JP2004244676A

JP2004244676A - Ion exchange membrane type electrolytic cell using gas diffusion cathode and its operation method

Info

Publication number: JP2004244676A
Application number: JP2003035369A
Authority: JP
Inventors: Kenji Nonomura; 健二野々村; Koji Saiki; 幸治斎木; Hiroaki Aikawa; 洋明相川
Original assignee: Chlorine Engineers Corp Ltd; Asahi Kasei Corp; Asahi Glass Co Ltd; Mitsui Chemicals Inc; Daiso Co Ltd; Toagosei Co Ltd; Kanegafuchi Chemical Industry Co Ltd; Tokuyama Corp; Tosoh Corp
Current assignee: Asahi Kasei Corp; Mitsui Chemicals Inc; Toagosei Co Ltd; Kanegafuchi Chemical Industry Co Ltd; Osaka Soda Co Ltd; Tokuyama Corp; Tosoh Corp; AGC Inc; ThyssenKrupp Nucera Japan Ltd
Priority date: 2003-02-13
Filing date: 2003-02-13
Publication date: 2004-09-02
Anticipated expiration: 2023-02-13
Also published as: JP4297694B2

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the damage of an ion exchange membrane and gas diffusion cathode by bringing the gas diffusion cathode into uniform and tight adhesion to the ion exchange membrane in electrolysis, such as ion exchange membrane brine electrolysis, and further to prevent the damage to gas diffusion cathode and the degradation in the electrolytic efficiency thereof due to current concentration. <P>SOLUTION: The electrolytic cell is constituted so as to press the gas diffusion cathode 7 toward the ion exchange membrane 2 by means of a porous plate 8 of a rigid body. As a result, the ion exchange membrane and the gas diffusion cathode are brought into contact with each other by nearly uniform force and the mechanical damage of the gas diffusion cathode and the ion exchange membrane is prevented. Further, caustic soda exists uniformly and therefore the current concentration to part of the gas diffusion cathode does not occur any more. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、ガス拡散陰極を使用したイオン交換膜型電解槽及びその運転方法、特にクロルアルカリ（食塩）電解槽及びその運転方法に関する。
【０００２】
【従来の技術】
クロルアルカリ電解を代表とする電解工業は、素材産業として重要な役割を果たしている。このような重要な役割を持つものの、クロルアルカリ電解に要する消費エネルギーが大きく、日本のようにエネルギーコストが高い国ではその省エネルギー化の達成を強く要望されている。
例えば、クロルアルカリ電解は、環境問題の解決と共に省エネルギー化を達成するために、水銀法から隔膜法を経てイオン交換膜法へと転換され、約２５年で約４０％の省エネルギー化を達成してきた。しかし、この省エネルギー化でも不十分で、エネルギーである電力コストが全製造費の約半分を占めているが、現行の方法を使用する限りこれ以上の電力節約は不可能なところまで来ている。更なる省エネルギー化を達成するためには電極反応を変換する等の抜本的な変更を行わなければならない。その例として燃料電池等で採用されているガス拡散電極の使用は現在考えられている中で最も可能性が高く、電力節約に対する有効な手段である。従来の金属陰極を使用する電解反応▲１▼が、陰極としてガス拡散陰極を使用し酸素を供給すると電解反応▲２▼に変換される。
【０００３】
▲１▼２ＮａＣｌ＋２Ｈ_２Ｏ→Ｃｌ_２＋２ＮａＯＨ＋Ｈ_２Ｅｏ＝２．１９Ｖ
▲２▼２ＮａＣｌ＋１／２Ｏ_２＋２Ｈ_２Ｏ→Ｃｌ_２＋２ＮａＯＨＥｏ＝１．１４Ｖ
【０００４】
つまり金属陰極をガス拡散陰極に変換し酸素を供給する電解反応にすることにより、電位が２．１９Ｖから１．１４Ｖに減少し、理論的には４０％以上の省エネルギー化が可能となる。このガス拡散陰極の使用によるクロルアルカリ電解の実用化に向けて種々の検討がなされているが、さらに電解電圧を低下させる方法としてガス拡散陰極をイオン交換膜に密着して設置し実質的に陰極液室をなくしてしまう、換言すると陰極室をガス室とする方法（陽極室と陰極ガス室の２つの部屋からなり２室法と総称する）が特許文献１等に提案されている。この方法を採用した場合、イオン交換膜と陰極との間にギャップがないため、陰極液がその間に最小限にしか存在せず、陰極液の電気抵抗が極限まで小さくなり電解電圧を最小に維持できるという利点を有する。
【０００５】
しかし一方では、この２室法電解槽では、ガス拡散陰極がイオン交換膜に均一に密着する状態を維持しなければ電解液（陰極液）が全面均一に保持できず、電流を流すことができない箇所を生じて十分な電流の通電は困難であるばかりか電流の集中によってイオン交換膜や陽極、ガス拡散陰極に回復しがたい損傷を生じてしまうという不安定な面も有している。
【０００６】
【特許文献１】
特開平１１−１２４６９８号公報
【０００７】
【発明が解決しようとする課題】
前述したようにイオン交換膜を陽−陰極間で狭持する電解槽の構造上の特徴は、ガス拡散陰極をイオン交換膜に均一に密着させてイオン交換膜の破損をさけるため及び陽−陰両電極間距離を最小に保つため、少なくとも一方の電極の極間距離方向への移動が自由な構造とし、電極を弾力性部材で押し狭持圧を調節できる点にある。
弾力性部材としては、金属ワイヤーからなる編物や織物又はこれを積層したもの、或いは三次元的に編んであるか、三次元的に編んだ後これにうねり加工等を施した形状、並びに金属繊維からなる不織物、コイルバネ（スプリング）、板バネなどであり、いずれも何らかのバネ弾性を有するものである。
【０００８】
バネ弾性にあっては、電解槽組み立て時に弾性部材は圧縮変形され反発力を生ずるが、この反発力が過度に大きければ、イオン交換膜は電極間に強く挟まれ機械的に変形し、ひいては破壊を生ずる。そこで、該反発力は電解槽下部に掛かる液ヘッド相当が適当であり、電解槽の運転時の圧力変動によるイオン交換膜の振動、ズレ等を抑制し得る程度で、可及的に小さくすることが望ましい。また、電解液の保持性、イオン交換膜に与える機械的損傷の面などから該反発力を全面均一にイオン交換膜に作用させることが好ましい。
従来のバネ弾性により電極を押圧する方式では、バネ弾性が直接電極に伝達されていたため、弾性力の調節が困難で、しかも弾性力が均一に電極に伝達され難かった。従って電極がイオン交換膜に均一に密着せず、しかも電極が破損したり電極内での電流が集中する等の不都合が生じていた。
本発明は、前述する課題つまりガス拡散陰極をイオン交換膜に均一に密着する状態を維持する方法を提案し、食塩電解等に実質的に使用が可能な２室法イオン交換膜電解槽及びその運転方法を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明者らは、ガス拡散陰極をイオン交換膜に実質的に均一密着する状態を維持できる電解槽の構造を鋭意探求した結果、下記の手段で上記の課題を解決した。
つまり本発明は、イオン交換膜により陽極を収容する陽極室とガス拡散陰極を収容する陰極室に区画されたイオン交換膜型電解槽において、前記ガス拡散陰極の前記イオン交換膜と反対側に透過性の押圧板を設置し、電解槽運転時に前記押圧板をガス室充填材の弾性力によりガス拡散陰極方向に押し付け、この押圧板から均一にガス拡散陰極に応力が作用してイオン交換膜とガス拡散陰極を全面的に密着する状態を維持することを特徴とするガス拡散陰極を用いたイオン交換膜型電解槽、及びイオン交換膜により陽極を収容する陽極室とガス拡散陰極を収容する陰極室に区画されたイオン交換膜型電解槽の前記ガス拡散陰極の前記イオン交換膜との反対側に透過性の押圧板を設置し、電解槽運転時に前記押圧板により前記ガス拡散陰極を前記イオン交換膜方向に押し付け、陽極室にハロゲン化アルカリを陰極室に酸素含有ガスを供給しながら両極間に通電して陰極室で水酸化アルカリを製造することを特徴とするイオン交換膜型電解槽の運転方法である。
【００１０】
以下本発明を詳細に説明する。
本発明の対象とする電解槽は、ガス拡散陰極がイオン交換膜に密着した陰極室がガス室として構成される前述した２室法電解槽である。又本発明の電解反応はクロルアルカリ（食塩）電解による水酸化アルカリ（水酸化ナトリウム）の生成反応であることが望ましいが、陰極室側で反応物質として酸素含有ガスを供給する反応であれば特に限定されない。
本発明ではこのような電解槽のガス拡散陰極を直接又は他の部材を介してイオン交換膜に実質的に均一密着させて、電流が偏ったり、イオン交換膜が損傷したりすることがないようにする。
【００１１】
この均一密着はガス拡散陰極にイオン交換膜に向けて力を加えれば良い。しかしながら、平滑面を有する押圧板をガス拡散陰極のイオン交換膜と反対側からイオン交換膜に向けて押圧することが望ましく、その押圧は、該押圧板と電解槽壁面等の間に収容した弾性力を有するガス室充填材により行うことが好ましい。このガス室充填材は電解槽組み込み前の厚さが前記押圧板と電解槽壁面との距離より大きいことが望ましい。このようなガス室充填材を前記押圧板と電解槽の壁面に組み込むと該ガス室充填材の厚さが縮小して反発力（又は弾性力）が生じる。この反発力は前記押圧板に向けて印加され、該押圧板がガス拡散陰極をイオン交換膜に向けて押圧する。前記反発力が均一に押圧板に印加されればガス拡散陰極がイオン交換膜に均一密着する。
【００１２】
従って均一密着のためには、ガス室充填材の反発力を押圧板に均一に伝えることが必要になる。
前記押圧板は酸素含有ガスをガス拡散陰極に供給するため、無孔の平板を使用することはできず、酸素含有ガスを均一にガス拡散陰極へ供給するための多数の孔を有する多孔板とする。そしてこの押圧板はガス室充填材の反発力をイオン交換膜の全面に均一に伝達するため、剛体であることが望ましい。つまり剛体であればガス室充填材の反発力が複数の点で押圧板に伝達されても、この反発力が剛体である押圧板全体に分散して特定の点に集中せずにガス拡散陰極に均一に伝達される。
【００１３】
更にこの押圧板を前記ガス室充填材を使用して押圧する際に、特に押圧板が剛体でない場合には、前記ガス室充填材の反発力が均一に押圧板に伝達されるようにする。この押圧板はガス及び液体透過性とする。
前記ガス室充填材も無孔性であると酸素含有ガスの供給に支障が生じる。このガス室充填材は弾性力を有することが必要であるため、通常は複数の金属ワイヤーを縦横に編み込み又は織り込んだ編物又は織物、つまり金網状とする。
ガス室充填材の金網では、縦横の金属ワイヤーの複数の交点がほぼ均一に分散すると共に、横方向に突き出している。このガス室充填材を電解槽内の押圧板と電解槽壁面間に収容すると、該ガス室充填材が横方向に収縮して反発力が生じると共に、均一に分散している前記複数の交点が押圧板に接触して押圧板全体を均一にガス拡散陰極方向に押圧し、これによりガス拡散陰極とイオン交換膜の均一密着が達成される。
【００１４】
本発明ではガス拡散陰極とイオン交換膜との間に炭素繊維性織物や金属繊維等の親水性材料から成る親水層を介在させても良い。この親水層はガス拡散陰極の反応点で生成した生成物である苛性ソーダ等を保持する機能を有し、この苛性ソーダ等は電解槽内下部から電解槽外へ取り出される。
このような構成から成るイオン交換膜電解槽を使用して、陽極室に食塩水溶液等の電解液を、陰極ガス室に酸素含有ガスを供給しながら、両極間に通電すると、ガス拡散陰極がイオン交換膜に均一密着しているため、ガス拡散陰極やイオン交換膜が機械的に損傷したりすることなく、更にガス拡散陰極の一部に電流集中が生ずることなく、苛性ソーダ等を高効率で製造できる。
【００１５】
【発明の実施の形態】
本発明による２室法型電解槽の一例を図１を参照して説明する。
電解槽本体１は、イオン交換膜２により陽極室３と陰極ガス室４に区画され、前記イオン交換膜２の陽極室３側にはメッシュ状の不溶性陽極５が密着し、イオン交換膜２の陰極ガス室４側には炭素繊維織物や金属繊維からなる親水層６を挟み、ガス拡散陰極７が密着している。ガス拡散陰極７の陰極ガス室４側には剛体で成形された押圧用剛体多孔板（押圧板）８が位置し、この多孔板８とガス室背板（陰極端子）１０の間、つまり陰極ガス室４内部には金属ワイヤーからなる編物又は織物等を複数枚積層して構成されるガス室充填材９が存在する。
図中、１１は陽極室３下部に設けられた陽極液導入口、１２は陽極室３上部に設けられた陽極液及びガス取出口、１３は陰極ガス室４上部に設けられた酸素含有ガス導入口、１４は陰極ガス室４下部に設けられた苛性ソーダ水溶液取出口である。
【００１６】
この電解槽本体１の陽極室３に陽極液導入口１１から食塩水を供給し、かつ陰極ガス室４に酸素含有ガス導入口１３から酸素含有ガスを供給しながら両電極５、７間に通電すると、ガス拡散陰極７では、予め苛性ソーダ水溶液で満たした親水層６側から水分が、反対面の陰極ガス室４側から酸素含有ガスが供給され、ガス拡散陰極７の反応点において苛性ソーダの生成反応が進行する。ガス拡散陰極７の反応点において生成した高濃度の苛性ソーダ水溶液は濃度勾配に従って親水層６へ拡散し直ちに吸収、保持され、また親水層６内部を流下して苛性ソーダ水溶液取出口１４から排出される。このとき、親水層６はガス室充填材９の弾力性を伝達された剛体多孔板８、及びガス拡散陰極７から均一にイオン交換膜２へ押し付けられる。つまりガス室充填材９の弾力性によりガス拡散陰極７を親水層６を介してイオン交換膜２に均一密着する状態を維持でき、電解液である苛性ソーダ水溶液を親水層６のほぼ全面に均一に保持することができる。ガス室充填材９で発生した反発力は結果的に陽極５によって支えることとなるため、陽極５は該反発力を支えるだけの剛性を有し、かつ平滑性を有していることが望ましい。
【００１７】
前述した反発力のバランス及び平滑性が崩れるとガス拡散陰極７とイオン交換膜２が不均一な密着となり苛性ソーダ水溶液は密着した点のみ親水層６に保持されることから、実質的な電流密度が上がり、槽電圧の上昇原因につながるばかりか、電流の集中によってイオン交換膜２や陽極５、ガス拡散陰極７に回復しがたい損傷を生じかねない。
剛体多孔板８の役割は、ガス室充填材９の弾力性を受け止め、ガス室充填材９の弾力性を均一にガス拡散陰極７、親水層６、更にイオン交換膜２に伝達することである。
【００１８】
ガス拡散陰極７をイオン交換膜２に均一に密着する状態を維持するために必要な剛体多孔板８とガス室充填材９についてさらに詳しく説明する。
剛体多孔板８は、平滑性を有する部材で、例えばエキスパンドメタル、パンチドメタル、剛性を持つ金属ワイヤー線で構成された金網、金属棒を格子状或いは縦方向に接続されたものが好ましい。エキスパンドメタルやパンチドメタル、平織金網等の場合、孔径は０．５〜５．０ｍｍが好ましい。孔径を０．５ｍｍより小さくすると酸素含有ガスの拡散に支障をきたしガス拡散陰極７の反応点までの到達が困難となることから槽電圧の上昇に繋がる。一方、５．０ｍｍより大きくすると剛体多孔板８のガス拡散陰極７に対する接触面積が著しく低下し、ガス拡散陰極７の機械的損傷や、ガス室充填材９の反発力をガス拡散陰極７に均一に伝達できない状態に陥り、延いては槽電圧の上昇に繋がる。開孔率（投影開孔率）は５０〜７０％程度が好ましいが、剛体多孔板８の材質、形状等によっては、７０％を越えても期待する剛性が維持され、かつ好ましい孔径が保たれている場合においては、前記開孔率は大きいほど透過能の観点からより好ましい。
【００１９】
ガス室充填材９は、電解槽１が組み立てられたとき、圧縮され、その反発力によって剛性多孔板８をガス拡散陰極７方向に押し付け、さらにガス拡散陰極７に反発力を伝達する機能を有する。このためガス室充填材９は金属ワイヤーを編んで網状とすることが好ましく、例えば０．０２〜０．５ｍｍ程度の径のワイヤーを編み、これを重ね合わせて又は三次元状に編み込んで網状体を構成する。編状体の最適な形体は表面に凸凹を付し反発力を付与した編状メッシュの積層体であり、この場合には見かけ厚さ０．５〜３ｍｍ程度のメッシュを１〜５枚積層したものが良い。この他の形体としては金属編物や織物又はこれを積層したもの、或いは金属繊維からなる不織物等、及び複数の長寸のワイヤーを互いにランダムに絡み合わせてフェルト状の網状体を構成することもできる。又ガス室充填材９の反発力は１ｍｍ圧縮したときの１平方センチメートル当り０．０３ｋｇから０．３ｋｇの応力で反発するものが好ましい。該反発力を０．０３ｋｇより小さくするとイオン交換膜２とガス拡散陰極７の密着性が低下し、親水層６に苛性ソーダ水溶液（電解液）を保持できなくなることがある。反対に反発力を０．３ｋｇより大きくするとイオン交換膜２や陽極５、ガス拡散陰極７に回復しがたい機械的損傷を生じさせることがある。
【００２０】
前記剛体多孔板８とガス室充填材９は陰極給電体（導電体）及び酸素含有ガス撹拌バッフルとしても機能する。
陰極給電体としての機能は、ガス室背板（陰極端子）１０からガス拡散陰極７へ給電する役割を果たす。給電をより効果的とするため剛体多孔板８、ガス室充填材９、さらにガス室背板（陰極端子）１０には銀メッキを施すことが好ましい。銀メッキは給電効果向上のほかガス室４の腐食防止にも寄与する。
酸素含有ガス撹拌バッフルとしての機能は、酸素含有ガスの流れを乱流化し、ガス拡散陰極７への拡散・供給効果を促進することに由来する。電解槽１では、物質移動の促進は効果的な電解反応を促すため非常に重要である。特に酸素の供給が重要である。酸素源として酸素濃度９０％以上の酸素含有ガスを使用したとしても、ガス拡散陰極７の反応点まで拡散していかなければ反応は進行しない。気体とガス拡散陰極７の界面における物質移動を促進するため酸素含有ガス撹拌バッフルとしての機能は一層重要な要素となる。
【００２１】
【実施例】
次に実施例により本発明を具体的に説明する。ただし、本発明はこれらの実施例に限定されるものではない。
【００２２】
（実施例１）
電解槽としては、有効面積が幅１００ｍｍ、高さ６００ｍｍの２室法電解槽を使用した。ガス拡散陰極としては、銀製マイクロメッシュを芯材とし、ＰＴＦＥ粉末、カーボン粉末を混練充填して製作されたガス拡散陰極を使用した。このガス拡散陰極はガス拡散層と反応層の２層構造からなり、反応層には銀微粒子触媒を担持させた。
剛体多孔板（押圧板）はニッケル製のエキスパンドメタル（孔径１．０〜１．５ｍｍ、厚さ０．６ｍｍ、開効率５６％）を使用した。ガス室充填材は、線形０．２ｍｍのニッケルワイヤーを三次元にニット形状に編み、目開きを１．５〜３．５ｍｍとした金網を４枚積層したもので、電解槽が組み立てられたとき、その厚みを３．０ｍｍから２．０ｍｍへ１ｍｍ圧縮され、その反発力は０．１５ｋｇｆ／平方センチメートルとなるように設置した。なお剛体多孔板、ガス室充填材、ニッケル製背板には厚みが１０μｍの銀メッキを施した。
【００２３】
親水層としては炭素繊維織物から成るシートを使用し、陽極としては、ＤＳＡ（ＴＭ）と呼ばれるチタンメッシュに酸化ルテニウムと酸化タンタルからなる金剛物を被覆した不溶性陽極を使用した。又イオン交換膜としては旭硝子製フレミオン８９３４を使用した。
ニッケル製背板、前記ガス室充填材、前記剛体多孔板、前記ガス拡散陰極、前記イオン交換膜及び前記陽極の順に重ねて電解槽を構成した。
【００２４】
陽極室に濃度が３０５ｇ／リットル、８７℃に加温した食塩水を供給し、次いでガス室に酸素含有ガス供給口よりＰＳＡ濃縮酸素（９４容量％）を酸素基準で０．７５Ｎリットル／ｍｉｎ（必要理論量の１．２倍）、温度８７℃に加熱して供給した。電解槽全体を８７℃に調節しながら電流を１分間に３３Ａ／平方メートルの上昇速度で１８０Ａまで上昇した。このときの電流密度は３ｋＡ／平方メートルである。定常状態に達した後の陽極液濃度は１２５ｇ／リットル、生成苛性ソーダ濃度は３２．４％であった。運転初期槽電圧は２．１０Ｖであったが、徐々に低下し１．９５Ｖで２ヶ月間以上安定推移した。このときの電流効率は９６％であった。
【００２５】
（比較例１）
電解槽に剛体多孔板を設置しなかった点を除き実施例１と同様の条件で電解を行ったところ、運転初期槽電圧は２．１０Ｖであったが、その後上昇傾向に推移し、６時間後２．７０Ｖを超え、また好転する見込みは見られなかった。水素発生の危惧、及び電解槽の構成部材に対して好ましくないので通電を停止した。
【００２６】
【発明の効果】
本発明の電解槽は、上記のような構成からなるため、イオン交換膜とガス拡散陰極がほぼ均一な力で接触し、ガス拡散陰極やイオン交換膜が機械的に損傷したりすることなく、更にガス拡散陰極の一部に電流集中が生ずることなく、苛性ソーダ等を高効率で製造できる。又イオン交換膜とガス拡散陰極間に親水層を設置すると、この親水層には苛性ソーダ水溶液等のアルカリ性電解液が全面均一に保持され、電解時には十分に電流が通電される状態を持続できる。
【図面の簡単な説明】
【図１】図１は本発明の２室法電解槽の構造を説明する図である。
【符号の説明】
１電解槽本体
２イオン交換膜
３陽極室
４陰極ガス室
５陽極
６親水層
７ガス拡散陰極
８剛体多孔板（押圧板）
９ガス室充填材
１０ガス室背板（陰極端子）
１１陽極液導入口
１２陽極液及びガス取出口
１３酸素含有ガス導入口
１４苛性ソーダ水溶液取出口[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ion exchange membrane type electrolytic cell using a gas diffusion cathode and its operating method, and more particularly to a chloralkali (salt) electrolytic cell and its operating method.
[0002]
[Prior art]
The electrolytic industry represented by chloralkali electrolysis plays an important role as a material industry. Although having such an important role, energy consumption required for chloralkali electrolysis is large, and in countries with high energy costs such as Japan, there is a strong demand for achieving energy saving.
For example, chloralkali electrolysis has been converted from the mercury method to the ion exchange membrane method through the diaphragm method in order to achieve environmental conservation as well as solving environmental problems, and has achieved energy saving of about 40% in about 25 years. . However, even this energy saving is not enough, and the power cost of energy accounts for about half of the total manufacturing cost, but no further power savings are possible using the current method. In order to achieve further energy saving, fundamental changes such as conversion of electrode reactions must be made. For example, the use of a gas diffusion electrode employed in a fuel cell or the like is the most probable among the currently considered and is an effective means for saving power. The conventional electrolytic reaction (1) using a metal cathode is converted into an electrolytic reaction (2) when oxygen is supplied using a gas diffusion cathode as a cathode.
[0003]
(1) 2NaCl + 2H ₂ O → Cl ₂ + 2NaOH + H ₂ Eo = 2.19V
(2) 2NaCl + 1 / 2O ₂ + 2H ₂ O → Cl ₂ + 2NaOH Eo = 1.14V
[0004]
That is, by converting the metal cathode into a gas diffusion cathode and performing an electrolytic reaction in which oxygen is supplied, the potential decreases from 2.19 V to 1.14 V, and theoretically energy saving of 40% or more can be achieved. Various studies have been made for the practical application of chloralkali electrolysis by using this gas diffusion cathode. However, as a method for further reducing the electrolysis voltage, the gas diffusion cathode is installed in close contact with the ion exchange membrane to substantially reduce the cathode. A method of eliminating the liquid chamber, in other words, using the cathode chamber as a gas chamber (consisting of two chambers, ie, an anode chamber and a cathode gas chamber) is proposed in Patent Document 1 and the like. When this method is used, there is no gap between the ion exchange membrane and the cathode, so the catholyte is only minimally present in between, and the electrical resistance of the catholyte is reduced to the limit to keep the electrolysis voltage to a minimum. It has the advantage of being able to.
[0005]
However, on the other hand, in this two-chamber electrolytic cell, the electrolytic solution (catholyte) cannot be maintained uniformly and the current cannot flow unless the gas diffusion cathode is kept in close contact with the ion exchange membrane. Not only is it difficult to energize with sufficient current due to the occurrence of a spot, but there is also an unstable aspect that the ion exchange membrane, the anode, and the gas diffusion cathode are irreparably damaged due to the concentration of the current.
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 11-124698
[Problems to be solved by the invention]
As described above, the structural characteristics of the electrolytic cell in which the ion exchange membrane is sandwiched between the positive and negative electrodes are that the gas diffusion cathode is uniformly adhered to the ion exchange membrane to prevent damage to the ion exchange membrane and the positive and negative electrodes. In order to keep the distance between the two electrodes to a minimum, the structure is such that at least one of the electrodes can move freely in the direction of the distance between the electrodes, and the holding pressure can be adjusted by pressing the electrode with an elastic member.
Elastic members include knitted or woven fabrics made of metal wires or laminates of these, or shapes that are three-dimensionally knitted or three-dimensionally knitted and then swelled, etc., and metal fibers Non-woven fabrics, coil springs (plate springs), leaf springs, etc., all of which have some spring elasticity.
[0008]
In spring elasticity, the elastic member is compressed and deformed during assembly of the electrolytic cell to generate a repulsive force. However, if this repulsive force is excessively large, the ion exchange membrane is strongly sandwiched between the electrodes and mechanically deformed and eventually destroyed. Is produced. Therefore, the repulsive force is appropriate for the liquid head applied to the lower part of the electrolytic cell, and should be made as small as possible so as to suppress vibrations and displacement of the ion exchange membrane due to pressure fluctuations during the operation of the electrolytic cell. Is desirable. In addition, it is preferable that the repulsive force is uniformly applied to the ion exchange membrane from the standpoint of electrolyte retention, mechanical damage to the ion exchange membrane, and the like.
In the conventional method in which the electrode is pressed by spring elasticity, since the spring elasticity is directly transmitted to the electrode, it is difficult to adjust the elastic force and it is difficult to uniformly transmit the elastic force to the electrode. Therefore, the electrodes are not uniformly adhered to the ion exchange membrane, and there are inconveniences such as damage to the electrodes and concentration of current in the electrodes.
The present invention proposes a method for maintaining the above-described problem, that is, a state in which the gas diffusion cathode is uniformly adhered to the ion exchange membrane, and a two-chamber ion exchange membrane electrolytic cell that can be substantially used for salt electrolysis and the like, and its The purpose is to provide a driving method.
[0009]
[Means for Solving the Problems]
As a result of earnestly searching for a structure of an electrolytic cell capable of maintaining a state in which the gas diffusion cathode is substantially uniformly adhered to the ion exchange membrane, the present inventors have solved the above-mentioned problems by the following means.
That is, the present invention relates to an ion exchange membrane type electrolytic cell partitioned into an anode chamber containing an anode by an ion exchange membrane and a cathode chamber containing a gas diffusion cathode, and transmits the gas diffusion cathode to the opposite side of the ion exchange membrane. When the electrolytic cell is operated, the pressure plate is pressed in the direction of the gas diffusion cathode by the elastic force of the gas chamber filling material, and stress is uniformly applied to the gas diffusion cathode from the pressure plate and the ion exchange membrane. An ion exchange membrane type electrolytic cell using a gas diffusion cathode, and an anode chamber containing an anode by an ion exchange membrane and a cathode containing a gas diffusion cathode A permeable pressure plate is installed on the opposite side of the gas diffusion cathode of the ion exchange membrane type electrolytic cell partitioned into the chamber from the ion exchange membrane, and the gas diffusion cathode is moved by the pressure plate during the operation of the electrolytic cell. An ion-exchange membrane-type electrolytic cell characterized in that alkali hydroxide is produced in the cathode chamber by applying current between both electrodes while pressing in the direction of the on-exchange membrane and supplying an alkali halide to the anode chamber and an oxygen-containing gas to the cathode chamber This is the driving method.
[0010]
The present invention will be described in detail below.
The electrolytic cell targeted by the present invention is the above-described two-chamber electrolytic cell in which the cathode chamber in which the gas diffusion cathode is in close contact with the ion exchange membrane is configured as the gas chamber. The electrolytic reaction of the present invention is preferably an alkali hydroxide (sodium hydroxide) formation reaction by chloralkali (sodium chloride) electrolysis, but is particularly a reaction that supplies an oxygen-containing gas as a reactant on the cathode chamber side. It is not limited.
In the present invention, the gas diffusion cathode of such an electrolytic cell is made to adhere substantially uniformly to the ion exchange membrane directly or through another member so that the current is not biased or the ion exchange membrane is not damaged. To.
[0011]
This uniform adhesion may be achieved by applying a force to the gas diffusion cathode toward the ion exchange membrane. However, it is desirable to press a pressing plate having a smooth surface toward the ion exchange membrane from the side opposite to the ion exchange membrane of the gas diffusion cathode, and the pressing is an elastic accommodated between the pressing plate and the electrolytic cell wall surface. It is preferable to use a gas chamber filling material having power. It is desirable that the gas chamber filler has a thickness before incorporation of the electrolytic cell larger than the distance between the pressing plate and the electrolytic cell wall surface. When such a gas chamber filler is incorporated in the pressing plate and the wall surface of the electrolytic cell, the thickness of the gas chamber filler is reduced to generate a repulsive force (or elastic force). This repulsive force is applied toward the pressing plate, and the pressing plate presses the gas diffusion cathode toward the ion exchange membrane. If the repulsive force is uniformly applied to the pressing plate, the gas diffusion cathode is uniformly adhered to the ion exchange membrane.
[0012]
Therefore, for uniform adhesion, it is necessary to uniformly transmit the repulsive force of the gas chamber filler to the pressing plate.
Since the pressing plate supplies an oxygen-containing gas to the gas diffusion cathode, a non-porous plate cannot be used, and a porous plate having a large number of holes for uniformly supplying the oxygen-containing gas to the gas diffusion cathode; To do. The pressing plate is preferably a rigid body in order to uniformly transmit the repulsive force of the gas chamber filler to the entire surface of the ion exchange membrane. In other words, even if the repulsive force of the gas chamber filler is transmitted to the pressing plate at a plurality of points if it is a rigid body, the repelling force is dispersed throughout the pressing plate, which is a rigid body, and does not concentrate on a specific point. Uniformly transmitted.
[0013]
Further, when the pressing plate is pressed using the gas chamber filler, particularly when the pressing plate is not a rigid body, the repulsive force of the gas chamber filler is uniformly transmitted to the pressing plate. This pressing plate is gas and liquid permeable.
If the gas chamber filler is also non-porous, it will hinder the supply of oxygen-containing gas. Since the gas chamber filling material needs to have elasticity, it is usually a knitted or woven fabric in which a plurality of metal wires are knitted or woven vertically or horizontally, that is, a wire mesh.
In the metal mesh of the gas chamber filler, a plurality of intersecting points of the vertical and horizontal metal wires are distributed almost uniformly and protrude in the horizontal direction. When the gas chamber filling material is accommodated between the pressing plate in the electrolytic cell and the electrolytic cell wall surface, the gas chamber filling material contracts in the lateral direction to generate a repulsive force, and the plurality of intersecting points that are uniformly dispersed include By contacting the pressing plate and pressing the entire pressing plate uniformly toward the gas diffusion cathode, uniform adhesion between the gas diffusion cathode and the ion exchange membrane is achieved.
[0014]
In the present invention, a hydrophilic layer made of a hydrophilic material such as carbon fiber woven fabric or metal fiber may be interposed between the gas diffusion cathode and the ion exchange membrane. This hydrophilic layer has a function of holding caustic soda, which is a product generated at the reaction point of the gas diffusion cathode, and this caustic soda is taken out from the lower part of the electrolytic cell to the outside of the electrolytic cell.
When an ion exchange membrane electrolytic cell having such a structure is used and an electrolyte such as a saline solution is supplied to the anode chamber and an oxygen-containing gas is supplied to the cathode gas chamber, the gas diffusion cathode is ionized. Because the gas diffusion cathode and ion exchange membrane are not mechanically damaged due to uniform adhesion to the exchange membrane, current concentration does not occur in a part of the gas diffusion cathode, and caustic soda, etc. can be produced with high efficiency. it can.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
An example of a two-chamber type electrolytic cell according to the present invention will be described with reference to FIG.
The electrolytic cell body 1 is divided into an anode chamber 3 and a cathode gas chamber 4 by an ion exchange membrane 2, and a mesh-like insoluble anode 5 is in close contact with the anode chamber 3 side of the ion exchange membrane 2. On the cathode gas chamber 4 side, a gas diffusion cathode 7 is in close contact with a hydrophilic layer 6 made of carbon fiber fabric or metal fiber. On the side of the cathode gas chamber 4 of the gas diffusion cathode 7, a pressing rigid porous plate (pressing plate) 8 formed of a rigid body is located, and between this porous plate 8 and the gas chamber back plate (cathode terminal) 10, that is, the cathode. Inside the gas chamber 4 is a gas chamber filler 9 formed by laminating a plurality of knitted or woven fabrics made of metal wires.
In the figure, 11 is an anolyte inlet provided in the lower part of the anode chamber 3, 12 is an anolyte and gas outlet provided in the upper part of the anode chamber 3, and 13 is an oxygen-containing gas inlet provided in the upper part of the cathode gas chamber 4. An opening 14 is a sodium hydroxide aqueous solution outlet provided in the lower part of the cathode gas chamber 4.
[0016]
A saline solution is supplied from the anolyte inlet 11 to the anode chamber 3 of the electrolytic cell main body 1, and the electrode 5 and 7 are energized while supplying the oxygen-containing gas from the oxygen-containing gas inlet 13 to the cathode gas chamber 4. Then, in the gas diffusion cathode 7, moisture is supplied from the hydrophilic layer 6 side previously filled with the caustic soda aqueous solution, and oxygen-containing gas is supplied from the cathode gas chamber 4 side of the opposite surface. Progresses. The high-concentration caustic soda aqueous solution generated at the reaction point of the gas diffusion cathode 7 diffuses into the hydrophilic layer 6 according to the concentration gradient and is immediately absorbed and held, and flows down inside the hydrophilic layer 6 and is discharged from the caustic soda aqueous solution outlet 14. At this time, the hydrophilic layer 6 is uniformly pressed against the ion exchange membrane 2 from the rigid porous plate 8 to which the elasticity of the gas chamber filler 9 is transmitted and the gas diffusion cathode 7. That is, due to the elasticity of the gas chamber filler 9, the gas diffusion cathode 7 can be kept in uniform contact with the ion exchange membrane 2 via the hydrophilic layer 6, and the aqueous solution of caustic soda as an electrolyte can be uniformly distributed over almost the entire surface of the hydrophilic layer 6. Can be held. Since the repulsive force generated in the gas chamber filling material 9 is supported by the anode 5 as a result, it is desirable that the anode 5 has sufficient rigidity to support the repulsive force and has smoothness.
[0017]
If the balance and smoothness of the repulsive force are lost, the gas diffusion cathode 7 and the ion exchange membrane 2 are in non-uniform contact, and the caustic soda aqueous solution is held in the hydrophilic layer 6 only at the point of contact, so that the substantial current density is In addition to increasing the cell voltage, the concentration of current may cause irreparable damage to the ion exchange membrane 2, anode 5, and gas diffusion cathode 7.
The role of the rigid porous plate 8 is to receive the elasticity of the gas chamber filler 9 and to transmit the elasticity of the gas chamber filler 9 uniformly to the gas diffusion cathode 7, the hydrophilic layer 6, and further to the ion exchange membrane 2. .
[0018]
The rigid perforated plate 8 and the gas chamber filler 9 necessary for maintaining the state in which the gas diffusion cathode 7 is in close contact with the ion exchange membrane 2 will be described in more detail.
The rigid perforated plate 8 is a member having smoothness, and is preferably, for example, an expanded metal, a punched metal, a wire mesh composed of a metal wire wire having rigidity, or a metal rod connected in a grid or longitudinal direction. In the case of expanded metal, punched metal, plain woven wire mesh, etc., the hole diameter is preferably 0.5 to 5.0 mm. If the hole diameter is smaller than 0.5 mm, the diffusion of the oxygen-containing gas is hindered and it is difficult to reach the reaction point of the gas diffusion cathode 7, which leads to an increase in the cell voltage. On the other hand, when the diameter is larger than 5.0 mm, the contact area of the rigid porous plate 8 with the gas diffusion cathode 7 is remarkably reduced, and mechanical damage to the gas diffusion cathode 7 and the repulsive force of the gas chamber filler 9 are uniformly applied to the gas diffusion cathode 7. It will be in the state which cannot be transmitted to, and will lead to a raise of a cell voltage by extension. The open area ratio (projected open area ratio) is preferably about 50 to 70%. However, depending on the material, shape, etc. of the rigid porous plate 8, the expected rigidity is maintained even when it exceeds 70%, and a preferable hole diameter is maintained. In this case, the larger the hole area ratio, the more preferable from the viewpoint of permeability.
[0019]
The gas chamber filler 9 is compressed when the electrolytic cell 1 is assembled, and has a function of pressing the rigid porous plate 8 toward the gas diffusion cathode 7 by the repulsive force and further transmitting the repulsive force to the gas diffusion cathode 7. . For this reason, it is preferable that the gas chamber filling material 9 be knitted into a net by knitting a metal wire. For example, a wire having a diameter of about 0.02 to 0.5 mm is knitted, and these are overlapped or knitted in a three-dimensional shape. Configure. The optimum shape of the knitted body is a laminated body of a knitted mesh having a surface with irregularities and a repulsive force. In this case, 1 to 5 meshes having an apparent thickness of about 0.5 to 3 mm are laminated. Things are good. Other forms include metal knitted fabrics, woven fabrics or laminates thereof, non-woven fabrics made of metal fibers, etc., and a plurality of long wires randomly entangled with each other to form a felt-like network. it can. The gas chamber filling material 9 preferably has a repulsive force of 0.03 kg to 0.3 kg per square centimeter when compressed by 1 mm. If the repulsive force is less than 0.03 kg, the adhesion between the ion exchange membrane 2 and the gas diffusion cathode 7 is lowered, and the hydrophilic layer 6 may not be able to hold the aqueous sodium hydroxide solution (electrolyte). On the contrary, if the repulsive force is larger than 0.3 kg, the ion exchange membrane 2, the anode 5, and the gas diffusion cathode 7 may cause irreparable mechanical damage.
[0020]
The rigid porous plate 8 and the gas chamber filler 9 also function as a cathode power supply (conductor) and an oxygen-containing gas stirring baffle.
The function as the cathode power feeder plays a role of feeding power from the gas chamber back plate (cathode terminal) 10 to the gas diffusion cathode 7. In order to make power supply more effective, the rigid porous plate 8, the gas chamber filler 9, and the gas chamber back plate (cathode terminal) 10 are preferably subjected to silver plating. The silver plating contributes to the prevention of corrosion of the gas chamber 4 in addition to improving the power supply effect.
The function as the oxygen-containing gas stirring baffle is derived from turbulent flow of the oxygen-containing gas and promoting the diffusion / supply effect to the gas diffusion cathode 7. In the electrolytic cell 1, the promotion of mass transfer is very important because it promotes an effective electrolytic reaction. The supply of oxygen is particularly important. Even if an oxygen-containing gas having an oxygen concentration of 90% or more is used as the oxygen source, the reaction does not proceed unless it diffuses to the reaction point of the gas diffusion cathode 7. The function as an oxygen-containing gas stirring baffle is an even more important factor for promoting mass transfer at the interface between the gas and the gas diffusion cathode 7.
[0021]
【Example】
Next, the present invention will be described specifically by way of examples. However, the present invention is not limited to these examples.
[0022]
Example 1
As the electrolytic cell, a two-chamber electrolytic cell having an effective area of 100 mm in width and 600 mm in height was used. As the gas diffusion cathode, a gas diffusion cathode manufactured by mixing and filling PTFE powder and carbon powder with a silver micromesh as a core material was used. This gas diffusion cathode has a two-layer structure of a gas diffusion layer and a reaction layer, and a silver fine particle catalyst was supported on the reaction layer.
As the rigid porous plate (pressing plate), an expanded metal made of nickel (pore diameter: 1.0 to 1.5 mm, thickness: 0.6 mm, open efficiency: 56%) was used. The gas chamber filler is made by laminating four linear meshes with a linear 0.2 mm nickel wire in a three-dimensional knitted shape and an opening of 1.5 to 3.5 mm. When the electrolytic cell is assembled The thickness was compressed 1 mm from 3.0 mm to 2.0 mm, and the repulsive force was set to 0.15 kgf / square centimeter. The rigid porous plate, the gas chamber filler, and the nickel back plate were subjected to silver plating with a thickness of 10 μm.
[0023]
As the hydrophilic layer, a sheet made of a carbon fiber fabric was used, and as the anode, an insoluble anode in which a titanium mesh called DSA (TM) was coated with a metal rigid material made of ruthenium oxide and tantalum oxide was used. As the ion exchange membrane, Flemion 8934 manufactured by Asahi Glass was used.
An electrolytic cell was constructed by layering a nickel back plate, the gas chamber filler, the rigid porous plate, the gas diffusion cathode, the ion exchange membrane, and the anode in this order.
[0024]
Saline solution having a concentration of 305 g / liter and heated to 87 ° C. was supplied to the anode chamber, and then PSA-concentrated oxygen (94 vol%) was supplied to the gas chamber from the oxygen-containing gas supply port at 0.75 N liter / min (on oxygen basis). 1.2 times the required theoretical amount) and heated to a temperature of 87 ° C. The current was increased to 180 A at a rate of 33 A / square meter per minute while adjusting the entire electrolytic cell to 87 ° C. The current density at this time is 3 kA / square meter. After reaching the steady state, the anolyte concentration was 125 g / liter, and the produced caustic soda concentration was 32.4%. The initial operation tank voltage was 2.10V, but gradually decreased and remained stable at 1.95V for 2 months or more. The current efficiency at this time was 96%.
[0025]
(Comparative Example 1)
When electrolysis was carried out under the same conditions as in Example 1 except that the rigid porous plate was not installed in the electrolytic cell, the initial cell voltage was 2.10 V, but after that it increased and increased for 6 hours. After 2.70V, there was no prospect of improvement. Since it was not preferable for the fear of hydrogen generation and the components of the electrolytic cell, the energization was stopped.
[0026]
【The invention's effect】
Since the electrolytic cell of the present invention is configured as described above, the ion exchange membrane and the gas diffusion cathode are in contact with each other with a substantially uniform force, and the gas diffusion cathode and the ion exchange membrane are not mechanically damaged. Furthermore, caustic soda and the like can be manufactured with high efficiency without causing current concentration in a part of the gas diffusion cathode. In addition, when a hydrophilic layer is provided between the ion exchange membrane and the gas diffusion cathode, an alkaline electrolyte such as an aqueous solution of caustic soda is uniformly held on the hydrophilic layer, and a state where a current is sufficiently passed during electrolysis can be maintained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the structure of a two-chamber electrolytic cell of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrolyzer main body 2 Ion exchange membrane 3 Anode chamber 4 Cathode gas chamber 5 Anode 6 Hydrophilic layer 7 Gas diffusion cathode 8 Rigid porous plate (pressing plate)
9 Gas chamber filler 10 Gas chamber back plate (cathode terminal)
11 Anolyte inlet 12 Anolyte and gas outlet 13 Oxygen-containing gas inlet 14 Caustic soda aqueous solution outlet

Claims

In a two-chamber ion exchange membrane type electrolytic cell divided into an anode chamber containing an anode by an ion exchange membrane and a cathode chamber containing a gas diffusion cathode, the gas diffusion cathode is permeable to the side opposite to the ion exchange membrane. A pressure plate is installed, and when the electrolytic cell is operated, the pressure plate is pressed toward the gas diffusion cathode by the elastic force of the gas chamber filling material, and stress is uniformly applied to the gas diffusion cathode from this pressure plate and the ion exchange membrane and the gas diffusion. An ion exchange membrane electrolytic cell using a gas diffusion cathode, characterized in that the cathode is maintained in a state of being in close contact with the entire surface.

2. The ion exchange membrane electrolytic cell according to claim 1, wherein the pressing plate is made of a metal and is an expanded metal, a punched metal, or a net-like rigid body having a hole diameter of 0.5 mm to 5.0 mm.

The ion exchange membrane electrolytic cell according to claim 1 or 2, wherein the gas chamber filler is accommodated between the pressing plate and the cathode chamber wall with elasticity.

When the gas chamber filling material is a knitted fabric and a woven fabric made of metal wires, a laminate of these, a three-dimensional knitted fabric and a three-dimensional knitted fabric, or a non-woven fabric made of metal and compressed by 1 mm The ion-exchange membrane electrolytic cell according to any one of claims 1 to 3, wherein the elastic stress per square centimeter is 0.03 kg to 0.3 kg.

The ion exchange membrane type electrolytic cell according to any one of claims 1 to 4, wherein the pressing plate and the gas chamber filler function as a power supply body for the gas diffusion cathode.

6. The ion exchange membrane type electrolytic cell according to claim 1, further comprising a hydrophilic layer between the ion exchange membrane and the gas diffusion cathode.

The ion exchange membrane type electrolytic cell according to claim 6, wherein the hydrophilic layer is a carbon fiber woven fabric.

A permeable pressure plate is provided on the opposite side of the gas diffusion cathode of the ion exchange membrane type electrolytic cell partitioned into an anode chamber containing an anode by an ion exchange membrane and a cathode chamber containing a gas diffusion cathode from the ion exchange membrane. When the electrolytic cell is operated, the gas diffusion cathode is pressed against the ion exchange membrane by the pressing plate, and an alkali halide is supplied to the anode chamber while supplying an oxygen-containing gas to the cathode chamber. An operation method of an ion exchange membrane electrolytic cell characterized by producing an alkali hydroxide.