Analytical and experimental study of switchgrass and agricultural plastic co-pyrolysis in a microwave reactor

Authors: Ellison, Candice; Mullen, Charles; Elkasabi, Yaseen

Submitted to: Fuel
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2025
Publication Date: 9/17/2025
Citation: Ellison, C.R., Mullen, C.A., Elkasabi, Y.M. 2025. Analytical and experimental study of switchgrass and agricultural plastic co-pyrolysis in a microwave reactor. Fuel. 406. https://doi.org/10.1016/j.fuel.2025.136771.
DOI: https://doi.org/10.1016/j.fuel.2025.136771

Interpretive Summary: Thermochemical conversion of biomass via pyrolysis can produce valuable renewable liquid fuels and chemicals from agricultural residues; however, the crude pyrolysis liquid product, bio-oil, is highly oxygenated, requiring upgrading to meet the specifications of petroleum-based liquids. Co-feeding plastic wastes, which are low in oxygen, with biomass can effectively reduce the oxygen content of the produced pyrolysis oil. Further, process electrification by microwave heating can enable the use of renewable energy, which is becoming increasingly available in rural locations. Compared to traditional heating, microwave heating can shorten processing times and improve energy efficiency compared to traditional heating, due to the unique heating mechanism of microwave. This article presents experimental results from microwave co-pyrolysis of switchgrass and waste polyethylene hay bale covers. In addition to pyrolysis oil, production of a waxy fraction resulted from the addition of plastic, which was subsequently converted into pitch which was analyzed for its potential as a coke precursor to further the applicability of the wax product.

Technical Abstract: This work describes initial results from microwave co-pyrolysis of switchgrass and agricultural plastic waste in the form of polyethylene (PE) hay bale covers. Analytical pyrolysis and thermogravimetric analysis (TGA) were used to better understand the volatile composition and thermal decomposition behavior during co-pyrolysis. Experimental microwave pyrolysis was carried out in a 1.2 kW multimode microwave cavity to pyrolyze 100 g of feedstock mixed with activated carbon absorber at different temperatures (350, 400, 500, 550, and 600 °C) and the product compositions were analyzed. The liquid and wax product compositions were found to have an additive effect, where switchgrass mainly contributed to the liquid fraction and PE mainly contributed to the hydrocarbon fraction. The greatest recovery of condensable organics was obtained at 400 °C with a greater proportion of organic liquids and 600 °C with a greater proportion of waxes. Further, the waxy fraction was converted into pitch to investigate a potential high value application for this fraction that is difficult to thermally decompose.