Hydrodeoxygenation Reactivity And Interaction Of Carbonyl Group And Carboxyl Group

Varieties of complex oxygen-containing compounds in bio-oil precursors strongly affect the properties of biofuels.Hydrodeoxygenation(HDO)is an effective way for biofuels upgrading.For providing a reference for studies on HDO of bio-oil precursors,levulinic acid(LA)was selected as a model compound of the complex oxygen-containing precursors in this work.The other two model compounds(2-pentanone and valeric acid)which have the same carbon number as LA and bear separately a carbonyl group and a carboxyl group were employed to help to elucidate HDO reactivity of LA and the interaction of carboxyl group with ketone carbonyl group.Firstly,Ru/HZSM-5 was prepared by an impregnation process and characterized by TEM,NH₃-TPD,H₂-TPR,Py-IR,BET and ICP techniques.The influence of preparation conditions on the catalytic performance was studied using 2-pentanone HDO as a model reaction.The suitable calcination conditions of 450?for 3 h and reduction conditions of350?for 4 h were obtained.The Ru/HZSM-5(Si/Al=21)catalyst was used to investigate the effects of catalyst dosage,reaction temperature,hydrogen pressure and reaction time on the HDO reaction of 2-pentanone and valeric acid.The suitable reaction conditions for 2-pentanone HDO were determined as follows:a catalyst weight percentage of 6 wt.%,a reaction temperature of 190?,a hydrogen pressure of 5 MPa and a reaction time of 6 h.Meanwhile,the selectivity to the target product pentane reached 77.6%with a 2-pentanone conversion of 91.8%.Whereas the selectivity of pentane was only 7.6%at a valeric acid conversion of 33.1%under the suitable reaction conditions of a catalyst weight percentage of 10 wt.%,a reaction temperature of 240?,a hydrogen pressure of 5 MPa and a reaction time of 4 h.To analyze the interaction of 2-pentanone with valeric acid,the HDO reaction of a mixture of 2-pentanone and valeric acid with a molar ratio of 1:1 was carried out under the conditions of a reaction temperature of 230?,a hydrogen pressure of 5 MPa and a reaction time of 4 h.The liquid reaction components were identified by GC-MS analysis.Subsequently,the reactions for each product formation in the system were speculated and a reaction network was established.The HDO reactions of 2-pentanone,valeric acid and their mixture were kinetically analyzed and their reaction activation energies were estimated.For HDO of 2-pentanone,the activation energy of 2-pentanone hydrogenation to 2-pentanol is32.56 k J·mol^-1(Ea₁)while the total activation energy of 2-pentanol dehydration and successive hydrogenation is 53.69 k J·mol^-1(Ea₂).For HDO of valeric acid,the activation energy is 73.37 k J·mol^-1(Ea₃).In HDO of the mixture of 2-pentanone and valeric acid,the activation energy of 2-pentanone HDO reaction is 10.99 k J·mol^-1(Ea₄)and that of valeric acid HDO reaction is 17.80 k J·mol^-1(Ea₅).By comparing the activation energy and reaction rate constant,HDO reactivity and interaction of 2-pentanone with valeric acid were primarily discussed.2-Pentanone promotes valeric acid HDO reaction while valeric acid impedes HDO of 2-pentanone.Then,HDO reaction of LA was evaluated using Ru/HZSM-5 catalyst under the conditions of a reaction temperature of 230?,a hydrogen pressure of 5 MPa,and a reaction time of 4 h.The liquid reaction components were qualitatively identified by GC-MS analysis and then the reactions for each product formation in the system were speculated.On this basis,a reaction network was established.The HDO reaction of LA was analyzed kinetically and the activation energy is 29.91 k J·mol^-1(Ea₆).By comparing HDO reaction activation energy and reaction rate constant of 2-pentanone,valeric acid,their mixture and LA,HDO reactivity of ketone carbonyl and carboxyl groups and their mutual influence were discussed.Ketone carbonyl group promotes the conversion of carboxyl group while carboxyl group inhibits the conversion of ketone carbonyl group.