A Study of Degradation and Liquefaction of Waste Plastics

Abstract

With a view to the environment protection and reduction of non-regeneration resource, recycling technology for converting to oil from plastic waste has drawn much attention in the world. India has also witnessed a substantial growth in the consumption of plastics and an increased production of plastic waste. Hence, the basis theories and the technology for industrialization of plastic liquefaction is the broad area of research today. The variety in plastic waste composition and differences in thermal degradation behavior makes modeling, design, and operation of thermal conversion systems a challenge. The aim of this study is to obtain detailed information on the pyrolysis characteristics like degradation ability with and without catalyst, chemical kinetics and the nature of liquefaction of most important waste plastics. A thermogravimetric analysis (TGA) including determination of kinetic parameters was performed at different constant heating rates of 5, 10, 15, 20oC/min in an inert atmosphere. The plastics polystyrene, polypropylene, low-density polyethylene and high-density polyethylene except PVC was modeled as single reactions to describe the degradation of hydrocarbon polymer. Using a semi batch reactor the experiments conducted for testing the nature of liquefaction of plastic waste individually. The maximum temperature maintained in the reactor was about 700oC. The catalytic degradation of waste PE and PP with poly-olefinic structure exhibited the liquid yield of 80-86 % and the solid yield below 2%, where as that of waste PS with polycyclic structure produced much more liquid, solid products than gases. The PVC diverted from the other plastics with the more generation of gaseous streams which included the production of HCL and with much less liquid yield. The comparison made between thermal and catalytic degradation of waste plastics for their liquefaction into fuel oils.