Structural characteristics of MCM-22 molecular sieve

MCM-22 molecular sieve has two sets of non-interconnected multi-dimensional channel systems. One set is a two-dimensional sinusoidal channel with an effective aperture of (0.4nmX0.59nm), and the other set is composed of a supercage (0.71nmX0.71mX 1.82nm) containing a twelve-membered ring, and its opening is also a ten-membered ring.

MCM-22 molecular sieve is slightly smaller than β zeolite, which is also a twelve-membered ring (the linear channel pore size is about 0.57nmX0.75nm, and the nonlinear tortuous channel pore size is about 0.56nmX0.65nm). Therefore, MCM-22 molecular sieve has better selectivity for certain reactions. For example, when benzene is alkylated with ethylene and propylene to produce styrene and cumene, the by-products of diethylbenzene and dicumyl -22 molecular sieve is blocked in the ten-membered ring channel, and has high selectivity. The MCM-22 molecular sieve has a larger pore volume than the ten-membered ZSM-5. When more branched hydrocarbon isomers participate in the reaction, its entry into the ZSM-5 ten-membered ring pores is blocked. However, MCM- The twelve-membered ring channel of 22 molecular sieve is unblocked for multi-branched compounds, and more I-Cs will be formed. In addition, the difference in the diffusion properties of different molecules also reflects its shape selectivity.