Production Of Furfural From Corncob By A Highly Efficient Two-step Process

As the second largest component after cellulose in lignocellulosic biomass, hemicelluloses consist of various monosaccharides, and can be conveted into multiple platform chemicals. Highly efficient conversion of hemicelluloses is the key technology for the utilization of the lignocellulosic biomass. Pentose in helicelluloses can be transformed into furfural by the dehydration. Due to the similar property with the chemicals derived from fossil energy, furfural can replace petroleum-based products in many fields such as fuel, chemicals engineering, and medicine industries. The furfural production from lignocellulosic biomass includes two key steps which contain the hydrolysis of hemicelluloses and the dehydration of pentose. According to whether the two steps occurred in one reactor, the furfural product process can be divided into one-step process and two-step process. In two-step process, the high yield of furfural is achieved as well as the sufficient utilization of the lignocellulosic biomass. Moreover, there are the homogeneous catalyst and the heterogeneous catalyst for furfural production. Solid acids as the heterogeneous catalyst have been highly concerned by the researchers because of their outstanding characteristics such as the strong acidity, the excellent thermal stability and the simple recycle process. The catalytic systems for furfural production include the monophase system and the biphasic system. Since the side reaction of furfural consumption can be restrained, the biphasic system is used extensively in furfural research. In this paper, a highly efficient two-step process was developed to produce furfural from corncob. In the first step, pentose-rich hydrolysats were produced by the hydrothermal pretreatment of corncob, and hydrolysats were converted into furfural via solid acids in the monophase system and the biphasic system in the second step. The results were as followed:(1) Furfural was produced by the autocatalysis hydrothermal pretreatment of corncob and then subsequent catalysis of hydrolysats using a new solid acid(SO42-/Si O2-Al2O3/La3+). The influences of pretreatment conditions on xylose yield in hydrolysats were discussed, and the catalytic effect of this solid acid on the pentose-rich hydrolysats was comparatively investigated as well was the recycle performance of solid acid. In the first step of the hydrothermal pretreatment of corncob, with increasing the reactor temperature or prolonging the reactor time, the degradation of hemicelluloses from the corncob cell wall and the xylose yield in the hydrolysta were enhanced. The highest xylose yield of 7.01 g/L was achieved at 190 oC for 60 min. Subsequently, the heterogeneous catalysis of the hydrolysate obtained from the hydrothermal pretreatment was performed using SO42-/Si O2-Al2O3/La3+ as a solid acid at 150 oC for 2.5 h. The maximum yield of furfural achieved was up to 21% under the investigated experimental conditions from the catalysis of hydrolysates obtained at 190 oC for 60 min in the hydrothermal process. After catalysis process, the solid acid was recycled and regenerated by impregnation with H2SO4. There was no obvious change in the catalytic activity of SO42-/Si O2-Al2O3/La3+ after four runs, and only a decline of 5.28% yield of furfural was observed.(2) A feasible approach for the production of xylose and xylooligomer from corncob was developed using oxalic acid-assisted ball milling, followed by the microwave-induced hydrothermal treatment. The effects of ball milling and microwave reactor conditions on the sugars yield in hydrolysates and the composition of treated corncob residues were studied, and the reactor condition was optimized. The treated corncob residues were characterized by SEM, XRD and FTIR. The maximum xylo-sugars yield of 86.10% was obtained after the ball milling process loaded by 15 m M oxalic acid(based on hydrolysate) for 60 min and further treated at 130 oC for 30 min under microwave. After the microwave-induced hydrothermal treatment, the solid residues of treated corncob were collected and converted into glucose with cellulase by enzymolysis process. It was found that the pretreatment was benefit for the enzymolysis, and the glucose yield of 80% was obtained after 48 h.(3) After the modification of the treated corncob residues by carbonization and sulfonation process, a sulfonated carbon-based catalyst(SCC) was prepared in this work. The concentrated pre-hydrolysis liquor(CPHL) containing 5 wt% xylose was catalyzed into furfural using SCC as a new solid acid catalyst in a new biphasic system(DCM/CPHL-Na Cl). Chemical and physical properties of this new biochar catalyst were analyzed by XRD, SEM, FT-IR, BET surface area, TGA, elemental analysis and XPS. The influence of the catalysis condition on furfural yield and the recyclability of SCC were researched. The highest furfural yield of 81.14 % with the furfural selectivity of 83.0% and nearly 100% C5-sugars conversions(99.9% for xylose and 99.2% for arabinose) were achieved under the reaction of 2 m L CPHL with 0.8 g Na Cl, 4 m L DCM and 0.02 g SCC at 170 oC for 60 min. With the regeneration process by sulfonation, the recycled catalyst displayed the good activity and the great stability, and the furfural yield was declined by 16%(from 81.4% for fresh SCC to 68.2% for 4th regenerated catalyst) after four runs.A highly efficient two-step process was developed for furfural production from corncob. Corncob was firstly milled with a tiny amount of oxalic acid, and was subjected to the mild microwave-assisted hydrothermal pretreatment. The xylo-sugars rich hydrolysate and the solid residue with cellulose and lignin were obtained. The hydrolyzed corncob residue was processed into a new biochar catalyst by carbonization and sulfonation, and can be converted into glucose by the enzyme hydrolysis. The biochar catalyst as the solid acid catalyst was applied for furfural product by a biphasic system(hydrolysate and DCM as the organic solvent). In this two-step process, the high furfural yield was achieved, and the major components of corncob were efficiently utilized by the classification directional conversion.