CA2244909A1

CA2244909A1 - Colloidal palladium-gold alloy catalyst for vinyl acetate production

Info

Publication number: CA2244909A1
Application number: CA002244909A
Authority: CA
Inventors: Robin S. Tanke
Original assignee: Individual
Current assignee: Celanese International Corp
Priority date: 1996-03-14
Filing date: 1997-02-10
Publication date: 1997-09-18
Also published as: EP0888183A1; KR19990087789A; JP2000506438A; BR9708288A; CZ292398A3; WO1997033690A1

Abstract

This invention provides a microemulsion process for the preparation of a supported palladium-gold catalyst for the production of vinyl acetate from ethylene, acetic acid and oxygen. A preferred catalyst composition has a content of colloidal palladium-gold alloy uniformly distributed on an .alpha.-alumina support. An invention catalyst exhibits a sustained level of selectivity for vinyl acetate production over an extended processing period.

Description

W O 97133690 PCTrUS97/02132 C O LLOIDAiL PA~LA~DIU~-G O LD A~LL O Y CATA~LYST
li'OR VINYL ACETATE PRODUCTION

5 Field of Invention The present invention relates generally to catalyst ~ic~lion and specifically toplG~dlion of a ~u~olled catalyst for use in the production of vinyl acetate (VA).

Background of the Invention A well-known commercial process for the pro~ etion of vinyl acetate is by the gas phase reaction of ethylene, acetic acid and oxygen in the plcse.lce of a supported catalyst which co~ s palladium.
A ~lefc,l~d type of vinyl acetate catalyst is one having a content of p~ m metal and gold metal distributed on the surface of a support substrate such as silica or alumina.
Numerous methods are known in the art for the production of a ~u~ol led catalyst for use in the production of VA. A general route employed by the art to prepare a supported catalyst for VA production involves iul~le~ a support (e.g., alumina or silica) with metal solution, fixing the metals onto the support, and re~lcing the metal. It has been found that when this general technique is employed for palladium and gold, it frequently yields a catalyst in which palladium and gold are partially or wholly segregated.
Prior art rererenccs which describe ~u~po~l~d p~ illm-gold catalysts for vinyl acetate production include United States Patent Numbers 3,761,513; 3,775,342; 3,822,308, 3,939,199;
4,048,096; 4,087,622; 4,133,962; 4,902,832; 5,194,417 5,314,858; and references cited therein;
incorporated by .~fe~ ce.
The activity and selectivity of a supported palladium-gold catalyst is affected by the physiochemical form of the palladium and gold metal content on the support surface. It is difficult to achieve a uniform microstructure of metal particles by some of the route(s) ~;ulle~Lly known in the art. The performance of a vinyl acetate m~nllf~rt-lring process is influenced by the ullifollllity of the palladium-gold catalyst microstructure.
In view of the above issues, the art is always searching for new techniques to develop a ~u~o.lt;d catalyst with improved microstructure, metal distribution, and selectivity for vinyl acetate pro-lucti~ n W 097/33690 PCT~US97tO2132 Summary of the Invention It is an object ofthis invention to provide a ~u~o-lc;d palladium-gold catalyst composition vvith improved selectivity in vinyl acetate production from ethylene, acetic acid and oxygen.
It is another object of this invention to provide a ~u~ull~d vinyl acetate catalyst which has a ullirollll microstructure of p~ m and gold metal on a support :iub ;Lla~
It is a further object of this invention to provide a process for producing a vinyl acetate catalyst which yields a ~ i r,-l ~ -- distribution of a colloidal p~ m-gold alloy on a support s~lrfz~r.e l 0 Other objects and advantages of the present invention shall become a~clll from the acconll~dl.ying description and examples.
The present invention relates generally to ~lG~Iion of a supported catalyst for use in the production of vinyl acetate. It relates speçific~lly to a process for the ~ n I iOI of a supported catalyst, and to the catalyst ~ ~. d from said process, for production of vinyl acetate from ethylene, acetic acid, and oxygen, which process c-~mpri~es 1) forming an aqueous solution of water-soluble p~ clitlm and gold coll~oui~ds;

2) tli~per~ing the aqueous solution in a hydlù~hobic solvent with an t;fr~.;live amount of s~ rt~nt to form a microemulsion miXIUl~i, 3) treating the micro~m~ n mixture with a re~ ring agent; and, 4~ impregn~ting a support with the mixture of step (3) to forrn a supported metal catalyst.
Optionally, the supported catalyst of step (4) may be washed and dried. This inventive ~lep~dlion differs from the art, in part, to its sequence of ~ inn Unlike the art, here, the metals are reduced before the s11bstr~te is hll~ e-1 This sequence differential has been found to result in a supported catalyst that has improved efficienry for the production of VA.
Description of the Invention One or more objects of the present invention are accol-l~ hed by a process for the pl~ 1 ior of a catalyst for pro~l11çtion of vinyl acetate from ethylene, acetic acid and oxygen, which process comprises 3û 1 ) forming an aqueous solution of water-soluble palladium and gold compounds, 2) dispersing the aqueous solution in a hydrophobic solvent with an effective amount of snrf~rt~nt to form a microPnntll~ic n ~
-W O 97/33690 PCT~US97/~2132 3) treating the microemulsion l~ lulG with a red--cing agent; and, 4) impre~n~ting a su~olL with the llli~Lule of step (3) to form a supported metal catalyst.
Optionally, the ~ olled catalyst of step (4) may be washed and dried.
The term "hydrophobic" as employed herein refers to an organic hydrocarbon soivent 5 which has a water-solubility of less than about one gram per one hundred grams of water at 100 ~C.
The term 'Imicro~o~nul~iQn'l as employed herein refers to a water-in-oil type of llliXLul~ in which the dis~ ed aqueous phase preferably has an average droplet size less than about five microns.
The term "alloy" as employed herein refers to a molecular llliX~Ul~i of at least two different metals. Discussion herein refers to the metals p~ lm and gold, and the term "alloy'~
is int~nfled to mean molecular ~ ul~s which are ~"I,~ lly free of segregated palladium and gold.
The terms "support", "support m~ m", and "sukstr~te" are used herein hll~ hallgeably.
The illV~ iVe process will be described relative to each step. The description illustrates a pl ~lled embo~1im~nt of the present invention. Generally it is dil~,Led to discussion of palladium and gold on ~lllmin~ or silica support. It is to be Imrlerstood by those of skill in the art that this technique is suitable for use with a variety of metal alloys and support sub~Ll~tes. The description herein is not int~n~lerl to be limited to p~ lm and gold alloy on ~Illmin~ or silica substrates. Other support sl~bstr~tes may be employed and will be ~iccllc~e~l in further detail below. Unless in~ t~rl otherwise, the order of addition of reagents within each step is not crucial to the invention.
Step (1): l;n the inventive process, the first step involves formirlg an aqueous solution of water-soluble palladiurn and gold compounds. Generally the route employed for step (1) involved dissolving the metal salts in water. It is l,le~ll~d to use water which is deionized or distilled to avoid ~ iti~ n~l salt hll~uliLies. The metal salts, sodium p~ m chloride (Na2PdCl4) and chloroauric acid (HAuC14-H20), were placed in a round bottom flask with a stir bar and water was added thereto. Stirring was accomplished at room ~IllpeldLul~: under atmospheric conditions. Stirring may be done under an inert atmosphere if desired.
Water is added in as m;";~ an amount as possible. The ~lu~l~ily of water is minimi7f-cl to facilitate the formation of a water-in-oil dispersion, in which the water droplets are in a micronized form, i.e., the droplets have an average size of about or less than 5 microns in W O 97/33690 PCT~US97/02132 diS mr~ter. It is ~,.,fc~,ed to add a s7-ffici--nt amount of water to the metal salts to form a saturated salt solution. A range consi~l~ of about l :l, (l g water: l g metal salt) to saturation of the metal salt in water. Preferably, the range is about l :3.
Step ~2~: Step (2) relates to dispersing the aqueous solution of step (l ) in a hydrophobic 5 solvent with an effective amount of s~rfS7r-tSlnt to form a microeml11eion mixture.
In t_e i~v~liv-e process, b.,Lw~ about 0.5-5 mi,71ilitr-re of water are employed per 30 millilit~r.~ of micro--mllleio l ~,ib~Lu~e in step (2) of the process. The micronized r1iepereion of water-in-oil solution of ps 11s7-7il1m and gold compounds erre~;Livt;ly provides a colloidal dispersion of ps 11slr3i11m-gold alloy in the step (3) metal recll7rtion step of the invention process.
l 0 Hydrophobic organic solvent~e suitable for use in step (2) include but are not limited to p~n7ts7ne, hexane, cyclohe~ 7ne~ heptane, octane, iso-octane, m phths7 ns phthr ne, benzene, chlorobenzene~ dichloromethS~nr, and the like. Pentane is the ~crc.-cd solvent.
The preferred amount of hydrophobic solvent is dependent on the pore volume of the support. Preferably a sufficient or effective amount of solvent is employed to saLu,dLe the pore 15 volurne of the ~ul~o, 1. It is desirable to avoid an excess of solvent. ~outine ~ .entSltion to test for abso,~liviLy of the support relative to ~e solvent will ~ e the ~lw~~ y of solvent to employ.
The ~--- r~ . I ingredient can be selecte~l from a wide range of non-ionic, anionic and cationic products which are commercially available. T11~ ive of suitable e1~rf-Slrtslntc are 20 ce~ylL,;nlethy1Slmmoni~Tn bromide; sodiurn lauryl sulfate; sodium dodecylb- n7--n- s~11fonate;
slmmoni~1m 1ignc-s1-1fonate; co n~nes tion products of ethylene oxide with fatty alcohols, arnines or alkylphenols; partial esters of fatty acids and hexitol anhydrides; and the like. A non-ionic surfactant is p,cfe~,cd for purposes of the present invention process. Preferred s11rfS~ctS nt~
include ~e~ ylene glycoldodecyl ether, triocty~phr7ephinr oxide, and Genepol~
25 (co...".e.eially available product from Hoechst Celanese Corporation), Wit~l the most ~,c~,ed sl-7~7ct~7nt being Genepol(~).
The s--rfS7ct~7nt ingredient can be employed in a ~lual~l;Ly between about 2-20 grams per 30 milliliter.e of micrc!pml7leion ~ Lwe. It was observed that too small an amount of s~1rf~7ct~7nt did not permit form~7tic-n of a microemulsion. Although no upper limit for an amount of e~ c tS7nt to 30 employ was ~letr-ctr-rl an excess of surfactant is wasteful. It is desirable to utilize a sufficient or effective amount of ~- ~, rS~ L to form a microemulsion. The amount of surf~7ct~nt will vary based on the amount of water employed in step (l) and the type of s11rf~- t~nt being used.

W O 97/33690 PCTrUS97/02132 s Generally, routine laboratory G~J' ~ ;.,.~..I;~lion can deterrnine a ~ti~f~rtory-minimllm amount of sllrf~rt~nt to employ.
The order of ~d~lition for step 2 genPr~lly involved adding solvent to ,~ rn.~ followed by mixing (mixing can be accomplished by any conventional means). Generally, thesolvent/sllrf~ct~nt lllixlw~; was mixed until a homogeneous, pourable, solution was obtained.
This pourable lllixlule was then added to the metal salt solution of step (1) and mixing was co~ ed until a micro~m~ ic n was formed. Employing p~ llm, and gold metal salts, and pentane as solvent, a color change was observed at step (2). The color will vary depending on the metal and solvent employed.
Step ~3~: Step (3) defines a particularly inventive aspect of the present invention process. In step (3) the microemulsion lllixLul~ is treated with an excess quantity of reducing agent, such as lly~d;~hle, ethylene gas, or ft)nn~lrlPhyde, to reduce the p~ lium and gold to the m~t~llic state and form a sl~pen~Pd colloidal alloy phase of p~ rlinm and gold metal in the microemnl~il n llliXLUlG.
In accordallce with the inventive process, the reduction step is con~ cted prior to the metal ~ Lure being i.l,~.e~ d on the support. If the reduction step is contl~7cted after the microemulsion lllixlule is hll~lG~ ed on the support, the 1~ catalyst has been found to have the palladium and gold metal se~ ed and be less selective for production of vinyl acetate from ethylene, acetic acid and oxygen.
It is highly bPnefici~l, and ,ecol~l.lçn~e-l to complete the reduction reaction to as near as possible. Generally, when employing lly~i~le, or a redllcing agent which causes the evolution of gas, the reaction can be m- nitc~red based on the evolution of gas, in which case, it is best to continue the reaction until gas ceases to evolve from the reaction.
In the ~Gr~ ,d embodiment, hydld~illc was added to the micr~t?m~ inn nlixlulc in a range of about 1 to 2 mls per 3 g of metal salts employed. The reslllt~nt reaction was exothPnnic The mixlulG was allowed to cool before prccee-1ing to step (4).
Step (4): Step (4) involves illl~ an inorganic support with the reduced metals-lllixLule of step (3) to form a supported metal catalyst. Illlplc2;.l~ )n may be con~ ct~P~
following convPntic-n~l procedures. The support ,ul)~Ll~ for the vinyl acetate catalyst can be selected from organic or inorganic support substrates. Due to their stability for the production of VA, inorganic ~u~olLs are ~lGrGll~ L Suitable inorganic ,u~po~L., include but are not limited to silica, ~1nmin~, silica/alumina lllixlule, zirconium dioxide, LiL~liulll dioxide, calcium dioxide, -W O 97/33690 PCTnUS97/02132 and the like, as well as other types of solid carriers widely employed for the ., li1l ,. . r;~ , . . c of vinyl acetate catalysts. Silica and z~ minzl are the ~.~fe~l~ed solid carriers to employ for the production of VA, with ~IITm;n~ being the most ~lerell~ d, and ~-z~lllminzl being most most ~ r~ d.
The vinyl acetate catalyst support me~ Tn' can be in the forrn of spheres, tablets, Raschig rings, and the like.
Generally for the present invention, the support .. ~.~;.. was used as received with no dLol ~ cil1 ~ ~ ~Pnt The support was added to the cooled llli~lule of step (3) under atmospheric conditions and mixed. Mixing occurred mzTmlz tly, however any conventional suitable means is acceptable.
The supported catalyst is hll~lc~ e~l with an a~liv~Lol ingredient such as an alkali metal ~lkz no?te (e.g., pot~ acetate, pUl~SSiulll borate), to provide a catalyst product with enhzlnr~ed selectivity for vinyl acetate production from ethylene, acetic acid and oxygen.
Optio~zll Step (5): Although not a i.~cf ssz~ step, the impre~nzlte~l catalyst support formed during step (4) was l~e~ledly washed with a co-solvent for water and solvent and sTlT~ctzlnt such as alcohol (ethanol? followed by a water wash. This washing removed any residual hydrophobic solvent, ~--- r~ , and salts from the supported catalyst. If desired, the wash step may be olnitte~T since catalyst residues would burn off in the reactor during use of the supported catalyst. The ~ul~oll~d catalyst was tnen dried in a standard convection oven or fluid bed drier. Drying by co~ ~lLional means is accc~l~ble. Drying ~ cLlUl~S employed ranged from about 150 ~C to about 300 ~C under a nitrogen atmosphere. If this step is employed, KOAc impregnation follows.

Discussion of Exarnples As demo,~L-aled in the Examples, ~lTTminzl is a pl cLl~d type of support . . .e.l;~
Although a ~u~,uullcd catalyst was ~ d utili7ing the present technique with silica, it was observed that greater metal retention to substrate was obtained when employing zllnminzl In Catalyst F.~z mples 1-3, the pz~ m-gold ~ olled catalysts have a silica ~ub~L~dl~.
It was observed that these supported catalysts did not possess as Ulli~llll, homogeneous physical appearance, as the catalyst ~u~olled on an ~ minzl 7UbSLldle. It was further observed that the catalyst examples 1-3, with a silica substrate, had insufficient metal loading on the surface to conduct ~rollll~lce testing. This is in contrast to Example 9, which exhibited a high retention of colloidal palladium-gold alloy on the ~Inmin~ sulr~ces of the substrate, and exhibited W O 97/33690 PCT~US97/02132 excellent selectivity for the production of vinyl acetate from ethylene, acetic acid and oxygen.

Su~ olled Catalyst Composition ~n addition to providing a process to prepare a supported catalyst, this invention provides 5 a catalyst composition for the ~ ~alion of vinyl acetate from ethylene, acetic acid and oxygen, which compri.~es colloidal p~ m-gold alloy on a support rne~ m preferably on an all~min~
support. "Colloidal" herein refers to a unirollll particle composition on the support with respect to palladium and gold; "Unifor n" as compound to ~u~l!ol~ed Pd/Au catalyst produced by prior art support techniques.
The colloidal palladium-gold alloy on the ~Inmin~ support typically has an average particle size between about 1-20 n~nom~ter~.
An invention vinyl acetate catalyst on alumina can have a p~ tlillm metal content between about 0.1-2.5 weight percent, and a gold metal content bt;lv~ about 0.05-0.6 weight percent based on the catalyst weight.
The catalyst p~ lium-gold weight ratio can vary bclw~en about 1-10:1.
A present invention catalyst colllL~osilion has particular advantage when utilized in the mz~mlf~ctllre of vinyl acetate monomer from ethylene, acetic acid and oxygen. A typical vinyl acetate process involves the reaction of ethylene, acetic acid and oxygen or air in the gas phase at about 100 -250 ~C and normal or elevated ~ W~ in the presence of a ~ulled catalyst which 20 colllaills palladiurn. Various vinyl acetate proces~in~ emborliment~ are ~esçribe(l in the references recited in the Background section The following examples are fur~er illustrative of the present invention. The colll~onelll~
and specific ingredients are l,.esellL~d as being typical, and various modifications can be derived in view of the foregoing disclosure within the scope of the invention.
FXAMP~.F~
General Procedure for VA Production When employing a Vinyl Acetate Stirred Tank Reactor (VAST) Unit in the F~mplç~ the following general procedure was employed. The VAST is a Berty reactor, or a continuous 30 stirred tank reactor of the rCcirc~ ting type that is run at con~t~nt oxygen cull~ ion (about 45%). The supported catalyst is loaded in a basket in the reactor, a measured amount of acetic acid, ethylene, and oxygen is added in a nitrogen diluent, and the reactor is brought up to W O 97/33690 PCTrUS97102132 Gl~lul~ by means of a heating m~ntle, The t~ c~dlu~e in the reactor is measured above and below the catalyst. The reaction is ~ k~l after approxim~tely 18 hours at a tt;lll~ c at which 45% oxygen co~ ion is ll~ n;~lrA Products are lllea~ul.,d by gas-phase chromatography. CO2 selectivities tend to be a little higher for the sarne catalyst when tested in S the VAST Unit cwll~c;d to the VAMU since the product vinyl acetate is recirculated in contact with the catalyst during the reaction sequence.
The Vinyl Acetate Micro Unit (VAMU) reaction in the F~c~mples is a plug flow type reaction system operated at co~-~ln--l lelll~ lu~. The VAMU reactor is a 3 ft-long, 16 mm i.d.
st~inlçce steel tube with a 3 mm co~ .l, ;c therrnocouple we}l. The reactor is e~uipped with a heating jacket through which hot water and steam are circ~ te~l Generally, a 30 cc sample of catalyst is diluted with support up to 150 cc and loaded to the reactor. The catalyst/support nli~Lul~ is topped with 30 cc of support. After a sing}e pass-through of the oxygen, ethylene and acetic acid in a nitrogen diluent at col~LallL te~l e~ , the products are analyzed by gas-phase chromatography.
Fx~mple 1 (SiO2 Support Example) This F~rnrle illu~Lldles the ~l ~dlion of a Pd-Au metal on a silica support type of catalyst by a microeml~leion method.
Na2PdCl4 (2.26 g, 7.8 mmol) and HAuCI4-3H2O (827 mg, 2.1 mmol) were dissolved in}.6 mL of deioni7ed water under nitrogen in a reaction flask. A solution of Genapol~) 26-L-60 (12.5 g, Hoechst CPI~n~ee~ in pentane ~35 mL) was p~ ,d. The two solutions were mixed to form a rnicro~m-~leion of the a~ueous ph~e in the organ~c solvent phase. Hy&~.e monohydrate (2 mL) re(l~cing agent was added under nitrogen, and the solution turned black and gas evolution was evident.
The reduced solution was applied to Aerosil 200 with MgO binder (Degussa). The forrned ~u~,~u~led catalyst was shaken for l0 min~ltee, and purged under nitrogen to remove the .I~.c solvent. The supported catalyst was washed with ethanol, and then washed with tl~rnin~r~li7f?~ water for 16 hours. The supported catalyst was dried in a flni~li7ecl bed drier for one hour at 100 ~C, and then dried at 150 ~C for 20 hours under nitrogen.
The supported catalyst was impregn~te~l with potassiurn acetate activator (6 g in 50 mL
of water), and dried in a fluidized bed drier at 100 ~C for one hour.

W O 97/33690 P~llu~7lo2l32 . g F.Y~mrle 2 (SiO2 Support Example) - ~
This F.Y~mple illu~LldL~s the ~dlion of a Pd-Au metal on a silica ~u~oll type ofcatalyst by a microemulsion m.~.thocl The ~u~olhd catalyst of this example was y-~ed in accol~ ce with example 1 employing the following reagents and qll~ntities ., S Na2PdCl4 2.26 g, 7.8 mmol HAUcl4-3H2o 827 mg, 2.1 mmol hyd~ e monohydrate 2 mL
Aerosil 300 with Kaolin binder (Degussa) 64.1 g pol~ .. acetate 6.0 g Example 3 (SiO2 Support F.x~mple) This Example illu~LldLes the ~lc~dlion of a Pd-Au metal on a silica support type of catalyst by a microemulsion method. The ~u~Ol L~d catalyst of this example was ~ d in 15 acc-aldallce with example 1 employing the following reagents and q~ ntiti~s.
Na2PdCl4 2.26 g, 7.8 mmol HAUcl4-3H2o 827 mg, 2.1 mmol hydrazine monohydrate 2 mL
Aerosil 300 with Al2O3 binder (Degussa) 56.6 g potassium acetate 5.0 g Example 4 This F.~mple illu~Llales the ~ç~dlion of a present invention type of Pd-Au metal alloy 25 on an ~lumin~ support catalyst by a microemulsion m~thn~ The ~u~polL~d catalyst of this example was ~ ed in acc-,r~ ce with to~mple 1 employing the following leagelll~ and quantities.
Na2PdCl4 2.26, 7.8 mmol HAUcl4-3H2o 827 mg, 2.1 mmol hydrazine monohydrate 2 mL
z~lumin~ Raschig rings 88.0 g puL~siulll acetate 4.0 g W O 97/33690 PCTnUS97/02132 X-ray absorption spectroscopy in~ ted a distribution of a colloidal Pd-Au alloy having an average particle size in the range of 1-20 n~nr~mete~rs~
The selectivity of the catalyst of example 4 was tested in a stirred tank process (VAST) for the ~ aldlion of vinyl acetate from ethylene, acetic acid and oxygen. The co~ udlive data 5 are s~mm~ri7~ in Tables I~

Example 5 (SiOt Support Example) This F.x~mrle ill~ s the ~L~JdLdLion of a Pd-Au metal on a silica support type of catalyst by a microPm~ eion mtothotl The ~u~o~Led catalyst of this example was yl~a~td in 10 accold~.ce with example 1 employing the following reagents and q l~nti~
NatPdCI4 2.26 g, 7.8 mmol HAuC14~3 H2O 827 mg, 2.1 mmol hydld;cille hydrate 2 mL
S~id Chemie T~358-E-1 59.3 g pulas~iulll acetate 5.0 g The selectivity of this catalyst was tested in a micro unit (VAMU) for the ~r,~dLion of vinyl acetate. The co~ v~uaLi.,e data are ~ ,. ;YPd in Tables II and III.

Fx~mple 6 (SiO2 Support ~Y~mrTe) This Exarnple illu~llales the ~ aLion of a Pd-Au metal on a silica support type of catalyst by a microemulsion method. The SU~V1 ~d catalyst of this example was ~ cd in accol.l~lce with example 1 employing the following reagents and qll~ntiti~s.
NatPdCL 2.26, 7.8 mmol HAuC14~3 HtO 827 mg, 2.1 mmol llydld~ e monohydrate 2 mL
Si~d Chemie T-4358-E-1 59.3 g pOlaSSilllll acetate 5.0 g The selectivity of this catalyst was tested in a micro unit for the yr~ inn of Yinyl acetate. The CO~ A~ V~: data are ~ in Tables I and III.
Example 7 This Example illllctr~t~s the ~.c~d~ion of a present invention type of Pd-Au metal alloy W O 97/33690 PCT~US97/OZ132 on an ~lumin~ support catalyst by a microemulsion method. The ~u~ ed catalyst of this example was ~,~aled in accordance with PY~mrle 1 employing the following reagents and q~l:mtiti ,P~,e .
Na2PdCl4 2.35 g, 8 mmol HAuC14-3 H2O 788 mg, 2 mmol hydrazine monohydrate l.S mL
-Al2O3 tablets (Aesar) lSS.0 g potassium acetate S.0 g The selectivity of this catalyst was tested in a micro unit for the ~ ,~dlion of vinyl 10 acetate. The coll~ualdLive data are ~ rrl in Tables I and IV.

Fx~mple 8 This Example illu~L dles the ~lGp~ )n of a present invention type of Pd-Au metal alloy on an ~lnmin~ support by a microemllleiQn method. The ~u~o1 Led catalyst of this example was 15 ~r~a~ed in accor lance with P~r~mple 1 employing the following reagents and qll~ntitip~s The ~ucedule was repeated to form a double coat of Pd-Au alloy on the ~Inmin~ support.
Na2PdCI4 2.65 g, 9 mmol HAuC43 H2O 394 mg, 1 mmol hydrazine monohydrate l.S mL
-Al2O3 tablets (Aesar) lSS.0 g pot~eeillm acetate (second coat) S.0 g The selectivity of this catalyst was tested in a microunit for the ~ inn of vinyl acetate. The c~ f i ve data are sllmm~ P~l in Tables I and IV.
F.~mI le 9 This Example illu~LLdL~s the p1~dLion of a present invention type of Pd-Au metal alloy on an ~lllmin~ support by a microemulsion method. The supported catalyst ûf this example was ~1.,pa1cd in acco1-l~1ce with example 1 employing the following reagents and q~l~ntities The 30 procedure was repeated to form a double coat of Pd-Au alloy on the alumina support.
Na2PdCl4 2.35 g, 8 mmol HAuCl4-3 ~2~ 788 mg, 2 mmol WO 97/33690 . PCT~US97/02132 hydld~ille monohydrate - 1.5 mL
-Al2O3 tablets (Aesar)155.0 g po~ acetate The selectivity of fhis catalyst was tested in a rnicro unit for the ~le~dlion of vinyl S acetate. The eo~p..~ data are summarized in Tables I and IV.

Example 10 This Fx~mple illusLldl~s the ~,r~>~ ~ ~ l ;on of a Pd-Au metal on an alumina support type of catalyst by a microemulsion mf~thofl, in which the p~ ml metal and the gold metal are applied 10 in separate CO?tin~s The supported catalyst of this exarnple was prepared in accol~ ce with example I employing the following reagents and qll~nfities l~;rst cn~tir~
Na2PdCI4 2.94 g, 10 rnmol hydrazine monohydrate 1.5 mL
lS -Al2O3 tablets (Aesar) 155 g Secon-l coZ3ti~
HAuC14-3 H2O 985 mg, 2.5 mmol hyd~ e monohydrate 1.0 mL
pO~SSi~ acetate 5.0g The selectivity of this catalyst was tested in a microunit for the pl~dlion of vinyl acetate. The co,~ udli~e data are s.. ~ 1 in Tables I and V.

Examples 11-12 These Examples illustrate the ~ ~dLion of present invention Pd-Au metal alloy on25 alumina support type of catalysts by a microemulsion method.
Na2PdCl4 4.41 g, 15 mmol HAuC14-3 H20 1.97 g, 5 rnmol hydl~ille monohydrate 3.0 mL
-Al2O3 tablets (Aesar) 310.0 g potassium acetate 5.0 g The initial ~U~JpOl led catalyst was pl~aled by a procedure similar to the microemulsion method of Example 1, and then the catalyst product was divided into two 155 g portions.

W O 97/33690 PCTrUS97/02132 One portion was dried at 150~~ for 16 hours under nitrogen, and i~ .e~ t~-1 withpok~;~iulll acetate (5 g in water), and dried at 100~C for one hour (Fx~mrle 11).
The second portion was c~lcin~d at 300 ~C for S hours in air, impregn~tPtl with pol~siu acetate (5 g in water), and dried at 100~C for one hour (Example 12).
S The selectivity of these catalysts were tested in a micro unit for the ~l c~ lion of vinyl acetate. The col"~alaliv-e data are s--mm~Tized in Tables I and V.

FY~mples 13-14 These F.Y~mples illTl~t-~t~ the ~ c~dlion of Pd-Au metal on alumina support type of catalysts by an inciri~nt wetness method.
-A1203 Raschig rings were impre~n~ted with a 32 mL aqueous solution c~ g Na2PdCl4 (3.47 g) and NaAuCl4 (3.47 g). NaOH (1.1 g in 120 mL of H2O) was added, and the lulci was allowed to stand for 20 hours.
The reS~lltin~ catalyst precursor was washed with de.~ i7~cl water, and dried. The catalyst then was impreEn~ted again with the same type of Pd-Au solution. The catalyst was dried at 100 ~C for one hour, then i,llplc~ ted with aqueous NaOH (1.1 g in 32 mL of H2O).
After st~n~ling for 15 hours, the catalyst was washed with clL ...i..~ Ialized water for 25 hours, dried at 100 ~C for one hour, and then at 150 ~C for 24 hours under nitrogen. The catalyst was impregn~t-~d with pof~ lm acetate (5 g in 32 mL of H2O), and dried at 100 ~C for one hour (Example 13).
The ~u~ led catalyst of F.Y~mple 14 was ~ d following the above described incipient wetness method, with Pd-Au in a 6: 1 ratio on a-alumina tablets.
The selectivity of the catalyst of Example 13 was tested in a stirred tank process for the ~re~dlion of vinyl acetate. The data are sllmnn~n7~d in Table II.
The selectivity of the catalyst of Example 14 was tested in a micro unit process for the lion of vinyl acetate. The CollllJ~dLivc data are ~ ;d in Table V.

Comm~nt~ regarding Tables Selectivity data is reported as being con~1llcte~1 in either VAMU or VAST unit. The 30 supported catalysts were analyzed by X-ray Fluorescence Spectroscopy (XFS) unless otherwise indicated. Shell Temp. is the telll~ ldLul~ of the hot water around the plug-flow reactor.
Double = means two catalyst coatings were placed on support or substrate.

W O 97/33690 PCTnUS97/02132 Abbreviations in Tables: -STY = space-time-yield ICP = inductively coupled plasma spectroscopy ADJ ~2 Conv= adjusted oxygen COll~c-~ion HE = heavy ends EtOAc = ethyl acetate HOAc = acetic acid TEM = tr~nemi~ion electron mi~l-.scoyy TTL = total AFB = after found bases - TABLE I
Data Of ('~t~lysts Prepared By Microem~ ion Process nF.~C~TPTION A~AT YSIS
Example 1, SiO2 0.23% Pd, 0.10% Au speckled catalyst Aerosil 200/MgO binder 75 ppm C1, 4.9% KOAc insufficient metal loading for analysis B~T SA = 186 m2/g Pore Vol. 0.82 cc/g 4: 1 Pd:Au Example 2, SiO2 0.30% Pd, 0.13% Au, speckled catalyst Aerosil 300/lcaolin binder <50 ppm Cl, 5.4% KOAc insllfficient metal loading for analysis BET SA = 245 m2/g Pore Vol. 0.81 cc/g 4:1 Pd:Au Example 3, SiO2 0.30% Pd, 0.13% Au, speckled catalyst Aerosil Al2O3 binder <50 ppm Cl, 5.3% KOAc insufficient metal loading for analysis BET SA= 238 m2/g Pore Vol. 1.02 cc/g 4:1 Pd:Au F~c~mple 4 0.58% Pd, 0.35%Au(ICP) VAST run a-Al2O3 Raschig rings 46.9 g catalyst BET SA = 0.7 m2/g Temp. 173 C
Pore Vol. 0.45 cc/g CO2 selectivity 12%
3:1 Pd:Au Catalyst 5, SiO2 0.86% Pd, 0.52% Au VAMU run Sud Chemie, T-4358-E-1 <50 ppm Cl, 5.1% KOAc 16.2 g catalyst BET SA = 235 m2g Post reaction analysis: Temp. 179 C
Pore Vol. 0.91 cc/g 0.63% Pd, 0.34% Au ~2 conv. 31.5%
3 :1 Pd:Au 9.1% KOAc CO2 selectivity 10.7%
Example 6, SiO2 0.53% Pd, 0.25% Au VAMU run Sud Chemie, T-4358-E-1 <50 ppm Cl, 7.1% KOAc 16.3 g catalyst BET SA = 235 m2/g Post reaction analysis: Temp. 179 C
Pore Vol. 0.91 cc/g 0.43% Pd, 0.20% Au, ~2 conv. 18.8%
4:1 Pd:Au 8.4% KOAc CO2 selectivity 8.5%
,.
Example 7 0.37% Pd, 0.17% Au (ICP) VAMU run a-Al2O3 tablets 35.5 g catalyst BET SA = 4 m2/g Temp. 155 C; 160 C

W O 97/33690 PCT~US97/02132 TABT F I. continued Pore Vol. 0.25 cc/g O2 conv. 18.7% 21.1%
4: 1 Pd:Au C~2 selective. 7.1 % 7.7%
s Example 8 0.80% Pd, 0.21% Au (ICP) VAMU run ~-Al2O3 tablets 35.5 g catalyst BET SA = 4 m2/g Temp. 145 C, 150 C
Pore Vol. 0.25 cc/g 02 conv. 30.3%, 36.7%
7:1 Pd:Au, Double coat CO2 selectivity 7.1%, 7.7%
Example 9 0.502% Pd, 0.24% Au VAMU run ~-Al2O3 tablets 0.54% K (ICP) 35.1 g catalyst BFT SA = 4 m2fg Temp. 151 C
Pore Vol. 0.25 cc/g O2 conv. 35.6%
4: 1 Pd:Au, Double coat CO2 selectivity 7.7%
F~mple 10 0.47% Pd, 0.25% Au VAMU run ~-Al203 tablets 0.65% K (ICP) 35.9 g catalyst BET SA = 4 m2/g Temp. 155 C
Pore Vol. 0.25 cc/g O2 conv. 21.31 %
Pd coated then Au coated CO2 selectivity 8.39%
Examplell 0.30%Pd,0.18%Au VAMUrun o~-AI203 tablets 0.31% K (ICP) 35.5 g catalyst BET SA = 4 m2/g Temp. 155 C
Pore Vol. 0.25 cc/g ~2 conv. 24%
3.1: 1 Pd:Au dry at 150 ~C CO2 selectivity 7.1 %
Example 12 0.28% Pd, 0.17% Au VAMU run ~-Al2O3 tablets 0.88% K (ICP) 35.5 g catalyst BET SA = 4 m2/g Temp. 155 C
Pore Vol. 0.25 cc/g O2 conv. 23%
3: 1 Pd:Au c~cin~1 300 ~C CO2 selectivity 9.0%

W O 97/33690 PCT~US97/02132 TART.F II
(CO~ ~ali~e Table of Data) V;rlyl Acetate Stirred T~nk Process. With Pd-Au On a-Alumina Support Fx~mple Number 4 8 13 CatalystID 3.1:1AI2O3 7:1 Al2O3 2.2:1 Al2O3 Catalyst Age, Hrs. 18.00 20.000 19.500 Sel. to C~2 (a,b) 11.984 12.285 11.152 Sel. to HE 0.504 0.569 0.614 Sel. to ETOAC 0.068 0.144 0.063 STY g VA/I,/Hr (a,c~ 675.754 544.238 695.656 ADJ ~2 Conv. (d) 45.755 45.224 46.575 Reactor Top Deg. C (e) 172.800 156.300 164.270 Reactor Bot Deg. C (e) 175.500 160.800 167.230 Pl~ u e.PSIG 170.100 170.000 169.840 ~2 Feed, moles/hr 1.017 1.020 1.016 C2H4Feed, moles/hr 5.007 5.007 5 ooo HOAC Feed, moles /hr 1.976 1.908 1.937 N2 FEED, moles /hr 4.942 4.942 4.940 ~2 Account.% (f) 96.802 94.645 96.643 C2H4 Account.% (g) 99.083 98.057 99.152 HOAC Account.%(h) 101.118 99.994 106.462 Mass Account.% (i) 99.711 98.897 101.156 wt% Pd (ICP) 0.58% 0.80% 1.1%
wt% Au 0.35% 0.21% 0.89%
MeanTEM Particle Size(k) 10.7 nm 8.3 nm Notes:
30 (a) Nonns-ii7~ to 45% ~2 COllVt~ iOn.
(b) Adj. CO2 Sel = (moles CO2 product minus moles CO2 fed)l00/2 (adj. C2H4 conv.), where adj. C2H4 conv. = moles C2H4 accounted for minus moles C2H4 product.
(c) STY, g VA/l-hr = (VA produced, g/hr x 1000)/catalyst volume, ml.
(d) Adj. ~2 Conv. = (moles ~2 fed, AFB minus moles ~2 product~l00/moles ~2 fed, where AFB = accounted for basis.
(e) The reactor telll~ aLul~i, degrees C, is the average of the circulation gas t~ dlul~ above and below the catalyst.
(f) ~2 Account. = (total moles ~2 recovered, AFB/total moles ~2 fed) 100.
(g) C2H4 Account. = (total moles C2H4 recovered, AFB/total moles C2H4 fed)l00.
40 (h) HOAc Account. = (total moles HOAc recovered, AFB/total moles HOAc fed) 100.
(i) Mass Account. = (total grams product recovered/total grams fed) 100.
(k) TEM measurement ~.ro.nled after run in VAST unit.
!~

~rF

W O 97/33690 PCTrUS97/02132 - TA~TFIII
Vinyl Acetate Micro Unit Process. With Pd-Au On Silica Support Example Number 5 6 Catalyst ID 3:1 Pd/Au metal on 4:1 Pd/Au metal on Size 5 mm 5 mm Avg. Cat. Temp. 178.800 179.520 Shell Temp. 173.900 177.650 P~ e 100.000 100.000 ~2~N2 Rate (cc/min) 896.840 897.290 C2H4 Rate (cc/min) 1014.070 1014.580 HOAc Rate (mL/min) 0.800 0.800 STY (g/L~) 352.024 262.756 Mass Acct. (%) 100.001 99.826 ~2 Conv. (%) 31.502 18.776 C2H4 Conv. (%) 13.395 10.630 AcOH Conv. (%) 7.129 5.367 ~2 Acct. (%) 101.141 103.298 C2H4 Acct. (%) 98.466 98.709 AcOH Acct. (%) 101.370 100.390 VA Sel. (%) 88.751 90.911 CO2 Sel. (%) 10.745 8.555 EtOAc Sel. (%) 0.126 0.130 TTL HE Sel. (%) 0.379 0.403 Selectivity values are norm~li7Pcl and based on ethylene.

CA 02244909 l998-07-28 W O 97/33690 PCT~US97/02132 - TA~r F IV
V;r~yl Acetate Micro Unit Process. With Pd-Au On a-Alumina Support Example Number 7 7 8 8 9 CatalystID 4:1 alloyed- 4:1 alloyed 7:1 alloyed- 7:1 alloyed- 4:1 alloyed Pd/Au Pd/Au Pd/Au PdlAu PdJAu on Al203 on Al203 on Al2O3 on Al2O3 on Al203 no. coats Double r)ouble Double Size 3 mm 3 mm 3 mm 3 mm 3 mm Avg. Cat. Temp. 157.130 162.130 147.730 152.930 154.520 Shell Temp. 155.450 160.500 145.650 149.950 151.050 Pressure 100.000 100.000 100.000 100.000 100.000 O2/N2 (15/85) Rate 902.000 894.210 904.530 905.070 928.700 (cc/min) C2H4Rate 1015.090 1006.320 1023.700 1024.310 1056.420 (cc/min) HOAC Rate 0.810 0.820 0.820 0.820 0.800 (mL/min) STY (g/L~r) 251.442 309.747 417.847 492.272 435.261 Mass Acct. (%) 99.658 100.308 100.696 100.855 98.248 ~2 Conv. (%) 18.174 21.118 30.3S3 36.754 35.648 ~2EI4~onv. (%) 8.973 8.579 i3.~7 ~r*.892 20.5~8 AcOH Conv. (%) 6.364 7.564 7.685 9.858 9.820 ~2 Acct. (~/O) 101.807 104.459 102.739 103.375 98.985 C2H4 Acct. (%3 97.489 97.252 98.648 97.646 96.631 AcOH Acct. (%) 101.522 103.767 103.485 105.289 97.886 VA Sel. 91.952 91.416 92.185 91.617 91.361 CO2 Sel. 7.081 7.738 7.098 7.735 7.713 ~tOAc Sel. 0.149 0.132 0.198 0.186 0.175 Total H~ Sel. 0.817 0.714 0.518 0.462 0.751 wt. %Pd 0.37 0.37 0.80 0.80 0.50 wt. % Au 0.17 0.17 0.21 0.21 0.24 W O 97/33690 PCTrUS97/02132 - T~TF V
Vir~y~ Acetate Micro U~it Process. Witll Pd-Au On ~-AIumina Support Example Number 10 11 12 13 14 CatalystID Pd coat 3:1 Pd/Au 3:1 Pd/Au 3:1 Pd/Au 6:1 Pd/Au then Au coat incipient on Al2O3 wetness Size 3 mm 3 mln 3 mm 3 mm 3 m m Avg. Cat. Temp. 157.500 157.920 156.620 167.800 159.370 Shell Temp. 155.750 155.350 153.610 163.800 156.050 Pressure 100.000 100.000 100.000 100.000 100.000 ~2~2 (15/85) R~te 918.860 913.090 903.530 907.510 915.180 (cc/min) C2H4 R~te 1045.230 1038.670 1021.430 1030.460 1038.180 (cc/min) HOAc R~te 0.790 0.800 0.850 0.800 0.800 (mL/min) STY (g~L~) 236.543 321.512 279.441 375.372 443.986 Mass. Acct. (%) 98.350 99.232 99.539 99.378 99.253 ~l Conv. (%) 21.311 23.811 23.402 34.379 35.950 C2H4 Conv. (%) 11.611 13.351 9.962 14.937 19.988 AcOH Conv. 6.785 7.520 6.942 8.417 8.383 ~2 Acct- (%) 97.799 101.512 100.641 99.206 101.523 ~H4 Acct. (%) 96.788 97.295 97.397 97.447 98.371 AcOH Acct. (%) 98.517 100.213 101.125 100.856 98.664 VA Sel. 90.600 91.967 90.183 88.868 90.570 CO2 Sel. 8.395 7.169 9.046 10.458 8.778 ~tOAc Sel. 0.212 0.192 0.144 0.128 0.224 Total HE Sel. 0.793 0.672 0.627 0.546 0.429 ~. % Pd 0.47 0.30 0.28 0.28 0.36 wt. % Au 0.25 0.18 0.17 0.17 0.11

Claims

21

1. A process for the preparation of a catalyst for production of vinyl acetate from ethylene, acetic acid and oxygen, which process comprises 1) forming an aqueous solution of water-soluble palladium and gold compounds:
2) dispersing the aqueous solution in a hydrophobic solvent with an effective amount of surfactant to form a microemulsion mixture:
3) treating the microemulsion mixture with a reducing agent; and, 4) impregnating a support with the mixture of step (3) to form a support metal catalyst; and, optionally, washing and drying the supported catalyst of step (4).

2. The process in accordance with claim 1 wherein the hydrophobic solvent is a hydrocarbon medium.

3. The process in accordance with claim 1 wherein the quality of surfactant ingredient is between about 2-20 grams per 30 milliliters of microemulsion mixture.

4. The process in accordance with claim 1 wherein the surfactant ingredient is a nonionic surfactant.

5. The process in accordance with claim 1 wherein the reducing agent is hydrazine.

6. The process in accordance with claim 1 wherein the support is an inorganic support.

7. The process in accordance with claim 6 wherein the support is selected from the group consisting of silica, alumina, silica/alumina mixture, zirconium dioxide, titanium dioxide, and calcium dioxide.

8. The process in accordance with claim 7 wherein the support is alumina.

9. The process in accordance with claim 6 wherein the support is in the form ofspherical structures.

10. The process in accordance with claim 6 wherein the support medium is in the form of tablets.

11. The process in accordance with claim 6 wherein the support medium is in the form of Raschig rings.

12. The process in accordance with claim 7 wherein the alumina catalyst support is .alpha.-alumina.

13. The process in accordance with claim 1 wherein the support metal catalyst of step (4) has a palladium metal content between about 0.1-2.5 weight percent, and a gold metal content between about 0.05-0.6 weight percent, based on the catalyst weight.

14. The process in accordance with claim 1 wherein the supported metal catalyst of step (4) has a palladium:gold weight ratio between about 1-10:1.

15. The process in accordance with claim 1 further comprising the step of impregnating the supported metal catalyst of step (4) with an aqueous solution of an alkali metal alkanoate activator, and then drying the resultant catalyst.

16. The process in accordance with 15 wherein the activator additive is alkali metal acetate.

17. A catalyst composition for the preparation of vinyl acetate from ethylene, acetic acid and oxygen, which comprises calloidal palladium-gold alloy on a support medium, said composition prepared in accordance with any of claims 1-16.

18. The catalyst composition in accordance with claim 17 wherein the colloidal palladium-gold alloy on the support has an average particle size between about 1-20 nanometers.

19. The catalyst composition in accordance with claim 17 which has a palladium metal content between about 0.1-2.5 weight percent, and a gold metal content between about 0.05-0.6 weight percent, based on the catalyst weight.

20. The catalyst composition in accordance with claim 17 which has a palladium:gold weight ratio between about 1-10:1.

21. The catalyst composition in accordance with claim 17 which has a palladium content between about 0.1-2 weight percent, based on the catalyst weight.

22. The catalyst composition in accordance with claim 17 wherein the support medium is alumina in the form of spherical structures.

23. The catalyst composition in accordance with claim 17 wherein the support medium is alumina in the form of tablets.

24. The catalyst composition in accordance with claim 17 wherein the support medium is alumina in the form of Raschig rings.

25. The catalyst composition in accordance with claim 17 wherein the support medium is .alpha.-alumina.