Hydrothermal Conversion Of Fatty Acids To Alkanes

Nowadays,a large number of non-renewable fossil energy is consumed quickly and the energy crisis become prominent.Biomass resource is a kind of new green energy,which is abundant,renewable and environment friendly.The development and utilization of biomass resources is very important to relieve energy pressure and promote the sustainable development of society and economy.As one of the most promising biomass resources,fatty acids are used to produce alkanes as aviation fuel which has attracted more and more attention.The general method of preparing alkanes is hydrogenation of fatty acids,which requires not only the external gaseous hydrogen as a hydrogen source,the storage and transportation of hydrogen gas,but also unsafe and unenvironmental friendly organic solvents.And expensive metals（e.g.Pt,Pd）and complex supported catalysts are often used as catalyst.These catalysts can not be used directly but need a hydrogen pretreatment process before use which is costful and complicated.In this study,a new method of hydrothermal deoxygenation of fatty acids to alkanes via water splitting by Zn with Ni/Raney Ni was proposed.This study uses general nickel powder as a catalyst without pure hydrogen,expensive catalysts and organic solvents which is an efficient,simple and green process.At the same time,Raney nickel was used as a catalyst to catalyze the conversion of fatty acids to alkanes under hydrothermal conditions,which shortened the reaction time,reduced the amount of catalyst and Zn.Firstly,hydrothermal deoxygenation of fatty acids to alkanes via water splitting by Zn with cheap metal catalyst was studied.Ni was selected as the catalyst and the optimum reaction conditions were obtained by optimizing the amount of reductant and catalyst,reaction time,reaction temperature and water-filling ratio.Palmitic acid was used as the model compound and The optimal reaction conditions of hydrothermal deoxygenation of fatty acids to alkanes via water splitting by Zn with Ni are follows:0.1 mmol palmitic acid,2.0 mmol reductant Zn,1.0 mmol catalyst Ni,40%water filling,reaction time 16 h,and reaction temperature 300 ^oC,giving the highest pentadecane yield of 90%.Then,the stability of the catalyst nickel was discussed.It was found that the catalytic nickel remained high catalytic activity after recycling of three times,and the yield of pentadecane was over 85%.Stearic acid,dodecanoic acid and hexadecanoic acid methyl ester（the model compounds of fatty acids/ester）as raw materials,was respectively efficiently converted to C_n-1 alkanes under optimal reaction conditions mentioned before.This indicates that the reaction system has high universality.Next,shorten reaction time to investigate the intermediate products.Results shows that the intermediate products are aldehydes and alcohols.Thus the possible reaction path of hydrothermal deoxygenation of fatty acids to alkanes via water splitting by Zn with Ni was proposed,which may involve the decarbonylation of fatty acids.Finally,Raney nickel was used as a catalyst to catalyze the conversion of acids to alkanes under hydrothermal conditions.When palmitic acid was used as the model compound,Raney nickel was used as the catalyst,the optimal reaction conditions for the conversion of palmitic acid to pentadecane via water splitting with Zn under the hydrothermal condition were follows:0.1 mmol palmitic acid,1.0 mmol reductant Zn,Catalyst Raney nickel 3 mg,reaction time 8 h,reaction temperature 300°C,water filling 40%.Under the optimal reaction conditions,the highest yield of pentadecane is 89.2%,which is similar to the yield of pentadecene under the optimum reaction conditions when using nickel as the catalyst.But the reaction time is shortened and the amount of zinc and catalyst are reduced greatly.