Synthesis And Catalytic Effect On Glycerol Aromatization Of Nano-HZSM-5 Zeolite

With the increase of oil price and aromatic demands,the traditional route of aromatic hydrocarbons production from petroleum will be a great challenge.Therefore,it is imperative to explore an economic synthesis route for aromatic hydrocarbons.In recent years,with the rapid development of the biodiesel market,the utilization of the byproduc-glycerol has become a research hotspot.The production of high value-added aromatics from glycerol can not only provide a new way for the synthesis of aromatics,but also promote the sustainable development of biomass energy.HZSM-5 zeolite,as a catalyst with unique three-dimensiomal pore structure and adjustable acidic sites,shows good aromatic selectivity for glycerol aromatization.However,the sole presence of micropores with pore size below 1 nm seriously restricts the diffusion rates of coke precursors.Moreover,the coke precursors could easily polymerize to form coke on acid sites and led to the deactivation of the zeolite.In this paper,HZSM-5 zeolite will be modified from two aspects.On one hand,the nano-HZSM-5 zeolite,which could provide more active sites and reduce diffusion path,was synthesized by different additives.On the other hand,active metal was introduced to nano-HZSM-5 zeolite to adjust the acid sites,and thus improved the selectivity of aromatic hydrocarbons.Herein,the nano-HZSM-5 zeolites were synthesized by hydrothermal method with five different additives(CMC-Na,NaCl,SA,PEG-10000 and KH-560).The catalytic performance of the prepared zeolites was investigated in the aromatization of glycerol under 0.1 MPa,400°C,0.96 h~-11 WHSV.It was found that the HZSM-5zeolite modified with CMC-Na,NaCl and SA additives had smaller crystals(less than100 nm),while the zeolites modified with PEG-10000 and KH-560 additives had lower crystallinity and bigger crystals.Moreover,a certain number of mesopores could be introduced into the zeolite modified with PEG-10000 and KH-560 additives.Overall,the zeolite modified with SA had more acid sites,larger intercrystal mesopores and smaller crystals,which increased the BTX carbon yield from 22%to35%and service lifetime from 3.5 h to 8.5 h.Therefore,SA was chosen as the optimal additive and the influence of synthesis conditions on zeolite was investigated.The results showed that the prepared sample had higher crystallinity,moderate acidic properties,larger pore volume and higher aromatic selectivity in glycerol aromatization under the crystallization temperature of 170°C,crystallization time of48 h,the mass of SA took up the the total mass of raw materials of 0.009 and the addition after TEOS.The active metal Sn was introduced into the zeolite modified with SA by the impregnation method and isomorphous substitution method respectively.The isomorphous substitution method did not cause a decrease in service lifetime.Nevertheless,the metal introduced by impregnation method could block the pore of zeolite,which caused a barrier for the diffusion of coke precursor and a decrease in service lifetime.Then other active metals(Sn,Zn,Cd,Mn)were introduced into the zeolite by isomorphous substitution method.Higher BTX yield was achieved on the zeolite modified with Zn,which was up to 40%.The incorporated Zn may preferentially accelerate the dehydrogenation of naphthene,thereby increasing the selectivity of aromatics.