What is High Strength Low Salt Bleach?
Sodium hypochlorite (Bleach) is made with chlorine gas or liquid 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. Any sodium hypochlorite higher than 17% by weight that does not precipitate salt is an indication that the salt levels in the sodium hypochlorite solution has been reduced. Therefore, it is high strength low salt bleach.
Normally, high strength low salt bleach produced by Powell equipment is a minimum of 30% by weight with approximately 8% by weight NaCl.
What is low salt sodium hypochlorite?
Traditional sodium hypochlorite is specified in a weight % strength such as 12.5% by weight and it is sold commercially at this strength or other strengths depending on shipping or other commercial requirements. Based on the molecular weights of sodium hypochlorite versus the salt, salt content with no sodium chlorate in the bleach will be 78% of the weight percent of the salt. Therefore, a 12.5% sodium hypochlorite solution will normally have 9.75% salt depending on the quality of the product (i.e. no sodium chlorate.)
High strength low salt bleach from the Powell process is produced at 30% NaOCl by weight with 8% (typical) salt. 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.
What is the specific gravity of the low salt sodium hypochlorite?
The low salt sodium hypochlorite is lighter than traditional sodium hypochlorite due to the lower salt content. Some typical specific gravities for 30% low salt and diluted low salt bleach in wt% NaOCl are 30 % = 1.346; 25% = 1.294; 20% = 1.293; 15% = 1.182; and 12.5% = 1.153. Traditional bleach specific gravities are 15% = 1.231; and 12.5% = 1.191.
This lower specific gravity results in more gallons shipped in typical 50,000 pound loads since each gallon is lighter.
What happens to salt during production at the manufacturer’s site?
Usually the high strength low salt bleach is made in chlor/alkali plants that use salt as the raw material. These plants will produce various amounts of chlorine per day that are reacted for the sodium hypochlorite production. Let’s assume 50 STPD is used for bleach production. 25 STPD would be recovered and returned to the plant for use. This recovered salt is very pure, requires almost no additional treatment, and depending on the cost of the purchased salt, may be worth approximately $2,500 per day or $875,000 per year at 350 days a year production.
Why is there an advantage of reduced salt content in the sodium hypochlorite at the consumer or municipality point of use?
Reduced salt in the sodium hypochlorite 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 will be 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 significant lower salt content in the drinking water or waste water.
How can I learn more about the decomposition rates of high strength low salt bleach versus traditional bleach at different temperatures, strengths and storage times?
Powell has created a decomposition program that can be downloaded for free. The software can be accessed by Clicking here.
How is High Strength Low Salt Bleach shipped?
Traditional bleach up to about 15% by weight is shipped in FRP tankers or rubber lined steel tankers of approximately 5,000 gallons. As the bleach strength increases above 15% by weight up to 30%, the FRP tankers will fail quickly depending on concentration and shipping temperature. Therefore, rubber lined steel tanks are the better choice. Contact Powell for further details.
How much bleach can be transported in a tanker truck?
In order to correlate bleach volumes all calculaions should be done in grams per liter available chlorine. Assume a tanker can carry 50,000 pounds of bleach solution at 30% by weight NaOCl or 380 gpl. This would allow 50,000 pounds / 8.34/1.346 or 4,454 gallons of 380 gpl which calculates to 4,454 x 380/120 or 14,104 pounds of available chlorine. A typical 12.5% NaOCl solution can be shipped in a tanker at 50,000/8.34/1.191 or 5,033 gallons of bleach. 12.5% NaOCl is approx. 142 gpl av. Cl. Therefore 5,033 gallons of 12.5% bleach is 5,033x142/120 or 5,955 pounds of available chlorine. In summary one tanker of 4,454 gallons of 30% by weight bleach is 14,104/5,955 or 2.37 times more available chlorine than a 5,000 gallon tanker of 12.5% NaOCl.