Metal-doped high silica ZSM-5 nanocatalyst for efficient conversion of plastic to value-added hydrocarbons

Current methods for plastic waste recycling: Challenges and opportunities

The practical use of plastics has rapidly increased owing to their superior physicochemical properties. Despite their excellent physicochemical properties, the short lifespan of plastics has inevitably led to a substantial generation of plastic waste. As such, strategic mitigation of the hazardous potential of plastic waste has been regarded as significant in waste management. In particular, establishing a reliable recycling platform for packaging plastic waste is of great importance considering its massive generation. To identify a strategic means of abating the hazardous potential of plastic waste, legislative enactment for their legal management must also be implemented. This review emphasizes the mechanical and chemical recycling methods for polyethylene, polypropylene, polyethylene terephthalate, polystyrene, and polyvinyl chloride, and discusses a technical platform for converting plastic waste into value-added chemical products. This study also offers a perspective on sustainable valorization as a practical alternative to circular resources.

Optimization of process parameters of catalytic pyrolysis using natural zeolite and synthetic zeolites on yield of plastic oil through response surface methodology

This study aims to reach a sustainable solution for waste management of medical plastics through value-added product extraction. It uses the DOE technique to examine the effect of natural zeolite and synthetic Al2O3 and SiO2 as catalysts. A small lab-scale pyrolysis setup was used for medical plastic waste management treatment. Pyrolysis of medical plastics with temperature range (350-450 °C), three catalysts, and wt.% are examined. This process is designed for 3 factors and 3 levels, such as type of catalyst, catalyst wt.%, and temperature, to create an L9 orthogonal array. At the same time, the heating rate and residence time are maintained constant at 5 °C/min and 75 minutes, respectively. Furthermore, this study analyzed the input variables in catalytic pyrolysis using response surface methodology. As a result of the study, generating the regression equation for oil yield, F and P values assure the model is significant. Optimization result shows the type of catalyst, temperature, and catalyst concentration values are found as aluminum oxide, 376 °C, and 6.6 wt.%, respectively. HDPE and LDPE oil yield a value of 58.3648 and 61.2051 wt%, respectively, under the optimum variables condition. For oil yield prediction, HDPE and LDPE's correlation coefficient (R2) were 0.9949 and 0.9943, respectively. Authentication of the model response using a regression equation validated with the experimental result shows good agreement. The produced medical plastic oil has a density, viscosity, flash & fire point, carbon residue, and cetane number 904 kg/m3, 2.3 cSt, 42 & 45 °C, 7.1 wt.% and 51 respectively. Finally, this study concludes that plastic oil extraction from medical waste through catalytic pyrolysis can be a potential source of alternative fuels in IC engines. Priority to optimization and low-cost catalysts highlights medical plastics waste management under the socio-economic model.

Catalytic reforming of polyethylene pyrolysis vapors to naphtha range hydrocarbons with low aromatic content over a high silica ZSM-5 zeolite

In this study, the microwave-assisted pyrolysis coupled with ex-situ catalytic reforming of polyethylene for naphtha range hydrocarbons, with low aromatic content, was investigated. Experimental results revealed that ZSM-5 zeolites with low SiO₂/Al₂O₃ ratios led to high aromatic selectivity, while an extremely high SiO₂/Al₂O₃ ratio significantly reduced the aromatic selectivity. The high selectivity of C5-C12 hydrocarbons (98.9 %) with low selectivity of C5-C12 aromatics (28.5 %) was obtained over a high silica ZSM-5 zeolite at a pyrolysis temperature of 500 °C, catalytic cracking temperature of 460 °C, and a weight hourly space velocity of 7 h^-1. The liquid oil produced was mainly composed of C5-C12 olefins that can be easily converted into paraffin-rich naphtha by hydrogenation or hydrogen transfer reactions as the feedstock for new plastic manufacturing. 8 cycles of regeneration-reaction cycles were carried out successfully with little change on the product distribution, showing the great potential for continuous production of low-aromatic liquid oil. Catalyst characterization showed that the catalyst deactivation was primarily caused by coke deposition (approximately 16.0 wt%) on the surface of the catalysts, and oxidative regeneration was able to recover most of the pore structure and acidity of the zeolite by effectively removing coke. This study provides a better understanding for the plastic-to-naphtha process and even for scale-up studies.