CN108211807B

CN108211807B - Treatment method of molecular sieve membrane

Info

Publication number: CN108211807B
Application number: CN201810036033.XA
Authority: CN
Inventors: 李砚硕
Original assignee: Zhejiang Huiyong New Material Co ltd
Current assignee: Zhejiang Huiyong New Material Co ltd
Priority date: 2018-01-15
Filing date: 2018-01-15
Publication date: 2021-11-23
Anticipated expiration: 2038-01-15
Also published as: CN108211807A

Abstract

The invention discloses a method for treating a molecular sieve. The method includes the step of contacting the molecular sieve with a basic solution. The permeation flux of the molecular sieve membrane can be increased by a simple alkali treatment method, and in some cases, the permeation flux and the separation selectivity of the molecular sieve membrane can be increased even simultaneously. On the other hand, the adopted technical means is simple and easy to implement, has low cost and is easy to realize industrialized application. And the method can be simply butted with the existing production process, is beneficial to upgrading and transforming products by production enterprises, and increases the market competitiveness.

Description

Treatment method of molecular sieve membrane

Technical Field

The invention belongs to the technical field of membrane separation, in particular to the field of molecular sieve membranes, and relates to a molecular sieve membrane performance improvement technology.

Background

The molecular sieve membrane is a novel inorganic separation membrane material, has the advantages of good stability and high separation performance, and is widely applied to the fields of pervaporation and vapor permeation. Two important indicators characterizing the separation performance of molecular sieve membranes are permeation flux and separation selectivity. Usually, by optimizing the synthesis conditions, a molecular sieve membrane with ideal permeation flux and selectivity can be obtained, but in many cases, simultaneous optimization of both is difficult to achieve.

The performance of the molecular sieve membrane can be improved by utilizing a post-treatment method. For example, the defects on the molecular sieve membrane can be eliminated by means of chemical liquid phase deposition, chemical vapor deposition and the like, and the separation selectivity of the molecular sieve membrane is improved. The defects of the molecular sieve membrane can be eliminated through multiple times of synthesis, and the selectivity is improved. The above methods generally result in a reduction in permeate flux.

The present invention has been made in view of the above problems, and it is desirable to find a simple and easy method for effectively improving the performance of a molecular sieve or a molecular sieve membrane.

Disclosure of Invention

The invention aims to provide a simple and feasible method for improving the performance of a molecular sieve membrane. In order to achieve the above object, the present invention discloses a method for treating a molecular sieve, which comprises the step of contacting the molecular sieve with an alkaline solution. In our studies, we found that the permeation flux of the molecular sieve membrane can be increased by a simple alkali treatment method, and in some cases, the permeation flux and the separation selectivity of the molecular sieve membrane can be increased even at the same time. On the other hand, the adopted technical means is simple and easy to implement, has low cost and is easy to realize industrialized application. And the method can be simply butted with the existing production process, is beneficial to upgrading and transforming products by production enterprises, and increases the market competitiveness.

Drawings

FIG. 1, is a schematic diagram of an apparatus for testing parameters according to an embodiment of the present invention.

In the figure: 1, constant-temperature water bath; 2, a raw material tank; 3, a magnetic circulating pump; 4 a membrane module; 5, a heater; 6, a three-way valve; 7, a collector; 8, a buffer bottle; 9 diaphragm pump.

Detailed Description

The invention provides a method for treating a molecular sieve, which comprises the step of contacting the molecular sieve with an alkaline solution.

In a specific embodiment, the alkaline solution has a pH of 8 to 13. Preferably an aqueous alkaline solution prepared from an alkaline substance such as an inorganic base or an organic quaternary ammonium salt base. More specifically, the alkaline substance may be preferably exemplified by, but not limited to, NaOH, KOH, NH₃H₂O, TMAOH (tetramethylammonium hydroxide), TEAH (tetraethylammonium hydroxide), TPAOH (tetrapropylammonium hydroxide), or mixtures thereof. Wherein the mixture refers to one or a mixture of several of the substances according to any proportion. More preferably, the alkaline substance is selected from NaOH, KOH, NH₃H₂O or mixtures thereof. Among these, NaOH or KOH is most preferable.

In particular embodiments, the contacting may be understood in a general sense. The most common treatment modalities that can be defined as contact include, but are not limited to, soaking or rinsing. The soaking time is generally 5-60 min, preferably 15-40 min. The washing should ensure the sufficient contact between the molecular sieve and the alkaline solution, and the time is generally 15-60 min, preferably 20-30 min.

The molecular sieve after alkali treatment can be directly applied or washed to be neutral by water for use. If a rinse step is added, deionized water is preferably used. Whether washing has no substantial effect on the properties of the molecular sieve.

The invention will now be further described by way of specific examples, but the non-limiting examples set forth should not be construed as limiting the scope of the invention in any way.

Unless otherwise indicated, the parameters and results herein are obtained by the following methods:

1. test method

(1) The flexural strength was performed as specified in HY/T064-2002, 5.4.

(2) The separation performance was determined by the following method: and (3) inspecting the pervaporation dehydration performance of the molecular sieve membrane, wherein the operating temperature is 50 ℃, and the raw material liquid is ethanol water solution containing 90% of ethanol. The composition of the permeate and the mass of the permeate collected per unit time were analytically measured, and the water/ethanol separation coefficient and the permeate flux were calculated according to the following formulas.

Separation factor (separation factor): represents the ratio of the relative contents of two substances in the material before and after the molecular sieve membrane separation operation. It is defined as:

in the formula, alpha_i/jRepresents the separation coefficient of the molecular sieve membrane for i (preferential permeation membrane) and j components; x is the number of_i,p(x_j,p) Represents the mass fraction of i (j) components in the permeate; x is the number of_i,f(x_j,f) Represents the mass fraction of the i (j) component in the raw material.

Permeation flux (permeation flux): the mass of the material per unit membrane area per unit time is permeated according to the specified temperature and pressure. It is defined as:

wherein J represents permeation flux (kgm)^-2h^-1) (ii) a W represents the mass (kg) of the permeate fraction; Δ t represents a sampling interval time (h); a represents the effective area (m) of the membrane surface for separation²)。

The apparatus for measuring the above parameters is shown in fig. 1.

The test method comprises the following steps:

a) preparing an ethanol aqueous solution containing 90% of ethanol, encapsulating a molecular sieve membrane in a stainless steel membrane component by using a silicon rubber sealing ring, and effectively separating an area A according to an exposed area.

b) The system was kept at a constant temperature of 50 ℃ by adjusting the constant temperature water bath and the heater.

c) The raw material liquid is conveyed to the raw material side of the membrane component by a magnetic circulating pump, and the flow speed in the membrane component is not lower than 0.1 m/s; the permeate side was pumped down by a membrane pump (pressure below 1kPa) and the collector was placed in an ice salt bath to condense and collect the permeate.

d) And switching the collector for sampling at intervals after the operation is stable, weighing the permeate, detecting the mass fraction of water and ethanol by using a Karl Fischer water analyzer, and substituting the mass fraction into a formula to calculate the separation coefficient and the permeation flux of the molecular sieve membrane. Three samples were taken consecutively and their average was calculated.

Example 1

The A-type molecular sieve membrane I is synthesized by a seed crystal method (CN1467017A example 1). And (3) soaking the synthesized molecular sieve membrane in an aqueous solution of NaOH, wherein the pH value of the solution is 10, and the soaking time is 30 min. After soaking, washing the mixture with clear water to be neutral.

The separation performance of the molecular sieve membranes before and after treatment was compared using a pervaporation test. The working process is as follows:

The test results are shown in table 1:

TABLE 1

Molecular sieve membrane	Flux of permeation	Coefficient of separation
			Untreated molecular sieve membrane I	0.50kg/m²h	600
Alkali-treated molecular sieve membrane I	0.55kg/m²h	650

Example 2

The A-type molecular sieve membrane II (CN100337918C example 3) is synthesized by a microwave synthesis method. And (3) soaking the synthesized molecular sieve membrane in an aqueous solution of NaOH, wherein the pH value of the solution is 8, and the soaking time is 30 min. After soaking, washing the mixture with clear water to be neutral.

The separation performance of the molecular sieve membranes before and after treatment was compared using a pervaporation test. The pervaporation operation was as in example 1, and the results of the above test are shown in Table 2:

TABLE 2

Molecular sieve membrane	Flux of permeation	Coefficient of separation
			Untreated molecular sieve membrane II	0.60kg/m²h	1000
Alkali-treated molecular sieve membrane II	0.70kg/m²h	1250

Example 3

NaA molecular sieve membrane III is synthesized by adopting mesoporous zeolite crystals (CN104941451A example 1), the synthesized molecular sieve membrane is soaked in NaOH aqueous solution, the pH value of the solution is 9, and the soaking time is 30 min. After soaking, washing the mixture with clear water to be neutral.

The separation performance of the molecular sieve membranes before and after treatment was compared using a pervaporation test. The pervaporation operation is as in example 1, and the test results are shown in table 3:

TABLE 3

Molecular sieve membrane	Flux of permeation	Coefficient of separation
			Untreated molecular sieve membrane III	0.60kg/m²h	1000
Alkali-treated molecular sieve membrane III	0.80kg/m²h	950

Example 4

Composite MOR type molecular sieve membrane IV (CN106823837A example 1) was synthesized using hollow fiber as a support, and the synthesized molecular sieve hollow fiber membrane was immersed in an aqueous solution of KOH at a pH of 10 for 60 min. After soaking, washing the mixture with clear water to be neutral. The separation performance of the molecular sieve membranes before and after treatment was compared using a pervaporation test. The pervaporation operation was as in example 1, and the results of the above test are shown in Table 4:

TABLE 4

Molecular sieve membrane	Flux of permeation	Coefficient of separation
			Untreated molecular sieve membrane IV	0.80kg/m²h	500
Alkali-treated molecular sieve membrane IV	1.00kg/m²h	600

Example 5

Different types of molecular sieve membranes are synthesized by referring to the methods of examples 1-4, and the properties of the molecular sieves treated under different alkaline conditions are detected by using the detection method and conditions described in example 1. The permeation flux change ratio (Δ x) and selectivity change ratio (Δ y) of the alkali-treated molecular sieve membrane were calculated as a percentage based on the molecular sieve not subjected to alkali treatment under the same conditions as a reference, as shown in table 5.

TABLE 5

In Table 5, NaX, NaY, CHA, T and ZSM-5 type molecular sieves were synthesized according to the following references: j.membr.sci.,337(2009) 47-54; Sep.Sci.Tech.,40(2005) 1047-; Sep.Sci.Tech.,40(2005) 1047-; AIChE J,39(2013) 936-947; korean membr.J.,7(2005), 51-57.

Claims

1. A method for treating a molecular sieve membrane comprises the step of contacting the molecular sieve membrane with an alkaline solution at room temperature, wherein the alkaline solution is an aqueous solution of an alkaline substance and has a pH of 8-10;

the molecular sieve membrane is NaA type or NaX type molecular sieve membrane.

2. The process according to claim 1, characterized in that said alkaline solution is an aqueous solution of an alkaline substance selected from inorganic bases or organic quaternary ammonium bases.

3. The process of claim 2, wherein the alkaline substance is selected from the group consisting of NaOH, KOH, NH₃H₂O, TMAOOH, TEAH, TPAOH or mixtures thereof.

4. The process of claim 2, wherein the alkaline substance is selected from the group consisting of NaOH, KOH, NH₃H₂O or mixtures thereof.

5. The process of claim 1 wherein said contacting is soaking or rinsing.