DE2147115A1 - - Google Patents

Description

9 1 L 7 1 1

PATENTANWÄLTE A I * ♦ / I I DR. O. DITTMANN K. L. SCHIPP DR. A. ν. FIVE BR DIPL. ING. P. StRBHL

8 MUNICH Θ0 MARIAHILFPLATZ 2 ft S

DA-4447

Description of the patent application

of the company

AJINOMOTO CO., INC. 7, 1-chome, Takara-cho, Chuo-ku, Tokyo, Japan

concerning
Process "for the preparation of methyl formate

Priority Sept. 21, 1970 No. 45-81958, Japan

The invention relates to the production of methyl formate and, more particularly, to a process for the production of methyl formate from carbon monoxide and hydrogen.

The production of methyl formate from methanol and carbon monoxide in the gas phase or in the liquid phase at increased Pressure and in the presence of an alkaline catalyst [cf. Brit. Patents 970,072 and 108,454; Indian J. Technol., JSj. [8], 266-7 (1967)] and the production of methanol with

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good yield from a mixture of carbon monoxide and hydrogen in a molar ratio of 1: 2 [cf. Chem. & Process Engg., 1968 [6], 69; Brit. U.S. Patent 1,010,871, Hydrocarbon Processing, 40 [11], 202 (1969)] are known.

The synthesis of methyl formate by the methods described above would be a purification of the CO-E ^ mixture for the Methanol synthesis and the separation of the hydrogen gas from it the unconverted gases, because from the unconverted gases resulting from the methanol synthesis, no starting materials can be prepared which are suitable for methyl formate synthesis. The combination of the two known methods for the synthesis of methanol and for the synthesis of methyl formate from methanol would thus be a complex one Make procedural conduct necessary so that such a procedure is not economical "

It has now been found that methyl formate is produced continuously from a single stream of mixed carbon monoxide and hydrogen gas can be prepared in excellent yields if one follows the procedure outlined in the enclosed Flow sheet is explained.

First stage

Carbon monoxide and hydrogen in a molar ratio of at most

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2: 1 and methanol v / ground in the presence of an alkaline catalyst kept at elevated pressure until at most half of the carbon monoxide has reacted with the methanol to form methyl formate. It is with worked an amount of methanol that is at least sufficient for such a reaction.

Second step

The temperature of the reaction mixture is reduced, until the methyl formate formed separates as a liquid from the unconverted gases. Ss can then from the System.

Third step

The unconverted gases are washed with cold methanol to remove constituents not used in the second stage, whereupon the washing liquid can be returned to the first stage or, after fractionation, returned to the third stage.

Fourth stage

Bas washed gas, which consists essentially of pure carbon

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monoxide and hydrogen is in the presence of a catalyst for the methanol synthesis in itself known Way converted to methanol. Part of the methanol can be returned to the third stage and the remainder of the Reaction product can be passed into the first stage. The unreacted gas is returned to the fourth stage.

• As can be seen from the drawing, the initial gas mixture can be produced by partial oxidation of hydrocarbons in crude oil or natural gas. However, other known methods can also be used for this purpose, for example the partial oxidation of coke and the reforming of hydrocarbons in the presence of carbon dioxide and water vapor. Finally, suitable mixtures of carbon monoxide and hydrogen can be used, which are by-products of many industrial processes, for example the production of acetylene hydrocarbons from other hydrocarbons. The mixture should contain the carbon monoxide and hydrogen in a molar ratio of at most 2; 1 included. The ratio of 1: 1 to 1: 2 is preferably used. An excess of hydrogen, which corresponds to a ratio exceeding 1: 2, represents ballast which, although it does not interfere with the reaction, adversely affects the economic viability of the process.

BATH ORIGINAL

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The gas mixture should contain less than 10 ppm sulfur and a maximum of 0.5 % carbon dioxide and 1 % water. These values can easily be obtained by the usual methods. The catalysts used in the first stage are not poisoned by impurities that are present in the above-mentioned areas. The catalysts work satisfactorily over long periods of time despite the presence of these substances. The sulfur and the unsaturated hydrocarbons, such as olefins and dienes, are converted in the first stage into high-boiling compounds which can easily be separated from the unconverted gas. In this way, these substances do not impair the later stages, in particular the methanol synthesis in the fourth stage.

The alkaline catalysts used in the first stage include the alkoxides and salts of weak acids of the alkali metals, E.g. of lithium, sodium, potassium, rubidium and cesium as well as the salts of weaker- '. Alkaline earth metal acids, e.g. beryllium, magnesium, calcium, strontium and barium. Suitable starting materials for the preparation of the above Alkoxides are alkyl alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol and amyl alcohol, cycloalkyl alcohols such as cyclohexanol and hydroxy ethers, such as 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 3-methoxypropanol and 4-methoxybutanol. To manufacture the. mentioned salts suitable weak

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BATH ORIGINAL

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Acids are ζ. B. carbonic acid and carboxylic acids, such as Formic acid, acetic acid and benzoic acid.

The alkaline catalysts obtainable in this way can be advantageous with ethylene oxide and / or alkyl, cycloalkyl, aralkyl or aryl substituted Ethylene oxide (see British patents 970 072 and 1 084 549) are used.

The temperature de: reaction zone in the first stage of the process is from 20 to 140.degree. C., preferably at 80.degree up to 120 ° C. The ratio of I-ethanol to carbon monoxide should be between 1: 0.5 and 1: 5, preferably between 1: 1 and 1: 3. The residence time in the Reaction: one is adjusted so that no more than half of the carbon monoxide originally present is consumed will. The rest is available for the methanol synthesis in the fourth stage. The first stage is preferred carried out at a pressure between 50 and 200 at. The pressures maintained in the system can be very close to one another. Both reactions can occur with your same pressure to be carried out, eliminating the need the use of compressors within the system is avoided.

When carrying out the methyl formate formation reaction

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In the liquid phase, stirring is expediently carried out by blowing in or bubbling in the starting materials into the reaction mixture. The reaction mixture can be stirred more strongly and more effectively when r.:an into the reaction zone feeds the gases that contain gaseous hydrogen, which does not interfere with the formation of methyl formate. As a result After stirring, the temperature distribution in the reaction mixture becomes more uniform and a higher expansion can be achieved of methyl formate, based on the methanol used, can be obtained. Also results in the reaction of the gas phase the hydrogen gas has a uniform temperature distribution. In this way, the temperature control is much easier than it is in the synthesis of methyl formate Methanol and carbon monoxide, without hydrogen, is the case. However, the hydrogen represents in the process of the invention is not only a very good diluent, as it is used in the subsequent methanol synthesis.

When the reaction mixture cools in the second stage of the process, a condensate of methyl formate and unconverted methanol separates out of the gas mixture. This gas mixture consists essentially of carbon monoxide and hydrogen in a ratio of 2: 1 to 1: 4, depending on the initial composition and other variables. The condensate is fractionated to separate the methyl formate from higher-boiling components, such as methanol and the alkaline catalyst. Since the methyl formate formed is a very easy

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BATH ORIGINAL

represents volatile compound, can cause separation from others

higher boiling

Ingredients also by blowing through from the first Hot gases removed from the reaction zone happen through the condensate. The methyl formate can, if desired, further rectified while the higher boiling components are sent back to the first stage.

The gaseous material discharged from the condensation zone is used to separate the alkaline catalyst, methyl formate and impurities such as sulfur, washed with cold methanol. The washing liquid can be returned to the first stage or after fractionation be returned to the washing zone. A conventional extraction tower for countercurrent contact can be used here of the downward flowing liquid methanol cooled to 0 ° C or less is used with the ascending gas will. The alkaline catalyst and the remaining methyl formate are extracted from the gas and the methanol can if desired, can be recovered by heat exchange with the hot gases discharged from the fourth stage. That The scrubbed gas is practically free of such materials as the catalyst poisons for the catalysts of methanol synthesis in the fourth stage represent, like sulfur, unsaturated hydrocarbons that are readily available at a concentration can be maintained at less than 0.1 ppm.

In the fourth stage of methanol synthesis, the molar ratio must be nis carbon monoxide to hydrogen be less than 1: 2.

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In this stage, sufficient methanol should be formed that it is sufficient to charge the first stage. at The maintenance of the desired ratios can be adjusted by using the method of the invention the carbon monoxide / hydrogen mixture was only the first Stage is fed. If such an approach is not appropriate, then some of the feed gas will be used subjected to a water gas shift in the presence of a conventional catalyst system. Be that way the original impurities present in the raw gas are removed and the reaction product is used for methanol synthesis suitable.

The production of methanol from carbon monoxide and hydrogen can be carried out by conventional processes, for example by low-pressure processes, medium-pressure processes and high-pressure processes [cf. Brit. Patent Specification 1 010 871 and Hydrocarbon Processing, 40 , [11], 202 (1969)]. For this purpose, the known ■ catalysts _a for methanol synthesis, for example catalysts containing copper, can be used. The optimal gas pressure in the methanol synthesis reactor is in the range of 30 to 350 atm, depending on the catalyst used. However, as described above, it is also possible to operate in such a way that the pressures in the entire system are set very similar to one another. When the pressure of the cold scrubbed gas becomes low

/Zone

is lower than it is required for the methanol synthesis /, then the gas is

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at least compressed to 10 times the initial pressure. The gas can contain up to 30 % inert gases such as methane or nitrogen and relatively small amounts of carbon dioxide without the yield being impaired.

If a catalyst containing copper is used, the methanol synthesis is preferably carried out at catalyst temperatures of about 250 ° C. and gas pressures of 30 to 200 atmospheres, preferably 40 to 100 atmospheres. It is preferred to react one mole of carbon monoxide and carbon dioxide with 2 to 3 moles of hydrogen. The condensate obtained by cooling the reaction mixture consists of 99 % methanol. Bs is returned to the first stage after it has been dried if it contains moderate amounts of water, some of it being used in the third stage, as described above, in part. If the unreacted gas does not contain more than 30% inert substances, it can be returned to the methanol reactor. An excess of the inert gas is removed from the system by periodically or continuously withdrawing a portion of the gas from the high pressure system.

The invention is illustrated in more detail by the following examples.

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example 1

A gas mixture of 48% CO, 47 % hydrogen, 4 % CO ₂ , 0.3 % CH ^, 0.4% S and 0.3% other gases was produced in the conventional manner from crude oil, oxygen and water vapor. All percentages relate to the volume. The gas mixture was cooled to 40 ° C. and desulfurized with N-methyl-pyrrolidone, the sulfur and carbon dioxide contents in the gas being reduced to 2 ppm and 0.1 % , respectively.

Most of the purified gas was introduced as a continuous stream into a reactor filled with methanol was filled, which contained 48 g / l potassium methoxide. The pressure was 100 at, the temperature 80 ° C. Ini the reactor was with a rate of 50 mole percent of the carbon monoxide fed Introduced methanol containing potassium methoxide in the same concentration as above.

The gas continuously withdrawn from the reactor was cooled under its high pressure, whereby a liquid was condensed , the 69 wt .-% methyl formate, 26 wt .-% methanol, Contained 4% by weight potassium methoxide and 1% by weight water. The condensate was transferred to a low-pressure vessel in which the dissolved gases were released and then fractionated. the Methyl formate fraction was rectified. The heavier ones Compounds such as methanol, potassium methoxide and water were made

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diluted with methanol and pumped back into the reactor. Some of the higher-boiling compounds were removed from the system in order to keep the water content in the system at 0.1% or less before dilution with the methanol. The gases released at low pressure were freed from usable components by washing with methanol. Then they were either released into the atmosphere or burned down under a kettle.

The gas fraction not condensed by cooling contained hydrogen and carbon monoxide in a ratio of 1: 0.7. It was mixed with the rest of the purified raw gas. The resulting mixture was washed with cold methanol in a countercurrent washing tower. The washed gas emerged from this at a temperature of -40 ° C. The washed gas mixture was mixed with steam and, in the presence of a catalyst, subjected to a water gas shift in the usual manner. The resulting gas mixture of carbon monoxide, carbon dioxide and hydrogen was dried and introduced into the methanol reactor. It contained less than 0.5 ppm sulfur so that the catalyst was not poisoned.

Under typical operating conditions , the gas mixture fed to the methanol reactor consisted of 67 % hydrogen, 18 % carbon monoxide, 10 % carbon dioxide and 3 »5 % nitrogen and

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Methane (volume percent). In general, a volume ratio from 2 to 4 parts of hydrogen to 1 part of carbon monoxide and carbon dioxide.

The methanol reactor contained a catalyst composed of copper, zinc and chromium in an atomic ratio of 4: 2: 2 on a graphite support. The pressure is 50 at, the temperature 250 ° C. The gas mixture was in a ratio of 12 % at a space velocity of 6000 to 7000 / h, corresponding to a space-time yield of 0.26 kg / liter. Converted to methanol for an hour.

The gas discharged from the methanol reactor was cooled, whereby hydrous methanol was condensed with a purity of 99.5%. Part of the methanol was used to wash the gas fraction from the methyl formate reactor. The remainder was distilled at atmospheric pressure to remove the water and returned to the methyl formate reactor. The gas discharged from the methanol reactor and not condensed by cooling was returned to the methanol reactor until it contained 30% nitrogen. It was then partially released from the high pressure zone in order to keep the nitrogen concentration in the recirculated gas below 30 % . The discharged gas contained sufficient monoxide, hydrogen and methane to allow use as a fuel gas for water dispenser generators. Its expansion took away heat from the methanol used as the gas scrubbing liquid.

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Example 2

In a modification of the procedure of Example 1, that became off after the reaction mixture had cooled the gas fraction obtained from the methyl formate reactor washed with methanol at -40 ° C. The washing liquid was fractionated, to pure methanol, methyl formate and a small amount of a sulfur-containing material from each other to separate. The methanol was in the wash column, the methyl formate to the mixture after cooling of the reaction recycled liquid fraction obtained from the methyl formate reactor. The gradual loss of methanol in the The washing and fractionating columns were replaced with fresh methanol.

A portion of the methanol obtained from the gaseous effluent product of the methyl formate reactor was transferred to the methyl formate reactor after washing and a water gas shift, if this was necessary. Some of the unconverted gases from the methanol reactor were also transferred directly from the methanol reactor into the methyl formate reactor. The remainder of the gaseous reaction mixture was cooled to liquefy the methanol and allow a portion of the unreacted gas to be withdrawn. This was done in order to reduce the concentration of the inert gas (nitrogen) to less than 30 % . The liquefied methanol was in the

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Initiated methyl formate and the rest of the gas was returned to the methanol reactor.

Example 3

27 g of metallic potassium was dissolved in 1 liter of methanol, thereby obtaining 820 g of a solution containing 48 g of potassium methoxide. This solution was placed in a 2 liter reactor equipped with a stirrer. The reactor was then heated to 80 ° C. A synthesis gas consisting of hydrogen and carbon monoxide (H ₂ / CO = 1.67 in the molar ratio) containing 5 ppm sulfur and 0.1 % carbon dioxide was injected into the reactor until the pressure was 100 atm. While this pressure was maintained, 167 moles of synthesis gas were introduced into the reactor over a period of 26 minutes. After cooling to 25 ° C., the reaction mixture was taken out. Its weight was 1226 g. The reaction mixture was fractionated at normal pressure to give 842 g of methyl formate, 323 g: methanol and 61 g of a residue consisting of 48 g of potassium methoxide and 13 g of water. 58.1 % of the methanol had been converted to methyl formate, the rate of formation being 72.5 g / h g-potassium. The unreacted gas consisted essentially of 100 moles of hydrogen and 50 moles of carbon monoxide.

The unreacted gas was mixed with a synthesis gas composed of 5.5 moles of hydrogen and 5.5 moles of carbon monoxide. The GE-

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The mixture was washed with methanol which had a pressure of 23 kg / cm and a temperature of -40 ° C. The GE- ' scrubbed gas contained moisture levels less than 0.5 ppm.

The washed gas was mixed with water vapor at

a pressure of 85 kg / cm over a catalyst for the conventional water gas displacement passed and dried. In this way, 70 moles of hydrogen, 19 moles Carbon monoxide and 12 moles of carbon dioxide at a pressure of

ρ ρ

91 kg / cm obtained. This mixture was let down to 80 kg / cm, passed over a copper / zinc / chromium catalyst (40/20/20) at 250 ° C. and a space velocity of 10,000 per hour. Thereby, methanol was obtained with a conversion of 12 % . The space-time yield of the methanol was 770 g per liter of catalyst and hour. The methanol obtained from the reaction mixture by condensation contained less than 0.5 mol% of impurities.

• Claim

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Claims (1)

Patents n sprue _h 2H7115 Process for the production of methyl formate by reacting carbon monoxide and methanol in the gas phase at increased Pressure and elevated temperature in the presence of alkaline catalysts, characterized in that he a) in a first reaction zone carbon monoxide, hydrogen and methanol reacts with one another at elevated pressure, preferably from 50 to 200 atm, until at most half of them of the carbon monoxide has reacted with the methanol to form methyl formate, b) the reaction mixture thus obtained is cooled in a condensation zone until the methyl formate condenses and separates from the non-condensed gases, c) washes the uncondensed gas in a washing zone with cold methanol, d) the scrubbed gas with a catalyst for methanol synthesis at elevated temperature and elevated pressure, preferably from 30 to 350 atm, in a second reaction zone brings into contact until methanol is formed and that one e) the methanol formed in the first reaction zone for conversion with the carbon monoxide. 2 0 9 8 13/1829 Blank page