Efficient preparation of 5-hydroxymethylfurfural from cellulose via one-step combination of mechanical and chemical pre-treatment

In this study, an innovative method for the high-efficiency production of 5-hydroxymethylfurfural (5-HMF) from cellulose were developed, overcoming the inherent recalcitrant physicochemical properties of cellulose. The method initiated with the ultra-high-pressure homogenization (UHPH) of a cellulose and formic acid mixture. This pre-treatment could highly enhance the 5-HMF yield compared with the reported pretreatment method. Following this, a catalytic system comprising a metal-based ionic liquid, 1-butyl-3-methylimidazole chloroaluminate ([BMIM][AlCl4]) and acetic acid, was utilized to transform the pre-treated cellulose into 5-HMF. Reaction parameters such as temperature, duration, DMSO concentration, cellulose substrate amount, and the balance of ILs and organic acids were optimized to obtain the highest yield of 5-HMF. Besides, a combination of experimental characterization methods with quantum chemical calculations, aiming to elucidate the pre-treatment mechanisms was conducted. The integration of formyl groups into the cellulose structure and the intense shear forces applied during UHPH were observed. These factors contributed to disrupting the cellulose's chemical stability, reducing particle size, and shifting cellulose's structure towards a blend of crystalline cellulose and amorphous forms with decreasing crystallinity. These changes collectively heightened the reactivity of cellulose for subsequent catalytic transformations, fostering more effective interactions between the catalyst and substrate and thereby elevating the efficiency of cellulose conversion to 5-HMF.