JP2004074026A - Gas adsorbent and gas separation apparatus and gas storage apparatus using the gas adsorbent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas adsorbent having excellent characteristics compared to a conventional gas adsorbent. <P>SOLUTION: The gas adsorbent comprises a metal complex showing a hysteresis loop of the absorption and desorption isothermal curves for at least one kind of gas and having ≥0.2 the total number of hydrogen bonds when the total number of the coordinate bonds, covalent bonds, ion bonds and hydrogen bonds is represented as 1. <P>COPYRIGHT: (C)2004,JPO

Description

【００２６】
で表される金属錯体が好ましい。前記式（１）において、Ｍは金属原子であり、銅、コバルト、ニッケル、亜鉛、鉄などを挙げることができる。前記式（１）において、Ａは配位子であり、複数存在するＡは、同一であってもよく異なっていてもよい。配位子Ａとしては、窒素原子を有する芳香族化合物の基が挙げられる。窒素原子を有する芳香族化合物としては、例えば、ピラジン、４，４’−ビピリジン、トランス−１，２−ビス（４−ピリジル）エチレン、１，４−ジシアノベンゼン、４，４−ジシアノビフェニル、１，２−ジシアノエチレン、１，４−ビス（４−ピリジル）ベンゼンなどが挙げられる。また、配位子Ａとして、ＢＦ_４、ＰＦ_６、Ｃｌ、Ｂｒ、ＣＦ_３ＳＯ_３、ＣＨ_３Ｃ_６Ｈ_４ＳＯ_３、およびＨ_２Ｏからなる群より選択される１種以上が含まれていてもよい。ただし、これらに限定されるものではない。これらの配位子が組み合わさった複合配位子であってもよい。また、窒素原子を有する芳香族化合物の基とＢＦ_４など化合物との双方が配位子Ａとして含まれていても勿論よい。前記式（１）において、ｎはＡ配位数であり、具体的には、ｎは４、５、６などである。
【００２７】
本発明のガス吸着材のガス吸着量や所定のガスに対する選択性を向上させるためには、金属錯体に用いられる金属イオンや配位子の種類を選択することが有効である。特に、配位子における配位原子の原子間距離を制御することが有効であると考えられる。具体的には、配位子として、下記式（２）：
【００２８】
【化４】

【００２９】
で表される化合物を配位子として使い分けて、本発明のガス吸着材の吸着特性を制御してもよい。式（２）において、Ｌは、窒素原子を有する芳香族化合物の基であり、２つ存在するＬは、同一であっても異なっていてもよい。窒素原子を有する芳香族化合物としては、アニリン、ピリジン、ピリミジン、キノリン、アクリジンなどが挙げられる。また、式（１）において、Ｓは、脂肪族炭化水素の二価の基、芳香族炭化水素の二価の基、−ＮＨ−、−Ｏ−、−Ｃ（＝Ｏ）Ｏ−、−ＳＯ−、または−ＳＯ_２−である。脂肪族炭化水素は、飽和していてもよく、不飽和であってもよい。また、直鎖、分岐、環状のいずれの形状であってもよい。脂肪族炭化水素の具体例としては、メタン、エタン、プロパン、ブタン、シクロブタン、ｉ−ブタン、ペンタン、シクロペンタン、ヘキサン、シクロヘキサン、エチレン、プロピレンなどが挙げられる。芳香族炭化水素の具体例としては、ベンゼン、ナフタレン、アントラセンなどが挙げられる。ただし、Ｓを選択するに際しては、式（１）で表される配位子の配位が阻害されないように留意する必要がある。
【００３０】
また、同じ成分であっても、合成後に１００〜６００℃に予熱することによって、ヒステリシスループの形状を変えることも可能である。
【００３１】
本発明のガス吸着材の具体例としては、［Ｃｕ（ｂｐｙ）（ＢＦ_４）_２（Ｈ_２Ｏ）_２・（ｂｐｙ）］_ｎ（式中、ｂｐｙは４，４’−ビピリジンを表す。以下同じ。）や、［Ｃｕ（ｂｐｙ）（ＢＦ_４）_２（Ｈ_２Ｏ）_４・（ｂｐｙ）］_ｎなどを挙げることができる。
【００３２】
［ガス吸着材の製造］
ガス吸着材の調製方法はガス吸着材の種類によって異なるものであり、一義的に決定できるものではないが、ここでは、［Ｃｕ（ｂｐｙ）（ＢＦ_４）_２（Ｈ_２Ｏ）_２・（ｂｐｙ）］_ｎを合成する場合を例にとり説明する。
【００３３】
まず、４，４’−ｂｉｐｙｒｉｄｉｎｅ（以下ｂｐｙと略記）のアセトニトリル溶液を還流しながら、銅（ＩＩ）テトラフルオロボレート水和物を含む水溶液を添加する。生じた析出物を濾過し、ジエチルエーテルの蒸気を、窒素流を用いて母液中に拡散させ、母液を室温で数日間保存する。続いて、濾過により析出物を得て、減圧下で数時間乾燥させる。このような作業により、目的物を得ることができる。しかしながら、上記方法に限定されるものでは勿論なく、各種方法を用いて合成してもよいことは言うまでもない。
【００３４】
［ガス吸着材の利用用途］
本発明のガス吸着材は、ガスの吸脱着に関する特殊な性質を活用して各種用途に適用することができる。例えば、圧力スイング吸着方式（以下「ＰＳＡ方式」と略記）のガス分離装置における吸着材に適用した場合にあっては、本発明のガス吸着材の特性を活かして、非常に効率良いガス分離が可能である。また、圧力変化に要する時間を短縮でき、省エネルギーにも寄与する。さらに、ガス分離装置の小型化にも寄与しうるため、高純度ガスを製品として販売する際のコスト競争力を高めることができることは勿論、自社工場内部で高純度ガスを用いる場合であっても、高純度ガスを必要とする設備に要するコストを削減できるため、結局最終製品の製造コストを削減する効果を有する。
【００３５】
本発明のガス吸着材の他の用途としては、ガス貯蔵装置が挙げられる。本発明のガス吸着材をガス貯蔵装置（業務用ガスタンク、民生用ガスタンク、車両用燃料タンクなど）に適用した場合には、搬送中や保存中の圧力を劇的に低減させることが可能である。搬送時や保存中のガス圧力を減少させ得ることに起因する効果としては、形状自由度の向上がまず挙げられる。従来のガス貯蔵装置においては、保存中の圧力を維持しなくてはガス吸着量を高く維持できない。しかしながら、本発明のガス貯蔵装置においては、圧力を低下させても充分なガス吸着量を維持できる。このため、容器の耐圧性を低くすることができ、ガス貯蔵装置の形状をある程度自由に設計することができる。この効果は、例えば自動車などの車両用燃料ガスタンクとして本発明のガス貯蔵装置を用いた場合には絶大である。燃料タンクとして本発明のガス貯蔵装置を用いた場合には、上述のように耐圧性に関する制約が緩くなるため、形状をある程度自由に設計できる。具体的には、車両における車輪やシートなどの形状にフィットするようにガス貯蔵装置の形状を調節することが可能となる。その結果、車両の小型化、荷物スペースの確保、車両の軽量化による燃費向上などの各種実利が得られる。
【００３６】
ガス分離装置やガス貯蔵装置に適用する場合における、容器形状や容器材質、ガスバルブの種類などに関しては、特に特別の装置を用いなくてもよく、ガス分離装置やガス貯蔵装置に用いられているものを用いることが可能である。ただし、各種装置の改良を排除するものではなく、いかなる装置を用いたとしても、本発明のガス吸着材を用いている限りにおいて、本発明の技術的範囲に包含されるものである。
【００３７】
【実施例】
＜実施例１＞
テトラフルオロホウ酸銅（ＩＩ）６水和物（Ａｌｄｒｉｃｈ社製；０．６７４ｇ）を純水（５０ｍｌ）に溶解させ、テトラフルオロホウ酸銅（ＩＩ）の０．０４Ｍ溶液（Ａ_１液）を準備した。別途、トランス−１，２−ビス（４−ピリジル）エチレン（関東化学株式会社製特級；０．７２９ｇ、以下「ｔ−ｂｐａ」と略記）をアセトニトリル（１００ｍｌ）に溶解させて、ｔ−ｂｐａの０．０４Ｍ溶液（Ｂ_１液）を準備した。３５７Ｋの水浴を用いて還流させながら、Ｂ_１液にＡ_１液を１時間かけて滴下した。滴下終了後、放冷し、５Ｃ濾紙を用いて、微量の粉体を濾取し、青色の濾液を得た。
【００３８】
この濾液を室温で撹拌しながら、ジエチルエーテル（５００ｍｌ）を１２時間かけて滴下し、さらに室温で４８時間撹拌した。ロータリーエバポレーターを使用して、エーテル及びアセトニトリルを実質的に留去し、残留物を濾過することで、淡青色粉体を得た。この粉体を１０^−３Ｐａ以下の減圧下で乾燥し、本発明のガス吸着材である［Ｃｕ（ｔ−ｂｐａ）（ＢＦ_４）_２（Ｈ_２Ｏ）_２（ｔ−ｂｐａ）］_ｎ（０．４１７ｇ）を得た。
【００３９】
得られたガス吸着材の７７Ｋでの窒素吸着特性を調査した。測定には、ＢＥＴ自動吸着装置（日本ベル株式会社製）を用い、測定に先立って試料を３７３Ｋで３時間真空熱処理して、吸着サイトに予め吸着していたゲスト分子を脱離させた。約０．０１ＭＰａまでは窒素の吸着は観測されず、０．０１ＭＰａを超えるあたりで急激な吸着量の増加が確認された。
【００４０】
また、得られたガス吸着材の室温での二酸化炭素吸着特性を調査した。測定方法は、窒素吸着測定の場合と同様にした。約０．０４ＭＰａまでは二酸化炭素の吸着は観測されず、０．０４ＭＰａを超えるあたりで急激な吸着量の増加が確認された。また、脱着に際しては、約０．０３ＭＰａまでの脱着量は僅かであったのに対して、０．０２ＭＰａにさしかかるあたりで急激な吸着量の減少が確認された。
【００４１】
さらに、得られたガス吸着材の室温でのメタン吸着特性を調査した。試料は、測定に先立って３７３Ｋで３時間真空熱処理して、吸着サイトに予め吸着していたゲスト分子を脱離させた。約４ＭＰａまではメタンの吸着は観測されず、５ＭＰａにさしかかるあたりで急激な吸着量の増加が確認された。また、脱着に際しては、約３ＭＰａまでの脱着量は僅かであったのに対して、３ＭＰａを下回ったあたりで急激な吸着量の減少が確認された。メタンガスの吸着量の最大値は、ガス吸着材１ｃｍ^３あたり１６５ｃｍ^３（Ｎｏｒｍａｌ）であった。また、吸脱着を３サイクル繰り返したが、ヒステリシスループには殆ど変化が見られなかった。
【００４２】
＜実施例２＞
トリフルオロメタンスルホン酸銅（ＩＩ）６水和物（関東化学株式会社製；０．７２３ｇ、以下トリフルオロメタンスルホン酸銅（ＩＩ）を「Ｃｕ（ＯＴｆ）_２」と略記）を純水（５０ｍｌ）に溶解させ、Ｃｕ（ＯＴｆ）_２の０．０４Ｍ溶液（Ａ_２液）を準備した。別途、４，４’−ビピリジン（和光純薬工業株式会社製特級；０．６２５ｇ）をアセトニトリル（５０ｍｌ）に溶解させて、４，４’−ビピリジンの０．０８Ｍ溶液（Ｂ_２液）を準備した。３５７Ｋの水浴を用いて還流させながら、Ｂ_２液にＡ_２液を１時間かけて滴下した。滴下終了後、放冷し、５Ｃ濾紙を用いて、微量の粉体を濾取し、青色の濾液を得た。
【００４３】
この濾液を室温で撹拌しながら、ジエチルエーテルの蒸気を、体積が１５０ｍｌになるまで窒素気流を用いて母液中に拡散させた。さらにこの溶液を室温で４８時間撹拌した。ロータリーエバポレーターを使用して、エーテル及びアセトニトリルをほとんど留去し、残留物を濾過することで淡青色粉体を得た。この粉体を１０^−３Ｐａ以下の減圧下で乾燥し、本発明のガス吸着材である［Ｃｕ（ｂｐｙ）（ＯＴｆ）_２（Ｈ_２Ｏ）_２（ｂｐｙ）］_ｎ（０．４１７ｇ）を得た。
【００４４】
実施例１に記載の方法に準拠して、得られたガス吸着材の７７Ｋでの窒素吸着特性を調査した。約０．０１ＭＰａまでは窒素の吸着は観測されず、０．０１ＭＰａを超えるあたりで急激な吸着量の増加が確認された。
【００４５】
また、実施例１に記載の方法に準拠して、得られたガス吸着材の室温での二酸化炭素吸着特性を調査した。約０．０４ＭＰａまでは二酸化炭素の吸着は観測されず、０．０４ＭＰａを超えるあたりで急激な吸着量の増加が確認された。また、脱着に際しては、約０．０３ＭＰａまでの脱着量は僅かであったのに対して、０．０２ＭＰａにさしかかるあたりで急激な吸着量の減少が確認された。
【００４６】
さらに、実施例１に記載の方法に準拠して、得られたガス吸着材の室温でのメタン吸着特性を調査した。約４ＭＰａまではメタンの吸着は観測されず、４．８ＭＰａにさしかかるあたりで急激な吸着量の増加が確認された。また、脱着に際しては、約３ＭＰａまでの脱着量は僅かであったのに対して、３ＭＰａを下回ったあたりで急激な吸着量の減少が確認された。メタンガスの吸着量の最大値は、ガス吸着材１ｃｍ^３あたり１５８ｃｍ^３（Ｎｏｒｍａｌ）であった。また、吸脱着を３サイクル繰り返したが、ヒステリシスループには殆ど変化が見られなかった。
【００４７】
＜実施例３＞
テトラフルオロホウ酸銅（ＩＩ）６水和物（Ａｌｄｒｉｃｈ社製；０．６７４ｇ）を純水（５０ｍｌ）に溶解させ、テトラフルオロホウ酸銅（ＩＩ）の０．０４Ｍ溶液（Ａ_３液）を準備した。別途、４，４’−ビピリジン（和光純薬工業株式会社製特級；０．６２５ｇ）をアセトニトリル（５０ｍｌ）に溶解させて、４，４’−ビピリジンの０．０８Ｍ溶液（Ｂ_３液）を準備した。３５７Ｋの水浴を用いて還流させながら、Ｂ_３液にＡ_３液を１時間かけて滴下した。これにより、僅かにグレーがかった析出物を含む溶液を得た。滴下終了後、副反応物である沈殿を濾過して除去した。
【００４８】
次に、撹拌しながら、ジエチルエーテルの蒸気を、体積が１５０ｍｌになるまで窒素気流を用いて母液中に拡散させた。続いて、この母液を２日間室温で保存し、３５３Ｋに加熱することによって溶媒（アセトニトリル、ジエチルエーテル）を蒸発させた。
【００４９】
残存物を濾過し、１０^−３Ｐａ以下の減圧下において４時間乾燥することによって水を除去し、本発明のガス吸着材である［Ｃｕ（ｂｐｙ）（ＢＦ_４）_２（Ｈ_２Ｏ）_２（ｂｐｙ）］_ｎ（０．３ｇ）を得た。
【００５０】
実施例１に記載の方法に準拠して、得られたガス吸着材の７７Ｋでの窒素吸着特性を調査した。約０．０１ＭＰａまでは窒素の吸着は観測されず、０．０１ＭＰａを超えるあたりで急激な吸着量の増加が確認された。
【００５１】
また、実施例１に記載の方法に準拠して、得られたガス吸着材の室温での二酸化炭素吸着特性を調査した。約０．０４ＭＰａまでは二酸化炭素の吸着は観測されず、０．０４ＭＰａを超えるあたりで急激な吸着量の増加が確認された。また、脱着に際しては、約０．０３ＭＰａまでの脱着量は僅かであったのに対して、０．０２ＭＰａにさしかかるあたりで急激な吸着量の減少が確認された。
【００５２】
さらに、実施例１に記載の方法に準拠して、得られたガス吸着材の室温でのメタン吸着特性を調査した。約４ＭＰａまではメタンの吸着は観測されず、４．５ＭＰａにさしかかるあたりで急激な吸着量の増加が確認された。また、脱着に際しては、約３ＭＰａまでの脱着量は僅かであったのに対して、３ＭＰａを下回ったあたりで急激な吸着量の減少が確認された。メタンガスの吸着量の最大値は、ガス吸着材１ｃｍ^３あたり１６０ｃｍ^３（Ｎｏｒｍａｌ）であった。また、吸脱着を３サイクル繰り返したが、ヒステリシスループには殆ど変化が見られなかった。
【００５３】
＜比較例１＞
活性炭粉末（関東化学株式会社製；０．５ｇ）について、実施例と同様にして、窒素、二酸化炭素、メタンについての吸脱着特性を評価した。吸脱着等温線はいずれもヒステリシスループを示さず、図２に示すようなタイプの吸脱着等温線を示した。メタンガスの吸着量の最大値は、活性炭１ｃｍ^３あたり１００ｃｍ^３（Ｎｏｒｍａｌ）であった。しかしながら、吸脱着を繰り返すと、３サイクル目におけるメタンガスの吸着量の最大値は、活性炭１ｃｍ^３あたり７０ｃｍ^３（Ｎｏｒｍａｌ）にまで減少した。
【００５４】
【発明の効果】
本発明のガス吸着材は、少なくとも１種のガスに関する吸脱着等温線がヒステリシスループを示すガス吸着材であるため、従来のガス吸着材と比べて非常に優れた吸着特性を有する。
【図面の簡単な説明】
【図１】本発明のガス吸着材のガス吸着量とガス圧力との関係を示すグラフである。
【図２】従来のガス吸着材のガス吸着量とガス圧力との関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas adsorbent, and more particularly to an adsorbent that exhibits a behavior in which an adsorption isotherm and a desorption isotherm relating to gas coincide with each other. These gas adsorbents are suitably used for gas storage devices and gas separation devices.
[0002]
[Prior art]
The gas adsorbent has a characteristic of storing a large amount of gas at a low pressure as compared with pressurized storage and liquefied storage. For this reason, in recent years, development of a gas storage device and a gas separation device using a gas adsorbent has been active.
[0003]
As the gas adsorbent, activated carbon, metal complex, and the like are known. Examples of the metal complex include, for example, [Co (4,4′-bpy) in JP-A-9-227571. _1.5 (NO ₃ ) ₂ ] _n A metal complex having the following composition has been proposed. In recent years, it has been found that fine carbons such as fullerenes and carbon nanotubes have a hydrogen gas storage capacity, and their practical application has been studied.
[0004]
However, conventionally proposed gas adsorbents are not sufficiently satisfactory in terms of gas adsorption amount and workability, and development of gas adsorbents having more excellent characteristics is desired.
[0005]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a gas adsorbent having superior characteristics as compared with conventional gas adsorbents. Another object of the present invention is to provide a gas storage device and a gas separation device each containing a gas adsorbent having the above characteristics, and a vehicle equipped with the gas storage device.
[0006]
[Means for Solving the Problems]
In the present invention, the adsorption / desorption isotherm regarding at least one gas exhibits a hysteresis loop, and when the total number of coordination bonds, covalent bonds, ionic bonds, and hydrogen bonds is 1, the total number of hydrogen bonds is 0.2. It is a gas adsorbent comprising the above metal complex.
[0007]
In the present invention, the adsorption / desorption isotherm regarding at least one gas exhibits a hysteresis loop, and the total number of coordination bonds, covalent bonds, ionic bonds, and hydrogen bonds is 1, compared to the energy of hydrogen bonds. It is a gas adsorbent made of a metal complex having a total number of bonds having a bond energy in the range of ± 30% of 0.2 or more.
[0008]
Since the gas adsorbent having such characteristics has completely different characteristics from conventionally known gas adsorbents, it exhibits a very special effect when applied to various applications. Good examples of applications include gas storage devices and gas separation devices.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the gas adsorbent of the present invention, the adsorption / desorption isotherm regarding at least one gas exhibits a hysteresis loop. That is, as shown in FIG. 1, the gas pressure-gas adsorption amount curve at the time of adsorption is different from the gas pressure-gas adsorption amount curve at the time of desorption.
[0010]
The peculiarity of the gas adsorbent in which the gas pressure-gas adsorption amount curve of the present invention exhibits a hysteresis loop will be described with reference to the drawings. FIG. 1 is a graph showing the relationship between gas pressure and gas adsorption amount in the gas adsorbent of the present invention. FIG. 2 is a graph showing the relationship between gas pressure and gas adsorption amount in a conventional adsorbent. In the figure, the horizontal axis indicates the gas pressure, and the vertical axis indicates the gas adsorption amount per unit mass of the adsorbent.
[0011]
In the conventional gas adsorbent, the gas adsorption amount increases as the gas pressure increases, and the pressure-adsorption amount curve during adsorption coincides with the pressure-adsorption amount curve during desorption (FIG. 2). For example, the amount of adsorption to be adsorbed on a conventional gas adsorbent is A ₁ The gas pressure is p ₁ It is necessary to pressurize until the adsorption amount is A ₁ To keep the pressure at p ₁ Need to hold on. In contrast, in the gas adsorbent of the present invention, the pressure-adsorption amount curve during gas adsorption shows a hysteresis loop (FIG. 1).
[0012]
The mechanism by which such a hysteresis loop appears has not yet been fully understood. As a possible mechanism, the ligand binding at the molecular level has a structure that sticks and leaves like a joint valve of a magnet, and only a molecule having a predetermined kinetic energy can pass through. Since the valve structure exists, the adsorption amount suddenly increases when a certain pressure is reached. Examples of the valve structure at the molecular level include a hydrogen bond with a loose bond force or a valve having a bond energy similar to that of a hydrogen bond, which can be attached and separated like a small magnet, and therefore has a predetermined kinetic energy. Only gas molecules with a pass through the valve.
[0013]
The hydrogen bond is a bond that is an order of magnitude weaker than the coordinate bond, covalent bond, and ionic bond, and thus functions as a valve structure at the molecular level. The molecular level valve structure is not limited to hydrogen bonds alone, but may be other weak bonds that fall within a range of ± 30% in hydrogen bonds and bond energy. Even such a bond is thought to be able to act as a “valve”, similar to a hydrogen bond. However, these are merely mechanism estimates. In other words, even if the mechanism is not followed, it is included in the technical scope of the present invention as long as it satisfies the requirements defined in the present invention and exhibits a hysteresis loop with respect to a predetermined gas.
[0014]
The present inventors diligently investigated the correlation between the expression of the hysteresis loop and the molecular structure of the metal complex, and found that there is a relationship between the amount of relatively weak bonds contained in the metal complex and the hysteresis loop. I found out. In other words, when the total number of coordination bonds, covalent bonds, ionic bonds, and hydrogen bonds is 1, the total number of hydrogen bonds or the total number of bonds having a bond energy in the range of ± 30% compared to the energy of hydrogen bonds is It has been found that when a predetermined amount is included, a hysteresis loop suitable for gas adsorption / desorption is exhibited. Specifically, the total number of bonds having a bond energy in the range of ± 30% compared to hydrogen bonds or hydrogen bonds is 0 when the total number of coordination bonds, covalent bonds, ionic bonds, and hydrogen bonds is 1. .2 or more, and preferably 0.4 or more. In addition, hydrogen bonds are included in the bonds whose bond energy is within a range of ± 30% compared to hydrogen bonds, and the intention is not to exclude hydrogen bonds from the total number. The total number of hydrogen bonds and the total number of bonds having a bond energy in the range of ± 30% compared to the hydrogen bond energy are possible by analyzing the molecular structure. If it is difficult to directly measure whether or not the bond has a bond energy in the range of ± 30% compared to the hydrogen bond energy or the hydrogen bond energy, a reasonable inference method may be used. For example, when a certain degree of correlation between the shape of the hysteresis loop and the valve structure at the molecular level can be confirmed, the binding energy in the range of ± 30% compared to the energy of hydrogen bond is obtained from the shape of the obtained hysteresis loop. May be inferred. In some cases, such a method may be used to calculate the total number of hydrogen bonds.
[0015]
A coordinate bond refers to a bond formed by supplying electrons shared from only one atom. In this respect, it differs from a covalent bond that shares electrons with each other. Examples of coordinate bonds include [Co (NH ₃ ) ₆ ] ³⁺ In ammonia (NH ₃ ) Nitrogen atom unshared electron pair and Co ³⁺ Refers to the bond formed between A covalent bond refers to a bond that shares a deficient electron with each other. Examples of covalent bonds include hydrogen molecules (H ₂ ) And the like. An ionic bond refers to a bond formed by attracting positively charged atoms (positive ions) and negatively charged atoms (negative ions) by electrostatic attraction (Coulomb force). Examples of ionic bonds include Na in crystals of sodium chloride (NaCl). ⁺ And Cl ⁻ And the like. A hydrogen bond refers to a bond formed by a strong dipole attractive force between an atom having a high electronegativity and a high electron density and a hydrogen atom. Examples include a bond between one hydrogen atom and the other oxygen atom between two polarized water molecules.
[0016]
In the present invention, the determination of the hydrogen bond content in the metal complex can be performed by an X-ray structural analysis apparatus. Specifically, it is possible to follow a method performed in an embodiment described later.
[0017]
The metal complex is preferably a metal complex having a periodic crystal structure in consideration of ease of control of gas adsorption amount and molecular structure. As an aspect of the periodic crystal structure, a structure in which a two-dimensional sheet is laminated via a ligand is considered preferable in consideration of gas adsorption characteristics. That is, a two-dimensional sheet formed by a bond mediated by a predetermined ligand has a ligand such as pyrazine, 4,4′-bipyridine, trans-1,2-bis (4-pyridyl) ethylene. A stacked structure as a pillar ligand (Piller Ligand) is preferable. When the metal complex constituting the gas adsorbent has a periodic crystal structure in which a two-dimensional sheet is laminated via a ligand, the molecular level valve structure is not only in the lattice-like two-dimensional sheet, It may be present in the rank.
[0018]
The two-dimensional sheet is 2D in the laminated structure via the pillar ligand. ₁ 2D ₂ 2D ₃ 2D ₄ Are adjacent to each other, the adjacent two-dimensional sheets may be joined by pillar ligands (PL) (ie, 2D ₁ -PL-2D ₂ -PL-2D ₃ -PL-2D ₄ ).
[0019]
When the two-dimensional sheet has a structure laminated via a ligand, at least a part of the ligand is not between adjacent two-dimensional sheets but between two-dimensional sheets separated by one or more layers, Two two-dimensional sheets are preferably combined. When the two-dimensional sheet separated by at least one layer has a structure bonded by a ligand, the distance between the two-dimensional sheets becomes small. For this reason, it has been found by synthetic experiments of various metal complexes that a valve structure at a molecular level is densely present and a hysteresis loop is more easily developed. In the metal complex having a three-dimensional structure, it is considered that the larger the total number of valve structures at the molecular level, the easier it is to develop a hysteresis loop in gas adsorption characteristics.
[0020]
For example, when every other two-dimensional sheet is joined by a pillar ligand, “2D ₁ -PL-2D ₃ 2D ₂ -PL-2D ₄ And the like. If every other two-dimensional sheet is joined by a pillar ligand, 2D ₁ And 2D ₂ PL that intervenes is 2D ₂ The inside of the molecule is inserted. However, the present invention is not limited to such a structure, and is included in the technical scope of the present invention as long as the adsorption / desorption isotherm regarding a predetermined gas, which is a characteristic of the gas adsorbent of the present invention, shows a hysteresis loop. Is. Although the mechanism is not clear, the gas storage capacity of the gas adsorbent of the present invention is significantly increased when every other two-dimensional sheet is joined by pillar ligands.
[0021]
The gas adsorbent of the present invention is a material in which the adsorption / desorption isotherm relating to gas exhibits a hysteresis loop, but it is sufficient that a hysteresis loop is exhibited with respect to at least one kind of gas. Good.
[0022]
The gas that the gas adsorbent of the present invention needs to exhibit a hysteresis loop varies depending on the application of the gas adsorbent of the present invention. For example, when the gas adsorbent of the present invention is used in a methane gas storage device, it is necessary to show a hysteresis loop for methane gas. When the gas adsorbent of the present invention is used in a gas separation device that separates hydrogen gas from a mixed gas of hydrogen and oxygen, it is necessary to show a hysteresis loop for each gas. Generally speaking, if the gas adsorbent of the present invention is used for storage or separation of gas used in various applications, the gas in which the gas adsorbent of the present invention exhibits a hysteresis loop is hydrogen, hydrocarbon (methane , Ethane, propane, butane, isobutane, etc.), carbon monoxide, carbon dioxide, oxygen, nitrogen and the like. Of course, a hysteresis loop may be shown for these two or more gases so that a mixture of a plurality of hydrocarbon gases such as LNG can be stored. In addition, if the gas adsorbent of the present invention is used for gas removal, the gas in which the gas adsorbent of the present invention exhibits a hysteresis loop includes hydrogen sulfide, sulfur oxide (SOx), nitrogen oxide (NOx), and Ammonia is preferred. Of course, a hysteresis loop may be shown for these two or more gases. A hysteresis loop may be shown for gases other than those exemplified above.
[0023]
The material used as the gas adsorbent of the present invention may be selected according to the gas to be stored and the pressure required during adsorption. Although it does not restrict | limit in particular, What has a transition metal is mentioned.
[0024]
Specifically, the metal complex has the following formula (1):
[0025]
[Chemical 3]

[0026]
The metal complex represented by these is preferable. In the formula (1), M is a metal atom, and examples thereof include copper, cobalt, nickel, zinc, and iron. In the formula (1), A is a ligand, and a plurality of A may be the same or different. Examples of the ligand A include an aromatic compound group having a nitrogen atom. Examples of the aromatic compound having a nitrogen atom include pyrazine, 4,4′-bipyridine, trans-1,2-bis (4-pyridyl) ethylene, 1,4-dicyanobenzene, 4,4-dicyanobiphenyl, 1 , 2-dicyanoethylene, 1,4-bis (4-pyridyl) benzene and the like. In addition, as ligand A, BF ₄ , PF ₆ , Cl, Br, CF ₃ SO ₃ , CH ₃ C ₆ H ₄ SO ₃ And H ₂ One or more selected from the group consisting of O may be included. However, it is not limited to these. A composite ligand in which these ligands are combined may be used. In addition, aromatic group having nitrogen atom and BF ₄ Of course, both the compound and the like may be contained as the ligand A. In the formula (1), n is an A coordination number, specifically, n is 4, 5, 6, and the like.
[0027]
In order to improve the gas adsorption amount of the gas adsorbent of the present invention and the selectivity to a predetermined gas, it is effective to select the type of metal ion or ligand used in the metal complex. In particular, it is considered effective to control the interatomic distance of coordination atoms in the ligand. Specifically, as a ligand, the following formula (2):
[0028]
[Formula 4]

[0029]
The adsorption characteristic of the gas adsorbent of the present invention may be controlled by properly using a compound represented by In the formula (2), L is a group of an aromatic compound having a nitrogen atom, and two Ls may be the same or different. Examples of the aromatic compound having a nitrogen atom include aniline, pyridine, pyrimidine, quinoline, acridine and the like. In the formula (1), S represents a divalent group of an aliphatic hydrocarbon, a divalent group of an aromatic hydrocarbon, —NH—, —O—, —C (═O) O—, —SO. -, Or -SO ₂ -. The aliphatic hydrocarbon may be saturated or unsaturated. Further, it may be any of linear, branched and cyclic shapes. Specific examples of the aliphatic hydrocarbon include methane, ethane, propane, butane, cyclobutane, i-butane, pentane, cyclopentane, hexane, cyclohexane, ethylene, propylene, and the like. Specific examples of the aromatic hydrocarbon include benzene, naphthalene, anthracene and the like. However, when selecting S, it is necessary to pay attention so that the coordination of the ligand represented by the formula (1) is not inhibited.
[0030]
Moreover, even if it is the same component, it is also possible to change the shape of a hysteresis loop by preheating to 100-600 degreeC after a synthesis | combination.
[0031]
As a specific example of the gas adsorbent of the present invention, [Cu (bpy) (BF ₄ ) ₂ (H ₂ O) ₂ (Bpy)] _n (Wherein bpy represents 4,4′-bipyridine, the same shall apply hereinafter) and [Cu (bpy) (BF ₄ ) ₂ (H ₂ O) ₄ (Bpy)] _n And so on.
[0032]
[Manufacture of gas adsorbent]
The method for preparing the gas adsorbent differs depending on the type of the gas adsorbent, and cannot be determined uniquely, but here, [Cu (bpy) (BF ₄ ) ₂ (H ₂ O) ₂ (Bpy)] _n An example of combining these will be described.
[0033]
First, an aqueous solution containing copper (II) tetrafluoroborate hydrate is added while refluxing an acetonitrile solution of 4,4′-bipyridine (hereinafter abbreviated as “bpy”). The resulting precipitate is filtered, the vapor of diethyl ether is diffused into the mother liquor using a stream of nitrogen, and the mother liquor is stored at room temperature for several days. Subsequently, the precipitate is obtained by filtration and dried under reduced pressure for several hours. The object can be obtained by such work. However, it is needless to say that the method is not limited to the above method, and it may be synthesized using various methods.
[0034]
[Use of gas adsorbent]
The gas adsorbent of the present invention can be applied to various uses by utilizing the special properties relating to gas adsorption and desorption. For example, when applied to an adsorbent in a pressure swing adsorption method (hereinafter abbreviated as “PSA method”) gas separation device, the gas adsorption material of the present invention can be used to achieve very efficient gas separation. Is possible. In addition, the time required for pressure change can be shortened, contributing to energy saving. Furthermore, since it can contribute to downsizing of the gas separation device, it is possible to increase the cost competitiveness when selling high-purity gas as a product. Since the cost required for the equipment that requires high purity gas can be reduced, the manufacturing cost of the final product can be reduced.
[0035]
Another application of the gas adsorbent of the present invention is a gas storage device. When the gas adsorbent of the present invention is applied to a gas storage device (business gas tank, consumer gas tank, vehicle fuel tank, etc.), it is possible to dramatically reduce the pressure during transportation and storage. . As an effect resulting from the ability to reduce the gas pressure during transportation or storage, firstly, improvement in the degree of freedom of shape can be mentioned. In the conventional gas storage device, the gas adsorption amount cannot be maintained high unless the pressure during storage is maintained. However, in the gas storage device of the present invention, a sufficient gas adsorption amount can be maintained even if the pressure is lowered. For this reason, the pressure resistance of a container can be made low and the shape of a gas storage apparatus can be designed freely to some extent. This effect is enormous when the gas storage device of the present invention is used as a fuel gas tank for vehicles such as automobiles. When the gas storage device of the present invention is used as a fuel tank, restrictions on pressure resistance are relaxed as described above, and the shape can be designed freely to some extent. Specifically, the shape of the gas storage device can be adjusted so as to fit the shape of wheels, seats, and the like in the vehicle. As a result, it is possible to obtain various benefits such as miniaturization of the vehicle, securing of luggage space, and improvement of fuel consumption by reducing the weight of the vehicle.
[0036]
When applied to a gas separation device or gas storage device, there is no need to use a special device for the shape of the container, the material of the container, the type of gas valve, etc., and those used in the gas separation device and gas storage device Can be used. However, the improvement of various apparatuses is not excluded, and whatever apparatus is used is included in the technical scope of the present invention as long as the gas adsorbent of the present invention is used.
[0037]
【Example】
<Example 1>
Copper (II) tetrafluoroborate hexahydrate (Aldrich; 0.674 g) was dissolved in pure water (50 ml), and a 0.04 M solution of copper (II) tetrafluoroborate (A ₁ Liquid). Separately, trans-1,2-bis (4-pyridyl) ethylene (special grade manufactured by Kanto Chemical Co., Inc .; 0.729 g, hereinafter abbreviated as “t-bpa”) was dissolved in acetonitrile (100 ml), and t-bpa 0.04M solution (B ₁ Liquid). While refluxing using a 357K water bath, ₁ A in liquid ₁ The solution was added dropwise over 1 hour. After completion of the dropwise addition, the mixture was allowed to cool and a trace amount of powder was collected by filtration using 5C filter paper to obtain a blue filtrate.
[0038]
While stirring the filtrate at room temperature, diethyl ether (500 ml) was added dropwise over 12 hours, and the mixture was further stirred at room temperature for 48 hours. Using a rotary evaporator, ether and acetonitrile were substantially distilled off, and the residue was filtered to obtain a light blue powder. 10 of this powder ^-3 [Cu (t-bpa) (BF) which is dried under reduced pressure of Pa or less and is a gas adsorbent of the present invention. ₄ ) ₂ (H ₂ O) ₂ (T-bpa)] _n (0.417 g) was obtained.
[0039]
The nitrogen adsorption characteristic at 77K of the obtained gas adsorbent was investigated. For the measurement, a BET automatic adsorption device (manufactured by Nippon Bell Co., Ltd.) was used, and the sample was subjected to vacuum heat treatment at 373 K for 3 hours prior to the measurement to desorb the guest molecules previously adsorbed at the adsorption site. No adsorption of nitrogen was observed up to about 0.01 MPa, and a rapid increase in the amount of adsorption was confirmed around 0.01 MPa.
[0040]
Moreover, the carbon dioxide adsorption characteristic at room temperature of the obtained gas adsorbent was investigated. The measurement method was the same as in the case of nitrogen adsorption measurement. No adsorption of carbon dioxide was observed up to about 0.04 MPa, and a sudden increase in the amount of adsorption was confirmed around 0.04 MPa. In addition, during the desorption, the desorption amount up to about 0.03 MPa was slight, but a sudden decrease in the adsorption amount was confirmed when approaching 0.02 MPa.
[0041]
Furthermore, the methane adsorption property at room temperature of the obtained gas adsorbent was investigated. Prior to measurement, the sample was vacuum heat treated at 373 K for 3 hours to desorb the guest molecules previously adsorbed on the adsorption site. Up to about 4 MPa, no methane adsorption was observed, and a sudden increase in the amount of adsorption was confirmed around 5 MPa. In addition, during the desorption, the desorption amount up to about 3 MPa was slight, but a sudden decrease in the adsorption amount was confirmed around 3 MPa. The maximum amount of methane gas adsorbed is 1 cm of gas adsorbent. ³ Per 165cm ³ (Normal). Further, adsorption and desorption were repeated for 3 cycles, but almost no change was observed in the hysteresis loop.
[0042]
<Example 2>
Copper (II) trifluoromethanesulfonate hexahydrate (manufactured by Kanto Chemical Co., Inc .; 0.723 g, hereinafter referred to as “Cu (OTf)”) ₂ Abbreviated as “) in pure water (50 ml), Cu (OTf) ₂ 0.04M solution (A ₂ Liquid). Separately, 4,4′-bipyridine (special grade manufactured by Wako Pure Chemical Industries, Ltd .; 0.625 g) was dissolved in acetonitrile (50 ml) to obtain a 0.08M solution of 4,4′-bipyridine (B ₂ Liquid). While refluxing using a 357K water bath, ₂ A in liquid ₂ The solution was added dropwise over 1 hour. After completion of the dropwise addition, the mixture was allowed to cool and a trace amount of powder was collected by filtration using 5C filter paper to obtain a blue filtrate.
[0043]
While stirring the filtrate at room temperature, diethyl ether vapor was diffused into the mother liquor using a nitrogen stream until the volume reached 150 ml. The solution was further stirred at room temperature for 48 hours. Using a rotary evaporator, ether and acetonitrile were almost distilled off, and the residue was filtered to obtain a light blue powder. 10 powders ^-3 [Cu (bpy) (OTf)], which is dried under reduced pressure of Pa or less and is a gas adsorbent of the present invention. ₂ (H ₂ O) ₂ (Bpy)] _n (0.417 g) was obtained.
[0044]
Based on the method described in Example 1, nitrogen adsorption characteristics at 77K of the obtained gas adsorbent were investigated. No adsorption of nitrogen was observed up to about 0.01 MPa, and a rapid increase in the amount of adsorption was confirmed around 0.01 MPa.
[0045]
Moreover, based on the method described in Example 1, the carbon dioxide adsorption property at room temperature of the obtained gas adsorbent was investigated. No adsorption of carbon dioxide was observed up to about 0.04 MPa, and a sudden increase in the amount of adsorption was confirmed around 0.04 MPa. In addition, during the desorption, the desorption amount up to about 0.03 MPa was slight, but a sudden decrease in the adsorption amount was confirmed when approaching 0.02 MPa.
[0046]
Furthermore, according to the method described in Example 1, the obtained gas adsorbent was examined for methane adsorption characteristics at room temperature. No adsorption of methane was observed up to about 4 MPa, and an abrupt increase in the amount of adsorption was confirmed around 4.8 MPa. In addition, during the desorption, the desorption amount up to about 3 MPa was slight, but a sudden decrease in the adsorption amount was confirmed around 3 MPa. The maximum amount of methane gas adsorbed is 1 cm of gas adsorbent. ³ 158cm per ³ (Normal). Further, adsorption and desorption were repeated for 3 cycles, but almost no change was observed in the hysteresis loop.
[0047]
<Example 3>
Copper (II) tetrafluoroborate hexahydrate (Aldrich; 0.674 g) was dissolved in pure water (50 ml), and a 0.04 M solution of copper (II) tetrafluoroborate (A ₃ Liquid). Separately, 4,4′-bipyridine (special grade manufactured by Wako Pure Chemical Industries, Ltd .; 0.625 g) was dissolved in acetonitrile (50 ml) to obtain a 0.08M solution of 4,4′-bipyridine (B ₃ Liquid). While refluxing using a 357K water bath, ₃ A in liquid ₃ The solution was added dropwise over 1 hour. This gave a solution containing a slightly grayish precipitate. After completion of the dropwise addition, the precipitate as a side reaction product was removed by filtration.
[0048]
Next, while stirring, the vapor of diethyl ether was diffused into the mother liquor using a nitrogen stream until the volume reached 150 ml. Subsequently, the mother liquor was stored at room temperature for 2 days and the solvent (acetonitrile, diethyl ether) was evaporated by heating to 353K.
[0049]
The residue is filtered and 10 ^-3 Water is removed by drying for 4 hours under reduced pressure of Pa or less, and the gas adsorbent of the present invention [Cu (bpy) (BF ₄ ) ₂ (H ₂ O) ₂ (Bpy)] _n (0.3 g) was obtained.
[0050]
Based on the method described in Example 1, nitrogen adsorption characteristics at 77K of the obtained gas adsorbent were investigated. No adsorption of nitrogen was observed up to about 0.01 MPa, and a rapid increase in the amount of adsorption was confirmed around 0.01 MPa.
[0051]
Moreover, based on the method described in Example 1, the carbon dioxide adsorption property at room temperature of the obtained gas adsorbent was investigated. No adsorption of carbon dioxide was observed up to about 0.04 MPa, and a sudden increase in the amount of adsorption was confirmed around 0.04 MPa. In addition, during the desorption, the desorption amount up to about 0.03 MPa was slight, but a sudden decrease in the adsorption amount was confirmed when approaching 0.02 MPa.
[0052]
Furthermore, according to the method described in Example 1, the obtained gas adsorbent was examined for methane adsorption characteristics at room temperature. Up to about 4 MPa, no methane adsorption was observed, and a sudden increase in the amount of adsorption was confirmed around 4.5 MPa. In addition, during the desorption, the desorption amount up to about 3 MPa was slight, but a sudden decrease in the adsorption amount was confirmed around 3 MPa. The maximum amount of methane gas adsorbed is 1 cm of gas adsorbent. ³ Per 160cm ³ (Normal). Further, adsorption and desorption were repeated for 3 cycles, but almost no change was observed in the hysteresis loop.
[0053]
<Comparative Example 1>
The activated carbon powder (manufactured by Kanto Chemical Co., Inc .; 0.5 g) was evaluated in the same manner as in the Examples for the adsorption / desorption characteristics of nitrogen, carbon dioxide, and methane. None of the adsorption / desorption isotherms showed a hysteresis loop, and showed a type of adsorption / desorption isotherm as shown in FIG. The maximum amount of methane gas adsorbed is 1 cm of activated carbon. ³ Per 100cm ³ (Normal). However, when adsorption / desorption is repeated, the maximum value of the adsorption amount of methane gas in the third cycle is 1 cm of activated carbon. ³ 70cm per ³ (Normal).
[0054]
【The invention's effect】
The gas adsorbent of the present invention is a gas adsorbent in which an adsorption / desorption isotherm relating to at least one kind of gas exhibits a hysteresis loop, and therefore has an excellent adsorption characteristic as compared with a conventional gas adsorbent.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between gas adsorption amount and gas pressure of a gas adsorbent according to the present invention.
FIG. 2 is a graph showing the relationship between gas adsorption amount and gas pressure of a conventional gas adsorbent.

Claims (16)

The adsorption / desorption isotherm for at least one gas exhibits a hysteresis loop,
A gas adsorbent comprising a metal complex in which the total number of hydrogen bonds is 0.2 or more, where the total number of coordination bonds, covalent bonds, ionic bonds, and hydrogen bonds is 1. The adsorption / desorption isotherm for at least one gas exhibits a hysteresis loop,
Metal whose total number of bonds having a bond energy in the range of ± 30% relative to the energy of hydrogen bonds is 0.2 or more when the total number of coordination bonds, covalent bonds, ionic bonds, and hydrogen bonds is 1. Gas adsorbent consisting of complex. The gas adsorbent according to claim 1, wherein the gas adsorbent has a periodic crystal structure. The gas adsorbent according to claim 3, wherein the periodic crystal structure is a structure in which a two-dimensional sheet is laminated via a ligand. 5. The gas adsorbent according to claim 4, wherein at least a part of the ligand bonds the two-dimensional sheets separated by one or more layers, not between the adjacent two-dimensional sheets. The metal complex has the following formula (1):

(Wherein M is a metal atom, A is the same or different ligand, and n is the coordination number of A)
The gas adsorbent according to claim 1, which has a unit structure represented by: The gas adsorbent according to claim 6, wherein M is copper, cobalt, nickel, or zinc. The gas adsorbent according to claim 6 or 7, wherein at least one of A is a group of an aromatic compound having a nitrogen atom. The group of the aromatic compound having a nitrogen atom is pyrazine, 4,4′-bipyridine, trans-1,2-bis (4-pyridyl) ethylene, 1,4-dicyanobenzene, 4,4-dicyanobiphenyl, 1 The gas adsorbent according to claim 8, which is 1,2-dicyanoethylene or 1,4-bis (4-pyridyl) benzene. One or more selected from the group consisting of BF ₄ , PF ₆ , Cl, Br, CF ₃ SO ₃ , CH ₃ C ₆ H ₄ SO ₃ , and H ₂ O is included as the A. Item 10. The gas adsorbent according to any one of Items 6 to 9. Following formula (2):

(In the formula, L is a group of an aromatic compound having a nitrogen atom, which may be the same or different, and S is a divalent group of an aliphatic hydrocarbon, a divalent group of an aromatic hydrocarbon, -NH -, - O -, - C (= O) O -, - SO-, or -SO ₂ - and is)
11. The gas adsorbent according to claim 6, wherein a compound represented by the formula: The adsorption / desorption isotherm for at least one gas selected from the group consisting of hydrogen, hydrocarbon, carbon monoxide, carbon dioxide, oxygen, and nitrogen exhibits a hysteresis loop. The gas adsorbent according to claim 1. The adsorption / desorption isotherm regarding at least one gas selected from the group consisting of hydrogen sulfide, sulfur oxide, nitrogen oxide, and ammonia exhibits a hysteresis loop. The gas adsorbent described in 1. A pressure swing adsorption type gas separation apparatus using the gas adsorbent according to any one of claims 1 to 13. A gas storage device comprising the gas adsorbent according to any one of claims 1 to 13 contained therein. A vehicle comprising the gas storage device according to claim 15.

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