Microwave dielectric properties of Malaysian palm oil and agricultural industrial biomass and biochar during pyrolysis process

Abstract

Advancement in the design and development of microwave (MW) processing technology greatly depends on the knowledge of dielectric properties. This study is dedicated to provide new and useful data on the dielectric properties of five different types of biomass generated from Malaysian agricultural (oil palm shell, empty fruit bunch, rice husk, and coconut shell) and wood (sawdust) based industries. The dielectric properties were measured from room temperature to ~ 700 °C and at six different frequencies (397 MHz, 912 MHz, 1429 MHz, 1948 MHz, 2466 MHz, and 2986 MHz) using a cavity perturbation method. The dielectric properties (dielectric constant and loss factor) dropped slightly in the drying region (24 °C to 200 °C) due to removal of moisture and further it decreased in the pyrolysis region (200 °C to 450 °C) due to decomposition or removal of volatile matter. However, dielectric properties increased drastically beyond temperature 450 °C. Minimum MW absorption (maximum penetration depth) was observed in temperature range of 300 to 400 °C. Biochar which was formed after the pyrolysis process, showed high loss tangent as compared to the original biomass, suggesting it as a suitable material for MW absorber and catalyst applications. Thus, the data can be used to design and simulate MW biomass processing system for large scale application, assisting with selection of frequency and optimization of process parameters and system dimensions.