Conversion of Waste Plastics to Fuel Oil

Abstract

Waste plastic disposal and excessive use of fossil fuels have caused environment
concerns in the world. Both plastics and petroleum derived fuels are hydrocarbons that
contain the elements of carbon and hydrogen. The difference between them is that plastic
molecules have longer carbon chains than those in LPG, petrol, and diesel fuels. Therefore, it
is possible to convert waste plastic into fuels.
The main objectives of this study were to understand and optimize the processes of plastic
pyrolysis for maximizing the diesel range products. Pyrolysis of polyethylene (PE) and
polypropylene (PP) has been investigated both theoretically and experimentally in a lab-scale
pyrolysis reactor. The key factors have been investigated and identified. High reaction
temperature and heating rate can significantly promote the production of light hydrocarbons.
Long residence time also favor’s the yield of the light hydrocarbon products. The effects of
other factors like type of reactor, catalyst, and pressure and reflux rate have also been
investigated in the literature review.
From the literature review, the pyrolysis reaction consists of three progressive steps:
initiation, propagation, and termination. Initiation reaction cracks the large polymer
molecules into free radicals. The free radicals and the molecular species can be further
cracked into smaller radicals and molecules during the propagation reactions. β-scission is
the dominant reaction in the PE propagation reactions. There are three types of cracking
of the polymers: random cracking, chain strip cracking, and end chain cracking. The major
cracking on the polymer molecular backbone is random cracking. Some cracking occurs at
the ends of the molecules or the free radicals, which is end chain cracking. Some polymers
have reactive functional side group on their molecular backbones. The functional groups will
break off the backbone, which is chain strip cracking. Chain strip cracking is the dominant
cracking reaction during polystyrene pyrolysis. The reaction kinetics was investigated in this
study. The activation energy and the energy requirement for the pyrolysis are dependent on
the reaction process and the distribution of the final products