JP3644629B2 - Separation method of hydrocarbons by separation membrane - Google Patents

Description

【０００７】
（但し、繰り返し単位構造内の主鎖部分にメタ結合を有し、Ａ ₁ とＡ ₂ は下記式（化１１）で表される４価の有機基を示し、Ｒ ₁ とＲ ₂ は下記式（化１２）〜（化１７）のいずれかで表される２価の有機基を示し、ｍ，ｎは正の自然数で重合度を示す。）
【０００８】
【化１１】

【０００９】
【化１２】

【００１０】
【化１３】

【００１１】
【化１４】

【００１２】
【化１５】

【００１３】
【化１６】

【００１４】
【化１７】

【００１５】
本発明においては、フッ素含有ポリイミド樹脂が、下記式（化１８）で表される繰り返し単位を主成分とすることが好ましい。
【００１６】
【化１８】

【００１７】
（但し、ｍは正の自然数で重合度を示す。）
【００１８】
【発明の実施の形態】
本発明者らは、特定炭化水素を含む炭化水素混合物を、フッ素含有ポリイミド樹脂から成る膜の一方の面に接触させ、この膜を通して、前記特定炭化水素を選択的に透過させ高度に分離する方法を見いだし、本発明に至ったものである。フッ素含有ポリイミドの多くは、耐熱性、気体分離性等に優れた膜分離材料として知られている。例えば、特開平５−７７４９号公報、米国特許第３８２２２０２号、米国特許第３８９９３０９号、米国特許第４５３２０４１号、米国特許第４６４５８２４号、米国特許第４７０５５４０号、米国特許第４７１７３９３号、米国特許第４７１７３９４号、米国特許第４８３８９００号、米国特許第４８９７０９２号、米国特許第４９３２９８２号、米国特許第４９２９４０５号、米国特許第４９８１４９７号、米国特許第５０４２９９２号各明細書等には含フッ素系の芳香族ポリイミドが開示されている。
【００１９】
本発明に用いる膜を構成する樹脂は、不飽和炭化水素、芳香族炭化水素等の特定炭化水素の分離性能に寄与する樹脂であって、そのガラス転位温度が２００〜２８０℃の範囲にあり、且つ繰り返し分子単位構造内の主鎖部分にメタ結合を有し、前記式（化１０）で表される繰り返し単位を主成分とするフッ素含有ポリイミド樹脂を主成分とする。ここで主成分とは、７０モル％以上をいう。また好ましい重量平均分子量は20,000〜800,000の範囲である。
【００２０】
均質ポリマーへの気体の透過性は、気体のポリマーへの溶解過程とポリマー中での拡散過程により決定され、具体的には、ポリマーへの溶解度係数とポリマー中における気体の拡散係数の積で表されることがよく知られている。このため、混合気体を溶解性あるいは拡散性の差を利用して、個別成分に分離することが可能となる。炭素数Ｃ３以上の炭化水素を透過させる場合は、一般的に膜素材高分子が透過成分により可塑化され、その結果、高分子の自由体積が増大し、拡散性の向上がみられる。この際、ポリイミドなどのガラス状高分子の場合、過度に可塑化されると、自由体積の増大率が大きくなり、その結果、特定透過成分を分子サイズの違いを利用して篩い分けるといった分離機能が低下する。このような過度の可塑化はポリイミドの熱運動性や３次元の分子構造に強く関係している。本発明者らは、この点に着眼し、鋭意検討した結果、ガラス転位温度が２００〜２８０℃の範囲にあり、且つ繰り返し分子単位構造内の主鎖部分にメタ結合を有し、前記式（化１０）で表される繰り返し単位を主成分とするフッ素含有ポリイミドを主成分とする樹脂を膜素材として用いた場合に、炭化水素による極端な可塑化を抑えることができ、特定炭化水素に対して高い分離能を有する分離膜が得られることを見いだした。
【００２１】
本発明において、ガラス転位温度とは、一般的な走査型示差熱量測定法に準じて測定される。上述のフッ素含有ポリイミド樹脂にガラス転位温度が２００℃未満のものを用いると、炭化水素の溶解に有効なフッ素含有ポリイミドの未緩和体積が過度に減少し、その結果、炭化水素の透過性が過度に低下する恐れがあるため好ましくない。また、ガラス転位温度が２８０℃を超えると、分子鎖の剛直性が過度に増大し、その結果、分子鎖充填性が悪くなり、炭化水素により過度に可塑化しやすくなる恐れがあるため好ましくない。また、上述の主鎖へのメタ結合の導入は、フッ素含有ポリイミド分子の屈曲性を増大させ、その結果、樹脂形成の際に分子鎖の高率的な充填が可能となると考えられ、炭化水素により可塑化しにくくなる傾向があるため好ましい。
【００２２】
本発明に用いられるフッ素合有ポリイミド樹脂は５０モル％以下であればフッ素合有ポリイミド樹脂以外のポリスルホン、ポリエーテルスルホンなどのポリマーとの共重合体、もしくは混合物であってもよい。
【００２３】
本発明で用いられるフッ素合有ポリイミド樹脂は、テトラカルボン酸二無水物とジアミン成分を用いて、例えば、米国特許第３９５９３５０号明細書に記載されているような公知の重合方法で得られる。例えば、テトラカルボン酸二無水物とジアミン化合物をほぼ等モル量を用い、極性溶媒中、約８０℃以下の温度、好ましくは、０〜６０℃で攪拌し、ポリアミック酸を重合する。ここで用いられる極性溶媒は特に限定されないが、Ｎ一メチルピロリドン、ピリジン、ジメチルアセトアミド、ジメチルホルムアミド、ジメチルスルホキシド、テトラメチル尿素、フェノール、クレゾールなどが好適に用いられる。
【００２４】
得られたポリアミック酸の極性溶媒溶液にトリメチルアミン、トリエチルアミン、ピリジン等の第３級アミン化合物、無水酢酸、塩化チオニル、カルボジイミドなどのイミド化促進剤を添加し、５〜１５０℃の温度で攪拌し、イミド化する。イミド化反応を行う際、イミド化促進剤を添加することなく、上記ポリアミック酸溶液を１００〜４００℃、好ましくは、１２０〜３００℃で加熱してイミド化してもよい。
【００２５】
イミド化反応後、重合時の極性溶媒やイミド化促進剤を除去するために、多量のアセトン、アルコールまたは水等の溶液に滴下し精製することにより、膜材料として好適なポリイミド樹脂が得られる。
【００２６】
また、イミド化促進剤を添加することなく、イミド化反応を行う場合は、ポリアミック酸溶液を多量のアセトン、またはアルコール等の溶液に滴下して得られたポリアミック酸粉末やポリアミック酸溶液から溶媒を蒸発させて得られたポリアミック酸の固体（蒸発の際、沈殿剤等を加えてポリアミック酸粉末を形成させ、濾別してもよい）を１００〜４００℃に加熱してイミド化することにより、膜材料として好適なポリイミド樹脂が得られる。
【００２７】
本発明で用いられる膜の製膜法は、特に限定されないが、例えば、上述のフッ素含有ポリイミド樹脂を適正な溶媒に溶解して製膜液を調製し、製膜液をガラス、金属、プラスチック等の平滑な表面を有する平板や管、あるいは、不織布等の多孔質支持体上に一定の厚さで流延し、次いで、加熱処理することにより得る方法（乾式製膜法）、および、上記製膜液をガラス、金属、プラスチック等の平板や管、あるいは、織布、不織布等の多孔質支持体上に一定の厚さで流延し、凝固液（製膜液中のフッ素含有ポリイミド樹脂は溶解しないが、製膜液中の有機溶媒と相溶性のある溶媒）に浸漬するか、または、製膜液を同心円状の多重構造のノズルから押し出し、上記凝固液に浸漬して中空糸状非対称膜を調製し、その後、膜を乾燥する方法（湿式製膜法）をとることができる。
【００２８】
フッ素含有ポリイミド樹脂の溶媒としては、特に限定されないが、Ｎ−メチル−２−ピロリドン、ジメチルアセトアミド、ジメチルホルムアミド、ジメチルスルホキシド、ジエチレングリコールジメチルエーテル、１，２−ジメトキシメタン等が挙げられる。
【００２９】
製膜液のポリイミド溶液濃度は３〜４０重量％、好ましくは１０〜３０重量％である。また、製膜液を調整する場合に必要に応じて、膨潤剤、分散剤、増粘剤等を加えてもよい。製膜液を流延する手段としては、例えば、ドクターナイフ、ドクタープレート、アプリケーター等を利用することができる。
【００３０】
製膜液流延後の加熱処理は、製膜液中の溶媒を十分に除去できる温度で、且つポリイミド樹脂のガラス転移点以下であることが望ましい。
【００３１】
上記湿式製膜法において、上記有機溶媒を浸漬し除去する際に用いられる凝固液は用いるフッ素含有ポリイミド樹脂を溶解しないが、製膜液中の溶媒と相溶性を有する溶媒であれば、とくに限定されないが、水やエタノール、メタノール、イソプロピルアルコール等のアルコール類およびこららの混合液が用いられ、特に水が好適に用いられる。製膜液中の有機溶媒を浸漬除去する際の凝固液の温度は特に限定されないが、好ましくは０〜５０℃の温度で行われる。
【００３２】
また、本発明における膜の形状は特に限定されないが、チューブ状（中空糸状を含む）、平膜状のものが好適に用いられる。
【００３３】
【実施例】
以下に実施例を挙げて本発明を説明するが、本発明はこれらの実施例に限定されるものではない。
【００３４】
（実施例）
5,5’-2,2’-トリフルオロ-1-（トリフルオロメチル）エチリデン-ビス-1,3-イソベンゾフランジオン(6FDA)0.0761mo1と、3,3 ’ - ジアミノジフェニルメタン (33 ’ DDM)0.0761mo1および溶媒としてＮ-メチル-２-ピロリドン(NMP)を加え、窒素雰囲気下室温で攪拌し、ポリアミック酸溶液を調製した。この際、ポリアミック酸溶液は、ポリアミック酸10wt%以内とした。次いで、このポリアミック酸溶液に無水酢酸0.305mo1を少量のピリジンとともに添加し、窒素雰囲気下室温で攪拌し、イミド化反応を行った。反応終了後、室温まで冷却し、重合液を過剰量の水中に高速攪拌下、滴下し沈澱精製させた。さらにメタノールで精製し、下記式（化１９）で表される繰り返し分子構造単位から成るフッ素含有ポリイミド樹脂を得た。
【００３５】
【化１９】

【００３６】
（但し、ｍは正の自然数で重量平均分子量140,000）
次に、前記（化１９）で表される繰り返し分子構造単位から成るフッ素合有ポリイミド１８重量部を希釈し、有機溶媒としてＮＭＰを８２重量部を加え、１００℃で６時間攪拌し溶解した。その後、濾過し、静置して十分に脱泡し、製膜液を調製した。製膜液をアプリケータを用いガラス板上に、幅２０ｃｍ、厚さ３００μｍで流延し、１１０℃で１時間、１５０℃で３時間、２００℃で３時間、さらに真空下にて２００℃で７２時間加熱処理を施し、厚さ２０−４０μｍのフッ素合有ポリイミド樹脂より成る均質膜を得た。このフッ素含有ポリイミド樹脂は繰り返し分子単位構造内の主鎖部分にメタ結合を有するもので、また、１０℃／分の昇温速度で走査型示差熱量測定をおこなったところ、ガラス転位温度は２１７℃であった。したがって、上記フッ素含有ポリイミド樹脂は、本発明の条件を満足するものであった。次に、得られた均質膜について、２５℃、供給圧力２ａｔｍにて、プロピレン／プロパン５０／５０ｍｏｌ％混合ガスを供給した時の定常状態における分離性能、透過性能評価結果を後にまとめて表１に示す。
【００３７】
（比較例）
実施例において、3,3'- ジアミノジフェニルメタン (33'DDM)のかわりに、4,4’-ジアミノジフェニルメタン(44’DDM)を用いた以外は同様にして下記式（化２０）で表される繰り返し分子単位構造から成るフッ素含有ポリイミド樹脂による均質膜を得た。
【００３８】
【化２０】

【００３９】
（但し、ｍは正の自然数で重量平均分子量120,000）
このフッ素含有ポリイミド樹脂について１０℃／分の昇温速度で走査型示差熱量測定を実施したところ、ガラス転位温度は２８６℃であった。したがって、このフッ素含有ポリイミド樹脂は本発明の条件を満足するものではなかった。次に、この均質膜について、実施例と同様にして、２５℃、供給圧力２ａｔｍにて、プロピレン／プロパン５０／５０ｍｏｌ％混合ガスを供給した時の定常状態における分離性能、透過性能評価結果を後にまとめて表１に示す。
【００４０】

（備考）
ＰＣ₃Ｈ₆：２５℃、２ａｔｍにて、プロパン／プロピレン50/50 mol％混合ガスを供給した場合のプロピレンの透過係数[cm³(STP)cm/cm² s cmHg]
α（ＰＣ₃Ｈ₆／ＰＣ₃Ｈ₈）：２５℃、２ａｔｍにて、プロパン／プロピレン50/50 mol％混合ガスを供給した場合のプロピレンとプロパンの分離係数［−］
【００４１】
表１に示した通り、本発明の実施例品は、比較例品と比べて、プロピレンの分離係数が高く、特定炭化水素に対する分離能が高いことが確認された。
【００４２】
【発明の効果】
本発明は、ガラス転位温度が所定範囲内にあり、主鎖にメタ結合を有するフッ素含有ポリイミド樹脂から膜を調製することで、炭化水素混合物中の特定炭化水素に対して高度な分離能を有する膜が得られ、この膜を用いて、性能面、コスト面においても実用的に満足しうる特定炭化水素を含む炭化水素混合物からの前記特定炭化水素の分離方法を提供することができる。[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for separating specific hydrocarbons from a mixture containing hydrocarbons. 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 the petroleum refining industry, petrochemical industry and the like.
[0002]
[Prior art]
In the petroleum refining industry and petrochemical industry, the method of separating specific hydrocarbons from hydrocarbon-containing mixtures using membranes has been studied for many years from the scientific and economic viewpoints. Has been reported. For example, U.S. Pat. No. 2,958,656 supplies a hydrocarbon mixture, i.e., naphtha, to a non-porous cellulose ether membrane, allowing a portion of the membrane to permeate and from the permeate side of the membrane using a cleaning gas or cleaning liquid. A method of separating unsaturated compounds, saturated compounds and aromatic compounds by removing permeate is disclosed. U.S. Pat. No. 2,930,754 selectively permeates a portion of a mixture distilling at a temperature in the boiling range of gasoline through a non-porous cellulose ether membrane, and the permeate is washed with a cleaning gas or a cleaning liquid. A method for separating hydrocarbons such as unsaturated hydrocarbons and aromatic compounds by removing them from the permeate side of the membrane is disclosed.
[0003]
[Problems to be solved by the invention]
However, according to the conventionally proposed membrane separation method using a membrane, most of the separation membranes are not yet sufficiently resistant to aromatic hydrocarbons, unsaturated hydrocarbons, saturated hydrocarbons, etc., or the separation ability for specific hydrocarbons, or In addition, a cleaning gas or a cleaning liquid for removing or recovering the hydrocarbons that have passed through the membrane is necessary, and the apparatus becomes complicated, and there is a problem in terms of economy. For this reason, the membrane separation method for specific hydrocarbons from a mixture containing hydrocarbons is not widely used on an industrial scale because of performance, workability, and cost.
[0004]
The present invention has been made in order to solve these problems, and has high resistance to hydrocarbons. For specific unsaturated hydrocarbons, aromatic hydrocarbons and the like in a mixture containing hydrocarbons. An object of the present invention is to provide a membrane separation method for specific hydrocarbons from a hydrocarbon-containing mixture that has high separation performance and is practically satisfactory both in terms of performance and cost.
[0005]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the hydrocarbon separation method of the present invention comprises a hydrocarbon mixture containing a specific hydrocarbon having a glass transition temperature in the range of 200 to 280 ° C. and a main structure in a repeating molecular unit structure. The fluorine-containing polyimide resin is a method in which the specific hydrocarbon is selectively permeated and separated through contact with one surface of a film mainly composed of a fluorine-containing polyimide resin having a meta bond in a chain portion. Is characterized by having as a main component a repeating unit represented by the following formula (Formula 10).
[0006]
[Chemical Formula 10]

[0007]
(However, it has a meta bond in the main chain portion in the repeating unit structure, A ₁ and A ₂ represent a tetravalent organic group represented by the following formula (Chemical Formula 11), and R ₁ and R ₂ represent the following formula: The divalent organic group represented by any one of (Chemical Formula 12) to (Chemical Formula 17) is shown, and m and n represent the degree of polymerization as a positive natural number.)
[0008]
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[0009]
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[0010]
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[0011]
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[0012]
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[0013]
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[0014]
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[0015]
In the present invention, the fluorine-containing polyimide resin preferably contains a repeating unit represented by the following formula (Formula 18) as a main component.
[0016]
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[0017]
(However, m is a positive natural number and indicates the degree of polymerization.)
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention contact a hydrocarbon mixture containing a specific hydrocarbon with one surface of a membrane made of a fluorine-containing polyimide resin, and selectively permeate the specific hydrocarbon through the membrane to highly separate the mixture. As a result, the present invention has been achieved. Many of the fluorine-containing polyimides are known as membrane separation materials having excellent heat resistance, gas separation properties, and the like. For example, JP-A-5-7749, US Pat. No. 3,822,202, US Pat. No. 3,899,309, US Pat. No. 4,320,041, US Pat. No. 4,645,824, US Pat. , U.S. Pat. No. 4,838,900, U.S. Pat. No. 4,899,092, U.S. Pat. No. 4,932,982, U.S. Pat. Is disclosed.
[0019]
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 in the range of 200 to 280 ° C. and repeatedly have a meta bond in the main chain portion of the molecular units within the structure, as a main component fluorine-containing polyimide resin consisting mainly of repeating units represented by the formula (formula 10). Here, the main component means 70 mol% or more. A preferred weight average molecular weight is in the range of 20,000 to 800,000.
[0020]
The permeability of a gas to a homogeneous polymer is determined by the dissolution process of the gas 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 For this reason, it is possible to separate the mixed gas into individual components using the difference in solubility or diffusivity. When permeating hydrocarbons having C3 or more carbon atoms, the membrane material polymer is generally plasticized by the permeation component, resulting in an increase in the free volume of the polymer and an improvement in diffusibility. At this time, in the case of a glassy polymer such as polyimide, if it is excessively plasticized, the rate of increase in the free volume increases, and as a result, the separation function of sieving specific permeation components using the difference in molecular size Decreases. Such excessive plasticization is strongly related to the thermal mobility and three-dimensional molecular structure of polyimide. The present inventors have paid attention to this point, a result of intensive studies, the range of the glass transition temperature of 200 to 280 ° C., have a meta bond in the main chain portion of and repeating the molecular unit structure, the formula ( When a resin mainly composed of a fluorine-containing polyimide having a repeating unit represented by chemical formula 10) as a main component is used as a membrane material, extreme plasticization by hydrocarbons can be suppressed, and for specific hydrocarbons It has been found that a separation membrane having high separation performance can be obtained.
[0021]
In the present invention, the glass transition temperature is measured according to a general scanning differential calorimetry. When the above-mentioned fluorine-containing polyimide resin having a glass transition temperature of less than 200 ° C. is used, the unrelaxed volume of the fluorine-containing polyimide effective for dissolving hydrocarbons is excessively reduced, resulting in excessive hydrocarbon permeability. It is not preferable because it may be lowered. On the other hand, if the glass transition temperature exceeds 280 ° C., the rigidity of the molecular chain is excessively increased. As a result, the molecular chain filling property is deteriorated, and there is a possibility that the hydrocarbon is likely to be excessively plasticized. In addition, the introduction of a meta bond to the main chain described above increases the flexibility of the fluorine-containing polyimide molecule, and as a result, it is considered that a high-efficiency filling of the molecular chain is possible during resin formation. Is preferred because it tends to be difficult to plasticize.
[0022]
The fluorine-containing polyimide resin used in the present invention may be a copolymer with a polymer such as polysulfone and polyethersulfone other than the fluorine-containing polyimide resin, or a mixture as long as it is 50 mol% or less.
[0023]
The fluorine-containing polyimide resin used in the present invention is obtained by a known polymerization method as described in, for example, US Pat. No. 3,959,350, using a tetracarboxylic dianhydride and a diamine component. 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 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.
[0024]
To the obtained polar solvent solution of polyamic acid, a tertiary amine compound such as trimethylamine, triethylamine and pyridine, an imidization accelerator such as acetic anhydride, thionyl chloride, carbodiimide, and the like, stirred at a temperature of 5 to 150 ° C., Imidize. When performing the imidation reaction, the polyamic acid solution may be imidized by heating at 100 to 400 ° C, preferably 120 to 300 ° C, without adding an imidization accelerator.
[0025]
After the imidation reaction, a polyimide resin suitable as a film material can be obtained by dripping and purifying a large amount of acetone, alcohol, water or the like in order to remove a polar solvent or imidization accelerator during polymerization.
[0026]
In addition, when an imidation reaction is performed without adding an imidization accelerator, a solvent is removed from a polyamic acid powder or a polyamic acid solution obtained by dripping a polyamic acid solution into a large amount of acetone or an alcohol solution. Membrane material is obtained by heating to 100-400 ° C. to imidize a solid of polyamic acid obtained by evaporation (a precipitant etc. may be added during evaporation to form a polyamic acid powder, which may be filtered off). A suitable polyimide resin can be obtained.
[0027]
The film forming method of the film used in the present invention is not particularly limited. For example, a film forming solution is prepared by dissolving the above-described fluorine-containing polyimide resin in an appropriate solvent, and the film forming solution is made of glass, metal, plastic, or the like. A method (dry film forming method) obtained by casting at a constant thickness on a flat support or tube having a smooth surface, a porous support such as a nonwoven fabric, and then heat-treating, The membrane liquid is cast at a certain thickness on a flat support such as glass, metal, plastic, or a porous support such as woven fabric or non-woven fabric, and a coagulation liquid (the fluorine-containing polyimide resin in the film-forming solution is A non-dissolvable but compatible solvent with an organic solvent in the membrane-forming solution), or the membrane-forming solution is extruded from a concentric multiple-structure nozzle and immersed in the coagulation solution to form a hollow fiber asymmetric membrane How to prepare and then dry the membrane (wet It is possible to take a film-forming method).
[0028]
The solvent for the fluorine-containing polyimide resin is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, diethylene glycol dimethyl ether, and 1,2-dimethoxymethane.
[0029]
The polyimide solution concentration of the film-forming solution is 3 to 40% by weight, preferably 10 to 30% by weight. Moreover, when adjusting a film forming liquid, you may add a swelling agent, a dispersing agent, a thickener, etc. as needed. As means for casting the film-forming solution, for example, a doctor knife, a doctor plate, an applicator, or the like can be used.
[0030]
The heat treatment after casting the film-forming solution is desirably at a temperature at which the solvent in the film-forming solution can be sufficiently removed and below the glass transition point of the polyimide resin.
[0031]
In the wet film forming method, the coagulating liquid used for immersing and removing the organic solvent does not dissolve the fluorine-containing polyimide resin used, but is particularly limited as long as it is compatible with the solvent in the film forming liquid. Although not used, water, alcohols such as ethanol, methanol, isopropyl alcohol and the like and mixed liquids thereof are used, and water is particularly preferably used. Although 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, it is preferably performed at a temperature of 0 to 50 ° C.
[0032]
In addition, the shape of the membrane in the present invention is not particularly limited, but a tube shape (including a hollow fiber shape) and a flat membrane shape are preferably used.
[0033]
【Example】
EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
[0034]
( Example )
Bis-1,3-isobenzofurandione (6FDA) 0.0761mo1, 3,3 - 5,5' -2,2'- trifluoro-1- (trifluoromethyl) ethylidene '- diaminodiphenylmethane (33' DDM) 0.0761 mol and N-methyl-2-pyrrolidone (NMP) as a solvent were added and 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. Subsequently, acetic anhydride 0.305mo1 was added to this polyamic acid solution together with a small amount of pyridine, and the mixture was stirred at room temperature in a nitrogen atmosphere to carry out an imidization reaction. After completion of the reaction, the reaction solution was cooled to room temperature, and the polymerization solution was dropped into an excess amount of water with high-speed stirring , and purified by precipitation. Furthermore, it refine | purified with methanol and obtained the fluorine-containing polyimide resin which consists of a repeating molecular structural unit represented by a following formula (Formula 19 ).
[0035]
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[0036]
(However, m is a positive natural number and a weight average molecular weight of 140,000 )
Next, 18 parts by weight of the fluorine-containing polyimide composed of the repeating molecular structural unit represented by the above ( Chemical Formula 19 ) was diluted, 82 parts by weight of NMP was added as an organic solvent, and the mixture was dissolved by stirring at 100 ° C. for 6 hours. Then, it filtered, left still and fully degas | foamed and prepared the film forming liquid. The film-forming solution is cast on a glass plate with an applicator at a width of 20 cm and a thickness of 300 μm, 110 ° C. for 1 hour, 150 ° C. for 3 hours, 200 ° C. for 3 hours, and further under vacuum at 200 ° C. 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, and when the scanning differential calorimetry was performed at a temperature rising rate of 10 ° C./min, the glass transition temperature was 217 ° C. Met. Therefore, the fluorine-containing polyimide resin satisfied the conditions of the present invention. Next, for 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 is supplied at 25 ° C. and a supply pressure of 2 atm are summarized in Table 1 later. Show.
[0037]
( Comparative example )
In the examples , the following formula ( Chemical Formula 20 ) is similarly used except that 4,4′-diaminodiphenylmethane (44′DDM) is used instead of 3,3′ -diaminodiphenylmethane (33′DDM). A homogeneous film made of a fluorine-containing polyimide resin having a repeating molecular unit structure was obtained.
[0038]
Embedded image

[0039]
(Where m is a positive natural number and a weight average molecular weight of 120,000)
When this fluorine-containing polyimide resin was subjected to scanning differential calorimetry at a rate of temperature increase of 10 ° C./min, the glass transition temperature was 286 ° C. Therefore, this fluorine-containing polyimide resin did not satisfy the conditions of the present invention. Next, with respect to this homogeneous membrane, the results of evaluation of separation performance and permeation performance in the steady state when propylene / propane 50/50 mol% mixed gas was supplied at 25 ° C. and supply pressure of 2 atm in the same manner as in the examples are described later. These are summarized in Table 1.
[0040]

(Remarks)
PC ₃ H ₆ : Propylene permeability coefficient [cm ³ (STP) cm / cm ² s cmHg] when propane / propylene 50/50 mol% mixed gas is supplied at 25 ° C. and 2 atm
α (PC ₃ H ₆ / PC ₃ H ₈ ): Propylene / propane separation factor [−] when propane / propylene 50/50 mol% mixed gas is supplied at 25 ° C. and 2 atm
[0041]
As shown in Table 1, it was confirmed that the example product of the present invention had a higher propylene separation factor and higher separation ability for specific hydrocarbons than the comparative product.
[0042]
【The invention's effect】
The present invention has a high resolution for a specific hydrocarbon in a hydrocarbon mixture by preparing a membrane from a fluorine-containing polyimide resin having a glass transition temperature within a predetermined range and having a meta bond in the main chain. A membrane is obtained, and by using this membrane, it is possible to provide a method for separating the specific hydrocarbon from a hydrocarbon mixture containing the specific hydrocarbon that is practically satisfactory in terms of performance and cost.

Claims (4)

One of the films of a hydrocarbon mixture containing a specific hydrocarbon , the glass transition temperature of which is in the range of 200 to 280 ° C., and the main component is a fluorine-containing polyimide resin having a meta bond in the main chain portion in the repeating molecular unit structure. It is brought into contact with the surface, through the membrane, a method of separating by selectively transmitting the particular hydrocarbon, the fluorine-containing polyimide resin, as a main component a repeating unit represented by the following formula (formula 1) Method.

(However, the main chain portion in the repeating unit structure has a meta bond, A ₁ and A ₂ represent a tetravalent organic group represented by the following formula (Chemical Formula 2), and R ₁ and R ₂ represent the following formula: The divalent organic group represented by any one of (Chemical Formula 3) to (Chemical Formula 8) is shown, and m and n are positive natural numbers indicating the degree of polymerization.)

The method according to claim 1, wherein the fluorine-containing polyimide resin contains a repeating unit represented by the following formula (Chemical Formula 9) as a main component.

(However, m is a positive natural number and indicates the degree of polymerization.) It is a film | membrane used for the method of Claim 1, Comprising: The glass transition temperature exists in the range of 200-280 degreeC, and the fluorine-containing polyimide resin which has a meta bond in the principal chain part in a repeating molecular unit structure is a main component. The fluorine-containing polyimide resin is a film containing a repeating unit represented by the formula (Formula 1) as a main component. It is a film | membrane used for the method of Claim 2, Comprising: The glass transition temperature exists in the range of 200-280 degreeC, and the fluorine-containing polyimide resin which has a meta bond in the principal chain part in a repeating molecular unit structure is a main component. The fluorine-containing polyimide resin is a film containing a repeating unit represented by the formula (Chemical Formula 9) as a main component.