JP3238874B2 - Selective separation membrane for unsaturated hydrocarbon and method for selective separation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a membrane and a separation method for selectively separating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons. More particularly, the present invention relates to a method for selectively separating and concentrating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons generated in petroleum refining industry, petrochemical industry, and the like, and a separation membrane used for the method. .

[0002]

2. Description of the Related Art In the petroleum refining and petrochemical industries,
The method of separating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons using a membrane has been studied for many years from a scientific and economic point of view, and some studies have been reported to date. ing. For example, US Pat.
No. 8656 discloses supplying a hydrocarbon mixture, ie, naphtha, to a non-porous cellulose ether membrane, allowing a portion of the membrane to permeate, and removing the permeate from the permeate side of the membrane using a cleaning gas or cleaning liquid. Thus, a method for separating an unsaturated compound, a saturated compound, and an aromatic compound is disclosed. U.S. Pat. No. 2,930,754 discloses that a portion of the mixture that distills at a temperature in the range of the boiling point of gasoline is selectively permeated through a non-porous cellulose ether membrane and the permeate is purified using a cleaning gas or cleaning liquid. It discloses a method for separating hydrocarbons such as unsaturated hydrocarbons and aromatic compounds by removing them from the permeate side. In addition, many of the fluorine-containing polyimides have a high glass transition temperature and a rigid and bulky molecular chain structure, so they have heat resistance, chemical resistance,
It is known as a membrane separation material having excellent gas separation properties.
For example, Japanese Patent Application Laid-Open No. 5-7749, U.S. Pat.
No. 2202, U.S. Pat. No. 3,899,309, U.S. Pat. No. 4,532,041, U.S. Pat.
No. 645824, U.S. Pat. No. 4,705,540, U.S. Pat. No. 4,717,393, U.S. Pat. No. 4,717,394, U.S. Pat. No. 4,838,900, U.S. Pat. No. 4,897,092, U.S. Pat. Specification, US Pat. No. 4,929,405
No. 4,981,497, U.S. Pat. No. 5,429,992, and the like, disclose fluorinated aromatic polyimides.

[0003]

However, in the method of separating unsaturated hydrocarbons using a membrane proposed in the prior art, most of the separation membranes still have insufficient separation performance with respect to unsaturated hydrocarbons, and also have sufficient permeability. There was a problem that was not. Therefore, the membrane separation method of unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons is not widely used on an industrial scale because of performance and cost problems. .

The present invention has been made to solve these problems, and has a high separation property and a high permeability to unsaturated hydrocarbons, and is practically satisfactory in both performance and cost. It is an object of the present invention to provide a method for separating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons, and a separation membrane used for the method.

[0005]

In order to achieve the above object, a selective separation membrane for unsaturated hydrocarbons according to the present invention is provided for selectively separating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons. A separation membrane used for permeation and separation, wherein a rotation barrier of a main chain per unit van der Waals volume in a minimum repeating unit molecular structure obtained by a molecular mechanics method using DREIDING 2 as a molecular force field. Energy of 150 cal / cm ³ or more,
A fluorine-containing polyimide resin having a d-spacing value of 0.53 to 0.7 nm (5.3 to 7.0 angstroms) determined by a wide-angle X-ray diffraction method as a main component; Has a repeating unit represented by the above formula (Formula 1) as a main component.

In the separation membrane, it is preferable that the membrane containing fluorine-containing polyimide as a main component is at least one membrane selected from a dense membrane and an asymmetric membrane. Here, the dense film refers to a film in a region where there is no porous structure and hydrocarbon permeability is controlled by solubility in the film and diffusivity in the film. An asymmetric film is a film in which one surface of the film is a dense layer, and the internal structure and the back surface are porous. These concepts are generally well known in the art.

Next, in the method for selectively separating unsaturated hydrocarbons according to the present invention, a mixture containing unsaturated hydrocarbons and saturated hydrocarbons is brought into contact with one surface of the selective separation membrane according to the present invention,
It has a configuration in which unsaturated hydrocarbons are selectively permeated and separated through this membrane.

According to the structure of the present invention described above, a mixture containing an unsaturated hydrocarbon and a saturated hydrocarbon is converted into a minimum repeating unit molecular structure obtained by a molecular mechanics method using DREIDING 2 as a molecular force field. The rotational barrier energy of the main chain per unit van der Waals volume is 1
50 cal / cm ³ or more, and the value of d-spacing determined by the wide-angle X-ray diffraction method is 0.53 to 0.7.
nm (5.3 to 7.0 angstroms), and a fluorine-containing polyimide resin as a main component, wherein the fluorine-containing polyimide resin is one of films mainly containing a repeating unit represented by the above formula (Formula 1). Surface, and selectively permeate and separate unsaturated hydrocarbons through this membrane to provide high separation and permeability to unsaturated hydrocarbons. Thus, a method for selectively separating unsaturated hydrocarbons, which is satisfactory in terms of efficiency, can be realized.

The selective separation method can be realized by a pervaporation method depending on the physical properties of the hydrocarbon to be handled and the pressure / separation operation of the separation operation. Polymers used as separation membrane materials can be roughly classified into glassy polymers and rubbery polymers. Glassy polymer membranes often utilize the space between segments with poor thermal motion to selectively permeate and separate specific molecules due to differences in diffusivity due to the size and shape of the transmitted molecules. Used.
Therefore, in order to obtain a membrane with high separability using a glassy polymer, a material that can stably retain the space between segments that can selectively transmit a specific molecule in a polymer matrix is used. It is considered effective to use it as a material. The establishment of such a space between segments depends on the thermal kinetics and packing structure of the segments. The present inventor has focused on this point and as a result of intensive studies, as a result, the main chain of the main chain per unit van der Waals volume in the minimum repeating unit molecular structure obtained by the molecular mechanics method using DREIDING 2 as the molecular force field. A polymer having a rotation barrier energy of 150 cal / cm ³ or more and a d-spacing value of 0.53 to 0.7 nm (5.3 to 7.0 angstroms) determined by a wide-angle X-ray diffraction method. The main component of the membrane is that it easily retains a packing structure capable of more selectively diffusing unsaturated hydrocarbons, has high separation and high permeability to unsaturated hydrocarbons, and has one surface of this membrane. It has been found that by contacting a mixture containing an unsaturated hydrocarbon with a saturated hydrocarbon, the unsaturated hydrocarbon can be selectively permeated and highly separated.

In the above, the rotational barrier energy per unit van der Waals volume is 150 cal / cm ^3.
If it is less than 1, the thermal mobility in the twisting direction of the segments increases, the space between the segments that can contribute to separation disappears, and there is a possibility that the separating property may decrease, which is not preferable.

In the above, if the value of d-spacing is less than 0.53 nm (5.3 angstroms), the transmittance tends to be too low and the practicality tends to be reduced, and 7.0 nm (7.0 angstroms) tends to decrease. If it exceeds, the separability may be too small, which is not preferable.

In the above, the rotation barrier energy refers to the maximum value of a potential energy barrier that must be exceeded when rotating a dihedral angle formed by four atoms of a polymer chain constituting a film by 360 °. More specifically, structural optimization calculations are performed for various structures in which the dihedral angle is changed at predetermined angle intervals in the range of 0 to 360 ° by a molecular mechanics method using driving (DREIDING) 2 as a molecular force field. It can be obtained as the difference between the maximum value and the minimum value of the potential energy of the various optimized structures obtained.

In the above, the driving (DREI)
DING) The rotation barrier energy of the main chain per unit van der Waals volume in the minimum repeating unit molecular structure obtained by the molecular mechanics method using the molecular force field as 2 is the molecular weight of the main chain in the minimum repeating molecular structure of the polymer. This is a value obtained by dividing the sum of the rotational barrier energies of all the constituent dihedral corners by the van der Waals volume.

In the above description, the driving (DREID)
ING) 2 is a molecular field for simulation for obtaining a sterically stable structure of a wide range of compounds using a parameter depending on an orbital hybridization mode in principle (Reference: The Journal of Physical Chemistry,
Vol. 94, No. 26, 1990, pp. 8897-8909 (The Journal
of Physical Chemistry, Vol.94, No.26, 1990.8897-8
909).

In the above description, the structure optimization calculation by the molecular mechanics method is not particularly limited as long as it is a method capable of obtaining a structure in which the potential energy of the molecular model has a minimum value. For example, the target molecular model is divided into a plurality of unit models, and after finding a structure in which the potential energy becomes the minimum value, the structures are connected, and the potential energy again takes the minimum value. The stable structure may be calculated.

In the above description, d-spacing refers to a plane spacing obtained from the well-known Bragg equation according to a wide-angle X-ray diffraction method. In the above, it is preferable to use a fluorine-containing polyimide resin as a main polymer constituting the membrane in order to obtain a separation membrane having both high permeability and high selectivity to unsaturated hydrocarbons.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The fluorine-containing polyimide resin used in the present invention may be used alone or as a mixture of two or more kinds. Further, if it is 50 mol% or less, it may be a copolymer or a mixture with a polymer such as polysulfone or polyethersulfone other than the fluorine-containing polyimide resin.

The fluorine-containing polyimide resin used in the present invention can be prepared, for example, by using tetracarboxylic dianhydride and a diamine compound (provided that at least one of the acid component or the amine component contains a fluorine-containing group). ,
It can be obtained by a known polymerization method as described in U.S. Pat. No. 3,959,350. For example, approximately equimolar amounts of tetracarboxylic dianhydride and a diamine compound (provided that at least one of the acid component or the amine component contains a fluorine-containing group) are used in a polar solvent in an amount of about 80%.
The mixture is stirred at a temperature of not higher than 0 ° C, preferably at 0 to 60 ° C to polymerize the polyamic acid. The polar solvent used here is not particularly limited, but N-methylpyrrolidone, pyridine,
Dimethylacetamide, dimethylformamide, dimethylsulfoxide, tetramethylurea, phenol, cresol, tetrahydrofuran and the like are preferably used.

A tertiary amine compound such as trimethylamine, triethylamine and pyridine, and an imidization accelerator such as acetic anhydride, thionyl chloride and carbodiimide are added to the obtained polar solvent solution of polyamic acid. Stir and imidize. When performing an imidation reaction,
Without adding an imidization accelerator, the polyamic acid solution is heated at 100 to 400 ° C, preferably at 120 to 30 ° C.
It may be imidized by heating at 0 ° C.

After the imidization reaction, in order to remove the polar solvent and the imidization accelerator during the polymerization, a large amount of a solution such as acetone, alcohol or water is dropped and purified to obtain a polyimide resin suitable as a film material. can get.

When the imidization reaction is carried out without adding an imidization accelerator, a polyamic acid powder or polyamic acid solution obtained by dropping a polyamic acid solution into a large amount of a solution of acetone or alcohol is used. By heating the solvent to 100-400 ° C. to imidize the solid of polyamic acid obtained by evaporating the solvent from the mixture (in the case of evaporation, a polyamic acid powder may be formed by adding a precipitant or the like and filtered). Thus, a polyimide resin suitable as a film material is obtained.

The method for forming a dense film used in the present invention is not particularly limited. For example, a film-forming solution is prepared by dissolving the above-mentioned fluorine-containing polyimide resin in an appropriate solvent, and the film-forming solution is made of glass, A method of casting a fixed thickness on a flat plate or a tube having a smooth surface such as a metal or a plastic, and then removing the solvent by heat treatment is preferably used.

The method for producing the asymmetric membrane used in the present invention is as follows.
Although not particularly limited, a wet phase inversion film forming method is preferably used in terms of productivity and cost. For example, the above-mentioned fluorine-containing polyimide resin is dissolved in a predetermined organic solvent to prepare a film-forming solution, and the film-forming solution is made of glass, metal, a flat plate or a tube of plastic, or a porous support such as a woven or nonwoven fabric. It is cast on the body at a certain thickness and immersed in a coagulation liquid (a solvent that does not dissolve the fluorine-containing polyimide resin in the film-forming solution but is compatible with the organic solvent in the film-forming solution), or A film forming solution can be extruded from a concentric double-structured nozzle, immersed in the coagulation solution to prepare an asymmetric film, and then the film can be dried.

The solvent for the fluorine-containing polyimide resin is not particularly restricted but includes N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide, diethylene glycol dimethyl ether, 1,2-dimethoxymethane and the like.

These organic solvents can be used alone,
It is also used as a mixed solvent of two or more. The organic solvent is preferably a solvent having a small polarity and a low affinity for a solvent used as a coagulating liquid, and examples thereof include diethylene glycol dimethyl ether and 1,2-dimethoxyethane. When a solvent with low affinity for the solvent used as the coagulating liquid is used for the film forming liquid, the solvent in the film forming liquid advances into the solvent used as the coagulating liquid rather than forming a skin-like thin layer during wet phase inversion film forming. Speed becomes sufficiently small. As a result, it is possible to obtain, over a wide range, an asymmetric membrane having a skin-like thin layer and a porous structure layer that do not have pinholes that greatly degrade the separation performance.

The coagulating solution used for immersing and removing the organic solvent does not dissolve the fluorine-containing polyimide resin used, but is not particularly limited as long as it is a solvent compatible with the solvent in the film forming solution. And alcohols such as ethanol, methanol, and isopropyl alcohol, and a mixture thereof, and water is particularly preferably used.
The temperature of the coagulation liquid at the time of immersing and removing the organic solvent in the film forming liquid is not particularly limited, but is preferably at a temperature of 0 to 50 ° C.

The polyimide solution concentration of the film forming solution is 3 to 40% by weight, preferably 10 to 30% by weight. When adjusting the film forming solution, a swelling agent, a dispersant, a thickener, and the like may be added as necessary. As a means for casting the film-forming solution, for example, a doctor knife, a doctor plate, an applicator or the like can be used. Further, the shape of the membrane in the present invention is not particularly limited, but a tubular (including a hollow fiber) or a flat membrane is preferably used.

[0028]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to this embodiment.

Example A fluorine-containing polyimide as a repeating unit represented by the above formula (Chemical Formula 1) was synthesized by the following method. 5,5'-2,
2'-trifluoro-1- (trifluoromethyl) ethylidene-bis-1,3-isobenzofurandione (6F
DA) 0.0761 mol and 3,3′-dimethoxy-
0.0761 mol of 4,4'-diaminobiphenyl dihydrochloride (DSH) and N-methyl-2-pyrrolidone (NMP) (200 ml) as a solvent and o-
Dichlorobenzene (50 ml) was added, and the flask was heated from room temperature to 170 ° C. while stirring under an argon atmosphere, and an imidization reaction was performed while azeotropically dehydrating water generated at 170 ° C.

After completion of the reaction, the reaction mixture was cooled to room temperature, and the polymerization solution was dropped into an excessive amount of water under high-speed stirring to precipitate and purify. Further purification with methanol yielded a fluorine-containing polyimide resin having the minimum repeating unit represented by the above formula (Formula 1) as a structural unit. Next, 9 parts by weight of a fluorine-containing polyimide having the minimum repeating unit represented by the formula (Formula 1) as a structural unit was diluted, and 91 parts by weight of NMP was added as an organic solvent,
The mixture was stirred and dissolved at 100 ° C. for 6 hours. Thereafter, the mixture was filtered, allowed to stand, and sufficiently defoamed to prepare a film-forming solution. The film forming solution was applied on a glass plate using an applicator, and the width was 20 cm and the thickness was 30.
Cast at 0 μm, 110 ° C. for 1 hour, 150 ° C. for 1 hour, 200 ° C. for 3 hours, and vacuum at 200 ° C. for 7 hours.
Heat treatment was performed for 2 hours to obtain a dense film made of a fluorine-containing polyimide having a thickness of 20 to 30 μm. Regarding the fluorine-containing polyimide resin constituting this film, Biosym / M
When the rotational barrier energy of the main chain per unit van der Waals volume in the minimum repeating unit molecular structure was calculated by a molecular mechanics method employing DREIDING2 as a molecular force field using software Cerius2 of molecular simulations, 218 cal /
cm ³ . Where the van der Waals volume is B
It was determined according to the atomic group contribution method using the value of ondi. The d-spacing of the fluorine-containing polyimide resin constituting the film was measured by a wide-angle X-ray diffraction method.
It was at 649 nm (6.49 Å). Therefore, this film satisfied the conditions of the polymer film in the present invention. Next, this film was treated at a temperature of 25 ° C. and a supply pressure of 2 atm with 50 vol of propylene.
Table 1 summarizes the results of evaluating the separation performance of a mixed gas of 1% and 50 vol% of propane.

Comparative Example A polysulfone resin was used in place of the fluorine-containing polyimide resin, and 82 parts by weight of NMP as an organic solvent was added to 18 parts by weight of the polysulfone resin, followed by stirring at 100 ° C. for 12 hours to dissolve. Thereafter, the mixture was filtered, allowed to stand, and sufficiently defoamed to prepare a film-forming solution. The obtained film-forming solution was cast on a glass plate using an applicator at a width of 20 cm and a thickness of 300 μm, and was subjected to a heat treatment at 110 ° C. for 1 hour, 150 ° C. for 3 hours, and further under vacuum at 150 ° C. for 72 hours. Alms, thickness 20-3
A dense membrane of 0 μm polysulfone was obtained. For the polysulfone resin constituting this membrane, the rotation barrier energy of the main chain per unit van der Waals volume in the minimum repeating unit molecular structure was calculated in the same manner as in the example, and it was 132 cal / cm ³ . The d-spacing of the polysulfone resin constituting this film was measured by a wide-angle X-ray diffraction method.
(5.10 angstroms). Therefore, this film did not satisfy the conditions of the polymer film in the present invention. Next, the results of evaluating the mixed gas separation performance of this membrane in the same manner as in the examples are summarized in Table 1 below.

(Table 1) Abbreviation of film material ΔEt d PC ₃ H ₆ PC ₃ H ₆ / PC ₃ H ₈ Example 6 FDA-DSH 218 6.49 9.0 × 10 ^-12 45 Comparative Example PSF 132 5.10 4.5 × 10 ^-12 3.5 (Remarks) ΔEt: High molecular weight obtained by molecular mechanics method using driving (DREIDING) 2 as a molecular force field. Rotation barrier energy of the main chain per unit van der Waals volume in the minimum repeating unit molecular structure [cal / cm ³ ] d: d-spacing [angstrom] obtained by wide-angle X-ray analysis PC ₃ H ₆ : propylene 50 vol%, Propane 50vo
Permeability coefficient of propylene [cm ³ (STP) cm / cm ² sc when 1% mixed gas is supplied at 2 atm and 25 ° C.
mHg] PC ₃ H ₆ / PC ₃ H ₈ : Separation coefficient (permeation coefficient ratio) of propylene and propane when a mixed gas of 50 vol% of propylene and 50 vol% of propane is supplied at 2 atm and 25 ° C. [−]

As is evident from Table 1, it was confirmed that the products of Examples of the present invention have high separation and high permeability to unsaturated hydrocarbons.

[0034]

As described above, according to the present invention, the main chain per unit van der Waals volume in the minimum repeating unit molecular structure determined by the molecular mechanics method using DREIDING 2 as a molecular force field. The rotation barrier energy of the fluorine-containing polyimide resin is a predetermined value or more, and the value of d-spacing determined by wide-angle X-ray diffraction method is a fluorine-containing polyimide resin present in a predetermined range as a main component, the fluorine-containing polyimide resin, the following By using a membrane containing a repeating unit represented by the formula (Formula 1) as a main component, a membrane having both high separation and high permeability to unsaturated hydrocarbons can be obtained. It is possible to provide a method for separating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons, which is practically satisfactory in performance and cost.

Continuing from the front page (72) Inventor Kenichi Ikeda 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Masatoshi Maeda 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto (56) References JP-A 8-173778 (JP, A) JP-A 8-173779 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53 / 22 B01D 61/00-71/82 510

Claims (3)

(57) [Claims] 1. A separation membrane used for selectively permeating and separating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons, comprising a drying (DREI)
DING) 2, the rotational barrier energy of the main chain per unit van der Waals volume in the molecular structure of the minimum repeating unit determined by a molecular mechanics method using 2 as a molecular force field is 150 cal.
/ Cm ³ or more, and the value of d-spacing determined by the wide-angle X-ray diffraction method is 0.53 to 0.7 nm (5.
Fluorine-containing port present in 3 to 7.0 Å)
This polyimide containing fluorine as the main component
The resin mainly comprises a repeating unit represented by the following formula (Formula 1).
Min and unsaturated hydrocarbons selective separation membrane. Embedded image 2. A composition containing a fluorine-containing polyimide resin as a main component.
At least one film selected from a dense film and an asymmetric film.
2. The method of claim 1 wherein the unsaturated hydrocarbon is a single membrane.
Separation membrane. 3. A mixture containing an unsaturated hydrocarbon and a saturated hydrocarbon.
The compound is used as one of the selective separation membranes according to claim 1 or 2.
Surface, and select unsaturated hydrocarbons through this membrane.
Selective separation of unsaturated hydrocarbons for selective permeation and separation.
Law.