Enhancement of fuel and physicochemical properties of canola residues via microwave torrefaction

Abstract Conversion of low value agricultural residues to better-quality products e.g. biofuel, bioproducts can solve the issues related to energy crisis as well as environmental challenges. Torrefaction, a thermochemical pretreatment was employed on canola residue (CR) to augment the physicochemical properties of biomass for heat and energy applications. In the present study, the effects of microwave torrefaction on canola residue have been investigated for the following operating parameters: microwave power (250–450 W), residence time (10–20 min), and feeding load (70–110 g). Box Behnken design method was used to design the experiments and find the interaction between process parameters. Both mass and energy yields diminished with rise in microwave power and torrefaction reaction time. The results show that the carbon content significantly increased with degree of torrefaction while oxygen content had a reverse trend, therefore the atomic ratio of torrefied biomass reduced remarkably. Torrefied biomass shows higher carbon percentages than that for the bituminous coal. In addition, a noticeable decrease in volatile matter was observed with growth in torrefaction severity and thus increased fixed carbon content. The higher heating value (HHV) was boosted up by 26% (promoted from 17.8 MJ/kg to 22.4 MJ/kg). HHV of highly torrefied canola residue is very close to bituminous coal. Fourier transform infrared spectroscopy (FTIR) analysis showed that surface functional groups for example O H, C H, and C O decreased with torrefaction severity indicating the improvement of hydrophobicity of torrefied biomass. Scanning electron microscopy (SEM) results represent a more porous structure at highest torrefaction conditions which happened due to thermal cracking and decomposition of lignin and decreased the grinding energy by 89% compared to that for raw biomass. Moreover, inductively coupled plasma-mass spectrometry (ICP) analysis data showed that concentrations of minerals, alkaline and other essential element amplified with degree of torrefaction. The influence of microwave power was the highest on properties of torrefied biomass, followed by residence time and feeding load. The optimum torrefaction conditions were found at 450W with 90 g feeding load for residence time of 20 min.