First characterization of the ecotoxicity of paraffin particles: assessment of biochemical effects in the marine polychaete Hediste diversicolor

Recent advances in liquid fuel production from plastic waste via pyrolysis: Emphasis on polyolefins and polystyrene

The management of plastic waste (PW) has become an indispensable worldwide issue because of the enhanced accumulation and environmental impacts of these waste materials. Thermo-catalytic pyrolysis has been proposed as an emerging technology for the valorization of PW into value-added liquid fuels. This review provides a comprehensive investigation of the latest advances in thermo-catalytic pyrolysis of PW for liquid fuel generation, by emphasizing polyethylene, polypropylene, and polystyrene. To this end, the current strategies of PW management are summarized. The various parameters affecting the thermal pyrolysis of PW (e.g., temperature, residence time, heating rate, pyrolysis medium, and plastic type) are discussed, highlighting their significant influence on feed reactivity, product yield, and carbon number distribution of the pyrolysis process. Optimizing these parameters in the pyrolysis process can ensure highly efficient energy recovery from PW. In comparison with non-catalytic PW pyrolysis, catalytic pyrolysis of PW is considered by discussing mechanisms, reaction pathways, and the performance of various catalysts. It is established that the introduction of either acid or base catalysts shifts PW pyrolysis from the conventional free radical mechanism towards the carbonium ion mechanism, altering its kinetics and pathways. This review also provides an overview of PW pyrolysis practicality for scaling up by describing techno-economic challenges and opportunities, environmental considerations, and presenting future outlooks in this field. Overall, via investigation of the recent research findings, this paper offers valuable insights into the potential of thermo-catalytic pyrolysis as an emerging strategy for PW management and the production of liquid fuels, while also highlighting avenues for further exploration and development.

Catalytic pyrolysis of harmful plastic waste to alleviate environmental impacts

Wax is a detrimental byproduct of plastic waste pyrolysis causing challenges upon its release into the environment owing to persistence and potential toxicity. In this study, the valorization of wax materials through conversion into BTEX (i.e., benzene, toluene, ethylbenzene, and xylene) was achieved via catalytic pyrolysis using zeolite-based catalysts. The potential of two types of waxes, spent wax (SW), derived from the pyrolysis of plastic waste, and commercial paraffin wax (PW), for BTEX generation, was investigated. Using HZSM-5, higher yields of oil (54.9 wt%) and BTEX (18.2 wt%) were produced from the pyrolysis of SW compared to PW (32.3 and 14.1 wt%, respectively). This is due to the improved accessibility of lighter hydrocarbons in SW to Brønsted and Lewis acid sites in HZSM-5 micropores, promoting cracking, isomerization, cyclization, Diels-Alder, and dehydrogenation reactions. Further, the use of HZSM-5 resulted in significantly larger yields of oil and BTEX from SW pyrolysis compared to Hbeta and HY. This phenomenon is ascribed to the well-balanced distribution of Brønsted and Lewis acid sites and the identical geometric structure of HZSM-5 micropores and BTEX molecules. The addition of Ga to HZSM-5 further led to 2.24% and 28.30% enhancements in oil and BTEX yields, respectively, by adjusting the acidity of the catalyst through the introduction of new Lewis acid sites. The regeneration of the Ga/HZSM-5 catalyst by removing deposited coke on the spent catalyst under air partially recovered catalytic activity. This study not only offers an efficient transformation of undesirable wax into valuable fuels but also provides an environmentally promising solution, mitigating pollution, contributing to carbon capture, and promoting a healthier and more sustainable environment. It also suggests future research directions, including catalyst optimization and deactivation management, feedstock variability exploration, and techno-economic analyses for sustainable wax conversion into BTEX via catalytic pyrolysis.