JP2838062B2 - Method for selective separation of unsaturated hydrocarbon gas by asymmetric membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an unsaturated hydrocarbon gas.
(Hereinafter simply referred to as "unsaturated hydrocarbons") and a method for separating unsaturated hydrocarbons from a mixture gas (hereinafter simply referred to as "mixture") containing a saturated hydrocarbon gas (hereinafter simply referred to as "saturated hydrocarbons") It is. More specifically, the present invention relates to a method for separating and concentrating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons generated in a petroleum refining industry, a petrochemical industry, or the like.

[0002]

2. Description of the Related Art In a petroleum refining industry or a petrochemical industry, a method of separating unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons by using a membrane has been used for many years from a scientific and economic viewpoint. It has been studied and some studies have been reported to date. For example, U.S. Pat.
No. 56 discloses supplying a hydrocarbon mixture, i.e., 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 solution. This discloses a method for separating unsaturated hydrocarbons, saturated compounds, and aromatic compounds.
U.S. Pat. No. 2,930,754 discloses that a portion of a mixture distilled at a temperature in the boiling range of gasoline is selectively permeated through a non-porous cellulose ether membrane, and the permeate is removed using a cleaning gas or a cleaning liquid. It discloses a method for separating unsaturated hydrocarbons and aromatic hydrocarbons by removing them from the permeate side of the asymmetric membrane.

[0003]

However, in the conventional method for separating unsaturated hydrocarbons using a membrane, most of the separation membranes still have insufficient separating ability for unsaturated hydrocarbons, and furthermore, insufficient permeability. There's a problem. for that reason,
At present, the membrane separation method of unsaturated hydrocarbons from a mixture containing unsaturated hydrocarbons and saturated hydrocarbons has not been widely used on an industrial scale due to performance and cost problems.

The present invention has been made in order to solve the above-mentioned conventional problems, and has a high separation ability and a high permeability for unsaturated hydrocarbons, and is practically usable 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.

[0005]

In order to achieve the above object, a method for selectively separating unsaturated hydrocarbons by an asymmetric membrane according to the present invention comprises the steps of: mixing a mixture containing unsaturated hydrocarbons and saturated hydrocarbons with a fluorine-containing polyimide; The resin is used as a main component, and it is brought into contact with one surface of an asymmetric membrane composed of a skin-like thin layer that selectively transmits unsaturated hydrocarbons and a porous structure layer that supports the skin-like thin layer. It is provided with a structure for selectively permeating and separating hydrocarbons.

In the above structure, the relationship between the solubility coefficient of the unsaturated hydrocarbon in the fluorine-containing polyimide resin and the solubility coefficient of the saturated hydrocarbon is measured at 25 ° C. and 50 torr or more. Preferably, when the sorption is at equilibrium, the {solubility coefficient ratio (unsaturated hydrocarbon / saturated hydrocarbon) ≧ 1.2}. The sorption refers to the dissolution of gas into the polymer. The term “50 torr or more” means that, depending on the physical properties of the hydrocarbon, when the liquid is a liquid at atmospheric pressure or higher, the liquid is evacuated (depressurized) to a gas to be measured.

In the above structure, the repeating molecular structural unit constituting the fluorine-containing polyimide resin preferably has at least three fluorine atoms. Further, in the above configuration, at least one of -CF ₃ is contained in the repeating molecular structural unit constituting the fluorine-containing polyimide resin.
It preferably has a group.

In the above structure, the fluorine-containing polyimide resin preferably contains a repeating unit substantially represented by the formula (1) as a main component. Further, in the above configuration, it is preferable that the fluorine-containing polyimide resin mainly contains a repeating unit substantially represented by the above formula (Formula 2).

According to the constitution of the present invention described above, a skin-like thin layer comprising a mixture containing an unsaturated hydrocarbon and a saturated hydrocarbon, which is mainly composed of a fluorine-containing polyimide resin, and which allows the unsaturated hydrocarbon to permeate selectively, Contacting one surface of an asymmetric membrane composed of a porous structure layer supporting the polymer, and selectively permeating and separating unsaturated hydrocarbons through the membrane, thereby achieving a high separation ability for unsaturated hydrocarbons. Thus, a method for selective membrane separation of unsaturated hydrocarbons having practically satisfactory performance and cost can be realized.

In the above description, the relationship between the solubility coefficient of unsaturated hydrocarbons and the solubility coefficient of saturated hydrocarbons in the fluorine-containing polyimide resin is determined by measuring the yield of hydrocarbons in the fluorine-containing polyimide resin at 25 ° C. and 50 torr or more. When the deposition is equilibrium, it is more preferable that the ratio of the solubility coefficient (unsaturated hydrocarbon / saturated hydrocarbon) ≧ 1.2, so that the selective membrane separation of unsaturated hydrocarbon can be performed. Here, the solubility coefficient indicates the volume of gas dissolved per unit pressure and polymer unit volume at a constant temperature. Therefore, the solubility coefficient can be used as an index of the affinity between the polymer and the gas. The permeability of a gas into a homogeneous polymer is determined by the process of dissolving the gas in the polymer and the process of diffusion of the gas in the polymer. Specifically, the product of the solubility coefficient in the polymer and the diffusion coefficient of the gas in the polymer is determined. Is well known. For this reason, the mixed gas can be separated into individual components by utilizing the difference in the solubility coefficient. The present inventor focused on this point, and as a result of intensive study, 25 ° C.
When the sorption of hydrocarbons is in equilibrium at a measurement of 50 torr or more, the solubility coefficient ratio (unsaturated hydrocarbon / saturated hydrocarbon)
When a fluorine-containing polyimide resin satisfying the condition of ≧ 1.2｝ is used as a skin-like thin layer material constituting an asymmetric membrane, an asymmetric separation membrane having high separation ability and high permeability to unsaturated hydrocarbons is obtained. Was found to be able to.

In the measurement at 25 ° C. and 50 torr or more, when the sorption of hydrocarbons is in equilibrium, if the solubility coefficient ratio (unsaturated hydrocarbon / saturated hydrocarbon) is less than 1.2, the skin-like thin layer of the asymmetric membrane The affinity between the polymer constituting the unsaturated hydrocarbon and the unsaturated hydrocarbon is reduced, so that the permeability of the unsaturated hydrocarbon tends to decrease.

In the above, the {solubility coefficient ratio (unsaturated hydrocarbon / saturated hydrocarbon) ≧ 1.2} means that the solubility coefficient of the unsaturated hydrocarbon in the fluorine-containing polyimide resin is smaller than that of the saturated hydrocarbon. It shows that it is 1.2 times.

In the above, at least 3 of the repeating molecular structural units constituting the fluorine-containing polyimide resin are contained.
When it has two fluorine atoms, more preferable selectivity is exhibited.

Further, in the above structure, when at least one --CF ₃ group is contained in a repeating molecular structural unit constituting the fluorine-containing polyimide resin, more preferable selectivity is exhibited.

Further, the fluorine content of the fluorine-containing polyimide resin is preferably 6 to 12 (the number of fluorine atoms in the repeating molecular unit), and the fluorine-containing polyimide resin has a substantially stable and high-quality unsaturated hydrocarbon separation. Preferred for obtaining a membrane. On the other hand, when the number exceeds 12, the raw material cost tends to increase, and the practicality tends to decrease.

In the above, it is preferable that the fluorine-containing polyimide resin contains a repeating unit substantially represented by the above formula (Chemical Formula 1) as a main component because it is low in cost and practical.
Further, in the above configuration, the fluorine-containing polyimide resin,
When the repeating unit represented by the above formula (Formula 2) is used as a main component, it is practically preferable because the cost is low.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a skin-like thin layer comprising a mixture containing an unsaturated hydrocarbon and a saturated hydrocarbon, which is mainly composed of a fluorine-containing polyimide resin and selectively allows the unsaturated hydrocarbon to permeate. The present inventors have found a method of contacting one surface of an asymmetric membrane composed of a supporting porous structure layer and selectively permeating and separating unsaturated hydrocarbons through the asymmetric membrane, thereby leading to the present invention. Many fluorine-containing polyimides have a high glass transition temperature and a rigid and bulky molecular chain structure, and thus are known as membrane separation materials having excellent heat resistance, chemical resistance, gas separation properties, and the like. For example, Japanese Patent Application Laid-Open No. 5-7749, U.S. Pat.
No. 02, U.S. Pat. No. 3,899,309, U.S. Pat.
No. 32041, U.S. Patent No. 4,645,824, U.S. Patent No. 4,705,540, U.S. Patent No. 4,717,393, U.S. Patent No. 4,717,394, U.S. Patent No. 4,838,900
U.S. Pat. No. 4,897,092, U.S. Pat.
No. 982, U.S. Pat. No. 4,929,405, U.S. Pat.
No. 981497 and US Pat. No. 5,049,992 disclose fluorine-containing aromatic polyimides. In the present invention, an asymmetric film having a skin-like thin layer containing the above-mentioned known fluorine-containing polyimide resin as a main component can be applied.

An example of a skin-like thin layer mainly composed of a fluorine-containing polyimide resin usable in the present invention is as follows.
In the formula (Formula 2), as the tetravalent organic group having at least three fluorine atoms, one in which a tetravalent proton of A ¹ or A ² is replaced by a fluorine atom or a group containing a fluorine atom is used. For example, a tetravalent organic group represented by the following formula (Formula 3) is preferably used.

[0019]

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The organic group having at least three fluorine atoms is not particularly limited as long as the proton of the divalent organic group represented by R1 or R2 is substituted by a fluorine atom or a group containing a fluorine atom. Is R1
Alternatively, one in which at least one proton of the divalent organic group of R2 is replaced by one —CF ₃ group is used. Specifically, divalent organic groups represented by the following formulas (Formula 4) to (Formula 7) are preferably used.

[0021]

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[0022]

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[0023]

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[0024]

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Further, it is more preferable that the fluorine-containing polyimide resin used in the present invention substantially contains a repeating unit represented by the above formula (Chemical Formula 2) as a main component. 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 comprises tetracarboxylic dianhydride and a diamine component (provided that at least one of the acid component or the amine component contains a fluorine-containing group) in an approximately equimolar amount. Used in a polar solvent at a temperature of about 80 ° C. or lower, preferably 0 to 60 ° C.
Stir at ℃ to polymerize the polyamic acid. The polar solvent used here is not particularly limited, but N-methyl-2-
Pyrrolidone, pyridine, dimethylacetamide, dimethylformamide, dimethylsulfoxide, tetramethylurea, phenol, cresol 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 imidation reaction,
In order to remove the polar solvent and imidization accelerator during polymerization,
A polyimide resin suitable as a skin-like thin layer material for an asymmetric membrane can be obtained by dropping and purifying a large amount of a solution such as acetone, alcohol or water.

When the imidization reaction is carried out without adding an imidization accelerator, a polyamic acid powder or a 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 to 400 ° C. to imidize a solid of polyamic acid obtained by evaporating the solvent from the mixture (a polyamic acid powder may be formed by adding a precipitant or the like during evaporation to form a polyamic acid powder). Thus, a polyimide resin suitable as a skin-like thin layer material for an asymmetric film can be obtained.

The method for forming an 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 formed on a flat plate or tube of glass, metal, plastic, or the like, or on a support such as a woven fabric or a nonwoven fabric. And then immersed in a coagulation solution (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 The liquid can be extruded from a concentric double-structured nozzle, immersed in the coagulation liquid to prepare an asymmetric membrane, and then dried.

The organic solvent in the film-forming solution used in the present invention is not particularly limited, but includes N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide, diethylene glycol dimethyl ether, 1,2-dimethoxymethane and the like. No. These organic solvents are used alone or as a mixed solvent of two or more kinds. The organic solvent is preferably a solvent having a small polarity and a low affinity for the solvent used as the coagulating liquid. For example, diethylene glycol dimethyl ether, 1,2-dimethoxymethane and the like are preferably used. When a solvent having a low affinity for the solvent used as the coagulating liquid is used for the film forming liquid, the solvent in the film forming liquid leaches into the solvent used as the coagulating liquid rather than the formation of a skin-like thin layer during wet phase inversion film forming. The speed becomes sufficiently low. As a result, it is possible to obtain an asymmetric membrane having a homogeneous skin-like thin layer and a porous structure layer free of pinholes that greatly degrade the separation performance over a wide range.

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

The polyimide solution concentration of the film forming solution in the present invention is 3 to 40% by weight, preferably 10 to 30% by weight. In addition, a swelling agent, a dispersing agent, a thickening agent and the like may be added as needed when preparing a film forming solution.

The asymmetric film used in the present invention is preferably further coated on the surface of the fluorine-containing polyimide thin film using an elastomer polymer. Forming and laminating a thin film of an elastomeric polymer is preferable in order to close the defects on the surface of the asymmetric film and prevent the surface from being damaged. The elastomer polymer refers to a polymer having a flexible film-forming ability, and specific examples thereof include polypropylene, polyvinyl chloride, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, polybutadiene, and polyisoprene. Of an ethylenic monomer or a conjugated diene monomer such as chloroprene rubber, poly (4-methyl-pentene-1), butadiene-styrene copolymer, isoprene-isobutylene copolymer, or polyisobutylene A polymer or a copolymer, in addition to the above monomer components, a copolymer containing a monomer component having a functional group such as acrylonitrile, (meth) acrylate, (meth) acrylic acid, Or polyether polyol, polyurethane polyether, polyurethane polyester or It can be mentioned a copolymer having both a so-called soft and hard segments, such as Li amide polyesters. Further, in addition to the above, an epoxy resin, an ethyl cellulose, a butoxy resin, or the like that is cured by a linear long-chain curing agent can be used as the elastomer polymer in the present invention. In the present invention, a crosslinkable silicone resin is particularly preferably used as the elastomer polymer.
Such a crosslinkable silicone resin is a silicone resin which is soluble in an organic solvent before crosslinking, but becomes insoluble in an organic solvent after crosslinking.
The film can be formed according to the method described in JP-A-705.

The shape of the asymmetric membrane in the present invention is not particularly limited, but a tube (including a hollow fiber) or a flat membrane is preferably used.

[0035]

EXAMPLES Examples will be described below with reference to specific examples.
The present invention is not limited to these examples.

[0036]

Example 1 A fluorine-containing polyimide as a recurring unit represented by the above formula (Formula 6) was synthesized by the following method.
0.1 mol of 5,5′-2,2′-trifluoro-1- (trifluoromethyl) ethylidene-bis-1,3-isobenzofurandione (6FDA) and 2,2-bis (4
-Aminophenyl) hexafluoropropane (BAA
F) 0.1 mol of N-methyl-2-pyrrolidone (NM
P) The solution was reacted in the solution for 4 hours to obtain a polyamic acid. Thereafter, 0.3 mol of pyridine and 0.3 mol of acetic anhydride were added, and an imidization reaction was performed for 15 hours. After the reaction, further N
MP and diluted to 8% by weight, and the N
After the MP solution was added dropwise, purification was performed to obtain a fluorine-containing polyimide having a repeating unit represented by the above formula (Formula 2) as a structural unit. Physical properties of the obtained fluorine-containing polyimide,
Glass transition temperature is 301 ° C and weight average molecular weight is 15
It was 9,000.

With respect to the obtained fluorine-containing polyimide,
When the solubility coefficient of propylene and propane was evaluated at a temperature of 25 ° C. and a supply pressure of 2 atm, the solubility coefficient ratio (propylene / propane) at the time of sorption equilibrium was 1.4.

Therefore, the material of the film and the solubility coefficient ratio are:
This satisfied the conditions for the skin-like thin film material of the asymmetric film in the present invention. Next, 82 parts by weight of diethylene glycol dimethyl ether was added to 18 parts by weight of a fluorine-containing polyimide having a repeating unit represented by the above formula (Chemical Formula 2) as a structural unit, and the mixture was stirred at 100 ° C. for 6 hours and dissolved. Thereafter, the mixture was filtered, allowed to stand, and sufficiently defoamed to prepare a film-forming solution. The film forming solution was cast on a polyester non-woven fabric with a width of 20 cm and a thickness of 300 μm using an applicator, and immersed in water of 5 ° C. as a coagulating solution for 1 hour. Thereafter, the membrane was washed with water and air-dried at room temperature to obtain an asymmetric membrane. The surface of such asymmetric membrane is crosslinked with a crosslinkable silicone resin solution of elastomer polymer (Si
(3 wt% solution of RTV615 of licones) and heat-treated at 110 ° C. for 30 minutes to form and laminate a thin film of an elastomeric polymer. Table 1 summarizes the results of evaluating the separation and permeation performance of propylene and propane at a temperature of 25 ° C. for the obtained asymmetric membrane having an elastomer thin film layer.

[0039]

Example 2 The solubility coefficient in a fluorine-containing polyimide resin at the time of sorption equilibrium was determined in the same manner as in Example 1 except that n-butane, 1-butene, and 1,3-butadiene were used instead of propylene and propane. As a result of the evaluation, the solubility coefficient ratio (1-butene / n-butane) was 1.4, and the solubility coefficient ratio (1,3-butadiene / n-butane) was 1.7. Therefore, the material of the film and the solubility coefficient ratio satisfied the conditions as the skin-like thin film material of the asymmetric film in the present invention. Next, n-butane, 1-butene,
For 1,3-butadiene, the results of evaluating the separation and permeation performance in the same manner as in Example 1 are summarized in Table 1 below.

[0040]

[Table 1]

As is clear from Table 1, it was confirmed that the products of Examples of the present invention had a high separation ability and a high permeability for unsaturated hydrocarbons.

[0042]

As described above, according to the present invention, the solubility coefficient of the unsaturated hydrocarbon satisfies the ratio of a predetermined value or more as compared with the solubility coefficient of the saturated hydrocarbon due to the difference in affinity between the polymer and the permeating component. By preparing an asymmetric membrane having a skin-like thin layer composed of a fluorine-containing polyimide resin, an asymmetric membrane having a high permeability and a high separation ability for unsaturated hydrocarbons can be obtained. Using,
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.

Continuation of the front page (51) Int.Cl. ⁶ identification code FI C10G 31/09 C10G 31/09 (56) References JP-A-5-7749 (JP, A) JP-A-5-146650 (JP, A) JP-A-6-182167 (JP, A) JP-A-3-267130 (JP, A) JP-A-7-178311 (JP, A) JP-A-62-1114628 (JP, A) JP-A-60-22902 JP-A 7-324047 (JP, A) JP-A 8-173779 (JP, A) JP-A 8-173778 (JP, A) JP-A 50-95205 (JP, A) 53-105402 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 61/36 B01D 71/64 C07C 7/144 C07C 11/02 C08G 73/10 C10G 31/09

Claims (6)

(57) [Claims] 1. A method of separating the unsaturated hydrocarbon gas from a mixture gas containing a saturated hydrocarbon gas <br/> unsaturated hydrocarbon gas, a mixture gas containing an unsaturated hydrocarbon gas and saturated hydrocarbon gas The asymmetric membrane composed mainly of a fluorine-containing polyimide resin and composed of a skin-like thin layer that selectively transmits unsaturated hydrocarbon gas and a porous structure layer that supports the skin-like thin layer, Through the membrane
Selective separation method unsaturated hydrocarbon gas by asymmetric membrane and separating selectively transmits an unsaturated hydrocarbon gas. 2. A fluorine-containing solubility coefficient of saturated hydrocarbon gas and solubility coefficient of the unsaturated hydrocarbon gas to the polyimide resin relationship, 25 ° C., in the measurement of more than 50 torr, a hydrocarbon gas to the fluorine-containing polyimide resin 2. The method for selective separation of unsaturated hydrocarbon gas by an asymmetric membrane according to claim 1, wherein, when the sorption is at equilibrium, the ratio of solubility coefficient (unsaturated hydrocarbon gas / saturated hydrocarbon gas ) ≧ 1.2. 3. The method for selectively separating unsaturated hydrocarbon gas by an asymmetric membrane according to claim 1, wherein the repeating molecular structural unit constituting the fluorine-containing polyimide resin has at least three fluorine atoms. 4. The method for selectively separating unsaturated hydrocarbon gas by an asymmetric membrane according to claim 1, wherein the repeating molecular structural unit constituting the fluorine-containing polyimide resin has at least one —CF ₃ group. 5. The unsaturated hydrocarbon according to claim 1, wherein the fluorine-containing polyimide resin contains a repeating unit substantially represented by the following formula (1) as a main component.
Gas selective separation method. Embedded image 6. A fluorine-containing polyimide resin, substantially selective of the formula (Formula 2) as a main component a repeating unit represented by claim 1 or 2 unsaturated hydrocarbon gas in an asymmetric membrane according to Separation method. Embedded image