Study Of Bio-oil Mild Hydrogenation Based On The Molecular Distillation

Biomass is the unique renewable resource that can be converted into liquid fuels.Crude bio-oil produced by biomass fast pyrolysis needs further upgrading process to improve its inferior properties such as high oxygen content,low calorific value and strong corrosiveness.However,the composition of bio-oil is complex and direct upgrading faces rapid catalyst deactivation and reactor clogging.The distilled fraction,which enriched acids,aldehydes and ketones via molecular distillation is more suitable for the subsequent upgrading process.Therefore,this article focuses on the high-efficiency separation of crude bio-oil and the mild hydrogenation of bio-oil distilled fraction and its model compounds.Acids,aldehydes and ketones and other small molecules of bio-oil have a high conversion capacity,while large-molecular-weight phenols and sugars tend to produce coke in the upgrading process.In this paper,the wiped-film molecular distillation apparatus was used to investigate the separation properties of simulated bio-oil under different factors including distillation temperature,distillation pressure and feed rate,respectively.Then,the response surface method was used to study the the effects of multi-factors on the molecular distillation.The concentration of the acid,aldehyde and ketone in the light fraction was set as the response value and the optimum condition of 69.83 ?,1498.31 Pa and 5.54 mL/min was determined.And the fit value of the acid aldehyde ketone concentration was 39.12 wt%.The results show that the concentration of the acid aldehyde ketone concentration in distillate is 38.96 wt%,which is in good agreement with the response surface model.The concentration of acid,aldehyde and ketone via molecular distillation increased from 28.50 wt%to 38.96 wt%,and the concentration of phenols decreased from 37.50 wt%to 25.14 wt%,which was good for subsequent hydrotreating.On the basis of the optimal operating condition,the study of mild hydrogenation was conducted under different temperatures based on four bimetallic catalysts(Pt-Fe,Pt-Ni,Pd-Fe and Pd-Ni),comparing with Pd and Pt catalysts.The physical and chemical properties of the catalyst were characterized by BET,XRD,TEM and H2-TPR.The results showed that the addition of Ni promoted the saturation of benzene ring and furan ring,and significantly promoted the conversion of phenols.Under the Pt-Ni/SiO2 catalyst,The optimum conversion rates of guaiacol and phenol were as high as 97.8%and 99.6%respectively.The addition of Fe promoted the protonation of acetic acid and thus significantly improve the conversion of acetic acid.Under the Pt-Fe/SiO2 catalyst,acetic acid was completely converted at all thetemperatures.The saturation degree of the liquid products after the hydrogenation over bimetallic catalytsts was obviously improved,which was favorable for the subsequent catalytic cracking to obtain the liquid hydrocarbon fuel.Based on the study of the model compouds,the Pt-Ni/SiO2 catalyst was selected for the mild hydrogenation of the mixture of bio-oil distilled fraction and ethanol,and the effect of reaction pressures and blend ratios of ethanol on the hydrogenation of bio-oil was investigated.It was found that the increase of reaction pressure and the blend ratio of ethanol are beneficial to the hydrogenation of bio-oil distilled fraction.When the pressure was 3.0 MPa and the blend ratio of ethanol reached 60%,the properties of feedstock was significantly improved,and a satisfying hydrogenation effect was achieved.