Organosilicon membrane having loose transition layer and preparation method therefor and use thereof

Abstract

The present invention belongs to the technical field of membrane separation, and disclosed are an organosilicon membrane having a loose transition layer and a preparation method therefor and the use thereof. The present invention involves reacting carbon nanotubes with an acid, followed by washing and drying to obtain carboxylated carbon nanotubes (COOH-CNTs); uniformly mixing same with an SiO2-ZrO2 sol to obtain a COOH-CNTs / SiO2-ZrO2 sol; applying the sol onto a tubular ceramic support, and calcining same to obtain a ceramic support having a loose transition layer; and applying an organosilicon sol onto the resulting ceramic support having a loose transition layer, and heat-treating same to form a separation layer, so as to obtain the organosilicon membrane. The COOH-CNTs of the present invention enable sol particles to be dispersed in a linear network and inherently have hydrophilicity and a channel structure, allowing more water molecules to pass through same rapidly, and reducing the permeation resistance of water molecules in the transition and separation layers, resulting in a better separation performance in pervaporation separation of a solvent / water solution.

Description

An organosilicon film with a loose transition layer, its preparation method and application Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to an organosilicon membrane with a loose transition layer, its preparation method, and its application. Background Technology

[0002] There is a significant industrial demand for pervaporation membranes used for solvent / water separation. However, pervaporation technology for dehydrating acidic organic compounds, such as acetic acid or organic solvents in acidic environments, places high demands on the acid resistance of the membranes.

[0003] Organosilicon membranes exhibit better stability than polymer and inorganic membranes in acidic and hydrothermal environments. Organosilicon membranes are generally multilayered asymmetric structures consisting of a support and a separation layer. The support primarily provides sufficient mechanical strength, while the separation layer mainly functions as a separator. Ceramic supports have relatively large pore sizes and rough surfaces, thus requiring the introduction of a transition layer to reduce pore size and surface roughness. However, traditional transition layer preparation processes are complex. Typically, structurally similar materials such as silica sol or alumina sol particles are loaded onto the support, and multiple coatings are applied to reduce the pore size by reducing the interparticle porosity. This method results in a transition layer with low porosity and a long mass transfer path, leading to a loss of membrane permeation flux during pervaporation.

[0004] Currently, silicone membranes are typically prepared using either a wiping or dipping method (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 wiping method usually results in low reproducibility of the prepared membrane and is prone to incomplete coating defects, while the dipping method forms a thicker membrane layer that is prone to cracking and exhibits a lower separation factor during pervaporation. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to address the shortcomings of existing technologies by providing an organosilicon film with a loose transition layer, its preparation method, and its application.

[0006] Technical solution: The objective of this invention is achieved through the following technical solution:

[0007] This invention provides a method for preparing an organosilicon film with a loose transition layer, comprising the following steps:

[0008] (1) Carbon nanotubes were reacted with acid, washed and dried to obtain carboxylated carbon nanotubes COOH-CNTs;

[0009] (2) Add water to the COOH-CNTs and SiO2-ZrO2 sol obtained in step (1) and mix evenly to obtain COOH-CNTs / SiO2-ZrO2 sol;

[0010] (3) Coat the COOH-CNTs / SiO2-ZrO2 sol obtained in step (2) onto the tubular ceramic support and calcine to obtain a ceramic support with a loose transition layer;

[0011] (4) The organosilicon sol is coated onto the ceramic support with a loose transition layer obtained in step (3), and heat-treated to form a separation layer to obtain the organosilicon film.

[0012] The COOH-CNTs of this invention enable sol particles to be dispersed in a linear grid and have hydrophilicity and a porous structure, allowing more water molecules to pass through quickly. This reduces the permeation resistance of water molecules in the transition and separation layers, resulting in better separation performance in solutions where solvent / water is separated by pervaporation.

[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℃, and the reaction time is 2-4h.

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

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

[0016] A further preferred embodiment of the present invention is that, in step (1), the COOH-CNTs are prepared by placing carbon nanotubes in sulfuric acid (98%) and nitric acid (68%) at 100°C for 4 hours, washing them alternately with deionized water and ethanol until neutral, and then drying them to obtain COOH-CNTs.

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

[0018] In this invention, the SiO2-ZrO2 sol is prepared according to the preparation method described in CN113058447A.

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

[0020] Preferably, in step (3), the coating method is spin coating, which involves fixing a tubular ceramic support on an iron rod and rotating it, placing COOH-CNTs / SiO2-ZrO2 sol below, loading it onto the support at low speed, and then performing rotary evaporation at high speed.

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

[0022] Preferably, in step (3), preheating is performed before calcination, and 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 coating and calcination are repeated 2-6 times.

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

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

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

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

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

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

[0030] In a further preferred embodiment of the present invention, the spin coating method involves coating an organosilicon sol onto a tubular ceramic support containing a loose transition layer at a low rotation speed of 20 rpm, and then increasing the rotation speed to 1000 rpm and holding it for 30 seconds.

[0031] Preferably, in step (4), the heat treatment is calcination at 100-250°C in an air atmosphere for 30-60 minutes.

[0032] The present invention also provides an organosilicon film with a loose transition layer prepared by the above preparation method.

[0033] The present invention also provides the application of the above-mentioned organosilicon membrane with a loose transition layer in pervaporation technology.

[0034] The aforementioned organosilicon membrane with a loose transition layer is placed in a membrane module for pervaporation separation of solvent / aqueous solution.

[0035] The present invention also provides a method for dehydrating an acidic system by pervaporation, wherein the above-mentioned organosilicon membrane with a loose transition layer is used for pervaporation of an aqueous acetic acid solution with a mass fraction of 90 wt%, wherein the aqueous acetic acid solution is heated to 75°C and a vacuum (<400 Pa) is drawn on the pervaporation side. Beneficial effects

[0036] This invention prepares an organosilicon membrane with a porous transition layer by doping COOH-CNTs into a SiO2-ZrO2 sol and then spin-coating the sol onto a tubular ceramic support. By doping with COOH-CNTs, the sol particles are dispersed within a nanotube network, reducing the density of the silicon-zirconium network structure and decreasing the number of coating passes. When applied to the dehydration separation of acetic acid / water solution via pervaporation, this improves the water permeation flux and separation factor. On one hand, COOH-CNTs disperse dense sol particles and possess porous structures that serve as additional transport channels for water molecules. Furthermore, the carboxyl groups they contain act as hydrophilic sites, enhancing water adsorption. All of these factors improve the transport efficiency of water molecules within the membrane, facilitating increased water flux during pervaporation separation of solvent and water. On the other hand, spin-coating reduces the defects associated with wiping and dip-coating, thereby increasing the membrane's separation performance. Attached Figure Description

[0037] Figure 1 is a SEM image of the organosilicon film prepared in Example 1;

[0038] Figure 2 is a SEM image of the organosilicon film prepared in Comparative Example 1;

[0039] Figure 3 is a schematic diagram of water molecules passing through the organosilicon membrane transition layer. Detailed Implementation

[0040] The technical solution of the present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0041] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0042] The SiO2-ZrO2 sol used in the embodiments and comparative examples of this invention was prepared according to the preparation method in CN113058447A.

[0043] According to the molar ratio of tetraethyl orthosilicate: zirconium butoxide: ethanol: hydrochloric acid of 1:5:10:2, these four substances are mixed together. By adjusting the water content, the mass fraction of tetraethyl orthosilicate and zirconium butoxide is kept at 2wt%. The solution is then heated to 100℃ and kept boiling for 6 hours to form a stable SiO2-ZrO2 sol.

[0044] Example 1: Preparation of an organosilicon film with a loose transition layer

[0045] (1) Place single-walled carbon nanotubes in a mixture of concentrated sulfuric acid (98%) and concentrated nitric acid (68%) (V H2SO4 / V HNO3 =3 / 1), stirred and refluxed at 100℃ for 4h, and then washed alternately with deionized water and ethanol until neutral. Finally, it was placed in a vacuum drying oven at 80℃ for 24h to obtain carboxylated carbon nanotubes COOH-CNTs.

[0046] (2) Take 3 mg of COOH-CNTs and 5 g of 2 wt% SiO2-ZrO2 sol, add deionized water to a total system of 20 g, and sonicate for 1 h to obtain a uniformly dispersed COOH-CNTs / SiO2-ZrO2 sol. The mass ratio of COOH-CNTs to SiO2-ZrO2 sol in the obtained sol is 3 wt%.

[0047] (3) Fix the tubular ceramic support on the iron rod and rotate it. Place COOH-CNTs / SiO2-ZrO2 sol below it and load the sol onto the support at a low speed of 20 rpm, then remove the sol. Increase the speed to 1000 rpm and maintain it for 60 s for rotary evaporation. Preheat the tubular ceramic support in an oven at 200 ℃ for 5 min, then heat it in a tube furnace at 550 ℃ for 20 min. Repeat this process 6 times to obtain a ceramic support with a loose transition layer.

[0048] (4) 1 g of 1,2-bis(triethoxysilyl)ethane (BTESE) was added to 10 g of ethanol, followed by the addition of 10 g of water and 0.05 g of hydrochloric acid for catalysis. The mixture was stirred at room temperature for 2 h to obtain an organosilicon sol. A separation layer was prepared by spin coating. The organosilicon sol was coated onto a tubular ceramic support containing a loose transition layer at a low speed of 20 rpm. The speed was increased to 1000 rpm and maintained for 30 s. After coating, the mixture was calcined in air at 250 °C for 30 min to obtain an organosilicon film. Figure 1 is a SEM image of the prepared organosilicon film. It can be seen from the figure that the surface of the prepared film is continuous and without obvious defects.

[0049] An organosilicon membrane was used for pervaporation testing of a 90 wt% acetic acid aqueous solution, with the acetic acid aqueous solution heated to 75 °C and a vacuum (<400 Pa) applied to the permeate side. The resulting separation performance was a flux of 2.13 kg·m³. -2 ·h -1 The separation factor is 1312.

[0050] Example 2

[0051] The process for preparing the organosilicon film is basically the same as in Example 1, except that in the COOH-CNTs / SiO2-ZrO2 sol, the amount of SiO2-ZrO2 sol remains constant, and the COOH-CNTs and SiO2-ZrO2 sol are mixed. 2- The ZrO2 sol has a mass ratio of 1 wt%.

[0052] An organosilicon membrane was used for pervaporation testing of a 90 wt% aqueous acetic acid solution, with the acetic acid solution heated to 75 °C and a vacuum (<400 Pa) applied to the permeate side. The resulting separation performance was a flux of 1.94 kg·m³. -2 ·h -1 The separation factor is 1033.

[0053] Example 3

[0054] The process of preparing the organosilicon film is basically the same as in Example 1, except that in the COOH-CNTs / SiO2-ZrO2 sol, the amount of SiO2-ZrO2 sol is kept constant, and the mass ratio of COOH-CNTs to SiO2-ZrO2 sol is 5wt%.

[0055] An organosilicon membrane was used for pervaporation testing of a 90 wt% aqueous acetic acid solution, with the acetic acid solution heated to 75 °C and a vacuum (<400 Pa) applied to the permeate side. The resulting separation performance was a flux of 2.33 kg·m³. -2 ·h -1 The separation factor is 596.

[0056] Example 4

[0057] The process of preparing the organosilicon film is basically the same as in Example 1, except that in the COOH-CNTs / SiO2-ZrO2 sol, the amount of SiO2-ZrO2 sol is kept constant, and the mass ratio of COOH-CNTs to SiO2-ZrO2 sol is 7wt%.

[0058] An organosilicon membrane was used for pervaporation testing of a 90 wt% acetic acid aqueous solution, where the acetic acid aqueous solution was heated to 75 °C and a vacuum (<400 Pa) was applied to the permeate side. The resulting separation performance was a flux of 2.45 kg·m³. -2 ·h -1 The separation factor is 312.

[0059] As can be seen from Examples 1-4, as the doping amount increases, the membrane flux increases accordingly, and the separation factor first increases and then decreases. The reason for the decrease is that when the doping amount is large enough, COOH-CNTs will agglomerate, which leads to an increase in the interface defects of the transition layer and a decrease in the separation factor.

[0060] Comparative Example 1

[0061] A tubular ceramic support was fixed to an iron rod, and a SiO2-ZrO2 sol was placed underneath. The sol was loaded onto the support at a low rotation speed of 20 rpm, and then the rotation speed was increased to 1000 rpm and maintained for 60 seconds for rotary evaporation. Finally, the tubular ceramic support was preheated in an oven at 200°C for 5 minutes, and then heated in a tube furnace at 550°C for 20 minutes. This process was repeated 6 times.

[0062] The BTESE separation layer was prepared by spin coating. The organosilicon sol prepared in Example 1 was coated onto a tubular ceramic support containing a transition layer at a low speed of 20 rpm. The speed was then increased to 1000 rpm and maintained for 30 s. After coating, the film was calcined in air at 250°C for 30 min to obtain an organosilicon film. Figure 2 is a SEM image of the prepared organosilicon film. As can be seen from the figure, the surface of the prepared BTESE film is smooth and continuous.

[0063] An organosilicon membrane was used for pervaporation testing of a 90 wt% aqueous acetic acid solution, with the acetic acid solution heated to 75 °C and a vacuum (<400 Pa) applied to the permeate side. The resulting separation performance was a flux of 1.31 kg·m³. -2 ·h -1 The separation factor is 1429.

[0064] Comparative Example 2

[0065] The transition layer was prepared by a wiping coating method. SiO2-ZrO2 sol was wiped onto a tubular ceramic support, and after coating, it was calcined at 550℃ for 20 min. This process was repeated 6 times to complete the coating of the transition layer.

[0066] The separation layer was prepared by a wiping method. The organosilicon sol prepared in Example 1 was wiped onto a tubular ceramic support containing a transition layer, and then calcined at 250°C for 30 min to obtain an organosilicon film.

[0067] An organosilicon membrane was used for pervaporation testing of a 90 wt% acetic acid aqueous solution, with the acetic acid aqueous solution heated to 75 °C and a vacuum (<400 Pa) applied to the permeate side. The resulting separation performance was a flux of 1.53 kg·m³. -2 ·h -1 The separation factor is 977.

[0068] Comparative Example 3

[0069] The transition layer was prepared by a wiping method. SiO2-ZrO2 sol was wiped onto a tubular ceramic support and calcined at 550℃ for 20 min. This process was repeated 10 times to complete the coating of the transition layer.

[0070] The separation layer was prepared by a wiping method. The organosilicon sol prepared in Example 1 was wiped onto a tubular ceramic support containing a transition layer, and then calcined at 250°C for 30 min to obtain an organosilicon film.

[0071] An organosilicon membrane was used for pervaporation testing of a 90 wt% acetic acid aqueous solution, with the acetic acid aqueous solution heated to 75 °C and a vacuum (<400 Pa) applied to the permeate side. The resulting separation performance was a flux of 1.23 kg·m³. -2 ·h -1 The separation factor is 1450.

[0072] Comparing Comparative Example 1 with Examples 1-4, it can be seen that the organosilicon film with the COOH-CNTs-doped transition layer has a higher flux. Figure 3 is a schematic diagram of water molecules passing through the transition layer of the organosilicon film. It can be seen from the figure that in the undoped COOH-CNTs-doped transition layer, water molecules can only pass through the gaps between the SiO2-ZrO2 sol, while in the COOH-CNTs-doped transition layer, water molecules can also be rapidly transported through the channels within the COOH-CNTs. Comparing Comparative Examples 2-3 with Comparative Example 1, it can be seen that the films prepared by spin coating and wipe coating have comparable performance, but spin coating requires fewer coating passes.

[0073] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for preparing an organosilicon film with a loose transition layer, characterized in that, Includes the following steps: (1) Carbon nanotubes were reacted with acid, washed and dried to obtain carboxylated carbon nanotubes COOH-CNTs; (2) Add water to the COOH-CNTs and SiO2-ZrO2 sol obtained in step (1) and mix evenly to obtain COOH-CNTs / SiO2-ZrO2 sol; (3) Coat the COOH-CNTs / SiO2-ZrO2 sol obtained in step (2) onto the tubular ceramic support and calcine to obtain a ceramic support with a loose transition layer; (4) The organosilicon sol is coated onto the ceramic support with a loose transition layer obtained in step (3), and heat-treated to form a separation layer to obtain the organosilicon film.

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℃, and the reaction time is 2-4h.

3. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of COOH-CNTs to SiO2-ZrO2 sol is 1-7%. 4.4 The preparation method according to claim 1, characterized in that, In step (3), the coating method is spin coating. Spin coating involves fixing a tubular ceramic support on an iron rod and rotating it, placing COOH-CNTs / SiO2-ZrO2 sol below, loading it onto the support at a low speed, and then performing rotary evaporation at a high speed. The low speed is 10-100 rpm, and the high speed is 600-6000 rpm, maintained 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℃ and the preheating time is 5-10 min.

6. The preparation method according to claim 1, characterized in that, In step (3), the calcination temperature is 450-550℃, the calcination time is 20-60min, 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 and polymerization of 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 at 100-250°C in an air atmosphere for 30-60 minutes.

9. The organosilicon film with a loose transition layer prepared by the preparation method according to any one of claims 1-8.

10. The application of the organosilicon membrane with a loose transition layer as described in claim 9 in pervaporation technology, characterized in that, The organosilicon membrane with a loose transition layer as described in claim 9 is placed in a membrane module for pervaporation separation of solvent / aqueous solution.

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