General physical and chemical properties of MCM-22 molecular sieve

General physical and chemical properties of MCM-22 molecular sieve

(1) Pore characteristics: By measuring the adsorption properties of MCM-22 molecular sieve, it was found that the shape of N in MCM-22 adsorption isotherm is Langmuir II type, and its BET specific surface area can reach more than 500 m'/g. According to the pore size distribution of the MCM-22 sample calculated by the H-K method, the pore size distribution curve appears double peaks (see Figure 1-8). It can be seen that it has two regular pore structures, and its average pore size is 0.5nm. Because MCM-22 is composed of a 10MR sinusoidal channel system and a 12MR supercage, its pore volume is larger than that of ZSM-5, which is composed of 10 MR cross channels, and is also larger than the SSZ-24 molecular sieve with one-dimensional 12 MR. But it is smaller than Y-type and Beta molecular sieves with three-dimensional 12MR channel system.

(2) Acidity: As shown in the NH;-TPD spectrum of MCM-22 shown in Figure 1-9, MCM-22 has two strengths of acid centers 96, and the maximum desorption peak temperature of the weak acid center is located near 254°C. The maximum desorption peak temperature of the strong acid center is located near 431°C, which is basically the same as that of ZSM-5 molecules.

Catalytic performance of MCM-22 molecular sieve

Due to its unique pore structure and acidic characteristics, MCM-22 molecules show good catalytic performance in many reaction processes, mainly in the following aspects:

1 Alkylation reaction

MCM-22, MCM-49, MCM-56 and other MWW structural molecules are very good catalysts for the alkylation reaction of olefins and benzene. Abroad, MCM-22 has been industrialized as a process for the conversion of hydrocarbons, especially the alkylation reaction of benzene with ethylene and propylene [0. Compared with USY, Beta and ZSM-5 molecular sieves, MWW molecular sieves have high selectivity for monoalkyl products when the olefin conversion rate is high, and by-products such as olefin oligomerization products, polyalkyl benzene and heavy components are eliminated. rare. In addition, the MCM-22 molecular sieve catalyst also has the characteristics of mild reaction conditions, low benzene-to-ene ratio, and environmental friendliness. Meng w et al. [1106] compared the alkylation reaction performance of benzene and propylene between MCM-22 and Beta molecular sieves. The results show that Beta molecular sieve with a three-dimensional 12 MR channel structure has higher initial alkylation activity, while MCM-22 molecules with 12 MR supercage and 10 MR channels have higher alkylation stability.

Cejka J et al. investigated the alkylation reaction performance of toluene and propylene of MCM-22 and MCM-58 molecular sieves. The results show that the MCM-22 molecular sieve has a very low selectivity for methylcumene, while the ZSM-5 molecular sieve with a 10 MR channel has a high selectivity for methylcumene. This shows that the alkylation reaction of toluene and propylene on MCM-22 molecular sieve may mainly occur on the outer surface (or 12MR holes) or acid sites close to the outer surface (or 12MR supercage closer to the outer surface) 11071.Chen, L et al. 0] investigated the effect of silicon to aluminum ratio (20~60) on the propylene and benzene alkylation performance of MCM-22 molecular sieve. The results show that when the silicon-to-aluminum ratio is 40, the selectivity of cumene and n-propylbenzene reaches the highest, and the selectivity of dicumene and tricumene reaches the lowest.

2 Aromatization reaction

Ga-MCM-22 molecular sieve [9] is used in reforming reaction, and its aromatization performance is comparable to Pt-Re/AlzO; precious metal catalyst. Zn/MCM-22 and Ga/MCM-22 molecular sieves have high activity and selectivity for n-butane aromatization reaction [109]. Mo/MCM-22 molecular sieve has received a lot of research in the oxygen-free aromatization reaction of methane. Su Yy10) and others have shown that the activity of Mo/MCM-22 and Mo/ZSM-5 catalysts are equivalent, but the selectivity and stability of the former are significantly better than the latter: Bai Jie et al. [Research shows that Mo/MCM-22 The reason for the high stability of the catalyst may be that the 12 MR supercage of MCM-22 molecular sieve has a high carbon holding capacity.

3 Catalytic cracking

Corma et al. f2 used n-heptane as raw material to study the cracking performance of MCM-22. The results showed that the catalytic cracking performance of MCM-22 molecular sieve is between 10MR molecules and 12MR molecules. MCM-22[131 molecular sieve is used as FCC catalyst additive. Compared with ZSM-5 molecules, its total gas and dry gas yields are reduced, gasoline losses are reduced, and propylene/propane and butene/butane ratios are increased. It shows that MCM-22 molecular sieve is an excellent catalyst additive for the production of new formulation gasoline. However, the addition amount of MCM-22 molecular sieve is relatively high (mass fraction 13%)3. Our research group applied MCM-22 to the process of cracking C4 and C5 olefins to produce ethylene and propylene, and achieved good propylene selectivity.

In addition, MCM-22 molecular sieve can also be used for toluene disproportionation! 51, 1-butene skeletal isomerization!, olefin oligomerization, hydrocracking, etherification, desulfurization, NOx elimination, n-butane dehydrogenation skeletal isomerization! and other reactions. . .