JPH0613085B2 - Method for producing volatile organic liquid concentrate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a volatile organic liquid by concentrating and separating an organic liquid component for volatilization from its aqueous solution.

[Prior Art] In recent years, the technology related to the membrane separation method has been remarkably developed as a technology such as reverse osmosis method, ultrafiltration method, diffusion dialysis method, hemodialysis method, electrodialysis method, gas separation method, and pervaporation method. is doing.

In general, there is a great need to separate and take out an aqueous solution of an organic liquid that is produced or accumulated in a reaction system or various processes while separating it from the system.

The pervaporation method, which is currently attracting attention, uses a membrane having a non-porous dense layer, supplies an aqueous solution to be separated to the primary side of the membrane, depressurizes the secondary side and takes out permeated components as vapor. This is a method of collecting the permeated vapor in a trap whose temperature is low. When attempting to separate an organic liquid from an aqueous solution by this method, almost all membrane materials allow water to permeate selectively. Among them, a membrane that selectively permeates volatile organic liquids is silicone. Non-porous membranes such as rubber membranes and polyolefins are disclosed in JP-A-52-68078. Recently, a silicone rubber film coated with polytrimethylsilylpropyne (JP-A-60-75306) and polyfluoroalkyl acrylate graft polystyrene has been proposed (Polymer Preprints Japan 34, (7) 1).
841 (1985).

[Problems to be Solved by the Invention] However, these techniques had practical problems such as extremely low separation selectivity and / or permeation rate, and performance stability.

Further, there is a problem that an energy-intensive process is required to keep a large-capacity device at a high degree of vacuum and to keep the trap at a low temperature.

That is, the present invention is intended to solve the drawbacks of the prior art, and is a volatile organic liquid that is preferentially permeated to a volatile organic liquid having improved separation selectivity and permeation rate of a membrane and separation efficiency. It is an object of the present invention to provide a method for producing a liquid concentrate.

[Means for Solving Problems] The present invention has the following configurations in order to achieve the above object.

That is, according to the present invention, a porous membrane made of a hydrophobic polymer is used to supply a volatile organic liquid aqueous solution to the primary side of the separation membrane and keep the secondary side in a gas phase to vaporize the separation. When the volatile organic liquid aqueous solution is concentrated, it is cooled and collected in a trap for recovery. The average pore size of the porous membrane is 10 times or more the Stokes radius of the substance to be separated, and the aqueous solution is substantially impermeable to the membrane. The secondary side of the separation membrane is kept at a pressure of 150 mmHg or more, and c. A method for producing a volatile organic liquid concentrate, comprising continuously flowing an inert gas to the secondary side of the separation membrane and satisfying at least one of the following (i) and (ii).

(I) The flow velocity of the inert gas is 0.05 m / s or more and 1.0 m / s
It is the following.

(Ii) The ratio of the volumetric flow rate of the inert gas to the volumetric permeation rate of the permeated vapor is 0.02 or more and 1.0 or less.

Regarding

The material of the dry porous membrane composed of the hydrophobic polymer used in the present invention may be any polymer as long as it does not show wettability with respect to the aqueous solution to be separated. if, the solubility parameter claim δH based on hydrogen bonding solubility parameters of the Hansen 5cal ^1/2 · cm ^-3/2 or less, and the solubility parameter δP based on dipole coupling 9
It is in the range of cal ^1/2 · cm ^-3/2 or less. However, even within this range, the preferential permeation to non-volatile components may be lost in the process of preparing a dry film, and it is difficult to completely limit it by the general physicochemical properties of the material. However, as a practical method, when a dry film is formed from the water-containing film by the solvent substitution drying method described below, those values of the dry film are compared with the average pore radius and volume porosity of the initial water-containing film. However, if each has a change of about 50% or more, it can be regarded as the hydrophobic polymer in the present invention.

Examples of such a polymer include polysulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, fluorine-containing polymers such as polyhexafluoropropylene or copolymers thereof, polyethylene, polypropylene, polystyrene, polyvinyl chloride. , Vinyl-based polymers such as polyacrylonitrile or their copolymers, polyphenylene oxide, poly (4-methylpentene-1)
Etc. can be mentioned. Polysulfone, polyvinylidene fluoride, polyacrylonitrile, polyphenylene oxide and the like can be particularly preferably used because the fine pore structure of the film can be adjusted appropriately and the film forming property is excellent.

As the method for producing the porous membrane used in the present invention, a usual method for producing a separation membrane, that is, a wet film forming method, a dry wet film forming method, a dry film forming method, a melt film forming method, sintering or fusion bonding It can be manufactured by a method or the like.

The shape of the membrane may be any shape such as a flat membrane, a tubular membrane, or a hollow fiber membrane, which can be preferably used in the present invention by assembling these into a membrane module having an appropriate structure and shape. In particular, the hollow fiber membrane is the most suitable shape because of the self-supporting property and mechanical / mechanical properties of the membrane.

In order to form a porous structure in the film forming process, a solvent, a plasticizer,
Alternatively, when the step of extracting and washing the micropore forming agent is involved, it is necessary to prepare the membrane in a dry state. In this case, in the case of drying from a solvent having a relatively small polarity, it can be prepared by a normal air-drying method or a drying method using warm air without any problem in many cases, but in the case of drying from a polar solvent or especially water, in many cases Whether the micropores disappear and the porous structure is destroyed and the permeation rate of solute in the membrane is significantly reduced,
It may lose transparency at all. In such a case, once the non-polar solvent is replaced with a solvent that is well soluble in both the polar solvent to be washed and the water or the water to be replaced, and then the non-polar solvent is further replaced and dried to obtain the above-mentioned product. Large changes in the porous structure can be avoided. in this case,
If the nature of the solvent to be initially substituted is appropriately selected, the step of further substituting with a more nonpolar solvent can be omitted, and the dry porous membrane can be prepared by one substitution. For example, in the case of polysulfone, polyvinylidene fluoride, polyacrylonitrile, etc., a method in which water is replaced with methanol or ethanol, and then it is replaced with n-hexane and dried is a preferred embodiment, but it is replaced with sufficiently dried methanol. If so, a suitable dry porous membrane can be prepared without substituting with n-hexane or the like.

The average micropore radius of the porous film used in the present invention will be described. In order to selectively permeate organic liquid molecules larger than water molecules as a solvent, the relative relationship between the micropore radius of the membrane and the molecular size of the substance to be separated is important. The ratio (Rp / rs) of the average micropore radius Rp (Å) to the Stokes radius rs (Å) of the solute molecule is
It must be 10 or more. When the value of Rp / rs is less than 10, it is not possible to preferentially permeate organic liquid components such as methanol, ethanol, n-propanol, and n-ptanol having a larger molecular size than water molecules.

Regarding the upper limit of the average fine pore radius, the larger the fine pore radius is, the more advantageous it is to the selectivity. However, from the viewpoint of water permeability, when the pore diameter becomes larger than a certain value, the pressure on the secondary side becomes primary. In the present invention, the aqueous solution becomes permeable when operated under a pressure lower than the side pressure, and the separation method of the present invention cannot be carried out. It is preferable to have a pore size in the range of being impermeable, and in the present invention, “substantially impermeable” means that an aqueous solution permeates in a gas state but is impermeable in a liquid state. Indicates that. The permeation of aqueous solution is
It depends not on the upper limit of the average micropore radius but on the maximum micropore radius. In addition to the physicochemical properties of the polymer, the coexistence in addition to the nature and concentration of the organic liquid contained in the aqueous solution to be separated Since other components are involved and are determined by the operating pressure, it is difficult to make a general decision, but the upper limit of the average micropore radius is considered to be around 1000 Å when constrained by the general classification based on the pore size of the separation membrane and typical operating conditions. be able to.

In the present invention, the aspect of the membrane separation method is similar to the pervaporation method, but the characteristics of the membrane used and the conditions on the secondary side are different from those of the pervaporation method. That is, supplying the volatile organic liquid aqueous solution to be separated to the primary side is the same, but keep the secondary side at a pressure of 150 mmHg or more,
At the same time, the flow rate of the inert gas is 0.05 m / s or more and 1.0 m / s or less, and / or the ratio of the volume permeation rate of the permeated vapor and the volume flow rate of the inert gas is 0.02 or more and 1.0 or less. Under the conditions, the permeated vapor is guided to the outside of the membrane module and collected in the cooled trap.

The pressure on the secondary side is 150mmHg or more, preferably 250mm
When it is Hg or more, more preferably 300 mmHg or more, the separation selectivity is remarkably improved.

The separation performance of the membrane strongly influences not only the pressure but also the flow rate of the inert gas and / or the ratio of the amount of permeated vapor and the flow rate of the inert gas, so that the preferable range of the pressure on the secondary side is
It is determined by considering the relationship between the flow rate of inert gas and the amount of permeated vapor. Further, the upper limit of the secondary pressure is generally 760 mmHg or less, which shows sufficient performance.

For the inert gas, the lower limit of the flow rate is advantageous in terms of separation selectivity and running cost, as long as the permeated vapor is sufficiently removed outside the system and does not condense in the membrane module. However, as the amount of the inert gas is reduced, the separation selectivity rapidly decreases, so the lower limit of the flow rate of the inert gas is determined by the total conditions such as the solution to be separated, the characteristics of the membrane module, and the operating conditions. The reason why the separation selectivity rapidly decreases near the lower limit of the amount of the inert gas is considered to be that the permeated vapor is condensed in the membrane module and the membrane is wet with the solution of the permeated component. Further, when the flow rate of the inert gas is increased, the total amount of the permeated vapor tends to increase, but the increase rate of water is predominant with respect to the increase of the volatile organic liquid component, and as a result, the separation selectivity decreases. . Therefore, the inert gas has a linear velocity of the film surface on the secondary side of 0.05 m / s or more and 1.0 m / s or less, preferably 0.1 m / s or more and 0.5 m / s or less, Alternatively,
If specified by (permeated vapor volume velocity / inert gas volume velocity), the separation selectivity is high when the condition of 0.02 or more and 1.0 or less is satisfied.

A volatile organic liquid aqueous solution that can be concentrated and separated by the method of the present invention is basically a substance whose composition of the volatile organic liquid substance in the vapor phase in the vapor-liquid equilibrium of the aqueous solution is larger than that in the liquid phase. Can be applied to Examples of such substances include methanol, ethanol, n-propanol, iso-propanol, n-butanol, t-butanol, acetone, tetrahydrofuran, 1,4-dioxane, methylamine, ethylamine, dimethylamine, diethylamine. , Acetonitrile, acetaldehyde, ethyl methyl ketone, methyl acetate, ethyl acetate and the like.

The concentration of the aqueous solution of these substances to which the present invention can be applied is preferably in a relatively low concentration range from the viewpoint of taking advantage of the features of the method of the present invention, 50% by weight or less, and further 0.5 to 20.
Weight percent is optimal. When the aqueous solution is higher than 50% by weight, the aqueous solution to be separated is not suitable for wetting the membrane regardless of other operations such as pressure.

The upper limit of the heat resistance of the membrane and the heat resistance of the liquid to be separated is limited in the temperature of the aqueous solution to be separated, which is circulated and supplied to the membrane module, but generally, the higher the temperature, the better.

EXAMPLES Next, the present invention will be specifically described by way of examples, but the scope of application of the present invention is not limited by the following examples. The experiment of the method for concentrating the volatile organic liquid aqueous solution of the present invention was performed by the method schematically shown in FIG. That is, a 5% aqueous solution of a volatile organic liquid from the supply liquid tank 1
The temperature is adjusted to 30 ° C. in the constant temperature bath 3, and the membrane module 4 is supplied and circulated. On the other hand, on the secondary side of the membrane, nitrogen gas is passed as an inert gas from the inlet 12 on the secondary side of the membrane module through the needle valve 5, and the permeated component is collected from the outlet 11 together with the permeated vapor in the cold trap 6 into the cold trap 6. . The cold trap 6 is a vacuum pump via a cold trap 7 for maintenance of the apparatus, and a pressure adjusting device 8 for maintaining a predetermined degree of pressure reduction.
Connected to 19. In the experiment, the device was assembled as shown in Fig. 1, the aqueous solution was circulated, the operation was started under predetermined conditions, and the pressure, the flow rate of nitrogen and the permeation state were made steady by using the cock 16, trap 13, and cock 18. After that, the cock 16 and the cock 18 are closed, the cocks 15 and 17 are opened, and the permeated liquid necessary for the measurement of the permeation amount and the analysis of the permeation component is cooled by the liquid nitrogen trap 6
Collected and sampled. The amount of permeation was determined by weighing, and the composition of the permeate was determined by gas chromatography or differential refractometer to determine the solute concentration. The separation factor was calculated by the following formula. C ₁ is the concentration (weight fraction) of the solute of the feed liquid and C ₂ is the permeate.

The same applies to solutes other than ethanol.

The average micropore radius of the porous film is measured by the method described below. That is, the water permeability of the membrane (Lp), the diffusion permeability of the solute (Pm methanol, which is a substance to be separated, ethanol,
It is obtained by measuring propanol, butanol, acetone, etc. and calculating using the relationship of the following equation.

Pm = (D / L) · (H / ts ² ) (1) Lp = (H / L) · {Rp ² / (8η)} (2) where D: solute diffusion coefficient, L: film thickness , H: water content,
ts: curved solute ratio, Rp: average micropore radius, η: water viscosity. ts is calculated from the following formula.

f ° sw = RT / D (3) fsw (RT / Pm-Vs / Lp) ・ (H / L) (4) ts = fsw / f ° sw R is gas constant, T is temperature at measurement (K) , Vs is the partial molar volume of the solute, f ° sw is the friction coefficient between the solute and the solvent in the solution, and fsw is the friction coefficient between the solute and the solvent in the film.

Example 1 Polyvinylidene fluoride hollow fibers having an average pore diameter of 230Å, a volume porosity of 0.717, an outer diameter of 1037 μm and an inner diameter of 738 μm were cut into a length of 40 cm, 14 pieces were bundled and inserted into an acrylic case, and both ends were epoxy. Potting was performed with an adhesive to prepare a test membrane module. The polyvinylidene fluoride hollow fiber membrane was spun and washed with water to replace the spinning solvent with methanol, and dried so that the membrane structure was not significantly changed. Using this test membrane module for ethanol aqueous solution by the method described above,
The membrane separation performance was measured by conducting experiments by variously changing the flow rate of nitrogen gas, the ratio of the amount of permeated vapor and the flow rate of nitrogen gas, and the atmospheric pressure on the secondary side of the separation membrane. When ethanol is the solute, the tortuosity Ts is 2.88. The experimental results are shown in Table 1, the ratio of the permeated vapor amount to the nitrogen gas flow rate, and the separation coefficient. The relationship with is shown in FIG.

Comparative Example 1 Example 1 except that the atmospheric pressure was set to 5 mmHg without passing nitrogen gas.
The same results as in Example 1 of Table 1 were obtained except that the nitrogen gas was flowed at 0.005 m / s and the pressure was 150 mmHg. .2 again
In the preferred range of the present invention, the nitrogen gas is permeated and the pressure is 5 mmHg.
Comparative Examples Nos. 3 to 5 in Table 1 show the results of various experiments performed in the same manner as in Example 1 except that the above was used. In addition, the ratio of the amount of permeated vapor and the flow rate of nitrogen gas, and the separation coefficient The relationship with is shown in FIG.

Example 2. A polysulfone hollow fiber having an average pore diameter of 96Å, a volume porosity of 0.68, a tortuosity ratio to ethanol ts = 1.94, an outer diameter of 1039 μm, and an inner diameter of 863 μm was prepared in a membrane module in the same manner as in Example 1, and an ethanol aqueous solution was used to apply pressure 640mmHg, linear velocity 0.2
The experiment was conducted with nitrogen gas at 16 m / s. Ethanol permeation rate Q = 0.036kg m ^-2 h ^-1 , Water permeation rate Q = 0.082kg m
^-2 h ^-1 , Comparative Example 2 Example 2 except that the pressure was set to 5 mmHg without passing nitrogen gas.
Membrane separation experiments were conducted in the same manner as above to investigate the separation performance. Ethanol permeation rate Q = 0.663 kg m ^-2 h ^-1 , Water permeation rate Q =
3.414kg m ^-2 h ^-1 , Met.

Example 3 A membrane module was prepared in the same manner as in Examples 1 and 2 using polyphenylene oxide hollow fibers having an average pore diameter of 27Å, a volume porosity of 0.59, a tortuosity ratio to ethanol ts = 1.94, an outer diameter of 445 μm, and an inner diameter of 359 μm. The separation performance was measured using an ethanol aqueous solution. Nitrogen gas is passed through at a linear velocity of 0.186 m / s, pressure is 640 mmHg, and the ratio of the amount of permeated vapor and the flow rate of nitrogen gas is
Experimented with 0.0376. Permeation rate of ethanol Q = 0.022 kg
m ^-2 h ^-1 , water permeation rate Q = 0.027 kg m ^-2 h ^-1 , Met.

Comparative Example 3 Example 3 except that the pressure was set to 5 mmHg without passing nitrogen gas.
Membrane separation experiments were conducted in the same manner as above to investigate the separation performance. Ethanol permeation rate Q = 0.123 kg m ^-2 h ^-1 , water permeation rate Q =
1.406kg m ^-2 h ^-1 , Met.

Example 4 Using the membrane module used in Example 1, a membrane separation experiment was conducted with a 2.24% acetone aqueous solution to measure the membrane separation performance. Flow nitrogen gas at a speed of 0.216 m / s, pressure 640 mmHg,
The ratio of the amount of permeated vapor and the flow rate of nitrogen gas was measured at 0.0495.
Acetone transmission rate 0.157 kg m ^-2 h ^-1 , water transmission rate Q =
0.094kg m ^-2 h ^-1 , Met.

Comparative Example 4 Example 4 except that the atmospheric pressure was set to 5 mmHg without passing nitrogen gas.
Membrane separation experiments were conducted in the same manner as above to investigate the separation performance. Acetone permeation rate Q = 0.511 kg m ^-2 h ^-1 , water permeation rate Q = 1.
857kg m ^-2 h ^-1 , Met.

Example 5 Using the membrane module used in Example 1, 1.0% n-
Membrane separation experiments were conducted with butanol aqueous solution to measure the membrane separation performance. Flow nitrogen gas at a speed of 0.216 m / s, pressure 640 m
The ratio of the amount of mHg permeated vapor to the flow rate of nitrogen gas was measured at 0.0495. Permeation rate of n-butanol 0.009 kg m ^-2 h ^-1 , water permeation rate 0.152 kg m ^-2 h ^-1 , Met.

Comparative Example 5 Example 5 was repeated except that the pressure was set to 5 mmHg without passing nitrogen gas.
Membrane separation experiments were conducted in the same manner as above to investigate the separation performance. Permeation rate Q of n-butanol Q = 0.075 kg m ^-2 h ^-1 , water permeation rate Q = 2.065 kg m ^-2 h ^-1 , Met.

Example 6 Using the membrane module used in Example 1, a membrane separation experiment was carried out with an aqueous solution of 20.0% ethanol to measure the membrane separation performance. Flow nitrogen gas at a speed of 0.377 m / s, pressure 76
The ratio of the amount of 0 mmHg permeated vapor and the flow rate of nitrogen gas was measured at 0.0292. The ethanol permeation rate is 0.179 kg m ^-2 h ^-1 , and the water permeation rate is 0.117 kg m ^-2 h ^-1 , and 20% ethanol aqueous solution
Concentrated to 60%, Met.

Comparative Example 6 Example 5 was repeated except that the pressure was set to 5 mmHg without passing nitrogen gas.
Membrane separation experiments were conducted in the same manner as above to investigate the separation performance. Ethanol permeation rate 1.188 kg m ^-2 h ^-1 , water permeation rate 2.568 kg
At m ^-2 h ^-1 , 20% aqueous ethanol solution was concentrated to 31.6%, It was 5.

EFFECTS OF THE INVENTION According to the present invention, remarkably high separation selectivity can be achieved, and furthermore, the volatile organic liquid component can be efficiently concentrated and separated from the volatile organic liquid aqueous solution at a sufficiently high permeation rate.

Further, according to the method of the present invention, it is possible to sufficiently efficiently perform the concentration separation without raising the temperature of the liquid to be separated to near the boiling point as in the conventionally known so-called thermopervaporation method, and to perform membrane separation. The separation operation under mild conditions, which is an advantage of the method, can be realized.

Further, unlike the pervaporation method, it is not necessary to have a high degree of vacuum, so that the energy required for the vacuum pump can be saved. In addition, even in the step of collecting the permeated vapor, there is an advantage that it can be carried out sufficiently efficiently without using a very low temperature trap unlike the pervaporation method.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an apparatus for producing a volatile organic liquid concentrate used in an example of the present invention. 1 is a supply liquid tank, 2 is a supply liquid circulation pump, 3 is a supply liquid heat exchanger,
4 is a membrane module, 5 is a needle valve for a flow regulator of an inert gas, and 6, 7 and 13 are cold traps. Reference numeral 8 is a pressure regulator, and 9 and 10 are inlets and outlets of the feed liquid membrane module. 11 is an outlet of the permeated vapor membrane module. Reference numeral 12 is a supply port of the inert gas to the membrane module. 14, 15, 16, 17, and 18 are cooks. 19 is a vacuum pump. FIG. 2 shows the amount of permeated vapor (v of Example 1 of the present invention and Comparative Example 1).
It is a plot of the relationship between the separation coefficient and the ratio of the ol / h) to the nitrogen gas amount (vol / h).

Claims (4)

[Claims] 1. A porous membrane made of a hydrophobic polymer is used to supply an aqueous volatile organic liquid solution to the primary side of the separation membrane, and the secondary side is kept in a gas phase to permeate the separation membrane. When the vapor is cooled and collected in a trap to be collected and the volatile organic liquid aqueous solution is concentrated, a. The average pore size of the porous membrane is 10 times or more the Stokes radius of the substance to be separated, and the aqueous solution is substantially impermeable to the membrane. The secondary side of the separation membrane is kept at a pressure of 150 mmHg or more, and c. A method for producing a volatile organic liquid concentrate, comprising continuously flowing an inert gas to the secondary side of the separation membrane and satisfying at least one of the following (i) and (ii). (I) The flow velocity of the inert gas is 0.05 m / s or more and 1.0 m / s
It is the following. (Ii) The ratio of the volumetric flow rate of the inert gas to the volumetric permeation rate of the permeated vapor is 0.02 or more and 1.0 or less. 2. A volatile organic liquid aqueous solution having a concentration of 50% by weight or less.
Method for producing volatile organic liquid concentrate according to item 3. A volatile organic liquid concentrate according to claim 1, wherein the volatile organic liquid aqueous solution has a concentration of 0.5% by weight or more and 20% by weight or less. Method 4. The volatile organic liquid concentrate according to claim 1, wherein the hydrophobic polymer is at least one selected from polysulfone, polyvinylidene fluoride, polyacrylonitrile, and polyphenylene oxide. Liquid manufacturing method.