Sol-gel derived Ti-doped mesoporous silica–alumina: an efficient catalyst to recover energy sources from environmental hazard waste plastics

Abstract

Waste plastics have been regarded as a chronic environmental threat because of their disposal problem. If we do not find a sustainable technology for waste plastic conversion, it will cover the whole planet and collapse the ecosystem. Waste low-density polyethylene (LDPE) and high-density polyethylene were pyrolyzed over sol-gel derived silica–alumina (ASA) and Ti-doped silica–alumina (ASA + Ti) catalysts. The catalysts were calcined at 500 °C and characterized using different conventional techniques, e.g., XRD, FTIR, TG/DTA, SEM, EDS, and BET. Based on characterization, it can be predicted that the nanoparticles are formed of rings via Si–O–M (Al or Ti) linkages, which improved their thermal stability and catalytic activity. The polymer and catalyst were taken at an optimized ratio of 25 m m−1 in a batch reactor for degradation. The Ti-doped silica–alumina catalyst showed the maximum conversion (96%) and gasoline selectivity (45.33%) at comparatively low temperatures (376 °C). The highest specific surface area, uniform mesoporosity, and bimetallic skeleton of the Ti-doped catalyst helped to achieve the best performance. The obtained liquid product comprised both branched aliphatic and aromatic hydrocarbons. The obtained result proves that the catalytic pyrolysis of polyolefin generally advances through carbonium ions, where the catalyst acts as a Lewis acid and Lewis base consecutively. Moreover, the synthesized catalyst plays a significant role in isomerization, cyclization, and aromatization reactions. Sources of approximately 44.13 MJ of energy can be recovered from 1 kg of postconsumer waste plastic. This waste-to-fuel technology should be commercialized because it is eco-friendly and cost-effective. Graphical abstract: [Figure not available: see fulltext.].