JPH0773666B2 - Membrane separation and concentration method of alcoholic aqueous solution - Google Patents

Description

Detailed Description of the Invention

The present invention relates to a method of dehydrating and concentrating an aqueous alcohol solution in which a water-soluble alcohol such as methanol, ethanol, propanol or butanol is dissolved by a pervaporation membrane separation method using a polyamino acid derivative membrane over the entire concentration range.

[0002]

BACKGROUND OF THE INVENTION Various methods for separating a specific compound from a homogeneous mixed solution are known, and distillation, extraction,
There are various methods such as adsorption, ion exchange, and crystallization, and they are widely used industrially.

[0003]

However, in the distillation method, which is a typical method of separating organic substances, it is necessary to perform phase conversion from a mixed solution into vapor during the separation process. It requires a certain amount of heat and is a typical energy-consuming separation and purification technology. For example, when ethanol is separated from water, the boiling point difference is 22.5 ° C, but ethanol and water are associated by hydrogen bonds,
A large amount of energy is required to break off this strong affinity and separate efficiently. Also, the ethanol solution is 9
Since azeotropic distillation occurs at a concentration of 5.5 wt%, it is necessary to perform azeotropic distillation in a complicated process to produce completely dehydrated ethanol. Therefore, in order to dehydrate and concentrate an organic solvent such as ethanol by the distillation method, there are drawbacks that complicated steps must be taken and a large amount of energy is consumed.

[0004]

SUMMARY OF THE INVENTION The present invention overcomes the drawbacks of the distillation method, which is a conventional multi-energy consuming separation method,
It was made to provide a method for dehydration / concentration of an alcohol aqueous solution, which is capable of efficiently performing a large amount of dehydration / concentration with a simple operation, and which is advantageous for industrial implementation.

Due to the strong demand for energy saving starting from the first oil crisis and the remarkable progress of science and technology on artificial membranes, pervaporation method is used as a new separation / concentration technology to supplement or replace distillation. Technology was developed. In particular, great expectations are placed on the technology for concentrating and separating the alcohol aqueous solution of biomass. Another major application field of the pervaporation method is dehydration / concentration of a water-containing organic solvent such as an alcohol aqueous solution.

In this membrane separation process, power is required to make the permeate side negative pressure, but a large amount of latent heat of vaporization and energy required for entrainer recovery required in the azeotropic distillation method are unnecessary. The biggest feature is energy conservation.

The pervaporation membrane separation method, which is attracting attention as a new separation process for organic liquid mixtures, has some characteristics as a separation / concentration method as taught in US Pat. No. 2,953,502. It is more energy-saving than conventional methods such as distillation, and is suitable for separating thermally unstable substances, and is effective for separating systems (azeotropic mixtures and near-boiling mixtures) that are difficult to separate by conventional methods. It is a big feature. The pervaporation membrane separation method takes the same process as distillation in terms of phase change from liquid to vapor, but there is a notable difference in that the latent heat of vaporization uses waste heat which does not cost fuel. In addition, the pervaporation membrane separation method separates and concentrates by three processes of dissolution in the membrane, diffusion in the membrane, and evaporation to the outside of the membrane, and by making good use of these processes, it will be used in the distillation method in the future. It is expected that it will be widely applied in various industrial fields in the future as an alternative high-level separation technology.

The conventional pervaporation separation membrane used for the purpose of removing water contained in an organic solvent such as alcohol and concentrating and purifying the organic solvent is a high concentration region of the organic solvent, that is, a low water content. However, it has a drawback that it cannot be used for dehydration of high and medium water-containing organic solvents. At the same time, in the conventional method, the permeation rate did not increase so much, so the amount of discharged water was small and it was inefficient. The present invention is a membrane separation and concentration method that overcomes these drawbacks. In other words, the present invention provides a membrane concentration method used in a dehydration / concentration separation process of an alcohol aqueous solution, which has a high discharge water amount, for the purpose of dehydration / concentration of alcohol over the entire concentration range of the alcohol aqueous solution including high-medium water content. It was done by.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies on a means for separating and concentrating an aqueous alcohol solution by a pervaporation membrane separation method, particularly a means for dehydrating, and as a result, a polyamino acid copolymer membrane has been obtained. It was found that the aqueous solution of alcohol can be efficiently separated and concentrated at room temperature by adopting the pervaporation method using the above method, and the present invention has been completed based on this finding. Preferably, L-leucine having a hydrophobic structure and Nε-carbobenzoxy-L-lysine capable of having a hydrophilic structure are randomly copolymerized, and decarbobenzoxy in hydrobromic acetic acid in a film-formed state. Poly (L-leucine-L-
By a pervaporation method using a derivative film of a lysine) copolymer, water is separated with good selectivity from an aqueous alcohol solution such as methanol, ethanol, or propanol,
It was found that a concentrated aqueous alcohol solution can be recovered, and the present invention has been completed. The membrane concentration method of the present invention can be applied not only to aqueous alcohol solutions, but also to removing water in general organic solvents and concentrating and purifying the organic solvents.

The synthetic polyamino acid copolymer membrane used in the membrane separation / concentration method of the present invention comprises the following four types of poly (L-leucine-
It is a derivative film of an L-lysine) copolymer.

(1) L-leucine having a hydrophobic structure and Nε-carbobenzoxy-L-lysine, which can have a hydrophilic structure, are randomly copolymerized, and depolymerized in hydrobromic acetic acid in a film-formed state. Poly (L-leucine-L-lysine) copolymer membrane obtained by carbobenzoxylation

(2) L-leucine having a hydrophobic structure and Nε-carbobenzoxy-L-lysine capable of having a hydrophilic structure are randomly copolymerized, and then depolymerized in hydrobromic acetic acid in a film-formed state. Separation membrane obtained by further treating a poly (L-leucine-L-lysine) copolymer membrane obtained by carbobenzoxylation with an aqueous sodium hydroxide solution

(3) L-leucine having a hydrophobic structure and Nε-carbobenzoxy-L-lysine, which can have a hydrophilic structure, are randomly copolymerized, and depolymerized in hydrobromic acetic acid in a film-formed state. Separation membrane obtained by further treating a poly (L-leucine-L-lysine) copolymer membrane obtained by carbobenzoxylation with an aqueous hydrochloric acid solution

(4) R-leucine having a hydrophobic structure and Nε-carbobenzoxy-L-lysine, which can have a hydrophilic structure, are randomly copolymerized, and depolymerized in hydrobromic acetic acid in a film-formed state. Separation membrane obtained by further treating a poly (L-leucine-L-lysine) copolymer membrane obtained by carrying out carbobenzoxylation with an ether solution of adipic acid dichloride

[0015]

According to the present invention, by using the above-mentioned membrane as a separation membrane of the pervaporation method, water can be removed from an aqueous solution of methanol, ethanol, propanol or the like.
The aqueous alcohol solution can be concentrated or dehydrated and purified with high purity by allowing selective permeation over the entire concentration range.

Each of the separation membranes used in the present invention has a strong hydrophobicity rather than a hydrophilicity, that is, a small action against water and resistance in view of the measurement result of the swelling degree in an aqueous alcohol solution. , Suggests that relaxation of the microstructure of the membrane is unlikely to occur in an aqueous alcohol solution. Furthermore, the strength of the hydrophobicity can be adjusted by the balance between the hydrophilic monomer and the hydrophobic monomer, that is, the copolymer composition. Therefore, the separation membrane used in the present invention, unlike the treatment object of the conventional separation membrane, not only a small amount of water, for example, 30%, 50%, 80%, further containing water, medium and high water content. It can be used for dehydration and concentration, which has a wide range of applications and has a concentration range as a separation target. When the water content is high as described above, a large amount of discharged water, that is, a permeation rate is inevitably required, and in this respect also, the separation membrane used in the present invention has high performance requirements. In other words, the transmission speed is several Kg / 〓h
It is also useful as a dehydration separation membrane when the water content is high, medium, and low.

The present invention is advantageous in that it avoids costly, energy-intensive distillation processes. To perform dehydration / concentration of an aqueous alcohol solution by the method of the present invention,
The raw material alcohol aqueous solution is supplied to the primary side of the membrane, that is, the supply side under atmospheric pressure or under pressure. On the secondary side, the permeate can be collected by sweeping it with another inert gas or vapor, or it can be collected under reduced pressure. That is, the membrane potential is 1 more than the chemical potential on the secondary side of the membrane, that is, the permeate collecting side.
By maintaining a large chemical potential on the secondary side, that is, the supply side, dehydration / concentration of the aqueous alcohol solution by the membrane can be performed. Each temperature on the supply side and the permeation side can be applied over a wide temperature range, but in the present invention, since the primary side of the membrane is liquid and the secondary side is vapor, in principle, the temperature is below the freezing point of alcohol and water. Alternatively, the temperature range above the boiling point cannot be used.

The poly (α-amino acid) used as a separation membrane material in the present invention has a rigid structure in which the main chain has an α-helix, and different free volumes are formed between the main chain structures depending on the side chains. There is. Therefore, it is considered that the permeation of small molecules occurs through this part of the free volume, and the chemical properties of the side chains (hydrophilicity, hydrophobicity, etc.) and the bulky property that influence the formation of the free volume affect the permeation separation behavior. It is expected to be greatly involved. Certainly, the separation membrane of the present invention has a hydrophilic group in its side chain, and therefore exhibits a water selective permeation type behavior. However, unexpectedly, it was found that the rigid main chain structure was destroyed by the aqueous alcohol solution and swelled greatly, and the fine structure of the film could not be maintained.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

EXAMPLE 1 A solution of L-leucine and Nε-carbobenzoxy-L-lysine amino acid anhydride in a molar ratio of 70:30 in a benzene-dioxane mixed solvent (molar ratio 1: 3) at a concentration of about 10 wt%. The resulting mixture was dissolved in the above solution, and triethylamine (1/200 mol of all monomers) was used as a polymerization initiator to carry out polymerization at room temperature for about 1 week. The film was formed by the solution casting method, but the L-leucine-Nε-carbobenzoxy-L-lysine copolymer solution obtained by polymerization will never dissolve in the solvent again if the solvent is dried. The polymerization solution was diluted with benzene as it was to a concentration of about 0.5 wt%, the casting solution was poured on a glass plate, and dried to form a film. Next, the copolymer film was immersed in a hydrobromic acid acetic acid solution for 2 days for decarbobenzyloxylation, and finally a poly (L-leucine-L-lysine) copolymer film (22.6 μm) was obtained.

The selection of the solvent for forming the polyamino acid copolymer by the solution casting method was carried out by examining the solubility of the polyamino acid copolymer in various solvents and determining the optimum solvent. When the charging ratio of the poly (L-leucine-L-lysine) copolymer is 90/10, 85/15 and 80/20, benzene can be used as a solvent during film formation. Further, since the charging ratio of poly (L-leucine-L-lysine) copolymer was 70/30, L-
When the lysine content is high, a benzene solution containing 20 wt% of dichloroacetic acid can be used. Regardless of which solvent was used, a benzene solution of the copolymer was cast on a glass plate, and then the solvent was gradually evaporated at room temperature to form a film. If necessary, a method of evaporating by heating and depressurizing can be adopted. The thin film obtained by peeling from the glass plate is usually 20 to 200 μm thick.

Next, in the examples, the permeation rate and the separation coefficient were measured by using an ordinary measuring device for pervaporation. FIG. 1 shows a schematic view of an apparatus for carrying out a pervaporation method using a separation membrane according to the present invention.

To conduct a membrane separation experiment using this apparatus,
The separation membrane 12 is attached to the liquid permeation cell 6, and the aqueous alcohol solution 13 is supplied onto the separation membrane. In this case, the pressure on the supply side is atmospheric pressure. On the other hand, the transmission side 14 is 13.3 by the vacuum pump 1.
Hold at a reduced pressure of ~ 66.5Pa. In the membrane separation experiment, the alcohol aqueous solution 13 to be concentrated was supplied and left overnight, after which the stirring motor 7 was measured while continuously stirring. The entire liquid permeation cell 6 was immersed in a constant temperature water bath 11 to keep the temperature constant. At this time, the effective area of the separation membrane is 15.9c〓
Met.

The vapor permeated through the separation membrane is collected in one of the branch pipes 5 cooled with liquid nitrogen, the branch pipe 5 is melted and cut after a predetermined time, and then the next branch pipe is cooled with liquid nitrogen. Then, the work of collecting the vapor and spray cutting after a predetermined time was continued. The weight of the content was obtained from the weight measurement of the branch pipe 5 in which the permeated liquid was sealed, and the permeation rate (Kg / 〓hr) was calculated.

Next, the alcohol-water mixed composition of the collected permeated liquid was determined using a gas chromatograph, and the separation coefficient was obtained. Indicated by. The separation factor (α) is defined as the concentration ratio of the two substances A and B in the feed liquid divided by the concentration ratio of the corresponding substances in the permeate. Here, CA and CB respectively indicate the concentration of the component that can selectively preferentially permeate and the concentration of the other component. In the case of the membrane separation experiment of the present invention, CA indicates the concentration of water and CB indicates the concentration of alcohol. Α (W / A) shown below is the separation coefficient (α) of water with respect to alcohol.

[0026]

[Table 1]

Example 2 A membrane preparation and concentration experiment were conducted in exactly the same manner as in Example 1 except that the aqueous alcohol solution to be dehydrated / concentrated was an aqueous ethanol solution. The results of dehydration / concentration by pervaporation are shown in Table 2.

[Table 2]

Example 3 A membrane preparation and concentration experiment were conducted in exactly the same manner as in Example 1 except that the aqueous alcohol solution to be dehydrated and concentrated was changed to an aqueous 2-propanol solution. The results of dehydration / concentration by pervaporation are shown in Table 3.

[Table 3]

Example 4 L-leucine and Nε-carbobenzoxy-L-lysine were copolymerized at a molar ratio of amino acid anhydride of 80:20, and the film was formed by solution casting in hydrobromic acetic acid. Decarbobenzoxylation is performed, and in order to further suppress the degree of swelling in water, it is immersed in a caustic soda aqueous solution of pH = 10 to 12 at room temperature for 48 hours,
A crosslinking treatment was performed. The membrane was thoroughly washed with deionized water and dried to obtain a separation membrane having a thickness of 21,82 μm. This separation membrane was attached to the liquid permeation cell 6 of the apparatus shown in FIG. 1 and a membrane separation experiment of an aqueous methanol solution was conducted. Table 4 shows the results of dehydration and concentration by pervaporation.

[0030]

[Table 4]

Example 5 A membrane preparation and concentration experiment were conducted in exactly the same manner as in Example 4 except that the aqueous alcohol solution to be dehydrated / concentrated was an aqueous ethanol solution. Table 5 shows the results of dehydration / concentration by pervaporation. The thickness of the separation membrane at this time is 21μ
It was m.

[Table 5]

Example 6 Membrane preparation and concentration experiments were conducted in exactly the same manner as in Example 4, except that the alcohol aqueous solution to be dehydrated and concentrated was changed to the 1-propanol aqueous solution. Table 6 shows the results of dehydration and concentration by pervaporation. The thickness of the separation membrane at this time is
It was 82 μm.

[Table 6]

Example 7 Copolymerization of L-leucine and Nε-carbobenzoxy-L-lysine with an amino acid anhydride molar ratio of 70:30 and film formation by a solution casting method in hydrobromic acetic acid Decarbobenzoxylation is performed and the lysine residue is quaternized by further immersing in hydrochloric acid (pH = 1.5), then thoroughly washed with deionized water, dried and separated to a thickness of 193 μm. A film was obtained.
This separation membrane was attached to the liquid permeation cell 6 of the apparatus shown in FIG. 1, and an ethanol aqueous solution membrane separation experiment was conducted. Table 7 shows the results of dehydration / concentration by pervaporation.

[0034]

[Table 7]

Example 8 A membrane preparation and concentration experiment were conducted in exactly the same manner as in Example 7, except that the aqueous alcohol solution to be dehydrated and concentrated was changed to the 2-propanol aqueous solution. Table 8 shows the results of dehydration and concentration by pervaporation.

[Table 8]

Example 9 L-leucine and Nε-carbobenzoxy-L-lysine amino acid anhydride were copolymerized at a molar ratio of 90:10, and film-formed by solution casting method in hydrobromic acetic acid. Decarbobenzoxylation is performed and the lysine residue is quaternized by further immersing in hydrochloric acid (pH = 1.5), then thoroughly washed with deionized water, dried, and separated with a thickness of 27 μm. Got Attach this separation membrane to the liquid permeation cell 6 of the device shown in FIG.
A membrane separation experiment of an aqueous propanol solution was conducted. Table 9 shows the results of dehydration and concentration by pervaporation.

[0037]

[Table 9]

Example 10 L-leucine and Nε-carbobenzoxy-L-lysine were copolymerized at a molar ratio of 80:20 amino acid anhydride, and the film was formed by a solution casting method in hydrobromic acetic acid. After decarbobenzoxylation, the product was immersed in diethyl ether in which adipic acid chloride was dissolved and the cross-linking reaction was performed for 72 hours.
A separation membrane with a thickness of m was obtained. This separation membrane was attached to the liquid permeation cell 6 of the apparatus shown in FIG. 1, and an ethanol aqueous solution membrane separation experiment was conducted. Table 10 shows the results of dehydration / concentration by pervaporation.

[0039]

[Table 10]

Example 11 A membrane preparation and concentration experiment were conducted in exactly the same manner as in Example 10 except that the alcohol aqueous solution to be dehydrated and concentrated was changed to the 1-propanol aqueous solution. Dehydration by pervaporation
Table 11 shows the concentration results.

[Table 11]

[0041]

According to the present invention, by using the above-mentioned separation membrane as a separation membrane for pervaporation,
From the aqueous solution of methanol, ethanol, 1-propanol, 2-propanol, etc., it is possible to selectively permeate only high-concentration water over the entire concentration range to efficiently dehydrate and concentrate the alcohol aqueous solution.

In concentrating a high water content region for an aqueous alcohol solution, a method of collecting alcohol having a small content is more efficient. Although there is a distillation method as a conventional separation / concentration method for this, a large amount of latent heat of vaporization is required because the liquid is once vaporized and separated, which is energetically inefficient. On the other hand, a highly efficient separation membrane that preferentially permeates alcohol rather than water and concentrates it has not yet been developed and cannot be adopted.

Even in the case of dehydration and concentration of the separation target in the high and medium water content region, the water is removed as well as the concentration adjustment, and the purity is as high as possible. From the viewpoint of purification, the purpose is to preferentially permeate water. It is correct. In this respect, the distillation method fractionates alcohol earlier than water because of the boiling point,
From the ethanol-water vapor-liquid equilibrium data, if the fractional distillation ratio is expressed as the same ratio as the separation coefficient, only a number of 10 or less can be obtained, but in reality, the number of distillation stages is large, so purification by distillation is not efficient. Good. With respect to the membrane concentration method of the present invention, it is considered that separation efficiency can be improved by performing a cascade method instead of performing a single-step membrane treatment.

[Brief description of drawings]

FIG. 1 is a schematic view showing an apparatus for carrying out the membrane separation and concentration method of the present invention.

[Explanation of Codes] 1 vacuum pump 2 cold trap 3 glass cock 4 rotating McLeod meter 5 cold trap for collecting permeated vapor 6 liquid permeation cell 7 stirring motor 8 stirrer 9 throw-in heater 10 electronic relay 11 constant temperature water tank 12 separation Membrane 13 Aqueous alcohol solution 14 Lower cell

Claims (4)

[Claims] 1. L-leucine and Nε-carbobenzoxy-
Using a poly (L-leucine-L-lysine) copolymer film obtained by copolymerizing an amino acid anhydride of L-lysine and performing decarbobenzoxylation in hydrobromic acetic acid in a film-formed state,
A method for concentrating an aqueous alcohol solution, which comprises dehydrating and concentrating an aqueous alcohol solution by a pervaporation membrane separation method. 2. The poly (L-leucine-L-
A method for concentrating an aqueous alcohol solution, which comprises dehydrating and concentrating an aqueous alcohol solution by a pervaporation membrane separation method using a membrane obtained by treating a lysine) copolymer membrane with an aqueous sodium hydroxide solution. 3. The poly (L-leucine-L-
A method for concentrating an aqueous alcohol solution, which comprises dehydrating and concentrating an aqueous alcohol solution by a pervaporation membrane separation method using a membrane obtained by treating a lysine) copolymer membrane with an aqueous hydrochloric acid solution. 4. The poly (L-leucine-L-
A method for concentrating an aqueous alcohol solution, which comprises dehydrating and concentrating an aqueous alcohol solution by a pervaporation membrane separation method using a membrane obtained by treating a lysine) copolymer membrane with an ether solution of adipic dichloride.