Canexus converted the plant from diaphragm technology to membrane technology. Chemical plants around the world are moving to this new process as it produces a superior product with less impact on the environment.

With this conversion our plant has become an international leader in the implementation of this new technology.

In the diaphragm cell process, an asbestos diaphragm is used to separate the anode and cathode compartments of the cell. Saturated brine enters the anode compartment and the chlorine gas liberated at the anode during electrolysis exits from the anode compartment. Sodium ions are transported from the anode compartment to the cathode compartment by the flow of the solution and by electromigration where they combine with the hydroxyl ions generated at the cathode during the formation of the hydrogen from the water molecules. The diaphragm resists the back migration of the hydroxyl ions, which would otherwise react with the chlorine in the anode compartment. In the cathode compartment, the concentration of the sodium hydroxide is ~12 percent, and the salt concentration is ~14 percent.

The membrane cell process, an ion specific membrane is sandwiched between the anode and the cathode separating the anode and cathode compartments. The saturated brine is fed to the anode compartment where chlorine is liberated at the anode, and the sodium ion migrates to the cathode compartment. Unlike the diaphragm cells, only the sodium ions and some water migrate through the membrane. The unreacted sodium chloride and other inert ions remain in the anolyte. About 30 percent caustic soda is fed to the cathode compartment, where sodium ions react with hydroxyl ions produced during the course of the hydrogen gas evolution from the water molecules. This forms caustic, which increases the concentration of caustic solution to ~33 percent. The hydrogen gas, saturated with water, exits from the catholyte compartment. Only part of the caustic soda product is withdrawn from the cathode compartment. The remaining caustic is diluted to ~30 percent and returned to the cathode compartment.

There are several significant advantages being realized with the conversion to membrane technology

• greenhouse gas emissions at the plant are reduced by over 80 per cent,
• asbestos has been removed from the manufacturing process,
• solids discharge into the Burrard Inlet has been reduced,
• the plant has a smaller footprint and
• the amount of natural gas used in the chemical process has been significantly reduced.

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