Technical challenges in scaling up the microwave technology for biomass processing

Microwave (MW)-assisted heating is one of the emerging technologies for biomass conversion into energy, fuels, and chemicals. It is claimed to be energy efficient, time-saving, and improves throughput compared to conventional processing systems mainly due to its unique heating nature. Yet, the issues hindering the scale-up of MW biomass processing technology has not been discussed much in the open literature. Previous review articles have mainly focused on the pyrolysis process parameters and product yields. This paper aims to present the challenges faced to scale-up the MW technology for biomass processing. The effects of materials’ dielectric properties and penetration depth, MW hotspots and non-thermal effects, MW absorbers and catalysts, temperature, sample size, retention time and MW power on product characteristics are addressed in detail. Importantly, energy analysis, batch vs continuous MW operation, and reactor/cavity design are presented to advance the scale-up of MW technology for processing a wide variety of biomass wastes. The article also covers different biomass thermo-chemical processes such as pyrolysis, gasification, liquefaction and torrefaction.