Sodium hydroxide (NaOH) is an important basic chemical raw material, widely used in the papermaking, textile, chemical, petroleum, pharmaceutical, and food industries. Its industrial production primarily utilizes the electrolysis of brine.

Production Process Overview:

Brine Refining

Crude salt is dissolved into saturated brine

Impurities such as Ca²⁺, Mg²⁺, and Fe³⁺ are removed through clarification, filtration, and the addition of chemicals (such as soda ash and barium hydroxide).

High-purity brine for electrolysis is obtained.

Electrolysis (primarily ion-exchange membrane electrolysis)

The purified brine is passed through the electrolytic cell.

Under the action of direct current, chlorine (Cl₂) is produced at the anode, hydrogen (H₂) is produced at the cathode, and sodium hydroxide solution is produced.

Main Reactions:

Anode: 2Cl⁻ → Cl₂↑ + 2e⁻

Cathode: 2H₂O + 2e⁻ → H₂↑ + 2OH⁻

Overall Reaction: 2NaCl + 2H₂O → 2NaOH + Cl₂↑ + H₂↑

Separation and Collection

Approximately 30% is obtained in the cathode chamber. Caustic soda solution

Chlorine and hydrogen are also produced as by-products.

Concentration and refining

The caustic soda solution is concentrated to different specifications of 32%, 42%, and 50% using a multi-effect evaporator.

It can also be further cooled and crystallized to produce solid sodium hydroxide (caustic soda flakes/beads).

Process Features:

Ion-exchange membrane electrolysis is the mainstream process, offering low energy consumption, high product purity, and excellent environmental performance.

The by-products chlorine and hydrogen can be comprehensively utilized to improve economic efficiency.

Summary: The core of sodium hydroxide production is brine refining → electrolysis → separation → concentration → finished product. Product forms include liquid caustic soda (32%-50%) and solid caustic soda (caustic soda flakes/beads).