Microwave pretreatment of biomass for conversion of lignocellulosic materials into renewable biofuels

Abstract

For the conversion of lignocellulosic material into renewable biofuels the microwave pretreatment of raw material is a new and promising technology. This work presents a numerical simulation of microwave heating of materials derived from sugar cane, african palm and green algae in microwave domestic oven. The power absorption of biomasses is studied in cylindrical and spherical shapes, with volumes varying from 10−5 m3 to 100 × 10−5 m3, as function of humidity (from 20% to 80%). Maxwell equations were employed to calculate the microwave electromagnetic field distribution in the microwave cavity and in the samples, coupled to heat equation when the humidity is varied. Penetration depth varied from 2 × 10−2 to 10 m and tanδ from 2 × 10−3 to 7 × 10−1 as function of humidity. Plots of electric field and temperature distribution inside the oven were done for sugar cane, palm oil and green algae for cylindrical and spherical samples for 30% and 65% of humidity in the samples. The coefficient of variation (COV) varied between 0.05 and 0.18. The rate of heating efficiency was evaluated using the degree of thermal runaway ΔT (5K<ΔT<75K) and evolution of average temperature T‾ (300K<T‾<370K) and their relationship with the energy absorbed by the samples and COV, respectively. The comprehensive evaluation coefficient, that describes the usability of a specific lignocellulosic material in industry, varied between 0.3 and 10.0, was calculated for the biomasses shapes and sizes as function of power and humidity.