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

Catalytic performance of SAPO-11/HZSM-5 composite supported Cr_2O_3 in the transformation of LPG to light olefins

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。

HZSM-5(core)/SAPO-l1(shell)composite molecular sieves were hydrothermally synthesized by crystallization of SAPO-11outside HZSM-5surface.After loading10%Cr203,the pore distribution,acidity,and catalytic activity of the composite supported Cr203in the transformation of liquefied petroleum gas(LPG)to ethene and propene were investigated.The results showed the HZSM-5surface was coated with SAPO-11microcrystalline 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 Cr2O3exhibits superior activity in the transformation of LPG to olefins than the single molecular sieves or mechanically mixed ones.The Cr2O3catalyst supported on the composite by crystallization for12h gives the highest activity and selectivity to the target products;the feed conversion and the selectivity to ethene and propene are42.63%and65.89%,respectively,while the selectivities to CH4and C5+are6.32%and15.48%,respectively.