GB1598314A

GB1598314A - Process for the manufacture of acetic acid by the oxidation of acetaldehyde

Info

Publication number: GB1598314A
Application number: GB5348277A
Authority: GB
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1976-12-22
Filing date: 1977-12-22
Publication date: 1981-09-16
Also published as: IT1089981B; NL7713977A; FR2375183A1; DE2658043A1; CA1107758A; ES465131A1; BR7708545A; DE2658043B2; CH630600A5; JPS5379814A; BE862177A

Abstract

Acetic acid is prepared by oxidising acetaldehyde at elevated temperature in the liquid phase with oxygen or oxygen-containing gases in the presence of one or more heavy metal compounds as catalyst; to initiate the reaction, the reaction mixture is admixed at the beginning of the oxygen feed with one or more organic peroxides which, under the reaction conditions, decompose with a half-life of up to 350 minutes into free radicals.

Description

(54) PROCESS FOR THE MANUFACTURE OF ACETIC ACID BY THE OXIDATION OF ACETALDEHYDE (71) We, HOECHST AKTIENGESELLSCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the preparation of acetic acid.

Processes for the manufacture of acetic acid by oxidising acetaldehyde at elevated temperature in the liquid phase with oxygen or gases containing oxygen in the presence of soluble heavy metal compounds as catalysts, have been disclosed. Suitable heavy metal compounds include manganese and/or cobalt compounds (see Ullmann's "Encyclopädie der technischen Chemie", Vol. 6, 3rd edition, 1955, page 781 ff. and DT-OS 2 513 678).

The reaction mixture that leaves the reactor generally still contains 3 to 5% by weight of unreacted acetaldehyde because the reaction was carried out with a deficiency of oxygen.

An embodiment of the process disclosed in DT-OS 2 514 095 uses a second reactor. This reactor works with a small excess of oxygen thus producing a crude acid that is practically free from acetaldehyde. At the same time, using this process, it is possible to recycle the heavy metal salts used as catalysts without any loss in activity. Both variants of the process work in continous operation without difficulty. However, difficulties do occur if, after a shut-down, for example as a result of a power failure, the plants have to be set in operation again. This is especially true if there is an interval of ten or more minutes between the shut-down and re-starting.

Experience has shown that when the acetaldehyde and oxygen are again supplied to the reactor the reaction does not begin immediately. The delay in the starting of the reaction may sometimes last for several hours.

There is thus an interest in ensuring that the reaction begins immediately after such an interruption or when the reaction is started with fresh reactor contents.

The addition of isobutyraldehyde as a start accelerator, preferably used in an amount of 0.3 to 5% by weight, is described in German Auslegeschrift 2, 520,976. In the example given therein, the mixture used for the oxidation contains 3 % of isobutyraldehyde, in addition to acetic acid and 3 % of acetaldehyde. It is indicated that the reaction then starts immediately.

Comparison experiments carried out (see comparison Examples 1 and 2 herein) resulted in an approximate halving of the start-up time from about 56 minutes (without the addition) to about 28 minutes (with the addition of 3 % of isobutyraldehyde), under otherwise identical operating conditions. However, the delay in the start-up of the reaction depends on various circumstances, for example the period of interruption in operation and the content of acetaldehyde, of impurities and of catalyst. The results can therefore be compared exactly only when the same reaction mixture is used. However, it can be concluded from the statements made in German Auslegeschrift 2,520,976 and on the basis of the comparison experiments carried out that in order to achieve a short start-up time for the reaction, considerably amounts of isobutyraldehyde should be added to the reaction mixture.

However, this has the disadvantageous result that in order to separate off the isobutyric acid formed in the reaction, a rather difficult distillation is required in working up the reaction mixture to give industrially pure acetic acid. In the case of an industrial reactor having a capacity of about 20 m3, an addition of 3 % of iosbutyraldehyde would means an amount of isobutyraldehyde of 600 kg, giving about 730 kg of isobutyric acid.

The present invention provides a process for the preparation of acetic acid which comprises oxidising acetaldehyde in the liquid phase, using a gas comprising oxygen as oxidant and a heavy metal compound as a catalyst and wherein there is added to the reaction mixture to initiate the reaction an organic peroxide other than peracetic acid having a half-life under the reaction conditions of not more than 350 minutes.

Preferably the reaction is carried out at elevated temperature. The gaseous oxidant may be pure oxygen or it may be a mixture of two or more gases one of which is oxygen.

Preferably the peroxide has a half-life for decomposition into free radicals of from 2 to 100 minutes. Suitably the peroxide is added to the reaction mixture immediately before the addition of oxygen begins or during the beginning of the addition of oxygen.

In general, the acetic acid synthesis is carried out under a pressure in the range of from 1 to 20 atmospheres, preferably 1 to 2 atmospheres, and at a temperature in the range of from 35 to 1500C, preferably 50 to 70". A manganese compound, cobalt compound or nickel compound or a mixture of two or more thereof is preferably used as the catalyst.

Examples of suitable peroxides are t-butyl hydroperoxide, cumene hydroperoxide, cyclohexanone peroxide and t-butyl perpivalate. t-Butyl hydroperoxide, cumene hydroperoxide and cyclohexanone peroxide are especially preferred. These peroxides generally have a very high activity, even additions of 0.01 to 0.1 weight %, relative to the capacity of the reactor, may start the reaction in a very short time. The addition of amounts of this order is thus preferred. Larger amounts can, of course, be added; however, the amounts given are generally sufficient for the intended purpose.

An advantage of these peroxides is that either their decomposition products are separated off with the first runnings in the working up by distillation of the crude acetic acid, or their decomposition products are already present in the reaction mixture.

Since the reaction mixture always contains some water, decomposition products such as t-butanol, cumene and cyclohexanone, are present in the first runnings of the crude acetic acid distillation in the form of an azeotrope with water.

The half-life (that is, the time after which 50 % decomposition of the peroxide has occured) for certain peroxides at 60 in acetic acid in the presence of catalytic amounts of heavy metal salts (Mn acetate, Co acetate and Ni acetate) was determined and is shown in the following Table.

Peroxide Half-life in minutes cyclohexanone peroxide 8 t-butyl hydroperoxide 40 cumene hydroperoxide 90 t-buty perpivalate 350 The peroxide is preferably fed into the main reaction zone, generally somewhat above the oxygen inlet, preferably as a solution in acetic acid and preferably directly at the start of the oxygen addition. This procedure is particularly advisable in the case of peroxides having a low half-life, for example cyclohexanone peroxide.

The following examples illustrate the invention. In order to ensure that the result of separate experiments can be compared meaningfully, a reaction mixture originating from an industrial installation, obtained when operation was interrupted, was used for the experiments. Two series of experiments were carried out. These were based on two interruptions in operation which took place 4 weeks apart. In each series of experiments, the individual tests were carried out in rapid succesion. It was therefore possible to assess the activity of each additive on a comparable basis.

In the start-up time data in the Examples, the symbol ' denotes minutes and the symbol " denotes seconds.

The reactor used in the Examples consisted of a double-walled glass tube, length 2,050 mm, inside diameter 34 mm. The jacket is used for heating by means of circulating water, and, after the reaction has started, for cooling. The reaction mixture containing acetaldehyde is fed in at the bottom of the reactor. The oxygen is metered into the reactor by means of a glass frit which is 100 mm above the reaction mixture inlet. For safety reasons, the gas space at the reactor head is flushed with a stream of N. The reaction mixture leaves the reactor through an overflow at the reactor head and is cooled to about 25 by a downstream cooler. The capacity of the reactor when not charged with gas is 18 1.

An inlet in the side 300 mm above the 2 inlet was added to the reactor for the experiments described in Examples 5 to 7 and 8 to 11.

EXPERIMENTAL SERIES I Comparison Example I The reactor described above was filled with a mixture of 97 % of crude industrial acetic acid and 3 % of acetaldehyde. The industrial crude acid contained, in addition to acetic acid, only traces of acetaldehyde, small amounts of water and a mixture of manganese acetate, cobalt acetate and nickel acetate as the catalyst, the total amount of catalyst being about 0.1 %.

The mixture was warmed to 60 by means of the jacket heating. 24 1/hour of oxygen were then metered in via the frit. At the same time, a mixture of 90 % of the industrial crude acid described above and 10 % of acetaldehyde was fed in from the bottom in an amount of 1,000 g/hour. The temperature in the reactor was kept at 600. The head of the reactor was flushed with 100 1/hour of nitrogen.

Under these conditions, the reaction started up after 55'55". The start-up could be recognised easily by an increase in temperature in the reactor to a maximum of 70" and by the collapse of the bubble column as a result of the consumption of oxygen. The start-up was immediately preceded by a brownish discolouration of the contents of the reactor.

Comparison Example 2 The reactor was filled with a mixture of 94 % of the industrial crude acid described in Comparison Example 1, 3 % of acetaldehyde and 3 % of isobutyraldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. The reaction started up after 27'37".

Example 1: The reactor was filled with a mixture of 96.7 % of the industrial crude acid described in Comparison Example 1. 3 % of acetaldehyde and 0.3 % of t-butyl hydroperoxide. All the remaining reaction conditions were the same as those in Comparison Example 1.

The reaction started up after 1'15". that is almost immediately.

Example 2: The reactor was filled with a mixture of 96.9 % of the industrial crude acid described in comparison Example 1, 3% of acetaldehyde and 0.1 % of t-butyl hydroperoxide. All the remaining reaction conditions were the same as those in Comparison Example 1.

The reaction started up after 2'45".

Example 3: The reactor was filled with a mixture of 96.97 % of the industrial crude acid used in Comparison Example 1, 3 % of acetaldehyde and 0.03 of t-butyl hydroperoxide. All the remaining reaction conditions were the same as those in Comparison Example 1.

The reaction started up after 5'6".

Example 4 The reactor was filled with a mixture of 96.99 % of the industrial crude acid used in Comparison Example 1, 3 % of acetaldehyde and 0.01 % of t-butyl hydroperoxide. All the remaining reaction conditions were the same as those in Comparison Example 1.

The reaction started up after 11'50".

Example 5: The reactor was filled with a mixture of 97 % of the industrial crude acid used in Comparison Example 1 and 3 % of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of t-butyl hydroperoxide in acetic acid was fed into the reactor through the inlet in the side above the O2 inlet; 10 ml of a 5.6 % strength solution were fed in by means of a metering pump over the course of 25". This corresponded to a t-butyl hydroperoxide addition of 0.03 % relative to the total contents of the reactor.

The reaction started up after 1'45".

EXPERIMENTAL SERIES II Comparison Example 3 The reactor described above was filled with a mixture of 97 % of industrial crude acid, which originated from another interruption in operation, and 3 % of acetaldehyde. All the other experimental conditions were the same as those in Comparison Example 1. The reaction had not started up after 70'; the experiment was therefore discontinued.

Example 6: The reactor was filled with a mixture of 97% of the industrial crude acid used in Comparison Example 3 and 3 % of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of t-butyl hydroperoxide in acetic acid was fed into the reactor through the inlet in the side above the oxygen inlet. 10 ml of a 5.4 % strength solution were fed in by means of a metering pump over the course of 20". This corresponded to a t-butyl hydroperoxide addition of 0.03 % relative to the total contents of the reactor.

The reaction started up after 1'25".

Example 7: The reactor was filled with a mixture of 97 % of the industrial crude acid used in Example 3 and 3 % of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of cumene hydroperoxide in acetic acid was fed into the reactor through the inlet in the side above the oxygen inlet; 10 ml of a 5.4 % strength solution were fed in by means of a metering pump over the course of 20". This corresponded to cumene hydroperoxide addition of 0.03 % relative to the total contents of the reactor.

The reaction started up after 4'15".

Example 8: The reaction was filled with a mixture of 97 % of the industrial crude acid used on Comparison Example 3 and 3 % of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of cyclohexanone peroxide in acetic acid was fed into the reactor through the inlet in the side above the oxygen inlet; 10 ml of a 5.4 % strength solution were fed in by means of a metering pump in the course of 20". This corresponded to a cyclohexanone peroxide addition of 0.03 % relative to the total contents of the reactor.

The reaction started up after 17'25".

Example 9: The reactor was filled with a mixture of 97 % of the industrail crude acid used in Comparsion Example 3 and 3% of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of t-butyl perpivalate in acetic acid above the oxygen inlet; 10 ml of a 5.4 % strength solution were fed in by means of a metering pump over the course of 20". This corresponded to a t-butyl perpivalate addition of 0.03 % relative to the total contents of the reactor.

The reaction started up after 41'50".

WHAT WE CLAIM IS: 1. A process for the preparation of acetic acid which comprises oxidising acetaldehyde in the liquid phase, using a gas comprising oxygen as oxidant and a heavy metal compound as a catalyst, and wherein there is added to the reaction mixture to initiate the reaction an organic peroxide other than peracetic acid having a half-life under the reaction conditions of not more than 350 minutes.

2. A process as claimed in claim 1, wherein the peroxide is t-butyl hydroperoxide, cumene hydroperoxide, cyclohexanone peroxide or t-butyl perpivalate.

3. A process as claimed in claim 1, wherein the peroxide has a half-life for decomposition into free radicals under the reaction conditions in the range of from 2 to 100 minutes.

4. A process as claimed in any one of claims 1 to 3, wherein the peroxide is used in an amount of from 0.01 to 0.1 by weight relative to the total weight of the reaction mixture.

5. A process as claimed in any one of claims 1 to 4, wherein the catalyst is a manganese, cobalt or nickel compound or a mixture of two or more thereof.

6. A process as claimed in any one of claims 1 to 5, carried out at a temperature in the range of from 35 to 1500C and a pressure in the range of from 1 to 20 atmospheres.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 6: The reactor was filled with a mixture of 97% of the industrial crude acid used in Comparison Example 3 and 3 % of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of t-butyl hydroperoxide in acetic acid was fed into the reactor through the inlet in the side above the oxygen inlet. 10 ml of a 5.4 % strength solution were fed in by means of a metering pump over the course of 20". This corresponded to a t-butyl hydroperoxide addition of 0.03 % relative to the total contents of the reactor. The reaction started up after 1'25". Example 7: The reactor was filled with a mixture of 97 % of the industrial crude acid used in Example 3 and 3 % of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of cumene hydroperoxide in acetic acid was fed into the reactor through the inlet in the side above the oxygen inlet; 10 ml of a 5.4 % strength solution were fed in by means of a metering pump over the course of 20". This corresponded to cumene hydroperoxide addition of 0.03 % relative to the total contents of the reactor. The reaction started up after 4'15". Example 8: The reaction was filled with a mixture of 97 % of the industrial crude acid used on Comparison Example 3 and 3 % of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of cyclohexanone peroxide in acetic acid was fed into the reactor through the inlet in the side above the oxygen inlet; 10 ml of a 5.4 % strength solution were fed in by means of a metering pump in the course of 20". This corresponded to a cyclohexanone peroxide addition of 0.03 % relative to the total contents of the reactor. The reaction started up after 17'25". Example 9: The reactor was filled with a mixture of 97 % of the industrail crude acid used in Comparsion Example 3 and 3% of acetaldehyde. All the remaining reaction conditions were the same as those in Comparison Example 1. At the start of the addition of oxygen, a solution of t-butyl perpivalate in acetic acid above the oxygen inlet; 10 ml of a 5.4 % strength solution were fed in by means of a metering pump over the course of 20". This corresponded to a t-butyl perpivalate addition of 0.03 % relative to the total contents of the reactor. The reaction started up after 41'50". WHAT WE CLAIM IS:

1. A process for the preparation of acetic acid which comprises oxidising acetaldehyde in the liquid phase, using a gas comprising oxygen as oxidant and a heavy metal compound as a catalyst, and wherein there is added to the reaction mixture to initiate the reaction an organic peroxide other than peracetic acid having a half-life under the reaction conditions of not more than 350 minutes.

7. A process as claimed in claim 6, carried out at a temperature in the range of from 50

to 700C and a pressure in the range of from 1 to 2 atmospheres.

8. A process as claimed in claim 1, carried out substantially as described in any one of Examples 1 to 9 herein.

9. Acetic acid which has been prepared by a process as claimed in any one of claims 1 to 8.