A composite membrane for separating acetone and isoprene gas and a method for preparing the same

Abstract

The present application relates to a kind of for the separation of acetone and isoprene gas in human exhaled gas Composite membrane and its preparation method, polydimethylsiloxane (PDMS) modified polymer-based hollow fiber composite membrane is prepared by dip coating method.The above-mentioned modification, while covering the macropore of base film surface, improve the adsorption capacity of functional layer to acetone gas, so as to improve the separation effect of composite membrane to isoprene / acetone.The present application has the characteristics of simple operation, gas separation effect is remarkable, gas molecule is measured quickly, accurately, efficiently etc., provides a new way of thinking for the selective separation of organic components in human exhaled gas.

Description

Technical Field

[0001] This invention relates to the field of separating volatile organic compounds (VOCs) from human exhaled gases, and particularly to a separation membrane for separating acetone and isoprene from human exhaled gases and its preparation method. Background Technology

[0002] Lung cancer is one of the most common malignant tumors worldwide, and effective screening methods for early diagnosis remain scarce. Isoprene gas is one of the potential respiratory biomarkers for lung cancer. Infrared absorption spectroscopy shows that the highly polar acetone gas and the less polar isoprene gas show similar activity at 2970 cm⁻¹. -1 The absorption cross-sections near the wavelength overlap. Therefore, the presence of high concentrations of acetone (ppmv level) in human exhaled breath can interfere with the measurement of isoprene (ppbv level). Thus, selective separation of the two is necessary to achieve high-sensitivity, high-resolution, and high-stability detection and analysis of isoprene in human exhaled breath.

[0003] Traditional gas separation technologies include absorption, adsorption, and condensation, but these methods are not suitable for separating exhaled gases from the human body and for clinical medical testing. Membrane separation technology has advantages such as simple operation, high separation efficiency, and low cost. With the continuous development of this technology, gas separation membranes have shown broad prospects in the production of industrial product gases, comprehensive utilization of waste gases, and environmental protection. It has become a highly efficient, energy-saving, and environmentally friendly new separation technology and has been successfully applied in various processes. Traditional organic membrane materials, such as polyvinylidene fluoride (PVDF) and polysulfone (PSF), have good physicochemical properties and have been used in gas separation. However, these membranes have low selectivity for polar gases such as acetone. To improve the adsorption and separation performance of membrane materials for acetone, further post-modification of the base membrane is required. Polydimethylsiloxane (PDMS) is a rubbery polymer. Its special alternating -Si-O- structure gives it good main chain flexibility and high free volume, thus exhibiting good permeability to most organic solvent molecules. It is one of the most ideal organic materials for the recovery of highly polar VOCs. Coating the surface of the base membrane with PDMS can enhance the interaction between organic functional groups and acetone gas, thereby increasing the membrane's adsorption capacity for acetone and achieving precise separation of isoprene / acetone.

[0004] Chinese invention patent (CN202011524982.6) discloses a high-permeability organic gas separation membrane prepared using a hydroxyl-terminated PDMS polymer with a molecular weight greater than 100,000 as the separation layer. This membrane is used for the recovery of solvents such as methyl tert-butyl ether, acetone, or petroleum ether in chemical and pharmaceutical production processes. Adding the organic gas separation membrane after the compression and condensation process increases solvent recovery by 10-30% and achieves a nitrogen purity of 99.5%, enabling nitrogen recovery and utilization. This method reduces the preparation cost of the separation membrane, but the steps are relatively cumbersome and time-consuming. Chinese invention patent (CN201610112477.8) describes a high-performance hollow fiber organic gas separation composite membrane prepared by sequentially coating a silane coupling agent solution and a polydimethylsiloxane solution, for use in the field of hexane / nitrogen gas separation and recovery technology. Chinese invention patent (CN202010392588.5) has successively prepared a SAPO-34 / PDMS organic gas permeation membrane by methods such as molecular sieve modification, casting solution preparation and composite membrane preparation. When this method is used to recover low molecular weight hydrocarbons from air and organic mixed gases, the separation factor is greatly improved, but the cost is high.

[0005] This invention first prepares a PDMS solution-modified polymer-based hollow fiber composite membrane using a dip-coating method. Through this modification, the aim is to increase the acetone adsorption capacity without affecting the isoprene concentration, thereby improving the isoprene / acetone separation efficiency of the composite membrane. This invention features simple operation, significant gas separation effect, and rapid, accurate, and efficient gas molecule measurement, providing a new approach for the separation of isoprene / acetone gases in human exhalation. Summary of the Invention

[0006] This invention uses a self-made or commercially available polyvinylidene fluoride (PVDF) or polysulfone (PSF) hollow fiber membrane as the base membrane. First, the base membrane is hydroxylated using a mixture of acetone, ethanol, and water. Then, a coating solution is prepared by mixing tetraethyl orthosilicate (TEOS) and dibutyltin dilaurate (BTB) as crosslinking agents and catalysts with hexane and polydimethylsiloxane (PDMS) in a specific ratio. Finally, a PDMS-coated PVDF hollow fiber membrane is prepared by dip-coating. This modified membrane can improve the acetone adsorption and separation capacity without affecting the isoprene permeation concentration, thus improving the separation efficiency of isoprene and acetone. The preparation of the above gas separation membrane mainly includes the following steps:

[0007] (1) Base membrane pretreatment: Take a section of base membrane with an inner diameter of 0.1-0.25 cm, an outer diameter of 0.2-0.5 cm, and a length of 5-10 cm, rinse it with ethanol and water, place it in an oven for vacuum drying, and then seal both ends with glue. Take acetone, ethanol, and water in a volume ratio of 1:1:1, and immerse the sealed hollow fiber membrane in the prepared solution. After soaking for 5-20 minutes, remove it and let it air dry. Repeat the above operation to prepare three identical hydroxylated modified membranes;

[0008] (2) Preparation of coating solution: The mass ratio of n-hexane:polydimethylsiloxane:tetraethyl orthosilicate:dibutyltin dilaurate is 10-20:1-2:1-2:0.1-0.2. First, dissolve polydimethylsiloxane in n-hexane and stir continuously at 45°C for 20-50 min. Then, add tetraethyl orthosilicate and dibutyltin dilaurate respectively and continue stirring for 0.5-1 h. Then, let it stand for 1-2 h to allow it to pre-crosslink.

[0009] (3) Preparation of modified film: When the solution becomes viscous, vertically immerse the hydroxylated modified film obtained in step (1) into the coating solution obtained in step (2), and after 0.5 to 3 minutes, vertically and uniformly pull it out and let it air dry naturally. Finally, put it into a vacuum oven at 30 to 60°C and dry it for 6 to 15 hours before taking it out for use.

[0010] The molecular weight of polydimethylsiloxane (PDMS) used in step (2) above can be 2 to 60 kDa, or one of the PDMS mixed solutions with different molecular weights.

[0011] The present invention has the following beneficial technical effects: simple operation, good adsorption and separation effect of modified membrane on acetone, no obvious interference with the permeation of isoprene, and significant separation effect of isoprene / acetone gas. Attached Figure Description

[0012] Figure 1 This is a comparison chart of the permeate concentrations for the separation of acetone and isoprene gases by the PVDF-based membrane and the PDMS-modified membrane (PVDF / PMDS1.5) prepared in Implementation Case 2.

[0013] Figure 2 This is a comparison chart of the permeate rates of acetone and isoprene gas separation by the PVDF-based membrane and the PDMS-modified membrane (PVDF / PMDS1.5) prepared in Implementation Case 2. Detailed Implementation

[0014] Example 1:

[0015] (1) Clean a commercial polysulfone (PSf) hollow fiber membrane with a length of 5cm, a hollow inner diameter of 2mm, and an outer diameter of 4mm with ethanol and water.

[0016] (2) Place the cleaned PVDF hollow fiber membrane in an oven for vacuum drying; take 5g each of acetone, ethanol and water, mix them evenly and dry them; vertically immerse the base membrane in the prepared solution, soak for 20 minutes and then take it out to dry naturally.

[0017] (3) Mix 1g of PDMS (molecular weight 50kDa) and 10g of n-hexane in a beaker. Place the beaker in a magnetic stirrer, heat to 45℃ and stir for 45min. Then add 0.125g of crosslinking agent tetraethyl orthosilicate (TEOS) and 0.1g of catalyst dibutyltin dilaurate (BTB) in sequence, and continue stirring for 1.5h. After stirring, let stand at room temperature for about 1h to allow it to fully crosslink.

[0018] (4) When the coating solution prepared above is viscous, immerse the hydroxylated membrane prepared in step (1) in it, react for 1 minute, take it out, let it air dry vertically, and then dry it at 45°C under vacuum for 8 hours. Name it PVDF / PDMS1.

[0019] Example 2:

[0020] (1) A commercial PVDF hollow fiber membrane with a length of 5cm, a hollow inner diameter of 2mm, and an outer diameter of 4mm was washed with ethanol and water.

[0021] (2) Place the cleaned PVDF hollow fiber membrane into an oven for vacuum drying. After drying, seal both ends with glue. Mix 5g each of acetone, ethanol and water evenly, then vertically immerse the sealed hollow fiber membrane in the prepared solution. After soaking for 8 minutes, remove and air dry.

[0022] (3) Mix 1g of PDMS (molecular weight 2kDa) and 10g of n-hexane in a beaker. Place the beaker in a magnetic stirrer, heat to 45℃ and stir for 30min. Then add 2.5g of crosslinking agent tetraethyl orthosilicate (TEOS) and 0.05g of catalyst dibutyltin dilaurate (BTB) in sequence, and continue stirring for 1h. After stirring, let stand at room temperature for about 1h to allow it to fully crosslink.

[0023] (4) When the coating solution prepared above is viscous, immerse the hydroxylated membrane in it, react for 1.5 min, take it out, let it air dry vertically, and then dry it at 45℃ under vacuum for 7 h. Name it PVDF / PDMS1.5.

[0024] Example 3:

[0025] (1) Clean the self-made PVDF hollow fiber membrane with a length of 5cm, a hollow inner diameter of 2mm and an outer diameter of 4mm with ethanol and water.

[0026] (2) Place the cleaned membrane in an oven for vacuum drying; take 5g each of acetone, ethanol and water, mix them, soak the dried membrane in the prepared solution, soak for 10 minutes and then take it out to dry naturally.

[0027] (3) Mix 1g of PDMS (molecular weight 50kDa) and 10g of n-hexane in a beaker. Place the beaker in a magnetic stirrer, heat to 45℃ and stir for 30min. Then add 0.1g of crosslinking agent tetraethyl orthosilicate (TEOS) and 0.05g of catalyst dibutyltin dilaurate (BTB) in sequence, and continue stirring for 1h. After stirring, let stand at room temperature for about 30min to allow it to fully crosslink.

[0028] (4) The coating solution prepared above is viscous. The hydroxylated membrane is immersed in it and reacted for 2 minutes. Afterward, it is removed, allowed to air dry vertically, and then dried under vacuum at 45°C for 10 hours. This solution is named PSF / PDMS2. Experimental comparative example:

[0029] A commercial PVDF hollow fiber membrane with an inner diameter of 2 mm, an outer diameter of 4 mm, and a length of 5 cm was rinsed with an ethanol solution and then vacuum dried to obtain the PVDF blank membrane required for this experiment. Experimental results:

[0030] This invention designs and prepares a separation membrane for separating acetone and isoprene gases. The modification method is simple to operate, provides significant gas separation effect, and exhibits good membrane stability during use. A comparison is made between the PVDF / PDMS1.5 modified membrane prepared in Example 2 and the original PVDF membrane obtained in the experimental control example:

[0031] (1) Gas permeation performance tests were conducted on the original and modified membranes using acetone gas at a concentration of 1000 ppbv and isoprene gas at a concentration of 489.27 ppbv. The acetone concentration permeating the modified PVDF / PDMS1.5 membrane was lower than that of the original PVDF membrane, decreasing from 996.29 ppbv in the original membrane to 551.40 ppbv in the modified membrane, a decrease of approximately 44.65%. However, the isoprene concentration after filtration showed no significant change, decreasing from 484.77 ppbv (original membrane) to 447.01 ppbv (modified membrane), a decrease of only approximately 9.28% (see the instruction manual appendix). Figure 1 This indicates that the modified membrane can improve the adsorption and separation performance of acetone.

[0032] (2) The permeation rate of the gas was tested using acetone gas with a concentration of 1000 ppbv and isoprene gas with a concentration of 489.27 ppbv. The unit of gas permeation rate R was GPU (gaspermeation unit), a commonly used unit in gas membrane separation. Under the conditions of 0℃ and 0.1013 MPa, 1 GPU = 7.5 × 10⁻⁶.-12 m 3 / m2×s×Pa). ​​The acetone permeation rate decreased from 30192.58 GPU (original PVDF membrane) to 10227.08 GPU (PVDF / PDMS1.5 modified membrane), a decrease of approximately 66.13%; the isoprene permeation rate decreased from 21200.35 GPU (original membrane) to 13694.16 GPU (modified membrane), a decrease of approximately 35.41%. The isoprene / acetone gas selectivity coefficient increased from 0.72 for the original membrane to 1.34 for the modified membrane (see the instruction manual appendix). Figure 2 ).

Claims

1. A composite membrane for separating acetone and isoprene gases in human exhaled breath, characterized in that, The composite membrane uses a hollow fiber membrane made of polyvinylidene fluoride or polysulfone as the base membrane. First, the base membrane is pretreated with a ternary mixed solution of acetone, ethanol, and water in a volume ratio of 1:1:

1. Then, polydimethylsiloxane with a molecular weight of 2-60 kDa is dissolved in hexane. Hexane:polydimethylsiloxane:tetraethyl orthosilicate:dibutyltin dilaurate are added sequentially as a crosslinking agent (10-20:1-2:1-2:0.1-0.2), followed by stirring and allowing the mixture to stand for pre-crosslinking to prepare the coating solution. Finally, a polydimethylsiloxane-modified hollow fiber composite membrane is prepared by dip-coating. This composite membrane can improve the adsorption and separation of acetone in human exhalation without affecting the permeation concentration of isoprene, thus improving the separation effect of isoprene and acetone.

2. The composite membrane for separating acetone and isoprene gases in human exhaled gas according to claim 1, characterized in that, The base membrane is selected from commercial membranes or self-made membranes, with a hollow inner diameter of 0.1-0.25 cm, an outer diameter of 0.2-0.5 cm, and a length of 5-10 cm.

3. The composite membrane for separating acetone and isoprene gases in human exhaled gas according to claim 1, characterized in that, The specific preparation method of the composite membrane is as follows: (1) Base membrane pretreatment: Take a section of base membrane, rinse it with ethanol and water, put it in an oven for vacuum drying, and seal both ends with glue. Take acetone, ethanol and water in a volume ratio of 1:1:1, immerse the hollow fiber membrane with both ends sealed in the prepared solution, soak for 5-20 minutes, take it out and dry it naturally to obtain a uniform hydroxylated modified base membrane. (2) Preparation of coating solution: First, dissolve polydimethylsiloxane in hexane and stir continuously at 45°C for 20-50 min. Then, add tetraethyl orthosilicate and dibutyltin dilaurate respectively and continue stirring for 0.5-1 h. Then, let it stand at room temperature for 1-2 h to allow it to pre-crosslink. (3) Preparation of modified film: When the coating solution becomes viscous, vertically immerse the modified base film in the coating solution for 0.5 to 3 minutes, vertically and uniformly pull it out and let it air dry naturally. Place it in a vacuum oven at 30 to 60°C for 6 to 15 hours to obtain the target composite film.

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