JPS6154206A - Thermopervaporation apparatus - Google Patents

Abstract

PURPOSE:To keep high efficiency in removing a solute for a long period even when org. materials are deposited on a membrane by superposing a finely pored membrane as a protective membrane on the second finely pored membrane as a separation membrane to form a fine pored membrane. CONSTITUTION:A protective membrane 2 consisting of the first finely pored membrane is provided in an outer tube 1, and a separation membrane 3 is furnished on the rear surface close to the membrane 2 to form a membrane tube 4. An untreated liquid passage is constituted between the membrane tube 4 and the outer tube 1 to form a thermopervaporation apparatus. The untreated liquid, heated at a specified temp., is introduced into the untreated liquid passage 5. The generated steam permeates the membrane tube 4, enters a steam diffusion space 12, and diffuses. Then the steam is cooled by a heat-transfer tube 11 to generate condensed water which is discharged from a discharge pipe 15. The apparatus is appropriately used for concentrating an aq. mixture contg. org. substances and for separating water from the aq. mixture.

Description

[Detailed description of the invention] The present invention relates to a thermopervaporation device.

For example, as a device for separating water from an aqueous mixture such as an aqueous solution or for condensing an aqueous solution, a hydrophobic microporous membrane that allows water vapor to pass through but does not allow the aqueous solution itself to pass through is heated to a predetermined temperature. A heated stock solution, for example, hot sea water, is passed through, and the water vapor generated from the stock solution is passed through the microporous membrane and cooled by a low-temperature heat transfer wall placed opposite the other side of the membrane. A liquid separation device using a thermopervaporation method is already known, in which a raw liquid is condensed on one side of a microporous membrane, and a condensate is obtained on the other side.

For example, in Japanese Patent Publication No. 49-45461, a pair of membrane walls made of microporous membranes are arranged in parallel to form a high-temperature stock solution passage between them, and the membrane walls are transmitted through the membrane walls to the outside of each membrane wall. A vapor diffusion space is provided to diffuse the water vapor.
Thermopervaporation involves installing a low-temperature heat transfer wall in each case, allowing the water vapor generated from the high-temperature stock solution to permeate the vapor diffusion space, cooling it on the heat transfer wall, condensing it, and separating water from the stock solution. The equipment is described.

For concentrating and separating liquids using the thermopervaporation device described above, a hydrophobic heat-resistant microporous membrane made of a fluororesin such as polytetrafluoroethylene is typically used as the separation means. mixtures, e.g.
It is suitable for concentrating an aqueous solution and separating water from this aqueous solution. However, on the other hand, if the liquid to be treated, that is, the stock solution, contains organic substances, these organic substances will adhere to the microporous membrane over the course of the treatment time, causing the microporous membrane to lose its hydrophobicity. As a result, the microporous membrane becomes permeable to liquid, leading to a decrease in the removal rate for solutes. In particular, when the stock solution is an aqueous liquid containing organic substances such as protein, starch, and fiber, such as tangerine juice, soybean protein, and fish juice in the food industry, microporous membranes are The solute removal rate is significantly reduced due to the attachment of organic substances, and the solute recovery rate and concentration rate of the undiluted solution are reduced.At the same time, the undiluted solution is mixed into the condensed water, resulting in a decrease in its purity.

In order to solve the above-mentioned problems, the present inventors developed 61
1. As a result of our research, we found that in a thermopervaporation device, the above microporous membrane is used as a first microporous membrane that directly contacts the stock solution as a protective film, and as a separation membrane that is layered on the back side of this BW preservation membrane. The inventors have discovered that even if organic substances adhere to the microporous membrane that directly contacts the stock solution, the solute removal rate can be maintained at a high rate for a long period of time by comprising a second microporous membrane. This led to the present invention.

In the thermopervaporation device according to the present invention, an aqueous mixture is brought into contact with one side of a hydrophobic microporous membrane that does not allow water to pass through, but allows water vapor to pass through, generates water vapor from this aqueous mixture, and transfers it to the above-mentioned single pores. In a thermopervaporation device in which the aqueous mixture is permeated to the other side of the membrane, and is cooled and condensed, the first microporous membrane as a protective membrane in which the aqueous mixture is in direct contact with the aqueous mixture; It is characterized by comprising a second microporous membrane as a separation membrane layered on the back surface.

In the thermopervaporation device of the present invention,
A microporous membrane that does not allow the permeation of the stock solution but allows the permeation of water vapor is formed from at least two microporous membranes. That is, it is formed from a first microporous membrane as a protective film that comes into direct contact with the stock solution, and a second microporous membrane as a separation membrane that is stacked on the back side of this protective film.

These protective membranes and separation membranes are not in complete contact with each other, and it is necessary to have a gap between the I-retaining membrane and separation membrane for the undiluted solution to enter, but they are not adhered to each other. There is no need for them to be present; they may just be superimposed. However, if necessary, they can also be partially glued together.

The microporous membrane used as the above-mentioned retention 8W membrane or separation membrane needs to be hydrophobic to the aqueous mixture that is the high-temperature stock solution, and has the property of not allowing the stock solution to pass through, but allowing water vapor to pass through. It is necessary. Therefore, the micropore 'zH
1A is usually about 0.05 to 50 μm, preferably 0
．． It has micropores of about 1 to 10 μm, and the porosity is preferably 50% or more. In addition, the thickness of the microporous membrane is 1 to 300 mm.
μm1 is preferably 5 to 50 μm, but is not limited thereto.

Specifically, as such a microporous membrane, a microporous membrane made of a fluororesin such as polytetrafluoroethylene resin, vinylidene fluoride resin, ethylene-tetrafluoroethylene copolymer resin, etc. is heat-resistant. It is particularly preferably used because it has both hydrophobicity and hydrophobicity. However, even for microporous membranes made of hydrophilic resins such as polysulfone or cellulose resin, when the surface is coated with a water-repellent resin such as fluororesin or silicone resin to provide a hydrophobic microporous surface. These resin films can also be used.

In addition, since microporous membranes generally have low strength, the separation membrane may be supported on an appropriate support.Such a support not only reinforces the microporous membrane but also prevents water vapor. It is sufficient that the material can be permeated, and for example, a woven or non-woven fabric made of polyamide or a porous tube made of ceramic is preferably used.

In this way, in a thermopervaporation device, by bringing the protective film into direct contact with the stock solution and layering the separation membrane on the back side of this protective film, even if the stock solution contains organic substances, it can be protected. The membrane functions as a filtration membrane for organic substances, and organic substances adhere to this protective membrane, so even if the protective 8W membrane loses its hydrophobicity and the undiluted solution passes through the protective membrane, the undiluted solution will not pass through the protective membrane. Organic substances are being filtered out and come into contact with the separation membrane. Since the separation membrane has a hydrophobic surface that is not contaminated with organic substances, it does not allow the undiluted solution to pass through it, but only allows water vapor to pass therethrough, so that the undiluted solution does not get mixed into the condensed water. Further, if the protective film becomes noticeably contaminated with organic substances, it can be replaced with a new microporous film as necessary.

In the device of the present invention, it is preferable that the back surface of the microporous membrane serving as the protective membrane, that is, the surface facing the surface of the separation membrane, be made hydrophilic. As mentioned above, when an organic substance adheres to the protective 8W membrane and its hydrophobicity is lost, and the undiluted solution permeates through the protective membrane, the undiluted solution will pass through the protective membrane because the back side of the protective membrane is hydrophilic. This is because the membrane is uniformly wetted, so the contact area between the stock solution and the separation membrane is large, and thus a large amount of water vapor permeation can be maintained.

In order to make the back side of the protective film hydrophilic in this way, when the protective film is made of polytetrafluoroethylene resin, for example,
The back surface may be subjected to corona discharge treatment, alkali metal treatment, sputter etching treatment in a hydrophilic gas atmosphere such as water vapor, or the like.

On the other hand, the surface of the protective film can be sputter-etched under an inert gas such as argon to make it more hydrophobic or roughened to facilitate the attachment of organic substances.

Furthermore, in the device of the present invention, the porosity and micropore diameter of the protective membrane are preferably larger than those of the separation membrane. Generally, it is already known that in the treatment of liquids using thermopervaporation equipment, the permeation rate of water vapor does not greatly depend on the thickness of the microporous membrane, that is, it does not decrease in proportion to the membrane thickness. However, as mentioned above,
By increasing the porosity and micropore diameter of the protective membrane compared to the separation membrane, the water vapor transmission rate becomes dependent almost solely on the properties of the separation membrane, and the reduction in water vapor transmission rate due to the protective membrane is eliminated. be.

Therefore, in the device of the present invention, in addition to the above-mentioned microporous membrane, for example, 5
A resin mesh such as polyamide or a metal mesh having micropores of 0 to 1000 meshes, preferably 200 to 500 meshes can also be used.

1 and 2 show an example of a thermopervaporation device according to the present invention.

That is, a tubular protective film 2 made of a first microporous membrane is disposed coaxially within the outer tube 1, and a second microporous membrane also made of a second microporous membrane is disposed adjacent thereto. Tubular separation membranes 3 are arranged coaxially, and these tubular membranes constitute a membrane tube 4.

A stock solution passage 5 for the stock solution heated to a predetermined temperature is formed between the membrane tube 4 and the outer tube.

An inlet pipe 6 and an outlet pipe 7 for the stock solution are connected to the stock solution passage 5 to form a stock solution circuit, and a heater 8 is disposed in this circuit as required. The stock solution is supplied through a stock solution supply pipe 1 equipped with a valve 9.
The stock solution circuit is appropriately replenished from zero to the stock solution circuit and circulated through the stock solution circuit. If necessary, the stock solution is heated to a predetermined temperature by these heaters 8 . Also,
Although not shown, a portion of the stock solution is discharged from the stock solution circuit via a discharge pipe as necessary.

A heat transfer tube 11 having a heat transfer wall is further disposed coaxially inside the membrane tube 4, and is spaced at an appropriate distance so as to have a vapor diffusion space 12 between it and the membrane tube. There is. The heat exchanger tube is made of a material with high heat conductivity, such as a thin-walled metal tube. These heat transfer tubes include an inlet pipe 13 and an outlet pipe 1 for the cooling medium.
4 are connected, and a cooling medium such as cooling water is circulated through the heat transfer tube.

An outlet pipe 15 is connected to the lower end of the vapor diffusion space for taking out condensed water that has been cooled and condensed by the heat transfer tube 11 in the vapor diffusion space.

In the above-mentioned apparatus, a high-temperature stock solution heated to a predetermined temperature is introduced into the stock solution passage 5, and the water vapor generated from the stock solution passes through the membrane tube 4, reaches the vapor diffusion space 12, and diffuses through the vapor diffusion space. The condensed water is cooled in the heat exchanger tube 11 to produce condensed water, and this condensed water flows down the surface of the heat exchanger tube to the condensed water outlet tube 1.
5 to the outside of the device.

According to the thermopervaporation device of the present invention, as described above, the protection 11 made of the first microporous membrane is brought into direct contact with the stock solution, and the second microporous membrane is Since the separation membranes made of membranes are arranged in an overlapping manner, when the stock solution contains an organic substance, the protective film functions as a filtration membrane for the organic substance, and the organic substance adheres to the protective membrane. Therefore, even if the protective membrane loses its hydrophobicity and the undiluted solution passes through the retaining 8W membrane, the undiluted solution from which organic substances have been filtered comes into contact with the hydrophobic separation membrane, and this separation membrane only contains water vapor. permeates, so the undiluted solution does not mix with /ge condensed water.

Furthermore, if the retention 8W membrane is replaced as appropriate depending on the state of attachment of organic substances, the solute removal rate can be maintained at a high level for a longer period of time.

Furthermore, by making the back side of the microporous membrane as a protective iW membrane hydrophilic, the stock solution that has passed through the protective film will uniformly wet the back side of the protective film, increasing the contact area between the stock solution and the separation membrane. , Thus, the water vapor transmission rate can be maintained high.

Therefore, the thermopervaporation device according to the present invention is suitable for concentrating aqueous mixtures containing organic substances and separating water from aqueous mixtures, for example, for concentrating and separating useful components in the food and pharmaceutical industries, wastewater treatment, etc. Specifically, it can be suitably applied to the concentration of fish and shellfish extracts, the concentration of fruit juices such as mandarin oranges, the treatment of pectin and gelatin aqueous solutions, and the treatment of wastewater such as potato wastewater, dyeing, and pulp wastewater.

Examples of the present invention are listed below.

Comparative Example 1 As shown in Fig. 1, a polytetrafluoroethylene microporous material having a thickness of 60 μm, a porosity of 70%, and micropores with an average pore diameter of 0.2 μm was placed inside a synthetic resin outer tube with a diameter of 40 m1. A membrane tube with a diameter of approximately 281 m was formed by arranging the membranes coaxially, and a stainless steel heat transfer tube was further placed within this membrane tube so that the width of the vapor diffusion space was 2.3 fins. A thermopervaporation device was constructed for this purpose. The effective membrane area in the device was 240 clIt.

In this device, tangerine juice with a temperature of 40° C. and a sugar content of 12° Br was passed through the stock solution passage, and cooling water with a temperature of 4° C. was passed through the heat transfer tube to concentrate the tangerine juice and obtain condensed water.

At the time when tangerine juice was concentrated twice, it was confirmed that essential oils, ash, fibers, etc. contained in tangerine juice were significantly attached to the membrane surface, and the sugar content of the obtained condensed water was O'B.
However, when this was cooled to a temperature of 5° C., a slight insoluble precipitate was formed, and it was confirmed that some of the fruit juice had permeated through the membrane.

In addition, the acquisition rate of condensed water is 4.0 kg/
n(・It was.

Example 1 In the apparatus of Comparative Example 1, the thickness was 80 μm, the porosity was 8
0%, a polytetrafluoroethylene microporous membrane having micropores with an average pore diameter of 2.0 μm is used as a protective film, and
Thickness: 60 μm, porosity: 70%, average pore size: 0.2
Comparative Example 1 above except that a polytetrafluoroethylene microporous membrane having micropores of μm was used as the separation membrane, and these were coaxially arranged very close to each other to form a membrane tube with a diameter of about 28 mm. The same device was configured.

In this apparatus, mandarin orange juice was concentrated and condensed water was obtained in the same manner as in Comparative Example (2). As a result, at the time of double concentration, essential oils and fibrous substances were observed on the protective membrane as in Comparative Example 1, but no such organic substances were observed on the separation membrane. The condensed water is O”Br
Moreover, even when this was cooled to 5° C., it was confirmed that no water-insoluble precipitate was formed and no fruit juice permeated through the membrane.

Also, 1! The acquisition speed of condensed water is 3.5 kg at the beginning.
/rd·hr, and although the thickness of the membrane tube was approximately twice that of the comparative example, there was only a slight decrease in the condensed water acquisition rate.

After this, replace the protective film and add tangerine juice in the same way.
When the juice was concentrated, it was possible to concentrate it 4 times without the juice passing through the membrane.

Example 2 The back surface of the same protective film used in Example 1 was made hydrophilic by corona discharge treatment under a water vapor atmosphere at a voltage of 15 kV. When tangerine juice was concentrated using the same device as in Example 1 except for using this 8W membrane, the properties of the obtained condensed water were the same as in Example 1, and the acquisition rate of condensed water was 3.9 k at
g/m·hr, which was increased compared to Example 1.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing an example of thermopervaporation according to the present invention, and FIG.
It is a sectional view along the A line. 1... Outer tube, 2... Protective membrane, 3... Separation membrane, 4...
... Membrane tube, 5... Stock solution passage, 6... Stock solution introduction tube, 7
...Stock solution outlet pipe, 10...Stock solution supply pipe, 11...
Heat exchanger tube, 12... Vapor diffusion space, 13... Cooling medium introduction pipe, 14... Cooling medium outlet pipe, 15... Condensed water extraction pipe. 11th'1

Claims (2)

[Claims] (1) An aqueous mixture is brought into contact with one side of the hydrophobic microporous membrane that does not allow water to pass through, but allows water vapor to pass through, and water vapor is generated from this aqueous mixture, which is then transferred to the other side of the microporous membrane. In a thermopervaporation device that permeates, cools and condenses, the microporous membrane has a first microporous membrane as a protective film in direct contact with the aqueous mixture, and a separation membrane stacked on the back side of the first microporous membrane. A thermopervaporation device comprising: a second microporous membrane; (2) The thermopervaporation device according to claim 1, wherein the surface of the protective film facing the separation membrane is hydrophilic.