Catalytic Microwave Pyrolysis of Lignocellulosic Biomass for Fuels and Chemicals

The undesirable properties (e.g., low heating value, high viscosity, and thermal and chemical instability) of the pyrolyzed products have prompted us to enhance the selectivity of desired products by using catalysts during biomass pyrolysis. Microwave-assisted pyrolysis (MAP) induces heating within the core of the substance through a direct energy conversion, which improves the products selectivity and energy efficiency and reduces the capital cost comparing with conventional pyrolysis. The present study evaluated the development of catalytic MAP of lignocellulosic biomass for fuels and chemicals. Metal oxides and zeolites (such as CaO, NiO, K₂CO₃, MgO, CuSO₄, AlCl₃, MgCl₂, HZSM-5) are the two types of catalysts that are most commonly used for catalytic MAP of lignocellulosic biomass. Results showed that the addition of catalysts/additives (such as activated carbon, silicon carbide, char) usually had a positive effect on heating rate and volatiles yield, and the biomass conversion rate and the products selectivity (such as phenols, guaiacols, hydrocarbons, furfural, furans contained in liquid product, H₂, CO included in syngas) were obviously improved. Technoeconomic assessments suggested that small distributed biomass energy production systems were technologically more feasible and economically more viable for MAP of biomass, and microwave-assisted ex situ catalytic pyrolysis of plants was profitable. However, before its industrial scale up, a lot of technical barriers need to be overcome for catalytic MAP of biomass, such as the design of reactor, development of cost-effective catalyst, heating uniformity, optimization of reaction conditions, kinetics study, and reaction mechanism disclosure.