分離技術シリーズ 31

ガス分離膜プロセスの基礎と応用

原

谷

賢

治・伊

藤 直

分 離 技 術 会

次

｢分離技術シリーズ｣ の継続刊行に当たって研究開発とは，新しい原理や現象を発見することばかりではなく，原理・現象は既知であっても新しい方法を案出するとか，あるいは新しい組み合わせを創案することによって，新しい技術，商品，品質，機能，用途，方法等々を創出することである．
本会は主に化学品の製造に関わる分離技術を包括的に扱う専門の学会である
が，研究者・技術者を糾合して正に関連分野の研究・開発の進展を目指し，急激な変化に対応しようと心がけている．
すでに何冊か刊行された本シリーズのなかには，本会会誌 ｢分離技術｣ 誌に掲載された論文によっているものもある．しかし，論文に記載された技術を取捨選択し，それらの組み合わせを考えて執筆されたものであるから，上述の視点から成書としての価値は高いといえるであろう．
さて，最近あらたな構想のもとに，本委員会よりいろいろな分野の権威者に執筆を依頼し，本シリーズに書き下ろしの著作物が加えられることになったのは誠に慶賀に堪えない次第である．分離技術の益々の発展に寄与することは勿論，読者諸兄姉に研鑽のお役に立つものと信じている．
分離技術シリーズ出版委員会
委員長

白

石

浩

は し が き

最初の市販ガス分離膜が登場して以来約 35 年が経過し，膜を用いたガス分離法(水素分離，CO2 分離，窒素分離，水蒸気分離など)は少しずつ普及を拡大してきている．加えて近年，温暖化対策や水素エネルギー社会の実現に貢献する技術としても期待が高まっており，産学官あげて研究開発が盛んになっている．その結果，新たな研究者や技術者の輪も広がりつつあることは，この分野で研究活動を続けてきた著者らにとってはたいへん喜ばしいことである．
一方で，膜によるガス分離法は歴史が浅いため体系だった書物が少なく，特に初めてガス分離膜について学ぶあるいは取り組もうという学生や研究開発者
にとって拠り所となる入門書が必要であると感じてきた．今回，分離技術会から執筆の機会をいただき，是非とも実現したいと考えたことは初歩から応用までの解説書であった．
第一部では，ガス分離膜の作製からプロセス設計までの一連の作業を行うことを想定し，基礎的事項と応用に関して実験法や計算法を解説した．設計法など数式の扱いについては習得の助けとなるように例題をもうけた．第二部では，化学反応が有する課題を膜の導入によって解決できる可能性があるという立場から，分離機能を有するだけでなく厳しい使用条件でも耐えることのできる無機複合膜の必要性，それらを反応器に組み込むことによって反応分離同時操作が可能になるメンブレンリアクター(膜反応器)の基本設計と操作方法，さらには得られる平衡移動効果などについて具体例を挙げて説明した．
執筆にあたり，重要な事項を漏らさず分かりやすくを心掛けたつもりである．
拙著がガス分離膜および応用技術の研究開発や実用の促進に少しでも役に立てれば幸いである．
2015 年 5 月
原

谷

賢

治

伊

藤

直

次

目

次

第一部：ガス分離膜の基礎とプロセス設計
ガス分離膜概説 ·································································

1

はじめに ···················································································

1

1．1

膜によるガス分離の原理 ·····················································21．2

分離係数と理想分離係数 ·····················································

41．3

ガス分離膜の開発 ······························································

4

第１章

1．3．1

膜開発の歴史·····························································

4

1．3．2

ガス分離膜の種類と製膜法···········································

5

1．3．3

膜モジュール·····························································

12

1．3．4

各種膜の特長的透過性と開発トレンド····························

14

1．4

分離プロセスの事例 ···························································

17

第２章

膜の透過機構と透過速度式 ··················································

20

2．1

膜の種類と透過機構 ···························································

20

2．2

実験系の透過速度式 ···························································

22

2．3

摩擦モデルによる透過の基本概念 ·········································

23

2．4

透過機構別の透過係数式 ·····················································

25

2．4．1

ゴム状高分子膜の理想的な溶解拡散·······························

25

2．4．2

ガラス状高分子膜の二元移動········································

25

2．4．3

キャリアーによる促進輸送···········································

27

2．4．4

パラジウム系金属膜の水素透過·····································

28

2．4．5

多孔質膜のガス透過····················································

28

2．4．6

表面拡散···································································

30

2．4．7

分子ふるい································································

31

2．5

混合型の透過係数式 ···························································

2．5．1

レジスタンスモデル····················································

2．5．1．1

32
32

例題 ·································································

33

Maxwell モデル ··························································

35

第３章

ガス分離膜の評価実験法 ·····················································

37

3．1

細孔径の評価法 ·································································

37

2．5．2

3．1．1

ガス透過法································································

37

3．1．2

パームポロメトリー法·················································

37

3．1．3

サブナノ孔の評価法····················································

39

透過特性値の測定法 ···························································

39

3．2

3．2．1

定容積圧力変化法による透過量の測定····························

40

3．2．2

ガスクロマトグラフを用いた透過量の測定······················

41

3．2．3

定圧容積変化法による透過量の測定·······························

42

3．2．4

収着量の測定·····························································

42

3．2．5

濃度依存透過特性値の平均値········································

44

混合ガスの分離実験 ···························································

45

3．3

3．3．1

混合ガス成分の透過係数測定········································

45

3．3．2

膜面での濃度分極現象·················································

46

主な膜の透過特性 ······························································

48

3．4

3．4．1

透過係数の温度依存····················································

48

3．4．2

ガス物性の影響··························································

50

3．4．3

膜物性の影響·····························································

52

理想的流れモデル ·················

54

4．1

モジュール内の物質収支 ·····················································

54

4．2

設計の前提条件と準備 ························································

55

4．3

理想流れモデルのモジュール ···············································

56

第４章

ガス分離膜モジュールの設計１

4．3．1

完全混合モデル··························································

56

4．3．2

高圧側流れがプラグフローのモデル·······························

60

4．3．2．1

片側混合プラグフロー ·········································

61

4．3．2．2

十字流プラグフロー ············································

62

4．3．2．3

並流プラグフロー ···············································

62

4．3．2．4

向流プラグフロー ···············································

62

4．3．2．5

例題 ·································································

63

非理想的要因への対応 ···········

65

5．1

ガス成分間相互作用 ···························································

65

5．2

膜外の流体力学的な要因 ·····················································

66

第５章

ガス分離膜モジュールの設計２

5．2．1

モジュール内圧力損失·················································

66

5．2．2

濃度分極···································································

69

5．2．2．1

膜外表面での分極 ···············································

69

5．2．2．2

多孔質支持層での分極 ·········································

70

5．2．3

混合拡散···································································

71

5．2．4

その他の問題·····························································

73

5．2．5

CFD ソフトによる設計計算 ·········································

73

第６章

膜モジュール構造と連結法の工夫 ·········································

74

6．1

内部二段式モジュール ························································

74

6．2

二種膜充填モジュール ························································

75

6．3

モジュール連結の工夫 ························································

76

6．3．1

並流＋向流の連結·······················································

76

6．3．2

ツリー型連結·····························································

78

供給流直列連結の実用的モジュール配列 ································

79

6．4

6．4．1

例題·········································································

81

第７章

ガス分離膜による高分離プロセスの設計 ································

84

7．1

分離性能のインデックス ·····················································

84

7．2

加圧・減圧モードと所要動力 ···············································

86

7．3

多段カスケードプロセス ·····················································

87

7．4

循環型プロセス ·································································

88

7．5

プロセス設計計算 ······························································

89

7．6

経済性比較のインデックス ··················································

94

7．7

コスト概算の例 ·································································

96

第二部：気相系メンブレンリアクターの基礎と設計
第１章
1．1

化学反応における課題と反応分離 ········································· 101
課

題 ·········································································· 1011．1．1

反応平衡による制約···················································· 1011．1．2

反応選択性の向上······················································· 1021．1．3

反応活性種の生成······················································· 1031．1．4

反応物や生成物の分離精製··········································· 103

1．1．5

反応熱の供給と除去···················································· 1031．2反応を促進するための分離 ·················································· 104

1．3

反応分離操作における無機系膜 ············································ 1051．3．1

反応と分離との結合···················································· 105

1．3．2

無機膜の優位性·························································· 107

第２章

無機系複合膜と透過速度式 ·················································· 109

2．1

複合膜化の意義 ································································· 109

2．2

分離活性層中の定常拡散 ····················································· 110

2．2．1

モデルおよび基礎式···················································· 110

2．2．2

支持体による流束低下················································· 112

2．3

多孔質複合膜の透過性能の評価 ············································ 114

2．3．1

気体透過速度式·························································· 114

2．3．2

分離活性層の透過係数と厚さの影響······························· 116

2．4パラジウム複合膜の透過性能 ··············································· 117

2．4．1

水素透過速度式·························································· 117

2．4．2

水素透過速度への操作圧の影響····································· 118

2．4．3

分離選択性································································ 120

第３章

反応・膜分離操作と定量的効果 ············································ 124

3．1

膜分離駆動力と操作方式 ····················································· 1243．2

反応分離の定量的効果 ························································ 125

3．2．1

完全混合流································································ 126

3．2．2

完全混合槽反応器での平衡反応····································· 1283．2．3

生成物の分離を伴う完全混合槽反応器···························· 129

第４章

パラジウムメンブレンリアクターのモデル化 ·························· 132

4．1

脱水素反応と反応平衡 ························································ 1324．1．1

平衡転化率································································ 1324．1．2

反応機構と水素分離効果·············································· 133

4．2

基礎式と各操作モデル ························································ 133

4．2．1

並流操作··································································· 1354．2．2

向流操作··································································· 136

4．2．3

減圧・真空操作·························································· 139

4．2．4

各操作とモデル計算との比較········································ 1404．3

限界水素回収率 ································································· 141

4．4

反応性スイープガスを使用した場合 ······································ 1444．4．1

等温操作··································································· 1444．4．2

断熱操作··································································· 145

4．5

CFD を利用したメンブレンリアクター内の可視化 ··················· 1484．5．1

多管式反応器····························································· 148

4．5．2

空気恒温槽内に置いた場合··········································· 151

4．5．3

テープヒータ加熱の場合·············································· 152

第５章

分離膜の選択性と膜反応器性能との関係 ································ 155

5．1

原料の透過損失による転化率低下 ········································· 1555．2

膜性能と反応成績 ······························································ 1565．2．1

反応温度と圧力の影響················································· 157

5．2．2

分離選択性の影響······················································· 158

5．3

予備触媒層 ······································································· 158

第６章

多孔質膜利用メンブレンリアクター ······································ 163

6．1

メタン水蒸気改質反応への応用 ············································ 1636．1．1

反応モデル································································ 163

6．1．2

膜反応器モデル·························································· 164

6．2

シミュレーション結果 ························································ 166

6．2．1

膜性能の影響····························································· 166

6．2．2

並流操作(スイープガス：窒素あるいは水蒸気)················ 167

6．2．3

並流操作および向流操作の比較(スイープガス：窒素)······· 169

使用記号 ······················································································ 172
索

引 ························································································· 174