Sustainable conversion of agricultural waste: bio-oil production from castor stalk via pyrolysis

Abstract

This study investigates the potential of castor stalk, an abundant agricultural residue in Gujarat, India, as a feedstock for sustainable bioenergy production through pelletization and pyrolysis. The castor stalk was processed and characterized to determine its proximate and ultimate composition, bulk density, and higher heating value. Pelletization significantly enhanced the energy density from 2665.66 MJ.m-3 to 7406.12 MJ.m-3. Pyrolysis experiments were conducted in a batch-scale pyrolyzer across a temperature range of 400 °C to 600 °C. The optimal temperature for maximum bio-oil yield (42.80 wt. %) was found at 450 °C, accompanied by bio-char (33.60 wt. %) and pyro-gas (23.60 wt. %) production. Gas chromatography analysis revealed the presence of energy-rich gases such as H2, CO, and CH4 in the pyro-gas, with a maximum higher heating value of 14.80 MJ m-3. The bio-char exhibited both favourable fuel properties and potential for use in agriculture and industrial applications. Overall, the study demonstrates the viability of castor stalk as a cost-effective and renewable biomass source for thermochemical conversion into valuable biofuels.