JP4911417B2 - Hollow fiber carbon membrane introduced with metal ions and dehydration method of aqueous alcohol solution using the same - Google Patents

Description

The present invention relates to a method for dehydrating an aqueous alcohol solution, characterized in that water is separated from the aqueous alcohol solution using a hollow fiber carbon membrane introduced with metal ions.
The present invention can perform water separation from an aqueous alcohol solution with high efficiency and high selectivity in an arbitrary concentration range by using a carbon membrane having excellent separation performance and acid resistance in the dehydration of the aqueous alcohol solution. A separation method is provided.

  In recent years, in the ethanol purification process produced from biomass ethanol and the like that have attracted attention, it is necessary to dehydrate to a concentration of about 99.5 wt%. Conventionally, an azeotropic distillation method and an adsorption method using an adsorbent such as zeolite (PSA method) are used in the dehydration process, but these methods require large-scale equipment and a large amount of energy. It was a problem in terms of manufacturing costs. On the other hand, since the membrane separation method can save 10 to 30% of energy compared to these methods, an organic membrane (Patent Literatures 1 to 3) and a zeolite membrane (Patent Literature 4) are used in this ethanol dehydration step. Proposed. However, organic membranes generally have poor heat resistance, and zeolite membranes have poor acid resistance. The hollow fiber carbon membrane has an advantage that it can be applied to a dehydration of an alcohol aqueous solution even in a separation system that requires acid resistance and under excessive water conditions, but has a problem that the separation performance is not so high.

Japanese Patent Laid-Open No. 5-168865 "Method for Dehydrating Organic Aqueous Solution" JP-A-11-76774 “Separation membrane for dehydration and production method thereof” JP-A-5-226 “Method for Dehydrating and Concentrating Organic Aqueous Solution” Special table 2008-521738 “Zeolite membrane and production method thereof” JP2009-34614 "Hollow fiber carbon membrane and method for producing the same"

  The present invention provides a technique for highly dehydrating and dehydrating alcohol, particularly ethanol, in any concentration range by using a carbon membrane that is excellent in both heat resistance and acid resistance and has excellent separation performance. To do.

In order to solve the above problems, the present inventors calcined a derivative polymer of poly (2,6-dimethyl-1,4-phenylene oxide) (hereinafter sometimes referred to as “PPO derivative”). As a result of further earnest research on the obtained carbon membrane, it was possible to introduce hydrophilic metal ions into the carbon membrane by utilizing the ion exchange ability of the sulfone group present in the PPO derivative. The knowledge that it has a big influence on
The present invention has been studied based on this finding, and as a result, by highly dispersing metal ions in the film, the surface of the carbon film is made hydrophilic and the adsorption of alcohol is suppressed, so that the excellent dehydrating performance of the alcohol aqueous solution can be achieved. It has been found that it can be obtained.

The carbon film of the present invention has substantially the following:
as well as
(Wherein R ^{11 to} R ¹² each independently represent a hydrogen atom or —SO ₃ H. However, R ^{11 to} R ¹² are not both hydrogen atoms). A part or all of the protons (hydrogen ions) of the sulfo group of the polyphenylene oxide derivative in which the ratio A (%) of the repeating unit (b) to (a) + (b) is 15% <A <60% Can be obtained by firing a hollow fiber membrane in which is exchanged for metal ions. The amount of metal ions introduced is preferably 3 to 20% with respect to the weight of the carbon film after firing.
Furthermore, in order to obtain the carbon film of the present invention, the firing is preferably performed at 450 to 850 ° C. under a reduced pressure of 10 ⁻⁴ atm or less or in an inert gas atmosphere, and the inert gas is argon gas. , One selected from helium gas and nitrogen gas.
Furthermore, when obtaining the carbon film of the present invention, it is preferable to perform preheating at about 150 to 300 ° C. for 30 minutes to 4 hours prior to firing.

The hollow fiber carbon membrane of the present invention is excellent in acid resistance and heat resistance, and has better separation performance in dehydration of an alcohol aqueous solution by introducing metal ions. Separation of water can be performed with high efficiency and high selectivity over an arbitrary concentration range.
Further, since the hollow fiber carbon membrane of the present invention is excellent in module processability, it is possible to produce a membrane module in which a hollow fiber carbon membrane is compactly filled in a container, and a small and efficient alcohol dehydration apparatus is manufactured. It becomes possible to do.

In an Example, it is the schematic of the pervaporation separation apparatus used for evaluation of water / ethanol separation performance. It is an adsorption isotherm of water at 25 ° C. for the sample of Example 5 and the sample of Comparative Example 1. 2 is an adsorption isotherm of ethanol at 25 ° C. for the sample of Example 5 and the sample of Comparative Example 1;

  The hollow fiber carbon membrane used in the present invention consists of the repeating units represented by the above (a) and (b), and the ratio A (%) of the repeating unit (b) to (a) + (b) is A polyphenylene oxide derivative in which 15% <A <60% is dissolved in an organic solvent, the solution is extruded simultaneously with the coagulation liquid, a hollow fiber membrane is spun, dried and fired for production. Metal ions may be mixed in the organic solvent, or the hollow fiber membrane after spinning may be impregnated with an aqueous solution containing metal ions. The metal ions used here are sodium, potassium, magnesium, aluminum and the like, and are mixed in the form of nitrate or acetate.

That is, first, the polyphenylene oxide derivative polymer is dissolved in an arbitrary solvent to prepare a film forming stock solution. At this time, the metal ion salt may be added to the solvent in an amount within the intended range. Examples of the solvent used here include methanol, ethanol, tetrahydrofuran, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, and the like, and these can be used as a mixture.
Next, the film-forming stock solution is extruded into the coagulation bath from the outer tube of the hollow tube spinning nozzle having a double-pipe annular structure, and is mixed with the solvent of the film-forming stock solution from the inner tube of the spinning nozzle. On the other hand, a hollow fiber membrane is spun by simultaneously extruding an insoluble core liquid. The metal ion salt may not be added to the solvent of the membrane forming stock solution, and the spun hollow fiber membrane may be impregnated with an aqueous solution containing metal ions for a certain period of time.

  The obtained hollow fiber membrane can be dried to obtain a precursor polymer membrane into which metal ions have been introduced. The precursor polymer film may be carbonized as it is. For example, the precursor polymer film is infusible by performing heat treatment at a temperature lower than the carbonization temperature at about 150 to 300 ° C. for 30 minutes to 4 hours. It is advantageous to do so. By applying this infusibilization treatment, the heat resistance of the hollow fiber carbon membrane is particularly improved.

The precursor polymer membrane or precursor infusibilized membrane thus obtained can be carbonized by a known method to produce a hollow fiber carbon membrane. For example, the precursor is housed in a container, and heated under a reduced pressure of 10 ⁻⁴ atm or less or under an inert gas atmosphere substituted with helium, argon gas, nitrogen gas, etc. A carbon film is manufactured. The heating conditions vary depending on the type and amount of the material constituting the precursor, but are from 450 to 850 ° C. for 30 minutes to 4 hours in a reduced pressure of 10 ⁻⁴ atm or less or in an inert gas atmosphere.

  Hereinafter, the present invention will be described in detail based on examples. However, the present invention is not limited to the following examples.

The evaluation methods of the hollow fiber carbon membranes obtained in the examples and comparative examples are as follows.
(Evaluation method of water / alcohol separation performance)
The water / alcohol separation performance of the carbon membrane in this example was evaluated by the pervaporation apparatus shown in FIG. One end of the hollow fiber carbon membrane 1 was sealed with an adhesive, and the opposite end was bonded to the stainless steel tube so as to maintain an airtight state. The hollow fiber carbon membrane 1 was immersed in a container 3 containing a supply liquid 2 made of a water / alcohol mixed liquid maintained at a constant temperature by a constant temperature bath 4. The cooling trap 6 was immersed in liquid nitrogen 7 (−196 ° C.), the supply pressure of the separation liquid was set to atmospheric pressure, and the permeation pressure was set to 1 Pa by the vacuum pump 13. After a predetermined time from the start of evaluation, the permeation flux (g · m ⁻² · h ⁻¹ ) was determined from the weight of the permeate deposited on the cooling trap 6. Further, the permeate was analyzed by TCD gas chromatograph, the concentration of the permeate was determined, and the separation factor α was calculated.
(Calculation of separation performance)
As an index of the separation performance of the carbon membrane, a permeation flux (g · m ⁻² · h ⁻¹ ) obtained by the following formula (I) and a separation coefficient α represented by the following formula (II) were used.
Permeation flux = (permeate weight [g]) ÷ {membrane area (m ² ) × time (h)} − (I)
Separation factor α (water / alcohol) = {water concentration in permeate [wt%] / alcohol concentration in permeate [wt%]} ÷ {water concentration in feed liquid [wt%] / alcohol concentration in feed liquid [wt%] ]}-(II)
The results are shown in Table 1.

<Example 1>
(Manufacture of hollow fiber carbon membrane)
A membrane-forming stock solution was prepared by dissolving 5.0 g of sulfonated PPO of A = 45% and 0.9 g of sodium acetate in 7.1 g of DMAc and 7.1 g of methanol. This was extruded into the coagulation bath from the outer tube of a hollow tube spinning nozzle having a double-pipe annular structure, and from the inner tube of the spinning nozzle, a 15% by weight aqueous ammonium nitrate solution was simultaneously extruded and spun. A molecular film was obtained. Next, the obtained precursor polymer film is heated to 270 ° C. at a rate of 8 ° C./min in an air atmosphere, heated at this temperature for 1 hour, and then allowed to cool, so that the precursor polymer film is infusible. went. Subsequently, the hollow fiber carbon membrane intermediate obtained above was carbonized using a vacuum electric furnace. In this operation, first, the inside of the vacuum electric furnace was depressurized to 10 ⁻⁵ torr or less, the temperature was raised to 600 ° C. at a rate of 10 ° C./min, heated at this temperature for 2 hours, allowed to cool, and hollow fiber carbon A membrane was obtained.
(Evaluation of the obtained hollow fiber carbon membrane)
The amount of sodium introduced into the hollow fiber carbon membrane obtained in Example 1 was measured by thermal analysis (TG), and the dehydration performance of a 90 wt% ethanol aqueous solution by pervaporation separation at 75 ° C. was evaluated. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 2>
The hollow fiber carbon membrane obtained in Example 1 was used to evaluate the dehydration performance of a 90 wt% ethanol aqueous solution by a vapor permeation method at 130 ° C. The results are shown in Table 1.
As is apparent from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity and exhibited excellent heat resistance and dewatering performance.

<Example 3>
A hollow fiber carbon membrane was obtained in the same manner as in Example 1 except that the amount of sodium acetate added was changed to 1.8 g. The dehydration performance of a 90 wt% ethanol aqueous solution was evaluated by the pervaporation separation method at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 4>
The hollow fiber carbon membrane obtained in Example 3 was used to evaluate the dehydration performance of a 90 wt% aqueous ethanol solution by a vapor permeation method at 130 ° C. The results are shown in Table 1.
As is apparent from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity and exhibited excellent heat resistance and dewatering performance.

<Example 5>
A film-forming stock solution was prepared by dissolving 5.0 g of sulfonated PPO with A = 45% in 7.1 g of DMAc and 7.1 g of methanol. This was extruded into the coagulation bath from the outer tube of a hollow tube spinning nozzle having a double tube annular structure, and 15 wt% ammonium nitrate aqueous solution was simultaneously extruded from the inner tube of the spinning nozzle and spun into a 20 wt% sodium chloride aqueous solution. After being immersed for 2 hours and washed with ion exchange water, it was air dried at room temperature to obtain a precursor polymer membrane. Next, the obtained precursor polymer film is heated to 270 ° C. at a rate of 8 ° C./min in an air atmosphere, heated at this temperature for 1 hour, and then allowed to cool, so that the precursor polymer film is infusible. went. Subsequently, the hollow fiber carbon membrane intermediate obtained above was carbonized using a vacuum electric furnace. In this operation, first, the inside of the vacuum electric furnace was depressurized to 10 ⁻⁵ torr or less, the temperature was raised to 600 ° C. at a rate of 10 ° C./min, heated at this temperature for 2 hours, allowed to cool, and hollow fiber carbon A membrane was obtained.
(Evaluation of the obtained hollow fiber carbon membrane)
The amount of sodium introduced into the hollow fiber carbon membrane obtained in Example 5 was measured by thermal analysis (TG), and the dehydration performance of a 90 wt% ethanol aqueous solution by pervaporation separation at 75 ° C. was evaluated. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 6>
The hollow fiber carbon membrane obtained in Example 5 was used to evaluate the dehydration performance of a 50 wt% ethanol aqueous solution by pervaporation separation at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 7>
The hollow fiber carbon membrane obtained in Example 5 was used to evaluate the dehydration performance of a 10 wt% ethanol aqueous solution by pervaporation separation at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 8>
The hollow fiber carbon membrane obtained in Example 5 was used to evaluate the dehydration performance of a 90 wt% ethanol aqueous solution by a vapor permeation method at 130 ° C. The results are shown in Table 1.
As is apparent from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity and exhibited excellent heat resistance and dewatering performance.

<Example 9>
The hollow fiber carbon membrane obtained in Example 5 was used to evaluate the dehydration performance of a 90 wt% 2-propanol aqueous solution by pervaporation separation at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 10>
The hollow fiber carbon membrane obtained in Example 5 was used to evaluate the dehydration performance of a 90 wt% 1-butanol aqueous solution by pervaporation separation at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 11>
A hollow fiber carbon membrane was obtained in the same manner as in Example 5 except that the immersion liquid after spinning was changed to a 20 wt% aqueous potassium chloride solution. The dehydration performance of a 90 wt% ethanol aqueous solution was evaluated by the pervaporation separation method at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 12>
The hollow fiber carbon membrane obtained in Example 11 was used to evaluate the dehydration performance of a 90 wt% aqueous ethanol solution by a vapor permeation method at 130 ° C. The results are shown in Table 1.
As is apparent from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity and exhibited excellent heat resistance and dewatering performance.

<Example 13>
A hollow fiber carbon membrane was obtained in the same manner as in Example 5 except that the immersion liquid after spinning was changed to a 20 wt% magnesium nitrate aqueous solution. The dehydration performance of a 90 wt% ethanol aqueous solution was evaluated by the pervaporation separation method at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Example 14>
A hollow fiber carbon membrane was obtained in the same manner as in Example 5 except that the immersion liquid after spinning was changed to a 20 wt% aluminum nitrate aqueous solution. The dehydration performance of a 90 wt% ethanol aqueous solution was evaluated by the pervaporation separation method at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the obtained hollow fiber carbon membrane separated only water with high selectivity, and showed excellent dewatering performance.

<Comparative example 1>
A film-forming stock solution was prepared by dissolving 5.0 g of sulfonated PPO with A = 45% in 7.1 g of DMAc and 7.1 g of methanol. This was extruded into the coagulation bath from the outer tube of a hollow tube spinning nozzle having a double-pipe annular structure, and from the inner tube of the spinning nozzle, a 15% by weight aqueous ammonium nitrate solution was simultaneously extruded and spun. A molecular film was obtained. Next, the obtained precursor polymer film is heated to 270 ° C. at a rate of 8 ° C./min in an air atmosphere, heated at this temperature for 1 hour, and then allowed to cool, so that the precursor polymer film is infusible. went. Subsequently, the hollow fiber carbon membrane intermediate obtained above was carbonized using a vacuum electric furnace. In this operation, first, the inside of the vacuum electric furnace was depressurized to 10 ⁻⁵ torr or less, the temperature was raised to 600 ° C. at a rate of 10 ° C./min, heated at this temperature for 2 hours, allowed to cool, and hollow fiber carbon A membrane was obtained.
(Evaluation of the obtained hollow fiber carbon membrane)
The hollow fiber carbon membrane obtained in Comparative Example 1 was evaluated for the dehydration performance of a 90 wt% ethanol aqueous solution by pervaporation separation at 75 ° C. The results are shown in Table 1.
As is clear from Table 1, the hollow fiber carbon membrane into which metal ions were not introduced had a small separation factor and insufficient dehydration performance.

<Comparative example 2>
The hollow fiber carbon membrane obtained in Comparative Example 1 was used to evaluate the dehydration performance of a 90 wt% ethanol aqueous solution by a vapor permeation method at 130 ° C. The results are shown in Table 1.
As is clear from Table 1, the hollow fiber carbon membrane into which metal ions were not introduced had a small separation factor and insufficient dehydration performance.

(Consideration of excellent effect of hollow fiber carbon membrane of the present invention)
Water and ethanol adsorption isotherms (FIGS. 2 and 3) at 25 ° C. were prepared for the sample of Example 5 and the sample of Comparative Example 1, respectively, and the excellent dehydration performance of the aqueous alcohol solution of the hollow fiber carbon membrane of the present invention Was considered.
As apparent from FIG. 2, the sample of Example 5 into which sodium ions were introduced had a larger amount of water adsorption because the hydrophilicity of the carbon membrane was increased compared to the sample of Comparative Example 1 into which sodium ions were not introduced. It can be seen that it has increased. On the other hand, as shown in FIG. 3, the ethanol adsorption amount of the sample of Example 5 was smaller than that of the sample of Comparative Example 1. That is, by introducing sodium ions, the difference in the amount of adsorption between water and ethanol is increased, so that an excellent permeation flux and separation factor are exhibited.

  The dehydration method of the present invention makes it possible to separate water from an aqueous alcohol solution in an arbitrary concentration range, but is particularly effective for dehydration of bioethanol containing acid, dehydration of 2-propanol, etc., and has industrial utility value. It is expensive.

DESCRIPTION OF SYMBOLS 1 ... Hollow fiber carbon membrane 2 ... Supply liquid 3 ... Container 4 ... Constant temperature tank 5 ... Stirrer 6 ... Cooling trap 7 ... Liquid nitrogen 8 ... Thermometer 9 ... Insulation tape 10 ... Stop valve 11 ... Pressure gauge 12 ... Stop valve 13 ... Vacuum pump 14 ... Stirrer

Claims (3)

A method for dehydrating an aqueous alcohol solution, characterized in that water is separated from the aqueous alcohol solution using a hollow fiber carbon membrane introduced with metal ions as a highly selective and hydrophilic membrane ,
As a hollow fiber carbon membrane introduced with metal ions,
below

as well as

(Wherein R ^{11 to} R ¹² each independently represent a hydrogen atom or a sulfone group, provided that R ^{11 to} R ¹² are not both hydrogen atoms). The ratio A (%) of the repeating unit (b) to (a + b) was 15% <A <60%. A polyphenylene oxide derivative was dissolved in an organic solvent and extruded into a coagulating liquid using a nozzle to form a hollow fiber. When a hollow fiber carbon membrane is produced by firing later, a metal ion is added to the organic solvent, or after forming the hollow fiber, the hollow fiber is impregnated with a solution containing the metal ion, so that the hollow fiber is obtained before the firing. Characterized by using a hollow fiber carbon membrane into which metal ions are introduced, and
A method wherein the metal ion is sodium ion or potassium ion . The method according to claim 1, wherein the alcohol in the aqueous alcohol solution is ethanol, 2-propanol, or 1-butanol. The method according to claim 1 or 2, wherein an alcohol aqueous solution in the entire concentration range is a dehydration target.