THE PRODUCTION OF FORMIC ACID OR FORMALDEHYDE FROM CARBON DIOXIDE

Abstract

The invention concerns a process and modular system for producing formic acid from a source of carbon dioxide. The process according to the invention comprises (a) a carbon capture step wherein a source of carbon dioxide is contacted with an alkaline solution to obtain a solution comprising carbonate and/or bicarbonate; optionally (b) subjecting the solution comprising carbonate and/or bicarbonate to alkaline water electrolysis, wherein carbonate present in the solution comprising carbonate and/or bicarbonate is converted to bicarbonate and H.sub.2O is converted into H.sub.2 and O.sub.2; (c) subjecting the solution comprising carbonate and/or bicarbonate to a hydrogenation step in the presence of a catalyst to obtain a solution comprising formate; and (d) subjecting the solution comprising formate obtained in step (c) to bipolar membrane electrodialysis to obtain a concentrated formic acid solution and a recovered alkaline solution, wherein the recovered alkaline solution obtained in step (d) is recycled back to step (a). The concentrated formic acid solution obtained from step (d) may be subjected to a hydrogenation step in the presence of a hydrogenation catalyst to obtain a concentrated formaldehyde solution.

Claims

1. A process for producing formic acid, comprising: (a) a direct air capture step wherein a source of carbon dioxide is contacted with an alkaline solution to obtain a solution comprising carbonate and/or bicarbonate; (c) subjecting the solution comprising carbonate and/or bicarbonate to a hydrogenation step in the presence of a catalyst to obtain a solution comprising formate; and (d) subjecting the solution comprising formate obtained in step (c) to bipolar membrane electrodialysis to obtain a concentrated formic acid solution and a recovered alkaline solution, wherein the recovered alkaline solution obtained in step (d) is recycled back to step (a).

2. The process according to claim 1, wherein the process is for producing formaldehyde and further comprises: (e) subjecting the concentrated formic acid solution obtained from step (d) to a hydrogenation step in the presence of a hydrogenation catalyst to obtain a concentrated formaldehyde solution.

3. The process according to claim 1, wherein the recovered alkaline solution comprises 1-20 wt. % formate on total weight.

4. The process according to claim 1, wherein in step (d) less than 80% of the formate of the solution comprising formate obtained in step (c) is converted to formic acid.

5. The process according to claim 1, wherein the concentrated formic acid solution comprises less than 2 wt. % inorganic salts on formic acid weight.

6. The process according to claim 1, wherein the amount of carbon dioxide in the source of carbon dioxide is in the range of 50 200000 ppmv.

7. The process according to claim 1, wherein the alkaline solutions comprises deep eutectic solvents or an inorganic salt.

8. The process according to claim 1, further comprising (b) subjecting the solution comprising carbonate and/or bicarbonate to alkaline water electrolysis prior to step (c), wherein carbonate present in the solution comprising carbonate and/or bicarbonate is converted to bicarbonate and H.sub.2O is converted into H.sub.2 and O.sub.2.

9. The process according to claim 1, wherein H.sub.2 gas required in step (c) and/or (e) originates from electrolysis of water.

10. The process according to any claim 1, wherein the alkaline solution is a solution comprising one or more selected from the list consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, and lithium hydroxide.

11. A modular system for performing the process according to claim 1, comprising: (a) an absorber having a first inlet for receiving an alkaline solution, a second inlet for receiving a source of carbon dioxide, an outlet for discharging a gas stream depleted in carbon dioxide, and an outlet for discharging a solution comprising carbonate and/or bicarbonate; (c) a hydrogenation reactor, comprising an inlet for receiving the solution comprising carbonate and/or bicarbonate, an inlet for receiving H.sub.2 gas and an outlet to discharge a solution comprising formate; and (d) a bipolar membrane electrodialysis reactor, comprising an inlet for receiving the solution comprising formate, an inlet for receiving an electrolyte solution, an outlet for discharging the concentrated formic acid solution and an outlet for discharging a recovered alkaline solution, wherein the modular system comprises a recycle loop which connects the outlet for discharging the recovered alkaline solution to the inlet for receiving an alkaline solution.

12. The modular system according to claim 11, further comprising one or more modules selected from: (b) an alkaline water electrolysis reactor, comprising an inlet for receiving the solution comprising carbonate and/or bicarbonate, an outlet for discharging the solution comprising carbonate and/or bicarbonate bicarbonate and one or more outlets for discharging H.sub.2 and O.sub.2; and (e) a second hydrogenation reactor, comprising an inlet for receiving the concentrated formic acid solution from module (d), an inlet for receiving H.sub.2 gas and an outlet for discharging formaldehyde.

Description

DESCRIPTION OF THE DRAWINGS

[0087] The present invention is illustrated with two preferred embodiments depicted in the figures.

[0088] FIG. 1 depicts a process flow diagram of the process according to the invention, in which flue gas is the source of carbon dioxide, typically with a CO.sub.2 content in the range of 0.04-20 wt. %. Flue gas (1) and an alkaline solution (5) enter absorber (2), wherein absorption of CO.sub.2 into the solution of step (a) takes place. Typically, over 50% of the CO.sub.2 present in the source of carbon dioxide is captured during step (a). A gaseous stream depleted in carbon dioxide (4) is discharged from the top of the absorber, while a solution comprising carbonate and/or bicarbonate (6) is discharged from the bottom. Solution (6) is fed to hydrogenation reactor (7), together with H.sub.2 gas (8) which is typically generated in water electrolyzer (9), which is fed with water (10) and in addition to H.sub.2 gas also generates O.sub.2 gas (11). In hydrogenation reactor (7), step (c) occurs, which typically operates with a yield of over 80%, and the carbonate and/or bicarbonate are hydrogenated into formate (12). The resulting solution comprising formate (12) that is obtained from reactor (7) is fed to BMED reactor (13). A second liquid (14), typically an electrolyte solution, enters the BMED reactor (13). Step (d) occurs in BMED reactor (13), wherein formate is converted into formic acid, and a recovered alkaline solution, which is depleted in formate (5), which usually has a pH of above 9.5, is fed back to absorber (2) as the alkaline solution. A concentrated formic acid solution (16) leaves the BMED reactor (13), together with some stripped carbon dioxide (15). The thus formed formic acid may be the product (17) of the process, or may be fed to hydrogenation reactor (18) to perform step (e). H.sub.2 gas (10) from water electrolyzer (9) is fed to reactor (18), and formic acid is converted into formaldehyde (19), which typically operates with a yield of over 80%. The resulting concentrated formaldehyde stream (19) is discharged from reactor (18).

[0089] FIG. 2 depicts a process flow diagram of the process according to the invention, in which air is the source of carbon dioxide (direct air capture). Air (1) and an alkaline solution (5) enter absorber (2), wherein absorption of CO.sub.2 into the solution of step (a) takes place. Typically, about 50% of the CO.sub.2 of the source of carbon dioxide is captured during step (a). A gaseous stream depleted in carbon dioxide (4) is discharged from the top of the absorber, while a solution comprising carbonate and/or bicarbonate (20) is discharged from the bottom. Solution (20) is subjected to alkaline water electrolysis in reactor (21). A KOH solution (24) is fed into reactor (21), and electrolysis of water of step (b) affords gaseous H.sub.2 (22) and O.sub.2 (23), that are discharged from the electrodes. The acidified solution comprising carbonate and/or bicarbonate (6) is discharged from reactor (21). The H.sub.2 gas (22) formed in reactor (21) may be fed to hydrogenation reactor (7) and/or (18). Alternatively or additionally, additional H.sub.2 gas (8) may be generated in water electrolyzer (9) and fed to hydrogenation reactor (7) and/or (18). The acidified solution (6) obtained from reactor (21) is fed to hydrogenation reactor (7), together with H.sub.2 gas (8) which is typically generated in water electrolyzer (9), which is fed with water (10) and in addition to H.sub.2 gas also generates O.sub.2 gas (11). In hydrogenation reactor (7), step (c) occurs, which typically operates with a yield of over 80%, and the carbonate and/or bicarbonate are hydrogenated into formate (12). The resulting solution comprising formate (12) that is obtained from reactor (7) is fed to BMED reactor (13). A second liquid (14), typically an electrolyte solution, enters the BMED reactor (13). Step (d) occurs in BMED reactor (13), wherein formate is converted into formic acid, and a recovered alkaline solution, which is depleted in formate (5), which usually has a pH of above 9.5, is fed back to absorber (2) as the alkaline solution. A concentrated formic acid solution (16) leaves the BMED reactor (13), together with some stripped carbon dioxide (15). The thus formed formic acid may be the product (17) of the process, or may be fed to hydrogenation reactor (18) to perform step (e). H.sub.2 gas (10) from water electrolyzer (9) is fed to reactor (18), and formic acid is converted into formaldehyde (19), which typically operates with a yield of over 80%. The resulting concentrated formaldehyde stream (19) is discharged from reactor (18).

EXAMPLES

[0090] The modelling approach for a bipolar membrane electrodialysis for separation and protonation of formate to formic acid is according to the publications of Jaime Ferrer et al. (Jaime-Ferrer et al., J. Memb. Sci. 2006, 280 (1-2), 509-516; Jaime-Ferrer et al., J. Memb. Sci. 2008, 325 (2), 528-536; Jaime-Ferrer et al., Modelling. J. Memb. Sci. 2009, 328 (1-2), 75-80). The results presented in this example are based on a 2-compartment bipolar membrane electrodialysis cells. The cells comprise a diluate compartment, which is the cathode compartment to which the solution comprising formate is introduced, and a concentrate compartment, which is the anode compartment to which the electrolyte solution is fed. The compartments are separated by an anion exchange membrane. Each compartment is bordered by a bipolar membrane. Concentration curves for all species in solution in the two compartments are provided as a function of processing time. The model produced the volume variations per compartment as a function of time, and the differential current efficiency as a function of time, which is related to the overall efficiency of the process for formic acid production from formate.

[0091] The governing mechanisms in the bipolar membrane electrodialysis process are the alkalinization of the diluate compartment and the concomitant acidification of the concentrate compartment due to the action of the bipolar membranes. The alkalinization and acidification fluxes, which are equivalent to the water splitting flux at the bipolar membrane, is regulated by the applied electric current. The water splitting flux determines the migration of the different ions in the electrodialysis process. When one molecule of water is split into hydroxide anions towards the diluate compartment, and hydronium cations towards the concentrate compartment, one anion molecule crosses the anion exchange membrane from diluate to concentrate. The crossover of cations through the bipolar membrane (sodium, potassium, etc.) due to migration hinders the water splitting action in the bipolar membrane.

[0092] Other modelled phenomena in the bipolar membrane electrodialysis process are the mass transfer of formic acid through the bipolar membranes and the anion exchange membrane due to concentration gradient between compartments, the migration of monovalent ions in the direction of the electric field as a function of both the concentration in the compartment from which the ion migrates, and the applied electric current; the electro-osmotic effect of solvent transfer through anion exchange membrane from diluate to concentrate compartments, the homogeneous reactions coming from the buffer equilibria of formate-formic acid and solubilized carbon dioxide-bicarbonate-carbonate, and water auto-ionization, and the carbon dioxide desorption at the concentrate compartment when a carrier gas is bubbled at the bottom of an hypothetical buffer vessel in which the concentrate compartment stream is recirculated. The model equations for these phenomena can all be found in the above publications of Jaime Ferrer et al.

[0093] The main assumptions of the model are the following: a constant current density is applied throughout the whole process, with no effect on the total cell potential; the model considers an infinite set of cells, diluate and concentrate compartments, being both compartments separated by an anion exchange membranes, and each cell separated from each other by a bipolar membrane, thus meaning that the electrode compartments have not been taken into account; the anion transfer rate for bicarbonate and formate through the anion exchange membranes is taken to be the same for both; only monovalent anions are transferred through the different ion exchange membranes, thus meaning specifically that carbonate does not cross any of the membranes; constant temperature has been taken throughout the whole process.

[0094] All necessary parameters for the mathematical model, as mass transfer coefficients of the different species in solution through ion exchange membranes, the migration terms for charged species through ion exchange membranes, and the parameters for the electro-osmotic effect of volume transfer between different compartments, have been taken from Jaime Ferrer et al. When data was not available for a specific parameter, reasonable assumptions were made based on presented data in Jaime Ferrer et al.

[0095] The described model can predict the loss of efficiency in the bipolar membrane electrodialysis process as the conversion of formate to formic acid proceeds. In Table 1, the different values of Differential Current Efficiency as a function of the conversion of formate present at the diluate compartment to formic at the concentrate compartment. The Differential Current Efficiency is defined as the quotient between the formic acid transfer rate at the concentrate compartment and the total acidification rate at the bipolar membrane, which is the driving force of the bipolar membrane electrodialysis process. The initial conditions for the results in table 1 are: initial concentrations of bicarbonate, carbonate and formate at the diluate compartment are 250, 75 and 3000 mol.Math.m.sup.?3, respectively; initial concentrations of bicarbonate, carbonate and formic acid at the concentrate compartment are 0, 0 and 10 mol.Math.m.sup.?3, respectively; constant current density applied is 250 A.Math.m.sup.?2, total membrane area of the bipolar membrane electrodialysis cell is 0.02 m.sup.2; initial volume of the diluate and concentrate compartment solutions is 10.sup.?4 and 10.sup.?4 m.sup.3, respectively.

TABLE-US-00001 TABLE 1 Results of the model for the Differential Current Efficiency for formic acid removal as a function of the formate to formic acid conversion. Conversion formate Differential Current to formic acid Efficiency [] [] 10% 94% 20% 88% 30% 83% 40% 78% 50% 72% 60% 66%

[0096] The simulation as represented in table 1 demonstrate a linear decrease of differential current efficiency upon a higher conversion of formate to formic acid. A loss of differential current efficiency directly relates to a higher energy usage and to a less efficient process.