Potassium hydroxide is prepared by chemical process. At present, most manufacturers adopt ion-exchange membrane method. The core process of the process flow is primary refining of brine, and the key equipment is electrolytic cell and ion-exchange membrane. The main processes are as follows:

1、盐水一次精制

1. Primary refining of brine

一次盐水工序的任务是将氯化钾、回收盐水、离子膜电槽经过脱氯处理的淡盐水，进行处理成符合要求的过滤盐水。由于这些盐水中含有隔膜所不能允许的杂质（有机物、菌藻类、SO42-、Ca2+、Mg2+、NH3、重金属、SS等），特别是SO42-、Ca2+、Mg2+在电解槽里会阻塞隔膜或离子膜，导致电解槽盐水液面上升，使电流效率下降、槽电压升高、电解槽寿命缩短，甚会造成停车。在盐水中分别加入精制剂氯化钡（或采用膜过滤，但许多中小型装置还是采用钡法）、氢氧化钾、次氯酸钾、碳酸钾、絮凝剂、亚硫酸钾等，以分别除去盐水中的SO42-、Mg2+杂质后，再经过滤器除去SS、CaCO3等杂质以达到工艺要求。

The task of primary brine process is to treat potassium chloride, recovered brine and light brine dechlorinated by ion-exchange membrane electrolyzer into qualified filtered brine. Because these brine contains impurities (organic matter, bacteria and algae, SO42 -, Ca2 +, Mg2 +, NH3, heavy metals, SS, etc.) that cannot be allowed by the diaphragm, especially SO42 -, Ca2 +, Mg2 + will block the diaphragm or ion membrane in the electrolytic cell, resulting in the rise of brine level in the electrolytic cell, the decrease of current efficiency, the increase of cell voltage, the shortening of cell life, and even shutdown. Add refining agent barium chloride (or membrane filtration, but many small and medium-sized devices still use barium method), potassium hydroxide, potassium hypochlorite, potassium carbonate, flocculant and potassium sulfite to remove SO42 - and Mg2 + impurities in the brine respectively, and then remove SS, CaCO3 and other impurities through the filter to meet the process requirements.

2、盐水二次精制

2. Secondary refining of brine

离子膜电解对盐水的质量要求高，从一次盐水工序来的过滤精盐水还需经过离子交换，进一步降低Ca、Mg离子。离子交换树脂塔有两塔流程和三塔流程之分。采用三塔流程，正常情况下两塔串联运行，一塔再生。

Ion membrane electrolysis has high requirements for the quality of brine. The filtered refined brine from the primary brine process needs to undergo ion exchange to further reduce Ca and Mg ions. Ion exchange resin tower can be divided into two tower processes and three tower processes. Three tower process is adopted. Under normal conditions, two towers operate in series and one tower regenerates.

3、电解

3. Electrolysis

经过二次精制，即盐水进入螯合树脂塔除去其中的钙、镁，泵入高位槽后流入离子膜电解槽的阳极室。通入直流电后，在阳极室产生氯气和流出淡盐水经分离器分离，氯气输送到氯气总管，淡盐水一般含氯化钾200-220g/l，经脱氯气去饱和槽。在电解槽的阴极室产生氢气和30-32%液碱同样也经过分离器，氢气输送到氢气总管。30-32%的液碱可以作为商品出售，也可以送到蒸发装置蒸浓到48%的液碱。

After secondary refining, that is, the brine enters the chelating resin tower to remove calcium and magnesium, which is pumped into the high-level tank and then flows into the anode chamber of the ion-exchange membrane electrolyzer. After DC power is applied, chlorine gas and outgoing light brine are generated in the anode chamber and separated by the separator. The chlorine gas is transmitted to the chlorine main pipe. The light brine generally contains 200-220g / L potassium chloride and passes through the dechlorination gas desaturation tank. Hydrogen and 30-32% liquid alkali generated in the cathode chamber of the electrolytic cell also pass through the separator, and the hydrogen is transmitted to the hydrogen main pipe. 30-32% of liquid alkali can be sold as a commodity, or it can be sent to the evaporation unit to evaporate to 48% of liquid alkali.

4、蒸浓与氯气、氢气、废气处理

4. Steam concentration and treatment of chlorine, hydrogen and waste gas