Making Caustic Soda with Less Salt Using a Special Electrolysis Cell

This patent describes a method to make purer caustic soda and chlorine gas using a two-chamber electrolysis cell with a gas diffusion electrode by carefully controlling pressure differences.

What it covers

The patent claims a method for electrolyzing brine (saltwater) in a "two-chamber ion exchange membrane electrolytic cell" (Claim 1). This cell has an "anode chamber" and a "cathode gas chamber" separated by an "ion exchange membrane." The cathode chamber uses a "gas diffusion electrode." The core idea is "reducing a differential pressure" between the liquid pressure in the anode chamber and the gas pressure in the cathode gas chamber (Claim 1). This pressure difference is precisely controlled, for example, reduced to "2.4 kPa or less" (Claim 1) or "-21.6 kPa or more" (Claim 2), by adjusting a "sealing pot or a valve" (Claim 1). This precise pressure control helps in "decreasing a salt concentration in the caustic soda aqueous solution" (Claim 1). For example, by carefully adjusting the valve downstream of the cathode chamber, the pressure inside the cathode chamber can be increased, which reduces the pressure difference across the membrane, leading to purer caustic soda.

What it doesn't cover

• —Electrolysis methods that do not use a "two-chamber ion exchange membrane electrolytic cell."
• —Electrolysis cells that do not employ a "gas diffusion electrode" as the cathode.
• —Methods that do not involve reducing the differential pressure between the anode liquid and cathode gas.
• —Methods where the differential pressure is not controlled to be "2.4 kPa or less" or "-21.6 kPa or more."
• —Electrolysis processes for producing chemicals other than chlorine gas and caustic soda.

The clever bit

The novelty lies in precisely managing the pressure difference across the ion exchange membrane in a two-chamber cell with a gas diffusion electrode. By reducing this "differential pressure" to specific narrow ranges (e.g., 2.4 kPa or less), the method significantly lowers the unwanted salt concentration in the produced caustic soda solution.

Why it matters

Caustic soda (sodium hydroxide) and chlorine gas are fundamental chemicals used in countless industries, from making paper and plastics to purifying water. Producing these chemicals with lower salt impurities, as described in this patent, means the final products are cleaner and more valuable. This improved purity can reduce downstream processing costs and enhance the quality of products made using these chemicals.

Real-world examples

• 1.Chlor-alkali plants
• 2.Manufacturing of PVC (polyvinyl chloride)
• 3.Water treatment facilities
• 4.Pulp and paper production
• 5.Textile bleaching