CA1036617A

CA1036617A - Production of acetic acid or mixtures of the same with methyl acetate

Info

Publication number: CA1036617A
Application number: CA190,215A
Authority: CA
Inventors: Franz J. Mueller; Nikolaus Von Kutepow
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1973-01-24
Filing date: 1974-01-15
Publication date: 1978-08-15
Also published as: DE2303271C3; JPS49109311A; NL7400658A; FR2327217B1; DE2303271B2; FR2327217A1; GB1450993A; IT1007574B; BE808716A; DE2303271A1

Abstract

ABSTRACT OF THE DISCLOSURE:
An improved process for the production of acetic acid alone or mixed with methyl acetate by reaction of methanol with carbon monoxide in the presence of a cobalt catalyst and of free or combined bromine and/or iodine at elevated temperature and superatmospheric pressure, in which there is additionally used at least one of the metals palladium, platinum, iridium, ruthenium and copper as catalyst and the reaction is carried out at a temperature of from 80 to 190°C
and at a pressure of from 100 to 300 atmospheres. Acetic acid is used for the production of its esters which are employed as solvents.

Description

~036617 This invention xelates to an improved process for the production of acetic acid or mixtures of the same with methyl acetate by reaction of methanol with carbon monoxide in the presence of a cobalt catalyst and in the presence of free or combined iodine and/or bromine at elevated temperature and super-atmospheric pressure.
It is known that acetic acid or a mixture thereof with methyl acetate is obtained by reaction of methanol with carbon - monoxide at superatmospheric pressure and at elevated temperature in the presence of a cobalt catalyst with the additional use of iodine in free or combined form (cf. German Patent 1,115,234 issued April 19, 1962 in the name of the Applicants). However, the disadvantage of this method when carried out on an industrial scale is that fairly high temperatures, for example 250C, and pressures of from 600 to 700 atmospheres have to be used in order to achieve suitable conversion rates. For a long time attempts have therefore been made to modify this process so that industrially viable conversions are obtained at lower temperatures and pressures.
According to a process disclosed in German Laid-Open Specification , DOS 1,767,151 on January 27, 1972 in the name of Monsanto Co., St-Louis, Mo. (V. St. A.) it is possible to carry out the reaction of methanol with carbon monoxide using rhodium catalysts at much lower temperatures and pressures. The disadvantage of the process is however that very expensive noble metal catalysts have to be used and there is a risk of considerable losses of the expensive rhodium catalyst. Moreover it is only possible to carry out the reaction under mild conditions when a high iodine content is used.
Since most of the iodine is present in the reaction mixture as hydrogen iodide the equipment has to be made of very expensive, : 30 extremely corrosion-resistant materials. It is known from Ge~man Laid-Open Specification DOS 1,939,286 of October 29, 1970 in the name of Monsanto CO., St. Louis, Mo. (V. St. A.) that it is possible ' ~' ,'.'; '., ~0366~7 to decrease the rhodium content by increasing the effectiveness of the rhodium by using another metal component, for example chromium, tungsten, titanium, zirconium, vanadium, molybdenum or iron. The disadvantage here however is that the catalyst has to be applied to a carrier. The carriers introduce a large amount of inert filler material into the reactor, thus restricting the reaction space.
Moreover the reaction is carried out in the gas phase so that very great reaction volumes are required. The main disadvantage however is that again a considerable content of iodine is necessary in the 10 reaction mixture in order to achieve viable industrial yields. -It is an object of the invention to provide a process in which acetic acid is obtained using cobalt as the mai~ catalyst constituent and employing fairly low temperatures and pressures.
It is further an object of the invention to achieve industrially viable yields of acetic acid without a high content of free or combined halogen which causes corrosion being necessary.
In accordance with this invention these and other objects and advantages are achieved in an improved process for the production of acetic acid or a mixture of the same with methyl acetate by reaction of methanol with carbon monoxide in the presence of a cobalt catalyst and free or combined bromine and/or iodine at eleva-ted temperature and superatmospheric pressure in which the improve~
ment consists in additionally using at least one of the metals palladium, platinum, iridium, ruthenium and copper as catalyst and carrying out the reaction at a temperature of from 80 to 190C and a pressure -~

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., 1036617 Z 29,658 of from 100 to ~00 atmospheres.
The new process is remarkable because nelther cobalt alone nor any of the additional metals alone will catalyze to any useful extent the reaction of methanol with carbon dloxide.
The startlng material may be not only ¢ommercial grade metha~ol but also crude methanol which contains for example up to 4 to 5% by welght of impurltles contained in crude methanol such as water and small amounts of methyl formate and methyl acetate. Moreover lt ls also posslble to replace some of the methanol, for example up to about 40 mole%, by dlmethyl ether. When dimethyl ether is used an amount of water corresponding stolchlometrically to the proportlon of dlmethyl ether has to be used.
Carbon monoxide ls convenlently used ln a stol¢hlometrlc amount but advantageously ln an excess of for example up to 70 mole%, based on the methanol used. It ls also posslble to use a gas contaln-lng oarbon monoxlde, advantageou~ly one whlch contalns more than 80% by volume of oarbon monoxide. Suoh a gas may contaln lnert oon-stltuents such as carbon dloxlde, nltrogen, rare gases or saturated lower hydrocarbons ln addltlon to carbon monoxlde.
The reaction ls carrled out at a pressure of from 100 to 300 atmospheres. A pressure of from 120 to 250 atmospheres has proved to be partlcularly sultable. It has also proved to be advantageous to malntaln durlng the reactlon a carbon monoxlde partlal pressure of from 50 to 250 atmospheres of the total pressure of from 100 to - 300 atmospheres and partloularly of from 100 to 200 atmospheres o~
the total pressure of from 150 to 250 atmospheres.
A temperature of from 80 to 190C ls maintalned durln~ the - reactlon. Partl¢ularly good results are obtalned when a temperature of from 100 to 180C ls used.
. ~0 The reaction is ¢arried out in the presence of oobalt as oatalystmetal. It ls possible to use cobalt in metalllc form. The cob&lt ls advantageously employed ln the form of an inorganlc or organic salt . '~. '' .. . : --0 Z 29,658 such as cobalt nitrate, cobalt carbonate but advantageously in the form of a salt of a fatty acid. It is also possible to use cobalt carbonyls or carbonyl complexes which may contain, as ligands, halogens, phosphines, phosphites, stibines, arsines, amines, nitriles, ketones, olefins or acetylene. It is also possible to add the said complexing agents separately to the reaction mixture. It has proved to be suitable to use the cobalt in a concentration of from 0.001 to 3% by weight and particularly from 0.3 to 100% by weight calculat-ed as metal and based on the reactlon mixture. Examples of suitable 10 forms in which cobalt may be used are Co(CH3C00)2-4H20, cobalt halides, cobalt formate and Co2(C0)8. It ls particularly preferred to use cobalt in the form of carboxylic acid salts and halides.
There is also used additionally as catalyst metal at least one of the metals palladium, platinum, iridium, ruthenium and copper.
It has to be especlally suitable to use palladlum, platinumg iridium and ruthenium, and particularly palladium or platinum. The said metals are, like cobalt, conveniently used in the ~orm of inorganic or organic salts. Examples of suitable forms are the simpLe and complex halides.
It has proved to be particularly advantageous to uæe the said [( 6 5)3P~2PdC12, PtC14, H2PtC16, IrCl RuCl The additional metals are used ln an amount of from 0.001 to 1% by weight and preferably in an amolmt of from 0.05 to 0.3% by weight calculated as metal and based on the reaction mixture.
Bromlne and/or iodine in elementary, ionic form or in organic combination are used additionally. The use of iodine or compounds of iodine has proved to be particularly suitable. Examples of appropriate forms in which bromine or iodine may be used (apart from the elemen- -tary form) are hydrobromic acid, hydroiodic acld or salts Or the same with an alkall metal or alkallne earth metal and also alkyl ~4~

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bromides and alkyl iodides. The addition of bromine or iodine in the form of an alkali metal saltJ a halohydracid or in elementary form ls particularly advantageous.
Bromine and/or iodine are as a rule used in an amount (calcu-lated as bromine or iodine) of from 0.05 to 4% by weight and prefer-ably from 1 to 3.0% by weight based on the reaction mixture. The concentration of halogen is limited by the occurrence o~ corrosion even when Ni-Cr-Mo alloys (Hastelloy C and B) are used. The use of halogen salts such as potassium iodide makes it possible to increase the halogen concentration to 5%.
The exact chemical constitution of the active catalyst system whlch is formed from cobalt, additional metal or metals and bromine and/or iodine during the reaction is not known. It is assumed how-ever that it is a mononuclear or polynuclear carbonyl complex whlch in addition to carbon monoxide contains inter alia bromine or iodine as ligands.
me reaction is advantageously carried out continuously in the liquid phase. It is also possible however to use the catalytically active metals, namely cobalt and the additional metals palladium, platinum, iridium, ruthenlum or copper, precipitated ontola conven-tional carrier such as silica gel, carbon or pumice, and to allow the methanol to trickle thereover or to pass methanol thereover in vapor phase under the said carbon monoxide pressure and the said reaction conditions with the addition o~ halogen compounds.
It has proved to be suitable ~or better temperature control to recycle the liquid reaction mixture or to recycle excess carbon ;
monoxide if necessary after it has been replenished with fresh carbon monoxide.
If importance is attached to obtaining mainly acetic acid as the process product it is advantageous to use as the starting material ;~
not pure methanol but aqueous methanol having for example a water content of from 25 to 35% by weight. The format,ion of methyl acetate -5- ~
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` O.Z. 29,658 ~ 036617 and carbon dioxide is suppressed by using water. It has proved to be advantageous to maintain a pressure of from 140 to 250 atmospheres -gauge when water is usedO
The process according to the invention may be carried out for example by supplying to the bottom of a vertical high pressure tube carbon monoxide and methanol in which the said additional metals and the said halogen are dissolved and carrying out the reaction in the liquid phase under the said pressure and temperature conditions.
Excess carbon monoxide after it has been replenished with fresh carbon monoxide may be used again or processed in separate equipment into pure carbon monoxide. The liquid reaction mixture is convenient-ly cooled and flashed and the main portion of the reaction mixture is distllled off~ a catalyst solution is obtained as bottoms which can be returned to the reaction together with methanol, if necessary after replenishing the amount lost.
Acetic acid and methyl acetate prepared accordlng to the inven-tlon are suitable as solvents and for the production of esters which can be used as solvents.
The process of the invention is illustrated ln the following Examples. TAC is th~ total acetic acid content consisting of free acetic acid and acetic acid combined in the form of methyl acetate, and FAC is the free (i.e. uncombined) acetic acld contained ln the : reaction mixture.

120 g of methanol, 2.7 g of cobalt acetate (4H20), 3 g of iodine, 1.2 g of bistriphenylphosphine palladium dichloride and 2.4 g of adiponitrile are plaoed in a high pressure vessel having a capaoity of o.8 liter and whi¢h is lined with Hastelloy C. Carbon monoxide is forced in up to a pressure of 50 atmospheres gauge.
The mixture is then heated to 120C and the pressure is ad~usted to 25C atmospheres gauge by forcing in more carbon monoxide. mis pressure ls maintained throughout the reaction period of slx hours : -, ~. . . . : -, . :.

1036617 o.z. 29,658 by forcing in more carbon monoxide. The mixture is then cooled and rlashed. According to the acid number and saponification number of the reaction product it contains 5.1~ by weight of free acetic acid and 44.8% by weight of methyl acetate. me total acetic acid content (TAC) of ~2.9% by weight is calculated therefrom.
me examples listed in the following Table I are carried out analogouslyO
It wlll be seen from the comparative experiments that the use Or a single catalyst metal gives much worse results.
The following abbreviations are used in Table I:
Ex = Example; T = temperature in C; P = pressure in atmospheres gauge; FAC , free acetic acid content; MA = methyl acetate in % by weight; TAC = total acetic acid content in ~ by weight.
+) 6 g of water additionally used ++) 2.1 g Or hydroiodic acid additionally used.
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An improved process for the production of acetic acid or a mixture of the same with methyl acetate by reaction of methanol with carbon monoxide in the presence of a cobalt catalyst and free or combined bromine and/or iodine at elevated temperature and at superatmospheric pressure wherein the improvement consists in additionally using at least one of the metals palladium, platinum, iridium, ruthenium and copper as catalyst and in carrying out the reaction at a temperature of from 80° to 190°C and at a pressure of from 100 to 300 atmospheres.

2. A process as claimed in claim 1 wherein palladium or platinum is used as the additional catalyst metal.

3. A process as claimed in claim 1 wherein a cobalt catalyst is used in an amount of from 0.001 to 3% by weight calcu-lated as metal and based on the reaction mixture.

4. A process as claimed in claim 1 wherein the additional metal is used in an amount of from 0.001 to 1% by weight calculated as metal and based on the reaction mixture.

5. A process as claimed in claim 1 wherein a temperature of from 100° to 180°C is used.

6. A process as claimed in claim 1 wherein a methanol/
dimethyl ether mixture is used.

7. A process as claimed in claim 1 carried out at a pressure of from 120 to 250 atmospheres.

8. A process as claimed in claim 1 wherein the additional metal is used in an amount of from 0.05 to 0.3% by weight calculated as metal and based on the reaction mixture.

9. A process as claimed in claim 1 wherein the bromine and/or iodine is used in an amount of from 0.05 to 4% by weight based on the reaction mixture.

10. A process as claimed in claim 9 wherein the amount of free or combined bromine and/or iodine used is from 1 to 3.0% by weight based on the reaction mixture.

11. A process as claimed in claim 1 wherein potassium iodide is used as the iodine compound.

12. A process as claimed in claim 1 wherein water is additionally used.

13. A process as claimed in claim 12 carried out at a pressure of from 140 to 250 atmospheres gauge.