Catalytic Microwave-Assisted Pyrolysis of the Main Residue of the Brewing Industry

Abstract

Most agro-industrial wastes are lignocellulosic biomass. Several technologies have been developed to convert these residues to value-added products. Among these processes, pyrolysis refers to the thermal degradation of organic materials. Microwave-assisted pyrolysis (MAP) is more advantageous than conventional pyrolysis because it offers time savings, increases heating efficiency, and promotes a more precise process control. In this work, the microwave-assisted pyrolysis (MAP) of brewer’s spent grain (BSG), the main waste of the brewing industry, was studied, focusing on its liquid product. The effects of temperature, moisture content, and catalyst (calcium oxide) percentage on the product distribution and hydrocarbon content in the liquid product obtained were investigated. Although a high liquid yield of 71.8% was achieved with a BSG moisture content of 14%, the quality of the product (hydrocarbon yield) in this condition was not so attractive (21.60%). An optimization study was carried out to simultaneously maximize bio-oil yield and quality. The optimum conditions obtained were a temperature of 570 °C and a catalyst/biomass ratio of 12.17%. The results of the liquid product composition at the optimum point are promising given the presence of aromatic hydrocarbons, organic compounds of great interest to the industry.