METHOD OF PRODUCING FORMIC ACID

Description

TECHNICAL FIELD

This disclosure relates to methods of producing formic acid, more particularly to methods of producing formic acid using catalytic gas diffusion electrodes and ion-selective membranes.

BACKGROUND

Systems and methods exist for distillation of formic acid from water mixtures. Currently available methods do not adequately address certain impurities in the inlet formic acid and water feed.

These current methods have some limitations in ion loss and loss of anolyte during the process. Formate ion loss occurs via crossover of the membrane in an uncontrolled, undesired, and normally unexpected manner while undergoing acidification of potassium formate to formic acid in electrodialysis. This loss may reach as high as 25% of the total formate ion generation. This loss is unrecoverable if it happens in the anolyte stream.

The loss of formate in the anolyte during the electrodialysis process leads to increase in capacity of electrolyzers to generate sufficient formate to make up the loss of formate in the electrodialysis process, raising the costs of the process.

Current approaches to producing formic acid sometimes involve producing carbon monoxide (CO) gas, a highly poisonous gas that cannot be transported so it had to be generated where it is consumed. Carbon monoxide cannot be purchased as a feedstock, but it is the starting material for the production of formic acid. The generation of CO uses high levels of energy, which also makes the production of CO more expensive.

Many approaches manufacture formic acid in a one-step process from CO₂. These approaches generally require expensive and novel membrane materials. These approaches do not generate formic acid in very high concentrations. Some processes generate formate as an end product rather than formic acid. These processes involve custom membranes and have high energy requirements.

Examples of prior approaches include those discussed in U.S. Pat. No. 9,145,615, issued Sep. 29, 2015, (“the '615 patent”), and U.S. Pat. No. 10,253,420, issued Sep. 20, 2015, (“the '420 patent”). The '615 patent described a process of using a three-chamber electrochemical reactor of reducing carbon dioxide to formate and formic acid. The '420 patent described a process of reducing carbon dioxide to formate using a three-chamber electrochemical reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a process of producing formate and formic acid from carbon dioxide.

FIG. 2 shows a more detailed view of an embodiment of producing formate and formic acid from carbon dioxide.

FIGS. 3-6 show alternative embodiments of producing formate and formic acid from carbon dioxide.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments herein involve a process of producing an alkali formate and formic acid from carbon dioxide and hydrogen obtained from electrolysis by water by a first process to create alkali formate, and then a second process to produce formic acid from an alkali formate. Each of these processes may stand on their own or may be combined.

This discussion uses several terms that have specific meanings. The term “alkali formate” means a formate (HCOO—) with an added alkali metal molecule, such as potassium formate (HCOOK). While some of the discussion may specifically mention potassium formate, other alkali metals may also be used including lithium, sodium, rubidium, cesium, and francium. The term “alkali” as used here refers to alkali metals.

As used here, the term “electrolysis” means any form of electrochemical reduction that employs a conductive cathode in an electrochemical chamber that also contains a catholyte and an anolyte, even if not conventionally considered electrolysis.

The term “electrodialysis” as used here encompasses any ion selective membrane process that uses electric fields to move ions through semipermeable membranes, such as cation membranes, anion membranes, and bipolar membranes.

FIG. 1 shows an embodiment of a process of producing formic acid from carbon dioxide and water. As a first part of the overall process, an electrolyzer, meaning any device that can apply electricity to an electrically conductive cathode in a chamber having a catholyte, and an anolyte, produces alkali formate. Note that the formula for alkali formate is “HCOOA,” where A could be any alkali metal. The ion membrane process 14 takes the alkali formate and produces formic acid (HCOOH). A unique part of this process lies in the recycling of the alkali metal back to the electrodialysis process. This results from a matching of the input and output process chemistry and feeds the alkali back to the electrolyzer. This reduces the need for additional alkali materials, making the process both environmentally responsible and less expensive.

The formic acid produced from the membrane process 14 may then undergo an optional distillation process 16. While the distillation of formic acid from an aqueous solution is not novel, the distillation process here differs in that it removes impurities introduced in the previous two processes. These are not typically observed in conventional distillation of formic acid from water since the conventional process does not involve alkali formate salts.

The distillation process comprises an optional component of the overall process. The electrolysis process 12 and the ion selective membrane process 14 produce formic acid without distillation. Further, as mentioned above, the electrolysis process that produces formate, and the production of formic acid from formate, can each stand alone.

FIG. 2 shows a more detailed view of one of the options/variations or methods for the process of FIG. 1. The electrolyzer 12 receives CO₂, water, and electricity (shown in FIG. 1) as inputs. In addition, an inlet 20 provides an inlet solution of alkali formate such as potassium formate (HCOOK) and alkali bicarbonate such as potassium bicarbonate (KHCO₃) as a catholyte to the cathode (negative) electrode chamber 122. For ease of discussion and the chemical formulas, potassium will represent the alkali portion with the understanding that it could be any one of the alkali metals listed above. In an embodiment, the concentrations of the alkali formate have a range of 0 to 0.6 mol per liter. In an embodiment, the concentration of the alkali formate has a range of 4.0 to 6 mol per liter. In an embodiment, the concentration of the alkali bicarbonate has a range of 0.01 to 2 mol per liter. In an embodiment, the alkali bicarbonate may have a concentration of 0.1 to 0.6 mol per liter. An anolyte also resides in the anode chamber 124.

The inlet 20 receives CO₂ as an input and may receive water or remove water, but usually not at the same time. The process might have to remove water by a process such as membrane distillation to meet the composition requirements of the catholyte inlet to the cathode chamber. In another separate case, water might need to be added. This depends on both the composition needs of the catholyte in the electrolysis process and the electrodialysis process where the choice of membrane and operation conditions might change the water content in a way that addition or subtraction/removal of water may be required.

Applying electricity to the cathode in the presence of the catholyte such as alkali formate and alkali bicarbonate mentioned above causes the formation of alkali formate. The electrolyzer converts CO₂ into alkali formate. CO₂ crosses the gas diffusion electrode and meets the catholyte on the electrode where H+, CO₂, and two electrons react to form HCOO—. Side products like H₂ and CO and any excess CO₂ enter the catholyte chamber. The anolyte supplies the H+ ions used in the reaction at the cathode and passes through a membrane separating the anolyte from the catholyte. In addition to protons, based on the choice of anolyte solution composition, the anolyte may also supply alkali+, such as K+, ions to the catholyte to form HCOOK.

In the method described in FIG. 2, fresh anolyte is supplied at a proprietary fixed ratio of H+ to K+ ions, which may equal 1 or higher, all the way to K+ equaling 0 M, at the exit, shown as the beginning of the USED ANOLYTE arrow in FIG. 2, the point where H+ and alkali+ such as K+ need to be replenished to the inlet ratio. This avoids impact of concentration changes on the CO₂ reduction at the catholyte.—If the anolyte is not refreshed, the ratio of H+ to alkali+ continues to increase which might affect the performance of the cell. In one embodiment, this replenishment of K+ and neutralization of excess H+ is done in the first part of an electrodialysis or other ion selection membrane process, shown by the REFRESHED ANOLYTE arrow, discussed in more detail later. However, other forms of replenishment may be used to maintain the desired ratio. In a variation, an acidic anolyte contains only H+ and no K+ is employed. Here, since there is no K+ in the anolyte (fresh or used), no correction of K+ concentration is required.

The catholyte also has alkali bicarbonate (KHCO₃) both to regulate the pH of the catholyte and to supply K+ to the desired reaction. The concentration of KHCO₃ drops from an inlet value to a low value and needs to be refreshed. As discussed above, this may be accomplished by a following electrodialysis or other ion selection membrane process or could be done by providing KOH with CO₂ added to it. In embodiments where the catholyte returns to the cathode, the catholyte solution is at least partially comprised of recycled catholyte solution. As shown in FIG. 2, the alkali formate output from the electrolyzer may split between the following ion selective membrane process, and some of it being returned as part of the catholyte solution directly, and some being returned to the inlet with dilute KOH to then return as part of the catholyte solution.

As discussed above, the process could end here with the alkali formate output, besides that being recycled into the electrolyzer, making up the final product. This process produces a high-quality alkali formate of approximately 40 wt % of the output product. Similarly, the ion selective membrane process, the embodiments here use electrodialysis as an example of such a process, may also stand alone, receiving alkali formate as an input and producing formic acid at a high concentration when compared to other existing commercial approaches to producing formic acid. The following discussion described the alkali formate to alkali process in conjunction with the electrodialysis process to demonstrate how the two processes can interact to make a more efficient overall process, with the understanding that the two processes can stand alone.

FIG. 2 shows the ion selective membrane process, referred to here as electrodialysis for brevity, has two sets of cells. These cells may comprise a combination of cation membranes and bipolar membranes. The formate output and the used anolyte output from the formate process of the embodiments, or some other formate process, may enter the cells of the first set in a first direction and the cells of the second set in the opposite direction. The process may have two subparts.

In the first set of cells, 140, two different processes occur. In one process, the cells are generating KOH to be added to the catholyte and acidification of the formate ion to formic acid. The generation of KOH is occurring from recycling a more dilute KOH) such that it finally reaches the desired concentration of KOH, referred to here as concentrated KOH. The resulting concentrated KOH then splits such that part of the concentrated KOH is sent to the electrolyzer 12, and remainder added with water and recycled within the same electrodialysis unit to make more KOH at the desired concentration. The concentrated KOH is then reacted with CO₂ to form KHCO₃ and added into the catholyte recycle to the electrolyzer.

In the second set of cells, 142, a process of regeneration of anolyte occurs by the addition of K+ and OH− in the electrodialysis process. On the other side of the membrane, the formate ions are undergoing acidification ions to formic acid, which will be sent to the first set of cells by the arrow 144 between the sets. In this embodiment, the used anolyte has higher H+ and lower K+ than the inlet anolyte concentrations used in the electrolysis conversion of CO₂ to formate. The used anolyte is flown such that it received K+ and OH− ions to bring K+ to the same concentration as the inlet anolyte for the electrolysis process. In addition, OH− also neutralizes the excess H+ to help reduce the H+ concentration to the same H+ as needed for the inlet. The resulting solution returns as the REFRESHED ANOLYTE to the electrolyzer 12.

In one embodiment, the number of cells in set 1, 140, may comprise 15-20% of the total number of cells, and the cells in set 2 142 may comprise 80-85% of the total number.

The resulting output solution of formic acid, HCOOH, may have a concentration of 20-30 wt % in the overall aqueous solution, with the formic acid comprises more than 99% formic acid, and less than 1% alkali formate. The removal of the water to produce the formic acid may occur in several ways. In the embodiment of FIG. 2, a distillation process 16 distills the formic acid out of the water. The process may recycle the water removed, and the formic acid product may have a concentration in a range of 80 wt % to 99.9 wt % of the product solution, the rest being water. As discussed above, the distillation process is optional.

FIGS. 3-6 describe different ways in which the two processes may interact. The electrolysis process for the electrolyzer 12 will essentially be the same up to the point where it produces the alkali formate. For simplicity, the discussion of the parts of FIGS. 2-5 that have already been discussed will not be repeated with the understanding that all of the embodiments of FIGS. 3-6, as examples, will include those portions of the overall system.

FIG. 3 shows an embodiment of a relationship between a formate producing process and an ion selective membrane process used to generate formic acid. In this embodiment, the formate input into the ion selective membrane process splits between the first set of cells and the second set of cells. The formate input also cycles back to the electrolysis process if the electrolysis process is included. The anolyte refreshing and the catholyte recycling are the same as in FIG. 2. However, in this embodiment, the output of the second set of cells does not go to the first set of cells. Instead, the outputs of both sets of cells are mixed at the output, shown by arrow 146. While this particular embodiment uses three sets of cells, the system may only use one set, as shown in FIG. 6, or may use more than three sets.

FIG. 4 shows another embodiment of a relationship between a formate producing process and an ion selective membrane process used to generate formic acid. In this embodiment, the formate input splits, but only between the second set of cells 142 and the recycling path back to the catholyte. The second set of cells 142 sends its outputs of the refreshed anolyte, as in other embodiments, and to the first set of cells 140, shown by arrow 144. The formic acid output in this embodiment comes only from the first set of cells 140, shown by arrow 148.

FIG. 5 shows another embodiment of a relationship between a formate producing process and an ion selective membrane process used to generate formic acid. FIG. 5 shows the same relationship as FIG. 2, but without the distillation system. The alkali formate is split between the two sets of dialysis cells, with no return path of formate to the electrolysis process.

FIG. 6 shows another embodiment of a relationship between a formate producing process and an ion selective membrane process used to generate formic acid. In this embodiment, the ion selective membrane cells have only one set of cells 149. The alkali formate from the formate process splits and one portion of it enters one side of the cells, and the other portion enters the other sides of the cells. The formic acid is produced as a result. The two paths enter the same cells but go in opposite directions through the cells. In this embodiment, the anolyte is only comprised of H+ (as in dilute acid) and does not include any K+ like it did in all embodiments indicated in FIGS. 2-5. In this embodiment, no regeneration of anolyte is performed, but only the addition of KHCO₃ to catholyte (HCOOK stream split stream) is performed. The KOH is first formed in the HCOOK containing split stream in the electrodialysis cells, and then CO2 is added to create the right concentration of KHCO₃ and HCOOK to have this as the inlet catholyte in the electrolyzer. It should also be noted that water may be added or removed from this stream as indicated in FIG. 6 to attain the right inlet concentration.

Each of the above embodiments are within the scope of the invention as claimed. FIGS. 3 to 6 variations or pathways. Formate ion loss via uncontrolled/undesired/unexpected crossover across the membrane while undergoing acidification of alkali formate to formic acid in the ion selective membrane process is directly proportional to the ratio of formic acid to un-acidified formate. The higher this ratio is, the greater the loss. This loss may result from limitations of the membranes, and process requirements of different situations.

This loss may equal 25% of the total formate ion generation in the ion selective membrane process 14 in the above figures. This loss is unrecoverable if it happens in the anolyte stream, on other side of the formate/formic acid stream.

To avoid such a loss, the embodiments do partial acidification of the formate product stream to formic acid in a first part of the electrodialysis process, where the anolyte on the other side is being refreshed. At this point, the amount of formic acid is minimal, so formate ion crossover loss is minimal. In the second part of the process, the formic acid/formate is converted to all formic acid. At the same time on the other side, KOH is generated in the formate stream as part of the catholyte regeneration or recycling.

Any loss of formate ion via crossover will be reversible since this formate with additional KOH is recycled to the electrolyzer as the regenerated catholyte. This could reduce the 20-25% potential formate loss to less than 10%. Further tuning of the process chemistry can reduce this loss to less than 5%. using a process such as that shown by FIG. 5. Using the process such as that shown in FIG. 6 could eliminate the formate loss, meaning approximately 0%.

Another advantage lies in the above processes using robust, commercially available, “off the shelf,” membranes, including those in development No custom membranes specifically designed for this system are needed.

One embodiment comprises a method of producing formic acid, including: receiving, from a formate process, a stream comprised of an alkali formate having a wt % of less than 50 wt % of the stream and splitting the stream into two smaller streams; routing the at least two smaller streams to one or more sets of ion selective membrane cells; applying electricity to the one or more sets of ion selective membrane cells; producing, as a result of the applying of electricity, an output stream of formic acid having a wt % of at least 20 wt % from the one or more sets of ion selective membrane cells; and producing one or more return streams to be returned to the formate process.

One embodiment is the method above, wherein producing the one or more return streams comprises producing one or more streams comprised of catholyte and refreshed anolyte.

One embodiment is the method above, wherein producing the one or more return streams comprises producing a return stream comprised of refreshed catholyte and one or either adding or removing water from the return stream.

One embodiment is the method above, wherein receiving the stream comprised of alkali formate comprises receiving a stream of alkali formate in which the alkali is selected from the group consisting of: potassium, sodium, cesium, lithium, francium, and rubidium.

One embodiment is the method above, wherein routing the at least two smaller streams comprise routing one of the at least two smaller streams to a first set of ion selective membrane cells, and another of the at least two smaller streams to a second set of ion selective membrane cells.

One embodiment is the method above, wherein the first set of ion selective membrane cells comprises a percentage of all of the cells having a range of 15 to 20 percent, and the second set of ion selective membrane cells comprises a percentage of all of the cells having a range of 80 to 85 percent.

One embodiment is the method above, wherein producing one or more return streams comprises a return stream of catholyte produced by the first set of cells.

One embodiment is the method above, wherein producing one or more return streams comprises producing a stream of refreshed anolyte from the second set of cells.

One embodiment is the method above, wherein producing the output stream of formic acid only results from the first set of cells.

One embodiment is the method above, wherein producing the output stream of formic acid comprises combining output streams from the first set of cells and the second set of cells.

One embodiment is the method above, wherein routing the at least two smaller streams comprises routing the at least two smaller streams to different portions of a same set of ion selective membrane cells.

One embodiment is the method above, wherein producing the one or more return streams comprises produce a return stream comprised of catholyte.

One embodiment is a method of producing formic acid, including: receiving, from a formate process, a stream comprised of an alkali formate having a wt % of less than 50 wt % of the stream and splitting the stream into two smaller streams; routing the at least two smaller streams to two different regions of one set of ion selective membrane cells; applying electricity to the one or more sets of ion selective membrane cells; producing, as a result of the applying of electricity, an output stream of formic acid having a wt % of at least 20 wt % from the one or more sets of ion selective membrane cells; and producing a return stream of catholyte to the formate process.

One embodiment is the method above, wherein producing the return stream of catholyte further comprises adding water to the return stream.

One embodiment is the method above, wherein producing the return stream of catholyte further comprises removing water from the return stream.

One embodiment is the method above, wherein receiving the stream comprised of alkali formate comprises receiving a stream of alkali format in which the alkali is selected from the group consisting of: potassium, sodium, cesium, lithium, francium, and rubidium.

One embodiment is a method of producing formic acid, including: receiving, from a formate process, a stream comprised of potassium formate having a wt % of less than 50 wt % of the stream and splitting the stream into two smaller streams; routing the at least two smaller streams to one or more sets of ion selective membrane cells; applying electricity to the one or more sets of ion selective membrane cells; producing, as a result of the applying of electricity, an output stream of formic acid having a wt % of at least 20 wt % from the one or more sets of ion selective membrane cells; and producing one or more return streams to be returned to the formate process.

One embodiment is the method above, wherein routing the at least two smaller streams to the one or more sets of ion selective membrane cells comprises one of either routing one of the at least two smaller streams to a first set of ion selective membrane cells and routing one of the at least two smaller streams to a second set of ion selective membrane cells, or routing the at least two smaller streams to different portions of a same set of ion selective membrane cells.

One embodiment is the method above, wherein producing the output stream of formic acid comprises one of either producing the output stream of formic acid from only one set of ion selective membrane cells, or combining output streams from two sets of ion selective membrane cells.

One embodiment is the method above, wherein producing one or more return streams to the formate process comprises producing one or more return streams comprised of one or more of catholyte and refreshed anolyte.

One embodiment is a method of producing formic acid, including: using an electrolyzer to produce alkali formate from a catholyte solution, n anolyte solution, carbon dioxide; taking the alkali formate from the electrolyzer as an input into an ion selective membrane process; and producing formic acid by converting the alkali formate; and returning recycled catholyte solution to the electrolyzer.

One embodiment is the method above, further comprising taking used anolyte from the electrolyzer as an input to the ion selective membrane process.

One embodiment is the method above, further comprising producing refreshed anolyte from the used anolyte and returning the refreshed anolyte to the electrolyzer.

One embodiment is the method above, wherein producing the refreshed anolyte comprises: taking the alkali formate as an input to the ion selective membrane process comprises splitting a stream of the alkali formate between two sets of ion selective membrane cells; and acidifying the used anolyte solution using one set of the two sets of the ion selective membrane cells to produce the refreshed anolyte, prior to the one set producing formic acid.

One embodiment is the method above, further comprising taking the formic acid from the ion selective membrane process as an input to a distillation process to produce a formic acid product having a higher concentration than the formic acid received from the ion selective membrane process.

One embodiment is the method above, further comprising producing oxygen as an output from the electrolyzer.

One embodiment is the method above, wherein taking the alkali formate from the electrolyzer as an input into the ion selective membrane process comprises splitting a stream of alkali formate between two sets of ion selective membrane cells.

One embodiment is the method above, further comprising returning a portion of the stream of the alkali formate to the electrolyzer.

One embodiment is the method above, wherein producing the formic acid comprises outputting formic acid from both sets of ion selective membrane cells.

One embodiment is the method above, wherein producing the formic acid comprises output formic acid from only one set of the two sets of ion selective membrane cells.

One embodiment is the method above, further comprising sending the formic acid produced by one of the two sets of ion selective membrane cells to the other of the ion selective membrane cells.

One embodiment is the method above, wherein taking the alkali formate from the electrolyzer comprises: splitting a stream of the alkali formate into two streams; sending one stream of the two streams through one set of ion selective membrane cells in a first direction; and sending the other stream of the two streams through the same set of ion selective membrane cells in an opposite direction.

One embodiment is the method above, wherein returning the recycled catholyte solution comprises refreshing the catholyte solution by adding an alkali hydroxide and carbon dioxide to the catholyte.

One embodiment is the method above, wherein the refreshing of the catholyte solution occurs during the ion selective membrane process.

One embodiment is the method above, wherein the refreshing of the catholyte solution occurs during the returning of the catholyte solution to the electrolyzer.

One embodiment is the method above, wherein the returning of the recycled catholyte solution comprises adding or subtracting water from the recycled catholyte as needed.

Additionally, this written description makes reference to particular features. It is to be understood that the disclosure in this specification includes all possible combinations of those particular features. For example, where a particular feature is disclosed in the context of a particular aspect, that feature can also be used, to the extent possible, in the context of other aspects.

Also, when reference is made in this application to a method having two or more defined steps or operations, the defined steps or operations can be carried out in any order or simultaneously, unless the context excludes those possibilities.

All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise.

Although specific aspects of this disclosure have been illustrated and described for purposes of illustration, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.