Study On Upgrading Of Bio-oil Derived From Biomass Thermal Chemical Conversion

Octanoic acid was chosen to be the model compound for bio-oil derived from biomass pyrolysis to study the effect of catalytic hydrogenation and catalytic esterification on the upgrading of bio-oil.For the catalytic hydrogenation,when 5%Ni-ZrO2 catalyst,the conversion of ocatnoic acid reached the maximum of 92.79% with a yield of 69.68% for heptane derived from octanal decarbonylation as the main product at the condition of hydrogen pressure of 3MPa and the reaction temperature of 320 oC.Besides,there were few ligheter alkanes,octane,octanal,octanol and octyl octanoate generated during the process.However,after being doped with 10 wt.% Mo to generate 10Mo/Ni-ZrO2 catalyst,the main product of heptane transformed into octane with a yield of 77.07% at a complete octanoic acid conversion.Meanwhile,the yields of lighter alkanes,heptanes,octene,octanal,octanol and octyl octanoate were 2.31%,10.67%,0.99%,3.56%,4.89% and 1.10%,respectively.The catalysts were characterized by nitrogen sorption,TEM,XRD,TPR and TPD methods,and the results demonstrated that the doping Mo particles to the Ni-ZrO2 catalyst resulted in the transformation of ZrO2 support from cubic form?c-ZrO2?to monoclinic form?m-Zr O2?and the improvement of the hydrogen adsorption capacity and acid property of the catalyst.Thus,the doping of Mo favored the dehydration-hydrogenation reactions of octanol intermediate which in turn facilitated octanoic acid HDO to C8 alkane.For the catalytic esterification of ocatnoic acid with methanol,the conversion of octanoic acid was 92.56% and the yield of target product-methyl octanoate was 89.08% on the effect of SO₄^2-/Al₂O₃ catalyst at the condition of reaction temperature of 160 oC and methanol/octanoic acid molar ratio of 4.5:1.Once introducing a certain amount of SiO2 to SO₄^2-/Al₂O₃ to generate SAS-5,the octanoic acid conversion reached 99.11%,meanwhile,the yield of methyl octanoate reached 99.07%,and no byproducts were detected.The catalysts samples were characterized by nitrogen sorption,XRD,NH3-TPD,FTIR and FTIR-pyridine adsorption methods,and the results demonstrated that the doping SiO2 to the SO₄^2-/Al₂O₃ catalyst resulted in the increase of BET surface areas and amount of surface sulfur species which led to an increase in acid sites,especially the Br?nsted acid sites,which consequently boosted the catalytic esterification activity.In addition,the introduction of SiO2 can also increase the thermal stability of surface sulfur species which resulted in the alleviation of catalyst deactivation.This explains why SAS-5 could matain considerable catalytic activity after being recycled for nine times.In addition,the amount of Br?nsted acid sites of the used catalyst decreased distinctly,which illustrated that the esterification reaction was proton acid promoted,and the reduction of Br?nsted acid sites was the main reason for catalyst deactivation.