Caustic soda is the common name for sodium hydroxide, one of the most widely used industrial alkalis. It is sold in three main forms: solid flakes, solid prills or pearls, and a liquid solution called lye.
The chemistry is the same in every form. What changes is the concentration, how it is packed and shipped, and how easily your plant can handle it.
How it is made
Caustic soda is made by the chlor-alkali process. An electric current passes through purified salt brine in a membrane cell. That splits it into chlorine gas, hydrogen and a sodium hydroxide solution. Modern plants in Gujarat use membrane cells, which give a cleaner product than older mercury or diaphragm cells.
The solution leaves the cell at around 32% strength. Plants concentrate it to about 48 to 50% lye by evaporation. To make solids, they evaporate it further into a molten form, then cool it into flakes or spray it into prills. Chlor-alkali plants cluster around Bharuch, Dahej, Vadodara and other estates on the Golden Corridor.
The three forms
- Flakes are thin solid chips, usually sold at about 98% sodium hydroxide and packed in 25 or 50 kg lined bags.
- Prills or pearls are small solid beads of similar purity, which flow and dose more easily than flakes.
- Lye is a solution, usually 48 to 50% sodium hydroxide, shipped in drums, IBCs or tank containers, and sometimes sold at 32%.
Choosing a form
Solids make sense when you import in smaller lots, dose by hand, or have no tank storage. You do not pay to ship water, and bags are easy to store. But you must dissolve them on site, which releases a lot of heat and needs careful handling.
Lye suits plants with tanks and pumps that use large volumes, such as alumina refineries, pulp mills and soap and detergent makers. You pay freight on the water content, so long sea voyages favour solids. Lye at 50% also freezes at a relatively mild temperature, so tanks may need heating in a cold climate.
What to check
A certificate of analysis for caustic soda should cover these points at least:
- Sodium hydroxide content, stated as a percentage by mass.
- Sodium carbonate, which forms when the product absorbs carbon dioxide from air.
- Sodium chloride, which tells you something about the cell type and purification.
- Iron and heavy metals, which matter for food, pharmaceutical and fine chemical users.
- Packing condition, because solid caustic absorbs moisture fast through a damaged bag.
Safety and handling
Caustic soda causes severe burns to skin and eyes in every form. Dissolving solids releases a lot of heat, so staff must always add caustic to water slowly, never water to caustic. Your site needs eye protection, gloves, an eyewash and a written handling procedure before the first delivery.
Storage matters too. Solids must stay dry and sealed, because they absorb moisture and carbon dioxide from the air, which lowers purity and turns flakes into a hard lump.
Next step
Caustic soda is dangerous goods in every form, so packing and paperwork must be correct before it leaves the plant. Our article on whether caustic soda is dangerous cargo covers that. We audit producers, check samples and documents, and supervise packing and loading. To plan your order, book a free sourcing review.