JP3361770B2 - Hydrocarbon separation method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating a specific hydrocarbon from a mixture containing hydrocarbons,
More specifically, it relates to a method for separating and concentrating unsaturated hydrocarbons, aromatic hydrocarbons, etc. from a mixture containing hydrocarbons generated in the petroleum refining industry, petrochemical industry and the like.

[0002]

2. Description of the Related Art In the petroleum refining industry and petrochemical industry,
The method of separating a specific hydrocarbon from a mixture containing hydrocarbons using a membrane has been studied for many years from a scientific and economic standpoint, and some studies have been reported so far. For example, U.S. Pat.No. 2,958,656 discloses a hydrocarbon mixture, i.e., naphtha, fed to a non-porous cellulose ether membrane, a portion of which is permeated through a membrane and a permeate from the permeate side of the membrane using a cleaning gas or liquid. The method of separating an unsaturated compound, a saturated compound, and an aromatic compound by removing is disclosed. U.S. Pat.No. 2,930,754 discloses that a portion of a mixture distilled at a boiling point range of gasoline is selectively permeated through a non-porous cellulose ether membrane, and the permeate is washed with a cleaning gas or a cleaning liquid. It discloses a method for separating hydrocarbons such as unsaturated hydrocarbons and aromatic compounds by removing them from the permeate side of the membrane.

Most of the fluorine-containing polyimides have heat resistance,
It is known as a membrane separation material having excellent gas separation properties.
For example, JP-A-5-7749, U.S. Patent No. 3822202, U.S. Patent No. 3899309, U.S. Patent No. 4532041, U.S. Patent No.
4645824, U.S. Pat.No. 4,705,540, U.S. Pat.No. 4717393
U.S. Pat.No. 4,717,394, U.S. Pat.No. 4,838,900, U.S. Pat.No. 4,897,902, U.S. Pat.No. 4,902,982, U.S. Pat.
29405, U.S. Pat. No. 4,981,497, U.S. Pat. No. 5,042,992, and the like disclose synthetic fluorine-based aromatic polyimides.

[0004]

However, in the conventionally proposed methods for separating hydrocarbons by membranes, most of the separation membranes have resistance to aromatic hydrocarbons, unsaturated hydrocarbons, saturated hydrocarbons, etc. Separation ability for hydrocarbons is not yet sufficient, and a cleaning gas or cleaning solution for removing or recovering hydrocarbons that have permeated the membrane is required, which complicates the apparatus and is economically problematic. Therefore, at present, the membrane separation method of a specific hydrocarbon from a mixture containing hydrocarbons is not widely used on an industrial scale because of problems of performance, workability, and cost.

The present invention has been made to solve the above-mentioned conventional problems and has a high resistance to hydrocarbons, and a specific unsaturated hydrocarbon or aromatic compound in a mixture containing hydrocarbons. It is an object of the present invention to provide a membrane separation method for a specific hydrocarbon from a mixture containing the hydrocarbon, which has a high separation ability for hydrocarbons and the like and is practically satisfactory in terms of performance and cost.

[0006]

In order to achieve the above object, the method for separating hydrocarbons according to the present invention is a method for separating a mixture containing hydrocarbons having 3 or more carbon atoms into a free volume fraction at 25 ° C. One side of a film containing as a main component a copolymer of a fluorine-containing polyimide resin having a value of 0.180 to 0.220 and a fluorine-containing polyimide resin having at least one -OH group in a repeating molecular structural unit. And the hydrocarbon having 3 or more carbon atoms is selectively permeated and separated through the membrane.

In the above method, it is preferable that the repeating molecular structural unit constituting the fluorine-containing polyimide resin has at least one --CF ₃ group.

[0008] In the above method preferably composed mainly of repeating units fluorine-containing polyimide resin represented by the front following formula (Formula 1).

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 its free volume fraction at 25 ° C. is O. The main component is a copolymer of a fluorine-containing polyimide resin in the range of 180 to 0.220 and a fluorine-containing polyimide resin having at least one —OH group in the repeating structural unit. The gas permeability to a homogeneous polymer is determined by the gas dissolution process in the polymer and the diffusion process in the polymer. Specifically, it is expressed by the product of the solubility coefficient in the polymer and the diffusion coefficient of the gas in the polymer. It is well known that Therefore, it becomes possible to separate the mixed gas into individual components by utilizing the difference in solubility or diffusivity. In the case of permeating a hydrocarbon having a carbon number of C ₃ or more, the membrane material polymer is generally plasticized by the permeation component, and as a result, the free volume of the polymer is increased and the diffusion property is improved. At this time, in the case of a glassy polymer such as polyimide, when it is excessively plasticized, the rate of increase in free volume increases, and as a result, a separation function such as sieving the specific permeation component using the difference in molecular size. Is reduced. On the other hand, if the hydrocarbon to be separated is not excessively plasticized, the permeability becomes too small, which is not preferable. The present inventor has paid attention to this point, and as a result of diligent studies, the free volume fraction at 25 ° C. is O.180 to O.220.
When a resin containing a fluorine-containing polyimide resin in the range of 10 and a copolymer of a fluorine-containing polyimide resin having at least one —OH group in a repeating molecular structural unit as a main component is used as a membrane material, It has been found that it is possible to suppress the extreme plasticization and obtain a separation membrane having a high separation ability for specific hydrocarbons. The reason why the introduction of the —OH group suppresses plasticization of the film containing the above-mentioned copolymer as a main component by the hydrocarbon is generally caused by intermolecular hydrogen bonding, and the hydrocarbon is dissolved to fill the molecular chain. This is probably because the state is less likely to collapse. Here, the free volume fraction (FF
V) was calculated from the following equation (Equation 1).

[0010]

FFV = (V ₂₉₈ -V _o ) / V ₂₉₈ (1) (where V ₂₉₈ is the molar volume of the polyimide resin at 25 ° C, and the molecular weight of the unit structure of the polyimide resin is It was calculated by dividing by the density.
V _o is the formula of Bondi (Bondi) (A. Bondi, J.Phys . Chem., 6
8, 441-451 (1964)), which is the molar volume of the polymer in OK determined by 1.3% of the van der Waals volume of the polyimide resin.
Double the value.

In the film material containing the above-mentioned copolymer as a main component, -O
When the H group is not contained, plasticization due to hydrocarbon becomes remarkable and the separation function may be deteriorated, which is not preferable.

If one of the fluorine-containing polyimide resins constituting the above-mentioned copolymer has a free volume fraction of less than 0.18 at 25 ° C., the molecular chain packing property of the copolymer is excessively improved, and The hydrogen permeability may be too low, which is not preferable. Further, if one of the fluorine-containing polyimide resins constituting the above-mentioned copolymer has a free volume fraction at 25 ° C. of more than O.20, plasticization due to hydrocarbon becomes remarkable and the separation function may deteriorate. Is not preferred.

Further, in the present invention, at least one of the repeating molecular structural units constituting the polyimide resin is
It is preferable to have —CF ₃ groups.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION
Fluorine-containing polyimide resin having a free volume fraction in the range of O.180 to O.220 and -O in the repeating molecular structural unit.
The method of contacting one side of a film containing a copolymer of a fluorine-containing polyimide resin having at least one H group as a main component, and selectively permeating and separating a specific hydrocarbon through this film, the present invention It came to.

In the present invention, a film containing a known fluorine-containing polyimide resin as a main component, which has been described in the above-mentioned prior art, can be applied.

The fluorine-containing polyimide resin used in the present invention preferably contains a repeating molecular structural unit represented by the general formula (Formula 1) as a main component. The tetravalent organic group having one or more —CF ₃ groups is not particularly limited, and for example, the following formula (Formula 2)

[0017]

[Chemical 2]

A tetravalent organic group represented by the following is preferably used.

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 3) to (Formula 8) are preferably used.

[0020]

[Chemical 3]

[0021]

[Chemical 4]

[0022]

[Chemical 5]

[0023]

[Chemical 6]

[0024]

[Chemical 7]

[0025]

[Chemical 8]

Of the above R ₁ or R ₂ , the divalent organic group containing at least one —OH group is not particularly limited, but is, for example, a divalent organic group represented by the following formulas (Formula 9) to (Formula 12). The organic groups and the like are preferably used.

[0027]

[Chemical 9]

[0028]

[Chemical 10]

[0029]

[Chemical 11]

[0030]

[Chemical 12]

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

The fluorine-containing polyimide resin used in the present invention can be obtained by using a tetracarboxylic dianhydride and a diamine component by a known polymerization method as described in, for example, US Pat. No. 3,959,350. . For example, using tetracarboxylic dianhydride and diamine compound in approximately equimolar amounts, in a polar solvent, at a temperature of about 80 ° C. or lower, preferably O.
Stir at ~ 60 ° C to polymerize 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 solution of the obtained polyamic acid in a polar solvent was added to a third solution of trimethylamine, triethylami, pyridine or the like.
Add an imidization promoter such as a primary amine compound, acetic anhydride, thionyl chloride, or carboximide, and stir at a temperature of 5 to 150 ° C to effect imidization. When performing the imidization reaction, the polyamic acid solution may be heated at 100 to 400 ° C., preferably 120 to 300 ° C. for imidization without adding an imidization accelerator.

After the imidization reaction, in order to remove the polar solvent and the imidization accelerator during the polymerization, the solution was dropped into a large amount of a solution of acetone, alcohol, water or the like 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, alcohol or the like. The solid of polyamic acid obtained by evaporating the solvent from (at the time of evaporation, a precipitating agent or the like is added to form a polyamic acid powder, which may be separated by filtration) is heated to 100 to 400 ° C. for imidization. Thus, a polyimide resin suitable as a film material can be obtained.

The method for forming the film used in the present invention is not particularly limited. For example, the fluorine-containing polyimide resin is dissolved in an appropriate solvent to prepare a film forming solution, and the film forming solution is made of glass, metal, Method obtained by casting a flat plate or tube having a smooth surface such as plastic or the like, or a porous support such as non-woven fabric at a constant thickness, and then subjecting to heat treatment
(Dry film forming method), and the above film forming solution is cast on a flat plate or tube of glass, metal, plastic or the like, or on a porous support such as woven or non-woven fabric at a constant thickness to obtain a coagulating liquid. (While the fluorine-containing polyimide resin in the film-forming solution does not dissolve, it is immersed in a solvent that is compatible with the organic solvent in the film solution), or, the film-forming solution is extruded from a concentric multiple structure nozzle, A method (wet film forming method) in which a hollow fiber-shaped asymmetric membrane is prepared by immersing the membrane in a coagulating liquid and then drying the membrane can be adopted.

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

The concentration of the polyimide solution in the film forming solution is 3 to 40 weight.
%, Preferably 10 to 30% by weight. In addition, a swelling agent, a dispersant, a thickener, and the like may be added if necessary when adjusting the film-forming liquid.

As means for casting the film-forming solution, for example,
A doctor knife, a doctor plate, an applicator, etc. 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 wet film forming method, the coagulating liquid used when dipping and removing the above organic solvent does not dissolve the fluorine-containing polyimide resin used, but is a solvent which is compatible with the solvent in the film forming liquid. Although not particularly limited, a mixed solution of water and alcohols such as ethanol, methanol, isopropyl alcohol and the like is used, and water is particularly preferably used. The temperature of the coagulating liquid when the organic solvent in the film forming liquid is removed by immersion is not particularly limited, but preferably 0
It is performed at a temperature of ~ 50 ° C.

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

[0043]

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) O-0761mo1 and 2,4,6-trimethyl-
1,3-Phenylenediamine (TMMPD): O.0381mo1 and 3,3'-dihydroxy-4,4'-diaminobiphenyl (DHDB): 0.0381
Mo1, and N-methyl-2-pyrrolidone (NMP) as a solvent were added, and the mixture was stirred at room temperature under a nitrogen atmosphere to prepare a polyamic acid solution. At this time, the polyamic acid solution was within 10 wt% of the polyamic acid. Then, acetic anhydride O.305mo1 was added to this polyamic acid solution together with a small amount of pyridine, and the mixture was stirred at room temperature under a nitrogen atmosphere to carry out an imidization reaction. After completion of the reaction, the mixture was cooled to room temperature, and the polymerization solution was added dropwise to excess water under high speed stirring for precipitation purification. The product was further purified with methanol and the following formula (Chemical formula 13, in which m = 0.5, n
= 0.5) to obtain a fluorine-containing polyimide resin copolymer having a repeating molecular structural unit.

[0045]

[Chemical 13]

Next, 14 parts by weight of a fluorine-containing polyimide composed of the repeating molecular structural unit represented by the chemical formula (13) was diluted, 86 parts by weight of NMP was added as an organic solvent, and the mixture was stirred at 100 ° C. for 6 hours. And dissolved. Then, it filtered and left still and deaerated sufficiently, and the film forming liquid was prepared. The film-forming solution was cast on a glass plate using an applicator with a width of 20 cm and a thickness of 300 μm, and the temperature was 11 ° C. for 1 hour, 150 ° C. for 3 hours, 200 ° C. for 3 hours, and further 200% under vacuum.
Heat treatment was carried out at 72 ° C. for 72 hours to obtain a homogeneous film made of a fluorine-containing polyimide resin having a thickness of 20-40 μm. Further, in the above polyamic acid solution preparation, in the diamine component, 2,4,
6-trimethyl-1,3-phenylenediamine (TMMPD) 0.0761mo
A fluorine-containing polyimide resin composed of a repeating molecular structural unit represented by the following formula (Formula 14), which is a constituent component of the above copolymer, was prepared in the same manner except that only l was used.

[0047]

[Chemical 14]

The free volume fraction of this fluorine-containing polyimide resin at 25 ° C. was 0189 when calculated in accordance with the equation (1). Therefore, the above-mentioned fluorine-containing polyimide resin copolymer satisfied the conditions of the present invention. Next, with respect to the obtained homogeneous film, at 25 ° C. and a supply pressure of 2 atm, propylene / propane 50/50 mol% mixed gas or at 25 ° C. and a supply pressure of 1.1 atm, 1,3-butadiene / n.
-Separation performance and permeation performance evaluation results in steady state when 50/50 mol% mixed gas of butane was supplied are summarized later in Table 1.
Shown in.

[Comparative Example 1] The same procedure as in Example 1 was carried out except that only the fluorine-containing polyimide resin having the repeating molecular structural unit represented by Chemical formula 14 prepared in Example 1 was used as the polyimide resin constituting the film. Similarly, a homogeneous film made of a fluorine-containing polyimide resin was obtained. The obtained fluorine-containing polyimide resin forming the homogeneous film did not satisfy the conditions of the present invention because it did not contain a —OH group. Next, for this homogeneous film, in the same manner as in Example 1, 25 ° C., supply pressure 2 at
Separation in steady state when 50/50 mol% 1,3-butadiene / n-butane mixed gas is supplied at 25 ° C and a supply pressure of 1.1 atm at m, m or propylene / propane 50/50 mol% mixed gas. The performance and transmission performance evaluation results are shown together in Table 1 below.

[0050]

[Table 1]

As shown in Table 1, the products of Examples of the present invention are
It was confirmed that the separation ability for specific hydrocarbons such as propylene and 1,3-butadiene was higher than that of the comparative product.

[0052]

EFFECTS OF THE INVENTION The present invention is to prepare a film from a copolymer of a fluorine-containing polyimide resin having a free volume fraction within a predetermined range at 25 ° C. and a fluorine-containing polyimide resin containing at least one —OH group. in the carbon of the hydrocarbons mixture
A membrane having a high degree of separation from hydrocarbons having a number of 3 or more can be obtained, and by using this membrane , hydrocarbons having a carbon number of 3 or more, which are practically satisfactory in terms of performance and cost, can be obtained. A method of separating the above hydrocarbon from the mixture containing can be provided.

─────────────────────────────────────────────────── --- Continuation of the front page (72) Kenichi Ikeda Inventor Kenichi Ikeda 1-2-1, Shimohozumi, Ibaraki-shi, Osaka, Nitto Denko Corporation (56) Reference JP-A-8-294616 (JP, A) JP-A-9-75679 (JP, A) JP-A-10-180063 (JP, A) JP-A-9-898 (JP, A) JP-A-9-896 (JP, A) JP-A-8-173779 (JP , A) JP-A-6-142433 (JP, A) JP-A-9-897 (JP, A) JP-A-8-173778 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) (Name) B01D 53/22 B01D 67/00-71/82 510

Claims (3)

(57) [Claims] 1. A mixture containing a hydrocarbon having 3 or more carbon atoms has a free volume fraction of 0.180 to 0.2 at 25 ° C.
A fluorine-containing polyimide resin having a range of 20 and a fluorine-containing polyimide resin copolymer having at least one —OH group in a repeating molecular structural unit are brought into contact with one surface of a film as a main component, and through this film. , The carbon number is 3
A method for separating hydrocarbons which selectively permeates and separates the above hydrocarbons. 2. The method for separating hydrocarbons according to claim 1, wherein at least one —CF ₃ group is contained in the repeating molecular structural unit constituting the fluorine-containing polyimide resin. 3. A method for separating hydrocarbons according to claim 1 or 2 fluorine containing polyimide resin as a main component a repeating unit represented by the following formula (Formula 1). [Chemical 1] (However, A ₁ and A ₂ represent a tetravalent organic group consisting of an aromatic, alicyclic or aliphatic hydrocarbon group, and R ₁ and R ₂ are divalent aromatic, aliphatic or aliphatic hydrocarbons. Group or a divalent organic group in which these hydrocarbon groups are bonded by a divalent organic bonding group, and at least one of A ₁ and A ₂ is —CF ₃
An organic group having at least one group, and at least one of R ₁ and R ₂ is an organic group having at least one —OH group,
Indicates m + n = 1. )