Catalytic Microwave-Assisted Co-Pyrolysis of soybean husk and HDPE: Optimization, Kinetics, and enhanced bio-oil production using ZSM-5

Abstract

Soybean husk (SH), a readily available agricultural residue, holds promise as a sustainable feedstock for biofuel production. Its abundance and potential for efficient conversion via pyrolysis make it particularly promising in renewable energy applications. The primary results of this study demonstrate that adding the ZSM-5 catalyst reduces the mean activation energy (Ea) from 209 to 187  kJ/mol, thereby facilitating the pyrolysis process. The bio-oil composition analysis revealed that the catalyst promoted the formation of cyclic hydrocarbons, increasing their proportion from 26 % to 53 %. When High-Density Polyethylene (HDPE) was added, most of the products generated were hydrocarbons, ranging from 78 % to 93 %. Additionally, an increase in pyrolysis temperature results in a decrease in phenolic compounds, highlighting the catalyst’s role in deoxygenation reaction and enhancing bio-oil quality. Optimization studies indicated that a SH to HDPE mass ratio of 3.3 and a temperature of 539 °C maximized bio-oil production during the co-pyrolysis process. However, reuse and regeneration tests reveal a decline in the catalyst’s performance after successive runs, as indicated by a reduced surface area of the catalyst, lower hydrocarbon content, and increased phenolic composition. This suggests that additional treatment during catalyst regeneration is necessary to maintain bio-oil quality. These findings underscore the potential for the use of agricultural waste and waste plastics in co-pyrolysis to produce valuable pyrolytic products. These results suggest opportunities for large-scale applications and further optimization studies.