RU135533U1 - THERMOPERVAPORATION MODULE - Google Patents

Abstract

1. Thermo-evaporation module for the separation and concentration of organic substances from liquid mixtures by thermogradient pervaporation separation, containing a chamber with a separated mixture and a chamber with a refrigerant, separated by a membrane selective for the target component and a solid surface, the temperature of which is lower than the temperature of the separated mixture, the condensation chamber is an air gap supported between the specified membrane and a solid surface, characterized in that the membrane is a polymer film reinforced setkoy.2 metal. The module according to claim 1, characterized in that the polymer film is made of polytrimethylsilylpropine, or polydimethylsiloxane, or polyvinylidene fluoride, or ethylene-propylene rubber, or a PTMSP composition and polydimethylsilmethylene with a PDMSM content of 0.5-5 wt.%, Or a polyester block polyamide with a proportion of polyester units of 40-60%. 3. The module according to claim 1, characterized in that the metal mesh is made of stainless steel or bronze, or brass. The module according to claim 1, characterized in that the diameter of the cells of the metal mesh is 30-70 microns.

Description

The utility model relates to the field of chemistry, namely to the separation of liquid mixtures and can be applied in various industries and agriculture. At the same time, the use of membrane technology allows not only solving technological problems, but also preventing environmental problems associated with environmental pollution.

One of the membrane processes of separation of liquid mixtures, still limitedly used on an industrial scale, is pervaporation. The pervaporation process allows the separation of various aqueous-organic mixtures (for example, to drain organic solvents and carry out wastewater treatment) and mixtures of organic substances. The prospectivity of pervaporation is related both to the relevance of the tasks being solved and to the high efficiency of the pervaporation process compared to other separation processes, with the possibility of separation of azeotropic mixtures, low energy consumption, non-reactivity and compactness of equipment.

Pervaporation is the process of membrane separation of liquids, in which the liquid separated mixture (feed) is brought into contact with one side of a selectively permeable non-porous membrane, and the components (permeate) penetrated through the membrane are removed as vapor from its reverse side, and then condense at a temperature below temperature of the mixture to be separated.

Most often in practice, the driving force of the process is the activity gradient, which is achieved by lowering the vapor pressure of the separated liquid mixture from the back of the membrane using one of the methods:

- either by evacuation;

- either by blowing off the vapor of the penetrating mixture with gas;

- either by condensation on the surface of the cooled heat exchanger located in the immediate vicinity of the membrane (about 1 mm).

Only the first method found industrial application (for economic reasons) in plants for the dehydration of organic solvents, when the permeate is continuously condensed in an evacuated cooled heat exchanger and removed from the system. {Jonquiures A. et. al. Industrial state-of-the-art of pervaporation and vapor permeation in the western countries // J.Membr. Sci. 2002. V.206. P.87-117.) Two other methods are more commonly used in laboratory research.

One of the most promising areas of pervaporation application is the isolation of bioalcohols from fermentation mixtures. The fermentation process is accompanied by the constant formation of non-condensing and well penetrating through the membrane carbon dioxide (as well as hydrogen in the case of ABE fermentation).

It is important to emphasize that in the case of vacuum pervaporation, the pumps are switched on periodically to pump non-condensable gases. All the rest of the time, a reduced vapor pressure of substances penetrating through the membrane is achieved by condensation in the refrigerator, where the temperature is maintained below 0 ° C. Therefore, this approach is unacceptable in terms of energy consumption in case of pervaporation separation of alcohols during fermentation and separation of liquid mixtures of other gases containing dissolved or sparged impurities.

It is also worth noting that to maintain a low temperature (less than 0 ° C), the use of special refrigeration equipment is required, leading to additional capital and operating costs for separation.

For these reasons, vacuum pervaporation has not found industrial use at the moment for the isolation and concentration of organic substances from liquid mixtures.

In this regard, of interest is the least studied variant of pervaporation, thermo-vaporization, in which the permeate condensation is realized on a cold wall directly in the membrane module at atmospheric pressure. The condensation of permeate in the process of thermal evaporation occurs, as a rule, at temperatures above 10 ° C, which distinguishes it favorably in comparison with vacuum pervaporation.

A known installation for isolating a dissolved component using a vapor-permeable membrane and a cooled wall on which vapor condensation occurs is described in US patent 3563860, IPC B01D 1/22, publ. 02.16.1971. In this case, a membrane is used that allows only one component of the mixture to be separated (the second usually is the salt or surfactant that does not pass into the gas phase). The installation consists of a chamber closed on both sides by a membrane. A hot liquid stream circulates through it, from which the desired component, for example water vapor, must be isolated. The installation also contains a chamber, closed on both sides by a waterproof heat-conducting wall. Coolant circulates through this chamber, which can also be used as a shared liquid mixture. Between these chambers there is a condensed permeate collection chamber, one wall of which is a specified membrane that transmits steam, and the other is a specified waterproof heat-conducting wall on which steam condenses. Hot and cold liquid flows from distribution pipelines connected to the heat exchanger and pump for the mixture to be separated and cold water, respectively, are supplied in parallel flows to each respective chamber and circulate in countercurrent.

The scope of the described technical solution is limited, since it is almost impossible to choose a membrane that passes only one component of the solution. This installation is mainly used for desalination of water, since salts dissolved in water do not pass into steam. However, for the isolation and concentration of organic compounds from aqueous media, it is not applicable.

It is known that using an asymmetric polyvinyltrimethylsilane (PVTMS) membrane, thermo-vaporization separation of inorganic substances can be carried out if the PVTMS membrane is modified in a plasma of a low-frequency glow discharge in an air atmosphere (A.B.Gilman, I. B. Elkina, V.V. Ugrov, VVVolkov “Plasma-chemical modification of the polyvinyltrimethylsilane membrane for thermo-vaporization” High Energy Chemistry, 1998, Volume 32, No. 4, pp. 305-309).

But installations using such a membrane are not suitable for the isolation and concentration of organic substances from liquid mixtures, since the surface of a plasma-modified PVTMS membrane acquires hydrophilic properties and is applicable only for the isolation of water.

A known membrane module for thermo-evaporation for the purpose of efficient heat recovery during pervaporation separation by using the condensation heat of permeate to directly heat the flow of the separated mixture (raw material), described in ESFernandez, P. Geerdink, ELV Goether, Desalination, 2010, V.250, PP. 1053-1055. It consists of a chamber with a separable mixture bounded on one side by a non-porous membrane, and a chamber with a refrigerant bounded on one side by an impermeable plate. The membrane chamber and the condensation chamber are located close to each other (distance - 2 mm) so that the membrane is opposite the impermeable plate. Between the liquid chambers there is an air gap (condensation chamber), in which the permeate condenses on a cold impermeable plate and is subsequently removed from the module by gravity. The separated mixture is fed into the condensation chamber and is heated by the enthalpy of condensation of permeate. Then the separated mixture is heated using an external heat source and fed into the membrane chamber. Due to the difference in vapor pressure on both sides of the membrane (from the side of the initial flow and permeate), liquid vapor penetrates through the membrane and condenses on an impermeable plate in the condensation chamber. This principle was experimentally investigated for the separation of ethanol from ethanol-water mixtures and it was shown that it is possible to obtain a heat recovery of up to 33% and realize permeate flows through the membrane up to 0.5 kg / m ² h with an ethanol / water separation factor of about 3.

From the point of view of the tasks of separation and concentration of organic substances from aqueous media, the main disadvantage of the described module is the low permeate flux of up to 0.5 kg / m ² h and a separation factor of about 3. In addition, the permeate flux of 0.5 kg / m ² h obtained at a concentration of more than 50% ethanol in ethanol-water mixture. It is known that pervaporation is used only when a component with a low concentration in the separated mixture selectively penetrates through the membrane (N. Winn, Chem. Eng. Prog. 2001, V.97, PP.66-72). This is due to the fact that when the permeate passes through the membrane, the latent heat of evaporation is expended to transfer the permeate from a liquid to a vapor state. However, when the ethanol concentration in the ethanol-water mixture is reduced to 10%, as the authors of the work indicate, the permeate flow decreases to values below 0.2 kg / m ² h.

The closest in technical essence and the achieved result is a pervaporation module for the isolation and concentration of organic substances described in Russian Patent No. 2432984, IPC B01D 61/00, publ. November 10, 2011, in which poly (1-trimethylsilyl-1-propine) is used as the membrane material. In the assembled state, two flowing liquid chambers of the membrane thermo-evaporation module - a thermostatic container with a refrigerant (chambers with a refrigerant) and a thermostatic tank with a shared liquid (chambers with a shared mixture) - are separated by a membrane and a solid surface, between which there is an air gap (condensation chamber). Refrigerant and liquid are circulated in separate circuits by pumps. Condensate drains from a solid surface under the influence of gravity and accumulates in a container for collecting permeate.

A disadvantage of the known module is the low permeate flow through the membrane and the separation factor. In addition, with a small difference in the temperature of the separated mixture and the condensation temperature, the efficiency of the module decreases. In the process of thermo-vaporization, the problem arises of supplying heat to the membrane surface and, as a result, temperature polarization (lowering the temperature in a thin membrane-gas boundary layer due to evaporation of permeate from the membrane surface). This effect can be most pronounced at a low temperature of the separated mixture and at a low condensation temperature, when the temperature polarization is maximum. So, for example, under fermentation conditions (at a temperature of 40 ° C), when additional heat is not supplied to the mixture to be separated.

The introduction of a thermo-evaporation module for the separation and concentration of organic substances from aqueous media into industry requires further improvement, which will lead to an increase in the flow of permeate through the membrane and the separation factor.

The objective of the proposed utility model is to increase the flow of permeate by increasing the thermal conductivity of the membrane and, as a result, maximizing the reduction of temperature polarization.

The problem is solved by the fact that a thermo-evaporation module for the separation and concentration of organic substances from liquid mixtures by thermogradient pervaporation separation is proposed, containing a chamber with a separated mixture and a chamber with a refrigerant separated by a membrane selective for the target component and a solid surface whose temperature is lower than the temperature of the separated mixture, condensation chamber — an air gap maintained between said membrane and a solid surface in which the membrane represents Second polymeric film reinforced with metal mesh.

The polymer film is preferably made of polytrimethylsilylpropine (PTMSP), or polydimethylsiloxane (PDMS), or polyvinylidene fluoride (PVDF), or ethylene propylene rubber (EPDM), or a composition of PTMSP and polydimethylsilmethylene (PDMSM) at a content of 0.5% PDMM. or polyester block polyamide (PEBA) with a proportion of polyester units of 40-60%.

The metal mesh is preferably made of stainless steel or bronze, or brass.

The mesh diameter of the mesh is preferably 30-70) microns.

The technical result that can be obtained from the use of the proposed technical solution is to increase the flow of permeate during the separation and concentration of organic substances from liquid mixtures.

The figure shows a diagram of a thermal vaporization installation containing the proposed module. The thermo-vaporization unit consists of the thermo-vaporization module (1) and two circuits of different temperatures. In the primary circuit, the refrigerant from the thermostatic chamber with the refrigerant (2) is circulated by the pump (3). In the second circuit, the shared fluid is circulated from a thermostatic chamber with the shared fluid (4) using a peristaltic pump (5). In the assembled state, the thermo-evaporation module contains a thermostatic chamber with a refrigerant and a thermostatic chamber with a shared liquid, which are separated by a membrane (6) and a solid surface (7), between which an air gap of 0.5-4.0 mm (8) is maintained (condensation chamber) . Maintaining the required temperature in the first circuit is provided by the cooling heat exchanger (9), in the second - by the heating heat exchanger (10).

The module works as follows. The separated liquid heated by the heat exchanger (10), through a peristaltic pump (5) enters the chamber (4). The permeate vapor evaporates from the surface of the membrane (6) and, passing into the condensation chamber (8), condenses on a solid surface (7). The solid surface is cooled by the refrigerant from the chamber (2), after the heat exchanger (9) by means of a pump (3) entering the chamber (4). Condensate drains from a solid surface under the influence of gravity and accumulates in a container for collecting permeate (not shown).

The concentrations of the substances of the initial mixture and permeate are determined refractometrically and by gas chromatography and using a Crystallux 4000M chromatograph using a flame ionization detector.

The total permeate flow is determined by the weight method according to the formula:

where m is the mass of permeate (kg), penetrated through a membrane with an area of S (m ² ), during time t (h).

The separation factor a is determined by the formula:

where x _о and x _в are mass fractions of the organic component and water, respectively, in the mixture to be separated, and y _о and y _в are mass fractions of the organic component and water, respectively, in permeate.

The following examples illustrate the proposed technical pawning, but in no way limit its scope.

Examples 1-12

Thermal pervaporation is carried out and 1-butanol is concentrated from a 1-butanol / water mixture with a concentration of 1-butanol in a separable solution equal to 2.0 wt%, changing the condensation temperature from 0 to 25 ° С. In examples 1-6 (comparative), a continuous film of polytrimethylsilylpropine (PTMSP) is used as a membrane; in examples 7-12, a PTMSP membrane reinforced with a stainless steel metal mesh with a mesh size of 40 μm is used.

The temperature of the shared initial mixture is maintained equal to 40 ° C. The thickness of the selective PTMSP - membrane layer is 40 μm. The thickness of the air gap is 2.5 mm.

The results of the isolation and concentration of 1-butanol are presented in table 1.

As can be seen from table 1. the flow for a reinforced PTMSP membrane is much higher than for an unreinforced membrane. So, for example, at a condensation temperature of 25 ° C, the permeate flow for the reinforced membrane is 7 times higher. It is worth noting that in all the examples, the separation factor for the reinforced membrane is higher than for the non-reinforced, for which at 25 ° C the separation factor is 0. Thus, the reinforced PTMSP membranes allow thermo-vaporization separation at higher condensation temperatures.

Table 1 Example No. one 2 3 four 5 6 Condensation temperature, ° С 0 5 10 fifteen twenty 25 PTMSP Flow kg / m ² h 0.05 0.05 0.04 0.04 0.02 0.01 Separation factor 41 40 40 twenty 2,5 0

Example No. 7 8 9 10 eleven 12 PTMSP / mesh Flow kg / m ² h 0.21 0.20 0.17 0.14 0.1 0,07 Separation factor 51 45 38 24 10 2

Examples 13-24

Thermo-vaporization separation and concentration of 1-butanol from a 1-butanol / water mixture with a concentration of 1-butanol in a shared solution equal to 1.0 wt% is carried out, changing the mesh size of a stainless steel mesh in a reinforced PTMSP membrane from 30 to 70 μm ( examples 13-21). In examples 22-24 (comparative) as a membrane using a continuous film PTMSP.

The temperature of the shared initial mixture is maintained equal to 40 ° C. The condensation temperature ranged from 0 to 15 ° C. The thickness of the selective PTMSP - membrane layer is 16 μm.

The results of the isolation and concentration of 1-butanol are presented in table 2.

table 2 Condensation temperature, ° С Permeate flow, kg / m ² h Cell 30 μm (examples 13-15) Cell 40 μm (examples 16-18) Cell 70 μm (examples 19-21) No mesh (examples 22-24) 0 0.22 0.42 0.31 0.20 5 0.20 0.37 0.29 0.19 fifteen 0.16 0.30 0.25 0.13

Membranes reinforced with metal meshes exhibit higher permeate fluxes compared to PTMSP films, and the maximum permeate flux is observed for a membrane reinforced with a mesh with a cell of 40 μm.

Examples 25-40.

Thermal pervaporation isolation and concentration of 1-butanol from a 1-butanol / water mixture with a concentration of 1-butanol in a shared solution equal to 1.0 wt% is carried out, changing the material of the metal mesh in a reinforced PTMSP membrane from 30 to 70 μm (examples 25- 36). In examples 37-40 (comparative) as a membrane using a continuous film PTMSP.

The temperature of the shared initial mixture is maintained equal to 40 ° C. The thickness of the selective PTMSP - membrane layer is 16 μm. The condensation temperature ranged from 0 to 15 ° C. The thickness of the air gap is 2.5 mm.

The results of the separation, isolation and concentration of 1-butanol are presented in table 3.

Table 3 Condensation temperature, ° С Permeate flow, kg / m ² h Stainless steel (examples 25-28) Bronze (examples 29-32) Brass (Examples 33-36) Without mesh (examples 37-40) 0 0.24 0.27 0.33 0.20 5 0.22 0.24 0.30 0.19 10 0.20 0.22 0.28 0.17 fifteen 0.17 0.20 0.26 0.13

With an increase in the thermal conductivity of the mesh material (thermal conductivity, W / mK: stainless steel - 15, bronze - 40, brass - 110), the permeate flow increases. The permeate flow through the reinforced PTMSP membranes is higher than through the PTMSP films of the same thickness.

Examples 41-44.

Thermogradient pervaporation separation and concentration of ethanol from ethanol / water mixture with ethanol concentration in the solution to be separated equal to 5.0 wt% were carried out, changing the temperature of the mixture to be separated from 40 to 60 ° С (examples 43-44). In examples 41-42 (comparative), a PTMSP continuous film is used as a membrane; in examples 43-44, a PTMSP membrane reinforced with a stainless steel metal mesh with a mesh size of 40 μm is used.

The thickness of the selective PTMSP - membrane layer is 16 μm. The condensation temperature was 10 ° C. The thickness of the air gap is 2.5 mm.

The results of the separation and concentration of ethanol are presented in table 4.

Table 4 Example No. 41 42 The temperature of separation, ° C 40 60 PTMSP Flow kg / m ² h 0.19 0.75 Separation factor 2.2 4.2 Example No. 43 44 PTMSP / mesh Flow kg / m ² h 0.59 1.42 Separation factor 4.0 6.1

As can be seen from table 4, membranes reinforced with metal grids show large values of the permeate flux and the ethanol / water separation factor in comparison with continuous PTMSP films, as in the case of the separation of water-butanol solutions.

The proposed technical solution also allows you to increase the values of the permeate flow and the separation factor for the target organic matter in comparison with traditional thermal vaporization (using an impermeable condensation surface).

In addition, the proposed module can be effectively used for pervaporation isolation and concentration of organic substances in the processes of their production by biomass fermentation, for example, the enzymatic production of ethanol or the enzymatic production of 1-butanol, the so-called acetone-1-butanol-ethanol fermentation (ABE fermentation) . Upon receipt of alcohols in this way, a large amount of non-condensing CO ₂ gas is formed, which makes the use of vacuum pervaporation for this application uneconomical. This is due to the fact that continuous evacuation (operation of a vacuum pump) is necessary to remove penetrating together with organic components through the CO ₂ membrane from the vacuum part of the system. The proposed module is devoid of these disadvantages.

Claims (4)

1. Thermo-evaporation module for the separation and concentration of organic substances from liquid mixtures by thermogradient pervaporation separation, containing a chamber with a separated mixture and a chamber with a refrigerant, separated by a membrane selective for the target component and a solid surface, the temperature of which is lower than the temperature of the separated mixture, the condensation chamber is an air gap supported between the specified membrane and a solid surface, characterized in that the membrane is a polymer film reinforced metal mesh. 2. The module according to claim 1, characterized in that the polymer film is made of polytrimethylsilylpropine, or polydimethylsiloxane, or polyvinylidene fluoride, or ethylene-propylene rubber, or a PTMSP composition and polydimethylsilmethylene with a PDMSM content of 0.5-5 wt.%, Or polyester -block polyamide with a proportion of polyester units of 40-60%. 3. The module according to claim 1, characterized in that the metal mesh is made of stainless steel or bronze, or brass. 4. The module according to claim 1, characterized in that the diameter of the cells of the metal mesh is 30-70 microns.

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