A preparation method of DDR molecular sieve membrane

Abstract

The present invention relates to a method for preparing a DDR molecular sieve membrane. The method comprises preparing a seed suspension of Sigma-1 molecular sieve seeds obtained by ball milling, and coating the seed suspension onto a support. A synthesis solution is prepared by hydrothermal synthesis of a mixture of adamantaneamine, ethyleneamine, deionized water, and silica sol. The membrane is then calcined with ozone to obtain an activated DDR molecular sieve membrane. Compared to the prior art, the method employs a high-boiling-point ethyleneamine compound as a mineralizer, thereby eliminating the problem of toxic gas volatilization associated with the use of ethylenediamine as a mineralizer. Furthermore, the thickness of the prepared DDR molecular sieve membrane is significantly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve membranes, and specifically provides a method for preparing a DDR molecular sieve membrane. Background Art

[0002] Gas separation membranes are an emerging membrane separation technology. Compared to traditional separation technologies, they offer advantages such as low separation energy consumption, small footprint, and zero pollution. Among the numerous membrane materials, molecular sieve membranes have become a hot topic for researchers both domestically and internationally due to their regular pore structure, excellent adsorption properties, thermochemical stability, and mechanical stability. Molecular sieve membranes consist of a continuous and dense layer of molecular sieve grown on a porous support. DDR molecular sieve is a special octahedral molecular sieve that exhibits strong preferential adsorption for CO2. Its effective pore size is 0.36 × 0.44 nm, giving it an inherent advantage in separating small molecule gases.

[0003] In order to promote the practical application of DDR molecular sieve membranes in the field of gas separation, the preparation of highly permeable molecular sieve membranes is key. The gas permeability of molecular sieve membranes is closely related to the thickness of the membrane layer. Increasing the thickness will increase the mass transfer resistance, resulting in a decrease in permeability. Therefore, reducing the thickness of the membrane layer as much as possible while ensuring the density of the membrane layer is an effective solution to improve the permeability. In addition, a large amount of ethylenediamine needs to be added as a mineralizer during the synthesis process of the DDR molecular sieve membrane. Ethylenediamine has a low boiling point and is volatile. It is easy to cause environmental pollution problems and also brings higher requirements for sealing during the high-temperature aging process of the casting liquid. The above factors have hindered the industrial application of DDR molecular sieve membranes. Summary of the Invention

[0004] The present invention provides a method for preparing a DDR molecular sieve membrane, which is characterized by addressing the problem that the thickness of the DDR molecular sieve membrane is difficult to control, resulting in low permeability.

[0005] The present invention provides a method for preparing a DDR molecular sieve membrane, comprising the following steps:

[0006] Step 1: Preparation of a support for loading seed crystals: ball-milled Sigma-1 molecular sieve seed crystals are dissolved in water to form a seed crystal suspension, which is then coated onto a porous support;

[0007] Step 2, preparation of DDR molecular sieve membrane: prepare a synthetic solution by mixing adamantaneamine, ethyleneamine, deionized water and silica sol in a certain molar ratio, and prepare the molecular sieve membrane by a secondary hydrothermal synthesis method.

[0008] Step 3: Activation of DDR molecular membrane: The synthesized DDR molecular sieve membrane is treated with ozone atmosphere to obtain an activated DDR molecular sieve membrane.

[0009] In the first step, the mass concentration of the Sigma-1 seed crystal suspension is 0.1wt.%-2wt.%, and the coating method is immersion pulling.

[0010] In the first step, the support layer is made of porous ceramic.

[0011] In the second step, the ethyleneamine is one or more of diethylenetriamine, triethylenetetramine and tetraethylenepentamine.

[0012] In the second step, the molar ratio of SiO2, adamantaneamine, ethyleneamine and water in the synthetic liquid silicon source is 1:0.01-0.06:0.2-1:20-80.

[0013] In the second step, the temperature of the secondary hydrothermal synthesis is 120-180° C., and the reaction time is 3-48 hours.

[0014] In the third step, the synthesized DDR molecular sieve membrane is treated with ozone atmosphere for 72-192 hours at a temperature of 200-250°C.

[0015] The present invention also provides a DDR molecular sieve membrane prepared by the above preparation method.

[0016] The present invention also provides a use of the above-mentioned DDR molecular sieve membrane in gas separation.

[0017] The gas separation refers to CO2 / CH4 gas separation.

[0018] Compared with the existing technology, the present invention uses high-boiling-point ethyleneamine as a mineralizer to prepare DDR molecular sieve membranes, avoiding the environmental pollution and high sealing problems caused by using volatile ethylenediamine as a mineralizer. In addition, the higher molecular weight of ethyleneamine makes the DDR molecular sieve membrane prepared under the same conditions thinner, which is conducive to the preparation of DDR molecular sieve membranes with higher flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 These are SEM images of the surface and cross-section of the DDR molecular sieve membrane prepared in Example 1.

[0020] Figure 2 These are SEM images of the surface and cross-section of the DDR molecular sieve membrane prepared in Comparative Example 1. DETAILED DESCRIPTION

[0021] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0022] Example 1

[0023] Sigma-1 molecular sieve (approximately 2 μm in particle size) was ball-milled in a high-energy planetary ball mill using a 1:30 ratio of the original molecular sieve to deionized water. After milling, a defined mass fraction of ball-milled Sigma-1 molecular sieve suspension was obtained by adding a predetermined amount of deionized water to clean the molecular sieve in the mill. A 0.5 wt.% ball-milled Sigma-1 molecular sieve seed solution was prepared. A pretreated hollow fiber support was then slowly and vertically lowered into the seed solution. After immersion for 15 seconds, the support was slowly removed vertically and placed in a 60°C oven to dry.

[0024] A synthetic liquid precursor was prepared using amantadine, triethylenetetramine, deionized water, and silica sol in a molar ratio of silane: amantadine: triethylenetetramine: water = 1:0.03:0.5:40. The specific steps are as follows: First, amantadine and triethylenetetramine were mixed and stirred with ultrasonication to dissolve the amantadine. Then, deionized water was quickly added and stirred in a water bath at 60°C for 20 minutes to clarify the synthetic liquid. Finally, silica sol was slowly added dropwise while stirring and aged in a water bath at 60°C for 1 hour. A hollow fiber substrate coated with a dense seed layer was placed vertically in a polytetrafluoroethylene reactor filled with the synthetic liquid. The oven temperature was set to 150°C for 24 hours. The prepared membrane was then calcined in an ozone atmosphere at 210°C for 4 days to remove the template.

[0025] Figure 1 This is a SEM image of the DDR molecular sieve membrane prepared in Example 1. The molecular sieve membrane surface exhibits good crystallinity, with prismatic morphology, well-intergrown, continuous, and dense particles. The molecular sieve membrane thickness is relatively uniform, approximately 3 μm.

[0026] The resulting DDR molecular sieve membrane was tested for CO₂ / CH₄ gas separation under the following conditions: room temperature, equimolar feed, and a feed pressure of 0.1 MPa. The permeate flow rate was measured using a soap bubble flowmeter. The permeate gas composition was analyzed using a gas chromatograph using a HAYES EP-DB column.

[0027] The calculation formula of gas permeability is: P = J / ΔP. Where P is gas permeability, unit is mol·m -2 ·s -1 ·Pa -1 , J is the average flux per unit time, mol·m -2 ·s -1 ; ΔP is the transmembrane pressure difference.

[0028] Separation selectivity calculation formula: α=P CO2 / P CH4 , that is, the ratio of the permeability of CO2 to CH4.

[0029] The CO2 / CH4 gas separation test results of the DDR molecular sieve membrane are shown below. At 0.1 MPa, the average CO2 permeability is 1.1×10 -7 mol·m -2 ·s -1 ·Pa -1 , the separation selectivity of CO2 / CH4 is 462.

[0030] Comparative Example 1

[0031] The difference from Example 1 is that ethylenediamine is used as the mineralizer, the temperature is set to 140° C., the time is 44 h, and the remaining steps are the same as Example 1.

[0032] Figure 2 This is a SEM image of the DDR molecular sieve membrane prepared in Comparative Example 1. The crystals on the membrane surface show a sharp morphology and good crystallinity. The membrane thickness is about 5 μm, and there are many miscellaneous crystals on the membrane surface.

[0033] The CO2 / CH4 gas separation test results of the DDR molecular sieve membrane are shown below. At 0.1 MPa, the average CO2 permeability is 0.4×10 -7 mol·m -2 ·s -1 ·Pa -1 , the separation selectivity of CO2 / CH4 is 315.

Claims

1. A method for preparing a DDR molecular sieve membrane, characterized in that: The steps include: Step 1: Preparation of a support for loading seed crystals: ball-milled Sigma-1 molecular sieve seed crystals are dissolved in water to form a seed crystal suspension, which is then coated onto a porous support; Step 2: Preparation of DDR molecular sieve membrane: a synthesis solution is prepared by mixing adamantane amine, ethyleneamine, deionized water, and silica sol in a certain molar ratio, and a molecular sieve membrane is prepared by a secondary hydrothermal synthesis method; Step 3: Activation of DDR molecular membrane: The synthesized DDR molecular sieve membrane is treated with ozone atmosphere to obtain an activated DDR molecular sieve membrane.

2. The method for preparing a DDR molecular sieve membrane according to claim 1, wherein: In the first step, the mass concentration of the Sigma-1 seed crystal suspension is 0.1wt.%-2wt.%, and the coating method is immersion pulling.

3. The method for preparing a DDR molecular sieve membrane according to claim 1, characterized in that: In the first step, the porous support is made of porous ceramics.

4. The method for preparing a DDR molecular sieve membrane according to claim 1, wherein: In the second step, the ethyleneamine is one or more of diethylenetriamine, triethylenetetramine and tetraethylenepentamine.

5. The method for preparing a DDR molecular sieve membrane according to claim 1, characterized in that: In the second step, the molar ratio of SiO2, adamantaneamine, ethyleneamine and water in the synthetic liquid silicon source is 1:0.01-0.06:0.2-1:20-80.

6. The method for preparing a DDR molecular sieve membrane according to claim 1, characterized in that: In the second step, the temperature of the secondary hydrothermal synthesis is 120-180° C., and the reaction time is 3-48 hours.

7. The method for preparing a DDR molecular sieve membrane according to claim 1, characterized in that: In the third step, the synthesized DDR molecular sieve membrane is treated with ozone atmosphere for 72-192 hours at a temperature of 200-250°C.

8. A DDR molecular sieve membrane prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the DDR molecular sieve membrane according to claim 8 in gas separation.

10. The use according to claim 9, characterized in that The gas separation refers to CO2 / CH4 gas separation.

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