Comparative evaluation of microwave-assisted acid, alkaline, and inorganic salt pretreatments of sugarcane bagasse for sugar recovery

Microwave heating technology has attracted great attention in biorefineries to generate biofuels and biomass-derived chemicals. NaOH and H2SO4 pretreatments are often applied to improve the process efficiency. Traditional heating pretreatments require long reaction times and contribute to rapid sugar degradation. Although effective, H2SO4 pretreatment suffers from the disadvantages of equipment corrosion, inhibitors generation, and waste water production. Herein, we performed NaOH, H2SO4, and FeCl3 pretreatments on sugar cane bagasse under microwave heating, and compared their effects on the biomass physical features, chemical compositions, and sugar release during pretreatment process. Our results showed that high amounts of sugar were obtained, and xylose and glucose were selectively recovered in the pretreatment liquor within 5–10 min of microwave heating by changing pretreatment media. NaOH efficiently fractionated biomass, generated xylose as the major product in pretreatment liquor, and left the solid residue more digestible. H2SO4 and FeCl3 effectively degraded both the hemicellulose and cellulose, producing glucose as the major product in the pretreatment liquor. Compared with H2SO4, FeCl3 pretreatment more efficiently removed lignin and recovered 48% glucose within only 5 min. Biomass chemical composition and morphological characteristics were studied and compared, confirming that microwave assisted FeCl3 pretreatment is a new and feasible approach to replace H2SO4 for biofuel and biomass-derived chemicals production.