Research On The Catalytic Hydrothermal Conversion Of Biomass Into Platform Chemicals With Solid Catalysts

Biomass is the only renewable carbon-containing energy in nature.Converting biomass into liquid fuel achieves high value-added utilization of biomass,which can reduce the consumption of fossil fuels,and is one of the most promising utilization routes for biomass.Platform compounds such as 5-hydroxymethylfurfural（HMF）,levulinic acid（LA）and furfural（FF）can be prepared by hydrothermal conversion of biomass,followed by condensation and hydrodeoxygenation to produce liquid fuels.solid acid catalyst for hydrothermal conversion of biomass to produce platform compounds was developed and studied in water and biphase solvent systems.All the related work is supported by the National Key R&D Program of China.Firstly,Zr O₂was impregnated with sulfuric acid.Solid acid catalysts with different SO₄^2-loads were prepared and tested by a variety of characterization methods.The characterization results showed that an appropriate amount of SO₄^2-load not only enhanced the acidity,but also increased the pore diameter and surface area.However,excessive SO₄^2-load would lead to the collapse of the pore structure and the change of the acid sites distribution of the catalyst.Four catalysts with different SO₄^2-loads were applied to the catalytic conversion of xylose,fructose and glucose in water to explore the influence of SO₄^2-loads on the performance of catalysts and the differences in the hydrothermal conversion characteristics of different sugars.Xylose is a pentose,which is converted into furfural by dehydration in water.The maximum furfural yield of 59.27%can be obtained by using 20%SO₄^2-/Zr O₂.Fructose and glucose are belonging to hexoses,which can be dehydrated to form HMF in the presence of catalysts and then hydrated to form LA and FA.Glucose is more difficult to convert than fructose,the maximum HMF yields were 27.72%and 17.68%for fructose and glucose respectively under the catalysis of 10%SO₄^2-/Zr O₂.The LA yield increased with the increase of SO₄^2-load.However,many side reactions occur in pure water,resulting in a low yield of high value-added HMF.In order to obtain high yield of HMF,Na Cl-THF/H₂O was applied to hydrothermal conversion of glucose.Because of the salting out effect of Na Cl,the original miscible THF/H₂O phase was separated into biphase.The HMF generated in the aqueous phase can be efficiently extracted into the organic phase THF,which reduces the consumption of HMF and greatly improves the yield of HMF.In addition,the effects of reaction conditions and catalyst composition on hydrothermal conversion of glucose were studied,and it was found that high temperature is a necessary condition for efficient conversion of glucose,while appropriate reaction time and acid distribution are keys to realize high selectivity of HMF.The maximum yield of 61.84%HMF could be obtained by using 20%SO₄^2-/Zr O₂as catalyst for glucose conversion at 160℃for 2h.The prepared catalysts and Na Cl-THF/H₂O two-phase solvent system were applied to hydrothermal conversion of disaccharides,polysaccharides and cellulose with six-carbon sugar to test the performances of the catalysts and solvent system.The results showed that different substrates obtained the highest HMF yield under the catalysis of 20%SO₄^2-/Zr O₂,which was due to its suitable acidity and stable pore structure.The hydrothermal conversion characteristics of different sugars are different,depending on the type of sugar unit,degree of polymerization and type of glycoside bond.