Sodium hydroxide (caustic soda) and potassium hydroxide (caustic potash) are the most widely used industrial alkalis, found in soap and detergent manufacture, pulp and paper production, petroleum refining, water treatment and general chemical synthesis. Both are strong, highly corrosive bases requiring careful handling.
Key points
- Sodium hydroxide is used across pulp and paper, textiles, soap and detergent manufacture, and gas scrubbing to remove acidic emissions.
- Most caustic soda is supplied as an aqueous solution (at least 50% NaOH) rather than solid, for handling and transport reasons.
- Potassium hydroxide is used in agricultural fertilisers, alkaline batteries, cosmetics and biodiesel manufacture, among other applications.
- Dissolving dry caustic in water is strongly exothermic, and both dry and dissolved forms present significant burn risk to skin, eyes and lungs.
How Alkalis Are Used in Manufacturing
Alkalis are incorporated through aqueous blending or as reactants in reaction chemistry, requiring corrosive chemical processing capability - relevant to cleaning chemicals and industrial detergents.
Regulatory Considerations
Alkali handling falls under COSHH corrosive-substance controls, with exothermic dilution behaviour a specific process safety consideration - see COSHH responsibilities.
Common Alkalis and What They Do
Alkalis raise pH and are used for neutralising acidity, saponification, cleaning formulations and as processing aids across a wide range of products. Sodium and potassium hydroxides are the strong, widely used options; carbonates and amines offer milder alternatives where a strong base would be excessive or would damage other formulation components.
Choice between them is not only a matter of strength. The counter-ion matters - sodium and potassium salts have different solubilities, which can affect clarity and stability - and amine bases bring their own odour and regulatory considerations. Substituting one alkali for another is therefore rarely a straight swap even where the pH outcome is the same.
Handling Considerations
Strong alkalis are corrosive and are, in practice, a greater hazard to eyes and skin than many people expect - alkali burns can be more damaging than equivalent acid exposure because they penetrate tissue rather than coagulating it. Handling controls and COSHH assessment should reflect that rather than treating alkalis as the milder option.
Like acids, dissolving solid alkali and neutralising with it release significant heat, so cooling and controlled addition are required. Solid caustic also absorbs moisture from air and can set solid in storage, which affects handling and charging. Alkalis attack aluminium and some other materials, so construction materials need checking as carefully as for acid service - a system suitable for one is not automatically suitable for the other.
Solid Versus Solution
Strong alkalis are available both as solids and as solutions, and the choice affects handling more than the chemistry. Solutions avoid dust and dissolution heat but cost more to transport and have a lower active content by weight; solids require dissolving equipment and controlled addition. Manufacturers usually have a preference based on their plant, so it is worth asking which they handle rather than assuming either.
Questions to Ask a Manufacturer
- What alkali concentrations and forms (solid or solution) do you have experience handling?
- How do you manage the exothermic risk of diluting concentrated caustic solutions?
- What personal protective equipment and engineering controls are in place for alkali handling?
- Do you have corrosive-handling capability separate from general production lines?
Related Pages
Frequently Asked Questions
Is caustic soda the same as caustic potash?
No - they're different compounds (sodium hydroxide and potassium hydroxide respectively) with overlapping but distinct application areas. Your manufacturer can advise which suits your formulation's requirements.
Is diluting concentrated alkali solutions straightforward?
Not without proper controls - the process is strongly exothermic and requires appropriate procedures and equipment to manage safely. This is a genuine process safety consideration, not a routine mixing step.
Find a Manufacturer
Find a UK Contract Chemical Manufacturer
Search the directory of UK contract and toll manufacturers by process, industry and capability.
Search the DirectoryLast reviewed: August 2026. Regulation and guidance change — verify anything you rely on against the primary source. Tell us if something here is out of date.