Preparation of Modified β Zeolite Catalysts and Research on Alkylation of Toluene with Tert-butylalcohol

Author:Wang Yuan Yuan

Supervisor:song hua

Database:Doctor

Degree Year:2016

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Pages:127

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The 4-tert-butyltoluene(PTBT)is an important chemical material,which is widely used in the chemical industry.The traditional processes for toluene butylation reaction are typically associated with problems of great acid consumption,corrosion,waste disposal and separation of catalyst.In order to overcome these drawbacks,considerable effort has been put into the development of environmentally friendly zeolites with high catalytic activity and high selectivity for alkylation of toluene with tert-butyl alcohol(TBA).In this work,selective synthesis of PTBT by alkylation of toluene and TBA was performed as probe reaction to study the catalytic activity of different zeolites,transitional metal oxide modified Hβ,acid modified Hβ and heteropolyacid modified Hβ.The correlations of catalytic activity and para-selectivity with acidity and pore structure were revealed.The kinetics model and hermodynamic model were established.The reaction mechanism for the alkylation reaction system was also proposed.The main research results were listed as follows.1.Alkylation of toluene with TBA over different zeolite catalysts(Hβ(Si/Al=25),HM(Si/Al=25),HZSM-5(Si/Al=25)and HY(Si/Al=12))were studied,the results showed that the order of catalytic activity for alkylation of toluene with TBA over different zeolite catalysts was Hβ>HY>HM>HZSM-5.However,this order did not match with the order of total acid(Hβ>HY>HZSM-5>HM)or the order of B acid(HZSM-5>Hβ>HY>HM).This result confirmed that acidity alone was an insufficient factor for catalytic activity.The channel structure of individual zeolite also played an important role in the catalytic activity.Hβ(0.66nm×0.67nm)with high acidity was found to be the most efficient catalyst for this particular alkylation process.Despite HZSM-5 has the highest amount of B acidity,the dimensions(0.54nm×0.56 nm and 0.51nm×0.55nm)of 10-ring portals in HZSM-5 were too short,as a consequence the conversion of toluene over HZSM-5 was low.The toluene conversion of 58.4% with PTBT selectivity of 67.3% could be obtained at the following optimal conditions: the cyclohexane amount of 60 mL,the Hβ zeolite amount of 1.0 g,the n(TBA):n(toluene)ratio of 3,the reaction temperature of 190 °C and the reaction time of 4 h.The kinetics of alkylation of toluene with TBA over Hβ could be described by the pseudo first order model,and the apparent activation energy(Ea)was 19.5kJ/mol.2.Alkylation of toluene with TBA over transitional metal oxide modified Hβ catalysts Fe2O3/Hβ,MnO/Hβ,Co2O3/Hβ,NiO/Hβ and CuO/Hβ)were studied.Compared with parent Hβ zeolite,the catalytic activity of transitional metal oxide modified Hβ catalysts decreased slightly,while the PTBT selectivity increased significantly.The order of catalytic activity over different transitional metal oxide modified Hβ catalysts was Fe2O3/Hβ>MnO/Hβ>Co2O3/Hβ>NiO/Hβ>CuO/Hβ,Fe2O3/Hβ was found to be the most efficient catalyst for this particular alkylation process.Modification of Hβ with Fe2O3 could decrease the strong acidity of Hβ and deactivate the acid sties on the surface,which were beneficial to increase selectivity to PTBT by suppressing further isomerization of the formed PTBT on acid sties.In addition,the narrowed pores after loading of Fe2O3 were beneficial to increase selectivity to PTBT,since PTBT with lower kinetic diameter can diffuse through the narrowed pores of Fe2O3(x)/Hβ much easier than MTBT.The appropriate Fe2O3 loading was 20% and the appropriate calcination temperature was 350°C.The toluene conversion of 57.9% with PTBT selectivity of 82.0% could be obtained at the following optimal conditions: the cyclohexane amount of 60 mL,the Fe2O3(20%)/Hβ amount of 1.0 g,the n(TBA):n(toluene)ratio of 3,the reaction temperature of 180 °C and the reaction time of 4 h.The kinetics of alkylation of toluene with TBA over Fe2O3(20%)/Hβ could be described by the pseudo first order model,and the apparent activation energy(Ea)was 22.7kJ/mol.3.Alkylation of toluene with TBA over acid modified Hβ catalysts(HNA/Hβ,HHA/Hβ,HPA/Hβ,HCA/Hβ,HTA/Hβ and HAA/Hβ)were studied.Compared with parent Hβ zeolite,the catalytic activity of inorganic acid modified Hβ decreased,while that of organic acid modified Hβ increased.The order of catalytic activity over different acid modified Hβ catalysts was HCA/Hβ>HTA/Hβ>HAA/Hβ>HPA/Hβ>HNA/Hβ>HHA/Hβ,HCA/Hβ was found to be the most efficient catalyst for this particular alkylation process.The frame construction of Hβ was not destroyed when using lower concentration of HCA,and the number of micropores,medium strong acid and B acid increased,thus the catalytic activity and the PTBT selectivity increased.However,both non-framework aluminum and framework aluminum can be washed out when using high concentration of HCA,the frame construction of Hβ was destroyed,thus the catalytic activity decreased.The appropriate concentration of HCA was 0.25 mol/L and the appropriate calcination temperature was 550 °C.The toluene conversion of 67.0% with PTBT selectivity of 80.4% could be obtained at the following optimal conditions: the cyclohexane amount of 60 mL,the HCA(0.25)/Hβ amount of 1.0 g,the n(TBA):n(toluene)ratio of 3,the reaction temperature of 180 °C and the reaction time of 4 h.The kinetics of alkylation of toluene with TBA over HCA(0.25)/Hβ could be described by the pseudo first order model,and the apparent activation energy(Ea)was 18.2kJ/mol.4.Alkylation of toluene with TBA over heteropolyacid modified Hβ catalysts(HPW/Hβ,HPMo/Hβ,HSiW/Hβ and HSiMo/Hβ)were stuied.Compared with parent Hβ zeolite,both catalytic activity and para-selectivity of heteropolyacid modified Hβ catalysts increased.The order of catalytic activity over different heteropolyacid modified Hβ catalysts was HPW/Hβ>HSiW/Hβ>HPMo/Hβ>HSiMo/Hβ,the HPW/Hβ was found to be the most efficient catalyst for this particular alkylation process.Modification of Hβ with HPW could increase the total acidity,especially the B acidity of Hβ,which was beneficial for increasing the catalytic activity.In addition,the narrowed pores after loading the HPW were beneficial for increasing selectivity to PTBT,since PTBT with lower kinetic diameter can diffuse through the narrowed pores of HPW(x)/Hβ much easier than MTBT.The appropriate HPW loading was 30% and the appropriate calcination temperature was 450 °C.The toluene conversion of 73.1% with PTBT selectivity of 80.8% could be obtained at the following optimal conditions: the cyclohexane amount of 60 mL,the HPW(30%)/Hβ amount of 1.0 g,the n(TBA):n(toluene)ratio of 3,the reaction temperature of 180 °C and the reaction time of 4 h.The kinetics of alkylation of toluene with TBA over HPW(30%)/Hβ could be described by the pseudo first order model,and the apparent activation energy(Ea)was 15.2kJ/mol.5.The alkylation of toluene with TBA is an electrophilic substitution reaction on the aromatic ring.The tert-butylation of toluene was commonly considered to proceed via carbenium ion mechanisms.Thermodynamics of toluene alkylation with TBA was studied,and the main reactions could be described as follows.The TBA reacted with zeolite to form isobutene,along with removal of water(R(1)).The isobutene reacted with toluene to form PTBT(R(2)).The isobutene reacted with toluene to form MTBT(R(3)).PTBT reacted with the isobutene to form 3,5-DTBT(R(4)).During the temperature range of 313.15 K-473.15 K,the enthalpy of R(1)>0,which showed that the reaction of TBA over zeolite to form isobutene was endothermic reaction.While the enthalpies of R(2),R(3)and R(4)<0,which showed the above three reactions were exothermic reactions.Thus,it suggested that increase in the reaction temperature was favorable to R(1)and unfavorable to R(2),R(3)and R(4).During the temperature range of 313.15 K-473.15 K,the gibbs free energy of R(1)>0,which showed that R(1)could not occur spontaneously.While the gibbs free energies of R(2),R(3)and R(4)<0,which showed that R(2),R(3)and R(4)could occur spontaneously.In addition,the gibbs free energies of R(2),R(3)and R(4)increased with the increasing of temperature,which showed that too high temperature was not beneficial for the alkylation of toluene with TBA,it was necessary to strictly control the reaction temperature.