Calcium hypochlorite [Ca(ClO)₂] is one of the most widely produced chlorine-based disinfectants in the world, with global production exceeding 500,000 metric tons annually. Its manufacturing involves controlled chemical reactions between chlorine gas and calcium compounds. Understanding the production process is essential for procurement managers, quality assurance teams, and water treatment engineers who need to evaluate supplier capabilities and product quality.
As a manufacturer of calcium hypochlorite granular and calcium hypochlorite tablets, Everglory Industrial provides this technical overview of the two primary production methods, quality control parameters, and industry specifications.
There are two industrial methods for producing calcium hypochlorite:
| Parameter | Calcium Process | Sodium Process |
|---|---|---|
| Primary Feedstock | Calcium hydroxide (slaked lime) | Sodium hydroxide + calcium hydroxide |
| Chlorine Source | Chlorine gas (Cl₂) | Chlorine gas (Cl₂) |
| Byproduct | Calcium chloride | Sodium chloride (salt) |
| Available Chlorine | 60-70% | 70-75% |
| Product Purity | Lower (more impurities) | Higher (more refined) |
| Global Market Share | ~30% | ~70% |
| Preferred For | Cost-sensitive markets | High-grade applications |
The sodium process is the dominant production method worldwide because it produces higher-purity calcium hypochlorite with 70-75% available chlorine. Here are the key steps:
Chlorine gas (Cl₂) is passed through a sodium hydroxide (NaOH) solution to produce sodium hypochlorite (NaClO):
2NaOH + Cl₂ → NaClO + NaCl + H₂O
This reaction takes place in a cooled reactor at 15-25°C to prevent decomposition. The resulting sodium hypochlorite solution typically has 10-15% available chlorine concentration.
The sodium hypochlorite solution is then mixed with a calcium hydroxide [Ca(OH)₂] slurry in a precipitation reactor. This reaction forms calcium hypochlorite as a solid precipitate:
2NaClO + Ca(OH)₂ → Ca(ClO)₂ + 2NaOH
The reaction is carefully controlled at 30-40°C with continuous stirring. The calcium hypochlorite forms as a crystalline solid suspended in the solution, while sodium hydroxide is regenerated and recycled back to Step 1.
The calcium hypochlorite crystals are separated from the mother liquor using centrifugal filters or vacuum filters. The filter cake is then washed with chilled water to remove residual sodium chloride, sodium hydroxide, and other impurities. The washing process is critical — insufficient washing leaves salt and alkali residues that reduce product stability.
The wet calcium hypochlorite cake (containing 30-40% moisture) is dried in a rotary dryer or fluidized bed dryer at controlled temperatures (60-80°C). Temperature control is critical — temperatures above 100°C can cause thermal decomposition and create a fire hazard. The dried product should have moisture content below 5-7%.
Calcium hypochlorite drying is the most hazardous step in production. The wet product is relatively stable, but as it dries, it becomes increasingly reactive. Modern facilities use nitrogen-inerted drying systems and strict temperature monitoring to prevent decomposition events. All equipment must be spark-proof and regularly cleaned to prevent contamination buildup.
The dried calcium hypochlorite is processed through granulation equipment to achieve the desired particle size distribution. Common specifications:
Finished calcium hypochlorite is packaged in moisture-proof HDPE drums (typically 40kg or 45kg) with inner PE bags. Each drum is sealed, labeled with UN 2880 classification, and tested for moisture content before shipping. Proper packaging is essential — moisture ingress during storage can accelerate decomposition and create safety risks.
The calcium process is simpler and less expensive but produces a lower-grade product. In this method, chlorine gas is directly passed through a calcium hydroxide slurry:
2Ca(OH)₂ + 2Cl₂ → Ca(ClO)₂ + CaCl₂ + 2H₂O
The resulting product is a mixture of calcium hypochlorite and calcium chloride, typically yielding 60-70% available chlorine. The calcium chloride byproduct is difficult to separate completely, which is why this method produces a less pure product. However, it requires fewer processing steps and lower capital investment, making it popular in developing markets.
| Parameter | Premium Grade | Standard Grade | Test Method |
|---|---|---|---|
| Available Chlorine | ≥70% | ≥65% | Iodometric titration |
| Moisture Content | ≤5% | ≤7% | Karl Fischer / oven drying |
| Particle Size | Per spec | Per spec | Sieve analysis |
| Water Insolubles | ≤5% | ≤10% | Filtration / gravimetric |
| Stability (72hr @ 80°C) | ≥90% retention | ≥85% retention | Accelerated aging test |
| Heavy Metals (as Pb) | ≤10 ppm | ≤20 ppm | ICP-MS |
| Iron Content | ≤100 ppm | ≤200 ppm | AAS / ICP |
Quality calcium hypochlorite should meet one or more of these standards:
Request these certifications from your supplier and verify them with third-party test reports (SGS, Intertek, or Bureau Veritas) before bulk purchasing.
The sodium process uses sodium hydroxide as an intermediate, producing higher-purity calcium hypochlorite with 70-75% available chlorine. The calcium process directly chlorinates calcium hydroxide, producing a less pure product (60-70% available chlorine) with calcium chloride as a byproduct. The sodium process accounts for ~70% of global production due to its superior quality.
The primary raw materials are chlorine gas (Cl₂), sodium hydroxide (NaOH, for the sodium process), and calcium hydroxide (Ca(OH)₂, also known as slaked lime). Chlorine gas is typically produced on-site via chlor-alkali electrolysis of brine (salt water), which also co-produces sodium hydroxide and hydrogen gas.
Yes, production involves significant hazards: toxic chlorine gas, exothermic reactions, and a reactive final product. Modern facilities mitigate these risks with closed-loop systems, chlorine gas detection and scrubbing, temperature-controlled reactors, nitrogen-inerted drying, and strict safety protocols. Workers require specialized training and PPE including self-contained breathing apparatus for certain operations.
Key quality tests include: iodometric titration for available chlorine content, Karl Fischer titration for moisture, sieve analysis for particle size, accelerated aging (72 hours at 80°C) for thermal stability, and ICP-MS for heavy metals. Reputable manufacturers test every batch and provide certificates of analysis (COA) with each shipment.
The CAS number is 7778-54-3. The UN number for shipping is UN 2880, classified as Class 5.1 (Oxidizing Substance), Packing Group II. This classification applies to calcium hypochlorite with more than 39% available chlorine (6.8% active oxygen), which covers all commercial grades (65-75% available chlorine).
