WO2013004577A1

WO2013004577A1 - Process for the preparation of formic acid by reacting carbon dioxide with hydrogen

Info

Publication number: WO2013004577A1
Application number: PCT/EP2012/062518
Authority: WO
Inventors: Thomas Schaub; Donata Maria Fries; Rocco Paciello; Peter Bassler; Martin Schäfer; Stefan Rittinger
Original assignee: Basf Se
Priority date: 2011-07-07
Filing date: 2012-06-27
Publication date: 2013-01-10
Also published as: CN103649036A; CA2838907A1; ZA201400863B; EP2729438A1; RU2014104137A; BR112013033528A2; JP2014522823A; KR20140044891A

Abstract

Process for the preparation of formic acid by reacting carbon dioxide with hydrogen in a hydrogenation reactor in the presence of a catalyst comprising an element from the 8th, 9th or 10th group of the Periodic Table of the Elements, of a tertiary amine and of a polar solvent, with formation of formic acid-amine adducts, which are then cleaved thermally to give formic acid and tertiary amine.

Description

Process for the preparation of formic acid by reaction of carbon dioxide with hydrogen

description

The invention relates to a process for the preparation of formic acid by reacting carbon dioxide with hydrogen in a hydrogenation reactor in the presence of a catalyst containing an element from the 8th, 9th or 10th group of the periodic table, a tertiary amine and a polar solvent, with formation of formic acid-amine adducts, which are then thermally cleaved to formic acid and tertiary amine.

Adducts of formic acid and tertiary amines can be thermally cleaved into free formic acid and tertiary amine and therefore serve as intermediates in the preparation of formic acid.

Formic acid is an important and versatile product. It is used, for example, for acidification in the production of animal feed, as a preservative, as a disinfectant, as an adjuvant in the textile and leather industry, as a mixture with their salts for de-icing of airplanes and runways and as a synthesis component in the chemical industry.

The said adducts of formic acid and tertiary amines can be prepared in various ways, for example (i) by direct reaction of the tertiary amine with formic acid, (ii) by hydrolysis of methyl formate to formic acid in the presence of the tertiary amine, (iii) by catalytic Hydration of carbon monoxide in the presence of the teriary amine or (iv) by hydrogenation of carbon dioxide to formic acid in the presence of the tertiary amine. The latter method of catalytic hydrogenation of carbon dioxide has the particular advantage that carbon dioxide is available in large quantities and is flexible in its source.

EP 0 095 321 describes a process for the preparation of trialkylammonium formates, ie of an adduct of formic acid and a tertiary amine, by hydrogenation of carbon dioxide in the presence of a tertiary amine, a solvent and a transition metal catalyst of VIII. Subgroup of the Periodic Table (Groups 8, 9, 10 according to IUPAC). The catalyst used is preferably ruthenium trichloride. As tertiary amine and solvent, triethylamine and a mixture of isopropanol and water are preferred. The reaction takes place in an autoclave at 82 bar and 80 ° C. The working up of the reaction mixture is carried out by distillation, whereby a first fraction containing isopropanol, water and triethylamine and a second fraction containing the adduct of formic acid and triethylamine are obtained. The thermal decomposition of the adduct of formic acid and triethylamine to formic acid is not described in EP 0 095 321.

EP 0 151 510 also describes a process for the preparation of adducts of formic acid and triethylamine, wherein the catalyst used is a rhodium-containing complex catalyst. The reaction is also carried out in an autoclave, the work-up of the resulting reaction mixture is carried out as in EP 0 095 321 by distillation.

EP 0 126 524 and EP 0 181 078 describe a process for the preparation of formic acid by thermal cleavage of adducts of formic acid and a teriary amine. According to EP 0 181 078, the process for producing formic acid comprises the following steps: i) reacting carbon dioxide and hydrogen in the presence of a volatile tertiary amine and a catalyst to obtain the adduct

Formic acid and the volatile tertiary amine, ii) separation of the adduct of formic acid and volatile tertiary amine from the catalyst and the gaseous components in an evaporator, iii) separation of the unreacted volatile tertiary amine in a distillation column or in a phase separator of the adduct of formic acid and the volatile tertiary amine, iv) base exchange of the volatile tertiary amine in the adduct of formic acid and the volatile tertiary amine by a less volatile and weaker nitrogen base, such as 1-n-butylimidazole, v) thermal cleavage of the adduct of formic acid and the less volatile and weaker nitrogen base to give formic acid and the less volatile and weaker nitrogen base.

In EP 0 126 524 and EP 0 181 078, the volatile tertiary amine in the formic acid adduct must be exchanged by a less volatile and weaker nitrogen base, such as, for example, 1-n-butylimidazole, before the thermal cleavage. The processes according to EP 0 126 524 and EP 0 181 078 are therefore very complicated, in particular with regard to the compulsory base exchange. A further significant disadvantage of the processes according to EP 0 126 524 and EP 0 181 078 is the fact that the separation of the adduct of formic acid and volatile tertiary amine according to the above-described step ii) of EP 0 126 524 and EP 0 181 078 in one Evaporator is carried out in the presence of the catalyst.

As a result, the cleavage of the adduct of formic acid and volatile tertiary amine to carbon dioxide, hydrogen and volatile tertiary amine is catalyzed according to the following reaction equation:

Kat

HCOOH * NR ₃ ►CO ₂ + H ₂ + NR ₃

Δ

The cleavage leads to a significant reduction in the yield of adduct of formic acid and volatile tertiary amine and thus to a reduction in the yield of the target product formic acid.

EP 0 329 337 proposes the addition of an inhibitor which reversibly inhibits the catalyst in order to solve this problem. Preferred inhibitors include carboxylic acids, carbon monoxide and oxidizing agents. The production of formic acid therefore comprises the steps i) to v) described above for EP 0 126 524 and EP 0 181 078, the addition of the inhibitor taking place after step i) and before or during step ii). A disadvantage of the process according to EP 0 329 337 in addition to the complex base exchange (step iv)) that the inhibitor passes together with the recycled tertiary amine in the hydrogenation (step (i)) and there the synthesis to the adduct of formic acid and volatile tertiary Amin disturbs. A further disadvantage of EP 0 329 337 is that a large part of the catalyst in the process is inhibited. Therefore, in the process according to EP 0 329 337, the inhibited catalyst must be reactivated before reuse in the hydrogenation (step i)).

WO 2010/149507 describes a process for the preparation of formic acid by hydrogenation of carbon dioxide in the presence of a tertiary amine, a transition metal catalyst and a high boiling polar solvent with an electrostatic factor> 200 * 10 ^"30 cm, such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1, 3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, dipropylene glycol, 1,5-pentanediol, 1,6-hexanediol and glycerol to give a reaction mixture which contains the formic acid amine. Adduct, the tertiary amine, the high-boiling polar solvent and the catalyst The reaction mixture is worked up according to WO 2010/149507 according to the following steps: 1) phase separation of the reaction mixture to obtain an upper phase containing the tertiary amine and the catalyst and a lower phase containing the formic acid-amine adduct, the high-boiling polar solvents and residues of the catalyst; Recycling of the upper phase for hydrogenation,

2) extracting the lower phase with the tertiary amine to obtain an extract containing the tertiary amine and the residues of the catalyst and a raffinate containing the high boiling point polar solvent and the formic acid amine adduct; Recycling of the extract for hydrogenation,

3) thermal cracking of the raffinate in a distillation column to obtain a distillate containing the formic acid and a bottoms mixture containing the free tertiary amine and the high-boiling polar solvent; Recycling of the high-boiling polar solvent for hydrogenation.

The process according to WO 2010/149507 has the advantage over the processes according to EP 0 095 321, EP 0 151 510, EP 0 126 524, EP 0 181 078 and EP 0 329 337 that it can be carried out without the complex base exchange step (step (iv)). ) and allows separation and recycling of the catalyst in its active form. However, a disadvantage of the process of WO 2010/149507 is that the separation of the catalyst despite phase separation (step 1)) and extraction (step 2)) is not always completely successful, so that traces of catalyst contained in the raffinate in the thermal cracking in the distillation column in Step 3) can catalyze the cleavage of the formic acid-amine adduct to carbon dioxide and hydrogen and the tertiary amine. It is also disadvantageous that esterification of the formic acid formed with the high-boiling polar solvents (diols and polyols) occurs in the thermal cleavage of the formic acid-amine adduct in the distillation column. This leads to a reduction in the yield of the target product formic acid.

The object of the present invention was to provide a process for the preparation of formic acid by hydrogenation of carbon dioxide, which does not have the disadvantages of the prior art or only to a significantly reduced extent and which leads to concentrated formic acid in high yield and high purity , Furthermore, the method should allow a simpler process control, as described in the prior art, in particular a simpler process concept for working up the discharge from the hydrogenation reactor, simpler process steps, a smaller number of process stages or simpler Apparatuses. Furthermore, the method should also be able to be carried out with the lowest possible energy requirement. Since a complete separation of the homogeneously dissolved active catalyst from the product stream can be realized only with great effort and even small amounts of catalyst in the thermal cleavage due to the high temperatures would lead to significant losses of formic acid, should also ensure that Catalyst traces are transferred before the distillation in non-active species, without the hydrogenation is disturbed. The object is achieved by a process for the preparation of formic acid, comprising the steps

(A) homogeneously catalyzed reaction of a reaction mixture (Rg) containing carbon dioxide, hydrogen, at least one catalyst containing at least one element selected from groups 8, 9 and 10 of the

Periodic Table, at least one polar solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and water and at least one tertiary amine of the general formula ( A1)

NR ¹ R ² R ³ (A1),

in the

R ¹ , R ² , R ³ independently of one another are unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic

Represent radicals having in each case 1 to 16 carbon atoms, wherein individual carbon atoms can be substituted independently of one another by a hetero group selected from the groups -O- and> N- and two or all three radicals connected to form a chain comprising at least four atoms in each case in a hydrogenation reactor to obtain, optionally after addition of water, a biphasic hydrogenation mixture (H) containing an upper phase (01) containing the at least one catalyst and the at least one tertiary amine (A1), and a lower phase (U 1 ) containing the at least one polar solvent, radicals of the at least one catalyst and at least one formic acid-amine adduct of the general formula (A2), _NR i _{R2 R3} * _x . HCOOH (A2),

in the

X, is in the range of 0.4 to 5 and

R ¹ , R ² , R ^{3 have} the meanings given above,

Working up of the hydrogenation mixture (H) obtained in step (a) according to one of the following steps

(b1) phase separation of the hydrogen mixture (H) obtained in step (a) in a first phase separation device into the upper phase (01) and the lower phase (U1) or

(b2) Extraction of the at least one catalyst from the hydrogen mixture (H) obtained in step (a) in an extraction unit with an extractant containing at least one tertiary amine (A1) to obtain a raffinate (R1) containing the at least one formic acid-amine adduct (A2) and the at least one polar solvent and an extract (E1) containing the at least one tertiary amine (A1) and the at least one catalyst or

(b3) phase separation of the obtained in step (a) Hydnergemischs (H) in a first phase separation device in the upper phase (01) and the lower phase (U1) and extraction of the residues of the at least one catalyst from the lower phase (U1) in an extraction unit with a Extraction agent comprising the at least one tertiary amine (A1) to obtain a raffinate (R2) containing the at least one formic acid-amine adduct (A2) and the at least one polar solvent and an extract (E2) containing the at least one tertiary amine (A1) and the radicals of the at least one catalyst, (c) at least partially separating the at least one polar solvent from the lower phase (U 1), from the raffinate (R1) or from the raffinate (R2) in a first distillation apparatus to obtain a distillate (D1) containing the at least one polar solvent, which is recycled to the hydrogenation reactor in step (a) and a biphasic bottoms mixture (S1) containing an upper phase (02) containing the at least one tertiary amine (A1) and a lower phase (U2) containing the at least one formic acid amine Adduct (A2), (d) optionally working up of the first bottoms mixture (S1) obtained in step (c) by phase separation in a second phase separation device into the upper phase (02) and the lower phase (U2),

(E) cleavage of the at least one formic acid-amine adduct contained in the bottom mixture (S1) or optionally in the bottom phase (U2)

(A2) in a thermal cleavage unit to obtain the at least one tertiary amine (A1) which is recycled to the hydrogenation reactor in step (a) and formic acid discharged from the thermal cleavage unit, immediately before and / or during step (C) the lower phase (U 1), the raffinate (R1) or the raffinate (R2) is added at least one inhibitor selected from the group consisting of carboxylic acids other than formic acid, of carboxylic acid derivatives other than formic acid derivatives and oxidizing agents.

It has been found that formic acid can be obtained in high yield with the process according to the invention. It is particularly advantageous that in the process according to the invention the base exchange (step (iv)) according to the processes of EP 0 126 524 and EP 0 181 078 can be saved. The process according to the invention enables an effective separation of the catalyst in its active form and the recycling of the separated catalyst into the hydrogenation reactor in step (a). In addition, the use of an inhibitor prevents the cleavage of the formic acid-amine adduct (A2), which leads to an increase in the yield of formic acid. By separating the polar solvent used according to the invention, in addition, esterification of the formic acid obtained in the thermal splitting unit in step (e) is prevented, which also leads to an increase in the formic acid yield. In addition, it has surprisingly been found that the use of the polar solvents according to the invention leads to an increase in the concentration of the formic acid-amine adduct (A2) in the hydrogenation mixture (H) obtained in step (a) compared to the polar solvents used in WO2010 / 149507 , This allows the use of smaller reactors, which in turn leads to a cost savings.

The terms "step" and "process step" are used synonymously below. Preparation of Formic Acid-Amine Adduct (A2); Process step (a)

In the process according to the invention, a reaction mixture (Rg) which comprises carbon dioxide, hydrogen, at least one catalyst containing at least one element selected from groups 8, 9 and 10 of the Periodic Table, at least one polar solvent selected from the Group consisting of methanol, ethanol, 1-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and water and at least one tertiary amine of the general formula (A1). The carbon dioxide used in process step (a) can be solid, liquid or gaseous. It is also possible to use gas mixtures containing large quantities of carbon dioxide, provided they are substantially free of carbon monoxide (volume fraction of <1% CO). The hydrogen used in the hydrogenation of carbon dioxide in process step (a) is generally gaseous. Carbon dioxide and hydrogen may also contain inert gases, such as nitrogen or noble gases. However, their content is advantageously below 10 mol% based on the total amount of carbon dioxide and hydrogen in the hydrogenation reactor. Although quantities may also be tolerable, they generally require the use of a higher pressure in the reactor, requiring further compression energy.

Carbon dioxide and hydrogen can be fed to process stage (a) as separate streams. It is also possible to use a mixture containing carbon dioxide and hydrogen in process step (a).

In the process according to the invention, at least one tertiary amine (A1) is used in process step (a) in the hydrogenation of carbon dioxide. In the context of the present invention, "tertiary amine (A1)" is understood as meaning both one (1) tertiary amine (A1) and mixtures of two or more tertiary amines (A1).

The tertiary amine (A1) used in the process according to the invention is preferably selected in such a way or with the polar solvent that the hydrogenation mixture (H) obtained in process step (a), if appropriate after the addition of water, is at least biphasic. The hydrogenation mixture (H) contains an upper phase (01) containing the at least one catalyst and the at least one tertiary amine (A1), and a lower phase (U 1) containing the at least one polar solvent, residues of the catalyst and at least one formic acid Amine adduct (A2).

The tertiary amine (A1) should be enriched in the upper phase (01), i. the upper phase (01) should contain the main part of the tertiary amine (A1). In the context of the present invention, by "enriched" or "main part" with respect to the tertiary amine (A1) is a weight fraction of the free tertiary amine (A1) in the upper phase (01) of> 50% based on the total weight of the free tertiary Amine (A1) in the liquid phases, ie the upper phase (01) and the lower phase (U 1) in the hydrogenation mixture (H) to understand.

By free tertiary amine (A1) is meant the tertiary amine (A1) which is not bound in the form of the formic acid-amine adduct (A2).

The weight fraction of the free tertiary amine (A1) in the upper phase (01) is preferably> 70%, in particular> 90%, in each case based on the total weight of the free tertiary amine (A1) in the upper phase (01) and the lower phase ( U 1) in the hydrogenation mixture (H).

The selection of the tertiary amine (A1) is generally carried out by a simple experiment in which the phase behavior and the solubility of the tertiary amine (A1) in the liquid phases (upper phase (01) and lower phase (U1)) under the process conditions in the process stage (a) be determined experimentally. In addition, non-polar solvents such as aliphatic, aromatic or araliphatic solvents may be added to the tertiary amine (A1). Preferred non-polar solvents are, for example, octane, toluene and / or xylenes (o-xylene, m-xylene, p-xylene).

The preferred tertiary amine to be used in the process according to the invention is an amine of the general formula

NR ¹ R ² R ³ (A1) in which the radicals R ¹ , R ² , R ^{3 are} identical or different and independently of one another are an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having in each case 1 to 16 carbon atoms, preferably 1 to 12 carbon atoms, wherein individual carbon atoms can be substituted independently of one another by a hetero group selected from the groups -O- and> N- and two or all three radicals with formation a chain comprising at least four atoms each can also be connected to each other. In a particularly preferred embodiment, a tertiary amine of the general formula (A1) is used, with the proviso that the total number of carbon atoms is at least 9.

Examples of suitable tertiary amines of the formula (A1) are:

Tri-n-propylamine, tri-n-butylamine, tri-n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decylamine, tri -n-undecylamine, tri-n-dodecylamine, tri-n-tridecylamine, tri-n-tetradecylamine, tri-n-pentadecylamine, tri-n-hexadecylamine, tri (2-ethylhexyl) amine.

Di-methyl-decylamine, dimethyldodecylamine, dimethyl-tetradecylamine, ethyl-di (2-propyl) amine, dioctyl-methylamine, dihexyl-methylamine.

Tricyclopentylamine, tricyclohexylamine, tricycloheptylamine, tricyclooctylamine and their substituted by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups derivatives. Dimethylcyclohexylamine, methyldicyclohexylamine, diethylcyclohexylamine, ethyldicyclohexylamine, dimethylcyclopentylamine, methyldicyclopentylamine.

• triphenylamine, methyldiphenylamine, ethyldiphenylamine, propyldiphenylamine, butyldiphenylamine, 2-ethylhexyldiphenylamine, dimethylphenylamine, diethylphenylamine, dipropylphenylamine, dibutylphenylamine, bis (2-ethylhexyl ) - phenylamine, tribenzylamine, methyl-dibenzylamine, ethyl-dibenzylamine and theirs by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2- propyl groups substituted derivatives. Nd-bis-C 1-4 -alkyl-piperidines, N, N-di-d-bis-C 1-4 -alkyl-piperazines, N-crib-C ₁₂ -alkyl-pyrrolidones, NC-bis-C 1-4 -alkyl-imidazoles and theirs one or more methyl. Ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups substituted derivatives. 1, 8-diazabicyclo [5.4.0] undsec-7-ene ("DBU"), 1, 4-diazabicyclo [2.2.2] octane ("DABCO"), N-methyl-8-azabicyclo [3.2 .1] octane ("tropane"), N-methyl-9-azabicyclo [3.3.1] nonane ("garnetane"), 1-azabicyclo [2.2.2] octane ("quinuclidine").

In the process according to the invention, mixtures of two or more different tertiary amines (A1) can also be used.

Particularly preferred in the process according to the invention as the tertiary amine of the general formula (A1) is an amine in which the radicals R ¹ , R ² , R ^{3 are} independent are selected from the group (to C ₁₂ alkyl, C ₅ - to C ₈ cycloalkyl, benzyl and phenyl, a.

In the process according to the invention, it is particularly preferable to use as the tertiary amine a saturated amine, i. containing only single bonds of the general formula (A1).

An especially suitable amine in the process according to the invention is a tertiary amine of the general formula (A1) in which the radicals R ¹ , R ² , R ^{3 are} independently selected from the group C ₅ - to C ₈ -alkyl, in particular tri -n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine,

Dimethylcyclohexylamine, methyldicyclohexylamine, dioctylmethylamine and dimethyldecylamine. In one embodiment of the process according to the invention, one (1) tertiary amine of the general formula (A1) is used.

In particular, the tertiary amine used is an amine of the general formula (A1) in which the radicals R ¹ , R ² and R ³ are selected independently of one another from C ₅ - and C ₆ -alkyl. Most preferably, in the process according to the invention, tri-n-hexylamine is used as the tertiary amine of the general formula (A1).

The tertiary amine (A1) in the process according to the invention is preferably liquid in all process stages. However, this is not a mandatory requirement. It would also be sufficient if the tertiary amine (A1) were dissolved at least in suitable solvents. Suitable solvents are in principle those which are chemically inert with respect to the hydrogenation of carbon dioxide, in which the tertiary amine (A1) and the catalyst dissolve well and in which, conversely, the polar solvent and the formic acid-amine adduct (A2) dissolve poorly , In question, therefore, in principle, chemically inert, nonpolar solvents such as aliphatic, aromatic or araliphatic hydrocarbons, such as octane and higher alkanes, toluene, xylenes.

In the process of the invention, at least one polar solvent is selected in process step (a) in the hydrogenation of carbon dioxide from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1 - propanol and water used.

In the context of the present invention, "polar solvent" is understood to mean both one (1) polar solvent and mixtures of two or more polar solvents. The polar solvent used in the process according to the invention is preferably selected or matched with the tertiary amine (A1) so that it preferably meets the following criteria with regard to the phase behavior in the hydrogenation reactor in process step (a): The polar solvent should preferably be selected such that the hydrogenation mixture (H) obtained in process step (a) is at least biphasic. The polar solvent should be enriched in the lower phase (U 1), ie the lower phase (U 1) should contain the main part of the polar solvent. In the context of the present invention, "enriched" or "main part" with respect to the polar solvent is a weight fraction of the polar solvent in the lower phase (U 1) of> 50%, based on the total weight of the polar solvent in the liquid phases (upper phase ( 01) and lower phase (U 1)) in the hydrogenation reactor to understand.

The weight fraction of the polar solvent in the lower phase (U 1) is preferably> 70%, in particular> 90%, in each case based on the total weight of the polar solvent in the upper phase (01) and the lower phase (U 1).

The selection of the polar solvent satisfying the above criteria is generally accomplished by a simple experiment in which the phase behavior and the solubility of the polar solvent in the liquid phases (upper phase (01) and lower phase (U 1)) under the process conditions in Process step (a) are determined experimentally.

The polar solvent may be a pure polar solvent or a mixture of two or more polar solvents as long as the polar solvent or mixture of polar solvents meets the above-described phase behavior and solubility criteria in the upper phase (01) and the above Subphase (U 1) in the hydrogenation reactor in process step (a).

In one embodiment of the process according to the invention, in step (a), first of all a single-phase hydrogenation mixture is obtained, which is converted into the biphasic hydrogenation mixture (H) by the addition of water. In a further embodiment of the process according to the invention, the biphasic hydrogenation mixture (H) is obtained directly in step (a). The biphasic hydrogenation mixture (H) obtained in this embodiment can be directly fed to the work-up of step (b). It is also possible to additionally add Waser to the biphasic hydrogenation mixture (H) before further processing in step (b). This can lead to an increase of the distribution coefficient P _K. In the event that a mixture of alcohol and water is used as the polar solvent, the ratio of alcohol to water is chosen so that together with the formic acid-amine adduct (A2) and the tertiary amine (A1) at least two-phase Hydrogenation mixture (H) containing the upper phase (01) and the lower phase (U 1) is formed.

It is also possible that, in the event that as a polar solvent, a mixture of alcohol (selected from the group consisting of methanol, ethanol, 1 - propanol, 2-propanol, 1-butanol, 2-butanol and 2-methyl- 1 -propanol) and water is used, the ratio of alcohol to water is chosen so that, together with the formic acid-amine adduct (A2) and the tertiary amine (A1) first a single-phase hydrogenation mixture is formed, which is subsequently by addition of Water is transferred to the biphasic hydrogenation mixture (H). In a further particularly preferred embodiment, the polar solvent used is water, methanol or a mixture of water and methanol.

The use of diols and their formic acid esters, polyols and their formic acid esters, sulfones, sulfoxides and open-chain or cyclic amides as the polar solvent is not preferred. In a preferred embodiment, these polar solvents are not contained in the reaction mixture (Rg).

The molar ratio of the polar solvent or solvent mixture used in the process according to the invention in process step (a) to the tertiary amine (A1) used is generally 0.5 to 30 and preferably 1 to 20.

The catalyst used in the process according to the invention in process step (a) for the hydrogenation of carbon dioxide comprises at least one element selected from groups 8, 9 and 10 of the periodic table (nomenclature according to I UPAC). Groups 8, 9 and 10 of the Periodic Table include Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt. In process step (a), one (1) catalyst or a mixture of two or more catalysts can be used. Preferably, one (1) catalyst is used. In the context of the present invention, "catalyst" is understood to mean both one (1) catalyst and mixtures of two or more catalysts.

Preferably, the catalyst contains at least one element selected from the group consisting of Ru, Rh, Pd, Os, Ir and Pt, more preferably at least one element selected from the group consisting of Ru, Rh and Pd. Most preferably, the catalyst contains Ru. As the catalyst, a complex-type compound (complex catalyst) of the above-mentioned elements is preferably used. The reaction in process step (a) is preferably carried out homogeneously catalyzed. In the context of the present invention, homogeneously catalyzed means that the catalytically active part of the complex-like compound (of the complex catalyst) is present at least partially dissolved in the liquid reaction medium. In a preferred embodiment, at least 90% of the complex catalyst used in process step (a) is dissolved in the liquid reaction medium, more preferably at least 95%, especially preferably more than 99%, most preferably the complex catalyst is completely dissolved in the liquid reaction medium (100%). ), in each case based on the total amount of complex catalyst present in the liquid reaction medium. The amount of the metal components of the complex catalyst in process step (a) is generally from 0.1 to 5000 ppm by weight, preferably from 1 to 800 ppm by weight and more preferably from 5 to 800 ppm by weight, based in each case on the entire liquid reaction mixture (Rg) in the hydrogenation reactor. The complex catalyst is selected so that it is enriched in the upper phase (01), ie the upper phase (01) contains the main part of the catalyst. In the context of the present invention, a "enriched" or "main part" with respect to the complex catalyst is a distribution coefficient of the complex catalyst P _K = [concentration of the complex catalyst in the upper phase (01)] / [concentration of the complex catalyst in the lower phase (U 1). ] of> 1 to understand. A distribution coefficient P _K > 1.5 is preferred, and a distribution coefficient P _K > 4 is particularly preferred. The complex catalyst is generally selected by a simple experiment in which the phase behavior and the solubility of the complex catalyst in the liquid phases (upper phase (01) and lower phase (U 1)) under the process conditions in process step (a).

Because of their good solubility in tertiary amines used in the process according to the invention as catalysts preferably homogeneous catalysts, in particular an organometallic complex compound containing an element from the 8th, 9th or 10th group of the periodic table and at least one phosphine group with at least one unbranched or branched, acyclic or cyclic, aliphatic radical having 1 to 12 carbon atoms, wherein individual carbon atoms may also be substituted by> P-. In the sense of branched cyclic aliphatic radicals, radicals such as, for example, -CH 2 -C ₆ HH are thus also included. Suitable radicals are, for example, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 1- (2-methyl) propyl, 2- (2-methyl) propyl, 1-pentyl, 1-hexyl, 1 - Heptyl, 1-octyl, 1 -nonyl, 1-decyl, 1-undecyl, 1-dodecyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl, methylcyclopentyl, methylcyclohexyl, 1- (2-methyl) -pentyl, 1- (2-ethyl ) -hexyl, 1 (2-propyl) heptyl and norbornyl. Preferably contains the unmasked or branched, acyclic or cyclic, aliphatic radical of at least 1 and preferably not more than 10 carbon atoms. In the case of an exclusively cyclic radical in the above-mentioned sense, the number of carbon atoms is 3 to 12 and preferably at least 4 and preferably at most 8 carbon atoms. Preferred radicals are ethyl, 1-butyl, sec-butyl, 1-octyl and cyclohexyl.

The phosphine group can contain one, two or three of the above-mentioned unbranched or branched, acyclic or cyclic, aliphatic radicals. These can be the same or different. Preferably, the phosphine group contains three of the above-mentioned unbranched or branched, acyclic or cyclic, aliphatic radicals, with particular preference, all three radicals are the same. Preferred phosphines P (nC _n H _2n + i) 3 with n equal to 1 to 10, more preferably tri-n-butylphosphine, tri-n-octylphosphine and 1, 2-bis (dicyclohexalphosphino) ethane. As already mentioned above, in the stated unbranched or branched, acyclic or cyclic, aliphatic radicals, individual carbon atoms may also be substituted by> P-. Thus, multidentate, for example, bidentate or tridentate phosphine ligands are also included. These preferably contain the

> P-CH ₂ CH ₂ -P <> P-CH ₂ CH ₂ -P-CH ₂ CH ₂ -P <grouping or

If the phosphine group contains radicals other than the abovementioned unbranched or branched, acyclic or cyclic, aliphatic radicals, these generally correspond to those which are customarily used in the case of phosphine ligands for organometallic complex catalysts. As examples of its called phenyl, tolyl and xylyl.

The organometallic complex compound may contain one or more, for example two, three or four, of the abovementioned phosphine groups having at least one unbranched or branched, acyclic or cyclic, aliphatic radical. The remaining ligands of the organometallic complex may be of different nature. Examples which may be mentioned are hydride, fluoride, chloride, bromide, iodide, formate, acetate, propionate, carboxylate, acetylacetonate, carbonyl, DMSO, hydroxide, trialkylamine, alkoxide.

The homogeneous catalysts can be used both directly in their active form and starting from customary standard complexes such as [M (p-cymene) Cl ₂ ] ₂ , [M (benzene) Cl ₂ ] _n , [M (COD) (allyl)], [MCI ₃ × H ₂ O], [M (acetylacetonate) ₃ ], [M (COD) Cl ₂ ] ₂ , [M (DMSO) ₄ Cl ₂ ] with M being the same element from the 8th, 9th or 10th Group of the periodic table with the addition of the corresponding or the corresponding phosphine ligands are produced only under reaction conditions. In the process according to the invention preferred homogeneous catalysts

[Ru (P ⁿ -Bu ₃₎ 4 (H) _2], [Ru (P ^n-octyl ₃₎ 4 (H) _2], [Ru (P ⁿ -Bu ₃₎ ₂ (1, 2-bis (dicyclohexylphosphino) - ethane ) (H) ₂ ], [Ru (P ⁿ octyl ₃ ) ₂ (1, 2-bis (dicyclohexylphosphino) ethane) (H) ₂ ], [Ru (PEt ₃ ) ₄ (H) ₂ ]

[Ru (P ^n-octyl ₃₎ 1, 2-bis (dicyclohexylphosphino) ethane) (CO) (H) _2],

[Ru (P ^n-octyl ₃₎ 1, 2-bis (dicyclohexylphosphino) ethane) (CO) (H) (HCOO)],

[Ru (P ⁿ butyl ₃ ) 1,2-bis (dicyclohexylphosphino) ethane) (CO) (H) ₂ ],

[Ru (P ⁿ butyl ₃ ) 1,2-bis (dicyclohexylphosphino) ethane) (CO) (H) (HCOO)],

[Ru (P ethyl ₃ ) 1,2-bis (dicyclohexylphosphino) ethane) (CO) (H) ₂ ],

[Ru (P ethyl ₃ ) 1,2-bis (dicyclohexylphosphino) ethane) (CO) (H) (HCOO)],

[Ru (P ⁿ octyl ₃ ) 1, 1-bis (dicyclohexylphosphino) methane) (CO) (H) ₂ ],

[Ru (P ^n-octyl ₃₎ 1, 1-bis (dicyclohexylphosphino) methane) (CO) (H) (HCOO)],

[Ru (P ⁿ butyl ₃ ) 1, 1-bis (dicyclohexylphosphino) methane) (CO) (H) ₂ ],

[Ru (P ⁿ butyl ₃ ) 1, 1-bis (dicyclohexylphosphino) methane) (CO) (H) (HCOO)],

[Ru (P ethyl ₃ ) 1, 1-bis (dicyclohexylphosphino) methane) (CO) (H) ₂ ],

[Ru (P ethyl ₃ ) 1, 1-bis (dicyclohexylphosphino) -methane) (CO) (H) (HCOO)],

[Ru (P ^n-octyl ₃₎ 1, 2-bis (diphenylphosphino) ethane) (CO) (H) _2],

[Ru (P ^n-octyl ₃₎ 1, 2-bis (diphenylphosphino) ethane) (CO) (H) (HCOO)],

[Ru (P ⁿ butyl ₃ ) 1,2-bis (diphenylphosphino) ethane) (CO) (H) ₂ ],

[Ru (P ⁿ butyl ₃ ) 1,2-bis (diphenylphosphino) ethane) (CO) (H) (HCOO)],

[Ru (P ethyl ₃ ) 1,2-bis (diphenylphosphino) ethane) (CO) (H) ₂ ],

[Ru (P ethyl ₃ ) 1,2-bis (diphenylphosphino) ethane) (CO) (H) (HCOO)],

[Ru (P ^n-octyl ₃₎ 1, 1-bis (diphenylphosphino) methane) (CO) (H) _2],

[Ru (P ⁿ octyl ₃ ) 1, 1-bis (diphenylphosphino) -methane) (CO) (H) (HCOO)],

[Ru (P ⁿ butyl ₃ ) 1, 1-bis (diphenylphosphino) -methane) (CO) (H) ₂ ],

[Ru (P ⁿ butyl ₃ ) 1, 1-bis (diphenylphosphino) -methane) (CO) (H) (HCOO)],

[Ru (P ethyl ₃ ) 1,1-bis (diphenylphosphino) -methane) (CO) (H) ₂ ],

[Ru (P ethyl ₃ ) 1, 1-bis (diphenylphosphino) -methane) (CO) (H) (HCOO)].

With these, in the hydrogenation of carbon dioxide, TOF values (turn-over-frequency) of greater than 1000 r.sup.- ¹ can be achieved.

The hydrogenation of carbon dioxide in process step (a) is preferably carried out in the liquid phase at a temperature in the range of 20 to 200 ° C and a total pressure in the range of 0.2 to 30 MPa abs. Preferably, the temperature is at least 30 ° C and more preferably at least 40 ° C and preferably at most 150 ° C, more preferably at most 120 ° C and most preferably at most 80 ° C. The total pressure is preferably at least 1 MPa abs and more preferably at least 5 MPa abs and preferably at most 15 MPa abs.

In a preferred embodiment, the hydrogenation is carried out in process step (a) at a temperature in the range of 40 to 80 ° C and a pressure in the range of 5 to 15 MPa abs. The partial pressure of the carbon dioxide in process step (a) is generally at least 0.5 MPa and preferably at least 2 MPa and generally at most 8 MPa. In a preferred embodiment, the hydrogenation in process step (a) is carried out at a partial pressure of the carbon dioxide in the range of 2 to 7.3 MPa.

The partial pressure of the hydrogen in process step (a) is generally at least 0.5 MPa and preferably at least 1 MPa and generally at most 25 MPa and preferably at most 10 MPa. In a preferred embodiment, the hydrogenation is carried out in process step (a) at a partial pressure of hydrogen in the range of 1 to 10 MPa.

The molar ratio of hydrogen to carbon dioxide in the reaction mixture (Rg) in the hydrogenation reactor is preferably 0, 1 to 10 and more preferably 1 to 3.

The molar ratio of carbon dioxide to tertiary amine (A1) in the reaction mixture (Rg) in the hydrogenation reactor is preferably 0, 1 to 10 and more preferably 0.5 to 3.

In principle, all reactors which are suitable for gas / liquid reactions under the given temperature and the given pressure can be used as hydrogenation reactors. Suitable standard reactors for gas-liquid reaction systems are described, for example, in KD Henkel, "Reactor Types and Their Industrial Applications", Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007, b04_087, Chapter 3.3 "Reactor for gas-liquid reactions". As examples of his called stirred tank reactors, tubular reactors or bubble column reactors.

The hydrogenation of carbon dioxide can be carried out batchwise or continuously in the process according to the invention. In the batchwise procedure, the reactor is equipped with the desired liquid and optionally solid feedstocks and auxiliaries, and then carbon dioxide and the polar solvent are pressed to the desired pressure at the desired temperature. After the end of the reaction, the reactor is normally depressurized and the two liquid phases formed are separated from one another. In the continuous mode of operation, the feedstocks and auxiliaries, including carbon dioxide and hydrogen, are added continuously. Accordingly, the liquid phases are continuously discharged from the reactor, so that the liquid level in the reactor remains the same on average. Preference is given to the continuous hydrogenation of carbon dioxide. The average residence time of the components in the hydrogenation reactor contained in the reaction mixture (Rg) is generally from 5 minutes to 5 hours. In the homogeneous-catalyzed hydrogenation, a hydrogenation mixture (H) is obtained in process step (a) which contains the catalyst, the polar solvent, the tertiary amine (A1) and the at least one formic acid-amine adduct (A2). In the context of the present invention, "formic acid-amine adduct (A2)" is understood as meaning both one (1) formic acid-amine adduct (A2) and mixtures of two or more formic acid-amine adducts (A2) or more formic acid-amine adducts (A2) are obtained in process step (a), if in the reaction mixture used (Rg) two or more tertiary amines (A1) are used.

In a preferred embodiment of the process according to the invention, a reaction mixture (Rg) is used in process step (a) which comprises a (1) tertiary amine (A1), a hydrogenation mixture (H) being obtained which comprises one (1) formic acid amine. Adduct (A2) contains.

In a particularly preferred embodiment of the process according to the invention, a reaction mixture (Rg) is used in process step (a) which comprises tri-n-hexylamine as the tertiary amine (A1) to give a hydrogenation mixture (H) which comprises the formic acid amine. Adduct of tri-n-hexylamine and formic acid and corresponds to the following formula (A3)

N (n-hexyl) ₃ * Xj HCOOH (A3). In the formic acid-amine adduct of the general formula (A2) or (A3), the radicals R ¹ , R ² , R ^{3 have} the meanings given above for the tertiary amine of the formula (A1), where the preferences mentioned there apply correspondingly. In the general formulas (A2) and (A3), x is in the range of 0.4 to 5. The factor X indicates the average composition of the formic acid-amine adduct (A2) and (A3), ie, the ratio of bound tertiary amine (A1) to bound formic acid in the formic acid-amine adduct (A2) or (A3). The factor x can be determined, for example, by determining the formic acid content by acid-base titration with an alcoholic KOH solution against phenolphthalein. In addition, a determination of the factor x, by determining the amine content by gas chromatography is possible. The exact composition of the formic acid-amine adduct (A2) or (A3) depends on many parameters, such as the concentrations of formic acid and tertiary amine (A1), the pressure, the temperature and the presence and nature of other components, in particular of the polar solvent. Therefore, the composition of the formic acid amine adduct (A2) or (A3), ie the factor x ,, can also change over the individual process stages. For example, after removal of the polar solvent, a formic acid-amine adduct (A2) or (A3) with a higher formic acid content generally forms, the excess bound tertiary amine (A1) being formed from the formic acid-amine adduct (A2 ) is split off and forms a second phase.

In process step (a), a formic acid-amine adduct (A2) or (A3) is generally obtained in which x is in the range from 0.4 to 5, preferably in the range from 0.7 to 1.6 ,

The formic acid-amine adduct (A2) is enriched in the lower phase (U 1), i. the lower phase (U 1) contains the major part of the formic acid-amine adduct. In the context of the present invention, the term "enriched" or "main part" with respect to the formic acid-amine adduct (A2) refers to a weight proportion of the formic acid-amine adduct (A2) in the lower phase (U 1) of> 50% to understand the total weight of the formic acid-amine adduct (A2) in the liquid phases (upper phase (01) and lower phase (U 1)) in the hydrogenation reactor.

The weight fraction of the formic acid-amine adduct (A2) in the lower phase (U 1) is preferably> 70%, in particular> 90%, in each case based on the total weight of the formic acid-amine adduct (A2) in the upper phase (01 ) and the lower phase (U 1).

Workup of the Hvdriergemischs (H); Process stage (b)

The hydrogenation mixture (H) obtained in the hydrogenation of carbon dioxide in process step (a) preferably has two liquid phases and is further worked up in process step (b) according to one of the steps (b1), (b2) or (b3).

Working up according to process step (b1) In a preferred embodiment, the hydrogenation mixture (H) is worked up further in step (b1). The invention therefore also provides a process for the preparation of formic acid, comprising the steps

(a) homogeneously catalyzed reaction of a reaction mixture (Rg) comprising carbon dioxide, hydrogen, at least one catalyst comprising at least one element selected from groups 8, 9 and 10 of the Periodic Table, at least one polar solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and water and at least one tertiary amine of the general formula (A1)

NR ¹ R ² R ³ (A1),

in the

R ¹ , R ² , R ³ independently represent an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical each having 1 to 16 carbon atoms, wherein individual carbon atoms independently of one another by a hetero group selected from the groups -O- and > N- may be substituted and two or all three radicals may also be linked together to form a chain comprising at least four atoms, in a hydrogenation reactor to obtain, optionally after addition of water, a biphasic hydrogenation mixture (H) containing an upper phase (01 ), which contains the at least one catalyst and the at least one tertiary amine (A1), and a lower phase (U1) containing the at least one polar solvent, residues of the at least one catalyst and at least one formic acid-amine adduct of the general formula (A2 contains)

R2R ^{3 *} ^ HCOOH (A2),

in the

X, is in the range of 0.4 to 5 and

R ¹ , R ² , R ^{3 have} the meanings given above,

(b1) phase separation of the hydrogenation mixture (H) obtained in step (a) in a first phase separation device into the upper phase (01) and the lower phase (U1),

(c) at least partially separating the at least one polar solvent from the lower phase (U1) in a first

Distillation device with preservation a distillate (D1) comprising the at least one polar solvent which is recycled to the hydrogenation reactor in step (a) and a biphasic bottom mixture (S1) containing an upper phase (O 2) containing the at least one tertiary amine (A 1) and a Subphase (U2) containing the at least one formic acid amine adduct (A2),

(d) optionally working up of the first bottoms mixture (S1) obtained in step (c) by phase separation in a second phase separation device into the upper phase (02) and the lower phase (U2),

(e) cleavage of the at least one formic acid-amine adduct (A2) contained in the bottom mixture (S1) or, if appropriate, in the bottom phase (U2) in a thermal splitting unit to give the at least one tertiary amine (A1) which is the hydrogenation reactor in step (a) is recycled, and formic acid derived from the thermal

Slitting unit is discharged, immediately before and / or during step (c) of the lower phase (U 1) at least one inhibitor selected from the group consisting of carboxylic acids other than formic acid, carboxylic acid derivatives different from formic acid derivatives and oxidizing agents is added.

In this case, the hydrogenation mixture (H) obtained in process step (a) is further worked-up in a first phase separation by phase separation to obtain a lower phase (U 1) comprising the at least one formic acid-amine adduct (A2) containing at least one polar solvent and radicals of the at least one catalyst and an upper phase (01) comprising the at least one catalyst and the at least one tertiary amine (A1). In a preferred embodiment, the upper phase (01) is recycled to the hydrogenation reactor. The lower phase (U 1) is supplied in a preferred embodiment of the first distillation apparatus in process step (c). Optionally, it is also advantageous to recycle a further liquid phase comprising both liquid phases containing unreacted carbon dioxide and a gas phase containing unreacted carbon dioxide and / or unreacted hydrogen to the hydrogenation reactor. Optionally, for example, it is desirable for the discharge of unwanted by-products or impurities, a portion of the upper phase (01) and / or a portion of the carbon dioxide or carbon dioxide and Hydrogen-containing liquid or gaseous phases auszuschleusen from the process.

The separation of the hydrogenation mixture (H) obtained in process step (a) is generally carried out by gravimetric phase separation. Suitable phase separators are, for example, standard apparatuses and standard methods, which are described, for example, in E. Müller et al., "Liquid-liquid Extraction", in Ullman's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007.b93_06, Chapter 3 Find "Apparatus". In general, the liquid phase enriched with the formic acid-amine adducts (A2) and the polar solvent is heavier and forms the lower phase (U 1).

The phase separation may take place, for example, after relaxation to about or near atmospheric pressure and cooling of the liquid hydrogenation mixture, for example at about or near ambient temperature.

In the present invention, it has been found that in the present system, that is, one with the formic acid-amine adducts (A2) and the polar solvent-enriched lower phase (U 1) and one with the tertiary amine (A1) and the Catalyst-enriched upper phase (02), both liquid phases with a suitable combination of the polar solvent and the tertiary amine (A1) very well separated even at a significantly increased pressure. Therefore, in the process according to the invention, the polar solvent and the tertiary amine (A1) can be selected such that the separation of the lower phase (U 1) enriched with the formic acid-amine adducts (A2) and the polar solvent from the tertiary amine (A1 ) and catalyst-enriched upper phase (01) and the return of the upper phase (01) to the hydrogenation reactor can be carried out at a pressure of 1 to 30 MPa abs. According to the total pressure in the hydrogenation reactor, the pressure is preferably at most 15 MPa abs. It is thus possible, without prior relaxation, to separate both liquid phases (upper phase (01) and lower phase (U 1)) in the first phase separation device and to recirculate the upper phase (01) to the hydrogenation reactor without appreciable pressure increase.

It is also possible to carry out the phase separation directly in the hydrogenation reactor. In this embodiment, the hydrogenation reactor functions simultaneously as the first phase separation device and the process steps (a) and (b1) are both carried out in the hydrogenation reactor. In this case, the upper phase (01) remains in the hydrogenation reactor and the lower phase (U 1) is fed to the first distillation apparatus in process stage (c).

In one embodiment, the process according to the invention is carried out in such a way that the pressure and the temperature in the hydrogenation reactor and in the first phase separation device are the same or approximately the same, under approx equal to a pressure difference of up to +/- 0.5 MPa or a temperature difference of up to +/- 10 ° C is understood.

Surprisingly, it has also been found that in the present system both liquid phases (upper phase (01) and lower phase (U 1)) separate very well even at elevated temperature, which corresponds to the reaction temperature in the hydrogenation reactor. In this respect, the phase separation in process stage (b1) also requires no cooling and subsequent heating of the upper phase (01) to be recycled, which likewise saves energy.

Work-up according to process step (b3)

In a further preferred embodiment, the hydrogenation mixture (H) is worked up further in step (b3). The invention therefore also provides a process for the preparation of formic acid, comprising the steps of homogeneously catalyzed reaction of a reaction mixture (Rg) containing carbon dioxide, hydrogen, at least one catalyst comprising at least one element selected from groups 8, 9 and

10 of the Periodic Table, at least one polar solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and water and at least one tertiary amine of the general Formula (A1)

NR ¹ R ² R ³ (A1),

in the

R ¹ , R ² , R ³ independently represent an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical each having 1 to 16 carbon atoms, wherein individual carbon atoms independently of one another by a hetero group selected from the groups -O- and > N- may be substituted and two or all three radicals may also be linked together to form a chain comprising at least four atoms, in a hydrogenation reactor to obtain, optionally after addition of water, a biphasic hydrogenation mixture (H) containing an upper phase (01 ) containing the at least one catalyst and the at least one tertiary amine (A1), and a lower phase (U1) which contains the at least one polar solvent, residues of the at least one catalyst and at least one formic acid-amine adduct of the general formula (A2),

NR ¹ R ² R ³ * Xi HCOOH (A2),

in the range of 0.4 to 5 and

R ² , R ^{3 have} the meanings given above,

(b3) phase separation of the hydrogenation mixture (H) obtained in step (a) in a first phase separation device into the upper phase (01) and the lower phase

(U1) and extraction of the residues of the at least one catalyst from the lower phase (U1) in an extraction unit with an extractant containing the at least one tertiary amine (A1) to obtain a raffinate (R2) containing the at least one formic acid-amine adduct (A2 ) and the at least one polar solvent and an extract (E2) containing the at least one tertiary amine (A1) and the radicals of the at least one catalyst,

(c) at least partially separating the at least one polar solvent from the raffinate (R2) in a first distillation apparatus to obtain a distillate (D1) containing the at least one polar solvent which is recycled to the hydrogenation reactor in step (a) and a biphasic mixture of bottoms (S1) comprising an upper phase (02) containing the at least one tertiary amine (A1), and a lower phase (U2) containing the at least one formic acid-amine adduct (A2), (d) optionally working up of the first bottoms mixture (S1) obtained in step (c) by phase separation in a second phase separation device into the upper phase (02) and the lower phase (U2), (e) cleavage in the bottoms mixture (S1) or optionally in the Subphase (U2) contained at least one formic acid-amine adduct (A2) in a thermal cleavage unit, to give the at least one tertiary amine (A1), which is recycled to the hydrogenation reactor in step (a), and of formic acid, which from the thermal Slitting unit is discharged, immediately before and / or during step (c) the raffinate (R2) is added at least one inhibitor selected from the group consisting of carboxylic acids other than formic acid, of carboxylic acid derivatives other than formic acid derivatives and oxidizing agents.

In this case, the hydrogenation mixture (H) obtained in process step (a) is separated into the lower phase (U 1) and the upper phase (01), which is recycled to the hydrogenation reactor, as described above for process step (b1) in the first phase separation device. With regard to the phase separation, the statements and preferences made for process step (b1) apply correspondingly to process step (b3). Also in the work-up according to step (b3), it is possible to carry out the phase separation directly in the hydrogenation reactor. In this embodiment, the hydrogenation reactor simultaneously acts as the first phase separation device. The upper phase (01) then remains in the hydrogenation reactor and the lower phase (U 1) is fed to the extraction unit.

The lower phase (U 1) obtained after phase separation is subsequently subjected in an extraction unit to extraction with at least one tertiary amine (A1) as extractant to remove the residues of the catalyst to obtain a raffinate (R2) containing the at least one formic acid-amine adduct (A2) and the at least one polar solvent and an extract (E2) containing the at least one tertiary amine (A1) and the residues of the catalyst.

In a preferred embodiment, the same tertiary amine (A1) used in process step (a) in the reaction mixture (Rg) is used as extractant, so that the statements and preferences with respect to the tertiary amine (A) for the process step (a) A1) apply correspondingly to process step (b3). The extract (E2) obtained in process step (b3) is recycled in a preferred embodiment to the hydrogenation reactor in process step (a). This allows efficient recovery of the expensive catalyst. The raffinate (R2) is fed in a preferred embodiment of the first distillation apparatus in process step (c).

The extractant used in process step (b3) is preferably the tertiary amine (A1) which is obtained in the thermal splitting unit in process step (e). In a preferred embodiment, in the thermal splitting unit in FIG

Process step (e) obtained tertiary amine (A1) to the extraction unit in process step (b3) recycled. The extraction is carried out in process step (b3) generally at temperatures in the range of 30 to 100 ° C and pressures in the range of 0, 1 to 8 MPa. The extraction can also be carried out under hydrogen pressure.

The extraction of the catalyst may be carried out in any suitable apparatus known to those skilled in the art, preferably in countercurrent extraction columns, mixer-settler cascades or combinations of mixer-settler cascades and countercurrent extraction columns.

If appropriate, in addition to the catalyst, fractions of individual components of the polar solvent from the lower phase (U 1) to be extracted in the extraction agent, the tertiary amine (A1), are also dissolved. This is not a disadvantage for the process, since the already extracted amount of polar solvent does not have to be supplied to the solvent removal and thus may save evaporation energy.

Work-up according to process step (b2)

In a further preferred embodiment, the hydrogenation mixture (H) is further worked up according to step (b2). The invention therefore also provides a process for the preparation of formic acid, comprising the steps

(a) homogeneously catalyzed reaction of a reaction mixture (Rg) comprising carbon dioxide, hydrogen, at least one catalyst comprising at least one element selected from groups 8, 9 and 10 of the Periodic Table, at least one polar solvent selected from the group consisting of methanol, ethanol, 1 - propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and water and at least one tertiary amine of the general formula (A1) NR ¹ R ² R ³ (A1),

in the R ¹ , R ² , R ³ independently represent an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical each having 1 to 16 carbon atoms, wherein individual carbon atoms independently of one another by a hetero group selected from the groups -O- and > N- may be substituted and two or all three radicals may also be linked together to form a chain comprising at least four atoms, in a hydrogenation reactor to obtain, optionally after addition of water, a biphasic hydrogenation mixture (H) containing an upper phase (01 ), which contains the at least one catalyst and the at least one tertiary amine (A1), and a lower phase (U1) containing the at least one polar solvent, residues of the at least one catalyst and at least one formic acid-amine adduct of the general formula (A2 contains)

_NR i _R2R3 * _x . HCOOH (A2),

in the X, ranging from 0.4 to 5 and

R ¹ , R ² , R ^{3 have} the meanings given above,

(b2) Extraction of the at least one catalyst from the hydrogenation mixture (H) obtained in step (a) in an extraction unit with an extractant containing the at least one tertiary amine (A1)

Obtaining a raffinate (R1) containing the at least one formic acid-amine adduct (A2) and the at least one polar solvent and an extract (E1) containing the at least one tertiary amine (A1) and the at least one catalyst

(c) at least partially separating the at least one polar solvent from the raffinate (R1) in a first distillation apparatus to obtain a distillate (D1) comprising the at least one polar solvent which is recycled to the hydrogenation reactor in step (a) and a biphasic bottom mixture (S1) containing an upper phase (O 2) containing the at least one tertiary amine (A 1) and a Subphase (U2) containing the at least one formic acid amine

Contains adduct (A2),

(e) cleavage of the at least one formic acid-amine adduct (A2) contained in the bottom mixture (S1) or, if appropriate, in the bottom phase (U2) in a thermal splitting unit to give the at least one tertiary amine (A1) which is the hydrogenation reactor in step

(a) is recycled and from formic acid discharged from the thermal cleavage unit, wherein immediately before and / or during step (c) the raffinate (R1) at least one inhibitor selected from the group consisting of

Formic acid is added to various carboxylic acids, carboxylic acid derivatives other than formic acid derivatives and oxidizing agents.

In this case, the hydrogenation mixture (H) obtained in process step (a) is fed directly to the extraction unit without prior phase separation. With regard to extraction, for process step (b2), the statements and preferences made for process step (b3) apply accordingly.

The hydrogenation mixture (H) is in this case subjected in an extraction unit to extraction with at least one tertiary amine (A1) as extractant to remove the catalyst to obtain a raffinate (R1) containing the at least one formic acid-amine adduct (A2) and the at least a polar solvent and an extract (E1) containing the at least one tertiary amine (A1) and the residues of the catalyst.

In a preferred embodiment, the extraction medium used is the same tertiary amine (A1) which is present in process stage (a) in the reaction mixture (Rg), so that the statements made for process stage (a) and Preferences with respect to the tertiary amine (A1) for the process step (b2) apply accordingly.

The extract (E1) obtained in process step (b2) is recycled in a preferred embodiment to the hydrogenation reactor in process step (a). This allows efficient recovery of the expensive catalyst. The raffinate (R1) is supplied in a preferred embodiment of the first distillation apparatus in process step (c). The tertiary amine (A1) which is obtained in the thermal splitting unit in process step (e) is preferably used as extractant in process step (b2). In a preferred embodiment, the tertiary amine (A1) obtained in the thermal splitting unit in process step (e) is recycled to the extraction unit in process step (b2).

The extraction is carried out in process step (b2) generally at temperatures in the range of 30 to 100 ° C and pressures in the range of 0, 1 to 8 MPa. The extraction can also be carried out under hydrogen pressure. The extraction of the catalyst may be carried out in any suitable apparatus known to those skilled in the art, preferably in countercurrent extraction columns, mixer-settler cascades or combinations of mixer-settler cascades and countercurrent extraction columns. If appropriate, in addition to the catalyst, fractions of individual components of the polar solvent from the hydrogenation mixture (H) to be extracted in the extraction agent, the tertiary amine (A1), are also dissolved. This is not a disadvantage for the process, since the already extracted amount of polar solvent does not have to be supplied to the solvent removal and thus may save evaporation energy.

Inhibition of traces of the catalyst

Immediately before and / or during step (c), the lower phase (U 1) obtained according to process step (b1), the raffinate (R1) obtained according to process step (b2) or the raffinate (R2) obtained according to process step (b3) are at least one inhibitor added.

Although the work-up of the hydrogenation mixture (H) allows effective separation and recycling of the catalyst into the hydrogenation reactor in step (a), residues of the catalyst are still present in the lower phase (U 1) during the work-up according to process step (b1). In the workup according to process step (b2) contains the raffinate (R1) still traces the catalyst. Also in the workup according to process step (b3), the raffinate (R2) still contains traces of the catalyst.

The lower phase (U 1), which is obtained according to process step (b1), contains residues of the catalyst in amounts of <100 ppm, preferably <80 ppm and in particular of <60 ppm, in each case based on the total weight of the lower phase (U 1).

The raffinate (R1) obtained according to process step (b2) contains traces of the catalyst in amounts of <5 ppm, preferably <3 ppm and in particular of <1 ppm, in each case based on the total weight of the raffinate (R1).

The raffinate (R2) obtained according to process step (b3) contains traces of the catalyst in amounts of <5 ppm, preferably <3 ppm and in particular <1 ppm, in each case based on the total weight of the raffinate (R2).

The residues or traces of the catalyst in the lower phase (U 1), the raffinate (R 1) or the raffinate (R 2) lead in the further workup to a cleavage of the formic acid-amine adduct (A2) to tertiary amine (A1), carbon dioxide and hydrogen. The cleavage of free formic acid, which is optionally contained in the lower phase (U 1), the raffinate (R 1) or the raffinate (R 2) or in the further work-up from the formic acid-amine adduct (A2) is formed by the radicals or catalyses traces of the catalyst. The formic acid is split into carbon dioxide and hydrogen. In order to prevent or minimize this cleavage, at least one inhibitor is added immediately before and / or during step (c) to the lower phase (U 1), the raffinate (R 1) or the raffinate (R 2).

In one embodiment of the present invention, the at least one inhibitor is added either immediately before or during step (c). In a further embodiment of the present invention, the at least one inhibitor is added immediately before and during step (c). In a further embodiment, the at least one inhibitor is added only immediately before step (c). In a further embodiment, the at least one inhibitor is added only during step (c).

For the purposes of the present invention, "immediately before step (c)" is understood to mean addition of the inhibitor to the lower phase (U 1), the raffinate (R 1) or the raffinate (R 2) after removal from the first phase separation device or the extraction unit and before being fed to the first distillation apparatus in process step (c) The addition of the inhibitor may be continuous or discontinuous. In the context of the present invention, inhibitor is understood as meaning both one (1) inhibitor and mixtures of two or more inhibitors. The inhibitor converts the catalyst into an inactive form, so that it can no longer catalyze the cleavage of the formic acid-amine adduct (A2) or of the free formic acid.

The inhibitor is selected from the group consisting of carboxylic acids other than formic acid, derivatives of carboxylic acids other than formic acid derivatives, and oxidizing agents.

In one embodiment, the inhibitor used is a mixture of at least one carboxylic acid and at least one oxidizing agent.

The inhibitor is used in a molar ratio of 0.5 to 1000, preferably 1 to 30, based on the catalytically active metal component of the catalyst, which in the lower phase (U1), the raffinate (R1) or the raffinate (R2) is.

Preferred carboxylic acids are those having at least one carboxy group (-COOH) and another functional group, such as hydroxy groups (-OH), carboxy groups or thiol groups (-SH), since such carboxylic acids due to the chelate Effect effectively bind to the metal component of the catalyst, and convert the catalyst into an inactive form.

Particularly suitable carboxylic acids are, for example, oxalic acid, lactic acid, maleic acid, phthalic acid, tartaric acid, citric acid, iminodiacetic acid, ethylenediaminetetraacetic acid (EDTA), nitriloacetic acid, methylglycinediacetic acid, diethylenetriaminepentaacetic acid (DTPA), dimercaptosuccinic acid.

Carboxylic acid derivatives are understood in the context of the present invention to mean organic compounds whose functional group is formally derived from the

Derive carboxy group (-COOH). Suitable carboxylic acid derivatives are, for example, carboxylic acid esters, carboxylic acid amides, carboxylic acid halides (e.g.

Carboxylic acid chlorides), carboxylic acid salts (e.g., lithium, sodium, potassium,

Trialkylammonium and ammonium salts of carboxylic acids), carboxylic anhydrides, carboxylic acid hydrazides, carboxylic acid azides, dithiocarboxylic acids, thiocarboxylic acids,

Hydroxamic acids, ketenes, imidocarboxylic acids, imidocarboxylic acid esters, amidines,

Amitrazones and nitriles.

Preference is given to carboxylic acid derivatives which can be prepared from the carboxylic acids described above, so that the above-described preferences for carboxylic acids apply correspondingly to the carboxylic acid derivatives. Particularly suitable carboxylic acid derivatives are carboxylic acid salts and carboxylic anhydrides the above-mentioned carboxylic acids, wherein among the carboxylic acid salts, alkali metal salts and trialkylammonium salts are particularly preferred.

Examples of particularly suitable carboxylic acid derivatives which may be mentioned are maleic anhydride, phthalic anhydride, the trisodium salt of methylglycinediacetic acid (available as Trilon ^M® ) and thioacetamide.

The carboxylic acids can thus be added both in the form of the free acid, as well as in the form of their derivatives (carboxylic acid derivatives), wherein among the carboxylic acid derivatives Carbonsäurealkalimetallsalze or

Carboxylic acid trialkylammonium salts are preferred. The carboxylic acids and / or carboxylic acid derivatives can be added in bulk or in the form of a solution. Suitable oxidizing agents are hydrogen peroxide, peroxycarboxylic acids, diacyl peroxides and trialkyl N-oxides. Preferred oxidizing agents are hydrogen peroxide, peroxo formic acid and trihexyl N-oxide, since these oxidizing agents decompose under the process conditions in step (c) and / or the process conditions in step (e) to substances which are present anyway in the process according to the invention for the preparation of formic acid , Preferably, the inhibitor is selected so that it is enriched in the phase which also contains the formic acid-amine adduct (A2).

In a preferred embodiment, thioacetamide is used as the inhibitor.

In a preferred embodiment, the inhibitor used is a mixture of hydrogen peroxide and EDTA.

In a preferred embodiment, a mixture of hydrogen peroxide and diethylenetriaminepentaacetic acid is used as the inhibitor.

In a preferred embodiment, EDTA is used as the inhibitor.

In a preferred embodiment, Trilon M is used as inhibitor.

In a preferred embodiment, meso-dimercaptosuccinic acid is used as inhibitor.

In a preferred embodiment, the inhibitor used is a mixture of hydrogen peroxide and meso-dimercaptosuccinic acid.

With regard to the inhibitor, "enriched" for process step (c) is a distribution coefficient Pi (c) = [concentration inhibitor in the lower phase (U2)] / [concentration inhibitor in the upper phase (02)] of> 1 to understand. Preferably, the distribution coefficient P | _(c) at> 2, and more preferably at> 5.

With regard to the inhibitor, "enriched" for the optional process step (d) is a distribution coefficient

Pi (d) ⁼ [concentration inhibitor in the lower phase (U2)] / [concentration inhibitor in the upper phase (02)] of> 1 to understand. Preferably, the distribution coefficient P | _(d ) at> 2 and more preferably at> 5.

With regard to the inhibitor, a distribution coefficient P | ₍ e) = [concentration of inhibitor in the lower phase (U3)] / [concentration of inhibitor in the upper phase (03)] is "enriched" for process step (e).

To understand from> 1. Preferably, the distribution coefficient P | _(e) > 2, and more preferably> 5.

This makes it possible to return the upper phase (02) or the upper phase (03) to the hydrogenation reactor without significant amounts of the inhibitor being recycled to the hydrogenation reactor, which could disturb the hydrogenation reactor in process stage (a).

Separation of the polar solvent; Process step (c)

In process step (c), the polar solvent is at least partially separated from the lower phase (U1), from the raffinate (R1) or from the raffinate (R2) in a first distillation apparatus. In the first distillation apparatus, a distillate (D1) and a two-phase bottoms mixture (S1) are obtained. The distillate (D1) contains the separated polar solvent and is added to the hydrogenation reactor in step (a) returned. The bottoms mixture (S1) contains the upper phase (02) containing the tertiary amine (A1) and a lower phase (U2) containing the formic acid-amine adduct (A2). In one embodiment of the process according to the invention, in the first distillation apparatus in process stage (c), the polar solvent is partly removed, so that the bottom mixture (S1) contains not yet separated polar solvent. In process step (c), for example, from 5 to 98% by weight of the polar solvent contained in the lower phase (U 1), in the raffinate (R 1) or in the raffinate (R 2), preferably 50 to 98% by weight, more preferably 80 to 98 wt .-% and particularly preferably 80 to 90 wt .-% are separated, in each case based on the total weight of the in the lower phase (U 1) in the raffinate (R1) or in the raffinate (R2) polar solvent.

In a further embodiment of the process according to the invention, the polar solvent is completely separated off in the first distillation apparatus in process stage (c). In the context of the present invention, "completely separated off" is a separation of more than 98% by weight of the polar solvent present in the lower phase (U 1), in the raffinate (R 1) or in the raffinate (R 2), preferably more than 98.5 wt .-%, particularly preferably more than 99 wt .-%, in particular more than 99.5 wt .-%, understood, in each case based on the total weight of the in the lower phase (U 1), in the raffinate (R1) or in the raffinate (R2) contained polar solvent.

The distillate (D1) separated in the first distillation apparatus is recycled in a preferred embodiment to the hydrogenation reactor in step (a). In the event that a mixture of one or more alcohols and water is used as the polar solvent, it is also possible to remove from the first distillation apparatus a low-water distillate (D1 _wa ) and a water-rich distillate (D1 _wr ). The water-rich distillate (D1 _wr ) contains more than 50 wt .-% of the water contained in the distillate (D1), preferably more than 70 wt .-%, especially more than 80 wt .-%, in particular more than 90 wt .-% , The low-water distillate (D1 _wa ) contains less than 50 wt .-% of the water contained in the distillate D1, preferably less than 30 wt .-%, more preferably less than 20 wt .-%, in particular less than 10 wt .-%. In a particularly preferred embodiment, the low-water distillate (D1 _wa ) is recycled to the hydrogenation reactor in step (a). The water-rich distillate (D 1 _wr ) is fed to the upper phase (01). The separation of the polar solvent from the lower phase (U 1), the raffinate (R 1) or the raffinate (R 2) can be carried out, for example, in an evaporator or in a distillation unit consisting of evaporator and column, the column containing packings, fillers and / or trays filled, done. The at least partial removal of the polar solvent preferably takes place at a bottom temperature at which no free formic acid is formed from the formic acid-amine adduct (A2) at a given pressure. The factor x, of the formic acid-amine adduct (A2) in the first distillation apparatus is generally in the range of 0.4 to 3, preferably in the range of 0.6 to 1, 8, particularly preferably in the range of 0.7 to 1, 7.

In general, the bottom temperature in the first distillation apparatus is at least 20 ° C, preferably at least 50 ° C and more preferably at least 70 ° C, and generally at most 210 ° C, preferably at most 190 ° C. The temperature in the first distillation apparatus is generally in the range of 20 ° C to 210 ° C, preferably in the range of 50 ° C to 190 ° C. The pressure in the first distillation apparatus is generally at least 0.001 MPa abs, preferably at least 0.005 MPa abs and more preferably at least 0.01 MPa abs and generally at most 1 MPa abs and preferably at most 0, 1 MPa abs. The pressure in the first distillation apparatus is generally in the range of 0.0001 MPa abs to 1 MPa abs, preferably in the range of 0.005 MPa abs to 0.1 MPa abs and more preferably in the range of 0.01 MPa abs to 0.1 MPa abs. In the removal of the polar solvent in the first distillation apparatus, the formic acid-amine adduct (A2) and free tertiary amine (A1) can be obtained in the bottom of the first distillation apparatus, since the removal of the polar solvent gives formic acid-amine adducts with a lower amine content , This forms a bottom mixture (S1) which contains the formic acid-amine adduct (A2) and the free tertiary amine (A1). The bottom mixture (S1) contains, depending on the separated amount of the polar solvent, the formic acid-amine adduct (A2) and optionally the free tertiary amine (A1) formed in the bottom of the first distillation apparatus. If appropriate, the bottoms mixture (S1) is further worked up in process step (d) for further work-up and then fed to process step (e). It is also possible to feed the bottoms mixture (S1) from process step (c) directly to process step (e).

In process step (d), the bottoms mixture (S1) obtained in step (c) can be separated in a second phase separation device into the upper phase (02) and the lower phase (U2). The lower phase (U2) is then further worked up according to process step (e). In a preferred embodiment, the upper phase (02) from the second phase separation device to the hydrogenation reactor in step (a) recycled. In a further preferred embodiment, the upper phase (02) is recycled from the second phase separation device to the extraction unit. For method step (d) and the second phase separation device, the statements and preferences for the first phase separation device apply accordingly.

In one embodiment, the method according to the invention thus comprises the steps (a), (b1), (c), (d) and (e). In a further embodiment, the method according to the invention comprises the steps (a), (b2), (c), (d) and (e). In a further embodiment, the method according to the invention comprises the steps (a), (b3), (c), (d) and (e). In a further embodiment, the method according to the invention comprises the steps (a), (b1), (c) and (e). In a further embodiment, the method according to the invention comprises the steps (a), (b2), (c) and (e). In a further embodiment, the method according to the invention comprises the steps (a), (b3), (c) and (e).

In one embodiment, the method according to the invention consists of the steps (a), (b1), (c), (d) and (e). In a further embodiment, the process according to the invention consists of the steps (a), (b2), (c), (d) and (e). In a further embodiment, the process according to the invention consists of the steps (a), (b3), (c), (d) and (e). In a further embodiment, the process according to the invention consists of the steps (a), (b1), (c) and (e). In a further embodiment, the process according to the invention consists of the steps (a), (b2), (c) and (e). In a further embodiment, the process according to the invention consists of the steps (a), (b3), (c) and (e).

Cleavage of the formic acid-amine adduct (A2); Process stage (s)

The bottom mixture (S1) obtained according to step (c) or the lower phase (U2) optionally obtained after the work-up according to step (d) is fed to a thermal splitting unit for further reaction.

The formic acid-amine adduct (A2) present in the bottom mixture (S1) or optionally in the bottom phase (U2) is cleaved in the thermal splitting unit to give formic acid and tertiary amine (A1). The formic acid is discharged from the thermal splitting unit. The tertiary amine (A1) is recycled to the hydrogenation reactor in step (a). The tertiary amine (A1) from the thermal cleavage unit can be recycled directly to the hydrogenation reactor. It is also possible to first recycle the tertiary amine (A1) from the thermal splitting unit to the extraction unit in process stage (b2) or process stage (b3), and subsequently from the extraction unit to the hydrogenation reactor in step (a), this embodiment is preferred.

In a preferred embodiment, the thermal splitting unit comprises a second distillation apparatus and a third phase separation apparatus, wherein the cleavage of the formic acid-amine adduct (A2) is carried out in the second distillation apparatus to obtain a distillate (D2) discharged from the second distillation apparatus (taken ), and a biphasic bottoms mixture (S2) comprising an upper phase (03) containing the at least one tertiary amine (A1), and a lower phase (U3) containing the at least one formic acid-amine adduct (A2) and the at least contains an inhibitor.

The removal of the formic acid from the second distillation apparatus obtained in the second distillation apparatus can be carried out, for example, (i) overhead, (ii) overhead and via a side draw, or (iii) only a side draw. If the formic acid is removed overhead, formic acid with a purity of up to 99.99% by weight is obtained. When taken off via a side draw, aqueous formic acid is obtained, in which case a mixture with about 85% by weight of formic acid is particularly preferred. Depending on the water content of the sludge mixture (S1) or, if appropriate, the lower phase (U2) fed to the thermal splitting unit, the formic acid can be withdrawn increasingly as top product or reinforced via the side draw. If necessary, it is also possible to remove formic acid only on the side draw, preferably with a formic acid content of about 85 wt .-%, in which case optionally the required amount of water can also be adjusted by adding additional water in the second distillation apparatus. The thermal cleavage of the formic acid-amine adduct (A2) is generally carried out according to the process parameters known in the prior art with respect to pressure, temperature and apparatus design. These are described, for example, in EP 0 181 078 or WO 2006/021 41 1. As a second distillation apparatus, for example, distillation columns are suitable, which generally contain packing, packings and / or trays.

In general, the bottom temperature in the second distillation apparatus is at least 130 ° C, preferably at least 140 ° C and more preferably at least 150 ° C, and generally at most 210 ° C, preferably at most 190 ° C, particularly preferably at most 185 ° C. The pressure in the second distillation apparatus is generally at least 1 hPa abs, preferably at least 50 hPa abs and more preferably at least 100 hPa abs, and generally at most 500 hPa, more preferably at most 300 hPa abs and more preferably at most 200 hPa abs. The bottoms mixture (S2) obtained in the bottom of the second distillation apparatus is biphasic. In a preferred embodiment, the bottoms mixture (S2) is fed to the third phase separation device of the thermal splitting unit and there in the upper phase (03) containing the tertiary amine (A1), and the lower phase (U3), the formic acid-amine adduct ( A2) and the inhibitor, separated. The upper phase (03) is discharged from the third phase separator of the thermal splitting unit and recycled to the hydrogenation reactor in step (a). The recycling can be carried out directly to the hydrogenation reactor in step (a) or the upper phase (03) is first supplied to the extraction unit in step (b2) or step (b3) and forwarded from there to the hydrogenation reactor in step (a). The lower phase (U3) obtained in the third phase separation device is then supplied again to the second distillation device of the thermal splitting unit. The formic acid-amine adduct (A2) present in the lower phase (U3) is then subjected to further cleavage in the second distillation apparatus, again giving formic acid and free tertiary amine (A1) and again in the bottom of the second distillation unit of the thermal splitting unit forming a two-phase bottoms mixture (S2), which is then fed again to the third phase separation device of the thermal splitting unit for further processing.

As already explained above, the inhibitor preferably remains in the phase in which the formic acid-amine adduct (A2) is also present, ie. in the lower phase (U3). This has the advantage that the upper phase (03) containing the tertiary amine (A1) can be recycled to the hydrogenation reactor without significant amounts of inhibitor being recycled to the upper phase (03) in process stage (a), which hinder the hydrogenation reaction there could.

The feeding of the bottom mixture (S1) or optionally of the bottom phase (U2) to the thermal splitting unit in process step (e) can take place in the second distillation device and / or the third phase separation device. In a preferred embodiment, the feed of the bottom mixture (S1) or optionally the lower phase (U2) in the second distillation device of the thermal separation unit takes place. In a further embodiment, the feed of the bottoms mixture (S1) or optionally the lower phase (U2) into the third phase separation vessel of the thermal splitting unit.

In a further embodiment, the feed of the bottom mixture (S1) or optionally the lower phase (U2) takes place both in the second distillation device of the thermal splitting unit, as well as in the third phase separation device of the thermal splitting unit. For this purpose, the bottom mixture (S1) or optionally the Subphase (U2) divided into two partial streams, wherein a partial stream of the second distillation device and a partial stream of the third phase separator are fed to the thermal splitting unit. The drawings show in detail: a block diagram of a preferred embodiment of the method according to the invention, a block diagram of a further preferred embodiment of the method according to the invention, a block diagram of a further preferred embodiment of the method according to the invention, a block diagram of a further preferred embodiment of the method according to the invention, a block diagram of a further preferred one Embodiment of the method according to the invention,

FIG. 6 shows a block diagram of a further preferred embodiment of the method according to the invention.

In FIGS. 1 to 6, the reference symbols have the following meanings:

FIG. 1

I-1 hydrogenation reactor

II- 1 first distillation apparatus

111-1 third phase separation device (the thermal splitting unit)

IV-1 second distillation device (the thermal splitting unit)

1 stream containing carbon dioxide

2 stream containing hydrogen

3 stream containing formic acid-amine adduct ((A2), residues of

Catalyst, polar LM; (Lower phase (U 1))

4 current containing inhibitor

5 stream containing polar solvent; (Distillate (D1))

6 stream containing tertiary amine (A1) (upper phase (02)) and formic acid

Amine adduct (A2) (lower phase (U2)); Swamp mixture (S1) 7 stream containing formic acid-amine adduct (A2) and inhibitor; Lower phase (U3)

8 stream containing tertiary amine (A1) (upper phase (03)) and

Formic acid-amine adduct (A2) and inhibitor (lower phase (U3)); Swamp mixture (S2)

9 stream containing formic acid; (Distillate (D2))

10 stream containing tertiary amine (A1); Upper phase (03)

FIG. 2

I- 2 hydrogenation reactor

II- 2 first distillation device

II 1-2 third phase separator

IV-2 second distillation apparatus

V-2 first phase separator

VI-2 extraction unit

1 1 stream containing carbon dioxide

12 stream containing hydrogen

13a stream containing hydrogenation mixture (H)

13b current containing lower phase (U 1)

13c stream containing raffinate (R2)

14 current containing inhibitor

15 stream containing distillate (D1)

16 stream containing bottoms mixture (S1)

17 current containing lower phase (U3)

18 stream containing swamp mixture (S2)

19 stream containing formic acid; (Distillate (D2))

20 current containing upper phase (03)

21 stream containing extract (E2)

22 current containing upper phase (01)

Figure 3 I-3 hydrogenation reactor

II- 3 first distillation apparatus

II I- 3 third phase separator

IV- 3 second distillation apparatus

V- 3 first phase separation device

VI-3 extraction unit 31 Electricity containing carbon dioxide

32 Electricity containing hydrogen

33a stream containing hydrogenation mixture (H)

33b stream containing lower phase (U 1)

33c stream containing raffinate (R2)

34 Current containing inhibitor

35 stream containing distillate (D1)

36 stream containing swamp mixture (S1)

37 current containing lower phase (U3)

38 Stream containing swamp mixture (S2)

39 stream containing formic acid; (Distillate (D2))

40 current containing upper phase (03)

41 stream containing extract (E2)

42 current containing upper phase (01)

FIG. 4

I-4 hydrogenation reactor

II-4 first distillation apparatus

II I-4 third phase separator

IV-4 second distillation device

V-4 first phase separator

VI-4 extraction unit

VI I-4 second phase separator

51 stream containing carbon dioxide

52 Stream containing hydrogen

53a stream containing hydrogenation mixture (H)

53b stream containing lower phase (U 1)

53c stream containing raffinate (R2)

54 current containing inhibitor

55 Stream containing distillate (D1)

56a stream containing bottoms mixture (S1)

56b current containing lower phase (U2)

56c stream containing upper phase (02)

57 current containing lower phase (U3)

58 Stream containing Sumpfgemisch (S2)

59 stream containing formic acid; (Distillate (D2))

60 current containing upper phase (03) Stream containing extract (E2) stream containing upper phase (01)

hydrogenation reactor

first distillation device

third phase separator

second distillation device

first phase separation device

extraction unit

71 Electricity containing carbon dioxide

72 Electricity containing hydrogen

73a stream containing hydrogenation mixture (H)

73b stream containing lower phase (U 1)

73c stream containing raffinate (R2)

74 Current containing inhibitor

75 stream containing low-water distillate (D 1wa)

76 stream containing swamp mixture (S1)

77 current containing lower phase (U3)

78 stream containing swamp mixture (S2)

79 stream containing formic acid; (Distillate (D2))

80 current containing upper phase (03)

81 stream containing extract (E2)

82 current containing upper phase (01)

83 Stream containing water-rich distillate (D1wr)

hydrogenation reactor

first distillation device

third phase separator

second distillation device

extraction unit

91 Electricity containing carbon dioxide

92 stream containing hydrogen

93a stream containing hydrogenation mixture (H)

93c stream containing raffinate (R1) 94 Current containing inhibitor

95 stream containing distillate (D1)

96 stream containing bottoms mixture (S1)

97 current containing lower phase (U3)

98 Stream containing swamp mixture (S2)

99 stream containing formic acid; (Distillate (D2))

100 current containing upper phase (03)

101 Stream Containing Extract (E1) In the embodiment according to FIG. 1, a stream 1 containing carbon dioxide and a stream 2 containing hydrogen are fed to a hydrogenation reactor 1-1. It is possible to supply the hydrogenation reactor 1-1 further streams (not shown) to compensate for any losses incurred by the tertiary amine (A1) or the catalyst.

In the hydrogenation reactor 1-1, carbon dioxide and hydrogen are reacted in the presence of a tertiary amine (A1), a polar solvent and a catalyst containing at least one element from Groups 8, 9 and 10 of the Periodic Table. In this case, a two-phase hydrogenation mixture (H) is obtained which has an upper phase (01) comprising the catalyst and the tertiary amine (A1) and a lower phase (U 1) containing the polar solvent, residues of the catalyst and the formic acid-amine adduct (A2 ) contains.

The lower phase (U 1) is supplied as stream 3 to the distillation apparatus 11-1. The upper phase (01) remains in the hydrogenation reactor 1-1. In the embodiment according to FIG. 1, the hydrogenation reactor 1-1 simultaneously acts as the first phase separation device.

The current 3 is added continuously or discontinuously, the inhibitor as stream 4. In the first distillation apparatus, the lower phase (U 1) is separated into a distillate (D1) containing the polar solvent, which is recycled as stream 5 to the hydrogenation reactor 1-1, and into a biphasic mixture (S1) containing an upper phase (02), containing the tertiary amine (A1) and the lower phase (U2) containing the formic acid-amine adduct (A2), inhibited residues of the catalyst and the inhibitor.

The bottoms mixture (S1) is fed as stream 6 to the third phase separation device 111-1 of the thermal splitting unit.

In the third phase separation device 111-1 of the thermal splitting unit, the sump mixture (S1) is separated to obtain an upper phase (03) containing the tertiary amine (A1) and a lower phase (U3) containing inhibited residues of the catalyst, the inhibitor and the formic acid-amine adduct (A2).

The upper phase (03) is recycled as stream 10 to the hydrogenation reactor 1-1. The lower phase (U3) is supplied as stream 7 to the second distillation device IV-1 of the thermal splitting unit. The formic acid-amine adduct (A2) present in the lower phase (U3) is cleaved in the second distillation apparatus IV-1 into formic acid and free tertiary amine (A1). In the second distillation apparatus IV-1, a distillate (D2) and a two-phase bottoms mixture (S2) are obtained.

The distillate (D2) containing formic acid is discharged as stream 9 from the distillation apparatus IV-1. The biphasic bottoms mixture (S2) containing the upper phase (03) containing the tertiary amine (A1) and the lower phase (U3) containing the formic acid-amine adduct (A2) inhibited residues of the catalyst and the inhibitor is referred to as Stream 8 is returned to the third phase separation device 111-1 of the thermal splitter unit. In the third phase separation device 111-1, the sump mixture (S2) is separated into upper phase (03) and lower phase (U3). Di upper phase (03) is recycled as stream 10 to the hydrogenation reactor 1-1. The lower phase (U3) is recycled as stream 7 to the second distillation device IV-1.

In the embodiment according to FIG. 2, a stream 11 containing carbon dioxide and a stream 12 containing hydrogen are fed to a hydrogenation reactor I-2. It is possible to supply the hydrogenation reactor I-2 with further streams (not shown) in order to compensate for any losses of the tertiary amine (A1) or of the catalyst which may occur.

In the hydrogenation reactor I-2, carbon dioxide and hydrogen are reacted in the presence of a tertiary amine (A1), a polar solvent and a catalyst containing at least one element from Groups 8, 9 and 10 of the Periodic Table. In this case, a two-phase hydrogenation mixture (H) is obtained which has an upper phase (01) comprising the catalyst and the tertiary amine (A1) and a lower phase (U 1) containing the polar solvent, residues of the catalyst and the formic acid-amine adduct (A2 ) contains.

The hydrogenation mixture (H) is fed as stream 13a to a first phase separator V-2. In the first phase separation device V-2, the hydrogenation mixture (H) is separated into the upper phase (01) and the lower phase (U 1). The upper phase (01) is recycled as stream 22 to the hydrogenation reactor I-2. The lower phase (U 1) is supplied as stream 13b of the extraction unit VI-2. In it, the lower phase (U 1) is extracted with the tertiary amine (A1), which is recycled as stream 20 (upper phase (03)) from the third phase separation II I-2 to the extraction device VI-2.

In the extraction unit VI-2, a raffinate (R2) and an extract (E2) are obtained. The raffinate (R2) contains the formic acid-amine adduct (A2) and the polar solvent and is supplied as stream 13c to the first distillation apparatus I I-2. The extract (E2) contains the tertiary amine (A1) and the residues of the catalyst and is recycled as stream 21 to the hydrogenation reactor I-2.

The current 13c is continuously or discontinuously added to the inhibitor as stream 14. In the first distillation apparatus I I-2, the raffinate (R 2) is separated into a distillate (D 1) containing the polar solvent, which is recycled as stream 15 to the hydrogenation reactor I-2, and into a biphasic sump mixture (S 1).

The bottoms mixture (S1) contains an upper phase (02) containing the tertiary amine (A1) and a lower phase (U2) containing the formic acid-amine adduct (A2) inhibited residues of the catalyst and the inhibitor. The bottoms mixture (S1) is fed as stream 16 to the second distillation device IV-2.

The formic acid-amine adduct present in the bottom mixture (S1) is cleaved in the second distillation device IV-2 into formic acid and free tertiary amine (A1). In the second distillation apparatus IV-2, a distillate (D2) and a bottoms mixture (S2) are obtained.

The distillate (D2) containing formic acid is discharged as stream 19 from the second distillation device IV-2. The biphasic bottoms mixture (S2) containing the upper phase (03) containing the tertiary amine (A1) and the lower phase (U3) containing the formic acid-amine adduct (A2), inhibited residues of the catalyst and the inhibitor is recycled as stream 18 to the third phase separation II I-2 of the thermal splitting unit. In the third phase separation device II-2 of the thermal cleavage unit, the bottom mixture (S2) is separated to obtain an upper phase (03) comprising the tertiary amine (A1) and a lower phase (U3) containing inhibited residues of the catalyst, the inhibitor and the formic acid Amine adduct (A2). The upper phase (03) is recycled from the third phase separator 111-2 as stream 20 to the extraction unit VI-2. The lower phase (U3) is supplied as stream 17 to the second distillation device IV-2 of the thermal splitting unit. The formic acid-amine adduct (A2) present in the lower phase (U3) is cleaved in the second distillation apparatus IV-2 into formic acid and free tertiary amine (A1). In the second distillation apparatus IV-2, as stated above, a distillate (D2) and a bottom mixture (S2) are again obtained.

In the embodiment according to FIG. 3, a stream 31 containing carbon dioxide and a stream 32 containing hydrogen are fed to a hydrogenation reactor 1-3. It is possible to supply the hydrogenation reactor 1-3 further streams (not shown) in order to compensate for any losses of the tertiary amine (A1) or of the catalyst. In the hydrogenation reactor 1-3, carbon dioxide and hydrogen are reacted in the presence of a tertiary amine (A1), a polar solvent and a catalyst containing at least one element from Groups 8, 9 and 10 of the Periodic Table. In this case, a two-phase hydrogenation mixture (H) is obtained which has an upper phase (01) comprising the catalyst and the tertiary amine (A1) and a lower phase (U 1) containing the polar solvent, residues of the catalyst and the formic acid-amine adduct (A2 ) contains.

The hydrogenation mixture (H) is supplied as stream 33a to a first phase separation device V-3. In the first phase separation device V-3, the hydrogenation mixture (H) in the upper phase (01) and the lower phase (U 1) is separated.

The upper phase (01) is recycled as stream 42 to the hydrogenation reactor I-3. The lower phase (U 1) is supplied as stream 33b to the extraction unit VI-3. In it, the lower phase (U 1) is extracted with the tertiary amine (A1), which is recycled as stream 40 (upper phase (03)) from the third phase separator II I-3 of the thermal splitting unit to the extraction unit VI-3.

In the extraction unit VI-3, a raffinate (R2) and an extract (E2) are obtained. The raffinate (R2) contains the formic acid-amine adduct (A2) and the polar solvent and is supplied as stream 33c to the first distillation device 11-3. The extract (E2) contains the tertiary amine (A1) and the residues of the catalyst and is recycled as stream 41 to the hydrogenation reactor I-2.

The flow 33c is added continuously or discontinuously to the inhibitor as stream 34. In the first distillation apparatus 11-3, the raffinate (R2) separated into a distillate (D1) containing the polar solvent, which is recycled as stream 35 to the hydrogenation reactor I-3, and into a two-phase bottoms mixture (S1).

The bottoms mixture (S1) contains an upper phase (02) containing the tertiary amine (A1) and a lower phase (U2) containing the formic acid-amine adduct (A2), inhibited residues of the catalyst and the inhibitor.

The sump mixture (S1) is supplied as stream 36 of the third phase separation device I I I-3 to the thermal splitting unit.

In the third phase separation device II-3 of the thermal cleavage unit, the bottom mixture (S1) is separated to obtain a top phase (03) comprising the tertiary amine (A1) and a lower phase (U3) containing inhibited residues of the catalyst, the inhibitor and the formic acid Amine adduct (A2).

The upper phase (03) is recycled as stream 40 to the extraction unit VI-3. The lower phase (U3) is supplied as stream 37 to the second distillation device IV-3 of the thermal splitting unit. The formic acid-amine adduct (A2) present in the lower phase (U3) is cleaved in the second distillation apparatus IV-3 into formic acid and free tertiary amine (A1). In the second distillation apparatus IV-3, a distillate (D2) and a bottoms mixture (S2) are obtained.

The distillate (D2) containing formic acid is discharged as stream 39 from the distillation device IV-3. The biphasic bottoms mixture (S2) containing the upper phase (03) containing the tertiary amine (A1) and the lower phase (U3) containing the formic acid-amine adduct (A2) inhibited residues of the catalyst and the inhibitor is referred to as Stream 38 to the third phase separation II I-3 of the thermal splitting unit recycled. In the third phase separation device I I I-3, the sump mixture (S2) is separated. The upper phase (03) is recycled to the extraction unit VI-3. The lower phase (U3) is recycled to the second distillation device IV-3.

In the embodiment according to FIG. 4, a stream 51 containing carbon dioxide and a stream 52 containing hydrogen are fed to a hydrogenation reactor I-4. It is possible to supply the hydrogenation reactor I-4 with further streams (not shown) in order to compensate for any losses of the tertiary amine (A1) or of the catalyst which may occur. In the hydrogenation reactor 1-4, carbon dioxide and hydrogen are reacted in the presence of a tertiary amine (A1), a polar solvent and a catalyst containing at least one element from Groups 8, 9 and 10 of the Periodic Table. In this case, a two-phase hydrogenation mixture (H) is obtained which has an upper phase (01) comprising the catalyst and the tertiary amine (A1) and a lower phase (U 1) containing the polar solvent, residues of the catalyst and the formic acid-amine adduct (A2 ) contains.

The hydrogenation mixture (H) is fed as stream 53a to a first phase separator V-4. In the first phase separation device V-4, the hydrogenation mixture (H) is separated into the upper phase (01) and the lower phase (U 1).

The upper phase (01) is recycled as stream 62 to the hydrogenation reactor I-4. The lower phase (U 1) is supplied as stream 53b to the extraction unit VI-4. Therein, the lower phase (U 1) is extracted with the tertiary amine (A1), the current 60 (upper phase (03)) from the third phase separation II I-4 of the thermal splitting unit and the current 56c from the second phase separation VI 1-4 to the extraction unit VI-4 is recycled.

In the extraction unit VI-4, a raffinate (R2) and an extract (E2) are obtained. The raffinate (R2) contains the formic acid-amine adduct (A2) and the polar solvent and is supplied as stream 53c to the first distillation apparatus 11-4. The extract (E2) contains the tertiary amine (A1) and the residues of the catalyst and is recycled as stream 61 to the hydrogenation reactor I-4.

The current 53c is added continuously or discontinuously to the inhibitor as stream 54. In the first distillation apparatus I I-4, the raffinate (R 2) is separated into a distillate (D 1) containing the polar solvent, which is recycled as stream 55 to the hydrogenation reactor I-4, and into a biphasic sump mixture (S 1).

The bottoms mixture (S1) contains an upper phase (02) containing the tertiary amine (A1) and a lower phase (U2) containing the formic acid-amine adduct (A2) inhibited residues of the catalyst and the inhibitor. The bottoms mixture (S1) is fed as stream 56a to the second phase separation VI I-4. In the second phase separation device VII-4, the bottom mixture (S1) is separated into the upper phase (02) and the lower phase (U2). The upper phase (02) is recycled from the second phase separator VI I-4 as stream 56c to the extraction unit VI-4. The lower phase (U2) is supplied as stream 56b to the second distillation device IV-4.

The formic acid-amine adduct (A2) present in the lower phase (U2) is cleaved in the second distillation apparatus IV-4 into formic acid and free tertiary amine (A1). In the second distillation apparatus IV-4, a distillate (D2) and a bottoms mixture (S2) are obtained.

The distillate (D2) containing formic acid is discharged as stream 59 from the second distillation device IV-4. The biphasic bottoms mixture (S2) containing the upper phase (03) containing the tertiary amine (A1) and the lower phase (U3) containing the formic acid-amine adduct (A2) inhibited residues of the catalyst and the inhibitor is referred to as Stream 58 to the third phase separation 111-4 of the thermal splitting unit recycled.

In the third phase separation device 111-4 of the thermal cleavage unit, the bottom mixture (S2) is separated to obtain a top phase (03) comprising the tertiary amine (A1) and a lower phase (U3) containing inhibited residues of the catalyst, the inhibitor and the formic acid Amine adduct (A2).

The upper phase (03) is recycled from the third phase separation device I I I-4 as stream 60 to the extraction unit VI-4. The lower phase (U3) is supplied as stream 57 to the second distillation device IV-4 of the thermal splitting unit. The formic acid-amine adduct (A2) present in the lower phase (U3) is cleaved in the second distillation apparatus IV-4 into formic acid and free tertiary amine (A1). In the second distillation apparatus IV-4, as stated above, a distillate (D2) and a bottoms mixture (S2) are again obtained.

In the embodiment according to FIG. 5, a stream 71 containing carbon dioxide and a stream 72 containing hydrogen are fed to a hydrogenation reactor I-5. It is possible to supply the hydrogenation reactor I-5 further streams (not shown) to compensate for any losses of the tertiary amine (A1) or the catalyst occurring.

In the hydrogenation reactor I-5, carbon dioxide and hydrogen are reacted in the presence of a tertiary amine (A1), a polar solvent and a catalyst containing at least one element from Groups 8, 9 and 10 of the Periodic Table. In this case, a biphasic hydrogenation mixture (H) is obtained which has a top phase (01) containing the catalyst and the tertiary amine (A1) and a Subphase (U 1) containing the polar solvent, residues of the catalyst and the formic acid-amine adduct (A2).

The hydrogenation mixture (H) is supplied as stream 73a to a first phase separation device V-5. In the first phase separation device V-5, the hydrogenation mixture (H) in the upper phase (01) and the lower phase (U 1) is separated.

The upper phase (01) is recycled as stream 82 to the hydrogenation reactor I-5. The lower phase (U 1) is supplied as stream 73b of the extraction unit VI-5. Therein, the lower phase (U 1) is extracted with the tertiary amine (A1), which is recycled as stream 80 (upper phase (03)) from the third phase separator of the thermal splitting unit to the extraction unit VI-5.

In the extraction unit VI-5, a raffinate (R2) and an extract (E2) are obtained. The raffinate (R2) contains the formic acid-amine adduct (A2) and the polar solvent and is supplied as stream 73c to the first distillation device 11-5. The extract (E2) contains the tertiary amine (A1) and the residues of the catalyst and is recycled as stream 81 to the hydrogenation reactor I-5.

The current 73c is added continuously or discontinuously to the inhibitor as stream 74. In the first distillation apparatus I I-5, the raffinate (R 2) is separated into a water-rich distillate (D 1 wr), a low-water distillate (D 1wa) and a biphasic bottom mixture (S1). The water-rich distillate (D1 wr) is supplied as stream 83 to the stream 73a. The low-water distillate (D1 wa) is recycled as stream 75 to the hydrogenation reactor I-5. The embodiment according to FIG. 5 presupposes that the polar solvent used is a mixture of one or more alcohols with water.

The sump mixture (S1) is fed as stream 76 to the third phase separator I I I-5 of the thermal splitting unit.

In the third phase separation device I II-5 of the thermal cleavage unit, the bottom mixture (S1) is separated to obtain an upper phase (03) containing the tertiary amine (A1) and a lower phase (U3) containing inhibited residues of the catalyst, the inhibitor and the formic acid Amine adduct (A2). The upper phase (03) is recycled as stream 80 to the extraction unit IV-5. The lower phase (U3) is supplied as stream 77 to the second distillation device IV-5 of the thermal splitting unit. The formic acid-amine adduct (A2) present in the lower phase (U3) is cleaved in the second distillation apparatus IV-5 into formic acid and free tertiary amine (A1). In the second distillation apparatus IV-5, a distillate (D2) and a bottoms mixture (S2) are obtained.

The distillate (D2) containing formic acid is discharged as stream 79 from the distillation apparatus IV-5. The biphasic bottoms mixture (S2) containing the upper phase (03) containing the tertiary amine (A1) and the lower phase (U3) containing the formic acid-amine adduct (A2) inhibited residues of the catalyst and the inhibitor is referred to as Stream 78 to the third phase separation II I-5 recycled thermal splitting unit. The sump mixture (S2) is separated in the third phase separation device I I I-5. The upper phase (03) is recycled as stream 80 to the extraction unit VI-5. The lower phase (U3) is recycled as stream 77 to the second distillation device IV-5.

In the embodiment according to FIG. 6, a stream 91 containing carbon dioxide and a stream 92 containing hydrogen are fed to a hydrogenation reactor I-6. It is possible to supply the hydrogenation reactor I-6 with further streams (not shown) in order to compensate for any losses of the tertiary amine (A1) or of the catalyst which may occur.

In the hydrogenation reactor I-6, carbon dioxide and hydrogen are reacted in the presence of a tertiary amine (A1), a polar solvent and a catalyst containing at least one element from Groups 8, 9 and 10 of the Periodic Table. In this case, a two-phase hydrogenation mixture (H) is obtained which has an upper phase (01) comprising the catalyst and the tertiary amine (A1) and a lower phase (U 1) containing the polar solvent, residues of the catalyst and the formic acid-amine adduct (A2 ) contains.

The hydrogenation mixture (H) is fed as stream 93a to the extraction unit VI-6. In it, the hydrogenation mixture (H) is extracted with the tertiary amine (A1), which is recycled as stream 100 (upper phase (03)) from the third phase separation device I II-6 of the thermal splitting unit to the extraction unit VI-6. In the extraction unit VI-6, a raffinate (R1) and an extract (E1) are obtained. The raffinate (R1) contains the formic acid-amine adduct (A2) and the polar solvent and is supplied as stream 93c to the first distillation apparatus I I-6. The extract (E1) contains the tertiary amine (A1) and the catalyst and is recycled as stream 101 to the hydrogenation reactor I-6.

The current 93c is added continuously or discontinuously to the inhibitor as stream 94. In the first distillation apparatus I I-6, the raffinate (R1) is separated into a distillate (D1) containing the polar solvent, which is recycled as stream 95 to the hydrogenation reactor I-6, and into a biphasic mixture (S1). The bottoms mixture (S1) contains an upper phase (02) containing the tertiary amine (A1) and a lower phase (U2) containing the formic acid-amine adduct (A2), inhibited residues of the catalyst and the inhibitor.

The sump mixture (S1) is supplied as stream 96 to the third phase separation device I I I-6 of the thermal splitting unit. In the third phase separation device 111-6 of the thermal cleavage unit, the bottom mixture (S1) is separated to obtain an upper phase (03) containing the tertiary amine (A1) and a lower phase (U3) containing inhibited residues of the catalyst, the inhibitor and the formic acid Amine adduct (A2).

The upper phase (03) is recycled as stream 100 to the extraction unit VI-6. The lower phase (U3) is supplied as stream 97 to the second distillation device IV-6 of the thermal splitting unit. The formic acid-amine adduct (A2) present in the lower phase (U3) is cleaved in the second distillation apparatus IV-6 into formic acid and free tertiary amine (A1). In the second distillation apparatus IV-6, a distillate (D2) and a bottoms mixture (S2) are obtained.

The distillate (D2) containing formic acid is discharged as stream 99 from the distillation device IV-6. The biphasic bottoms mixture (S2) containing the upper phase (03) containing the tertiary amine (A1) and the lower phase (U3) containing the formic acid-amine adduct (A2) inhibited residues of the catalyst and the inhibitor is referred to as Stream 98 to the third phase separation II I-6 of the thermal cleavage unit recycled. The bottom mixture (S2) is separated in the third phase separation device II-6. The upper phase (03) is called current 100 to Extraction unit VI-6 recycled. The lower phase (U3) is recycled as stream 97 to the second distillation device IV-6.

The invention will be explained in more detail below with reference to embodiments and a drawing.

EXAMPLES Inventive Examples A-1 to A-17 (Hydrogenation and Phase Separation, Workup of the Output from the Hydrogenation Reactor)

A 250 ml Hastelloy C autoclave equipped with a magnetic stir bar was charged under inert conditions with tertiary amine (A1), polar solvent and homogeneous catalyst. The autoclave was then closed and pressed at room temperature C0 ₂ . Subsequently, H _{2 was} pressed in and the reactor was heated with stirring (700 rpm). After the desired reaction time, the autoclave was cooled and the hydrogenation mixture (H) was depressurized. Unless otherwise stated, a two-phase hydrogenation mixture (H) was obtained, the upper phase (01) containing the still free tertiary amine (A1) and the homogeneous catalyst, and the lower phase (U 1) containing the polar solvent and the formic acid-amine adduct (A2) formed was enriched. The total content of formic acid in the formic acid-amine adduct (A2) was determined by titration with 0.1 N KOH in MeOH potentiometrically using a "Mettler Toledo DL50" titrator and the Turnover Frequency (= TOF; : JF Hartwig, Organotransition Metal Chemistry, 1st Edition, 2010, Universtiy Science Books, Sausalito, Calif., P.545) and the reaction rate The composition of the two phases was determined by gas chromatography and the ruthenium content was determined by atomic adsorption spectroscopy (= AAS) The parameters and results of the individual experiments are given in Tables 1 .1 to 1 .5.

Examples A-1 to A-17 show that in the process according to the invention even with variation of the tertiary amine (A1), the polar solvent, the catalyst with respect to the ligands and the metal component, the amount of catalyst, and the amount of water added high to very high reaction rates of up to 0.98 mol kg ^-1 r ¹ can be achieved. All investigated systems formed two phases, the upper phase (01) in each case with the still free tertiary amine (A1) and the homogeneous catalyst, and the lower phase (U 1) in each case with the polar solvent and the formed formic acid-amine adduct (A2) was enriched. Table 1.1

Table 1.2

Table 1.3

Table 1.4

Table 1.5

Example A-17

Tertiary amine (A1) 75 g trihexylamine

Polar solvent 25.0 g 1-Propanol (used) 8.0 g water

Catalyst 0.16 g [Ru (P ⁿ Oct ₃ ) ₄ (H) ₂ ], 0.08 g

1, 2

ethane bis (dicyclohexylphosphino)

Pressing on C0 ₂ With 20.3 g on 2.5 MPa abs

Pressing on H _{2 to} 10.5 MPa abs

Heating to 50 ° C

Pressure change to 1 1.4 MPa abs

Reaction time 2 hours

Special feature -

Upper phase (01) 37.1 g

2.6% water 3.9% 1-propanol 93.5% trihexylamine

Lower phase (U 1) 74.5 g

6.2% formic acid

9.4% water 31.5% 1-propanol 52.9% trihexylamine

K _Ru (C _Ru Upper Phase (01) / 3.9

c _Ru subphase (U 1))

TOF 437 h ¹

Reaction rate 0.45 mol kg ¹ h ¹

Examples A-18 to A-21 (hydrogenation with diols and methanol as solvent)

A 100 mL or 250 mL Hastelloy C autoclave equipped with a paddle or magnetic stirrer was charged under inert conditions with the tertiary amine (A1), polar solvent and catalyst. Subsequently, the autoclave was sealed and C0 _{2 were} pressed at room temperature. Subsequently, H _{2 was} pressed in and the reactor was heated with stirring (700-1000 rpm). After the reaction time, the autoclave was cooled and the hydrogenation mixture (H) was depressurized. After the reaction, water was optionally added to the reaction and stirred for 10 minutes at room temperature. A biphasic hydrogenation mixture (H) was obtained in which the upper phase (01) with the tertiary amine (A1) and the homogeneous catalyst, and the lower phase (U1) with the polar solvent and the formic acid-amine adduct formed (A2 ) was enriched. The phases were then separated and the formic acid content of the lower phase (U1) was determined. The total content of formic acid in the formic acid-amine adduct (A2) was determined by titration with 0.1 N KOH in MeOH potentiometrically using a "Mettler Toledo DL50" titrator. The parameters and results of the individual experiments are shown in Table 1.1

Examples A-18 to A-21 show that under comparable conditions using methanol-water mixtures as the polar solvent higher formic acid concentrations in the lower phase can be achieved compared to diols as the polar solvent.

Table 1.6

5

Example B-1 to B-3 (Extraction of Catalyst)

A 100 ml Hastelloy C autoclave equipped with a paddle stirrer was charged under inert conditions with the tertiary amine (A1), polar solvent and the catalyst. Subsequently, the autoclave was sealed and C0 _{2 were} pressed at room temperature. Subsequently, H _{2 was} pressed on and the reactor was heated with stirring (1000 rpm). After the reaction time, the autoclave was cooled and the hydrogenation mixture (H) was depressurized. A biphasic hydrogenation mixture (H) was obtained, the upper phase (01) containing the still free tertiary amine (A1) and the homogeneous catalyst, and the lower phase (U 1) containing the polar solvent and the formic acid amine formed. Adduct (A2) was enriched. The lower phase (U 1) was separated and added under inert conditions three times with the same amount (mass of amine corresponds to the mass of the lower phase (U 1)) fresh tertiary amine (A1) (10 minutes at room temperature and then separate phases) added to the catalyst extraction , The total content of formic acid in the formic acid-amine adduct (A2) was determined by titration with 0.1 N KOH in MeOH potentiometrically using a "Mettler Toledo DL50" titrator The ruthenium content was determined by AAS The parameters and results of the individual Experiments are shown in Table 1 .6.

Examples B-1 to B-3 show that in the process according to the invention tertiary amine (A1) obtained in process step (e) can be used to extractively reduce the amount of ruthenium catalyst in the lower phase (U 1). By further extraction steps or a continuous countercurrent extraction, this value could be lowered further.

Table 1.7

Inventive Examples C-1 to C-16 (Hydrogenation and Phase Separation, Addition of Water after Reaction;) A 250 ml Hastelloy C autoclave equipped with a magnetic stir bar was placed under inert conditions with tertiary amine (A1), polar solvent, and homogeneous catalyst filled. The autoclave was then closed and pressed at room temperature C0 ₂ . Subsequently, H _{2 was} pressed in and the reactor was heated with stirring (700 rpm). After the desired reaction time, the autoclave was cooled and the hydrogenation mixture (H) was depressurized. Unless otherwise stated, after the addition of water, a two-phase hydrogenation mixture (H) was obtained, the upper phase (01) containing the still free tertiary amine (A1) and the homogeneous catalyst, and the lower phase (U 1) containing the polar solvent , Water and the formed formic acid-amine adducts (A2) was enriched. The total content of formic acid in the formic acid-amine adduct (A2) was determined by titration with 0.1 N KOH in MeOH potentiometrically with a "Mettler Toledo DL50" titrator, and the Turnover Frequency (= TOF, for the definition of TOF see : JF Hartwig, Organotransition Metal Chemistry, 1st Edition, 2010, Universtiy Science Books, Sausalito / California, p.545) and the reaction rate was determined by atomic absorption spectroscopy and the composition of the two phases was determined by gas chromatography The parameters and results of the individual experiments are reproduced in Tables 1 .7 to 1 .1 1. In the embodiments in Experiments C-1 to C-16, unfavorable Ru distribution coefficients k are present after the reaction _Ru before. the product phase current (3,13a), 33a), 53a), 73a), 93 a)) was, therefore, then mixed with water to give a two-phase mixture formed, the upper phase (0 1) consisted mainly of amine and the alcohol and the lower phase (U 1) of the formic acid-amine adducts (A2), the alcohol and water, which were adjusted by the addition of water improved Ru distribution coefficients between these two phases. In the embodiments in the comparative experiments for C3, C7 and C15 (experiments C-17 to C-19 in Table 1 .12), the entire amount of water was already added in the reaction. Here it can be clearly seen that in the case of solvents and catalysts used here, the addition of this amount of water in the hydrogenation leads to inferior ruthenium partitioning coefficients after the reaction and / or lower reaction rates. Table 1.8

Table 1.9

Table 1.10

Table 1.11

Table 1.12

Table 1.13: Comparative Experiments - Addition of Water in the Reaction

Example D1-D4 (extraction of the catalyst);

A 100 ml Hastelloy C autoclave equipped with a paddle stirrer was charged under inert conditions with the tertiary amine (A1), polar solvent and the catalyst. Subsequently, the autoclave was sealed and C0 _{2 were} pressed at room temperature. Subsequently, H _{2 was} pressed on and the reactor was heated with stirring (1000 rpm). After the reaction time, the autoclave was cooled and the hydrogenation mixture (H) was depressurized. After the reaction, water was added to the reaction effluent and stirred at room temperature for 10 minutes. A biphasic hydrogenation mixture (H) was obtained, the upper phase (01) containing the free tertiary amine (A1) and the homogeneous catalyst, and the lower phase (U 1) containing the polar solvent and the formic acid amine formed. Adduct (A2) was enriched. The lower phase (U 1) was separated and stirred under inert conditions three times with the same amount (mass of amine corresponds to the mass of the lower phase) of fresh trialkylamine (stir for 10 minutes at room temperature and then separate phases). The total content of formic acid in the formic acid / amine adduct was determined potentiometrically by titration with 0.1 N KOH in MeOH using a "Mettler Toledo DL50" titrator The ruthenium content was determined by AAS The parameters and results of the individual experiments are in Table 1 .13 reproduced.

Examples D-1 to D-4 show that by varying the catalyst and the amount of water added in the formation of formic acid, the ruthenium in the product phase can be depleted to levels below one ppm ruthenium.

Table 1.14

Example E1 -E9 (Reuse of Catalyst and Catalyst Extraction);

A 100 ml Hastelloy C autoclave equipped with a paddle stirrer was charged under inert conditions with the tertiary amine (A1), polar solvent and the catalyst. Subsequently, the autoclave was sealed and C0 _{2 were} pressed at room temperature. Subsequently, H _{2 was} pressed on and the reactor was heated with stirring (1000 rpm). After the reaction time, the autoclave was cooled and the hydrogenation mixture (H) was depressurized. After the reaction, water was added to the reaction effluent and stirred at room temperature for 10 minutes. There was obtained a two-phase product mixture, wherein the upper phase (01) with the still free tertiary amine (A1) and the homogeneous catalyst, and the lower phase (U 1) with the polar solvent and the formed formic acid-amine adduct (A2 ) was enriched. The phases were then separately determined the formic acid content of the lower phase (U 1) and the ruthenium content of both phases by the methods described below. The upper phase (01) containing ruthenium catalyst was then supplemented with fresh tertiary amine (A1) to 37.5 g and used again with the same solvent under the same reaction conditions as previously for C0 ₂ hydrogenation. After completion of the reaction and addition of water, the lower phase (U 1) was separated and under inert conditions three times with the same amount (mass of amine corresponds to the mass of the lower phase) fresh tertiary amine (A1) (10 minutes at room temperature stirring and then separate phases) for catalyst extraction added. The total content of formic acid in the formic acid-amine adduct (A2) was determined by titration with 0.1 N KOH in MeOH potentiometrically using a "Mettler Toledo DL50" titrator The ruthenium content was determined by AAS The parameters and results of the individual Experiments are shown in Tables 1 .14 to 1 .19.

Examples E-1 to E-9 show that by varying the catalyst, the amount of water added (both before and after the reaction) and the reaction conditions, the active catalyst can be used again for the C0 ₂ hydrogenation and the ruthenium in deplete the product phase down to 2 ppm with only one extraction. Table 1.15

Table 1.16

Table 1.17

Table 1.18

Table 1.19

Table 1.20

Examples F1-F4 (Thermal Separation of the Polar Solvent from the Trialkylamine-Solvent-Formic Acid Mixtures Present as a Product Phase After Extraction); -

Alcohol and water are distilled off from the product phase (containing the formic acid-amine adduct, lower phase (U1), raffinate (R1) or raffinate (R2)) under reduced pressure using a rotary evaporator. In the bottom a biphasic mixture (trialkylamine and formic acid-amine adduct phase, bottom mixture (S1)), the two phases are separated and the formic acid content of the lower phase (U2) by potentiometric titration with 0.1 N KOH in MeOH with The amine and alcohol content are determined by gas chromatography and the parameters and results of the individual experiments are given in Table 1.20.

Examples F-1 to F-4 show that in the process according to the invention, various polar solvents can be separated under mild conditions from the product phase (lower phase (U1), raffinate (R1) or raffinate (R2)), a lower phase containing lower U2 (U2 ) and an upper phase (02), consisting predominantly of tertiary amine, is obtained.

Table 1.21

Examples G1 and G2 (Thermal Separation of the Polar Solvent from the Trialkylamine Solvent-Formic Acid Mixtures and Cleavage of the Formic Acid-Amine Adduct) Alcohol and water are separated from the product phase (containing the formic acid amine subduct (U 1), raffinate ( R1) or raffinate (R2)) distilled off under reduced pressure by means of a rotary evaporator. A biphasic mixture is formed in the bottom (trialkylamine and formic acid-amine adduct phase, bottom mixture (S1)) and the two phases are separated. The composition of the distillate (containing most of the methanol and water; distillate (D1)), the upper phase (containing the free trialkylamine, upper phase (02)) and the lower phase (containing the formic acid-amine adduct; lower phase (U2)) was determined by gas chromatography and by titration of the formic acid against 0.1 N KOH in MeOH potentiometrically with a "Mettler Toledo DL50" titrator The formic acid is then removed from the lower phase (U2) from the first step in a vacuum distillation apparatus over a 10 cm Vigreux column After complete removal of the formic acid, a single-phase bottom product (S2) consisting of the pure tertiary amine (A2) is obtained, which can be used for extraction of the catalyst and recycling into the hydrogenation The composition of the sump (S2) and of the distillate was determined by Ga chromatography and by titration of the formic acid with against 0.1 N KOH in MeOH determined potentiometrically with a "Mettler Toledo DL50" titrator. The parameters and results of the individual experiments are shown in Table 1 .21.

Examples G-1 and G-2 show that in the process according to the invention, various polar solvents can be separated from the product phase under mild conditions, with a lower (U3) formic acid and an upper phase (03) consisting predominantly of tertiary amine (A1). , From this formic acid-rich lower phase (U3), the formic acid can then be cleaved off at higher temperatures from the tertiary amine (A1), the free tertiary amine (A1) being obtained. The formic acid thus obtained still contains some water, which, however, can be separated off from the formic acid by a column having a greater separation efficiency. The resulting in both the separation of the solvent and in the thermal cleavage tertiary amine (A1) can be used to extract the catalyst. Table 1.22

Examples H1 to H4 (preferred solubility of the inhibitors according to the invention in a biphasic mixture of formic acid-amine adduct (A2) and tertiary amine (A1))

20 g of formic acid-amine adduct of formic acid and tri-n-hexylamine (A3) (20.4% HCOOH), 10 g of trihexylamine and 0.5 g each of the inhibitors mentioned in the table are weighed together and for 2 hours at room temperature touched. Subsequently, both liquid phases are separated (with EDTA and Trilon M, some solid forms, which is decanted off) and the content of the inhibitor in each phase is determined by HPLC (detection limit for EDTA and trioin M: 0.01 g / 100g, for citric acid and DL tartaric acid: 0.1 g / 100g)

Examples H-1 to H4 show that the inhibitors preferably accumulate in the formic acid-amine adduct (A3) phase in the process according to the invention and thus do not enter the hydrogenation stage.

Examples

Examples 11 and 12: Decomposition of formic acid in the hydrogenation mixture (H) from the C0 ₂ hydrogenation without addition of an inhibitor (reference values, Comparative Example 11) and with addition (Inventive Example AI2) in the solvent removal. Comparative Example 11: A 250 mL Hastelloy C autoclave equipped with a magnetic stirring bar was placed under inert conditions with trihexylamine (65.0 g), methanol (25.0 g), water (2.0 g), [Ru (PnOct ₃ ) ₄ (H) ₂ ] (82 mg) and 1, 2-bis (dicyclohexylphosphino) ethane (= dcpe, 20 mg). The autoclave was then closed and pressed at room temperature C0 ₂ (25.0 g). Subsequently, it was pressed onto 120 bar with H ₂ and the reactor was heated to 70 ° C. with stirring (700 rpm). After 8 hours of reaction time, the autoclave was cooled and the hydrogenation mixture (M) relaxed. The total content of formic acid in the formic acid-amine adduct (A3) in the lower phase (U 1) was determined by titration with 0.1 N KOH in MeOH potentiometrically using a "Mettler Toledo DL50" titrator

8.1%, wherein the hydrogenation mixture (M) (96.2 g) consisted of 85.5% of the lower phase (U 1). The hydrogenation mixture (H) was then heated at atmospheric pressure under reflux (oil bath temperature 80 ° C) in a glass flask, and hourly determines the ratio of upper phase (01) to lower phase (U 1) and the formic acid content by titration.

Inventive Example 12: A 250 mL Hastelloy C autoclave equipped with a magnetic stir bar was placed under inert conditions with trihexylamine (65.0 g), Metahnol (25.0 g), water (2.0 g), [Ru (PnOct ₃ ) ₄ (H) ₂ ] (82 mg) and 1, 2-bis (dicyclohexylphosphino) ethane (20 mg). The autoclave was then closed and pressed at room temperature C0 ₂ (25.0 g). Subsequently, it was pressed onto 120 bar with H ₂ and the reactor was heated to 70 ° C. with stirring (700 rpm). After 8 hours of reaction time, the autoclave was cooled and the hydrogenation mixture (H) relaxed. The total content of formic acid in the formic acid-amine adduct (A3) in the lower phase (U 1) was determined potentiometrically by titration with 0.1 N KOH in MeOH using a "Mettler Toledo DL50" titrator

8.2%, wherein the hydrogenation mixture (H) (95.7 g) consisted of 83.5% of the lower phase (U 1). The hydrogenation mixture (H) was treated with H ₂ 0 ₂ (136 mg of a 30% solution in water) and then heated at atmospheric pressure under reflux (oil bath temperature 80 ° C) in a glass flask. Hourly the ratio of upper phase (01) to lower phase (U 1) and the formic acid content was determined by titration.

FIG. 7 shows the development of the percentage content of the lower phase (U 1) based on the total weight of the hydrogenation mixture (H).

FIG. 7 and Examples 11 and 12 show that the formic acid present in the formic acid-amine adduct (A3) in the lower phase (U 1) decomposes significantly more slowly at the temperatures of the methanol separation (80 ° C.) (removal of the polar solvent) when small amounts of an inhibitor such as H ₂ 0 _{2 are} added (Example 12). In the formic acid-amine adduct (A3) cleavage, however, the decomposition rate is much faster than in the step of separation of the polar solvent and thus more relevant due to the higher bottom temperatures (> 130 ° C), so that further investigations for inhibitors Process step (e), ie the cleavage of the formic acid-amine adduct (A3) relate (Examples 13-125).

Comparative Examples 13-15: decomposition of formic acid in the cleavage of the formic acid-amine adduct (A3) without addition of an inhibitor; Simulation of process step (e) without addition of an inhibitor.

Comparative Examples 13-15: 80.0 g of formic acid-amine adduct (A3), ie, adduct of formic acid and tri-n-hexylamine, (1: 1, 5, 20 wt .-% formic acid) and the ruthenium catalyst were in a glass flask weighed. The reaction mixture was refluxed to 130 ° C in the open system, forming an upper phase and a lower phase. The content of formic acid in the formic acid-amine adduct (A3) in the lower phase was determined by titration with 0.1 N KOH in MeOH potentiometrically hourly with a "Mettler Toledo DL50" - titrator, and also the ratio between upper and lower phase in Reaction mixture was determined.

Table 1

Examples 13 and 15 show that the formic acid decomposes very rapidly in the lower phase at the temperatures of the cleavage (> 130 ° C.) (process step (e)), if ruthenium compounds (with or without phosphine ligand) are present and no inhibitor has been added

Inventive Examples 16-130: decomposition of formic acid in the cleavage of the formic acid-amine adduct (A3) with the addition of an inhibitor; Simulation of process step (e) with the addition of an inhibitor

Inventive Examples 16-130: 80.0 g formic acid-amine adduct (A3), i. Adduct of formic acid and tri-n-hexylamine, (1: 1.5, 20 wt .-% formic acid) and the ruthenium catalyst and the inhibitor were weighed into a glass flask. The reaction mixture was refluxed to 130 ° C in the open system to form a lower phase and an upper phase. The content of formic acid in the formic acid-amine adduct (A3) in the lower phase was determined by titration with 0.1 N KOH in MeOH potentiometrically hourly with a "Mettler Toledo DL50" - titrator, and also the ratio between upper and lower phase in Reaction mixture was determined.

Examples 16 and 130 according to the invention show that the decomposition of formic acid in the cleavage (> 130 ° C.) (process stage (e)) can be markedly slowed down by the addition of inhibitors according to the invention and thus significantly lower formic acid losses occur during work-up.

Table 2:

Table 4:

Table 5:

Table 6:

Table 7:

Table 8:

Claims

claims

A process for producing formic acid comprising the steps

NR ¹ R ² R ³ (A1),

in the

NR ¹ R ² R ³ * Xi HCOOH (A2),

in the

X, is in the range of 0.4 to 5 and

R ¹ , R ² , R ^{3 have} the meanings given above, (b) Working up of the hydrogenation mixture (H) obtained in step (a) according to one of the following steps

(b2) extraction of the at least one catalyst from the hydrogen mixture (H) obtained in step (a) in an extraction unit with an extractant containing the at least one tertiary amine (A1) to obtain a raffinate (R1) containing the at least one formic acid amine Adduct (A2) and the at least one polar solvent and an extract (E1) containing the at least one tertiary amine (A1) and the at least one catalyst or

(b3) Phase separation of the hydrogen mixture (H) obtained in step (a) in a first phase separation device into the upper phase (01) and the lower phase (U1) and extraction of the residues of the at least one catalyst from lower phase (U1) in an extraction unit with an extraction agent containing the at least one tertiary amine (A1) to obtain a raffinate (R2) containing the at least one formic acid-amine adduct (A2) and the at least one polar solvent and an extract (E2) containing the at least one tertiary amine (A1) and the radicals of the at least one catalyst, (c) at least partially separating the at least one polar solvent from the lower phase (U 1), from the raffinate (R1) or from the raffinate (R2) in a first distillation apparatus to obtain a distillate (D1) containing the at least one polar solvent, which is recycled to the hydrogenation reactor in step (a) and a biphasic bottoms mixture (S1) containing an upper phase (02) containing the at least one tertiary amine (A1) and a lower phase (U2) containing the at least one formic acid amine Contains adduct (A2),

(d) optionally working up of the first bottoms mixture (S1) obtained in step (c) by phase separation in a second phase separation device into the upper phase (02) and the lower phase (U2), (e) cleavage in the bottoms mixture (S1) or optionally in the Subphase (U2) containing at least one formic acid-amine adduct (A2) in a thermal cleavage unit to give the at least one tertiary amine (A1) which is recycled to the hydrogenation reactor in step (a) and formic acid resulting from the thermal cleavage unit is discharged immediately before and / or during step (c) of the lower phase (U 1), the raffinate (R1) or the raffinate (R2) at least one inhibitor selected from the group consisting of carboxylic acids other than formic acid, of carboxylic acid derivatives other than formic acid derivatives and

Oxidizing agents is added.

2. The process according to claim 1, wherein the hydrogenation mixture (H) obtained in step (a) is further worked up according to step (b1) and the first upper phase (01) is recycled to the hydrogenation reactor in step (a) and the

Subphase (U 1) of the first distillation apparatus in step (c) is supplied.

3. The process according to claim 1, wherein the hydrogenation mixture (H) obtained in step (a) is further worked up according to step (b2), wherein the extractant used is the at least one tertiary amine (A1) obtained in step (e) in the thermal cleavage unit and the extract (E1) in the Hydrogenation reactor in step (a) is recycled and the raffinate (R1) of the first distillation apparatus in step (c) is supplied.

Process according to claim 1, wherein the hydrogenation mixture (H) obtained in step (a) is further worked up according to step (b3), wherein the extractant used is the at least one tertiary amine (A1) obtained in step (e) in the thermal splitting unit, and the extract (E2) is recycled to the hydrogenation reactor in step (a) and the raffinate (R2) is fed to the first distillation apparatus in step (c).

A process according to any one of claims 1 to 4, wherein the thermal splitting unit comprises a second distillation apparatus and a third phase separation apparatus, and the cleavage of the formic acid-amine adduct (A2) in the second distillation apparatus is carried out to obtain a distillate (D2) containing formic acid the second distillation apparatus is discharged and a biphasic bottom mixture (S2) containing an upper phase (03) containing the at least one tertiary amine (A1) and a lower phase (U3) containing the at least one formic acid-amine adduct (A2) and the contains at least one inhibitor.

A process according to claim 5, wherein the bottoms mixture (S2) obtained in the second distillation apparatus is separated into the upper phase (03) and the lower phase (U3) in the third phase separator of the thermal splitter unit and the upper phase (03) is added to the hydrogenation reactor in step (a ) and the lower phase (U3) is recycled to the second distillation device of the thermal splitter unit.

A method according to claim 6, wherein the upper phase (03) is recycled to the extraction unit in step (b2) or (b3).

A process according to any one of claims 1 to 7, wherein the first sump mixture (S1) obtained in step (c) or optionally the lower phase (U2) of the second distillation apparatus is fed to the thermal splitting unit. Method according to one of claims 1 to 8, wherein the obtained in step (c) first bottoms mixture (S1) or optionally the lower phase (U2) of the third phase separation device of the thermal splitting unit is supplied.

Method according to one of claims 1 to 9, wherein the bottom mixture (S1) obtained in step (c) is further worked up according to step (d) and the top phase (02) is returned to the extraction unit in step (b2) and the bottom phase (U2) the thermal splitting unit in step (e) is supplied.

A process as claimed in any of claims 1 to 10, wherein the tertiary amine used is a tertiary amine of the general formula (A1) in which the radicals R ¹ , R ² and R ³ are selected independently of one another from the group consisting of C ₅ to C ₆ alkyl, C ₅ to C ₈ cycloalkyl, benzyl and phenyl.

A process according to any one of claims 1 to 11, wherein the tertiary amine (A1) used is tri-n-hexylamine.

A process according to any one of claims 1 to 12, wherein the polar solvent used is water, methanol or a mixture of water and methanol.

A method according to any one of claims 1 to 13, wherein as inhibitor at least one carboxylic acid selected from the group consisting of oxalic acid, lactic acid, maleic acid, phthalic acid, tartaric acid, citric acid, iminodiacetic acid, ethylenediaminetetraacetic acid (EDTA), nitriloacetic acid, methylglycinediacetic acid, diethylenetriaminepentaacetic acid (DTPA), dimercaptosuccinic acid is used.

Method according to one of claims 1 to 13, wherein as inhibitor at least one oxidizing agent selected from the group consisting of peroxycarboxylic acids, diacyl peroxides and trialkyl-N-oxides is used.