Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Processes for the manufacture of acetic acid by oxi-
dizing acetaldehyde at elevated temperature in the liquid ph--_e
using oxygen or gases containing oxygen in the presence of
soluble heavy metal compounds as catalysts are already kno~m,
S Manganese compounds and/or cobalt compounds are preferably us~d
as the heavy metal compounds (see Ullmann~s "Enzyklopadie der
technischen Chemie" ("Encyclopaedia o~ Industrial Chemistry"~,
volume 6, 3rd edition, 1955, page 781 et seq, and German
Offenlegungsschrift 2,513,678),
? a - In general, the reaction mixture leaving the reactor
still contains 3 - 5 % by wQight of unreacted acetaldehyde,
since less than the equivalent amount of oxygen is employed.
A specific embodiment of the process, described in German
Offenlegungsschrift 2,514,095, u~es an additional second reacto.,
In this, a slight excess of oxygen is employed and a viriual~-~-
aldehyde-free crude acid is-thus obtained, At the same t ~,
this also makes it possible for the heavy metal salts used as
the catalyst to be recycled without loss in activity. Bot:^
process variants are operated continuously without ~roblems.
However, there are difficulties if the installations must ce
set in operation agai.n after being disconnected, for ex~mpl b,~
power failure, This is particularly true if there is ~
period of ten minutes or more bet~een the disconnectlon and ~h
re-operation.
Experience has sho~ that tne re~ction does not ~e~^in
immediately when acetaldehyde and ox~en are fed in ag?~n,
Un~er certain circwmstan^es, the delay in t~e start-u~ o4 th~
reaction can be several hours.
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There is thus a particular 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,
and in particular in an amount of 0.3 - 5 % by weight, is thus
claimed in German Auslegeschrift 2,520,976. In the example given
therein, the mixture used for the oxidation additionally 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) 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 identical
operating conditions. However, the delay with respect to time in
the start-up of the reaction depends on various circumstances,
such as, 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 u~sed. However, it can be concluded from the statements
made in German Auslegeschrift 2,520,97~ and on the basis of the
comparison experiments carried out that in order to achieve a good
effect, that is to say a short start-up time of the reaction,
consi~erable amounts of isobutyraldehyde must certainly be added to
the reaction mixture.
2~ However, this has the disadvantageous result that in order
to separate off the iso~utyric acid formed in the reaction particular
distillation measures are required in working up the reaction
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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 ~ would mean an amount of isobutyraldehyde of 600 kg, which
correspond to about 730 kg of isobutyric acid.
The problem was to find start accelerating additives of
high activity which do not have the disadvantage mentioned.
It has now been found, surprisingly, that certain peroxidic
compounds are quite outstanding start accelerators. The process
according to the invention for tXe manufacture of acetic acid by
oxidizing acetaldehyde at elevated temperature in the liquid phase
using oxygen or gases containing oxygen in the presence of one or
more heavy metal compounds as a catalyst comprises adding to the
reaction mixture at the start of the addition of oxygén one or
more organic peroxides which under the reaction conditions decompose,
with a half-life of up to 350 minutes, into fee radicals in order
to initiate the reaction. Peroxides with a half-life of 2 to 100
minutes are preferably used.
- In general, the acetic acid synthesis is carried out under
pressures of 1 - 20 atmospheres, preferably 1 - 2 atmospheres, and
at temperatures from 35 to 150C, preferably 50~ - 70C. Manganese
compounds, cobalt compounds or nickel compounds or a mixture of
these heavy me~al compounds are preferahly used as the catalyst.
These conditions also apply to the initiation of the reac-
tion by the addition of peroxides. Examples of suitable peroxides
are peracetic acid, t-butyl hydroperoxide, cumene hydroperoxide,
cyclohexanone peroxide or t-butyl perpivalate. Peracetic acid, t-
butyl hydxoperoxide, cumene hyroperoxide and cyclohexanone peroxide
are preferredO These peroxides have a very high activity, that is
to say even additions of 0.01 - 0.1 we~ght ~, relative to
the capacity of the reactor, start the reaction in a
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very short time. The addition of amounts of this type is thus
preferred.
Larger amounts can, of course, also be added; however, the
amounts given are c ~ letely sufficient for the intended purpose.
A particular 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 that
only substances are formed which are in any case already present in
the reaction mixture. Thus, the desired reaction product itself,
that is to say acetic acid, is formed from peracetic acid. Since
the reaction mixture always contains some water, the 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 suitability of the peroxides to be employéd for the
abovementioned purpose can be deduced from the half-lives. The
half-life (that is to say the time after which 50 ~ decomposition
of the peroxides has occurred) for some 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 (see the
following Table~.
Peroxide Half-life in
minutes
peracetic acid 2 - 3
cyclohexanone peroxide
t-butyl hydroperoxide 40
cumene hydroperoxide 9O
t-butyl perpivalate 350
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The peroxides are preferably fed into the main reaction
zone, that is to say somewhat above the oxygen inlet, as a solution
in acetic acid directly at the start of the oxygen addition. This
procedure is particularly advisable in the case of peroxides having
a low half-life, such as, for example, peracetic acid and cyclo-
hexanone peroxide.
In the abovementioned German Auslegeschrift 2,520,976 itis indicated that the delay in the start-up can be "up to 5 hours".
In order to ensure that the results can be compared exactly,
a reaction mixture originating from an industrial installation,
10 such as is obtained therefrom when operation is interrupted, was
used for the experiments and 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 succession. It was thereby possible
to determine the activity of the additives on a comparable basis
in each case.
In the start-up time data in the Examples, the symbol '
denotes minutes and the symbol" denotes seconds.
Examples
Apparatus:
The reactor consists of a double-walled glass tube, length
2,050 mm, inside diameter 34 mm. The jacket is used, by means of
circulating water, for heating and, aft~r the reaction has started,
for cooling. The reaction mixture containing acetaldehyde is fed
in at the bottom of the reacotr. 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
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head is flushed with a stream of N2. 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 1.~ 1.
An inlet in the side 300 mm above the 2 inlet was added
to the reactor for the experiments according to Example 5 - 7 and
8 - 11.
Experimental series I
Comparison Example 1
The reactor described above is filled with a mixture consist-
ing of 97 ~ of crude industrial acetic acid and 3 % of:acetaldehyde.
The industrial crude acid also contains, 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 is warmed to 60 by means of the ja~ket heating.
24 l/hour of oxygen are then metered in via the frit. At the same
time, a mixture consisting of 90 ~ of the industrial crude acid
described above and 10 % of acetalaehyde is fed in from the bottom
in an amount of 1,000 g/hour. The temperature in the reactor is
kept a~ 60. The head of the reactor is flushed with 100 l/hour of
nitrogen.
Under these conditions, the reaction starts up after 55'55".
The start-up can be recognised exactly, namely by an increase in
temperature in the reactor to a maximum of 70 and the collapse of
the bubble column as a result of the consumption of oxygen. The
start-up is immediately preceeded by a brownish discoloration of
the contents of the reactor.
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Comparison Example 2
The reactor is filled with a mixture consisting of 94 ~ of
the industrial crude acid described in Comparison Example 1, 3 %
of acetaldehyde and 3 % of isobutyraldehyde. All the remaining
reaction conditions correspond precisely to those from Comparison
S Example 1. The reaction starts up after 27'37".
Example 1:
The reactor is filled with a mixture consisting 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
! 10 remaining reaction conditions correspond precisely to those from
Comparison Example 1.
The reaction starts up after 1'15", that is to say almost
immediately.
Example 2: -
The reactor is filled with a mixture consisting 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 correspond precisely to those from
Comparison Example 1.
The reaction starts up after 2'45".
Exam~le 3:
The reactor is filled with a mixture consisting of 9~.97 %
of the industrial crude acid used in Comparison Example 1, 3 ~ of
acetaldehyde and 0.03 % of t-butyl hydroperoxide. A11 the remaining
reaction conditions correspond precisely to those from Comparison
Example 1.
The reaction starts up after 5'6".
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Example 4:
The reactor is filled with a mixture consisting 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 remain-
ing reaction conditions correspond precisely to those from Comparison
Example 1.
The reaction starts up after 11'50".
Example S:
The reactor is filled with a mixture consisting of 97 % of
the industrial crude acid used in Comparison Example 1 and 3 ~ of
acetaldehyde. All the remaining reaction conditions correspond to
those from Comparison Example 1. However, at the start of the
addition of oxygen, a solution of peracetic acid is fed into the
reactor through the inlet in the side above the 2 inlét. 25 ml =
26.3 g of a 5.6% strength peracetic acid solution are fed in by
means of a metering pump in the course of one minute. This
corresponds to a peracetic acid addition of 0.08 %, relative to
the total contents of the reactor.
The reaction has already started up when the addition has
ended, that is to say in the course of one minute.
2Q Example 6:
The reactor is filled with a mixture consisting of 97 % of
the industrial crude acid used in Comparison Example 1 and 3 ~ of
acetaldehyde as in Example 5. All the remaining reaction conditions
correspond to those from Comparison Example 1. At the start of the
addition of oxygen, 16.6 ml = 17.4 g of a 5.6 ~ strength solution
of peracetic acid in acetic acid are fed into the reactor through
the inlet in the side in the course of about 3 minutes.
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This corresponds to a peracetic acid addition of 0.054 %,
relative to the total contents of the reactor.
The reaction starts up immediately after the addition of
the amount indicated has ended, i.e. after 3'20".
Example 7:
The reactor is filled with a mixture consisting of 97 ~ of
the industrial crude acid used in Comparison Example 1 and 3 ~
of acetaldehyde. all the remaining reaction conditions correspond
to those from Comparison Example 1. At the start of the addition
of oxygen, a solution of t-butyl hydroperoxide in acetic acid is
fed into the reactor through the inlet in the side above the 2
inlet. 10 ml of a 5.6 ~ strength solution are fed in by means of
a metering pump in the course of 25". This corresponds to a t-butyl
hydroperoxide addition of 0.03 %, relative to the total contents of
the reactor.
The reaction starts up after 1'45". c
EXPERIMENTAL SERJES ~I
. . .
Comparison Example 3
The reactor described above was filled with a mixture
consisting of 97 % of industrial crude acid, which originated from
another interruption in operation, and ~ % of acetaldehyde. All
the other experimental conditions correspcnd precisely to ~ose from Go~ri-
son Example 1. The reaction had not yet started up after 70'; the
experiment was therefore discontinued.
Example 8:
The reactor is filled with a mixture consisting of 97 % of
the industrial crude acid used in Comparison Example ~ and 3 ~ of
acetaldehyde. All the remaining reaction conditions correspond to
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those from Comparison Example 1. At the start of the addition of
oxygen, a solution of t-butyl hydroperoxide in acetic acid is fed
into the reactor through the inlet in the side above the oxygen
inlet. 10 ml of a 5.4 ~ strength solution are fed in by means of
a metering pump in the course of 20". This corresponds to a t-butyl
hydroperoxide addition of 0.03 ~, relative to the total contents of
the reactor.
The reaction thereby starts up after 1'25".
Exam le 9:
The reactor is filled with a mixture consisting of 97 % of
the industrial crude acid used in Example 3 and 3 ~ of acetaldehyde.
All the remaining reaction conditions correspond to those from
Comparison Example 1. At the start of the addition of oxygen, a
solution of cumene hydroperoxide in acetic acid is fed~into the
reactor through the inlet in the side above the oxygen inlet. 10 ml
of a 5.4 ~ strength solution are fed in by means of a metering pump
in the course of 20". This corresponds to a cumene hydroperoxide
addition of 0.03 %, relative to the total contents of the reactor.
The reaction thereby starts up after 4'15".
Exam~le 10:
The reactor is filled with a mi~ture consisting of 97 % of
the industrial crude acid used on Comparison Example 3 and 3 ~ of
acetaldehyde. All the remaining reaction conditions correspond to
those from Comparison Example 1. At the start of the addition of
oxygen, a solution of cyclohexanone peroxide in acetic acid is fed
~5 into the reactor through the inlet in the side a~ove the oxygen
inlet. 10 ml o~ a 5.4 ~ stren~th solution are fed~in ~y means of
a meterin~ pump in the course of 20". This corresponds to a
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cyclohexanone peroxide addition of 0.03 %, relative to the total
contents of the reactor.
The reaction thereby starts up after 17'25".
Example 11:
The reactor is filled with a mixture consisting of 97 % of
the industrial crude acid used in Comparison Example 3 and 3 % of
acetaldehyde. All the remaining reaction conditions correspond to
those from Comparison Example l. At the start of the addition of
oxygen, a solution of t-butyl perpivalate in acetic acid is fed into
the reactor through the inlet in the side above the oxygen inlet.
lO ml of a 5.4 % strength solution ar~ fed in by mean5 of a meter-
ing pump in the course of 20". This corresponds to a t-butyl perpi-
valate addition of 0.0~ %, relative to the total contents of the
reactor. The reaction thereby starts up after 41'50".,
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