Catalyst used for isomeric pour point depression of middle distillate in F-T synthesis and special core-shell structure composite molecular sieve of catalyst

Abstract

The invention provides a catalyst used for isomeric pour point depression of middle distillate in F-T synthesis and a special core-shell structure composite molecular sieve of the catalyst. The composite molecular sieve takes a microporous ZSM-22 molecular sieve as a core and takes a mesoporous MCM-41 molecular sieve as a shell, wherein a relative proportion of the microporous ZSM-22 molecular sieve to the mesoporous MCM-41 molecular sieve is adjustable. A preparation method for the composite molecular sieve comprises the steps of: firstly, preparing the ZSM-22 molecular sieve; then, adding alkaline and an organic template agent into a mixed system containing the ZSM-22 molecular sieve for pre-crystallization; and regulating the pH value to 6.5-13.5, and carrying out crystallization treatment, thereby obtaining the composite molecular sieve. The catalyst, which is prepared by taking the core-shell structure ZSM-22 / MCM-41 composite molecular sieve as a carrier, is applied to hydroisomerization reaction of the middle distillate in F-T synthesis, and shows high isomeric selectivity; and especially, highly branched alkane selectivity is obviously improved. In the case that the conversion rate is 91.4%, the isomeric selectivity is kept to be higher than 90%, and the highly branched isomeric selectivity reaches 55.6%.

Description

technical field [0001] The invention relates to a catalyst for the isomerization depreciation of F-T synthetic middle distillate oil and its special core-shell structure composite molecular sieve. Background technique [0002] ZSM-22 molecular sieve has a strong acid center, good hydrothermal stability and unique shape selectivity, and exhibits excellent catalytic performance in long-chain alkane isomerization reactions. However, the active site of the molecular sieve at the orifice is highly acidic, resulting in a strong cracking activity based on the molecular sieve catalyst; and the one-dimensional ten-membered ring pore structure has a large diffusion limit, resulting in the isomerization of the single-branched paraffin as the main product. Mainly, while multi-branched alkanes have lower freezing point and better low temperature fluidity. Generally speaking, the introduction of mesopores into the microporous molecular sieve system can effectively improve the diffusion p...

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Problems solved by technology

However, using this method to treat molecular sieves will destroy the molecular sieve skeleton, resulting in a decrease in its hydrothermal stability, which will inevitably lead to a decrease in the yield of molecular sieves (J.Catal.319(2014)232), and the process needs to be treated by pickling The Al component deposited on the surface of the molecular sieve, the process conditions are very complicated

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