Catalytic Synthesis of p-xylene from Biomass-derived 2,5-dimethylfuran Over Modified Al-rich H-Beta Zeolites and Functionalized MCM-41
Author:Zhao Rong Rong
Supervisor:zhang wei ping
As a main source of synthetic polyester,p-xylene(PX)is the most widely used one among o,m,p-xylene.It can be obtained from the cycloaddition of biomass-derived 2,5-dimethylfuran(DMF)and ethylene(dehydrated from ethanol)via Diels-Alder reaction and subsequent dehydration process.This route to renewable PX has great significance on the sustainable development of the petrochemical industry.In this thesis the catalytic processes for PX synthesized by 2,5-DMF and ethylene over dealuminated Al-rich H-Beta zeolites as well as by 2,5-DMF and ethanol over sulfonic-group functionalized MCM-41 were developed.The relationship between structure,acidity and reaction performances of modified H-Beta zeolites for the reaction of 2,5-DMF and ethylene was systematically explored.The stability and regeneration ability of modified H-Beta were also investigated in detail.Through the comparative study of reaction performances of 2,5-DMF and ethanol to PX over H-Beta zeolite and functionalized MCM-41,the formation rule of carbonceous species was revealed,which further improves the sustainability of PX production.The main findings of this thesis are summarized as follows:(1)A series of H-Beta zeolites with different Si/Al ratios,derived from the acid treating Al-rich H-Beta from organo-template free synthesis,were employed to catalyze 2,5-DMF and ethylene to produce PX.Among which,H-Beta zeolite with Si/Al ratio of 22 dealuminated from Al-rich H-Beta zeolite was found to be an excellent catalyst for the production of PX.2,5-DMF conversion of 99%and the PX yield of 97%were obtained under the optimized conditions.Solid-state NMR characterization results show that the excellent performance of dealuminated H-Beta is closely related to its proper acid strength,acid amount,B/L acid ratio and the presence of secondary pore system.Besides,H-Beta-22 zeolite also exhibits good stability.After five successive regeneration cycles,the yield of PX is still as high as 85%without obvious dealumination.(2)The influences of different modification methods on the structure and acidity of dealuminated H-Beta zeolite as well as on the reaction performances and coke deposit for 2,5-DMF and ethylene were systematically studied.When H-Beta zeolite modified by Al(NO)3,the contents of framework Al and Bronsted acid sites increase obviously,producing more carbonceous species with low H/C ratio.While for H-Beta zeolite modified by Al(O-i-Pr)3,more extraframework Al are formed,leading to severer coke deposit.However,the PX yield reaches as high as 97%for H-Beta zeolite doped with low γ-Al2O3 dosage.Moreover,the amount of coke deposit decreases from 12 wt%to 7 wt%.(3)The reaction between 2,5-DMF and ethanol was studied comparatively over dealuminated H-Beta zeolite and functionalized mesoporous MCM-41.It is found that the sulfonic group functionalized MCM-41 shows better catalytic performances.2,5-DMF conversion of 79%,PX selectivity of 80%and its yield of 63%were obtained under the optimized conditions,which is better than the literature results.Solid-state NMR,TG and TPO characterizations show that silylated MCM-41-SO3H with NH3 pre-treatment has proper amount and strength of Bronsted acid sites,which result in the increase of PX selectivity and reduction of the coke deposit amount to 4 wt%.This significantly enhances the utilization efficiency of carbon atoms.