HZSM-5/SAPO-11负载Cr_2O_3催化转化LPG制低碳烯烃活性研究

SAPO-11晶化液中预置HZSM-5合成了HZSM-5(核)/SAPO-11(壳)复合分子筛。以复合分子筛为载体负载10%Cr_2O_3,研究了其孔分布、酸性质及其对液化石油气(LPG)转化制乙烯和丙烯反应的催化性能。结果表明,复合分子筛由HZSM-5表面包覆不同厚度的SAPO-11微晶组成,随着晶化时间延长,复合分子筛壳层厚度增加。复合分子筛负载Cr_2O_3催化剂的介孔率先增加后降低;弱酸量先增加后降低,强酸强度增加,强酸量先降低后增加,强酸密度减小。复合分子筛载体在LPG选择转化反应中催化性能优于单个分子筛和机械混合分子筛,其中,晶化12 h合成样品负载Cr_2O_3用于LPG转化反应对原料总转化率和乙烯+丙烯选择性最高,分别为42.63%和65.89%,CH_4和C_(5+)选择性分别为6.32%和15.48%。通过控制晶化时间可调变壳层厚度、复合分子筛介孔率以及酸性质,改善产物分布。

Catalytic performance of SAPO-11/HZSM-5 composite supported Cr2O3 in the transformation of LPG to light olefins

HZSM-5(core)/SAPO-11(shell) composite molecular sieves were hydrothermally synthesized by crystallization of SAPO-11 outside HZSM-5 surface. After loading 10% Cr₂O₃, the pore distribution, acidity, and catalytic activity of the composite supported Cr₂O₃ in the transformation of liquefied petroleum gas (LPG) to ethene and propene were investigated. The results showed the HZSM-5 surface was coated with SAPO-11 microcrystalline of different thicknesses. With the increase of crystallization time, the shell thickness of the composite molecular sieves is increased; the mesoporosity and acidity can then be regulated by controlling the shell thickness. The composite supported Cr₂O₃ exhibits superior activity in the transformation of LPG to olefins than the single molecular sieves or mechanically mixed ones. The Cr₂O₃ catalyst supported on the composite by crystallization for 12 h gives the highest activity and selectivity to the target products; the feed conversion and the selectivity to ethene and propene are 42.63% and 65.89%, respectively, while the selectivities to CH₄ and C₅₊ are 6.32% and 15.48%, respectively.