Conversion of Waste Polyethylene into Hydrocarbon Fuel - Analysis of the Effect of Set Temperature on Reaction Time and Liquid Yield.

Abstract

Disposal of plastic waste has become one of the major environmental issues in Sri Lanka. The methods available to date such as incineration and land filling are cost­intensive and less accepted due t(f environmental impacts. Attention is thus being paid to new recycling methods which are more environmentally attractive. Pyrolysis is one such promising method for the treatment of mixed and contaminated plastic wastes. In pyrolysis, plastics are thermally degraded to produce liquid, gases and solid hydrocarbons. Pyrolysis of waste plastics was investigated in a reactor system which consists of a semi-batch reactor, a condenser and a liquid-gas separator developed reactor system is capable of converting waste plastics (polyethylene, polypropylene and polystyrene) into hydrocarbon fuel. Polyethylene waste samples of 3000 g by weight were used for the experiments carried out to investigate the effects of set temperature on reaction time and liquid yield. The reaction time was found to decrease from 300 min to 170 min, when the set temperature of the reactor increased from 425 °C to 525 °C. The liquid yield was found to increase from 31.0% to 60. 7%, when the set temperature of the reactor increased from 425 °C to 4 75 °C and further it was found to decrease from 60.7% to 39.9%, when the set temperature of the reactor increased from 475 °C to 525 °C. The solid residue left in the reactor was decreased from 41.6% to 27.4%, when the set temperature of the reactor increased from 425 °C to 450 °C and it was found to remain around 26.0% beyond 450 °C. Set temperature of 425 °C drastically increased the solid residue amount and drastically decrease the liquid yield. Higher set temperatures such as 500 and 525 °C were found to decreased liquid yield and reaction time at an approximately same solid residue amount. Set temperatures such as 450 and 475 °C were found to give decent liquid yield at comparatively low solid residue amount. The best set temperature for waste polyethylene pyrolysis was 4 75 °C in terms of obtaining higher liquid yield and gas yield with low solid residue amount at comparatively small reaction time.