Note: Descriptions are shown in the official language in which they were submitted.
~ 110~ ~5/~ 66
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The present invention rela-tes to a process ~or -the con
tinuous manufact1lre of ace-tic acid ester by addition o~
acetic acid to ethylene.
It is known to react ace-tic acid in the pre.sence of
acidic catalysts wi-th ethylene to yield ace-tic acid ethyl
ester. In the litera-ture several proposals have been made
concerning the catalysts and -the operation rnethods. A sum-
mary of these proposals has been published by ~. ~lurakami,
T. Ha-ttori and H. Uchida in J. Chem. Soc~ Japan, Ind. Chem.
Sect. (l~ogyo I~agaku Zasshi) 72 (9), 19~15 - 19l~ (-1969).
' It can be-seen therefrom that catalys-ts con-taining oxides
of chromium, molybdenum and wolfram in -the form of diffe-
rent heteropoly acids~ which are used for the ca-talysis in
the gaseous phase, show a certain ini-tial activity at reL~
tively high -tempera-ture of more than 200 C and under a
pressure of up -to 150 bars, but become nearly inactive atfter
a few hours already. Ca-talysts containing phosphoric acid
H3P0~ to be used for the reac-tion in a gaseous phase are un-
suitable because of their low activity. ~cidic :ion exchange
resins cannot be used owing to t;heir instability already at
temperatures even below -the required reaction -temperature.
Considerable difficulties also arise ~hen performing
the reaction in the liquid phase. For -this rea~son a por-tion
of 67 % of a sulfur:ic acid of 96 /0 strength, calculated on
~5 acctic acid to be reactecl, -t'or example, has been proposecl in
the reaction zone~ for the manufacture of acetic ac:id e-thyl
ester f~rom acetic acid and ethylene.
It is~ however, known -tha-t h:igh concerltrations of rmine-
ral acids lead -to a partial polymerization of et;hylene a1~d,
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consequently9 to losses o~ ethylene and -to polymer by-
produc-ts, which can only be removed ~lth d;~ficul-ties ~`rc)m
the cataly~st solu-tion. A ~urther substantial disadvantage
of mineral acids o~ high concentration resides in the -~act
-that they bring about considerable corrosion problems, which
hinder their use on an inclus-trial scale~
As a summary i-t can be said tha-t none of the me-thods
proposed in the li-terature has proved appropriate ~or an
economic manu~acture of acetic acid es-ters on an indus-trial
scale~
The present invention consequen-tly provides a process
~or the manut'acture o~ acetic acid ethyl ester by reac-tion
o~ acetie acid and ethylene in the gaseous phase in -the pre-
sence o~ acidic ca-talysts~ which comprises passing ehtylene
over a -~ixed-bed catalys-t wi-th periodically al-ternating quan-
tities of acetic acid a-t a temperature ~rom 130 -to i70 C~
the catalyst being composed of silicon dioxide, ~hich has a
sur~ace ~rom 50 to 200 m /g and is impregnated with ~l2SOl~ or
; diethyl sulfate or ethylsul~ate acid or mixtures o~ these
compounds, the ace-tic acid concentration, calculated on
ethylene, varying constantly over a range ~rom o.o1 to 40 %
by mole.
The process according to the invention has surprisingly
; decisive advantages as compared to the previously proposecl
2S methods. One advantage resides in -the ~act -tha-t the e~fi~
ciency o~ the catalyst according to the invention is nearly
~mchanged under -the reaction concl:Ltions even a~-ter more
than 100 hours. The other a~vantage resides in the fact
that -there are prac-tically no losses o~ ethylene due to
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~ /F 266
polymerizat:ion A :~orma-tion o~ by-pro~ucts or unclesired
consecutive produc-ts can nvt at all be ohserved~
The process according -to -the inven-tion can be performed
in the fo~1lowing manner generally: Ethylene and acetic acid
in a gaseous state are passed -through a reaction zone in a
reactor, in which -the ca-talys-t is arranged as a iixed-bed.
In this process acetic acicl may ei-ther be passecl ove:r a pre-
evaporator or be lead directly to the reaction zone, where
~ it vaporizes immediately under -the reac-tion conditions
A hea-table -tube, which may be made of glass or stai.n-
less steel, ~or example~ may serve as a reaction zone~ in
which the catalys-t is arranged as a fixed-bed. Other reac-
tor forms and materials may also be used, however
The reaction tempera-ture is in the range ~rom 130 to
15 170 C, preferably from 140 to I50 C~ sligh-tly higher or
lower temperatures being also possible~
A pressure range from 0.5 -to 10 bars is suitable for
the process according to the invention, but hig:her pressures~
for e~ample up to I00 bars~ may also be applied without ~!
di~ficulty.
The service life of the catalyst as well as the space-
time-yield o~ the catalys-t in -the process o~ -the invention
a:re defined in characteristic manner by the ace-tic acid con-
centration in the reactor. The permanent varlation o:f -the
ace-t;ic acid concentration in the reac-tor is in a :range
between a min:imwn value and a maximum value f:rom 0.01 to
40 % by mole~ calcula-ted on e-thylene, is particula:rly advan-
ta~eously achieved in definite lnterva:Ls.
Th:is peImanent variation may be achieved rnos-t easily,
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for example by continuously regulating the acetic acid ad-
r~ssion in ~eriods, durinq which aeld is added~d d~r~la whieh ~2
addition is dieontinued by mec~s of a t~ switeher.
The duration of these intervals with or withou-t acid
addition depencls subs-tan-tially on -the desorp-tion veloci-ty
Or the ace-t:ic acid ~rom -the catalys-t under -the reaCtior1 con-
ditions. ~s acetic aci.d is absor'bed by the catalyst -to a
higher degree than ethylene, -the cataly-tically ac-tive sur-
. face o~ the.ca-talys-t woulcl be subs-tan-tially covered wi-th
ace-tic acid alone already af-ter a shor-t period of -time,when
~orking withou-t'inte:rruption of the ace-tic acid addition,
and as a consequence thereof only a ~ery small part o~ ethy
lene would be ac-tivated, -thus considerably red-1ci.ng -the
ester formation veloci-ty. I:n practice it may also be advan-
tageously opera-ted in the ~ollowing manner: Ace-tic acid is
introduced into -the reac-tor during an in-ter~al from 2 -to 60
minutes, :for example 9 preferably 5 to 30 minutes, and -the
addition ls -then interrup-ted ~or each time 0.1 -to '15 minutes~
p:referably 1 -to 10 mi:nu-tes, while e-thylene is adcled -~i-t'hou-t
in-terruption. ~s a consecluence of such a repea-ted discon-
tinuance of -the ace-tic acid adclition a part of -the acetic
acid absorbed by the ca-talys-t is desorbed again and again
so t:hat a su~`ficien-t quan-tity of ethylene is likewise ab-
sorbed genera:lly~
Si02 used ~or t:he manufac-ture of -the ca-talyst :has a
specific surrace from 50 -to 200 m /g, p:ref`erably ~rom ~0 to
170 m /g. Considerably larger or s~aller .ju:r:faces may 'Leac1
to no-ticeably reduced yields of ace-tic ac:id e-thyl es-te:r.
The ca-talyst ma-~ generally -be prepa:rec1 in -the following
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manner: SiO2 is impregn~ted with ~12SOLI and/or diethylsul~`ate
or ethylsul~uric acld o:r with mix-tures of these compoul1ds,
preferably in admix-ture with acetic acid, and dried subse
quently under a reduced pressure at a temperature of abou-t
lL~o C. Among the catalys-ts prepared in said manner there
are preferably used those having a conten-t of H2S04 ancl/or
diethylsulfa-te and/or e-thyl.sul~uric acid or mixtures of
these compounds from about 10 to 30 % by- weight, op-tionally
a~ter removal o~ the acet:ic acid by drying.
I~ -the material load of the catalyst is too high duri.ng
the reaction a small discharge and, consequently~ losses of
the impregna-tion may occur whereby the space--time--yield o:f
the catalyst may be sligh-tly reduced in the course of seve-
ral hundred hours. In such cases it has proved advantage-
ous to introduce H2S04 and/or diethylsulfate and/or ethy].~
sulfuric acid dissolved in acetic acirl into the reactor to-
gether with the reaction components in an amount f:rom about
O.i to about 2 /0 by weight, calculated on the acetic acid
introduced into -the reactor.
The reaction product may be worked up continuou~sly or
discontinuously by applying the known methods. The preferr-
ed method consists in separating the reac-tion mixture con-ti-
nuously while isolating p-ure acetic acid ethyl este-r. For
this purpose the reaction mixtnre is cooled af-ter having
le~t the reac-tor9 whe:reby e-thylacetate and non conver-ted
acetic acid condense, whereas non convertecl eth~lene is se
para-ted in a gaseous state and recycled to the reactor. The
condensate is preferablr con-t:inuously submlt-ted to a frac-
tionnated distillation~ whereby non converted acetic acid
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is recovercd from the bottom prod-uct of the distillation
column and recycled to the reac-tor, whereas pure acetic acid
ethyl. ester is obtained at -the top of -the column.
The selectivity of the process according to the inven-
tion is extremely high; i-t is nearly 100 o~h, referring to
acetic acid as well as to ethylene.
Ace-tic acid ethyl ester is used to a considerable ex~
tent, for example, as a solven-t for lacquers and adhesives.
. - The follo~ing examples illustra-te the invention:
E X A M P L E S 1 to 3:
- A -total of 10 rnl/h of acetic acid is introduced by
pump,ing alterna-tingly by means of a dosage pump, while simul-
taneously adding 20 Nl/h of ethylene~ at the top o.f a verti-
cally arranged glass -tube reactor of 30 cm length and 100 ml
volune~ ~hich is filled wi-th about 100 ml of a catalyst com-
posed of SlO2, impregnated with 25 % by weight of H~SOl~ and
having a certain-surface as indicatecl in Table 1 and which
is hea-ted to a tempera-ture of 138 C, the acetic acid addi
tion being inte:rrupted constantly for 2 min-u-tes a.~ter 6 mi-
nutes. The reaction mixture leaving the reactor is broughtto normal temperature, liberated from e~cess ethylene and
analysed. It contai.ns besides non converted ace-tic acid
only ace-tic acid ethyl ester so that the selectivitles cal
culated on conver-ted ethylene as well as on converted acetic
acid are practically 'lO0 %. Table 1 indicate.s the conten-t
of ace-tic acid ethyl cster in -the react,ion mixture libera-t-
ed ~rom ethylene of the ~xamples 1 to 3. The non convertcd
portions of ethylene and acetic acid may be :recycled to the
reactor wlthout particular purifying operations.
. . .
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T ~ B L E
Influence of` the ca-talyst surf`ace on the conve:rsion
Example SiO2-surface /c by weight of acetic acid e~yl
2 es-ter in the reaction mixture
(m /g) .. ~
1 l10 3~.2
2 120 60,0
3 160 37.4
. . . . __
C 0 M P-A ~ A T I V E E X A M P L E S 1 and 2: -
It is operated in the same manner as in E~amples 1 to
3~ e~Ycept that comparable catalysts are used having a SiO2
surface other than that according -to the inven-tion. Table 2
shows the results obtained. The portions of acetic ac:id
ethyl ester in the reaction mixture are noticeably smaller.
T A B L E II
Influence of -the ca-talyst surface on the conversion
Compara-tive SiO2-surface % by weight of acetic acid
Example (In /g) ethyl ester in the reaction
mi~ture
._ .. . _. _ _ . ~
20 1 o.6 1L~.6
2 35 _ 10.0
E X A M P L E S 4 to 7:
The apparatus described in the Examples 1 to 3 is :t`ill-
ed each time with 100 m] of a ca-talyst (carriero SiO2 ha~ing
a surface of 120 m /g) pr~vided with the impregnation indi-
cated in Table 3 and fed with ethylene and acetic acid in an
analogous manner to Examples 1 to 3. The reaction tempera-
ture in the reactor is 11~4 C. Table 3 indicates the por-
tions of acetic acid ethyl ester in the reaction mixture.
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The selectivl-ti.es, calcula-ted on conver-ted ace-tic acid
as well a.s on con~er-ted ethy1.ene)in the Examples 4 to 7 are
1 0 0 % .
T A B L E III
5 Influence of the catalyst impregnation on the conversion
Example Impregna-tion by weigh-t /0 by weight of ace-tic
(each time 20 % by acid e-thyl es-ter in
. weigh-t) the reac-tion mix-ture
4 H2S04 61.5
. di.ethylsulfate 59.2
.. . 6 ethylsulfuric acid 59-7
_ _ ,. . ., ..... __ .. _. ._ ' O 1
E X A M P L E S 8 to 10:
c~00 Nl/h of ethylene as well as alternatingly acetic
acid having a content of diethylsulfate of 0~7 % by weight
are introdueed continuously at the top of a vertically ar-
ranged V4A steinless steel reactor of 100 cm leng-th, whieh
is filled with 250 ml of catalys-t (SiO2, 120 m /g, 25 o~b by
weight of diethylsulfate), at a -temperature of 147 C. The
alternating acetic acid addition is carried out in the fol-
lowing manner: The acldi-tion is interrupted each -time for
one interval af-ter 5 dosing intervals. A total of 150 ml/h
of acetic acid is metered into the reactor, The pressure in
the reactor is 6 bars. The reaction mi~ture leaving the
reactor is worked up continuously. The e~cess ethylene is
recycled to the reac-tor. The portion of the reac-tion mi.x-
ture liquid ~t normal temperature is fractiona-ted in a di.
s-tillation column. The acetic ac:id ethyl ester is withdrawn
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at the top of the column. A mixture containing besides small
quantitie~ of acetic acid ethyl ester unconverted acetic acid
is recycled to the reactor continuously from the bottom.
Table 4 indicates the different intervals of the alternating
acetic acid addition of the Examples 8 to 10 as well as the
space-time-yields obtained. The selectivities for acetic
acid ethyl ester, calculated on converted ethylene and con-
verted acetic acid, are in all cases 100 ~.
T A B L E IV
Example Intervals of the acetic Space-time-yield of the
acid addition (min) acetic acid ethyl ester
addition without formation (g/l.h)
addition
8 5 1 205
9 12.5 2.5 178
164
The same values for the space-time-yield of the acetic
acid ethyl ester formation as well as the same selectivities
are obtained even after a continuous operation time of more
than 1000 hours.
C 0 M P A R A T I V E E X ~ M P L E 3:
~ len operating in the same manner as in the Examples 8
to 10, except that the acetic acid addition is not perform-
ed alternatingly, but that 150 ml/h of acetic acid are added
without interruption, the space-time-yield of the acetic
acid ethyl ester formation is only 100 g/l . h.
-- 1 0
