Study On The In Situ Hydrogenation Of Model Compounds In Biomass Pyrolysis Oil

Biomass is considered as one of the most promising resources for fuel and it can be converted into liquid biofuels by fast pyrolysis,which is known as biomass pyrolysis oil or bio-oil.However,some undesired properties of bio-oil such as instability and acidity limit its direct utilization as fuel and should be upgraded firstly.The in situ hydrogenation is a novel upgrading method of pyrolysis oil.For this method,hydrogen is produced by the reforming of hydrogenation liquid donor and in situ used to upgrade pyrolysis oil,which can simplify the process and reduce the cost.In this research,the in situ hydrogenation of model compounds in biomass pyrolysis oil over the mixed catalysts of zeolite solid acids and Raney Ni was systematically investigated.Phenol,acetone,n-butanal and acetic acid were selected as the model compounds of pyrolysis oil.Methanol was used as the solvent to produce hydrogen.Firstly,the effect of zeolite solid acids on the in situ hydrogenation of bio-oil was investigated.The zeolite solid acids included Hbeta and HZSM-5 with different Si/Al ratio of 25,40,60 and 25,50.The results indicated that the conversion of phenol increased with the addition of zeolite solid acids and Hbeta（Si/Al=60）showed the best catalytic performance.The reaction pathway was discussed and the main reaction pathway was hydrogenated for benzene ring of phenol to produce cyclohexanone and cyclohexanol.And the effect of the quantity of Hbeta（Si/Al=60）and Raney Ni on the in situ hydrogenation of phenol and its reusability were also studied.The results show that the quantity of Hbeta（Si/Al=60）and Raney Ni had great impact on the carbon loss,but little effect on both the conversion and the products distribution.The Raney Ni was indispensable to the aqueous phase reforming of methanol to produce hydrogen and hydrogenation of benzene ring.While the zeolite solid acid was responsible for providing a larger catalytic specific surface area and more contact sites to the reactants.In addition,the mixed catalysts of Raney Ni and Hbeta（Si/Al=60）still exhibited good catalytic activity after reusing 6 times.Then,the effects of the reaction conditions on the in situ hydrogenation of phenol were investigated and the optimum conditions were as follows:reaction temperature was 220°C,initial pressure of N₂ was 1 MPa,water and methanol volume ratio was 30m L:10m L,reaction time was 4 h.The average hydrogen pressure obtained from the aqueous phase reforming of methanol was about 1.075MPa/h.Finally,the in situ hydrogenation of acetone,n-butanal and acetic acid were carried out and found that they all could be converted into the corresponding alcohols or esters by the in situ hydrogenation or esterification.The effect of one other model compound on the in situ hydrogenation of phenol was investigated and found that the presence of acetic acid would reduce the conversion of phenol significantly.The interactions of different model compounds were investigated and found that acetic acid had little effect on the conversion of acetone and n-butanal,but still had a significant effect on the conversion of phenol.In all,phenol,acetone,n-butanal and acetic acid could be converted into stable,combustible alcohols or esters by the in situ hydrogenation or esterification.Therefore,a novel upgrading method of biomass pyrolysis oil was proposed,named the in situ hydrogenation esterification.