Method for separating trace organic matters in water based on non-isothermal pervaporation

Abstract

The invention provides a method for separating trace organic matters in water based on non-isothermal pervaporation, which comprises the following steps: additionally arranging a conductive porous support membrane (carbon nanotube membrane) on one side of pervaporation separation membrane penetrating fluid, and electrically heating the support membrane part; the temperature of the penetrating fluid side of the pervaporation separation membrane is higher than that of the raw material liquid side of the pervaporation separation membrane, so that the micro-temperature gradient of the pervaporation separation membrane is formed. According to the method, the temperature trade-off effect influencing flux and separation factors is eliminated in a mode of actively creating temperature gradient (non-isothermal) in a microenvironment, high selectivity and good treatment capacity can be achieved at the same time, and the method has a remarkable effect on improvement of pervaporation performance.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a method for separating trace organic matter in water based on non-isothermal pervaporation. Background Technology

[0002] Pervaporation (PV) is an effective method for dehydrating trace organic matter in water or organic solvents containing small amounts of water. It utilizes the chemical potential difference between upstream and downstream components of a pervaporation membrane to achieve mass transfer, and leverages the differences in affinity and mass transfer resistance of the pervaporation membrane for different components in the feed solution to achieve selectivity. Selectivity and processing capacity are the two most important indicators for evaluating the industrial feasibility of PV technology. Under the same experimental conditions, better selectivity results in greater processing capacity, separation efficiency, and effectiveness. In pervaporation, the parameter characterizing selectivity is the separation factor (α), which is the ratio of the concentration of the component to be separated in the permeate to that of other components in the feed solution under certain experimental conditions. The parameter characterizing processing capacity is the flux (J), which is the mass (or number of moles) of permeate passing through a unit effective membrane area per unit time under certain experimental conditions.

[0003] See Figure 1 Solvent molecules pass through the pervaporation separation membrane from one side to the other. The resulting vapor is then cooled at a low temperature to obtain the permeate. The process consists of three steps: The solvent in the feed liquid swells and enters the upstream of the polymer membrane (pervaporation separation membrane). This is a selective step. This step is very fast and has little impact on the processing capacity (flux), but has a great impact on the selectivity (separation factor), mainly determining the selectivity (separation factor) of the pervaporation process. Solvent molecules that swell and enter the upstream of the polymer membrane (pervaporation separation membrane) diffuse into the downstream of the polymer membrane (pervaporation separation membrane) under the drive of the chemical potential difference on both sides of the membrane. This is also a selective step, which is relatively slow and affects both processing capacity and selectivity. 3) Solvent molecules downstream of the polymer membrane (pervaporation separation membrane) are desorbed in a vacuum (or purge gas). This step has virtually no selectivity and is relatively slow. It mainly determines the processing capacity (flux) and has almost no effect on selectivity (separation factor).

[0004] To increase the driving force of the process and improve the permeation flux of the components, raising the temperature of the feed solution is the most common method. However, in most cases, increasing the feed solution temperature will lead to a decrease in selectivity, which is the typical "trade-off" effect. The "trade-off" effect means that most pervaporation separation membranes cannot simultaneously meet the requirements of high flux and high selectivity, thus reducing the practical application value of pervaporation technology.

[0005] Therefore, pervaporation technology that simultaneously possesses high selectivity and high flux is the goal pursued by pervaporation membrane separation methods. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for separating trace organic matter in water based on non-isothermal pervaporation. This method uses a temperature gradient in the microenvironment of the separation membrane to eliminate the temperature "trade-off" effect that affects flux and separation factor, thereby achieving both high selectivity and good processing capacity.

[0007] This invention provides the following technical solution: This invention provides a method for separating trace organic matter in water based on non-isothermal pervaporation. The method involves: attaching a porous conductive support membrane to the permeate side of a pervaporation separation membrane and heating the porous conductive support membrane so that the temperature on the permeate side of the pervaporation separation membrane is higher than the temperature on the feed liquid side of the pervaporation separation membrane, forming a microscopic temperature gradient; and using the non-isothermal pervaporation separation membrane to separate trace organic matter in water.

[0008] The fundamental reason for the “trade-off” effect is that temperature has opposite effects on the swelling and diffusion during pervaporation. At low temperatures, the swelling selectivity is high while the diffusion rate is slow, resulting in high selectivity but low flux. At high temperatures, the swelling selectivity is low while the diffusion rate is fast, resulting in low selectivity but high flux.

[0009] This invention heats an additional porous conductive support membrane on the permeate side of a pervaporation separation membrane to create a temperature gradient, thereby generating a certain temperature gradient within the separation membrane. This allows for highly selective swelling at a lower temperature (the first step described in the background art) and rapid diffusion of the swollen components at a higher temperature (the second and third steps described in the background art), thus maximizing both selectivity and permeation flux and improving the overall effect of pervaporation.

[0010] Furthermore, the process of separating trace organic matter in water includes: constructing a pervaporation device and using the pervaporation device to separate trace organic matter in water.

[0011] Furthermore, the pervaporation device includes a raw material tank, a membrane pool, and a cold trap. The membrane pool is equipped with a pervaporation separation membrane. An additional porous conductive support membrane is provided on the permeate side of the pervaporation membrane. The porous conductive support membrane is connected to a heating device. The raw material side of the pervaporation separation membrane is connected to the raw material tank through a circulation pump, and the permeate side of the pervaporation separation membrane is connected to the cold trap.

[0012] Furthermore, the porous conductive support film is a carbon nanotube film with a thickness ranging from 10 to 50 µm.

[0013] Furthermore, the heating is performed using low-voltage direct current heating.

[0014] Furthermore, the voltage is 0.5~5V.

[0015] Furthermore, the temperature on the feed liquid side of the pervaporation separation membrane is 30℃~60℃, and the temperature on the permeate side of the pervaporation separation membrane is 60℃~90℃.

[0016] The present invention has the following beneficial effects: 1. This invention creates a temperature gradient in the separation membrane, causing the selective swelling (physicochemical equilibrium step) of pervaporation to occur on the lower temperature side of the membrane, ensuring high selectivity, while the diffusion (rate control step) affecting flux occurs on the higher temperature side, resulting in higher permeation flux. This simultaneously improves both the selectivity and permeation flux of pervaporation.

[0017] 2. This invention is based on non-isothermal pervaporation separation of trace organic matter in water, which can achieve in-situ separation of organic matter, while meeting the requirements of high throughput and having high selectivity, thus improving the separation effect. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the pervaporation separation process; Figure 2 This is a schematic diagram of the non-isothermal pervaporation process in this invention; Figure 3 This is a schematic diagram of the pervaporation device in this invention.

[0020] In the diagram: 1: Liquid level line, 2: High-pressure circulating pump, 3: Raw material tank, 4: Liquid flow meter, 5: Membrane tank (including pervaporation separation membrane and additional porous conductive support membrane), 6: Cold hydrazine, 7: Cooling liquid nitrogen tank, 8: Vacuum pump, 9: Heater, T: Temperature control system, P: Vacuum gauge. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a method for separating trace organic matter in water based on non-isothermal pervaporation. An additional porous conductive support membrane on the permeate side of the pervaporation separation membrane is heated to form a temperature gradient between the feed liquid side and the permeate side of the pervaporation separation membrane; the pervaporation membrane is then used to separate trace organic matter in water.

[0023] The process of separating trace organic matter from water includes: setting up a pervaporation device and using the pervaporation device to separate trace organic matter from water.

[0024] The pervaporation device includes a feed tank, a membrane pool, and a cold trap. The membrane pool is equipped with a pervaporation separation membrane and an additional porous conductive support membrane. The feed liquid side of the pervaporation separation membrane is connected to the feed tank via a high-pressure circulating pump, and the permeate side of the pervaporation separation membrane is connected to the cold trap.

[0025] Furthermore, to optimize the pervaporation process, a liquid flow meter, a coolant nitrogen tank, a vacuum pump, a heater, a temperature control system, and a vacuum gauge can be installed in the aforementioned pervaporation device. Specifically, the pervaporation test employs, for example... Figure 3 The pervaporation apparatus shown in the diagram operates with a pervaporation separation membrane (polymer membrane) and an additional porous conductive support membrane fixed on a porous titanium plate. The effective contact area between the membrane and the feed liquid is 34.32 cm². 2 The circulating feed flow rate was 30 L / h, which was sufficiently high that concentration polarization was negligible. Before each permeate collection, the pervaporation experiment was run for approximately 0.5–1 h to allow the swelling and diffusion between the pervaporation membrane and the feed to reach a stable state. After reaching a stable state, the permeate gas was collected using liquid nitrogen cooling; the actual collection time was 0.5 h, and the selection factor and flux were analyzed. Subsequent examples and comparative examples followed this method, differing only in the use of DC heating and the pervaporation membrane. Example 1:

[0026] A PDMS pervaporation separation membrane was selected and an electrically heated carbon nanotube membrane (as a support membrane) was added after it.

[0027] Carbon nanotube membranes are a type of polymer material membrane with good electrical conductivity. When an electric current is applied, a temperature difference is generated on both sides of the membrane, achieving a non-isothermal effect. In this embodiment, the thickness of the carbon nanotube membrane selected is 30 µm.

[0028] A 2.15 wt.% butanol aqueous solution was selected for pervaporation test; A voltage of 0.5V was applied to both ends of the carbon nanotube-supported membrane. After stabilization, the temperatures on both sides of the pervaporation separation membrane were 45℃ and 63℃, respectively. In this embodiment, the separation factor was calculated to be 42, and the flux was 86.1 g / m³. 2 h.

[0029] The separation factor described in this embodiment is a key indicator for measuring membrane selectivity. It represents the membrane's ability to enrich butanol in the mixed solution during the pervaporation process.

[0030] The larger the separation factor in this embodiment, the better the selectivity of the membrane, meaning that the membrane can more effectively separate the target component from the feed mixture.

[0031] In this embodiment, the separation factor (α) is defined as the ratio of the butanol concentration in the permeate to that in the feed solution.

[0032] The formula for calculating the separation factor (α) in this embodiment is as follows:

[0033] in: Y A The mass fraction of butanol in the permeate; Y B : The mass fraction of water in the permeate; X A The mass fraction of butanol in the feed solution; X B : The mass fraction of water in the raw material liquid.

[0034] The flux mentioned in this embodiment is a key indicator for measuring membrane separation efficiency or productivity. It represents the mass or volume of permeate passing through a unit membrane area per unit time.

[0035] In this embodiment, the higher the flux, the faster the membrane permeation rate, which means that more permeation products can be obtained under the same conditions, resulting in higher separation efficiency.

[0036] In this embodiment, the flux (J) refers to the total flux, expressed in g / (m³). 2 •h).

[0037] The flux (J) calculation formula described in this embodiment is as follows:

[0038] in: m: The total mass (g) of permeate collected within time t; A: Effective membrane area (m²) 2 ); t: Collection time (h).

[0039] Example 2: PTMSP pervaporation separation membrane was selected, and a voltage of 1V was applied to both ends of the carbon nanotube membrane. Other settings were the same as in Example 1.

[0040] After stabilization, the temperatures on both sides of the pervaporation membrane were 48°C and 76°C, respectively. In this embodiment, the calculated separation factor was 47, and the flux was 968.6 g / m³. 2 h. Example 3:

[0041] A PU-HBPEV pervaporation membrane (preparation process is described in Mingjie, Hu, Le, et al. High-performance interpenetrating polymer network polyurethane pervaporation membranes for butanol recovery[J]. Journal of Chemical Technology & Biotechnology, 2015.DOI:10.1002 / jctb.4533.) was selected to separate a 3.42 wt.% butanol aqueous solution. A 5V voltage was applied across the carbon nanotube membrane, and other settings were the same as in Example 1.

[0042] After stabilization, the temperatures on both sides of the pervaporation membrane were 53℃ and 88℃, respectively. In this embodiment, the separation factor was calculated to be 10, and the flux was 537.8 g / m³. 2 h. Example 4:

[0043] An IPU-HBPEV pervaporation membrane (preparation process is described in Mingjie, Hu, Le, et al. High-performance interpenetrating polymer network polyurethane pervaporation membranes for butanol recovery[J]. Journal of Chemical Technology & Biotechnology, 2015.DOI:10.1002 / jctb.4533.) was selected to separate a 3.42 wt.% butanol aqueous solution. A 5V voltage was applied across the carbon nanotube membrane, and other settings were the same as in Example 1.

[0044] After stabilization, the temperatures on both sides of the pervaporation separation membrane were 57°C and 85°C, respectively. In this embodiment, the separation factor was calculated to be 64, and the flux was 607.9 g / m³. 2 h.

[0045] Comparative Example 1: This comparative example is the comparative example of Example 1. It uses isothermal pervaporation (without an additional porous conductive support membrane) to separate trace organic matter in water. The initial temperature on both sides of the pervaporation membrane is 45°C, and other settings are the same as in Example 1.

[0046] After stabilization, the membrane temperature on both sides of the pervaporation separation membrane remained at 45°C, and the calculated separation factor was 45 (slightly higher than in Example 1), with a flux of 53.2 g / m³. 2 h (far lower than in Example 1).

[0047] Comparative Example 2: This comparative example is the comparative example of Example 1. It uses isothermal pervaporation (without an additional porous conductive support membrane) to separate trace organic matter in water. The initial temperature on both sides of the pervaporation membrane is 63°C, and other settings are the same as in Example 1.

[0048] After stabilization, the membrane temperature on both sides of the pervaporation separation membrane remained at 63°C, and the calculated separation factor was 30 (far lower than in Example 1), with a flux of 92.2 g / m³. 2 h (slightly higher than in Example 1).

[0049] Comparative Example 3: This comparative example is the comparative example of Example 2. It uses isothermal pervaporation (without an additional porous conductive support membrane) to separate trace organic matter in water. The initial temperature on both sides of the pervaporation membrane is 48°C, and other settings are the same as in Example 2.

[0050] After stabilization, the membrane temperature on both sides of the pervaporation separation membrane remained at 48°C, and the calculated separation factor was 50 (slightly higher than in Example 2), with a flux of 587.3 g / m³. 2 h (far lower than in Example 2).

[0051] Comparative Example 4: This comparative example is the comparative example of Example 2. It uses isothermal pervaporation (without an additional porous conductive support membrane) to separate trace organic matter in water. The initial temperature on both sides of the pervaporation membrane is 76°C, and other settings are the same as in Example 2.

[0052] After stabilization, the membrane temperature on both sides of the pervaporation separation membrane remained at 76°C, and the calculated separation factor was 29 (far lower than in Example 2), with a flux of 983.1 g / m³. 2 h (slightly higher than in Example 2).

[0053] Comparative Example 5: This comparative example is the comparative example of Example 3. It uses isothermal pervaporation (without an additional porous conductive support membrane) to separate trace organic matter in water. The initial temperature on both sides of the pervaporation membrane is 53°C, and other settings are the same as in Example 3.

[0054] After stabilization, the membrane temperature on both sides of the pervaporation separation membrane remained at 53°C, and the calculated separation factor was 11 (slightly higher than in Example 3), with a flux of 321.9 g / m³. 2 h (far lower than in Example 3).

[0055] Comparative Example 6: This comparative example is the comparative example of Example 4. It uses isothermal pervaporation (without an additional porous conductive support membrane) to separate trace organic matter in water. The initial temperature on both sides of the pervaporation membrane is 57°C, and other settings are the same as in Example 4.

[0056] After stabilization, the membrane temperatures on both sides of the pervaporation separation remained at 57°C, and the calculated separation factor was 65 (slightly higher than in Example 4), with a flux of 343.6 g / m³. 2 h (far lower than in Example 4).

[0057] The data from the above embodiments and comparative examples are summarized in Table 1: Table 1

[0058] As can be seen from Examples 1-4 and their corresponding Comparative Examples 1-6 in Table 1, when different pervaporation separation membranes are used with the non-isothermal pervaporation technology of this application for the separation of low-concentration organic matter, the selectivity (separation factor) remains basically unchanged at low temperatures, while the flux is significantly improved.

[0059] In summary, this invention uses a gradient temperature approach to eliminate the temperature "trade-off" effect that affects flux and separation factor, thereby achieving both high selectivity and good processing capacity, and playing a positive role in improving pervaporation performance.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for separating trace organic matter in water based on non-isothermal pervaporation, characterized in that, The method is as follows: a porous conductive support membrane is attached to the permeate side of the pervaporation separation membrane and the porous conductive support membrane is heated so that the temperature of the permeate side of the pervaporation separation membrane is higher than the temperature of the feed liquid side of the pervaporation separation membrane, forming a microscopic temperature gradient; the pervaporation membrane is used to separate trace organic matter in water.

2. The method as described in claim 1, characterized in that: The process of separating trace organic matter from water includes: setting up a pervaporation device and using the pervaporation device to separate trace organic matter from water.

3. The method as described in claim 2, characterized in that: The pervaporation device includes a feed tank, a membrane pool, and a cold trap. The membrane pool is equipped with a pervaporation separation membrane. A support membrane and a porous conductive support membrane are provided on the permeate side of the pervaporation separation membrane. The porous conductive support membrane is connected to a heating device. The feed liquid side of the pervaporation separation membrane is connected to the feed tank through a circulation pump, and the permeate side of the pervaporation separation membrane is connected to the cold trap.

4. The method as described in claim 1, characterized in that: The porous conductive support film is a carbon nanotube film with a thickness ranging from 10 to 50 µm.

5. The method as described in claim 1, characterized in that: The heating is performed using low-voltage direct current.

6. The method as described in claim 5, characterized in that: The voltage is 0.5~5V.

7. The method as described in claim 1, characterized in that: The temperature on the feed liquid side of the pervaporation separation membrane is 30℃~60℃, and the temperature on the permeate side of the pervaporation separation membrane is 60℃~90℃.

Images