Isomerization Cracking of n -Octane and n-Decane on Regulated Acidity Pt/WO_x-SO_4-ZrO_2 Catalysts

摘要

The effect of WO_3 loading on the acidity and specific surface area of catalysts composed of Pt supported on ZrO_2 and double-promoted with SO_4~(2-) and WO_3 catalysts (PtWSZ) was studied. The catalysts were tested in the isomerization cracking of heavy alkanes, and the objective was to assess their ability to produce branched shorter alkanes, contributing to the gasoline pool. As a consequence, the focus was put on the maximization of the yield of C_4-C_7 isomers (i-C_(4-7)). The catalysts were characterized by several techniques. The crystalline structure was analyzed by XRD. The acidity of the catalysts was measured by thermal desorption of pyridine. A screening and first selection of the most promising catalysts was done by means of the reaction of n-octane at 300 ℃, 0.1 MPa, WHSV = 1 and H_2C_8 = 6 mol/mol. A high yield of i-C_8 was obtained with the Pt/ WO_3—ZrO_2 catalyst. The incorporation of SO_4~(2-) as a promoter increased the acidity and the cracking activity. Pt/SO_4~(2-)-ZrO_2 displayed very strong acid sites and generated the highest amount of light hydrocarbons. Catalysts of regulated acidity combining both promoters yielded the best results. The most promising PtWSZ catalyst was obtained with 5% W and 1.4% S. The test reaction of n-decane at near-industrial conditions (1.5 MPa, 300 ℃, WHSV = 4, H_2-C_(10) = 6 mol/mol) was used for a further assessment of the catalytic properties. This test confirmed that the double-promoted catalyst (PtWSZ, 5% W, 1.4% S) had high activity and stability and produced an isomerizate with the highest i-C_(4-7)/i-C_(total) molar ratio in comparison to the sulfated zirconia (PtSZ) and tungstated zirconia (PtWZ) catalysts.