RU2392038C1 - Device for mass exchange between liquid and gas phase - Google Patents

Abstract

FIELD: technological processes. ^ SUBSTANCE: invention relates to the field of mass exchange processes in liquid-gas system with the help of porous membranes. Device for mass exchange between liquid and gas includes facilities for supply and discharge of exchanging phases, mass exchange chamber formed by two membranes from porous polymer material, which is not soaked with exchanging liquid phase, between which there is a layer of porous polymer material non-soaked with liquid phase with a system of through channels, besides through channels are arranged with identical dimensions, are arranged in parallel and equidistantly from each other, have permanent configuration and area of cross section in the whole length and are directed from supply system to system of exchanging liquid phase discharge. ^ EFFECT: improved efficiency of mass exchange processes in liquid-gas system. ^ 3 tbl, 3 ex, 1 dwg

Description

The invention relates to the field of mass transfer processes in a liquid-gas system using porous membranes used to separate or isolate substances, as well as for directional mass transfer of substances from one exchanging phase to another, for example, to concentrate these substances for their subsequent determination.

A number of devices are known for mass transfer between a liquid and a gas phase, in which exchanging phases are located on opposite sides of membranes made of porous polymeric materials, the pores of which are filled with a gas phase [1-10]. The mass transfer process in known devices is carried out on the side of the membrane in contact with the liquid phase, which does not wet the membrane material, and the intensity of mass transfer is determined by the rate of diffusion mass transfer through the pore space of the membrane and the size of the interface between the exchanged phases, thereby reducing the efficiency of mass transfer.

Known devices in which the increase in the surface of the interphase contact in the unit of mass transfer space is achieved through the use of membranes in the form of hollow fibers [11-12]. However, this greatly complicates the design of mass transfer devices. In addition, in these devices the cavity does not exclude the possibility of one of the exchanging phases entering the flow of the other phase.

A device is known that is more efficient than the known devices, which performs mass transfer, which is closest to the claimed invention in terms of the task and technical implementation and which is selected as a prototype [13]. In the known device, the mass transfer chamber contains two membranes of a polymeric non-wettable material, between which a layer of a non-wettable porous polymeric material with a pore size of 0.003-1.0 μm, having a system of through channels of arbitrary shape, is placed. The flow of exchanging fluid is passed directly through the porous layer, and the gas stream is introduced into the porous layer and removed from it through membranes that are not permeable to the liquid phase at operating pressures. The presence in the porous material of two types of pores, significantly differing in size, makes it possible to simultaneously pass flows of exchanging phases through it: the gas phase fills and moves through the pores of the polymer material, and the liquid phase that does not wet this material fills and moves through a system of through channels. The impossibility of one of the exchanging phases getting into the flow of the other phase is ensured by the maintenance of certain pressures of these phases. The gas phase cannot get into the flow of the liquid phase due to the fact that the pressure of the liquid phase in the porous layer is maintained greater than the pressure of the gas phase. For this purpose, an adjustable choke is installed on the flow line of the liquid phase at the outlet of the porous material. The aqueous phase cannot get into the gas phase flow due to the fact that its pressure in the porous material is maintained less than the sum of the gas phase pressure and capillary pressure that occurs in the pores of the material and membranes. The capillary pressure is regulated by choosing the material of the porous layer and membranes and the pore sizes in them. By increasing the surface of the interphase contact and eliminating the diffusion limitations of the mass transfer rate, which is carried out by convective mixing of each phase, the device provides higher mass transfer efficiency compared to devices in which the flows of exchanging phases contact each other through a membrane.

A disadvantage of the known device is the insufficiently high efficiency of mass transfer due to the fact that in the prototype device the channels in the porous polymer material through which the flow of the liquid phase moves have an arbitrary shape and, therefore, an arbitrary cross-sectional area. This inevitably leads to uneven fluid flow over the cross section and length of the porous layer, and also causes uneven flow and the gas phase, since the channels filled with liquid, which are not permeable to the gas phase flow, are unevenly distributed over the layer. Such uneven flow of phases leads to a significant erosion of the zones of the released components and, ultimately, significantly reduces the efficiency of mass transfer.

The claimed invention is devoid of this drawback and its technical result is to increase the efficiency of mass transfer.

The specified technical result is achieved by the fact that in the device for mass transfer between liquid and gas, including means for supplying and outputting flows of exchanging phases, a mass transfer chamber formed by two membranes of porous polymeric material not wettable by the exchanged liquid phase, between which a layer of non-wettable liquid is placed the phase of the porous polymer material with a system of through channels, in accordance with the claimed invention, the through channels have the same dimensions, are parallel and equal remote from each other, have a constant configuration and a cross-sectional area along the entire length and are directed from the supply system to the output system of the exchanging liquid phase.

The effect of increasing mass transfer is achieved by the fact that the through channels in the polymer material are not of arbitrary shape and not uniform in cross section, as is the case in the device adopted as a prototype, but, as indicated above, have the same dimensions, are parallel and equidistant from each other, and they have a constant configuration and cross-sectional area along the entire length and are directed from the supply system to the liquid phase withdrawal system. The identity, parallelism and equidistance from each other of the channels through which the liquid phase moves together provide a uniform flow of the liquid and gas phases through the porous material and thereby significantly increase (compared with the prototype) the efficiency of mass transfer between the liquid and gas phase.

The effectiveness of the mass transfer process in the proposed device depends on the size and number of channels in the porous material. The smaller the size of the channels and the greater their number per unit cross-sectional area of the porous material, the ceteris paribus the higher the efficiency of the process. However, this reduces the productivity of the process, since the permeability of the porous layer decreases and, accordingly, the maximum possible costs of the exchanging phases through the porous material are reduced. The optimal size of the channels and their number already depend on the particular utilitarian problem being solved.

The claimed device is illustrated in the drawing.

The main unit of the device is a mass transfer chamber. Polymeric porous membranes 1, 2 are installed in the mass transfer chamber. A layer of polymeric porous material is placed in the intermembrane space 3, in which parallel channels having a constant configuration and a cross-sectional area along the entire length are made equally spaced from each other 4, which are directed from the fluid supply manifold 5 to the fluid outlet manifold 6. The remaining elements of the device are similar in purpose to the device adopted as a prototype. The collectors for supplying and discharging liquids 5 and 6, as well as the collectors for supplying and discharging gas 7 and 8, serve for uniform intake and uniform removal of flows exchanging the liquid and gas phases. The device comprises means for regulating the pressure of the liquid and gas phase 9 at the entrance to and exit from the mass transfer chamber, as well as means measuring the pressure of the liquid and gas 10, for example, pressure gauges.

The proposed device operates as follows. A fluid flow is introduced through the manifold 5. After filling channels 4 in the intermembrane layer 3 with liquid and the free volumes of the collectors 5 and 6, which is visually checked by the absence of gas bubbles in the liquid stream at the outlet of the manifold 6, a gas stream is supplied through the manifold 7 under a pressure lower than the liquid pressure at the outlet of the manifold 6 The ratio of the flow rates of the exchanging phases, which is necessary under the conditions of a specific mass transfer process, is maintained by means of pressure control means at the outlet of the mass transfer chamber.

The operability of the proposed device, which was tested in laboratory conditions at St. Petersburg State University, and also subsequently under real production conditions, is illustrated by various examples of mass transfer processes in a liquid-gas system: gas extraction and liquid absorption.

Example 1

Continuous gas extraction water purification from dissolved oxygen.

The flow of purified distilled water saturated with atmospheric oxygen with a dissolved oxygen concentration of 9 mg / kg was passed through a proposed device and prototype device using a peristaltic pump with a certain flow rate and filled with equal volumes (6 cm ³ ) of a porous polymeric material (4-PN polytetrafluoroethylene) ) and identical membranes from the same material. The diameter of the channels in the proposed device was 1 mm, the length was 3 cm, and the number of channels per 1 cm ^{2 of the} cross section of the porous layer was 10. After filling the devices with purified water, a flow was passed simultaneously with the water supply through the devices with a certain flow rate extractant gas - high purity nitrogen (oxygen content less than 0.001 vol.%). The residual concentration of oxygen dissolved in water at the outlet of the devices was measured by control and using an oxygen analyzer brand AKPM - 01T. The results are presented in table 1.

Table 1 The residual concentration of dissolved oxygen using the proposed device and the device of the prototype at different costs of the gas extractant (W _G ) and purified water (W _L ) W _G , ml / min W _L , ml / min W _G / W _L Residual oxygen concentration, mcg / kg Proposed device Prototype device fifteen thirty 0.5 240 ± 20 320 ± 20 thirty thirty 1,0 84 ± 7 150 ± 10 60 thirty 2.0 39 ± 4 62 ± 5 120 thirty 4.0 15 ± 2 Not functioning thirty 60 0.5 104 ± 8 220 ± 20 60 60 1,0 28 ± 3 59 ± 5 120 60 2.0 11 ± 1 27 ± 2 240 60 4.0 5 ± 1 Not functioning

It was found that the maximum possible ratio of the flow rate of the extractant gas and the purified water, on which, all other things being equal, determines the degree of purification of water from dissolved oxygen, in the case of the prototype device is 2: 1, while for the proposed device 4: 1. This is due to a more uniform distribution in the porous layer of channels that are not permeable to the gas phase, through which the fluid flow moves in the proposed device compared to the prototype. With the same costs of exchanging phases, the proposed device provides a higher degree of water purification from dissolved oxygen, which indicates a higher mass transfer efficiency in the proposed device compared to the prototype.

Example 2

Continuous saturation of saline with atmospheric oxygen.

A pre-degassed stream of physiological saline (1% NaCl + 4.5% glucose) pre-degassed with a dissolved oxygen concentration of less than 0.1 mg / kg using a peristaltic pump with a certain flow rate was passed through the proposed device and the prototype device, filled with equal volumes (6 ³ cm) of a porous polymeric material (polytetrafluoroethylene grade 4-PN) and identical membranes from the same material. The diameter, length and number of channels in the proposed device are the same as in the previous example. After filling the devices with physiological saline, simultaneously with the flow of the solution through the devices with a certain flow rate, the flow of atmospheric air was carried out. Using an AKPM - 01T oxygen analyzer, the concentration of dissolved oxygen in physiological saline was measured at the outlet of the devices. The degree of saturation of the physiological solution with atmospheric oxygen was taken as a percentage of the concentration of oxygen in the solution to the limiting solubility of atmospheric oxygen in this solution. The results are presented in table 2.

table 2 The degree of saturation of the physiological solution with atmospheric oxygen using the proposed device and the prototype device at various air flow rates (W _G ) and physiological saline (W _L ) W _G , ml / min W _L , ml / min W _G / W _L The degree of saturation,% Proposed device Prototype device fifteen thirty 0.5 61 42 thirty thirty 1,0 88 66 45 thirty 1,5 96 84 60 thirty 2.0 one hundred 95 thirty 60 0.5 55 38 60 60 1,0 81 63 90 60 1,5 94 82 120 60 2.0 99 92

As can be seen from table 2, at the same costs of the exchanging phases, the proposed device provides a more complete saturation of the physiological solution with atmospheric oxygen compared to the prototype device. This indicates a higher mass transfer efficiency of the claimed device.

Example 3

Liquid absorption absorption of phenol vapor from an air stream into an aqueous solution with its subsequent fluorescence determination.

Using a pump, mass-exchange chambers of equal volume (5 cm ³ ) of the proposed device and prototype device were filled with an absorbing aqueous solution, which contain the same amount of porous polymeric material (4-PN polytetrafluoroethylene) and identical membranes from the same material. The volume of the absorbent solution in the channels of the porous material in both cases was 1.0 cm ³ . The diameter of the channels in the proposed device was 1 mm, their length was 5 cm, and the number of channels per 1 cm ^{2 of the} cross section of the porous layer was 10. After filling the mass transfer chamber with an absorbent solution, the input and output liquid phase collectors were blocked. Then, an air stream with a known concentration of phenol vapor (10, 20, and 50 μg / m ³ ) was passed through the device using an electroaspirator with a flow rate of 1 l / min for 10 minutes. After passing the analyzed air, the gas phase collectors were closed, the liquid phase collectors were opened, and the absorbed aqueous solution with phenol absorbed from the air was displaced with a distilled water pump into a flow fluorescence detector (excitation wavelength - 254 nm, radiation detection wavelength range 320-340 nm) . The obtained fractograms measured the height and peak area of phenol. The peak area is proportional to the amount of phenol in the absorbent solution, and the peak height is proportional to the phenol concentration at the maximum of the displacement zone. The results are shown in table 3.

Table 3 The parameters of the phenol peaks when using the proposed device and the prototype device for various concentrations of phenol The concentration of phenol in the air, mcg / m ³ Phenol Peak Parameters (Relative Units) Peak area Peak height Proposed device Prototype Device Proposed device Prototype Device 10 100 ± 5 74 ± 4 100 ± 4 41 ± 2 twenty 210 ± 10 138 ± 6 205 ± 8 88 ± 4 fifty 520 ± 20 360 ± 15 491 ± 16 223 ± 10

As can be seen from table 3, in the case of the proposed device, the peak areas of phenol are approximately 30% larger, and the peak heights are 2-3 times greater than in the case of the prototype. The large values of the peak areas when using the proposed device indicate a higher degree of phenol extraction from the analyzed air stream with an absorbing aqueous solution, which can be explained by a higher mass transfer efficiency. Significantly higher peak heights in the case of the proposed device also indicate a significantly less erosion of the phenol zone when it is displaced in the proposed device. Together, these effects can reduce the detection limits of phenol in air by several times.

Based on the studies, the above examples clearly confirm the significantly higher (not less than twice) the efficiency of mass transfer processes in the liquid-gas system using the new design of the claimed invention.

The claimed invention is in demand in industry, as well as in laboratory and industrial conditions, when a highly effective deep and continuous treatment of water from oxygen dissolved in it is required.

Information sources

1. Hwang S.T. Kammermeyer K. Membrane separation methods. Per. from English M .: Chemistry, 1981, p. 68.

2. Babcoch W.C., Bakez R.W., Kelly D. J. at al. "U. S. government research reports", 1980, 7, PB80-110430, p. 1174.

3. US patent N 345589 (1969).

4. U.S. Patent No. 4,451,562 (1984).

5. Patent of Germany N 2758546 (1978).

6. Patent of South Africa N 7903581 (1980).

7. Application for the invention of EP N 0223626 (1987).

8. Japan Patent N 63-1860 (1988).

9. Japanese Patent N 63-17465 (1988).

10. Patent BBP N 1471308 (1977).

11. Japan Patent N 63-1860 (1988).

12. Japan Patent N 63-17465 (1988).

13. RF patent N 2023488 (1991) is a prototype.

Claims (1)

A device for carrying out mass transfer between a liquid and a gas, including means for supplying and outputting flows of exchanging phases, a mass transfer chamber formed by two membranes of a porous polymer material that is not wettable by the exchanging liquid phase, between which a layer of a non-wettable liquid phase porous polymer material with a through-channel system is placed, characterized the fact that the through channels are made with the same dimensions, are parallel and equidistant from each other, have a constant configuration s and the cross-sectional area along the entire length and are directed from the feed system to the output system of the exchanging liquid phase.