WO2013092157A1

WO2013092157A1 - Process for preparing formic acid

Info

Publication number: WO2013092157A1
Application number: PCT/EP2012/073930
Authority: WO
Inventors: Peter Bassler; Stefan Rittinger; Daniel Schneider; Donata Maria Fries; Klaus-Dieter Mohl; Joaquim Henrique Teles; Martin Schäfer; Jürgen PASCHOLD
Original assignee: Basf Se; Basf Schweiz Ag
Priority date: 2011-12-20
Filing date: 2012-11-29
Publication date: 2013-06-27
Also published as: ZA201405237B; JP2015505857A; KR20140105577A; CN103998409A; BR112014015187A8; EP2794540A1; BR112014015187A2; RU2014129627A; SG11201402587UA; CA2859128A1; CN103998409B

Abstract

Process for obtaining formic acid by thermal separation of a stream comprising formic acid and a tertiary amine (I), in which a liquid stream comprising formic acid and tertiary amine (I) is produced by combining tertiary amine (I) and a formic acid source, secondary components comprised therein are separated off, formic acid is removed by distillation from the resulting liquid stream in a distillation apparatus, where the bottom output from the distillation apparatus is separated into two liquid phases, and the upper liquid phase is recirculated to the formic acid source and the lower liquid phase is recirculated to the separation of the secondary components and/or to the distillation apparatus, wherein low boilers are removed by distillation from the upper liquid phase and recirculated to the depleted stream.

Description

Process for the preparation of formic acid

Description The present application incorporates by reference the US Provisional Application No. 61 / 577,701 filed December 20, 2011.

The present invention relates to a process for the production of formic acid by thermal separation of a stream comprising formic acid and a tertiary amine (I) which comprises contacting a liquid stream comprising formic acid and tertiary amine (I) by combining tertiary amine (I) and a formic acid source. produced in a molar ratio of 0.5 to 5, 10 to 100 wt .-% of the secondary components contained therein, and from the resulting liquid stream in a distillation apparatus at a bottom temperature of 100 to 300 ° C and a pressure of 30 to 3000 hPa abs removed formic acid by distillation, wherein separating the bottoms discharge from the distillation apparatus into two liquid phases and the upper liquid phase to the formic acid source and the lower liquid phase for separating the secondary components and / or the distillation apparatus returns.

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 currently most common process for the production of formic acid is the hydrolysis of methyl formate, which can be obtained, for example, from methanol and carbon monoxide. The aqueous formic acid obtained by hydrolysis is then subsequently concentrated, for example using an extraction aid such as a dialkyl formamide (DE 25 45 658 A1).

In addition, the recovery of formic acid is also known by thermal cleavage of compounds of formic acid and a tertiary nitrogen base. These compounds are generally acidic ammonium formates of tertiary nitrogen bases, in which formic acid has reacted with the tertiary nitrogen bases beyond the classical salt formation step to form stable, hydrogen-bonded bridged addition compounds. The addition compounds of formic acid and tertiary nitrogen bases can be formed by combining the tertiary nitrogen base and a formic acid source. For example, WO 2006/021, 41 1 discloses the preparation of such addition compounds in general (i) by direct reaction of the tertiary nitrogen base with formic acid, (ii) by transition-metal-catalyzed hydrogenation of carbon dioxide to formic acid in the presence of the tertiary nitrogen base, (iii) by reaction of methyl formate with water and subsequent extraction of the formic acid formed with the tertiary nitrogen base, and (iv) by reaction of methyl formate with water in the presence of the tertiary nitrogen base. The general advantages of using addition compounds of formic acid and tertiary nitrogen bases for the production of formic acid are that on the one hand, the addition compounds formic acid bind strong enough first to the formic acid as free formic acid from the medium, for example, the reaction medium in which the formic acid only by chemical synthesis is formed, or for example to withdraw from a dilute formic acid solution and the formic acid in the form of their addition compounds thereby easier to separate, but on the other hand are weak enough to subsequently dissolve the formic acid from the addition compounds by thermal cleavage again to concentrate and purified to win in free form.

EP 0 001 432 A discloses a process for the recovery of formic acid by hydrolysis of methyl formate in the presence of a tertiary amine, especially an alkylimidazole, to form addition compounds of formic acid and the tertiary amine. The obtained hydrolysis mixture, which contains unreacted methyl formate, water, methanol, addition compounds and tertiary amine, is freed from the low-boiling components methyl formate and methanol in a first distillation column. In a second column, the remaining bottoms product is dewatered. The dewatered bottom product of the second column, which still contains addition compounds and tertiary amine, is then fed to a third column and therein the addition compounds are thermally cleaved into formic acid and tertiary amine. The released formic acid is removed as an overhead product. The tertiary amine accumulates in the bottom and is recycled to the hydrolysis.

DE 34 28 319 A discloses a process for the recovery of formic acid by hydrolysis of methyl formate. The hydrolysis mixture obtained, which contains unreacted methyl formate, water, methanol and formic acid, is freed from the low-boiling components methyl formate and methanol in a first distillation column. The aqueous formic acid obtained in the bottom is then extracted with a higher-boiling amine, in particular a longer-chain, hydrophobic C6 to Cu trialkylamine, in the presence of an additional hydrophobic solvent, in particular an aliphatic, cycloaliphatic or aromatic hydrocarbon, thereby forming a reacted aqueous addition compound of formic acid and the amine. This is dehydrated in a second distillation column. The dewatered addition compound arising in the sump will now be described according to the teaching of

DE 34 28 319 A the top bottom of a distillation column (in Fig. 1 referred to as "K4") supplied and thermally split. The hydrophobic solvent is found both in the top and in the bottom of the column. The gaseous overhead stream contains, in addition to the hydrophobic solvent, especially the released formic acid. This stream is re-liquefied in the condenser. Two phases are formed, namely a polar formic acid phase and a hydrophobic solvent phase. The formic acid phase is removed as product and the solvent phase is recycled as reflux into the column. By the presence of the hydrophobic solvent, a complete cleavage of the adduct can be achieved, which according to the teaching of the DE-Offenlegungsschrift allegedly without decomposition of ant acid takes place. The (almost) formic acid-free bottoms contain the hydrophobic amine as well as the hydrophobic solvent. This is returned to the extraction stage.

EP 0 181 078 A and EP 0 126 524 A describe processes for obtaining formic acid by hydrogenating carbon dioxide in the presence of a transition metal catalyst and a tertiary amine such as a d- to do-trialkylamine to form an addition compound of formic acid and the tertiary amine, working up the hydrogenation with removal of the catalyst and the low boilers, replacement of the amine base by a weaker, higher-boiling tertiary amine, in particular by an alkylimidazole, with separation of the first tertiary amine and subsequent thermal cleavage of the newly formed addition compound in a distillation column. For this purpose, according to EP 0 181 078 A, FIG. 1, the stream containing formic acid and amine is fed into the central region of the column "30". The formic acid released during the thermal decomposition is removed as top product. The weaker, higher-boiling tertiary amine accumulates in the sump and is recycled to the stage of base exchange.

WO 2008/1 16,799 discloses a process for recovering formic acid by hydrogenating carbon dioxide in the presence of a transition metal catalyst, a high boiling polar solvent such as an alcohol, ether, sulfolane, dimethyl sulfoxide or amide, and a polar amine bearing at least one hydroxyl group to form an addition compound of formic acid and the amine. According to the doctrine of

WO 2008/1 16,799, the hydrogenation effluent for thermal cleavage of the addition compound can be fed directly to a distillation apparatus. This may include a distillation column and, if short residence times are desired, also a thin film or falling film evaporator. The released formic acid is removed as an overhead product. The polar amine and the polar solvent and, if appropriate, not separated catalyst collect in the bottom and can be recycled to the hydrogenation stage.

WO 2006/021, 41 1 describes a process for the recovery of formic acid by thermal cleavage of an addition compound of formic acid and a tertiary amine (quaternary ammonium formate), in which the tertiary amine has a boiling point of 105 to 175 ° C. Preferred tertiary amines are alkylpyridines. The special boiling range of the tertiary amines increases the color stability of the formic acid obtained. The addition compound to be used can generally be obtained from the tertiary amine and from an acid source. Advantageously, the discharge from the adduct synthesis is first freed from volatile components and then fed to the thermal cleavage. The thermal cleavage is carried out as usual in a distillation column, wherein the stream containing formic acid and amine as shown in FIG. 1 of WO 2006/021, 41 1 in the central region of the column (C) is supplied. The released formic acid is removed as an overhead product. The tertiary amine, which may optionally still contain residues of formic acid, collects in the bottom and can be recycled to the formic acid source. EP 0 563 831 A discloses an improved process for the thermal cleavage of an addition compound of formic acid and a tertiary amine (quaternary ammonium formate) with the obtainment of formic acid. The addition compound to be used can generally be obtained from the tertiary amine and a formic acid source. Advantageously, the discharge from the synthesis is first freed from volatile components and then fed to the thermal cleavage in the middle of a distillation column. The improvement is essentially to carry out the thermal cleavage of the addition compound in the presence of a secondary formamide, which increases the color stability of the formic acid obtained. The released formic acid is removed as an overhead product. The tertiary amine and the secondary formamide accumulate in the bottom and can be recycled to the formic acid source.

PCT / EP201 / 060770 teaches a process for recovering formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I) which comprises combining a tertiary amine (I) and a formic acid source with a liquid stream containing formic acid and a tertiary amine Amine (I) produced in a molar ratio of 0.5 to 5, 10 to 100 wt .-% of the minor components contained therein, and from the resulting liquid stream in a distillation apparatus at a bottom temperature of 100 to 300 ° C and a pressure of 30 to 3000 hPa abs removed formic acid by distillation, wherein separating the bottom product from the distillation apparatus into two liquid phases, of which the upper liquid phase of tertiary amine (I) is enriched and recycled to the formic acid source and the lower liquid phase is enriched in formic acid and Separation of the secondary components and / or the distillation device rückgefü is heard. The object of the present invention was to find an improved process for the production of formic acid by thermal separation of a stream containing formic acid and a tertiary amine, which has advantages over the prior art and which is able to obtain formic acid in high yield and high concentration. In particular, the improved process should continue to function stably over longer operating times and produce formic acid in consistently high purity. Of course, the process should be as simple as possible and as energy-efficient as possible.

Surprisingly, a process for the recovery of formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I), which at a pressure of 1013 hPa abs has a boiling point higher by at least 5 ° C than formic acid, found in which

(a) producing a liquid stream comprising formic acid and tertiary amine (I) by contacting tertiary amine (I) and a formic acid source and having a molar ratio of formic acid to tertiary amine (I) of from 0.5 to 5; (b) separating from the liquid stream obtained from step (a) from 10 to 100% by weight of the minor components contained therein;

(c) from the liquid stream obtained from step (b) containing formic acid and tertiary amine (I) by distillation in a distillation apparatus at a bottom temperature of 100 to 300 ° C and a pressure of 30 to 3000 hPa abs of formic acid, wherein the in Step (a) to be used tertiary amine (I) and the separation rate in said distillation apparatus so chooses that form two liquid phases in the bottom discharge; (d) separating the bottoms discharge from the distillation apparatus mentioned in step (c) into two liquid phases, wherein the upper liquid phase has a molar ratio of formic acid to tertiary amine (I) of 0 to 0.5 and the lower liquid phase a molar ratio of formic acid to tertiary Amine of (I) from 0.5 to 4; (e) recycling the upper phase of liquid phase separation from step (d) to step (a); and

(F) the lower liquid phase of the phase separation from step (d) to step (b) and / or (c) is recycled, and which is characterized in that

(g) from the upper liquid phase of the phase separation from step (d) in a distillation apparatus at a bottom temperature of 100 to 300 ° C and a pressure of 1 to

1000 hPa abs low boilers, which at a pressure of 1013 hPa abs by at least 5 ° C lower boiling point than the tertiary amine (I), separated by distillation and the depleted of low boilers stream to one of the aforementioned steps (a) to ( f) returns.

The tertiary amine (I) to be used in the process according to the invention in step (a) has at a pressure of 1013 hPa abs a boiling point which is at least 5 ° C. higher than formic acid. The tertiary amine (I) to be used preferably has a boiling point higher than at least 10 ° C., more preferably at least 50 ° C. and very particularly preferably at least 100 ° C., than formic acid. A restriction with regard to an upper limit for the boiling point is not necessary since for the process according to the invention the lowest possible vapor pressure of the tertiary amine (I) is in principle of advantage. In general, the boiling point of the tertiary amine (I) in a, optionally by known methods from vacuum to 1013 hPa abs projected pressure, below 500 ° C. The formic acid source mentioned in step (a) is understood as meaning a stream which comprises formic acid in dilute, contaminated and / or chemically bound form, or which contains a precursor which produces formic acid by chemical reaction. Finally, the formic acid source in step (a) ensures the direct or indirect supply of formic acid. The addition in chemically bound form may be, for example, in the form of a complex, a salt or an addition compound between the formic acid and an amine other than the tertiary amine (I). In principle, all chemical reactions in which formic acid is produced can be considered as chemical reactions. Of particular industrial importance at the time of this patent application, however, the production of formic acid by hydrolysis of methyl formate and the production of formic acid by transition metal-catalyzed hydrogenation of carbon dioxide. Both of these synthesis options are well known in the art and described in various variants and embodiments. Another technically relevant possibility for the production of formic acid by chemical reaction is, for example, the direct reaction of carbon monoxide with water.

In the case of the hydrolysis of methyl formate, usually methyl formate, water and tertiary amine (I) are added to the hydrolysis reactor together or sequentially to trap the formic acid formed by the hydrolysis with the tertiary amine (I) in the form of an addition compound and thus to the hydrolysis equilibrium to withdraw. As a result, a high conversion of methyl formate can be achieved and a particularly advantageous separation of the unreacted water by a subsequent distillation possible.

In the case of transition metal catalyzed hydrogenation of carbon dioxide, the tertiary amine (I) is generally added to the hydrogenation reactor to form a stream containing formic acid and a tertiary amine (I) already in the hydrogenation. Preference is given in step (a) to the generation of the stream comprising formic acid and tertiary amine (I) by hydrolysis of methyl formate in the presence of water and tertiary amine (I). Further preferred in step (a) is the production of the stream comprising formic acid and tertiary amine (I) from dilute formic acid by concentration in the presence of tertiary amine (I). However, particularly preferred in step (a) is the generation of the stream comprising formic acid and tertiary amine (I) by hydrolysis of methyl formate in the presence of water and tertiary amine (I).

The contacting of the tertiary amine (I) and the formic acid source in step (a) may be carried out in the presence of water. In the preferred hydrolysis of methyl formate, water is even needed as a reactant for the reaction of the methyl formate. When the tertiary amine (I) and the formic acid source are combined in the presence of water in step (a), the content of water is generally adjusted by taking the amount of chemically spent water into account such that the liquid Current in addition to formic acid and tertiary amine (I) also contains water.

The bringing together of tertiary amine (I) and the formic acid source can be done in a variety of ways. If the formic acid source is one Stream containing formic acid in dilute, contaminated and / or chemically bound form, so often a mere contact, preferably with mixing, with the tertiary amine (I) is sufficient. This can be done, for example, in pipes which preferably contain suitable mixing internals. Likewise, the contacting can also take place in other devices, such as stirred kettles. Also, a stepped contacting in which the tertiary amine (I) is added to the formic acid source or, conversely, the formic acid source added to the tertiary amine (I) is added is possible and may even be advantageous. If the formic acid source is a material stream from which the formic acid is to be produced only by chemical reaction of several substances, it is generally advantageous to produce the formic acid source only by combining the individual components in the reactor. Suitable reactors are in particular the reactors known to the person skilled in the art for the type of reaction. For example, the tertiary amine (I) may already be initially charged, fed to the formic acid source in parallel with the individual components, supplied in the course of the chemical reaction, or supplied only at the end of the chemical reaction. It is also possible to distribute these individual steps over several reactors. Depending on the exothermicity of the contacting of tertiary amine (I) and the formic acid source, it may be advantageous to cool the device itself or the stream obtained therefrom. Suitable procedures for contacting tertiary amine (I) and the formic acid source can be determined with the usual expertise without much effort.

The liquid stream produced in contacting tertiary amine (I) and a formic acid source in step (a) has a formic acid to tertiary amine (I) molar ratio of 0.5 to 5. The molar ratio is preferably at 1 and preferably at 3. The said molar ratio refers to the total liquid flow, irrespective of whether it is mono- or polyphase.

The liquid stream comprising formic acid and tertiary amine (I) produced in step (a) generally has a concentration of formic acid plus tertiary amine (I) of from 1 to 99% by weight, based on the total amount of the stream. Preferably, said stream has a concentration of formic acid plus tertiary amine (I) of> 5% by weight and more preferably of> 15% by weight and preferably of <95% by weight and more preferably of <90% by weight. % on.

From the liquid stream obtained from step (a) 10 to 100 wt .-% of the minor components contained therein are separated. The stated range of values is based on the concentration of secondary components that the liquid stream generated in step (a) has. In the following, this concentration is called "C-component (stream from step (a))". The secondary component-depleted liquid stream corresponds to the stream fed to the distillation apparatus in step (c). Its concentration is referred to below as "CNebenkom o nents (feed stream to step (c)). "Thus, the above separation of minor components refers to the quotient

₁ C _{minor components} (feed stream to step (c)) [g / L] _wt%

^C Nebenkom _P ones, s (βΐΤΟΤΠ ÜUS step (ii)) [g / L]

In step (b), preferably 20% by weight and more preferably> 30% by weight and preferably <99.99% by weight and more preferably <99.9% by weight of the secondary components are separated off. The term secondary components are all components contained in the liquid stream obtained in step (a), which are neither formic acid nor tertiary amine (I). Examples include water, methanol (in particular in the hydrolysis of methyl formate), dissolved non-hydrolyzed methyl formate (in particular in the hydrolysis of methyl formate), possible degradation products of the tertiary amine (I), dissolved inert gases, homogeneous catalyst (especially in the hydrogenation of Carbon dioxide), dissolved carbon dioxide or dissolved hydrogen (in particular in the hydrogenation of carbon dioxide), solvents, other components.

The manner in which the secondary components are separated is irrelevant to the process according to the invention. Thus, for example, the customary and known methods for the separation of liquid mixtures can be used. First and foremost, distillative separation is mentioned here. In this, the liquid mixture is separated in a distillation apparatus. For example, low-boiling secondary components such as methanol, methyl formate or water can be separated overhead or as a side draw. However, it is also conceivable to separate high-boiling secondary components via bottoms and the formic acid and tertiary amine (I) -containing mixture as side stream or overhead product. In addition to the distillative separation, however, membrane, absorption, adsorption, crystallization, filtration, sedimentation or extraction methods are also possible. Extraction methods are preferred in the concentration of dilute aqueous formic acid and the use of tertiary amines (I), which are not or only partially miscible with water.

Of course, it is also possible to combine several separation steps, which can also be based on different methods. The interpretation of the separation step or the separation steps can be made with the usual expertise.

Between steps (a) and (c), of course, further method steps can be carried out in the method according to the invention in addition to step (b).

From the liquid stream obtained from step (b), formic acid is finally removed by distillation in a distillation apparatus at a bottom temperature of 100 to 300 ° C. and a pressure of 30 to 3000 hPa abs. As distillation devices for this purpose are basically the one skilled in the art for such separation tasks known, or auszulegende with its general skill devices in question.

Usually, the distillation device comprises, in addition to the actual column body with internals, among other things, a top condenser and a bottom evaporator. In addition, this may of course also include other peripheral devices or internal installations, such as a flash tank in the inlet (for example, for separation of gas and liquid in the inlet to the column body), an intermediate evaporator (for example, for improved heat integration of the method) or internals for avoidance or reduction aerosol formation (such as tempered soils, demisters, coalescers or deep bed diffusion filters). The column body can be equipped, for example, with packings, fillers or trays. The number of separation stages required depends in particular on the type of tertiary amine (I), the concentration of formic acid and tertiary amine (I) in the feed of the distillation apparatus in step (c) and the desired concentration or purity of formic acid, and determined by the skilled person in the usual way. In general, the number of required separation stages is at 3, preferably at 6 and more preferably at 7. In principle, there are no limits. For practical reasons, it should be common, usually ^ 70, optionally use -i 50 separation stages or even <30 separation stages.

The stream comprising formic acid and tertiary amine (I) from step (b) can be fed to the column body in the distillation apparatus, for example as a side stream.

Optionally, the addition may be preceded by, for example, a flash evaporator. In order to minimize the thermal load on the supplied stream in the distillation apparatus, it is generally advantageous to supply it to the lower portion of the distillation apparatus. Thus, it is preferred in step (c) to supply the stream comprising formic acid and a tertiary amine (I) in the region of the lower quarter, preferably in the region of the lower fifth and particularly preferably in the region of the lower sixth of the present separation stages, in which case Of course, a direct feed into the swamp is included.

Alternatively, however, it is also preferred in step (c) to feed the said stream from step (b) comprising formic acid and a tertiary amine (I) to the bottom evaporator of the distillation apparatus.

The distillation apparatus is operated at a bottom temperature of 100 to 300 ° C and a pressure of 30 to 3000 hPa abs. The distillation apparatus is preferably operated at a bottom temperature of> 120 ° C., more preferably of> 140 ° C. and preferably of -i 220 ° C. and particularly preferably of <200 ° C. The pressure is preferably about 30 hPa abs, more preferably> 60 hPa abs, and preferably <1500 hPa abs and particularly preferably <500 hPa abs. Depending on the composition and origin of the formic acid and a feed containing tertiary amine (I) to the distillation apparatus, formic acid can be obtained as top and / or side product from the distillation apparatus. If the feed contains boiling components easier than formic acid, it may be advantageous to separate them by distillation as the top product and the formic acid in the side draw. In the case of gases possibly dissolved in the feed (such as, for example, carbon monoxide or carbon dioxide), it is generally also possible to separate the formic acid together with the latter as the top product. Contains the feed higher than formic acid boiling ingredients, formic acid is preferably removed by distillation as a top product, but optionally instead or additionally in the form of a second stream in the side take. The higher boiling than formic acid components are then preferably withdrawn via an additional side stream in this case. If necessary, the side stream with secondary components can be recycled to separate off the secondary components in step (b).

In this way, formic acid can be obtained with a content of up to 100 wt .-%. In general, formic acid contents of 75 to 99.995 wt .-% are easily achievable. The residual content which is missing at 100% by weight is mainly water, and according to the substances introduced into the distillation apparatus in addition to formic acid and the tertiary amine (I), of course other components such as solvents or also possible decomposition products are conceivable. Thus, for example, water may already be present in the feed of the distillation apparatus but may also be formed by decomposition of formic acid itself during the thermal separation in small amounts.

In the production of concentrated formic acid with a content of 95 to 100 wt .-% as top or side product, water is discharged with a part of the eliminated formic acid in a side stream. The formic acid content of this side stream is typically 75 to 95% by weight. The aqueous formic acid from the side stream may optionally be recycled to separate the water in step (b).

However, it is also possible to discharge the water and the split-off formic acid in a common overhead or side stream. The formic acid content of the product thus obtained is then usually at 85 to 95 wt .-%.

In order in particular to suppress the formation of organic degradation products of tertiary amine (I) caused by oxidation as far as possible, it is particularly advantageous when operating the distillation apparatus at pressures below 0.1 MPa abs, the penetration of oxygen by the lowest possible number on connections, nozzles and flanges, by a special care in the installation, by using particularly dense

Flange connections (such as those with comb profile seals or weld lip seals) or nitrogen-covered flange connections should be avoided or at least eliminated. keep languages low. A suitable flange connection is disclosed for example in DE 10 2009 046 310 A1.

The formic acid obtainable by the process according to the invention has a low color number and a high color number stability. In general, a color number of <20 APHA, and in particular even <10 APHA and possibly even <5 APHA can be achieved without problems. Even with several weeks of storage, the color number remains almost constant or increases only insignificantly. Due to the separation according to the invention of the organic degradation products of the tertiary amine (I) in step (b) can be obtained without further effort, a particularly pure formic acid in which said degradation products generally at 70 ppm by weight, preferably at -i 30 wt . ppm and most preferably at 20 ppm by weight. The content of secondary components is extremely low and is usually included

-i 100 ppm by weight, preferably at 50 ppm by weight and most preferably at 25 ppm by weight.

Depending on this, it may also be advantageous to use a plurality of distillation apparatuses in step (c), especially if in addition to the free formic acid and the amine (I) -containing

Still further fractions, for example containing by-products, reaction by-products, impurities and / or formic acid fractions of different purities and concentrations, are to be obtained. Of course, the distillation apparatus for separating the formic acid can also be configured as thermally coupled distillation columns or as a dividing wall column.

In the process according to the invention, the tertiary amine (I) to be used in step (a) and the separation rate in the distillation apparatus mentioned in step (c) are selected such that two liquid phases form in the bottom effluent of the distillation apparatus mentioned in step (c).

The formation of two liquid phases is mainly determined by the chemical and physical properties of the two phases. These, in turn, can be influenced by the choice of the tertiary amine (I) to be used, by the separation rate in the distillation apparatus, but also by the presence of any additional components, such as solvents and their concentrations.

The separation rate is the quotient m acid (feed stream to step (c)) [g I h] - m _{formic acid} (bottoms discharge) [g / h] _

^ _^ (Feed stream to step (c)) [g / h] in which "formic acid (feed stream to step (c))" the amount of formic acid fed per unit time of the distillation apparatus and "formic acid (Surripfaustrag)" corresponds to the amount of formic acid discharged per unit time via the bottom discharge. In general, in this preferred form of the process according to the invention, a separation rate of> 10%, preferably> 25% and particularly preferably> 40%, and in general of <99.9%, preferably <99.5% and particularly preferably <99 is selected , 0%. For example, the separation rate can be easily influenced by the temperature and pressure conditions in the distillation apparatus and by the residence time in the distillation apparatus. It can be determined by simple tests, if appropriate also during operation of the method according to the invention.

The suitability of a tertiary amine (I) or an optionally additionally desired solvent can be determined, for example, in simple experiments in which the phasicity is determined under the intended conditions.

The phase separation can be carried out, for example, in a separate phase separator, which is connected downstream of the distillation apparatus. However, it is also possible to integrate the phase separator in the bottom region of the distillation apparatus, in the region of the bottom evaporator or else in the region of the bottom evaporator circulation. Here, for example, the use of a centrifugal separator is possible or possibly even advantageous.

Since the formation of two liquid phases in addition to the chemical and physical properties of the two phases also influenced by the temperature, which usually miscibility increases with temperature, it may be advantageous to improve the phase separation, this at a lower temperature than to operate the previously selected bottom temperature. For this purpose, the bottoms discharge is usually cooled in an intermediate heat exchanger to a temperature in the range of 30 to 180 ° C. Preferably, the phase separation is carried out at a temperature of> 50 ° C or at a temperature of <160 ° C and more preferably at a temperature of <130 ° C.

The upper liquid phase in step (d) has a molar ratio of formic acid to tertiary amine (I) of generally from 0 to 0.5, preferably> 0.005 and more preferably 0.015, and preferably <0.25 and more preferably <0.125 , The lower liquid phase in step (d) has a molar ratio of formic acid to tertiary amine (I) of generally from 0.5 to 4, preferably> 0.75 and more preferably> 1, and preferably <3.5 and more preferably < 3 on. However, depending on the choice of amine, it may of course also be possible for the formic acid-containing phase to form the upper phase and the amine phase with a molar formic acid-amine ratio of 0 to 0.5, the lower phase. It is important only that there is a phase separation, wherein one phase has a molar ratio of formic acid to tertiary amine generally from 0 to 0.5 and a second phase, a molar ratio of formic acid to tertiary amine generally from 0.5 to 4. Preferably, the upper phase those having a molar ratio of formic acid to tertiary amine generally from 0 to 0.5 and the lower phase those having a molar ratio of formic acid to tertiary amine generally from 0.5 to 4. Furthermore, it is advantageous in the inventive method, to select the separation rate in the distillation apparatus mentioned in step (c) so that the molar ratio of formic acid to tertiary amine (I) in the bottom effluent is from 0.1 to 2.0. Bottom discharge is the entirety of the liquid bottoms condensates which leave the distillation apparatus and are separated into two liquid phases according to step (d). It is irrelevant whether the bottom condensates originate, for example, directly from the bottom of the distillation apparatus itself, the bottom of the bottom evaporator, or from both. The separation rate in the distillation apparatus mentioned in step (c) is preferably selected such that the molar ratio of formic acid to tertiary amine (I) in the bottom effluent is preferably <1.5. As a result of the recycling of the upper liquid phase of the phase separation from step (d) to step (a) in step (e), the tertiary amine (I) contained in the upper liquid phase can be obtained by combining with the formic acid source to further produce a formic acid and tertiary amine ( I) are used. In general, from 10 to 100%, preferably from 50 to 100%, particularly preferably from 80 to 100%, very particularly preferably from 90 to 100% and in particular from 95 to 100% of the upper liquid phase is recycled to step (a).

It has surprisingly been found within the scope of the present invention that the upper liquid phase of the phase separation from step (d) is enriched in particular with low-boiling, organic degradation products of the tertiary amine (I) in comparison with other low-formic acid streams.

The term "organic degradation products of the tertiary amine (I)" is to be understood as meaning compounds which undergo a chemical transformation of the tertiary amine (I) with separation of originally present bonds, recombination of nitrogen-carbon bonds or chemical conversion of the nitrogen-bonded radicals form. Thus, it has been recognized within the scope of the invention that tertiary amines (I) tend, for example, in the presence of formic acid under elevated temperature and elevated pressure, as in individual stages of the process according to the invention, in the corresponding, with the remains of the tertiary Amines (I) z, Ν-substituted formamide and the corresponding, the rest of the tertiary amine (I) containing formate decompose. In the case of a tertiary amine (I) having three identical radicals R, such as Cs to Cs-alkyl, the said decomposition reaction would be, for example, as follows:

(A) in which case the corresponding dialkylformamide and the corresponding alkyl formate form as organic degradation products of the tertiary amine (I). Furthermore, it has been recognized within the scope of the invention that tertiary amines (I), for example, also tend to react in the presence of formic acid and traces of oxygen at elevated temperature, as may be present in individual stages of the process according to the invention the radicals of the tertiary amine (I) N, N-substituted formamide and to decompose, from the aldehyde formed from the other rest. In the case of a tertiary amine (I) having three identical radicals Ch-R, such as, for example, Cs to Cs-alkyl, the said decomposition reaction would be, for example, as follows:

in which case the corresponding dialkylformamide and the corresponding alkanal form as organic degradation products of the tertiary amine (I).

Further, it has been recognized in the invention that tertiary amines (I) in the presence of methyl formate, which is used in the recovery of formic acid by hydrolysis of methyl formate, tend to be methylated to the corresponding methylammonium cation. In the case of a tertiary amine (I) having three identical radicals R, such as Cs to Cs-alkyl, the said methylation reaction would be, for example, as follows, where Me is methyl:

This can back-split, whereby also a tertiary amine with a methyl group is formed. In the case of the above-mentioned system, this reaction equation would be as follows:

[MeNR ₃ ] ⁺ [HCOO] - MeNR ₂ +

According to reaction equation (A), the tertiary amine containing a methyl group then likewise leads to the formation of dialkylformamide:

Organic degradation products of the tertiary amine (I) can lead to impurities of the formic acid to be obtained according to step (c). In addition, organic degradation products of the tertiary amine (I) having a boiling point between the formic acid and the tertiary amine (I) tend to be concentrated in the distillation apparatus used in step (c) and thereby increase the energy consumption in the distillation apparatus.

In the context of the invention, it has been recognized that it is precisely those interfering components which are particularly readily and simply distillative from the said upper liquid phase of the phase separation

Step (d) are separable. In the method according to the invention, therefore, in step (g) from the upper liquid phase of the phase separation from step (d) in a distillation apparatus at a bottom temperature of 100 to 300 ° C and a pressure of 1 to 1000 hPa abs light-lowers which at a pressure of 1013 hPa abs have a boiling point which is lower by at least 5 ° C. than the tertiary amine (I), are separated off by distillation and the stream removed from low-boiling components is recycled to one of the abovementioned steps (a) to (f).

Under low boilers are generally secondary components, as defined in the present specification to understand, which, as mentioned, at a pressure of 1013 hPa abs a lower by at least 5 ° C boiling point than the tertiary amine (I). These preferably have a boiling point which is lower by at least 7 ° C. and more preferably by at least 10 ° C. than the tertiary amine (I). A restriction with respect to a lower limit for the boiling point is not necessary, since particularly low-boiling low boilers can also be removed particularly easily by distillation. In general, however, the boiling point of the low boilers is above 100 ° C. at the stated pressure of 1013 hPa abs.

The low boilers to be removed in the process according to the invention are either already contained in step (a) and contain tertiary amine (I) and / or are first formed in the course of the process up to the present step (g). Thus, for example, it is possible that the tertiary amine (I) fed in step (a) already contains various organic degradation products of the tertiary amine (I) because of its preparation or pretreatment. However, it is also possible and usually also the case that the low boilers to be removed are formed exclusively or in addition to those already supplied in the tertiary amine (I) under appropriate conditions in steps (a) to (c).

The separation of said low boilers in step (g) is carried out by distillation. As distillation devices for this purpose, in principle, those skilled in the art for such separation tasks known or auszulegende with its general skill devices in question. The distillation apparatus is at a bottom temperature of 100 to 300 ° C and a operated at a pressure of 1 to 1000 hPa abs. Preferably, the distillation apparatus at a bottom temperature of> 120 ° C, more preferably of> 140 ° C and preferably from

<220 ° C and more preferably operated by <200 ° C. The pressure is preferably> 5 hPa abs, particularly preferably> 10 hPa abs, and preferably <500 hPa abs and more preferably <250 hPa abs.

The depleted of low boilers stream generally accumulates as bottom product. However, it is also possible to obtain this as a side stream, especially if, in the course of the distillation of the low boilers, any high boilers present, that is to say generally higher than the tertiary amine (I) boiling components, are to be removed.

In the process according to the invention, 0.01 to 50% of the upper liquid phase is generally added to the phase separation from step (d) in step (g). This amount is sufficient, on the one hand to keep the existing low boilers at a sufficiently low level, on the other hand, but also to keep the effort, such as the size of the distillation apparatus or the current energy requirements, within limits. Preference is given to> 0.1% and more preferably> 0.5%, and preferably <20%, particularly preferably <10% and very particularly preferably <5% of the upper liquid phase of the phase separation from step (d) to step (g) ,

By the separation according to the invention of the low-boiling components in step (g), their amount in the process can be kept at a low level. Above all, this also effective and cleverly counteracted, with increasing time accumulation. The concentration of low boilers can thus, based on a stream comprising the bottom product from step (g) and the remaining, not to step (g), the upper liquid phase from step (e), easily to a value of <25 wt .-%, prefers

<15% by weight and particularly preferably <10% by weight. In general, the mentioned concentration is 0,00 0.001% by weight, usually ä 0.1% by weight. The degree of depletion of low boilers _m low _boilers (protected stream) [g / h] _m _% mLeemMsieder (feed stream to step (g)) [g / h]) is generally from 1 to 100%, preferably at 10% , particularly preferably at 50%.

The separated low boilers can be disposed of, for example.

The low-boiling-point-depleted stream obtained in step (g) is recycled to one of the aforementioned steps (a) to (f) in the process of the present invention. In general, from 10 to 100%, preferably from 50 to 100%, particularly preferably from 80 to 100%, very particularly preferably from 90 to 100% and in particular from 95 to 100% of the weight of low-boiling components are used. enriched stream back to steps (a) to (f). It is of course possible to recycle the depleted of low boilers stream, for example, to a selected location, so also, for example, to split and recycle to different locations. The current depleted of low-boiling components is preferably recycled to one of the abovementioned steps (a) to (e). In a particularly preferred embodiment, the stream depleted of low-boiling components is returned to step (a). In another, particularly preferred embodiment, the depleted of low boilers stream back to step (b).

In general, in the recycling of the upper liquid phase of the phase separation from step (d) to step (a), in addition to step (g), of course, also further process steps can be integrated. Also in terms of the nature of the intermediate process steps, in principle, there are no limits. It is also possible to deliberately remove part of the upper liquid phase as so-called "purge stream". Missing or lost amounts of tertiary amine (I) can, of course, be supplemented again by newly supplied tertiary amine (I), this for example via the recycle stream or directly to step (a) or to any point in the process, for example in step (b) or step (c) can be supplied.

In the process according to the invention, according to step (f), the lower liquid phase of the phase separation from step (d) is recycled to step (b) and / or (c). As a result, the formic acid present in the lower liquid phase can likewise be used for the production of formic acid by distillative removal. Depending on the desired embodiment, the lower liquid phase can thus be recycled (i) to step (b), (ii) split to step (b) and (c) or (iii) to step (c). In general, however, the return to step (c) is preferred since this usually places the loading of the lower liquid phase containing formic acid and tertiary amine (I) at a minimum and the material flow in step (b) is not increased quantitatively, which would otherwise be correspondingly greater Dimensioning would result. In general, from 10 to 100%, preferably from 50 to 100%, particularly preferably from 80 to 100%, very particularly preferably from 90 to 100% and in particular from 80 to 100% of the lower liquid phase is recycled to step (b) and / or (c) ,

However, it is also possible, in addition to the mentioned recycling of the lower liquid phase to step (b) and / or (c), also to recycle a further part to step (a). This is advantageous, for example, in the case of the production of formic acid by transition-metal-catalyzed hydrogenation of carbon dioxide, since this generally takes place in the presence of a polar solvent, which also accumulates in the lower liquid phase and thus can be recycled back to step (a).

Of course, further process steps can also be integrated in the recycling of the lower liquid phase. As a non-limiting example may also be mentioned here a purification of the recirculating lower liquid phase or of the tertiary amine (I) contained therein and / or the formic acid contained therein of undesirable accompanying substances, Reaction by-products or other impurities. Also in terms of the nature of the intermediate process steps, in principle, there are no limits. It is also possible to purposely discharge a portion of the lower liquid phase as a so-called "purge stream" in order to remove, for example, unwanted accompanying substances, reaction by-products or other impurities.

The tertiary amine (I) which is preferably used in the process according to the invention has the general formula (Ia) NR-R ² R ³ (Ia), in which the radicals R ¹ to R ^{3 are} identical or different and independently of one another are 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 can also be substituted independently of one another by a hetero group selected from the group -O- and> N- and two or all three radicals may also be linked together to form a chain comprising at least four atoms each. Examples of suitable amines are:

Tri-n-propylamine (Sdpioi3 hPa = 156 ° C), tri-n-butylamine, tri-n-pentylamine, tri (3-methylbutyl) amine, 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, tri- (2-propylheptyl) amine.

Dimethyl-decylamine, dimethyl-dodecylamine, dimethyl-tetradecylamine, ethyl-di- (2-propyl) -amine (5-propeno hPa = 127 ° C.), di-n-octyl-methylamine, di-n-hexyl-methylamine, n-hexyl- (2-methylpropyl) -amine, di-n-hexyl- (3-methylbutyl) -amine, methyl-di- (2-ethylhexyl) -amine, di-n-hexyl- (1-methyl-n -hexyl) amine, di-2-propyl-decylamine.

Tricyclopentylamine, tricyclohexylamine, tricycloheptylamine, tricyclooctylamine and theirs

by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups substituted derivatives.

Dimethylcyclohexylamine, methyldicyclohexylamine, diethylcyclohexylamine, ethyldicyclohexylamine, dimethylcyclopentylamine, methyldicyclopentylamine, methyldicyclohexylamine. Triphenylamine, methyldiphenylamine, ethyldiphenylamine, propyldiphenylamine, butyldiphenylamine, 2-ethylhexyldiphenylamine, dimethylphenylamine, diethylphenylamine, dipropylphenylamine, dibutylphenylamine, bis (2-ethyl -hexyl) -phenylamine, tribenzylamine, methyl- dibenzylamine, ethyl-dibenzylamine 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, 5-di- (1-piperidyl) -pentane, N-Ci-bis-Ci2-alkyl-piperidine, N, N-di-Ci-bis-Ci2-alkyl-piperazines, N-Ci-bis-Ci2 Alkyl-pyrrolidines, N-Ci-bis-Ci2-alkyl-imidazoles and their by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2- Methyl-2-propyl groups substituted derivatives.

1, 8-diazabicyclo [5.4.0] undec-7-ene ("DBU"), 1, 4-diazabicyclo [2.2.2] octane, N-methyl-8-azabicyclo [3.2.1] octane ("Tropan "), N-methyl-9-azabicyclo [3.3.1] nonane (" garnetan "), 1 -

Azabicyclo [2.2.2] octane ("quinuclidine"), 7,15-diazatetracyclo [7.7.1.0 ² ' ⁷ .0 ^{10 15} ] heptadecane ("Spartein").

Of course, mixtures of different tertiary amines (I) can also be used in the process according to the invention. Of course, then all tertiary amines (I) used are of course at a pressure of 1013 hPa abs a boiling point higher by at least 5 ° C than formic acid.

Among the tertiary amines of the general formula (Ia) described above, those are preferred in which the radicals R ¹ to R ^{3 are} identical or different and independently of one another are an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic radical each having 1 to 16 carbon atoms, preferably 1 to 12 carbon atoms represent, wherein 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 to form one at least four Atoms, saturated chain can also be interconnected.

Preferably, at least one of the radicals on the alpha carbon atom, ie on the carbon atom bonded directly to the amine nitrogen atom, carries two hydrogen atoms.

In the process according to the invention, particular preference is given to using as tertiary amine (I) an amine of the general formula (Ia) in which the radicals R ¹ to R ^{3 are} independently selected from the group C 1 to C 12 alkyl, C to Cs Cycloalkyl, benzyl and phenyl. Very particularly preferably, in the process according to the invention, the tertiary amine (I) used is a saturated amine of the general formula (Ia).

In particular, in the inventive process as a tertiary amine (I) an amine of the general formula (la) a, in which the radicals R ¹ to R ^{3 are} independently selected from the group Cs to Cs-alkyl, in particular tri-n- pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, dimethylcyclohexylamine, methyldicyclohexylamine, dioctylmethylamine and dimethyl-decylamine. In another embodiment, amines are used which are attached to the alpha carbon atom (the carbon atom bonded directly to the amine nitrogen atom), to the beta carbon atom (the second carbon atom bonded by the amine nitrogen atom) or the gamma carbon atom (the third to the amine nitrogen atom bonded carbon atom) have a branching. Here are alkyl, aryl and other substituents in principle conceivable, preferred are alkyl groups such as methyl, ethyl or propyl groups, or piperidyl groups. In this embodiment, particular preference is given to N-ethylpiperidine, tri (3-methylbutyl) amine, di-n-hexyl (2-methylpropyl) amine, di-n-hexyl (3-methylbutyl) amine, methyl di (2-ethylhexyl) amine, di-n-hexyl (1-methyl-n-hexyl) -amine, di-2-propyl-decylamine, methyl-dicyclohexylamine, 1,5-di- (1-piperidyl ) pentane.

The formic acid and tertiary amine (I) containing streams formed in the process according to the invention, in addition to the free formic acid and the free tertiary amine (I) in a mixture containing the formic acid and the tertiary amine (I) in various other forms. The type and amount of the individual forms may, depending on the present conditions, such as the relative proportions of formic acid to tertiary amine (I), the presence of other components (for example, water, solvents, by-products, impurities) and thus ultimately also the concentration of formic acid and tertiary amine (I), the temperature and the pressure be different. For example, mention may be made of the following conceivable forms:

Ammonium formate (molar ratio of formic acid to tertiary amine (I) of 1) or formic acid-rich adduct with the tertiary amine (I) (molar ratio of formic acid to tertiary amine (I) of> 1).

- ionic liquid.

For carrying out the method according to the invention, the type and quantity of the individual forms is irrelevant. The liquid stream from step (b) to be fed to step (c) may optionally also contain so-called solvents.

If a solvent is to be used, it is advantageous, in particular in the case of the preferred variant in which two liquid phases form in the bottom discharge from the distillation apparatus mentioned in step (c), that this is not or only slightly with the tertiary amine (I), but is well miscible with the formic acid-containing amine phase and thus in step (d) is more likely to be found in the lower liquid phase. To this end, has established itself as yardstick, an electrostatic factor, abbreviated EF, obtained from preferably> 200 x 10 ^"30 Cm at 25 ° C, exposed. The electrostatic factor EF is defined as the product of the relative Dielekt- s rizitätskonstante _r and the dipole moment μ of the solvent (see, for example, C.

Reichardt, "Solvent and Solvent Effects in Organic Chemistry", 3rd edition, Wiley-VCH Verlag GmbH & Co KGaA, Weinheim 2003, Chapter 3.2, page 67 below to page 68 above). This preferred value ensures that the optional solvent has a certain minimum polarity and in step (d) is miscible with the lower liquid phase.

The use of solvents, depending on the particular system (for example, type of tertiary amine (I), concentrations, temperature, pressure and the like), for example, improve the separation of the two liquid phases.

Suitable classes of substances which are particularly suitable as an optional solvent are in particular formic acid esters, diols and their formic acid esters, polyols and their formic acid esters, sulfones, sulfoxides, open-chain or cyclic amides and mixtures of the substance classes mentioned.

Examples of suitable diols and polyols are ethylene glycol (EF =

290.3 · 10 ³⁰ cm), diethylene glycol (EF = 244.0 · 10 ^"30 cm), triethylene glycol, polyethylene glycol, 1, 3-propanediol (EF = 285.6 · ^{10" 30} cm), 2-methyl- 1, 3-propanediol, 1, 4-butanediol (EF = 262.7 · ^10-30 Cm), dipropylene glycol, 1, 5-pentanediol (EF = 212.5 · 10 ^"30 Cm), 1, 6-hexanediol and Diols and polyols can be esterified in the presence of formic acid owing to their OH groups, in the process according to the invention especially in step (c) in the thermal separation of the stream comprising formic acid and tertiary amine (I) in said distillation apparatus. Since the resulting formic acid esters show a very similar phase behavior, they are generally equally suitable as solvents, and the water formed in the esterification is harmless in the thermal separation this small one Quantities can be separated in the distillation apparatus via a side draw.

Suitable sulfoxides are dialkyl sulfoxides, for example, preferably d- to C6 dialkyl sulfoxides, particularly dimethyl sulfoxide (EF = 627.1 · 10 ^"30 cm) called. Suitable chain or cyclic amides are for example formamide (EF =

1243.2 · 10 ³⁰ cm), N-methylformamide (EF = 2352.9 · 10 ^"30 cm), Ν, Ν-dimethylformamide (EF = 396.5 · 10 ³⁰ cm), N-methylpyrrolidone (EF = 437.9 x 10 ^"30 cm), acetamide and N-methylcaprolactam. But depending on it can also be advantageous to use just a rather non-polar solvent with <200 x 10 ^"30 Cm, related to 25 ° C. Non-polar solvents may optionally reduce the concentration of formic acid in the upper liquid phase.

However, the process according to the invention is preferably carried out without addition of a solvent. In a preferred variant of the process according to the invention, in step (a), in the presence of water, a formic acid source which contains methyl formate and from which a liquid stream comprising formic acid, tertiary amine (I) and methanol is obtained by hydrolysis of methyl formate. About step (b) is separated in this variant then usually in addition to excess water and the resulting methanol from the hydrolysis of methyl formate. The separated methanol can then be used, for example, again in the synthesis of methyl formate. Since methanol has a significantly lower boiling point than water and thus is more easily separable by distillation from a corresponding mixture containing methanol, water, formic acid and tertiary amine (I), it is advantageous in this variant, methanol as a separate stream from the from step ( a) separate the stream obtained.

If methanol is separated off in the variant mentioned in the preceding paragraph, it is particularly advantageous to separate a further stream containing unreacted methyl formate in step (b) and to recycle the latter to step (a). As a result, the yield of formic acid based on the methyl formate used can be significantly increased. Since methyl formate has a significantly lower boiling point than methanol and thus is even more easily separable by distillation from a corresponding mixture containing methyl formate, methanol, water, formic acid and tertiary amine (I), it is advantageous in this variant, methyl formate and methanol as a separate Separate streams from the stream obtained from step (a). This can be done, for example, in two separate distillation apparatuses, in which methyl formate is separated off in the first column and methanol in the second column. However, it is also possible, for example, to separate both components in a single distillation device in separate streams. Methyl formate can be obtained, for example, as a top product and methanol as a side stream product.

The hydrolysis of methyl formate in step (a) is usually carried out in a temperature range of 80 to 150 ° C and a pressure range of 0.4 to 25 MPa abs. As a device for carrying out the hydrolysis in step (a), in principle all devices can be used in which an exothermic conversion of fluid streams is possible. As examples are about

Rührkessel, tubular reactors or tube bundle reactors, each without internals or with internals (such as beds, packing, perforated plates and the like) called. The hydrolysis is preferably carried out with heat removal or adiabatic. In another preferred variant of the process according to the invention, in step (a) a formic acid source is used which contains carbon dioxide, hydrogen and a homogeneous catalyst and from which a liquid stream containing formic acid and tertiary amine (I) is obtained by homogeneously catalyzed hydrogenation of carbon dioxide becomes. Was step (a) also carried out in the presence of water and / or methanol, which is a particularly preferred embodiment of this variant, then separated usually in step (b) water and / or methanol again, wherein in the case of the separation of Methanol this preferably back to step (a) is returned. Methanol and water are used in this variant primarily as polar solvents.

The specific steps and process features for the homogeneous-catalyzed hydrogenation of carbon dioxide to formic acid in the presence of water and methanol are in

PCT / EP 201 1/060012.

The homogeneous catalyst used here is preferably an organometallic complex compound containing an element from the 8th, 9th or 10th group of the periodic table. The complex compound furthermore preferably contains at least one phosphine group having at least one unbranched or branched, acyclic or cyclic aliphatic radical having 1 to 12 carbon atoms, where individual carbon atoms may also be substituted by> P-. The hydrogenation is preferably carried out at 20 to 200 ° C and 0.2 to 30 MPa abs. The discharge from the hydrogenation stage (a) is preferably biphasic. The upper phase contains tertiary amine (I) and homogeneous catalyst, the lower phase formic acid, tertiary amine (I), water, methanol and also homogeneous catalyst. Both phases are separated and the tertiary amine (I) and homogeneous catalyst containing upper phase recycled to the hydrogenation stage (a). The lower phase, containing formic acid, tertiary amine (I), water, methanol and homogeneous catalyst, is preferably extracted with tertiary amine (I) in order to extract the majority of the homogeneous catalyst present therein and also together with the tertiary amine (I) to the hydrogenation stage ( a) return. The remainder of the lower phase containing formic acid, tertiary amine (I), water and methanol is then fed to step (b) to separate methanol and water and organic degradation products of the tertiary amine (I) as described above.

With regard to the further work-up, reference should also be made to the specific steps and process features mentioned in PCT / EP 201 1/060012.

1 shows a simplified block diagram of a general embodiment of the method according to the invention. In it, the individual letters have the following meaning:

A = apparatus for producing a formic acid and tertiary amine (I)

containing stream

B = device for the separation of by-products

C = distillation apparatus

D = phase separation vessel

F = distillation apparatus

Via stream (1), a formic acid source and, via stream (8c), tertiary amine (I) are fed to device A for producing a stream containing formic acid and tertiary amine (I). As already explained above, the formic acid source to be supplied may contain, for example, formic acid in chemically bound form or a precursor which is produced in device A formic acid by chemical reaction. Stream (2) containing formic acid and tertiary amine (I) is withdrawn from device A and fed to device B for separation of minor components. This may, for example, be a distillation apparatus in which low-boiling secondary components are removed by distillation. Separated minor components are taken via stream (3). Through stream (4), the concentrated formic acid and tertiary amine (I) stream of the distillation apparatus C is supplied. This is the distillative removal of formic acid as stream (5). The bottom of the distillation apparatus C is fed to the phase separation vessel D as stream (6) for phase separation. The lower liquid phase is recycled as stream (7) to the distillation apparatus C. The upper liquid phase is withdrawn as stream (8a) and fed to the distillation apparatus F. In this low boilers are removed by distillation as stream (8z) and the depleted of low boilers stream as stream (8c) returned to the device A. Fig. 2 shows a simplified block diagram of a modified preferred embodiment in which only a portion of the upper liquid phase from the phase separation vessel D is fed to the distillation apparatus F for the removal of low-boiling components. The other part is returned via current (8b) and subsequently (8c) directly to the device A. The recycling of the low-boiling-point-depleted stream from the distillation apparatus F can be made to other locations in the process. Thus, by means of the streams (8y (i)) to (8y (iii)) shown in dashed lines, FIG. 3 shows, for example, recirculations to the device A, to the device B and to the phase separation vessel D. The streams shown in dashed lines are to be understood as alternatives, each individually or in combination. However, the recirculation can also take place, for example, at other points of the process, for example in the distillation apparatus C.

4 shows a preferred embodiment in which the separation according to the invention of the low boilers according to the variant shown in FIG. 2 is combined with a special variant for the separation of the secondary components. This particular variant is advantageous above all in the presence of water as a secondary component and makes it possible in one step to separate organic degradation products of the tertiary amine (I) which form in the process according to the invention, without passing them on to a significant extent into the distillation apparatus C. In FIG. 4, the additional letter E has the following meaning: E = phase separation vessel

The formic acid, tertiary amine (I) and water-containing stream (2) is withdrawn from device A and fed to device B for the separation of water and organic degradation products of the tertiary amine (I). This may, for example, be a distillation apparatus. Separated water and organic degradation products of the tertiary amine (I) are removed via stream (3) and fed to the phase separation vessel E. In it, two liquid phases are formed. The lower, water-containing liquid phase is called Current (3x) returned to the device A. The upper liquid phase enriched in organic degradation products of the tertiary amine (I) is taken off as stream (3y) and discharged from the process. Through stream (4), the concentrated formic acid and tertiary amine (I) stream of the distillation apparatus C is supplied.

In the area of the distillation apparatus C and the phase separation D, various embodiments are possible. They differ not only in whether the phase separation takes place in a separate container or integrated in the bottom of the distillation column, but also in the place of addition of the formic acid and tertiary amine (I) containing stream to the distillation device and in the current flow between the column container and the bottom evaporator and the withdrawal point of the bottom discharge. The in PCT / EP-Az. 201 1 / 060,770 in Figs. 2 to 7 illustrated and described in the text embodiments are also applicable in the context of the preferred method according to the invention. Two preferred embodiments of preferred fields of application of the method according to the invention are described below.

Recovery of formic acid by hydrolysis of methyl formate A preferred embodiment for the recovery of formic acid by hydrolysis of methyl formate is shown in Fig. 5 by a simplified block diagram.

In this, the individual letters have the following meaning: A = apparatus for the hydrolysis of methyl formate and production of a formic acid, tertiary amine (I) and water-containing stream

B = distillation apparatus for the separation of methyl formate, methanol and

water

C = distillation apparatus for the production of formic acid

D = phase separation vessel

F = distillation apparatus

Methyl formate (streams (1 a) and (3b)), water (streams (1 b) and (3c)) and tertiary amine (I) (stream (8c)) are fed to the apparatus A. Hydrolysis of methyl formate produces a formic acid, tertiary amine (I), methanol, water and methyl formate-containing stream which is taken as stream (2) from the apparatus A and fed to the apparatus B. The methyl formate conversion and thus the composition of the stream (2) depends primarily on the relative feed amounts of the three feed streams methyl formate, water and tertiary amine (I) to the apparatus A, the type of tertiary amine (I) used, the residence time and the reaction temperature from. The conditions which are meaningful for the respective reaction system can easily be determined by the person skilled in the art, for example by preliminary experiments. In electricity (2) is the Molar ratio of formic acid to tertiary amine (I) usually 0.5 to 5, preferably 0.5 to 3, of course, deviations from this range are possible.

In the distillation apparatus B of stream (2) now unreacted Methylform iat (stream (3b)), formed in the hydrolysis of methanol (stream (3a)) and water and organic degradation products of the tertiary amine (I) (stream (3c)) separated. Stream (3b) containing the unreacted starting materials methyl formate is recycled to device A. The methanol separated off via stream (3a) can be reused, for example, for the preparation of methyl formate. Current (3c) is also returned to device A. Formic acid and tertiary amine (I) are taken off via stream (4). This also contains residual quantities

Water. Depending on the design of the process, these may constitute a few percent by weight or even a few tens of percent by weight of the stream (4). The water content in stream (4) is preferably ^ 20% by weight, more preferably ^ 10% by weight and very particularly preferably-5% by weight. The molar ratio of formic acid to tertiary amine (I) is not or only slightly changed by the distillation apparatus B, so that this in stream (4) is usually 0.5 to 5, preferably 0.5 to 3, which of course also deviations are possible from this area.

Stream (4) is fed to the distillation apparatus C. In it, the formic acid is removed by distillation via stream (5) as overhead product, via stream (5a) as side product and / or via stream (5b) as side product. Depending on the framework conditions, ie above all the composition of the feed stream (4) to the distillation apparatus C and the desired purity of formic acid, in the present embodiment formic acid can be obtained as stream (5) overhead or as stream (5a) as side product. Water-containing formic acid is then taken off as side product via stream (5a) or (5b). In individual cases, it may even be sufficient to remove formic acid or hydrous formic acid only via stream (5) as the top product. Depending on the specific embodiment, the side stream (5b) or even both side streams (5a) and (5b) can thus be dispensed with. Of course, the distillation apparatus C can also have the embodiments disclosed in FIGS. 2 to 7 of PCT / EP-A-1 201 07070.

The bottom product of the distillation apparatus C is fed as stream (6) to the phase separation vessel D. Alternatively, the phase separator D can also be integrated into the distillation apparatus C. In the phase separation vessel D, the bottom product is separated into two liquid phases. Between the distillation apparatus C and the phase separation vessel D may optionally be interposed, for example, a heat exchanger for cooling the withdrawn bottom stream, for example. Although a lower phase separation temperature generally leads to a somewhat better separation in terms of the formic acid content, but causes due to the use of a heat exchanger additional effort and energy consumption. Advantages and disadvantages should therefore be weighed in each case. The lower liquid phase from the phase separation vessel D is recycled via stream (7) to the distillation apparatus C. In this case, the lower liquid phase can also be preheated. This can be done by an energetically separate heat exchanger or by heat integration with the heat exchanger used for cooling the bottoms discharge from the distillation apparatus C or a combination of both.

The upper liquid phase from the phase separation vessel D is removed via stream (8a). A partial stream (8x) is fed to the distillation apparatus F. In this, low boilers are distillatively removed as stream (8z) and the stream depleted of low boilers recycled as stream (8y) and subsequently (8c) to the apparatus A. The remaining, other partial stream (8b) is returned directly to the device A via stream (8c). In another preferred embodiment for the production of formic acid by hydrolysis of methyl formate, the methyl formate stream (1a) is introduced into the distillation apparatus B according to FIG. This embodiment is generally advantageous when the current as (1 a) available methyl formate is still contaminated with residual amounts of methanol, for example by a preceding methyl formate iat synthesis step with partial methanol conversion and incomplete workup of the methyl formate. As a result of the direct supply of stream (1 a) to the distillation apparatus B, the methanol contained can thus be separated off as stream (3a) and recycled, for example, to the methyl formate synthesis stage. This variant makes it possible to dispense with completely methyl formate / methanol separation in the methyl formate synthesis stage and thus to save an entire distillation column and thus energy during operation.

In a further preferred embodiment for the production of formic acid by hydrolysis of methyl formate, both the methyl formate stream (1a) and the water stream (1b) are introduced into the distillation apparatus B according to FIG. With regard to the water flow (1 b), this embodiment is generally advantageous when hot condensate or steam is available as a water source, as this can be used in the distillation device B, the thermal energy stored therein.

For the sake of completeness it should be mentioned that in a further embodiment it is of course also possible to add the methyl formate stream (1a) into the device A, but the water stream (1b) into the distillation device B. Dies For example, it is advantageous if low pressure excess steam is available.

Of course, in the production of formic acid by hydrolysis of methyl formate, it is also possible and even advantageous to combine the variants shown in FIGS. 5 to 7 with the special separation of the secondary components shown in FIG. 4. By way of example, this is shown as a combination of the variants of FIGS. 4 and 5 in FIG. 8.

It is likewise possible, in the variants shown in FIGS. 5 to 8, similar to that already mentioned in connection with FIG. 3, not only to recycle the light-depleted stream from the distillation apparatus F to the apparatus A, but also or exclusively to it to lead other bodies in the proceedings. Thus, FIG. 9 is shown by the dashed lines shown in FIG. For example, (8y (i)) to (8y (iv)) represent repatriations to device A, device B (two different addition sites), and phase separation vessel D. The streams shown in dashed lines are to be understood as alternatives, each individually or in combination can. Of course, not shown returns, such as in the distillation device C, also conceivable.

In the variants of FIGS. 5 to 9, with regard to the embodiment of the distillation apparatus B, specific variants with one, two or even three distillation columns are possible. Fig. 10a shows an embodiment with a distillation column. 10b to 10e show different embodiments with two distillation columns. Fig. 1 1 a to 1 1 c show different embodiments with three distillation columns. Preferred for the embodiment of the distillation apparatus B are the variants with one or two distillation columns. For the sake of completeness, it should be mentioned that, in particular in the embodiments with one or two distillation columns, these can also be configured as a thermally coupled or dividing wall column.

Production of formic acid by hydrogenation of carbon dioxide

A preferred embodiment for the recovery of formic acid by hydrogenation of carbon dioxide is shown in Fig. 12 by a simplified block diagram.

In it, the individual letters have the following meaning:

A = Device for the hydrogenation of carbon dioxide and production of formic acid, tertiary amine (I) and water-containing stream

A1 = hydrogenation reactor

A2 = phase separation vessel

A3 = extraction unit

B = distillation apparatus for the separation of methanol, water and

organic degradation products of the tertiary amine (I)

C = distillation apparatus for the production of formic acid

D = phase separation vessel

F = distillation apparatus carbon dioxide (stream (1 a)), hydrogen (stream (1 b)) and tertiary amine (I) (stream (8c)) are fed to the hydrogenation reactor A1 in device A. In the hydrogenation reactor A1, the hydrogenation is carried out in the presence of a homogeneous catalyst and of water and methanol as solvent to form a formic acid, tertiary amine (I), methanol, water and homogeneous catalyst-containing stream (2a). This is fed to the phase separation vessel A2, in which form two liquid phases. The upper liquid phase containing tertiary amine (I) and

Homogeneous catalyst is recycled via stream (2b) to the hydrogenation reactor A1. The lower liquid phase containing formic acid, tertiary amine (I), water, methanol and also mogenkatalysator, is passed via stream (2c) to the extraction unit A3. In this, the residues of the remaining homogeneous catalyst are largely extracted via the supplied as stream (8) tertiary amine (I) and recycled together with the tertiary amine (I) as stream (2d) to the hydrogenation reactor A1. As stream (2), thus, a formic acid, tertiary amine (I) and water-containing stream are obtained and supplied to the distillation apparatus B.

In the distillation apparatus B, methanol (stream (3b)) and water and organic degradation products of the tertiary amine (I) (stream (3c)) are separated from stream (2). Stream (3b) containing methanol is recycled to the hydrogenation reactor A1 in device A. Stream (3c) is also recycled to the hydrogenation reactor A1 in apparatus A. Formic acid and tertiary amine (I) are removed via stream (4) and passed to the distillation apparatus C. With regard to the process steps relating to the distillation apparatus C, the phase separation vessel D and the distillation apparatus F, reference is made to the above description for the recovery of formic acid by hydrolysis of methyl formate.

Of course, it is also possible in the recovery of formic acid by hydrogenation of carbon dioxide, similar to that already mentioned in connection with FIG. 3, to recycle the stream of light ends from the distillation apparatus F not only to the apparatus A but also or exclusively to others To lead in the procedure.

The process according to the invention enables the recovery of formic acid in high yield and high concentration by thermal separation of a stream containing formic acid and a tertiary amine. By the separation according to the invention of low-boiling components from the upper liquid phase of the phase separation of the bottom discharge from the thermal separation of the formic acid and tertiary amine-containing stream, their concentration in the system can be kept at a low level. This effectively avoids creeping up of low boilers and thus effectively counteracts a slow increase in energy consumption in the distillation apparatus for thermal separation of the formic acid and tertiary amine-containing stream and a slow deterioration of formic acid quality due to increasing low-level contamination. The process according to the invention thus enables a very stable operation over a longer period of operation while maintaining the constant high purity of the formic acid produced. The formic acid to be obtained has a low color number and a high color stability. The process is simple, reliable and energy-efficient feasible.

The process according to the invention can also be used particularly advantageously in conjunction with the hydrolysis of methyl formate as the formic acid source and has technical and economic advantages over the currently industrially practiced methylformate hydrolysis with subsequent dewatering by means of an extraction aid or two-pressure distillation. Examples

Laboratory Equipment 1 (for Comparative Example 1)

Laboratory equipment 1 was used to study the continuous process without application of the present invention. The simplified block diagram of laboratory equipment 1 is shown in FIG. 13. In it, the individual letters have the following meaning:

= Stirred tank (volume 0.3 L, electrically heated)

= each tubular reactor (inner diameter 80 mm, length 1200 mm,

filled with 2 mm glass balls, electrically heated)

= Mixing container (volume 5 L)

= Container (volume 5 L)

Distillation device with column body (inside diameter 55 mm, equipped with two tissue packs, each with 1, 3 m packing height and a specific surface area of 750 m ² / m ³ , wherein the feed of stream (2) was between the two tissue packs), oil-heated falling film evaporator and Condenser and adjustable reflux divider at the top of the column

Distillation apparatus with column body (inside diameter 55 mm, equipped with 12 bubble trays in the stripping section and 10 bubble trays in the

Reinforcement part, wherein the inflow of electricity (3d) between the two

Parts and the inlet of stream (5b) in the stripping section was), oil-heated falling film evaporator and condenser and adjustable reflux divider at the top of the column

= Column body (inner diameter 43 mm, equipped with a

Tissue packing above the sump with a packing height of 0.66 m and a specific surface area of 500 m ² / m ³ and a further fabric packing with a packing height of 1, 82 m and a specific surface area of 750 m ² / m ³ , wherein the Side stream (5b) between the two fabric packs) and condenser and adjustable reflux divider at the top of the column

= Oil-heated falling film evaporator

= Separate phase separation vessel (volume 0.3 L, oil-heated)

The apparatus and lines consisted of a nickel-based alloy with the material number 2.4610. The mass flow was measured using a Coriolis flowmeter. Laboratory system 1 was operated continuously. In all experiments in the laboratory system 1, the content of formic acid was determined in each case by potentiometric titration with 0.5 N NaOH in water and the content of water according to Karl Fischer. determined. All other organic components were determined by gas chromatography.

Laboratory plant 2 (for example 2 according to the invention)

Laboratory equipment 2 is the laboratory equipment 1 extended by a separate phase separation vessel for electricity (3c) and was used to study the continuous process using the present invention. The simplified block diagram of laboratory equipment 2 is shown in FIG. 14. Therein the supplemented letter has the following meaning:

E = phase separation vessel

F = distillation apparatus with column body (inner diameter 30 mm,

equipped with 1 m Sulzer CY packing (750 m ² / m ³ ), with the feed of stream (9a) below the packing), oil-heated bottoms vessel and adjustable reflux divider at the top of the column

Incidentally, reference is made to the description of the laboratory 1.

example 1

(Comparative Example)

Example 1 was carried out in the laboratory 1. About stream (1 a) 1760 g / h of methyl formate were metered via metering pumps and 849 g / h of water in the stirred tank A1 via stream (1 c). Stream (1 c) was taken from the mixing tank X, which was composed of fresh water via stream (1 b) and recycle water from the distillation apparatus B2 via stream (3c). Current (1 b) was chosen such that the sum of current (1 b) and current (3c) gave the desired current (1 c). The stirred tank A1 was operated at 1 10 ° C and 1, 3 MPa abs. The discharge was passed in tubular reactor A2, which was also operated at 1 10 ° C and 1, 3 MPa abs. The output of tubular reactor A2 was passed in tube reactor A3. In these 1964 g / h of tri-n-hexylamine were fed via stream (8a). The output of tube reactor A3 was passed in tube reactor A4. In these, an additional 1661 g / h of tri-n-hexylamine were fed via stream (8b). The streams (8a) and (8b) were taken from the container Y, which was used to distribute the recirculated via stream (8) tri-n-hexylamine on the two tube reactors A3 and A4. The operation of tubular reactor A3 was carried out at 1 15 ° C and 1, 3 MPa abs, of tubular reactor A4 at 1 10 ° C and 1, 3 MPa abs. Stream (2) was a product mixture containing 58.4% by weight of tri-n-hexylamine, 16.4% by weight of formic acid, 12.3% by weight of methanol, 7.8% by weight of water and 6 , 9 wt .-% methyl formate won.

Stream (2) was depressurized and passed into the column body of the distillation apparatus B1. At a top pressure of 0.18 MPa abs and a reflux ratio of 2.5, the top product Stream (3ab) was stripped off a mixture containing formed methanol and unreacted methyl formate. The bottom product obtained as stream (3d) was 5012 g / h of a mixture. retaining 71, 2 wt .-% of tri-n-hexylamine, 9.1 wt .-% water, 20.7 wt .-% formic acid and 0.1 wt .-% methanol. The bottom temperature in B1 was 1 17 ° C.

Stream (3d) was sent to the column body of the distillation apparatus B2. In addition, via stream (5b), 277 g / h of the side draw off from the column body was fed to the distillation apparatus C1, which contained 79.3% by weight of formic acid and 16.6% by weight of water. The top product of the distillation apparatus B2 was at a head pressure of

0.10 MPa abs and a reflux ratio of 0.71 450 g / h of stream (3c) deducted.

Stream (3c) containing 98.8% by weight of water and 0.3% by weight of formic acid was fed to the mixing vessel X for recycling to the stirred tank A1.

Via stream (4) were 482 g / h of a mixture containing 75.3 wt .-% of tri-n-hexylamine, 26.0 wt .-% formic acid and 1, 2 wt. As bottom product at a bottom temperature in B2 of 160 ° C 4821 g / h .-% water and fed from above onto the evaporator C2. The evaporator C2 and the column body C1 were operated in vacuum. The temperature at the lower outlet of the evaporator C2 was 161 ° C. The gaseous discharge of the evaporator was fed as stream (6x) to the column body C1. This was operated at a top pressure of 0.015 MPa abs and with a reflux ratio of reflux to distillate of 4. The top product of C1 was obtained as stream (5) 907 g / h of 99.6 wt .-% formic acid. 277 g / h as stream (5b) were withdrawn as side draw and returned to the column body B2. The liquid effluent of the column body C1 was fed as stream (6a) at the top of the evaporator C2.

The liquid discharge of the evaporator C2 was passed as stream (6b) to the phase separation vessel D. This was operated at normal pressure and at a temperature of 80 ° C. Two liquid phases formed. The upper liquid phase was withdrawn continuously as stream (8) at 3587 g / h and fed into the container Y. Stream (8) contained 95.7% by weight of tri-n-hexylamine and 1.2% by weight of formic acid. The lower liquid phase was continuously fed as stream (7) to the evaporator C2. The remaining stream was fed into the top of evaporator C2.

To ensure the above operating conditions, the system was initially run for seven days. During this time, the methyl-di-n-hexylamine concentration in stream (8) increased to 0.31% by weight and steadily continued to increase in subsequent days. 9 days after retraction, the concentration was already at 0.77 wt .-%. An end to the rise was not apparent. The methyl-di-n-hexylamine concentration is tabulated in Table 1 and graphically in FIG.

Example 1 shows that without the use of the measure according to the invention for the selective separation and removal of low-boiling components, in the present example in particular of methyl-di-n-hexylamine, its concentration in stream (8) increases continuously. In addition, example 1 is also proof that methyl-di-n-hexylamine is also under the real operating conditions. Disadvantages in the long-term operation of such a method would be preprogrammed.

Example 2 (Inventive Example)

Example 2 was carried out in the laboratory plant 2. About stream (1 a) 2280 g / h of methyl formate were metered via metering pumps and 950 g / h of water (1 c) in the stirred tank A1 over stream. Stream (1 c) was taken from the mixing tank X, which was composed of fresh water via stream (1 b) and recycle water from the distillation apparatus B2 via stream (3c). Current (1 b) was chosen such that the sum of current (1 b) and current (3c) gave the desired current (1 c). The stirred tank A1 was operated at 1 10 ° C and 1, 3 MPa abs. The discharge was passed in tubular reactor A2, which was operated at 108 ° C and 1, 3 MPa abs. The output of tubular reactor A2 was passed in tube reactor A3. In these, 1603 g / h of tri-n-hexylamine were fed via stream (8a). The output of tube reactor A3 was passed in tube reactor A4. In these, an additional 1603 g / h of tri-n-hexylamine were fed via stream (8b). The

Streams (8a) and (8b) were taken from the container Y, which was used to distribute the recirculated via stream (8) tri-n-hexylamine on the two tube reactors A3 and A4. The operation of tubular reactor A3 was carried out at 105 ° C and 1, 3 MPa abs, of tubular reactor A4 at 106 ° C and 1, 3 MPa abs. Stream (2) was a product mixture containing 49.8% by weight of tri-n-hexylamine, 16.9% by weight of formic acid, 12.3% by weight of methanol, 7.9% by weight of water and 1 1, 5 wt .-% methyl formate won.

Stream (2) was depressurized and passed into the column body of the distillation apparatus B1. At a top pressure of 0.18 MPa abs and a reflux ratio of 1.4, the head product stream (3ab) was stripped off a mixture comprising formed methanol and unreacted methyl formate. The bottom product was as stream (3d) 5007 g / h of a mixture containing 59.5 wt .-% of tri-n-hexylamine, 9.9 wt .-% water, 26.3 wt .-% formic acid and 0.1 wt .-% methanol. The bottom temperature in (B1) was 1 17 ° C. Stream (3d) was sent to the column body of the distillation apparatus B2. In addition, via stream (5b), 265 g / h of the side draw off from the column body were fed to the distillation apparatus C1, which contained 83.2% by weight of formic acid and 16.6% by weight of water. The top product of the distillation apparatus B2 was at a head pressure of

0.18 MPa abs and a reflux ratio of 0.25 600 g / h of stream (3c) deducted. Stream (3c) containing 97.9% by weight of water and 2.0% by weight of formic acid was fed to the mixing vessel X for recycling to the stirred tank A1.

About stream (4) were 4512 g / h of a mixture containing 63.9 wt .-% of tri-n-hexylamine, 27.9 wt .-% formic acid and 1, 0 wt. As bottom product at a bottom temperature in B2 of 177 ° C 4512 g / h .-% water and fed from above onto the evaporator C2. The evaporator C2 and the column body C1 were operated in vacuum. The temperature at the lower outlet of the evaporator C2 was 161 ° C. The gaseous discharge of the evaporator was called electricity (6x) supplied to the column body C1. This was operated at a top pressure of 0.015 MPa abs and with a reflux ratio of reflux to distillate of 2.6. The top product of C1 was obtained as stream (5) 930 g / h of 99.9 wt .-% formic acid. As side draw 265 g / h were removed as stream (5b) and returned to the column body B2. The liquid effluent of the column body C1 was fed as stream (6a) at the top into the evaporator C2.

The liquid discharge of the evaporator C2 was passed as stream (6b) to the phase separation vessel D. This was operated at normal pressure and at a temperature of 80 ° C. Two liquid phases formed. The upper liquid phase was withdrawn continuously as stream (8) at 3250 g / h and fed into the container Y. Stream (8) contained 95.1% by weight of tri-n-hexylamine and 1.2% by weight of formic acid. The lower liquid phase was withdrawn continuously as stream (7) and fed to the top of the evaporator C2. From tank Y, 790 g were taken each working day (Monday to Friday) and distilled in the distillation apparatus F at a top pressure of 15 hPa abs and a bottom temperature of 162 ° C. In each case about 35 g of top product were obtained and discarded. The top product contained in each case about 67.1% by weight of methyl-di-n-hexylamine, about 0.2% by weight of tri-n-hexylamine and about 28.5% by weight of formic acid. The remaining bottoms discharge was again fed to the container Y. On the weekends (Saturday and Sunday) no distillative work-up was carried out via the distillation apparatus F.

The methyl-di-n-hexylamine concentration in stream (8) was followed analytically during the experiment. It is shown in tabular form in Table 2 and graphically in FIG. 16. The dashed, vertical lines in FIG. 16 are each intended to symbolize the weekend (Saturday and Sunday) on which no distillative workup via the distillation apparatus F took place.

Example 2 shows that without the measure according to the invention for the selective removal and removal of low-boiling components, in the present example in particular of methyl-di-n-hexylamine, its concentration steadily increases. For example, on the first weekend of measurements, there was an increase in current (8) from 2.99% by weight to 3.08% by weight of methyl-di-n-hexylamine. In contrast, by the measure according to the invention in the following five working days (Monday to Friday), the concentration of methyl-di-n-hexylamine again be reduced accordingly.

As a result, under the given process conditions, the concentration of methyl-di-n-hexylamine could be kept at a value around 3% by weight.

Examples 3 to 4

(Decomposition of tri-n-hexylamine compared to methyl-di-n-hexyl-amine) Example 3

(Decomposition of tri-n-hexylamine in the presence of formic acid and water)

95.3 g (0.35 mol) of tri-n-hexylamine, 16.3 g (0.35 mol) of formic acid (98-100% by weight) and 6.3 g (0.35 mol) of water were in Laboratory mixed in an ice bath. Subsequently, the resulting solution was warmed to room temperature (about 20 ° C) and degassed by applying three times vacuum (2 hPa abs) and gassing with pure nitrogen. A biphasic solution was obtained. This was then transferred to a 270 ml autoclave (material HC) in a so-called glove box under IS atmosphere and sealed. The autoclave was then pressed with nitrogen to 1, 0 MPa abs and heated to 160 ° C with vigorous stirring. After reaching the temperature, it was re-pressed with N2 to a total pressure of 2.5 MPa abs. The reaction mixture was then stirred at 160 ° C for 72 hours. The autoclave was then cooled to room temperature, depressurized to atmospheric pressure and the contents transferred to a glass jar. The discharge was divided into two phases. 48.1 g were obtained as the upper phase and 57.9 g as the lower phase. Both phases were analyzed by gas chromatography for their di-n-hexylformamide content. The upper phase contained 0.16 wt% (0.077 g), the lower phase 0.69 wt% (0.4 g) of di-n-hexylformamide.

Example 4

(Decomposition of methyl-di-n-hexylamine in the presence of formic acid and water)

69.8 g (0.35 mol) of methyl-di-n-hexylamine, 16.3 g (0.35 mol) of formic acid (98-100% by weight) and 6.3 g (0.35 mol) of water were mixed in the laboratory in an ice bath. Subsequently, the resulting solution was warmed to room temperature (about 20 ° C) and degassed by applying three times vacuum (2 hPa abs) and gassing with pure nitrogen. A biphasic solution was obtained. This was then transferred into a 270 ml autoclave (material HC) in a so-called glove box under N 2 atmosphere and sealed. The autoclave was then pressed with nitrogen to 1, 0 MPa abs and heated to 160 ° C with vigorous stirring. After reaching the temperature, it was re-pressed with N2 to a total pressure of 2.5 MPa abs. The reaction mixture was then stirred at 160 ° C for 72 hours. The autoclave was then cooled to room temperature, depressurized to atmospheric pressure and the contents transferred to a glass jar. The discharge was divided into two phases. 25.0 g were obtained as the upper phase and 54.3 g as the lower phase. Both phases were analyzed by gas chromatography for their di-n-hexylformamide content. The upper phase contained 0.52% by weight (0.13 g), the lower phase 1.1% by weight (0.597 g) of di-n-hexylformamide.

Examples 3 and 4 show that the acidolytic formation of di-n-hexylformamide from methyl-di-n-hexylamine is significantly faster than that from tri-n-hexylamine. Since the formation of di-n-hexylformamide is equivalent to a direct loss of tertiary amine (I), in the recovery of formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I), it is advantageous to reduce the amount of methyl-di -n-hexylamine to minimize. Example 5 to 7

(Influence of methyl-di-n-hexylamine on the energy consumption of the pure distillation of formic acid)

Example 5

In a distillation column (internal diameter 30 mm) with 25 bubble caps and oil-heated Sambay evaporator (thin film evaporator) 670 g / h of a mixture of electricity (4) were fed from the operation of the laboratory system at an oil temperature of 200 ° C and a top pressure of 150 hPa abs , The mixture used contained 20% by weight of formic acid, 74% by weight of tri-n-hexylamine, 2% by weight of water and 1% by weight of di-n-hexylformamide. The reflux ratio at the top of the column was 5: 1. Under these conditions, 105 g / h of 99.8% formic acid were obtained as overhead product, 10 g / h of 78% aqueous formic acid were withdrawn via a side draw on the 13th floor and 555 g / h drepfaustrag won. All streams were re-combined in a mixing vessel and fed back to the column. During the experiment, the entire energy supply was regulated by the oil temperature on the Sambay evaporator. Example 6

Example 6 was carried out as in Example 5, but fed from the operation of the laboratory plant using a 4 wt .-% methyl di-n-hexylamine-enriched mixture of stream (4). The mixture used contained 20% by weight of formic acid, 70% by weight of tri-n-hexylamine, 4% by weight of methyl-di-n-hexylamine, 2% by weight of water and 1% by weight of di-n - hexylformamide. In contrast to Example 5, only 90 g / h of 99.8% formic acid were obtained as top product using the methyl-di-n-hexylamine-containing feed stream. The amount of side draw was 14 g / h, in which case 80 wt .-% formic acid was recovered. The remainder was removed as bottoms stream.

Example 7

In Example 7 was tried by using the mentioned in Example 6, methyl-di-n-hexylamine-containing feed stream in the apparatus described in Example 5, by increasing the oil temperature, a similarly high amount of 99.8% formic acid as the top product win. To 666 g / h of the feed stream mentioned in Example 6 were supplied. At an oil temperature of 205 ° C finally 103 g / h of 99.8% formic acid could be obtained as the top product. In this case, 20 g / h of 79 wt .-% formic acid were withdrawn as a side stream. The remainder was removed as bottoms stream.

Examples 5, 6 and 7 show in the pure distillation of formic acid a significant negative effect by the presence of methyl-di-n-hexylamine. With otherwise constant Conditions falls the achievable amount of pure formic acid significantly. In the present case, in the presence of 4% by weight of methyldin-hexylamine instead of 105 g / h, only 90 g / h of 99.8% formic acid were obtained as the top product. To compensate for this waste, an increase in the bottom temperature and thus the energy input is required. In the present case, at least 103 g / h of 99.8% formic acid as the top product could be obtained by increasing from 200 ° C. to 205 ° C. again.

Example 8 In the distillation column described in Example 5, 650 g / h of the mixture from Experiment 7 containing 20% by weight of formic acid, 2% by weight of water, 4 Wt .-% of methyl-di-n-hexylamine and 70 wt .-% tri-n-hexylamine closed in the bottom. The reflux ratio at the top of the distillation column was 3: 1. Under these conditions, at the top of the distillation column, a top stream of 50 g / h of 99.8% formic acid, a side stream from the 6th bottom of the distillation column of 75 g / h of 75% aqueous formic acid and a bottom effluent of 515 g / h removed. The resulting side stream was analyzed for its content of tri-n-hexylamine and methyl-di-n-hexylamine. It contained 3000 ppm by weight of tri-n-hexylamine and 35000 ppm by weight of methyl-di-n-hexylamine.

Example 8 shows that a selective enrichment of methyl-di-n-hexylamine over tri-n-hexylamine of factor 10 in the side of the so-called formic acid pure column is possible.

Claims

claims

1 . Process for the recovery of formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I), which at a pressure of

1013 hPa abs has a boiling point at least 5 ° C higher than formic acid, in which one

(a) producing a liquid stream comprising formic acid and tertiary amine (I) by contacting tertiary amine (I) and a formic acid source and having a molar ratio of formic acid to tertiary amine (I) of from 0.5 to 5;

(b) separating from the liquid stream obtained from step (a) from 10 to 100% by weight of the minor components contained therein;

(c) from the liquid stream obtained from step (b) containing formic acid and tertiary amine (I) by distillation in a distillation apparatus at a bottom temperature of 100 to 300 ° C and a pressure of 30 to 3000 hPa abs of formic acid, wherein the in Step (a) to be used tertiary amine (I) and the separation rate in said distillation apparatus so chooses that form two liquid phases in the bottom discharge;

(d) separating the bottoms discharge from the distillation apparatus mentioned in step (c) into two liquid phases, wherein the upper liquid phase has a molar ratio of formic acid to tertiary amine (I) of 0 to 0.5 and the lower liquid phase a molar ratio of formic acid to tertiary Amine of (I) from 0.5 to 4;

(e) recycling the upper phase of liquid phase separation from step (d) to step (a); and

(f) the lower liquid phase of the phase separation from step (d) to step (b) and / or (c) returns, characterized in that

(G) from the upper liquid phase of the phase separation from step (d) in a distillation apparatus at a bottom temperature of 100 to 300 ° C and a pressure of 1 to 1000 hPa abs low boilers which at a pressure of 1013 hPa abs by at least 5 ° C lower boiling point than the tertiary amine (I), separated by distillation and the depleted of low boilers stream to one of the aforementioned steps (a) to (f).

2. The method according to claim 1, characterized in that one uses in step (a) in the presence of water, a formic acid source which contains methyl formate and from Wel- rather, a liquid stream containing formic acid, tertiary amine (I) and methanol is obtained by hydrolysis of methyl formate.

A process according to claim 1, characterized in that in step (a) a formic acid source is used which contains carbon dioxide, hydrogen and a homogeneous catalyst and from which a liquid stream containing formic acid and tertiary amine (I) is obtained by homogeneously catalyzed hydrogenation of carbon dioxide becomes.

Process according to claims 1 to 3, characterized in that the liquid stream produced in step (a) has a concentration of formic acid plus tertiary amine (I) of 1 to 99 wt .-% based on the total amount of the stream.

Process according to Claims 1 to 4, characterized in that the separation rate in the distillation apparatus mentioned in step (c) is selected such that the molar ratio of formic acid to tertiary amine (I) in the bottom effluent is from 0.1 to 2.0.

Process according to Claims 1 to 5, characterized in that 0.01 to 50% of the upper liquid phase is fed to the phase separation from step (d) in step (g).

Process according to Claims 1 to 6, characterized in that the stream depleted of low-boiling components is recycled from step (g) to step (a).

Process according to Claims 1 to 6, characterized in that the stream depleted of low-boiling components is recycled from step (g) to step (b).

Process according to Claims 1 to 8, characterized in that the tertiary amine (I) is an amine of the general formula (Ia)

NR R ² R ³ (Ia) in which the radicals R ¹ to R ^{3 are} identical or different and independently of one another represent an unbranched or branched, acyclic or cyclic, aliphatic, aliphatic or aromatic radical having in each case 1 to 16 carbon atoms, wherein individual Carbon atoms independently of one another can also be substituted by a hetero group selected from the group -O- and> N- and two or all three radicals can also be linked together to form a chain comprising at least four atoms each.

10. The method according to claim 9, characterized in that as the tertiary amine (I) an amine of the general formula (Ia), in which the radicals R ¹ to R ^{3 are} independently selected from the group d- to Ci2-alkyl, Cs to Cs cycloalkyl, benzyl and phenyl, starts.

A method according to claim 10, characterized in that the tertiary amine (I) is an amine of general formula (Ia), in which the radicals R ¹ to R ^{3 are} independently selected from the group Cs to Cs-alkyl, is used.