||||||III US005567839A United States Patent 19 11) Patent Number: 5,567,839 Gulliver et al. 45 Date of Patent: Oct. 22, 1996 54 PROCESS FOR THE PREPARATION OF 5,179,057 1/1993 Bartley. WNYLACETATE 5,185,308 2/1993 Bartley et al.. 5,189,004 2/1993 Bartley et al.. 75 Inventors: David J. Gulliver, Banstead; Simon J. 5,225.388 7/1993 Wunder et al.. 5,250,487 10/1993 Wirtz et al.. Kitchen, Doncaster, both of England 5,274,181 12/1993 Bartley et al.. (73) Assignee: BP Chemicals Limited, London, 5,292,931 3/1994 Wirtz et al.. England 5,342.987 8/1994 Bartley. 5,347,046 9/1994 White ...................................... 560/245 21 Appl. No.: 342,314 FOREIGN PATENT DOCUMENTS 22 Filed: Nov. 18, 1994 156674 11/1983 Canada. 2071698 12/1992 Canada. 30 Foreign Application Priority Data 2093610 10/1993 Canada. 563414 3/1992 European Pat. Off.. Nov. 19, 1993 (GB) United Kingdom ................... 932.3823 519435 12/1992 European Pat. Off. Nov. 19, 1993 (GB) United Kingdom ................... 9323857 519436 12/1992 European Pat. Off.. 565952 10/1993 European Pat. Off.. (51 Int. Cl. ............................ C07C 67/05 2121693 8/1972 France. 52 U.S. Cl. ........................... 560/245; 502/169; 502/243 1283T37 8/1972 United Kingdom. (58) Field of Search ............................................... 560/245 1288.299 9/1972 United Kingdom. 1333449 10/1973 United Kingdom. 56) References Cited 1500.67 21978 United Kingdom . 151869 5/1978 United Kingdon . U.S. PATENT DOCUMENTS 3,743,607 7/1973 Sennewald et al.. Primary Examiner-Michael L. Shippen 3,775,342 11/1973 Kronig .................................... 560/245 Attorney, Agent, or Firm-Fay, Sharpe, Beall, Fagan, Min 3,822,308 7/1974 Kronig et al. nich & McKee 3,939,199 2/1976 Fernholz et al. 4,048,096 9/1977 Bissot. (57) ABSTRACT 4,087,622 5/1978 Nakamura et al. 4,093,559 6/1978 Fernholz et al. In a process for the preparation of palladium and palladium/ 4,119,567 10/1978 Bartsch. gold shell type catalysts for vinyl acetate production, the 4,158,737 6/1979 Bartsch. improvement comprises using a barium salt to precipitate 4,347,383 8/1982 Isshiki ..................................... 564/249 water-insoluble palladium and optional gold compounds 4,370,261 1/1983 Wunder et al., onto a support prior to reduction with a reducing agent. A 4,370,492 1/1983 Wunder et al. barium salt additive may also be introduced to the catalyst 4,407,733 10/1983 Birkenstock ............................ 502/174 after reduction to reduce the tendency of the catalyst to 4.550,097 10/1985 Drake. deactivate with use. 4,668,819 5/1987 Fernholz et al. 4,902,823 2/1990 Wunder et al. 5,179,056 1/1993 Bartley. 15 Claims, 5 Drawing Sheets U.S. Patent 5,567,839 U.S. Patent Oct. 22, 1996 Sheet 3 of 5 5,567,839 A|-0091S/TWIWDN (8H LV)-1 WN5) LINV U.S. Patent Oct. 22, 1996 Sheet 4 of 5 5,567,839 e1S/TV/LV/DE TVIVUA0||SÅ & 00,7 088 099 OZE 00£ (8H LV) - / WAB • LAW 5,567,839 1. 2 PROCESS FOR THE PREPARATION OF The use of alkali metal acetates, in particular potassium WNYLACETATE acetate, as promoters for both non-shell and shell type catalysts for vinyl acetate production is known (see for example, U.S. Pat. No. 3,743,607; U.S. Pat. No. 3,822.308; The present invention relates to the preparation of cata U.S. Pat. No. 4,087,622; U.S. Pat. No. 5,179,056; U.S. lysts and in particular to the preparation of palladium and 5 5,185.308; U.S. Pat. No. 5,179,057; U.S. Pat. No. 5,189,004 palladium/gold catalysts useful in effecting the production of and U.S. Pat. No. 5,250,487). vinyl acetate from ethylene, acetic acid and oxygen contain According to GB 1,283,737 alkali metal or alkaline earth ing gas. metal salts of weak acids, both organic and inorganic acids The production of vinyl acetate by reacting ethylene, have been found to be especially useful as activators for acetic acid and oxygen together in the gas-phase in the 10 vinyl acetate catalysts. Sodium, lithium, potassium, presence of a catalyst containing palladium, gold and an rubidium and caesium salts and mixtures thereof are said to alkali metal acetate promoter is a known process. The have been found to be most effective. However, only potas sium acetate is used in the examples. catalyst components are typically supported on a porous GB 1,333,449 describes catalysts comprising a carrier carrier material such as silica or alumina. 15 impregnated with a palladium salt and a barium carboxylic In early examples of these catalysts, both the palladium acid aurate derived from a carboxylic acid having from 2 to and gold were distributed more or less uniformly throughout 10 carbon atoms, preferably barium aceto-aurate, barium the carrier (see for example U.S. Pat. No. 3,743,607 and GB propiono-aurate or barium butyro-aurate. According to GB 1,333,449). This was subsequently recognised to be a dis 1,333,449 the catalysts are prepared by impregnating the advantage because it was found that the material within the 20 carriers with a solution of the active components and drying. inner part of the carrier did not contribute to the reaction GB 1,333,449 does not therefore, describe the preparation of since the reactants did not diffuse significantly into the shell impregnated catalysts. carrier before reaction occurred. In other words a significant The use of barium auroacetate in catalysts is also amount of the palladium and gold never came into contact described in U.S. Pat. No. 4,370,492. 25 Canadian patent application CA 2,071.698 describes the with the reactants. use of barium as a component of palladium-containing In order to overcome this problem, new methods of catalysts in the absence of cadmium and gold. According to catalyst manufacture were devised with the aim of produc CA 2,071.698, the catalytically active substances are applied ing catalysts in which the most active components were to the supportin customary manner, for example by impreg concentrated in the outermost shell of the support (shell nating the support with a solution of the active substances, impregnated catalysts). For example GB 1,500,167 claims 30 subsequently drying it and if appropriate subjecting it to catalysts in which at least 90% of the palladium and gold is reduction. According to CA 2,071,698 the active substances distributed in that part of the carrier particle which is not can also be applied, for example, by precipitation on the more than 30% of the particle radius from the surface, whilst support or by spraying on, vapour deposition or dipping. In CA 2,071,698 the preparation processes described in all the GB 1,283,737 teaches that the degree of penetration into the 35 examples would be expected to produce non shell type porous carrier can be controlled by pretreating the porous catalysts. carrier with an alkaline solution of, for example, sodium Canadian patent application CA 2,093,610 describes the carbonate or sodium hydroxide. preparation of shell type catalyst by the steps of (1) dissolv Another approach which has been found to produce ing salts of palladium, potassium and (a) cadmium, (b) particularly active catalysts is described in U.S. Pat. No. barium or (c) gold in a solvent; (2) atomising the solution 4,048,096. In this patent, shell impregnated catalysts are ultrasonically; (3) impregnating the support with the atom produced by a process comprising the Steps of (1) impreg ised solution one or more times and (4) curing after each nating a catalyst support with an aqueous solution of water impregnation. soluble palladium and gold compounds, the total volume of It has now been found that a catalyst of high activity is the solutions being 95 to 100% of the absorptive capacity; 45 obtained by using a barium salt to precipitate water insoluble (2) precipitating water-insoluble palladium and gold com palladium and optionally gold compounds on the catalyst pounds on the catalyst support by contacting the impreg support during the production of shell impregnated catalysts. nated catalyst support with a solution of alkali metal silicate, According to the present invention there is provided a the amount of alkali metal silicate being such that, after the process for preparing a shell impregnated catalyst for use in alkali metal silicate has been in contact with the carrier for 50 the production of vinyl acetate from ethylene, acetic acid 12 to 24 hours, the pH of the solution is from 6.5 to 9.5; (3) and an oxygen containing gas, said catalyst comprising converting the water-insoluble palladium and gold con palladium and optionally gold deposited on a catalyst sup pounds into palladium and gold metal by treatment with a port characterised in that the process comprises the steps in sequence of: reducing agent; (4) washing with water; (5) contacting the 55 catalyst with alkali metal acetate and (6) drying the catalyst. (1) impregnating the catalyst support with aqueous solu U.S. Pat. No. 5,185,308 describes the preparation of tions of water-soluble palladium and optional gold palladium/gold shell impregnated catalysts for vinyl acetate compounds, production which are prepared by a series of steps including (2) contacting the impregnated support from Step (1) with impregnation, precipitation, reduction, washing, drying, a solution of a barium salt capable of reacting with the potassium acetate loading and final drying.