Sodium hypochlorite (Bleach) is made with chlorine and sodium hydroxide in solution with water.
Cl2 + NaOH = NaOCl + NaCl + H2O
When the bleach strength exceeds approximately 17% by weight, the salt is approximately 13.2% by weight and will be high enough in concentration to begin precipitating out of solution. The definition of high strength low salt bleach is any sodium hypochlorite higher than 17% by weight that does not precipitate salt. This is an indication that the salt levels in the sodium hypochlorite solution have been reduced. Normally, high strength low salt bleach produced by Powell equipment is a minimum of 30% by weight with approximately 8% by weight NaCl. Reducing the strength by water addition to the 12.5% by weight commercial-grade will result in approximately 3.5% by weight salt. This reduced salt content will improve the half-life of the sodium hypochlorite by a factor of 2 compared to traditional sodium hypochlorite at the same concentration and temperature.
In summary, low salt sodium hypochlorite is any product that has less salt in solution than traditional commercial-grade sodium hypochlorite at the same strength.
Low salt sodium hypochlorite is lighter than traditional sodium hypochlorite due to the lower salt content. Typical specific gravities for low salt bleach (in weight percent sodium hypochlorite) are 30 % = 1.346; 25% = 1.294; 20% = 1.293; 15% = 1.182; and 12.5% = 1.153. Traditional sodium hypochlorite specific gravities are 15% = 1.231; and 12.5% = 1.191.
This lower specific gravity results in more gallons per shipment because the product is lighter.
High strength low salt bleach is typically made in chlor-alkali plants that use salt as the raw material. These plants will produce various amounts of chlorine and sodium hydroxide to produce sodium hypochlorite. Let’s assume 50 STPD of chlorine is used for bleach production. 25 STPD of salt would be recovered and returned to the plant for reuse. This recovered salt is very pure, requires almost no additional treatment, and might be worth as much as $2,500 per day or $875,000 per year.
Lower salt content makes the product approximately 2 times more stable. In many formulations that are used in the household market, the reduced salt will allow for more varied formulations. Each formulator will have to test all products using the low salt content bleach, but results have typically been positive.
In the municipal market where the purchaser receives full 5,000-gallon loads of 13 wt% NaOCl, the total salt load is reduced by 3,900 pounds per tanker. Reduced salt content in the NaOCl will result in significantly lower salt content in the drinking or wastewater.
Powell has created a decomposition program that can be downloaded for free. View the software: https://powellsolutions.com/resources/calculators/sodium-hypochlorite-material-balance-english/
Traditional bleach (up to about 15% by weight) is shipped in FRP tankers or rubber lined steel tankers of approximately 5,000 gallons. Higher bleach strengths can typically cause FRP tankers to prematurely fail. Therefore, rubber lined steel tanks are the better choice.
Tanker Capacity: 50,000 pounds
High Strength Low Salt (HSLS) Bleach Strength: 30% by weight or 380 gpl available chlorine with a specific gravity of 1.346.
Traditional Bleach Strength: 12.5% by weight or 142 gpl available chlorine with a specific gravity of 1.191.
50,000/8.334/1.346 = 4,457 gallons of bleach. At 380 gpl strength, this is equivalent to approximately 14,177 pounds of chlorine.
50,000/8.334/1.191 = 5,037 gallons of bleach. At 142 gpl strength, this is equivalent to approximately 5,987 pounds of chlorine.
Therefore, there is approximately 2.37 times more chlorine per shipment.