Selective hydrogenation catalyst system and process for preparing the same and its use

This invention relates to a selective hydrogenation catalyst system, a method of preparing this catalyst system and a process for selectively hydrogenating acetylenic and diolefinic compounds in hydrocarbon feeds, especially in C 2 -C 10 hydrocarbon fractions, to mono-olefins employing the catalyst system. More particularly, this invention relates to a selective hydrogenation Pd- and Bi-containing catalyst system, and its preparation and use.

In the hydrocarbon feeds as a source of polymerization grade olefins such as ethylene; propylene, butylenes and aromatics hydrocarbons, for example in C 2 -C 10 hydrocarbons, such as in propylene-propane feeds, there exist significant amountic of diolefins and acetylenic compounds, for example about 0.3-3% acetylenes and diolefins, which must be pre-removed by selective hydrogenation because such impurities are poisons of polyolefin (such as polyethylene etc.) catalyst, and influence the polymerization of olefin. In order to avoid said catalyst poisoning, the selective catalystic hydrogenation to make acetylenic and diolefinic compounds convert to mono-olefins is generally used. However, in the reaction of acetylenes and diolefins removal by selective hydrogenation, the acetylenes and diolefins adsorbed on catalyst surface are easy to form unsaturated C 4 -C 8 hydrocarbons through a hydrogenating dimerization. In turn, said C 4 -C 8 hydrocarbons will react subsequently with other unsaturated hydrocarbons (acetylene or ethylene etc.) to form C 6 -C 24 oligomers (known as “green oil”) adhered unavoidably on the selective hydrogenation catalyst. Said adhesion will make the activity and selectivity of the catalyst decrease gradually, shorten the catalyst operation cycle period and service life and lead to more frequent regenerations, thus increase in production costs.

In terms of the support material in the prior art, most catalysts for selective hydrogenation of acetylenic and diolefinic compounds are alumina-supported Pd catalysts. It is also found that TiO 2 -supported Pd catalyst ( U.S. Pat. No. 4,839,329), SiO 2 -supported Pd—Zn catalyst (DE 2,156,544), CaCO 3 -supported Pd—Pb catalyst, and cellular iolite -supported Pd catalyst containing alkali and/or alkali-earth metal (CN 1,176,291A) be used, in this field.

In terms of the active component in the prior art, also included are Pd catalyst systems with a cocatalyst component. The cocatalyst component disclosed in U.S. Pat. No. 4,404,124 is Ag, that in EP 892,252 is Au, that in DE 1284403 and U.S. Pat. No. 4,577,047 is Cr, that in U.S. Pat. No. 3,912,789 is Cu, that in U.S. Pat. No. 3,900,526 is Fe, that in U.S. Pat. No. 3,489,809 is Rh, that in U.S. Pat. No. 3,325,556 is Li, that in CN 1,151,908A is K. Other cocatalyst components disclosed include Pb, Zn etc.

In the aforesaid catalyst systems, some cocatalyst components sacrificed Pd catalyst's selectivity for improving its activity, some of them although can improve the Pd catalyst's selectivity or reduce the green oil formation, their activity reduced significantly. Therefore, only the Pd—Ag catalyst is in common use at present But with respect to its activity and selectivity, Pd—Ag catalyst is still less than satisfactory.

It is an object of this invention to overcome said shortcomings of the prior art, to provide a high selective and high hydrogenation active catalyst system for selective hydrogenation with green oil formation reduced, the service life of the catalyst increased, and the production costs decreased.

It is a further object of the invention to provide a process for the preparation of the catalyst system.

It is another object of the invention that a process for using the catalyst system in a selective hydrogenation of acetylenic and diolefinic compounds in hydrocarbon feeds.

The selective hydrogenation catalyst system of this invention comprises a support material, a Pd-containing catalyst component, Bi-containing cocatalyst component, wherein

the weight percent of Pd-containing catalyst component is 0.001-1 wt. % based on the total weight of the catalyst system,

the weight ratio Bi/Pd is 0.01-50, and

the balance is the support material

The support material is selected from the group consisting of diatomaceous earth, SiO 2 , TiO 2 , Al 2 O 3 , and has a shape of granular, spherical, flake or strip, its specific surface area is 1-350 m 2 /g.

The preferred support material is Al 2 O 3 or SiO 2 , its preferred shape is strip or spherical, its preferred specific surface area is 5-280 m 2 /g, more preferably 8-280 m 2 /g. The preferred weight percent of Pd-containing catalyst component is 0.008-0.6 wt. %, more preferably 0.01-0.5 wt. %. The preferred weight ratio Bi/Pd is 0.1-10, more preferably 1-6.

The catalyst system of the invention can further contain optionally at least one other cocatalyst components selected from the group consisting of Ag, Cu, Zn, K, Mg and Ca. In one embodiment of this invention, the Bi-containing cocatalyst component is added on the Pd-containing catalyst component which has combined with one or more other cocatalyst components. Therefore, in the selective hydrogenation of this invention, the activity and selectivity of the catalyst system which has contained the aforesaid cocatalyst components, can be improved and the green oil formation reduced, thus the cycle of operation prolonged.

When using Ag as the aforesaid optional cocatalyst component, the Ag content is 0.001-10 wt. %, preferably 0.01-2 wt. %, based on the total weight of the catalyst system.

The catalyst system of this invention is manufactured by impregnating a support material simultaneously or separately with a Pd-containing solution, and a Bi-containing solution, and then drying at 100-300° C. for 5-24 hrs, and calcining at 350-650° C. for 4-20 hrs. Said Pd-containing solution is selected from an aqueous solution of palladium chloride, palladium nitrate, palladium acetate or the like, and Bi-containing solution is selected from the aqueous solution of bismuth nitrate, bismuth chloride or the like.

When this invention is practiced, the support material used in the selective hydrogenation catalyst system of the invention can be diatomaceous earth, Al 2 O 3 , SiO 2 , TiO 2 etc, the preferred support material is Al 2 O 3 . The shape of the support material can be granular, spherical, flake, or extruded strip. the preferred shape is an extrudate. The specific surface area of support material, such as Al 2 O 3 can be 1-350 m 2 /g, preferably is 5-280 m 2 /g, more preferably 8-28 m 2 /g. The preparation process for the support material such as Al 2 O 3 is not critical on the properties of the catalyst of the invention, and carbonization method, nitric acid method etc. can be used. The selective hydrogenation catalyst system of the invention comprises, based on the total weight of the supported catalyst system, 0.001-1% of Pd component and 0.001-10% of Group IB cocatalyst metal component, and a Group VA cocatalyst metal. The preferred Group IB cocatalyst metal is Ag and/ or Cu. the preferred Group VA cocatalyst metal is Bi.

When using the stepwise-impregnating method, the procedure is as follows:

firstly, impregnating the support material by using a Pd-containing solution. It is advantageous to impregnate with the largest amount of solution absorbable by the support material. The amount of the Pd-containing solution used should be sufficient such that the calcined catalyst would contain 0.001-1 wt. % of metal Pd. One skilled in the art is easy to determine the appropriate mixing ratio. The Pd-containing solution can be the aqueous solution of palladium chloride, palladium nitrate, palladium acetate, or the like. After impregnating by Pd-salt solution, drying at 100-300° C. for 5-24 hrs. The dried support material can either be impregnated with Bi-containing solution, or impregnated first with Ag-containing solution and then with Bi-containing solution. Preferably, the dried support material can be impregnated with the largest amount of the solution absorbable thereby completely.

When impregnating with Ag-containing solution, this solution is made up from silver nitrate, silver perchlorate, or the like., The amount of Ag-containing solution used should be sufficient such that the calcined catalyst system would contain 0.001-10 wt. % of metal Ag. One skilled in the art is easy to determine the appropriate mixing ratio. The Pd-treated support material that Ag salt solution impregnated is dried at 100-300° C. for 5-24 hrs, the dried support material is impregnated with a Bi-containing solution. Preferably, the dried support material can be impregnated with the largest amount of the solution absorbable thereby completely.

The Bi-containing solution is made up from bismuth nitrate, bismuth chloride, or the like. The amount of Bi-containing solution used should be sufficient such that the calcined catalyst would have a weight ratio Bi/Pd of 0.01-50, preferably 0.1-10, most preferably 1-6. One skilled in the art is easy to determine the appropriate mixing ratio. After impregnating with Bi salt solution, drying at 100-300° C. for 5-24 hrs, and calcining at 350-650° C. for 4-20 hrs. One skilled in the art is easy to determine the appropriate conditions of drying and calcining.

Owing to the addition of Group VA metal Bi as cocatalyst, the selective hydrogenation catalyst system of the invention has more improvement of the activity and selectivity than the prior art, decreases the formation of green oil and carbon deposit after long term operation of the catalyst, thus prolongs the service life of the present catalyst system, operation cycle period and reduces the production costs.

Comparative Example 1

According to the aforesaid process and operating conditions disclosed, alumina beads having a diameter range of 2.5-4.5 mm were impregnated with an aqueous solution of palladium nitrate. After drying, calcining, 0.03 wt. % Pd/alumina catalyst was prepared. Said catalyst was further impregnated with an aqueous solution of silver nitrate, after drying, calcining, 0.03 wt. % Pd-0.8 wt. % Ag/alumina catalyst (called catalyst A, i.e. equivalent to the catalyst in U.S. Pat. No. 4,404,124) was prepared.