The process of thermocatalytic conversion of polypropylene into liquid hydrocarbons using amorphous aluminum silicates with aluminum content of 1.6-12.9 wt.% as catalysts was studied. The aluminum silicates were synthesized by sol-gel method using hydrolysis of tetraethoxysilane in a presence of aluminum salt at pH=9. All samples possessed acidic sites with pKa value of 3.46-5.00 and had a developed surface. Textural properties of the aluminum silicates were determined. Thermocatalytic conversion of polypropylene was carried out in a flow fixed-bed reactor with a fixed layer of the mixture of the catalyst and the reagent at a mass ratio of polymer : catalyst of 3 : 1 in argon atmosphere with a gradual rise of temperature in the range of 300 – 450 ºС. The sample of silica, which did not contain aluminum, was demonstrated to be inactive in polypropylene degradation, while other catalysts provided conversion of polypropylene into liquid products. The highest yield of liquid products was 80% for a catalyst with an aluminum content of 8.1 wt.%. According to the results of GLC saturated hydrocarbons were identified among the products for all samples. The effect of the concentration of acidic centers on the chemical and fractional composition of the target products was shown. For the studied aluminum silicates with the same pKa values, an increase in the aluminum content favored the formation of a lighter hydrocarbon fraction. For the catalyst with the highest aluminum content the n-alkanes of С5-С10 composition were identified. These products were closest to gasoline oil fraction. This provides a possibility to consider secondary polyolefins as an alternative source of motor fuels. An influence of catalyst composition on maximal temperature of polyethylene degradation was determined by differential thermal analysis.

No abstract

No abstract

The catalytic activities of mesoporous H-MCM-41 aluminosilicates of different compositions in degradation of polypropylene and a polypropylene-polyethylene mixture into gasoline-range fraction hydrocarbons were compared. A higher yield of the target products (86 wt %) was observed for the sample with a lower aluminum content. Using the results of chromatographic analysis of the catalyzate for the content of the gasoline-range fraction, both saturated and unsaturated hydrocarbons, dominated by products with cyclic structure, were identified in all the samples studied. In the presence of the H-MCM-41 sample with a lower silica modulus, a larger amount of condensation products with a higher calorific value arose from polypropylene degradation. Mesoporous aluminosilicates H-MCM-41 can be regarded as effective catalysts for thermocatalytic conversion of polypropylene to produce the gasoline-range fraction.