CA2031429A1

CA2031429A1 - Process for the preparation of vinyl acetate

Info

Publication number: CA2031429A1
Application number: CA002031429A
Authority: CA
Inventors: Friedrich Wunder; Peter Wirtz; Gunter Roscher; Klaus Eichler
Original assignee: Hoechst AG
Current assignee: Celanese GmbH
Priority date: 1989-12-05
Filing date: 1990-12-04
Publication date: 1991-06-06
Also published as: MX173115B; EP0431478A2; ES2060905T3; KR0169111B1; AU629072B2; EP0431478B1; KR910011745A; DE59007054D1; EP0431478A3; AU6771890A; JPH04108759A; BR9006142A; DE3940125A1; JP2854143B2

Abstract

Abstract of the disclosure Process for the preparation of vinyl acetate The invention relates to a process for the preparation of vinyl acetate in the gas phase 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 and/or gold compounds and which contains as activators alkali metal compounds and,if desired,addition-ally cadmium compounds on a support which is composed 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 particles have a particle size of 4 to 9 mm, 5 to 20% of the pore volume of the support being formed of pores having radii of 200 to 3000 .ANG. and 50 to 90% of the pore volume being formed of pores having radii of 70 to 100 .ANG.. The support particles are compressed with the aid of an Li, Mg, Al, Zn or Mn salt of a C2-C20 carboxylic acid or a mixture of such salts as binder.

Description

2~3~2~
,~ , 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 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).

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~

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 , .
, 2 ~

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.

.. .
~ .

31~2~

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~

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.

~3;~2~

_I
o ~r o~
O~
~ I~ O
,1 ~ ~
~W
~ ~ ~ C~ .
o ~ .
X ~ W
a~ ~u IQ ~ a~

~D CC O ,~
~ ~ :

h ,~ ~ ~D o ,~
U ~ ~ O

O N
.~, a) ~1 ,~ ~ n o P~
U ~ ~ ~ .

O _i_ q~
~a ` ~
o ~r o ~ .~, -~1 O ~C '~r N 4) OÇ~

~ ~I) -~1 ,, U ~ O

.C
~1 u ~q a) O~ 1 0 a1 ~
I ~ ~ plU~ S;l ~d : . , ~ , - . . :

Claims

1. A process for the preparation of vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases on a catalyst which contains palladium and/or its compounds and, if desired, addition-ally gold and/or gold compounds and which contains as activators alkali metal compounds and,if desired,additionally cadmium compounds on a support which is composed 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 particles have a particle size of 4 to 9 mm, 5 to 20% of the pore volume of the support being formed of pores having radii of 200 to 3000 .ANG. and 50 to 90% of the pore volume being formed of pores having radii of 70 to 100 .ANG., which comprises compressing the support particles with the aid of an Li, Mg, Al, Zn or Mn salt of a C2-C20 carboxylic acid or a mixture of such salts as binder.

2. The process as claimed in claim 1, wherein carboxylates of Al or Mg are employed as binders.

3. The process as claimed in claim 1, wherein Mg carboxylates are employed as binders.