Effect of Addition of K to Ni/SiO_2 and Ni/Al_2O_3 Catalysts on Hydrothermal Cracking of Bitumen

摘要

Hydrothermal cracking of Canadian Athabasca bitumen was performed over Ni/SiO_2 and Ni/Al_2O_3 catalysts under 703 K and 5.0 MPa of hydrogen pressure in a batch reactor. Comparing with thermal cracking under the same reaction conditions, hydrothermal cracking process obviously suppressed the formation of coke from 5.5 to 3.5 wt% (Ni/SiO_2) and to 3.0 wt% (Ni/Al_2O_3), and the formation of gaseous hydrocarbon products. To decrease coke formation further, a small amount of potassium was impreganted in the catalysts. The spectroscopy of NH_3-TPD showed that the amount of acidic sites in both catalysts, Ni/Al_2O_3 and Ni/SiO_2, was dramtically decreased by K_2O modification. The acid-catalyzed polymerization of residuum indiced by acidic sites in the catalyst, that might result in the formation of coke, was suppressed by neutralization of the acidic sites. Adding 3% of potassium onto Ni/SiO_2 decreased the yield of coke from 3.5 to 2.1 wt%.