Preparation of magnesium metal modified low-silicon SSZ-13 molecular sieve and MTO reaction performance thereof

Abstract

The invention provides a preparation method of a magnesium metal modified low-silicon molecular sieve material. The magnesium metal modified low-silicon molecular sieve material comprises 0.1-6% of magnesium (calculated by magnesium oxide), 5.36-20% of aluminum (calculated by aluminum oxide), 69-94.5% of silicon (calculated by silicon oxide) and 0.01-5% of alkali metal (calculated by oxide), and has a CHA type topological structure, and the specific surface (through the BET method) of the magnesium metal modified low-silicon molecular sieve material is no smaller than 565 m2 / g after the magnesium metal modified low-silicon molecular sieve material is calcinated at 630 DEG C for 4 h. The preparation method of the magnesium metal modified low-silicon molecular sieve material comprises the steps that a template agent and a sodium hydroxide aqueous solution are added into an alkaline silica sol to be uniformly stirred, aluminum sulfate is added to be uniformly stirred, and chabasite crystalline phase seed crystal is added to be stirred at room temperature for 4 h to obtain uniform gel; and a product is obtained through crystallization, calcination and magnesium ion exchange, wherein magnesium ions can also be led in the molecular sieve synthesization process by one step. The molecular sieve material prepared through the preparation method has the advantages that the molecular sieve material is low in silicon-aluminum ratio, adjustable in acid center concentration, low in acid strength and high in MTO diolefin selectivity, and a large amount of ammonium chloride waste liquid does not exist in the preparation process.

Description

technical field [0001] The invention relates to a preparation method of metal magnesium-modified low-silicon SSZ-13 molecular sieve and its application as a methanol-to-olefin (MTO) catalyst. Background technique [0002] Methanol-to-olefins (MTO) is a new process that can replace the traditional petroleum route to produce low-carbon olefins. In recent years, with the shortage of petroleum resources, this process has attracted widespread attention from all over the world. The core of the MTO process is the catalyst problem. At present, the active component of MTO catalyst commonly used in the market is SAPO-34 molecular sieve. At the same time, the MTO properties of silico-alumina zeolite molecular sieves with the same CHA structure as SAPO-34 molecular sieves have also been intensively studied. [0003] SSZ-13 molecular sieve was invented by American Chevron (Chevron) Petroleum Company and disclosed in patent US4544538. Since the SSZ-13 molecular sieve synthesized in thi...

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Problems solved by technology

However, with the increase of the silicon-aluminum ratio of the SSZ-13 molecular sieve, the specific surface area of ​​the molecular sieve product decreases, the crystallinity decreases, and the acidity increases.

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