چكيده به لاتين
Abstract:
The presence of acetylene in ethylene flow produced in olefin plant of petrochemical complexes, is a permanent poison for the polymerization catalysts. The ethylene feedstock of polymerization should have acetylene content lower than 5ppm. The acetylene in the catalytic reactor converts to ethylene. The optimum catalyst should adsorb acetylene in ethylene rich feedstock and in the semi-hydrogenation reaction produce ethylene and no effect on the other components. The best performance in selective hydrogenation of acetylene is done by palladium catalysts.
In this thesis, the role of support was studied primary. A series of alumina phases were produced by heat treatment and also some metal aluminates (metal: nickel, copper, and zinc) were prepared by sol-gel and impregnation methods. The physical and chemical characters were identified and the palladium and silver were impregnated on the selected supports, respectively. The catalysts properties and performances were investigated. Also some preparation parameters that effect on the silver deposition on the catalysts like; surface reduction by hydrogen, type of impregnation methods and precursors, pH, and calcination temperature were evaluated.
The theta and delta alumina phases had the best performance as the support of palladium. The uniform distribution and similar active sites was shaped on them. The aluminates prepared by impregnation method had high surface area compared to sol-gel method. The type of metal ions had effect on the alumina phase transformation rate and the copper ions was accelerates alumina phase transformation more than other ions. The nickel aluminates had lower acidity than zinc aluminate and the acidity both of them in lower than alumina. The multicoordination active sites of palladium were formed on the metal aluminate supports that increased the acetylene conversion to 80%.
The active sites blocking by silver was decreased by using surface reduction of hydrogen in impregnation process so the acetylene conversion was increased from 40% to 60%. The pH of precursor had more effect on the performance than other impregnation parameters. The acetylene conversion of samples prepared at pH equal 11 and 4 were 45% and 30% ,respectively. The dry and wet impregnation of silver precursor had 50% and 30% acetylene conversion .
Keywords: hydrogenation;acetylene; palladium; alumina; ethylene
