Process for the preparation of formic acid

Abstract

The invention relates to a method for preparing formic acid from carbohydrates or raw materials containing them, comprising a step of mixing carbohydrates or raw materials containing them with vanadium oxide (V2O5) in an aqueous medium and an oxidation reaction of the carbohydrates to formic acid. Figure for abstract: no figure

Description

Title of the invention: Process for the preparation of formic acid

[0001] The invention relates to a process for preparing formic acid from carbohydrates, and in particular from biomasses of plant origin, such as those from agriculture.

[0002] Formic acid is a volatile, non-toxic and easily biodegradable organic acid; it is widely used in the fields of agriculture, pharmacy, rubber, leather, textile and in food companies. In addition, this molecule is a renewable energy vector for hydrogen storage.

[0003] In the food industry, it is used as a food additive for its acidifying, antibacterial, digestive, and preservation-aiding properties. At the same time, its use in the decontamination and disinfection of food products contributes to maintaining the hygiene of the entire production chain.

[0004] The production of formic acid based on fossil resources is mainly carried out by a process of carbonylation of methanol by carbon monoxide into methyl formate, from reagents from the petrochemical industry; it is followed by hydrolysis of the ester at 120°C, 10 bars.

[0005] The oxidative conversion of biomass carbohydrates into formic acid has also been achieved via a two-step process: i) hydrolysis of the biomass to the formation of monosaccharides, such as glucose or fructose, and ii) carbon bond cleavage by catalytic oxidation. Known conversion pathways include, for example, fast pyrolysis, acid hydrolysis, wet oxidation, or catalytic or advanced oxidation (photocatalysis, electrocatalysis).

[0006] Shen et al. (Green Chem, 2021, 23, 1536-1561) review the different reaction pathways for converting biomass into formic acid.

[0007] Li et al. (Chem SusChem 2012, 5, 1313-1318) describe the oxidation of glucose in the presence of different catalytic systems. He concludes that the use of polyoxometallates based on vanadium and molybdenum, such as H5PV2MO10O40, allows formic acid formation yields of up to 36%.

[0008] Wang et al (Green Chem, 2014, 16, 2614 - 2618) describe an oxidation reaction using sodium metavanadate (NaVO3) dissolved in water.

[0009] CN106977388 describes the preparation of formic acid by catalytic oxidation of the biomass, using a synergistic catalytic mixture comprising, based on water-soluble metavanadate and ferric chloride (FeCl3).

[0010] Polyoxometalates, in particular the heteropolyacid HPA-5 ([H8PV5Mo704o]) are known to efficiently activate the conversion of the substrate into formic acid and carbon dioxide.

[0011] Nevertheless, the synthesis of this type of catalyst represents a relatively complex and expensive step. The establishment of a catalyst synthesis process would require heavy equipment, generating costs related to raw materials (solvents, reagents, etc.) as well as higher energy costs.

[0012] There is therefore still a need for a process for producing formic acid using renewable or recyclable raw materials, while exhibiting good yield and good selectivity. It is therefore desirable to have a process based on simple, commercially available and inexpensive catalysts.

[0013] Surprisingly, it has been found that the oxidation of biomass using vanadium oxide as a catalyst makes it possible to limit CO2 emissions and to obtain significant yields of formic acid.

[0014] This is why the present invention relates to a process for preparing formic acid from carbohydrates or raw materials containing them, comprising the following steps:

[0015] a) mixture of carbohydrates or raw materials containing them with vanadium oxide (V2O5) in aqueous medium,

[0016] b) oxidation reaction of carbohydrates in an aqueous medium, in the presence of vanadium oxide, at a pH of 1.5 to 4, at a temperature Tl of 80 to 180°C, preferably of 80°C to 130°C and in particular of 80°C to 110°C, and under an oxygen pressure PI of 3 to 50 bars, preferably of 3 to 30 bars and in particular of 5 to 20 bars, to obtain formic acid,

[0017] c) separation of the formic acid formed at the end of step b by an organic solvent, to obtain an organic phase containing the formic acid and an aqueous phase containing the other reaction species,

[0018] d) introduction of a new quantity of carbohydrates or raw materials containing them, into the aqueous phase obtained at the end of step c,

[0019] e) oxidation reaction of the carbohydrates in the aqueous phase obtained at the end of step d, at a pH of 1.5 to 4, at a temperature T2 of 80 to 180°C, preferably of 80°C to 130°C and under an oxygen pressure P2 of 3 to 30 bars and preferably of 5 to 20 bars, P2 being less than or equal to PI, to obtain formic acid,

[0020] f) separation of the formic acid formed at the end of step e by at least one organic solvent, to obtain an organic phase containing the formic acid and an aqueous phase containing the other reaction species,

[0021] g) recovery of the formic acid present in the organic phases obtained at the end of steps c and f.

[0022] The process according to the invention makes it possible to limit carbon emissions compared to conventional methods of producing formic acid, to combat the re global warming and thus meet the challenges of chemistry with an improved environmental footprint. It is inexpensive and uses vanadium oxide as a catalyst, a commercially available, inexpensive reagent with a relatively simple chemical structure. In addition, vanadium oxide has a low molecular weight, which allows the use of smaller quantities of catalyst compared to other catalysts known in the state of the art such as polyoxometalates and in particular HPA 5.

[0023] The process also meets the recyclability criteria.

[0024] Indeed, at the end of a first cycle of formic acid production, the reaction medium is recovered and reused. The substrate, carbohydrates or raw materials containing them, is added to the medium from which the formic acid has been extracted (step d). A new cycle of formic acid production can then be carried out, using the reaction species, and in particular the active catalytic species, present in the aqueous medium.

[0025] Carrying out several reaction cycles improves the yield of formic acid, with cycles of rank 2 and higher being able to be carried out at a pressure lower than the reaction pressure of the first cycle.

[0026] According to one of the embodiments of the invention, steps d to f are repeated n times, n being from 1 to 50, in particular from 1 to 30; n being for example from 2 to 20, in particular from 2 to 10. Several oxidation reaction cycles are thus carried out, recovering the formic acid at the end of each cycle and adding reaction substrate to the aqueous medium. At the end of the process, all of the fractions containing the formic acid are combined.

[0027] The oxygen pressure Pn of the cycles of rank n is lower than the pressure PI of the 1st reaction cycle. Pn is lower than or equal to the pressure P2.

[0028] Generally, the pressures PI and P2 (and therefore the pressures Pn of the successive cycles) are from 3 to 20 bars.

[0029] In particular, P2 is less than 20 bars, in particular less than 15 bars. P2 can in particular be from 3 to 10 bars, and makes it possible to obtain good yields of formic acid.

[0030] By aqueous medium is meant a medium comprising as solvent water and optionally one or more hydrophilic co-solvents; such co-solvents may for example be of an alcoholic nature, such as methanol, ethanol, tert-butanol, isopropyl alcohol or isobutyl alcohol. Advantageously, water represents at least 90% of the solvent of the aqueous medium, preferably at least 95% of the solvent. The aqueous phase preferably contains, in addition to water, at least one mineral acid, formic acid and the catalyst and / or the catalytic species generated.

[0031] Advantageously, the carbohydrates are chosen from glycerol, monosac- charides, oligosaccharides, polysaccharides and / or their mixtures in any proportions.

[0032] The carbohydrates can be provided in the first stage of the process in pure form or as a raw substrate, in particular in the form of a raw material containing them.

[0033] Such raw materials are notably made up of biomass, in particular agricultural biomass; this is made up of organic matter generated by activities linked to agriculture and livestock farming (meat, milk, crops, grasses, crop residues, etc.). The raw material containing carbohydrates is for example chosen from celluloses, molasses, corn cobs, lignins, chicory pulps, beet pulps or mixtures thereof.

[0034] The process can thus be carried out from all multi-carbon saccharide derivatives such as molasses, methylcellulose, isomaltulose, maltodextrin, corn cobs or chicory pulp.

[0035] Oligosaccharides are molecules composed of a combination of simple sugars (also called oses or monosaccharides) linked by alpha or beta osidic bonds. They generally comprise from 2 to 20 oses, in particular from 2 to 10 oses. They can be linear, branched or cyclic. Oligosaccharides include in particular fructo-oligosaccharides, galacto-oligosaccharides, gluco-oligosaccharides and mannan-oligosaccharides.

[0036] Polysaccharides (also called polyholosides or polyosides) are complex carbohydrates made up of a large number of simple sugars, generally greater than 20, linked together by glycosidic bonds.

[0037] They can be linear, such as cellulose, or branched, such as gum arabic, amylopectin, dextran, hemicellulose; they can also be mixed, such as starch.

[0038] The pH of the oxidation reaction of the process according to the invention will be adjusted in a known manner, by the addition of at least one acid in the mixture of substrate (carbohydrates or raw material containing them) and vanadium oxide in aqueous medium. The acid will advantageously be a mineral acid and may in particular be chosen from phosphoric acid, sulfuric acid, hydrochloric acid, hydrobromic acid, nitric acid and their mixtures in all proportions. This adjustment is carried out for example in steps b) or e) of the process according to the invention, or during their reiteration during cycles of rank n.

[0039] An acid that is particularly suitable for implementing the process according to the invention is phosphoric acid. The use of phosphoric acid makes it possible to produce formic acid with good yields. In addition, this molecule is commonly used in the food industry and leads to products suitable for food applications, particularly in animal feed.

[0040] The use of phosphoric acid is particularly advantageous.

[0041] Indeed, the catalyst activated in an acid medium, for example by adding H3PO4, is highly selective under mild conditions. It can be reused over several reaction cycles (for example 5 <n<10 cycles).

[0042] In particular, the process according to the invention may comprise oxidation reactions in an aqueous medium at temperatures T1, T2 and T(2+n), with n being from 1 to 50, and in particular from 1 to 30; n being for example from 2 to 20, in particular from 2 to 10. The reaction temperatures will generally be from 80 to 180°C, but may be lower, for example from 80 to 130°C, in particular from 80 to 120°C, and for example from 90°C to 120°C.

[0043] Good yields of formic acid will be obtained for temperatures T1 ranging, for example, from 90°C to 120°C, in particular from approximately 95°C to 110°C. The reaction temperature of the subsequent cycles, T2 and T(2+n) is advantageously less than or equal to the temperature TL. It may, for example, be from 90 to 110°C, in particular from 90 to 105°C. According to one of the embodiments, T1 and T2 are each approximately 100°C (plus or minus 3°C).

[0044] Surprisingly, it has been demonstrated in the context of the invention that the process makes it possible to reduce the production of CO2 under these conditions in comparison with conventional methods. This constitutes an additional advantage, the carbon footprint of the formic acid produced according to the invention can be up to 10 times lower than for a formic acid produced from petroleum derivatives.

[0045] The formation of CO2 during the oxidation reactions is thus generally less than or equal to 50 mol%, or even 40 mol%. This formation of CO2 decreases in particular when the cycles are repeated, in particular when steps d to f are repeated at least once to carry out an additional reaction cycle.

[0046] The selectivity of the formic acid production process is particularly notable during the recycling reactions (steps d and following). An increase in formic acid yields is observed during the following cycles, which is accompanied by a relative decrease in CO2 production.

[0047] The amount of vanadium oxide will be adapted to improve the yield. In particular the concentration of vanadium oxide in step a) is 5 to 20 mol%, in particular approximately 10 mol%.

[0048] As mentioned above, the formic acid is extracted from the reaction medium at the end of each oxidation reaction, preferably by at least one organic solvent by liquid / liquid extraction; in particular the organic solvent comprises at least ethers. A recyclable and potentially bio-sourceable solvent is preferably used, such as tert-butylmethyl ether (MTBE), 2-methyl-tetrahydrofuran; other possible solvents are fatty alcohols such as hexan-1-ol or heptan-l-ol. It is understood that the solvents can be used pure or in mixtures in any proportions.

[0049] The organic solvent (or mixture of organic solvents) is then evaporated and additional formic acid extraction steps may be carried out, including filtration and distillation.

[0050] All of the organic phases recovered at the end of the different oxidation reaction cycles can be combined to undergo these subsequent extraction steps.

[0051] According to one embodiment of the method according to the invention, the treatment of carbohydrates or raw materials containing them is carried out in batches.

[0052] According to another embodiment of the invention, the process for preparing formic acid is carried out continuously or semi-continuously.

[0053] Formic acid can be extracted semi-continuously from the reaction medium, which is recharged with substrate. The active solution is recycled to which the substrate is added again. The pH, pressure and temperature parameters are checked and adjusted if necessary at the start of each new oxidation cycle.

[0054] According to one embodiment of the invention, the method as described in the present application further comprises an acid treatment step before step a. This embodiment is particularly suitable when the method is applied to a substrate such as oligosaccharides, a raw substrate and / or raw materials containing carbohydrates and other residues, such as for example corn cobs, chicory or beet pulps.

[0055] Thus, before step a, the raw material containing carbohydrates is subjected to an acid treatment. This treatment is preferably carried out at a high temperature, for example from about 80°C to 100°C. For example, the raw substrate, in particular the raw material containing the carbohydrates, is placed in an acid medium and the mixture is maintained at a high temperature for a time allowing hydrolysis; this time will be adapted by a person skilled in the art depending on the type of raw material and the reaction temperature. The reaction mixture is then filtered to remove any solid residues that may be present depending on the raw material used. The filtrate is introduced into an aqueous medium in the presence of V2O5, to carry out step a of the process described above.

[0056] The acid or mixture of acids used for this treatment will be adapted by a person skilled in the art, but will advantageously be the same as that used to adjust the pH during the oxidation reaction step. The acid is in particular a mineral acid; it may in particular be preferably chosen from phosphoric acid, sulfuric acid, hydrochloric acid, hydrobromic acid and their mixtures in all proportions.

[0057] The duration of the carbohydrate oxidation reaction will be adapted by the person skilled in the art. job depending on the type of substrate.

[0058] Generally, the oxidation reaction of carbohydrates or raw materials containing them, in steps b or e, is carried out for a period of 10 min to 5 hours, in particular 30 min to 3 hours, but the duration will be adjusted by a person skilled in the art according to the volume of carbohydrate or raw material to be treated; the duration can thus be increased and go up to 10 hours, or even 24 hours.

[0059] The invention also relates to the use of a composition containing formic acid obtained by the preparation process described above, as a food additive, in particular in animal feed. Such a composition contains formic acid and traces of reaction species, such as, for example, catalytic residues and / or the starting substrate. These are in particular compositions containing formic acid obtained by using phosphoric acid as the acid. Treatment on activated carbon of the solution containing the formic acid can be carried out in order to eliminate any residues. Brief description of the figures

[0060] The invention will be better understood by reading the following examples. In these examples, reference will be made to the appended figures, in which:

[0061] [Fig-1] represents the yields of formic acid (FA) and CO2 after a cycle of reaction and recycling

[0062] [Fig.2] is a graph showing the oxidation kinetics by V2O5 of corn cobs

[0063] [Fig.3] is a diagram showing the influence of V2O5 recycling in sucrose oxidation, with formic acid (FA) and CO2 levels

[0064] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art.

[0065] Example 1: Oxidation of sucrose to formic acid catalyzed by vanadium (V) oxide in an acid medium

[0066] The catalytic oxidation device consists of an IL stainless steel autoclave equipped with mechanical stirring with a Rushton turbine and a heating collar, connected to a regulator.

[0067] 20 g of sucrose dissolved in 500 mL of distilled water as well as 7.5 mL of acid Phosphoric acid (75% by weight) are introduced into the IL autoclave. 1.1g of vanadium (V) oxide are added. The autoclave is closed, purged twice with 10 bars of O2 and then the pressure is adjusted to 20 bars of O2. The autoclave is heated to 100°C, the temperature is monitored using a thermocouple placed in the medium. After the temperature rise, the pressure is adjusted to 20 bars and the medium is left stirring at 100°C for 4 hours.

[0068] The autoclave is then cooled, the gas phase is extracted, collected in a tube of Schlenk and analyzed by gas chromatography to quantify the CO2 produced by the reaction. The autoclave is opened, the formic acid is extracted from the aqueous phase by liquid-liquid extraction with tert-butyl methyl ether MTBE (5*500ml). The solvent is evaporated under reduced pressure (500 mbar, 40°C), the distillate is recovered for finalization of the extractions. The concentrated formic acid phase is filtered through charcoal, then the rest of the solvent is evaporated (80 mbar, 40°C).

[0069] The molar yield of Formic Acid is calculated as a function of the formic acid concentration in the organic phase according to the following equation:

[0070] y _ cFAxVOrg mol~

[0071] The mass yield of Formic Acid is calculated according to the following equation:

[0072] [Math.2] y _ CF^VOr^mwFA * m “ mSacc

[0073] The molar yield of CO2 is calculated as a function of the partial pressure of CO2 in the collected gas phase, by assimilating to the ideal gas regime, according to the following equation:

[0074] [Math.3] 1 COI — RxTxnSaaxi2

[0075] For the recycling experiments, 20 g of sucrose are dissolved in the aqueous phase before repeating the reaction under the same conditions.

[0076] The results are presented in the following table and in [Fig.3]

[0077] [Tables 1] Cycle v A mol Ym YcO2 1 51% 83% 41% 2 72% 116% 40% 3 69% 111% 32% 4 51% 83% 23% 5 69% 112% 22% 6 83% 134% 35%

[0078] Example 2: Oxidation of glucose to formic acid catalyzed by vanadium (V) oxide in acidic medium

[0079] The catalytic oxidation device consists of an IL stainless steel autoclave equipped with mechanical stirring with a Rushton turbine and a heating collar, connected to a regulator.

[0080] 20 g of glucose dissolved in 500 mL of distilled water as well as 5 mL of phos- phoric (75% by weight) are introduced into the autoclave, 1.85 g of vanadium (V) oxide are suspended. The autoclave is closed, purged twice with 10 bars of O2 then the pressure is adjusted to 20 bars of O2. The autoclave is heated to 110°C, the temperature monitoring is carried out using a thermocouple placed in the medium. After the temperature rise, the pressure is adjusted to 20 bar and the medium is left stirring at 110°C for 3 hours.

[0081] The autoclave is then cooled, the gas phase is extracted, collected in a Schlenk tube and analyzed by gas chromatography to quantify the CO2 produced by the reaction. The autoclave is opened, the formic acid is extracted from the aqueous phase by liquid-liquid extraction with tert-butylmethyl ether (5*500ml). The solvent is evaporated under reduced pressure (500 mbar, 40°C), the distillate is recovered for finalizing the extractions. The concentrated formic acid phase is filtered through carbon, then the rest of the solvent is evaporated (80 mbar, 40°C).

[0082] The molar yield of Formic Acid is calculated as a function of the formic acid concentration in the organic phase according to the following equation

[0083] [Math.4] y _ 1 evil — nGi^6

[0084] The mass yield of Formic Acid is calculated according to the following equation:

[0085] [Math.5] y _ rm~ mGlc

[0086] The molar yield of CO2 is calculated as a function of the partial pressure of CO2 in the collected gas phase, by assimilating to the ideal gas regime, according to the following equation:

[0087] [Math.6] CO2 RxTxnGIlx6

[0088] For the recycling experiments, 20 g of glucose are dissolved in the aqueous phase before repeating the reaction under the same conditions.

[0089] The results are presented in the following table

[0090] [Tables2] Cycle v A mol Ym YcO2 1 10% 16% 30% 2 46% 71% 51% 3 49% 75% 40% 4 69% 106% 37% 5 56% 86% 53% 6 59% 90% 39% 7 69% 105% 33% 8 67% 103% 41% 9 63% 96% 39%

[0091] Example 3: oxidation of beet molasses

[0092] An oxidation reaction with V2O5 as catalyst is carried out under the following conditions: 1g of molasses, 0.1mmol V2O5, 200 pL H3PO4, 10 mL H2O, 20 bars O2, at 100°C.

[0093] The reaction shows a linear conversion over the first hour of reaction. An optimal conversion of 40 mol% is obtained after 1.5 h. Very few solid residues are observed at the end of the reaction.

[0094] The same reaction is carried out in an IL reactor.

[0095] The conditions are as follows: 50g of molasses, 5 mmol V2O5, 10 mL H3PO4, 500 mL H2O, 20 bars O2, at 100°C.

[0096] Formic acid yields of 40 mol% are obtained. The same selectivity is maintained when recycling the catalytic phase after extraction of the formic acid.

[0097] The results are shown in [Fig. 1]

[0098] Example 4: oxidation of corn cob

[0099] The corn cob is placed in a 10%wt phosphoric acid solution maintained at 90°C overnight (16 hours).

[0100] The reaction mixture is then filtered and the filtrate is introduced into an autoclave under catalytic oxidation conditions (20 bars O2, 100°C) in the presence of the V2O5 catalyst.

[0101] After two hours of reaction, for a formic acid yield of 36 mol%, 46 mol% of CO2 are obtained with a treated corn cob. A formic acid yield of 28 mol% and 72 mol% of CO2 are obtained with a corn cob not treated with phosphoric acid after 8 hours of reaction.

[0102] The pretreatment, which is of interest in terms of catalytic performance, makes it possible to avoid the introduction of insoluble materials into the reactor and thus prevent obstruction of the conduits, the negative impact on agitation and decantation and limit impurities.

[0103] The results are shown in [Fig.2]

Claims

Claims

1. Process for the preparation of formic acid from carbohydrates or raw materials containing them, comprising the following steps: a) mixing carbohydrates or raw materials containing them with vanadium oxide (V2O5) in an aqueous medium, b) oxidation reaction of the carbohydrates in an aqueous medium, in the presence of vanadium oxide, at a pH of 1.5 to 4, at a temperature T1 of 80 to 180°C and under an oxygen pressure PI of 3 to 50 bars, to obtain formic acid, c) separation of the formic acid formed at the end of step b by at least one organic solvent, to obtain an organic phase containing the formic acid and an aqueous phase containing the other reaction species, d) introduction of a new quantity of carbohydrates or raw materials containing them, into the aqueous phase obtained at the end of step c, e) oxidation reaction of the carbohydrates in the aqueous phase obtained at the end of step c, the outcome of step d, at a pH of 1,5 to 4, at a temperature T2 of 80 to 180°C and under an oxygen pressure P2 of 3 to 30 bars, P2 being less than or equal to PI, to obtain formic acid, f) separation of the formic acid formed at the end of step e by an organic solvent, to obtain an organic phase containing the formic acid and an aqueous phase containing the other reaction species, g) recovery of the formic acid present in the organic phases obtained at the end of steps c and f.,

2. Process for the preparation of formic acid according to claim 1, characterized in that the carbohydrates are chosen from glycerol, monosaccharides, oligosaccharides and polysaccharides or their mixtures.

3. Process for the preparation of formic acid according to at least one of claims 1 or 2, characterized in that the raw material containing carbohydrates is chosen from celluloses, molasses, corn cobs, lignins, chicory pulps and beet pulps or mixtures thereof.

4. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that the pressures P1 and P2 are from 3 to 20 bars.

5. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that P2 is less than 20 bars.

6. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that the temperatures T1 and T2 are from 80 to 120°C.

7. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that steps d to f are repeated n times, where n is an integer ranging from 1 to 50.

8. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that before step a, the raw material containing carbohydrates is subjected to an acid treatment.

9. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that the concentration of vanadium oxide in step a) is 5 to 20 mol%.

10. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that the pH is adjusted by adding at least one acid chosen from phosphoric acid, sulfuric acid, hydrochloric acid, hydrobromic acid, nitric acid or mixtures thereof.

11. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that the organic solvent is chosen from the group comprising tert-butylmethyl ether (MTBE), 2-methyl-tetrahydrofuran and their mixtures.

12. Process for the preparation of formic acid according to at least one of the preceding claims, characterized in that the formation of CO2 during the oxidation reactions is less than or equal to 40 mol%.

13. Use of a composition containing formic acid obtained by the preparation process according to at least one of the preceding claims as a food additive, in particular in animal feed.

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