Synthesis of gasoline range fuels by the catalytic cracking of waste plastics using titanium dioxide and zeolite

The current study examined the carbon recycling application of waste materials. Thermal catalytic cracking reactions were carried out in a fixed bed to synthesize gasoline-range hydrocarbon fuels from used plastics. Titanium (IV) oxide (TiO2) and zeolite were tested as catalysts for pyrolysis using low-density polyethylene (LDPE), polyvinylchloride (PVC), and polystyrene (PS) reactants. In addition to the catalyzed pyrolysis reactions, we also investigated non-catalyzed thermal degradation of the plastic substrates for negative control. The liquid yield, reaction temperature profile, and physical appearance of the synthesized liquid products were determined. The pyrolysis reactions demonstrated that the optimum catalyst–polymer ratio is 40%. The distillate collection temperatures ranged between 82 and 198 °C (LDPE), 68–172 °C (PVC), and 40–168 °C (PS). Our experiments showed that LDPE, PVC, and PS can readily be pyrolyzed to produce 44% (LDPE), 13% (PVC), and 89% (PS) hydrocarbon liquid products using zeolite catalyst. Gas chromatography–mass spectrometry (GC–MS) was used to analyze the structure and chemical composition of the products. The main products were C5 (1,2-dimethylcyclopropane), C6 (2-methylpentane), C7 (1,3-dimethylcyclopentene, 1-heptene), and C8 (2-octene, 4-octene, octane, 3-ethylhexane), indicating gasoline-range hydrocarbon molecules. The highest liquid yield of 89.3% was obtained from zeolite catalyst over polystyrene in comparison to all plastics cracked while the lowest liquid yield of 3.9% was obtained from the cracking of PVC under no catalyst condition.