JP2002159822A - Method for separating hydrocarbon by separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for separating specific hydrocarbon from a hydrocarbon mixture, capable of being practically satisfied from the stand points of capacity and cost, by using a membrane comprising a fluorine- containing polyimide resin having high separation capacity with respect to specific hydrocarbon. SOLUTION: The hydrocarbon mixture is brought into contact with one surface of a membrane based on the fluorine-containing polyimide resin with a glass transition temperature of 200-280 deg.C having a metal bond in the main chain portion within its repeating molecular unit structure and the specific hydrocarbon is selectively passed through the membrane to be separated. For example, the membrane comprising the fluorine-containing polyimide resin based on a repeating unit represented by formula 1 (wherein, m is a positive natural number and shows a degree of polymerization) or formula 2 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for separating a specific hydrocarbon from a mixture containing the hydrocarbon. More specifically, the present invention relates to a method for separating and concentrating unsaturated hydrocarbons, aromatic hydrocarbons, and the like from a mixture containing hydrocarbons generated in a petroleum refining industry, a petrochemical industry, or the like.

[0002]

2. Description of the Related Art In the petroleum refining industry and the petrochemical industry, methods for separating specific hydrocarbons from hydrocarbon-containing mixtures using membranes have been studied for many years from a scientific and economic viewpoint. Some examples have been reported.
For example, U.S. Pat. No. 2,958,656 discloses that a hydrocarbon mixture, i.e., naphtha, is supplied to a non-porous cellulose ether membrane, a portion of which is permeated through the membrane, and the permeate side of the membrane is cleaned using a cleaning gas or cleaning liquid. A method for separating unsaturated compounds, saturated compounds and aromatic compounds by removing permeate is disclosed. U.S. Pat. No. 2,930,754
The specification 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 passed through the permeate side of the membrane using a cleaning gas or a cleaning liquid. Discloses a method of separating hydrocarbons such as unsaturated hydrocarbons and aromatic compounds by removing the hydrocarbons.

[0003]

However, in the conventional method for separating hydrocarbons using a membrane, most of the separation membranes are resistant to aromatic hydrocarbons, unsaturated hydrocarbons, saturated hydrocarbons, or the like, or have specific hydrocarbons. The separation power is not yet sufficient, or a cleaning gas or cleaning liquid is required to remove or recover hydrocarbons permeated through the membrane,
The device becomes complicated and there is an economical problem. Therefore, at present, the membrane separation method of specific hydrocarbons from a mixture containing hydrocarbons is not widely used on an industrial scale due to problems in performance, workability, and cost.

[0004] The present invention has been made to solve these problems, and has a high resistance to hydrocarbons, a specific unsaturated hydrocarbon in a mixture containing hydrocarbon,
It has high separation ability for aromatic hydrocarbons, etc.
It is an object of the present invention to provide a method for membrane separation of a specific hydrocarbon from a mixture containing a hydrocarbon, which is practically satisfactory both in terms of cost.

[0005]

In order to achieve the above object, a method for selectively separating hydrocarbons according to the present invention is characterized in that a mixture containing hydrocarbons is mixed with a glass transition temperature in the range of 200 to 280 ° C. It is characterized by contacting one surface of a film mainly composed of a fluorine-containing polyimide resin having a meta bond in the main chain portion in the molecular unit structure, and selectively permeating and separating specific hydrocarbons through this film. I do.

In the present invention, it is preferable that at least one --CF ₃ group is contained in the repeating molecular unit structure constituting the fluorine-containing polyimide resin.

In the present invention, it is preferable that the fluorine-containing polyimide resin contains a repeating unit substantially represented by the following formula (4) as a main component.

[0008]

Embedded image

(However, A ₁ and A _{2 each} have a tetravalent organic group comprising an aromatic, alicyclic or aliphatic hydrocarbon group having a meta bond in the main chain portion in the repeating unit structure. ₁ and R ₂
Is a divalent aromatic, aliphatic or aliphatic hydrocarbon group or a divalent organic bonding group in which these hydrocarbon groups are bonded.
A organic group having a valence of at least one of A ₁ , A ₂ , R ₁ , and R ₂ is an organic group having at least one —CF ₃ group;
m and n are positive natural numbers and indicate the degree of polymerization. In the present invention, the fluorine-containing polyimide resin preferably contains a repeating unit substantially represented by the following formula (5) or (6) as a main component.

[0010]

Embedded image

(However, m and n are positive natural numbers and indicate the degree of polymerization.)

[0012]

Embedded image

(However, m and n are positive natural numbers and indicate the degree of polymerization.)

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors contact a mixture containing a hydrocarbon with one side of a film made of a fluorine-containing polyimide resin, and selectively permeate a specific hydrocarbon through this film to obtain a high degree. A method for separation has been found, and the present invention has been achieved. Many fluorine-containing polyimides are known as membrane separation materials having excellent heat resistance and gas separation properties. For example, Japanese Patent Application Laid-Open No. 5-7749, U.S. Pat.
No. 822202, U.S. Pat. No. 3,899,309, U.S. Pat. No. 4,532,041, U.S. Pat. No. 4,645,824,
U.S. Pat. No. 4,705,540, U.S. Pat.
No. 3, US Pat. No. 4,717,394, US Pat.
No. 8,900, U.S. Pat. No. 4,897,092, U.S. Pat. No. 4,932,982, U.S. Pat. No. 4,929,405, U.S. Pat. No. 4,981,497, U.S. Pat. .

The resin constituting the membrane used in the present invention is a resin that contributes to the separation performance of specific hydrocarbons such as unsaturated hydrocarbons and aromatic hydrocarbons, and has a glass transition temperature of 20%.
The main component is a fluorine-containing polyimide resin having a temperature in the range of 0 to 280 ° C. and having a meta bond in the main chain portion in the repeating molecular unit structure. Here, the main component means 70 mol% or more. The preferred weight average molecular weight is 20,000 to 800,
000 range.

The gas permeability of a homogeneous polymer is determined by the process of dissolving the gas in the polymer and the process of diffusion in the polymer. Specifically, the solubility coefficient of the gas in the polymer and the diffusion coefficient of the gas in the polymer are determined. It is well known that it is expressed as a product. For this reason, it becomes possible to separate the mixed gas into individual components by utilizing the difference in solubility or diffusivity. When a hydrocarbon having a carbon number of C3 or more is allowed to permeate, generally, the polymer of the membrane material is plasticized by the permeating component, and as a result, the free volume of the polymer is increased and the diffusivity is improved. At this time, in the case of a glassy polymer such as polyimide, if it is excessively plasticized, the rate of increase in free volume increases, and as a result, a separation function such as sieving a specific permeated component using a difference in molecular size. Decrease.
Such excessive plasticization is strongly related to the thermal mobility and three-dimensional molecular structure of polyimide. The present inventors have focused on this point and conducted intensive studies. As a result, the glass transition temperature was 20 ° C.
Extreme plasticization due to hydrocarbons occurs when a resin in the range of 0 to 280 ° C. and containing a fluorine-containing polyimide as a main component having a meta bond in a main chain portion in a repeating molecular unit structure is used as a film material. It has been found that a separation membrane which can be suppressed and has a high separation ability for specific hydrocarbons can be obtained.

In the present invention, the glass transition temperature is measured according to a general scanning differential calorimetry. The above-mentioned fluorine-containing polyimide resin has a glass transition temperature of 200.
It is not preferable to use a material having a temperature lower than 0 ° C., because the unrelaxed volume of the fluorine-containing polyimide effective for dissolving the hydrocarbon is excessively reduced, and as a result, the permeability of the hydrocarbon may be excessively reduced. On the other hand, if the glass transition temperature exceeds 280 ° C., the rigidity of the molecular chain is excessively increased, and as a result, the packing of the molecular chain is deteriorated, and there is a possibility that the polymer may be excessively easily plasticized. In addition, the introduction of a meta bond into the main chain described above increases the flexibility of the fluorine-containing polyimide molecule, and as a result, it is considered that high-efficiency filling of the molecular chain is possible during resin formation, and hydrocarbons are considered. This is preferred because it tends to be less plasticized.

In the present invention, it is possible to apply the known film containing a fluorine-containing polyimide resin as a main component, which has been described in the related art.

The fluorine-containing polyimide resin used in the present invention preferably contains a repeating molecular structural unit represented by the general formula (Formula 4) as a main component. The tetravalent organic group having one or more —CF ₃ groups is not particularly limited. For example, a tetravalent organic group represented by the following formula (Formula 7) is preferably used.

[0020]

Embedded image

The divalent organic group of R ₁ or R ₂ is not particularly limited, but a structure containing phenylene in the main chain is preferably used. Specifically, divalent organic groups represented by the following formulas (Formula 8) to (Formula 15) are preferably used.

[0022]

Embedded image

[0023]

Embedded image

[0024]

Embedded image

[0025]

Embedded image

[0026]

Embedded image

[0027]

Embedded image

[0028]

Embedded image

[0029]

Embedded image

The fluorine-containing polyimide resin used in the present invention may be a copolymer or a mixture with a polymer such as polysulfone or polyethersulfone other than the fluorine-containing polyimide resin as long as it is 50 mol% or less.

The fluorine-containing polyimide resin used in the present invention can be obtained by a known polymerization method, for example, as described in US Pat. No. 3,959,350, using a tetracarboxylic dianhydride and a diamine component. Can be For example, a tetracarboxylic dianhydride and a diamine compound are used in approximately equimolar amounts and stirred in a polar solvent at a temperature of about 80 ° C. or lower, preferably 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 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 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 100-400 ° 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 the 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 or metal. A method of casting a plate or tube having a smooth surface such as plastic or the like, or a porous support such as a non-woven fabric with a constant thickness, followed by heat treatment (dry film forming method), and , The above-mentioned film forming solution is made of glass, metal,
It is cast to a certain thickness on a porous support such as a plastic or other flat plate or tube, or a woven or non-woven fabric, and a coagulation solution (the fluorine-containing polyimide resin in the film formation solution does not dissolve, but the film formation solution A solvent that is compatible with the organic solvent in) or extrude the film-forming solution from a concentric multi-layered nozzle, and immerse in the coagulation solution to prepare a hollow fiber-like asymmetric membrane,
Thereafter, a method of drying the film (wet film forming method) can be employed.

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.

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.

The heat treatment after the casting of the film-forming solution is preferably carried out at a temperature at which the solvent in the film-forming solution can be sufficiently removed and at a temperature not higher than the glass transition point of the polyimide resin.

In the above-mentioned wet film-forming method, the coagulating liquid used for immersing and removing the above-mentioned organic solvent does not dissolve the fluorine-containing polyimide resin used, but any solvent having a compatibility with the solvent in the film-forming liquid. Although not particularly limited, water, alcohols such as ethanol, methanol, and isopropyl alcohol, and a mixture thereof are used, 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 shape of the membrane in the present invention is not particularly limited, but a tube (including a hollow fiber) or a flat membrane is preferably used.

[0041]

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

Example 1 5,5'-2,2'-trifluoro-1
-(Trifluoromethyl) ethylidene-bis-1,3-isobenzofurandione (6FDA) 0.0761mol and 3,4'-diaminodiphenylether (34'DPE) 0.0761mol and N-methyl-2-pyrrolidone (NMP ) And stirred at room temperature under a nitrogen atmosphere to prepare a polyamic acid solution. At this time, the content of the polyamic acid solution was adjusted to 10 wt% or less of the polyamic acid. Then, acetic anhydride was added to this polyamic acid solution at a concentration of 0.1%.
305 mol was added together with a small amount of pyridine, and the mixture was stirred at room temperature under a nitrogen atmosphere to perform an imidization reaction. After completion of the reaction, the mixture was cooled to room temperature, and the polymerization solution was dropped into an excess amount of water under high-speed stirring to precipitate and purify. Further purification with methanol yielded a fluorine-containing polyimide resin comprising a repeating molecular structural unit represented by the following formula (Formula 16).

[0043]

Embedded image

(Where m is a positive natural number and weight average molecular weight)
90,000) Next, 18 parts by weight of a fluorine-containing polyimide comprising a repeating molecular structural unit represented by the above formula (Chem. 16) was diluted, and 82 parts by weight of NMP was added as an organic solvent.
The mixture was stirred for a period of time to dissolve. 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 glass plate using an applicator at a width of 20 cm and a thickness of 300 μm, and was heated at 110 ° C. for 1 hour, 150 ° C. for 3 hours, 200 ° C. for 3 hours, and further under vacuum at 200 ° C. A heat treatment was performed for 72 hours to obtain a homogeneous film made of a fluorine-containing polyimide resin having a thickness of 20 to 40 μm. This fluorine-containing polyimide resin has a meta bond in the main chain portion in the repeating molecular unit structure. When the scanning differential calorimetry is performed at a heating rate of 10 ° C./min, the glass transition temperature is 237.
° C. Therefore, the above-mentioned fluorine-containing polyimide resin satisfied the conditions of the present invention. Next, with respect to the obtained homogeneous membrane, the separation performance and permeation performance evaluation results in a steady state when a propylene / propane 50/50 mol% mixed gas was supplied at 25 ° C. and a supply pressure of 2 atm are summarized in Table 1 below. Show.

Example 2 The procedure of Example 1 was repeated, except that 3,3′-diaminodiphenylmethane (33′DDM) was used instead of 3,4′-diaminodiphenylether. A homogeneous film made of a fluorine-containing polyimide resin having a repeating molecular unit structure represented by the following formula was obtained.

[0046]

Embedded image

(Where m is a positive natural number and weight average molecular weight)
140,000) This fluorine-containing polyimide resin has a meta bond in the main chain portion in the repeating molecular unit structure, and has a temperature of 10 ° C.
When the scanning differential calorimetry was performed at a heating rate of / min, the glass transition temperature was 217 ° C. Therefore,
The above-mentioned fluorine-containing polyimide resin satisfied the conditions of the present invention. Next, in the same manner as in Example 1, the separation performance and permeation performance evaluation results in the steady state when a propylene / propane 50/50 mol% mixed gas was supplied at 25 ° C. and a supply pressure of 2 atm in the same manner as in Example 1. Are summarized in Table 1 below.

Comparative Example 1 The procedure of Example 1 was repeated, except that 4,4′-diaminodiphenylmethane (44′DDM) was used instead of 3,4′-diaminodiphenylether. A homogeneous film made of a fluorine-containing polyimide resin having a repeating molecular unit structure represented by the following formula was obtained.

[0049]

Embedded image

(Where m is a positive natural number and weight average molecular weight
120,000) Scanning differential calorimetry at a heating rate of 10 ° C./min for this fluorine-containing polyimide resin revealed a glass transition temperature of 286 ° C. Therefore, this fluorine-containing polyimide resin did not satisfy the conditions of the present invention. Next, this homogeneous film was treated in the same manner as in Example 1 at 25 ° C. and a supply pressure of 2 atm.
Table 1 summarizes the separation performance and permeation performance evaluation results in the steady state when a 50/50 mol% mixed gas of propane was supplied.

[0051]

[Table 1]

As shown in Table 1, the product of the embodiment of the present invention
It was confirmed that the separation coefficient of propylene was higher and the separation ability for specific hydrocarbons was higher than that of the comparative example product.

[0053]

According to the present invention, by preparing a film from a fluorine-containing polyimide resin having a glass transition temperature within a predetermined range and having a meta bond in a main chain, a high degree of specific hydrocarbon in a hydrocarbon mixture can be obtained. By using this membrane, it is possible to provide a method for separating a specific hydrocarbon from a hydrocarbon-containing mixture which is practically satisfactory in performance and cost.

Continuing on the front page (72) Inventor Tsukasa Miyazaki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Kenichi Ikeda 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko shares Company F-term (reference) 4D006 GA27 KA12 MA01 MA02 MA03 MB04 MC58X MC79X MC87 NA03 NA05 NA62 PB18 PB68 4J043 PA04 QB31 QC02 RA35 SA06 SB03 TA14 TA22 TB02 UA131 UA132 VAUA1 UA151 UB011 UB061 UB061 UB061 ZB11

Claims (4)

[Claims] A film comprising a hydrocarbon-containing mixture having a glass transition temperature in the range of 200 to 280 ° C. and a fluorine-containing polyimide resin having a meta bond in a main chain portion in a repeating molecular unit structure as a main component. And selectively permeating and separating a specific hydrocarbon through the membrane. 2. The method for selectively separating hydrocarbons according to claim 1, wherein the fluorine-containing polyimide resin has at least one --CF ₃ group in a repeating molecular unit structure. 3. The method for selectively separating hydrocarbons 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. Embedded image (However, a meta bond in the main chain portion of the repeating unit structure, A ₁ and A ₂ represents an aromatic tetravalent organic radical consisting of alicyclic or aliphatic hydrocarbon group, R ₁ and R ₂ represents a divalent aromatic, aliphatic or aliphatic hydrocarbon group or a divalent organic group in which these hydrocarbon groups are bonded by a divalent organic bonding group, and A ₁ , A ₂ , R ₁ , At least one of R ₂ is -C
An organic group having at least one F ₃ group, where m and n are positive natural numbers and indicate the degree of polymerization. ) 4. The selection of hydrocarbons according to claim 1, wherein the fluorine-containing polyimide resin is mainly composed of a repeating unit substantially represented by the following formula (2) or (3). Separation method. Embedded image (However, m and n are positive natural numbers and indicate the degree of polymerization.) (However, m and n are positive natural numbers and indicate the degree of polymerization.)