The ultra-stable Y zeolite, modified β zeolite, and modified ZSM-5 zeolite were characterized by NH3-TPD analysis. The results showed that the acidic substance of modified β zeolite is between that of the Y zeolite and the ZSM-5 zeolite. These three kinds of zeolites were evaluated by using hexane, decane and light diesel serving as feedstocks with different molecular size. The results showed that these three kinds of zeolites had different cracking capability and product distribution obtained for cracking hydrocarbons with different molecular sizes as a result of the difference in pore structure and acidic substances. The modified β zeolite can produce much more C_5~= —C_8~= olefins, which are excellent precursors of propylene. Then the mixed samples of these three kinds of zeolites were tested in the VGO microreactor unit, and the test results showed that the modified β zeolite played a ‘relay role' between the ultra-stable Y zeolite and the modified ZSM-5 zeolite, so that the composite made of the ultra-stable Y zeolite, the modified β zeolite, and the modified ZSM-5 zeolite showed a highest propylene yield and selectivity.
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