NL8303355A - METHOD FOR PREPARING ACETIC ACID. - Google Patents

Description

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Method for the preparation of acetic acid.

This invention relates to a process for the preparation of acetic acid, and more particularly by catalytic rearrangement of methyl formate.

The conversion of methyl formate to acetic acid 5 is a known reaction. For example, U.S. Patent 2,508,513 discloses a liquid phase process in which methyl formate is heated in the presence of a carbonyl-forming metal catalyst and a halide, the catalyst being defined as one or more of the metals of the iron group, preferably nickel. Examples are given of the use of nickel iodide hexahydrate and of nickel carbonyl. The process is carried out at a relatively high temperature, and although no yields are mentioned, the reference to by-products shows that it is relatively low. US patent 1,697,109 describes a process in which methyl formate is converted in the vapor phase to acetic acid, in which acetates are used as catalyst and substances which can form acetates. Possible catalysts of that kind are the compounds of copper, tin, lead, zinc and aluminum. No implementation examples are given of this method.

More recently, precious metal catalysts have been mentioned for this reaction. For example, U.S. Patent 4,194,056 teaches us to prepare acetic acid by heating methyl formate in the presence of a soluble rhodium salt and an iodine-containing promoter. Relatively high yields are cited, and that patent teaches that cobalt iodide, cobalt iodine / triphenylphosphine, methyl iodide, copper chloride / triphenylphosphine, ferrous chloride / triphenylphosphine, tungsten hexacarbonyl, rhenium pentacarbonyl, molarbydyl ether, catalysts, for example, 2-hydroxydexyl reaction catalysts fit. Although rhodium gives good results, it is a very expensive catalyst, like all eighth grade precious metals. U.S. Pat. No. 3,839,428 uses Group VIII or Group IIB metals, but requires relatively high temperatures and pressures.

Dutch patent application 82.02188 describes a process for rearrangement or isomerization of methyl formate by means of a catalyst system containing no noble metal, but molybdenum / nickel or tungsten / nickel and an organophosphorus or organo-nitrogen compound as a promoter. While this nickel catalyst process allows for effective rearrangement of methyl formate without the use of a noble metal, it is useful to improve this reaction somewhat in terms of reaction speed and productivity without the need for organic promoters.

This invention aims to provide a better process for the preparation of acetic acid by rearrangement of methyl formate, which requires neither high temperatures nor noble 20 'metals of the eighth group, and which allows acetic acid without organic promoters in high yield and in short reaction time can make.

According to the invention, the rearrangement of methyl formate to acetic acid is carried out using a molybdenum / nickel / alkali metal or tungsten / nickel / alkali metal catalyst in the presence of a halide (iodide or bromide, especially iodide) and in the presence of carbon monoxide. The surprising finding was made that this catalyst system in the presence of the indicated medium allows rearrangement or isomerization of methyl formate to acetic acid at relatively low temperatures and pressures with rapid formation and good acetic acid yield.

The remarkable effect of the catalyst system of this invention is especially surprising due to the experimental data contained in European Patent Application Laid-Open No. 0.035.458, which application relates to the carbonylation of methanol to acetic acid in the presence of nickel an alkyl halide, an alkali metal or alkaline earth metal halide goes with tetraethyl sulfone or derivative thereof or an alkyl ether of polyethylene glycol or an amide as a solvent. The publication contains tests with nickel in combination with chromium, molybdenum and tungsten, in which there was no reaction at all even after 2 hours. It has also been observed that the nickel tends to volatilize and appear in the vapors of the reaction mixture under conditions common to carbonylations. It has surprisingly been found that with the catalyst system according to the invention the nickel volatility is strongly suppressed and a very stable catalyst results.

Thus, according to the invention, methyl formate is heated in the presence of carbon monoxide, a halide (in particular a lower alkyl halide such as methyl iodide) and in the presence of said catalyst combination.

Carbon monoxide is removed from the vapor phase and, if desired, recycled. Normally liquid and relatively volatile components of the final reaction mixture, such as alkyl halide, unreacted methyl formate and by-products, are easily removed by distillation and separated (for reuse), and the desired acetic acid is essentially the only final product.

In the case of a preferred liquid phase reaction, the organic compounds are easily separated from the metal compounds by distillation. The reaction is best carried out in a reaction zone to which the carbon monoxide, the methyl formate, the halide, the catalyst combination and the promoter are fed.

When carrying out the method according to the invention, a wide temperature range from 25 ° to 35 ° C is suitable, but preferably a temperature between 100 ° and 250 ° C is used, and the very best between 125 ° and 225 ° C. Temperatures lower than mentioned can be used, • -V "5] 4, but these have the negation to lead to lower reaction rates, and higher temperatures can also be used, but this does not give any clear advantage. The reaction time is not a parameter of this method either and depends largely on the temperature used, but generally it is between 0.1 and 20 hours The reaction takes place under elevated pressure, but it is an advantage of this invention, as already indicated, that excessively high pressures, for which one needs special equipment, not needed here In general, the reaction 10 is effectively conducted with a partial carbon monoxide voltage of at least 1 ata and at most 140 ata, and in particular between 2 ata and 14 ata, although CO voltages of up to 350 and even up to 750 ata can be applied By setting the partial carbon monoxide tension to the aforementioned value, sufficient amount of this compound is always present. The total voltage is, of course, that which gives the desired partial CO voltage and preferably is high to give a liquid phase, the reaction being advantageously carried out in an autoclave or the like.

After the desired residence time has elapsed, the reaction mixture is separated into its constituents, for example by distillation. Preferably, the reaction mixture is placed in a distillation zone which may be a fractional distillation column or else a series of columns arranged to separate liquid components from the acetic acid product and to separate that acetic acid from the less volatile catalyst components. The boiling points of the volatiles are so far apart that their separation by ordinary distillation presents no problems. Likewise, the higher boiling organics can be easily separated from the metal catalyst. The double catalyst and halide thus recovered can then be combined with fresh methyl formate and carbon monoxide from which a new portion of acetic acid can be prepared.

Although not absolutely necessary, the process can be performed in the presence of a solvent or diluent. The presence of a higher boiling solvent or diluent, for example the acetic acid itself, allows the total pressure to be lower. On the other hand, the solvent or diluent can be any organic liquid that is inert in this reaction, such as hydrocarbons (eg, octane, benzene, toluene, xylene and tetralien) or carboxylic acids. If a carboxylic acid is used, it is preferably acetic acid because it already exists in the system, although other carboxylic acids can also be used. If the solvent or diluent is not the product itself, one is chosen such that its boiling point differs sufficiently from that of the desired product so that it can be easily separated, which will be readily apparent to those skilled in the art. Mixtures of liquids can also be used.

The carbon monoxide is preferably used in the substantially pure form commercially available, but inert diluents such as carbon dioxide, nitrogen, methane and noble gases may be present if desired.

The presence of inert diluents does not affect the reaction, but their presence increases the total pressure required to maintain the desired partial CO stress. The presence of a small amount of water, as can be found in the commercial qualities of the starting materials, is entirely acceptable. Hydrogen, which may be present as an impurity, does not encounter any objection and even tends to stabilize the catalyst. In fact, to obtain a low partial CO voltage, the supplied CO may have been diluted with or some other inert gas. It has surprisingly been found that the presence of hydrogen does not lead to the formation of reduction products. The diluting gas, e.g., hydrogen, may generally be present up to a concentration of up to 95%, if desired.

The two components of the catalyst can be used in any suitable form. For example, nickel, molybdenum, tungsten and chromium can be used as finely divided metals, but also as organic or inorganic compounds. Representative of such compounds are the carbonates, oxides, hydroxides, bromides, iodides, chlorides, oxyhalides, hydrides, lower alkoxides (such as methoxide), phenoxides and carboxylates; these carboxylates can be derived from fatty acids with 1 to 20 carbon atoms, such as acetic acid, butyric acid, decanoic acid, lauric acid, benzoic acid, etc. Likewise, both metals can be used as complexes, for example as carbonyl compounds or metal alkyls, and also as chelates, association compounds and as enol salts. Examples of other complexes are bis (triphenylphosphine) nickel dicarbonyl, tricyclopentadienyl trinikkel diarbonyl, tetrakis (triphenylphosphite) nickel and corresponding complexes of the other components such as molybdenum hexacarbonyl and tungsten hexacarbonyl. Particular preference is given to the elemental forms, the halides (especially the iodides) and the organic salts such as the acetates.

The alkali metal (lithium, sodium, potassium or cesium) is suitably used as a salt, preferably as a halide (e.g. as iodide). The preferred alkali metal 20 is lithium. However, the alkali metal can also be used as hydroxide, carboxylate, alkoxide or in the form of another compound, as mentioned above in connection with the other catalyst components, and representative alkali metal compounds are sodium iodide, potassium iodide, cesium iodide, lithium iodide, lithium bromide, lithium chloride, lithium acetate and lithium hydroxide.

It will be understood that the above compounds and complexes serve only as examples; this is not an exhaustive list.

The said metal and metal compounds may contain the impurities normally found in the commercial grades and do not require further purification.

How much of each catalyst component 35 is taken is not so important and that is not a parameter of the process according to the invention and that can be done over a wide range.

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___ r 7 vary. As will be well known to those skilled in the art, the amount of catalyst to be used is that which gives an appropriate and reasonable reaction rate since this rate is generally determined by the amount of catalyst. However, any amount of catalyst will essentially cause the intended reaction and can thus be termed a "catalytically effective amount." Generally, however, at least 1 mmole per liter of reaction mixture is taken from each catalyst component, preferably 35 to 500 mmole, most preferably 15 to 150 mmole per liter.

The ratio of nickel to molybdenum, tungsten or chrome can vary. In general, the atomic ratio of nickel to other metal is between 1: 3000 and 3000: 1, better between 30: 1 and 3:20, and best between 1: 3 and 3:30.

Likewise, the nickel to alkali metal atomic ratio is generally at least 3: 1000 and is preferably between 1:30 and 1: 100, most preferably between 3:20 and 3:50.

The amount of iodide can also vary widely, but generally at least one atom per 20 atoms of nickel should be taken. Often, 1 to 300 moles, preferably 2 to 50 moles, of iodide are taken per nickel atom. Usually, no more than 200 moles of iodide will be taken per nickel atom.

It will be appreciated, however, that the iodide does not need to be added to the system as such, it may also be introduced as other organic iodide or as hydrogen iodide or as an alkali metal or other salt, and even as elemental iodine.

As already mentioned, the catalyst system according to the invention comprises an iodide and the combination of molybdenum or tungsten or chromium with nickel and alkali metal.

This system allows the preparation of acetic acid in high yield and in short reaction time, without the use of eighth grade precious metals, and this combination of alkali metal with molybdenum, tungsten or chromium allows these good results with, compared to the state the art, relatively smaller amounts of nickel.

A particular embodiment of the catalyst system 8 can be represented by the formula X: T: Z: Q, wherein X represents molybdenum, tungsten or chromium and T represents nickel (as metal or as halide, oxide, carboxylate, carbonyl compound or hydride), Q is some iodine-5 source (element hydrogen iodide, alkali metal iodide or alkyl iodide having 1 to 20 carbon atoms) and Q is an alkali metal compound. The preferred alkali metal is, as already said, lithium, and then in the form of iodide or bromide or carboxylate (as defined by X and T), the mol-10 ratio of X to T being between 1:10 and 10: 1 , the mole ratio of X + T to Q between 1:10 and 10: 1, and the mole ratio of Q to X + T between 100: 1 and 10: 1. The iodide may have been replaced by a bromide.

It will be understood that the described reaction occurs. borrows well for continuous operation, with reactants and catalyst continuously fed into a suitable reaction zone and the reaction mixture continuously distilled to remove volatile organic compounds therefrom and yield a net product which is essentially only acetic acid, whereby the other organic constituents are recycled, and also a liquid phase with catalyst residues is also recycled.

It will also be appreciated that, if desired, the catalytic reaction of this process may also be in vapor phase 25, by appropriate adjustment of the total pressure and temperature such that the reactants contact the catalyst in vapor form. In any case of a vapor phase reaction (and optionally also in a liquid phase operation), the catalyst components may be supported. which can be of the usual kind, such as A ^ Qj »

SiO2, SiC, ZrO2, carbon, bauxite, attapulgite, etc. The catalyst components can be applied to the supports in the usual manner, for example by impregnation. The concentrations on the carriers can vary widely, such as between Q, 0, 35 and 30% by weight, or even higher. Representative working conditions for vapor phase operation are a temperature between 100 ° C and 9 350 ° C (preferably between 150 ° and 275 ° C and most preferably between 175 ° and 255 ° C), a pressure between 0.07 and 350 ata (at preferably between 4 and 105 ata and most preferably between 10 and 35 ata) and a space velocity between 50 and 10,000 per hour (preferably between 5 and 6,000 per hour, most preferably between 500 and 4,000 per hour).

In the case of a supported catalyst, the iodide goes with the reactants and does not remain on the support.

The invention is now further illustrated by the following examples, which are not to be construed as limiting, in which all percentages and parts refer to weights unless otherwise indicated.

Example I

150 parts of methyl formate, 100 parts of methyl iodide, 101 parts of acetic acid, 7.5 parts of nickel iodide, 15 parts of molybdenum carbonyl and 60 parts of lithium iodide were introduced into a 1 liter Parr autoclave. The reactor was charged three times with 3 | Atmosphere 5 CO is rinsed out and then pressed with CO2 to ato and CO to 16 ato. The reactor was then heated to 200 ° C and kept at that temperature for 3 hours. After cooling, the contents were taken out of the reactor and analyzed by gas chromatography. The reaction mixture was found to contain, in addition to the acetic acid originally present, a net addition of 100 parts acetic acid, as well as unreacted methyl formate and methyl iodide and the catalyst components.

Example II

Into the autoclave of Example I, 150 parts of methyl formate, 100 parts of methyl iodide, 300 parts of acetic acid, 7.5 parts of nickel iodide, 15 parts of molybdenum carbonyl and 60 parts of cesium iodide were introduced. The reactor was rinsed three times with 3.5 ato CO-3Q and then spiked with 1 to 5 ato and with CO to 31 ato.

The reactor was now heated to 200 ° C and kept at that temperature for 5 hours. After cooling, the contents were taken out of the reactor and analyzed by gas chromatography. In addition to the acetic acid originally present, 127 parts of acetic acid were found to have been added, and unreacted methyl formate and methyl iodide were also present, as well as the catalyst - - - I rf *

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Example III

150 parts of methyl formate, 100 parts of methyl iodide, 100 parts of acetic acid, 7.5 parts of nickel iodide, 15 parts of chromium carbonyl and 60 parts of lithium iodide were introduced into the reactor of Example 1. The reactor was rinsed three times with 3 atoms of CO and then charged with up to 5 atoms and with CO to 16 atoms.

The reactor was now heated to 200 ° C and left there for 3 hours.

After cooling, the contents were taken out of the reactor and gas-10 chromatography analyzed. In addition to the acetic acid originally present, 123 parts of acetic acid were found to have been added, and unreacted methyl formate and methyl iodide were also present, as were the catalyst components.

Example IV

Into the autoclave of Example 1, 150 parts of methyl formate, 100 parts of methyl iodide, 100 parts of acetic acid, 7.5 parts of nickel iodide, 15 parts of tungsten hexacarbonyl and 60 parts of lithium iodide were introduced. The reactor was rinsed three times with 3 ATo CO and then compressed with up to 5 ATO and with CO to 16 ATO. The reactor was now heated to 200 ° C and left there for 5 hours. After cooling, the contents were taken out of the reactor and analyzed by gas chromatography. In addition to the originally used acetic acid, it was found that 100 parts of acetic acid had been added, furthermore unreacted methyl formate and methyl 25 iodide and the catalyst components were present.

Example V

Into the Parr autoclave of Example 1, 150 parts of methyl formate, 100 parts of methyl iodide, 100 parts of acetic acid, 7.5 parts of nickel iodide, 15 parts of molybdenum hexacarbonyl and 30.60 parts of lithium iodide were introduced. The reactor was rinsed three times with 3J ata CO and then pressed to 35 ato CO. The reactor was heated to 200 ° C and held there for 5 hours.

After cooling, the reactor contents were taken out and analyzed by gas chromatography. In addition to the originally present acetic acid, it appeared that 149 parts of acetic acid had been added, there were also unreacted methyl formate and methyl iodide and the

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catalyst components are present. There was a substantially complete conversion of the methyl formate used.

Claims (5)

1. Process for the preparation of acetic acid by rearrangement of methyl formate in the presence of carbon monoxide and a catalyst system, characterized in that the catalyst system consists of a combination of molybdenum, tungsten or chromium with nickel and alkali metal and that the reaction happens in the presence of an iodide or bromide. 2. Process according to claim 1, characterized in that the catalyst is a combination of molybdenum with nickel and alkali metal. A method according to claim 1 or 2, characterized in that the alkali metal is lithium. Process according to any one of the preceding claims, characterized in that the iodide or bromide is methyl iodide. 5. Method mainly according to description and / or examples. 20. ........... A