Conversion of polyethylene into gasoline-range fuels by two-stage catalytic degradation using silica-alumina and HZSM-5 zeolite

A two-stage catalytic degradation of polyethylene using amorphous silica-al umina and HZSM-5 zeolite catalysts in series has been developed for convert ing the polymer into high-quality gasoline-range fuels. Compared with the o ne-stage degradation over each catalyst, the two-stage method provides some advantages. They are an improved gasoline yield and a high octane number d espite low aromatics content. Significant results were obtained when silica -alumina and HZSM-5 were used in a weight ratio of 9:1 as upper and lower c atalysts, respectively, in a flow reactor. The reverse sequence of catalyst s showed no advantage. It was suggested that large pores and moderate acidi ty of the silica-alumina loaded in the upper layer operated favorably to ca talyze the degradation of polyethylene into Liquid hydrocarbons. The result ing oils showed low quality, and they were transformed into high-quality ga soline on the strongly acidic sites,of the HZSM-5 loaded in the lower layer at the expense of oil yield. Increases in concentration of isoparaffins an d aromatics contributed to the upgrading.