What are the disadvantages of too high a content of ZSM-5 in catalytic cracking catalysts?
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I would like to ask everyone: increasing the proportion of ZSM-5 selective molecular sieve in catalytic cracking catalysts can improve the octane number of gasoline as well as the yield of propylene； But what will be the consequences if the proportion of ZSM-5 shape-selective molecular sieves increases too much?
Following your reasoning, the gas output of the device should increase, which in turn will raise the load on the compressor; therefore, careful attention is needed to pressure control for both devices. You can continue to derive further along this line of thought......
Increasing the octane rating of gasoline also means increasing the olefin content, but there are also standards for the olefin and aromatic content in gasoline.
ZSM-5 selective molecular sieves have the effect of reducing the olefin content and increasing the octane rating of gasoline; (reducing the olefin content inevitably lowers the octane rating of gasoline.) ZSM-5 selective molecular sieves exhibit three reaction characteristics: 1. They promote hydrogen transfer reactions to saturate the olefins. 2. Selective cracking, which converts the olefins in gasoline into C3-C4 olefins. 3. Increase the content of saturated hydrocarbons and the degree of isomerization. If the proportion of ZSM-5 selective molecular sieve is increased, the hydrogen transfer reaction has a significant impact on the selectivity of the product; increasing the silica-alumina ratio of the zeolite **enhances the isomerization reaction.
Molecular sieves have small pore sizes, making them unsuitable for cracking large molecules, which results in an increase in gas volume.