EP2139837A1

EP2139837A1 - Method for producing formic acid

Info

Publication number: EP2139837A1
Application number: EP08717979A
Authority: EP
Inventors: Nina Challand; Xavier Sava; Michael Röper
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2007-03-23
Filing date: 2008-03-18
Publication date: 2010-01-06
Also published as: WO2008116799A1; AR065807A1; NO20093037L; BRPI0809156A2; CA2681508A1; JP2010521533A; KR20090123972A; CN101663259A; US20100063320A1

Abstract

The invention relates to a method for producing formic acid by generating the corresponding ammonium formate by means of catalytic hydrogenation of carbon dioxide with hydrogen on a catalyst comprising a metal of groups 8 through 10 of the periodic system, in the presence of a primary, secondary, and/or tertiary amine, and by cleaving the ammonium formate by heating it in formic acid and the amine, characterized in that the primary, secondary, or tertiary amine is selected from the amines of formula I or the mixtures thereof, R1 through R3 being identical or different and being hydrogen, linear or branched alkyl radicals having 1 to 18 carbon atoms, cycloaliphatic radicals having 5 to 7 carbon atoms, aryl radicals and/or aryl alkyl radicals, at least one of the radicals R1 to R3 carrying a hydroxyl group, and that said hydrogenation is performed in a solvent having a boiling point of =105°C at normal pressure, and that the formic acid is obtained in the hydrogenation reaction mixture comprising the high-boiling solvent by thermal cleavage of the ammonium formate and distillation of the formic acid.

Description

Process for the preparation of formic acid

description

The present invention relates to a process for the preparation of formic acid.

It is known to produce ammonium formates of primary, secondary and / or tertiary amines by catalytic hydrogenation of carbon dioxide with hydrogen over hydrogenation catalysts in the presence of the primary, secondary and / or tertiary amines in a solvent. From the ammonium formates can be released by heating formic acid.

Formic acid is industrially produced mainly by carbonylation of methanol with carbon monoxide to methyl formate and subsequent hydrolysis to formic acid with the recovery of methanol (K. Weissermel, H. -J. Arpe, Industrial Organic Chemistry, fourth edition, VCH-Verlag, pages 45 to 46 ).

Instead of carbon monoxide, carbon dioxide can also be used for the production of formic acid. The d-component carbon dioxide is available in gaseous form or bound in large quantities as carbonate on earth.

From numerous studies it is known that carbon dioxide can be converted by electrochemical or photochemical reduction, but also by transition metal-catalyzed hydrogenation with hydrogen in formic acid or its salts (W. Leitner, Angewandte Chemie 1995, 107, pages 2391 to 2405).

In particular, the catalytic hydrogenation of carbon dioxide in the presence of amines appears to be industrially promising. The ammonium formates formed in this case can be z. B. thermally split into formic acid and the used, traceable into the hydrogenation amine.

From EP 0 095 321 B1 (BP Chemicals) is known, carbon dioxide with hydrogen in the presence of tertiary aliphatic, cycloaliphatic or aromatic amines, homogeneously dissolved compounds as catalysts containing metals of the eighth subgroup and lower alcohols or alcohol / water mixtures as solvents to implement corresponding ammonium formates. In Example 1 triethylamine, i-propanol / water mixtures and ruthenium trichloride are used. A disadvantage is the complicated workup of the hydrogenation: First, the low boilers i-propanol (boiling point 82 ° C / 1013 mbar), water and excess Amine (boiling point triethylamine 89.5 ° C / 1013 mbar) are separated by distillation from the ammonium formates formed as high boilers.

To obtain the formic acid from the ammonium formates obtained after removal of the low boilers, these can be split thermally. However, the formic acid distilled off at the top (boiling point 100 ° C./1013 mbar) is contaminated by the amine with a similar boiling point, which partly passes with the formic acid, with reformation of the ammonium formate. Also problematic is the separation and recycling of the homogeneous catalysts.

Also according to DE-A 44 31 233, Examples 1 to 4, carbon dioxide is hydrogenated in the presence of triethylamine, water and alcohols. As catalysts heterogeneous catalysts such. B. ruthenium on Al ₂ O ₃ as a carrier or ruthenium-containing complex compounds on silica as a carrier. This alleviates the problem of catalyst recycle. The work-up of the product mixture of the hydrogenation to obtain formic acid, however, has the same problems as in the process according to EP 0 095 321 B1.

From EP 357243 B1 (BP Chemicals) it is known to hydrogenate carbon dioxide in the presence of tertiary nitrogen bases such as triethylamine in a mixture of two different solvents having a miscibility gap. In Example 1 z. B. carbon dioxide in the presence of triethylamine, ruthenium trichloride, tri-n-butylphosphine and the two solvents toluene and water. The hydrogenation product decomposes into a toluene phase containing the ruthenium catalyst and an aqueous phase containing the formed triethylammonium formate. On page 3, line 56, to page 4, line 27, the suitable for the implementation of the invention nitrogen bases are discussed. Mention is also made of hydroxyl-substituted primary, secondary or tertiary amines.

It is also known to use in the hydrogenation of carbon dioxide in the presence of amines and [(mC ₆ H ₄ Sθ ₃ ^" Na ⁺ ) ₃ P] ₃ RhCl as a transition metal catalyst in aqueous solution also ethanolamines (Leitner, W. et al. in "Aqueous Phase Organometallic Catalysis", edited by B. Cornils and WA Herrmann, Verlag WILEY-VCH, page 491ff.). However, the use of ethanolamines leads to significantly lower formate yields and lower TOF values than The use of triethylamine and dimethylamine Within the ethanolamine series, formate yield and TOF value from monoethanolamine via diethanolamine decrease to triethanolamine (page 491, Figure 2). The object of the present invention is to remedy the disadvantages mentioned and in particular to simplify the work-up of the reaction effluents which occur in the catalytic hydrogenation of carbon dioxide in the presence of amines.

This object is surprisingly achieved by providing a process for preparing formic acid comprising reacting by catalytic hydrogenation of carbon dioxide with hydrogen on a catalyst containing a metal of groups 8 to 10 of the periodic table in the presence of a primary, secondary and / or tertiary Amines generates the corresponding ammonium formate and cleaves the ammonium formate by heating in formic acid and the amine, characterized in that the primary, secondary or tertiary amine is selected from the amines of the formula I or mixtures thereof,

NR ₂ I

where Ri to R _{3 are} identical or different and denote hydrogen, linear or branched alkyl radicals having 1 to 18 carbon atoms, cycloaliphatic radicals having 5 to 7 carbon atoms, aryl radicals and / or arylalkyl radicals and at least one of the radicals Ri to R ₃ carries a hydroxyl group, and one, the hydrogenation is carried out in a solvent having a boiling point ≥ 105 ⁰ C at atmospheric pressure, and one in which the high boiling solvent the reaction mixture containing the hydrogenation wins the formic acid by thermal cleavage of the ammonium formate and distillation of the formic acid.

The reaction of the invention can be z. B. when using triethanolamine as the tertiary base and [RuH ₂ (PPh ₃ ) ₄ ] as a hydrogenation catalyst by the following reaction equation:

CO ₂ + H ₂ + N (CH ₂ -CH ₂ -OH) ₃ ^ _H COO-HN ⁺ (CH ₂ -CH ₂ -OH) ₃

[RuH ₂ (PPh ₃ ) J

Carbon dioxide can be used solid, liquid or gaseous, it is preferably used in gaseous form.

In the amines of the formula I, the radicals R 1 to R _{3 are} identical or different and denote hydrogen, linear or branched alkyl radicals having 1 to 18 carbon atoms, cycloaliphatic radicals having 5 to 8 carbon atoms, aryl radicals having 6 to 12 carbon atoms atoms or arylalkyl radicals. At least one of Ri to R3 carries a hydroxyl group. The compounds of formula I thus contain an amino group and at least one hydroxyl group in the same molecule.

As linear alkyl radicals z. For example, methyl, ethyl, n-butyl, n-propyl, n-hexyl, n-decyl, n-dodecyl radicals in question.

Suitable branched alkyl radicals are derived from linear alkyl radicals and carry as side chains alkyl radicals having one to four carbon atoms, such as methyl, ethyl, propyl or butyl radicals. Preferred are linear or branched alkyl radicals having a maximum of 14, more preferably not more than 10 carbon atoms.

As cycloaliphatic radicals having 5 to 8 carbon atoms z. As cyclopentyl or cyclohexyl radicals in question, which may be unsubstituted or substituted by methyl or ethyl radicals.

Suitable aryl radicals are unsubstituted phenyl radicals or phenyl radicals which may be monosubstituted or polysubstituted by C 1 to C ₄ -alkyl radicals.

Suitable aralkyl groups are, for example phenylalkyl radicals of the formula -CH ₂ -C H _O _5, whose phenyl group may be mono- or poly-substituted by d- to C ₄ -alkyl radicals.

At least one of Ri to R3 contains a hydroxyl group. But it is also possible that two or three of the radicals Ri to R ₃ each contain a hydroxyl group. It may be a primary, secondary or tertiary hydroxyl group.

Preferably, a total of two, more preferably three hydroxyl groups in the radicals R ₁ to R _{3 are} included. Due to the presence of hydroxyl groups, the radicals Ri to R ₃ become aliphatic or cycloaliphatic alcohols or phenols.

Very particular preference is given to amines I having radicals R ₁ to R ₃ which are selected from the group consisting of C 1 -C ₁₄ -alkyl, benzyl, phenyl and cyclohexyl, where the radicals R ₁ to R ₃ carry a total of 1 to 3 hydroxyl groups.

Examples of the amines I according to the invention are ethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, ethyldiethanolamine, dodecyldiethanolamine, phenyldiethanolamine, diphenylethanolamine, p-hydroxyphenyldiethanolamine, p-hydroxycyclohexylethylethanolamine, diethylethanolamine, dimethylethanolamine. Tertiary amines I are preferred over primary and secondary amines I, for example the previously mentioned in detail tertiary amines. Very particular preference is triethanolamine.

Particularly preferred mixtures of amines I are mixtures of monoethanolamine, diethanolamine and triethanolamine, as obtained in the reaction of ethylene oxide with ammonia with variation of the molar ratio (K. Weissermel, H. -J. Arpe, Industrielle Organische Chemie, fourth edition, VCH -Verlag, pages 172 to 173, 1994). These contain, for example, 10 to 75 mol% monoethanolamine, 20 to 25 mol% diethanolamine and 0 to 70 mol% triethanolamine.

In general, the boiling point of the amines used according to the invention at normal pressure (1013 mbar) is at least 130 ^° C., preferably at least 150 ^° C.

The hydrogenation catalyst contains as catalytically active components one or more metals or compounds of these metals of groups 8 to 10 of the Periodic Table, ie the metals of the iron, cobalt and nickel group (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir , Pt). Of these, the noble metals (Ru, Rh, Pd, Os, Ir, Pt) are preferred, with palladium, rhodium and ruthenium being most preferred. The catalytically active components include the metals themselves, but also their compounds, such as. Ruthenium trichloride and the complexes bis (triphenylphosphine) ruthenium dichloride and tris (triphenylphosphine) rhodium chloride. The metals mentioned and their compounds can be used suspended or dissolved homogeneously. However, it is also possible to apply the metals or their compounds to inert catalyst supports and to suspend the heterogeneous catalysts thus prepared in the reaction according to the invention or to use them as fixed bed catalysts.

As an inert catalyst carrier z. B. SiO ₂ , Al ₂ O ₃ , ZrO ₂ , mixtures of these oxides or graphite are used.

Particularly preferred catalysts are compounds of the formula RuH ₂ L ₄ or RuH ₂ (LL) ₂ in which L is a monodentate phosphorus-based ligand and LL is a bidentate phosphorus-based ligand.

When using homogeneously dissolved metal compounds, the catalyst concentration is 0.1 to 1000, preferably 1 to 800, particularly preferably 5 to 500 ppm of catalytically active metal, based on the entire reaction mixture.

Particularly preferred as a homogeneous catalyst is the ruthenium complex compound [RuH ₂ (triphenylphosphine) ₄ ]. When using heterogeneous catalysts, the amount of metal on the support is generally from 0.1 to 10% by weight of the heterogeneous catalyst.

The hydrogenation is carried out in the presence of a high-boiling, generally organic solvent which boils at atmospheric pressure (1013 mbar) at least 5 ^° C., in particular at least 10 ^° C. higher than formic acid. Formic acid boils at atmospheric pressure at 100 to 101 ⁰ C. Suitable solvents are, for. As alcohols, ethers, sulfolanes, dimethyl sulfoxide, open-chain or cyclic amides such as dialkylformamide, dialkylacetamides, N-formylmorpholine (boiling point 240 ° C / 1013 mbar) or 5- to 7-membered lactams or mixtures of the compounds mentioned. In general, under the conditions of the hydrogenation, a homogeneous reaction mixture of high-boiling solvent and the one or more amines without miscibility gap is present.

Preferably, the boiling point of the organic solvent is above 105 ⁰ C, more preferably above 1 15 ⁰ C.

Preferred solvents include dialkylformamides, dialkylacetamides and dialkyl sulphoxides, preferably d-Cβ-alkyl groups and, in particular, N, N-dibutylformamide (boiling point 119 to 120 ⁰ C, 15 mm) of N, N-Dibutylacetamid (boiling point 77-78 ° C / 6 mm Hg) and dimethyl sulfoxide (bp 189 ⁰ C).

It is also possible to carry out the reaction according to the invention without the addition of solvents which boil at atmospheric pressure higher than 105 ^° C. and form only a liquid phase under the hydrogenation reaction conditions. In this case, the amines of the formula I themselves act as solvents.

The solvent mixture may contain up to 5% by weight of water. Small amounts of water can be formed, for example, by esterification of alkanolamine and formic acid in the thermal cleavage of the ammonium formates and the distillative removal of formic acid.

The amount of solvent is 5 to 80 wt .-%, in particular 10 to 60 wt .-%, based on the total feed mixture.

The catalytic hydrogenation can be carried out batchwise or preferably continuously in the liquid phase.

The reaction temperature in the catalytic hydrogenation is generally from 30 to 150 ⁰ C, preferably 30 to 100 ⁰ C, particularly preferably 40 to 75 ⁰ C. The partial pressure of the carbon dioxide is generally from 5 bar to 60 bar, in particular from 30 bar to 50 bar, the partial pressure of hydrogen from 5 bar to 250 bar, in particular 10 to 150 bar.

The molar ratio of carbon dioxide to hydrogen is generally from 10: 1 to 0.1: 1, preferably from 1: 1 to 1: 3.

The molar ratio of carbon dioxide to amine may be varied in the range of from 10 to 1 to 0.1 to 1, preferably in the range of 0.5 to 1 to 2 to 1.

The residence time is generally 10 minutes to 8 hours.

The inventive method is characterized by a higher solubility of carbon dioxide in the reaction mixture containing the amines I, compare the solubility of CO ₂ in triethylamine: IG Podvigaylova at al. So V. Chem. Ind. 5, 1970, pages 19 to 21 with the solubility of CO ₂ in triethanolamine: RE Meissner, U. Wagner, OiI and Gas Journal, Feb. 7, 1983, pages 55 to 58.

The ammonium formates prepared according to the invention can be thermally cleaved into formic acid and amine. This is done according to the invention in the reaction mixture of the hydrogenation, which contains the high-boiling solvent, optionally after prior separation of the catalyst. The inventive method is characterized in that a distillative separation of formic acid from the reaction mixture is easily possible because formic acid is the component with the lowest boiling point. As a result, it can easily be distilled off from the reaction mixture containing the high-boiling solvent and the amine I.

For this purpose, the hydrogenation is distilled in a distillation apparatus at pressures of 0.01 to 2 bar, preferably 0.02 to 1 bar, more preferably at 0.05 to 0.5 bar. The liberated formic acid passes overhead and is condensed. The bottoms product, which consists of liberated amine I, solvent and optionally catalyst, is recycled to the hydrogenation stage. The bottom temperatures are, depending on the set pressure, 130 to 220 ⁰ C, preferably 150 to 200 ⁰ C.

Heterogeneous hydrogenation catalysts, the z. B. are used in suspension, are generally separated by filtration from the hydrogenation before the thermal cleavage of the formates. Depending on the thermal stability of the homogeneous hydrogenation catalysts, separation prior to thermal cleavage of the ammonium formates may be advantageous, for example by extraction, adsorption or ultrafiltration. For thermal cleavage are especially distillation equipment such as distillation columns, z. B. packed, packed and bubble tray columns. As a filler z. B. to avoid corrosion preferably ceramic packing. Furthermore, thin film or falling film evaporators may be advantageous if short residence times are desired.

After the formic acid separation, the mixture of high boiling solvent and amine can be recycled to the carbon dioxide hydrogenation. Preference is given to a continuous process in which the solvent / amine mixture, if appropriate after separation of a purge stream, is recycled.

The invention is further illustrated by the following examples.

Examples

General procedure for the experiments on the catalytic hydrogenation of carbon dioxide with hydrogen

In an autoclave, a mixture of an amine and a solvent in which [RuH ₂ (PPh ₃ ) ₄ ] catalyst was dissolved was vigorously stirred (600 revolutions per minute). At room temperature hydrogen was then pressed to a pressure of 10 bar. The mixture was then warmed to 50 ^° C. and hydrogen was repressed to a pressure of 30 bar. By pressing carbon dioxide, the pressure was increased up to 60 bar. The mixture was then stirred at 50 ^° C. for one hour.

Then the autoclave was cooled and relaxed. The formate content of the reaction effluent was determined by IC analysis. In Table 1, the feedstocks and their amounts together with the formate amounts found and the TOF values (turn over frequency) are compiled.

Example 1 and Comparative Example 1

The experimental results show that TOF values of the same order of magnitude as when working with triethylamine in methanol are achieved when working with triethanolamine in dibutylformamide. Example 2 and Comparative Examples 2a and 2b

The three examples were carried out with a quarter of the catalyst amount of Example 1 and Comparative Example 1. They show that significantly better TOF values are achieved when working with triethanolamine in dibutylformamide than when working with triethylamine in dibutylformamide or a dibutylformamide / water mixture.

The results of Examples 1 and 2 are also surprising insofar as the carbon dioxide hydrogenation in water as a solvent with ethanolamines leads to significantly worse results than with dimethyl and triethylamine, see W. Leitner et al. in "Aqueous Phase Organometallic Catalysis", edited by B. Cornils and WA Herrmann, published by WILEY-VCH, page 491.

Table 1

¹⁾ TOF (turn over frequency) = mole of target product per mole of cat. Metal and hour; TON (turn over number); TOF = TON per hour; All experiments were carried out for 5 hours

Claims

claims

1. A process for the preparation of formic acid, which is obtained by catalytic hydrogenation of carbon dioxide with hydrogen over a catalyst containing a metal of groups 8 to 10 of the Periodic Table, in the presence of a primary, secondary and / or tertiary amine, the corresponding ammonium formate and the ammonium formate is split by heating in formic acid and the amine, characterized in that the primary, secondary or tertiary amine is selected from the amines of the formula I or mixtures thereof,

R ^X 1

NO,

where R 1 to R ₃ are identical or different and denote hydrogen, linear or branched alkyl radicals having 1 to 18 carbon atoms, cycloaliphatic radicals having 5 to 7 carbon atoms, aryl radicals and / or arylalkyl radicals and at least one of the radicals R 1 to R ₃ bears a hydroxyl group, and carrying out the hydrogenation in a solvent which has a boiling point ≥ 105 ⁰ C at atmospheric pressure, and the formic acid in the high-boiling solvent reaction mixture of the hydrogenation by thermal cleavage of the ammonium formate and distilling off the formic acid wins.

2. The method according to claim 1, characterized in that one uses as the amine monoethanolamine, diethanolamine or triethanolamine or a mixture of two or three of these compounds.

3. The method according to claim 1 or 2, characterized in that the catalyst contains ruthenium, rhodium and / or palladium.

4. Process according to claims 1 to 3, characterized in that the catalyst is a homogeneous catalyst or a suspended or fixed heterogeneous catalyst.

5. The method according to claims 1 to 4, characterized in that the catalyst is a compound of the formula RuH ₂ L ₄ or RuH ₂ (LL) _2, wherein L Nigen a monodentate phosphorus-containing ligand and LL one bidentate phosphorus-containing ligand means includes.

6. The method according to claims 1 to 5, characterized in that the catalyst comprises the compound [RuH ₂ (PPh ₃ ) ₄ ], wherein the compound in the reaction mixture can be homogeneously dissolved or heterogeneous on a support.

7. The method according to claims 1 to 6, characterized in that the high-boiling solvent is selected from the group consisting of alcohols, ethers, sulfolanes, sulfoxides, open-chain or cyclic amides or mixtures thereof.

8. Process according to claim 7, characterized in that the solvent is selected from the group consisting of N, N-dialkylformamides, N, N-dialkylacetamides, N-formylmorpholine, 5- to 7-membered N-alkyllactams and dialkylsulfoxides, where alkyl is in each case C 1 - to C ₅ -alkyl, and their mixtures see.

9. Process according to claims 1 to 8, characterized in that the high-boiling solvent is N, N-dibutylformamide or dimethyl sulfoxide.

10. The method according to claims 1 to 9, characterized in that the catalytic hydrogenation is carried out at temperatures of 30 ⁰ C to 150 ⁰ C.

1 1. The method according to any one of claims 1 to 10, characterized in that amine I and high-boiling solvent form a single-phase mixture under the conditions of hydrogenation.

12. The method according to any one of claims 1 to 11, characterized in that after distilling off the formic acid, the mixture of amine I and high-boiling solvent is recycled to the hydrogenation.