Study Of Mild Hydrogenation And Co-Cracking Of Bio-oil Fractions

The crude bio-oil produced from biomass fast pyrolysis is required to be upgraded due to its inferior properties.However,because of the complicated composition,effective conversion of the whole bio-oil could not be achieved by single upgrading technique.Molecular distillation could divide bio-oil into the distilled fraction rich in small molecules and the residue fraction rich in sugars and pyrolytic lignin.Distilled fraction exhibits high activity in the catalytic reactions,in favor of subsequent upgrading.Besides,mild hydrogenation and co-cracking with ethanol were both introduced as hydrogen donor to improve the activity and stability of oxygenated compounds during the conventional cracking process.Therefore,in this paper,the mild hydrogenation-cocracking of distilled fractions and their model compounds was carried out.The mild hydrogenation of simulated bio-oil was performed,aimed at investigating the effect of reaction conditions on the hydrogenation efficiency.Based on the conversion of reactants,the selectivity of products and the effective hydrogen to carbon ratio of liquid products,300?/4 MPa was chosen as an optimum condition for the mild hydrogenation.Under this condition,the overall conversion of simulated bio-oil reached to 93.8%,and maximum effective hydrogen to carbon ratio of 1.554 for liquid products was achieved.In addition,the contents of phenols and acids decreased obviously.Therefore,the activity of simulated bio-oil was improved significantly and in favor of subsequent catalytic cracking.The diversity of bio-oil in composition from different biomass feedstock cause difficulties to the conversion and utilization of bio-oil.For some bio-oils which consist of large amounts of carboxylic acids and show strong corrosiveness,the technical route of mild hydrogenation-esterification was proposed.The catalytic upgrading of acid-rich bio-oil and typical model compounds was performed upon Cu/SBA-15 catalyst prepared by homogeneous deposition precipitation.The synergetic effect between acetic acid and other oxygenated compounds was found,and the reaction pathways of model compounds were proposed according to the quantitative determination of products.In addition,Cu/SBA-15catalyst exhibited good stability and the catalytic efficiency remained stable during 40 h.Consequently,the corrosive bio-oil with high unsaturation degree could be converted into the improved bio-oil,mainly consisting of alcohols,esters and hydrocarbons.As for the problems during the upgrading process caused by phenol-rich bio-oil,which is difficult to convert via hydrogenation,serial Pt-Ni bimetallic catalysts were prepared for mild hydrogenation.Three typical phenols,like phenol,guaiacol and catechol,were chosen,and their hydrogenation behaviors and the activity of catalysts were investigated.It was found that the addition of Ni on Pt/SiO₂ catalyst obviously promoted the conversions of three phenols,while the yields of liquid products showed a decreasing trend.Based on the yield of liquid product and conversion of reactant,3Pt6Ni/SiO₂ catalyst exhibited superior activity,upon which effective conversion of phenols and satisfying yield of liquid product could be achieved.As for the improvement of cracking stage,serial Ga₂O₃/HZSM-5 zeolite catalysts with different Si/Al ratios and preparation methods were prepared for the catalytic cracking of simulated bio-oil.It was found that the catalyst activity decreased with the increase of Si/Al ratio.In detail,the conversions of reactants significantly decreased,and the selectivity and quality of oil-phase product declined.The active components upon the Ga₂O₃/HZSM-5-M catalyst were not well dispersed,and thus the activity was worst and the coke deposition of spent catalysts was serious.The activity of Ga₂O₃/HZSM-5-P catalyst was not bad,while the content of polyaromatic hydrocarbons was relatively high.The Ga₂O₃/HZSM-5-I?25?catalyst showed the superior activity.Upon this catalyst,the oil-phase selectivity of 35.5 wt%was obtained,and the content of aromatic hydrocarbons and monoaromatic hydrocarbons reached to 92.3%and 80.3%,respectively.Based on the improvement of hydrogenation and cracking stage,the study of mild hydrogenation-cocracking of bio-oil was performed.Firstly,the comparative study of hydrogenation-cracking and single-stage cracking of simulated bio-oil was carried out,in order to verify the necessity of the introduction of mild hydrogenation.Afterwards,the hydrogenation-cracking behavior of bio-oil distilled fraction derived from walnut shell was studied.The experimental results revealed that the yield of oil-phase product increased from24.6 wt%to 38.6 wt%with the addition of hydrogenation pretreatment.The oil-phase product entirely consisted of hydrocarbons,63.7 wt%of which were BTX?benzene,toluene,xylene?products.Besides,the coke yield was only 3.1 wt%.Aforementioned results revealed that the mild hydrogenation-cocracking of bio-oil based on the separation of molecular distillation will be promising.