A Study On Ni-based Catalytic Preparation Of Long-chain Hydrocarbons From Fatty Acids

With the over-exploitation of non-renewable fossil fuels,the increasing of environmental pollution and demand of fuels and chemicals made the conversion of biomass to produce long chain hydrocarbons got great attention.Nowadays,the main method to produce hydrocarbons from lipids is hydrodeoxygenation.However,the high hydrogen consumption and complex separation of products restricted its development.To solve these problem,the decarbonylated/decarboxylated obtained great attention and developed fast recently.This research had followed the preparing of long chain hydrocarbons from decarbonylation/decarboxylation of fatty acid using Ni basedcatalyst in solvent and H2 free.The study included the catalyst synthsis,catalyst characterization and reaction mechanism for decarbonylation/decarboxylation of fatty acids.Then,Ni/AC-xPt bimetallic catalyst was prepared to regulate the selectivity of ?-olefin.Finally,a new method for the preparation of long chain hydrocarbons with controlable products selectivity over Ni based catalyst was established.The main contents are generalized as follows:Firstly,the catalytic activities of decarbonylation of stearic acid over Ni supported on different supports(Al2O3,ZrO2,TiO2 and AC),without using a solvent or H2,were evaluated.Then 5 wt%Ni/AC,which had the best performence on decarbonylation of stearic acid,was characterrized by N2-BET,TEM,XRD,H2-TPR,FTIR.The influences of Ni loading,reaction time and reaction tenperature were investigated.The results indicated that Ni/AC showed a better activity compared with Ni/TiO2,Ni/Al2O3 and Ni/ZrO2 with the same Ni loading.At 350?,57.9%yeild of C17 was achieved after 5 h over 5wt%Ni/AC.The increase of Ni loading had little influence on the stearic acid conversion and C17 selectivity and 1 wt%Ni/AC also had high activity in decarbonylation of stearic acid(41.7%selectivity of C17).According to the catalyst characterization,the small size particles of Ni fcc crystal structure and high Ni dispersion were the key factors to high activity.After analyzing the product distribution,the pathway of decarbonylation of stearic acid by Ni/AC was established.The first step of decarbonylation of stearic acid was to produce carbocation,then the gas,pyrolysis products,heptadecane,heptadecene,aromatics and coke were formed via Ni/AC catalysis.Secondly,in order to expand the selection range of raw materials,the catalytic activities of decarbonylation/decarboxylation of oleic acid without using a solvent or H2 over Ni/AC catalysts were evaluated.The catalysts were characterized by XRD,TEM,CH3COOH-TPD,CO-TPD and the influences of reaction time,reaction temperature and catalysts addition on catalytic activity were investigated.The results indicated that 54.2%yeild of heptadecane and aromatics was achieved after 4 h at 350?.Ni/AC catalyst had good reusability under this condition,which recycling the catalysts at least three times did not shown any reduction in activity.With the increasing of Ni loading,the selectivity of heptadecane and aromatics increased.From the characterization of catalyst,the fcc crystal structure and high dispersion of Ni particles(9.6 um)were the key factors for Ni/AC catalyst to decarboxylate oleic acid.The 40%Ni/AC showed a lower activity compared with 30%Ni/AC because of over Ni loading,leading the decrease of Ni dispersion on the catalyst,and further aggravating during the cracking and coking.Finally,the decarbonylation of stearic acid in H2 free over Ni/AC-xPt catalysts,synthesized by atomic layer deposition(ALD),was evaluated.The influences of different Pt deposition cycles,reaction temperature,DPEphos ligand adding and using dodecane as solvent were investigated.The result showed that 40.5%selectivity of 1-heptadecene and 57.2%selectivity of heptadecane with the 39.0%stearic acid conversion over Ni/AC-45Pt were achieved at 350? after 1 h in presence of DPEphos ligand,acetic anhydride and dodecane.DPEphos ligand increased the selectivity of 1-heptadecene.The conversion of stearic acid to prepare 1-heptadecene was sensitive to temperature,high temperature led to enhanced hydrogenation reaction,which caused a decrease in selectivity of 1-heptadecene.The hydrogenation reaction of ALD-Ni/AC-xPt limited the selectivity of 1-heptadecene.The presence of a dodecane solvent could control the rate of the process of the 1-heptadecene to heptadecane,then increased the selectivity of 1-heptadecene.