Boron modified HZSM-5 molecular sieve, preparation method and application thereof

Abstract

The invention discloses a method for preparing nanoscale boron modified HZSM-5 by seed crystal directing. The method comprises the steps as follows: (1) mixing an aluminum source, a silicon source, an alkali source, a boron source, ZSM-5 molecular sieve seed crystals and water, adjusting the pH of an obtained mixture to 10-12 and mixing the mixture uniformly to form gel; (2) crystallizing the gel in a reactor, and performing solid-liquid separation, washing and drying on a crystallized product to obtain a dried crystallized product; (3) adding the dried crystallized product in an ammonium salt solution for ion exchange to obtain an ammonia type ZSM-5 molecular sieve; (4) roasting the ammonia type ZSM-5 molecular sieve to obtain HZSM-5. The invention further discloses a molecular sieve prepared by the method and application of the molecular sieve in a reaction of methanol to propylene. The boron modified HZSM-5 requires no roasting of a template agent and is environment-friendly, the propylene yield and the service life are greatly increased, the selectivity of propylene reaches 44.0wt% or higher, and the service life reaches 500 h or longer.

Description

technical field [0001] The invention belongs to the technical field of molecular sieve preparation, and relates to a method for preparing modified ZSM-5, in particular to a seed-guided method for preparing nano-scale boron-modified HZSM-5 molecular sieve, the prepared molecular sieve and its application in methanol to propylene in the application. Background technique [0002] ZSM-5 is an important solid acid catalyst in the chemical industry and the main active component of methanol to propylene (MTP) catalyst. Improving the selectivity of propylene and the service life of the catalyst are particularly important for the MTP process, and one of the research focuses is the preparation and modification of ZSM-5. [0003] The nano-scale ZSM-5 molecular sieve has the advantages of large specific surface area, short pore channel, high catalytic activity, strong anti-coking ability and good stability (CN 1608990 A). The reaction of methanol on ZSM-5 molecular sieve is seriously ...

AI Technical Summary

Problems solved by technology

However, it is usually necessary to add an organic template agent during hydrothermal synthesis, which will not only increase the cost, but also cause environmental pollution caused by the waste liquid discharged after hydrothermal synthesis, and when the ratio of silicon to aluminum is increased, crystallization will form in the early stage. The viscosity and density of the gel will increase, and the amount of water required will also increase, which will reduce the yield

In addition, if the reaction gel mixture is too thick, miscellaneous crystals such as mordenite and quartz will easily appear, which will affect the synthesis effect of ZSM-5 molecular sieve

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