Production of valuable chemicals through the catalytic pyrolysis of harmful oil sludge over metal-loaded HZSM-5 catalysts

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.

Thermocatalytic conversion of wood-plastic composite over HZSM-5 catalysts

Air gasification of the Wood-Plastic Composite (WPC) was performed over Ni-loaded HZSM-5 catalysts to generate H₂-rich gas. Increasing SiO₂/Al₂O₃ ratio (SAR) of HZSM-5 adversely affected catalytic activity, where the highest gas yield (51.38 wt%) and H₂ selectivity (27.01 vol%) were acquired using 20 %Ni/HZSM-5(30) than those produced over 20 %Ni/HZSM-5(80) and 20 %Ni/HZSM-5(280). Reducing SAR was also favorably conducive to increasing the acyclic at the expense of cyclic compounds in oil products. These phenomena are attributed to enhanced acid strength and Ni dispersion of 20 %Ni/HZSM-5(30) catalyst. Moreover, catalytic activity in the terms of gas yield and H₂ selectivity enhanced with growing Ni loading to 20 %. Also, the addition of promoters (Cu and Ca) to 20 %Ni/HZSM-5(30) boosted the catalytic efficiency for H₂-rich gas generation. Raising temperature indicated a positive relevance with the gas yield and H₂ selectivity. WPC valorization via gasification technology would be an outstanding outlook in the terms of a waste-to-energy platform.

Synthesis of Micromesoporous Zeolite-Alumina Catalysts for Olefin Production from Heavy Crude Oil

Maximizing the production of high-value olefins from heavy crude oil is a crucial topic in the downstream refining industry. However, converting heavier fractions is a major challenge due to the small pore size of the zeolites. Therefore, this work aimed to develop extrudate zeolite catalysts posing adequate micromesoporous pore network and moderate acidity by combining microporous zeolite with the boehmite phase of alumina. These extruded zeolite-alumina catalysts are expected to allow sufficient diffusion of heavy fractions, thus leading to high cracking of heavy oil into valuable olefins. Different zeolite-alumina catalysts of varying alumina content ranging from 25 to 75% (AlZ-25, AlZ-50, and AlZ-75) were prepared in the laboratory to study the optimum zeolite-alumina ratios for maximum olefin production from heavy oil. The catalysts were characterized for their chemical and physical properties using nitrogen adsorption (N2 adsorption), X-ray diffraction (XRD), inductively coupled plasma (ICP) spectrometry, Fourier transform infrared (FT-IR) spectroscopy, and NH3 temperature programmed desorption (TPD). A gradual increase in the average pore diameter (APD) of the catalysts was observed due to the alumina ratio with a distinct range of acidity that is in the range of 125 to 375°C, and also the geometry of pores is not the same for all of the supports. Catalytic performance tests were conducted in a fixed-bed reactor at 450°C, 10 bar, and liquid hourly space velocity (LHSV) of 1 h−1. The results revealed that the prepared catalysts were thermally stable and effective in heavy oil conversion to olefins. Moreover, the selectivity of propylene was higher than that of ethylene (P/E) due to the modified textural and acidic properties of the catalysts. The results showed that the catalysts prepared with moderate acidity and adequate mesopores exhibited a considerable effect on the conversion of heavy crude oil into olefins. Hence, the acidity and mesoporosity of the catalysts play a vital role in determining the catalyst performance.