A silicone film having a loose transition layer and a method of making and using the same

Abstract

The application discloses a kind of organic silicon membrane with loose transition layer and its preparation method and application, belong to membrane separation technical field.The application is reacted with carbon nanotube and acid, washing, drying, obtain carboxylated carbon nanotube COOH-CNTs;And with SiO2-ZrO2 Sol mixed evenly, obtain COOH-CNTs / SiO2-ZrO2 Sol;It is coated to tubular ceramic support, calcination obtains ceramic support with loose transition layer;Organic silicon sol is coated to the ceramic support with loose transition layer obtained, heat treatment forms separation layer, obtains the organic silicon membrane.COOH-CNTs of the application can be dispersed into linear grid with sol particle, and itself has hydrophilic and pore structure, can make more water molecules pass quickly, reduce the permeation resistance of water molecule in transition layer and separation layer, in pervaporation separation solvent / water solution, it shows better separation performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of membrane separation technology, and particularly relates to an organic silicon membrane with a loose transition layer and a preparation method and application thereof. BACKGROUND

[0002] Pervaporation membranes for solvent / water separation have a significant demand in industry. The pervaporation technology for the dehydration of acidic organic substances, such as the dehydration of acetic acid or the dehydration of organic solvents in an acidic environment, has a high requirement for the acid resistance of the membrane.

[0003] The stability of the organic silicon membrane in an acidic environment and a hydrothermal environment is better than that of polymer membranes and inorganic membranes. The organic silicon membrane is generally a multilayer asymmetric structure composed of a support and a separation layer. The support mainly provides sufficient mechanical strength, and the separation layer mainly plays a screening role. The pore size of the ceramic support is large and the surface is rough, so a transition layer needs to be introduced to reduce the pore size and surface roughness. However, the conventional transition layer preparation process is complex, and a material with a similar structure, such as silica sol or alumina sol, is usually selected to be loaded on the support, and the inter-particle stacking pores are reduced in size through multiple coating, which results in a low porosity of the transition layer formed, a long mass transfer path, and a loss of permeation flux in pervaporation.

[0004] Currently, the organic silicon membrane is usually prepared by rubbing coating or dip coating (Waseem Raza, et al. HCl modification and pervaporation performance of BTESE membrane for the dehydration of acetic acid / water mixture [J]. Separation and Purification Technology, 2020, 235: 116102; Hessel L. Castricum, et al. High-performance hybrid pervaporation membranes with superior hydrothermal and acid stability [J]. Journal of Membrane Science, 2008, 324: 111-118). The rubbing coating method usually results in low repeatability of the prepared membrane and is prone to defects such as incomplete coating. The membrane layer formed by the dip coating method is thick and is prone to cracking, and exhibits a low separation factor in pervaporation. SUMMARY

[0005] Purpose of the invention: The purpose of the present invention is to address the deficiencies of the prior art and provide an organic silicon film with a loose transition layer and a preparation method and application thereof.

[0006] Technical solution: The purpose of the present invention is achieved through the following technical solution:

[0007] The present invention provides a method for preparing an organic silicon film having a loose transition layer, comprising the following steps:

[0008] (1) reacting carbon nanotubes with acid, washing, and drying to obtain carboxylated carbon nanotubes COOH-CNTs;

[0009] (2) adding water to the COOH-CNTs and SiO2-ZrO2 sol prepared in step (1), mixing them uniformly, and obtaining a COOH-CNTs / SiO2-ZrO2 sol;

[0010] (3) coating the COOH-CNTs / SiO2-ZrO2 sol prepared in step (2) onto a tubular ceramic support and calcining the support to obtain a ceramic support having a loose transition layer;

[0011] (4) coating the organic silicon sol onto the ceramic support having the loose transition layer obtained in step (3), and heat-treating the ceramic support to form a separation layer to obtain the organic silicon film.

[0012] The COOH-CNTs of the present invention enable sol particles to be dispersed into a linear grid, and the COOH-CNTs themselves have hydrophilicity and a pore structure, which allows more water molecules to pass through quickly, reducing the permeation resistance of water molecules in the transition layer and the separation layer, and showing good separation performance in the pervaporation separation solvent / water solution.

[0013] Preferably, in step (1), the acid is a mixture of concentrated sulfuric acid and concentrated nitric acid, with a volume ratio of 3:1; the reaction temperature is 60-100° C., and the reaction time is 2-4 h.

[0014] Preferably, in step (1), the washing method is to wash with deionized water and ethanol alternately until neutral.

[0015] Preferably, in step (1), the drying temperature is 50-80° C., and the drying time is 12-24 hours.

[0016] A further preferred embodiment of the present invention is that in step (1), the preparation method of COOH-CNTs is to place carbon nanotubes in sulfuric acid (98%) and nitric acid (68%) at 100°C for a reaction time of 4 hours, and then wash them alternately with deionized water and ethanol until neutral, and then dry them to obtain COOH-CNTs.

[0017] Preferably, in step (2), the mass ratio of the COOH-CNTs to the SiO2-ZrO2 sol is 1-7%.

[0018] In the present application, the SiO2-ZrO2 sol is prepared according to the preparation method of CN113058447A.

[0019] According to the molar ratio of tetraethyl orthosilicate: zirconium n-butoxide: ethanol: hydrochloric acid 1:5:10:2, the four substances are mixed together, the mass fraction of tetraethyl orthosilicate and zirconium n-butoxide is kept at 2wt% by adjusting the water content, then the solution is heated to 100℃ and kept boiling for 6h, forming a stable SiO2-ZrO2 sol.

[0020] Preferably, in step (3), the coating method is spin coating, the spin coating is to fix the tubular ceramic support on an iron rod and rotate, place the COOH-CNTs / SiO2-ZrO2 sol below, load it onto the support at low speed, and perform spin evaporation at high speed.

[0021] The low speed is 10-100rpm, and the high speed is 600-6000rpm, and the speed is maintained for 30-60s.

[0022] Preferably, in step (3), preheating is performed before calcination, the preheating temperature is 100-200℃, and the preheating time is 5-10min.

[0023] Preferably, in step (3), the calcination temperature is 450-550℃, the calcination time is 20-60min, and the number of times of repeating coating and calcination is 2-6 times.

[0024] Preferably, in step (4), the organosilica sol is prepared by hydrolysis and polymerization reaction of an organosilica source precursor under the catalysis of an acidic catalyst.

[0025] Further, the organosilica source precursor can be 1,2-bis(triethoxysilyl)ethane (BTESE) or bis(triethoxysilyl)methane (BTESM).

[0026] In a further preferred embodiment of the present application, the organosilica source precursor is 1,2-bis(triethoxysilyl)ethane (BTESE).

[0027] Further, the acidic catalyst can be hydrochloric acid, sulfuric acid or nitric acid.

[0028] Further, the acidic catalyst is selected from hydrochloric acid.

[0029] Preferably, in step (4), the coating method is spin coating.

[0030] In a specific further preferred embodiment of the present application, the spin coating is performed by applying the sol-gel on a tubular ceramic support with a loose transition layer at a low rotation speed of 20 rpm, and then increasing the rotation speed to 1000 rpm for 30 s.

[0031] Preferably, in step (4), the heat treatment is calcination in air at 100-250℃ for 30-60 min.

[0032] The present application also provides the silicone membrane with a loose transition layer prepared by the above method.

[0033] The present application also provides the use of the above silicone membrane with a loose transition layer in pervaporation technology.

[0034] The above silicone membrane with a loose transition layer is placed in a membrane module for pervaporation separation of solvent / water solution.

[0035] The present application also provides a method for pervaporation dehydration of an acidic system, wherein the above silicone membrane with a loose transition layer is used for pervaporation of an aqueous acetic acid solution with a mass fraction of 90wt%, and the aqueous acetic acid solution is heated at a temperature of 75℃, and the permeation side is vacuumized (<400 Pa).

[0036] Advantages:

[0037] The present application prepares a silicone membrane with a loose transition layer by doping COOH-CNTs into SiO2-ZrO2 sol-gel and coating the sol-gel on a tubular ceramic support by spin coating. By doping COOH-CNTs, the sol-gel particles are dispersed in the nanotube network, which reduces the density of the silicon-zirconium network structure, and reduces the coating times. When applied to the dehydration separation of acetic acid / water solution by pervaporation, the water permeation flux and separation factor are improved. On the one hand, COOH-CNTs disperse the dense sol-gel particles, and the structure itself has pores, which can serve as an additional transport channel for water molecules, and the contained carboxyl group further serves as a hydrophilic site to enhance water adsorption, which all improve the transport efficiency of water molecules in the membrane, and are beneficial to improve the water flux in the pervaporation separation of solvent and water. On the other hand, by spin coating, the defect problems caused by rubbing and dipping are reduced, and the separation performance of the membrane is improved. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 SEM image of the silicone membrane prepared in Example 1;

[0039] Figure 2 SEM image of the silicone membrane prepared in Comparative Example 1;

[0040] Figure 3Schematic diagram of water molecules passing through the organic silicon film transition layer. DETAILED DESCRIPTION

[0041] The technical solutions of the present application will be described in detail below through specific examples, but the protection scope of the present application is not limited to the examples.

[0042] If a specific technology or condition is not specified in the examples, it is performed according to the technology or condition described in the literature in the field, or according to the product manual. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be purchased through a regular channel.

[0043] The SiO2-ZrO2 sol used in the examples and comparative examples of the present application was prepared according to the method of CN113058447A.

[0044] The four substances were mixed together according to the molar ratio of tetraethyl orthosilicate: zirconium n-butoxide: ethanol: hydrochloric acid 1:5:10:2, the mass fraction of tetraethyl orthosilicate and zirconium n-butoxide was kept at 2wt% by adjusting the water content, then the solution was heated to 100℃ and kept boiling for 6h, forming a stable SiO2-ZrO2 sol.

[0045] Preparation of the organic silicon film with a loose transition layer in Example 1

[0046] (1) The single-walled carbon nanotubes were placed in a mixture of concentrated sulfuric acid (98%) and concentrated nitric acid (68%) (V H2SO4 / V HNO3 = 3 / 1) and stirred at reflux at 100℃ for 4h. After the end, they were washed with deionized water and ethanol alternately until neutral, and finally dried in a vacuum drying oven at 80℃ for 24h to obtain carboxylated carbon nanotubes COOH-CNTs.

[0047] (2) 3mg of COOH-CNTs and 5g of 2wt% SiO2-ZrO2 sol were taken, deionized water was added to a total system of 20g, and after ultrasonic treatment for 1h, a uniformly dispersed COOH-CNTs / SiO2-ZrO2 sol was obtained. The mass ratio of COOH-CNTs to SiO2-ZrO2 sol in the obtained sol was 3wt%.

[0048] (3) The tubular ceramic support was fixed on an iron rod and rotated, and the COOH-CNTs / SiO2-ZrO2 sol was placed below. The sol was loaded onto the support at a low rotation speed of 20rpm, and then the sol was removed. The rotation speed was increased to 1000rpm, and rotation evaporation was performed for 60s. The tubular ceramic support was placed in an oven at 200℃ for preheating for 5min, and then placed in a tube furnace at 550℃ for heating for 20min. The above process was repeated 6 times to obtain a ceramic support with a loose transition layer.

[0049] (4) 1 g of 1,2-bis(triethoxysilyl)ethane (BTESE) was added to 10 g of ethanol, then 10 g of water and 0.05 g of hydrochloric acid were added for catalysis, and stirred at room temperature for 2 h to obtain a silicone sol. The separation layer was prepared by a spin coating method, the silicone sol was coated on a tubular ceramic support containing a loose transition layer at a low rotation speed of 20 rpm, the rotation speed was increased to 1000 rpm for 30 s, and after the coating was completed, the silicone film was obtained by calcining at 250°C in air for 30 min. Figure 1 is an SEM image of the prepared silicone film, from which it can be seen that the prepared film has a continuous surface and no obvious defects.

[0050] The silicone film was used for a pervaporation test of an aqueous acetic acid solution with a mass fraction of 90wt%, wherein the heating temperature of the aqueous acetic acid solution was 75°C, and the permeation side was vacuumized (<400 Pa), and the obtained separation performance was: a flux of 2.13 kg·m -2 ·h -1 , and a separation factor of 1312.

[0051] Example 2

[0052] The process for preparing the silicone film was basically the same as that in Example 1, except that in the COOH-CNTs / SiO2-ZrO2 sol, the amount of SiO2-ZrO2 sol was kept unchanged, and the mass ratio of COOH-CNTs to SiO2-ZrO2 sol was 1wt%.

[0053] The silicone film was used for a pervaporation test of an aqueous acetic acid solution with a mass fraction of 90wt%, wherein the heating temperature of the aqueous acetic acid solution was 75°C, and the permeation side was vacuumized (<400 Pa), and the obtained separation performance was: a flux of 1.94 kg·m -2 ·h -1 , and a separation factor of 1033.

[0054] Example 3

[0055] The process for preparing the silicone film was basically the same as that in Example 1, except that in the COOH-CNTs / SiO2-ZrO2 sol, the amount of SiO2-ZrO2 sol was kept unchanged, and the mass ratio of COOH-CNTs to SiO2-ZrO2 sol was 5wt%.

[0056] The silicone film was used for a pervaporation test of an aqueous acetic acid solution with a mass fraction of 90wt%, wherein the heating temperature of the aqueous acetic acid solution was 75°C, and the permeation side was vacuumized (<400 Pa), and the obtained separation performance was: a flux of 2.33 kg·m -2 ·h -1 , and a separation factor of 596.

[0057] Example 4

[0058] The process for preparing the silicone membrane of Example 1 was substantially the same, except that in the COOH-CNTs / SiO2-ZrO2 sol, the amount of SiO2-ZrO2 sol was kept unchanged, and the mass ratio of COOH-CNTs to SiO2-ZrO2 sol was 7wt%.

[0059] The silicone membrane was used for pervaporation test of 90wt% acetic acid aqueous solution, wherein the heating temperature of the acetic acid aqueous solution was 75℃, and the permeation side was vacuumized (<400Pa), and the obtained separation performance was: flux was 2.45kg·m -2 ·h -1 , and separation factor was 312.

[0060] As can be seen from Examples 1-4, with the increase of the doping amount, the membrane flux increased, and the separation factor first increased and then decreased, and the reason for the decrease was that when the doping amount was large to a certain extent, the COOH-CNTs would be aggregated, resulting in the increase of interface defects of the transition layer, and the decrease of the separation factor.

[0061] Comparative Example 1

[0062] The tubular ceramic support was fixed on an iron rod, and SiO2-ZrO2 sol was placed below, the sol was loaded onto the support at a low speed of 20rpm, and then the speed was increased to 1000rpm, and rotation evaporation was carried out for 60s. Finally, the tubular ceramic support was placed in an oven at 200℃ for preheating for 5min, and then was placed in a tube furnace at 550℃ for heating for 20min, and the process was repeated for 6 times.

[0063] The BTESE separation layer was prepared by spin coating method, the silicone sol prepared in Example 1 was coated onto the tubular ceramic support containing the transition layer at a low speed of 20rpm, the speed was increased to 1000rpm for 30s, and after the coating was completed, calcination was carried out at 250℃ in air for 30min, to obtain the silicone membrane. Figure 2 is the SEM image of the prepared silicone membrane, and from the image, it can be seen that the prepared BTESE membrane has smooth and continuous surface.

[0064] The silicone membrane was used for pervaporation test of 90wt% acetic acid aqueous solution, wherein the heating temperature of the acetic acid aqueous solution was 75℃, and the permeation side was vacuumized (<400Pa), and the obtained separation performance was: flux was 1.31kg·m -2 ·h -1 , and separation factor was 1429.

[0065] Comparative Example 2

[0066] The transition layer was prepared by rubbing method. The SiO2-ZrO2 sol was rubbed on the tubular ceramic support, and after coating, it was calcined at 550℃ for 20min, and repeated 6 times to complete the coating of the transition layer.

[0067] The separation layer was prepared by rubbing method. The silicone sol prepared in Example 1 was rubbed on the tubular ceramic support containing the transition layer, and then calcined at 250℃ for 30min to obtain a silicone membrane.

[0068] The silicone membrane was used for the pervaporation test of 90wt% acetic acid aqueous solution, wherein the heating temperature of the acetic acid aqueous solution was 75℃, and the permeation side was vacuumized (<400Pa), and the obtained separation performance was: flux was 1.53kg·m -2 ·h -1 , and separation factor was 977.

[0069] Comparative Example 3

[0070] The transition layer was prepared by rubbing method. The SiO2-ZrO2 sol was rubbed on the tubular ceramic support, and after coating, it was calcined at 550℃ for 20min, and repeated 6 times to complete the coating of the transition layer.

[0071] The separation layer was prepared by rubbing method. The silicone sol prepared in Example 1 was rubbed on the tubular ceramic support containing the transition layer, and then calcined at 250℃ for 30min to obtain a silicone membrane.

[0072] The silicone membrane was used for the pervaporation test of 90wt% acetic acid aqueous solution, wherein the heating temperature of the acetic acid aqueous solution was 75℃, and the permeation side was vacuumized (<400Pa), and the obtained separation performance was: flux was 1.23kg·m -2 ·h -1 , and separation factor was 1450.

[0073] Comparing Comparative Example 1 with Examples 1-4, it can be seen that the flux of the silicone membrane doped with COOH-CNTs transition layer is higher. Figure 3 A schematic diagram of water molecules passing through the transition layer of the silicone membrane, from which it can be seen that the transition layer without doping COOH-CNTs, water molecules can only pass through the gap between SiO2-ZrO2 sol, while the transition layer doped with COOH-CNTs, water molecules can also pass through the channel in COOH-CNTs for fast transmission. Comparing Comparative Examples 2-3 with Comparative Example 1, it can be seen that the performance of the membrane prepared by spin coating method is equivalent to that of the membrane prepared by rubbing method, but the coating times of the spin coating method are less.

[0074] While the application has been described and illustrated with reference to specific preferred embodiments, it is not intended that it be limited to these particulars. Various changes in form and detail can be made without departing from the spirit and scope of the application as defined by the appended claims.

Claims

1. A method for preparing an organosilicon film having a loose transition layer, characterized in that: The following steps are involved: (1) reacting carbon nanotubes with acid, washing, and drying to obtain carboxylated carbon nanotubes COOH-CNTs; (2) adding water to the COOH-CNTs and SiO2-ZrO2 sol prepared in step (1), mixing them uniformly, and obtaining a COOH-CNTs / SiO2-ZrO2 sol; (3) coating the COOH-CNTs / SiO2-ZrO2 sol prepared in step (2) onto a tubular ceramic support and calcining the support to obtain a ceramic support having a loose transition layer; (4) coating the organic silicon sol onto the ceramic support having the loose transition layer obtained in step (3), and heat treating the ceramic support to form a separation layer to obtain the organic silicon film; The organosilicon sol is prepared by hydrolysis and polymerization of an organosilicon source precursor, 1,2-bis(triethoxysilyl)ethane or bis(triethoxysilyl)methane.

2. The preparation method according to claim 1, characterized in that In step (1), the acid is a mixture of concentrated sulfuric acid and concentrated nitric acid, with a volume ratio of 3:1; the reaction temperature is 60-100°C, and the reaction time is 2-4 hours.

3. The preparation method according to claim 1, characterized in that In step (2), the mass ratio of the COOH-CNTs to the SiO2-ZrO2 sol is 1-7%.

4. The preparation method according to claim 1, characterized in that In step (3), the coating method is spin coating, and the spin coating is to fix the tubular ceramic support on the iron rod and rotate it, place the COOH-CNTs / SiO2-ZrO2 sol underneath, load it onto the support at a low speed, and perform rotary evaporation at a high speed; the low speed is a rotation speed of 10-100 rpm, and the high speed is a rotation speed of 600-6000 rpm, and maintain it for 30-60 seconds.

5. The preparation method according to claim 1, characterized in that In step (3), preheating is performed before calcination, the preheating temperature is 100-200°C, and the preheating time is 5-10 minutes.

6. The preparation method according to claim 1, characterized in that In step (3), the calcination temperature is 450-550° C., the calcination time is 20-60 min, and the coating and calcination are repeated 2-6 times.

7. The preparation method according to claim 1, characterized in that In step (4), the organosilicon sol is prepared by hydrolysis polymerization of an organosilicon source precursor under the catalysis of an acidic catalyst.

8. The preparation method according to claim 1, characterized in that In step (4), the heat treatment is calcination in an air atmosphere at 100-250°C for 30-60 minutes.

9. The organic silicon film having a loose transition layer prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the organic silicon membrane with a loose transition layer according to claim 9 in pervaporation technology, characterized in that: The organic silicon membrane with a loose transition layer as claimed in claim 9 is placed in a membrane assembly to perform pervaporation separation of solvent / water solution.

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