CA1094101A - Process for the manufacture of acetic acid ethyl ester - Google Patents

Abstract

Process for the Manufacture of Acetic Acid Ethyl Ester Abstract of the Disclosure:
Acetic acid ethyl ester is prepared by passing ethylene over a fixed-bed catalyst composed of silicon dioxide, which has a surface from 50 to 200 m2/g and which is impregnated with H2SO4, diethylsulfate or ethylsulfuric acid or mixtures of these compounds, with periodically alternating quantities of acetic acid, at a temperature from 130 to 170°C, the acid concentration, calculated on ethylene, varying constant-ly over a range from 0,01 to 40 % by mole,

Description

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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 - 3 ~

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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 - 5 ~

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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 "- 6 _ - - : ; :' -, ,: i' ;

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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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I-lOi~ 7'~ ?6-6 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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:~ :: : - - 'l ~ 1l01~'-~ F 266 --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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10~4101 ~IOF 75/F ~>6 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 9 12.5 2.5 178 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.

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of acetic acid ethyl ester in the gaseous phase in which ethylene is passed over a fixed-bed catalyst with periodically alternating quantities of acetic acid at a temperature of from 130 to 170°C, the catalyst being composed of silicon dioxide having a surface of from 50 to 200 m2/g which is impregnated with at least one member of the group of H2SO4, diethylsulfate and ethylsulfuric acid, the acetic acid concentration, calculated on ethylene, varying constantly over a range of from 0.01 to 40% by mole.

2. A process as claimed in claim 1, in which the acetic acid ethyl ester is separated continuously from the reaction mixture, unreacted portions of acetic acid and ethylene are sepa-rated and these unreacted portions are returned to the reaction.

3. A process as claimed in claim 1, in which any lost H2SO4, diethylsulfate or ethylsulfuric acid is recovered.

4. A process as claimed in claim 1, claim 2 or claim 3 in which the acetic acid is added alternatingly by interrupting the addition in certain intervals.

5. A process as claimed in claim 1, claim 2 or claim 3 in which the reaction is carried out at a temperature from 140 to 150°C.

6. A process as claimed in claim 1, claim 2 or claim 3 in which the silicon dioxide used has a surface from 80 to 170 m2/g.

7. A process as claimed in claim 1, claim 2 or claim 3 in which the acetic acid concentration varies over a range from 0.1 to 30% by mole.