WITHDRAWN- Mechanisms for Fast Co-pyrolysis Initial Reactions of Rice Straw and Polystyrene Explored Using A Pyroprobe Integrated With an Ion Trap Mass Spectrometer

Co-pyrolysis of rice straw with hydrogen atom-rich polystyrene is a promising approach to improve bio-yield and quality, alleviate the dependency on crude oil-derived fuels and products, and contribute to waste management. Optimization of the co-pyrolysis process requires structural identification of initial co-pyrolysis products and molecular-level understanding of reactions producing these products. This study employed a pyroprobe directly integrated with a linear quadrupole ion trap (LQIT) and LQIT/Orbitrap tandem mass spectrometers having an atmospheric pressure chemical ionization (APCI) source to decipher the identities of initial fast co-pyrolysis products of rice straw and polystyrene. This analytical approach, not involving gas chromatography, facilitates rapid cooling of the initial products and their immediate ionization by APCI for further analysis. Quantum chemical calculations were employed to elucidate the likely co-pyrolysis reaction mechanisms. Different blending ratios of (rice straw: polystyrene, by wt.%) were used to perform co-pyrolysis experiments. Detected initial co-pyrolysis products of blends were similar to products formed via individual pyrolysis of either rice straw or polystyrene. Co-pyrolysis at blending ratios 90:10, 85:15, and 70:30 synergistically enhanced the production of furan-related compounds (e.g., 5-hydroxymethylfurfural) and monoaromatic hydrocarbon compounds (styrene and 2-phenyl-1,3-butadiene). This occurred probably due to intermolecular H atom transfer reactions between intermediates derived from polystyrene and rice straw during co-pyrolysis, based on calculations. Proposed co-pyrolysis reaction mechanisms involved both concerted (e.g., dehydration, pinacol rearrangement, etc.) and free radical reactions. Along with the blending ratio, operating parameters, i.e., final temperature, heating rate, and final temperature holding time, were found to influence the distribution of co-pyrolysis products significantly.