Microwave Assisted Production Of Furfural Compounds And Extraction Of Hemicellulose From Bamboo

As an important biomass resource,bamboo is the most widely distributed and resource-rich variety among bamboos in China.However,a large amount of waste is generated during the cutting and processing process of bamboo,which not only causes serious waste of bamboo resources,but also pollutes the environment.Therefore,it is necessary to utilize bamboo resources.Furfural compounds represented by furfural(FF)and 5-hydroxymethylfurfural(HMF)are precursors for the preparation of a variety of high value-added chemicals and biofuels.They are also an important bridge connecting biomass and chemical products.As one of the three major components of lignocellulosic biomass,hemicellulose has important application potential due to its non-toxic and biodegradable characteristics.Therefore,finding a suitable way to convert the polysaccharides from bamboo waste into furfural compounds or extraction hemicellulose polysaccharides can not only solve the environmental pollution problem caused by bamboo waste,but also help to improve the high-value conversion and utilization of bamboo waste.In this paper,FF and HMF were prepared by one-pot reaction in biphasic reaction system using pretreated bamboo as raw materials.The effects of different catalytic systems and reaction conditions on the yields of FF and HMF were investigated.Hemicellulosic polysaccharides were extracted from ionic liquid pretreatment of bamboo powder by using alkaline extrant.The main research contents and conclusions are as follows:1.Using H₂SO₄ as the catalyst and bamboo powder pretreated with Bmim Ac as the reaction materials,two platform compounds of FF and HMF were prepared by one-pot microwave-assisted heating in a H₂O/MIBK biphasic reaction system.The effects of sulfuric acid concentration,reaction temperature and reaction time on the yields of FF and HMF were investigated.The results showed that the highest total yields of FF and HMF were 67.00mol%and 25.52mol%,respectively,under the catalysis dosage of2m L 1.0wt%H₂SO₄ at 180?for 30min.The conversion efficiency of hemicellulose to FF in bamboo was much higher than that of cellulose to HMF.Through the characterization of the reaction residue by FT-IR,XRD and Py-GC/MS,it was found that the content of lignin in the residue increased with the increase of reaction time and temperature,while the content of cellulose and hemicellulose decreased with the increase of reaction time and temperature.In addition,the physical and chemical properties of bamboo powder were changed to some extent after Bmim Ac pretreatment,such as the decrease of crystallinity of cellulose.2.H₂O/MIBK was also used as the reaction system to study the synergistic effect of metal salts,metal salts-sulfuric acid on the production of FF and HMF from bamboo.It was found that Fe Cl₃ had the best effect on the production of FF and HMF from hemicellulose and cellulose in bamboo powder at the same time.Under the optimal conditions:0.1g pretreated bamboo powder was used as the reaction substrate,24mg Fe Cl₃ was used as the catalyst,and microwave heating at 180?for 20min in H₂O/MIBK(1.5:10,m L:m L),the highest total yields of FF and HMF were 87.03%and51.25%,respectively.The solid acid catalyst ATP-S-Fe was prepared by loading Fe Cl₃on ATP.The yield of bamboo powder converted to FF and HMF by ATP-S-Fe was57.16%and 19.59%,respectively,which were close to the date when 1wt%H₂SO₄(62.79%and 23.54%)was used as catalyst under the same conditions.Finally,the organic phase in the reaction system was separated and purified by vacuum distillation,and the purity of the obtained FF and MIBK was higher than 95%.3.Microwave-assisted IL(Bmim Cl and Bmim Ac)was used to pretreat bamboo under different conditions,and then hemicellulose was extracted by alkali extractant and followed by alcohol precipitation.The results showed that the optimum conditions for separating hemicellulose were as follows:microwave-assisted Bmim Ac was heated to 150°C for 60 min to pretreat the bamboo powder,and then 5%Na OH was used to extract hemicellulose with a yield of 20.33%.Comparing the physicochemical properties of hemicellulose extraction,it was found that the microwave-assisted IL pretreatment had no significant effect on the main structure of the extracted hemicellulose,the main chain was arabinoxylan,the glucose content in the side chain was significantly reduced,and the molecular weight and thermal stability were slightly improved.The hemicellulose extracted by microwave-assisted Bmim Ac pretreatment has high purity.Although the yield of hemicellulose extracted by microwave-assisted Bmim Cl pretreatment is significantly increased,it contains more impurities such as lignin.