DE102012016959A1 - Preparing formic acid, comprises e.g. reacting a reaction mixture comprising carbon dioxide, hydrogen, polar solvent and tertiary amine in presence of cationic complex catalyst into hydrogenation mixture including formic acid-amine-adduct - Google Patents

Abstract

Preparing formic acid, comprises (a) reacting a reaction mixture comprising carbon dioxide, hydrogen, a polar solvent and a tertiary amine of (Ia) in the presence of a cationic complex catalyst, in a hydrogenation reactor (I) to obtain a hydrogenation mixture containing a formic acid-amine-adduct (A1) of (II), and (b) processing the hydrogenation mixture comprising (b1) separating the polar solvent from the hydrogenation mixture to obtain a distillate containing a formic acid-amine-adduct (A2), and (b2) splitting the formic acid-amine-adduct (A2) to obtain tertiary amine and formic acid. Preparing formic acid, comprises (a) reacting a reaction mixture comprising carbon dioxide, hydrogen, at least one polar solvent and at least one tertiary amine of the formula (NR 1>R 2>R 3>) (Ia) in the presence of at least one cationic complex catalyst, which contains at least one element from groups 8, 9 and 10, in a hydrogenation reactor (I) to obtain a hydrogenation mixture containing at least one polar solvent, at least one cationic catalyst and at least one formic acid-amine-adduct (A1) of formula (NR 1>R 2>R 3>x x 1HCOOH) (II), and (b) processing the hydrogenation mixture comprising (b1) separating at least one polar solvent from the hydrogenation mixture in a distillation apparatus (II) to obtain a distillate containing at least one polar solvent and a bottom mixture comprising at least one formic acid-amine-adduct (A2), and (b2) splitting at least one formic acid-amine-adduct (A2) contained in the bottom mixture, in a thermal cracking unit (III) to obtain at least one tertiary amine and formic acid, where the cationic complex catalyst is immobilized before processing the hydrogenation mixture in the step (b) by at least one carrier material having acidic functional groups, which is insoluble in the hydrogenation mixture. Either R 1>-R 3>(1-16C) aliphatic, (1-16C) araliphatic or (1-16C) aromatic group (all optionally branched or cyclic, and C of all groups are optionally substituted by -N- or -O-); or 2 or 3 of R 1>-R 3>chain containing at least 4 atoms; and x 10.4-5.

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 cationic complex catalyst which contains an element from the 8th, 9th or 10th group of the periodic table and can be immobilized on a support material, a tertiary one Amines and a polar solvent to form 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.

In particular, the catalytic hydrogenation of carbon dioxide in the presence of amines ( W. Leitner, Angewandte Chemie 1995, 107, pages 2391 to 2405 ; PG Jessop, T. Ilkariya, R. Noyori, Chemical Reviews 1995, 95, pp. 259-272 ). The adducts of formic acid and amines formed in this process can be thermally cleaved into formic acid and the amine which can be recycled into the hydrogenation. In the hydrogenation catalysts are used which contain one or more elements from the 8th, 9th or 10th group of the periodic table. Preference is given to using a catalyst which comprises ruthenium.

• • Nicht vollständige Abtrennung und Rückführung würde zu großen Verlusten des teuren Katalysators führen und erhebliche Zusatzkosten generieren.
• • Der Katalysator kann die Rückspaltung des Addukts aus Ameisensäure und tertiärem Amin zu Kohlendioxid, Wasserstoff und tertiärem Amin gemäß folgender Reaktionsgleichung katalysieren:
  

In order to enable an economical process, the catalyst used must be separated as completely as possible from the product stream of the catalytic hydrogenation and recycled to the reaction of carbon dioxide with hydrogen in the presence of amines. The reasons are:

• • Inadequate separation and recycling would lead to large losses of the expensive catalyst and generate significant additional costs.
• The catalyst can catalyze the cleavage of the adduct of formic acid and tertiary amine to carbon dioxide, hydrogen and tertiary amine according to the following reaction equation:
  

The cleavage leads to a significant reduction in the yield of adduct of formic acid and tertiary amine and thus to a reduction in the yield of the target product formic acid. The transition-metal-catalyzed decomposition of formic acid has been reported in inter alia C. Fellay, N. Van, PJ Dyson, G. Laurenczy Chem. Eur. J. 2009, 15, 3752-3760 ; C. Fellay, PJ Dyson, G. Laurenczy Angew. Chem. 2008, 120, 4030-4032 ; A. Boddien, B. Loges, F. Gärtner, C. Torborg, K. Fumino, H. Junge, R. Ludwig, M. Beller J. Am. Chem. Soc. 2010, 132, 8924-8934 ; B. Loges, A. Boddien, H. Young, M. Beller Angew. Chem. 2008, 120, 4026-4029 ; F. Joó ChemSusChem 2008, 1, 805-808 ; S. Enthaler Chem. SuChem 2008, 1, 801-804 ; S. Fukuzumi, T. Kobayashi, T. Suenobu ChemSusChem 2008, 1, 827-834 and A. Boddien, B. Loges, H. Young, M. Beller ChemSusChem 2008, 1, 751-758 described. The catalysts used in this case are in principle also suitable for the hydrogenation of carbon dioxide to formic acid ( PG Jessop, T. Ilkariya, R. Noyori Chem. Rev. 1995, 95, 259-272; PG Jessop, F. Joó, CC Tai Coord. Chem. Rev. 2004, 248, 2425-2442 ; PG Jessop, Homogeneous Hydrogenation of Carbon Dioxide, in: The Handbook of Homogeneous Hydrogenation, Ed .: JG de Vries, CJ Elsevier, Volume 1, 2007, Wiley-VCH, pp. 489-511 ).

Thus, the catalyst used must be separated as completely as possible from the product stream of the catalytic hydrogenation and recycled to the hydrogenation of carbon dioxide.

• 1) Phasentrennung des Reaktionsgemischs unter Erhalt einer Oberphase enthaltend das tertiäre Amin und den Katalysator sowie einer Unterphase enthaltend das Ameisensäure-Amin-Addukt, das hochsiedende polare Lösungsmittel und Reste des Katalysators; Rückführung der Oberphase zur Hydrierung,
• 2) Extraktion der Unterphase mit dem tertiären Amin unter Erhalt eines Extrakts enthaltend das tertiäre Amin und die Reste des Katalysators sowie eines Raffinats enthaltend das hochsiedende polare Lösungsmittel und das Ameisensäure-Amin-Addukt; Rückführung des Extrakts zur Hydrierung,
• 3) Thermische Spaltung des Raffinats in einer Destillationskolonne unter Erhalt eines Destillats enthaltend die Ameisensäure und eines Sumpfgemischs enthaltend das freie tertiäre Amin und das hochsiedende polare Lösungsmittel; Rückführung des hochsiedenden polaren Lösungsmittels zur Hydrierung.

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 having 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. There is obtained a reaction mixture containing the formic acid-amine adduct, the tertiary amine, the high-boiling polar solvent and the catalyst. The reaction mixture is worked up 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 procedure is appropriate WO 2010/149507 thus allows separation and recycling of the catalyst.

A disadvantage of the method of WO 2010/149507 is, however, that the separation of the catalyst is very complex and includes a phase separation (step 1)) and an extraction (step 2)). Furthermore, it is disadvantageous that esterification of the formic acid formed with the high-boiling polar solvents (diols and polyols) can occur 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 management, as described in the prior art, in particular a simpler process concept for processing the discharge from the hydrogenation reactor, simpler process steps, a smaller number of process stages or simpler apparatus. Furthermore, the method should also be able to be carried out with the lowest possible energy requirement.

The workup of the discharge from the hydrogenation reactor should preferably be carried out exclusively with the substances already present in the process, without additional auxiliaries, and these should preferably be completely or substantially completely recycled in the process.

• (a) Umsetzung eines Reaktionsgemischs (Rg) enthaltend Kohlendioxid, Wasserstoff, mindestens ein polares Lösungsmittel sowie mindestens ein tertiäres Amin der allgemeinen Formel (A1) NR¹R²R³ (A1), in der R¹, R², R³ unabhängig voneinander einen unverzweigten oder verzweigten, acyclischen oder cyclischen, aliphatischen, araliphatischen oder aromatischen Rest mit jeweils 1 bis 16 Kohlenstoffatomen darstellen, wobei einzelne Kohlenstoffatome unabhängig voneinander auch durch eine Heterogruppe ausgewählt aus den Gruppen -O- und >N- substituiert sein können sowie zwei oder alle drei Reste unter Bildung einer mindestens jeweils vier Atome umfassenden Kette auch miteinander verbunden sein können, in Gegenwart mindestens einen kationischen Komplexkatalysators, der mindestens ein Element ausgewählt aus den Gruppen 8, 9 und 10 des Periodensystems enthält, in einem Hydrierreaktor, unter Erhalt eines Hydriergemischs (H) enthaltend das mindestens eine polare Lösungsmittel, den mindestens einen kationischen Katalysator sowie mindestens ein Ameisensäure-Amin-Addukt der allgemeinen Formel (A2) NR¹R²R³·x_iHCOOH (A2), in der x_i im Bereich von 0,4 bis 5 liegt und R¹, R², R³ die vorstehend genannten Bedeutungen haben, (b) Aufarbeitung des Hydriergemischs (H) umfassend die Schritte (b1) Abtrennung des mindestens einen polaren Lösungsmittels aus dem Hydriergemisch (H) in einer Destillationsvorrichtung unter Erhalt eines Destillats (D1) enthaltend das mindestens eine polare Lösungsmittel und eines Sumpfgemischs (S1) enthaltend das mindestens eine Ameisensäure-Amin-Addukt (A2), (b2) Spaltung des im Sumpfgemisch (S1) enthaltenen mindestens einen Ameisensäure-Amin-Addukts (A2) in einer thermischen Spalteinheit unter Erhalt des mindestens einen tertiären Amins (A1) und Ameisensäure,

wobei der kationische Komplexkatalysator vor der Aufarbeitung des Hydriergemischs (H) gemäß Schritt (b) durch mindestens ein Trägermaterial (T), das saure funktionelle Gruppen aufweist und im Hydriergemisch (H) unlöslich ist, immobilisiert wird.The object is achieved by a process for the preparation of formic acid, comprising the steps

• (a) reaction of a reaction mixture (Rg) comprising carbon dioxide, hydrogen, at least one polar solvent and at least one tertiary amine of the general formula (A1) NR ¹ R ² R ³ (A1), in which R ¹ , R ² , R ³ independently of one another represent an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having in each case 1 to 16 carbon atoms, where individual carbon atoms are also 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 be joined together to form a chain comprising at least four atoms, in the presence of at least one cationic complex catalyst containing at least one element selected from groups 8, 9 and 10 of Periodic table contains, in a hydrogenation reactor, to obtain a hydrogenation mixture (H) containing the at least one polar solvent, the at least one cationic catalyst and at least one formic acid-amine adduct of the general formula (A2) NR ¹ R ² R ³ · x _i HCOOH (A2), in which x _{i is} in the range from 0.4 to 5 and R ¹ , R ² , R ^{3 have} the abovementioned meanings, (b) Working up of the hydrogenation mixture (H) comprising the steps of (b1) separating off the at least one polar solvent the hydrogenation mixture (H) in a distillation apparatus to obtain a distillate (D1) comprising the at least one polar solvent and a bottom mixture (S1) containing the at least one formic acid-amine adduct (A2), (b2) cleavage in the bottom mixture (S1) containing at least one formic acid-amine adduct (A2) in a thermal splitting unit to obtain the at least one tertiary amine (A1) and formic acid,

wherein the cationic complex catalyst before the workup of the hydrogenation mixture (H) according to step (b) by at least one support material (T) having acidic functional groups and is insoluble in the hydrogenation mixture (H) is immobilized.

It has been found that formic acid can be obtained in high yield with the process according to the invention. The process according to the invention enables an effective separation of the catalyst in its active form and the immobilization of the cationic complex catalyst in the hydrogenation reactor in step (a). The separation of the polar solvent used according to the invention also prevents esterification of the formic acid obtained in the thermal splitting unit in step (b2), which likewise leads to an increase in the yield of formic acid. 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 those in WO2010 / 149507 used polar solvents - leads. 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, in process step (a), a reaction mixture (Rg) is reacted in a hydrogenation reactor containing carbon dioxide, hydrogen, at least one cationic complex catalyst containing at least one element selected from groups 8, 9 and 10 of the periodic table, at least one polar solvent and at least a 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 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 represent 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, where individual carbon atoms independently of one another may also be substituted by a hetero group selected from the groups -O- and> N-, and two or all three radicals may also be linked together to form a chain comprising at least four atoms each. 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.

• • Tri-n-propylamin, Tri-n-butylamin, Tri-n-pentylamin, Tri-n-hexylamin, Tri-n-heptylamin, Tri-n-octylamin, Tri-n-nonylamin, Tri-n-decylamin, Tri-n-undecylamin, Tri-n-dodecylamin, Tri-n-tridecylamin, Tri-n-tetradecylamin, Tri-n-pentadecylamin, Tri-n-hexadecylamin, Tri-(2-ethylhexyl)amin.
• • Dimethyl-decylamin, Dimethyl-dodecylamin, Dimethyl-tetradecylamin, Ethyl-di-(2-propyl)amin, Dioctyl-methylamin, Dihexyl-methylamin.
• • Tricyclopentylamin, Tricyclohexylamin, Tricycloheptylamin, Tricyclooctylamin und deren durch eine oder mehrere Methyl-, Ethyl-, 1-Propy-, 2-Propyl-, 1-Butyl-, 2-Butyl- oder 2-Methyl-2-propyl-Gruppen substituierte Derivate.
• • Dimethyl-cyclohexylamin, Methyl-dicyclohexylamin, Diethyl-cyclohexylamin, Ethyl-dicyclohexylamin, Dimethyl-cyclopentylamin, Methyl-dicyclopentylamin.
• • Triphenylamin, Methyl-diphenylamin, Ethyl-diphenylamin, Propyl-diphenylamin, Butyl-diphenylamin, 2-Ethyl-hexyl-diphenylamin, Dimethyl-phenylamin, Diethyl-phenylamin, Dipropyl-phenylamin, Dibutyl-phenylamin, Bis(2-Ethyl-hexyl)phenylamin, Tribenzylamin, Methyl-dibenzylamin, Ethyl-dibenzylamin und deren durch eine oder mehrere Methyl-, Ethyl-, 1-Propyl, 2-Propyl-, 1-Butyl-, 2-Butyl- oder 2-Methyl-2-propyl-Gruppen substituierte Derivate.
• • N-C₁-bis-C₁₂-Alkyl-piperidine, N,N-Di-C₁-bis-C₁₂-Alkyl-piperazine, N-C₁-bis-C₁₂-Alkyl-pyrrolidone, N-C₁-bis-C₁₂-Alkyl-imidazole und deren durch eine oder mehrere Methyl-, Ethyl-, 1-Propy-, 2-Propyl-, 1-Butyl-, 2-Butyl- oder 2-Methyl-2-propyl-Gruppen substituierte Derivate.
• • 1,8-Diazabicyclo[5.4.0]undec-7-en („DBU”), 1,4-Diazabicyclo[2.2.2]octan („DABCO”), N-Methyl-8-azabicyclo[3.2.1]octan („Tropan”), N-Methyl-9-azabicyclo[3.3.1]nonan („Granatan”), 1-Azabicyclo[2.2.2]octan („Chinuclidin”).

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.
• Dimethyl-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, methyl-diphenylamine, ethyl-diphenylamine, propyl-diphenylamine, butyl-diphenylamine, 2-ethyl-hexyl-diphenylamine, dimethyl-phenylamine, diethyl-phenylamine, dipropyl-phenylamine, dibutyl-phenylamine, bis (2-ethyl-hexyl ) 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.
• • NC ₁ -bis-C ₁₂ -alkyl-piperidines, N, N-di-C ₁ -bis-C ₁₂ -alkyl-piperazines, NC ₁ -bis-C ₁₂ -alkyl-pyrrolidone, NC ₁ -bis-C ₁₂ Alkyl imidazoles and their by one or more methyl, ethyl, 1-propy, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups substituted derivatives.
• • 1,8-diazabicyclo [5.4.0] undec-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.

The tertiary amine of the general formula (A1) used in the process according to the invention is particularly preferably an amine in which the radicals R ¹ , R ² , R ³ are selected independently of one another from the group C ₁ - to C ₁₂ -alkyl, C ₅ - to C ₈ cycloalkyl, benzyl and phenyl, a.

In the process according to the invention, particular preference is given to using a saturated amine as tertiary amine, ie. H. 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 principle, therefore, chemically inert, nonpolar solvents such as for example, aliphatic, aromatic or araliphatic hydrocarbons, for example octane and higher alkanes, toluene, xylenes (o-, p- and / or m-xylene).

In the process of the invention, at least one polar is used in process step (a) in the hydrogenation of carbon dioxide. Preferred are polar solvents having a boiling point at atmospheric pressure (1 atm) in the range of 20 to 150 ° C, preferably 20 to 120 ° C, more preferably 20 to 110 ° C and in particular in the range of 30 to 100 ° C.

• • Monoalkohole wie Methanol, Ethanol, 1-Propanol, 2-Propanol, 1-Butanol, 2-Butanol, 2-Methyl-1-propanol,
• • Ether wie Diethylether, Di-n-propylether, Dimethoxyethan, Methyl-tert-butylether, Ethyl tert-butylether, 1,4-Dioxan, Tetrahydrofuran, 2-Methyltetrahydrofuran,
• • Wasser.

Suitable polar solvents are, for example

• Monoalcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol,
• Ethers, such as diethyl ether, di-n-propyl ether, dimethoxyethane, methyl tert-butyl ether, ethyl tert-butyl ether, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran,
• • Water.

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.

Preferably, the reaction mixture (Rg) contains at least one polar solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, dimethoxyethane, methyl tert-butyl ether, tetrahydrofuran.

Particularly preferred polar solvents are mixtures of at least one of the abovementioned suitable monoalcohols and / or at least one of the abovementioned suitable ethers with water.

In a further particularly preferred embodiment, the polar solvent used is methanol, tetrahydrofuran or a mixture of water, methanol and tetrahydrofuran.

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 cationic complex 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 (IUPAC nomenclature). 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) cationic complex catalyst or a mixture of two or more cationic complex catalysts can be used. Preference is given to using one (1) cationic complex catalyst. In the context of the present invention, "cationic complex catalyst" is understood to mean both one (1) cationic complex catalyst and mixtures of two or more cationic complex catalysts.

Preferably, the cationic complex catalyst contains at least one element selected from the group consisting of Fe, Pd and Ir. Most preferably, the cationic complex catalyst contains Fe.

The cationic complex catalyst used is preferably a complex-like compound of the abovementioned elements, which is generally soluble in the reaction mixture (R _g ) prior to immobilization.

The amount of metal components used in the cationic 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 250 ppm by weight, in each case based on the total liquid reaction mixture in the hydrogenation reactor.

In the process according to the invention, the cationic complex catalysts used are in particular catalysts which are homogeneously soluble in the reaction mixture (Rg) before the immobilization, in particular organometallic complex compounds containing at least one element from the 8th, 9th or 10th group of the periodic table, at least one neutral ligand and at least one anionic ligand.

Neutral ligands are ligands that are in free, d. H. uncomplexed, form, have no charge. By anionic ligands ligands are understood that in free, d. H. uncomplexed, form, have at least one negative charge. Suitable neutral ligands are, for example, phosphine ligands, amine ligands (such as tertiary amines), carbon monoxide and DMSO. Examples of suitable anionic ligands are hydride, fluoride, chloride, bromide, iodide, formate, acetate, propionate, acetylacetonate, hydroxide and alcoholates (such as methanolate, ethanolate and propoxide).

Cationic complex catalysts are understood as meaning catalysts which can cleave off at least one anionic ligand under the reaction conditions in process step (a), giving rise to a catalyst species which has at least one positive charge.

Particularly suitable neutral ligands are phosphine ligands. The cationic complex catalyst preferably has at least one phosphine ligand.

The cationic complex catalyst or its salts used as a precursor can be dissolved to improve the solubility before use in process step (a) in a polar solvent, preferably an ether such as tetrahydrofuran.

Suitable phosphine ligands are phosphine groups which contain at least one unbranched or branched, acyclic or cyclic, aliphatic radical having 1 to 9 carbon atoms, where individual carbon atoms may also be substituted by> P-. For the purposes of branched cyclic aliphatic radicals, radicals such as, for example, -CH ₂ -C ₆ H _{11 are also} included. Examples of suitable radicals are methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 1- (2-methylpropyl, 2- (2-methylpropyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-methyl). Octyl, 1-nonyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl, methylcyclopentyl, methylcyclohexyl, 1- (2-methyl) -pentyl, 1- (2-ethyl) -hexyl and norbornyl, preferably containing the unbranched or branched, acyclic or cyclic In the case of an exclusively cyclic radical in the above-mentioned sense, the number of carbon atoms is 3 to 9 and preferably at least 4 and preferably at most 8. The preferred radicals are methyl, 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 are P (nC _n H _{2n + 1} ) ₃ where _n is 1 to 11, preferably n is 1 to 10.

Particular preference is given to phosphines of the general formula P (nC _n H _{2n + 1} ) ₂ -CH ₂ CH ₂ -P (nC _n H _{2n + 1} ) ₂ where n is 1 to 9, such as 1,2-bis (dimethylphosphino) ethane, 1,2-bis (diethylphosphino) ethane, 1,2-bis (dibutylphosphino) ethane, 1,2-bis (dioctylphosphino) ethane, 1,1 '- [2 - [(diethylphosphino) methyl] -2-methyl-1 , 3-propanediyl] bis [1,1-diethylphosphine ("Ethylphos Triphos") or tris [2- (diphenylphosphino) ethyl] phosphine and 1,2-bis [bis (methoxypropyl) phosphino] ethane {P (C ₄ H ₉ O) ₂ -CH ₂ CH ₂ -P (C ₄ H ₉ O) ₂ }.

As already mentioned above, in the stated unbranched or branched, acyclic or cyclic, aliphatic radicals, individual carbon atoms may also be substituted by> P-. Examples of suitable radicals are methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 1- (2-methyl) propyl, 2- (2-methyl) propyl, 1-pentyl, 1 Hexyl, 1-heptyl, 1-octyl, 1-nonyl. Thus, multidentate, for example, two- or tetradentate, phosphine ligands are also included.

wobei R^a C₁- bis C₉-Alkyl oder C₅- bis C₆-Aryl bedeutet.These preferably contain the

where R ^{a is} C ₁ - to C ₉ -alkyl or C ₅ - to C ₆ -aryl.

Suitable tetradentate phosphine ligands have, for example, the following general formulas: P (CH ₂ CH ₂ PR ^a ₂ ) ₃ , P (CH ₂ CH ₂ PR ⁴ ₂ ) ₃ , where the radicals R ^a and R ⁴ are as defined above and below Have meanings.

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 cationic complex catalyst 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, tetrafluoroborate, nitrate, sulfate, sulfite, hydrogen sulfite, oxalate, acetate, propionate, carboxylates, carbonate, acetylacetonate, carbonyl, DMSO, hydroxide, trialkylamine, alkoxide.

The cationic complex catalyst preferably contains at least one element selected from the group consisting of iron, palladium and iridium and at least one phosphine ligand selected from the group consisting of 1,2-bis (dimethylphosphino) ethane, 1,2-bis (diethylphosphino) ethane, 1 , 2-bis (dipropylphosphino) ethane and 1,2-bis (dibutylphosphino) ethane.

The cationic complex catalysts can be used both directly in their active form and starting from customary standard compounds or standard complexes such as iron (II) nitrate, iron (III) nitrate, iron (II) sulfate, iron (III) sulfate, iron (II ) chloride, iron (III) chloride, bis (cyclopentadienyl) iron, bis (pentamethylcyclopentadienyl) iron, cyclohexadiene-iron tricarbonyl, ferrous acetate, triene dodecacarbonyl, diisone nonacarbonyl, iron pentacarbonyl, ferrous tetrafluoroborate, iron (III ) phosphate, ammonium ferric sulfate, ammonium ferrous sulfate, ferrous oxalate, ferric oxalate, ammonium ferric oxalate trihydrate, iron phosphide (iron monophosphide, diiron phosphide, triiron phosphide), iron ( II) perchlorate, iron (III) perchlorate hydrate, iron (III) phosphate, iron (III) acetylacetonate, iron (II) bromide, iron (II) fluoride, iron (III) fluoride, iron (III ) bromide, ferrous iodide, ferric oxide, ferrous acetylacetonate, ammonium ferrous sulfate hexahydrate, ammonium ferric sulfate dodecahydrate, cyclopentadienyliron (II) dicarbonyl dimer, with the addition of the corresponding or the corresponding phosphine ligands only under reaction conditions in process step (a) are produced.

The cationic complex catalysts can also be used in their active form. Preferred cationic complex catalysts are, for example, selected from the group consisting of [Fe (PR ⁴ 3) ₄ X ¹ ] ⁺ [X ² ] ^- , [Fe (PR ⁴ ₃ ) ₄ (H ₂ ) X ¹ ] ⁺ [X ² ] ^- , [Fe (PR ⁴ ₃ ) ₄ (L) X ¹ ] ⁺ [X ² ] ^- , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ ₂ ) ₂ X ¹ ] ⁺ [X ² ] ^- , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ ₂ ) ₂ (H ₂ ) X ¹ ] ⁺ [X ² ] ^- , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ ₂ ) ₂ (L) X ¹ ] ⁺ [X ² ] ^- , [FeP (CH ₂ CH ₂ PR ⁴ ₂ ) ₃ X ¹ ] ⁺ [X ² ] ^- , [FeP (CH ₂ CH ₂ PR ⁴ ₂ ) ₃ (H ₂ ) X ¹ ] ⁺ [ X ² ] ^- , [FeP (CH ₂ CH ₂ PR ⁴ ₂ ) ₃ (L) X ¹ ] ⁺ [X ² ] ^- , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ (CH ₂ ) _n PR ⁴ ₂ ) X ¹ ] ⁺ [X ² ] ^- , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ (CH ₂ ) _n PR ⁴ ₂ ) (H ₂ ) X ¹ ] ⁺ [X ² ] ^- , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ (CH ₂ ) _n PR ⁴ ₂ ) (L) X ¹ ] ⁺ [X ² ] ^- ,
wherein X ¹ and X ² is identical or different, are each independently preferably selected from the group consisting of H ^-, Cl ^-, Br ^-, I ^-, HCOO ^-, BF ₄ ^-, NO ₃ ^- SO ₄ ^2-, SO ₃ ^2-, HSO ₄ ^- , C ₂ O ₄ ^2- , CH ₃ CO ₂ ^- , CH ₃ CH ₂ CO ₂ ^- , OH ^- , CH ₃ O ^- , CH ₃ CH ₂ O ^- , CH ₃ COCHCOCH ₃ ^- , HCO ₃ ^- , CO ₃ ^2- ,
wherein L is preferably selected from the group consisting of H ₂ O, N ₂ , CO, CO ₂ , polar solvent optionally present nonpolar solvent and tertiary amine (A1) and their combination and
wherein R ^{4 is} preferably selected from the group consisting of methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 1- (2-methyl) propyl, 2- (2-methyl) propyl, 1 -Pentyl, 1-hexyl, 1-heptyl, 1-octyl, 1-nonyl, cyclohexyl, phenyl and benzyl, wherein n is 1, 2, 3, 4, 5 or 6, preferably n is 2.

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 30 MPa abs and more 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 20 MPa. In a preferred embodiment, the hydrogenation in process step (a) is carried out at a partial pressure of the hydrogen in the range of 1 to 15 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 particularly 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, for example, in KD Henkel, "Reactor Types and Their Industrial Applications," in Ullmann's Encyclopedia of Industrial Chemistry, 2005 ,. Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007.b04_087, Chapter 3.3 "Reactors for gas-liquid reactions" specified. 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 usually depressurized. 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 catalyzed hydrogenation of carbon dioxide, a hydrogenation mixture (H) is obtained in process step (a) which contains the cationic complex catalyst, the polar solvent, optionally 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). Mixtures of two or more formic acid-amine adducts (A2) are obtained in process step (a) if two or more tertiary amines (A1) are used in the reaction mixture used (Rg).

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 · x _i 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 general formulas (A2) and (A3) x is in the range of 0.4 to 5. The factor x _i is the average composition of the formic acid-amine adduct (A2) or (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 _i 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 _i by determination of 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 _i , 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 _{i is} in the range from 0.4 to 5, preferably in the range from 0.7 to 1.6 ,

Before further working up of the hydrogenation mixture (H) in step (b), the cationic complex catalyst is immobilized (immobilized) by at least one support material (T) which has acidic functional groups and is insoluble in the hydrogenation mixture (H). As a result, an immobilized cationic complex catalyst is obtained.

Suitable support materials (T) are those which have acidic functional groups, for example sulfonic acid groups (-SO ₃ H) and / or carboxylic acid groups (COOH). Further suitable are those support materials (T) which contain chelate groups as acidic functional groups, for example iminodiacetic acid or aminophosphonic acid. In addition, inorganic support materials (T) with acidic functional groups, such as clay and bleaching earths, zeolites, phosphated Nb ₂ O ₅ , metal oxides, eg. As titanium oxide TiO ₂ , zirconium oxide ZrO ₂ , semi-metal oxides, z. B. SiO ₂ -Al ₂ O ₃ mixed oxides.

Particularly suitable as support materials (T) are strongly acidic cationic ion exchanger polymers, i. H. Ion exchange polymers having sulfonic acid groups. Also particularly suitable are weakly acidic cationic ion exchange polymers, d. H. Ion exchange polymers having carboxylic acid groups. It is also possible to use ion exchanger polymers which have sulfonic acid groups and carboxylic acid groups. Typically, said ion exchange polymers contain a matrix of divinylbenzene cross-linked polystyrene or crosslinked polyacrylate or of phenol-formaldehyde condensate. Depending on the degree of crosslinking one speaks of gel or macroporous ion exchange polymers. Depending on the type and number of functional groups, in particular in the case of sulfonated ion exchanger polymers, surface-sulfonated, mono- and bisulfonated ion exchanger polymers are used.

Examples of suitable strongly acidic cationic ion exchanger polymers are Amberlite 252H from Dow, Lewatit MonoPlus S100 H from Lanxess, Lewatit K 1131 from Lanxess, Purolite CT175 from Purolite, Purolite CT275 from Purolite, Amberlyst 15 from Dow, Amberlyst 16 from Dow, Amberlyst 35 from Dow, Amberlyst 36 from Dow and Amberlyst 39 from Dow, Amberlyst 15 from Dow, Amberlyst 16 from Dow, Amberlyst 35 of Dow, Amberlyst 36 of Dow and Amberlyst 39 of Dow. Suitable weakly acidic cationic ion exchange polymers are, for example, Amberlite IRC50 from Dow and Lewatit CNP80 from Lanxess. Suitable acidic cationic ion exchanger polymers which have chelate groups, in this case iminodiacetic acid, are, for example, Amberlite IRC748 from Dow.

In the immobilization of the cationic complex catalyst, this splits off at least one anionic ligand, whereby a positively charged catalyst species such as [Fe (PR ⁴ ₃ ) ₄ X ¹ ] ⁺ , [Fe (PR ⁴ ₃ ) ₄ (H ₂ ) X ¹ ] ⁺ , [Fe (PR ⁴ ₃ ) ₄ (L) X ¹ ] ⁺ , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ ₂ ) ₂ X ¹ ] ⁺ , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ ₂ ) ₂ (H ₂ ) X ¹ ] ⁺ , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ ₂ ) ₂ (L) X ¹ ] ⁺ , [FeP (CH ₂ CH ₂ PR ⁴ ₂ ) ₃ X ¹ ] ⁺ , [FeP (CH ₂ CH ₂ PR ⁴ ₂ ) ₃ (H ₂ ) X ¹ ] ⁺ , [FeP (CH ₂ CH ₂ PR ⁴ ₂ ) ₃ (L) X ¹ ] ⁺ , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ (CH ₂ ) _n PR ⁴ ₂ ) X ¹ ] ⁺ , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ (CH ₂ ) _n PR ⁴ ₂ ) (H ₂ ) X ¹ ] ⁺ , [Fe (PR ⁴ ₂ (CH ₂ ) _n PR ⁴ (CH ₂ ) _n PR ⁴ ₂ (L) X ¹ ] ⁺ ,
wherein X ^{1 is} preferably selected from the group consisting of H ^- , Cl ^- , Br ^- , I ^- , HCOO ^- , BF ₄ ^- , NO ₃ ^- SO ₄ ² , SO ₃ ^2- , HSO ₄ ^- , C ₂ O ₄ ^2- , CH ₃ CO ₂ ^- , CH ₃ CH ₂ CO ₂ ^- , OH ^- , CH ₃ O ^- , CH ₃ CH ₂ O ^- , CH ₃ COCHCOCH ₃ ^- , HCO ₃ ^- , CO ₃ ^2- ,
wherein L is preferably selected from the group consisting of H ₂ O, N ₂ , CO, CO ₂ , polar solvent optionally present nonpolar solvent and tertiary amine (A1) and their combination and
wherein R ^{4 is} preferably selected from the group consisting of methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 1- (2-methyl) propyl, 2- (2-methyl) propyl, 1 -Pentyl, 1-hexyl, 1-heptyl, 1-octyl, 1-nonyl, cyclohexyl, phenyl and benzyl, wherein n is 1, 2, 3, 4, 5 or 6, preferably n is 2.

This positively charged catalyst species ionically binds to the acidic functional groups of the support material (T), forming the immobilized cationic complex catalyst.

The immobilized cationic complex catalyst is largely insoluble in the hydrogenation mixture (H).

The immobilized cationic complex catalyst thus contains the positively charged catalyst species formed by cleavage of at least one anionic ligand from the cationic complex catalyst and the support material (T), in which formally the protons of the acidic functional groups through the positively charged catalyst species to form an ionic bond are replaced.

In one embodiment of the process according to the invention, the immobilization of the cationic complex catalyst can take place before the reaction of the reaction mixture (Rg). For this purpose, the cationic complex catalyst and the support material (T), optionally in the presence of the polar solvent and / or the tertiary amine (A1), are introduced into the hydrogenation reactor. The immobilization of the cationic complex catalyst takes place in this embodiment before the actual hydrogenation in step (a), so that the reaction of the reaction mixture (Rg) takes place from the beginning in the presence of the immobilized cationic complex catalyst. In this embodiment, the hydrogenation mixture (H) contains the cationic complex catalyst in immobilized form (immobilized cationic complex catalyst).

It is also possible to carry out the immobilization in a reactor upstream of the hydrogenation reactor and to supply the resulting immobilized cationic complex catalyst to the hydrogenation reactor in step (a).

In a further embodiment of the process according to the invention, the immobilization of the cationic complex catalyst can take place during and / or after the reaction of the reaction mixture (Rg). For this purpose, the reaction mixture (Rg) is fed to the hydrogenation reactor and converted to the hydrogenation mixture (H). The immobilization of the cationic complex catalyst is then carried out by adding the support material (T) in the hydrogenation reactor. The reaction of the reaction mixture (Rg) is homogeneously catalyzed in this embodiment until the immobilization of the cationic complex catalyst, d. H. the catalytically active part of the cationic complex catalyst is at least partially dissolved in the liquid reaction medium in step (a) before immobilization. Preferably, prior to immobilization, at least 90% of the cationic complex catalyst used in step (a) is dissolved in the liquid reaction medium, more preferably at least 95%, in particular at least 99%, based in each case on the total amount of the prior to immobilization in the liquid reaction medium in step (a ) contained cationic complex catalyst. After immobilization, the hydrogenation mixture (H) contains the cationic complex catalyst in immobilized form (immobilized cationic complex catalyst).

The immobilized cationic complex catalyst is largely insoluble in the hydrogenation mixture (H). This allows for easy separation of the immobilized cationic complex catalyst from the hydrogenation mixture (H) to give a hydrogenated hydrogenation mixture (Ha) containing the polar solvent and the formic acid-amine adduct (A2). The separation of the immobilized cationic complex catalyst can be carried out for example by filters. These can be installed, for example, at the reactor outlet of the hydrogenation reactor, so that the immobilized cationic complex catalyst remains in the hydrogenation reactor. It is also possible to install the support material (T) in the form of a fixed bed in the hydrogenation reactor

The efficiency (E) of immobilization is described by: E = B - A / B x 100 (%) A is defined as the amount of the metal component of the cationic complex catalyst in the reclaimed hydrogenation mixture (Ha).
B is defined as the amount of the metal component of the cationic complex catalyst in the hydrogenation mixture (H) before immobilization.

The value for E is preferably greater than 90%, particularly preferably greater than 95% and in particular greater than 99%.

The amount of the metal component (A) in the worked up hydrogenation mixture (Ha) and the amount of the metal component (B) in the hydrogenation mixture (H) before the immobilization can be determined by discontinuous experiments. The determination of the amounts of the metal components takes place, for example, by atomic emission spectrometry.

After separation of the immobilized cationic complex catalyst, the reclaimed hydrogenation mixture generally contains less than 0.1 g, preferably less than 0.01 g and in particular less than 0.001 g of the metal component of the cationic complex catalyst, each based on an amount of 100 g of the worked up hydrogenation mixture (Ha).

Selection of the cationic complex catalyst and support material (T) is generally accomplished by a simple experiment in which the cationic complex catalyst and support material (T) are contacted under the reaction conditions in step (a), and after completion of the reaction, the amount of metal components in the reaction mixture worked up hydrogenation mixture (Ha) and in the immobilized cationic complex catalyst is determined by elemental analysis.

The reclaimed hydrogenation mixture (Ha) can be mono-, bi- or polyphase. In the case where the hydrogenation mixture is single-phase, this can be converted into a two-phase hydrogenation mixture by adding additional polar solvent, in particular by adding water.

The worked up hydrogenation mixture (Ha) contains the polar solvent and the formic acid-amine adduct (A2). The worked-up hydrogenation mixture (Ha) may optionally additionally contain the tertiary amine (A1), free ligands and residues of the cationic complex catalyst.

This is not a disadvantage since the free ligands are soluble in the tertiary amine (A1) and thus can be recycled from the thermal cleavage unit in step (b2) together with the tertiary amine (A1) to the hydrogenation reactor in step (a).

From the worked-up hydrogenation mixture (Ha), the polar solvent is separated off in step (b1). The reclaimed hydrogenation mixture (Ha) can be passed directly to the distillation apparatus in step (b1).

It is possible to further work up the reclaimed hydrogenation mixture (Ha) prior to separation of the polar solvent in step (b1). In the event that the reclaimed hydrogenation mixture (Ha) is biphasic, it contains an upper phase (O1) containing the tertiary amine (A1), and optionally free ligands, and a lower phase (U1) containing the polar solvent, optionally residues of the cationic complex catalyst and the formic acid-amine adduct (A2). The reclaimed hydrogenation mixture (Ha) can then be fed to a phase separation device, where it is separated into the upper phase (O1) and the lower phase (U1). The upper phase (O1) can be recycled to the hydrogenation reactor in step (a). The lower phase (U1) is forwarded to the distillation apparatus in step (b1).

It is also possible to extract the worked-up hydrogenation mixture (Ha) with an extractant containing the at least one tertiary amine (A1) to obtain a raffinate (R1) containing the formic acid-amine adduct (A2) and the polar solvent and an extract ( E1) containing the tertiary amine (A1) and optionally free ligands. The extract (E1) can be recycled to the hydrogenation reactor in step (a). The raffinate (R1) is sent to the distillation apparatus in step (b1). It is also possible to further work up the worked-up hydrogenation mixture (Ha) before the separation of the polar solvent in step (b1) by a combination of phase separation and extraction.

Work-up of the worked-up hydrogenation mixture (Ha); Process stage (b)

Separation of the at least one polar solvent; Process Stage (b1) In process stage (b1), the polar solvent is separated off from the worked-up hydrogenation mixture (Ha) in a distillation apparatus. In the distillation apparatus, a distillate (D1) and a bottoms mixture (S1) are obtained. The distillate (D1) contains the separated polar solvent and is recycled to the hydrogenation reactor in step (a). The bottom mixture (S1) contains the formic acid-amine adduct (A2), optionally tertiary amine (A1) and optionally free ligands.

The swamp mixture can be biphasic. In this case, the bottoms mixture (S1) contains an upper phase (O2) which contains the tertiary amine (A1) and optionally free ligands, and a lower phase (U2) which contains the formic acid-amine adduct (A2).

In one embodiment of the process according to the invention, the polar solvent is partially removed in the distillation apparatus in process stage (b1), so that the bottom mixture (S1) contains not yet separated polar solvent. In process step (b1), for example, from 5 to 98% by weight of the polar solvent contained in the worked-up hydrogenation mixture (Ha), preferably from 50 to 98% by weight, more preferably from 80 to 98% by weight and especially preferably from 80 to 90% by weight .-% are separated, each based on the total weight of the recovered in the hydrogenation mixture (Ha) 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 (b1). In the context of the present invention, "completely separated off" is a separation of more than 98% by weight of the polar solvent contained in the worked-up hydrogenation mixture (HA), preferably more than 98.5% by weight, more preferably more than 99% by weight. %, in particular more than 99.5% by weight, understood, in each case based on the total weight of the polar solvent contained in the worked-up hydrogenation mixture (Ha).

The distillate (D1) separated in the first distillation apparatus is recycled in a preferred embodiment to the hydrogenation reactor in step (a).

The separation of the polar solvent from the worked-up hydrogenation mixture (Ha) can be carried out, for example, in an evaporator or in a distillation unit consisting of evaporator and column, the column being filled with packings, fillers and / or trays.

The separation of the polar solvent is preferably carried out 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 _{i of} the formic acid-amine adduct (A2) in the distillation apparatus is generally in the range from 0.4 to 3, preferably in the range from 0.6 to 1.8, particularly preferably in the range from 0.7 to 1 , 7th

In general, the bottom temperature in the 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 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 distillation apparatus is generally in the range of 0.001 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 separation of the polar solvent in the distillation apparatus, the formic acid-amine adduct (A2) and free tertiary amine (A1) can be obtained in the bottom of the distillation apparatus the removal of the polar solvent formic acid-amine adducts (A2) with lower amine content arise. 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 distillation apparatus.

The bottoms mixture (S1) can be forwarded directly to the thermal splitter unit in step (b2).

It is also possible to further work up the sump mixture (S1) before forwarding in step (b2). For example, it is possible to subject the bottoms mixture (S1) obtained in step (b1) to phase separation, to obtain an upper phase (O2) which contains the free tertiary amine (A1) and optionally free ligands, and a lower phase (U2) contains the formic acid-amine adduct (A2). The lower phase (U2) can then be further worked up according to process step (b2). The upper phase (O2) can be recycled to the hydrogenation reactor in step (a).

Cleavage of the formic acid-amine adduct (A2); Process step (b1)

The bottom mixture (S1) obtained according to step (b1) is fed to a thermal splitting unit for further reaction.

The formic acid-amine adduct (A2) present in the bottom mixture (S1) is cleaved in the thermal splitting unit to 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).

In a preferred embodiment, the thermal splitting unit comprises a second distillation device. In the second distillation apparatus, the thermal decomposition of the formic acid-amine adduct (A2) is carried out to obtain a distillate (D2) containing formic acid which is discharged from the second distillation apparatus and a sump mixture (S2) containing the tertiary amine (A1) and optionally free ligands.

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) fed to the thermal splitting unit, the formic acid can be taken off as an overhead product or more intensively 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 for example in EP 0 181 078 or WO 2006/021 411 described. 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 abs, more preferably at most 300 hPa abs and more preferably at most 200 hPa abs.

The invention is explained in more detail below with reference to embodiments and a drawing without limiting it thereto.

The drawings show in detail:

1 a schematic block diagram of a preferred embodiment of the method according to the invention.

In 1 the reference signs have the following meanings:

LIST OF REFERENCE NUMBERS

I

hydrogenation reactor

II

distillation apparatus

III

thermal splitting unit

1

Electricity containing carbon dioxide (CO ₂ )

2

Stream containing hydrogen (H ₂ )

3

Stream containing formic acid-amine adduct (A2), polar solvent; worked up hydrogenation mixture (Ha)

4

Stream containing polar solvent

5

Stream containing formic acid-amine adduct (A2); Swamp mixture (S1)

6

Stream containing tertiary amine (A1)

7

Stream containing formic acid; Distillate (D2)

In the embodiment according to 1 be carbon dioxide (electricity 1 ) and hydrogen (electricity 2 ) are fed to the hydrogenation reactor (I). In the hydrogenation reactor (I), these are reacted in the presence of an immobilized cationic complex catalyst containing as metal component a metal from the 8th, 9th or 10th group of the periodic table, a tertiary amine (A1) and a polar solvent to give a hydrogenation mixture (H ) containing the formic acid-amine adduct (A2) and the polar solvent. From the hydrogenation mixture (H), the immobilized cationic complex catalyst is separated. This remains in the hydrogenation reactor (I). The reactor discharge (current 3 ; worked up hydrogenation mixture (Ha)) is fed to a distillation apparatus (II). At the top of the recycled hydrogenation mixture (Ha) is the polar solvent as a stream ( 4 ) and recycled to the hydrogenation reactor (I). As the bottom of the distillation apparatus, the stream ( 5 ), which contains the formic acid-amine adduct (A2) (bottom mixture (S1)).

Electricity ( 5 ) is forwarded to the thermal cleavage unit (III) and there cleaved to tertiary amine (A1) and formic acid. The tertiary amine (A1) is obtained in the bottom of the thermal splitting unit (III) and used as stream ( 6 ) are recycled to the hydrogenation reactor (I). Formic acid is called electricity ( 7 ) taken at the head of the thermal splitting unit (III).

embodiments

1. Immobilization of the homogeneous cationic complex catalyst on the support material (T) in the hydrogenation reactor

A 250 mL Hastelloy C autoclave equipped with a magnetic stirrer bar was charged under inert conditions with the indicated tertiary amine, polar solvent and cationic complex catalyst, or its precursor dissolved in tetrahydrofuran (THF). The autoclave was subsequently tested for leaks with nitrogen (N ₂ ).

Subsequently, the autoclave was sealed. At room temperature, carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) were further pressed to the desired reaction pressure and kept constant. The reactor was heated with stirring (700 rpm). After the appropriate reaction time, the autoclave was cooled and the hydrogenation mixture (H) was depressurized.

The resulting hydrogenation mixture (H) was weighed and a sample was taken for analysis. In the analysis, the amount of the metal component of the cationic complex catalyst contained in the hydrogenation mixture (H) and the amount of formic acid contained in the hydrogenation mixture (H) in the form of the formic acid-Amdukkts were determined.

Subsequently, the carrier material (T) was added to the hydrogenation mixture (H) and shaken together with the hydrogenation mixture (H), wherein the cationic complex catalyst was immobilized on the carrier material (T). Subsequently, the immobilized cationic complex catalyst was separated. The recovered hydrogenation mixture (Ha) thus obtained was biphasic and was separated into the upper phase (O1) and the lower phase U1). Upper and lower phases were weighed and analyzed. In the analysis, the amount of the metal component of the cationic complex catalyst contained in upper or lower phase (H) and the amount of formic acid contained in the upper or lower phase in the form of the formic acid-amine adduct were determined.

The amounts of the metal component are given in g / 100 g of the respective phase. The amounts of formic acid are given in wt .-% based on the total weight of the respective phase.

The amount of formic acid contained in the formic acid-amine adduct was determined by titration with 0.1 KOH in 2-propanol against phenolphthalein. The formic acid was determined by ¹ H NMR spectroscopy together with CHCl ₃ as an internal standard and from this the turn-over number (TON) and the turn-over frequency (TOF) were calculated. The amount of the metal component of the cationic complex catalyst was determined by atomic emission spectrometry.

The parameters and results of the individual experiments are given in Table 1.

Examples A-1 and A-2 show that iron dichloride (FeCl ₂ ) together with the employed phosphine ligand 1,2-bis (diethylphosphino) ethane (DEPE) in the polar solvent in the presence of trihexylamine catalyzes the hydrogenation of CO ₂ , and that the cationic complex catalyst can be formed in situ. In the hydrogenation mixture (H) was determined 6.3 and 6.6% formic acid in the form of the formic acid-amine adduct. The homogeneous cationic complex catalyst was then immobilized on the support material (T) and separated. The recovered hydrogenation mixture (Ha) thus obtained was biphasic. The iron content in the upper phase (O1) and the lower phase (U1) of the worked up hydrogenation mixture (Ha) was determined. This resulted in a very high immobilization efficiency of 90% and 95%, respectively.

In Example A-3, Fe (DEPE) ₂ Cl _{2 was} used and Purolite CT 175 was used as support material (T). In the hydrogenation mixture (H) 6% formic acid in the form of the formic acid-amine adduct was determined. 99% of the homogeneous cationic complex catalyst was immobilized. Table 1 Example A-1 Example A-2 Example A-3 catalyst 0.271 g FeCl ₂ 1.324 g DEPE 0.271 g FeCl ₂ 1.324 g DEPE 1.153 g Fe (DEPE) ₂ Cl ₂ Polar solvent 5.0 g of THF 20.0 g of methanol 60.0 g of trihexylamine 5.0 g of THF 20.4 g of methanol 60.8 g of trihexylamine 5.0 g of THF 20.4 g of methanol 60.8 g of trihexylamine Pressing on CO ₂ with 20.2 g to 1.9 MPa abs with 20.2 g to 1.7 MPa abs with 20.4 g to 1.7 MPa abs Pressing H ₂ to 13.9 MPa abs to 13.8 MPa abs to 13.7 MPa abs Heat to 50 ° C to 50 ° C to 50 ° C pressure change to 15.0 MPa abs to 14.7 MPa abs to 14.9 MPa abs reaction time 4 hours 4 hours 4 hours Hydrogenation mixture (H) before immobilization 89.1 g (single-phase) Fe: 0.12 g / 100 g 6.3% formic acid 88.6 g (single-phase) Fe: 0.13 g / 100 g 6.6% formic acid 88.1 g (single-phase) Fe: 0.14 g / 100 g 6.0% formic acid TON mol _AS / mol _Fe 55 52 47 TOF mol _AS / mol _Fe / h 14 h ^-1 13 h ^-1 12 h ^-1 Carrier material (T) 12 g of Amberlite 252H 12 g Purolite CT 175 12 g Purolite CT 175 Upper phase (O1) in the worked-up hydrogenation mixture (Ha) 10 g Fe: <0.001 g / 100 g P: 0.13 g / 100 g 11.1 g Fe: <0.001 g / 100 g P: 0.009 g / 100 g 17.2 g Fe: <0.001 g / 100 g P: 0.003 g / 100 g Subphase (U1) in the worked up hydrogenation mixture (Ha) 56.8 g Fe: 0.012 g / 100 g 45 g Fe: 0.006 g / 100 g 35.5 g Fe: 0.002 g / 100 g Efficiency (E) of immobilization (0.12-0.012 / 0.12) x 100 = 90% (0.13 - 0.006 / 0.13) x 100 = 95% (0.14 - 0.002 / 0.14) x 100 = 99% 2. Immobilization of the cationic iron complex catalysts after hydrogenation Example A-4 catalyst 0.271 g FeCl ₂ 1.324 g DEPE Polar solvent 5.0 g of THF 20.4 g of methanol 60.8 g of trihexylamine Pressing on CO ₂ with 20.0 g to 1.8 MPa abs Pressing H ₂ to 13.8 MPa abs Heat to 50 ° C pressure change to 15.1 MPa abs reaction time 4 hours Hydrogenation mixture (H) before immobilization 89.1 g (single-phase) Fe: 0.14 g / 100 g 6.2% formic acid TON mol _AS / mol _Fe 51 TOF mol _AS / mol _Fe / h 13 h ^-1 Carrier material (T) 1 g of carrier material (T) per 8 g of hydrogenation mixture (H)

As described above, a hydrogenation mixture (H) was prepared.

Different carrier materials (T) were added to the hydrogenation mixture (H) thus obtained in order to determine the efficiency of the immobilization. The support materials (T) were shaken together with the hydrogenation mixture (H). The immobilized catalyst was subsequently separated. The recovered hydrogenation mixture (Ha) thus obtained was biphasic. The amount of iron in the upper phase (O1) and the lower phase (U1) were determined. From this, the efficiency of immobilization was calculated. Table 2 Carrier material (T) properties Fe upper phase (O1) in g / 100 g Fe lower phase (U1) in g / 100 g Efficiency (E) of immobilization (%) Amberlite 252H Strong acid macroporous cation exchange resin with styrene-divinylbenzene cross-linked polystyrene matrix and SO ₃ groups as functional groups <0.001 0,020 90 Purolite CT 175 Strong-acid, macroporous catalyst resin with styrene-divinylbenzene cross-linked polystyrene matrix and SO ₃ groups as functional groups <0.001 0,002 98 Purolite CT 275 Strong-acid, macroporous catalyst resin with styrene-divinylbenzene cross-linked polystyrene matrix and SO ₃ groups as functional groups - 0,007 94 Amberlyst 15 Strong-acid, macroporous, catalyst resin with styrene-divinylbenzene cross-linked polystyrene matrix and SO ₃ groups as functional groups - 0.005 96 Amberlyst 16 Strong-acid, macroporous catalyst resin with styrene-divinylbenzene cross-linked polystyrene matrix and SO ₃ groups as functional groups <0.001 0,006 95 Amberlyst 35 Strong-acid, macroporous, bisulfonated catalyst resin with styrene-divinylbenzene cross-linked polystyrene matrix and SO ₃ groups as functional groups - 0,004 97 Amberlyst 36 Strong-acid, macroporous, bisulfonated catalyst resin with styrene-divinylbenzene cross-linked polystyrene matrix and SO ₃ groups as functional groups - 0,004 97 Amberlyst 39 Strong-acid, macroporous, catalyst resin with styrene-divinylbenzene cross-linked polystyrene matrix and SO ₃ groups as functional groups <0.001 0,007 94

3. Hydrogenation of CO ₂ with an immobilized cationic iron complex catalyst

In Example B-1, the immobilized cationic complex catalyst was used in the hydrogenation of CO ₂ , which was separated in Example A-2. After the hydrogenation, the immobilized cationic complex catalyst was separated. The recovered hydrogenation mixture (Ha) thus obtained was biphasic. In the lower phase (U1) 3.9% formic acid in the form of the formic acid-amine adduct were determined.

In Example B-2, the immobilized cationic iron complex catalyst was prepared with the carrier material Amberlite 252H from Dow before starting the hydrogenation in situ in the hydrogenation reactor. 3.8% of formic acid in the form of the formic acid-amine adduct were determined in the lower phase (U1) of the worked-up hydrogenation mixture. Table 3 Example B-1 Example B-2 catalyst 12 g of Fe - Purolite CT 175 0.271 g of FeCl ₂ 1.324 g of DEPE (C ₂ H ₅ ) 12 g of Amberlite 252H polar solvent 20.4 g of methanol 60.8 g of trihexylamine 5.0 g of THF 20.4 g of methanol 60.8 g of trihexylamine Pressing on CO ₂ With 20.1 g to 2.5 MPa abs With 20.0 g to 2.0 MPa abs Pressing H ₂ At 14.5 MPa abs At 14.1 MPa abs Heat At 50 ° C At 50 ° C pressure change At 14.7 MPa abs At 14.9 MPa abs reaction time 4 hours 4 hours worked up hydrogenation mixture (Ha) 56.1 g (upper phase O1) Fe: <0.001 g / 100 g of 0.5% formic acid 49.3 g (upper phase O1) Fe: <0.001 g / 100 g of 0.5% formic acid 44.1 g (lower phase U1) Fe: 0.003 g / 100 g 3.9% formic acid 47.0 g (lower phase U1) Fe: 0.024 g / 100 g 3.8% formic acid TON mol _AS / mol _Fe - 18 TOF mol _AS / mol _Fe / h - 5

4. DMPE as a phosphine ligand in Fe-catalyzed CO ₂ hydrogenation

In Examples C-1 and C-2, the cationic complex catalyst was formed in situ from iron dichloride (FeCl ₂ ) to the phosphine ligand 1,2-bis (dimethylphosphino) ethane (DMPE). Table 4 Example C-1 Example C-2 catalyst 0.390 g FeCl ₂ 1.400 g DMPE (CH ₃ ) 0.108 g FeCl ₂ 0.385 g DMPE (CH ₃ ) polar solvent 15.4 g of THF 6.7 g of water 29.5 g of methanol 88.1 g of trihexylamine 4.1 g of THF 32.6 g of methanol 97.2 g of trihexylamine Pressing on CO ₂ With 20.0 g to 2.0 MPa abs With 20.0 g to 1.6 MPa abs Pressing H ₂ To 14.0 MPa abs At 13.6 MPa abs Heat At 50 ° C At 50 ° C pressure change At 13.5 MPa abs At 12.2 MPa abs reaction time 5 hours 5 hours worked up hydrogenation mixture (Ha) 12.2 g (upper phase O1) Fe: <0.001 g / 100 g of 1.0% formic acid 141.5 g (single-phase) Fe: 0.033 g / 100 g P: 0.11 g / 100 g 7.3% formic acid 133.2 g (lower phase U1) Fe: 0.091 g / 100 g 7.6% formic acid TON mol _AS / mol _Fe 76 245 TOF mol _AS / mol _Fe / h 15 49

In this case, in the lower phase (U1) of the worked-up hydrogenation mixture, 7.6% and 7.3%, respectively, of formic acid in the form of the formic acid-amine adduct were determined; with a TON of 75 and 245, respectively. When water is present during CO ₂ hydrogenation, two phases form and the iron complexes are enriched in the polar lower phase (U1).

In Example C-3, 1,2-bis (dimethylphosphino) ethane (DMPE) was used together with iron dichloride. The implementation and workup were as described above.

In Example C-3 in the hydrogenation mixture (H) 10.5% formic acid in the form of the formic acid-amine adduct were determined. The efficiency of immobilization was 91%. Example C-3 Example C-4 catalyst 0.136 g FeCl ₂ 0.482 g DMPE 0.136 g FeCl ₂ 1.079 g Ethylphos Triphos Polar solvent 5.1 g of THF 10.2 g of methanol 30.4 g of trihexylamine 5.1 g of THF 10.2 g of methanol 30.4 g of trihexylamine Pressing on CO ₂ with 20.3 g to 2.5 MPa abs with 20.0 g to 2.0 MPa abs Pressing H ₂ to 14.8 MPa abs to 14.0 MPa abs Heat to 50 ° C to 50 ° C pressure change to 14.0 MPa abs to 15.0 MPa abs reaction time 4 hours 5 hours Hydrogenation mixture (H) 48.9 g (single-phase) Fe: 0.12 g / 100 g 10.5% formic acid 48.8 g (single-phase) Fe: 0.16 g / 100 g 7.0% formic acid TON mol _AS / mol _Fe 122 67 TOF mol _AS / mol _Fe / h 31 h ^-1 13 h ^-1 Carrier material (T) 7 g of Amberlyst 35 7 g of Amberlite 252H Upper phase (O1) in the worked-up hydrogenation mixture (Ha) not determined not determined Subphase (U1) in the worked up hydrogenation mixture (Ha) 32.1 g of Fe: 0.011 g / 100 g 30.4 g of Fe: 0.001 g / 100 g Efficiency (E) of immobilization (0.12-0.011 / 0.12) x 100 = 91% (0.16 - 0.001 / 0.16) x 100 = 99%

The tridentate phosphorus ligand ethylphos triphos 1,1 '- (2 - [(diethylphosphino) methyl] -2-methyl-1,3-propanediyl] bis [1,1-diethylphosphine, together with Amberlite 252H in Example C- 4 a high efficiency of the immobilization of the cationic complex catalyst of 99% In the lower phase (U1) of the worked up hydrogenation mixture (Ha) only 0.001 g of iron are present relative to 100 g of lower phase (U1) In the hydrogenation mixture (H) 7% formic acid in Form of formic acid-amine adduct determined.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2010/149507 [0009, 0010, 0011, 0015]
• EP 0181078 [0113]
• WO 2006/021411 [0113]

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Claims (15)

Process for the preparation of formic acid, comprising the steps of (a) reacting a reaction mixture (Rg) comprising carbon dioxide, hydrogen, at least one polar solvent and at least one tertiary amine of the general formula (A1) NR ¹ R ² R ³ (A1), in which R ¹ , R ² , R ³ independently of one another represent an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical having in each case 1 to 16 carbon atoms, where individual carbon atoms are also 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 be joined together to form a chain comprising at least four atoms, in the presence of at least one cationic complex catalyst containing at least one element selected from groups 8, 9 and 10 of Periodic table contains, in a hydrogenation reactor, to obtain a hydrogenation mixture (H) containing the at least one polar solvent, the at least one cationic catalyst and at least one formic acid-amine adduct of the general formula (A2) NR ¹ R ² R ³ · x _i HCOOH (A2), in which x _{i is} in the range from 0.4 to 5 and R ¹ , R ² , R ^{3 have} the abovementioned meanings, (b) Working up of the hydrogenation mixture (H) comprising the steps of (b1) separating off the at least one polar solvent the hydrogenation mixture (H) in a distillation apparatus to obtain a distillate (D1) containing the at least one polar solvent and a bottom mixture (S1) containing the at least one formic acid-amine adduct (A2), (b2) cleavage in the bottom mixture (S1) containing at least one formic acid-amine adduct (A2) in a thermal cleavage unit to obtain the at least one tertiary amine (A1) and formic acid, wherein the cationic complex catalyst prior to the workup of the hydrogenation mixture (H) according to step (b) by at least one support material ( T) which has acidic functional groups and is insoluble in the hydrogenation mixture (H) is immobilized. Process according to claim 1, wherein the cationic complex catalyst is immobilized prior to the reaction of the reaction mixture (Rg). Process according to claim 1, wherein the cationic complex catalyst is immobilized during and / or after the reaction of the reaction mixture (Rg). A process according to any one of claims 1 to 3, wherein the immobilized cationic complex catalyst is separated from the hydrogenation mixture (H) to obtain a worked-up hydrogenation mixture (Ha), which is further worked up according to step (b). The method of claim 4, wherein the separated immobilized catalyst remains in the hydrogenation reactor. A process according to any one of claims 1 to 5, wherein the distillate (D1) obtained in step (b1) is recycled to the hydrogenation reactor in step (a). A process according to any one of claims 1 to 6, wherein the at least one tertiary amine (A1) obtained in step (b2) in the thermal cleavage unit is recycled to the hydrogenation reactor in step (a). A process according to any one of claims 1 to 7, wherein the cationic complex catalyst contains at least one element selected from the group consisting of iron, palladium and iridium. A process according to any one of claims 1 to 8, wherein the cationic complex catalyst comprises at least one phosphine ligand selected from the group consisting of 1,2-bis (dimethylethylphosphino) ethane, 1,2- Bis (diethylethylphosphino) ethane, 1,2-bis (dipropylethylphosphino) ethane, 1,2-bis (dibutylphosphino) ethane and 1,1 '- [2 - [(diethylphosphino) methyl] -2-methyl-1,3-propanediyl ] to [1,1-diethyl phosphine. Method according to one of claims 1 to 9, wherein a tertiary amine of the general formula (A1) is used, in which the radicals R ¹ , R ² , R ^{3 are} independently selected from the group consisting of C ₅ to C ₆ alkyl , C 5 to C ₆ cycloalkyl, benzyl and phenyl. A process according to any one of claims 1 to 10, wherein the tertiary amine (A1) used is tri-n-hexylamine. A process according to any one of claims 1 to 11, wherein the polar solvent used is water, methanol, tetrahydrofuran or a mixture of water, methanol and tetrahydrofuran. Method according to one of claims 1 to 12, wherein as support material (T) an ion exchange polymer is used which contains sulfonic acid groups (-SO ₃ H) and / or carboxylic acid groups (-COOH). Method according to one of claims 1 to 12, wherein as support material (T) an ion exchange polymer is used which contains chelate groups selected from the group consisting of iminodiacetic acid groups and aminophosphonic acid groups as the acidic functional group. Method according to one of claims 1 to 12, wherein as support material (T) an inorganic support material is used, selected from the group consisting of clay and bleaching earths, zeolites, phosphated Nb ₂ O ₅ , titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ) and SiO ₂ -Al ₂ O ₃ mixed oxides.

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