Progress on technologies and mechanism of furfural production from lignocellulose catalyzed by acids

Abstract: Furfural is an important high value-added platform chemical derived from lignocellulosic biomass. Domestic and foreign scholars launched various studies of furfural production from biomass, especially in the field of acid catalyzed hydrolysis. In this study, it was reviewed that the progress on technologies and mechanism of furfural production from lignocellulose catalyzed by acids, especially diluted Br?nsted acid. The progress status of traditional one-step furfural production technologies was summarized at first, and the problem of large amount of waste water treatment in traditional furfural industry was analyzed. To solve the shortages of one-step technologies, different types of two-step technologies were proposed to achieve the saccharides of hemicellulose to C5 sugars and the dehydration of C5 sugars to furfural separately. The first step of two-step technology was similar to the pretreatment in cellulose ethanol technology, so researchers mainly focus on the second step of furfural preparation from C5 sugars. They invented new methods (such as new solvent systems and catalysts) to increase furfural yields, or improve the economic efficiency of reaction progress by applying effective heating methods or by transferring furfural from reaction system as soon as its generation. In this section, methods of ionic liquid solvent, solid acid catalyst, microwave-assisted heating, organic solvent extraction, supercritical carbon dioxide extraction were studied. Then the new and hot technologies of simultaneous production of furfural and cellulose-derived chemicals, such as 5-hydroxymethylfurfural and levulinic acid were described and evaluated. In the second part, the reaction kinetics of xylose and lignocellulosic biomass catalyzed by diluted Br?nsted acids were comprehensively analyzed, and the research progress of related mechanisms was depicted. It was concluded that the kinetic models of the furfural production from lignocellulose were significantly influenced by the acid concentration and temperature. Under higher acid concentration and temperature, the kinetic model was more simple, and close to the "xylose-furfural-degradation products" path or the "xylan-xylose-furfural" path. In the third part, both the mechanisms of furfural generation from xylose and by-products generation from furfural were introduced. In the fourth part, due to Lewis acid catalysis was confirmed important and effective for xylose isomerization to xylulose, and xylulose conversion into furfural was more easier, we summarized the progress and mechanism of xylose conversion into furfural catalyzed by Lewis acid, such as FeCl3, SnCl4 and LiCl. Finally, the research status of the solvent effects in acid/organic solvent reaction systems was concluded, and due to quantum chemistry was used in platform chemical production progress recently, the application of related software was introduced, such as GROMACS. This paper aimed to provide sufficient information for relative scholars to carry out research on furfural production from biomass, and to help scholars to conduct selective research.