The effect of catalyst modification is difficult to balance
HZSM-5, SAPO-11, MCM-22 and other zeolites are promising catalysts for the preparation of 2, 6-dimethyl naphthalene (2,6-DMN) by methylation of naphthalene and methyl naphthalene with methanol.
MCM-22 molecular sieve contains two mutually unconnected multi-dimensional pore system with relatively small pore size, high conversion rate and good stability. A considerable part of naphthalene or methyl naphthalene reacts in the pores on the outer surface of the molecular sieve. As the reaction on the outer surface of the molecular sieve loses pore restriction, there are more side reactions, which leads to low selectivity of 2, 6-DMN.
SAPO-11 molecular sieve is a three-dimensional skeleton structure with non-crossed one-dimensional pore structure composed of ten-membered rings. The pore size of SapO-11 molecular sieve is between that of mesoporous and macroporous molecular sieve. In the alkylation reaction between naphthalene and methanol, Sapo-11 molecular sieve is not only conducive to the diffusion of reactants and products, but also plays a role in the screening of DMN isomers. At the same time, its weak acid content and acid strength can effectively inhibit the isomerization of 2, 6-DMN and improve the selectivity of 2, 6-DMN. As the one-dimensional pore is easy to be blocked by carbon molecules, thus blocking the molecular diffusion, SAPO-11 molecular sieve deactivation is fast and the activity stability is poor. With the progress of the reaction, the conversion rate decreases rapidly.
