High-value products from chickpea residues by thermal pyrolysis and its environmental impacts

Abstract

High value products could be obtained from chickpea residues (CR) by thermal pyrolysis. Biomass was previously characterized in terms of chemical composition and thermal behavior by elemental analysis, infrared spectroscopy (FTIR) and thermogravimetric studies. From temperature effect on products, 500 °C showed the highest yield to bio-oil (44 wt%). While higher temperatures promoted gas emissions from secondary cracking reactions. At this temperature, hydrocarbons, furans and alcohols, considered as desirable molecules, were improved in the liquid. From them, 2,5-dimethylfuran (DMF) showed an important production. This compound is considered a second-generation biofuel. In the gases, CO2 was the most emitted compound at this temperature, followed by CO from the thermal decomposition of cellulose and hemicellulose. On the other hand, CH4 emission is caused by the degradation of lignin and its concentration increases with temperature. In addition, volatile organic compounds (VOCs) in the gas phase, including toluene, 2-methylbutanal, 3-methylbutanal, 2-methylfuran, octane, 2-octene, dimethyl disulfide and 4-methylpentanenitrile, were identified under the experimental conditions in this study. The solid product, bio-char, shows useful properties including a Higher Heating Value (HHV) of 19.19 MJ/kg and a functional composition analyzed by FTIR and X-ray photoelectron spectroscopy (XPS) with a higher proportion of non-oxygenated groups. It could be considered for energy production, soil amendment and water or air treatment. Its highest yield (43 wt%) was obtained at 400 °C. Therefore, the three reaction products of CR pyrolysis reported several value-added compounds from renewable sources of great interest for industrial and chemical purposes.