MODIFIED POROUS MEMBRANE MATERIAL AND PREPARATION METHOD THEREOF, AND LIQUID MEMBRANE SEPARATION METHOD OF CARBON DIOXIDE

Abstract

A membrane modification method for improving liquid membrane separation of carbon dioxide (CO.sub.2) includes grafting an organic substance containing an amine group on a porous membrane material, and loading water into pore channels of the porous membrane material to prepare a supported liquid membrane for a gas mixture separation experiment of CO.sub.2. In the method, the amine group is introduced through chemical grafting to make the water being alkaline when used as membrane liquid. Compared with an alkaline solution as the membrane liquid, the method can avoid the loss of active alkaline substances and increase the permeation flux of CO.sub.2.

Claims

1. A use of a modified porous membrane material in improving a separation factor during a liquid membrane separation of carbon dioxide (CO.sub.2), wherein the modified porous membrane material is prepared by a preparation method comprising the following steps: dissolving a silane coupling agent containing an amine group in an organic solvent to serve as a modifier; immersing an inorganic porous membrane material in the modifier for a grating reaction; and after the grafting reaction is completed, performing washing and drying to obtain the modified porous membrane material, wherein the inorganic porous membrane material has an average pore size of 20-200 nm; and the liquid membrane separation of the CO.sub.2 comprises the following steps: loading water as a solvent into pore channels of the modified porous membrane material to form a liquid membrane; and allowing the liquid membrane to contact with a gas mixture containing the CO.sub.2 to make the CO.sub.2 permeate a membrane layer.

2. The use according to claim 1, wherein the amine group is one selected from the group consisting of a primary amine-containing group, a secondary amine-containing group, and a tertiary amine-containing group.

3. The use according to claim 1, wherein the inorganic porous membrane material is selected from the group consisting of porous alumina, porous titania, porous zirconia, and porous silica.

4. The use according to claim 1, wherein the inorganic porous membrane material geometrically has a flat-plate structure or a tubular structure.

5. (canceled)

6. The use according to claim 1, wherein the silane coupling agent containing the amine group is selected from the group consisting of N,N-dimethyl-3-aminopropyltrimethoxysilane and (3-aminopropyl)trimethoxysilane; and the organic solvent is at least one selected from the group consisting of ethanol, acetone, dimethylacetamide (DMAC), and tetrahydrofuran (THF).

7. The use according to claim 1, wherein the grafting reaction is performed at a temperature of 20-40° C. for 1-24 h.

8. (canceled)

9. The use of according to claim 1, wherein the gas mixture containing the CO.sub.2 further comprises at least one selected from the group consisting of N.sub.2, CH.sub.4, H.sub.2, O.sub.2, He, and CO.

10. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is an infrared spectrum of an amination-modified porous membrane material;

[0029] FIG. 2 shows an effect of a water-supported liquid membrane made of porous membrane materials before and after amination modification on gas permeance in a CO.sub.2 separation system; and

[0030] FIG. 3 shows an effect of temperature on gas permeance of CO.sub.2 of a porous membrane without amination modification.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In the technical scheme of the present invention, a silane coupling agent containing amine groups is added dropwise to an organic solvent to dissolve to prepare a modifying solution, a porous membrane material is immersed in the modifying solution for reaction, and washed and dried after the reaction to obtain a membrane material rich in amine groups. Under surface tension, water is loaded in membrane pore channels, and a prepared supported liquid membrane is used to separate a CO.sub.2 gas mixture.

[0032] In the present invention, the modification method of supported materials is simple and easy to implement. The method can help avoid membrane fluid loss caused by using ionic liquids (with relatively high requirements for the pore size), and the amine groups are introduced to improve the selective separation of CO.sub.2 by water-supported liquid membranes.

[0033] In the present invention, the membrane liquid used in the prepared water-supported liquid membrane is a green solvent with no pollution to the environment, low cost and easily-available source.

[0034] In the present invention, the porous membrane material has hydrophilicity, which makes it convenient to add water vapor to the CO.sub.2 gas mixture to repair liquid membrane by capillary condensation.

[0035] A modified porous membrane material is modified with an amine-containing group in pore channels.

[0036] In an embodiment, the amine-containing group is one selected from the group consisting of a primary amine-containing group, a secondary amine-containing group and a tertiary amine-containing group.

[0037] In an embodiment, the membrane material is an inorganic porous membrane material or a polymer porous membrane material.

[0038] In an embodiment, the inorganic porous material is selected from the group consisting of porous alumina, porous titania, porous zirconia and porous silica.

[0039] In an embodiment, the membrane material has an average pore size of 1-200 nm.

[0040] In an embodiment, the membrane material has a flat-plate structure or tubular structure.

[0041] A preparation method of the modified porous membrane material includes the following steps.

[0042] A silane coupling agent containing an amine group is dissolved in an organic solvent to serve as a modifier. A porous membrane material is immersed in the modifier for grafting reaction. After the grafting reaction is completed, washing and drying are performed to obtain the modified porous membrane material.

[0043] In an embodiment, the silane coupling agent containing the amine group is selected from the group consisting of N,N-dimethyl-3-aminopropyltrimethoxysilane and (3-aminopropyl)trimethoxysilane.

[0044] In an embodiment, the organic solvent is at least one selected from the group consisting of ethanol, acetone, DMAC and THF.

[0045] In an embodiment, the grafting reaction is performed at 20-40° C. for 1-24 h.

Example 1

[0046] An inner membrane of a tubular ceramic membrane with an average pore size of 100 nm (geometric dimensions of the membrane were as follows: an effective length was 8 cm, an outer diameter was 12 cm, an inner diameter was 8 cm and a porosity was about 40%) was washed and dried in a drying box for 1-2 h. A silane coupling agent N,N-dimethyl-3-aminopropyltrimethoxysilane (DMAPS) containing amine groups was added dropwise to absolute ethanol to dissolve to prepare a 15 mmol/L modifying solution. A porous membrane material was immersed in the modifying solution, to allow for full reaction for 12 h at a constant-temperature water bath of 35° C., and washing and drying were performed to obtain a membrane material with tertiary amine groups on a surface. A surface infrared spectrum of the modified membrane material is shown in FIG. 1. A structure of the DMAPS is as follows:

##STR00001##

[0047] Comparing the infrared spectra of the membrane before and after the modification, it can be seen that the modified ceramic membrane has new characteristic peaks, which are the characteristic peaks of —CH.sub.2—, N—C, —CH.sub.3 and Si—O—Al marked in the figure, respectively. Especially, N—C at 1610 cm.sup.−1 is a unique peak of the DMAPS, and there is a characteristic peak at 810 cm.sup.1 that demonstrates the Si—O—Al formed by the reaction of Si—OH and Al—OH.

[0048] The membrane material was soaked in water, and water was loaded in the membrane pores through surface tension, optionally this process could be accelerated by vacuuming. When no bubbles came out, the membrane material was taken out to gently wipe off the remaining water on the membrane surface, to obtain a supported liquid membrane that can separate the CO.sub.2 gas mixture.

[0049] The prepared water-supported liquid membrane was installed in a membrane module to determine gas permeance of pure gas and the ideal separation factor. A gas permeance test was performed under 0.6 Mpa and 25° C. The results are as follows. An ideal separation factor of CO/N.sub.2 is infinite. The unmodified membrane has a gas permeance of about 2.5±0.15 GPU for CO.sub.2, and the modified membrane has a gas permeance of about 3.83±0.19 GPU for CO.sub.2, which is about 53% higher than that of the unmodified membrane. The results are shown in FIG. 2.

Example 2

[0050] An inner membrane of a tubular ceramic membrane with an average pore size of 200 nm (geometric dimensions of the membrane were as follows: an effective length was 8 cm, an outer diameter was 12 cm, an inner diameter was 8 cm and a porosity was about 40%) was washed and dried in a drying box for 1-2 h. A silane coupling agent (3-aminopropyl)trimethoxysilane containing amine groups was added dropwise to acetone to dissolve to prepare a 50 mmol/L modifying solution. A porous membrane material was immersed in the modifying solution, to allows for full reaction for 24 h at a constant-temperature water bath of 30° C., and washing and drying were performed to obtain a membrane material with tertiary amine groups on a surface. The membrane material was used in gas adsorption of a gas-liquid membrane contactor, and water was used as an adsorbent. It is found that the CO.sub.2 has a mass transfer flux increased from an initial 0.15 mol/(m.sup.2.Math.h) to 0.209 mol/(m.sup.2.Math.h), with an increase of about 40% relative to an initial flux.

Example 3

[0051] An influence of different operating temperatures on the permeation rate of CO.sub.2 was investigated, as shown in FIG. 3.

[0052] For unmodified membranes (a tubular ceramic membrane with an average pore size of 20 nm was used, and geometric dimensions of the membrane were as follows: an effective length was 8 cm, an outer diameter was 12.5 cm, and an inner diameter was 7.5 cm; and a porosity was about 30%), and water was used as membrane liquid.

[0053] A permeation behavior of gas in the supported liquid membrane conformed to a dissolution-diffusion model: D (diffusion coefficient), S (solubility coefficient), J (gas permeance) and 1 (liquid membrane thickness).

P=S×D=J×

[0054] The diffusion coefficient increases with the increase of temperature, and the solubility coefficient decreases with the increase of temperature, such that the gas permeance J could have an optimal value point.