Method for synthesizing highly-oriented MFI (Melt Flow Index) molecular sieve membrane through controlled secondary growth of twin crystal

Abstract

The invention discloses a method for synthesizing a highly-oriented MFI (Melt Flow Index) molecular sieve membrane through controlled secondary growth of a twin crystal. The method comprises the following steps of: (1) preparing secondary growth synthetic fluid consisting of ethyl orthosilicate, tetrapropyl ammonium hydroxide, sodium hydroxide and water in the molar ratio of 1:(0.001-0.60):(0.001-0.20):(10-1000); (2) stirring the synthetic fluid at room temperature for 1-10 hours, putting the stirred synthetic fluid into a synthesis kettle, putting a support body coated with a b axis orientedcrystal seed layer into the synthesis kettle, sealing the synthesis kettle, heating, and synthesizing at the temperature of between 120 DEG C and 200 DEG C for 10-300 minutes; and (3) washing and drying to obtain the oriented MFI molecular sieve membrane from the support body. The MFI molecular sieve membrane synthesized by the method is highly oriented in a b axis, the method is easy to operate,a molecular sieve membrane layer has high orientation, the synthetic fluid can be recycled, cost is lowered, and pollution is reduced.

Description

technical field [0001] The invention relates to the synthesis of MFI molecular sieve membranes, and in particular provides a method for synthesizing highly oriented MFI molecular sieve membranes through controlled secondary growth of twins. Background technique [0002] Molecular sieve membrane has a regular pore structure, unique mechanical and electronic properties, and excellent thermal stability, chemical stability and biological stability, so it is widely used in material separation, membrane reactors, chemical sensors, electrodes, low dielectric Constant materials and anti-corrosion coatings and many other fields. At present, the molecular sieve membranes reported in the literature mainly include LTA type, T type, MFI type, FAU type, MOR type, etc., among which the MFI type molecular sieve membrane has attracted much attention. This is because: (1) the pore size of the MFI molecular sieve is equivalent to the molecular size of many important industrial chemicals; (2) ...

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Problems solved by technology

The advantages of the in-situ hydrothermal synthesis method are simple operation, strong applicability, and low cost; however, while the in-situ hydrothermal synthesis method forms a molecular sieve membrane on the support, a large number of molecular sieve crystals are also formed in the bulk phase, and it is difficult to avoid twinning. generation, making it difficult to synthesize highly oriented molecular sieve membranes

[0004] The secondary growth method for synthesizing oriented molecular sieve membranes can better control the oriented growth of molecular sieve crystals because of the use of oriented seed crystal layers; however, the secondary growth method needs to obtain a uniformly coated seed crystal layer, and the operation steps are relatively complicated The preparation cost is high, and the secondary growth process is often accompanied by the formation of other orientation twins, which affects the orientation of the molecular sieve membrane

In the secondary growth process, the preheated synthetic solution is the key, if using fresh synthetic solution will generate a large number of a Axis-oriented twins, cannot obtain height b Axial Oriented MFI Molecular Sieve Membrane

[0008] The above-mentioned secondary growth method either uses a special complex structure-directing agent, or the steps are cumbersome, or the energy consumption is high, the pollution is serious, and the cost is high

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