Torrefaction of Cassava Rhizome to Produce High-Grade Solid Biofuels

Abstract

This research studied solid fuel production from cassava rhizome by torrefaction technology to enable its use in the energy sector. Cassava rhizomes (CR) were treated at a temperature range of 250–300 °C under a nitrogen atmosphere. The residence time was 30 minutes. The solid products were characterized in terms of their fuel properties and functional groups, including mass and energy yield, energy densification, ash content, ultimate analysis, and calorific value. In addition, the functional groups of organic compounds were identified by the Fourier transform infrared spectroscopy technique, and the Van Krevelen diagram was used for comparisons of the fuel properties with coal. The results indicated that pretreatment using torrefaction had a significant impact on the quantity and physicochemical properties of the solid product. The torrefied-CR at 300 °C had the lowest mass yield (47.6%), energy yield (66.4%), and content of oxygen (22.0%), however, resulting in the highest calorific value (24.81 MJ/kg), energy densification (1.4), and content of carbon (62.51%). The calorific value of solid products ranged from 18 to 24 MJ/kg, showing an increase of 6% to 39% compared to the raw biomass. The peak of C–O and C=O stretching in hemicellulose began to disappear at temperatures above 275 °C. When the torrefaction temperature was increased to 300 °C, the ash content slightly increased from 6.18% to 8.76%. Moreover, the oxygen-to-carbon and hydrogen-to-carbon ratios of solid products decreased to become close to lignite coal. The results indicated torrefaction is a pretreatment method for converting cassava rhizome into high-grade biofuel.