HZSM-5/SAPO-5复合分子筛的制备及其在异丁烷芳构化反应中的催化性能研究

Synthesis of HZSM-5/SAPO-5 composites and their catalytic behavior in isobutane aromatization

以三乙胺为模板剂,将十六烷基三甲基溴化铵(CTAB)表面改性的HZSM-5投入SAPO-5合成母液中制备了HZSM-5/SAPO-5复合分子筛。采用XRD、FTIR、SEM、NH3-TPD和Py-IR等表征了合成样品结构、形貌和酸性,对比考察了HZSM-5、机械混合分子筛HZSM-5&SAPO-5(MZS)和复合分子筛HZSM-5/SAPO-5(CSZC)在异丁烷芳构化中的催化性能。结果表明:HZSM-5/SAPO-5为片状SAPO-5包覆于HZSM-5表面的复合结构,且由于弱酸型SAPO-5的引入和包覆,使复合分子筛的强、弱酸量和酸强度均低于MZS和HZSM-5,抑制了分子筛强酸位上异丁烷芳构化裂解副反应的发生,提高了其强弱酸协同芳构化作用,同时可能由于CTAB的改性使HZSM-5表面产生少量介孔,提高了CSZC的容炭能力,芳构化反应稳定性提高。CSZC上异丁烷芳构化生成苯、二甲苯等目标产物的选择性较之HZSM-5和MZS大幅提高。

HZSM-5/SAPO-5 composite molecular sieves were prepared by using triethylamine as a template and adding cetyltrimethylammonium bromide （CTAB） surface-modified HZSM-5 into SAPO-5 synthetic mother liquor. HZSM-5 were firstly modified by cetyhrimethylammonium bromide （CTAB）, then HZSM-5 （CTAB） were added into low temperature crystallized gel of SAPO-5 to adsorb SAPO-5 crystallites, followed by crystallization in 200℃ for 24h to obtain HZSM-5/SAPO-5 composites （CSZC）. XRD, FT-IR, SEM, NH3-TPD and Py-IR were used to characterize the structure and acidity of the molecular sieves, and their catalytic behavior in isobutane aromatization were investigated. The results showed that CSZC were composed of HZSM-5 covered by 1.5lxmxl.5μm lamellar SAPO-5, due to which the strong acid sites of HZSM-5 were partially covered and the acid amount and strength of CSZC were less than MZS and HZSM-5, thus the cracking of iso-butane on strong acid sites was supressed and the synergetic aromatization was promoted. At the same time the capability of carbon accomodation is also improved possibly because the modification of HZSM-5 by CTAB could lead to forming some mesopores. The aromatization selectivity and catalytic stability of of CSZC were higher than that of HZSM-5 and MZS. The highest selectivity of of benzene and xylene could be achieved on CSZC.