(183d) Microwave Catalytic Gasification of Mixed Plastics and Corn Stover for Clean Hydrogen Production

Of the 353 million metric tons of plastic waste produced worldwide in last two decades, only 9% of plastic waste is recycled, with bulk of plastic waste either landfilled or incinerated. Recycling and upcycling plastic waste are crucial to reduce environmental pollution. Gasification is the thermochemical conversion of solid carbon feedstock at high temperatures with the gasifying agent to generate hydrogen rich syngas. Existing gasification processes are energy intensive and requires high operating temperatures > 1000℃, making the process uncommercial. Microwave heating has attracted interest in a wide range of chemical processes because of its distinct advantages over conventional heating methods, such as quick and selective heating to increase process efficiency. Our research team recently demonstrated the synergistic effects of corn stover and mixed plastics to produce hydrogen rich syngas via microwave heating [1]. To further enhance H₂ yield and increase process efficiency, this work reports the addition of magnetite as a bifunctional catalyst to co-gasify plastic and corn stover. Fe catalysts are reported to show high activity in microwave plastic conversion to hydrogen both as a catalyst and microwave energy absorber. Two different sized magnetite was used in this work. A mixture of polyethylene, polystyrene and polypropylene was used as plastic feedstock, while Corn Stover was used as biomass. The catalysts were physically mixed with plastics and biomass at 1:1:1 weight ratio before they were loaded in the reactor to initiate gasification reaction under air flow while varying parameters including temperature and WHSV. The produced gas was directly sent to GC-MS system for analysis and the spent catalysts and char were later collected for deactivation study. The fresh and spent catalysts were analyzed by TGA, BET, Raman and XRD to study catalytic effects for various reaction conditions.

A comparative study was carried out to observe the maximize H₂ yield under microwave heating vs conventional heating at similar reaction conditions. The results indicate that under microwave, magnetite produce significantly higher H₂ yields compared to conventional reactor under similar reaction conditions. XRD [2] suggested that under microwave, magnetite got reduced (Figure 1a) to supply more oxygen radicals in the reaction, which helped to crack tar further down to produce additional H₂. Magnetite, being a good microwave absorber, also helped to minimize total power input, which resulted in lower total absorbed energy per gm feedstock, as compared to conventional runs. Decrease in tar and char production was observed in microwave vs conventional run, as the H₂ yield increased (Figure 1b), suggesting efficient catalytic gasification of the biomass-plastic feedstock.

Keywords: Plastic upcycling, gasification, microwave conversion, hydrogen, energy efficiency

Reference

1. Ashraf Abedin, Xinwei Bai, Mark Smith, Pranjali Muley, Microwave-assisted co-gasification of mixed plastics and corn stover: A synergistic approach to produce clean hydrogen, Energy Conversion and Management, 280, 2023, 116774, ISSN 0196-8904
2. Gupta, Yashpal & Sharma, Vipin & Kumar B V, Manoj. Issues in Determining Size of Nano-crystalline Particles by X-ray Diffraction. Materials Today: Proceedings. 2, 2015, 3534-3538. 10.1016/j.matpr.2015.07.330.