Hydrocracking of Polyethylene to Jet Fuel Range Hydrocarbons over Bifunctional Catalysts Containing Pt- and Al-Modified MCM-48

A low-density polyethylene was hydrocracked to liquid hydrocarbons in autoclave reactors over catalysts containing Pt- and Al-modified MCM-48. Two kinds of Al-modified MCM-48 were synthesized for the reaction: Al-MCM-48 was synthesized using a sol–gel method by mixing Al(iso-OC3H7)3 with Si(OC2H5)4 and surfactant in a basic aqueous solution before hydrothermal synthesis, and Al/MCM-48 was synthesized using a post-modification method by grafting Al3+ ions on the surface of calcined Al/MCM-48. X-ray diffraction (XRD) patterns indicated that both Al-MCM-48 and Al/MCM-48 had a cubic mesoporous structure. The Brunauer–Emmett–Teller (BET) surface areas of Al-MCM-48 and Al/MCM-48 were larger than 1000 m2/g. 27Al Magic Angle Spinning-NMR (MAS NMR) indicated that Al3+ in Al-MCM-48 was located inside the framework of mesoporous silica, but Al3+ in Al/MCM-48 was located outside the framework of mesoporous silica. The results of ammonia temperature-programmed desorption (NH3-TPD) showed that the acidic strength of various samples was in the order of H-Y > Al/MCM-48 > Al-MCM-48 > MCM-48. After 4 MPa H2 was charged in the autoclave at room temperature, 1 wt % Pt/Al/MCM-48 catalyst showed a high yield of C9−C15 jet fuel range hydrocarbons of 85.9% in the hydrocracking of polyethylene at 573 K for 4 h. Compared with the reaction results of Pt/Al/MCM-48, the yield of light hydrocarbons (C1−C8) increased over Pt/H-Y, and the yield of heavy hydrocarbons (C16−C21) increased over Pt/Al-MCM-48 in the hydrocracking of polyethylene. The yield of C9−C15 jet fuel range hydrocarbons over the used catalyst did not decrease compared to the fresh catalyst in the hydrocracking of polyethylene to jet fuel range hydrocarbons over Pt/Al/MCM-48.