氢氟酸改性纳米ZSM-5分子筛选择性催化生物乙醇制丙烯

Selective Catalytic Conversion of Bio-ethanol to Propene by Hydrofluoric AcidModified Nano-ZSM-5 Zeolites

采用不同含量氢氟酸(HF)后处理制备一系列HF改性的纳米ZSM-5分子筛催化剂,用于在温度500℃、压力0.1 MPa和质量空速(MHSV)为10 h^(-1)的条件下选择性转化生物乙醇制丙烯反应。采用X射线衍射、N2物理吸附、ICP-OES、热重分析及NH3-TPD等手段对改性和未改性的催化剂进行表征。结果表明:HF溶液改性不仅调变ZSM-5分子筛的酸性质,而且对ZSM-5分子筛孔道结构有较大的影响。ZSM-5分子筛酸性的减弱抑制反应过程中焦炭的生成,介孔增多提高产物的扩散能力,从而抑制焦炭的生成并增强催化剂的抗积炭能力。适量(HF质量分数为6%)的HF溶液改性处理,显著改善和延长纳米ZSM-5分子筛的丙烯选择性和使用寿命。此外,对失活催化剂进行表征可知,积炭和酸性减弱可能是催化剂失活的主要原因。

The modified nano-ZSM-5 zeolites were prepared by post-treatment with different contents of hydrofluoric acid(HF)solution for selective conversion of bio-ethanol to propene at temperature of 500℃,pressure of 0.1 MPa and MHSV of 10 h^(-1).The modified and unmodified catalysts were characterized by XRD,N_(2)physisorption,ICP-OES,TG and NH 3-TPD techniques.The results show that HF modification can not only change the acid properties of ZSM-5 zeolites,but also have a great effect on their pore structure.The decrease of acidity in ZSM-5 zeolites has inhibited the formation of coke during the reaction,and the increase of mesopores has enhanced the diffusion ability of products,thus inhibiting the formation of coke and improving the anti-coke ability of catalysts.Therefore,the propene selectivity and working life of nano-ZSM-5 zeolites have been significantly improved and prolonged by the modification of HF solution with suitable content(mass fraction of 6%).In addition,the characterization results of the deactivated catalysts indicate that carbon deposition and decreased acidity may be the main factors of catalyst deactivation.