Currently, the conversion of waste plastics into high-value products via catalytic pyrolysis enables the advancement of plastics’ open-loop recycling. However, enhancing selectivity remains a critical challenge. This study introduces a novel approach to catalytic pyrolysis, utilizing a combination of MCM-41 and modified gallium-based HZSM-5 catalysts, to achieve exceptional selectivity for aromatic liquid-phase products from linear low-density polyethylene. Firstly, to enhance the probability of dehydroaromatization optimization, the type and proportion of metal active sites within the HZSM-5 catalyst are fine-tuned, which would establish equilibrium with acid sites, resulting in a remarkable 15.72% increase in the selectivity of aromatic hydrocarbons. Secondly, to enhance the accessibility of volatiles to active sites, mesoporous MCM-41 with cracking capabilities is introduced. The doping ratio of MCM-41 is meticulously controlled to facilitate the diffusion of cracked volatiles to the active centers of modified gallium-based HZSM-5, enabling efficient reforming reactions. Experimental findings demonstrate that MCM-41 significantly enhances the dehydroaromatization activity of the modified gallium-based HZSM-5 catalyst. Under the influence of MCM-41:Zr₂Ga₃/HZSM-5 = 1:2 catalyst, the selectivity for aromatic hydrocarbons reaches an impressive 93.11%, with a notable 60.01% selectivity for benzene, toluene, ethylbenzene, and xylene. Lastly, this study proposes a plausible pathway for the generation of high-value aromatic hydrocarbons using the combined catalyst.

Separating monomeric cycloalkanes from naphtha obtained from direct coal liquefaction not only facilitates the valuable utilization of naphtha but also holds potential for addressing China’s domestic chemical feedstock market demand for these compounds. In extractive distillation processes of naphtha, relative volatility serves as a crucial parameter for extractant selection. However, determining relative volatility through conventional vapor-liquid equilibrium experiments for extractant selection proves challenging due to the complexity of naphtha’s compound composition. To address this challenge, a prediction model for the relative volatility of n-heptane/methylcyclohexane in various extractants has been developed using machine-learning quantitative structure-property relationship methods. The model enables rapid and cost-effective extractant selection. The statistical analysis of the model revealed favorable performance indicators, including a coefficient of determination of 0.88, cross-validation coefficient of 0.94, and root mean square error of 0.02. Factors such as α, E_HOMO, ρ, and logP_oct/water collectively influence relative volatility. Analysis of standardized coefficients in the multivariate linear regression equation identified density as the primary factor affecting the relative volatility of n-heptane/methylcyclohexane in the different extractants. Extractants with higher densities, devoid of branched chains, exhibited increased relative volatility compared to their counterparts with branched chains. Subsequently, the process of separating cycloalkane monomers from direct coal liquefaction products via extractive distillation was optimized using Aspen Plus software, achieving purities exceeding 0.99 and yields exceeding 0.90 for cyclohexane and methylcyclohexane monomers. Economic, energy consumption, and environmental assessments were conducted. Salicylic acid emerged as the most suitable extractant for purifying cycloalkanes in direct coal liquefaction naphtha due to its superior separation effectiveness, cost efficiency, and environmental benefits. The tower parameters of the simulated separation unit provide valuable insights for the design of actual industrial equipment.

With the advantages of low raw material cost and 100% atom utilization, the synthesis of high value-added chemical product cyclic carbonates by the cycloaddition of CO₂ to epoxides has become one of the most prospective approaches to achieve the industrial utilization of CO₂. In the reported catalytic systems, the complexity of the catalyst synthesis process, high cost, separation difficulties, and low CO₂ capture limit the catalytic efficiency and its large-scale application. In this paper, Ag nanoparticles loaded on polyethyleneimine (PEI)-modified UiO-66-NH₂ (Ag/PEI@UiO-66-NH₂) are successfully synthesized by in situ immersion reduction. The Ag nanoparticles and the amino groups on the surfaces of PEI@UiO-66-NH₂ contribute to the adsorption of CO₂ and polarization of C–O bonds in epoxides, thereby boosting the conversion capability for the CO₂ cycloaddition reaction. At the amount of propylene oxide of 0.25 mol and the catalyst dosage of 1% of the substrate, the yield and selectivity of propylene carbonate are up to 99%. In addition, the stability and recyclability of Ag/PEI@UiO-66-NH₂ catalyst are attained. The Ag/PEI@UiO-66-NH₂ catalyst also demonstrates a wide range of activity and distinctive selectivity toward cyclo-carbonates in the cycloaddition of CO₂ to epoxides. This work provides a guide to designing a highly efficient catalyst for in situ capture and high-value utilization of CO₂ in industrial applications.

Under optimal process conditions, pyrolysis of polyolefins can yield ca. 90 wt % of liquid product, i.e., combination of light oil fraction and heavier wax. In this work, the experimental findings reported in a selected group of publications concerning the non-catalytic pyrolysis of polyolefins were collected, reviewed, and compared with the ones obtained in a continuously operated bench-scale pyrolysis reactor. Optimized process parameters were used for the pyrolysis of waste and virgin counterparts of high-density polyethylene, low-density polyethylene, polypropylene and a defined mixture of those (i.e., 25:25:50 wt %, respectively). To mitigate temperature drops and enhance heat transfer, an increased feed intake is employed to create a hot melt plastic pool. With 1.5 g·min^–1 feed intake, 1.1 L·min^–1 nitrogen flow rate, and a moderate pyrolysis temperature of 450 °C, the formation of light hydrocarbons was favored, while wax formation was limited for polypropylene-rich mixtures. Pyrolysis of virgin plastics yielded more liquid (maximum 73.3 wt %) than that of waste plastics (maximum 66 wt %). Blending polyethylenes with polypropylene favored the production of liquids and increased the formation of gasoline-range hydrocarbons. Gas products were mainly composed of C₃ hydrocarbons, and no hydrogen production was detected due to moderate pyrolysis temperature.

Microwave-assisted pyrolysis is an effective method for recycling plastic wastes into oils that can be used for aviation fuels. In this study, energy and economic analyses of aviation oil production from microwave-assisted pyrolysis of polystyrene were performed. The total energy efficiency, recovered energy efficiency, unitary cost, unitary energy economic cost, relative cost difference, and energy economic factor were detailed. And the effects of microwave power, pyrolysis temperature, microwave absorbent loading, and microwave absorbent type on these parameters were covered. It was found that pyrolysis temperature has the most significant effect on the unitary cost and unitary energy economic cost of aviation oil, and-microwave absorbent type has a significant influence on energy economic factor during the whole microwave-assisted pyrolysis process. The optimum reaction conditions at the tonnage system for pyrolysis of 1 t polystyrene were microwave power of 650 W, pyrolysis temperature of 460 °C, and silicon carbide (microwave absorbent) at a loading of 2 t (twice than feedstock loading). At these optimal conditions, the total energy efficiency, recovered energy efficiency, unitary cost, unitary energy economic cost, relative cost difference, and energy economic factor were 62.78%, 96.51%, 3.21 × 10⁴ yuan·t^–1, 779 yuan·GJ^–1, 1.49, and 71.02%, respectively.