碱处理法制备微介孔ZSM-5及其加氢脱硫性能的研究

STUDY ON PREPARATION OF MICRO-MESOPOROUS ZSM-5 ZEOLITE BY ALKALI TREATMENT AND PROFORMANCE IN HYDRODESULFURIZATION OF FCC GASOLINE

以不同浓度Na2CO3和NaOH溶液对ZSM-5分子筛进行脱硅处理,采用XRD,SEM,BET,NH3-TPD手段对处理前后的分子筛进行表征,并考察不同浓度碱液处理并负载Co、Mo金属的催化剂对加氢脱硫性能的影响。结果表明:碱处理可以得到微介孔结构的ZSM-5分子筛,并可调变分子筛的酸性,提高脱硫效果与烯烃芳构化活性;NaOH溶液对ZSM-5分子筛的晶体结构影响较大,经低浓度的NaOH溶液(0.5mol/L)处理后,ZSM-5分子筛的相对结晶度下降至90.8%;NaOH溶液浓度为1.0mol/L时,ZSM-5分子筛的结晶度仅为78.3%,比表面积、孔体积和孔径均下降;采用Na2CO3溶液处理时,在得到微介孔结构ZSM-5分子筛的同时对ZSM-5分子筛的晶体结构影响较小,当Na2CO3溶液浓度为4.0mol/L时,得到的Co-Mo/ZSM-5催化剂在FCC汽油加氢脱硫及芳构化反应中,脱硫率高达94.2%,汽油中芳烃体积分数增加20.7百分点。

ZSM-5zeolites were treated by different concentrations of Na2CO3 and NaOH solution.The molecular sieves before and after alkali treatment were characterized by XRD,BET,SEM and NH3-TPD techniques.The effects of different concentrations of alkali solution for the performance of hydrodesulfurization and aromatization were investigated.The results showed that ZSM-5zeolite was apt to forming micro-mesoporous structure after alkali-treatment.Alkali-treatment could modulate the acidity,and significantly improve the activity of desulfurization and olefins aromatization.Also,NaOH solution impacts on the crystal structure of ZSM-5zeolite.ZSM-5zeolite was subjected to a decrease of the BET surface area,pore size and pore volume at the low concentration of NaOH solution（0.5mol/L）,and the relative crystallization declined to 90.8%.When the concentration of NaOH solution is 1.0mol/L,the crystallinity of ZSM-5zeolite is only 78.3%.Whereas,when ZSM-5zeolite was subjected to desilication in the Na2CO3 solution,micro-mesoporous ZSM-5zeolite can be obtained with the crystal structure hardly affected.When the Co-Mo/ZSM-5catalyst obtained at the Na2CO3 solution concentration of4.0mol/L was applied in the hydrodesulfurization and aromatization reaction of FCC gasoline,the desulfurization rate and the aromatics content in gasoline reached 94.2percentage points and 20.7percentage points,respectively.