氯碱工业Chloralkali process

阳极（钛基涂钌等氧化物的“尺寸稳定阳极”）上 Cl⁻ 被氧化：2 Cl⁻ − 2e⁻ → Cl₂↑；阴极（镍或钢）上水被还原：2 H₂O + 2e⁻ → H₂↑ + 2 OH⁻，阴极区生成 NaOH。必须把阳极产物与阴极产物隔开，否则 Cl₂ 会与 NaOH 反应生成 NaClO，H₂ 与 Cl₂ 混合还可能爆炸。

At the anode (a titanium 'dimensionally stable anode' coated with ruthenium and other oxides) Cl⁻ is oxidised: 2 Cl⁻ − 2e⁻ → Cl₂↑. At the nickel or steel cathode water is reduced: 2 H₂O + 2e⁻ → H₂↑ + 2 OH⁻, so NaOH forms in the cathode compartment. The products must be kept apart, or Cl₂ will react with NaOH to give NaClO, and H₂–Cl₂ mixtures can explode.

1890 年代出现隔膜法（石棉隔膜，碱液较稀且含盐）和汞阴极法（卡斯特纳-凯尔纳法，碱液纯但有汞污染）。1970 年代日本旭化成等公司把杜邦的全氟磺酸离子交换膜（Nafion）用于氯碱，只允许 Na⁺ 通过，得到 30–35% 的高纯碱液，能耗也最低。《水俣公约》生效后，汞法在全球逐步淘汰。

The diaphragm cell (asbestos, giving dilute, salty caustic) and the mercury cell (Castner–Kellner, giving pure caustic but mercury pollution) appeared in the 1890s. In the 1970s Asahi Chemical and others applied DuPont's perfluorosulfonic acid membrane (Nafion), which passes only Na⁺, producing 30–35% high-purity caustic with the lowest energy use. Mercury cells are being phased out worldwide under the Minamata Convention.

电解 1 吨 NaCl 约得 0.68 吨 Cl₂ 和 0.76 吨 NaOH，两种产品按固定比例产出，因此需要平衡市场需求。氯气约三分之一用于生产 PVC，也用于制盐酸、漂白剂和含氯有机物；烧碱用于造纸、氧化铝和化纤。氯碱是耗电大户，每吨碱约耗电 2200–2500 kWh。

Electrolysing one tonne of NaCl gives about 0.68 t of Cl₂ and 0.76 t of NaOH, a fixed ratio that has to be balanced against market demand. About a third of the chlorine goes into PVC, and the rest into hydrochloric acid, bleaches and chlorinated organics; caustic goes into paper, alumina and synthetic fibres. The process is power-hungry, using about 2200–2500 kWh per tonne of caustic.