NL8301890A - METHOD FOR PREPARING ACETIC ACID. - Google Patents

Description

t i 4

T

J

Method for the Preparation of Acetic Acid.

This invention relates to a process for the preparation of acetic acid by carbonylation of methanol.

Acetic acid has been known as an industrial chemical for many years and large amounts are used in the preparation of various products. Proposals for preparing carboxylic acid by the action of carbon monoxide on alcohols (carbonylation) have been described, inter alia, by Reppe et al. In U.S. Pat. No. 2,729,651 and by Holmes in U.S. Pat. Nos. 4,133,963 and 4,218,340. However, 10 previous carbonylation proposals required very high pressures. Carbonylations operating at lower pressures have also been suggested. French patent 1,573,130 discloses, for example, the carbonylation of methanol and mixtures of methanol with methyl acetate in the presence of compounds of Group VIII noble metals, such as platinum, iridium, palladium, osmium and ruthenium, and in the presence of bromine or iodine under lower pressures than those required by Reppe and Holmes.

According to U.S. Pat. Nos. 3,769,329 and 3,772,380, acetic acid is prepared from the same starting materials in the presence of iridium or rhodium and bromine or iodine. U.S. Pat. Nos. 3,689,533 and 3,717,670 describe a vapor phase process for the preparation of acetic acid using various supported rhodium-containing catalysts.

However, all these lower pressure processes require precious noble metals.

More recently, Belgian Pat. No. 860,557 describes the preparation of carboxylic acids by carbonylation of alcohols using nickel as the catalyst, which is strengthened by a compound of trivalent phosphorus and an iodide. Here one has a low-pressure carbonylation without precious metal. This method has an effect, but there is room for better yields of the desired acid.

An improved process is also described in US patent application 219,786 of December 24, 1980. This discloses the preparation of acetic acid by carbonylation of methanol in the presence of molybdenum nickel or tungsten nickel catalyst in the presence of iodide and in the presence of an organophosphorus or organo nitrogen compound as a promoter.

Now the surprising finding was made that the carbonylation can proceed significantly faster if a small but critical amount of water is present in the reaction system, which also helps to keep the catalyst in soluble form. Thus, according to the invention, methanol is carbonylated in the presence of molybdenum-nickel or tungsten-nickel as a catalyst, in the presence of an iodide and of an organophosphorus or organo-nitrogen compound as a promoter and now also in the presence of 2 to 8%, preferably 4 to 6% water (based on the total weight of the reaction mixture).

The process to which this invention relates relates to a wide temperature range, namely from 25 ° to 350 ° C, but preferably from 100 ° to 250 ° C, and most preferably from 125 ° to 225 ° C, Lower temperatures than those mentioned can be used but lead to lower reaction rates and higher temperatures are also applicable, but there is no advantage in this. The reaction time is also not a parameter of this method and depends mainly on the temperature used, but representative residence times are from 0.1 to 20 hours. The reaction takes place under elevated pressure, but exceptionally high pressures, which require special high-pressure equipment, are not required 3Q. In general, the reaction is effective with partial C0 voltages between 1 and 140 bar, even better between 1 and 70 bar (0.1 to 14MPa and 7 MPa, respectively). But CO voltages up to 350 bar and even up to 700 bar (35 MPa or 70 MPa) can also be used. By setting the partial CO voltages to those values, one always has enough of that starting material. The total pressure is, of course, that of the carbon monoxide 8301890 3 with the pressure required to keep the remaining substances in liquid phase, and in this case the reaction can advantageously be carried out in an autoclave or the like.

The final reaction mixture will normally contain volatile compounds, such as hydrocarbon iodide, unreacted alcohol, the acid to be prepared and optionally corresponding ester and / or ethers thereof, after separating the acid all those volatile components can be reused in the reaction . After the desired residence time has elapsed, the reaction mixture is separated into its constituents, usually by distillation. Preferably, the reaction mixture is to be distilled, for example, in a fractional distillation column or in a series of columns, operating well enough to separate the volatiles from the acid to be prepared and also the acid to be prepared from the less volatile catalyst. and the promoter ingredients. The boiling points of the volatiles are sufficiently far apart that normal distillation is not a problem.

Likewise, the higher boiling organic components can be easily distilled from the metal catalyst and an optional organic promoter in the form of a relatively low volatile complex. The thus-recovered catalyst and the promoter, including the iodide, can then be combined with new amounts of alcohol and carbon monoxide and reacted to form new carboxylic acid.

Although not necessary, the reaction can take place in the presence of an organic solvent or diluent. Since methanol has a relatively low boiling point, the presence of a higher boiling solvent or diluent, preferably acetic acid or the corresponding ester such as methyl acetate, allows to set more moderate total pressures. Alternatively, the solvent or diluent can be any organic solvent that is inert under the reaction conditions, such as hydrocarbons (eg, octane, benzene, toluene, xylene, and tetralien) and halocarbonaceous materials (eg, trichlorobenzene) and carboxylic acids or esters thereof (e.g. methoxyethyl acetate). Solvent mixtures can also be used, such as mixtures of methyl acetate and acetic acid. If a carboxylic acid is used, it is preferably acetic acid because this is already found in the reaction system. When using a solvent or diluent which is not already present in the reaction mixture of its own, one preferably has a boiling point sufficiently different from the boiling points of the components of the reaction mixture, so that it is easy to separate, which is a skilled person will understand.

The carbon monoxide is suitably used as a substantially pure substance, such as is 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 carbonylation, but their presence naturally increases the total pressure if the desired partial CO stress is to be achieved. Hydrogen may be present and tends to stabilize the catalyst. In fact, in order to set low CO voltages, it is possible to dilute the supplied carbon monoxide with hydrogen or one of the above-mentioned inert gases. It has been surprisingly found that the presence of hydrogen does not lead to the formation of reduced products. The diluent gas, e.g. hydrogen, may be used up to concentrations of 25-95%, if desired. Particularly desirable is the use of amounts of hydrogen such that the ratio between its partial voltage and partial CO voltage is between 0.05: 3 and 0.4: 3, preferably between 0.15: 1 and 0.25: 1 as also indicated in co-pending application 3Q. . Such use of hydrogen has been found to have a beneficial effect on the reaction rate in the system referred to here.

The catalyst components can be used in any suitable form, so both as an element and with higher valences. For example, nickel and molybdenum or tungsten can be used as finely divided metals, but also as 8301890 - organische 5 organic or inorganic compounds. Representative compounds are the carbonates, oxides, hydroxides, bromides, iodides, chlorides, oxyhalides, hydrides, lower alkoxides (methoxides) and phenoxides, and also the carboxylates derived from 5 fatty acids with 1 to 20 carbon atoms such as the acetates, butyrates, decanoates , laurates, benzoates, etc. Likewise, complexes of the catalytic metals can be used, e.g., the carbonyls and metal alkyls, as well as the chelates, association compounds and enol salts. Examples of other complexes are 10 bis (triphenylphosphine) nickel dicarbonyl, tricyclopentadienyl-trinikkel dicarbonyl, tetrakis (triphenylphosphite) nickel and the corresponding complexes of the other metals such as molybdenum hexacarbonyl and tungsten hexacarbonyl. Among the catalyst components mentioned, complexes of these metals with organic promoters as ligands are also derived from the organic promoters mentioned below.

Particular preference is given to the elemental forms, the halides (especially the iodides) and the organic salts, and in particular those of the monocarboxylic acid which is prepared therewith. It will be appreciated that the above compounds and complexes are only illustrative of the appropriate forms of the catalyst components, and should not be taken as limiting.

The listed catalyst precursors 25 may contain the impurities normally associated with commercial qualities, and they do not require further purification.

The organophosphorus promoter is preferably a phosphine of the formula PR2 wherein the three groups R30 may be the same or different and are alkyl, cycloalkyl, aryl, amide or halogen (having 1 to 20 carbon atoms in the alkyl and cycloalkyl groups and 6 to 18 carbon atoms in the aryl groups), e.g. hexamethylphosphoric triamide. Representative of the phosphines are trimethylphosphine, tri-propylphosphine, tricyclohexylphosphine and triphenylphosphine. When the promoter is an organo nitrogen compound it is preferably an 8301890 6 tertiary amine or a polyfunctional nitrogen containing compound such as an amide, a hydroxyamine, a ketoamine, a di-, tri- or other polyamine, or a nitrogen compound having two or more other functional groups. Representative of these 5 organo nitrogen promoters are 2-hydroxypyridine, 2,6-diamino-pyridine, 2- and 8-hydroxyquinoline, 1-methylpyrrolidi-non, 2-imidazolidone, Ν, Ν-dimethylacetamide, dicyclohexylacetamide, dicyclohexylmethylamine, Ν, Ν -diethyltoluamide and imidazole.

Although the organic promoter is usually added separately to the catalyst system, it is also possible to introduce it as a complex with one of the constituent metals, such as bis (triphenylphosphine) nickel dicarbonyl and tetrakis (triphenylphosphite) nickel. It is also possible to use both free and complex bound promoters. If a complex of an organic promoter with a metal is used, one can also add free organic promoter.

The amount of the catalyst components is immaterial and that is not a parameter of the process of the invention; this can vary over a wide range. As those skilled in the art know, so much catalyst is used that a reasonable and sufficient reaction speed is obtained. However, essentially any amount of catalyst supports the intended reaction and can thus be considered catalytically active. In general, however, 1 mole of catalyst will be used per 10 to 10,000 moles of alcohol, preferably 1 mole per 100 to 5000 moles of alcohol and most preferably 1 mole per 300 to 1000 moles of alcohol.

The ratio of nickel to the other metal can also vary. Generally, 1 mol of nickel has 3Q. per 0.01 to 100 mol of the other metal, preferably that ratio is 1 mol per 0.1 to 20 mol, most preferably 1 mol per 1 to 10 mol.

The amount of organic promoter can also vary widely, but generally 1 mole per 0.1 to 10 mole of catalyst components is used.

The amount of iodide can also vary widely, but in general at least 10 moles per 100 moles of alcohol must be present. In general, per 100 moles of alcohol there are 10 to 50 moles, preferably 17 to 35 moles of iodide. Usually no more than 200 moles of iodide per 100 moles of alcohol will be used. However, it should be recognized that the iodide does not necessarily have to be used as alkyl iodide, it can also be used as HJ or as inorganic iodide and even as elemental iodine.

A particularly favorable embodiment of the catalyst with molybdenum-nickel or full-grain nickel as metals can be represented by the formula X: T: Z: Q, wherein X is molybdenum or tungsten and T nickel (both with zero valency or as halide, oxide or carboxylate, carbonyl or hydride), ZJ2, HJ or alkyl iodide and Q is an organophosphorus or organo nitrogen compound in which phosphorus or nitrogen is trivalent. Preferred nitrogen and phosphorus compounds have already been indicated above, and most preferred is a phosphine of the formula PR2, also as defined above. The X to T molar ratio is between 0.1: 1 20 and 10: 1, the X + T to Q molar ratio is between 0.05: 1 and 20: 1, and the Z to X + T molar ratio is between 1: 1 and 1000: 1.

As already stated, the invention is based on the finding that in a system as described above, a small but critical amount of water in the reaction mixture, ie between 2 and 8% of the total weight of the reaction mixture, is a surprising and unexpected increase in the reaction rate and also keeps the catalyst in soluble form.

It will be appreciated that the described reaction lends itself well to a continuous operation in which the starting materials, water and catalyst are continuously fed into an appropriate reaction zone and the reaction mixture is continuously distilled so that the volatiles are separated therefrom, whereby a net yield of carboxylic acid and the other organic constituents are recycled, and the catalyst is also left in the liquid phase, which is also recycled.

8301890 1r 8

The invention is now further illustrated by the following non-limiting examples.

Example I

The preparation was carried out in a 1-liter auto-5 claaf with electrically heated jacket, a magnetically driven stirrer, gas and liquid feeds, and a bleed housing near the vapor-liquid separation. The test was carried out at a temperature of 200 ° C and a total pressure of 88 bar (the CO pressure of which was 66 bar). The CO voltage was maintained by continuously supplying this gas in the required amount. 250 g of the liquid feed was supplied per hour, which consisted of 38% by weight of methyl iodide, 33% by weight of methanol, 7% by weight of acetic acid, 6% by weight of methyl acetate and 5% by weight. % from water, with 0.2 wt% nickel (introduced as nickel iodide), 0.3 wt% molybdenum (introduced as molybdenum carbonyl) and 4 wt% triphenylphosphine.

After a steady state was set, the reaction was run continuously for about 16 hours. The effluent collected contained about 0.1 wt.% Solid, 20 and gas chromatography of the liquid showed that 3.2 µmoles of acetic acid were formed per liter per hour.

Comparative example A

The preparation of Example I was repeated in the same apparatus and under the same conditions, except that water was omitted from the feed. Now it turned out

effluent to contain 0.1 wt% solids, and the acetic acid formation rate was only 2.6 µmoles per hour per liter. Example II

The apparatus 30 described in Example I was used at a temperature of 200 ° C and a total pressure of 88 bar with a hydrogen / carbon monoxide mixture such that the partial pressures of CO were 61 bar and 4 bar, respectively. These partial stresses were maintained by continuously supplying those two gases in the required amounts. The liquid feed was the same as in Example I and was also operated at a flow rate of 250 grams per hour. The 8301890% ..... 2 * 9 other conditions were also as in example I.

The collected effluent was found to contain 0.1% by weight of solid and gas chromatography showed that 5.6 gmole of acetic acid was formed per hour per liter.

5 Comparative example B

Again, the apparatus described in Example I was used at a temperature of 200 ° C and a total pressure of 88 bar, with a hydrogen-carbon monoxide mixture such that the partial stresses of CO and 10 were 63 bar and 5.2 bar, respectively. . Those partial stresses were maintained by continuously supplying those two gases in the required amounts. 250 g / h of liquid feed was again used, with the same composition as in Example 1, except that the water was omitted. The other reaction conditions were also as in Example I.

The collected effluent was found to contain 4.5 wt% solids, and gas chromatography of the liquid found that the rate of acetic acid formation was now only 4.5 µmoles per hour per liter.

20 -j 3301890

Claims (3)

1. Process for the preparation of acetic acid, wherein methanol is reacted with carbon monoxide in the presence of molybdenum-nickel or tungsten-nickel, an iodide and an organophosphorus or organo-nitrogen compound as a promoter, characterized in that the reaction also takes place in the presence of 2 to 8% by weight of water (based on the total weight of reaction mixture). 2. Process according to claim 1, characterized in that the water content of the reaction mixture is between 4 and 6% by weight. 3. Method mainly according to description and / or examples. 15 8301890