Simultaneous conversion of C5 and C6 lignocellulosic polysaccharides to platform chemicals through microwave-assisted hydrolysis

Lignocellulosic biomass consists for ca. 70% of polysaccharides (cellulose microfibrils and hemicellulose) and ca. 30% lignin. Therefore, it is a valuable source for platform chemical production from polysaccharides. Even though biomass is relatively cheap and readily available, it is still a major challenge to break down the energy rich polysaccharides into platform chemicals that can be used in further processes. In this research, the possibility of microwave-assisted acid hydrolysis to convert lignocellulosic polysaccharides into platform chemicals (i.e. HMF and furfural) was investigated. A biphasic reaction system is applied to prevent the rapid rehydration of hydroxymethylfurfural (HMF) to levulinic acid and avoid polymerization to disperse polymers, the so-called humins. The biphasic reaction system consists of an acidified water phase (where the acid functions as the catalyst) and an organic solvent phase. The system has been heated by microwave radiation, which allows a quicker heating process and is said to have direct positive effects on the production of HMF. These advantages of a microwave heated biphasic reaction system contribute to the increase of the yields of the platform chemicals. In a first stage, the process parameters (temperature, acid concentration and reaction time) for the conversion of cellulose to HMF were optimized using response surface methodology (i.e., Box Behnken design). Then, under these optimized parameters, the simultaneous conversion of C5 and C6 polysaccharides (using xylan and cellulose as model components) to furfural and HMF was investigated. From the results it is clear that no humins are formed during the microwave treatment and that it is possible to convert C5 and C6 sugars into furfural and HMF respectively. A maximal HMF yield is found to be 32,98 w%(± 1,11w%). Furfural yields were within the same range. Previously named results were obtained using xylan and cellulose as model compounds for lignocellulosic polysaccharides. However, the lignocellulosic matrix itself (including lignin) can have a significant influence on the conversion pathways to the desired platform chemicals. Therefore the effect of the lignocellulosic matrix has also been investigated. In this research bamboo was applied as lignocellulosic biomass. In advance the cellulose and hemicellulose content of bamboo was determined using the Van Soest analysis. Also in this case C5 and C6 polysaccharides were simultaneous converted to furfural and HMF, while lignin remained after reaction.status: publishe