Study Of Catalytic Lignin Depolymerization By Multielement Compound Metal Oxides

Biomass energy,as a renewable energy with low-carbon emission,is definitely promising and worthy to be developed.Lignocellulose is an important part of biomass energy and mainly consists of cellulose,semicellulose and lignin.The oxygen content of lignin is less than cellulose and semicellulose so it has higher HHV than them.The lignin has immense potential value to be explored.For example,the conversion from the lignin to bio-fuel is promising.For the complicated three-dimensional amorphous polymer structure of the lignin,lignin is hard to be depolymerized and the catalytic methods of lignin depolymerization is an important part of the lignin conversion industry.In this paper,a series of catalysts were designed to depolymerize lignin.The proper solvent system was carefully chosen and the effects of these catalytic system in lignin depolymerization were researched in detail.Finally,efficient catalytic lignin depolymerization were realized.The compound solid superacid catalyst,Ni-S2O82-/TiO2,was prepared through impregnation-calcination and NaBH4 reduction methods.After researching the catalytic effects at different conditions,the reaction conditions with the maximal yields got were as follows:When the reaction temperature was 280? and the reaction time was 60 min,the maximal yields(74.67%and 42.33%)of the ethyl acetate soluble and the diethyl ether solubl product were got.When the reaction temperature was 260? and the reaction time was 60 min,the maximal yield(4.5%)of the monomer product was got.On the basis of S2O82-/TiO2,the acid-base compound catalyst,S2O82--K2O/TiO2,was prepared and it can catalytically depolymerize lignin more efficiently than the S2O82-/TiO2.After 12 h reaction at 320?,a very high yield of total monomers,28.96%,was got.Through the characterization of the S2O82--K2O/TiO2,it was found that when 40%of S2O82-and K2O were loaded,super strong acid and base sites came out.The catalytic property was improved with the emergence of the super strong acid and base sites.Besides,through the study of solvents,it was found that the 1,4-dioxane/methanol solvent system had the best effect of all.Adding the hydrogenation process in the catalytic depolymerization process can effectively improve the result of the reaction.The effects of mixing S2O82--K2O/TiO2 and Ru/C or loading Ni on S2O82--K2O/TiO2 and S2O82--K2O/ZrO2 were researched.These improvements effectively ehanced the efficiency of catalytic lignin depolymerization.After 24 h reaction at 320?,the lignin whose HHV is 25.7 MJ/kg was converted to the liquid product whose HHV is 34.4 MJ/kg with S2O82--K2O/TiO2 and Ru/C(the ratio was 3:1).After loading Ni on the S2O82--K2O/TiO2,the acidity and hydrogenation ability were both improved ald the yields were increased.For Ni-S2O82--K2O/ZrO2,it got better result at the high temperature(320?)after prolonging reaction time.The reason was that the load of Ni only enhanced the hydrogenation ability of Ni-S2O82--K2O/ZrO2.The previous catalysts had good catalytic performance,but their stability was poor.To improve this defect,a titanic metal solid solution was introduced into lignin depolymerization as a catalyst.The metal solid solution was composed of TiO2,MgO and NiO.After the WO3 was loaded on the carrier,the titanic metal solid solution catalyst,W/TiMgNiOx,was got.The yields of the W/TiMgNiOx were slighty less than the previous catalysts,but from the stability test of the catalyst,it was found that the W/TiMgNiOx was much more stable than other catalysts.Compared with the stability of S2O82--K2O/TiO2(about 32%reduction after 5-cycle reaction)and Ni-S2O82--K2O/TiO2(18%reduction after 5-cycle reaction),the stability of W/TiMgNiOx was obviously better(11%reduction after 5-cycle reaction).To improve the catalytic efficiency,the Sn-Al metal solid solution,which has stronger acidity,was employed as the carrier,and the WO3 and Ru were loaded on the carrier to prepare the Ru-W/SnAlOx catalyst.It has good catalytic efficiency and stability.The Ru-W/SnAlOx catalyst had the best combination property in the whole research.When the reaction temperature was 300? and the reaction time was 12 h,the yields of the liquid,petroleum ether soluble and monomer products were respectively 94.32%,59.86%and 15.69%.Besides,after 5-cycle reaction,the catalytic efficiency of Ru-W/SnAlOx was only reduced about 14%.