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What is Electrolysis?

Electrolysis is a chemical process where an electric current (DC) passes through a liquid (electrolyte) to create a non-spontaneous chemical reaction.

Large-scale industrial electrolysis technology is used for the manufacture of chlor-alkali products such as chlorine (Cl2), sodium hydroxide (NaOH / caustic soda) and Hydrogen (H2), through the electrolysis of sodium chloride (NaCl).

Other uses of the process include the production of potassium hydroxide (KOH / potash) or hydrochloric acid (HCI / muriatic) and sodium hypochlorite (bleach).


What is an Electrolyser?

An electrolyser is a system designed to house the electrolysis process and manage the process flows of inputs and outputs.

Membrane cell electrolysers feature a sealed module that consist of two chambers, separated by a flexible cation exchange membrane, to prevent chlorine and hydrogen gasses from mixing. The two chambers are formed by the anode and cathode pan assemblies respectively, and once connected to an electricity supply, is where the electrolysis takes place.

Each electrolyser consists of such modules arranged electrically in series within a frame. Typically a number of electrolysers are installed in a cell room side by side, with the quantity designed to meet the overall desired capacity of the plant.


Where do we get Chlorine from?

In industrial volumes, chlorine is produced from the electrolysis of saltwater (brine) by an electrolyser(s) housed in a cell room.

The majority of cell rooms now use the membrane electrolyser process. Diaphragm and mercury cell processes are used to a much lesser extent due to their use of asbestos and mercury respectively, with many areas of the world using environmental legislation to close any mercury plants still in existence. Non-asbestos diaphragm systems are available but feature a much higher power consumption than the membrane process.


How does electrolysis produce chlorine and hydrogen ?

The overall reaction for the electrolysis of brine is :
2NaCl + 2H2O → Cl2 + H2 + 2NaOH

  1. Electrolyte (brine to the anodes and caustic to the cathodes) enters the electrolysis cell
  2. Electrical current begins to flow through the electrodes of each cell
  3. Sodium (Na+) or Potassium (K+) ions pass through the semi-permeable ion exchange membrane
  4. Chlorine gas bubbles form at the anode and Hydrogen gas bubbles form at the cathode

What products are produced in the chlor-alkali process?

The chlor-alkali electrolysis process is used in the manufacture of chlorine (Cl2) and sodium hydroxide (NaOH / caustic soda), Hydrogen (H2), potassium hydroxide (KOH / potash), hydrochloric acid (HCI) or sodium hypochlorite (bleach).


What are the products of Chlor-Alkali used for?

Chlor-alkali chemicals serve as critical feedstock for the manufacture of many products such as PVC, fertilizers, detergents, pharmaceuticals and are used in water purification. Learn more about the products of each chlor-alkali application with our useful guide.


Which Type of Electrolyser is an INEOS BICHLOR Electrolyser?

BICHLOR electrolysers are of a zero-gap membrane bipolar design, featuring a modular approach that streamlines maintenance and minimises plant downtime. The technology delivers significant energy savings and long-lasting performance over a lifetime of chlor-alkali production.


Why are electrode coatings required for Electrolysers?

Each electrode (cathode and anode) is coated to improve power performance and efficiency of the electrolysis process.

Cathode coatings electro-catalytically promote H2 evolution and provide resistance to impurity poisoning and reverse currents at shutdown.

Anode pan coatings are for the electrocatalytic promotion of Cl2 evolution and have superior alkali wear performance and lower exit brine chlorate values.


How long will my coatings last before needing replacement?

Our cathode coatings are supplied with an industry-leading 8 or 16-year coating warranty, dependent on which of our coatings range is selected.

Our anode coatings feature up to 12-year warranties.


What is an electrode coating made of?

INEOS CHLORCOAT electrode coatings contain precious metals for resistance to lifetime-limiting events during the operation of the electrolyser.


Are INEOS' Electrolysers available in my country?

INEOS chlor-alkali electrolysers are available for installation in all countries and are already installed in over 35 countries across the world.


Are INEOS Electrolysers safe to operate?

BICHLOR electrolysers are inherently safe to operate. Design features such as a fully wetted membrane that prevents gasses mixing, and the ability to remove or add modules without personnel climbing on the structure ensure safe operation.


How much does an INEOS Bichlor Electrolyser cost?

INEOS BICHLOR electrolysers are designed to suit the individual requirements of each application and upstream / downstream process. There are a number of design factors that influence the cost, such as capacity, configuration and operational choices such as pressure and current density.

Contact Us to let us develop a design for your application.


Will I receive any Technical Service after plant commissioning?

INEOS Electrochemical Solutions offer a comprehensive Asset Care Program that includes Technical Service and Training on all of our electrolysers installations.



The membrane in a chlor-alkali electrolyser is a semi-permeable barrier separating the anode and cathode compartments which selectively allows the passage of specific ions (i.e. Na+ or K+) ensuring high product purity whilst also preventing the mixing of gases.


As temperature increases the membrane ion conductivity increases (reduced resistance / voltage) however it will also increase water transport and reduce selectivity. BICHLOR operating conditions are selected to deliver optimum performance and product qualities.