The overexploitation of fossil fuels has precipitated a global crisis marked by resource depletion and environmental degradation. Among diverse strategies for converting biomass into biofuels, thermochemical conversion stands out as the most commercially viable approach. However, direct biomass pyrolysis faces critical challenges: excessive generation of oxygenated compounds significantly reduces fuel quality due to elevating acidity and lowering calorific value. Furthermore, biomass inherently suffers from a low hydrogen-to-carbon ratio, limiting its utility as a premium fuel.
A compounding issue arises during agricultural residue recovery, where biomass is frequently contaminated with waste polyethylene film. Intriguingly, these polyolefin plastics, rich in carbon and hydrogen, exhibit complementary properties when co-processed with biomass. Through pyrolysis, such plastics can be valorized into liquid hydrocarbons, simultaneously addressing the hydrogen deficiency of biomass and enhancing oxygen removal efficiency.
In this study, researchers from Qingdao University of Science and Technology systematically investigated the co-pyrolysis behavior and product distribution of peanut straw and polyethylene film blends. Thermogravimetric analysis results revealed distinct pyrolysis temperature intervals. Synergistic effects, quantified through experimental-theoretical deviations, demonstrated enhanced mass conversion rates and accelerated pyrolysis kinetics in blended systems. All three blend ratios demonstrate synergistic promotion effects, with the 1:7 mixture exhibiting the most pronounced enhancement.
Gas chromatography-mass spectrometry analysis of bio-oil production showed significant compositional variations. As the mass ratio of peanut straw to polyethylene increases from 1:1 to 1:7, the bio-oil yield increased systematically from 62.1% to 76.86%, accompanied by elevated alkane from 20.84% to 31.41% and olefin from 24.73% to 42.89%. The co-pyrolysis demonstrated a pronounced synergistic interaction, significantly enhancing hydrocarbon yields compared to individual component pyrolysis. This enhancement can be attributed to hydrogen radicals generated from polyethylene pyrolysis interacting with oxygen-containing compounds derived from peanut straw decomposition.
Catalytic upgrading with HZSM-5 demonstrated bifunctional optimization. The catalyst achieved selective deoxygenation through Brønsted acid sites, converting oxygenates from 20.07% to 8.85% into hydrocarbons via decarbonylation pathways. These mechanisms synergistically increased bio-oil yield to 77.08%, with hydrocarbon yields reaching 81.85% (alkanes: 35.69%; olefins: 46.16%) at the optimal ratio of 1:7. Carbon chain distribution analysis indicated a polyethylene ratio-dependent shift toward short-chain alkanes (C6-C19), with HZSM-5 intensifying this trend through selective cracking of long-chain species (C20+).
This work provides fundamental insights into heterogeneous catalysis in lignocellulose-plastic co-conversion systems, advancing circular economy paradigms for non-recyclable plastic biomass wastes. The pyrolysis mechanism was proposed to elucidate the reaction process comprehensively.
DOI
10.1007/s11705-026-2624-z