JP2015505857A - Method for producing formic acid - Google Patents

Abstract

A method for obtaining formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I), comprising combining a tertiary amine (I) and a formic acid source together with a formic acid and a primary formic acid. Producing a liquid stream containing the tertiary amine (I), separating the secondary components contained therein, and separating the formic acid from the resulting liquid stream by distillation in a distillation apparatus; Separating the bottom discharge from the two liquid phases, returning the upper liquid phase to the formic acid source and returning the lower liquid phase to the secondary component separation and / or distillation apparatus. Separating the low boilers from the upper liquid phase by distillation and returning the reduced stream.

Description

  This application includes US Provisional Application No. 61 / 577,701, filed December 20, 2011 by reference.

  The present invention is a process for obtaining formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I), comprising combining a tertiary amine (I) and a formic acid source Gave a liquid stream containing formic acid and tertiary amine (I) in a molar ratio of 0.5 to 5, separating 10 to 100% by weight of the secondary components contained therein, and obtained From the liquid stream, formic acid is removed by distillation at a bottom temperature of 100-300 ° C. and a pressure of 30-3000 hPa (absolute pressure) in a distillation apparatus, and the bottom discharge from the distillation apparatus is separated into two liquid phases; It relates to said process wherein the upper liquid phase is returned to the formic acid source and the lower liquid phase is returned to the secondary component separation and / or distillation apparatus.

  Formic acid is an important and versatile product. Formic acid is, for example, for acidification in the production of feed, as a preservative, as a fungicide, as an aid in the textile and leather industries, as a mixture with its salts for defrosting airplanes and runways, and Used as a synthetic building block in the chemical industry.

  Currently, a very 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 subsequently subsequently concentrated using an extraction aid such as, for example, dialkylformamide (DE2545658A1).

  In addition, it is also known to obtain formic acid by thermal decomposition of a compound from formic acid and a tertiary nitrogen base. These compounds are generally tertiary ammonium base acidic ammonium formates, for which formic acid reacts with tertiary nitrogen bases through a classical salt formation step to form hydrogen bridge bonds. It is a stable addition compound that is crosslinked via Addition compounds consisting of formic acid and a tertiary nitrogen base can be formed by combining a tertiary nitrogen base and a formic acid source. Here, for example, WO2006 / 021,411 discloses the preparation of such adduct compounds, and generally (i) a tertiary nitrogen base and formic acid are reacted directly, and (ii) in the presence of a tertiary nitrogen base. Hydrogenation of carbon dioxide with a transition metal catalyst to obtain formic acid, (iii) reacting methyl formate with water, subsequently extracting the formed formic acid with a tertiary nitrogen base, and (iv) methyl formate and This is done by reacting with water in the presence of a tertiary nitrogen base.

  The general advantage of using an addition compound consisting of formic acid and a tertiary nitrogen base to obtain formic acid is that, on the one hand, the addition compound binds formic acid very well and the formic acid is free. As formic acid, the formic acid is first removed from the medium in which it is formed by chemical synthesis, for example from the reaction medium or from a diluted formic acid solution, and formic acid can thereby be more easily separated in the form of its adduct. On the other hand, the formic acid is less than sufficient to be obtained by subsequent elution from the adduct compound by pyrolysis, concentration, and purification to the free form.

  EP0001432A discloses a method for obtaining methyl formate while hydrolyzing it in the presence of a tertiary amine, in particular in the presence of an alkylimidazole, to form an adduct consisting of formic acid and a tertiary amine. From the resulting hydrolysis mixture containing unreacted methyl formate, water, methanol, adduct and tertiary amine, the low boiling point methyl formate and methanol are removed in the first distillation column. In the second column, the remaining bottom product is dehydrated. The dehydrated bottom product of the second column, which further contains an addition compound and a tertiary amine, is then fed to the third column, where the addition compound is pyrolyzed to form formic acid. And a tertiary amine. The liberated formic acid is removed as the top product. The tertiary amine collects at the bottom and is returned to the hydrolysis.

DE3428319A discloses a method for obtaining formic acid by hydrolysis of methyl formate. From the resulting hydrolysis mixture containing unreacted methyl formate, water, methanol and formic acid, the low boiling point methyl formate and methanol are removed in the first distillation column. The aqueous formic acid generated at the bottom is subsequently higher-boiling amines, in particular longer-chain hydrophobic C ₆ -C ₁₄ -trialkylamines, with additional hydrophobic solvents, in particular aliphatic, fatty It is extracted in the presence of a cyclic or aromatic hydrocarbon and reacts to form an aqueous addition compound consisting of formic acid and an amine. The compound is dehydrated in a second distillation column. The dehydrated addition compound generated at the bottom is now fed to the top stage of the distillation column (denoted “K4” in FIG. 1) and pyrolyzed according to the teaching of DE 3428319A. Hydrophobic solvents are present at the top and bottom of the column. The gaseous top stream contains, among other things, liberated formic acid in addition to the hydrophobic solvent. This stream is liquefied again in the condenser. In so doing, two phases are formed, one polar formic acid phase and one hydrophobic solvent phase. The formic acid phase is discharged as product and the solvent phase is returned to the column as a reflux. Due to the presence of the hydrophobic solvent, complete decomposition of the adduct can be achieved, and it is believed that the decomposition takes place without decomposition of formic acid according to the teachings of the aforementioned DE publication. The (substantially) formic acid free bottom contains a hydrophobic amine and a hydrophobic solvent. This is returned to the extraction step.

EP0181078A and EP0126524A, the transition metal catalyst and a tertiary amine, for example C ₁ -C ₁₀ - by hydrogenating carbon dioxide in the presence of a trialkylamine, to form an addition compound consisting of formic acid and a tertiary amine, The hydrogenation effluent is worked up to separate the catalyst and low boilers, and the amine base is replaced with weaker, higher boiling tertiary amines, especially alkyl imidazoles, to form the first tertiary Describes a process for obtaining formic acid by separating the amine and subsequently pyrolyzing the newly formed adduct in a distillation column. To that end, according to FIG. 1 of EP0181078A, a stream containing formic acid and an amine is fed to the middle region of column “30”. Formic acid liberated during pyrolysis is removed as the top product. The weaker, higher boiling tertiary amine collects at the bottom and is returned to the base exchange step.

  WO 2008 / 116,799 describes carbon dioxide in the presence of a transition metal catalyst, a high boiling polar solvent such as alcohol, ether, sulfolane, dimethyl sulfoxide or amide, and a polar amine having at least one hydroxyl group. Disclosed is a method for obtaining formic acid by hydrogenation to form an addition compound consisting of formic acid and an amine. According to the teachings of WO2008 / 116,799, the hydrogenation effluent can be fed directly to a distillation unit for the thermal decomposition of the addition compound. The apparatus may include a distillation column and may include a thin film evaporator or a falling film evaporator if a short residence time is desired. The liberated formic acid is removed as the top product. The polar amine and polar solvent and optionally unseparated catalyst collect at the bottom and can be returned to the hydrogenation step.

  WO2006 / 021,411 is a method for obtaining formic acid by thermal decomposition of an addition compound (quaternary ammonium formate) from formic acid and a tertiary amine, wherein the tertiary amine has a boiling point of 105 to 175 ° C. A method is disclosed. Preferred tertiary amines include alkyl pyridines. Due to the special boiling range of the tertiary amine, the color stability of the formic acid obtained is increased. The addition compounds to be used can then generally be obtained from tertiary amines and formic acid sources. Preferably, volatile components are first removed from the effluent from the adduct synthesis and then fed to the pyrolysis. The pyrolysis is carried out in the distillation column as usual, in which the stream containing formic acid and amine is fed into the middle region of the column C according to FIG. 1 of WO2006 / 021,411. The liberated formic acid is removed as the top product. The tertiary amine, which may still contain a formic acid residue, collects at the bottom and can be returned to the formic acid source.

  EP0563831A lists an improved method for thermally decomposing an adduct compound (quaternary ammonium formate) from formic acid and a tertiary amine to obtain formic acid. The addition compounds to be used can then generally be obtained from tertiary amines and formic acid sources. Preferably, volatile components are first removed from the synthesis effluent and then fed to the center of the distillation column for pyrolysis. The improvement consists essentially in the thermal decomposition of the addition compound in the presence of a secondary formamide that increases the color stability of the obtained formic acid. The liberated formic acid is removed as the top product. The tertiary amine and secondary formamide collect at the bottom and can be returned to the formic acid source.

  PCT / EP2011 / 060770 is a process for obtaining formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I), wherein the tertiary amine (I) and the formic acid source are combined To produce a liquid stream containing formic acid and tertiary amine (I) in a molar ratio of 0.5-5, separating 10-100% by weight of the secondary components contained therein, and Formic acid is separated from the obtained liquid stream by distillation at a bottom temperature of 100 to 300 ° C. and a pressure of 30 to 3000 hPa (absolute pressure) in a distillation apparatus, and the bottom discharge from the distillation apparatus is separated into two liquid phases. And the upper liquid phase is concentrated with respect to the tertiary amine (I) and returned to the formic acid source, and the lower liquid phase is concentrated with respect to formic acid to separate the secondary components and / or distillation apparatus. Teaches the method of returning to

  The object of the present invention is an improved process for obtaining formic acid by thermal separation of a stream containing formic acid and a tertiary amine, which has advantages over the prior art and has a high yield of formic acid and It was to find a method that could be obtained at high concentrations. In particular, the improved process should function stably over longer working hours and produce formic acid with a constant high purity. Of course, it is desirable that the method be as simple and low energy as possible.

Surprisingly, for obtaining formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I) having a boiling point at least 5 ° C. higher than formic acid at a pressure of 1013 hPa (absolute pressure) A method,
(A) Combining a tertiary amine (I) with a formic acid source contains formic acid and tertiary amine (I), and the molar ratio of formic acid to tertiary amine (I) is 0.5. Produces a liquid stream that is ~ 5,
(B) separating from 10 to 100% by mass of by-products contained therein from the liquid stream obtained from step (a);
(C) From the liquid stream containing formic acid and tertiary amine (I) obtained from step (b), in a distillation apparatus, a bottom temperature of 100 to 300 ° C. and a pressure of 30 to 3000 hPa (absolute pressure) The formic acid is separated by distillation at this time, the separation rate in the tertiary amine (I) to be used in step (a) and the distillation apparatus described above being such that two liquid phases are formed in the bottom discharge. Selected to
(D) The bottom discharge from the distillation apparatus mentioned in step (c) above is separated into two liquid phases, the upper liquid phase having a molar ratio of formic acid to tertiary amine (I) of 0 The lower liquid phase has a molar ratio of formic acid to tertiary amine (I) of 0.5 to 4,
(E) returning the liquid phase above the phase separation from step (d) to step (a), and (f) changing the liquid phase below the phase separation from step (d) to step (b) and / or Or in the method of returning to (c),
(G) From the liquid phase above the phase separation from step (d), in a distillation apparatus at a bottom temperature of 100-300 ° C. and a pressure of 1-1000 hPa (absolute pressure), a pressure of 1013 hPa (absolute pressure) A stream having a boiling point lower than that of the tertiary amine (I) by at least 5 ° C. is separated by distillation, and the stream having the reduced low boiling point is reduced to 1 of the above steps (a) to (f). It has been found that said method is characterized in that it is returned to one.

  The tertiary amine (I) to be used in step (a) in the process according to the invention has a boiling point at least 5 ° C. higher than formic acid at a pressure of 1013 hPa (absolute pressure). Preferably, the tertiary amine (I) to be used has a boiling point higher than that of formic acid by at least 10 ° C., particularly preferably by at least 50 ° C., particularly preferably by at least 100 ° C. No limitation on the upper limit for the boiling point is necessary for the process according to the invention, since the lowest possible vapor pressure of the tertiary amine (I) is basically preferred. In general, the boiling point of the tertiary amine (I) is less than 500 ° C., optionally in a pressure extrapolated from vacuum to 1013 hPa (absolute pressure) by known methods.

  The formic acid source mentioned in step (a) means that formic acid is contained in diluted, contaminated and / or chemically bound form, or formic acid is produced by a chemical reaction. Represents a material stream containing a precursor.

  Finally, the formic acid source in step (a) ensures a direct or indirect supply of formic acid. The addition in chemically bound form can be effected, for example, in the form of a complex, salt, or adduct between formic acid and an amine different from the tertiary amine (I). The chemical reaction basically corresponds to any chemical reaction that produces formic acid. However, what is particularly industrially important is the production of formic acid by hydrolysis of methyl formate and the production of formic acid by hydrogenation of carbon dioxide with a transition metal catalyst at the time of filing of the present application. Two named synthetic techniques are well known in the art and are defined in various variations and embodiments. One further industrially relevant approach for the production of formic acid by chemical reaction is, for example, the direct reaction of carbon monoxide with water.

  In the case of hydrolysis of methyl formate, usually the formic acid formed by hydrolysis is trapped in the form of an adduct with a tertiary amine (I) and thus escapes the hydrolysis equilibrium. And the tertiary amine (I) are added to the hydrolysis reactor together or back and forth. Thereby, a high conversion of methyl formate can be achieved and a particularly favorable separation of unreacted water by subsequent distillation is possible.

  In the case of hydrogenation of carbon dioxide with a transition metal catalyst, the tertiary amine (I) generally has a hydrogenation reaction because a stream containing formic acid and the tertiary amine (I) is formed during the hydrogenation. Add to vessel.

  Preferably, in step (a), a stream containing formic acid and tertiary amine (I) is produced by hydrolysis of methyl formate in the presence of water and tertiary amine (I). More preferably, in step (a), a stream containing formic acid and tertiary amine (I) is produced by concentration from formic acid diluted in the presence of tertiary amine (I). However, particularly preferably in step (a) a stream containing formic acid and tertiary amine (I) is produced by hydrolysis of methyl formate in the presence of water and tertiary amine (I). .

  Combining the tertiary amine (I) and the formic acid source in step (a) can be carried out in the presence of water. In the preferred hydrolysis of methyl formate, water is required rather as a reactant for the reaction of methyl formate. In the case where the tertiary amine (I) and the formic acid source are combined in the presence of water in step (a), the water content takes into account the amount of chemically consumed water, In general, the liquid stream produced in step (a) is adjusted to contain water in addition to formic acid and tertiary amine (I).

  Combining the tertiary amine (I) with the formic acid source can be done in a very wide variety of ways. When the formic acid source is a mass stream containing formic acid in diluted, contaminated and / or chemically bound form, often with tertiary amine (I), preferably with mixing Direct contact is sufficient. This contact can be made, for example, in a tube, preferably in a tube containing suitable mixing internal fittings. Similarly, the contacting can also be done in other devices such as a stirred tank. Alternatively, the tertiary amine (I) may be added stepwise to the formic acid source, or conversely, the formic acid source may be added stepwise to the tertiary amine (I) and combined stepwise. It is possible and even more preferred in some cases. In general, the formic acid source sends the individual components together to the reactor when the formic acid source is a mass stream from which the formic acid is to be generated only by a chemical reaction from multiple substances. It is preferable that it is generated for the first time. Reactors in this case are in particular those known to the person skilled in the art for the type of reaction. The tertiary amine (I) can then be charged, for example, in parallel with the individual components of the formic acid source, in the course of a chemical reaction, or in a chemical reaction. It may be supplied only upon completion. These individual steps can also be divided into a plurality of reactors. Depending on the exothermic reaction when the tertiary amine (I) and the formic acid source are combined, it is also preferred to cool the apparatus itself or the stream obtained therefrom.

  A suitable working mode for bringing together the tertiary amine (I) and the formic acid source can be determined with a great deal of labor with ordinary expertise.

  The liquid stream produced when the tertiary amine (I) and the formic acid source are combined in step (a) has a molar ratio of formic acid to tertiary amine (I) of 0.5-5. . The molar ratio is preferably 1 or more and preferably 3 or less. The molar ratios listed are for the total liquid stream, regardless of whether it is present in one or multiple phases.

  The liquid stream containing formic acid and tertiary amine (I) produced in step (a) is generally a formic acid and tertiary amine at a concentration of 1 to 99% by weight relative to the total amount of the stream. (I). Preferably, the concentration of formic acid and tertiary amine (I) in the above stream is not less than 5% by weight, particularly preferably not less than 15% by weight and preferably not more than 95% by weight, in particular Preferably it is 90 mass% or less.

に当てはまる。 From the liquid stream obtained from step (a), 10 to 100% by mass of the subcomponents contained therein is separated. The basis for the above value range is the concentration of the minor component of the liquid stream produced in step (a). This concentration is hereinafter referred to as “C _subcomponent (flow from step (a))”. The liquid stream with reduced secondary components corresponds to the stream supplied to the distillation apparatus in step (c). This concentration is hereinafter referred to as “C _subcomponent (feed flow to step (c))”. Therefore, the above-mentioned separation of subcomponents is a quotient.

Is true.

  Preferably, in step (b), 20% by weight or more, particularly preferably 30% by weight or more, and preferably 99.99% by weight or less, particularly preferably 99.9% by weight or less of the subcomponents are separated.

  The concept of accessory component represents in this case any component contained in the liquid stream obtained in step (a), which is neither formic acid nor tertiary amine (I). Examples include, for example, water, methanol (especially in the case of hydrolysis of methyl formate), dissolved unhydrolyzed methyl formate (especially in the case of hydrolysis of methyl formate), tertiary amine (I) Decomposition products, dissolved inert gases, homogeneous catalysts (especially for carbon dioxide hydrogenation), dissolved carbon dioxide or dissolved hydrogen (especially for carbon dioxide hydrogenation), solvents, etc. Of the ingredients.

  The manner and method in which the minor components are separated is not very important for the method according to the invention. Here, for example, conventional and known methods for the separation of liquid substance mixtures can be used. First of all, here, separation by distillation is mentioned. In this case, the liquid substance mixture is separated in a distillation apparatus. Here, for example, components with low boiling points, such as methanol, methyl formate or water, can be separated off via the top or as a side extract. However, it is also conceivable to separate the high-boiling by-components through the bottom and the mixture containing formic acid and the tertiary amine (I) as a side stream or top product. However, in addition to separation by distillation, membrane methods, absorption methods, adsorption methods, crystallization methods, filtration methods, precipitation methods or extraction methods are also possible. The extraction method is preferred when a tertiary amine (I) is used which is not miscible with water or is only miscible with water when concentrating diluted aqueous formic acid.

  Of course, it is also possible to combine a plurality of separation steps which can be based on different methods. The design of one or more separation steps can be done with normal expertise.

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

  From the liquid stream obtained from step (b), formic acid is finally separated in the distillation apparatus at a bottom temperature of 100-300 ° C. and a pressure of 30-3000 hPa (absolute pressure). The distillation apparatus for that purpose basically corresponds to an apparatus that is known for the separation work for those skilled in the art or that should be produced with general skills.

  Typically, the distillation apparatus includes, inter alia, a top condenser and a bottom evaporator in addition to a unique column with internal fittings. Furthermore, the distillation apparatus can, of course, also be used with further peripheral devices or internal fittings, such as flash vessels in the supply channel (for example for separation of gas and liquid in the supply channel to the column), intermediate evaporators ( Including internal fittings (eg temperature adjustable trays, demisters, coalescers or Tiefbettdiffusionsfilters, etc.) for avoiding or reducing aerosol formation (eg for improved heat integration of the method) Good. The tower may be provided with, for example, a packing, a packing or a tray. The number of separation stages required is, in particular, the type of tertiary amine (I), the concentration of formic acid and tertiary amine (I) in the distillation apparatus feed in step (c) and the desired or desired concentration of formic acid. Depending on the purity of and can be determined routinely by one skilled in the art. In general, the number of separation stages required is 3 or more, preferably 6 or more, particularly preferably 7 or more. In principle, no limit is imposed on the high price. However, for practical reasons it is common to use generally 70 or less, optionally 50 or less, or even 30 or less separation stages.

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

  Optionally, the addition may be pre-connected, for example with a flash evaporator. In order to keep the thermal load in the fed stream distillation apparatus as small as possible, it is generally preferred to feed the stream rather to the lower region of the distillation apparatus. Here, in step (c), the stream containing formic acid and tertiary amine (I) is present in the lower quarter region, preferably in the lower fifth region, of the existing separation stage, It is particularly preferred to supply in the lower sixth region, in which case, as a matter of course, also includes a direct supply at the bottom.

  However, alternatively, it is also possible to supply in step (c) the above stream from step (b) containing formic acid and tertiary amine (I) to the bottom evaporator of the distillation apparatus. preferable.

  The distillation apparatus is operated at a bottom temperature of 100-300 ° C. and a pressure of 30-3000 hPa (absolute pressure). Preferably, the distillation apparatus is operated at a bottom temperature of 120 ° C. or higher, particularly preferably 140 ° C. or higher and preferably 220 ° C. or lower, particularly preferably 200 ° C. or lower. The pressure is preferably 30 hPa (absolute pressure) or more, particularly preferably 60 hPa (absolute pressure), and preferably 1500 hPa (absolute pressure) or less, particularly preferably 500 hPa (absolute pressure).

  Depending on the composition and origin of the feed to the distillation unit containing formic acid and the tertiary amine (I), formic acid can be obtained from the distillation unit as a top product and / or as a side product. . If the feed contains components having a boiling point lower than that of formic acid, it is sometimes preferred to separate the components by distillation with the top product and formic acid as the side extract. In the case of a gas that is considered dissolved in the feed (such as carbon monoxide or carbon dioxide), however, it is also possible to separate formic acid with the gas as a top product. When the feed contains components having a boiling point higher than formic acid, formic acid is preferably separated by distillation as the top product, but alternatively or in addition, in the form of a second stream. Separated by distillation in the side extract. In this case, components having a boiling point higher than formic acid are then preferably withdrawn via an additional side stream. The side stream with subcomponents can optionally be returned to step (b) for separation of the subcomponents.

  Thus, formic acid having a content of up to 100% by mass can be obtained. In general, a formic acid content of 75-99.995% by weight can be achieved without problems. The residual content which is missing up to 100% by weight is mainly water, of course depending on the substances introduced into the distillation apparatus in addition to formic acid and the primary amine (I), Components such as solvents or possible decomposition products are also conceivable. Here, for example, water may already be present in the feed of the distillation apparatus, but in some cases it may also be produced only in small amounts by decomposition of formic acid itself only during the thermal separation.

  When concentrated formic acid having a content of 95-100% by weight is obtained as top or side product, water is discharged in the side stream together with a portion of the decomposed formic acid. . The formic acid content of this side stream is typically 75-95% by weight. Aqueous formic acid from the side stream can optionally be returned to step (b) for water separation.

  However, water and decomposed formic acid can also be discharged in a common top or side stream. The product thus obtained has a formic acid content of generally 85 to 95% by weight.

  In particular, in order to sufficiently suppress the formation of organic decomposition products of the tertiary amine (I) caused by oxidation, particularly when operating the distillation apparatus at a pressure of less than 0.1 MPa (absolute pressure), oxygen intrusion, By minimizing the number of connections, tube pieces and flanges, by being particularly careful during installation, and by using particularly tight flange connections (for example those having a comb-like contour seal or weld lip seal), Alternatively, it is particularly preferred to avoid by a flange connection covered with nitrogen or at least keep it very low. Suitable flange connections are disclosed, for example, in DE102009046310A1.

  The formic acid obtained by the process according to the invention has a low color number and a high color number stability. In general, it is possible to achieve an APHA color number of 20 or less, in particular, an APHA color number of 10 or less, possibly even an APHA color number of 5 or less, without problems. During weeks of storage, the number of colors stays almost constant or only slightly increased.

  Based on the separation according to the invention of the organic degradation products of the tertiary amine (I) in step (b), it is possible to obtain particularly pure formic acid without any further effort. In the pure formic acid, the above-mentioned degradation products are generally present at 70 ppm by weight or less, preferably at 30 ppm by weight or less, particularly preferably at 20 ppm by weight or less.

  The content of subcomponents is very low and generally present at 100 ppm by weight or less, preferably at 50 ppm by weight or less, particularly preferably at 25 ppm by weight or less.

  Accordingly, in addition to the free formic acid and amine (I) -containing bottom product, in addition to other fractions, for example accompanying substances, reaction by-products, impurities and / or formic acid fractions of various purity and concentration. If other fractions to be contained are to be obtained, it may be preferred to use a plurality of distillation apparatus in step (c).

  The distillation apparatus for the separation of formic acid can of course also be configured as a thermally connected distillation column or as a separation wall column (Trennwandkolonne).

  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) is the bottom discharge of the distillation apparatus mentioned in step (c). In the product, it is chosen to form two liquid phases.

  The formation of the two liquid phases is mainly determined from the chemical and physical properties of the two phases. They are also influenced by the choice of tertiary amine (I) to be used, by the separation rate in the distillation apparatus, but also by the presence of optional additional components, such as solvents, and even by their concentration. Can be done.

を表し、その際、「ｍ_ギ酸（ステップ（ｃ）への供給流れ）」は、単位時間あたりに蒸留装置に供給されるギ酸の量に相当し、そして「ｍ_ギ酸（底部排出物）」は、単位時間あたりに底部排出物を介して排出されるギ酸の量に相当する。一般に、本発明による方法のこの好ましい形態では、一般に１０％以上の、好ましくは２５％以上の、特に好ましくは４０％以上の、かつ一般に９９．９％以下の、好ましくは９９．５％以下の、特に好ましくは９９．０％以下の分離速度が選択される。分離速度は、例えば蒸留装置中の温度条件および圧力条件によって、ならびに蒸留装置中の滞留時間によって簡単に影響を受けることがある。分離速度は、簡単な実験によって、場合により本発明による方法の運転に際しても調査することができる。 The separation speed is the quotient

_Where “m _{formic acid} (feed stream to step (c))” corresponds to the amount of formic acid fed to the distillation unit per unit time and “m _{formic acid} (bottom discharge)” is , Corresponding to the amount of formic acid discharged through the bottom discharge per unit time. In general, in this preferred form of the process according to the invention, it is generally at least 10%, preferably at least 25%, particularly preferably at least 40% and generally at most 99.9%, preferably at most 99.5%. Particularly preferably, a separation rate of 99.0% or less is selected. The separation rate can be easily influenced, for example, by temperature and pressure conditions in the distillation apparatus and by the residence time in the distillation apparatus. The separation rate can be investigated by simple experiments and possibly also during the operation of the process according to the invention.

  The suitability of the tertiary amine (I) or optionally additionally desired solvent can be examined in a simple experiment, for example examining the nature of the phase under the intended conditions.

  The phase separation can be performed, for example, in a separate phase separator that is connected afterwards to the distillation apparatus. However, it is also possible to integrate the phase separator in the bottom area of the distillation apparatus, in the area of the bottom evaporator or in the area of the bottom evaporator circuit. In this case, for example, a centrifugal separator can be used or even preferred in some cases.

  The formation of the two liquid phases is influenced by temperature in addition to the chemical and physical properties of both phases, and generally the miscibility increases with temperature, so to improve phase separation In some cases, it may be preferable to do this at a temperature lower than the preselected bottom temperature. To that end, the bottom discharge is usually cooled to a temperature in the range of 30-180 ° C. in a heat exchanger connected in between. Preferably, the phase separation is carried out at a temperature of 50 ° C. or higher, or at a temperature of 160 ° C. or lower, particularly preferably at a temperature of 130 ° C. or lower.

  The upper liquid phase in step (d) is generally from 0 to 0.5, preferably not less than 0.005, particularly preferably not less than 0.015 and preferably not more than 0.25, particularly preferably 0. A molar ratio of formic acid to tertiary amine (I) of 125 or less. The lower liquid phase in step (d) is generally 0.5-4, preferably 0.75 or more, particularly preferably 1 or more and preferably 3.5 or less, particularly preferably 3 or less, It has a molar ratio of formic acid to tertiary amine (I). However, depending on the choice of amine, of course, the phase containing formic acid forms the upper phase and the amine phase having a molar ratio of formic acid to amine of 0-0.5 forms the lower phase. It is also possible. What is important is simply the presence of phase separation, where one phase has a formic acid to tertiary amine molar ratio of 0-0.5 and the second phase is a formic acid to The molar ratio of tertiary amine is generally 0.5-4. Preferably, the upper phase is a phase having a molar ratio of formic acid to tertiary amine generally from 0 to 0.5 and the lower phase is a molar ratio of 0.5 to 4 formic acid to tertiary amine. It is a phase having

  Furthermore, in the process according to the invention, the separation rate in the distillation apparatus mentioned in step (c) is such that the molar ratio of formic acid to tertiary amine (I) in the bottom discharge is 0.1 to 2.0. It is preferable to select as follows. Bottom discharge refers to the entire liquid bottom condensate that exits the distillation unit and is divided into two liquid phases according to step (d). In so doing, it is not very important whether the bottom condensate originates for example directly from the bottom of the distillation apparatus, from the bottom of the bottom evaporator or both. Preferably, 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 preferably not more than 1.5.

  By returning the liquid phase above the phase separation from step (d) to step (a) by step (e), the tertiary amine (I) contained in the upper liquid phase is converted to formic acid. By combining with a source, it can be used for further production of streams containing formic acid and tertiary amine (I). In general, from 10 to 100%, preferably from 50 to 100%, particularly preferably from 80 to 100%, particularly preferably from 90 to 100%, in particular from 95 to 100%, of step ( Returned to a).

  Surprisingly, within the scope of the present invention, the liquid phase above the phase separation from step (d) has a lower boiling point of tertiary amine (I), especially compared to another stream with reduced formic acid. It was found to be rich in organic degradation products.

その場合に、相応のジアルキルホルムアミドおよび相応のアルキルホルミエートが、第三級アミン（Ｉ）の有機分解産物として形成される。 At that time, the concept of the organic decomposition product of the tertiary amine (I) means that the bond that originally existed is separated under the chemical conversion of the tertiary amine (I), and the nitrogen-carbon bond is separated. Represents a compound that forms a new bond or a chemical conversion of a nitrogen-bonded group. Here, within the scope of the present invention, the tertiary amine (I) is a tertiary amine, for example in the presence of formic acid, at a higher temperature and pressure than is present in the individual steps of the process according to the invention. It was confirmed that there was a tendency to decompose into the corresponding formamide N- and N-substituted with the amine (I) residue and the corresponding formate containing another residue of the tertiary amine (I). In the case of a tertiary amine (I) having three different residues R, for example C ₅ -C ₈ -alkyl, the above described decomposition reaction is for example as follows:

In that case, the corresponding dialkylformamide and the corresponding alkylformate are formed as organic degradation products of the tertiary amine (I).

その場合に、相応のジアルキルホルムアミドおよび相応のアルカナールが、第三級アミン（Ｉ）の有機分解産物として形成される。 Furthermore, within the scope of the present invention, the tertiary amine (I) is, for example, also in the presence of formic acid and trace amounts of oxygen, at a higher temperature than is present in the individual steps of the process according to the invention, It was confirmed that there was also a tendency to decompose into the corresponding formamide N- and N-substituted with the residue of the tertiary amine (I) and the aldehyde from which the other formaldehyde was formed. In the case of a tertiary amine (I) having three different residues CH ₂ —R, for example C ₅ -C ₈ -alkyl, the above decomposition reaction is for example as follows:

In that case, the corresponding dialkylformamide and the corresponding alkanal are formed as organic degradation products of the tertiary amine (I).

その際、Ｍｅは、メチルを表す。 Furthermore, within the scope of the present invention, the tertiary amine (I) tends to be methylated to the corresponding methylammonium cation in the presence of methyl formate used when obtaining formic acid by hydrolysis of methyl formate. It was confirmed that In the case of a tertiary amine (I) having three identical residues R, for example C ₅ -C ₈ -alkyl, the methylation reaction described above is for example as follows:

In this case, Me represents methyl.

This is reverse decomposed, whereby a tertiary amine having a methyl group is formed. In the case of the system described above, this reaction equation is as follows:

According to Scheme A, a tertiary amine containing a methyl group then results in the formation of a dialkylformamide as well:

  The organic degradation products of the tertiary amine (I) can lead to formic acid contamination to be obtained by step (c). Furthermore, the organic degradation products of the tertiary amine (I) having a boiling point between formic acid and the tertiary amine are concentrated in the distillation apparatus used in step (c), whereby energy consumption in the distillation apparatus Tend to be increased.

  In the scope of the present invention, it has been found that the interfering components can be separated from the upper liquid phase of the phase separation from step (d), in particular by good and simple distillation. Thus, in the process according to the invention, in step (g), from the liquid phase above the phase separation from step (d) at the bottom temperature of 100 to 300 ° C. and the pressure of 1 to 1000 hPa (absolute pressure) in the distillation apparatus, At a pressure of 1013 hPa (absolute pressure), low boilers having a boiling point lower than that of the tertiary amine (I) by at least 5 ° C. are separated by distillation, and a reduced stream of low boilers is obtained from the steps (a) to Returned to one of (f).

  Low boilers are in this case generally subcomponents as defined in the detailed description of the invention, as described above, at least 5 more than the tertiary amine (I) at a pressure of 1013 hPa (absolute pressure). It should represent a minor component having a boiling point as low as ° C. Preferably, said subcomponent has a boiling point which is lower by at least 7 ° C., particularly preferably by at least 10 ° C. than said tertiary amine (I). The restriction on the lower limit for the boiling point is not necessary since low boiling substances with a particularly low boiling point can generally be separated by distillation in particular easily. In general, the boiling point of the low boilers exceeds 100 ° C., however, at the pressure of 1013 hPa (absolute pressure) described above.

  The low boilers to be separated in the process according to the invention are already contained in the tertiary amine (I) fed to step (a) and / or only in the course of the process up to this step (g). Either formed. Here, for example, the tertiary amine (I) supplied to step (a) can already contain various organic degradation products of the tertiary amine (I) based on its preparation or post-treatment. It is. However, the low boilers to be separated are also formed in steps (a) to (c) under corresponding conditions, either exclusively or in addition to the low boilers already supplied to the tertiary amine (I). This is usually the case.

  Separation of the aforementioned low boilers in step (g) is carried out by distillation. The distillation apparatus for that purpose basically corresponds to an apparatus that is known for the separation work for those skilled in the art or that should be produced with general skills. The distillation apparatus is operated at a bottom temperature of 100-300 ° C. and a pressure of 1-1000 hPa (absolute pressure). Preferably, the distillation apparatus is operated at a bottom temperature of 120 ° C. or higher, particularly preferably 140 ° C. or higher and preferably 220 ° C. or lower, particularly preferably 200 ° C. or lower. The pressure is preferably 5 hPa (absolute pressure) or more, particularly preferably 10 hPa (absolute pressure) or more, and preferably 500 hPa (absolute pressure) or less, particularly preferably 250 hPa (absolute pressure) or less. .

  A reduced stream of low boilers generally occurs as a bottom product. However, it is also possible to obtain the stream as a side stream, in particular in the range of distilling off the low boilers and at the same time optionally presenting high boilers, i.e. higher boiling points than the tertiary amine (I) in general. It is also possible to obtain the component if it is to be removed.

  In the process according to the invention, generally 0.01 to 50% of the liquid phase above the phase separation from step (d) is fed to step (g). This amount is sufficient on the one hand to keep the low boilers present at a sufficiently low level, but also on the other hand because the costs such as the size of the distillation unit or the continuous energy requirements do not exceed the degree. Enough. Preferably, the phase from step (d) is 0.1% or more, particularly preferably 0.5% or more and 20% or less, particularly preferably 10% or less, particularly preferably 5% or less. The liquid phase above the separation is fed to step (g).

  Due to the inventive separation of low boilers in step (g), the amount can be kept at a low level in the process. In particular, it also effectively and accurately resists the accumulation that increases over time.

は、一般に１〜１００％、好ましくは１０％以上、特に好ましくは５０％以上である。 Therefore, the low boiler concentration is easily based on the stream comprising the bottom product from step (g) and the remaining upper liquid phase from step (e) not led to step (g). Further, it can be maintained at a value of 25% by mass or less, preferably 15% by mass or less, particularly preferably 10% by mass or less. In general, the stated concentration is 0.001% by weight or more, usually 0.1% by weight or more. Reduction degree of low boiling point substances

Is generally 1 to 100%, preferably 10% or more, particularly preferably 50% or more.

  The separated low boiling point material can be discarded, for example.

  The reduced stream of low boilers obtained in step (g) is returned to one of the above-mentioned steps (a) to (f) in the process according to the invention. In general, 10 to 100%, preferably 50 to 100%, particularly preferably 80 to 100%, particularly preferably 90 to 100%, in particular 95 to 100%, of the reduced stream of low boilers as a whole, Returned to steps (a) to (f). In that case, of course, the reduced stream of low boilers can be returned, for example, at a selected location, and thus can also be returned, for example, separately at different locations. Preferably, the reduced stream of low boilers is returned to one of steps (a) to (e) described above. In one particularly preferred embodiment, the reduced stream of low boilers is returned to step (a). In another particularly preferred embodiment, the reduced stream of low boilers is returned to step (b).

  In general, in the return of the liquid phase above the phase separation from step (d) to step (a), in addition to step (g), naturally other method steps may also be integrated. Also, basically no restrictions are imposed on the types of method steps connected in between. It is also possible to take out part of the upper liquid phase intentionally as a so-called “purge flow”. The deficient or lost amount of tertiary amine (I) can of course be supplemented again with newly supplied tertiary amine (I), wherein the amine is, for example, via a return stream. Or directly to step (a) or at any position in the process, for example step (b) or step (c).

  In the method according to the invention, according to step (f), the liquid phase below the phase separation from step (d) is returned to steps (b) and / or (c). Thereby, the formic acid contained in the lower liquid phase can likewise be used to obtain formic acid by separation by distillation. Depending on the desired embodiment, the lower liquid phase is therefore divided into (i) step (b), (ii) step (b) and step (c), or (iii) step. Can be returned to (c). However, return to step (c) is generally preferred. This is because the loading of the lower liquid phase containing formic acid and tertiary amine (I) is usually the lowest and the mass flow in step (b) does not increase quantitatively. . This would otherwise result in a correspondingly larger scale. In general, from 10 to 100%, preferably from 50 to 100%, particularly preferably from 80 to 100%, particularly preferably from 90 to 100%, in particular from 80 to 100%, of the lower liquid phase, step ( b) and / or (c).

  However, in addition to the above return to the lower liquid phase steps (b) and / or (c), it is also possible to return further parts to step (a). This is preferred, for example, in the case of formic acid production by hydrogenation of carbon dioxide with a transition metal catalyst. This is because the production is generally carried out in the presence of a polar solvent, which can likewise be collected in the lower liquid phase and returned to step (a) again.

  Also, of course, further method steps may be integrated in the return of the lower liquid phase. As a non-limiting example, again the lower liquid phase to be returned, or the tertiary amine (I) contained therein and / or the formic acid contained therein, undesired accompanying substances, reaction byproducts. Alternatively, purification from impurities can be mentioned. Also, basically no restrictions are imposed on the types of method steps connected in between. It is also possible to deliberately discharge a part of the lower liquid phase as a so-called “purge stream” and to remove, for example, unwanted incidental substances, reaction by-products or further impurities.

The tertiary amines (I) that are advantageously used in the process according to the invention are those of the general formula (Ia)
NR ¹ R ² R ³ (Ia)
In which the radicals R ¹ to R ³ are the same or different and, independently of one another, are unbranched or branched, acyclic or cyclic, aliphatic, Represents an araliphatic or aromatic group each having 1 to 16 carbon atoms, preferably having 1 to 12 carbon atoms, wherein the individual carbon atoms are, independently of one another, a radical May be substituted by a heteroatom selected from -O- and> N-, and two or all three groups may be linked together forming a chain containing at least four atoms each. Good].

Suitable amines include, for example, the following:
Tri-n-propylamine (boiling point _{1013 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 (boiling point _{1013 hPa} = 127 ° C.), di-n-octyl-methyl Amine, di-n-hexyl-methylamine, 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, tricyclopentylamine, tricyclohexylamine, tricycloheptylamine, tricyclooctylamine and one or more methyl groups, with ethyl group Derivatives of the foregoing substituted with 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl, dimethyl-cyclohexylamine, methyl-dicyclohexyl Amines, diethyl-cyclohexylamine, ethyl-dicyclohexylamine, Dimethyl-cyclopentylamine, methyl-dicyclopentylamine, methyl-dicyclohexylamine, triphenylamine, methyl-diphenylamine, ethyl-diphenylamine, propyl-diphenylamine, butyl-diphenylamine, 2-ethyl-hexyl-diphenylamine, dimethyl-phenylamine, diethyl -Phenylamine, dipropyl-phenylamine, dibutyl-phenylamine, bis (2-ethyl-hexyl) phenylamine, tribenzylamine, methyl-dibenzylamine, ethyl-dibenzylamine and one or more methyl groups, Derivatives of the foregoing substituted with an ethyl group, 1-propyl group, 2-propyl group, 1-butyl group, 2-butyl group or 2-methyl-2-propyl group , 5-di (1-piperidyl) pentane, N-C _{1 ~C 12} - alkyl - piperidine, N, N-di -C ₁ -C ₁₂ - alkyl - piperazine, N-C _{1 ~C 12} - alkyl - pyrrolidine , N-C ₁ -C ₁₂ - alkyl - imidazole and, with one or more methyl groups, ethyl groups, 1-propyl, 2-propyl, 1-butyl group, or a 2-butyl group Derivatives of the foregoing substituted with a 2-methyl-2-propyl group: 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 ("Granatan"), 1-azabicyclo [ 2.2.2] Octane ("Chinucli din "), 7,15-diazatetracyclo [7.7.1.0 ^2,7 . 0 ^{10, 15]} heptadecane ( "Spartein")
Of course, mixtures of various tertiary amines (I) can also be used in the process according to the invention. Preferably, then, of course, all tertiary amines (I) used have a boiling point at least 5 ° C. higher than formic acid at a pressure of 1013 hPa (absolute pressure).

Of the tertiary amines of the general formula (Ia) above, the radicals R ¹ to R ³ are the same or different and, independently of one another, are unbranched or branched An acyclic or cyclic, aliphatic, araliphatic or aromatic each having 1 to 16 carbon atoms, preferably having 1 to 12 carbon atoms, Wherein each individual carbon atom may be, independently of one another, substituted by a heteroatom selected from the groups —O— and> N—, and two or all three groups are each at least four Preference is given to amines which may form a saturated chain containing atoms and which may be linked together.

  Preferably, at least one of said groups has two hydrogen atoms at the α-carbon atom, ie the carbon atom bonded directly to the amine nitrogen atom.

Particularly preferably, in the process according to the invention, the tertiary amine (I) is represented by the general formula (Ia), in which the radicals R ¹ to R ³ are, independently of one another, C ₁ -C ₁₂ - alkyl, C ₅ -C ₈ - cycloalkyl, amines selected from the group of benzyl and phenyl are used.

  Particularly preferably, in the process according to the invention, saturated amines of the general formula (Ia) are used as tertiary amine (I).

In particular, in the process according to the invention, the tertiary amine (I) is represented by the general formula (Ia), in which the radicals R ¹ to R ³ are independently of each other C ₅ -C ₈ -alkyl. Amines selected from the group consisting of tri-n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, dimethylcyclohexylamine, methyldicyclohexylamine, dioctylmethylamine and dimethyl Decylamine is used.

  In a further embodiment, to the α-carbon atom (carbon atom bonded directly to the amine nitrogen atom), to the β-carbon atom (second carbon atom bonded to the amine nitrogen atom), or γ-carbon. An amine having a branch at the atom (third carbon atom bonded to the amine nitrogen atom) is used. Here, alkyl substituents, aryl substituents and other substituents are conceivable in principle, preferably alkyl groups such as methyl, ethyl or propyl or piperidyl groups. In this embodiment, particularly preferably 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 stream containing formic acid and tertiary amine (I) formed by the process according to the invention is added to the formic acid and tertiary amine (I) in addition to the free formic acid and free tertiary amine (I) in the mixture. Amine (I) may be included in various other forms. The type and amount of the individual forms depends on the conditions present, for example the relative ratio of formic acid to the tertiary amine (I), further components (for example water, solvents, by-products, impurities ), And finally, depending on conditions such as concentration of formic acid and tertiary amine (I), temperature and pressure. Here, for example, the following possible forms:
An adduct of ammonium formate (molar ratio of formic acid to tertiary amine (I) is 1) or adduct with formic acid-rich tertiary amine (I) (molar ratio of formic acid to tertiary amine (I) is 1)
-Include ionic liquids.

  For the implementation of the method according to the invention, the type and amount of the individual forms are not very important.

  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, in a preferred variant in which two liquid phases are formed, particularly in the bottom discharge from the distillation apparatus mentioned in step (c), this solvent comprises a tertiary amine (I) and It is preferred that it is not miscible or only essentially immiscible but has good miscibility with the formic acid-containing amine phase and is therefore found again in the lower liquid phase in step (d). For this reason, an electrostatic coefficient (electrostatischer Faktor) (preferably shortened to EF) of preferably 200 · 10 ⁻³⁰ Cm or more with respect to 25 ° C. has been found. Its electrostatic coefficient EF is defined as the product of the relative dielectric constant ε _r of the solvent and the dipole moment μ (eg C. Reichardt, “Solvents and Solvent Effects in Organic Chemistry”, 3rd edition, Wiley-VCH Verlag (See GmbH & Co KGaA, Weinheim 2003, chapter 3.2, from the bottom of page 67 to the top of page 68). This preferred value ensures that any solvent has a predetermined minimum polarity and is miscible with the lower liquid phase in step (d).

  The use of a solvent can, for example, improve the separation of both liquid phases, depending on the particular system (for example the type, concentration, temperature, pressure, etc. of the tertiary amine (I)).

  Substance classes that are particularly suitable as optional solvents include in particular formate esters, diols and their formate esters, polyols and their formate esters, sulfones, sulfoxides, open-chain amides or cyclic amides and mixtures of the aforementioned substance classes.

Suitable diols and polyols include, for example, ethylene glycol (EF = 290.3 · 10 ⁻³⁰ Cm), diethylene glycol (EF = 244.0 · 10 ⁻³⁰ Cm), triethylene glycol, polyethylene glycol, and 1,3-propane. Diol (EF = 285.6 · 10 ⁻³⁰ Cm), 2-methyl-1,3-propanediol, 1,4-butanediol (EF = 262.7 · 10 ⁻³⁰ Cm), dipropylene glycol, 1, Examples include 5-pentanediol (EF = 212.5 · 10 ⁻³⁰ Cm), 1,6-hexanediol and glycerin. Diols and polyols may be esterified in the presence of formic acid based on their OH groups. It takes place in the process according to the invention, in particular during step (c), during the thermal separation of the stream containing formic acid and tertiary amine (I) in the distillation apparatus described above. The resulting formic acid esters exhibit very similar phase behavior so that they are generally very suitable as solvents as well. In addition, the water generated during esterification is not harmful during thermal separation. In the continuous operation of the process according to the invention, no water accumulation occurs. This is because this small amount of water can be separated in the distillation device via the side extraction.

Suitable sulfoxides include, for example, dialkyl sulfoxides, preferably C ₁ -C ₆ -dialkyl sulfoxides, especially dimethyl sulfoxide (EF = 627.1 · 10 ⁻³⁰ Cm).

Suitable open chain or cyclic amides include, for example, formamide (EF = 1243.2 · 10 ⁻³⁰ Cm), N-methylformamide (EF = 2352.9 · 10 ⁻³⁰ Cm), N, N-dimethylformamide (EF = 396.5 · 10 ⁻³⁰ Cm), N-methylpyrrolidone (EF = 437.9 · 10 ⁻³⁰ Cm), acetamide and N-methylcaprolactam.

However, it may also be preferred to use a non-polar solvent just below 200 × 10 ⁻³⁰ Cm for 25 ° C. accordingly. Non-polar solvents can optionally reduce the concentration of formic acid in the upper liquid phase.

  However, preferably the process according to the invention is carried out without the addition of a solvent.

  In a preferred variant of the process according to the invention, a formic acid source containing methyl formate is used in step (a) in the presence of water, which contains formic acid, tertiary amine (I) and methanol. A liquid stream is obtained by hydrolysis of methyl formate. Via step (b), in this variant, the methanol resulting from the hydrolysis of methyl formate as well as the excess water is generally separated off. The separated methanol can then be used, for example, freshly in the synthesis of methyl formate. In this variant, methanol has a significantly lower boiling point than water and can therefore be more easily separated by distillation from a corresponding mixture containing methanol, water, formic acid and tertiary amine (I). The methanol is preferably separated from the stream obtained from step (a) as a separate stream as well.

  If methanol is separated during the variant listed in the previous paragraph, again in step (b) again separate the further stream containing unreacted methyl formate and return it to step (a). Is particularly preferred. Thereby, the yield of formic acid can be clearly increased relative to the methyl formate used. Since methyl formate has a significantly lower boiling point than methanol and can therefore be more easily separated by distillation from a corresponding mixture containing methyl formate, methanol, water, formic acid and tertiary amine (I), In this variant, the methyl formate and methanol are preferably separated from the stream obtained from step (a) as separate streams as well. This can be done, for example, in two separate distillation units, in which methyl formate is separated in the first column and methanol is separated in the second column. However, for example, both components can also be separated in multiple separate streams in a single distillation apparatus. Methyl formate is then obtained, for example, as a bottom product, and methanol is obtained as a sidestream product.

  The hydrolysis of methyl formate in step (a) is usually performed at a temperature of 80 to 150 ° C. and a pressure range of 0.4 to 25 MPa (absolute pressure). As an apparatus for carrying out the hydrolysis in step (a), in principle, any apparatus capable of exothermic reaction of a fluid stream can be used. Examples include, for example, stirred tanks, tube reactors or tube bundle reactors, each with internal fittings (eg packed beds, packings, perforated plates and the like). It may not have. 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 containing carbon dioxide, hydrogen and a homogeneous catalyst is used, from which the formic acid and the tertiary amine (I ) Is obtained by homogeneous catalytic hydrogenation of carbon dioxide. If step (a) is further carried out in the presence of water and / or methanol, it is a particularly preferred embodiment of said variant, but generally in step (b) water and / or methanol Is separated again, in the case of methanol separation, this is preferably returned to step (a) again. Methanol and water are primarily used as polar solvents in this variant.

  Specific steps and process characteristics for homogeneous catalytic hydrogenation of carbon dioxide to formic acid in the presence of water and methanol are described in PCT / EP2011 / 060012.

  As the homogeneous catalyst, an organometallic complex compound containing an element from Group 8, Group 9 or Group 10 of the Periodic Table is preferably used. More preferably, the complex compound has at least one phosphine group having at least one unbranched or branched acyclic or cyclic aliphatic group having 1 to 12 carbon atoms. Wherein individual carbon atoms may be substituted by> P-. The hydrogenation is preferably performed at 20 to 200 ° C. and 0.2 to 30 MPa (absolute pressure). The effluent from the hydrogenation step (a) is preferably two-phase. The upper phase contains tertiary amine (I) and homogeneous catalyst, and the lower phase contains formic acid, tertiary amine (I), water, methanol and likewise homogeneous catalyst. The two phases are separated and the upper phase containing the tertiary amine (I) and the homogeneous catalyst is returned to the hydrogenation step (a). The lower phase containing formic acid, tertiary amine (I), water, methanol and homogeneous catalyst is preferably extracted with tertiary amine (I) so that most of the homogeneous catalyst contained therein is extracted. It is extracted and returned to the hydrogenation step (a) together with the tertiary amine (I). The remainder of the lower phase containing formic acid, tertiary amine (I), water and methanol is then fed to step (b) and then, as before, according to the invention as well as methanol. Water and organic degradation products of tertiary amine (I) are separated.

  With regard to further post-processing, the specific steps and method features mentioned in the supplementary PCT / EP2011 / 060012 are pointed out.

FIG. 1 shows a simplified block diagram of a general embodiment of the method according to the invention. The individual letters have the following meanings:
A = Equipment for producing a stream containing formic acid and tertiary amine (I) B = Equipment for separating by-products C = Distillation equipment D = Phase separation vessel F = Distillation equipment Formic acid source Via (1) and tertiary amine (I) is fed via stream (8c) to apparatus A for producing a stream containing formic acid and tertiary amine (I). . As already explained further above, the source of formic acid to be supplied can contain, for example, formic acid in chemically bound form or in the form of a precursor in which formic acid is produced by a chemical reaction in apparatus A. . Stream (2) containing formic acid and tertiary amine (I) is withdrawn from apparatus A and fed to apparatus B for separation of secondary components. This apparatus may be, for example, a distillation apparatus, in which low-boiling secondary components can be removed by distillation. The separated subcomponents are removed via stream (3). Through stream (4), the stream in which the formic acid and the tertiary amine (I) have been concentrated is fed to distillation apparatus C. There, the formic acid is separated by distillation as stream (5). The bottom of the distillation apparatus C is fed to the phase separation vessel D for phase separation as stream (6). The lower liquid phase is returned to the distillation apparatus C as stream (7). The upper liquid phase is removed as stream (8a) and sent to distillation apparatus F. In the apparatus, low boilers are withdrawn as a stream (8z) by distillation and the reduced low boiler stream is returned to apparatus A as stream (8c).

  FIG. 2 is a simplified block diagram of a preferred modified embodiment in which only a portion of the upper liquid phase from phase separation vessel D is fed to distillation apparatus F for the separation of low boilers. It is. The other part is returned directly to device A via stream (8b) and then via (8c).

  The return of the stream with reduced low boilers from the distillation unit F can be carried out elsewhere in the process. Here, FIG. 3 shows, for example, the return to the device A, the return to the device B, and the return to the phase separation vessel D by the flow (8y (i)) to (8y (iii)) shown by the broken lines. ing. The flows indicated by broken lines should be represented as options that may exist individually or in combination. However, the return can be carried out, for example, at another location of the process, for example to the distillation apparatus C.

FIG. 4 shows a preferred embodiment combining the separation according to the invention of low boilers according to the variant shown in FIG. 2 with a particular variant for the separation of secondary components. This particular variant is particularly preferred in the presence of water as a secondary component and allows for the separation of the tertiary amine (I) organic degradation products formed by the process according to the invention in one step. The degradation product is sent to the distillation apparatus C only to a small extent. In FIG. 4, the additional letter E has the following meaning:
E = phase separation vessel Stream (2) containing formic acid, tertiary amine (I) and water is withdrawn from apparatus A and for separation of water and organic degradation products of tertiary amine (I) To the apparatus B. The device may be a distillation device, for example. The separated water and organic decomposition product of tertiary amine (I) are removed via stream (3) and fed to phase separation vessel E. There are thus formed two liquid phases. The lower liquid phase containing water is returned to apparatus A as stream (3x). The upper liquid phase rich in organic degradation products of tertiary amine (I) is removed as stream (3y) and discharged from the process. Through stream (4), the stream in which the formic acid and the tertiary amine (I) have been concentrated is fed to distillation apparatus C.

  Various configurations are possible in the region of the distillation apparatus C and the phase separation D. These differ not only in that the phase separation is carried out in a separate vessel or integrated and carried out at the bottom of the distillation column, but also the stream containing formic acid and tertiary amine (I) to the distillation unit. And the point of addition, the point of the flow path between the column vessel and the bottom evaporator, and the point of the bottom discharge output. The embodiments shown in FIGS. 2 to 7 and described in the text of PCT / EP-Az. 2011 / 060,770 can also be used within the scope of the preferred method according to the invention.

  In the following, two preferred embodiments are described for preferred fields of use of the method according to the invention.

Obtaining formic acid by hydrolysis of methyl formate One preferred embodiment for obtaining formic acid by hydrolysis of methyl formate is illustrated by the simplified block diagram in FIG.

The individual letters have the following meanings:
A = Equipment for hydrolyzing methyl formate to produce a stream containing formic acid, tertiary amine (I) and water B = Distillation equipment for separating methyl formate, methanol and water C = Formic acid Distillation equipment for acquisition D = phase separation vessel F = distillation equipment methyl formate (streams (1a) and (3a)), water (streams (1b) and (3c)) and tertiary amine (I) (stream ( 8c)) is supplied to apparatus A. Hydrolysis of methyl formate produces a stream containing formic acid, tertiary amine (I), methanol, water and methyl formate, which is removed from apparatus A as stream (2) and into apparatus B Supplied with. The conversion of methyl formate and thus the composition of stream (2) is primarily based on the relative feeds of the three feed streams, methyl formate, water and tertiary amine (I), to apparatus A, and the first used. Depends on the type of tertiary amine (I), residence time and reaction temperature. Reasonable conditions for the respective reaction system can be easily determined by a person skilled in the art, for example by preliminary tests. In stream (2), the molar ratio of formic acid to tertiary amine (I) is usually from 0.5 to 5, preferably from 0.5 to 3, and of course may deviate from this range. Good.

  In distillation apparatus B, from stream (2), here unreacted methyl formate (stream (3b)), methanol formed by hydrolysis (stream (3a)) and organics of water and tertiary amine (I) The degradation product (stream (3c)) is separated. The stream (3b) containing unreacted material used, methyl formate, is returned to apparatus A. Methanol separated via stream (3a) can be used, for example, for the production of fresh methyl formate. Stream (3c) is returned to device A as well. Formic acid and tertiary amine (I) are removed via stream (4). This still contains the remaining amount of water. Depending on the performance of the method, these may constitute several mass percent or even tens of mass percent of stream (4). Preferably, the water content in stream (4) is not more than 20% by weight, particularly preferably not more than 10% by weight, particularly preferably not more than 5% by weight. Since the molar ratio of formic acid to the tertiary amine (I) is not changed by distillation apparatus B or is only changed essentially insubstantially, the molar ratio is also usually 0.5 in stream (4). -5, preferably 0.5-3, in which case it may of course deviate from this range.

  Stream (4) is fed to distillation apparatus C. There, formic acid is removed by distillation as a top product via stream (5), as a side product via stream (5a) and / or as a side product via stream (5b). Depending on the general conditions, i.e. in particular 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 is passed through the top as stream (5) or stream ( 5a) can be obtained as a side product. The hydrous formic acid is then withdrawn as a side product via stream (5a) or (5b). In special cases, it may instead be sufficient to simply remove formic acid or hydrous formic acid as the top product via stream (5). Thus, depending on the specific embodiment, the side flow (5b) or even both side flows (5a) and (5b) can be omitted. The distillation apparatus C may of course have the embodiment disclosed in FIGS. 2-7 of PCT / EP-Az. 2011 / 060,770.

  The bottom product of distillation apparatus C is fed to phase separation vessel D as stream (6). Optionally, the phase separator D may be integrated in the distillation apparatus C. In phase separation vessel D, the bottom product is separated into two liquid phases. Optionally, for example, a heat exchanger may be connected between the distillation apparatus C and the phase separation vessel D for cooling the bottom stream taken off. Lower phase separation temperatures do indeed generally lead to some better separation with respect to formic acid content, but cause additional costs and energy requirements based on the use of heat exchangers. Therefore, advantages and disadvantages should be considered respectively. The lower liquid phase from the phase separation vessel D is returned to the distillation apparatus C via stream (7). In that case, the lower liquid phase may be preheated. It is done through an energetically isolated heat exchanger, through a heat integration with a heat exchanger used for cooling the bottom effluent from the distillation unit C, or through a combination of both Can do.

  The upper liquid phase from the phase separation vessel D is removed via flow (8a). A partial stream (8x) is sent to the distillation unit F. In the apparatus, the low boilers are removed by distillation as a stream (8z), and the reduced low boiler stream is returned to apparatus A as stream (8y) and later as (8c). The remaining other partial stream (8b) is returned directly to apparatus A via stream (8c).

  In another preferred embodiment for obtaining formic acid by hydrolysis of methyl formate, according to FIG. 6, the methyl formate stream (1a) is placed in distillation apparatus B. This embodiment is generally a methyl formate synthesis step with methyl formate provided as stream (1a) still in the residual amount of methanol, for example with pre-methanol partial conversion and incomplete workup of methyl formate. It is preferable when it is contaminated by. Thus, by feeding stream (1a) directly to distillation apparatus B, the methanol contained is separated as stream (3a), which can be returned to, for example, the methyl formate synthesis step. This variant makes it possible to dispense with the methyl formate / methanol separation completely in the methyl formate synthesis step, and thus also to reduce the energy in the entire distillation column and thus in continuous operation.

  In a further preferred embodiment for obtaining formic acid by hydrolysis of methyl formate, according to FIG. 7, both the methyl formate stream (1a) and the water stream (1b) are placed in the distillation apparatus B. It is done. With respect to the water stream (1b), this embodiment is generally preferred when providing hot condensate or steam as the water source. This is because the thermal energy stored there can be used in the distillation apparatus B.

  For completeness, of course, in a further embodiment, the methyl formate stream (1a) is put into apparatus A, but the water stream (1b) can also be put into distillation apparatus B. I want to say. It is preferred, for example, when low pressure excess steam (Niederdruck-Ueberschussdampf) is provided.

  In obtaining formic acid by hydrolysis of methyl formate, it is of course possible to combine the modified method shown in FIGS. 5 to 7 with the special separation of subcomponents shown in FIG. This is illustrated in FIG. 8 as a combination of variants from FIGS.

  Similarly, in the variation shown in FIGS. 5-8, as already mentioned with respect to FIG. 3, not only is the stream with reduced low boilers from distillation unit F returned to unit A, It can also be sent elsewhere in the process or exclusively at that location. Here, FIG. 9 shows, for example, return to apparatus A, return to apparatus B (two different addition sites), and phase separation according to the flows (8y (i)) to (8y (iv)) indicated by broken lines. Return to container D is shown. The flows indicated by broken lines should be represented as options that may exist individually or in combination. It is self-evident that return not shown, for example, return to the distillation apparatus C, can be considered as well.

  In the variant from FIGS. 5 to 9, for the embodiment of the distillation apparatus B, a particular variant with one, two or even three distillation columns is possible. FIG. 10a shows an embodiment with one distillation column. Figures 10b to 10e show different embodiments with two distillation columns. Figures 11a to 11c show different embodiments with three distillation columns. For the embodiment of the distillation apparatus B, a variant with one or two distillation columns is preferred. For completeness, particularly in the case of embodiments having one or two distillation columns, these distillation columns may be configured as thermally connected columns or as separation wall columns.

Acquisition of Formic Acid by Hydrogenation of Carbon Dioxide One preferred embodiment for the acquisition of formic acid by hydrogenation of carbon dioxide is illustrated by the simplified block diagram in FIG.

The individual letters have the following meanings:
A = device for hydrogenating carbon dioxide to produce a stream containing formic acid, tertiary amine (I) and water A1 = hydrogenation reactor A2 = phase separation vessel A3 = extraction unit B = methanol, water And distillation apparatus for separating organic decomposition products of tertiary amine (I) C = distillation apparatus for obtaining formic acid D = phase separation vessel F = distillation apparatus carbon dioxide (stream (1a)), hydrogen (stream) (1b)) as well as the tertiary amine (I) (stream (8c)) are fed to the hydrogenation reactor A1 in apparatus A. In the hydrogenation reactor A1, by performing hydrogenation in the presence of a homogeneous catalyst and water and methanol as a solvent, a stream containing formic acid, tertiary amine (I), methanol, water and homogeneous catalyst (2a ) Is formed. The stream is fed to phase separation vessel A2, where two liquid phases are formed. The upper liquid phase containing tertiary amine (I) and homogeneous catalyst is returned to hydrogenation reactor A1 via stream (2b). The lower liquid phase containing formic acid, tertiary amine (I), water, methanol and also a homogeneous catalyst is introduced into the extraction unit A3 via stream (2c). In the extraction unit, the residual of the homogeneous catalyst still present is fully extracted via the tertiary amine (I) supplied as stream (8), together with the tertiary amine (I). Return to the hydrogenation reactor A1 as stream (2d). Thus, a stream containing formic acid, tertiary amine (I) and water is obtained as stream (2) and fed to distillation apparatus B.

  In distillation apparatus B, methanol (stream (3b)) and water and organic decomposition products of tertiary amine (I) (stream (3c)) are separated from stream (2). The stream (3b) containing methanol is returned to the hydrogenation reactor A1 in apparatus A. Stream (3c) is likewise returned to the hydrogenation reactor A1 in apparatus A. Formic acid and tertiary amine (I) are removed via stream (4) and introduced into distillation apparatus C. With regard to the method steps for the distillation apparatus C, the phase separation vessel D and the distillation apparatus F, reference is made to the detailed description given above for obtaining formic acid by hydrolysis of methyl formate.

  Of course, in obtaining formic acid by hydrogenation of carbon dioxide, the flow with reduced low boilers from the distillation apparatus F is not only returned to the apparatus A, but the present It is also possible to send to another part of the process or exclusively to that place.

  The process according to the invention makes it possible to obtain formic acid in high yields and concentrations by thermal separation of a stream containing formic acid and a tertiary amine.

  The separation according to the invention of the low boilers from the liquid phase above the phase separation of the bottom effluent from the thermal separation of the stream containing formic acid and a tertiary amine allows its concentration in the system to be kept at a low level. it can. Thereby, the potential accumulation of low boilers is avoided, thus increasing the energy consumption in the distillation unit for the thermal separation of streams containing formic acid and tertiary amines and the contamination by low boilers. The increase effectively counters the progressive deterioration of formic acid quality. Thus, the process according to the invention enables a very stable operation over a longer operating time with a constant high purity of the formic acid produced at the same time. The formic acid obtained has a low color number and a high color number stability. The method can be implemented simply, reliably and with low energy.

  The process according to the invention can be used in particular preferably in combination with the hydrolysis of methyl formate as the source of formic acid, and is preferably carried out in combination with dehydration by extraction aids or two-pressure distillation, which is currently carried out industrially. It has technical and economic advantages over the operating method of hydrolysis of methyl formate with

FIG. 1 shows a simplified block diagram of a general embodiment of the method according to the invention. FIG. 2 is a simplified block diagram of a preferred modified embodiment in which only a portion of the upper liquid phase from phase separation vessel D is fed to distillation apparatus F for the separation of low boilers. Is shown. FIG. 3 shows, for example, the return to the device A, the return to the device B, and the return to the phase separation vessel D by the flow (8y (i)) to (8y (iii)) indicated by broken lines. FIG. 4 shows a preferred embodiment combining the separation according to the invention of low boilers according to the variant shown in FIG. 2 with a particular variant for the separation of secondary components. FIG. 5 shows a simplified block diagram of a preferred embodiment for obtaining formic acid by hydrolysis of methyl formate. FIG. 6 shows another preferred embodiment for obtaining formic acid by hydrolysis of methyl formate. FIG. 7 shows a further preferred embodiment for obtaining formic acid by hydrolysis of methyl formate. FIG. 8 shows a combination of variants from FIGS. FIG. 9 shows, for example, return to apparatus A, return to apparatus B (two different addition sites), and to phase separation vessel D by the flow (8y (i)) to (8y (iv)) indicated by broken lines. Indicates return. FIG. 10 shows one embodiment with one distillation column at a, and different embodiments with two distillation columns from b to e. FIG. 11 shows different embodiments from a to c, with three distillation columns. FIG. 12 shows a simplified block diagram of a preferred embodiment for obtaining formic acid by carbon dioxide hydrogenation. FIG. 13 shows a simplified block diagram of the laboratory equipment 1. FIG. 14 shows a simplified block diagram of the laboratory equipment 2. FIG. 15 illustrates the methyl-di-n-hexylamine concentration. FIG. 16 illustrates the methyl-di-n-hexylamine concentration.

Example Laboratory equipment 1 (for comparative example 1)
Laboratory equipment 1 was used for the investigation of a continuous process that does not use the present invention. A simplified block diagram of the laboratory equipment 1 is shown in FIG. The individual letters have the following meanings:
A1 = stirring tank (capacity 0.3L, electric heating type)
A2, A3, A4 = tube reactors (inner diameter 80mm, length 1200mm, filled with 2mm glass spheres, electric heating type)
X = mixing container (capacity 5L)
Y = container (capacity 5L)
B1 = column (with an inner diameter of 55 mm, each loaded with two fabric packings having a packing height of 1.3 m and a specific surface area of 750 m ² / m ^{3, in} which the feed line of stream (2) is between both packing beds A distillation apparatus having an oil-heated falling film evaporator and condenser and a controllable reflux separator at the top of the column B2 = column (inner diameter 55 mm, with 12 bubble bell plates in the recovery section) The concentrating section is equipped with ten bubble plates, where the feed path for stream (3d) exists between the two sections and the feed path for stream (5b) exists in the recovery section); Distillation apparatus with oil-heated falling film evaporator and condenser and controllable reflux separator at the top of the column C1 = column (with an inner diameter of 43 mm, a packing height of 0.66 m and a specific surface area of 500 m ² / m ³ Having a fabric filling above the bottom Loading, and loading the additional fabric packings with a fill height and a specific surface area of 750m ² / m ³ of 1.82 m, when the lateral extraction of the flow (5b) is present in both packing alcove) And condenser and controllable reflux separator at the top of the column C2 = oil-heated falling film evaporator D = individual phase separation vessel (capacity 0.3L, oil-heated)
The device and conduit consisted of a nickel-base alloy having material number 2.4610. The mass flow rate was confirmed with a Coriolis type flow meter. Laboratory equipment 1 was operated continuously.

  During all tests in laboratory equipment 1, the formic acid content was measured by potentiometric titration with 0.5 N NaOH in water, respectively, and the water content was measured by the Karl Fischer method. All other organic components were each measured by gas chromatography.

Laboratory equipment 2 (for example 2 according to the invention)
Laboratory equipment 2 is a laboratory equipment 1 that is expanded around a separate phase separation vessel for the flow (3c), which was used for a continuous process study using the present invention. A simplified block diagram of laboratory equipment 2 is shown in FIG. Of these, the supplemented letters have the following meanings:
E = phase separation vessel F = column (with an inner diameter of 30 mm, 1 m of Sulzer CY packing (750 m ² / m ³ ), the flow (9a) feed line being below the packing), The description of the laboratory equipment 1 is referred to for a distillation apparatus having an oil-heated bottom vessel and a controllable reflux separator at the top of the column.

Example 1 (comparative example)
Example 1 was carried out in laboratory equipment 1. Via stream (1a), 1760 g / h methyl formate and 849 g / h water via stream (1c) were metered into stirred tank A1 by means of a metering pump. A flow (1c) composed of fresh water via the flow (1b) and recycled water via the flow (3c) from the distillation apparatus B2 was taken out from the mixing vessel X. Stream (1b) was selected such that the sum of stream (1b) and stream (3c) was the desired stream (1c). The stirring tank A1 was operated at 110 ° C. and 1.3 MPa (absolute pressure). The effluent was introduced into a tubular reactor A2 which was also operated at 110 ° C. and 1.3 MPa (absolute pressure). The discharge from the tubular reactor A2 was introduced into the tubular reactor A3. The reactor was fed with 1964 g / h tri-n-hexylamine via stream (8a). The discharge from the tubular reactor A3 was introduced into the tubular reactor A4. The reactor was further fed with 1661 g / h tri-n-hexylamine via stream (8b). Streams (8a) and (8b) are then removed from vessel Y, which separates the tri-n-hexylamine returned via stream (8) into both tubular reactors A3 and A4. Used for. The operation of the tubular reactor A3 was performed at 115 ° C. and 1.3 MPa (absolute pressure), and the operation of the tubular reactor A4 was performed at 110 ° C. and 1.3 MPa (absolute pressure). As stream (2), 58.4% by mass of tri-n-hexylamine, 16.4% by mass of formic acid, 12.3% by mass of methanol, 7.8% by mass of water, and 6.9% by mass of methyl formate. A product mixture containing was obtained.

  Stream (2) was depressurized and introduced into the column of distillation apparatus B1. At a top pressure of 0.18 MPa (absolute) and a reflux ratio of 2.5, a mixture containing methanol formed and unreacted methyl formate was withdrawn as the top product stream (3ab). As a bottom product, as stream (3d), a mixture consisting of 71.2% by weight of tri-n-hexylamine, 9.1% by weight of water, 20.7% by weight of formic acid and 0.1% by weight of methanol 5012 g / h was obtained. The bottom temperature in B1 was 117 ° C.

  Stream (3d) was introduced into the column of distillation apparatus B2. In addition, 277 g / h of a side extract containing 79.3% by weight of formic acid and 16.6% by weight of water from the column of distillation apparatus C1 were fed via stream (5b). . A 450 g / h stream (3c) was withdrawn as the top product of distillation apparatus B2 at a top pressure of 0.10 MPa (absolute pressure) and a reflux ratio of 0.71. A stream (3c) containing 98.8% by weight water and 0.3% by weight formic acid was fed to mixing vessel X for return to stirring tank A1.

  Via stream (4) as bottom product, at a bottom temperature in B2 of 160 ° C., 75.3% by weight of tri-n-hexylamine, 26.0% by weight of formic acid and 1.2% by weight of water Of 4821 g / h was obtained, which was fed to the evaporator C2 from above. The evaporator C2 and the column body C1 were operated in a vacuum. The temperature of the discharge part below the evaporator was 161 ° C. The gaseous discharge of the evaporator was fed to the column C1 as a stream (6x). It was operated at a top pressure of 0.015 MPa (absolute pressure) and a reflux to distillate reflux ratio of 4. As the top product of C1, 907 g / h of 99.6% by weight of formic acid were obtained as stream (5). As a side extract, 277 g / h was extracted as a flow (5b) and returned to the tower B2. The liquid effluent of the tower body C1 was fed upward to the evaporator C2 as stream (6a).

  The liquid discharge from the evaporator C2 was introduced into the phase separation vessel D as stream (6b). The phase separator was operated at normal pressure and a temperature of 80 ° C. Two liquid phases are formed. The upper liquid phase was withdrawn at 3587 g / h as continuous flow (8) and conveyed to 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 sent to evaporator C2 as continuous flow (7). The remaining stream was fed upward to the evaporator C2.

  In order to guarantee the above operating conditions, the equipment was first conditioned for 7 days. During this time, the methyl-di-n-hexylamine concentration in stream (8) increased to 0.31% by weight and continued to increase on subsequent days. After 9 days of running-in, the concentration was already 0.77% by weight. The end of the increase could not be confirmed. Methyl-di-n-hexylamine concentrations are listed in Table 1 and illustrated in FIG.

  Example 1 shows that if the measures according to the invention for the targeted separation and discharge of low boilers, in this case in particular methyl-di-n-hexylamine, are not used, the concentration in stream (8) is continuous. It shows that it will increase. Example 1 is further evidence that methyl-di-n-hexylamine forms even under actual operating conditions. The disadvantage of such a method in long-term operation is inevitable.

Example 2 (example according to the invention)
Example 2 was performed in laboratory facility 2. Via stream (1a), 2280 g / h of methyl formate and 950 g / h of water via stream (1c) were metered into stirred tank A1 by means of a metering pump. A flow (1c) composed of fresh water via the flow (1b) and recycled water via the flow (3c) from the distillation apparatus B2 was taken out from the mixing vessel X. Stream (1b) was selected such that the sum of stream (1b) and stream (3c) was the desired stream (1c). The stirring tank A1 was operated at 110 ° C. and 1.3 MPa (absolute pressure). The effluent was introduced into a tubular reactor A2 operated at 108 ° C. and 1.3 MPa (absolute pressure). The discharge from the tubular reactor A2 was introduced into the tubular reactor A3. 1603 g / h of tri-n-hexylamine was fed to the reactor via stream (8a). The discharge from the tubular reactor A3 was introduced into the tubular reactor A4. The reactor was further fed with 1603 g / h of tri-n-hexylamine via stream (8b). Streams (8a) and (8b) are then removed from vessel Y, which separates the tri-n-hexylamine returned via stream (8) into both tubular reactors A3 and A4. Used for. The tubular reactor A3 was operated at 105 ° C. and 1.3 MPa (absolute pressure), and the tubular reactor A4 was operated at 106 ° C. and 1.3 MPa (absolute pressure). As stream (2), 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 11.5% by weight of methyl formate A product mixture containing was obtained.

  Stream (2) was depressurized and introduced into the column of distillation apparatus B1. At a top pressure of 0.18 MPa (absolute) and a reflux ratio of 1.4, a mixture containing methanol formed and unreacted methyl formate was withdrawn as the top product stream (3ab). As bottom product, as stream (3d), a mixture consisting of 59.5% by weight of tri-n-hexylamine, 9.9% by weight of water, 26.3% by weight of formic acid and 0.1% by weight of methanol 5007 g / h was obtained. The bottom temperature in (B1) was 117 ° C.

  Stream (3d) was introduced into the column of distillation apparatus B2. In addition, 265 g / h of a side extract containing 83.2% by weight of formic acid and 16.6% by weight of water from the column of distillation apparatus C1 were fed via stream (5b). . A 600 g / h stream (3c) was withdrawn as the top product of distillation apparatus B2 at a top pressure of 0.18 MPa (absolute pressure) and a reflux ratio of 0.25. A stream (3c) containing 97.9% by weight water and 2.0% by weight formic acid was fed to mixing vessel X for return to stirring tank A1.

  Via stream (4) as bottom product at the bottom temperature in B2 at 177 ° C. 63.9% by weight of tri-n-hexylamine, 27.9% by weight of formic acid and 1.0% by weight of water Of 4512 g / h was obtained, which was fed into the evaporator C2 from above. The evaporator C2 and the column body C1 were operated in a vacuum. The temperature of the discharge part below the evaporator C2 was 161 ° C. The gaseous discharge of the evaporator was fed to the column C1 as a stream (6x). It was operated at a top pressure of 0.015 MPa (absolute pressure) and a reflux to distillate reflux ratio of 2.6. As the top product of C1, 99.9% by weight of formic acid as stream (5) was obtained at 930 g / h. As a side extract, 265 g / h was extracted as a stream (5b) and returned to column B2. The liquid effluent of the tower body C1 was fed upward to the evaporator C2 as stream (6a).

  The liquid discharge from the evaporator C2 was introduced into the phase separation vessel D as stream (6b). The phase separator was operated at normal pressure and a temperature of 80 ° C. Two liquid phases are formed. The upper liquid phase was withdrawn as a continuous flow (8) at 3250 g / h and conveyed to 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 as continuous flow (7), which was fed upward to the evaporator C2.

  From vessel Y, 790 g each was taken on weekdays (from Monday to Friday) and distilled in distillation apparatus F at a top pressure of 15 hPa (absolute pressure) and a bottom temperature of 162 ° C. In that case, about 35 g of top product was obtained, which was discarded. The top products each contained about 67.1% by weight methyl-di-n-hexylamine, about 0.2% by weight tri-n-hexylamine and about 28.5% by weight formic acid. . Each remaining bottom discharge was again fed to container Y. Distillative work-up by distillation unit F was not performed on weekends (Saturday and Sunday).

  The methyl-di-n-hexylamine concentration in stream (8) was observed analytically during the test. The concentrations are listed in Table 2 and illustrated in FIG. The vertical broken lines in FIG. 16 should symbolize weekends (Saturday and Sunday) where the post-distillation treatment by the distillation apparatus F was not performed.

  Example 2 shows that if the measures according to the invention for the targeted separation and discharge of low boilers, in this example in particular methyl-di-n-hexylamine, are not carried out, the concentration increases continuously. Yes. Here, for example, on the first weekend of the measurement, an increase in methyl-di-n-hexylamine in stream (8) was recorded from 2.99% to 3.08% by weight. In contrast, the measures according to the invention allowed the methyl-di-n-hexylamine concentration to be correspondingly lowered again on the following five weekdays (Monday to Friday).

  Therefore, in the final results, under the indicated process conditions, the concentration of methyl-di-n-hexylamine could be kept at a value of 3% by weight.

Examples 3-4
(Decomposition of tri-n-hexylamine compared to methyl-di-n-hexylamine)
Example 3
(Decomposition of tri-n-hexylamine in the presence of formic acid and water)
95.3 g (0.35 mol) tri-n-hexylamine, 16.3 g (0.35 mol) formic acid (98-100% by weight) and 6.3 g (0.35 mol) water In an ice bath. Subsequently, the resulting solution was warmed to room temperature (about 20 ° C.) and degassed by gassing with pure nitrogen over 3 vacuums (2 hPa (absolute pressure)). A two-phase solution was obtained. This was then refilled and closed in a so-called glove box with a 270 mL autoclave (material HC) under N ₂ atmosphere. The autoclave was subsequently pressurized to 1.0 MPa (absolute pressure) with nitrogen and heated to 160 ° C. with vigorous stirring. After reaching that temperature, N ₂ was used to post-pressurize to a total pressure of 2.5 MPa (absolute pressure). The reaction mixture was stirred here at 160 ° C. for 72 hours. Subsequently, the autoclave was cooled to room temperature, released to normal pressure, and the contents were transferred to a glass container. The effluent separated into two phases. 48.1 g was obtained as the upper phase and 57.9 g was obtained as the lower phase. Both phases were examined for their di-n-hexylformamide content by gas chromatography. The upper phase contains 0.16% by weight (0.077 g) of di-n-hexylformamide and the lower phase contains 0.69% by weight (0.4 g) of di-n-hexylformamide. It was.

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 Mixed in an ice bath in the laboratory. Subsequently, the resulting solution was warmed to room temperature (about 20 ° C.) and degassed by gassing with pure nitrogen over 3 vacuums (2 hPa (absolute pressure)). A two-phase solution was obtained. This was then refilled and closed in a so-called glove box with a 270 mL autoclave (material HC) under N ₂ atmosphere. The autoclave was subsequently pressurized to 1.0 MPa (absolute pressure) with nitrogen and heated to 160 ° C. with vigorous stirring. After reaching that temperature, N ₂ was used to post-pressurize to a total pressure of 2.5 MPa (absolute pressure). The reaction mixture was stirred here at 160 ° C. for 72 hours. Subsequently, the autoclave was cooled to room temperature, released to normal pressure, and the contents were transferred to a glass container. The effluent separated into two phases. 25.0 g was obtained as the upper phase and 54.3 g was obtained as the lower phase. Both phases were examined for their di-n-hexylformamide content by gas chromatography. The upper phase contains 0.52 wt% (0.13 g) di-n-hexylformamide and the lower phase contains 1.1 wt% (0.597 g) di-n-hexylformamide. It was.

  Examples 3 and 4 show that the acidolytic formation of di-n-hexylformamide from methyl-di-n-hexylamine occurs clearly more rapidly than that from tri-n-hexylamine. ing. Since the formation of di-n-hexylformamide should be equated with the direct loss of tertiary amine (I), thermal separation of the stream containing formic acid and tertiary amine (I) is obtained upon obtaining formic acid. Therefore, it is preferable to keep the amount of methyl-di-n-hexylamine as small as possible.

Examples 5-7
(Effect of methyl-di-n-hexylamine on the energy consumption of pure distillation of formic acid)
Example 5
Flow from operation of laboratory equipment in a distillation column (inner diameter 30 mm) with 25 bubble bell plates and an oil-heated Samay evaporator at an oil temperature of 200 ° C. and a top pressure of 150 hPa (absolute pressure) ( 670 g / h of material mixture from 4) was fed. The substance mixture used contained 20% by weight formic acid, 74% by weight tri-n-hexylamine, 2% by weight water and 1% by weight di-n-hexylformamide. The reflux ratio at the top of the column was 5: 1. Under these conditions, 99.8% formic acid 105 g / h was obtained as the top product, and 78% aqueous formic acid 10 g / h was withdrawn via the side withdrawal at the 13th stage, bottom discharge. A product of 555 g / h was obtained. All streams were recombined in the mixing vessel and fed fresh into the column. During the test, the total energy supply was regulated via the Sambay evaporator oil temperature.

Example 6
Example 6 was carried out in the same way as Example 5 but fed using the material mixture from stream (4) from the operation of the laboratory equipment rich in 4% by weight of methyl-di-n-hexylamine. . The substance mixture used was 20% by weight formic acid, 70% by weight tri-n-hexylamine, 4% by weight methyl-di-n-hexylamine, 2% by weight water and 1% by weight di-n. -Contained hexylformamide. Unlike Example 5, when using an input stream containing methyl-di-n-hexylamine, only 99.8% formic acid could be obtained as the top product. The amount of the side extract was 14 g / h, in which case 80% by weight of formic acid was obtained. The remaining residue was discharged as a bottom stream.

Example 7
In Example 7, using the input stream containing methyl-di-n-hexylamine listed in Example 6, in the apparatus described in Example 5, an increase in oil temperature caused a similar amount of 99.8%. Attempts were made to obtain formic acid as the top product. To that end, the input stream 666 g / h mentioned in Example 6 was fed. At an oil temperature of 205 ° C., finally 99.8% formic acid 103 g / h could be obtained as the top product. At that time, 79% by mass of formic acid 20 g / h was extracted as a lateral flow. The remaining residue was discharged as a bottom stream.

  Examples 5, 6 and 7 clearly support the adverse effect in the case of pure distillation of formic acid by the presence of methyl-di-n-hexylamine. Under otherwise the same conditions, the amount of pure formic acid that can be achieved is clearly reduced. In this case, when 4% by weight of methyl-di-n-hexylamine is present, only 90 g / h of 99.8% formic acid can be obtained as the top product for 105 g / h. It was. To compensate for the decrease, it is necessary to increase the bottom temperature and thus introduce energy. In this case, by raising from 200 ° C. to 205 ° C., at least 103 g / h of 99.8% formic acid could be obtained as the top product.

Example 8
In the distillation column described in Example 5, at an oil temperature of 194 ° C. and a top pressure of 150 hPa (absolute pressure), from test 7, 20% by weight formic acid, 2% by weight water, 4% by weight methyl-di- 650 g / h of a mixture containing n-hexylamine and 70% by weight tri-n-hexylamine was fed to 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 99.8% formic acid of 50 g / h and a side stream of 75 g / h of 75% aqueous formic acid from the sixth stage of the distillation column; A bottom discharge of 515 g / h was removed. The resulting side stream was analyzed for the tri-n-hexylamine and methyl-di-n-hexylamine content of the stream. The stream 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 increase of methyl-di-n-hexylamine over tri-n-hexylamine is 10 times possible in the so-called formic acid purification column side extract.

  A apparatus for producing a stream containing formic acid and tertiary amine (I), an apparatus for hydrolyzing methyl formate to produce a stream containing formic acid, tertiary amine (I) and water , An apparatus for hydrogenating carbon dioxide to produce a stream containing formic acid, tertiary amine (I) and water, A1 hydrogenation reactor, stirred tank, A2 phase separation vessel, tubular reactor, A3 Extraction unit, tubular reactor, equipment for separating B by-products, distillation equipment for separating methyl formate, methanol and water, separating organic decomposition products of methanol, water and tertiary amine (I) B1 tower body, oil-heated falling film evaporator and condenser, and distillation apparatus having a controllable reflux separator at the top of the tower, B2 tower body, oil-heated falling film steamer And condensers and distillation apparatus with controllable reflux separator at the top of the column, C distillation apparatus, distillation apparatus for formic acid acquisition, distillation apparatus for formic acid acquisition, C1 column body and condenser and column Controllable reflux separator at the top, C2 oil-heated falling film evaporator, D-phase separation vessel, E-phase separation vessel, F distillation unit, tower body, oil-heated bottom vessel and control at the top of the column Distillation device with possible reflux separator, X mixing vessel, Y vessel

Claims (11)

A method for obtaining formic acid by thermal separation of a stream containing formic acid and a tertiary amine (I) having a boiling point at least 5 ° C. higher than formic acid at a pressure of 1013 hPa (absolute pressure),
(A) By combining the tertiary amine (I) and the formic acid source, the formic acid and the tertiary amine (I) are contained, and the molar ratio of formic acid to the tertiary amine (I) is 0.5 to Producing a liquid stream having 5;
(B) separating from 10 to 100% by mass of by-products contained therein from the liquid stream obtained from step (a);
(C) From the liquid stream containing formic acid and tertiary amine (I) obtained from step (b), in a distillation apparatus, a bottom temperature of 100 to 300 ° C. and a pressure of 30 to 3000 hPa (absolute pressure) The formic acid is separated by distillation with the tertiary amine (I) to be used in step (a) and the separation rate in the distillation apparatus described above, so that two liquid phases are formed in the bottom discharge. Selected as
(D) The bottom discharge from the distillation apparatus mentioned in step (c) above is separated into two liquid phases, the upper liquid phase having a molar ratio of formic acid to tertiary amine (I) of 0 And the lower liquid phase has a molar ratio of formic acid to tertiary amine (I) of 0.5 to 4,
(E) returning the liquid phase above the phase separation from step (d) to step (a), and (f) changing the liquid phase below the phase separation from step (d) to step (b) and / or Or in the method of returning to (c),
(G) From the liquid phase above 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 (absolute pressure) at a pressure of 1013 hPa (absolute pressure). A low boiler having a boiling point lower than that of the tertiary amine (I) by at least 5 ° C. is separated by distillation, and the stream having the reduced low boiler is reduced to one of the steps (a) to (f) described above. Returning to the method.   2. The method according to claim 1, wherein a formic acid source containing methyl formate is used in step (a) in the presence of water, the formic acid source comprising formic acid, tertiary amine (I) and methanol. Wherein the liquid stream is obtained by hydrolysis of methyl formate.   The method according to claim 1, wherein in step (a), a formic acid source containing carbon dioxide, hydrogen and a homogeneous catalyst is used, from which the formic acid and the tertiary amine (I) are contained. A process characterized in that the liquid stream is obtained by homogeneous catalytic hydrogenation of carbon dioxide.   The method according to any one of claims 1 to 3, wherein the liquid stream produced in step (a) comprises formic acid at a concentration of 1 to 99% by weight relative to the total amount of the stream. A process comprising a tertiary amine (I).   5. A process according to any one of claims 1 to 4, wherein the separation rate in the distillation apparatus mentioned in step (c) is such that the molar ratio of formic acid to tertiary amine (I) in the bottoms discharge is A method characterized in that it is selected to be 0.1-2.0.   6. The method according to any one of claims 1 to 5, wherein 0.01 to 50% of the liquid phase above the phase separation from step (d) is fed to step (g). Feature method.   7. A method according to any one of claims 1 to 6, characterized in that the stream with reduced low boilers is returned from step (g) to step (a).   7. A method according to any one of claims 1 to 6, characterized in that the stream with reduced low boilers is returned from step (g) to step (b). 9. The process according to claim 1, wherein the tertiary amine (I) is represented by the general formula (Ia).
NR ¹ R ² R ³ (Ia)
In which the radicals R ¹ to R ³ are the same or different and, independently of one another, are unbranched or branched, acyclic or cyclic, aliphatic, Represents an araliphatic or aromatic group each having 1 to 16 carbon atoms, wherein the individual carbon atoms are independently of one another selected from the groups -O- and> N- Wherein two or all three groups may be bonded to each other, forming a chain containing at least four atoms each], characterized in that an amine is used. how to. 10. The process according to claim 9, wherein the tertiary amine (I) is represented by the general formula (Ia), in which the groups R ¹ to R ³ are independently of each other C ₁ -C _12. - alkyl, C ₅ -C ₈ - wherein the cycloalkyl, the amine is selected from the group of benzyl and phenyl are used. 11. The process according to claim 10, wherein the tertiary amine (I) is represented by the general formula (Ia), in which the radicals R ¹ to R ³ are independently of each other C ₅ -C _8. A process characterized in that an amine selected from the group of alkyls is used.

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