Studies On Hydroconversion Of Vegetable Oil To Produce Alternative Aviation Fuel

Currently,the necessity of developing renewable energy is highlighted due to the exhaustion of fossil resources and the serious environmental problems.The hydroconversion of vegetable oil to produce alternative fuel has attracted great attention owing to its green nature and cleanness.The catalyst is critical for the hydroconversion of vegetable oil,therefore it is of important to improve the catalytic activity of catalyst to increase the conversion and selectivity.In this work,the influence of active metals and support on hydroconversion of vegetable oil were deeply discussed with the aim at providing theoretical guidance for the hydroconversion of vegetable oil to produce highperformance biofuels.Firstly,Ni doped respective Pt and Mo were selected as active metals to investigate the role of composition of active metals in the hydroconversion of vegetable oil.It is found that the predominated pathways over NiPt bimetallic catalysts are decarboxylation and decarbonylation,and the highest selectivity of decarboxylation reaches to 62 %.The Pt2+ and Pt4+ species in NiPt bimetallic catalyst prefers the decarboxylation while the Pt0 species benefits for the decarbonylation.For NiMo bimetallic catalysts,the main deoxygenation pathways are decarboxylation(41 %)and hydrodeoxygenation(63 %).Larger amount ofNiMoO4-andMoO3 sulfided phases shows higher selectivity for decarboxylation,while the catalyst with more Mo4+ polymeric octahedral sulfided phases obtains mainly hydrodeoxygenation products.The results of H2-TPR and TEM show that the active metal-support interaction and metals dispersions are the key factors for deoxygenating.The stronger active metalsupport interaction and higher metals dispersions,the higher decarboxylation selectivity is obtained.The phase of active metal in catalyst is also affected by the acidity and surface groups of support.Then,hierarchical ZSM-5 was synthesized via hydrothermal crystallization,which was adopted as support for NiMo to study the influence of support on the hydroconversion of vegetable oil.This hierarchical ZSM-5 supported catalyst inhibits the deep cracking reaction and exhibites a potential application for C9-C15 hydrocarbons(45 %)in the hydroconversion of vegetable oil due to the interconnected intracrystal and intercrystal mesoporosity in ZSM-5.In order to obtain hierarchical ZSM-5 easier and more efficiently,the commercial ZSM-5 was treated with NaOH and NH4NO3 to control its pore structure and the acidity distribution.The impact of these two properties on the hydroconversion of vegetable oil are further investigated by employing the resulting ZSM-5 as supports of the catalysts.It is observed that the intercrystal mesopore size of the ZSM-5 is increased after NaOH treatment.When this ZSM-5 is loaded with Ni and Mo for the hydroconversion of vegetable oil,deep cracking reaction is inhibited while the aromatization reaction of C2-C8 olefins is promoted.As a result,a selectivity of 46 % for C9-C15 hydrocarbons is derived,which is similar to the value obtained with the hydrothermally synthesized ZSM-5.The ion exchange of ZSM-5 with NH4NO3 only increases the Br?nsted acidity while the Lewis acidity remains unchanged.In the hydroconversion of vegetable oil,the selectivity of aromatics increases with the increase of Br?nsted acidity and the Lewis acidity determines the formation of cycloalkanes.The mechanism of aromatic formation was also presumed: the cracking,dehydrogenation and dehydrogenation-aromatization occurred on Br?nsted acid sites and the Diels-Alder cyclization occurred on Lewis acid sites.So the aromatics formed under the combined effect of Br?nsted and Lewis acid.Above all,controlling the acidity and pore structure in support can quantitatively convert vegetable oil to high performance fuels.