Study On Product Distribution Of Hydrolysis Hydrogenation/Hydrogenolysis Of Biomass Sugars

As the most abundant organic carbon source in nature,efficient transformation of cellulose into various platform chemicals is an important means of remitting fossil energy crisis.The aim of this paper is to regulate the product distribution of hydrolysis hydrogenation/hydrogenolysis of cellulose.Our work concentrated on the retro-aldol condensation involved in the transformation of biomass sugars,and investigated the influence factors of product distribution in transforming cellulose into polyols through hydrolysis hydrogenation/hydrogenolysis by changing acid sites and hydrogenation sites in catalytic system.The retro-aldol condensation can directly influence product distribution of hydrolysis hydrogenation/hydrogenolysis of biomass sugars.Firstly,in order to find the acid sites in favour of cleavage of C-C bonds in monosaccharide by retro-aldol condensation.We investigated the effect of Br?nsted acid sites（BAS）and Lewis acid sites（LAS）on C-C bonds cleavage by retro-aldol condensation in monosaccharide.A series of solid acid catalysts with different acid sites and concentration were prepared,including γ-Al₂O₃,HZSM-5 zeolite,SnOPO₄,SnZrOPO₄（1:1）,and SO₄^2-/ZrO2.The catalytic conversion of fructose in methanol over the five solid acid catalysts was studied as the probe reaction.The results showed that LAS was beneficial to retro-aldol condensation of monosaccharide,fructose can undergo retro-aldol condensation to form glyceraldehyde,which can be converted into methyl lactate in methanol.However,BAS was not good for retro-aldol condensation of monosaccharide for the reason that fructose would converted into HMF derivatives by dehydration over BAS.In order to study the effect of solid acid catalysts on biomass sugars hydrolysis hydrogenation/hydrogenolysis,the hydrogenation/hydrogenolysis of glucose and cellobiose was conducted over different solid acid catalysts（WZr/SBA-15,γ-Al₂O₃ and HZSM-5）in combine with Ru/C and Ni/MC hydrogenation.It turned out that the conversion of cellobiose showed positive correlation with total acid amount of WZr/SBA-15,and the selectivity of C₂-C₄ polyols showed positive correlation with Lewis acid amount of WZr/SBA-15.The conversion of cellobiose and the selectivity of C₂-C₄ polyols maximized over W₃₀Zr₅/SBA-15 catalyst,with the cellobiose conversion of 97.6% and the C₂-C₄ polyols selectivity of 49.7%.W₃₀Zr₅/SBA-15 was in favour of generation of ethylene glycol with the obviously enhanced yield,γ-Al₂O₃ and HZSM-5 were prone to convert glucose into C3 polyols,namely the propylene glycol and glycerol.The conversion of glucose was improved over W₃₀Zr₅/SBA-15 and γ-Al₂O₃ catalysts;nevertheless,the conversion of glucose over HZSM-5 was almost same as the conversion without solid acid catalysts.Finally,the hydrolysis hydrogenation/hydrogenolysis of cellobiose and cellulose was conducted over WZr/SBA-15 in the presence of Ru/C or Ni/MC,in order to research the effect of metal catalyst on product distribution of hydrolysis hydrogenation/hydrogenolysis of biomass sugars.Results indicated that the total yields of C₂-C₄ polyols were similar over Ru/C and Ni/MC catalyst.The yield of sorbitol generated from hydrogenation was lower over Ni/MC catalyst than that of over Ru/C catalyst,and hydrolysis hydrogenolysis was the main reaction pathway.When the catalytic conversion of cellobiose was conducted over W₃₀Zr₅/SBA-15 at 180 °C with reaction time of 120 min,the yield of ethylene glycol was 35.4% and the yield of sorbitol was 12.9%.After the phosphoric acid pretreatment of cellulose,in the reaction condition of 225 °C and 30 min,the yield of ethylene glycol was 35.8% and the yield of sorbitol was only 5.5%.