Microwave-assisted formic acid extraction for high-purity cellulose production

The effective separation of hemicelluloses and cellulose is the prerequisite for creating high-value products using wood wastes. In this study, a novel process including mechanical pre-beating, microwave-assisted formic acid (MAFA) extraction, and bleaching treatment was developed for producing high-purity cellulose from the pulp fibers of hardwood waste. Most hemicelluloses and lignin were simultaneously removed (i.e., hemicelluloses were separated from cellulose) due to the MAFA treatment. The pulp fibers were pre-beaten for a loose fiber structure for the formic acid impregnation. The results showed that the introduction of microwave could significantly enhance hemicellulose removal and separation from pulp fibers. The MAFA treatment was performed under atmospheric pressure and mild condition (≤ 100 °C), which led to the significant increase in the lignin yield, cellulose content, crystallinity index, and crystallite homogeneity. After the beating pretreatment and MAFA process (88% formic acid, 100 °C, 4 + 4 h), the hemicellulose removal rate reached 75.5%, and the cellulose purity was as high as 93.2% along with a maximal cellulose crystallinity index (77.5%) and minimum crystallite cross-sectional area (12.40 nm²).