WO2012034991A1 - Method for producing formamides - Google Patents

Abstract

The invention relates to a method for producing formamides by reacting carbon dioxide (1) with hydrogen (2) in a hydrogenation reactor I in the presence of: a catalyst, containing an element from group 8, 9 or 10 of the Periodic Table, a tertiary amine containing at least 6 carbon atoms per molecule, and a polar solvent, forming formic acid/amine adducts as intermediates which are then reacted with ammonia or amines in a reactor, obtaining a two-phase liquid reaction product from which the liquid phase enriched with formamides is separated by distillation and the formamide is recovered.

Description

 Process for the preparation of formamides Description

The present invention relates to a process for the preparation of formamides, i. of formamide and its / V-substituted derivatives starting from carbon dioxide.

Formamide and its derivatives are important selective solvents and extractants because of their polarity. They are z. B. for the extraction of butadiene from C ₄ cuts, acetylene from C ₂ cracker fractions and aromatics used from aliphatic.

All large-scale production processes for the production of formamide and its alkyl derivatives use carbon monoxide as the d-block:

Formamide, / V-Alkylformamide and A / ./V-dialkylformamide are prepared by reacting methyl formate with ammonia, / V-alkylamines or A /, / V-dialkylamines. The liberated methanol can be recycled to the Methylformiatsynthese from carbon monoxide and methanol.

In another, also technically used synthesis, ammonia or the abovementioned amines are reacted at 20 to 100 ° C. and 2 to 10 MPa directly with carbon monoxide instead of methyl formate. Work is carried out in methanol as a solvent with alkoxides as catalysts (Hans-Jürgen Arpe, Industrial Organic Chemistry, 6th edition, 2007, pages 48 to 49).

A disadvantage of carbon monoxide is its toxicity, which makes working under strict safety precautions necessary. Furthermore, the relatively high pressures in the production of formamides from carbon monoxide are costly.

There has therefore been no lack of attempts to replace carbon monoxide with the cheap, non-toxic and abundantly available d-block carbon dioxide (eg Applied Homogeneous Catalysis with Organometallic Compounds, Volume 2, pages 1058 to 1072, 1996, VCH Verlagsgesellschaft and W. Leitner, Angew Chem, Int. Ed., Engl. 1995, 34, pages 2207 to 2221).

There are numerous studies on the hydrogenation of carbon dioxide in the presence of primary or secondary amines to ammonium formates and / or formamides using heterogeneous catalysts. A disadvantage, however, is that the activity of the heterogeneous catalysts decreases after their separation and recycling in the hydrogenation.

Therefore, homogeneous catalysts are preferred for the reaction.

US 3,530, 182 (Shell Oil Company, Prior. 26.12.1967) and Tetrahedron Letters No. 5, pages 365 to 368 (1970) show that even homogeneous catalysts for the hydrogenation of carbon dioxide in the presence of primary and secondary amines to form amides can be used. Suitable z. B. halogen-containing transition metal compounds, especially the elements copper, zinc, cadmium, palladium and platinum. According to Example 1, carbon dioxide is hydrogenated in the presence of dimethylamine and zinc bromide as a catalyst at 155 ° C, 2.76 MPa carbon dioxide and 2.76 MPa hydrogen. After 17 hours, dimethylformamide is obtained with a TOF value of 1.45. The TOF value (Turn Over Frequency) is a measure of the efficiency of the catalyst and indicates how many moles of product per mole of catalyst and hour are formed, cf. J.F. Hartwig: Organotransition Metal Chemistry, 1st Edition, 2010, University Science Books, Sausalito, California, p. 545).

Carbon dioxide can also be hydrogenated in the presence of dimethylamine and homogeneously dissolved platinum complex compounds of the formula ^ -Pt ₂ (Ph ₂ P-CH ₂ -PPh ₂ ) ₃ ) to dimethylformamide. At 100 ° C and 11.4 MPa total pressure, TOF values of 57.3 are achieved (Schreiner, S., et al., J. Chem. Soc., Chem. Commun., 1988, pages 602-603). An enormous increase in TOF was achieved by the use of homogeneously dissolved ruthenium complex compounds containing trialkyl phosphine ligands. In the hydrogenation of carbon dioxide in the presence of ammonia, primary or secondary amines or corresponding ammonium carbamates in single phase under supercritical conditions (reaction temperature> 31 ° C, C0 ₂ pressure> 7.4 MPa) worked (PG Jessop, Y. Hsiao, T Ikariya, R. Noyori, JACS 1996, 118, pp. 351-352, and EP 0 652 202 A1, pp. 5-6, 14, and Table 6, Research Development Corporation of Japan, Prior. 04.1, 1993, and 07.06.1994). Tables 6 and 7 in JACS and Table 6 in EP 0 652 202 A1 summarize the results. The highest TOF value was achieved after 70 hours with 6,000 in the hydrogenation of carbon dioxide at 100 ° C, 13 MPa carbon dioxide and 8 MPa hydrogen in the presence of dimethylamine in the form of ammonium carbamate. The catalyst used was RuCl ₂ [P (CH ₃ ) ₃ ] 4 (JACS, Table 7).

In the production of formic acid by hydrogenation of carbon dioxide in the presence of the same or similar catalysts and sub- or supercritical operation _on t _he v † j _amines worked which the formic acid in the form of of adducts with the tertiary amines. In contrast, the preparation of amides without addition of tertiary amines is used (JACS, page 346, column 2, lines 3 to 10). It can be assumed that the initially formed formic acid is absorbed by ammonia, the primary or secondary amines as salt. This salt reacts at supercritical conditions in homogeneous phase even at 100 ° C to formamides and water.

A further increase in the TOF values after 2 hours to 370,000 was achieved using ruthenium complexes with bidentate phosphines as ligands (O. Kröcher, RA Koppel, A. Baiker, Chem. Comm. 1997, pages 453 to 454, Table 1 ).

EP 0 095 321 A, EP 0 151 510 A and EP 0 181 078 A (BP Chemicals Ltd.) describe the hydrogenation of carbon dioxide in the presence of a homogeneous catalyst comprising a transition metal of subgroup VIII (group 8, 9, 10), a tertiary amine and a polar solvent to an adduct of formic acid and the tertiary amine known. Ruthenium-based carbonyl, halide and / or triphenylphosphine-containing complex catalysts and rhodium-phosphine complexes are mentioned as preferred homogeneous catalysts. The hydrogenation is carried out at a carbon dioxide partial pressure of up to 6 MPa, a hydrogen partial pressure of up to 25 MPa and a temperature of about room temperature to 200 ° C.

JP 1 1322687 shows that salts of formic acid and tertiary amines are obtained in the reaction of aliphatic aldehydes with formaldehyde in the presence of tertiary amines to give polyalcohols. These salts are previously unrecognizable by-products. The application teaches the salts at 20 to 130 ° C with primary or secondary amines to formamides, tertiary amines and water to implement. The water of reaction is preferably after addition of a solvent such as. B. toluene separated by azeotropic distillation. In the only embodiment triethylammonium formate and toluene were mixed and with piperidine (molar ratio of formate to piperidine = 1 to 1, 2) was added. Under reflux, the toluene / water heteroazeotrope was separated and discharged water. The yield of N-formylpiperidine and triethylamine was quantitative. From Chemie Ingenieur Technik (75), pages 877 to 883 (2003) is known to convert carbon dioxide with hydrogen in the presence of dimethylamine, toluene, water and rhodium or Rutheniumphosphinkomplexen to dimethylformamide. According to Figure 5, TOF values of around 260 were achieved at 120 ° C, a partial pressure ratio of hydrogen to carbon dioxide of 1: 1 (p _k ait = 5 MPa). Figure 7 shows an integrated process concept for the synthesis and work-up of dimethylformamide: The reaction effluent consists of two liquid phases, which are separated from each other. The upper, toluene and catalyst-containing phase is concentrated and then returned to the synthesis stage. The lower aqueous phase containing the target product dimethylformamide is back-extracted with toluene and worked up by distillation.

Information on which stage and at which pressure excess hydrogen and excess carbon dioxide are recycled, missing. Another disadvantage is that despite a subsequent extraction of the water phase with toluene noticeable catalyst losses are recorded. In addition, toluene is a foreign substance and must therefore be separated consuming before recycling the extract in the hydrogenation.

The prior art shows that in the hydrogenation of carbon dioxide in the presence of homogeneously dissolved ruthenium-phosphine complexes as catalysts and ammonia, primary or secondary amines, amide TOF values are obtained which are attractive for industrial processes. None of the cited documents, however, discloses how to work up the hydrogenation efficiencies in an economical manner and thereby separate the homogeneous catalyst from the reaction products and can be recycled to the hydrogenation stage (O. Kröcher, RA Koppel, A. Baiker, Chem. Commun. 1996, page 1497 , left column, 1st paragraph). In this case, it means that it is of great advantage if the carbon dioxide / hydrogen mixture which is under high pressure during the hydrogenation would not have to be partially or completely relaxed in the course of the work-up. After the expansion, the excess carbon dioxide / hydrogen mixture would have to be compressed again with high energy expenditure.

It is an object of the present invention to provide a preferably continuous, integrated process for the preparation of formamide and its alkyl, cycloalkyl, aryl and aralkyl derivatives based on the starting materials carbon dioxide, hydrogen and ammonia, mono- or diamines. The target products formamide and its derivatives should be made accessible with high yields and selectivities. The work-up of the reaction effluent from the reactor should be technically simple, require little energy, and be carried out exclusively with substances already present in the process, without additional auxiliaries. The separation and recycling of the homogeneous hydrogenation catalysts in the synthesis step should be as efficient as possible.

in der F und R₂ unabhängig voneinander Wasserstoff, lineare oder verzweigte Reste mit 1 bis 15 Kohlenstoffatomen, cycloaliphatische Reste mit 5 bis 10 Koh- lenstoffatomen, einen substituierten oder unsubstituierten Phenylrest und einenThis object is achieved by a process for the preparation of formamides of Formal la

in the F and R _{2 are} independently hydrogen, linear or branched radicals having 1 to 15 carbon atoms, cycloaliphatic radicals having 5 to 10 carbon atoms, a substituted or unsubstituted phenyl radical and a

Phenyl, and R 1 and R ₂ may be closed to a five- or six-membered ring which contains an oxygen atom, a Λ / -Η- or N-R radical, where R 1 has the abovementioned meaning,

by reacting carbon dioxide (1) with hydrogen (2) in a hydrogenation reactor I in the presence

- A catalyst containing an element from the 8th, 9th or 10th group of the Periodic Table, - A tertiary amine of the formula NR ₃ R ₄ R ₅ (IVa) in which the radicals R ₃ to R _{5 are the} same or different and independently represent an unbranched or branched, acyclic or cyclic, aliphatic, aromatic or araliphatic radical having in each case 1 to 16 carbon atoms, preferably 1 to 12 carbon atoms, wherein individual carbon atoms independently of one another also by a hetero group selected from the group -O- and

> N-substituted and two or all three radicals can also be linked together to form a chain comprising at least four atoms, with the proviso that the total number of C atoms per molecule is at least 6,

- a polar solvent

to form formic acid-amine adducts as intermediates of formula II a

NR ₃ R ₄ R ₅ .Xi HCOOH (IIa),

(Xi = 0.4 to 5) wherein in the reaction in the hydrogenation reactor I form two liquid phases, namely a lower phase containing predominantly the polar solvent in which the formic acid-amine adducts are enriched, and an upper phase containing predominantly the tertiary amine in which the homogeneous catalyst is enriched and wherein the effluent (3) from the hydrogenation reactor I is worked up according to the following process steps:

Separation of the two liquid phases from the hydrogenation reactor in a phase separation vessel,

 Recycling the upper phase from the phase separation vessel into the hydrogenation reactor and

Forwarding the lower phase from the phase separation vessel in an extraction unit, wherein

• residues of catalyst with the same tertiary amine that was used in the hydrogenation, extracted and the loaded with the catalyst tertiary amine is recycled to the hydrogenation reactor I, which is characterized in that the catalyst-free stream containing the formic acid / amine adducts of formula (IIa), and polar solvent (7) in a reactor IV passes, and therein the formic acid-amine adducts of the formula (IIa) at temperatures of 0 to 200 ° C with ammonia or amines of the formula (IIIa),

/ ^R 1

 H - N

 \ (purple),

in the R _\ and R ₂ for formula (la) have the meaning given, in which via the intermediate of formula (Va) of the corresponding

Adduct of formic acid with ammonia or an amine of the formula (IIIa)

NHR _! R ₂ · χ HCOOH (Va) the corresponding formamide of the formula (Ia) is obtained, and

(ii) separating the biphasic liquid effluent from reactor IV (stream 9) in a phase separation vessel V into a liquid phase (stream 10) enriched in formamides of formula (la) and a second tertiary amine enriched liquid phase (stream 12) tertiary amine-enriched liquid phase (stream 12) completely or partially returns to the extraction unit III, and (iii) distilling stream 10 in a distillation unit VI to yield the formamide of formula (Ia), removing water, recycling the polar solvent (stream 8) to the hydrogenation reactor I, and unreacted ammonia or amine of the formula (II) purple) in the reactor IV (stream 11).

Preferably, the partial stream not recycled to the extraction unit III is returned to the tertiary amine-enriched liquid phase in the hydrogenation reactor I.

The catalyst to be used in the hydrogenation of carbon dioxide in the process according to the invention is preferably a homogeneous catalyst. This contains an element from the 8th, 9th or 10th group of the periodic table, ie Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and / or Pt. Preferably, the catalyst contains Ru, Rh, Pd, Os, Ir and / or Pt, more preferably Ru, Rh and / or Pd, and most preferably Ru.

The elements mentioned above are homogeneously dissolved in the form of complex-like compounds in the reaction mixture. The homogeneous catalyst is to be selected so that it is enriched together with the tertiary amine in the liquid phase (B). Under "enriched" is a distribution coefficient of the homogeneous catalyst

P = [concentration of homogeneous catalyst in liquid phase (B)] / [concentration of homogeneous catalyst in liquid phase (A)] of> 1 to understand. Here, the liquid phase (A) is the phase containing the solvent enriched with the formic acid / amine adducts. The selection of the homogeneous catalyst is generally carried out by a simple experiment in which the partition coefficient of the desired homogeneous catalyst under the planned process conditions is determined experimentally.

Because of their good solubility in tertiary amines used in the process according to the invention as homogeneous catalysts preferably an organometallic complex compound containing an element from the 8th, 9th or 10th group of the periodic table and at least one phosphine group having 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-. For the purposes of branched cyclic aliphatic radicals, this also includes radicals such as -CH ₂ -C ₆ Hn. Suitable radicals are, for example, be mentioned methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 1- (2-methyl) propyl, 2- (2, "- _3nty | - | _ _Hexy | 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. The unbranched or branched, acyclic or cyclic, aliphatic radical preferably contains 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 are P (A7-C _n H ₂ n + i) 3 where n is 1 to 10, more preferably tri-n-butylphosphine, tri-n-octylphosphine and 1, 2-bis (dicyclohexylphosphino) 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 respectively.

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. Examples include 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 x H ₂ O], [M (acetylacetonate) ₃ ], [M (COD) Cl ₂ ] ₂ , [M ( DMSO) ₄ CI ₂ ] with M equal to element from the 8th, 9th or 10th group of the periodic table with the addition of the corresponding phosphine ligand or only under reaction conditions.

Preferred homogeneous catalysts in the process according to the invention are [Ru (Pn-Bu ₃ ) ₄ (H) ₂ ], [Ru (Pn-octyl ₃ ) ₄ (H) ₂ ], [Ru (Pn-Bu ₃ ) ₂ (1, 2 bis (dicyclohexylphosphino) ethane) (H) ₂ ], [Ru (Pn-Octyl ₃ ) ₂ (1, 2-bis (dicyclohexylphosphino) ethane) (H) ₂ ], [Ru (PEt ₃ ) ₄ (H) ₂ . With these, TOF values (turn-over frequency) of greater than 1000 h ^-1 can be achieved in the hydrogenation of carbon dioxide.

When using homogeneous catalysts, the amount of said metal component in the organometallic complex 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 entire liquid reaction mixture in the hydrogenation reactor.

The distribution coefficient of the homogeneous catalyst based on the amount of ruthenium in the amine phase and the product phase containing the formic acid / amine adduct after hydrogenation in the range of P is greater than 0.5, more preferably greater than 1.0, and most preferably greater than 4.

The tertiary amine is selected and matched with the polar solvent such that the hydrogenation product forms two liquid phases and the tertiary amine in the upper phase is enriched in the hydrogenation reactor. By "enriched" is meant a weight fraction of> 50% of the free, that is not bound in the form of the formic acid / amine adduct, tertiary amine in the upper phase based on the total amount of free, tertiary amine in both liquid phases. The proportion by weight is preferably> 90%. The choice of tertiary amine is generally made by a simple experiment in which the solubility of the desired tertiary amine in both liquid phases is determined experimentally under the intended process conditions. The upper phase may also contain parts of the polar solvent and a non-polar inert solvent. The preferred tertiary amine to be used in the process according to the invention is an amine of the general formula (IVa)

NR ₃ R ₄ R ₅ (IVa) in which the radicals R ₃ to R _{5 are} identical or different and independently of one another _ ^: - ^: __ _{3n QC} | _he branched, acyclic or cyclic, aliphatic, aromatic or araliphatic radical having in each case 1 to 16 carbon atoms, preferably 1 to 12 carbon atoms, where individual carbon atoms can be substituted independently of one another by a hetero group selected from the group -O- and> N- and two or all three radicals with formation a chain of at least four atoms each, with the proviso that the total number of carbon atoms is at least 6.

Examples of suitable amines of the formula (IVa) include: triethylamine, 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. Dimethyldecylamine, dimethyldodecylamine, dimethyl-tetradecylamine, ethyl-di (2-propyl) amine, dioctylmethylamine, dihexylmethylamine.

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, methyldibenzylamine, ethyldibenzylamine and theirs by a or a plurality of methyl, ethyl, 1-propy, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups substituted derivatives.

• A / -Crbis _{Ci-2-alkyl-piperidines,} A /, / V-di-Ci-Crbis -Alkylpiperazine _2, A / -Crbis-pyrrolidine Ci ₂ alkyl, A / -Crbis-Ci ₂ -Alkylimidazole and their derivatives substituted by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups.

• 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"). Of course, mixtures of any number of different tertiary amines IVa can also be used in the process according to the invention.

Particularly preferred in the present process the tertiary amine is an amine of general formula (IVa), in which the radicals R ¹ to R ^{3 are} independently selected from the group d- to C ₂ alkyl, C ₅ - to C ₈ - Cycloalkyl, benzyl and phenyl.

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 (IVa).

Very particularly preferably employed in the process according to the invention as a tertiary amine is an amine of the general formula (IVa) in which the radicals R ₃ to R _{5 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 particular, the tertiary amine used is an amine of the general formula (IVa) in which the radicals R ¹ to R ³ are selected independently of one another from C ₅ - and C ₆ -alkyl.

In the process according to the invention, the tertiary amine is preferably liquid in all process stages. However, this is not a mandatory requirement. It would also be sufficient if the tertiary amine were at least dissolved in suitable solvents. Suitable solvents are in principle those which are chemically inert with regard to the hydrogenation of carbon dioxide and the thermal cleavage of the adduct, in which the tertiary amine and, in the case of the use of a homogeneous catalyst, these also dissolve well, inversely polar solvent and formic acid / Dissolve amine adducts poorly. In principle, therefore, come chemically inert, non-polar solvents such as aliphatic, aromatic or araliphatic hydrocarbons, such as octane and higher alkanes, toluene, xylenes. The polar solvent to be used in the hydrogenation of carbon dioxide in the process according to the invention is to be selected or matched with the tertiary amine in such a way that the polar solvent is enriched in the lower phase. By "enriched" is meant a weight fraction of> 50% of the polar solvent in the lower phase based on the total amount of polar solvent in both liquid phases. Preferably, the proportion by weight of the polar solvent is generally given by a A simple experiment in which the solubility of the desired polar solvent in both liquid phases under the intended process conditions is determined experimentally. The polar solvent may be a pure polar solvent as well as a mixture of various polar solvents as long as the solvent, above-mentioned conditions, boiling point and phase behavior apply. Suitable classes of substances which are suitable as polar solvents are preferably alcohols and diols and also their formic esters and water.

Suitable alcohols include alcohols in which the trialkylammonium formates preferably dissolve in a mixture with water and this product phase has a mixture gap with the free trialkylamine. Examples of suitable alcohols are methanol, ethanol, 2-methoxyethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol. The ratio of alcohol to water should be selected such that, together with the trialkylammonium formate and the trialkylamine, a biphasic mixture is formed in which most of the trialkylammonium formate, water and polar solvent are in the lower phase, generally by a simple Experiment is determined by experimentally determining the solubility of the desired polar solvent mixture in both liquid phases under the intended process conditions. Suitable classes of compounds which are suitable as polar solvents are preferably diols and also their formic acid esters, polyols and also their formic acid esters, sulfones, sulfoxides, open-chain or cyclic amides and mixtures of the mentioned classes of substances. Examples of suitable diols and polyols are 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 called glycerin.

As a suitable sulfone especially tetramethylene sulfone (sulfolane) is called.

Examples of suitable sulfoxides are dialkyl sulfoxides, preferably C ₁ - to C ₆ -dialkyl sulfoxides, in particular dimethylsulfoxide. Examples of suitable open-chain or cyclic amides are formamide, N-methylformamide, A / ./V-dimethylformamide, / V-methylpyrrolidone, acetamide and / V-methylcaprolactam. The molar ratio of the polar solvent or solvent mixture to be used in the process according to the invention to the tertiary amine used is generally 0.5 to 30 and preferably 1 to 20.

The carbon dioxide to be used in the hydrogenation of carbon dioxide 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 to be used in the hydrogenation of carbon dioxide is generally gaseous. Carbon dioxide and hydrogen may also contain inert gases, such as nitrogen or noble gases. Advantageously, however, their content is below 10 mol% based on the total amount of carbon dioxide and hydrogen in the hydrogenation reactor. While larger amounts may also be tolerable, they generally require the use of a higher pressure in the reactor, requiring further compression energy.

The hydrogenation of carbon dioxide takes place in the liquid phase preferably at a temperature of 20 to 200 ° C and a total pressure 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.

The partial pressure of the carbon dioxide is generally at least 0.5 MPa and preferably at least 2 MPa and generally at most 8 MPa. The partial pressure of hydrogen 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. The molar ratio of hydrogen to carbon dioxide in the feed of the hydrogenation reactor is preferably 0, 1 to 10 and particularly preferably 1 to 3.

The molar ratio of carbon dioxide to tertiary amine in the feed of the hydrogenation reactor is generally 0, 1 to 10 and preferably 0.5 to 3. In principle, all reactors which are fundamentally suitable for gas / liquid reactions under the given temperature and the given pressure can be used as hydrogenation reactors. Suitable standard reactors for liquid-liquid reaction systems are described, 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". Examples which may be mentioned 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 hydrogen are pressed to the desired pressure at the desired temperature. After the end of the reaction, the reactor is generally 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 phase is continuously removed 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 in the hydrogenation reactor is generally 10 minutes to 5 hours. The formic acid / amine adducts formed in the hydrogenation of carbon dioxide in the presence of the catalyst to be used, the polar solvent and the tertiary amine generally have the general formula (IIa)

NR ₃ R 4 R ₅ · Xi HCOOH (IIa), in which the radicals R ₃ to R ₅ correspond to the radicals described for the tertiary amine (IVa) and x is from 0.4 to 5, preferably from 0.7 to 1.6. The respective average compositions of the amine-formic acid ratios in the product phases in the respective process steps, ie the factor x ,, can be determined, for example, by determining the formic acid content by titration with an alcoholic KOH solution against phenolphthalein and the amine content by gas chromatography. The composition of the formic acid / amine adducts, ie the factor x, can change during the different process steps. For example, adducts are generally formed after removal of the polar solvent a higher formic acid content with x ₂ > Xi with x ₂ 1 to 4, wherein the excess, free amine can form a second phase.

In the hydrogenation of carbon dioxide by the process according to the invention, two liquid phases are formed. The lower phase is enriched with the formic acid / amine adducts as well as the polar solvent. With regard to the formic acid / amine adducts, a distribution coefficient of the formic acid / amine adducts P = [concentration of formic acid / amine adduct (II) in liquid phase (A)] / [concentration of formic acid / amine adduct (II) in Liquid phase (B)] of> 1, where A and B have the meaning given above. Preferably, the distribution coefficient is> 2 and more preferably> 5. The upper phase is enriched with the tertiary amine. In the case of the use of a homogeneous catalyst this is also enriched in the upper phase.

The two liquid phases formed are separated from one another in the process according to the invention and the upper phase is recycled to the hydrogenation reactor. Optionally, it is also advantageous to recycle a further liquid phase comprising both liquid phases containing unconverted carbon dioxide and a gas phase containing unconverted 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, auszuschleusen a portion of the upper phase and / or a portion of the carbon dioxide or carbon dioxide and hydrogen-containing liquid or gaseous phases from the process.

The separation of the two liquid phases is generally carried out by gravimetric phase separation. Suitable phase separation vessels are, for example, standard apparatuses and standard methods, which are described, for example, in E. Müller et al. , "Liquid Liquid Extraction", in Ullmann's Encyclopaedia of Industrial Chemistry, 2005, Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007.b03_06, Chapter 3 "Apparatus". In general, the liquid phase enriched with the formic acid / amine adducts as well as the polar solvent is heavier and forms the lower phase.

The phase separation can be carried out, for example, after relaxation, for example to about or near atmospheric pressure, and cooling of the liquid reaction mixture, for example to about or near ambient temperature. However, it is to be feared that at least part of the at the higher reaction pressure in the Liquid phases of dissolved gas, in particular carbon dioxide, degassed in the relaxation and to compress separately as a gas stream and is recirculated to the hydrogenation reactor. Likewise, the lower phase before being returned to the hydrogenation reactor separately to bring to reaction pressure. In this case, a suitable, designed according to the pressure difference to be overcome designed compressor or a pump, which also consumes additional energy during operation for the recirculating gas and liquid phase.

In the context of the present invention, it has been found that in the present system, that is to say a subphase enriched with the formic acid / amine adducts and the polar solvent, and also with the tertiary amine and in the case of the use of a homogeneous catalyst This enriched upper phase, both liquid phases with a suitable combination of the solvent and the amine can be separated very well even at a significantly increased pressure. Therefore, in the process according to the invention, the solvent and the amine are preferably to be selected so that the separation of the one, enriched with the formic acid / amine adducts and the polar solvent lower phase of the other, enriched with the tertiary amine upper phase, and the return of the upper phase to Hydrogenating 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. Thus, it may even be possible to separate both liquid phases from each other without prior relaxation and to recycle the upper phase to the hydrogenation reactor without appreciable pressure increase. In this case, as well as in the case of only slight relaxation, it is possible to completely renounce a return of any gas phase. Whether this waiver is possible for the respective concrete system is to be determined in case of doubt beforehand by simple experimental examples.

The process according to the invention can thus preferably be carried out in such a way that the pressure in the hydrogenation reactor and in the phase separation vessel is the same or approximately the same.

The process according to the invention can thus preferably be carried out in such a way that the pressure and the temperature in the hydrogenation reactor and in the phase separation vessel are the same or approximately the same, whereby a pressure difference of up to +/- 0.5 MPa or approximately a temperature difference of up to +/- 5 ° C is understood.

Particularly preferably, the phase separation takes place at a pressure of at least 50%, very particularly preferably of at least 90% and in particular of at least "-gpression pressure. The pressure during the phase separation is particularly high preferably at most 105% and most preferably at most 100% of the reaction pressure.

Surprisingly, it has also been found that in the present system both liquid phases can separate very well even at an elevated temperature which corresponds to the reaction temperature. In this respect, the phase separation also no cooling and subsequent heating of the recirculating upper phase is required, which also saves energy. The findings for the phase separation under elevated pressure and elevated temperature are exceeded even more that just the upper phase according to the inventive system under pressure by suitable choice of the amine and the polar solvent can have a particularly high absorption capacity for carbon dioxide. This means that any excess carbon dioxide which is not reacted in the hydrogenation reaction is very preferably present in the upper phase and can thus be recycled without problems as a liquid to the reactor.

The majority of the polar solvent of the separated lower phase is thermally separated from the formic acid / amine adducts in a distillation unit, whereby the polar solvent removed by distillation is recycled to the hydrogenation reactor. The pure formic acid / amine adducts and free amine are obtained in the bottom of the distillation unit, since formic acid / amine adducts with a lower amine content are formed during the removal of the polar solvent, resulting in a two-phase bottom mixture consisting of an amine and a formic acid / amine Adduct phase forms (Figure 2).

The thermal separation of the polar solvent or mixture, see above, is preferably carried out at a bottom temperature at which no free formic acid forms from the formic acid / amine adduct having the higher (x1) or lower (x2) amine content at a given pressure , Generally, the bottom temperature of the thermal separation unit is at least 20 ° C, preferably at least 50 ° C and more preferably at least 70 ° C, and generally at most 210 ° C, more preferably at most 190 ° C. The pressure is generally at least 0.0001 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 0, 1 MPa abs.

The thermal separation of the polar solvent or mixture takes place either in an evaporator or in a distillation unit, consisting of evaporator and column, filled with packing, packing and / or trays. The solvent, - ^ _. _rT1 j _SC | _{ien- r rennun} g be condensed, again with the liberated condensation enthalpy can be used, for example, to preheat the solvent coming from the extraction with amine / formic acid adduct mixture to the evaporation temperature (FIG. 1). Alternatively, only parts of the solvent mixture can be separated. It is also possible to separate the polar solvent only in substep VI and to return it to the hydrogenation stage I.

The solution of tertiary amine adduct and formic acid is extracted with free tertiary amine streams from the appropriate phase separation vessels and recycled to the hydrogenation reactor. This is done to separate residual amounts of hydrogenation catalyst from the product stream. This extraction allows efficient recovery of the expensive, active noble metal catalyst for the hydrogenation reaction.

The extraction takes place at temperatures of 30 to 100 ° C and pressures of 0, 1 to 8 MPa. The extraction can also be carried out under hydrogen pressure.

The extraction of the hydrogenation catalyst can be carried out in any suitable apparatus known to the person skilled in the art, preferably in countercurrent extraction columns, mixer-settler cascades or combinations of mixer-settlers.

In certain circumstances, in addition to the catalyst, portions of individual components of the polar solvent from the liquid phase to be extracted in the extraction agent, the amine stream, are dissolved. This is not a disadvantage for the process, since the already extracted amount of solvent does not have to be supplied to the solvent removal and thus may save evaporation energy.

It may be advantageous to integrate a device for adsorbing traces of hydrogenation catalyst between the extraction apparatus and the thermal separation device. Many adsorbents are suitable for adsorption. Examples include polyacrylic acid and its salts, sulfonated polystyrenes and their salts, activated carbons, montmorillonites, bentonites, silica gels and zeolites. If the amount of hydrogenation catalyst in the product stream of the phase separation vessel II is less than 1 ppm, in particular less than 0.1 ppm, the adsorption device is sufficient for the separation of the hydrogenation catalyst and its recovery. Then, the extraction step can be omitted and the tertiary amine can be recycled together with the organic solvent in the hydrogenation. The formic acid adducts of the formula (IIa) are then reacted with ammonia (F and R ₂ in formula (IIIa) = hydrogen) or amines of the formula (IIIa) to formamides of the formula (Ia), tertiary amines IVa and water:

R1. ,

NR ₃ R ₄ R ₅ . X _| HCOOH + x _t HN H - IC - N ../. ^R1 + NR ₃ R ₄ R ₅ + H ₂ 0

 R2 R2

 I a IVa

 (Xi = 0.4 - 5)

In a preferred embodiment of the invention, the reaction is carried out in the presence of the polar solvent used in the hydrogenation reactor. In this case, the entire amount of polar solvent arriving in the reactor is preferably used.

The reaction is preferably carried out at temperatures of 80 to 200 ° C, preferably 100 to 180 ° C, particularly preferably 120 to 170 ° C. The pressure is 0.01 to 10 MPa, preferably 0.1 to 7 MPa, particularly preferably 0.2 to 5 MPa.

The reaction can also be carried out at temperatures of 0 to 80 ° C in the specified pressure ranges. This results in reaction effluents, in addition to formamides of the formula Ia, predominantly as intermediate formates of the formula Va, i. Adducts of formic acid with ammonia or an amine of the formula (IIIa).

NHR _! R ₂ · χ HCOOH (Va).

These mixtures can be converted at temperatures between 80 and 200 ° C as the adducts (IIa) in formamide of formula (Ia).

The molar ratio of formic acid in adduct IIa to ammonia or amine III is 1 to 5, preferably 1 to 2, particularly preferably 1 to 1. The reaction can be carried out batchwise, but preferably continuously.

The synthesis of formamides 1a can be carried out in standard reactors, as described, for example, in KD Henkel, "Reactor Types and their Industrial Applications" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH Verlag, Chapter 3.3 are indicated. Examples which may be mentioned stirred tank reactors, tubular reactors or bubble column reactors.

In a further preferred embodiment of the invention, part or all of the polar solvent is removed by distillation before being fed to the formamide reactor and recycled to the hydrogenation reactor (I). The amount of polar solvent removed can be from 25 to 99%, preferably from 35 to 97%, particularly preferably from 50 to 95%, of the amount of polar solvent present in the stream before being fed to the reactor.

This process variant is advantageous, for example, when used as the polar solvent in the hydrogenation of carbon dioxide primary alcohols such as methanol together with water. It is also possible in principle and may be advantageous to use a polar solvent other than the amidation step, in the reactor IV, in the hydrogenation step in the hydrogenation reactor I. For this purpose, the polar solvent is separated from the hydrogenation and recycled to the hydrogenation reactor I. In the amidation stage, a different polar solvent used in the hydrogenation step is used in reactor IV, which is separated again after amidation and in the reactor IV, in which the amidation is carried out, is recycled. Thus, for example, the carbon dioxide hydrogenation in the presence of methanol and water and the reaction of the adduct (IIa) can be carried out with ammonia in the presence of sulfolane. Suitable polar solvents for the amidation are, for example, sulfones, sulfoxides or open-chain or cyclic amides.

The distillation can be carried out in the separation of low-boiling polar solvents such as the monohydric alcohols methanol, ethanol, propanols and butanols at atmospheric pressure or in vacuo. In contrast, when using diols as polar solvents, working in a vacuum is preferred.

Depending on the separation problem, different apparatus can be used as distillation units. At far apart boiling points of the adduct IIa and the polar solvent can, for. B. evaporators such as falling film evaporator can be used. However, the distillation unit to be used generally comprises a distillation column containing packing, packing and / or trays.

In the reaction of formic acid adducts of the formula (IIa) with ammonia or amines of the formula (IIIa) according to the inventive method, both in the presence and in the absence of polar solvents, two liquid phases C ^-, - '-' ^■■ j _SS jgp | -iase C is linked to the formamide of formula (Ia), water and optionally unreacted ammonia or amine enriched purple. With regard to the formamide of the formula (Ia), a distribution coefficient is enriched under

P = [concentration of formamide of formula (Ia) in liquid phase C /

 To understand the concentration of the formamide of formula (Ia) in liquid phase D of> 1. Preferably, the distribution coefficient is> 2, and more preferably> 5. The liquid phase D is enriched with the tertiary amine resulting from the adduct II a.

The two liquid phases C and D formed are separated from one another in the process according to the invention. The liquid phase D is returned to the extraction apparatus and serves there for the extraction of residual amounts of homogeneous, dissolved hydrogenation catalyst. If appropriate, it is desirable, for example, for discharging unwanted by-products or impurities, to remove some of the liquid phases C or D from the process.

The separation of the two liquid phases C and D is generally carried out by gravimetric phase separation. Suitable for this purpose are, for example, standard apparatus and standard methods, which are described, for example, in E. Müller et. Al., "Liquid-Liquid Extraction," in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007. b03_06, Chapter 3 "Apparatus". The phase separation can be carried out, for example, after relaxation, for example to about or near atmospheric pressure, and cooling of the liquid reaction mixture, for example to about or near ambient temperature.

The liquid phase C is passed into a distillation unit VI and worked up there by distillation. It contains the target product formamide of the formula (Ia), optionally unreacted ammonia or amine of the formula (IIIa), water of reaction and polar solvents selected from the group of methanol, ethanol, propanols or butanols or from the group of diols. In a variant of this process, the polar solvents are separated before being fed to the formamide reactor and recycled to the hydrogenation stage I.

The distillation unit VI consists of at least one, preferably two to three distillation columns. These columns contain, depending on the separation problems z. B. packing, packages and / or floors. If the polar solvents have not previously been separated off, the ethanol / water and propanol / water homoazeotrope in the case of ethanol and heteroazeotrope in the case of butanols are to be taken into account. The water of reaction is discharged from the process. Polar solvents are recycled to the hydrogenation stage, unreacted ammonia and unreacted amines III a to the reactor. The target products, the formamides of the formula (Ia), are discharged from the process and, if necessary, fed to a preferably distillative fine purification.

In a further preferred embodiment, adducts of the formula (IIa), formates of the formula (Va) or mixtures of adducts of the formula (IIa) and formates of the formula (Va) with amines of the formula (IIIa), preferably with ammonia and polar solvents Implemented distillation conditions. The reaction takes place in a distillation apparatus, for example a distillation flask with attached distillation column. Aliphatic, cycloaliphatic or aromatic hydrocarbons, such as n-heptane, n-hexane, cyclohexane, methylcyclohexane, toluene, ethylbenzene, ortho, meta and para xylene and mixtures of these compounds can be used as nonpolar solvents. These compounds form heteroazeotrope with water. The bottom temperatures of this distillation are 80 to 200 ° C, preferably 110 to 200 ° C, particularly preferably 135 to 190 ° C. The pressure is 0.01 MPa to 10 MPa, preferably 0.1 MPa to 7 MPa, more preferably 0.2 to 5 MPa. The water of reaction is distilled off together with the polar solvent. From the resulting in the condensation liquid two-phase mixture, water is separated and discharged, the non-polar solvent returned to the distillation. The bottom product of the distillation is worked up. Formamide of the formula (Ia) is separated from tertiary amine of the formula IVa. The tertiary amine IVa is recycled to the hydrogenation stage I.

The process according to the invention has particular advantages when constructing a large-scale production plant with "economy of scale" for the preparation of adducts of the formula (IIa) from tertiary amines and formic acid, which is used for the production of formic acid and of formamides I a.

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

1. Carbon dioxide hydrogenation (in the hydrogenation reactor I) and phase separation of the discharge from the hydrogenation reactor (in the phase separation vessel II) (Examples A1 to A4)

A 250 ml Hastelloy C autoclave equipped with a magnetic stirrer bar was charged under inert conditions with the tertiary amine, polar solvent and homogeneous catalyst indicated in Table 1 below. 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 appropriate reaction time, the autoclave was cooled and the reaction mixture was depressurized. A biphasic product mixture was obtained in which the upper phase was enriched with free tertiary amine and the homogeneous catalyst, and the lower phase with the polar solvent and the formic acid / amine adduct formed. The total content of formic acid in the formic acid / amine adduct was determined by titration with 0.1 N KOH in methanol potentiometrically using a Mettler Toledo DL50 titrator ^®. From this, the turn-over frequency (TOF) and the reaction rate were calculated. The composition of the two phases was determined by gas chromatography. The ruthenium content was determined by atomic absorption spectroscopy (AAS). The parameters and results of the individual experiments are given in Table 1.

The two liquid phases were separated in a separatory funnel. Examples A-1 to A-4 show that high to very high reaction rates of up to 0.98 mol kg ^"1 h ^{" 1} (reaction rate = mol of formic acid / (kg weight reaction output xh reaction time) are achieved two phases, wherein the upper phase was enriched in each case with the free tertiary amine and the homogeneous catalyst, and the lower phase in each case with the polar solvent and the formed formic acid / amine adduct.

my

24

Table 1

EK10-0928PC

2. Extraction of Catalyst Residues (in Extraction Apparatus III) (Example B-1)

Example B-1, Table 2 shows that in the phase separation of a Wasserstoffrieraustrags 26.2 g of a lower phase were obtained which contained 6.1 wt .-% formic acid in the form of the formic acid / amine adduct and 33 ppm ruthenium. This lower phase was stirred at room temperature under inert conditions three times for 10 minutes each with 26.2 g of tri-n-hexylamine. The phases were separated. The ruthenium content of the extracted lower phase as determined by AAS analysis was 21 ppm ruthenium.

Example B-1 shows that the amount of ruthenium in the lower phase can be reduced by about 36% by extraction with the same tertiary amine already used in C0 ₂ hydrogenation. Additional extraction steps or continuous countercurrent extraction could further reduce the ruthenium content.

Table 2

Catalyst Extraction Example B-1

 Tertiary amine 37.5 g trihexylamine

 Polar solvent 12.0 g of methanol

 (used) 0.5 g of water

Catalyst 0.16 g [Ru (Pn-Octyl ₃ ) 4 (H) ₂ ]

Pressing on C0 ₂ At 1, 7 MPa

Pressing H _{2 to} 8.0 MPa

 Heating 50 ° C

 Reaction time 1, 5 hours

 Upper phase 23.3 g

 Lower phase 26.2 g

 6.1% formic acid

c _Ru upper phase after reaction 350 ppm

c _Ru lower phase after reaction 33 ppm

c _Ru lower phase after extraction 21 ppm 3. Distillative separation of the polar solvent before amide synthesis (in the distillation apparatus 111-1) (Example C-1)

Example C-1 shows the distillative separation of the polar solvents methanol and water from a hydrogenation. At 120 ° C and 0.02 MPa, a distillate was obtained on a rotary evaporator, which contained all the methanol, 0.3 wt .-% formic acid and almost all water. The biphasic bottom effluent (upper phase + lower phase) can be used for the amide preparation in reactor IV (FIGS. 1 and 2).

Table 3

Preparation of formamides by reaction of adducts of formic acid with tertiary amines with primary and secondary amine (n-butylamine or dimethylamine) or with ammonia (in reactor IV)

A 250 mL Hastelloy C autoclave equipped with a magnetic stirrer bar was placed under inert conditions with the formic acid tertiary amine adduct IIa and, optionally, a nominal solvent and water (see Table 4, Examples D-1 through D-19). filled. Subsequently, the autoclave was sealed. At room temperature dimethylamine, n-butylamine, or ammonia were pressed. Subsequently, the reactor was heated with stirring (700 rpm). After the desired reaction time, the autoclave was cooled and the reaction mixture was depressurized. A two-phase product mixture was obtained, the upper phase consisting of the tertiary amine and the lower phase consisting of the corresponding amide, water and optionally polar solvent and optionally ammonium formate. Both phases were separated and weighed using a separatory funnel. The composition of the two phases was determined by gas chromatography and proton NMR spectroscopy. The parameters and results of the individual experiments are shown in Tables 4 to 6.

4.1 Preparation of A /, / V-dimethylformamide (Examples D1 to D19)

Table 4

Example D-1 Example D-2 Example D-3 Example D-4 Example D-5

Amine 48 g 60 g 48 g 48 g 23 g / v ethyl

Trihexylamine trihexylamine trihexylamine trihexylamine diisopropylamine

Formic acid 16 g HCOOH 20 g HCOOH 16 g HCOOH 16 g HCOOH 17 g HCOOH

Solvent 72 g 1, 4- No LM 72 g 1, 4- No LM 73 g 1, 4- (LM) Butanediol Butanediol Butanediol

 6 g of water

 Dimethylamine 18 g DMA 21 g DMA 19 g DMA 19 g DMA 16 g DMA (DMA)

 Press to 0.33 MPa 0.21 MPa 0.36 MPa 0.32 MPa 0.28 MPa

Temperature 150 ^U C 150 ^U C 150 ^U C 150 ^U C 130 ^U C

Running time 4 hours 2 hours 2 hours 2 hours 2 hours

Upper phase 48 g 57 g 46 g 46 g 15 g / V ethyl

Trihexylamine trihexylamine trihexylamine trihexylamine diisopropylamine

Lower phase 102 g 40 g 1 12 g 33 g 109 g

 Yield GC 99.5% 94.0% 75.9% 99.4% 95.0% (Fl%)

dimethylformamide Example D-6 Example D-7 Example D-8 Example D-9 Example D-10

Amine 48 g 48 g 48 g 25 g 48 g

 Trihexylamine trihexylamine trihexylamine trihexylamine trihexylamine

Formic acid 16 g HCOOH 16 g HCOOH 16 g HCOOH 4 g HCOOH 16 g HCOOH

Solvent 72 g MeOH 72 g MeOH No 25 g methanol 72 g 1, 5-6 g water 6 g water pentanediol

Dimethylamine 18 g DMA 19 g DMA 20 g DMA 4 g DMA 16 g DMA (DMA)

 Press to 0,26 MPa 0,09 MPa 0,26 MPa 0,29 MPa 0,29 MPa

Temperature 130 ^U C 130 ^U C 130 ^U C 130 ^U C 130 ^U C

Running time 2 hours 2 hours 2 hours 2 hours 2 hours

Upper phase 48 g 46 g 46 g 23 g 47 g

 Trihexylamine trihexylamine trihexylamine trihexylamine trihexylamine

Lower phase 1 1 1 g 107 g 33 g 25 g 101 g

Yield GC 60.8% 82.9% 99.4% 20.7% 89.5% (Fl%)

 dimethylformamide

Example D-1 1 Example D-12 Example D- Example D-14 Example D-15

 13

 Amine 48 g 27 g 33 g 41 g 33 g N, N

Trihexylamine tripropylamine tributylamine tripentylamine dimethyldecylamine

Formic acid 16 g HCOOH 17 g HCOOH 17 g 17 g HCOOH 16 g HCOOH

 HCOOH

 Solvent 73 g 1, 6-72 g 1, 4-72 g 1, 4-72 g 1, 4-72 g 1, 4-butanediol

 Hexanediol butanediol butanediol butanediol

 Dimethylamine 17 g DMA 15 g DMA 16 g DMA 16 g DMA 16 g DMA (DMA)

 Press to 0.32 MPa 0.19 MPa 0.18 MPa 0.18 MPa 0.21 MPa

Temperature 130 ^U C 130 ^U C 130 ^U C 130 ^U C 130 ^U C

 Running time 2 hours 2 hours 2 hours 2 hours 2 hours

Upper phase 47 g 20 g 31 g 38 g 29 g N, N

Trihexylamine tripropylamine tributylamine tripentylamine dimethyldecylamine

Lower phase 102 g 106 g 101 g 101 g 104 g

 Yield GC 83.0% 87.2% 87.3% 86.2% 88.3%

(Area%)

dimethylformamide Example D-16 Example D-17 Example D-18 Example D-19

Amine 35 g / V methyl 23 g / V ethyl 64 g Tris (2-70 g

 dicyclohexylamine diisopropylamine ethylhexyl) amine trihexylamine

Formic acid 17 g HCOOH 17 g HCOOH 16 g HCOOH 5 g HCOOH

 Solvent 72 g of 1, 4-73 g of 1, 4-72 g of 1, 4-30 g of 1, 4-butanediol butanediol butanediol butanediol

 Dimethylamine (DMA) 16 g DMA 16 g DMA 16 g DMA 5 g DMA

 Pressure after pressing 0.18 MPa 0.28 MPa 0.32 MPa 0.30 MPa

Temperature 130 ^U C 130 ^U C 130 ^U C 130 ^U C

 Running time 2 hours 2 hours 2 hours 2 hours

 Upper phase 25 g / V methyl 15 g / V ethyl 64 g Tris (2-63 g

 dicyclohexylamine diisopropylamine ethylhexyl) amine trihexylamine

Lower phase 1 12 g 109 g 101 g 33 g

 Yield GC (Fl%) 86.4% 95.0% 89.7% 17.9%

dimethylformamide

In the experiments shown in Table 4 for the preparation of dimethylformamide from adducts IIa and dimethylamine (DMA) were in the presence of 1, 4-butanediol as a polar solvent (D-1, D-15) and in the absence of a polar solvent and water (D. -4, D-8) dimethylformamide yields of over 95% achieved.

In the presence of primary alcohols such as methanol as the polar solvent, the dimethylformamide yield dropped to 82.9% (D-7). Even more, the dimethylformamide yield dropped in the presence of methanol and water. In experiments D-6 and D-9 dimethylformamide yields of only 60.8% and 20.7% were achieved. Therefore, water, more preferably water together with primary alcohols as polar solvents is preferably already separated by distillation in process step 111-1 and recycled as stream 8 into the hydrogenation step.

4.2 Preparation of n-butylformamide (Example E1)

Table 5

 Example E-1

 Amine 48 g trihexylamine

 Formic acid 16 g HCOOH

 Solvent 72 g of 1,4-butanediol

N-butylamine 31 g n-BuNH ₂ Pressure after pressing 0.12 MPa

Temperature 150 ^U C

 Running time 4 hours

 Upper phase 35 g trihexylamine

 Lower phase 125 g

 Yield GC (Fl%) Butyl 99.5%

 formamide Butylformamide

Experimental result E-1 shows that the reaction of adduct IIa with n-butylamine in the presence of 1,4-butanediol as the polar solvent gives n-butylformamide in quantitative yield.

4.3 Preparation of Formamide (Examples F-1 to F-8)

Example F-1 Example F-2 Example F-3 Example F-4 Example F-5

Amine 48 g 44 g 50 g 60 g 58 g

 Trihexylamine trihexylamine trihexylamine trihexylamine trihexylamine

Formic acid 8 g HCOOH 5 g HCOOH 6 g HCOOH 20 g HCOOH 10 g HCOOH

Solvent 35 g methanol 41 g ethanol 37 g propanol 29 g methanol

 10 g water 9 g water 8 g water

Ammonia 4 g NH ₃ 3 g NH ₃ 2 g NH ₃ 8 g NH ₃ 5 g NH ₃

Press to 0,18 MPa 0,1 1 MPa 0,10 MPa 0,89 MPa 0,27 MPa

Temperature 160 ^U C 160 ^U C 160 ^U C 160 ^U C 160 ^U C

Running time 4 hours 4 hours 4 hours 4 hours 4 hours

Upper phase 47 g 46 g 85 g 56 g 57 g

 Trihexylamine trihexylamine trihexylamine trihexylamine

Lower phase 54 g 54 g 14 g 26 g 44 g

Yield GC 44.9% 48.0% 25.9% 71.4% 76.6% (F1%) formamide

 Yield NMR 43.0% 52.0% 65.0% Not 17.0% (mol%) true

ammonium

formate

Selectivity (from78.8% 100.0% 74.0% not be92.3% prey / turnover) is correct Example F-6 Example F-7 Example F-8

 Amine 60 g Trihexylamine 57 g Trihexylamine 16 g Trihexylamine

Ants Acid 20 g HCOOH 20 g HCOOH 3 g HCOOH

 Solvent 20 g methanol 20 g sulfolane 30 g 1, 4-butanediol

Ammonia 9 g NH ₃ 8 g NH ₃ 1 g NH ₃

 Pressure after pressing 0.45 MPa 0.99 MPa 0.95 MPa

Temperature 160 ^U C 160 ^U C 160 ^U C

 Running time 4 hours 4 hours 4 hours

 Upper phase 59 g Trihexylamine 54 g Trihexylamine 1 1 g Trihexylamine

Lower phase 46 g 45 g 25 g

 Yield GC (Fl%) 72.6% 89.6% 6.3%

formamide

 Yield NMR (mol%) 26.0% 10.0% Not determined Ammonium Formate

 Selectivity (recovery98, 1% 99.6% Not determined / turnover)

In the reaction of adducts IIa with ammonia to formamide, formamide yields of around 77 area% were achieved in methanol as the polar solvent. Ammonium formate (17 mol%) contained in the reaction mixture can be subsequently converted to formamide (F-5).

When sulfolane was used as the polar solvent, the formamide yield was about 90 area%, with 10 mol% of ammonium formate contained (F-7).

Deterioration of the yield is observed similarly to the preparation of dimethylformamide (D-6, D-9) in the presence of methanol and additional water (F-1).

Again, water, particularly preferably water together with primary alcohol as polar solvent already in process step II 1-1 separated by distillation and recycled as stream 8a in the hydrogenation step. The drawing shows in detail: a block diagram of a plant for a preferred process for the preparation of formamides starting from carbon dioxide by the process according to the invention and

Figure 2 is a block diagram of a further preferred method for the preparation of

 Formamides starting from carbon dioxide.

In the embodiment according to FIG. 1, carbon dioxide, stream 1, and hydrogen, stream 2, are fed into the hydrogenation reactor I. Therein they are reacted 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 to formic acid-amine adducts.

To compensate for losses of tertiary amine IVa, a supplementary stream of tertiary amine, (stream 4a) may be provided to the hydrogenation reactor I.

The two-phase discharge from the hydrogenation reactor I (stream 3) is passed into the phase separation vessel II. In the phase separation vessel II there is a lower phase which is enriched with formic acid-amine adducts and the polar solvent, and an upper phase 4, which contains predominantly the tertiary amine in which the homogeneous catalyst is enriched enriched, and from the Phase separation vessel II is recycled to the hydrogenation reactor I. The lower phase 5 is fed to an extraction apparatus III, wherein catalyst residues are extracted with the tertiary amine from the phase separation vessel V (stream 12). The tertiary amine with the catalyst residues (stream 6) from the extraction unit III is recycled to the hydrogenation reactor I, the product phase 7 from the extraction unit III is fed to the reactor IV, wherein the reaction with ammonia or amines, stream IIIa, takes place. The biphasic liquid effluent, stream 9, from the reactor IV is separated in a phase separation vessel V into a formamide-enriched liquid phase, stream 10, and a second tertiary amine-enriched liquid phase, stream 12, stream 12 being preferably introduced into the extraction apparatus III is recycled. The enriched with the target product formamide liquid phase, stream 10, is separated by distillation in a distillation unit VI to yield the formamide, stream la, discharge of water, H ₂ 0, and unreacted ammonia or amine, stream 1 1, in the reactor IV and polar solvent (stream 8) which is recycled to the hydrogenation reactor. The preferred embodiment shown in Figure 2 differs from the embodiment in Figure 1 only insofar as the extraction unit III is followed by a separation unit 111-1, for separating polar solvent. In the separation unit 111-1, the polar solvent is separated off and recycled as stream 8a into the hydrogenation reactor I. In the reactor IV, in which the amidation takes place, a different from the hydrogenation stage solvent can be supplied, which is separated again in the distillation unit VI and as stream 1 1 in the amidation, in the reactor IV, recycled. The product stream 7a from the separation unit 111-1 is substantially free of polar solvent, and is passed into the reactor IV.

Claims

Patent claims 1. Process for the production of formamides of the formula I a

in which F and R ₂ can independently represent hydrogen, linear or branched radicals with 1 to 15 carbon atoms, cycloaliphatic radicals with 5 to 10 carbon atoms, a substituted or unsubstituted phenyl radical and a phenylalkyl radical, and R ^ and R ₂ to a five-or six-membered ring can be closed, which contains an oxygen atom, a Λ/-Η or N-R radical, where R^ has the meaning given above, by reacting carbon dioxide (1) with hydrogen (2) in a hydrogenation reactor I in the presence - a catalyst containing an element from the 8th, 9th or 10th group of the periodic table, - a tertiary amine of the formula NR ₃ R ₄ R ₅ (IVa), in which the radicals R ₃ to R ₅ are the same or different and independently of one another an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical, each with 1 to 16 carbon atoms, preferably 1 to 12 carbon atoms, whereby individual carbon atoms can also be independently substituted by a heterogroup selected from the group -O- and >N-, as well as two or all three radicals to form a chain comprising at least four atoms each can also be connected to each other, provided that the total number of carbon atoms is at least 6, as well - a polar solvent with the formation of formic acid-amine adducts as intermediates of the formula II a NR ₃ R ₄ R ₅ .Xi HCOOH (IIa), (Xi = 0, 4 to 5) where two liquid phases are formed during the reaction in the hydrogenation reactor I, namely a lower phase containing predominantly the polar solvent in which the formic acid-amine adducts are present in enriched form, and an upper phase, containing predominantly the tertiary amine in which the homogeneous catalyst is enriched and the discharge (3) from the hydrogenation reactor I is processed according to the following process steps: Separation of the two liquid phases from the hydrogenation reactor I in a phase separation vessel II, Return of the upper phase (4) from the phase separation vessel II into the hydrogenation reactor I and Sub-phase forwarding (5) from the phase separation vessel (II) into an extraction unit III, in which Residues of catalyst are extracted with the same tertiary amine that was used in the hydrogenation and the tertiary amine loaded with catalyst (6) is recycled into the hydrogenation reactor I, characterized in that the catalyst-free stream containing the formic acid/amine adducts of the formula (IIa) and polar solvent (7) passes it on to a reactor IV, and reacts therein the formic acid-amine adducts of the formula (IIa) at temperatures of 0 to 200 ° C with ammonia or amines of the formula (purple), HN

in which R- _\ and R ₂ have the meaning given for formula (la), whereby via the intermediate with the formula (Va) of the corresponding adduct of formic acid with ammonia or an amine of the formula (purple) NHR _! R ₂ · χ HCOOH (Va) the corresponding formamide of the formula (la) is obtained, and (ii) the two-phase liquid reaction output from the reactor IV (stream 9) in a phase separation vessel V into a formamide of the formula (la) enriched liquid phase (stream 10) and a second liquid phase enriched with tertiary amine (stream 12), the liquid phase enriched with tertiary amine (stream 12) is completely or partially returned to the extraction unit III, and (iii) in a distillation unit VI stream 10 separated by distillation to obtain the formamide of the formula (la), removal of water, recycling of the polar solvent (stream 8) into the hydrogenation reactor I, and the unreacted ammonia or amine of the formula (purple) into reactor IV (stream 11). Method according to claim 1, characterized in that the partial stream of the liquid phase enriched with tertiary amine (stream 12) that is not returned to the extraction unit III is returned to the hydrogenation reactor I. Process according to claim 1 or 2, characterized in that the polar solvent is separated off from the stream 7 loaded with formic acid-amine adducts of the formula (la) before it is fed to the reactor IV. Method according to one of claims 1 to 3, characterized in that the polar solvents used are those selected from the group of methanol, ethanol, propanols, butanols, formic acid esters of the alcohols listed above and/or water. Process according to one of claims 1 to 3, characterized in that the polar solvents used are those from the group of diols, in particular 1,3-propanediol, 2-methyl-1,3-propanediol or 1,4-butanediol or their formic acid esters . Method according to one of claims 1 to 3, characterized in that sulfones, sulfoxides, open-chain or cyclic amides or mixtures thereof are used as polar solvents. Method according to one of claims 1 to 6, characterized in that the upper phase (4) is recycled from the phase separation vessel II into the hydrogenation reactor I at a total pressure of 0.2 to 30 MPa and a temperature of 20 to 200 ° C. 8. The method according to any one of claims 1 to 7, characterized in that the pressure in the hydrogenation reactor I and in the phase separation vessel II is the same or approximately the same. 9. Method according to one of claims 1 to 8, characterized in that the temperature in the hydrogenation reactor I and in the phase separation vessel II is the same or approximately the same.