Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/36—Preparation of carboxylic acid esters by reaction with carbon monoxide or formates
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C69/00—Esters of carboxylic acids; Esters of carbonic or haloformic acids
  • C07C69/02—Esters of acyclic saturated monocarboxylic acids having the carboxyl group bound to an acyclic carbon atom or to hydrogen
  • C07C69/04—Formic acid esters
  • C07C69/06—Formic acid esters of monohydroxylic compounds

Definitions

• the present invention relates to a process for the preparation of methyl formate by reacting methanol with carbon monoxide at a pressure of 0.5 to 10 MPa abs and a temperature of 50 to 150 ° C in the presence of a metal alcoholate as a catalyst in a reactor, in which the A gas stream is withdrawn from the reactor, methyl formate entrained in this gas stream is separated off by condensation and the remaining gas stream is returned to the reactor in whole or in part as a recycle gas stream.
• Methyl formate (methyl formate) is an important intermediate in the production of formic acid and is obtained industrially by continuous carbonylation of methanol in the liquid phase in the presence of sodium or potassium methylate as a catalyst at temperatures in the range from about 50 to 150 ° C (see Ullmann's Encyclopedia of Industrial Chemistry, th edition 6, 2000 electronic release, Chapter "FORMIC ACID - production",).
• the reaction is a homogeneously catalyzed equilibrium reaction in which the equilibrium is shifted towards methyl formate with increasing carbon monoxide partial pressure and falling temperature.
• the known methods are operated at a pressure of up to 30 MPa abs and a temperature of 50 to 150 ° C.
• alkali metal formate In the production of methyl formate mentioned, two undesirable side reactions occur in particular, which can lead to serious problems in the continuously operated process. Both side reactions lead to the formation of alkali metal formate.
• the alkali metal methylate used reacts with any traces of water introduced in a hydrolysis reaction to form alkali metal formate and methanol.
• the alkali metal methylate used also reacts with existing methyl formate to form alkali metal formate and wench ethyl ether. Due to its insufficient solubility in the reaction medium, the alkali metal formate can then lead to deposits in the apparatus and pipelines and even blockage of pipes and valves.
• the risk of salt precipitation is particularly high in the case of a high methanol conversion and thus a high concentration of methyl formate and can therefore in principle be reduced by setting a partial conversion while ensuring a low concentration of methyl formate.
• DE patent specification 926 785 describes a high-pressure process operating at 30 MPa, in which only a low catalyst concentration of 0.25% by weight sodium (corresponding to 0.59% by weight sodium methylate) is used to reduce salt separation becomes.
• the reactor contents are continuously stirred in order to keep the separated amounts of salt in suspension.
• the liquid reactor discharge which contains about 90% methyl formate, is expanded and worked up by distillation.
• DE-Auslegeschrift 1,046,602 describes a continuous, two-stage process in the presence of 0.5 to 5% by weight of alkali metal methylate at a pressure of 5 to 30 MPa. Deposits are to be prevented by ensuring a turbulent flow in the reactor. The total conversion of methanol is about 90%. The liquid reactor discharge is let down and worked up by distillation.
• DE-Auslegeschrift 1 147 214 describes a high-pressure process operating at 15 to 20 MPa, in which the reaction takes place in the presence of 0.12 to 0.3 mol% of alkali metal methylate in at least two successive reaction zones characterized by decreasing temperatures, and that Carbon monoxide is fed to the reactor in at least two substreams at different heights. Short-term, recurring changes in the proportions of carbon monoxide are intended to prevent the salt-like precipitation from settling. The total conversion of methanol is up to 97%. The liquid reactor discharge is let down and worked up by distillation.
• WO 96/26178 describes a high-pressure process in which the reaction is carried out in the presence of 0.05 to 0.2% by weight of alkali metal methylate at a pressure of 21 to 25 MPa.
• concentration of methyl formate in the reactor discharge is up to 97% by weight.
• the liquid reactor discharge is let down and worked up by distillation.
• DE-A 2 243 811 describes a process in which the reaction is carried out in the presence of 0.4 to 1.5% by weight of alkali metal methylate in countercurrent mode at a pressure of 4 to 30 MPa and which has a plurality of reaction zones connected in series. In particular, columns with flooded trays are mentioned as preferred apparatus.
• the reaction mixture obtained in the bottom of the column contains 20 to 70% by weight of methyl formate and is worked up by distillation after expansion.
• EP-A 0 617 003 describes a process in which the reaction is carried out in the presence of 0.4 to 1.5% by weight of alkali metal methylate at a pressure of 1 to 30 MPa. First, the reactants are brought together in a mixing zone and at least partially converted. The reaction solution obtained is finally saturated with carbon monoxide and fed to a post-reaction zone without the addition of further starting materials. The liquid reactor discharge is let down and worked up by distillation.
• WO 01/07392 describes a process in which the reaction takes place in the presence of 0.05 to 0.5% by weight of alkali metal methylate at a carbon onoxide pressure of 9 to 18 MPa.
• the liquid reactor discharge which contains about 60 to 95% by weight of methyl formate, is fed to a distillation column in order to remove the methyl formate.
• the remaining catalyst and methanol-containing bottom stream is recycled again, with residual catalyst and catalyst degradation products being withdrawn from a partial stream thereof via a desalination device.
• space-time yields in the range from 370 to 880 g / l-h of methyl formate were achieved.
• US 4,661,624 discloses a two-stage process with recycling of the catalyst-containing, methanolic solution.
• the reaction is carried out at a pressure of 0.48 to 6.9 MPa (70 to 1000 psia) and a concentration of alkali metal methylate of 1 to 8 mol% (corresponding to 1.7 to 13.5% by weight of sodium methylate).
• additional methanol is fed in countercurrent to convert the remaining carbon monoxide.
• the process is operated at an extremely low conversion, so that the liquid reactor discharge contains only about 2 to 20 mol% of methyl formate. It is fed to a distillation column to remove the methyl formate. The remaining bottom stream containing catalyst and methanol is recycled.
• No. 4,216,339 teaches a process in which the reaction takes place in the presence of 0.2 to 4% by weight of alkali metal methylate at a pressure of 2 to 11 MPa and in which the carbon monoxide supplied is passed through a self-priming jet nozzle, which is characterized by a sufficiently high Circulation flow is operated, is dispersed in the liquid reaction mixture.
• a corresponding amount of reaction mixture is continuously removed from the liquid circulating stream and worked up by distillation after the expansion.
• a concentration of methyl formate of 51% by weight was obtained at a pressure of 4.4 MPa in the reaction mixture.
• DE patent specification 863 046 teaches a continuously operating low-pressure process in which methanol and 1 to 2% by weight sodium (corresponding to 2.3 to 4.7% by weight sodium methylate) in a bubble column filled with packing elements from top to bottom and coal Lenmonoxide is fed in countercurrent from bottom to top and reacted at a pressure of about 2.5 to 3.0 MPa (25 to 30 atmospheres).
• the reaction mixture is continuously removed from the bottom of the reactor and led to working up by distillation.
• the gas withdrawn at the top of the reactor is passed through a cooler, freed of entrained methyl formate in a separator and returned to the reactor to ensure a sufficiently high gassing stream mixed with fresh carbon monoxide.
• the methyl formate condensed from the gas phase in the separator is also sent for workup by distillation.
• the pressure and temperature must be set so that the catalyst and its degradation products are kept in solution.
• a method improved compared to DE 863 046 is described in DE patent 880 588.
• methanol and 1.6 to 2.5% by weight of sodium are supplied in a bubble column with carbon monoxide in a cocurrent from the bottom upwards and implemented at a pressure of up to 3.0 MPa (up to 30 atmospheres).
• Liquid reaction mixture is removed from a gas dome located on the reactor head and fed back to the reactor base via a circulation pump.
• the gaseous phase is removed from the upper end of the gas dome, passed through a cooler, then freed of entrained methyl formate in a separator and returned to the reactor to ensure a sufficiently high gassing stream mixed with fresh carbon monoxide.
• all of the methyl formate is removed via the gas phase and, after the condensation, fed to the working-up by distillation.
• DE 880 588 shows that, using the 770 L reactor (8 m length and 35 cm clear width) at 3.0 MPa and 85 to 88 ° C. in continuous operation, 3.1 kg of methyl formate per Hour could be obtained. This corresponds to a space-time yield of only 4 g / lh methyl formate.
• the methyl formate concentration in the condensed raw discharge was about 60% by weight (38 to 40% by weight of methanol).
• a disadvantage of the process described is the very low space-time yield of 4 g / lh of methyl formate, which is approximately two orders of magnitude below the values achieved in the high-pressure process, and the very high catalyst concentration of 3.8 up to 5.9% by weight of sodium methylate and the high consumption of catalyst.
• the method described is therefore very uneconomical.
• a process for the preparation of methyl formate by reacting methanol with carbon monoxide at a pressure of 0.5 to 10 MPa abs and a temperature of 50 to 150 ° C in the presence of a metal alcoholate as a catalyst was found in a reactor in which the reactor withdraws a gas stream, separates methyl formate carried from this gas stream by condensation and returns the remaining gas stream to the reactor in whole or in part as a recycle gas stream, which is characterized in that in at least one area of the reactor in which the gas is essentially in one direction flows, sets an average gas empty pipe speed of 1 to 20 cm / s.
• an average empty gas pipe velocity of 1 to 15 cm / s, particularly preferably 2 to 10 cm / s and very particularly preferably 5 is set in at least one area of the reactor in which the gas flows essentially in one direction up to 10 cm / s.
• gas empty pipe speed is to be understood as the quotient of the volume flow of the gas flowing in this area and the free cross-sectional area of the reactor area to be considered.
• the volume flow of the gas u flowing in this area comprises the entire gas flow under the given pressure and the given temperature.
• the free cross-sectional area is to be understood as the cross-sectional area accessible to the fluid reaction medium. The part of any internals that are not accessible to the fluid reaction medium is not counted towards the free cross-sectional area. It should be pointed out that the liquid fraction present in the reactor area to be considered is by definition not taken into account when calculating the gas empty pipe speed.
• the reactor is, for example, a bubble column reactor
• the gas is generally introduced in the lower part of the reactor, the direction of flow of the gas in the reaction medium being essentially directed upwards due to the buoyancy.
• the bubble column reactor therefore usually contains only one area with respect to the direction of flow of the gas.
• the gas is introduced into a plug-in tube located in the center of the reactor through a nozzle.
• the impulse introduced also conveys further, gaseous and liquid reaction medium into the plug-in tube and induces an internal circuit in the reactor.
• the reaction medium flows through the insertion tube, is deflected at the end of the insertion tube by a so-called baffle plate, flows in the opposite direction between the inner reactor wall and the insertion tube, and is finally redirected again by the impulse generated by the nozzle and pulled into the insertion tube again.
• the jet loop reactor thus generally contains two areas with respect to the direction of flow of the gas, namely an area inside the insertion tube and an area outside the insertion tube, in which the gas flows in the opposite direction, at least one of these two areas in the method according to the invention has average gas empty tube speed of from 1 to 20 cm / s.
• a metal alcoholate or mixtures of different metal alcoholates are used as the catalyst.
• the reaction is carried out at a concentration of catalyst used of 0.01 to 2 mol / kg of liquid reaction mixture, preferably 0.02 to 1.5 mol / kg of liquid reaction mixture and particularly preferably 0.8 to 1.2 mol / kg of liquid reaction mixture.
• concentration of catalyst used is to be understood as the sum of the concentrations of metal alcoholate and its secondary products, in particular the metal form formed in an undesired side reaction.
• Suitable cations of the metal alcoholates are the cations of the metals of the 1st to 15th group of the periodic table.
• Suitable metals are, for example, alkali metals, alkaline earth metals or aluminum.
• the alkali metals and alkaline earth metals are preferred and the alkali metals are particularly preferred.
• Sodium and potassium, in particular potassium, may be mentioned as very particularly preferred metals.
• Suitable alcoholate anions are alcoholate anions with 1 to 12 carbon atoms, preferably unbranched or branched C ⁇ ⁇ to -C 2 alkanolate anions, such as methanolate, ethanol, 1-propanolate, 2-propanolate, 1-butanolate, 2-butanolate, 2-Me - Thyl-1-propanolate, 2-methyl-2-propanolate, 1-pentanolate, isoamylate, 1-hexanolate, 1-heptanolate, 1-octanolate, 1-nonanolate and 1-decanolate. Methanolate may be mentioned as a particularly preferred alcoholate.
• sodium methoxide and potassium methoxide, in particular potassium methoxide, are preferably used as the catalyst.
• the reaction of methanol with carbon monoxide in the presence of the metal alcoholate as catalyst in the process according to the invention is preferably carried out at a temperature from 50 to 110 ° C., particularly preferably from 60 to 100 ° C. and very particularly preferably from 60 to 85 ° C. Reaction temperatures of 60 to 85 ° C surprisingly lead to an increased carbon monoxide conversion compared to reaction temperatures above 85 ° C with the same residence time.
• the reaction is preferably carried out at a pressure of 0.5 to 6 MPa abs, particularly preferably from 1 to 5 MPa abs and very particularly preferably from 2 to 4 MPa abs.
• the molar ratio of the total amount of methanol fed to the reactor and the amount of freshly fed carbon monoxide in the process according to the invention is generally 1 to 5.
• the molar ratio mentioned is preferably 1 to 4 and very particularly preferably 1.4 to 3.3 ,
• the methanol fed to the reactor is composed of the freshly fed methanol and the optionally recycled methanol.
• the above molar ratio is based on the amount of freshly added carbon monoxide. Since in the process according to the invention, in addition to the supply of fresh carbon monoxide, a circulating gas stream containing carbon monoxide is also returned to the reactor, the molar methanol / carbon monoxide ratio actually present in the reactor is lower than the above-mentioned molar ratio and is generally dependent on the amount of carbon monoxide returned in the range of 0.06 to 0.2.
• all reactors which are suitable for gas / liquid reactions and which have an average empty gas pipe velocity of 1 to 20 cm / in at least one area of the reactor in which the gas flows in one direction can be used as reactors in the process according to the invention. s can be achieved.
• a reactor should also be understood as a series connection of several individual devices.
• the bubble column reactor and the loop reactor may be mentioned as suitable apparatus.
• the bubble column reactor and the jet loop reactor are preferred.
• the reactors can optionally be equipped with various internals such as packing, static mixers or heat exchangers.
• the supply of the methanol-containing liquid stream and the carbon monoxide-containing gas stream can take place in different ways, depending on the type of reactor used.
• the gas stream is generally added in the lower region of the reactor using the usual gassing devices.
• the methanol-containing liquid stream can be added, for example, in the upper area (countercurrent mode) or in the lower area (cocurrent mode).
• the gas stream is generally supplied in the upper region of the reactor, with the pulse direction pointing downward, or in the lower region of the reactor, with the pulse direction directed upward.
• the liquid stream containing methanol can be added at one or different points on the reactor.
• a bubble column When a bubble column is used, it is preferably operated in a direct current mode with respect to the supply of the liquid stream containing methanol and the gas stream containing carbon monoxide.
• the gas stream containing carbon monoxide and the gas stream containing methanol are thus added in the lower region of the bubble column.
• a gas stream is continuously withdrawn from the top of the reactor. This generally contains methyl formate, unreacted methanol and unreacted carbon monoxide.
• the entrained methyl formate is separated from this gas stream by condensation and the remaining gas stream is returned to the reactor in whole or in part as a recycle gas stream.
• the liquid stream which is condensed out of the removed gas stream and which generally contains methyl formate and unreacted methanol is distilled separated and the methanol obtained also returned to the reactor.
• Figure 1 shows a simplified process flow diagram of a preferred embodiment for the production of methyl formate using a bubble column reactor with recirculation of the circulating gas stream containing carbon monoxide and with recirculation of a liquid stream containing methanol.
• Freshly supplied carbon monoxide (I) is mixed with the recycle gas stream via line (3) and fed to the bubble column reactor (B) via a compressor (A). This is also supplied via line (7) and the compressor (G) with freshly fed methanol (III), with freshly fed catalyst (II) and with recycled methanol.
• the reactor contains a device for removing catalyst-containing reaction mixture (VI).
• a gaseous stream is withdrawn via line (1) and methyl formate carried along as well as methanol carried out are condensed out in a heat exchanger (C).
• the remaining gas stream is returned to the reactor via line (2) and (3), a device for discharging exhaust gas (V) generally being present.
• the liquid condensed out in the heat exchanger (C) is fed via line (4) to a condensate tank (D) and from this line (5) into a distillation column (E).
• the liquid stream obtained as the bottom product and containing methanol is returned to the reactor (B) via line (6) and the compressor (F).
• Methyl formate (IV) is obtained as the top product of the distillation column.
• a cascaded reactor is also to be understood to mean a series connection of a plurality of individual apparatuses, each of which can be cascaded or non-cascaded independently of one another.
• the cascaded bubble column is an example of a multi-cascaded apparatus. This is generally cascaded through sieve trays.
• a cascaded reactor in which the top zone is operated at a temperature of 80 to 150 ° C. and preferably 80 to 120 ° C. is particularly preferably used in the process according to the invention.
• the temperature range mentioned enables a particularly advantageous evaporation rate of the methyl formate formed.
• this is / are preferably operated at a reaction temperature of 60 to 85 ° C. Since the evaporation in the uppermost zone requires evaporation energy, it is particularly advantageous to introduce this energy by additionally heating the reaction mixture. To this end, it is particularly preferred to take reaction mixture from a previous zone, pass it through a heat exchanger and then into the uppermost zone.
• the particularly preferred process mentioned in the last paragraph has the particular advantage of evaporating the methyl formate formed at a temperature which ensures a particularly advantageous evaporation rate, while simultaneously carrying out the reaction of methanol with carbon monoxide in the presence of a metal alcoholate as a catalyst at a temperature which enables particularly high carbon monoxide conversion.
• Figure 2 shows a particularly preferred embodiment of a cascaded reactor using the example of a bubble column in which the reaction mixture is removed in the lower region via line (1), heated in a heat exchanger (D) and fed to the upper zone via line (2).
• This is preferably separated from the previous zone by a sieve plate (B) with a drain shaft (C).
• the sieve bottom enables the gas flowing from the preceding zone to pass through, so that it bubbles up in finely divided form through the reaction mixture in the uppermost zone and thus promotes the stripping effect.
• the gas stream containing carbon monoxide, methyl formate and methanol is removed via line (3).
• the liquid in the top zone which does not evaporate, runs back into the previous zone via the drain shaft.
• an analogous construction as shown in Figure 2 is also possible when using other devices, such as a loop reactor.
• a process is very particularly preferred in which the gas stream withdrawn from the reactor is separated in an amplification column into a bottom stream containing methyl formate and a top stream containing carbon monoxide and methyl formate, methyl formate entrained in the top stream is separated off by condensation and the remaining gas stream is wholly or partly as a circulating gas stream returns to the reactor.
• FIG 3 shows a simplified process flow diagram of a preferred embodiment for the production of methyl formate using a rectifying column with recirculation of the circulating gas stream containing carbon monoxide and with recirculation of a liquid stream containing methanol.
• Freshly supplied carbon monoxide (I) is mixed with the recycle gas stream from line (3) and fed to the bubble column reactor (B) via a compressor (A). This is also supplied via line (7) and the compressor (G) with freshly fed methanol (III), with freshly fed catalyst (II) and with recycled methanol.
• the reactor contains a device for removing catalyst-containing reaction mixture (VI).
• a rectifying column (H) which separates the gas stream from the reactor into a bottom stream containing methyl formate and a top stream containing carbon monoxide and methyl formate.
• the bottom stream of the rectification column (H) is passed via line (9) into a distillation column (E).
• the liquid stream obtained as the bottom product of column (E) and containing methanol is returned to the reactor (B) via line (6) and the compressor (F).
• Methyl formate (IV) is obtained as the top product of the distillation column.
• the top product of the rectification column (H) is passed via line (1) into a heat exchanger (C), in which methyl formate and methanol which are carried along are condensed out.
• the remaining gas stream is returned to the reactor via line (2) and (3), a device for discharging exhaust gas (V) generally being present.
• the liquid condensed out in the heat exchanger (C) is fed via line (4) to a condensate container (D) and methyl product (IV) is obtained from this via line (5) as a product.
• a portion of the condensed liquid is fed to the rectifying column (H) as reflux via line (8).
• the process according to the invention for the production of methyl formate is technically simple to carry out, leads to no or only very little deposition of salt-like deposits, requires only a small outlay in terms of apparatus, in particular because of the low pressure compared to the known processes, and has a low energy consumption and a low consumption of catalyst and enables a space-time yield of methyl formate of> 100 g / lh.
• the advantages mentioned are achieved in particular by the high gas empty tube speed and the removal of gaseous methyl formate from the reactor.
• Example 1 a test facility as shown in Figure 1 was used. A bubble column with an inner diameter of 55 mm and a total height of 1000 mm was used as the reactor.
• the total flow of the gas flowing through this area is calculated from the circulating gas flow and the gas flow of freshly supplied carbon monoxide, with only half of the freshly supplied carbon monoxide flow being calculated on account of the consumption of carbon monoxide.
• the total flow of gas flowing through was thus 15.5 kg / h, the average molar mass being approximately 28 g / mol, the pressure 3.0 MPa abs and the temperature 75 ° C.
• the volume flow of the gas flowing through is calculated to be 148 cm 3 / s.
• the mean empty gas pipe speed was 6.2 cm / s.
• Example 1 shows that a high space-time yield of about 200 g of methyl formate per liter of gassed volume and hour can be obtained by the process according to the invention at a relatively low pressure of 3.0 MPa abs and a relatively low reaction temperature of 75 ° C. ,
• the catalyst consumption is also very low with about 1 g of potassium methylate per kg of methyl formate formed. Due to the relatively low pressure of 3.0 MPa abs and the removal of gaseous methyl formate from the reactor, the process requires only a simple technical and apparatus expenditure.

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• 2002
  • 2002-04-19 DE DE10217528A patent/DE10217528A1/de not_active Withdrawn
• 2003
  • 2003-04-15 BR BR0308912-6A patent/BR0308912A/pt not_active IP Right Cessation
  • 2003-04-15 AU AU2003226810A patent/AU2003226810A1/en not_active Abandoned
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