JP4627111B2 - Operation method of ion exchange membrane method alkaline chloride electrolytic cell. - Google Patents
Operation method of ion exchange membrane method alkaline chloride electrolytic cell. Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、イオン交換膜法による塩化アルカリの電解槽の運転を安全に行うためのイオン交換膜法電解槽の運転方法に関する。
【０００２】
【従来の技術】
従来から、イオン交換膜を用いる食塩等の塩化アルカリを電気分解する方法（以下、「イオン交換膜法塩化アルカリ電解」という）が工業的規模で実施されている。
イオン交換膜法塩化アルカリ電解では、通常、有機材料からなるイオン交換膜を挟んで、一方の陽極側は塩素及び強い酸化性雰囲気、他方の陰極側は強いアルカリ溶液が存在するので、イオン交換膜はきわめて過酷な状況に曝されていることになる。したがって、長期間にわたる操業ではイオン交換膜の経時的な劣化は避けがたい。また、このような劣化は、単にイオン交換膜の性能上の劣化にとどまらず、一般にピンホールと言われるような破損が生じた場合には、陽極側の塩素と陰極側の水素が混合し、最悪の場合は爆発する危険もある。さらに、イオン交換膜にピンホールが発生すると、高圧側のアルカリが陽極室へ流入し、塩素と反応して次亜塩素酸を生成し、これが電槽ガスケットを腐食することによって、外部への液漏れの原因となり、電解槽の寿命を縮めることにもなる。
【０００３】
また、イオン交換膜法塩化アルカリ電解を停止している間は、電解槽の腐食等を防止するために、防食電流を流しておくのが一般的である。
しかしながら、防食電流を流しているにもかかわらず、イオン交換膜や電解槽の表面が損傷してしまう場合があり、その状態で運転を再開すると、陽極側の塩素と陰極側の水素が混合したり、電槽ガスケットを腐食して、外部への液漏れの原因となり、電解槽の寿命を縮めてしまうことになる。
【０００４】
したがって、イオン交換膜法塩化アルカリ電解にあっては、使用するイオン交換膜の劣化や電解槽の損傷等の異常をできるだけ早期に発見することが、事故防止及びコスト低減の意味からもきわめて重要となる。
【０００５】
従来、イオン交換膜法塩化アルカリ電解槽の運転方法としては、例えば、次のものが知られている。
▲１▼特開昭５５−６５３７９号公報には、複数個の電解槽の陽極室に共通の母管から分岐する枝管によって塩水を並列に供給し、陽極室液の一部を排出口より抜き出しながら電解を行うにあたり、排出口より抜き出される陽極室液のｐＨ値を測定し、これに基づいて各電解槽に個別的に塩酸を供給し、ｐＨ値を４以下に保つことを特徴とするハロゲン化アルカリのイオン交換膜法電解槽の運転方法が記載されている。
【０００６】
▲２▼特開昭５７−１２３９８９号公報には、電解槽に設けられた電流検出器及び電圧検出器によって電解槽運転時における電流量（Ｉ）及び電圧（Ｖ）を検出して電解槽の正常運転時における電流量（Ｉ）及び電圧（Ｖ）を用い、式：Ｖ＝ＫＩ＋ｅ（ｅは理論電解電圧である）に基づいて予め求めたＫ値、及び予め設定した許容値α0を用いた式：Ｖ＝ＫＩ＋ｅ＋αを比較し、｜α｜＞｜α0｜となったとき異常信号を発生するごとくして行う電解槽の運運制御方法が記載されている。
【０００７】
▲３▼また、特開平８−７４０８２号公報には、複数個のイオン交換膜法塩化アルカリ電解槽を運転するにあたり、各電解槽の陽極室からの塩素ガス中の酸素濃度及び各槽への塩素供給量を各槽毎に測定し、該測定値に基づいて塩素ガス中の酸素濃度を０．１〜０．５（容量）％に保つように各電解槽に個別的に塩酸を供給し、且つ各槽の塩素原単位（塩酸供給量／塩素発生量）を算出し、この算出価を予め定めた値と比較するか、或いは全槽の塩酸原単位の平均値との相対比較によって、電解槽の異常を検出することを特徴とする塩化アルカリのイオン交換膜法電解槽の運転方法が開示されている。
【０００８】
【発明が解決しようとする課題】
しかしながら、上記した従来のイオン交換膜法塩化アルカリ電解槽の運転方法のうち、陽極液のｐＨ値を測定する方法は、運転時にすべての電解槽についてｐＨ値を測定しなければならず、操作が非常に煩雑である。また、ｐＨ４を越える領域では電流効率の変動に対するｐＨ値の感度が非常に低いので、ｐＨ値の変化により異常を検出することが困難である。さらに、ｐＨ値は測定時の液温のばらつき、サンプリング時のガス放散の影響により誤差を生じやすいという問題がある。
【０００９】
また、電解槽運転時における電流量及び電圧を検出する方法は、ｐＨ値を測定することなく運転中に発生する電解槽の異常を早く発見できる点で比較的優れた方法であるといえる。しかしながら、電解槽の運転を停止した後、運転を再開する場合に、電解槽の運転が正常に再開できるか否か、及び電解槽の運転を正常に継続できるか否かの判断する場合には適用が難しい。
【００１０】
一方、特開平１１−６１４７６号公報には、イオン交換膜塩化アルカリ電解槽の陽極室に所定アルカリ金属濃度のアルカリ金属ハロゲン化物水溶液を満たし、陰極室に所定濃度のアルカリ金属水酸化物水溶液を満たし、所定温度で通電を開始する方法が提案されている。
【００１１】
この方法は、運転停止中において、陽極室と陰極室の電解液の濃度バランスが崩れることに着目し、この濃度バランスの崩れを正常に戻すことによって、正常な運転を開始する方法である。しかしながら、この方法はすべての電解槽の電解液の濃度測定を行わねばならず、煩雑であり、簡便性及び迅速性に欠けるという問題がある。
【００１２】
このように、従来のイオン交換膜法塩化アルカリ電解の運転開始法及び運転（制御）法は、電解槽の運転を停止した後、運転を再開する場合に、イオン交換膜や電解槽等に損傷がなく正常に運転を再開できるか否か、及び運転を再開した後、正常に運転を継続できるか否かの判断を簡便且つ速やかに行うことができる方法ではなかった。特に、冬季に積雪等によって発生しやすい送電線の短絡事故等により不時停電が生じるような場合には、イオン交換膜及び電解槽の損傷をできるだけ軽減し、製造コストの上昇を抑えるためには、停電後できるだけ速やかに正常な運転を再開できることが重要である。
【００１３】
本発明は、かかる実状に鑑みなされたものであって、イオン交換膜法塩化アルカリ電解において、電解槽の運転を停止した後、運転を再開する場合に、イオン交換膜や電解槽に損傷がなく正常に運転を開始し、継続できるか否かの判断を簡便且つ速やかに行うことができる、イオン交換膜法塩化アルカリ電解槽の運転方法を提供することを課題とする。
【００１４】
【課題を解決するための手段】
上記課題の解決を図るべく、本発明は、複数個のイオン交換膜法塩化アルカリ電解槽を運転するにあたり、運転を開始する前に電解槽を流れる防食電流の電圧Ａ（Ｖ）、及び運転を開始した後の所定電流における電解電圧Ｂ（Ｖ）を測定し、前記Ａ及びＢが設定値以上の場合には運転を継続し、Ａ又はＢのいずれかが設定値未満の場合には電解槽から発生する気体の分析を行い、該分析の結果から電解槽の運転を継続するか停止するかの判断を行うことを特徴とするイオン交換膜法塩化アルカリ電解槽の運転開始方法を提供する。
【００１５】
本発明の運転方法においては、前記Ａ又はＢのいずれかが設定値未満の場合には、前記電解槽の陽極室から発生する気体中に含まれる塩素ガスの濃度を測定し、得られた測定結果から電解槽の運転を継続するか停止するかを判断するのが好ましい。
【００１６】
本発明の運転方法においては、前記Ａ又はＢのいずれかが設定値未満の場合には、前記電解槽の陽極室から発生する気体中に含まれる塩素ガス及び酸素ガスの濃度を測定し、得られた測定結果から電解槽の運転を継続するか停止するかを判断するのがより好ましい。
【００１７】
本発明の運転方法においては、前記Ａ又はＢのいずれかが設定値未満の場合には、前記電解槽の陽極室から発生する気体中に含まれる塩素ガス、酸素ガス及び水素ガスの濃度を測定し、得られた測定結果から電解槽の運転を継続するか停止するかを判断するのがさらに好ましい。
【００１８】
本発明の運転方法においては、記Ａ又はＢのいずれかが設定値未満の場合には、前記電解槽の陽極室から発生する気体を分析し、前記気体の分析の結果、塩素ガス濃度が９５（容量）％以上の場合、又は塩素ガス濃度が９２（容量）％以上９５（容量）％未満であって、酸素ガス濃度が７（容量）％未満で、かつ水素ガス濃度が０．２５（容量）％未満の場合には運転を継続し、それ以外の場合には運転を停止するのが特に好ましい。
【００１９】
また、本発明の運転方法においては、前記防食電流の電圧Ａ（Ｖ）の設定値としては、陽極液のｐＨ値Ｐ、槽温度Ｔ（℃）及び陰極液の水酸化アルカリの濃度ＣOH（重量％）を種々の条件下で測定した値を、一般式（１）：ａ＋ｂＰ＋ｃＴ＋ｄＣOHに代入して、重回帰分析しすることによりａ、ｂ、ｃ及びｄを求め、得られた式から定められるものを用いるのが好ましい。
【００２０】
【発明の実施の形態】
以下、本発明を詳細に説明する。
本発明に用いられるイオン交換膜法塩化アルカリ電解槽の一例を図１に示す。
実際の電解槽は、図１に示す単位を多層（１０層〜２０層程度）積層して構成されている。図１において、陽極室３では塩素イオンが陽極１に電子を放出し塩素となり、塩素ガスが発生する。また、陰極室４では水が陰極２から電子を受け取って水素ガスの発生と水酸化物イオンを生ずる。一方、イオン交換膜５により選択的にアルカリ金属イオンが移動し、これが水酸化物イオンと反応して水酸化アルカリとなる。
【００２１】
また、各電解槽においては、イオン交換膜５により区切られた単位毎に陽極１と陰極２が備え付けられているが、それらは並列に接続されており、電解槽単位で電流及び電圧の測定が可能となっている。なお、イオン交換膜５としては、一般的には、カルボキシル基、スルホ基を側鎖に有する陽イオン交換性のフッ素樹脂が多く用いられる。また、塩化アルカリとしては、塩化ナトリウムが一般的である。
【００２２】
本発明は、複数個のイオン交換膜法塩化アルカリ電解槽を運転する方法であって、運転を開始する前（以下、「通電前」ともいう）の防食電流の電圧Ａ（Ｖ）、及び運転を開始した後（以下、「通電後」ともいう）の電解電圧Ｂ（Ｖ）を測定し、前記Ａ及びＢが設定値以上の場合には運転を継続し、Ａ又はＢのいずれかが設定値未満の場合には電解槽から発生する気体の分析を行い、該分析の結果から電解槽の運転を継続するか停止するかの判断を行うイオン交換膜法塩化アルカリ電解槽の運転方法である。本発明のイオン交換膜法塩化アルカリ電解槽の運転方法の概要のフローチャートを図２に示す。
【００２３】
本発明は、通電前に防食電流の電圧が所定値Ａ（Ｖ）以上になっているか否かを確認することを第１の特徴とする。
イオン交換膜法塩化アルカリ電解槽の運転を行っている場合に、何らかの理由により運転を停止する場合、あるいは運転を停止せざるを得ない場合がある。電解槽の運転を停止すると、電解槽の中は１種の電池のような状態になって、電解槽の中を電流が流れることが知られている。そして、この状態を放置しておくと、イオン交換膜に損傷を与えたり、電解槽や電極表面を腐食するおそれがある。
そのため、従来から電解槽の運転を停止している間、電解槽に防食電流を流すことにより、イオン交換膜に損傷を与えたり、電解槽や電極表面を腐食するのを防止している。
【００２４】
防食電流が流れている間、陽極室からは酸素ガスが発生し、陰極室から水素ガスが主に発生している。一定の防食電流が流れている状態では、ネルンストの式から、防食電流中の電槽電圧は陽極室及び陰極室のｐＨ値に依存することが導かれる。防食電流の電圧と陽極室の電解液のｐＨ値を実際に測定した結果を図３に示した。図３から、一般的に電解液のｐＨ値が高い場合には防食電流の電圧が低くなることがわかる（図３に示す例においては、寄与率は約０．６６である）。
【００２５】
通電後においては、図４に示す測定例から明らかなように、陰極液のｐＨ値と電槽電圧との間には相関関係は見られなかった。しかしながら、図５に示すように、通電前の陽極液のｐＨ値と通電後の陽極液のｐＨ値との間には一定の相関関係があることがわかった（図５に示す例においては、寄与率は約０．７である）。
【００２６】
したがって、▲１▼電解槽の運転再開前の防食電流の電圧が一定値以下の電解槽は、陽極液のｐＨ値が異常に高くなっていること、▲２▼通電前の陽極液のｐＨ値と通電後の陽極液のｐＨ値との間には一定の相関関係が見られること、及び、▲３▼陽極液のｐＨ値が異常である場合には運転再開後のトラブルが予測される。これらのことから、防食電流の電圧が所定値未満の場合には、電解槽の運転を再開後において再度運転が正常に継続できるか否かを判断することとした。
【００２７】
防食電流の電圧は、槽温度や陰極液である水酸化ナトリウム水溶液の濃度等の因子によって影響を受ける。したがって、防食電流の電圧Ｖの設定値は、例えば次のようにして決定することができる。
▲１▼防食電流の電圧に影響を及ぼす因子として、陰極液のｐＨ値Ｐ、槽温度Ｔ（℃）及び陰極液の水酸化ナトリウム濃度ＣOH（重量％）との間に１次の相関関係があると仮定して、一般式（１）：Ｖ＝ａ＋ｂＰ＋ｃＴ＋ｄＣOHが成り立つとする。
▲２▼そして、種々の条件で陰極液のｐＨ値Ｐ、槽温度Ｔ（℃）及び陰極液の水酸化ナトリウム濃度ＣOH（重量％）を測定し、前記一般式（１）のａ、ｂ、ｃ及びｄの値を重回帰分析法により求める。
【００２８】
▲３▼得られた一般式（１）は、種々の条件（槽温度、陽極液のｐＨ値、陰極液の水酸化ナトリウムの濃度）において、一般的に成り立つ。したがって、電解槽の運転を再開する前において、電解槽の運転を再開した後にトラブルの発生が予想される危険性の高い電解槽として、該電解槽の陽極液のｐＨ値が、例えばｐＨ１２以上の場合とすると、一般式（１）のＰに１２を代入し、そのときの槽温度Ｔ及び陰極液の水酸化ナトリウムの濃度ＣOHの測定値を代入することによって、防食電流の電圧の設定値Ａ（Ｖ）を定めることができる。
【００２９】
本発明は、防食電流の電圧が所定値以上であるか否かを判断することを特徴とするものであるから、該設定値を定める方法は上記に限定されることなく、他の方法、例えば、経験則等から定めることもできる。
【００３０】
本発明は、通電後において、所定電流における電解電圧が所定値Ｂ（Ｖ）以上になっているか否かを確認することを第２の特徴とする。
運転再開後、イオン交換膜法塩化アルカリ電解を実際に行う場合には、電解電流・電圧を徐々に増加させながら、電解が正常に再開できるか否かを逐次確認し、最終的に電解電流が５０ｋＡ〜１００ｋＡの状態で電解の運転を行う。
【００３１】
また、通電後においては陽極室からは塩素ガスが発生するが、電解槽に何らかのトラブルがある場合には、電解槽から発生する気体の成分組成が正常の場合と異なることが知られている。したがって、すべての電解槽の陽極室から発生する気体の分析を逐次行えば、電解槽が正常に運転されるものであるか否かを確認することができる。しかし、その操作は非常に煩雑であり、迅速性に欠ける。
【００３２】
そこで、本発明では、▲１▼陽極室から発生する塩素ガス濃度が低くなる場合には、電解槽に何らかのトラブルが発生していると判断されること、及び▲２▼電解槽の陽極室から発生する塩素ガス濃度と電解電圧との間には一定の相関関係があることから、通電後電解電流及び電圧を上昇させていく過程で、所定の電流での電解電圧が所定値Ｂ（Ｖ）未満の場合には、電解槽に何らかのトラブルが発生している可能性が高いと判断することとした。
【００３３】
電解槽の陽極室から発生する塩素ガス濃度と、電解電圧との間には一定の相関関係がある。したがって、電解電圧の所定値（Ｂ）は、塩素ガス濃度が低い場合の電解電圧の測定データーを解析することにより、経験的に定めることができる。
【００３４】
本発明は、通電前に防食電流の電圧が所定値Ａ（Ｖ）未満の場合、又は通電後に電解電圧が所定値Ｂ（Ｖ）未満の場合には、電解槽から発生する気体の分析を行い、該分析の結果から運転を継続できるか又は運転を停止して電解槽の安全点検を行うべきか否かの判断を行うことを第３の特徴とする。
【００３５】
本発明においては、分析する電解槽から発生する気体として、陽極室から発生する気体を分析するのが好ましい。陽極室から発生する可能性があるガスとしては、塩素ガス、酸素ガス及び水素ガスが挙げられる。電解槽が正常に運転されている場合には塩素ガスのみが発生するはずであり、電解槽に異常がある場合には塩素ガス濃度が相対的に低下し、酸素ガスや水素ガス濃度が高くなるからである。したがって、気体の分析としては、先ず塩素ガス濃度の測定を行い、塩素ガス濃度が所定値未満の場合には、酸素ガス濃度及び水素ガス濃度の測定を行うのがより好ましい。
【００３６】
より具体的には、陽極室から発生する気体の分析を、例えば、図６に示すフローチャートに示す▲１▼〜▲５▼の手順で行うことができる。なお、図６に示すスローチャートにおいて、ＹはＹｅｓを、ＮはＮｏを意味する（以下のフローチャートにて同じである。）。
▲１▼先ず、電解槽の陽極室から発生している気体に含まれる塩素ガス濃度を測定する。この段階で塩素ガス濃度がＸ（容量）％以上の場合には運転を継続できると判断する。
▲２▼塩素濃度がＹ（容量）％にも満たない場合には危険であると考えられるため，運転を停止して電解槽の安全点検を行う。
▲３▼塩素ガス濃度がＸ（容量）％未満であるがＹ（容量）％以上の場合には、酸素ガス濃度を測定する。酸素ガス濃度がＺ（容量）％以上の場合には危険であると考えられるため，運転を停止して電解槽の安全点検を行う。
▲４▼酸素ガス濃度がＺ（容量）％未満の場合には水素濃度の測定する。ここで、水素ガス濃度がＷ（容量）％以上の場合には危険であると考えられるため、運転を停止して電解槽の安全点検を行う。
▲５▼水素濃度がＷ（容量）％未満の場合には運転が継続できると判断する。
【００３７】
本発明においては、気体の分析の方法には格別の制約はなく、従来公知の分析装置及び分析手段を採用できる。
【００３８】
【実施例】
以下、実施例により本発明をさらに詳細に説明する。
実施例においては、図１に示す単位を１５層横に積層してなる電解槽を計３０槽用いた。また、イオン交換膜法塩化ナトリウム電解槽の運転は、図７に示すフローチャートに従って行った。
【００３９】
先ず、通常の電解槽の運転を行った後に電解槽の運転を停止した。運転を停止している間は、該電解槽に防食電流を一定電圧で流しつづけた。そのときの防食電流の電圧Ｖと陽極液のｐＨ値Ｐとを、種々の電解槽温度Ｔ（℃）及び陰極液の水酸化ナトリウム濃度ＣOH（重量％）の条件で測定した。電解槽温度Ｔが６５℃、陰極液の水酸化ナトリウム濃度ＣOHが２９重量％の場合の測定結果を図８に示す。その他、電解槽温度６０〜７０℃、水酸化ナトリウム濃度２８〜３０重量％の範囲で測定を行った。
【００４０】
次いで、一般式（１）：Ｖ＝ａ＋ｂＰ＋ｃＴ＋ｄＣOHが成立するとして、測定結果を用いて重回帰分析を行い、式：Ｖ＝１．６３３−０．０３５Ｐ−０．００１Ｔ＋０．０１５ＣOHを得た。すなわち、ａ＝１．６３３、ｂ＝−０．０３５、ｃ＝−０．００１、ｄ＝０．１５となった。
【００４１】
トラブルの発生のおそれが高いと判断される電解槽の陽極液のｐＨ値を１１．８、電解槽の平均温度Ｔを７０℃及び水酸化ナトリウムの平均濃度ＣOHを２６重量％として、これらを一般式（１）に代入してＶの値を求めると、Ｖ＝１．５４（Ｖ）が得られた。なお、トラブル発生のおそれが高いと判断される電解槽の陽極液のｐＨ値は一般的には１２以上と考えられるが、ｐＨ値は、安全性を考慮して１１．８と設定した。
【００４２】
運転再開後、電解電圧の測定を行った。本実施例では、電解槽の運転再開後の電解電圧を測定し、▲１▼電解電流２５ｋＡ（アンペア）での電圧が２．４５Ｖ以上であれば、電解槽は正常に作動しているので、運転は継続できるとし、▲２▼該電解電圧が２．４５Ｖ未満の場合には、電解槽に異常があるおそれがあるので、陽極室から発生する気体の分析を行うこととした。
【００４３】
また、電解電流１０ｋＡでは運転再開直後のため電圧が安定しておらず、電解電流が２５ｋＡになると電解電圧が次第に安定し、電解電圧はおよそ２．５４Ｖ〜２．７０Ｖで推移した。したがって、電解電圧が所定の値以上であるか否かの判断は、電流電圧２５ｋＡの場合で行うこととした。
【００４４】
また、基準となる電解電圧の所定値（２．５４Ｖ）は、次のようにして決定した。すなわち、電解電流（Ｉ）を０ｋＡ、１０ｋＡ、２５ｋＡと変化させた場合における運転再開後の電解電圧（Ｖ）の経時変化を測定した。測定結果の一例を図９に示す（図９中、横軸は経過時間、縦軸は電解電圧（Ｖ）を示す）。そして、種々の電解槽について測定した結果から、正常な電解槽の場合には、２５ｋＡの電解電流で電解電圧が２．５４Ｖ以上であることを経験的に見出した。
【００４５】
なお、電解電流０ｋＡ（防食電流が流れている状態）では、防食電流の電圧（Ｖ）は１．５４Ｖ〜１．７Ｖの間で推移しており、防食電流の電圧は正常であれば１．５４Ｖ以上であるとこともわかった（Ｉ＝０ｋＡの場合）。
【００４６】
電解電流が２５ｋＡで電解電流が２．５４Ｖ未満の電解槽の場合は、該電解槽の陽極室から発生する気体の分析を行った。通電後の電解電流２５ｋＡでの電解電圧（Ｖ）と陽極室から発生する気体に含まれる塩素ガス濃度（容量％）を測定した結果を図１０に示す。図１０から、電解電圧が異常に低い場合（電解電圧＝２．１Ｖ〜２．２Ｖ）には、陽極室から発生してくる塩素ガスの濃度は、電解電圧が約２．５４Ｖ〜２．６５Ｖの電解槽の場合に比して相対的に低いことがわかる。
【００４７】
気体の分析結果から、具体的に電解槽の運転を継続するか停止すかの判断は、図１０で得られた測定結果を参照して、次の手順で行うこととした。
▲１▼先ず、電解槽の陽極室から発生する気体の一定量を採集し、該気体中に含まれる塩素濃度を測定した。測定の結果、塩素ガス濃度が９５（容量）％以上の場合には正常であると判断し、運転を継続した。
▲２▼塩素ガス濃度が９２（容量）％以上であるが９５（容量）％未満の場合には、酸素ガス濃度を測定した。酸素ガス濃度が７（容量）％以上の場合には、危険槽であると判断し、電解槽の運転を停止して安全点検を行った。
▲３▼酸素濃度が７（容量）％未満の場合には、水素ガス濃度で判定した。水素ガス濃度が０．２５（容量）％未満の場合には正常であると判断し、運転を継続した。
▲４▼水素ガス濃度が塩素ガス濃度が０．２５（容量）％以上の場合には、危険槽であると判断し、電解槽の運転を停止して安全点検を行った。
【００４８】
この場合、塩素ガス濃度はオルザット分析法で測定し、酸素ガス濃度及び水素ガス濃度は、ガスクロマトグラフ法により測定した。
【００４９】
【発明の効果】
以上説明したように、本発明によれば、従来のように、すべての電解槽の陽極液のｐＨ値を測定するという煩雑な作業が不要であり、イオン交換膜法塩化アルカリ電解槽の運転を停止した後、運転を再開する場合に、イオン交換膜や電解槽に損傷がなく正常に運転を開始し、継続できるか否かの判断を簡便且つ迅速に行うことができる。
【図面の簡単な説明】
【図１】イオン交換膜法塩化アルカリ電解槽の１例の模式図（断面図）である。
【図２】本発明のイオン交換膜法塩化アルカリ電解槽の運転方法の手順を示すフローチャート図である。
【図３】通電前の防食電流の電圧と陽極液のｐＨ値との関係を表す図である。
【図４】通電後の電解電圧と陽極液のｐＨ値との関係を表す図である。
【図５】通電前と通電後の陽極液のｐＨ値の関係を表す図である。
【図６】通電後の電解電圧が所定値未満の場合に陽極室から発生する気体の分析を行い、分析結果から電解槽の運転を継続できるか、運転を停止するかの判断手順を示したフローチャート図である。
【図７】実施例におけるイオン交換膜法塩化ナトリウム電解槽の運転方法の手順を示すフローチャート図である。
【図８】通電前の防食電流の電圧と陽極液のｐＨ価との関係から重回帰式を求めた図である。
【図９】防食電流の電圧（Ｉ＝０）と電解電流（Ｉ＝１０ｋＡ，２５ｋＡ）での電解電圧の経時変化を表した図である。
【図１０】電解電圧と陽極室から発生する塩素ガス濃度との関係を表した図である。
【符号の説明】
１…陽極
２…陰極
３…陽極室
４…陰極室
５…イオン交換膜[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ion exchange membrane method electrolytic cell operating method for safely operating an alkali chloride electrolytic cell by an ion exchange membrane method.
[0002]
[Prior art]
Conventionally, a method of electrolyzing alkali chloride such as salt using an ion exchange membrane (hereinafter referred to as “ion exchange membrane method alkali chloride electrolysis”) has been carried out on an industrial scale.
In the ion-exchange membrane method alkali chloride electrolysis, usually an ion-exchange membrane made of an organic material is sandwiched, and one anode side contains chlorine and a strong oxidizing atmosphere, and the other cathode side contains a strong alkaline solution. Is exposed to extremely harsh conditions. Therefore, it is difficult to avoid the deterioration of the ion exchange membrane over time during long-term operation. In addition, such deterioration is not limited to the performance of the ion exchange membrane, and in general, when damage such as pinholes occurs, chlorine on the anode side and hydrogen on the cathode side mix, In the worst case, there is a risk of explosion. Furthermore, when a pinhole is generated in the ion exchange membrane, the alkali on the high pressure side flows into the anode chamber and reacts with chlorine to produce hypochlorous acid, which corrodes the battery case gasket, thereby causing liquid to the outside. It causes leakage and shortens the life of the electrolytic cell.
[0003]
Further, while the ion exchange membrane method alkali chloride electrolysis is stopped, it is common to pass a corrosion-proof current in order to prevent corrosion of the electrolytic cell.
However, the surface of the ion exchange membrane or the electrolytic cell may be damaged in spite of the anti-corrosion current, and when the operation is restarted in this state, the anode side chlorine and the cathode side hydrogen are mixed. In other words, the battery case gasket is corroded, causing liquid leakage to the outside and shortening the life of the electrolytic cell.
[0004]
Therefore, in ion exchange membrane method alkaline chloride electrolysis, it is extremely important from the standpoint of accident prevention and cost reduction to detect abnormalities such as deterioration of the ion exchange membrane used and damage to the electrolytic cell as early as possible. Become.
[0005]
Conventionally, as an operation method of an ion exchange membrane method alkaline chloride electrolytic cell, for example, the following is known.
(1) In Japanese Patent Laid-Open No. 55-65379, salt water is supplied in parallel by a branch pipe branched from a common mother pipe to the anode chamber of a plurality of electrolytic cells, and a part of the anode chamber liquid is discharged from the discharge port. When performing electrolysis while extracting, the pH value of the anode chamber liquid extracted from the discharge port is measured, and based on this, hydrochloric acid is individually supplied to each electrolytic cell, and the pH value is maintained at 4 or less. A method of operating an alkali halide ion exchange membrane electrolytic cell is described.
[0006]
(2) Japanese Patent Laid-Open No. 57-123989 discloses that the current amount (I) and voltage (V) during operation of the electrolytic cell are detected by a current detector and a voltage detector provided in the electrolytic cell, Using the amount of current (I) and voltage (V) during normal operation, using the K value obtained in advance based on the formula: V = KI + e (e is the theoretical electrolysis voltage), and the preset allowable value α 0 The equation: V = KI + e + α is compared, and the operation control method of the electrolytic cell is performed as if an abnormal signal is generated when | α |> | α 0 |.
[0007]
(3) In addition, in JP-A-8-74082, when operating a plurality of ion exchange membrane alkali chloride electrolytic cells, the oxygen concentration in the chlorine gas from the anode chamber of each electrolytic cell and the Measure the chlorine supply amount for each tank, and supply hydrochloric acid individually to each electrolytic tank so that the oxygen concentration in the chlorine gas is kept at 0.1 to 0.5 (volume)% based on the measured value. And, the chlorine basic unit (hydrochloric acid supply amount / chlorine generation amount) of each tank is calculated, and this calculated value is compared with a predetermined value or by relative comparison with the average value of the hydrochloric acid basic unit of all the tanks, An operating method of an alkali chloride ion-exchange membrane method electrolytic cell characterized by detecting an abnormality in the electrolytic cell is disclosed.
[0008]
[Problems to be solved by the invention]
However, among the operation methods of the conventional ion exchange membrane method alkaline chloride electrolytic cell described above, the method of measuring the pH value of the anolyte must measure the pH value of all the electrolytic cells during operation. It is very complicated. In addition, in the region exceeding pH 4, the sensitivity of the pH value with respect to fluctuations in current efficiency is very low, so it is difficult to detect an abnormality due to the change in pH value. Furthermore, there is a problem that the pH value is likely to cause an error due to variations in liquid temperature during measurement and gas diffusion during sampling.
[0009]
Moreover, it can be said that the method of detecting the electric current amount and voltage at the time of an electrolytic cell operation is a comparatively excellent method in that an abnormality of the electrolytic cell that occurs during the operation can be quickly discovered without measuring the pH value. However, when resuming operation after stopping the operation of the electrolyzer, when determining whether the operation of the electrolyzer can be resumed normally and whether the operation of the electrolyzer can be continued normally Difficult to apply.
[0010]
On the other hand, in Japanese Patent Application Laid-Open No. 11-61476, an anode chamber of an ion exchange membrane alkaline chloride electrolytic cell is filled with an alkali metal halide aqueous solution having a predetermined alkali metal concentration, and a cathode chamber is filled with an aqueous alkali metal hydroxide solution having a predetermined concentration. A method of starting energization at a predetermined temperature has been proposed.
[0011]
This method focuses on the fact that the concentration balance of the electrolyte solution in the anode chamber and the cathode chamber is lost during the operation stop, and the normal operation is started by returning the concentration balance to normal. However, this method has a problem that it is necessary to measure the concentration of the electrolytic solution in all the electrolytic cells, is complicated, and lacks simplicity and speed.
[0012]
As described above, the conventional ion exchange membrane method alkali chloride electrolysis start-up method and operation (control) method cause damage to the ion-exchange membrane or the electrolyzer when the operation is restarted after the operation of the electrolyzer is stopped. It is not a method that can easily and quickly determine whether or not the operation can be resumed normally and whether the operation can be continued normally after the operation is resumed. In particular, in the event that an unsuccessful power failure occurs due to a short-circuit accident of a transmission line that is likely to occur due to snow, etc. in winter, in order to reduce damage to the ion exchange membrane and the electrolytic cell as much as possible, and to suppress an increase in manufacturing costs It is important to be able to resume normal operation as soon as possible after a power failure.
[0013]
The present invention has been made in view of such circumstances, and in ion exchange membrane alkali chloride electrolysis, when the operation of the electrolytic cell is stopped and then restarted, there is no damage to the ion exchange membrane or the electrolytic cell. It is an object of the present invention to provide an operation method of an ion exchange membrane method alkaline chloride electrolytic cell capable of simply and promptly determining whether or not the operation can be normally started and continued.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention operates a plurality of ion-exchange membrane alkaline chloride electrolyzers. The voltage A (V) of the anticorrosion current flowing through the electrolyzer before the operation is started, and the operation are as follows. The electrolysis voltage B (V) at a predetermined current after the start is measured, and the operation is continued when A and B are equal to or higher than a set value, and when either A or B is less than the set value, the electrolytic cell An ion exchange membrane method alkaline chloride electrolytic cell operation starting method is provided, in which the gas generated from the gas is analyzed, and whether the electrolytic cell operation is continued or stopped is determined from the analysis result.
[0015]
In the operation method of the present invention, when either A or B is less than a set value, the concentration of chlorine gas contained in the gas generated from the anode chamber of the electrolytic cell is measured, and the obtained measurement It is preferable to determine from the results whether to continue or stop the operation of the electrolytic cell.
[0016]
In the operation method of the present invention, when either A or B is less than a set value, the concentration of chlorine gas and oxygen gas contained in the gas generated from the anode chamber of the electrolytic cell is measured and obtained. It is more preferable to determine whether to continue or stop the operation of the electrolytic cell from the measured results.
[0017]
In the operation method of the present invention, when either A or B is less than a set value, the concentration of chlorine gas, oxygen gas and hydrogen gas contained in the gas generated from the anode chamber of the electrolytic cell is measured. It is more preferable to determine whether to continue or stop the operation of the electrolytic cell from the obtained measurement result.
[0018]
In the operating method of the present invention, when either A or B is less than the set value, the gas generated from the anode chamber of the electrolytic cell is analyzed, and as a result of the analysis of the gas, the chlorine gas concentration is 95. (Volume)% or more, or chlorine gas concentration is 92 (Volume)% or more and less than 95 (Volume)%, oxygen gas concentration is less than 7 (Volume)%, and hydrogen gas concentration is 0.25 ( It is particularly preferable to continue the operation when the volume is less than (%), and to stop the operation otherwise.
[0019]
In the operation method of the present invention, the set values of the anticorrosion current voltage A (V) include the pH value P of the anolyte, the bath temperature T (° C.), and the alkali hydroxide concentration C OH ( COH ). a value obtained by measuring the weight%) under various conditions, the general formula (1): by substituting a + bP + cT + dC OH , calculated a, b, c, and d by multiple regression analysis, determined from the obtained equation It is preferable to use those that can be used.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
An example of an ion exchange membrane method alkaline chloride electrolytic cell used in the present invention is shown in FIG.
An actual electrolytic cell is formed by stacking the units shown in FIG. 1 in multiple layers (about 10 to 20 layers). In FIG. 1, in the
[0021]
In each electrolytic cell, an anode 1 and a
[0022]
The present invention is a method of operating a plurality of ion exchange membrane alkali chloride electrolytic cells, and the voltage A (V) of the anticorrosion current before the operation is started (hereinafter also referred to as “before energization”), and the operation Is measured (hereinafter also referred to as “after energization”), and if A and B are equal to or higher than the set value, the operation is continued, and either A or B is set. If the value is less than the value, the gas generated from the electrolytic cell is analyzed, and from the result of the analysis, the operation of the electrolytic cell alkaline chloride electrolytic cell is determined to determine whether to continue or stop the electrolytic cell operation. . FIG. 2 shows a flowchart of the outline of the operation method of the ion exchange membrane method alkaline chloride electrolytic cell of the present invention.
[0023]
The first feature of the present invention is to confirm whether or not the voltage of the anticorrosion current is equal to or higher than a predetermined value A (V) before energization.
When an ion exchange membrane method alkaline chloride electrolytic cell is operated, the operation may be stopped for some reason or the operation may be inevitably stopped. It is known that when the operation of the electrolytic cell is stopped, the electrolytic cell is in a state of a kind of battery, and a current flows through the electrolytic cell. If this state is left unattended, the ion exchange membrane may be damaged or the electrolytic cell or electrode surface may be corroded.
For this reason, while the operation of the electrolytic cell has been stopped, a corrosion-preventing current is applied to the electrolytic cell to prevent damage to the ion exchange membrane and corrosion of the electrolytic cell and the electrode surface.
[0024]
While the anticorrosion current flows, oxygen gas is generated from the anode chamber, and hydrogen gas is mainly generated from the cathode chamber. In a state where a certain anticorrosion current flows, it is derived from the Nernst equation that the cell voltage in the anticorrosion current depends on the pH values of the anode chamber and the cathode chamber. The results of actually measuring the voltage of the anticorrosion current and the pH value of the electrolyte in the anode chamber are shown in FIG. From FIG. 3, it can be seen that the voltage of the anticorrosion current generally decreases when the pH value of the electrolytic solution is high (in the example shown in FIG. 3, the contribution ratio is about 0.66).
[0025]
After energization, as is apparent from the measurement example shown in FIG. 4, no correlation was found between the pH value of the catholyte and the cell voltage. However, as shown in FIG. 5, it was found that there is a certain correlation between the pH value of the anolyte before energization and the pH value of the anolyte after energization (in the example shown in FIG. The contribution is about 0.7).
[0026]
Therefore, (1) the electrolytic cell in which the voltage of the anticorrosion current before the electrolytic cell restarts is below a certain value, the pH value of the anolyte is abnormally high, and (2) the pH value of the anolyte before energization There is a certain correlation between the anolyte and the pH value of the anolyte after energization, and (3) if the pH value of the anolyte is abnormal, a trouble after resuming operation is predicted. From these facts, when the voltage of the anticorrosion current is less than the predetermined value, it is determined whether or not the operation can be continued normally again after restarting the operation of the electrolytic cell.
[0027]
The voltage of the anticorrosion current is affected by factors such as the bath temperature and the concentration of the sodium hydroxide aqueous solution that is the catholyte. Therefore, the set value of the voltage V of the anticorrosion current can be determined, for example, as follows.
(1) The primary correlation among the catholyte pH value P, the bath temperature T (° C.) and the catholyte sodium hydroxide concentration C OH (wt%) as factors affecting the voltage of the anticorrosion current assuming that there is a general formula (1): and V = a + bP + cT + dC OH holds.
(2) The pH value P of the catholyte, the bath temperature T (° C.), and the sodium hydroxide concentration C OH (wt%) of the catholyte were measured under various conditions, and a, b in the general formula (1) were measured. , C and d are determined by multiple regression analysis.
[0028]
(3) The general formula (1) obtained generally holds under various conditions (bath temperature, anolyte pH value, catholyte sodium hydroxide concentration). Therefore, before resuming the operation of the electrolytic cell, as an electrolytic cell having a high risk of occurrence of trouble after resuming the electrolytic cell operation, the pH value of the anolyte in the electrolytic cell is, for example,
[0029]
Since the present invention is characterized by determining whether or not the voltage of the anticorrosion current is equal to or higher than a predetermined value, the method for determining the set value is not limited to the above, but other methods, for example, It can also be determined from rules of thumb.
[0030]
A second feature of the present invention is to confirm whether or not the electrolytic voltage at a predetermined current is equal to or higher than a predetermined value B (V) after energization.
When actually performing alkaline ionization using ion exchange membrane method after resuming operation, gradually check whether or not the electrolysis can be resumed normally while gradually increasing the electrolysis current and voltage. The electrolysis operation is performed in a state of 50 kA to 100 kA.
[0031]
In addition, chlorine gas is generated from the anode chamber after energization, but it is known that when there is some trouble in the electrolytic cell, the component composition of the gas generated from the electrolytic cell is different from the normal case. Therefore, if the gas generated from the anode chambers of all the electrolytic cells is sequentially analyzed, it can be confirmed whether or not the electrolytic cells are normally operated. However, the operation is very complicated and lacks quickness.
[0032]
Therefore, in the present invention, (1) when the chlorine gas concentration generated from the anode chamber is low, it is judged that some trouble has occurred in the electrolytic cell, and (2) from the anode chamber of the electrolytic cell. Since there is a certain correlation between the concentration of generated chlorine gas and the electrolysis voltage, the electrolysis voltage at a predetermined current becomes a predetermined value B (V) in the process of increasing the electrolysis current and voltage after energization. If it is less than that, it is determined that there is a high possibility that some trouble has occurred in the electrolytic cell.
[0033]
There is a certain correlation between the concentration of chlorine gas generated from the anode chamber of the electrolytic cell and the electrolysis voltage. Therefore, the predetermined value (B) of the electrolysis voltage can be determined empirically by analyzing the measurement data of the electrolysis voltage when the chlorine gas concentration is low.
[0034]
In the present invention, when the voltage of the anticorrosion current is less than the predetermined value A (V) before energization, or when the electrolysis voltage is less than the predetermined value B (V) after energization, the gas generated from the electrolytic cell is analyzed. The third feature is to judge whether the operation can be continued from the result of the analysis or whether the operation should be stopped and the electrolytic cell safety inspection should be performed.
[0035]
In the present invention, it is preferable to analyze the gas generated from the anode chamber as the gas generated from the electrolytic cell to be analyzed. Gases that may be generated from the anode chamber include chlorine gas, oxygen gas, and hydrogen gas. If the electrolyzer is operating normally, only chlorine gas should be generated, and if there is an abnormality in the electrolyzer, the chlorine gas concentration will decrease relatively and the oxygen gas and hydrogen gas concentrations will increase. Because. Therefore, as a gas analysis, it is more preferable to measure the chlorine gas concentration first, and when the chlorine gas concentration is less than a predetermined value, measure the oxygen gas concentration and the hydrogen gas concentration.
[0036]
More specifically, analysis of the gas generated from the anode chamber can be performed, for example, according to procedures (1) to (5) shown in the flowchart shown in FIG. In the slow chart shown in FIG. 6, Y means Yes and N means No (the same applies to the following flowcharts).
(1) First, the concentration of chlorine gas contained in the gas generated from the anode chamber of the electrolytic cell is measured. At this stage, if the chlorine gas concentration is X (volume)% or more, it is determined that the operation can be continued.
(2) If the chlorine concentration is less than Y (capacity)%, it is considered dangerous, so stop the operation and perform a safety check of the electrolytic cell.
(3) If the chlorine gas concentration is less than X (capacity)% but Y (capacity)% or more, the oxygen gas concentration is measured. If the oxygen gas concentration is more than Z (capacity)%, it is considered dangerous, so stop the operation and perform a safety check of the electrolytic cell.
(4) If the oxygen gas concentration is less than Z (volume)%, measure the hydrogen concentration. Here, since it is considered dangerous when the hydrogen gas concentration is W (capacity)% or more, the operation is stopped and the electrolytic cell is inspected for safety.
(5) If the hydrogen concentration is less than W (capacity)%, it is determined that the operation can be continued.
[0037]
In the present invention, the gas analysis method is not particularly limited, and conventionally known analysis devices and analysis means can be employed.
[0038]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
In the examples, a total of 30 electrolytic cells in which the units shown in FIG. The operation of the ion exchange membrane sodium chloride electrolytic cell was performed according to the flowchart shown in FIG.
[0039]
First, the operation of the electrolytic cell was stopped after the normal electrolytic cell was operated. While the operation was stopped, the anticorrosion current was continuously supplied to the electrolytic cell at a constant voltage. The voltage V of the anticorrosion current and the pH value P of the anolyte at that time were measured under conditions of various electrolytic cell temperatures T (° C.) and the sodium hydroxide concentration C OH (wt%) of the catholyte. FIG. 8 shows the measurement results when the electrolytic cell temperature T is 65 ° C. and the sodium hydroxide concentration C OH of the catholyte is 29% by weight. In addition, the measurement was performed at an electrolytic cell temperature of 60 to 70 ° C. and a sodium hydroxide concentration of 28 to 30% by weight.
[0040]
Next, assuming that the general formula (1): V = a + bP + cT + dC OH is established, a multiple regression analysis was performed using the measurement results to obtain the formula: V = 1.633-0.035P-0.001T + 0.015C OH . That is, a = 1.633, b = −0.035, c = −0.001, and d = 0.15.
[0041]
The pH value of the anolyte in the electrolytic cell that is judged to be highly likely to cause trouble is 11.8, the average temperature T of the electrolytic cell is 70 ° C., and the average concentration of sodium hydroxide COH is 26% by weight. Substituting into the general formula (1) to obtain the value of V, V = 1.54 (V) was obtained. Note that the pH value of the anolyte in the electrolytic cell, which is judged to have a high risk of occurrence of trouble, is generally considered to be 12 or more, but the pH value was set to 11.8 in consideration of safety.
[0042]
After resuming operation, the electrolysis voltage was measured. In this example, the electrolysis voltage after restarting the operation of the electrolyzer was measured. (1) If the voltage at an electrolysis current of 25 kA (ampere) was 2.45 V or more, the electrolyzer was operating normally. The operation can be continued. (2) When the electrolysis voltage is less than 2.45 V, there is a possibility that the electrolytic cell may be abnormal, so the gas generated from the anode chamber is analyzed.
[0043]
In addition, the voltage was not stable at the electrolytic current of 10 kA immediately after the restart of the operation. When the electrolytic current reached 25 kA, the electrolytic voltage gradually became stable, and the electrolytic voltage shifted from about 2.54 V to 2.70 V. Therefore, the determination as to whether or not the electrolytic voltage is equal to or higher than a predetermined value is made when the current voltage is 25 kA.
[0044]
Moreover, the predetermined value (2.54V) of the reference electrolysis voltage was determined as follows. That is, the time-dependent change of the electrolysis voltage (V) after restarting the operation when the electrolysis current (I) was changed to 0 kA, 10 kA, and 25 kA was measured. An example of the measurement results is shown in FIG. 9 (in FIG. 9, the horizontal axis indicates elapsed time, and the vertical axis indicates electrolytic voltage (V)). And from the result of measuring about various electrolytic cells, in the case of a normal electrolytic cell, it discovered empirically that the electrolysis voltage is 2.54V or more with the electrolysis current of 25 kA.
[0045]
In addition, in the electrolysis current of 0 kA (the state in which the anticorrosion current flows), the voltage (V) of the anticorrosion current changes between 1.54 V and 1.7 V. It was also found that the voltage was 54 V or more (in the case of I = 0 kA).
[0046]
In the case of an electrolytic cell having an electrolytic current of 25 kA and an electrolytic current of less than 2.54 V, gas generated from the anode chamber of the electrolytic cell was analyzed. FIG. 10 shows the results of measuring the electrolysis voltage (V) at an electrolysis current of 25 kA after energization and the chlorine gas concentration (volume%) contained in the gas generated from the anode chamber. From FIG. 10, when the electrolysis voltage is abnormally low (electrolysis voltage = 2.1 V to 2.2 V), the concentration of chlorine gas generated from the anode chamber is about 2.54 V to 2.65 V. It can be seen that it is relatively low compared to the case of the electrolytic cell.
[0047]
Based on the gas analysis results, the decision whether to continue or stop the operation of the electrolytic cell was made in the following procedure with reference to the measurement results obtained in FIG.
(1) First, a certain amount of gas generated from the anode chamber of the electrolytic cell was collected, and the concentration of chlorine contained in the gas was measured. As a result of the measurement, when the chlorine gas concentration was 95 (volume)% or more, it was judged to be normal and the operation was continued.
(2) When the chlorine gas concentration was 92 (volume)% or more but less than 95 (volume)%, the oxygen gas concentration was measured. When the oxygen gas concentration was 7 (capacity)% or more, it was judged as a dangerous tank, and the operation of the electrolytic cell was stopped to perform a safety check.
(3) When the oxygen concentration was less than 7 (volume)%, the determination was made based on the hydrogen gas concentration. When the hydrogen gas concentration was less than 0.25 (volume)%, it was judged normal and the operation was continued.
(4) When the hydrogen gas concentration was 0.25 (volume)% or more of the chlorine gas concentration, it was judged as a dangerous tank, and the operation of the electrolytic cell was stopped and a safety check was performed.
[0048]
In this case, the chlorine gas concentration was measured by an Orsat analysis method, and the oxygen gas concentration and the hydrogen gas concentration were measured by a gas chromatographic method.
[0049]
【The invention's effect】
As described above, according to the present invention, unlike the prior art, the troublesome work of measuring the pH value of the anolyte in all the electrolytic cells is unnecessary, and the operation of the ion exchange membrane method alkaline chloride electrolytic cell is not required. When the operation is resumed after stopping, it is possible to easily and quickly determine whether or not the ion exchange membrane and the electrolytic cell can be operated normally without any damage.
[Brief description of the drawings]
FIG. 1 is a schematic view (cross-sectional view) of an example of an alkali chloride electrolytic cell using an ion exchange membrane method.
FIG. 2 is a flow chart showing a procedure of an operation method of the ion exchange membrane method alkaline chloride electrolytic cell of the present invention.
FIG. 3 is a diagram showing the relationship between the voltage of the anticorrosion current before energization and the pH value of the anolyte.
FIG. 4 is a diagram showing the relationship between the electrolysis voltage after energization and the pH value of the anolyte.
FIG. 5 is a graph showing the relationship between the pH value of the anolyte before and after energization.
FIG. 6 shows a procedure for performing analysis of gas generated from the anode chamber when the electrolysis voltage after energization is less than a predetermined value and determining whether the operation of the electrolytic cell can be continued or stopped based on the analysis result. It is a flowchart figure.
FIG. 7 is a flowchart showing a procedure of an operation method of an ion exchange membrane method sodium chloride electrolytic cell in an example.
FIG. 8 is a diagram showing a multiple regression equation obtained from the relationship between the voltage of the anticorrosion current before energization and the pH value of the anolyte.
FIG. 9 is a diagram showing the change over time of the electrolysis voltage at the anticorrosion current voltage (I = 0) and the electrolysis current (I = 10 kA, 25 kA).
FIG. 10 is a diagram showing the relationship between the electrolysis voltage and the concentration of chlorine gas generated from the anode chamber.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ...
Claims (6)
請求項１記載のイオン交換膜法塩化アルカリ電解槽の運転方法。When either A or B is less than the set value, the concentration of chlorine gas contained in the gas generated from the anode chamber of the electrolytic cell is measured, and the operation of the electrolytic cell is continued from the obtained measurement result. The operation method of the alkali chloride electrolytic cell of the ion exchange membrane method of Claim 1 which determines whether to stop or to stop.
請求項１記載のイオン交換膜法塩化アルカリ電解槽の運転方法。When either A or B was less than the set value, the gas generated from the anode chamber of the electrolytic cell was analyzed, and the concentrations of chlorine gas and oxygen gas contained in the gas were measured and obtained. The operation method of an ion exchange membrane method alkali chloride electrolytic cell according to claim 1, wherein it is determined whether to continue or stop the electrolytic cell operation from the measurement result.
請求項１記載のイオン交換膜法塩化アルカリ電解槽の運転方法。When either A or B is less than a set value, the gas generated from the anode chamber of the electrolytic cell is analyzed, and the concentrations of chlorine gas, oxygen gas and hydrogen gas contained in the gas are measured, The operation method of an ion exchange membrane method alkali chloride electrolytic cell according to claim 1, wherein it is determined whether to continue or stop the operation of the electrolytic cell from the obtained measurement result.
請求項１記載のイオン交換膜法塩化アルカリ電解槽の運転方法。When either A or B is less than the set value, the gas generated from the anode chamber of the electrolytic cell is analyzed. As a result of the analysis, (1) the chlorine gas concentration is 95 (volume)% or more. Or (2) the chlorine gas concentration is 92 (volume)% or more and less than 95 (volume)%, the oxygen gas concentration is less than 7 (volume)%, and the hydrogen gas concentration is less than 0.25 (volume)%. The operation method of the ion-exchange membrane method alkaline chloride electrolytic cell according to claim 1, wherein the operation is continued in the case of (1), and the operation is stopped in other cases.
請求項１〜５のいずれかに記載のイオン交換膜法塩化アルカリ電解槽の運転方法。As the set values of the voltage A (V) of the anticorrosion current, the pH value P of the anolyte, the bath temperature T (° C.), and the alkali hydroxide concentration C OH (wt%) of the catholyte were measured under various conditions. The value is substituted into the general formula (1): a + bP + cT + dC OH , and a, b, c, and d are obtained by multiple regression analysis, and values determined from the obtained formula are used. ion-exchange membrane method OPERATION how the alkali chloride electrolytic cell according to.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS52149295A (en) * | 1976-06-08 | 1977-12-12 | Tokuyama Soda Co Ltd | Protecting method for electrolytic bath |
| JPS5425298A (en) * | 1977-07-29 | 1979-02-26 | Tokuyama Soda Co Ltd | Protection method of electrolyzer |
| JPS61153295A (en) * | 1984-12-26 | 1986-07-11 | Tokuyama Soda Co Ltd | Method for detecting breakage in ion exchange membrane |
| JPH0617278A (en) * | 1992-06-30 | 1994-01-25 | Asahi Glass Co Ltd | Method for restarting electrolytic cell |
| JPH07243079A (en) * | 1994-03-02 | 1995-09-19 | Sumitomo Chem Co Ltd | Interelectrode voltage measuring device |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS52149295A (en) * | 1976-06-08 | 1977-12-12 | Tokuyama Soda Co Ltd | Protecting method for electrolytic bath |
| JPS5425298A (en) * | 1977-07-29 | 1979-02-26 | Tokuyama Soda Co Ltd | Protection method of electrolyzer |
| JPS61153295A (en) * | 1984-12-26 | 1986-07-11 | Tokuyama Soda Co Ltd | Method for detecting breakage in ion exchange membrane |
| JPH0617278A (en) * | 1992-06-30 | 1994-01-25 | Asahi Glass Co Ltd | Method for restarting electrolytic cell |
| JPH07243079A (en) * | 1994-03-02 | 1995-09-19 | Sumitomo Chem Co Ltd | Interelectrode voltage measuring device |
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