Pyrolysis of polypropylene in the presence of oxygen

Abstract

The polypropylene (PP) was coated on porous α-alumina particles and then pyrolyzed in a flow of helium or a mixture of helium–oxygen at atmospheric pressure. The mass release from PP was dramatically enhanced in the presence of oxygen at temperatures in the range of 200–300°C. The temperature for the 50% mass release was ca. 250°C at an oxygen partial pressure ( P O 2 ) of 16.7 kPa and was lowered by 190°C as compared with a system which contained no oxygen. When P O 2 was higher than 4.2 kPa, the mass release rate obeyed first-order kinetics with respect to P O 2 , and the activation energy was calculated and found to be 65–75 kJ/mol. The activation energy was considerably lower than that for pyrolysis in the absence of oxygen (230 kJ/mol) and agreed well with the value for formation of peroxides on tertiary carbons. When the pyrolysis was conducted at 250°C under P O 2 =16.7 kPa, the carbon-based yield of volatiles exceeded 90%, and the yields of CS 2-soluble oil and wax were 76% and 6.0%, respectively. The carbon-based yields of other products were: Acetone, 2.5%; methanol, 1.5%; CO, 3.0%; CO 2, 2.2% and solid residue; 10%. Proton NMR (nuclear magnetic resonance) analysis showed that the CS 2-soluble oil possessed an elemental composition of C 100H 187O 11. The average number of carbon atoms per molecule of the oil was approximately 10, and –CH 2–OH, –C(CH 3)CO and CH 2 were typical end groups. Their formation is explained by the decomposition of peroxides formed on tertiary carbons.