| Summary: | 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-OC<sub>3</sub>H<sub>7</sub>)<sub>3</sub> with Si(OC<sub>2</sub>H<sub>5</sub>)<sub>4</sub> and surfactant in a basic aqueous solution before hydrothermal synthesis, and Al/MCM-48 was synthesized using a post-modification method by grafting Al<sup>3+</sup> 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 m<sup>2</sup>/g. <sup>27</sup>Al Magic Angle Spinning-NMR (MAS NMR) indicated that Al<sup>3+</sup> in Al-MCM-48 was located inside the framework of mesoporous silica, but Al<sup>3+</sup> in Al/MCM-48 was located outside the framework of mesoporous silica. The results of ammonia temperature-programmed desorption (NH<sub>3</sub>-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 H<sub>2</sub> was charged in the autoclave at room temperature, 1 wt % Pt/Al/MCM-48 catalyst showed a high yield of C<sub>9</sub>−C<sub>15</sub> 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 (C<sub>1</sub>−C<sub>8</sub>) increased over Pt/H-Y, and the yield of heavy hydrocarbons (C<sub>16</sub>−C<sub>21</sub>) increased over Pt/Al-MCM-48 in the hydrocracking of polyethylene. The yield of C<sub>9</sub>−C<sub>15</sub> 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.
|
|---|
