Catalytic cracking of polyethylene over all-silica MCM-41 molecular sieve.

The catalytic cracking of high-d. polyethylene was demonstrated over all-silica MCM- 41 catalysts. The cracking activity increases with the degree of crystallinity of the catalysts. The pore diam. of the samples has an effect on the level of the catalytic activity, with catalysts having small pore diams. giving higher activity. A carbenium ion-mediated mechanism is proposed for the cracking reaction, as high levels of isobutene and isobutane and low levels of C and C were produced. The product distribution was compared with those obtained from thermal cracking tests. The surface acidity of the all-silica MCM-41 is attributed to the presence of silanol groups. It is proposed that the formation and stabilization of carbenium ions in the pores of the catalyst are due to the adsorption interaction between the polyethylenic fragments with the surface of the channels

Catalytic cracking of polyethylene over all-silica MCM-41 molecular sieve.

The catalytic cracking of high-d. polyethylene was demonstrated over all-silica MCM- 41 catalysts. The cracking activity increases with the degree of crystallinity of the catalysts. The pore diam. of the samples has an effect on the level of the catalytic activity, with catalysts having small pore diams. giving higher activity. A carbenium ion-mediated mechanism is proposed for the cracking reaction, as high levels of isobutene and isobutane and low levels of C and C were produced. The product distribution was compared with those obtained from thermal cracking tests. The surface acidity of the all-silica MCM-41 is attributed to the presence of silanol groups. It is proposed that the formation and stabilization of carbenium ions in the pores of the catalyst are due to the adsorption interaction between the polyethylenic fragments with the surface of the channels

Catalytic Pyrolysis of Waste Plastics using Staged Catalysis for Production of Gasoline Range Hydrocarbon Oils

The two-stage pyrolysis-catalysis of high density polyethylene has been investigated with pyrolysis of the plastic in the first stage followed by catalysis of the evolved hydrocarbon pyrolysis gases in the second stage using solid acid catalysts to produce gasoline range hydrocarbon oil (C8-C12). The catalytic process involved staged catalysis, where a mesoporous catalyst was layered on top of a microporous catalyst with the aim of maximising the conversion of the waste plastic to gasoline range hydrocarbons. The catalysts used were mesoporous MCM-41 followed by microporous ZSM-5, and different MCM-41:zeolite ZSM-5 catalyst ratios were investigated. The MCM-41 and zeolite ZSM-5 were also used alone for comparison. The results showed that using the staged catalysis a high yield of oil product (83.15 wt.%) was obtained from high density polyethylene at a MCM-41:ZSM-5 ratio of 1:1 in the staged pyrolysis-catalysis process. The main gases produced were C2 (mainly ethene), C3 (mainly propene), and C4 (mainly butene and butadiene) gases. In addition, the oil product was highly aromatic (95.85 wt.% of oil) consisting of 97.72 wt.% of gasoline range hydrocarbons. In addition, pyrolysis-staged catalysis using a 1:1 ratio of MCM-41: zeolite ZSM-5 was investigated for the pyrolysis–catalysis of several real-world waste plastic samples from various industrial sectors. The real world samples were, agricultural waste plastics, building reconstruction plastics, mineral water container plastics and household food packaging waste plastics. The results showed that effective conversion of the real-world waste plastics could be achieved with significant concentrations of gasoline range hydrocarbons obtained