Development And Research Of High Performance ZSM-5 Catalyst For Alkylation Of Benzene With Dilute Ethylene To Ethylbenzene

In this thesis,a series of nanoscale HZSM-5 with high Si/Al ratios were synthesized with seeds under the hydrothermal synthesis method,modulating the H₂O/Si O₂ ratio and Si O₂/TPABr ratio,studying the effects of the amount of water and template agent on the molecular sieve morphology,crystallinity and grain size,and selecting the most suitable HZSM-5 synthesis formula.Using gallium nitrate as gallium source instead of aluminum source reagent,introducing Ga atoms into the above HZSM-5 formula to completely replace Al atoms to provide acidity.And a series of Ga-ZSM-5 with different Si/Ga ratios and HZSM-5 with different Si/Al ratios were synthesized,and the effects of Ga atom introduction on the acid properties of molecular sieves and the effects of acid properties on catalytic alkylation of benzene and ethylene were discussed in comparison.Finally,the HZSM-5 molecular sieve catalyst synthesized by the best HZSM-5 formula was used as the precursor,and modified with rare earth metals to obtain a series of ZSM-5 catalysts modified by different concentrations/different modification methods/different kinds of rare earth metals.The effect of rare earth metal modification on the performance of the catalyst was studied.In the experiment,XRD,SEM,N₂-BET,Ar-BET,NH₃-TPD,ICP,Py-IR and TG-DTA were used to characterize the synthesized catalysts,drawing the following conclusions:（1）The HZSM-5 molecular sieve synthesized by the crystalline seed-directed method is cross-shaped,with the length of about 300-500 nm in the a-axis direction and the thickness of about 70-120 nm in the b-axis direction,and changing the feeding H₂O/Si O₂ ratio has an effect on the length ratio of the a-and b-axis of the sample.The crystallinity of the catalyst decreases as the Si O₂/TPABr ratio increases,which means the amount of template agent added decreases,and when the Si O₂/TPABr ratio reaches 32,the crystallinity decreases significantly and a large number of amorphous Si O₂ particles appear,at which time the molecular sieve can no longer be completely crystallized.（2）A series of nanoscale Ga-HZSM-5 with different Si/Ga ratios are synthesized by using gallium nitrate hydrate as the gallium source.Ga-HZSM-5 has the same morphology and grain size as same as Al-HZSM-5,but its acid amount and acid strength are weaker than Al-HZSM-5,and it shows lower activity,high ethyl selectivity in catalytic alkylation reaction of benzene and dilute ethylene,and the by-product xylene is reduced by 30-50%compared with Al-HZSM-5,and it operates stably within 100 h with better anti-carbon accumulation ability.（3）Different kinds of rare earth metals are used to modify HZSM-5.It is found that both La and Y modification reduce the B/L value of the catalyst,and both of them have different degrees of improvement on the reaction performance of the catalyst,and the modification effect has the same trend,but the effect of Y modification is better than that of La modification;While Ce modification increases the B/L value of the catalyst,which leads to serious side reactions,carbon deposition,and the catalyst has a long induction period.From this,the relationship of the modification effect of Y>La>matrix>Ce is obtained.（4）The pickled and unpickled HZSM-5 samples are modified by 3%Yttrium respectively.It is found by comparison that nitric acid pickling treatment on the catalyst before Y modification can significantly improve the modification effect.There is almost no change in the conversion rate of benzene and the carbon deposition rate,which means the modification effect is weak;the B/L value of pickled-modified catalyst is significantly decreased,resulting the C_Benzene and S_EB+DEB are significantly improved,the selectivity of C₉ and C₁₀₊decrease,carbon deposition becomes slow,showing a better ability to resist carbon deposition.（5）The yttrium modification treatment of HZSM-5 within a certain modification ratio can weaken the strong acid strength of the catalyst and decrease the B/L value.At the moment the benzene conversion improves,both ethyl selectivity and carbon deposition resistance of the catalyst.When the modification ratio exceeds a certain value,the effect of yttrium modification starts to decrease,and the influence on the amount of B acid disappears,and a large amount of weak acids catalyzing ethylene oligomerization are introduced to generate carbon deposition precursors,which decrease ethyl selectivity,and increase C₉ selectivity,but the ability to resist carbon deposition is not improved significantly.