DIGESTION ACCELERATOR AND METHOD FOR PRODUCING PULP USING SAME

Description

TECHNICAL FIELD

The present disclosure relates to a digestion accelerator, and a method for producing pulp with the digestion accelerator.

BACKGROUND ART

Alkaline main agents are used for pulping materials including lignocellulose in digestion steps of methods for producing pulp. Digestion accelerators are used for efficiently performing digestion. As such a digestion accelerator, Patent Literature 1 discloses a digestion accelerator containing a quaternary ammonium compound. Patent Literature 2 discloses a digestion accelerator containing at least one of glucose and fructose.

CITATION LIST

Patent Literature

• Patent Literature 1: Unexamined Japanese Patent Application Publication No. 2019-65434
• Patent Literature 2: Unexamined Japanese Patent Application Publication No. 2020-2481

SUMMARY OF INVENTION

Technical Problem

In a case where an alkaline main agent and the digestion accelerator disclosed in Patent Literature 1 and Patent Literature 2 are used in a digestion step of a method for producing pulp, a material including lignocellulose can be efficiently digested as compared with digestion where only an alkaline main agent is used. However, there is a demand for a further increase in efficiency of digestion in order to efficiently produce pulp, from the viewpoint of price increase of wood according to the expansion of a demand for wood in recent years, suppression of deforestation according to global warming, and the like.

In view of the above circumstances, an objective of the present disclosure is to provide a digestion accelerator capable of efficiently digesting a material including lignocellulose in a digestion step of pulping a material including lignocellulose, and a method for producing pulp with the digestion accelerator.

Solution to Problem

The inventors of the present disclosure have made intensive studies for achieving the above objective, and as a result, have found that the above objective can be achieved by a digestion accelerator including a specified quaternary ammonium compound, and at least one amine compound selected from the group consisting of a specified primary monoamine, a specified secondary monoamine, and a specified tertiary monoamine, and a digestion accelerator including a specified quaternary ammonium compound, and a sulfur-containing compound that generates a sulfide ion, a polysulfide ion, or a hydrogen sulfide ion in the presence of the quaternary ammonium compound, thereby leading to completion of the present disclosure.

In order to achieve the above objective, [1] the digestion accelerator according to the present disclosure includes a quaternary ammonium compound represented by formula (1), and at least one amine compound selected from the group consisting of a primary monoamine represented by formula (2), a secondary monoamine represented by formula (3), and a tertiary monoamine represented by formula (4).

In formula (1), R¹ is an alkyl group having 8 to 22 carbon atoms, a hydroxyalkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, or a hydroxyalkenyl group having 8 to 22 carbon atoms,

• • R² is an alkyl group having 1 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group,
  • R³ and R⁴ are each independently an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, an aryl group, a benzyl group optionally having an alkyl group having 1 to 4 carbon atoms, a phenethyl group optionally having an alkyl group having 1 to 4 carbon atoms, a glycidyl group, or an (A¹O)_mY group,
  • N represents a nitrogen atom,
  • X^p− represents a counterion, and is an inorganic anion or an organic anion, and p represents a valence of an ion,
  • A¹O is an alkyleneoxy group having 2 to 4 carbon atoms, and Y is a hydrogen atom or an acyl group, and
  • n is an integer of 1 to 15 and m is an integer of 1 to 15.

In formula (2), R⁵ is an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A²O)_kZ group, A²O is an alkyleneoxy group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and k is an integer of 1 to 6.

In formula (3), R⁶ and R⁷ are each independently an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A³O)_rZ group, A³O is an alkyleneoxy group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and r is an integer of 1 to 12.

In formula (4), R⁸ and R⁹ are each independently an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_tZ group, A⁴O is an alkyleneoxy group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and t is an integer of 1 to 12, and

• • R¹⁰ is an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group, A⁵O is an alkyleneoxy group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and u is an integer of 1 to 12.

In addition, [2] a mass ratio between the quaternary ammonium compound and the amine compound may be 5:1 to 10000:1.

In addition, [3] the digestion accelerator according to the present disclosure includes a quaternary ammonium compound represented by formula (1), and a sulfur-containing compound that generates a sulfide ion, a polysulfide ion, or a hydrogen sulfide ion in the presence of the quaternary ammonium compound.

In formula (1), R¹ is an alkyl group having 8 to 22 carbon atoms, a hydroxyalkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, or a hydroxyalkenyl group having 8 to 22 carbon atoms,

• • R² is an alkyl group having 1 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group,
  • R³ and R⁴ are each independently an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, an aryl group, a benzyl group optionally having an alkyl group having 1 to 4 carbon atoms, a phenethyl group optionally having an alkyl group having 1 to 4 carbon atoms, a glycidyl group, or an (A¹O)_mY group,
  • N represents a nitrogen atom,
  • X^p− represents a counterion, and is an inorganic anion or an organic anion, and p represents a valence of an ion,
  • A¹O is an alkyleneoxy group having 2 to 4 carbon atoms, and Y is a hydrogen atom or an acyl group, and
  • n is an integer of 1 to 15 and m is an integer of 1 to 15.

In addition, [4] the sulfur-containing compound may include at least one compound selected from the group consisting of thiosulfate, hydrogen thiosulfate, sulfite, hydrogen sulfite, disulfite, dithionite, dithionate, disulfate, peroxosulfate, peroxodisulfate, and polythionate.

In addition, [5] a mass ratio between the quaternary ammonium compound and the sulfur-containing compound may be 1:2 to 100:1.

In addition, in order to achieve the above objective, [6] the method for producing pulp according to the present disclosure includes a digestion step of adding at least one main agent selected from the group consisting of an alkaline main agent and a sulfite-based main agent, and a digestion accelerator, to digest a material including lignocellulose, wherein the digestion accelerator is the digestion accelerator according to [1] or [3].

In addition, [7] a content of the digestion accelerator may be 0.001% by mass to 1.0% by mass relative to the material including the lignocellulose.

Advantageous Effects of Invention

According to the digestion accelerator and the method for producing pulp with the digestion accelerator of the present disclosure, a material including lignocellulose can be efficiently digested.

DESCRIPTION OF EMBODIMENTS

Hereinafter, each mode for carrying out the present disclosure (hereinafter, simply referred to as “Embodiment”.) is described in detail. The following Embodiments are illustrative for describing the present disclosure, and are not intended to limit the present disclosure to the following content. The present disclosure can be appropriately modified and carried out within the gist thereof.

Embodiment 1

A digestion accelerator of Embodiment 1 includes a quaternary ammonium compound, and at least one amine compound selected from the group consisting of a primary monoamine, a secondary monoamine, and a tertiary monoamine. First, the quaternary ammonium compound and the amine compound are described. Next, the digestion accelerator including them is described.

(Quaternary Ammonium Compound)

The quaternary ammonium compound included in the digestion accelerator of Embodiment 1 is a compound represented by the following formula (1).

• • N in formula (1) represents a nitrogen atom.
  • R¹ in formula (1) is an alkyl group having 8 to 22 carbon atoms, a hydroxyalkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, or a hydroxyalkenyl group having 8 to 22 carbon atoms.
  • R² in formula (1) is an alkyl group having 1 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group. Here, A¹O is an alkyleneoxy group having 2 to 4 carbon atoms. n represents the number of repeating units in the alkyleneoxy group, and is a number of 1 to 15. Y is a hydrogen atom or an acyl group. The “number of repeating units in the alkyleneoxy group” means the “average addition molar number of the alkyleneoxy group”. Hereinafter, the same also applies to all embodiments.
  • R³ and R⁴ in formula (1) are each independently an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, an aryl group, a benzyl group optionally having an alkyl group having 1 to 4 carbon atoms, a phenethyl group optionally having an alkyl group having 1 to 4 carbon atoms, a glycidyl group, or an (A¹O)_mY group. Here, A¹O is an alkyleneoxy group having 2 to 4 carbon atoms. m represents the number of repeating units in the alkyleneoxy group, and is a number of 1 to 15. Y is a hydrogen atom or an acyl group. The “benzyl group optionally having an alkyl group having 1 to 4 carbon atoms” includes a benzyl group (C₆H₅CH₂—), and a benzyl group in which an alkyl group having 1 to 4 carbon atoms is added to CH₂ in the benzyl group. The “phenethyl group optionally having an alkyl group having 1 to 4 carbon atoms” includes a phenethyl group (C₆H₅CH₂CH₂—), and a phenethyl group in which an alkyl group having 1 to 4 carbon atoms is added to CH₂ in the phenethyl group. C represents a carbon atom and H represents a hydrogen atom. Hereinafter, the same also applies to all Embodiments.
  • R¹, R², R³, and R⁴ in formula (1) each preferably have the following structure from the viewpoint of promotion of digestion.
  • R¹ is preferably an alkyl group having 10 to 18 carbon atoms, a hydroxyalkyl group having 10 to 18 carbon atoms, an alkenyl group having 10 to 18 carbon atoms, or a hydroxyalkenyl group having 10 to 18 carbon atoms. R¹ is more preferably a linear alkyl group having 10 to 16 carbon atoms, a linear hydroxyalkyl group having 10 to 16 carbon atoms, a linear alkenyl group having 10 to 16 carbon atoms, or a linear hydroxyalkenyl group having 10 to 16 carbon atoms.
  • R² is preferably an alkyl group having 1 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group. Here, A¹O is an alkyleneoxy group having 2 to 4 carbon atoms. n represents the number of repeating units in the alkyleneoxy group, and is a number of 1 to 6. Y is a hydrogen atom or an acyl group. R² is more preferably a linear alkyl group having 1 to 22 carbon atoms, a linear hydroxyalkyl group having 1 to 22 carbon atoms, a linear alkenyl group having 2 to 22 carbon atoms, a linear hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group. Here, A¹O is an alkyleneoxy group having 2 to 4 carbon atoms. n represents the number of repeating units in the alkyleneoxy group, and is a number of 1 to 4. Y is a hydrogen atom or an acyl group.
  • R³ and R⁴ are each independently preferably an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, an aryl group, a benzyl group optionally having an alkyl group having 1 to 4 carbon atoms, a phenethyl group optionally having an alkyl group having 1 to 4 carbon atoms, a glycidyl group, or an (A¹O)_mY group. Here, A¹O is an alkyleneoxy group having 2 to 4 carbon atoms. m represents the number of repeating units in the alkyleneoxy group, and is a number of 1 to 6. Y is a hydrogen atom or an acyl group. R³ and R⁴ are each independently more preferably an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, an aryl group, a benzyl group optionally having an alkyl group having 1 to 4 carbon atoms, a phenethyl group optionally having an alkyl group having 1 to 4 carbon atoms, a glycidyl group, or an (A¹O)_mY group. Here, A¹O is an alkyleneoxy group having 2 to 4 carbon atoms. m represents the number of repeating units in the alkyleneoxy group, and is a number of 1 to 4. Y is a hydrogen atom or an acyl group.

Furthermore, in a case where R², R³, and R⁴ in formula (1) are each a hydroxyalkyl group, a hydroxyalkenyl group, or an alkyleneoxy group, these each preferably have the following structure from the viewpoint of promotion of digestion.

In a case where R² is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, and n is preferably an integer of 1 to 15. The sum is more preferably 1 to 9, still more preferably 1 to 6.

In a case where R³ or R⁴ are each independently a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A¹O)_mY group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, and m is preferably an integer of 1 to 15. The sum is more preferably 1 to 9, still more preferably 1 to 6.

In a case where, in R² and R³ or R⁴, R² is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group and R³ or R⁴ is each independently a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A¹O)_mY group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, n, and m is preferably an integer of 2 to 15. The sum is more preferably 2 to 9, still more preferably 2 to 6.

In a case where, in R³ and R⁴, R³ and R⁴ are each independently a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A¹O)_mY group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, and m is preferably an integer of 2 to 15. The sum is more preferably 2 to 9, still more preferably 2 to 6.

In a case where, in R², R³, and R⁴, R² is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group and R³ and R⁴ are each independently a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A¹O)_mY group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, n, and m is preferably an integer of 3 to 15. The sum is more preferably 3 to 9, still more preferably 3 to 6.

X^p− in formula (1) represents a counterion. p represents the valence of an ion. p is 1 to 40, and is preferably 1 to 20, more preferably 1 to 3 from the viewpoint of productization, industrialization, and cost. The counterion is not limited as long as it is an anion capable of being taken with the quaternary ammonium compound to constitute a salt. Examples of the counterion include (i) an inorganic anion and (ii) an organic anion.

Examples of the inorganic anion (i) include halogen ions such as chloride ions and bromide ions, hydroxy ions, sulfate ions, nitrate ions, phosphate ions, borate ions, sulfonate ions, hypochlorite ions, nitrite ions, phosphite ions, diphosphite ions, sulfite ions, hydrogen sulfite ions, sulfide ions, hydrogen sulfide ions, polysulfide ions, thiol ions, thiosulfate ions, and thioglycollate.

Examples of the organic anion (ii) include i) an organic carboxylate ion, ii) phosphate ester ion, iii) a sulfonate ion, iv) an alkyl carbonate ion, v) a sulfate ester ion, and vi) an anionic polymer. Examples of the organic carboxylate ion i) include formate ions, acetate ions, propionate ions, gluconate ions, lactate ions, fumarate ions, maleate ions, and adipate ions. Examples of the phosphate ester ion ii) include polyoxyalkylene alkyl ether phosphate ester ions, alkyl phosphate monoester ions, alkyl phosphate diester ions, alkenyl phosphate ester ions, and aryl phosphate ester ions. Examples of the sulfonate ion iii) include alkylbenzenesulfonate ions and alkylsulfonate ions. Examples of the alkyl carbonate ion iv) include methyl carbonate ions and ethyl carbonate ions. Examples of the sulfate ester ion v) include alkyl sulfate ester ions and polyoxyalkylene alkyl ether sulfate ester ions. Examples of the anionic polymer vi) include polyacrylic acid, polymaleic acid, polyphosphoric acid, and polysulfuric acid compounds.

Among these counterions, the inorganic anion (i) is preferably a halogen ion such as a chloride ion or a bromide ion, a sulfate ion, a nitrate ion, a borate ion, or a phosphate ion from the viewpoint of promotion of digestion. The organic anion (ii) is preferably an alkyl phosphate monoester ion in which the number of carbon atoms in the alkyl group is 1 to 4, such as a butyl phosphate ester ion; an alkyl phosphate diester ion in which the number of carbon atoms in the alkyl group is 1 to 4, such as a dibutyl phosphate ester ion; an alkylbenzenesulfonate ion in which the number of carbon atoms in p-toluenesulfonate or the like is 1 to 4; or an alkyl sulfate ester ion in which the number of carbon atoms in the alkyl group is 1 to 4, such as a methyl sulfate ion (CH₃SO₄⁻) or an ethyl sulfate ion (C₂H₅SO₄⁻).

(Amine Compound)

The amine compound included in the digestion accelerator of Embodiment 1 includes at least one amine compound selected from the group consisting of a primary monoamine, a secondary monoamine, and a tertiary monoamine.

(Primary Monoamine)

The primary monoamine is a compound represented by the following formula (2).

In formula (2), R⁵ is an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A²O)_kZ group. Here, A²O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. k is an integer of 1 to 6.

R⁵ is preferably an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a hydroxyalkyl group having 1 to 18 carbon atoms, a hydroxyalkenyl group having 2 to 18 carbon atoms, or an (A²O)_kZ group from the viewpoint of promotion of digestion. Here, A²O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. k is an integer of 1 to 2. R⁵ is more preferably an alkyl group having 10 to 14 carbon atoms, an alkenyl group having 10 to 14 carbon atoms, a hydroxyalkyl group having 10 to 14 carbon atoms, a hydroxyalkenyl group having 10 to 14 carbon atoms, or an (A²O)_kZ group. Here, A²O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. k is 1.

(Secondary Monoamine)

The secondary monoamine is a compound represented by the following formula (3).

In formula (3), R⁶ is an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A³O)_r1Z group. Here, A³O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. r1 is an integer of 1 to 12. In formula (3), R⁷ is an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A³O)_r2Z group. Here, A³O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. r2 is an integer of 1 to 12. In addition, R⁶ and R⁷ may be the same as or different from each other.

Here, the (A³O)_r1Z group of R⁶ and the (A³O)_r2Z group of R⁷ may also be collectively designated as “(A³O)_rZ group”.

R⁶ and R⁷ in formula (3) each preferably have the following structure from the viewpoint of promotion of digestion.

R⁶ is preferably an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a hydroxyalkyl group having 1 to 18 carbon atoms, a hydroxyalkenyl group having 2 to 18 carbon atoms, or an (A³O)_r1Z group. Here, A³O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. r1 is an integer of 1 to 6. R⁶ is more preferably an alkyl group having 10 to 14 carbon atoms, an alkenyl group having 10 to 14 carbon atoms, a hydroxyalkyl group having 10 to 14 carbon atoms, a hydroxyalkenyl group having 10 to 14 carbon atoms, or an (A³O)_r1Z group. Here, A³O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. r1 is an integer of 2 to 4.

R⁷ is preferably an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a hydroxyalkyl group having 1 to 18 carbon atoms, a hydroxyalkenyl group having 2 to 18 carbon atoms, or an (A³O)_r2Z group. Here, A³O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. r2 is an integer of 1 to 6. R⁷ is more preferably an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkyl group having 1 carbon atom, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A³O)_r2Z group. Here, A³O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. r2 is an integer of 2 to 4.

Furthermore, in a case where R⁶ and R⁷ in formula (3) are each a hydroxyalkyl group, a hydroxyalkenyl group, or an alkyleneoxy group, R⁶ and R⁷ each preferably have the following structure from the viewpoint of promotion of digestion.

In a case where R⁶ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A³O)_r1Y group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, and r1 is an integer of 1 to 12. The sum is preferably 1 to 6, more preferably 1 to 4.

In a case where R⁷ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A³O)_r2Y group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, and r2 is an integer of 1 to 12. The sum is preferably 1 to 6, more preferably 1 to 4.

In a case where, in R⁶ and R⁷, R⁶ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A³O)_r1Y group and R⁷ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A³O)_r2Y group, preferably the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, r1, and r2 is an integer of 2 to 12. The sum is preferably 2 to 6, more preferably 2 to 4. In addition, R⁶ and R⁷ may be mutually the same in structure or may be mutually different in structure.

(Tertiary Monoamine)

The tertiary monoamine is a compound represented by the following formula (4).

In formula (4), R⁸ is an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t1Z group. A⁴O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. t1 is an integer of 1 to 12.

In formula (4), R⁹ is an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t2Z group. A⁴O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. t2 is an integer of 1 to 12. In addition, R⁸ and R⁹ may be mutually the same in structure or may be mutually different in structure.

Here, the (A⁴O)_tZ group of R⁸ and the (A⁴O)_t2Z group of R⁹ may also be collectively designated as “(A⁴O)_tZ group”.

In formula (4), R¹⁰ is an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group. A⁵O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. u is an integer of 1 to 12.

R⁸, R⁹ and R¹⁰ in formula (4) each preferably have the following structure from the viewpoint of promotion of digestion.

R⁸ is preferably an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a hydroxyalkyl group having 1 to 18 carbon atoms, a hydroxyalkenyl group having 2 to 18 carbon atoms, or an (A⁴O)_t1Z group. A⁴O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. t1 is an integer of 1 to 6. R⁸ is more preferably an alkyl group having 10 to 14 carbon atoms, an alkenyl group having 10 to 14 carbon atoms, a hydroxyalkyl group having 10 to 14 carbon atoms, a hydroxyalkenyl group having 10 to 14 carbon atoms, or an (A⁴O)_t1Z group. A⁴O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. t1 is an integer of 1 to 4.

R⁹ is preferably an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a hydroxyalkyl group having 1 to 18 carbon atoms, a hydroxyalkenyl group having 2 to 18 carbon atoms, or an (A⁴O)_t2Z group. A⁴O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. t2 is an integer of 1 to 6. R⁹ is more preferably an alkyl group having 10 to 14 carbon atoms, an alkenyl group having 10 to 14 carbon atoms, a hydroxyalkyl group having 10 to 14 carbon atoms, a hydroxyalkenyl group having 10 to 14 carbon atoms, or an (A⁴O)_t2Z group. A⁴O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. t2 is an integer of 1 to 4.

R¹⁰ is preferably an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group. A⁵O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. u is an integer of 1 to 6. R¹⁰ is more preferably an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group. A⁵O is an alkyleneoxy group having 2 to 4 carbon atoms, and Z is a hydrogen atom or an acyl group. u is an integer of 1 to 4.

Furthermore, in a case where R⁸, R⁹, and R¹⁰ in formula (4) are each a hydroxyalkyl group, a hydroxyalkenyl group, or an alkyleneoxy group, these each preferably have the following structure from the viewpoint of promotion of digestion.

In a case where R⁸ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_tZ group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, and t1 is an integer of 1 to 12. The sum is preferably 1 to 6, more preferably 1 to 4.

In a case where R⁹ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t2Z group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, and t2 is an integer of 1 to 12. The sum is preferably 1 to 6, more preferably 1 to 4.

In a case where R¹⁰ is a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, and u is an integer of 1 to 12. The sum is preferably 1 to 6, more preferably 1 to 4.

In a case where, in R⁸ and R⁹, R⁸ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t1Z group and R⁹ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t2Z group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, t1, and t2 is an integer of 2 to 12. The sum is preferably 2 to 6, more preferably 2 to 4. In addition, R⁸, and R⁹ may be mutually the same in structure or may be mutually different in structure.

In a case where, in R⁸ and R¹⁰, R⁸ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t1Z group and R¹⁰ is a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, t1, and u is an integer of 2 to 12. The sum is preferably 2 to 6, more preferably 2 to 4. In addition, R⁸ and R¹⁰ may be mutually the same in structure or may be mutually different in structure.

In a case where, in R⁹ and R¹⁰, R⁹ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t2Z group and R¹⁰ is a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, t2, and u is an integer of 2 to 12. The sum is preferably 2 to 6, more preferably 2 to 4. In addition, R⁹ and R¹⁰ may be mutually the same in structure or may be mutually different in structure.

In a case where, in R⁸, R⁹, and R¹⁰, R⁸ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t1Z group, R⁹ is a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_t2Z group, and R¹⁰ is a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group, the sum of the number of such hydroxyalkyl groups, the number of such hydroxyalkenyl groups, t1, t2, and u is an integer of 3 to 12. The sum is preferably 3 to 6, more preferably 3 to 4. In addition, R⁸, R⁹, and R¹⁰ may be the same as or different from each other.

The above amine compound is preferably the secondary monoamine, more preferably the primary monoamine, further preferably the tertiary monoamine from the viewpoint of promotion of digestion.

(Digestion Accelerator)

The digestion accelerator of Embodiment 1 includes the above quaternary ammonium compound and amine compound. The mass ratio between the quaternary ammonium compound and the amine compound is 5:1 to 10000:1. The mass ratio is preferably 10:1 to 10000:1, more preferably 10:1 to 1000:1 from the viewpoint of promotion of digestion.

The content of the digestion accelerator of Embodiment 1 is 0.001% by mass to 1.0% by mass relative to a material including lignocellulose. For example, the content of the digestion accelerator of Embodiment 1 is 1.0 to 1000 mg based on 100 g of a material including lignocellulose, and is preferably 2 to 500 mg, more preferably 5 to 200 mg from the viewpoint of promotion of digestion.

The digestion accelerator of Embodiment 1 may include two or more of such quaternary ammonium compounds different in structure. The digestion accelerator of Embodiment 1 may include two or more of such amine compounds.

The digestion accelerator of Embodiment 1 in which the specified quaternary ammonium compound and the specified amine compound are included, as described above, can be used in a digestion step, to efficiently digest a material including lignocellulose without any loss in activity of the quaternary ammonium compound.

Embodiment 2

Next, a digestion accelerator of Embodiment 2 is described.

The digestion accelerator of Embodiment 2 includes a quaternary ammonium compound, and a sulfur-containing compound that generates a sulfide ion, a polysulfide ion, or a hydrogen sulfide ion in the presence of the quaternary ammonium compound. First, the quaternary ammonium compound and the sulfur-containing compound are described. Next, the digestion accelerator including them is described.

(Quaternary Ammonium Compound)

The quaternary ammonium compound included in the digestion accelerator of Embodiment 2 is substantially the same as the quaternary ammonium compound described in Embodiment 1.

(Sulfur-Containing Compound)

The sulfur-containing compound included in the digestion accelerator of Embodiment 2 is a compound that generates a sulfide ion, a polysulfide ion, or a hydrogen sulfide ion in the presence of the quaternary ammonium compound. The sulfur-containing compound include, for example, at least one compound selected from the group consisting of thiosulfate, hydrogen thiosulfate, sulfite, hydrogen sulfite, disulfite, dithionite, dithionate, disulfate, peroxosulfate, peroxodisulfate, and polythionate. The sulfur-containing compound preferably includes at least one compound selected from the group consisting of sodium thiosulfate, ammonium thiosulfate, sodium hydrogen sulfide, and sodium sulfide from the viewpoint of promotion of digestion.

(Digestion Accelerator)

The digestion accelerator of Embodiment 2 includes the above quaternary ammonium compound and sulfur-containing compound. The mass ratio between the quaternary ammonium compound and the sulfur-containing compound is 1:1 to 100:1. The mass ratio is preferably 1:1 to 50:1, more preferably 1:1 to 20:1 from the viewpoint of promotion of digestion.

The content of the digestion accelerator of Embodiment 2 is 0.001% by mass to 1.0% by mass relative to a material including lignocellulose. For example, the content of the digestion accelerator of Embodiment 2 is 1.0 to 1000 mg based on 100 g of a material including lignocellulose, and is preferably 2 to 500 mg, more preferably 5 to 200 mg from the viewpoint of promotion of digestion.

The digestion accelerator of Embodiment 2 may include two or more of such quaternary ammonium compounds different in structure. The digestion accelerator of Embodiment 1 may include two or more of such sulfur-containing compounds.

The digestion accelerator of Embodiment 2 including the specified quaternary ammonium compound and the specified sulfur-containing compound as described above can be used in a digestion step, to efficiently digest a material including lignocellulose. In other words, the sulfur-containing compound is included in the digestion accelerator and thus a state is made in which a sulfide ion, a polysulfide ion, a hydrogen sulfide ion, or the like is much present around the quaternary ammonium compound. The digestion accelerator, when used in a digestion step, can digest lignocellulose by an irreversible reaction. For example, in the case of a digestion step in an alkaline digestion method, sodium sulfide or the like is separately used from such a digestion accelerator. A sulfide ion, a polysulfide ion, a hydrogen sulfide ion, or the like generated here is not much present around the quaternary ammonium compound, and it is thus difficult to generate an irreversible reaction. Therefore, it is difficult to efficiently digest lignocellulose.

[Solvent and Additive Capable of being Added in Embodiment 1 and Embodiment 2]

The above digestion accelerator of each of Embodiment 1 and Embodiment 2 may include water or an organic solvent. The digestion accelerator can be, for example, dissolved or emulsified in water or an organic solvent and then used. Examples of the organic solvent include lower alcohols in which the number of carbon chains is 1 to 6, such as methanol, ethanol, and propanol; alkylene glycols in which the number of carbon chains is 1 to 6, such as ethylene glycol, diethylene glycol, and propylene glycol; and 3-methyl-3-methoxybutanol.

The above digestion accelerator of each of Embodiment 1 and Embodiment 2 may further include an additive from the viewpoint of allowing the digestion accelerator to efficiently penetrate into a material including lignocellulose.

(Additive)

Examples of the additive include a non-ionic surfactant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, mineral oil, natural oil such as orange oil, an alkaline agent, and acid. The digestion accelerator may further include, for example, a defoamer and/or a washing agent from the viewpoint of enhancing washing properties of pulp. Such an additive can be added to the digestion accelerator as long as the effects of the digestion accelerator are not impaired.

Examples of the above alkaline agent include inorganic alkali. Examples of the inorganic alkali include sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia.

Examples of the above acid include inorganic acids such as hydrochloric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, formic acid, lactic acid, and oxalic acid.

The foregoing is the description of the compounds and the like included in the digestion accelerator of each of Embodiment 1 and Embodiment 2. Next, a production method of the quaternary ammonium compound included in the digestion accelerator of each of Embodiment 1 and Embodiment 2, and a production method of the amine compound in Embodiment 1 are described.

(Method for Producing Quaternary Ammonium Compound)

The quaternary ammonium compound can be synthesized by various methods. In such a synthesis method, for example, the quaternary ammonium compound is obtained by adding a quaternizing agent having R⁴ to a tertiary amine having R¹, R², and R³ to allow these to react at a temperature of 70 to 150° C.

In another synthesis method, in the case of a quaternary ammonium compound in which R⁴ is an (AO)H group, the quaternary ammonium compound is obtained by neutralizing a tertiary amine having R¹, R², and R³ with any acid and then adding an alkylene oxide in an equivalent amount to the amount of the tertiary amine, into the mixture after neutralization, to perform a quaternization reaction at a temperature of 70 to 120° C. Here, AO is an alkyleneoxy group.

In an example of still another synthesis method, in the case of a quaternary ammonium compound in which R², R³, and R⁴ are substituents respectively represented by an (AO)_nH group, an (AO)_m1H group, and an (AO)_m2H group, the quaternary ammonium compound is obtained by adding a predetermined amount of an alkylene oxide to trialkanolamine to add the above substituents at a temperature of 100 to 150° C., and then adding a quaternizing agent having R¹, to the resulting mixture, to allow these to react at a temperature of 60 to 130° C. n, m1 and m2 are each, for example, an integer of 1 to 9.

The amine compound included in the digestion accelerator of Embodiment 1, and the sulfur-containing compound included in the digestion accelerator of Embodiment 2 can be each synthesized by a known method. For example, the tertiary monoamine is obtained by a polymerization reaction of an alkylene oxide with an alkylamine having 1 to 22 carbon atoms at a temperature of 70 to 150° C.

(Method for Producing Pulp)

The digestion accelerator of each of Embodiment 1 and Embodiment 2, described above, is used in a digestion step of a method for producing pulp. Next, a method for producing pulp, with such a digestion accelerator, is described.

The method for producing pulp includes a digestion step of digesting a material including lignocellulose, with at least one main agent selected from the group consisting of an alkaline main agent and a sulfite-based main agent, and the digestion accelerator, a washing step of washing pulp obtained by digestion, a screening step of removing dust from the pulp, and a bleaching step of bleaching the pulp.

In the digestion step, for example, the digestion accelerator of any Embodiment, a material including lignocellulose, and an alkaline main agent are added to a digestion oven, and digested under conditions of high temperature and high pressure. Such digestion is made to take out a fibrous content (pulp) from lignocellulose.

The temperature, pressure and time in the digestion step are appropriately set depending on the type, shape, and size of the material including lignocellulose. For example, in a case where the material including lignocellulose is a wood chip, the temperature is, for example, 50 to 300° C., and is preferably 80 to 250° C. from the viewpoint of a reduction in load on facilities such as a digestion oven. The pressure is, for example, ordinary pressure to 10 MPa, and is preferably ordinary pressure to 5 MPa from the viewpoint of a reduction in load on facilities such as a digestion oven. The time is, for example, 1 to 5 hours from the viewpoint of a reduction in load on facilities such as a digestion oven.

Examples of the digestion method adopted in this digestion step include an alkaline digestion method and a sulfite digestion method. Such an alkaline digestion method can be further classified into a kraft method, a soda method, a soda method, a polysulfide method, and the like. Such a sulfite digestion method can be further classified into an alkaline sulfite method, a neutral sulfite method, a bisulfite method, and the like. The digestion method is preferably an alkaline digestion method from the viewpoint of promotion of digestion. Among these alkaline digestion methods, a kraft method and a polysulfide method are preferred from the viewpoint of promotion of digestion.

Examples of the alkaline main agent used in the alkaline digestion method include sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate. The amount of the alkaline main agent used in the digestion step differs depending on the type of the material including lignocellulose, and is 1 to 120 parts by mass based on 100 parts by mass of the material including lignocellulose. The amount is preferably 3 to 60 parts by mass, more preferably 5 to 60 parts by mass from the viewpoint that the digestion is efficiently performed to allow the effects of the digestion accelerator to be exerted.

A kraft method as one alkaline digestion method is a method of digestion with an alkaline main agent and sodium sulfide. For example, in a case where the alkaline main agent is sodium hydroxide, the amount of sodium sulfide used is 1 to 200 parts by mass based on 100 parts by mass of sodium hydroxide, and is preferably 10 to 100 parts by mass from the viewpoint that the digestion is efficiently performed.

A polysulfide method as one alkaline digestion method is a method of digestion with an alkaline main agent, sodium sulfide, and sodium polysulfide (Na₂Sx, x=2 to 5). For example, in a case where the alkaline main agent is sodium hydroxide, the amount of sodium sulfide used is 1 to 200 parts by mass based on 100 parts by mass of sodium hydroxide, and is preferably 10 to 100 parts by mass from the viewpoint that the digestion is efficiently performed. The amount of the sodium polysulfide used is 1 to 200 parts by mass based on 100 parts by mass of the sodium hydroxide, and is preferably 10 to 100 parts by mass from the viewpoint that the digestion is efficiently performed.

A soda method as one alkaline digestion method is a method of digestion with an alkaline main agent. For example, sodium hydroxide is used as the alkaline main agent.

Examples of the material including lignocellulose include wood and vegetation. Examples of the wood include wood of Laubholz with hardwood as a raw material and wood of Nadelholz with softwood as a raw material. Examples of the vegetation include bacchus, reed, kenaf, mulberry tree, and bamboo. Such wood and vegetation are, for example, shaped into chips and then used.

EXAMPLES

The present disclosure is described in further detail with reference to the following Examples and Comparative Examples, but the present disclosure is not limited to the following Examples at all. In Examples and Comparative Examples, the following quaternary ammonium compound, amine compound, sulfur-containing compound, and material including lignocellulose were used.

(Quaternary Ammonium Compound)

R¹, R², R³, R⁴, and the counterion of each quaternary ammonium compound (E1 to E8, e9 to e10) used in Example and Comparative Example have a structure shown in Table 1. These quaternary ammonium compounds (E1 to E8, e9 to e10) were each synthesized.

Quaternary

ammonium

Functional group

compound	R1	R2	R3	R4	Counterion
E1	C12H25	CH3	CH3	C2H5	C2H5SO4−
	(Lauryl)
E2	C12H25	CH3	CH3	Benzyl	Cl−
	(Stearyl)
E3	C12H25	C2H4OH	C2H4OH	C2H5	C2H5SO4−
	(Lauryl)
E4	C12H25	C2H4OH	C2H4OH	C2H4OH	NO3−
	(Lauryl)
E5	C18H37	CH3	CH3	CH3	CH3SO4−
	(Stearyl)
E6	C8H17	CH3	CH3	C2H4OH	Phosphate ion
	(Octyl)				(PO33−)

E7

C12H25

(EO)8H

C2H4OH

p-Toluene-

	(Lauryl)				sulfonate ion
					(C6H4(CH3)SO3−)
E8	C10H21	C10H21	CH3	CH3	Cl−
	(Decyl)	(Decyl)

e9

C12H25

(EO)32H

CH3

CH3SO4−

	(Lauryl)
e10	C6H13	C2H4OH	C2H4OH	C2H5	C2H5SO4−
	(Hexyl)

(Synthesis of Quaternary Ammonium Compound E1)

To a four-necked flask equipped with a reflux condenser, 1 molar equivalent of lauryldimethylamine was added, and the resultant was heated to 85 to 95° C. Thereto was dropped and simultaneously stirred 1.1 molar equivalents of diethyl sulfate, to perform a quaternization reaction, and thus a quaternary ammonium compound E1 was obtained.

(Synthesis of Quaternary Ammonium Compound E2)

To a four-necked flask equipped with a reflux condenser, 1 molar equivalent of lauryldimethylamine and distilled water in an amount of two times the mass of lauryldimethylamine were added, and the resultant was heated to 85 to 95° C. Thereto was dropped and simultaneously stirred 1.1 molar equivalents of benzyl chloride, to perform a quaternization reaction, and thus E2 was obtained.

(Synthesis of Quaternary Ammonium Compound E3)

To a pressure-resistant reaction vessel, 1 molar equivalent of laurylamine was added, purged with nitrogen, and then heated to 120 to 130° C. Thereinto was blown 2 molar equivalents of ethylene oxide, and thus an adduct in which 2 molar equivalents of ethylene oxide was added to laurylamine was obtained. Next, 1 molar equivalent of the adduct obtained was added to a four-necked flask equipped with a reflux condenser, and heated to 85 to 95° C. Thereto was dropped and simultaneously stirred 1.1 molar equivalents of diethyl sulfate, to perform a quaternization reaction, and thus a quaternary ammonium compound E3 was obtained.

(Synthesis of Quaternary Ammonium Compound E4)

To a pressure-resistant reaction vessel, 1 molar equivalent of laurylamine was added, purged with nitrogen, and then heated to 120 to 130° C. Thereinto was blown 2 molar equivalents of ethylene oxide, and thus an adduct in which 2 molar equivalents of ethylene oxide was added to laurylamine was obtained. Next, distilled water in an amount of two times the mass of the adduct obtained was added to the pressure-resistant reaction vessel, and 1 molar equivalent of nitric acid was added for neutralization. Thereafter, the pressure-resistant reaction vessel was heated to 85 to 95° C., and 1.1 molar equivalents of ethylene oxide was blown, to perform a quaternization reaction. Finally, water was removed under reduced pressure with an evaporator under a condition of 70° C., and a quaternary ammonium compound E4 was obtained.

(Synthesis of Quaternary Ammonium Compound E5)

To a four-necked flask equipped with a reflux condenser, 1 molar equivalent of stearyldimethylamine was added, and heated to 85 to 95° C. Thereto was dropped and simultaneously stirred 1.1 molar equivalents of dimethyl sulfate, to perform a quaternization reaction, and thus a quaternary ammonium compound E5 was obtained.

(Synthesis of Quaternary Ammonium Compound E6)

To a four-necked flask equipped with a reflux condenser, 1 molar equivalent of octyldimethylamine was added, distilled water in an amount of two times the mass of octylamine was added, and 0.7 molar equivalents of phosphoric acid was added. Thereafter, the pressure-resistant reaction vessel was heated to 85 to 95° C., 1.1 molar equivalents of ethylene oxide was blown, to perform a quaternization reaction, and thus a quaternary ammonium compound E6 was obtained.

(Synthesis of Quaternary Ammonium Compound E7)

To a pressure-resistant reaction vessel, 1 molar equivalent of laurylamine was added, purged with nitrogen, and then heated to 120 to 130° C. Thereinto was blown 8 molar equivalents of ethylene oxide, and thus an adduct in which 8 molar equivalents of ethylene oxide was added to laurylamine was obtained. Next, distilled water in an amount of two times the mass of the adduct obtained was added to the pressure-resistant reaction vessel, and 1.0 molar equivalent of para-toluenesulfonic acid was added for neutralization. Thereafter, the pressure-resistant reaction vessel was heated to 85 to 95° C., 1.1 molar equivalents of ethylene oxide was blown, to perform a quaternization reaction, and thus a quaternary ammonium compound E7 was obtained.

(Quaternary Ammonium Compound E8)

Didecyldimethylammonium chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was used.

(Synthesis of Quaternary Ammonium Compound e9)

To a pressure-resistant reaction vessel, 1 molar equivalent of laurylamine was added, purged with nitrogen, and then heated to 120 to 130° C. Thereinto was blown 32 molar equivalents of ethylene oxide, and thus an adduct in which 32 molar equivalents of ethylene oxide was added to laurylamine was obtained. To a four-necked flask equipped with a reflux condenser, 1 molar equivalent of the adduct obtained was added, and heated to 85 to 95° C. Thereto was dropped and simultaneously stirred 1.1 molar equivalents of dimethyl sulfate, to perform a quaternization reaction, and thus a quaternary ammonium compound E9 was obtained.

(Synthesis of Quaternary Ammonium Compound e10)

To a pressure-resistant reaction vessel, 1 molar equivalent of hexylamine was added, purged with nitrogen, and then heated to 120 to 130° C. Thereinto was blown 2 molar equivalents of ethylene oxide, and thus an adduct in which 2 molar equivalents of ethylene oxide was added to laurylamine was obtained. Next, 1 molar equivalent of the adduct obtained was added to a four-necked flask equipped with a reflux condenser, and heated to 85 to 95° C. Thereto was dropped and simultaneously stirred 1.1 molar equivalents of diethyl sulfate, to perform a quaternization reaction, and thus a quaternary ammonium compound E10 was obtained.

(Amine Compound)

The amine compounds used here were the following amine compounds.

A1 tetradecylamine was used as the primary monoamine.

A2 diethanolamine was used as the secondary monoamine.

A3 N,N-dimethyldecylamine, A4 N-lauryldiethanolamine, or A5 triethanolamine was used as the tertiary monoamine.

These amine compounds used here were those manufactured by Tokyo Chemical Industry Co., Ltd.

Tertiary monoamines a6 and a7 were synthesized as follows.

(Synthesis of Tertiary Monoamine a6)

To a pressure-resistant reaction vessel, 1 molar equivalent of laurylamine was added, purged with nitrogen, and then heated to 120 to 130° C. Thereinto was blown 30 molar equivalents of ethylene oxide, and thus an adduct a6 in which 30 molar equivalents of ethylene oxide was added to laurylamine was obtained.

(Synthesis of Tertiary Monoamine a7)

To a pressure-resistant reaction vessel, 1 molar equivalent of laurylamine was added, purged with nitrogen, and then heated to 120 to 130° C. Thereinto was blown 50 molar equivalents of ethylene oxide, and thus an adduct a7 in which 50 molar equivalents of ethylene oxide was added to laurylamine was obtained.

(Sulfur-Containing Compound)

Sulfur-containing compounds used here were B1 sodium thiosulfate, B2 ammonium thiosulfate, B3 sodium hydrogen sulfide, B4 sodium sulfide, B5 sodium tetrasulfide, B6 potassium sulfite, B7 sodium hydrogen sulfite, and b8 sodium sulfate.

These sulfur-containing compounds of B1 to B4, B6 to B7, and b8 used here were those manufactured by FUJIFILM Wako Pure Chemical Corporation. The sulfur-containing compound of B5 used here was one manufactured by NAGAO Co., Ltd.

(Material Including Lignocellulose)

A wood chip was used as the material including lignocellulose.

Laubholz, wood chip with hardwood (acacia:eucalyptus=7:3) as a raw material,

Nadelholz, wood chip with softwood (Pinus densiflora) as a raw material.

The above quaternary ammonium compounds, amine compounds, sulfur-containing compounds, and materials including lignocellulose were each used and variously evaluated.

Example 1, Laubholz, Kraft Method, Digestion Accelerator Including Amine Compound

Laubholz as a wood chip, and a digestion accelerator including a quaternary ammonium compound and an amine compound were used to perform digestion by a kraft method. First, Laubholz was subjected to a stainless sieve having an aperture of 710 μm, and Laubholz remaining on the sieve was dried at 60° C. for 24 hours. The digestion accelerator was prepared so that the contents of the quaternary ammonium compound E4 (pure content) and the amine compound A1 (pure content) relative to Laubholz (wood chip) were each 0.03% by mass and the mass ratio between the quaternary ammonium compound E4 (pure content) and the amine compound A1 (pure content) was 100:1. Specifically, 14.85 mg of the quaternary ammonium compound E4 (pure content) and 0.15 mg of the amine compound A1 (pure content), with respect to 50.0 g of Laubholz (wood chip), were placed in a vessel, and dissolved in distilled water, and thus the digestion accelerator to be used in Example 1 was obtained.

Next, 6.9 g (3.2 g in terms of pure content of single sodium sulfide) of a sodium sulfide pentahydrate salt and 11.2 g of sodium hydroxide were added to a beaker and distilled water was added thereto so that the total mass was 145 g, thereby obtaining an alkaline aqueous solution. The digestion accelerator prepared in advance was added to this aqueous solution, distilled water was added thereto so that the total mass was 150 g, and the resultant was stirred to obtain a digestion liquid.

Into a pot (MINI COLOR, manufactured by Texam Giken Co., Ltd.) were placed 50.0 g of Laubholz and 150 g of the digestion liquid prepared, and digestion was performed at 150° C. for 50 minutes.

After the digestion, the wood piece residual rate, the yield, and the Kappa number were evaluated with respect to Example 1, and the results were shown in Table 2. The wood piece residual rate, the yield, and the Kappa number were evaluated respectively by the following procedures.

<Wood Piece Residual Rate (Wood Chip Residual Ratio)>

The degree of progression of digestion of a wood piece (wood chip) can be determined by examining the wood piece residual rate (wood chip residual ratio). The wood piece residual rate can also be called wood chip residual ratio.

The wood piece residual rate was determined from the following expression.

Wood piece residual rate (%)=(Mass (g) of residue object after digestion/Mass (g) of sample before digestion)×100

Here, one subjected to the following treatment was adopted as a residue object after digestion. First, the mixture obtained by digestion was sieved. Next, a residue remaining on a stainless sieve having an aperture of 710 μm was washed with water, and such washing was repeated until the water used in washing was colorless. Thereafter, the residue was dried at 105° C. for 10 hours, and the resultant was adopted as a residue object. The sample before digestion here corresponds to a wood chip sieved before digestion and dried. For example, the sample before digestion of Example 1 is Laubholz sieved before digestion.

The evaluation criteria of the wood piece residual rate in the case of use of a kraft method and Laubholz were as follows.

Excellent: a wood piece residual rate of less than 0.5%,

Good: a wood piece residual rate of 0.5% or more and less than 1.5%,

Poor: a wood piece residual rate of 1.5% or more and less than 2.5%,

Bad: a wood piece residual rate of 2.5% or more.

<Yield>

The yield is the yield of the pulp obtained after digestion. It was determined from the following expression.

Yield (%)=(((i) Mass (g) of pulp recovered+(ii) Mass (g) of wood piece residual×½)/(iii) Mass (g) of sample before digestion)×100

• • (i) The mass of the pulp recovered was defined as the mass of pulp obtained after the following treatment. First, the mixture obtained by digestion was subjected to a stainless sieve having an aperture of 710 μm, and the mixture passing through the sieve was subjected to a finer stainless sieve having an aperture of 75 μm. The remaining residue in this sieve was washed with water, and such washing was repeated until water used in washing was colorless. Thereafter, the residue was dried at 105° C. for 10 hours. Thereafter, the mass of the residue after drying was measured, and this was defined as the mass of the pulp recovered.
  • (ii) The mass of a wood piece residual was defined as the mass of a residue obtained after the following treatment. First, the mixture obtained by digestion was subjected to a stainless sieve having an aperture of 710 μm, the remaining residue was washed with water, and such washing was repeated until the water used in washing was colorless. Thereafter, the residue was dried at 105° C. for 10 hours. Thereafter, the mass of the residue after drying was measured, and this was defined as the mass of the wood piece residual. Here, under the assumption that the residue after digestion is again digestion-treated, the mass obtained by multiplying the mass of the residue after treatment (mass of wood piece residual) with ½ is regarded as the pulp mass expected to be able to be further recovered, and this is added to the numerator in the expression.
  • (iii) The sample before digestion is a wood chip sieved and dried before digestion. For example, the sample before digestion of Example 1 is Laubholz sieved and dried before digestion.

The evaluation criteria of the yield in the case of use of a kraft method and Laubholz were as follows.

Excellent: a yield of 52.5% or more,

Good: a yield of less than 52.5% and 52.0% or more,

Poor: a yield of less than 52.0% and 51.5% or more,

Bad: a yield of less than 51.5%.

<Kappa Number>

The Kappa number indicates the content of the residual lignin. The Kappa number of the pulp obtained after digestion is small because the content of the residual lignin is low. The Kappa number of the pulp obtained after digestion can be examined to determine the degree of progression of digestion of the wood piece (wood chip).

One subjected to the following treatment was adopted as pulp obtained after digestion. First, the mixture obtained by digestion was subjected to a stainless sieve having an aperture of 710 μm, and the mixture passing through the sieve was subjected to a finer stainless sieve having an aperture of 75 μm. The remaining residue in this sieve was washed with water, and such washing was repeated until the water used in washing was colorless. Thereafter, the residue was dried at 105° C. for 10 hours. This was defined as pulp. The Kappa number was determined by a method described in JIS P 8211(2011).

The evaluation criteria of the Kappa number in the case of use of a kraft method and Laubholz were as follows.

Excellent: a Kappa number of less than 15.5,

Good: a Kappa number of 15.5 or more and less than 16.0,

Poor: a Kappa number of 16.0 or more and less than 16.5,

Bad: a Kappa number of 16.5 or more.

Examples 2 to 17 and Comparative Examples 1 to 17, Laubholz, Kraft Method, Digestion Accelerator Including Amine Compound

The same method as in Example 1 was used to perform digestion and evaluation in each of Examples 2 to 17 and Comparative Examples 1 to 17 except that the types, the amounts of use, and the mass ratios of the quaternary ammonium compound and the amine compound were changed as shown in Table 2 and Table 3. In Comparative Example 1, digestion was performed without any digestion accelerator, and evaluation was made.

	Digestion accelerator

		Content
	Mass ratio of	(% by mass)
	quaternary	of digestion	Evaluation item

	Quaternary		ammonium	accelerator	Wood piece
	ammonium	Amine	compound/amine	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

1	E4	A1	100/1	0.03	0.4	52.3	15.5
					Excellent	Good	Good
2	E4	A2	100/1	0.03	0.4	52.2	15.5
					Excellent	Good	Good
3	E4	A3	100/1	0.03	0.4	52.4	15.3
					Excellent	Good	Excellent
4	E4	A4	100/1	0.03	0.4	52.4	15.3
					Excellent	Good	Excellent
5	E4	A5	100/1	0.03	0.4	52.3	15.4
					Excellent	Good	Excellent
6	E4	A6	100/1	0.03	0.4	52.1	15.8
					Excellent	Good	Good
7	E1	A4	100/1	0.03	0.5	52.3	15.4
					Good	Good	Excellent
8	E2	A4	100/1	0.03	0.5	52.5	15.4
					Good	Excellent	Excellent
9	E3	A3	100/1	0.03	0.4	52.5	15.3
					Excellent	Excellent	Excellent
10	E5	A5	100/1	0.03	0.6	52.2	15.6
					Good	Good	Good
11	E6	A5	100/1	0.03	0.7	52.2	15.6
					Good	Good	Good
12	E7	A1	100/1	0.03	1.0	52.1	15.7
					Good	Good	Good
13	E8	A2	100/1	0.03	1.1	52.0	15.7
					Good	Good	Good
14	E3	A3	10/1	0.03	0.4	52.3	15.5
					Excellent	Good	Good
15	E3	A3	1000/1	0.03	0.4	52.3	15.5
					Excellent	Good	Good
16	E3	A3	100/1	0.1	0.2	52.6	15.2
					Excellent	Excellent	Excellent
17	E3	A3	100/1	0.01	1.2	52.0	15.6
					Good	Good	Good

	Digestion accelerator

		Content (%
	Mass ratio	by mass) of
	of quaternary	digestion	Evaluation item

	Quaternary		ammonium	accelerator	Wood piece
Comparative	ammonium	Amine	compound/amine	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

1	—	—	0/0	0	3.1	49.8	16.5
					Bad	Bad	Bad
2	E1	—	100/0	0.03	0.5	51.3	16.1
					Good	Bad	Poor
3	E2	—	100/0	0.03	0.5	51.3	16.1
					Good	Bad	Poor
4	E3	—	100/0	0.03	0.4	51.3	16.1
					Excellent	Bad	Poor
5	E4	—	100/0	0.03	0.4	51.3	16.0
					Excellent	Poor	Poor
6	E5	—	100/0	0.03	0.7	51.2	16.2
					Good	Bad	Poor
7	E7	—	100/0	0.03	0.9	51.1	16.3
					Good	Bad	Poor
8	E8	—	100/0	0.03	1.3	51.2	16.3
					Good	Bad	Poor
9	—	A1	0/100	0.03	2.9	49.9	16.5
					Bad	Bad	Bad
10	—	A2	0/100	0.03	3.0	49.9	16.5
					Bad	Bad	Bad
11	—	A3	0/100	0.03	3.0	49.9	16.4
					Bad	Bad	Poor
12	—	A4	0/100	0.03	2.9	49.9	16.5
					Bad	Bad	Bad
13	—	A5	0/100	0.03	3.0	49.8	16.5
					Bad	Bad	Bad
14	e9	A3	100/1	0.03	1.6	51.3	16.3
					Poor	Bad	Poor
15	e10	A4	100/1	0.03	1.8	51.3	16.4
					Poor	Poor	Poor
16	E3	a6	100/1	0.03	0.4	Bad	16.2
					Excellent	Poor	Poor
17	E3	a7	100/1	0.03	0.4	51.5	16.2
					Excellent	Poor	Poor

Example 18, Nadelholz, Kraft Method, Digestion Accelerator Including Amine Compound

Nadelholz as a wood chip, and a digestion accelerator including a quaternary ammonium compound and an amine compound were used to perform digestion by a kraft method.

In Example 18, substantially the same procedure as in Example 1 was performed for digestion and evaluation except that the quaternary ammonium compound was E1, the amine compound was A4, the wood chip was Nadelholz, and the amounts of the sodium sulfide pentahydrate salt and the sodium hydroxide added were changed. In Example 18, 7.75 g (3.6 g in terms of pure content of single sodium sulfide) of a sodium sulfide pentahydrate salt and 12.6 g of sodium hydroxide were added to the digestion liquid.

The evaluation criteria in the case of use of a kraft method and Nadelholz were as follows.

(1) Evaluation Criteria of Wood Piece Residual Rate

Excellent: a wood piece residual rate of less than 0.5%,

Good: a wood piece residual rate of 0.5% or more and less than 1.5%,

Poor: a wood piece residual rate of 1.5% or more and less than 2.5%,

Bad: a wood piece residual rate of 2.5% or more.

(2) Evaluation Criteria of Yield

Excellent: a yield of 52.5% or more,

Good: a yield of less than 52.5% and 52.0% or more,

Poor: a yield of less than 52.0% and 51.5% or more,

Bad: a yield of less than 51.5%

(3) Evaluation Criteria of Kappa Number

Excellent: a Kappa number of less than 29.0,

Good: a Kappa number of 29.0 or more and less than 29.5,

Poor: a Kappa number of 29.5 or more and less than 30.0,

Bad: a Kappa number of 30.0 or more.

Examples 19 to 22 and Comparative Examples 18 to 26, Nadelholz, Kraft Method, Digestion Accelerator Including Amine Compound

The same method as in Example 18 was used to perform digestion and evaluation in each of Examples 19 to 22, and Comparative Examples 18 to 26 except that the types, the amounts of use, and the mass ratios of the quaternary ammonium compound and the amine compound were changed as shown in Table 4 and Table 5. In Comparative Example 18, digestion was performed without any digestion accelerator, and evaluation was made.

	Digestion accelerator

		Content (%
	Mass ratio	by mass) of
	of quaternary	digestion	Evaluation item

	Quaternary		ammonium	accelerator	Wood piece
	ammonium	Amine	compound/amine	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

18	E1	A4	100/1	0.03	0.6	52.7	28.9
					Good	Excellent	Excellent
19	E3	A3	100/1	0.03	0.4	52.8	28.8
					Excellent	Excellent	Excellent
20	E4	A3	100/1	0.03	0.4	52.8	28.8
					Excellent	Excellent	Excellent
21	E4	A2	100/1	0.03	0.5	52.4	29.1
					Good	Good	Good
22	E7	A1	100/1	0.03	0.9	52.2	29.3
					Good	Good	Good

	Digestion accelerator

		Content (%
	Mass ratio	by mass) of
	of quaternary	digestion	Evaluation item

	Quaternary		ammonium	accelerator	Wood piece
Comparative	ammonium	Amine	compound/amine	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

18	—	—	0/0	0	3.2	51.3	30.8
					Bad	Bad	Bad
19	E1	—	100/0	0.03	0.6	51.7	30.2
					Good	Poor	Bad
20	E3	—	100/0	0.03	0.4	51.7	30.2
					Excellent	Poor	Bad
21	E7	—	100/0	0.03	1.0	51.5	30.6
					Good	Poor	Bad
22	—	A1	0/100	0.03	2.9	51.4	30.8
					Bad	Bad	Bad
23	—	A2	0/100	0.03	3.0	51.3	30.7
					Bad	Bad	Bad
24	—	A3	0/100	0.03	3.0	51.4	30.7
					Bad	Bad	Bad
25	e9	A3	0/100	0.03	1.8	51.9	30.0
					Poor	Poor	Bad
26	e10	A4	0/100	0.03	1.7	51.8	29.9
					Poor	Poor	Poor

Example 23, Nadelholz, Polysulfide Method, Digestion Accelerator Including Amine Compound

Nadelholz as a wood chip, and a digestion accelerator including a quaternary ammonium compound and an amine compound were used to perform digestion by a polysulfide method.

In Example 23, substantially the same procedure as in Example 1 was performed for digestion and evaluation except that the quaternary ammonium compound was E1, the amine compound was A4, the wood chip was Nadelholz, the amounts of the sodium sulfide pentahydrate salt and the sodium hydroxide added were changed, and a sodium tetrasulfide solution (manufactured by NAGAO Co., Ltd.) was newly used. In Example 23, 6.2 g (2.88 g in terms of pure content of single sodium sulfide) of the sodium sulfide pentahydrate salt, 12.6 g of sodium hydroxide, and 2.4 g (0.72 g in terms of pure content of single sodium tetrasulfide) of the sodium tetrasulfide solution were added to the digestion liquid.

The evaluation criteria in the case of use of a polysulfide method and Nadelholz were as follows.

(1) Evaluation Criteria of Wood Piece Residual Rate

Excellent: a wood piece residual rate of less than 0.5%,

Good: a wood piece residual rate of 0.5% or more and less than 1.5%,

Poor: a wood piece residual rate of 1.5% or more and less than 2.5%,

Bad: a wood piece residual rate of 2.5% or more.

(2) Evaluation Criteria of Yield

Excellent: a yield of 52.5% or more,

Good: a yield of less than 52.5% and 52.0% or more,

Poor: a yield of less than 52.0% and 51.5% or more,

Bad: a yield of less than 51.5%.

(3) Evaluation Criteria of Kappa Number

Excellent: a Kappa number of less than 29.0,

Good: a Kappa number of 29.0 or more and less than 29.5,

Poor: a Kappa number of 29.5 or more and less than 30.0,

Bad: a Kappa number of 30.0 or more.

Examples 24 and 25, and Comparative Examples 27 to 31, Nadelholz, Polysulfide Method, Digestion Accelerator Including Amine Compound

The same method as in Example 23 was used to perform digestion and evaluation in each of Examples 24 and 25, and Comparative Examples 27 to 31 except that the types, the amounts of use, and the mass ratios of the quaternary ammonium compound and the amine compound were changed as shown in Table 6 and Table 7. In Comparative Example 27, digestion was performed without any digestion accelerator, and evaluation was made. Each evaluation was made according to the same evaluation criteria as the evaluation criteria in Example 23.

	Digestion accelerator

		Content (%
	Mass ratio	by mass) of
	of quaternary	digestion	Evaluation item

	Quaternary		ammonium	accelerator	Wood piece
	ammonium	Amine	compound/amine	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

23	E1	A4	100/1	0.03	0.4	52.6	28.6
					Excellent	Excellent	Excellent
24	E3	A3	100/1	0.03	0.3	52.8	28.4
					Excellent	Excellent	Excellent
25	E8	A2	100/1	0.03	0.8	52.4	29.3
					Good	Good	Good

	Digestion accelerator

		Content (%
	Mass ratio	by mass) of
	of quaternary	digestion	Evaluation item

	Quaternary		ammonium	accelerator	Wood piece
Comparative	ammonium	Amine	compound/amine	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

27	—	—	0/0	0	3.1	51.4	30.5
					Bad	Bad	Bad
28	E1	—	100/0	0.03	0.4	51.8	29.9
					Excellent	Poor	Poor
29	E3	—	100/0	0.03	0.4	51.9	29.9
					Excellent	Poor	Poor
30	—	A2	0/100	0.03	3.1	51.6	30.5
					Bad	Poor	Bad
31	—	A3	0/100	0.03	3.0	51.6	30.5
					Bad	Poor	Bad

Example 26, Laubholz, Soda Method, Digestion Accelerator Including Amine Compound

Laubholz as a wood chip, and a digestion accelerator including a quaternary ammonium compound and an amine compound were used to perform digestion by a soda method.

In Example 26, the quaternary ammonium compound was E1, the amine compound was A4, the wood chip was Laubholz, the alkaline main agent was only sodium hydroxide, and the amounts thereof added were changed. In addition, preparation was made so that the contents of the quaternary ammonium compound E1 (pure content) and the amine compound A4 (pure content) relative to Laubholz (wood chip) were each 0.06% by mass and the mass ratio between the quaternary ammonium compound E1 (pure content) and the amine compound A4 (pure content) was 100:1. Specifically, 29.7 mg of the quaternary ammonium compound E1 (pure content) and 0.3 mg of the amine compound A4 (pure content), with respect to 50.0 g of Laubholz (wood chip), were placed in a vessel, and dissolved in water, and thus the digestion accelerator to be used in Example 26 was obtained. Other procedure was substantially the same as the procedure in Example 1 to perform digestion and evaluation. In Example 26, 16.2 g of sodium hydroxide was added to the digestion liquid.

The evaluation criteria in the case of use of a soda method and Laubholz were as follows.

(1) Evaluation Criteria of Wood Piece Residual Rate

Excellent: a wood piece residual rate of less than 1.0%,

Good: a wood piece residual rate of 1.0% or more and less than 1.5%,

Poor: a wood piece residual rate of 1.5% or more and less than 2.5%,

Bad: a wood piece residual rate of 2.5% or more.

(2) Evaluation Criteria of Yield

Excellent: a yield of 52.0% or more,

Good: a yield of less than 52.0% and 51.5% or more,

Poor: a yield of less than 51.5% and 51.0% or more,

Bad: a yield of less than 51.0%.

(3) Evaluation Criteria of Kappa Number

Excellent: a Kappa number of less than 18.5,

Good: a Kappa number of 18.5 or more and less than 19.0,

Poor: a Kappa number of 19.0 or more and less than 19.5,

Bad: a Kappa number of 19.5 or more.

Examples 27 and 28, and Comparative Examples 32 to 36, Laubholz, Soda Method, Digestion Accelerator Including Amine Compound

The same method as in Example 26 was used to perform digestion and evaluation in each of Examples 27 and 28 and Comparative Examples 32 to 36 except that the types, the amounts of use, and the mass ratios of the quaternary ammonium compound and the amine compound were changed as shown in Table 8 and Table 9, and the evaluation was made according to the same evaluation criteria as the evaluation criteria in Example 26. In Comparative Example 32, digestion was performed without any digestion accelerator, and evaluation was made.

	Digestion accelerator

		Content (%
	Mass ratio	by mass) of
	of quaternary	digestion	Evaluation item

	Quaternary		ammonium	accelerator	Wood piece
	ammonium	Amine	compound/amine	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

26	E1	A4	100/1	0.06	0.8	52.1	18.6
					Excellent	Excellent	Good
27	E4	A3	100/1	0.06	0.7	52.2	18.6
					Excellent	Excellent	Good
28	E8	A1	100/1	0.06	1.3	51.8	18.9
					Good	Good	Good

	Digestion accelerator

		Content (%
	Mass ratio	by mass) of
	of quaternary	digestion	Evaluation item

	Quaternary		ammonium	accelerator	Wood piece
Comparative	ammonium	Amine	compound/amine	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

32	—	—	0/0	0	3.8	50.9	20.0
					Bad	Bad	Bad
33	E1	—	100/0	0.06	0.9	51.2	19.3
					Excellent	Poor	Poor
34	E4	—	100/0	0.06	0.8	51.2	19.2
					Excellent	Poor	Poor
35	—	A4	0/100	0.06	3.5	50.9	19.9
					Bad	Bad	Bad
36	—	A3	0/100	0.06	3.6	50.9	19.8
					Bad	Bad	Bad

Example 29, Laubholz, Kraft Method, Digestion Accelerator Including Sulfur-Containing Compound

Laubholz as a wood chip, and a digestion accelerator including a quaternary ammonium compound and a sulfur-containing compound were used to perform digestion by a kraft method. Laubholz was subjected to a stainless sieve having an aperture of 710 μm, and Laubholz remaining on the sieve was dried at 60° C. for 24 hours. The digestion accelerator was prepared so that the contents of the quaternary ammonium compound E3 (pure content) and the amine compound B1 (pure content) relative to Laubholz (wood chip) were each 0.03% by mass and the mass ratio between the quaternary ammonium compound E3 (pure content) and the sulfur-containing compound B1 (pure content) was 6:1. Specifically, 12.86 mg of the quaternary ammonium compound E3 (pure content) and 2.14 mg of the sulfur-containing compound B1 (pure content), with respect to 50.0 g of Laubholz (wood chip), were placed in a vessel, and dissolved in distilled water, and thus the digestion accelerator to be used in Example 29 was obtained

Next, 6.9 g (3.2 g in terms of pure content of single sodium sulfide) of a sodium sulfide pentahydrate salt and 11.2 g of sodium hydroxide were added to a beaker and distilled water was added thereto so that the total mass was 145 g, thereby obtaining an alkaline aqueous solution. The digestion accelerator prepared in advance was added to this aqueous solution, distilled water was added thereto so that the total mass was 150 g, and the resultant was stirred to obtain a digestion liquid.

Into a pot (MINI COLOR, manufactured by Texam Giken Co., Ltd.), 50.0 g of Laubholz and 150 g of the digestion liquid prepared were placed, and digestion was performed at 150° C. for 50 minutes.

After digestion, the wood piece residual rate, the yield, and the Kappa number were evaluated with respect to Example 29, and the results were shown in Table 10. The wood piece residual rate, the yield, and the Kappa number in Example 29 were evaluated according to the same evaluation criteria as the evaluation criteria in Example 1.

Examples 30 to 44 and Comparative Examples 37 to 44, Laubholz, Kraft Method, Digestion Accelerator Including Sulfur-Containing Compound

The same method as in Example 29 was used to perform digestion and evaluation in each of Examples 30 to 44 and Comparative Examples 37 to 44 except that the types, the amounts of use, and the mass ratios of the quaternary ammonium compound and the sulfur-containing compound were changed as shown in Table 10 and Table 11.

The digestion accelerator of Comparative Example 44 was obtained by separately using the quaternary ammonium compound and the sulfur compound, unlike the digestion accelerator of Example 29. Specifically, only 12.86 mg of the quaternary ammonium compound E3 (pure content) was placed in a vessel, and dissolved in distilled water, and thus the digestion accelerator to be used in Comparative Example 44 was obtained. Next, 2.14 mg of the sulfur-containing compound B1 (pure content) not used in preparation of the digestion accelerator, 6.9 g (3.2 g in terms of pure content of single sodium sulfide) of the sodium sulfide pentahydrate salt, and 11.2 g of sodium hydroxide were added to a beaker, distilled water was added so that the total mass was 145 g, and thus an alkaline aqueous solution was obtained. The digestion accelerator prepared in advance was added to this aqueous solution, distilled water was added thereto so that the total mass was 150 g, and the resultant was stirred to obtain a digestion liquid. Into a pot (MIN COLOR, manufactured by Texam Giken Co., Ltd.) were placed 50.0 g of Laubholz and 150 g of the digestion liquid, and digestion was performed at 150° C. for 50 minutes. As described above, Comparative Example 44 was different from Example 29 in that the sulfur-containing compound B1 (pure content) was not used in preparation of the digestion accelerator and was used in preparation of the digestion liquid. The evaluation criteria were the same as the evaluation criteria in Example 1, as in Example 29.

	Digestion accelerator

	Mass ratio	Content (%
	of quaternary	by mass) of
	ammonium	digestion	Evaluation item

	Quaternary	Sulfur-	compound/sulfur-	accelerator	Wood piece
	ammonium	containing	containing	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

29	E3	B1	6/1	0.03	0.4	52.3	15.2
					Excellent	Good	Excellent
30	E3	B3	6/1	0.03	0.4	52.2	15.3
					Excellent	Good	Excellent
31	E3	B4	6/1	0.03	0.4	52.1	15.3
					Excellent	Good	Excellent
32	E3	B5	6/1	0.03	0.4	52.2	15.3
					Excellent	Good	Excellent
33	E3	B7	6/1	0.03	0.4	52.0	15.4
					Excellent	Good	Excellent
34	E1	B2	6/1	0.03	0.5	52.2	15.3
					Good	Good	Excellent
35	E2	B3	6/1	0.03	0.6	52.3	15.3
					Good	Good	Excellent
36	E4	B5	6/1	0.03	0.4	52.2	15.3
					Excellent	Good	Excellent
37	E5	B1	6/1	0.03	0.7	52.2	15.4
					Good	Good	Excellent
38	E6	B3	6/1	0.03	0.8	52.0	15.5
					Good	Good	Good
39	E7	B4	6/1	0.03	1.0	52.0	15.6
					Good	Good	Good
40	E8	B6	6/1	0.03	1.1	52.0	15.7
					Good	Good	Good
41	E3	B1	15/1	0.03	0.4	52.2	15.3
					Excellent	Good	Excellent
42	E3	B1	2/1	0.03	0.4	52.2	15.3
					Excellent	Good	Excellent
43	E3	B1	6/1	0.1	0.2	52.5	15.1
					Excellent	Excellent	Excellent
44	E3	B1	6/1	0.01	1.4	52.0	15.7
					Good	Good	Good

	Digestion accelerator

	Mass ratio	Content (%
	of quaternary	by mass) of
	ammonium	digestion	Evaluation item

	Quaternary	Sulfur-	compound/sulfur-	accelerator	Wood piece
Comparative	ammonium	containing	containing	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

37	—	B1	0/1	0.03	3.0	51.2	16.4
					Bad	Bad	Poor
38	—	B3	0/1	0.03	2.9	51.1	16.5
					Bad	Bad	Bad
39	—	B4	0/1	0.03	3.0	51.1	16.5
					Bad	Bad	Bad
40	—	B5	0/1	0.03	3.0	51.0	16.5
					Bad	Bad	Bad
41	—	B7	0/1	0.03	2.9	51.1	16.5
					Bad	Bad	Bad
42	e10	B1	6/1	0.03	1.9	51.3	16.2
					Poor	Bad	Poor
43	E3	b8	6/1	0.03	0.4	51.3	16.2
					Excellent	Bad	Poor
44	E3	B1	6/1	0.03	0.4	51.3	16.2
					Excellent	Bad	Poor

Example 45, Nadelholz, Kraft Method, Digestion Accelerator Including Sulfur-Containing Compound

Nadelholz as a wood chip, and a digestion accelerator including a quaternary ammonium compound and a sulfur-containing compound were used to perform digestion by a kraft method.

In Example 45, substantially the same procedure as in Example 18 was performed for digestion and evaluation except that the quaternary ammonium compound was E2, the sulfur-containing compound was B1, the wood chip was Nadelholz, and the amounts of the sodium sulfide pentahydrate salt and the sodium hydroxide added were changed. In Example 45, 7.75 g (3.6 g in terms of pure content of single sodium sulfide) of the sodium sulfide pentahydrate salt, and 12.6 g of sodium hydroxide were added to the digestion liquid. The wood piece residual rate, the yield, and the Kappa number in Example 45 were evaluated according to the same evaluation criteria as the evaluation criteria in Example 18.

Examples 46 to 49 and Comparative Examples 45 to 50, Nadelholz, Kraft Method, Digestion Accelerator Including Sulfur-Containing Compound

The same method as in Example 45 was used to perform digestion and evaluation in each of Examples 46 to 49 and Comparative Examples 45 to 50 except that the types, the amounts of use, and the mass ratios of the quaternary ammonium compound and the sulfur-containing compound were changed as shown in Table 12 and Table 13. In Comparative Example 50, the quaternary ammonium compound and the sulfur compound were separately used. This Comparative Example was different from Example 46 in that the sulfur-containing compound B2 (pure content) was not used in preparation of the digestion accelerator and the sulfur-containing compound B2 (pure content) was used in preparation of the digestion liquid.

	Digestion accelerator

	Mass ratio	Content (%
	of quaternary	by mass) of
	ammonium	digestion	Evaluation item

	Quaternary	Sulfur-	compound/sulfur-	accelerator	Wood piece
	ammonium	containing	containing	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

45	E2	B1	6/1	0.03	0.6	52.6	28.9
					Good	Excellent	Excellent
46	E3	B2	6/1	0.03	0.4	52.7	28.7
					Excellent	Excellent	Excellent
47	E4	B5	6/1	0.03	0.4	52.6	28.8
					Excellent	Excellent	Excellent
48	E6	B4	6/1	0.03	0.6	52.4	29.1
					Good	Good	Good
49	E8	B7	6/1	0.03	1.0	52.3	29.3
					Good	Good	Good

	Digestion accelerator

	Mass ratio	Content (%
	of quaternary	by mass) of
	ammonium	digestion	Evaluation item

	Quaternary	Sulfur-	compound/sulfur-	accelerator	Wood piece
Comparative	ammonium	containing	containing	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

45	—	B1	0/1	0.03	3.3	51.4	30.7
					Bad	Bad	Good
46	—	B5	0/1	0.03	3.4	51.4	30.8
					Bad	Bad	Excellent
47	e9	B1	6/1	0.03	1.8	51.8	30.1
					Poor	Poor	Poor
48	e10	B1	6/1	0.03	1.7	51.7	30.0
					Poor	Poor	Poor
49	E3	b8	6/1	0.03	0.6	51.6	30.0
					Good	Poor	Poor
50	E3	B2	6/1	0.03	0.4	51.6	30.0
					Excellent	Poor	Good

Example 50, Nadelholz, Polysulfide Method, Digestion Accelerator Including Sulfur-Containing Compound

Nadelholz as a wood chip, and a digestion accelerator including a quaternary ammonium compound and a sulfur-containing compound were used to perform digestion by a polysulfide method.

In Example 50, substantially the same procedure as in Example 23 was performed for digestion and evaluation except that the quaternary ammonium compound was E2, the sulfur-containing compound was B3, the wood chip was Nadelholz, the amounts of the sodium sulfide pentahydrate salt and the sodium hydroxide added were changed, and a sodium tetrasulfide solution (manufactured by NAGAO Co., Ltd.) was newly used. In Example 50, 6.2 g (2.88 g in terms of pure content of single sodium sulfide) of the sodium sulfide pentahydrate salt, 12.6 g of sodium hydroxide, and 2.4 g (0.72 g in terms of pure content of single sodium tetrasulfide) of the sodium tetrasulfide solution were added to the digestion liquid. The wood piece residual rate, the yield, and the Kappa number in Example 50 were evaluated according to the same evaluation criteria as the evaluation criteria in Example 23.

Examples 51 and 52, and Comparative Examples 51 to 55, Nadelholz, Polysulfide Method, Digestion Accelerator Including Sulfur-Containing Compound

The same method as in Example 50 was used to perform digestion and evaluation in each of Examples 51 and 52 and Comparative Examples 51 to 55 except that the types, the amounts of use, and the mass ratios of the quaternary ammonium compound and the sulfur-containing compound were changed as shown in Table 14 and Table 15. The wood piece residual rate, the yield, and the Kappa number were evaluated according to the same evaluation criteria as the evaluation criteria in Example 23.

The digestion accelerator of Comparative Example 55 was obtained by separately using the quaternary ammonium compound and the sulfur compound, unlike the digestion accelerator of Example 51. Specifically, only 12.86 mg of the quaternary ammonium compound E4 (pure content) was placed in a vessel, and dissolved in distilled water, and thus the digestion accelerator to be used in Comparative Example 55 was obtained. Next, 2.14 mg of the sulfur-containing compound B1 (pure content) not used in preparation of the digestion accelerator, 6.2 g (2.88 g in terms of pure content of single sodium sulfide) of the sodium sulfide pentahydrate salt, 12.6 g of sodium hydroxide, and 2.4 g (0.72 g in terms of pure content of single sodium tetrasulfide) of the sodium tetrasulfide solution were added to a beaker, distilled water was added so that the total mass was 145 g, and thus an alkaline aqueous solution was obtained. The digestion accelerator prepared in advance was added to this aqueous solution, distilled water was added thereto so that the total mass was 150 g, and the resultant was stirred to obtain a digestion liquid. Into a pot (MIN COLOR, manufactured by Texam Giken Co., Ltd.) were placed 50.0 g of Nadelholz and 150 g of the digestion liquid, and digestion was performed at 150° C. for 50 minutes. As described above, Comparative Example 45 was different from Example 51 in that the sulfur-containing compound B1 (pure content) was not used in preparation of the digestion accelerator, but used in preparation of the digestion liquid.

	Digestion accelerator

	Mass ratio	Content (%
	of quaternary	by mass) of
	ammonium	digestion	Evaluation item

	Quaternary	Sulfur-	compound/sulfur-	accelerator	Wood piece
	ammonium	containing	containing	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

50	E2	B3	6/1	0.03	0.3	52.6	28.6
					Excellent	Excellent	Excellent
51	E4	B1	6/1	0.03	0.3	52.7	28.4
					Excellent	Excellent	Excellent
52	E7	B6	6/1	0.03	0.8	52.3	29.4
					Good	Good	Good

	Digestion accelerator

	Mass ratio	Content (%
	of quaternary	by mass) of
	ammonium	digestion	Evaluation item

	Quaternary	Sulfur-	compound/sulfur-	accelerator	Wood piece
Comparative	ammonium	containing	containing	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

51	E2	—	6/1	0.03	0.4	51.9	30.0
					Excellent	Poor	Bad
52	E4	—	6/1	0.03	0.4	51.9	29.8
					Excellent	Poor	Poor
53	—	B1	6/1	0.03	3.1	51.6	30.5
					Bad	Bad	Bad
54	—	B3	6/1	0.03	3.1	51.6	30.4
					Bad	Poor	Bad
55	E4	B1	6/1	0.03	0.4	51.8	29.8
					Good	Poor	Poor

Example 53, Laubholz, Soda Method, Digestion Accelerator Including Sulfur-Containing Compound

Laubholz as a wood chip, and a digestion accelerator including a quaternary ammonium compound and a sulfur-containing compound were used to perform digestion by a soda method. In Example 53, the quaternary ammonium compound was E2, the sulfur-containing compound was B4, the wood chip was Laubholz, the alkaline main agent was only sodium hydroxide, and the amounts thereof added were changed. In addition, preparation was made so that the contents of the quaternary ammonium compound E2 (pure content) and the sulfur-containing compound B4 (pure content) relative to Laubholz (wood chip) were each 0.06% by mass and the mass ratio between the quaternary ammonium compound E2 (pure content) and the sulfur-containing compound B4 (pure content) was 6:1. Specifically, 25.71 mg of the quaternary ammonium compound E2 (pure content) and 4.29 mg of the sulfur-containing compound B4 (pure content), with respect to 50.0 g of Laubholz (wood chip), were placed in a vessel, and dissolved in distilled water, and thus the digestion accelerator to be used in Example 53 was obtained. Other procedure was substantially the same as the procedure in Example 26 to perform digestion and evaluation. Here, 16.2 g of sodium hydroxide was added to the digestion liquid. The wood piece residual rate, the yield, and the Kappa number were evaluated according to the same evaluation criteria as the evaluation criteria in Example 26.

Examples 54 and 55, and Comparative Examples 56 to 61, Laubholz, Soda Method, Digestion Accelerator Including Sulfur-Containing Compound

The same method as in Example 53 was used to perform digestion and evaluation in each of Examples 54 and 55 and Comparative Examples 56 to 61 except that the types, the amounts of use, and the mass ratios of the quaternary ammonium compound and the sulfur-containing compound a were changed as shown in Table 16 and Table 17. In Comparative Example 61, the quaternary ammonium compound and the sulfur compound were separately used. This Comparative Example was different from Example 54 in that the sulfur-containing compound B2 (pure content) was not used in preparation of the digestion accelerator and the sulfur-containing compound B2 (pure content) was used in preparation of the digestion liquid. The wood piece residual rate, the yield, and the Kappa number were evaluated according to the same evaluation criteria as the evaluation criteria in Example 26.

	Digestion accelerator

	Mass ratio	Content (%
	of quaternary	by mass) of
	ammonium	digestion	Evaluation item

	Quaternary	Sulfur-	compound/sulfur-	accelerator	Wood piece
	ammonium	containing	containing	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

53	E2	B4	6/1	0.06	0.9	52.1	18.6
					Excellent	Excellent	Good
54	E3	B2	6/1	0.06	0.7	52.0	18.4
					Excellent	Excellent	Excellent
55	E7	B2	6/1	0.06	1.4	51.5	18.9
					Good	Good	Good

	Digestion accelerator

	Mass ratio	Content (%
	of quaternary	by mass) of
	ammonium	digestion	Evaluation item

	Quaternary	Sulfur-	compound/sulfur-	accelerator	Wood piece
Comparative	ammonium	containing	containing	relative to	residual	Yield	Kappa
Example	compound	compound	compound	wood chip	rate (%)	(%)	number

56	E2	—	—	0.06	0.9	51.1	19.4
					Excellent	Poor	Poor
57	E3	—	—	0.06	0.8	51.2	19.3
					Excellent	Poor	Poor
58	—	B2	—	0.06	3.9	50.6	19.9
					Bad	Bad	Bad
59	—	B4	—	0.06	3.9	50.7	19.8
					Bad	Bad	Bad
60	E3	B2	6/1	0.06	0.9	51.2	19.3
					Excellent	Poor	Poor
61	E3	B2	6/1	0.06	0.9	51.3	19.3
					Excellent	Poor	Good

It was found that the digestion accelerators of Examples 1 to 55 each exhibited favorable wood piece residual rate, yield, and Kappa number in digestion by a kraft method, digestion by a polysulfide method, and digestion by a soda method.

As described above, the digestion accelerator of the present disclosure can efficiently digest a material including lignocellulose.

(Supplementary Notes)

(Supplementary Note 1)

A digestion accelerator including:

• • a quaternary ammonium compound represented by formula (1); and
  • at least one amine compound selected from the group consisting of a primary monoamine represented by formula (2), a secondary monoamine represented by formula (3), and a tertiary monoamine represented by formula (4),

• • wherein, in formula (1), R¹ is an alkyl group having 8 to 22 carbon atoms, a hydroxyalkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, or a hydroxyalkenyl group having 8 to 22 carbon atoms,
  • R² is an alkyl group having 1 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group,
  • R³ and R⁴ are each independently an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, an aryl group, a benzyl group optionally having an alkyl group having 1 to 4 carbon atoms, a phenethyl group optionally having an alkyl group having 1 to 4 carbon atoms, a glycidyl group, or an (A¹O)_mY group,
  • N represents a nitrogen atom,
  • X^p− represents a counterion, and is an inorganic anion or an organic anion, and p represents a valence of an ion,
  • A¹O is an alkyleneoxy group having 2 to 4 carbon atoms, and Y is a hydrogen atom or an acyl group, and
  • n is an integer of 1 to 15 and m is an integer of 1 to 15;

• • in formula (2), R⁵ is an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A²O)_kZ group, A²O is an alkyleneoxy group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and k is an integer of 1 to 6;

• • in formula (3), R⁶ and R⁷ are each independently an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A³O)_rZ group, A³O is an alkyleneoxy group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and r is an integer of 1 to 12; and

• • in formula (4), R⁸ and R⁹ are each independently an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A⁴O)_tZ group, A⁴O is an alkyleneoxy group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and t is an integer of 1 to 12, and
  • R¹⁰ is an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, or an (A⁵O)_uZ group, A⁵O is an alkyleneoxy group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and u is an integer of 1 to 12.

(Supplementary Note 2)

The digestion accelerator according to Supplementary Note 1, wherein a mass ratio between the quaternary ammonium compound and the amine compound is 5:1 to 10000:1.

(Supplementary Note 3)

A digestion accelerator including:

• • a quaternary ammonium compound represented by formula (1); and
  • a sulfur-containing compound that generates a sulfide ion, a polysulfide ion, or a hydrogen sulfide ion in the presence of the quaternary ammonium compound,

• • wherein, in formula (1), R¹ is an alkyl group having 8 to 22 carbon atoms, a hydroxyalkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, or a hydroxyalkenyl group having 8 to 22 carbon atoms,
  • R² is an alkyl group having 1 to 22 carbon atoms, a hydroxyalkyl group having 1 to 22 carbon atoms, an alkenyl group having 2 to 22 carbon atoms, a hydroxyalkenyl group having 2 to 22 carbon atoms, or an (A¹O)_nY group,
  • R³ and R⁴ are each independently an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydroxyalkenyl group having 2 to 4 carbon atoms, an aryl group, a benzyl group optionally having an alkyl group having 1 to 4 carbon atoms, a phenethyl group optionally having an alkyl group having 1 to 4 carbon atoms, a glycidyl group, or an (A¹O)_mY group,
  • N represents a nitrogen atom,
  • X^p− represents a counterion, and is an inorganic anion or an organic anion, and p represents a valence of an ion,
  • A¹O is an alkyleneoxy group having 2 to 4 carbon atoms, and Y is a hydrogen atom or an acyl group, and
  • n is an integer of 1 to 15 and m is an integer of 1 to 15.

(Supplementary Note 4)

The digestion accelerator according to Supplementary Note 3, wherein the sulfur-containing compound includes at least one compound selected from the group consisting of thiosulfate, hydrogen thiosulfate, sulfite, hydrogen sulfite, disulfite, dithionite, dithionate, disulfate, peroxosulfate, peroxodisulfate, and polythionate.

(Supplementary Note 5)

The digestion accelerator according to Supplementary Note 4, wherein a mass ratio between the quaternary ammonium compound and the sulfur-containing compound is 1:2 to 100:1.

(Supplementary Note 6)

A method for producing pulp, the method including a digestion step of adding at least one main agent selected from the group consisting of an alkaline main agent and a sulfite-based main agent, and a digestion accelerator, to digest a material including lignocellulose, wherein

• • the digestion accelerator is the digestion accelerator according to any of Supplementary Note 1 to Supplementary Note 5.

(Supplementary Note 7)

The method for producing pulp according to Supplementary Note 6, wherein a content of the digestion accelerator is 0.001% by mass to 1.0% by mass relative to the material including the lignocellulose.

The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled.

This application claims the benefit of Japanese Patent Application No. 2022-106468, filed on Jun. 30, 2022, the entire disclosure of which is incorporated by reference herein.