Research On The Heteropolyacid Catalyzed Hydrothermal Conversion Of Biomass Into Furfural And Levulinic Acid

Biomass,as the sole carbon-containing renewable resource,not only facilitates the transformation of energy structure and carbon dioxide emission reduction but also provides support for agricultural economy.The utilization of biomass involves the directed depolymerization of hemicellulose and cellulose through hydrothermal processing,yielding platform compounds such as furfural and levulinic acid.Subsequent aldol condensation and cooperative hydrogenation deoxygenation lead to the synthesis of high-value fuel-grade molecules and valuable chemicals.This endeavor aids in diminishing reliance on finite fossil energy sources while alleviating the environmental pollution associated with such resources.This study,supported by the National Key Research and Development Program,has developed a heterogeneous catalytic conversion technology based on heteropolyacids,achieving efficient directed transformation of cellulose-based biomass into furfural and levulinic acid.Firstly,addressing the challenge posed by the low efficiency of hydrothermal depolymerization caused by the high polymerization degree and compact structure of typical cellulose-based biomass,namely corn stalks,we explore the impact of various hydrolysis parameters in the low-acid hydrolysis process of corn stalks on the production of xylose and glucose.By separating xylose and glucose from the hydrolyzed biomass under different temperature conditions,an optimal temperature separation scheme is established at 130°C and 160°C,yielding a two-stage hydrolysis process.Under the optimal conditions,the highest concentrations achieved are 24.38g*L^-1 for xylose and 26.64 g*L^-1 for glucose.To enhance conversion efficiency,computational fluid dynamics（CFD）simulations are employed to investigate the influence of reactor structure on the flow field within the reaction system.By optimizing parameters such as impeller design and installation height,as well as operating conditions such as rotational speed,the directed synthesis of the desired product is intensified,leading to an 11.2%increase in xylose concentration.Subsequently,a study is conducted on the dehydration conversion of biomass-derived sugars to furfural and levulinic acid.A reaction system is developed employing heteropolyacids as catalysts in a single-phase green solvent system composed of GVL and water,enabling the conversion of biomass-derived sugars into furfural and levulinic acid.Research findings indicate that silicotungstic acid（with a Br（?）nsted/Lewis acid ratio of 1.03）exhibits the highest catalytic activity,yielding conversion rates of 87.7%for glucose to levulinic acid and 9%for furfural.The effect of GVL addition on silicotungstic acid catalyzed glucose conversion is thoroughly studied,revealing a positive correlation between GVL addition under aqueous conditions and glucose conversion rate as well as levulinic acid yield.Furthermore,the influence of silicotungstic acid on the hydrothermal conversion of xylose to furfural is investigated.The impact of GVL addition,substrate and catalyst loading,reaction time,and temperature on silicotungstic acid catalytic efficiency is systematically studied.The highest furfural yield of 83.5%is achieved at 190°C after a 5-minute reaction.Additionally,a kinetic analysis of the dehydration conversion of glucose and xylose to levulinic acid and furfural,respectively,is conducted within the GVL-water system over a temperature range of 160-200°C.Moreover,to address the issue of difficult recovery and reuse of homogeneous heteropolyacids after hydrothermal reactions,a solid acid catalyst with excellent hydrothermal stability and recyclability is synthesized by combining Ti O₂ with heteropolyacids.This catalyst demonstrates high efficiency in the dehydration conversion of xylose to furfural and exhibits certain catalytic activity in the dehydration conversion of glucose to levulinic acid.The acidity of the catalyst and the distribution of Lewis/Br（?）nsted acidity can be controlled by adjusting the loading of active heteropolyacid components.Furthermore,a biphasic solvent system of methyl isobutyl ketone（MIBK）and water is found to enhance the conversion of xylose and glucose in the feedstock,as well as the selectivity towards furfural and levulinic acid in the products.Under optimized reaction conditions,using TPA-Ti O₂-3 as the catalyst and conducting the reaction at 190°C for 60 minutes,a maximum furfural yield of 76.71%is achieved,significantly surpassing catalysts composed of the same mass of Ti O₂ and heteropolyacid.Even after five cycles of catalyst use,the furfural yield remains above80%of the initial yield,demonstrating favorable hydrothermal stability and recyclability.Additionally,significant progress is made in the catalytic dehydration conversion of glucose to levulinic acid.Under optimized conditions,a reaction time of120 minutes at 200°C using the TPA-Ti O₂-4 catalyst yields the highest conversion rate of 100%for glucose and a 41.6%yield of levulinic acid.Finally,combining the advantages of both homogeneous and heterogeneous heteropolyacids,a temperature-responsive bifunctional catalyst,Ch Al _XH_3-3XSi W₁₂O₄₀,is developed.This catalyst is used for the dehydration conversion of glucose to levulinic acid in a biphasic MIBK-water solvent system.By reacting choline chloride with silicotungstic acid,the resulting catalyst exhibits temperature-responsive characteristics,enabling a transition between homogeneous and heterogeneous catalysis at the temperature inflection point of 90°C.By controlling the content of the Lewis metal Al,the ratio of Br（?）nsted/Lewis acidity in the heteropolyacid is optimized,enhancing the selectivity of the target platform compounds.Ultimately,the optimized catalyst,Ch Al_2/3HSi W₁₂O₄₀,achieves the best performance with a glucose conversion rate of100%and an levulinic acid yield of 62.01%at 150°C for 8 hours.Additionally,performance tests on catalyst recyclability demonstrate good hydrothermal stability,allowing for multiple reuse cycles without loss of catalytic activity,providing reliable support for the industrial application of catalysts.