Hydrocracking Of Long-chain Bio-alkanes Over Pt/Al-MCM-41 For Jet Fuel Production

Many countries in the world increase the research and development on bio-jet fuels in order to reduce the greenhouse gas emission and the traditional fossil fuel usage.The two-step hydrogenation technique used to convert oil into bio-jet fuel has the most potential for industrial application because of the mature technology.The selection of bifunctional catalyst is important to the two-step hydrogenation process especially the second step of hydrocracking/hydroisomerization process.Molecular sieves especially mesoporous molecular sieves with larger pore size are widely used as the the catalyst support in hydrocracking processes.Their larger pore is advantageous to the diffusion of long-chain alkanes in catalyst channel resulting in high selectivity to C9~C15 alkanes.Mesoporous molecular sieve MCM-41 was used as the catalyst support in this paper.Pt/Al-MCM-41 catalyst was developed for hydrocracking of long-chain bio-alkanes for bio-jet fuel production.Firstly,the effects of different synthesis methods of Al-MCM-41 catalyst support,including hydrothermal synthesis method and post-grafting method on the catalyst activity and selectivity were studied in the paper.X-ray diffraction(XRD),X-ray fluorescence(XRF),N2 physisorption(BET),temperature-programmed desorption of ammonia(NH3-TPD)and transmission electron microscope(TEM)were characterized on these samples.The optimal Al-MCM-41 preparation method is hydrothermal synthesis method with long-range ordered,more total acid amount and moderate acid sites,and higher conversion and kerosene/gasoline ratio.Under this method,the BET surdace area,pore volume,and the most probable pore of the Al-MCM-41 were 726.1 m2/g,1.40 mL/g and 2.55 nm,respectively.Secondly,the effects of different synthesis conditions,including Si/Al ratio,aging time,calcination time,P modification,types of the noble metal and various platinum loadings on the catalyst activity and selectivity were examined.The optimal synthesis conditons were: Si/Al ratio of 10,aging time of 20 h,calcination time of 8h,without P modification of the support,platinum loading and with the platinum loading of 0.7%The effects of reaction conditions,including temperature,pressure,weight hour space velocity and hydrogen/oil volume ratio,on the catalyst activity and selectivity were investigated.The optimal temperature,pressure,weight hour space velocity and hydrogen/oil volume ratio were 310 ?C,2MPa,1 h-1 and 1500,respectively,under which the bio-alkanes conversion of 68.6 % and the kerosene /gasoline ratio of 2.0.Finally,the stability of Pt/Al-MCM-41 catalyst and the quality of the jet fuel produced from hydrocracking of bio-alkanes were analyzed.Stable catalyst performance was observed within continuous reaction for 48 h.All the properties of bio-jet fuel product by atmospheric/vacuum distillation were reached the ASTM D7566 standard,especially the freezing point reached up to-73.8 ?C.