JP2623487C

JP2623487C -

Info

Publication number: JP2623487C
Authority: JP
Publication date: 1999-06-07

Description

【発明の詳細な説明】〔産業上の利用分野〕本発明は分子ふるい炭素の選択的吸着特性を利用して、窒素を含む混合ガスよ
り高濃度の窒素ガスを分離する方法に関する。〔従来技術〕金属の熱処理、半導体の製造、化学プラントの防爆シートなどに広く利用され
ている工業用窒素ガスは、従来主として深冷分離装置により製造され、パイピン
グ、タンクローリー、ボンベ等によりユーザーへ供給されてきた。近年になり、新しい窒素ガスの製造法として、例えば特公昭５４−１７５９５
号公報に開示された分子ふるいコークスを充填剤とした吸着塔に原料ガスを加圧
下で送入し、酸素を選択的に吸着させ窒素ガスを分離する方法の如きいわゆる圧
力スイング吸着（ＰｒｅｓｓｕｒｅＳｗｉｎｇＡｄｓｏｒｐｔｉｏｎ；ＰＳ
Ａ）式窒素ガスの製造法が開発されてきている。このＰＳＡ式窒素ガスの分離法は、深冷分離法に比較して装置が、小型となり
操作が簡便で無人連続運転が可能などの利点が注目され、現在もなお種々の装置
改良が提案されている。このＰＳＡ式窒素ガスの分離法においては、装置構成、吸着剤、操作サイクル
等種々の条件により、発生窒素ガスの純度や発生量、所要動力等がきまってくる
ため、これまでにも種々の提案がなされてきている。しかしながら窒素ガス純度
、発生量、エネルギー原単位について、あるいは装置のより一層のコンパクト化
に関し克服すべき課題が多々残されているのが現状である。〔発明が解決しようとする課題〕本発明者らは、この様な現状に鑑み鋭意研究の結果本発明を完成させたもので
あり、その目的とするところは、高純度窒素ガスを低いエネルギー原単位で多量
に発生することができる窒素ガスの分離方法を提供するにある。〔目的を達成するための手段〕上述の目的は、少なくとも２塔以上の吸着塔に窒素を含む混合ガスを供給し、
高圧吸着工程と、低圧再生工程とを各吸着塔で交互に繰り返し、窒素ガスを分離
するＰＳＡ法において、（Ａ）分子ふるい炭素として（ａ）粒径０．８〜１２０μｍの多数の球状炭素粒子が三次元的に不規則に重な
り且つ合体された構造を有し、（ｂ）該多数の炭素粒子の間には三次元的に不規則に走る連続通路が存在し（ｃ）該炭素粒子の夫々は、該粒子の間の通路に連通する多数の細孔を有し、そ
して（ｄ）少なくとも８５重量％の炭素含有率を有し、かつ、（ｅ）２．５ｋｇｆ／ｃｍ²・Ｇの加圧下で単成分吸着を行なった際の酸素と窒
素の１分後の吸着量の容量比が３．５〜２０である分子ふるい炭素を用い、（Ｂ）吸着塔１塔当りの有効容積が製品ガス取出量（Ｎｌ／ｍｉｎ）の０．３
〜１０倍であり、かつ、製品貯留槽有効容積が吸着塔１塔当りの有効容積の１．
４〜２倍であり、（Ｃ）吸脱着操作サイクルとして、吸着、均圧、再生の各工程を含み、再生の
工程では大気圧再生を行い、かつ、均圧工程と吸着工程の間に強制的に、あるい
は吸着工程初期に自動的に製品貯留槽より吸着塔に窒素富化ガスが還流する工程
を含み、（Ｄ）吸着工程が１３０〜２１０秒間であることを特徴とする窒素ガスの分離方法により達成される。本発明の窒素ガスの分離に用いる上述の如き構造と特性を有する分子ふるい炭
素の製造法は特開昭６４−６１３０６号公報に詳述されているが、その要点は以
下の如くである。即ち、（ａ）粒径１〜１５０μｍの球状熱硬化性フェノール樹脂粉末、を１
００重量部当り、（ｂ）フェノール樹脂またはメラミン樹脂よりなる熱硬化性樹脂の溶液、５〜
５０重量部（固形分として）（ｃ）ポリビニルアルコールおよび水溶性又は水膨潤性セルロース誘導体から
選ばれる高分子バインダー１〜３０重量部である均一混合物を準備し、この均一混合物を粒状物に成形し、そして、この粒状物
を非酸化性雰囲気下、５００〜１１００℃の範囲の温度で、加熱処理して炭化し
、粒状分子ふるい炭素とする方法である。また、この分子ふるい炭素は、好ましくは、多数の球状炭素粒子が粒径２〜３
０μｍを有し、好ましくは多数の炭素粒子の間の連続通路の平均直径は０．１〜
２０μｍである。この分子ふるい炭素は、上記（Ａ），（Ｂ）の特徴と相俟って、上記多数の炭
素粒子の夫々が、上記粒子間の通路に連通する多数の細孔を有する。この多数の
細孔の存在が分子ふるい炭素の選択吸着性の発現に大きく寄与している。多数の炭素粒子の中の該細孔は好ましくは約１０Å以下の平均直径を有する。また、該細孔の占める容積は分子ふるい炭素の重量１ｇ当り好ましくは０．１
〜０．７ｃｃであり、より好ましくは０．１５〜０．５ｃｃであり、さらに好ま
しくは０．２〜０．４ｃｃである。該分子ふるい炭素は、組成上の特徴として、少なくとも８５重量％の炭素含有
率を有し、好ましくは少なくとも９０重量％の炭素含有率を有する。また、該分子ふるい炭素は、気孔率が好ましくは２５〜５０容積％であり、よ
り好ましくは３０〜４５容積％である。また、嵩密度が好ましくは０．７〜１．２ｇ／ｃｃであり、より好ましくは０
．８〜１．１ｇ／ｃｃである。該分子ふるい炭素は、上記の如く、好ましくは、平均直径１０Å以下の細孔を
有するが好ましくはこの細孔は平均直径３〜５Ａの範囲に最も多く分布している
。この分子ふるい炭素の比表面積は、Ｎ₂吸着によるＢ．Ｅ．Ｔ．法により測定
した値として、通常１〜６００ｍ²／ｇ、好ましくは１０〜４００ｍ²／ｇ、最も
好ましくは２０〜３５０ｍ²／ｇ程度である。該分子ふるい炭素は、例えば直径０．５〜５ｍｍ長さ１〜１０ｍｍ程度の円柱
状、あるいは直径０．５〜１０ｍｍ程度の球状の形態で提供され、その充填密度
は通常０．５〜０．７５ｇ／ｃｍ³であり、好ましくは０．５０〜０．７０ｇ／
ｃｍ³である。上記製法に従い２．５ｋｇｆ／ｃｍ²・Ｇの加圧下で単成分吸着を行なった際
の酸素と窒素の１分後の吸着量の容量比が３．５〜２０であるように製造された
分予ふるい炭素は窒素を含む混合ガスより、窒素ガスを分離するＰＳＡ法におい
て極めて有効に働き、高純度の窒素ガスを極めて効率よく分離することが可能で
あり、特にＰＳＡ装置の構成と操作条件を以下の如く設定し、本ＭＳＣと組合せ
ることによりその効果が極めて顕著であることを見出した。即ち、少なくとも２塔以上の吸着塔を有するＰＳＡ装置において、（１）吸着塔１塔当りの有効容積が製品ガス取出量（Ｎｌ／ｍｉｎ）の０．３
〜１０倍であり、かつ製品貯留槽有効容積が吸着塔１塔当りの有効容積の１．４
〜２倍であり、（２）吸脱着操作サイクルとして、吸着、均圧、再生の各工程を含み、再生の
工程では大気圧再生を行い、かつ、均圧工程と吸着工程の間に強制的にあるいは
吸着工程初期に自動的に製品貯留槽より吸着塔に窒素富化ガスが還流する工程を
含み（３）吸着工程が１３０〜２１０秒であるＰＳＡ装置の構成と操作条件である。本発明におけるＭＳＣの特性は、後述の測定法により測定した２．５ｋｇｆ／
ｃｍ²・Ｇの加圧下での単成分吸着において、酸素と窒素の１分後の吸着量の容
量比が３．５〜２０である。この吸着容量比は、好ましくは４．５〜２０であり
、最も好ましくは９〜２０である。また、このＭＳＣは、同一の測定法における
１分後の酸素吸着容量が通常ＭＳＣ１ｇ当り６×１０^-4〜９×１０^-4モルであり
、好ましくは７×１０^-4〜９×１０^-4モル、最も好ましくは７．５×１０^-4〜９
×１０^-4モルである。本発明のＰＳＡ装置は、主として、ＭＳＣを充填した２塔以上の吸着塔、コン
プレッサーなどの原料混合ガス供給装置、製品窒素ガスを貯留するための製品貯
留槽、及びこれらの構成要素を連結する配管及びガスの流れを制御するための自
動弁とその制御系、流量調整計及びガス濃度分析計などから構成されている。本発明の極めて効率的な窒素ガスの分離法においては、上記装置構成において
吸着塔１塔当りの有効容積は、製品ガス取出量（Ｎｌ／ｍｉｎ）の０．３〜１０
倍であり好ましくは０．５〜７倍、最も好ましくは０．７〜４倍である。また、
製品貯留槽有効容積は吸着塔１塔当りの有効容積の１．４〜２倍である。製品取
出量に対し、吸着塔容積が小さい場合には、吸着塔容量当りの生産性が向上し、
製品単位量当りの動力消費量、即ち動力原単位も少なくて済むが、製品の窒素純
度が低下する。本発明において得られる製品窒素ガスの純度は、吸着工程、再生
工程の塔内圧力等により変動するが、本発明の吸着塔容積と製品ガス取出流量（Ｎｌ／ｍｉｎ）の比率の範囲内では、通常窒素純度（Ｎ₂＋Ａｒ）９９．９９９
９〜９９ｖｏｌ％の範囲の製品ガスを得ることが可能である。従って本発明の比
率の範囲内で高純度の窒素ガスを得たい場合には、吸着塔容積を大きく、また比
較的純度の低い窒素ガスで良い場合には吸着塔容積を小さくすればよい。また、
製品貯留槽容積が小さ過ぎる場合には、ＰＳＡ操作サイクルの均圧工程と吸着工
程の間に強制的にあるいは吸着工程初期に自動的に製品貯留槽より吸着塔に還流
する窒素富化ガスの還流量が少なくなり過ぎ、効率良く、高純度の製品窒素ガス
を得ることが困難となり、また、製品窒素ガスの供給圧力が低下し、好ましくな
い。一方、製品貯留槽容積が大き過ぎる場合には、装置起動時に製品貯留槽の窒
素濃度が所定の定常値に到達するのに時間がかかり過ぎ待ち時間が長くなる。本発明の上述の如き構成のＰＳＡ装置による実際の窒素ガスの分離操作の実施
態様の一例を第１図に基づいて説明すると以下の通りである。第１図において、（１）は空気圧縮機、（２）はエアドライヤ、（３），（３
ａ）…は吸着塔、（４），（４ａ），（７），（７ａ），（１０），（１０ａ）
，（１３），（１３ａ）…は弁、（５），（５ａ），（１８），（９），（９ａ
），（１１），（１２），（１６）…はパイプ、（１４）はリザーバータンク、
（１５）はバルブである。同図において、空気圧縮機（１）により供給された原料空気は、必要ならば除
湿機（２）で除湿した後、自動弁（４）または（４ａ）を通して吸着塔（３）ま
たは（３ａ）に供給される。例えば、吸着塔（３）が吸着工程の場合には、この
吸着塔に原料空気が供給され、吸着塔（３ａ）は再生工程となる。吸着工程にあ
る吸着塔の塔内圧力は通常３〜９ｋｇｆ／ｃｍ²・Ｇ、好ましくは４〜８．５ｋ
ｇｆ／ｃｍ²・Ｇ、最も好ましくは５〜８ｋｇｆ／ｃｍ²・Ｇである。また、吸着
塔の再生は、通常大気開放（以下大気圧再生と記す）により実施されるので、再
生工程にある吸着塔の内圧は、大気圧にまで低下する。また、第１図は、配管（
１８）、自動弁（１９）により製品貯留槽より窒素富化ガスを強制的に還流する
工程が含まれる場合の例示であるが、この配管（１８）、自動弁（１９）がなく
、吸着塔と製品貯留槽の圧力バランスの結果として、配管（１１），（９），（
９ａ）、自動弁（１０），（１０ａ）を通じて還流が自動的に起こる場合も本発明の範囲に含まれる。また再生工程には、製品貯留槽内の窒素富化ガスを逆流して吸着塔内を洗浄す
るいわゆるパージ法を採用してもよい。次に吸着工程の終了した吸着塔（３）と再生工程の終了した吸着塔（３ａ）は
、吸着塔製品ガス取出側または、吸着塔原料ガス送入側あるいは、吸着塔製品ガ
ス取出側と原料ガス送入側とで連結し、吸着工程の終了した吸着塔内に存在する
混合ガスの一定量を再生工程の終了した吸着塔に移動させる所謂均圧工程に移る
。通常吸着塔製品ガス取出側を連結した場合を塔頂均圧、吸着塔製品ガス取出側
どうし及び製品ガス送入側どうしを連結した場合を上下均圧、吸着塔製品ガス取
出側と製品ガス送入側とを連結した場合をクロス均圧と呼んでいるが、これらの
均圧方法あるいは、その他の均圧方法も含め均圧工程を実施することが本発明の
範囲内である。均圧工程の終了後、製品貯留槽より窒素富化ガスを配管（１８）および自動弁
（１９）により強制的に吸着塔（３ａ）に還流させてもよいが、強制的な還流工
程が行なわれない場合、あるいは、強制的な還流量が吸着塔と製品貯留槽の完全
な圧力バランスに到達するに至らない程度に少ない場合には、次の吸着塔（３ａ
）の吸着工程初期に、吸着塔（３ａ）内の圧力が製品貯留槽内（１４）の内圧よ
り低いことにより自動的に還流がおこる。この自動的な還流は、吸着塔への原料
空気の送入及び製品貯留槽からの窒素富化ガスの還流により吸着塔の内圧が上昇
し、製品貯留槽と圧力がバランスすることにより自動的に停止し、吸着塔より製
品貯留槽への窒素富化ガスの取出しに移行していく。この吸着塔（３ａ）の吸着工程の間、吸着塔（３）は再生工程にある。そして
吸着工程の終了した吸着塔（３ａ）と再生工程の終了した吸着塔（３）は連結さ
れ、均圧工程に移る。この様にして、吸着−均圧−還流−再生−均圧の工程が順
次繰り返される。上記の本発明ＰＳＡサイクルに於て吸着工程の時間は１３０〜２１０秒である
。また、その他の工程については、その長さを特に限定するものではないが、通
常均圧は０．１〜１０秒程度、還流も０．１〜１０秒程度であり、再生工程の長
さは吸着工程との兼ね合いにより自動的に決まってくる。〔発明の効果〕本発明の窒素ガスの分離方法は、優れた窒素、酸素の分離能を賦与した独自の
微細孔構を有する分子ふるい炭素と特定のＰＳＡ装置構成及び特定のＰＳＡ操作
法を組合せることにより、製品窒素ガスの純度が高く、発生量が大きく、かつ、
動力原単位の小さい窒素ガスの分離方法を提供するものである。即ち、本発明の窒素ガス分離方法に於ては、多数の球状炭素粒子が三次元的に
不規則に重なり且つ合体された構造を有し、該多数の炭素粒子の間には三次元的
に不規則に走る連続通路が存在し、該炭素粒子の夫々には、該粒子の間の通路に
連通する多数の細孔を有する独特の微細構造を持つ、通常ペレット状の優れた窒
素、酸素分離能を賦与した分子ふるい炭素を用い、その分子ふるい炭素を充填剤
とした特定の装置構成、特定の操作法に於てはじめて到達しうる顕著な効果を有
する、窒素ガスの分離方法である。本発明に於ては、例えば、製品窒素ガス純度（窒素＋アルゴンの容量％）は９
９〜９９．９９９９％程度の高純度とすることが可能であり、その吸着塔容積当
りの製品発生量〔（Ｎｌ／ｍｉｎ）／ｌ〕も純度により異なるが、０．１〜３．
３倍と大きい範囲まで取ることが可能である。また、本発明の窒素ガス分離を実
施するのに要する所要動力は、装置条件や操作条件、製品純度等により異なるが
従来技術に比較し一段と低減されており、その利点は極めて大なるものがある。以下に実施例を挙げて本発明を具体的に説明する。なお本発明に用いた測定法
をまとめて示すと次の通りである。（１）細孔容積、細孔径分布の測定：本発明の分子ふるい炭素の細孔容積及び細孔径分布は、細孔直径６０Å〜５０
０μｍの範囲の細孔については、ポロシメーターによる水銀圧入法（島津製作所
製、ポアサイザー９３１０）により測定した。また、細孔直径６０Å以下の細孔については、窒素ガスの吸着等温線により、
下記のいわゆるケルビン式により求めた。Ｐ：吸着ガスが細孔に吸着するときの飽和蒸気圧、Ｐ₀：常態での吸着ガスの飽和蒸気圧、 γ：表面張力、Ｖ：液体窒素の１分子体積、Ｒ：ガス定数、Ｔ：絶対温度、 γＫ：細孔のケルビン半径、細孔のケルビン半径に対する補正は、Ｃｒａｎｓｔｏｎ−Ｉｎｋｌｅｙ法によ
りおこなった。（２）酸素及び窒素の１分後の吸着量及び平衡吸着量の測定：本発明に用いる分子ふるい炭素の酸素・窒素の吸着容量を第２図に示す吸着特
性測定装置により測定した。第２図において、（１）は真空ポンプ、（２），（３），（８），（１１），
（１２），（１３）…はバルブ、（４）は試料室、（５）は調整室、（６），（
７）は圧力センサー、（９）は記録計、（１０）は圧力計、（１４），（１５）
はガスレギュレーター、（１６）は窒素ボンベ、（１７）は酸素ボンベである。同図において、試料室（４）（２２６．９ｍｌ）に約３ｇの試料を入れ、バル
ブ（１１），（８）を閉じ、バルブ（２），（３）を開けて３０分間脱気した後
バルブ（２），（３）を閉じ、バルブ（１１）を開けて調整室（５）（２３１．
７ｍｌ）内に酸素ガスまたは窒素ガスを送り込み、設定圧になったところでバル
ブ（１１）を閉じ、バルブ（３）を開け所定時間における内部圧力の変化を測定
して、酸素および窒素の各々の吸着量の経時変化を測定し、吸着開始１分後の酸
素吸着量（Ｑ₁）窒素吸着量（Ｑ₂）を求めた。また上記経時変化が一定値に安定
するまで測定を継続し、酸素平衡吸着量（Ｑ₃）及び窒素平衡吸着量（Ｑ₄）も測
定した。測定は測定開始１分後の吸着塔内圧あるいは平衡吸着塔測定時の内圧が２．５
ｋｇｆ／ｃｍ²・Ｇより大または小となる点、数点が測定できる様初期設定圧を
変えて測定し、それより２．５ｋｇｆ／ｃｍ²・Ｇにおける酸素及び窒素の１分
後の吸着量及び平衡吸着量を求めた。実施例１４００ｌの反応容器に、塩酸１８％およびホルムアルデヒド９％からなる混合
水溶液３００ｋｇを入れ、温度を２０℃とした。つぎに、この反応容器に、濃度
９８％（２％は水）のフェノールと水とを用いて調製した濃度９０％のフェノー
ル水溶液（２０℃）を１２ｋｇ添加した。添加後３０〜４０秒間攪拌し、反応容
器内の内容物が急激に白濁すると同時に攪拌を中止し静置した。静置をつづける
と内温が徐々に上昇し、内容物は次第に淡いピンクに変色し、白濁してから３０
分後にはいずれもスラリー状あるいは樹脂状物の生成がみられた。上記工程の後
、引き続いて内容物を７５〜７６℃まで３０分間で昇温し、この温度で攪拌しな
がら４０分間保持した。つぎに、この内容物を水洗した後、濃度０．１％のアン
モニア水溶液中で、５０℃において６時間中和処理し、ついで水洗濾過し８０℃
において６時間乾燥した。その結果、平均粒子径２８μｍの粒子形状が球状のフ
ェノール樹脂粉末が得られた。つぎに上記方法により製造した球状フェノール樹脂１０ｋｇを計量し、更に該
球状フェノール樹脂粉末１００重量部に対し、水溶性メラミン樹脂（住友化学（
株）製、スミテックスレジンＭ−３、固形分濃度８０％）を固形分の量で２０重
量部、重合度１７００けん化度８８％のポリビニルアルコール４重量部、馬鈴薯
澱粉２０重量部およびエチレングリコール４重量部を計量した。上記原料のうちポリビニルアルコールを温水で２０重量％の水溶液となるよう
に溶解し、このビニルアルコール水溶液に水溶性メラミン樹脂、馬鈴薯澱粉およ
びエチレングリコールを加えニーダーで１０分間混合した。その後球状フェノー
ル樹脂を加えて更に１０分間混合した。この混合組成物を２軸押出造粒機（不二パウダル（株）製、ペレッタダブル、
ＥＸＤＦ−１００型）で押出し、平均粒子径が３ｍｍφ×６ｍｍＬの粒状体を造
粒した。該粒状体を８０℃で２４時間熱処理し、分子ふるい炭素前駆体組成物を
得た。該前駆体組成物は前記作業の繰り返しにより約２００ｋｇ作製した。この前駆体組成物を３バッチに分け、それぞれ有効寸法８００ｍｍφ×２００
０ｍｍＬのロータリーキルンに入れ、窒素雰囲気下６０℃／Ｈで昇温し、８００
℃で１時間保持し、その後、炉冷し、平均粒子径２．４ｍｍφ×４ｍｍＬのペレット状分子ふるい炭素を合計で１００ｋｇ製造した。この分子ふるい炭素は、（ａ）平均粒径約２０μｍ程度の多数の球状炭素粒子が三次元的に不規則に重
なり且つ合体された構造を有し、（ｂ）該多数の炭素粒子の間には、平均孔径約２μｍの三次元的に不規則に走
る連続通路が存在し、（ｃ）該炭素粒子の夫々は、該粒子の間の通路に連通する多数の細孔を有し、
そして（ｄ）炭素含有率は、９６％であった。更に（ｅ）２．５ｋｇｆ／ｃｍ²・Ｇの加圧下で酸素吸着を行なった際の１分後の
酸素吸着量（Ｑ₁）は７．５０×１０^-4ｍｏｌ／ｇ、窒素吸着量（Ｑ₂）は１．０
４×１０^-4ｍｏｌ／ｇで１分後の酸素・窒素の吸着容量比は７．２１であった。また、該分子ふるい炭素の２．５ｋｇｆ／ｃｍ²・Ｇでの酸素の平衡吸着量（
Ｑ₃）は８．９×１０^-4ｍｏｌ／ｇであった。また、該分子ふるい炭素のペレッ
ト状粒子の嵩密度は１．０２ｇ／ｃｍ³、充填密度は０．６５３ｇ／ｃｍ³であっ
た。次に第１図に示す２塔の吸着塔と製品貯留槽及び原料空気圧縮機、除湿機及び
それらを連続する配管及び自動弁よりなる窒素ガス分離装置により空気を原料と
して窒素ガスの濃縮分離実験を行なった。本実施例では第１図に於て、吸着塔内
径は２００ｍｍφ×１，０００ｍｍＬ（内容積Ｖ_A＝３１．４ｌ）、製品貯留槽
は内径２５０ｍｍφ×１，１５０ｍｍＬ（内容積Ｖ_R＝５６．４ｌ：Ｖ_R／Ｖ_A＝
１．７９６）、コンプレッサー定格は２．２ｋＷとした。このガス分離装置を用
い第１表に示す操作サイクル及び操作時間で運転し製品ガス取出量と製品窒素ガ
ス純度の関係について検討した結果を第２表に示す。尚、本実施例に於ては、吸
着塔の最高到達圧力を７ｋｇｆ／ｃｍ²・Ｇとし、再生は大気圧再生とした。上表から吸着塔１塔当りの有効容積が製品ガス取出量（Ｎｌ／ｍｉｎ）の０．
３以下の場合には製品窒素ガスの純度が低くなり多くの工業的用途に対して適用
不可能となり、また１０以上の場合には製品取出量が装置サイズに比較して小さ
くなり過ぎ、動力原単位も増大することがわかる。実施例２実施例１と同様の第１図に示した装置構成のガス分離装置で実施例１と同一の
分子ふるい炭素を用い製品貯留槽と吸着塔の有効容積の比率をかえて空気を原料
とする窒素ガス濃縮分離実験を行なった。コンプレッサー定格は２．２ｋＷとし
、吸着塔は内径２００ｍｍφ×１，０００ｍｍＬ（内容積Ｖ_A＝３１．４ｌ）と
した。また、ＰＳＡ操作条件は実施例１の場合と同一とした。その結果を第３表に示す。上表より製品貯留槽容積の吸着塔容積に対する比率が小さ過ぎる場合には製品
窒素ガスの純度が低下し、また、製品貯留槽内容積が大き過ぎる場合には、装置
起動時の濃度安定に要する時間が長くなることがわかる。実施例３実施例１と同様の分子ふるい炭素の製造法により、焼成時の最高到達温度をか
えることにより２．５ｋｇｆ／ｃｍ²・Ｇでの酸素と窒素の１分後の吸着量比が
異なる第４表に示す５種類の分子ふるい炭素を製造した。第４表に示す吸着特性を有する分子ふるい炭素を実施例１と同一の装置を用い
空気を原料とする窒素ガスの濃縮分離実験を行った。操作サイクルとしては第５
表に示す工程を採用した。自動弁の作動条件としては還流時間は設定しなかった
が、本操作サイクルに於ては、吸着工程初期に吸着圧力の高い製品貯留槽より昇
圧の完了していない吸着塔に製品窒素ガスが自動的に還流する。この還流は吸着
塔圧力と製品貯留槽圧力がバランスするまで継続し、その後は、吸着塔より製品
貯留槽へ製品窒素ガスが流入することになる。上記操作サイクルにより窒素ガス濃縮実験を行なった結果を第６表に示す。本
実験での窒素ガス取出量は２５ｌ／ｍｉｎとした。上表から試料Ｎｏ．２〜４では比較的良好な結果が得られたことがわかる。Description: TECHNICAL FIELD The present invention relates to a method for separating nitrogen gas having a higher concentration than a mixed gas containing nitrogen by utilizing the selective adsorption characteristics of molecular sieve carbon. [Prior art] Industrial nitrogen gas, which is widely used for heat treatment of metals, semiconductor production, and explosion-proof sheets for chemical plants, is conventionally produced mainly by cryogenic separation equipment and supplied to users by piping, tank lorries, cylinders, etc. It has been. In recent years, as a new method for producing nitrogen gas, for example, Japanese Patent Publication No. 54-17595
So-called Pressure Swing Adsorption such as a method in which a raw material gas is fed under pressure to an adsorption tower using molecular sieve coke as a filler disclosed in Japanese Patent Publication No. ; PS
A) A method for producing nitrogen gas has been developed. In this PSA type nitrogen gas separation method, attention is paid to any advantage that the apparatus is small in size, easy to operate, and capable of unmanned continuous operation as compared with the cryogenic separation method, and various apparatus improvements have been proposed at present. I have. In this PSA-type nitrogen gas separation method, various conditions such as an apparatus configuration, an adsorbent, and an operation cycle determine the purity, generation amount, required power, and the like of the generated nitrogen gas. Is being done. However, at present, there are still many issues to be overcome regarding nitrogen gas purity, generation amount, unit energy consumption, or further downsizing of the apparatus. [Problems to be Solved by the Invention] The present inventors have completed the present invention as a result of intensive studies in view of such current situation, and the purpose is to convert high-purity nitrogen gas into a low energy source. An object of the present invention is to provide a method for separating nitrogen gas which can be generated in a large amount in units. [Means for Achieving the Object] The above object is to supply a mixed gas containing nitrogen to at least two or more adsorption columns,
In the PSA method of alternately repeating the high-pressure adsorption step and the low-pressure regeneration step in each adsorption tower to separate nitrogen gas, (A) molecular sieving carbon (a) a large number of spherical carbon particles having a particle size of 0.8 to 120 μm Has a three-dimensionally irregularly overlapping and coalesced structure, and (b) a continuous three-dimensionally irregular passage exists between the plurality of carbon particles. Each has a number of pores communicating with the passages between the particles, and (d) has a carbon content of at least 85% by weight, and (e) a 2.5 kgf / cm ² · G Using a molecular sieve carbon having a volume ratio of the adsorbed amount of oxygen and nitrogen after 1 minute of performing single component adsorption under pressure of 3.5 to 20; 0.3 of product gas extraction (Nl / min)
And the product storage tank effective volume is 1.10 times the effective volume per adsorption tower .
A 4 to 2 times, as (C) adsorption-desorption operation cycle, adsorption, pressure equalization, comprising the steps of reproducing, then play atmospheric pressure in the regeneration step, and forced between the pressure equalization step and the adsorption step And / or automatically at the beginning of the adsorption step, wherein the nitrogen-enriched gas is returned from the product storage tank to the adsorption tower, and (D) the adsorption step is performed for 130 to 210 seconds. Achieved by the method. The method for producing molecular sieve carbon having the above-mentioned structure and characteristics used for separating nitrogen gas according to the present invention is described in detail in JP-A-64-61306, the main points of which are as follows. That is, (a) a spherical thermosetting phenol resin powder having a particle size of 1 to 150 μm
(B) a solution of a thermosetting resin composed of a phenol resin or a melamine resin,
50 parts by weight (as a solid content) (c) A homogeneous mixture of 1 to 30 parts by weight of a polymer binder selected from polyvinyl alcohol and a water-soluble or water-swellable cellulose derivative is prepared, and the uniform mixture is formed into granules. Then, the granular material is subjected to a heat treatment at a temperature in the range of 500 to 1100 ° C. in a non-oxidizing atmosphere to be carbonized, thereby forming granular molecular sieve carbon. The molecular sieve carbon preferably has a large number of spherical carbon particles having a particle size of 2 to 3 particles.
0 μm, and preferably the average diameter of the continuous passage between the large number of carbon particles is from 0.1 to
20 μm. This molecular sieve carbon has a large number of pores in which each of the large number of carbon particles communicates with a passage between the particles, in combination with the features of the above (A) and (B). The presence of the large number of pores greatly contributes to the expression of selective adsorption of molecular sieve carbon. The pores in the multiplicity of carbon particles preferably have an average diameter of about 10 ° or less. The volume occupied by the pores is preferably 0.1 g / g of molecular sieve carbon.
To 0.7 cc, more preferably 0.15 to 0.5 cc, and still more preferably 0.2 to 0.4 cc. The molecular sieve carbon has, as a compositional feature, a carbon content of at least 85% by weight, preferably at least 90% by weight. The molecular sieve carbon preferably has a porosity of 25 to 50% by volume, more preferably 30 to 45% by volume. The bulk density is preferably 0.7 to 1.2 g / cc, more preferably 0 to 1.2 g / cc.
. 8 to 1.1 g / cc. As described above, the molecular sieve carbon preferably has pores having an average diameter of 10 ° or less, and preferably these pores are most frequently distributed in an average diameter of 3 to 5A. The specific surface area of the molecular sieve carbon, B. by N ₂ adsorption E. FIG. T. As a value measured by the method, it is usually about 1 to 600 m ² / g, preferably about 10 to 400 m ² / g, and most preferably about ²⁰ to 350 m ² / g. The molecular sieve carbon is provided, for example, in the form of a column having a diameter of about 0.5 to 5 mm and a length of about 1 to 10 mm, or a spherical form having a diameter of about 0.5 to 10 mm. 75 g / cm ³ , preferably 0.50 to 0.70 g / cm ³
cm ³ . According to the above-mentioned production method, when the single component adsorption was performed under a pressure of 2.5 kgf / cm ² · G, the volume ratio of the adsorbed amounts of oxygen and nitrogen after 1 minute was 3.5 to 20. Pre-sieved carbon works extremely effectively in the PSA method of separating nitrogen gas from a mixed gas containing nitrogen, and it is possible to separate high-purity nitrogen gas very efficiently. It was found that the effect was extremely remarkable by setting as follows and combining with the present MSC. That is, in a PSA apparatus having at least two or more adsorption towers: (1) The effective volume per adsorption tower is 0.3% of the product gas extraction amount (Nl / min).
And the product storage tank effective volume is 1.4 times the effective volume per adsorption tower.
A 2 times, (2) as adsorption-desorption operation cycle, adsorption, pressure equalization, comprising the steps of reproducing, then play atmospheric pressure in the regeneration step, and forced between the pressure equalization step and the adsorption step Or a step of automatically refluxing the nitrogen-enriched gas from the product storage tank to the adsorption tower at the beginning of the adsorption step. (3) The configuration and operating conditions of the PSA apparatus in which the adsorption step is 130 to 210 seconds . The characteristics of the MSC in the present invention were determined to be 2.5 kgf /
In the single-component adsorption under a pressure of cm ² · G, the capacity ratio of the adsorption amounts of oxygen and nitrogen after one minute is 3.5 to 20. This adsorption capacity ratio is preferably from 4.5 to 20, and most preferably from 9 to 20. The MSC has an oxygen adsorption capacity after 1 minute in the same measuring method of usually 6 × 10 ^{-4 to} 9 × 10 ^-4 mol, preferably 7 × 10 ^{-4 to} 9 × 10 ^-4 mol per gram of MSC. Mol, most preferably 7.5 × 10 ^{-4 to} 9
× 10 ^-4 mol. The PSA device of the present invention is mainly composed of two or more adsorption columns filled with MSC, a raw material mixed gas supply device such as a compressor, a product storage tank for storing product nitrogen gas, and a pipe connecting these components. And an automatic valve for controlling the flow of gas and its control system, a flow controller, a gas concentration analyzer and the like. In the very efficient nitrogen gas separation method of the present invention, the effective volume per one adsorption tower in the above-described apparatus configuration is 0.3 to 10 of the product gas extraction amount (Nl / min).
And preferably 0.5 to 7 times, and most preferably 0.7 to 4 times. Also,
The effective volume of the product storage tank is 1.4 to 2 times the effective volume per adsorption tower. If the capacity of the adsorption tower is small relative to the product withdrawal, the productivity per capacity of the adsorption tower is improved,
The power consumption per product unit amount, that is, the power consumption unit is also small, but the nitrogen purity of the product is reduced. The purity of the product nitrogen gas obtained in the present invention varies depending on the column pressure in the adsorption step and the regeneration step, but within the range of the ratio between the adsorption tower volume and the product gas extraction flow rate (Nl / min) of the present invention, Normal nitrogen purity (N ₂ + Ar) 99.999
It is possible to obtain a product gas in the range of 9 to 99 vol%. Therefore, when it is desired to obtain high-purity nitrogen gas within the range of the present invention, the capacity of the adsorption tower may be increased, and when relatively low-purity nitrogen gas is sufficient, the capacity of the adsorption tower may be reduced. Also,
If the volume of the product storage tank is too small, the return of the nitrogen-enriched gas refluxing from the product storage tank to the adsorption tower is forced between the pressure equalization step and the adsorption step of the PSA operation cycle or automatically at the beginning of the adsorption step. The flow rate is too small, and it becomes difficult to efficiently obtain high-purity product nitrogen gas, and the supply pressure of the product nitrogen gas decreases, which is not preferable. On the other hand, when the volume of the product storage tank is too large, it takes too much time for the nitrogen concentration of the product storage tank to reach a predetermined steady-state value when the apparatus is started, and the waiting time becomes longer. One example of an embodiment of the actual operation of separating nitrogen gas by the PSA device having the above-described configuration of the present invention will be described below with reference to FIG. In FIG. 1, (1) is an air compressor, (2) is an air dryer, (3), (3)
a) is an adsorption tower, (4), (4a), (7), (7a), (10), (10a)
, (13), (13a)... Are valves, (5), (5a), (18), (9), (9a
), (11), (12), (16) ... are pipes, (14) is a reservoir tank,
(15) is a valve. In the figure, the raw material air supplied by the air compressor (1) is dehumidified by a dehumidifier (2) if necessary, and then is passed through an automatic valve (4) or (4a) to the adsorption tower (3) or (3a). Supplied to For example, when the adsorption tower (3) is in the adsorption step, the raw material air is supplied to the adsorption tower, and the adsorption tower (3a) is a regeneration step. The pressure inside the adsorption tower in the adsorption step is usually 3 to 9 kgf / cm ² · G, preferably 4 to 8.5 k.
gf / cm ² · G, most preferably 5 to 8 kgf / cm ² · G. In addition, since the regeneration of the adsorption tower is usually performed by opening to the atmosphere (hereinafter, referred to as atmospheric pressure regeneration), the internal pressure of the adsorption tower in the regeneration step decreases to the atmospheric pressure. FIG. 1 shows a pipe (
18) and an example in which a step of forcibly refluxing the nitrogen-enriched gas from the product storage tank by the automatic valve (19) is included. However, the pipe (18) and the automatic valve (19) are not provided, and the adsorption tower is not provided. And (11), (9), (
9a) and the case where reflux occurs automatically through the automatic valves (10) and (10a) is also included in the scope of the present invention. In the regeneration step, a so-called purge method may be employed in which the nitrogen-enriched gas in the product storage tank is back-flowed to wash the inside of the adsorption tower. Next, the adsorption tower (3) for which the adsorption step has been completed and the adsorption tower (3a) for which the regeneration step has been completed are separated from the adsorption tower product gas take-out side, the adsorption tower raw material gas feed side, or the adsorption tower product gas take-out side. The process is shifted to a so-called pressure equalization process in which a fixed amount of the mixed gas existing in the adsorption tower after the adsorption step is transferred to the adsorption tower after the regeneration step, which is connected to the gas inlet side. Normally, when the product gas outlet side of the adsorption tower is connected, the top pressure is equalized.When the product gas outlet sides of the adsorption tower and the product gas inlet side are connected, the upper and lower pressure is equalized. The case where the inlet side is connected to the inlet side is referred to as cross equalization, but it is within the scope of the present invention to perform the equalizing step including these equalizing methods or other equalizing methods. After completion of the equalizing step, the nitrogen-enriched gas may be forcibly refluxed from the product storage tank to the adsorption tower (3a) by the pipe (18) and the automatic valve (19). If not, or if the amount of forced reflux is small enough not to reach a perfect pressure balance between the adsorption tower and the product storage tank, the next adsorption tower (3a
At the beginning of the adsorption step (1), reflux is automatically caused by the pressure in the adsorption tower (3a) being lower than the internal pressure in the product storage tank (14). This automatic reflux is automatically performed by feeding the raw material air into the adsorption tower and refluxing the nitrogen-enriched gas from the product storage tank, thereby increasing the internal pressure of the adsorption tower and balancing the pressure with the product storage tank. The operation will be stopped and the process will be shifted to the removal of nitrogen-enriched gas from the adsorption tower to the product storage tank. During the adsorption step of the adsorption tower (3a), the adsorption tower (3) is in a regeneration step. The adsorption tower (3a) for which the adsorption step has been completed and the adsorption tower (3) for which the regeneration step has been completed are connected, and the process proceeds to the pressure equalization step. In this way, the steps of adsorption, pressure equalization, reflux, regeneration, and pressure equalization are sequentially repeated. In the above-mentioned PSA cycle of the present invention, the time of the adsorption step is 130 to 210 seconds . The length of the other steps is not particularly limited, but usually equalization is about 0.1 to 10 seconds, reflux is also about 0.1 to 10 seconds, and the length of the regeneration step is It is automatically determined by the balance with the adsorption process. [Effect of the Invention] The nitrogen gas separation method of the present invention combines a molecular sieve carbon having a unique micropore structure imparted with excellent nitrogen and oxygen separation ability, a specific PSA device configuration and a specific PSA operation method. By doing so, the purity of the product nitrogen gas is high, the amount generated is large, and
An object of the present invention is to provide a method for separating nitrogen gas having a small power consumption unit. That is, in the nitrogen gas separation method of the present invention, a large number of spherical carbon particles have a three-dimensionally irregularly overlapping and united structure, and the three-dimensional Excellent nitrogen and oxygen separation, usually in the form of pellets, with a continuous passage running irregularly and each of the carbon particles having a unique microstructure with a large number of pores communicating with the passage between the particles This is a method for separating nitrogen gas which has a remarkable effect that can be achieved only in a specific apparatus configuration and a specific operation method using molecular sieve carbon imparted with a function and using the molecular sieve carbon as a filler. In the present invention, for example, the product nitrogen gas purity (volume% of nitrogen + argon) is 9%.
The purity can be as high as about 9 to 99.9999%, and the amount of product generated per volume of the adsorption tower [(Nl / min) / l] varies depending on the purity.
It is possible to take up to three times as large a range. Further, the power required for performing the nitrogen gas separation of the present invention differs depending on the equipment conditions, operating conditions, product purity, etc., but is further reduced as compared with the conventional technology, and the advantages are extremely large. . Hereinafter, the present invention will be described specifically with reference to examples. The measurement methods used in the present invention are summarized below. (1) Measurement of pore volume and pore size distribution: The pore volume and pore size distribution of the molecular sieve carbon of the present invention are as follows.
The pores in the range of 0 μm were measured by a mercury intrusion method using a porosimeter (Pore Sizer 9310, manufactured by Shimadzu Corporation). For pores having a pore diameter of 60 ° or less, the nitrogen gas adsorption isotherm indicates
It was determined by the following so-called Kelvin equation. P: Saturated vapor pressure when the adsorbed gas is adsorbed in the pores, P ₀ : Saturated vapor pressure of the adsorbed gas in a normal state, γ: Surface tension, V: One molecular volume of liquid nitrogen, R: Gas constant, T: Absolute temperature, γK: Kelvin radius of pore, Kelvin radius of pore were corrected by Cranston-Inkley method. (2) Measurement of Adsorption and Equilibrium Adsorption of Oxygen and Nitrogen After One Minute: The adsorption capacity of molecular sieve carbon for oxygen and nitrogen used in the present invention was measured by an adsorption characteristic measuring apparatus shown in FIG. In FIG. 2, (1) is a vacuum pump, (2), (3), (8), (11),
(12), (13) ... are valves, (4) is a sample chamber, (5) is an adjustment chamber, (6), (
7) is a pressure sensor, (9) is a recorder, (10) is a pressure gauge, (14) and (15).
Is a gas regulator, (16) is a nitrogen cylinder, and (17) is an oxygen cylinder. In the same figure, about 3 g of a sample was put in the sample chamber (4) (226.9 ml), valves (11) and (8) were closed, and valves (2) and (3) were opened and degassed for 30 minutes. The valves (2) and (3) are closed, the valve (11) is opened, and the adjustment chamber (5) (231.
Oxygen gas or nitrogen gas is fed into the reactor (7 ml), and when the pressure reaches the set pressure, the valve (11) is closed, the valve (3) is opened, and the change in the internal pressure during a predetermined time is measured. The change in the amount over time was measured, and the amount of oxygen adsorbed (Q ₁ ) and the amount of adsorbed nitrogen (Q ₂ ) one minute after the start of adsorption were determined. The measurement was continued until the change with time became stable to a constant value, and the oxygen equilibrium adsorption amount (Q ₃ ) and the nitrogen equilibrium adsorption amount (Q ₄ ) were also measured. The measurement was carried out at an internal pressure of the adsorption tower one minute after the start of the measurement or at an internal pressure of 2.5 when the equilibrium adsorption tower was measured.
The initial set pressure was changed so that several points larger or smaller than kgf / cm ² · G could be measured, and the adsorption amount of oxygen and nitrogen after 1 minute at 2.5 kgf / cm ² · G And the equilibrium adsorption amount. Example 1 A 400 l reaction vessel was charged with 300 kg of a mixed aqueous solution composed of 18% hydrochloric acid and 9% formaldehyde, and the temperature was adjusted to 20 ° C. Next, 12 kg of a 90% concentration aqueous phenol solution (20 ° C.) prepared using 98% (2% water) phenol and water was added to the reaction vessel. After the addition, the mixture was stirred for 30 to 40 seconds, and the contents in the reaction vessel suddenly became cloudy, and the stirring was stopped and the mixture was allowed to stand. When the container is left standing, the internal temperature gradually rises, and the contents gradually turn pale pink and become cloudy.
Minutes later, formation of a slurry or resinous material was observed. After the above step, the content was subsequently heated to 75 to 76 ° C. for 30 minutes and kept at this temperature for 40 minutes with stirring. Next, the content was washed with water, neutralized in a 0.1% aqueous ammonia solution at 50 ° C for 6 hours, and then washed with water and filtered.
For 6 hours. As a result, a phenol resin powder having an average particle diameter of 28 μm and a spherical particle shape was obtained. Next, 10 kg of the spherical phenol resin produced by the above method was weighed, and 100 parts by weight of the spherical phenol resin powder was added to a water-soluble melamine resin (Sumitomo Chemical (
Co., Ltd., Sumitex Resin M-3, solid content concentration 80%), 20 parts by weight of solid content, 4 parts by weight of polyvinyl alcohol having a degree of polymerization of 1700 and a saponification degree of 88%, 20 parts by weight of potato starch, and ethylene glycol 4 Parts by weight were weighed. Of the above raw materials, polyvinyl alcohol was dissolved in warm water to give a 20% by weight aqueous solution, and a water-soluble melamine resin, potato starch and ethylene glycol were added to the vinyl alcohol aqueous solution and mixed for 10 minutes with a kneader. Thereafter, the spherical phenol resin was added and mixed for another 10 minutes. This mixed composition is subjected to a twin-screw extrusion granulator (Fuji Paudal Co., Ltd., Peretta Double,
EXDF-100) to granulate a granular material having an average particle size of 3 mmφ × 6 mmL. The granules were heat-treated at 80 ° C. for 24 hours to obtain a molecular sieve carbon precursor composition. About 200 kg of the precursor composition was prepared by repeating the above operation. This precursor composition was divided into three batches, each having an effective size of 800 mmφ × 200.
Place in a 0 mmL rotary kiln, raise the temperature at 60 ° C / H under nitrogen atmosphere,
C. for 1 hour, and then cooled in a furnace to produce a total of 100 kg of pelletized molecular sieve carbon having an average particle diameter of 2.4 mmφ × 4 mmL. The molecular sieve carbon has the following structure: (a) a structure in which a large number of spherical carbon particles having an average particle size of about 20 μm are three-dimensionally irregularly overlapped and united; Has a three-dimensionally irregular continuous passage having an average pore diameter of about 2 μm, and (c) each of the carbon particles has a large number of pores communicating with the passage between the particles,
And (d) the carbon content was 96%. (E) When oxygen adsorption was performed under a pressure of 2.5 kgf / cm ² · G, the oxygen adsorption amount (Q ₁ ) after one minute was 7.50 × 10 ^-4 mol / g, and the nitrogen adsorption amount (Q ₁ ) Q ₂ ) is 1.0
The oxygen / nitrogen adsorption capacity ratio after one minute at 4 × 10 ⁻⁴ mol / g was 7.21. In addition, the equilibrium adsorption amount of oxygen at 2.5 kgf / cm ² · G of the molecular sieve carbon (
Q ₃ ) was 8.9 × 10 ⁻⁴ mol / g. The bulk density of the molecular sieve carbon pellets was 1.02 g / cm ³ , and the packing density was 0.653 g / cm ³ . Next, a nitrogen gas concentration and separation experiment was performed using air as a raw material by a nitrogen gas separation device comprising two adsorption towers, a product storage tank, a raw material air compressor, a dehumidifier, and piping and an automatic valve connecting them as shown in FIG. Was performed. In the present embodiment At a first figure, the adsorption tower inner diameter 200mmφ × 1,000mmL (internal volume V _A = 31.4l), the product reservoir is the inside diameter 250mmφ × 1,150mmL (internal volume V _R = 56.4l : V _R / V _A =
1.796), and the compressor rating was 2.2 kW. Table 2 shows the results obtained by operating this gas separation apparatus at the operation cycle and operation time shown in Table 1 and examining the relationship between the product gas extraction amount and the product nitrogen gas purity. In this example, the maximum pressure of the adsorption tower was 7 kgf / cm ² · G, and the regeneration was at atmospheric pressure. From the above table, the effective volume per adsorption tower is 0.1% of the product gas output (Nl / min).
If it is less than 3, the purity of the product nitrogen gas will be low and it will not be applicable to many industrial applications. If it is more than 10, the product removal will be too small compared to the equipment size, and It can be seen that the unit also increases. Example 2 A gas separation apparatus having the same configuration as that of Example 1 and shown in FIG. 1 and using the same molecular sieve carbon as in Example 1 and changing the effective volume ratio between the product storage tank and the adsorption tower to produce air as raw material A nitrogen gas concentration separation experiment was performed. The compressor rating was 2.2 kW, and the adsorption tower had an inner diameter of 200 mmφ × 1,000 mmL (internal volume _VA = 31.4 l). The PSA operation conditions were the same as those in Example 1. Table 3 shows the results. From the table above, if the ratio of the product storage tank volume to the adsorption tower volume is too small, the purity of the product nitrogen gas will be reduced, and if the product storage tank internal volume is too large, it will be necessary to stabilize the concentration when starting the device. It turns out that time becomes long. Example 3 By the same method for producing molecular sieved carbon as in Example 1, the ratio of the amount of adsorbed oxygen and nitrogen after one minute at 2.5 kgf / cm ² · G was changed by changing the maximum temperature during firing. Five types of molecular sieve carbons shown in Table 4 were produced. Using the same apparatus as in Example 1, molecular sieve carbon having the adsorption characteristics shown in Table 4 was subjected to a nitrogen gas concentration / separation experiment using air as a raw material. The fifth operation cycle
The steps shown in the table were employed. Although the reflux time was not set as the operating condition of the automatic valve, in this operation cycle, the product nitrogen gas was automatically transferred from the product storage tank having a high adsorption pressure to the adsorption tower whose pressure was not completely increased at the beginning of the adsorption process. Reflux. This reflux is continued until the pressure in the adsorption tower and the pressure in the product storage tank are balanced, and thereafter, the product nitrogen gas flows into the product storage tank from the adsorption tower. Table 6 shows the results of a nitrogen gas enrichment experiment performed by the above operation cycle. The amount of nitrogen gas taken out in this experiment was 25 l / min. From the above table, sample No. It can be seen that comparatively good results were obtained in Nos. 2 to 4.

【図面の簡単な説明】第１図は本発明の実施態様の一例に用いる装置の説明図である。同図において
、（１）……空気圧縮機、（２）……エアドライヤ、（３），（３ａ）……吸着
塔、（４），（４ａ），（７），（７ａ），（１０），（１０ａ），（１３），
（１３ａ）……弁、（５），（５ａ），（１８），（９），（９ａ），（１１）
，（１２），（１６）……パイプ、（１４）……リザーバータンク、（１５）…
…バルブである。第２図は分子ふるい炭素の分子ふるい特性を評価するための吸着特性測定装置
の説明図である。同図において、（１）……真空ポンプ、（２），（３），（８
），（１１），（１２），（１３）……バルブ、（４）……試料室、（５）……
調整室、（６），（７）……圧力センサー、（９）……記録計、（１０）……圧
力計、（１４），（１５）……ガスレギュレーター、（１６）……窒素ボンベ、
（１７）……酸素ボンベである。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of an apparatus used as an example of an embodiment of the present invention. In the figure, (1) ... air compressor, (2) ... air dryer, (3), (3a) ... adsorption tower, (4), (4a), (7), (7a), (10) ), (10a), (13),
(13a) ... valve, (5), (5a), (18), (9), (9a), (11)
, (12), (16) ... pipe, (14) ... reservoir tank, (15) ...
... a valve. FIG. 2 is an explanatory view of an adsorption characteristic measuring apparatus for evaluating molecular sieve characteristics of molecular sieve carbon. In the figure, (1)... Vacuum pump, (2), (3), (8)
), (11), (12), (13) ... valve, (4) ... sample chamber, (5) ...
Adjustment chamber, (6), (7) pressure sensor, (9) recorder, (10) pressure gauge, (14), (15) gas regulator, (16) nitrogen cylinder ,
(17) An oxygen cylinder.

Claims

Claims: 1. A mixed gas containing nitrogen is supplied to at least two or more adsorption towers,
The high-pressure adsorption step and the low-pressure regeneration step are alternately repeated in each adsorption tower, and pressure swing adsorption (Pressure Swing Adsorb-tio) for separating nitrogen gas.
n; PSA) method: (A) as molecular sieve carbon (a) having a structure in which a large number of spherical carbon particles having a particle diameter of 0.8 to 120 μm are three-dimensionally irregularly overlapped and united; ) There is a continuous path running irregularly in three dimensions between the multiple carbon particles, and (c) each of the carbon particles has multiple pores communicating with the pathway between the particles. And (d) having a carbon content of at least 85% by weight, and (e) one minute after the oxygen and nitrogen have been subjected to the single-component adsorption under a pressure of 2.5 kgf / cm ² · G. (B) The effective volume per adsorption column is 0.3% of the product gas extraction amount (Nl / min) using a molecular sieve carbon having a capacity ratio of the adsorption amount of 3.5 to 20.
And the product storage tank effective volume is 1.10 times the effective volume per adsorption tower .
A 4 to 2 times, as (C) adsorption-desorption operation cycle, adsorption, pressure equalization, comprising the steps of reproducing, then play atmospheric pressure in the regeneration step, and forced between the pressure equalization step and the adsorption step And / or automatically at the beginning of the adsorption step, wherein the nitrogen-enriched gas is returned from the product storage tank to the adsorption tower, and (D) the adsorption step is performed for 130 to 210 seconds. Method.