Fast pyrolysis of algae model compounds for bio-oil: In-depth insights into the volatile interaction mechanisms based on DFT calculations

Abstract

Fast pyrolysis of algae biomass is a promising approach to produce high value-added bio-oil, while the interaction mechanisms among the pyrolytic volatiles of algae components remain unclear. To simplify the pyrolysis process and better investigate the intermediates distribution, glucose (Glc), alanine (Ala), and glycerol (Gly) were selected as the model compounds for algae biomass. The fast pyrolysis behaviors, volatile release properties, and bio-oil compositions of model compounds and their binary mixers were performed using TG-FTIR and Py-GC/MS to reveal the volatile interaction mechanisms combined with density functional theory (DFT) calculations. Experimental results showed that co-pyrolysis of Ala with Glc and Gly displayed a synergistic effect on the weight loss and CO2 release at lower temperatures, and the volatile interactions inhibited the weight loss and CO production at higher temperatures during co-pyrolysis of model compounds. Compared with individual pyrolysis, the contents of pyrazines, furans, and pyridines in the bio-oils from co-pyrolysis of Glc+Ala, Glc+Gly, and Ala+Gly increased by 14.47%, 18.59%, and 12.07%, respectively. Ethylamine generated from Ala and small molecular aldehydes and ketones derived from Glc and Gly were the main precursors. Based on the products evolution, the possible volatile interaction pathways were proposed at the molecular level and the energy profiles were assessed by DFT calculations. Calculation results manifested that the Maillard and acetal reactions with lower free energy barriers were the initial reactions driving the formation of heterocyclic compounds. These findings could offer insights into the fast pyrolysis mechanisms of algae biomass and provide theoretical support for the feedstock and pyrolysis process optimization and the bio-oil composition regulation, thereby promoting the efficient utilization of algae.