COMPOSITIONS AND METHODS FOR THE REMOVAL OF SCALE BUILD-UP IN PULP AND PAPER PROCESS

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 63/714,140, filed 31 Oct. 2024, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to compositions and methods for on-the-run or real-time removal of scale in pulp and paper processes, such as pulp digesters, evaporators, liquor heaters, etc. . . . More particularly, the composition includes one or more chelating ligands, one or more copolymers, and one or more surfactants. The composition can be added continuously and in real-time to the black liquor in pulping and paper processes to remove scale, without the need to shut down the process.

BACKGROUND

Scaling formation arises primarily from the presence of dissolved inorganic salts in the aqueous system that exists under supersaturation conditions of the process. The salts are formed when water is heated or cooled in heat transfer equipment, such as digestors, heat exchangers, condensers, evaporators, cooling towers, boilers, and pipe walls. Changes in temperature or pH lead to scaling and fouling via the accumulation of undesired solid materials at interfaces. The accumulation of scale on heated surfaces causes the heat transfer coefficient to decline with time and will eventually, under heavy fouling, cause production rates to be unmet. Ultimately, the only option is often to shut down the process and perform a cleanup. This requires a shut down in production as well as use of corrosive acids and chelating agents. The economic loss due to fouling is one of the biggest problems in all industries dealing with heat transfer equipment. Scaling is responsible for equipment failures, production losses, costly repair, higher operating costs, and maintenance shutdowns.

The Kraft pulping process is one of the major pulping processes in the pulp and paper industry. Spent liquor resulting from the kraft pulping process (black liquor or “BL”) contains various organic materials as well as inorganic salts, the deposition of which detracts from an efficient chemical recovery cycle. Inorganic pulping chemicals and energy are recovered by incinerating BL in a recovery boiler. For an efficient combustion in the recovery furnace, BL coming from the pulp digesters with relatively low solids concentration has to be evaporated and concentrated to at least 60% solids, typically in a multistage process (i.e., a multi-effect evaporator).

Kraft pulp mill evaporator systems can be the bottleneck in chemical recovery limited mills. Scaling from calcium compounds such as calcium carbonate, calcium silicate, calcium sulfate, calcium oxalate, etc., or composite scales mainly composed of calcium compounds generally cause issues and the reason for shut-downs and scale removal.

Calcium salts, as well as sodium salts, are heavily loaded in black liquor as it is concentrated by evaporation up to 50+% in the evaporator train before transfer to a crystallizer. These salts can crystallize together in varying proportions to give scales of different hardness and solubility. Although some salts are water-soluble, others are not. Calcium salts in particular, have low water solubility, and extreme conditions in pulp mills (high temperature, pressure and pH) accelerates their formation and deposition on surfaces, causing issues with heat transfer, flow rate, and process efficiency. The maintenance of the digestor or evaporator has to be performed offline and generally requires the entire system needs to be shut down, sometimes for days, for a proper clean-up of the scale.

This requires the production of pulp to be decreased resulting in a decrease in production and thus loss in profits.

To this point, steps have been taken to prevent scaling, e.g., a number of scale inhibitors are often employed in the field to prevent, delay, inhibit or otherwise control the scaling process but not the real-time removal of scale.

However, despite the application of inhibitors, scales still form, causing a need for scheduled shut downs to clean them (via hydroblasting, acid washing etc). Even with scheduled shut downs, scaling can be formed prematurely, before the shutdown period. When this happens mills have no options other than to do an unscheduled shut down or continue operations despite the buildup of scale. Both of these options result in a significant loss of production, efficiency and profit. Accordingly, it is desirable to develop a product that can on a continuous, real-time, and on-the-run basis, actively remove the buildup of scale.

Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

Provided are scale removing compositions for the “real-time” or “on-the-run” removal of scale build-up, such as from calcium carbonates and oxalates, on surfaces in contact with the black liquor in pulping and paper processes. The composition comprises one or more chelating ligands, one or more polymers and/or copolymers, and one or more surfactants.

Also, provided is a method for the real-time or on-the-run removal of scale build-up on surfaces in contact with the black liquor in pulping and paper processes on a continuous basis.

The method comprises adding to the black liquor of a pulp and paper process, a scale removing composition that includes one or more chelating ligands, one or more polymers and/or copolymers, and one or more surfactants.

Finally, provided is a method for the minimization of scale build-up on surfaces in contact with the aqueous system of pulping and papermaking processes on a continuous basis.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

FIG. 1, displays the performance of the developed formulation (hereafter called “New Composition”, when applied in real-time versus a simulated laboratory scale “EDTA dump” test.

FIG. 2, compares performance of “New Composition” to that of EDTA when both applied in real-time, to a batch MK-Digestor.

FIG. 3, depict dosage-response of “New Composition” indicating a linear dose-response rate.

FIG. 4, depict dosage-response of “New Composition” indicating a linear dose-response rate.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims.

Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 5%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. “About” can alternatively be understood as implying the exact value stated. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

Provided are compositions and methods for the removal of scale build-up on surfaces in contact with the black liquor in a pulping and paper processes. In particular, the composition includes one or more chelating ligands, one or more polymers and/or copolymers, and one or more surfactants.

The composition was found to remove scaling, for example, scaling from calcium salts from surfaces in contact with the black liquor stream in pulping and paper processes, for example, the surfaces of digestors and evaporators. The composition can be added continuously to the black liquor of a pulp and paper processing plant thereby removing and preventing scale build-up in real-time.

In some aspects of the composition, the chelating ligand includes organophosphates containing 2 to 6 phosphonate groups. Other examples of suitable chelants generally include those with independent functionality as a scale inhibitor, and may comprise organic and inorganic phosphonates, organophosphonates, polyphosphates, organic chelants, polymeric chelants, and various combinations thereof. The chelant may provide activity and/or functionality to the composition apart from chelation and/or sequestration activity, and may be described in terms of such activity. For example, in some embodiments, the chelant component comprises one or more strong acids (e.g., phosphonic acids, phosphoric acids, phosphorous acids, phosphonate/phosphonic acids, etc.), aminopolycarboxylic acids, chelating agents, polymeric scale inhibitors (e.g., polymaleic acid), as well as various salts thereof and combinations thereof.

In aspects of the composition, the chelant comprises an organic phosphonate. Examples of suitable organic phosphonates include 2-phosphonobutane-1,2,4-tricarboxylic acid (“PBTC”), 1-hydroxyethane 1,1-diphosphonic acid (“HEDP”), bis(phosphonomethyl)aminotris(methylenephosphonic acid) (“ATMP”), bis(hexamethylene triamine penta (methylene phosphonic acid)) (“BHMTPMPA”), hexamethylenediaminetetra (methylene phosphonic acid) (“HMDTMPA”), diethylene triamine pentamethylene phosphonic acid (“DETPMPA”), and the like, as well as combinations thereof. In some embodiments, the organic phosphonate is 2-phosphonobutane-1,2,4-tricarboxylic acid (“PBTC”).

In some embodiments, the chelant comprises, alternatively is, an inorganic phosphate having the formula (I):

where Y is Na, K, H, or combinations thereof, and n is an integer having a value of at least 6.

With regard to inorganic phosphates of formula (I), Y is typically Na, and the integer n of has a value of at least 2, alternatively at least 6, alternatively at least 8, alternatively at least 9, alternatively at least 10, alternatively at lease 11, alternatively at least 12, or alternatively at least 21. In some embodiments, the integer n of formula (I) may have a value of from 2 to 30, alternatively from 6 to 30, alternatively from 8 to 30, or alternatively from 10 to 30.

Examples of inorganic phosphates of formula (I) suitable for use in the composition may include sodium hexametaphosphate (Na₈P₆O₁₉), sodium heptaphosphate (Na₉P₇O₂₂), sodium octaphosphate (Na₁₀P₈O₂₅), sodium nonaphosphate (Na₁₁P₉O₂₈), sodium decaphosphate (Na₁₂P₁₀O₃₁), sodium hendecaphosphate (Na₁₃P₁₁O₃₄), and sodium dodecaphosphate (Na₁₄P₁₂O₃₇), and sodium henicosphosphate (Na₂₃P₂₁O₆₄). In certain embodiments, the inorganic phosphate of formula (I) includes sodium dodecaphosphate, where n of formula (I) is an integer having a value of 12. In other embodiments, the inorganic phosphate of formula (I) includes sodium henicosphosphate, where n is an integer having a value of 21. Additional examples of inorganic phosphates include tetrasodium pyrophosphate (Na₄P₂O₇) (“TSPP”), sodium triphosphate (Na₅P₃O₁₀) (“STPP”), sodium trimetaphosphate (NaPO₃)₃(“STMP”), and combinations thereof.

In some embodiments, the composition comprises one or more additional scale inhibitors selected from polymeric scale inhibitors, such as polycarboxylic aids, salts of acrylamido-methyl propane sulfonate/acrylic acid copolymer (AMPS/AA), polymaleic acid, phosphinated maleic copolymer (PHOS/MA), salts of acrylic acid/t-butylacrylamide/acrylamido-methyl propane sulfonate terpolymers (AA/tBAM/AMPS), polyaspartic acids, and the like, as well as combinations thereof.

In some aspects, the chelant component comprises one or more organic chelants (i.e., organic chelating compounds). Example of suitable chelating compounds include aminopolycarboxylates and aminopolycarboxylic acids (APCAs), such as iminodiacetic acid (IDA), N-(hydroxyethyl) ethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), as well as organophosphinic and organophosphonic compounds such as ethylenediaminetetramethylene-phosphonic acid (EDTMP), diethylene triaminepentamethylenephosphonic acid (DTPMP), nitrilotrimethylenephosphonic acid (NTMP), and also other classes of organic chelators such as gluconates, citrates, and the like, as well as combinations thereof.

In some embodiments, the chelant is, alternatively comprises, a green chelant, i.e., a chelating compound that is derived from a natural and/or renewable source and/or is readily biodegradable. Such compounds may fall within the specific examples listed above, or may be described in independent groupings based on base functionality. For example, green chelant examples typically include various APCAs, derivatives of glutamate, amino acids, etc., as well as combinations thereof. Specific examples include N-2-acetamidoiminodiacetic acid (ADA), ethylenediglutamic acid (EDGA), ethylenediamine dimalonic acid (EDDM), N,N-bis(carboxymethyl)-L-glutamic acid tetrasodium salt (GLDA), iminodisuccinic acid (IDSA), ethylenediamine disuccinic acid (EDDS), methyl glycine diacetic acid trisodium salt (MGDA), N-bis[2-(1,2-dicarboxymethoxy)ethyl]glycine, N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid, and 2,6-pyridinedicarboxylic acid. It will be appreciated that such compounds may be utilized in the acidic and/or salt forms, which are readily available and known in the art.

In yet other aspects of the composition, the one or more chelating ligands is present in the composition in an amount of from about 25 wt. % to about 60 wt. %, or from about 35 wt. % to about 45 wt. % of the total composition.

In some aspects of the composition, the one or more polymers and/or copolymers can be chosen from sulfonated copolymers of acrylic acid, polyaspartate, maleic anhydride and acrylic acid copolymer (MA/AA), poly(isopropenylphosphonic) acid, polycarboxilic acid, polyhydroxyalkanoates, polyepoxysuccinic acid and combinations thereof.

In other aspects of the composition, wherein the one or more polymers and/or copolymers is present in the composition in an amount of from about 5 wt. % to about 30 wt. %, or from about 15 wt. % to about 20 wt. % of the total composition.

In yet other aspects of the composition, the one or more polymers and/or copolymers has a weight average molecular weight of from about 8000 to about 20000 g/mol, or from about 12000 to about 15000 g/mol.

In some aspects of the composition, the surfactant is chosen from a linear alkylbenzene sulfonic acid, polyethylene glycol, alcohol ethoxylates, and combinations thereof.

In other aspects of the composition, the surfactant is present in the composition in an amount of from about 1 wt. % to about 10 wt. %, or from about 3 wt. % to about 6 wt. % of the total composition.

In yet other aspects of the composition, the one or more surfactants are emulsified prior to combining with the chelating ligand and polymer and/or copolymer.

In yet other aspects of the composition, the composition further comprises additional additives chosen from amino acids, tannins, nanoparticles, dispersants, and combinations thereof.

Also provided is a method for the removal of scale build-up on surfaces in contact with the black liquor of a pulp and paper process, the method comprising: adding to the pulp and paper process a scale removing composition that includes a chelating ligand, a copolymer having chelating properties, and a surfactant.

In some aspects of the method, the scale removing composition is present in the aqueous system in an amount of from about 50 ppm to about 400, or from about 100 ppm to about 200 ppm.

In some aspects of the method, the scale removing composition is added continuously or in real-time to the black liquor of the pulp and paper process.

In some aspects of the method, the scale removing composition is added to the black liquor of the pulp and paper process at a digestor, evaporator, or a combination thereof.

In some aspects of the method, the scale comprises calcium carbonate and/or calcium oxalate.

Also provided, is a method for the minimization of scale build-up on surfaces in contact with the aqueous systems in a pulp and paper making process. The method includes adding a composition that includes one or more chelating ligands, one or more copolymers, and one or more surfactants to the aqueous system of the pulp and paper process.

In some aspects of the method, the surfaces in contact with the aqueous system are surfaces of heat transfer equipment, digestors, heat exchangers, condensers, evaporators, cooling towers, boilers, and pipe walls.

In other aspects of the method, the composition is present in the aqueous system in an amount of from about 50 ppm to about 400, or from about 100 ppm to about 200 ppm of the aqueous system.

Although, such removal of scale is of particular importance in pulp and papermaking processes, it is envisioned that the formulation could be used in other applications where scale buildup is an issue, such as, in waste water and water treatment applications.

EXAMPLES

The examples below have been described with reference to a particular embodiment, those skilled in the art will understand that changes can be made and equivalent substitutions made for certain components without departing from the scope of the claims. Additionally, modifications may be made to adapt to specific conditions or materials without departing from the scope thereof. It is intended that the compositions and methods to not be limited to a particular embodiment disclosed but will include all embodiments falling with the scope of the claims.

Example 1

A method to measure removal of calcium carbonate scale and evaluate effectiveness of treatments was developed as outlined herein. A Parr bomb reactor was used to run tests on a real-time continuous basis using a pulp mill digester condition (160° C. and 100 pounds per square inch (psi)) and using a black liquor (18.98% solid, 7.99 g/L sulfidity and pH of 13.5) as the medium. A pre-weighed piece of 100% calcium carbonate crystal was used as a representation for the industrial scale.

A composition was prepared according to Table 1 below:

TABLE 1
Mass Removal of CaCO3
New Composition

Chemistry	Weight %

ethylenediamine tetra(methylene phosphonic acid) salt	55.40
Sulfonated polyacrylate	29.25
Linear alkylbenzene sulfonic acid	1.63
polyethylene glycol	1.25
C12-14 linear alcohol 7 EO	12.28
Biocide	0.20

The “New Composition” was compared with a composition using a 25 wt. % aqueous solution of ethylenediaminetetraacetic acid (EDTA) in a laboratory scale “chelant dump” test, i.e., pouring the EDTA composition (20-25 wt. %) at a pH of 11 to 12 on a pre-weighed piece of 100% CaCO₃ in a beaker and letting it sit for a specified amount of time, no circulation/stirring was used.

FIG. 1 compares results from the EDTA “chelant dump” treatment vs “continuous” treatment using the new scale removing composition for 8 hours. The amount of calcium carbonate removed from the pre-weighed piece of 100% calcium carbonate crystal was measured gravimetrically, using a scientific scale (0.001 g accuracy) and compared. The mass amount of CaCO₃ removed calculated using the following equation:

Mass ⁢ Removal ⁢ ( mg ) = Final ⁢ weight ⁢ ( mg ) - Initial ⁢ weight ⁢ ( mg ) .

Results can be found in Table 2 and FIG. 1.

TABLE 2
Comparison of Mass CaCO3 Removal.

	Test Method	CaCO3 Mass Removal (mg)

	EDTA “Chelant Dump”	48
	“Continuous Treatment”	75
	(New Composition)

Results indicate that the continuous treatment using the “New Composition” outperforms the formulations containing EDTA both in the EDTA “dump” test and in the continuous treatment of EDTA versus New Composition (via the M/K digester) described in Example 2. Since EDTA is only used in the field in the form of a “chelant dump” treatment, the data presented in Example 1 for EDTA is used as a benchmark for the “New Composition”.

Example 2

The “New Composition” and “EDTA composition” described in Example 1, were used in this example. The test would compare the efficacy of the two formulations in a 10 hour continuous trial using the M/K digester described below.

The following steps were used in this test. 1) the weight of a piece of calcium carbonate (CaCO₃) crystal was recorded (initial weight) and placed inside the MK digestor on a false bottom screen, 2) the M/K digestor was then filled with 1.6 L of black liquor for the medium, 3) the compositions comprising 5000 ppm actives were added to their respective digestors, 4) the experiments were run for 10 hours at 160° C. and 100 psi (black liquor recirculates through the system continuously), 5) after 10 hours, the piece of crystal was removed, gently washed and dried, and 7) the crystal mass removal was measured by subtracting the final weight of the crystal from the initial weight using the equation in Example 1. Results can be found in Table 3 below and FIG. 2, which shows the milligram mass removal of CaCO₃ at the end of the 10 hour treatment cycle.

TABLE 3
Mass CaCO3 Removal.

M/K Digester Test	CaCO3 Mass Removal (mg)

EDTA Composition	103
Continuous Treatment (New Composition)	780

EDTA performance peaks at pH of 12, which was used in the laboratory “dump” test to maximize efficiency of the benchmark. The application of EDTA composition on a continuous basis or on-the-run was found to be not practical in the field. This is confirmed by the underperformance of the EDTA composition in Example 2.

Although not to be bound by theory, the extreme operating conditions of a digester (high temperature, high pressure, high pH in form of black liquor medium) used in the M/K digester test, may be responsible for EDTA degradation and hence lack of performance. The EDTA was expected to perform very well in high alkalinity conditions, so the degradation could be attributed to extended exposure to high temperature and pressure. This degradation was not seen when using the “New Composition” and hence outperforms EDTA in the M/K digester test.

Example 3

The process and procedures used in Example 2, were used here. In these tests, the dose response of the “new” scale removal formulation was measured as described below. A piece of 100% calcium carbonate was weighed and put inside the reactor on a false bottom as described above. Each data point in Table 4 below, represents an individual batch experiment. The following steps were followed: 1) a magnetic stir bar was placed inside a Parr reactor; a false bottom was placed over the magnetic stir bar, 2) a pre-weighed piece of CaCO₃ crystal was placed on the false bottom in the reactor, 3) 100 milliliters (ml) of black liquor was added to the reactor, 4) the desired amount of the formulation (either 0, 100, 250, 500 or 1000 ppm) was added to the black liquor (active basis), 5) the reactor was closed and the contents stirred at 500 revolutions-per-minute (rpm), 6) the experiment was run for the desired amount of time (1, 2, 4 or 8 hours), and 7) a 25 ml sample of black liquor was taken, without shutting the digestor down, and filtered through a 25 micron filter and submitted for ICP analysis. The amount of calcium carbonate found in the sample was measured each hour via Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for 10 hours.

Sample preparation for ICP analysis were according to manufactures recommendations. In this case, the sample of black liquor was transferred to a test tube and an appropriate amount of 30% H₂O₂ was added to the black liquor sample and after 5 minutes an appropriate amount of HCl followed by HNO₃ was added to the sample, 3). The test tubes were capped, and the sample gently shaken. The samples were placed in the digestor at 85° C. for 60 minutes at which time the samples were removed from the digestor and allowed to cool down to room temperature. An appropriate amount of water was added to each test tube to reach a final desired volume. The total final mass of the tube and sample was determined, and the dilution factor (DF) calculated using the following equation:

D ⁢ F = ⁢ ( Final ⁢ mas ⁢ of ⁢ Tube ⁢ and ⁢ Sample ) - 
 ( Mass ⁢ of ⁢ Tube ) / ( Mass ⁢ of ⁢ Sample ) .

ICP results (in the form of soluble Ca⁺ levels in parts-per-million (ppm)) are shown in Table 4 and Table 5 below.

TABLE 4
Dosage Response of CaCO3 Removal

Dosage (ppm) →

0

100

250

500

1000

	Time (hr) ↓	Soluble Ca (ppm)

	1		69.85	63.95	103	108.33
	2	40	74.45	89.5	126.67	149.15
	4		56.9	66.25	76.8	100.55
	8		51.7	56.15	80.25	100.45

The new composition shows a linear dose-response rate which is evident in FIG. 3 and FIG. 4. This indicates a direct relationship between increasing dosage and increase in CaCO₃ mass removal. Maximum removal effect is observed at 2 hours for all dosages.

While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the present disclosure. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims.