NaClO

Sodium Hypochlorite（NaClO）Production

1. Properties of Sodium Hypochlorite
Chemical formula: NaClO, molecular weight: 74.44 g/mol.
Solubility: 29.3 g/100mL at 0°C.
pKa value: The pKa of hypochlorous acid is 7.5185, indicating that it undergoes hydrolysis in water.
Hazard information: Corrosive. May cause irritation to skin and eyes. Rinse with plenty of water upon contact.
Storage conditions: Should be stored away from light and at low temperature to extend shelf life.
Appearance: Pale yellowish-green transparent liquid.
Concentration and density:

2. Chemical Properties of Sodium Hypochlorite
（1）Sodium hypochlorite is unstable at room temperature and readily decomposes during storage. It exhibits strong oxidizing properties, which can lead to side reactions forming sodium chlorate.

3NaClO == NaClO₃ + 2NaCl

The above reaction proceeds vigorously at temperatures above 40℃, accompanied by a significant decrease in pH. To prevent this side reaction, the pH must be maintained above 11.
（2）Peroxidation reaction

NaClO+ Cl₂ + H₂O == NaCl + 2HClO
NaClO + 2HClO == NaClO₃ + 2HCl
NaClO + 2HCl == NaCl + H₂O + Cl₂

In sodium hypochlorite production, if the chlorination reaction exceeds the endpoint, the sodium hypochlorite will completely decompose.
（3）Photochemical decomposition

2NaClO == 2NaCl + O₂

Approximately 90% of the available chlorine will decompose upon exposure to sunlight. To prevent this, the addition of protective colloids such as gelatin, casein, and sugars is effective.
（4）Thermal decomposition

2NaClO == 2NaCl + O₂

The decomposition rate increases with rising temperature.
（5）Acid decomposition

NaClO + 2HCl == NaCl + HClO
2HClO == 2HCl + O₂

（6）Reduction of available chlorine caused by heavy metal catalysts.

2MO + NaClO == M₂O₃ + NaCl

（7）Reduction of available chlorine caused by pH decrease.

2NaClO == 2NaCl + O₂

3. Quality Specifications of Sodium Hypochlorite

4.Production Methods of Sodium Hypochlorite
Reaction equation for sodium hypochlorite production:

Cl₂ + 2NaOH == NaCl + NaClO + H₂O + 106kJ/mol

There are two main production methods for sodium hypochlorite:
（1）Two-tower co-current flow with tail gas tower
（2）Falling film absorption with tail gas tower
Process description for the two-tower co-current flow with tail gas tower:

Chlorine gas, after flow rate regulation, enters the lower section of the first-stage absorption tower, where it comes into counter current contact with caustic soda solution to react and form sodium hypochlorite. The unreacted chlorine gas then passes to the second-stage absorption tower for further counter current contact with caustic soda solution. The tail gas is discharged to atmosphere through the tail gas tower and the induced draft fan.
The prepared caustic soda solution, after flow rate regulation, enters the first-stage absorption tower circulation tank. The absorption liquid from the circulation tank is pumped by the first-stage circulation pump through a plate heat exchanger, where it is cooled with chilled water, and then enters the upper section of the first-stage absorption tower for contact reaction with chlorine gas. The reacted absorption liquid leaves from the tower bottom and is split into two streams: one stream is returned to the first-stage circulation tank, and the other stream is sent to the second-stage absorption tower circulation tank through a level control valve.
The absorption liquid in the second-stage absorption tower circulation tank is pumped by the second-stage circulation pump through a plate heat exchanger, where it is cooled with chilled water, and then enters the second-stage absorption tower for contact reaction with chlorine gas. The reacted absorption liquid leaves from the tower bottom and is split into two streams: one stream is returned to the second-stage circulation tank, and the other stream, after passing through an online analyzer and meeting the quality specifications, flows to the finished product intermediate tank. It is then pumped by the product pump through a heat exchanger for cooling and delivered to the end user or to the market for sale.

Process Description for Falling Film Absorption with Tail Gas Tower
Chlorine gas, after flow rate regulation, enters the lower section of the falling film absorber, where it reacts with caustic soda solution on the tube wall to form sodium hypochlorite. The heat of reaction is removed by chilled water circulating through the shell side. Unreacted chlorine gas leaves from the upper section of the falling film absorber and enters the tail gas tower, where it comes into counter current contact with the caustic soda solution fed to the falling film absorber. Non-condensable gases are extracted and vented to atmosphere by a hydraulic jet pump.
The prepared caustic soda solution is delivered by the alkali preparation pump to the hydraulic jet pump for reaction with tail gas, and then enters the absorption alkali tank. It is then pumped by the absorption alkali pump through a plate heat exchanger for cooling, and enters the tail gas tower to react with the chlorine gas from the falling film absorber. The absorption liquid flows from the bottom of the tail gas tower through a liquid seal to the top of the falling film absorber, where it is distributed by a film distributor to form a film along the falling film tubes, flowing downward in contact with chlorine gas for reaction. The finished product discharged from the lower section of the falling film absorber is analyzed by an online analyzer. Qualified product enters the finished product intermediate tank for delivery by the product pump, while off-spec product is sent to the off-spec storage tank for reprocessing or reuse.
Process Features:
（1）Two-tower co-current flow with tail gas tower: The first tower has a larger diameter and serves as the primary reactor, ensuring product concentration and facilitating automatic control.
（2）Falling film absorption with tail gas tower: Compact footprint, low equipment investment, low power consumption, easy control, and suitable for large-scale production.

5. Consumption Quota