Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~3~2~
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HOECHST ARTIENGESELLSCHAFT Dr.MA/gm HOE 89/F 384
Description
Proces~ for the preparation of vinyl acetate
It is known ~hat ethylene can be reacted in the gas phase
with acetic acid and oxygen or oxygen-containing gases on
solid bed catalys~s to give vinyl ace~ate. Sui~able
catalysts ~ontain a noble metal component and an aetiva-
tor component~ ~he noble me~al component i8 preferably
composed of palladium and/or i~s compounds; gold and/or
its compounds can additionally also be present (U5 Patent
3,939ll99, DE-OS 2,100,778, US Patent 4,668,819). ~he
activator component is composed in this case of compounds
of elements of the 1st main group and/or the 2nd main
group and/or cadm.ium. Potas~ium i~ preferred as an
element o~ the ls~ main group. These active components
are applied to supports in finely divided form, silica or
alumina in general being u#ed as 6upport material~
The specific ~urface area of the ~upports i~ in general
40 _ 350 m2/g. According to US Pa~ent 3,939,199, the total
pore volume should be 0.4 - 1.2 ml/g, and o this less
than 10~ should be formed of "micropores" having a pore
diame~er below 30 A (A = angs~rom = 10-~ cm). Suitable
supports having these properties are, for example,
aerogenic SiO2 or an aerog~nic SiO2-Al2O3 mixture. The
support particles in the vinyl acetate preparation in
general have the form of spheres. However, tablets and
cylinder~ ha~e al80 already been employed.
The still unpublished German Pakent Application
P 39 19 524.4 describes a support which i8 compo~ed of
SiO2 or an SiO2-Al2O3 mixture having a surface area of
50 ~- 250 m2/g and a pore volume of 0.4 - 1.2 ml/g and
whose particle~ have a particle size of 4 to 9 ~m, 5 to
20% of the pore vol~me of the support being ormed of
pores having radii of 200 to 3000 A and 50 to 90% of the
pore volume being formed o pores having radii of 70 to
.~
~3:~2~3
100 ~.
It has now been found tha~ it is very advant~geous if the
suppor~ particles are compressed wi~h the aid o c~rboxy-
la~es of Li, Mg, Al, Zn or Mn as binders.
S The invention relates to a process for the prepara~ion of
vinyl ace~ate in the gas pha~e from ethylene, acetic acid
and oxygen or oxygen~containing gases on a catalyst which
contains palladium and/or its compounds and, if desired,
additionally gold andJor gold compound~ and also alkali
metal compounds as activators and, if de6ired, addition-
ally cadmium compounds on a ~uppor~ which i5 composed of
SiO2 or an SiO2-Al2O3 mixture having a surface area of
50 - 250 m2/g and a pore volum2 of 0.4 - 1.2 ml/g land
whose particles have a particle siz~ of 4 to 9 mm, 5 to
20% of the pore volume of ~he support being formed of
pores having radii of 200 to 300G ~ and 50 to 90% of the
pore volumP being formed of pores having radii of 70 to
100 A, which comprises compressing the suppoxt particles
with the aid of an ~i, Mg, Al, ~n or Mn salt of a C~ C20
carboxylic acid or a mixture of ~uch salts as binder.
The carboxylate or carboxylates ~re employed in amounts
such that the sum of the amounts of ~i, Mg, Al, Zn and
Mn, calculated as elemen~s, is 0.1 to 5% by weight, ba.sed
on the support material, preferably 0.3 to 1.5~ by
weight.
Al carboxylates or Mg carboxylate~, in particular ~g
carbo~ylates, are preferably employed. The carbo~ylic
acids preferably have 12 to 18 carbon atoms. The support
particles according to the claim~ can be prepared, for
exampler as follows:
glass mlcro~pheres are initially prepared, for example by
flame hydrolysis of silicon tetrachlorida or a silicon
tetrachloride/aluminum tr.1chloxide mixture in an o~y-
hydrogen flame (UB Patent 3,939,1~9). The microspheres
can also be prepared by mel~ing very fine SiOz dust in a
" 2~3:~L29
-- 3 --
sufficiently hot flame and then cooling rapidly. The
microspheres prepared in one of the two ways have a
surface area of 100 - 300 m2/g. Microspheres having a
surface area of 150 - 250 m2~g, which are composed of at
least 95~ by weight of SiO2 and at most 5~ by weight of
Al2O3, in particular of at least 99% by weight of SiO2 and
at most 1% by weight of ~12O3, are par~icularly ~uitable~
Microspheres having ~aid surface area are a~ailable
commercially, for example under the name ~Aerosil or
~Cabosil or as ~highly di~perse silicic acid".
Support particlesare then pre6sed ~rom the microspheres
with the addition of one or more carboxylates o Li, Mg,
Al, Zn or Nn and with ~he addition of organic fillers
(such as ~ugar, urea, higher fatty acids, long chain
paraffins, microcrystalline cellulose) and lubricants
(such as kaolin, yraphite, me~al soaps), for example by
tableting (after precompression) or extruding. Thesupp
particlesare then calcined in O2-containing gases. When
using the Li, Mg, Al, Zn or Mn ~alt~ of higher carboxylic
acids (Cl6-C20) these "~oaps" simultaneously act in the
tableting as lubricants~ so that a ~epaxate lubric~nt
does not have ~o be added. The surf ace area of the
finished support, its pore volume and the proportion of
the pore volume which pores of a certain radius form
("pore radii di~tribution") i~ determined by the type of
6haping (tablets, extrudate pressings etc.), the tempera-
ture and duration of calcining, the relative amount~ of
fillers, lubricants and microspheres and the ~uxface area
of the microspheres. Which are the most suitable values
3Q for these determining parameter~ can be deteLmined by
sLmple prelLminary experiments.
The finished support obtained by this method has a
~urface area of 50 to 250 m2/g and a pore volume of 0O4
to 1.2 ml/g and a particle ~ize of 4 to 9 mm (adjustable
by tableting or extruding support particles of suitable
size).
-- 4 --
By using the support~ according to the claLms, it is
possible to increase substan~ially the space-time yield
of the catalysts compared to conventional suppor~s with
- otherwise identical conditions (the same content of
active substances on the support and the same reaction
conditions) and at the same time ~o lower ~he mo~t severe
side reaction, the combustion of ~he ethylene to give
CO2, by 75~. ~he ethyl acetate formation occurring as a
further side reaction is also distinctly reduc~d. ~s a
result of this increase in the selectivity from about 92%
to about 97%, substantial savings can be achieved and
additionally as a result of ~he increa~ing efficiency,
together with distinctly increased selec~ivity, the
amount of catalyst and reactor vol~me can be reduced in
new plants, which lead~ to considerable xeductions in the
pl~nt cost~, or th~ capacity can be signif icantly in-
creased without alterations in already existing plants,
so that the investment costs for ~he plant expansion are
s aved .
The surface area of said supports is always the so-called
BET surface areal measured by the method of Brunauer,
Emmett and Teller. It indicates the total surface area of
1 0 of ~upport material, i . e . the sum of the external
surface area of the support and of ~he internal surface
area of all open pores. The total pore volume and the
proportion thereof which pores of a certain size ~for
ex~mple those haYing a diameter of 70 to 100 ~) contri-
bute can be measured with the aid of mercury porosLmetry.
Suitable measuring apparatuses are manufactured, for
example, by the firm8 Carlo Erba or Micxomeritics.
The catalytically active sub~ances are applied to the
support in a customary manner, for example by impxegnat-
ing the support with a solution of the active substances,
then drying and, if appropriate, reducing. However, the
active substance~ can also be applied, for example, by
depositing on the support, by sprayin~ on, evaporating
on or immersing.
203~2~
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Suitable solvents for the catalytically active substances
are in particular unsubstituted carboxylic acids having
2 to 10 carbon atoms in the molecule, such as acetic
acidl propionic acid, n- and i~o-butyric acid and the
various valeric acids. Owing to their physical properties
and also fox economic reason~, acetic acid i~ preferably
employed as the solvent. ~he additional u~e of an in~rt
solvent is expedient if the substances a:re insufficiently
soluble in the carbo~ylic acid. Thus, for example,
lQ palladium chloride can be dissolved substan~ially b~tter
in an aqueous acetic acid ~han in glacial acetic acid.
Possible additional solvents are those which are inert
and miscible with ~he carboxylic acid. In addition to
water, those which may be mentioned are, for example,
ketones such as acetone and acetylacetone, in addition
ethers such a~ tetrahydrofuran or dioxane, but also
hydrocarbons such as benzene.
The catalyst contains palladi~m and/or its compounds as
the noble metal component and alkali metal compounds as
the activator component. I~ can contain gold and/or its
compounds as an additional noble metal component, and it
can contain cadmium compound~ as an additional ctivator
component.
Possible compounds of palladium are all the salts and
complexes which are soluble (and, i appropriat~, reduc-
ible) and which leave behind no deactivatin~ substances
such as halogen or sulfur in the finished catalyst.
Particularly suitable compounds are the carboxylates/
preferably the ~alts of aliphstic monocarbo~ylic cids
having 1 to 5 carbon atoms~ for example the acetate, the
propionate or the butyrate. In addition, for example, the
nitrate, n.itrite, hydrated oxide, oxalate, acetylaceto-
nate or the acetoacetate are suitable. However, compounds
such as the sulfate and the halides can also be used if
care is talcen that the sulfate radical is removed, for
example by precipitating with barium acetate, or ~he
halogen is removed, for example by precipitating ~ith
,
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2 ~
-- 6 --
silver nitra~e, before Lmpregnation so that the sulfate
or halogen anion does not get on~o the support. Owing to
its solubility and its availabili~y, palladium acetate i~
the particularly preferred palladium compound.
In general, ~he content of palladium in the catalyst is
1.0 to 3% by weight, preferably 1.5 to 2.5% by weight, in
particular 2 to 2.5% by weight, based on ~he total weight
of the supported catalyst.
In addition to palladium and/or its compounds, gold
and~or its compounds can additionally also be present. A
particularly suitable ~old compound is barium aceto-
aurate. In general, gold or one of its compounds, if it
is employed, is added in an amount of 0.2 to O.7~ by
weight, relative to the total weight of the supported
catalyst, only the gold componPnt being calcula~ed in the
case of a gold compound.
The catalyst contains alkali metal compounds and, if
appropriate, additionally cadmium compounds as activa-
tors. Suitable compounds are, for example, alkali metal
carboxylate~ æuch as, for example, potassium acetate,
sodium acetate, lithium acet~te and fiodium propionate.
Suitable alkali metal compounds are al~o those which
change into the carbogylates under the reaction condi-
tionsO such asl for example, hydroxides, oxides and
carbonates. Suitable compounds of cadmium are those which
contain no halogen or sulfur, for example the carboxylate
Ipreferred), oxide~ hydroxide, carbonate, citrate,
tartrate/ nitrate, acetylacetonate~ benzoylacetonate and
acetoacekate. Cadmium acetate i5 particularly ~uitable.
Mixture~ of variou~ activator~ can also bo employed. Each
individual activator i5 in general added in an amount of
0.5 - 4% by weight, only the metal component of the
actlvator being calculated, in particular relative to the
total w~ight of the supported cataly~t.
.. .
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31~2~
-- 7 --
The following catalysts are preferred:
palladium/cadmium/alkali metal element and palladium~
gold/alkali metal element, it being possible for pal-
ladium or gold to be pre~ent as metals or as compounds in
the finished ca~alys~ and potassium being preferred as
the alkali metal element ~in the form of a carboxylate3.
The ratio K:Pd or K (Pd+Au) is in this casa preferably
0.7.1 to 2~ he ratic Cd:Pd or Cd:(Pdl~3 is preferably
0.6:1 to 2:1, in par~icular 0.6:1 to 0~9 1o In this case,
Pd, Au, Cd and K are always calculated as elements, i.e.,
for example, only the me~al components of Pd acetate,
Cd acetate and K acetate on ~he support are compared with
one another.
The catalysts palladium acetate/cadmium acetate/potassium
ace~ate and palladium ace~ate/barium acetoaurate/potas-
sium ace~ate are particularly preferred.
The impregnation of the catalyst support with the
solution of the active components i~ preferably carried
out in such a way that the suppor~ material is covered
with the solution and the excess solution iB then poured
off or filtered off. With regard to solu$ion losses, it
is advantageous to employ only the solution corresponding
to the integral pore vo.1ume of the catalyst and to mix
carefully ~o that the particles of the support material
are uniformly wetted. ~his thorough mixing can be
achieved, for e$ample, by stirring. It i8 e~pedient to
carry out the impregnation process and the thorough
mixing at the same time, for example in 8 ro~ating drum
or a tumble dryer, it being possible for the drying to
follow immediately. It i8 furthermors e~epedient to
measure the ~mount and the composikion of the ~olution
used f~r impregnating the catalyst ~upport such that it
corresponds to the pore volume Qf the support material
and that the desired amount of acti~e substances is
applied by impregnating only once.
2~3~
-- 8 --
The catalyst support impregnated with the solution of the
active substances i5 preferably dried under reduced
pressure. The temperature during the drying should be
below 120C, preferably b~low 90C. It is furthermore in
general recommended to carry out the dryins in a stre~m
of inert gas, for e~ample in a stream of nitrogen or
carbon dioxide. The residual solvent con~ent ~f~er drying
should preferably be less than 8% by weight, in parti-
cular less than 6% by weight.
If reduction of the palladium compounds (and if desired
of the gold compounds~ is carried out, which may some-
times ~e useful~ this can be carried out in vacuo, at
normal pressure or at elevated pressure up to 10 bar. In
this case it is recommended to dilute the reductant all
the more strongly with an inert gas, the higher the pres-
sure. The reduction temperature is b~tween 40 and 260C,
preferably between 70 and 200C. In general, it i8
expedient to use an inert gas/reductant mixture which
contains O.Dl to 50 vol.-%, preferably 0.5 to 20 vol.-~
reductant, for the reduction. Ni~rogen, carbon dio~ide or
a rare gas, for example, can be used as the inert gas.
Suitable reductants are, for example, hydrogen~ methanol,
formaldehyde, ethylene, propylene, ifiobutylene, bu~ylene
and other olefins. The amount o~ the reductant depends on
the amount of palladium and, if appropriate, of gold emp-
loyed; the reduction equivalent should be at lea~k 1 to
105 tLmes the oxidation equivalent/ but larger amounts of
reductant are not harm~ul. For example, at least 1 mo3. of
hydrogen should be u~ed rPlative to 1 mol of palladium.
The reduction can be carried out in the same unit follow-
ing the drying.
The vinyl acetate i8 in general prepared by passing
acetic acid, ethylene and oxygen or o~ygen-containing
gases at temperatures of 100 to 220C, preferably 120 to
200C, and at pressures of 1 to 25 bar, preferably 1 to
20 bar, over the finished catalyst, it being possible to
circulate unreacted components. The oxygen concentration
,
~ ~ 3 ~
g
is expediently kept below 10 vol.-% (relative to the
acetic acid-free gas mixture). Undex certain circ~m-
stances, however, dilution with inPrt gases such as
nitrogen or carbon dioxide is also advantageous. CO2 is
particularly suitable for dilution in circula~ion proces-
ses, since it is formed in Rmall amounts during the
reaction.
The following examples are intended to illustrate the
invention.
Compari~on ~ample 1
tSpherical support particles of conventional silica gel)
. .
200 g of a binder-free silicic acid support which con-
sisted of annealed (800C) silica gel spheres of 5 - 8 mm
diameter were employed. The ~commercial) support formed
from these spherical particles had a BET ~urfac0 area of
169 m2/g and a pore volume of 0.48 ml/g, which was com-
posed to 8% of pore~ having 70 - 100 A diameter and to
29% of pores having 200 ~ 3000 ~ diameter. The support
was Lmpregnated wi~h a solution (corxesponding to this
pore volume) of 11.5 g of Pd acetate, 10.0 g of Cd
acetate and 10.8 g of K acetate in 66 ml of glacial
acetic acid and dried at 60C under nitrogen at a pres-
sure of 200 mbar to a residual solvent content of 2~ by
weight. This ga~e a doping of 2.3~ by weight of Pd, 1.8%
by weight of Cd and 2.0% by weight of K ~Cd:Pd = 0.78:1,
K:Pd = 0.87:1).
50 ml of the finished catalyst were packed into a reac-
tion tu~e of 8 mm in~ernal diameter and of a length of
1.5 m. The gas to be reacted was then pass~d over the
catalyst at a pressure of 8 bar (reactor .inlet~ and a
catalyst temperature of 150C. This ~as consisted at the
reactor inlet of 27 vol.-% of ethylene, 55 vol.-% of N2;
12 vol.-% of acetic acid and 6 vol.-~ Of 2- The results
can ~e seen from the table.
`` 2~3~3
-- 10 ~
ComparisQn ~xa~ple ~
(Spherical support particles of conventional SiO2)
200 g of a silicic acid support were employed which had
been compre~ed without binder from b~ntonite which had
been calcined and then washed with ~Cl (96~ by weight SiO2
cont4nt after this wash) to give spheres of S 6 mm
diameter. The suppoxt made of these ~pherical particles
had a BET surace area of 121 m2/g and a pore volume of
0.66 mltg, which was composed to 21~ vf por~s having
10 70 - loo A diametex and to 42~ o:~ pores having
200 - 3000 ~ diameter. The support particles were i~preg-
nated as in Comparison Example 1 (except tha~ 114 ml of
glacial acetic acid were used ins~ead of 66 ml) and dried
so that ~he same doping was present as in that c~se. The
catalyst was then tested as in Comparison ~xample l. The
results can be seen from the table.
Comparison ~ample 3
A support was irst prepared from SiO2 microspheres having
a surface area of 200 mZ/g and also microc~ystalline
cellulose as a filler, graphi~e as a lubricant and kaolin
as a binder. The finished support had a pore volume of
0.80 ml/g, which was composed to 62% of pores having
70 ~ 100 A diameter and to 9% of pores ha~ing
200 - 3000 A diameter. The support par~icles had the
shape of cylinders having curved end surfaces (6 mm
diameter and 6 mm height; the ~hape i~ simil2r to the
shape of the known pharmaceutical capsules). The ~urface
area of the aupport particleæ was 185 m2/g.
The support particles (200 g) were impregnated as in
Comparison Example 1 (except that 141 ml of glacial
acetic acid were used instead of 6~ ml) and dried so that
the same doping was present as in that case. The catalyst
was then tested as in Comparison Example 1. The results
can be ~een from the table.
, :
,: ,
~ ~3~9
Compari60n ~ ple 4
A support was irst prepared from SiO2-Al2O3 micxospheres
~97% by weight of SiO2, 3% by weight of Al2O3) having a
surface area of 170 m2/g and suyar as a filler, graphite
S as a lubricant and kaolin as a binder. The finished
support had a pore volume of 0.75 mltg, which was com-
posed to 58% of pores having 70 - 100 ~ diameter and to
12% of pores having 200 - 3000 A diameter. The support
particles had the same form and size as in Compari60n
Example 3, but they now had a surface area of 132 m2~g.
The support particles (200 g) were impregnated a~ in
Comparison Example 1 (except ~hat 131 ml of glacial
acetic acid were used instead of 66 mlj and dried so that
the same doping was present a~ in that case. The catalyst
was then tested as in Comparison Example 1. The results
can be seen from the table.
~a~ple 1
The support was prepared as in Compaxison Exa~ple 3,
except that about 10% by weigh~ of Mg stearate was used
as a hinder; ~he finish0d support contained 0.4% by
weight of Mg. It had a surface area of 186 mZ/g and a pore
volume of 0.8 ml/g, 78% of the pore vol~me being formed
of pores having radii of 70 - 100 A and 16% o~ the pore
volume of pores having radii of 200 - 3000 A. The support
particles had the ~ame form and size as in Compari.son
Example 3 and 4.
The support particles (200 g) were Lmpregnated as in
Compariqon Example 1 (except that because of the higher
pore volume 141 ml of glacial acetic acid were usad
in~tead of 66 ml) and dried 80 that the same doping wa~
pre~ent as in that case. The catalyst was then te6ted as
in Comparison F.xample 1. ~he re6ult~ can be seen from the
table.
,
. ~ :
- 12 - ~ ~ 3 ~
~Emple 2
The support was prepared as in Example 1~ except that 10%
- by weight of Al stearate were now employed instead of Mg
stearate; the finished suppor~ contained 0.3% by w~ight
of ~l. It had a surface area of 164 m2/g and a pore volume
of Q.91 ml/g, 76% of ~he pore volume being formed of
pores having radii of 70 ~ 100 A and 18% of the pore
volume of pores having radii of 200 - 3000 A. The support
particles had the same shape and size as in Example 1 and
Comparison ~xamples 3 and 4.
The support particles ~200 g) were impregnated as in
Comparison Example 1 ~except that because of the higher
pore volume 160 ml of glaci~l acetic acid were u~ed
instead of 66 ml) and dri~d 80 ~hat the same doping was
present as in that case. The catalyst was then tested as
in Comparison Exampl~ he results can be seen from the
table.
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-- 13 --
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