What Does Caustic Soda Do in Soap and Detergent Manufacturing?
Caustic soda (sodium hydroxide, NaOH) is the alkali behind both soap and synthetic detergent — but it does a different job in each. In soap it saponifies oils and fats. In detergents its main job is to neutralise LABSA (linear alkylbenzene sulphonic acid) into LAS, the active surfactant in most laundry and dishwashing products. This guide covers the detergent side in depth.
Saponification
Oils and fats + caustic soda give soap and glycerol. Grades, SAP values and kg of NaOH per tonne of soap are covered in our guide to caustic soda in soap making.
triglyceride + 3 NaOH → 3 soap + glycerolNeutralisation
LABSA + caustic soda gives LAS and water. This page covers the chemistry, how much caustic soda you need, which grade suits each detergent and how to buy it.
R–C₆H₄–SO₃H + NaOH → R–C₆H₄–SO₃Na + H₂O- ≈ 134 kgNaOH (100%) per tonne of LABSA 96%
- ≈ 136 kgas 98% flakes
- ≈ 1,026 kgLAS formed per tonne of LABSA 96%
- pH 7.5–8.5typical neutralisation end point
LABSA Neutralisation: The Main Job of Caustic Soda in Detergents
LABSA is a strong organic acid; LAS, its sodium salt, is the detergent. Caustic soda turns one into the other. One mole of sodium hydroxide neutralises one mole of sulphonic acid, and the small amount of free sulphuric acid left over from sulphonation takes two moles of NaOH per mole. The reaction gives off heat, so it is run with stirring and cooling, finishing at a slightly alkaline pH.
Where the ≈ 134 kg per tonne figure comes from
For LABSA 96% with an average molecular weight of 322 g/mol and 1.77% free sulphuric acid, per tonne of LABSA:
Sulphonic acid: 960 kg ÷ 322 × 40.0 = 119.2 kg NaOH Free H₂SO₄: 17.7 kg ÷ 98.08 × 2 × 40.0 = 14.4 kg NaOH Total = 133.7 kg NaOH (100% basis) → 136.4 kg flakes 98% → 267.4 kg liquid 50%The same tonne of LABSA yields about 1,026 kg of active LAS (sodium salt, molecular weight ≈ 344). Plants usually allow a small excess and control the final addition by pH rather than by weight.
| Form of caustic soda | NaOH content | Quantity per tonne of LABSA 96% |
|---|---|---|
| Pure NaOH (100% basis) | 100% | ≈ 134 kg |
| Caustic soda flakes | 98% | ≈ 136 kg |
| Caustic soda pearls | 99% | ≈ 135 kg |
| Liquid caustic soda | 50% | ≈ 267 kg |
| Liquid caustic soda | 32% | ≈ 418 kg |
Stoichiometric figures from molecular weights, using the LABSA 96% certificate-of-analysis values above. Your own LABSA may differ in active matter, molecular weight (typically about 318–326 for commercial C10–C13 blends) and free acid, so use the calculator below with your own COA.
Caustic Soda Calculator for LABSA Neutralisation
Enter your LABSA tonnage and the values from its certificate of analysis. The calculator returns the caustic soda to buy in your chosen form, the LAS produced and the number of 25 kg bags. Calculated in your browser only.
Defaults are the LABSA 96% COA values used above. The final end point in the plant should always be set by pH, not by the calculated weight.
Indicative sizing for planning an order, not a process specification. Confirm with a plant trial.
Where Caustic Soda Is Used in Each Type of Detergent
How caustic soda is used depends on the product format. In most household detergents it is consumed during manufacture; in heavy-duty cleaners it is the active ingredient itself.
| Product | What caustic soda does | Usual form |
|---|---|---|
| Liquid laundry and dishwashing detergent | Neutralises LABSA to LAS; adjusts the final pH of the liquid | Liquid 50%, or flakes made up as solution |
| Spray-dried powder detergent | Neutralises LABSA in the slurry before spray drying; soda ash and other builders add alkalinity | Liquid or flakes |
| Dry-mix and agglomerated powder | Often replaced by soda ash for dry neutralisation; caustic soda used where a stronger alkali is needed | Flakes or pearls |
| Detergent cakes and bars | Neutralises LABSA in the mix alongside soda ash and fillers | Flakes |
| Industrial degreasers, oven and drain cleaners | Is the active cleaning alkali, dissolving fats and proteins | Flakes, pearls or liquid |
| Clean-in-place (CIP) and bottle washing | Hot caustic solution removes organic soil in food, dairy and beverage plants | Liquid 50% |
| Bar and toilet soap | Saponifies oils and fats — see caustic soda in soap making | Flakes or pearls |
Caustic Soda vs Soda Ash in Detergent Making
Both are sodium alkalis and both appear in detergent plants, but they are not interchangeable. Caustic soda is the strong base used to neutralise; soda ash (sodium carbonate) is the milder base that also works as a builder.
| Point | Caustic soda (NaOH) | Soda ash (Na₂CO₃) |
|---|---|---|
| Strength | Strong base, pH ≈ 13.4 at 1% | Weaker base, pH ≈ 11 at 1% |
| Neutralising LABSA | Fast and clean; only water is formed | Works, but releases carbon dioxide |
| Best suited to | Liquid detergents, slurry neutralisation, heavy-duty cleaners | Powder detergents, dry neutralisation, building and water softening |
| Builder function | No | Yes |
| Handling | Corrosive, Class 8 dangerous goods | Irritant, not dangerous goods |
Soda ash grades: soda ash light and soda ash dense.
Which Form of Caustic Soda Suits a Detergent Plant?
Liquid 50%
Metered straight into the neutraliser by pump, with no dissolving step and no dust. Needs corrosion-resistant tanks, and heating in cold climates because 50% solution starts to crystallise near 12 °C. Shipped in ISO tanks.
Flakes 98%
The standard export grade. Dissolved on site to the working strength; stores well in sealed 25 kg bags and makes the most of every container when the plant is far from the supply point.
Pearls 99%
Small, nearly dust-free beads that flow freely in screw feeders and dissolve evenly — useful for automated solid dosing and for plants where dust exposure is the main concern.
What to Check on the Caustic Soda COA for Detergent Production
Four parameters on the batch certificate of analysis decide how caustic soda behaves in a detergent plant. Ask for all four, and compare several recent batches rather than one sample.
| Parameter | Why it matters in detergents |
|---|---|
| NaOH assay | Sets the dose. Dose against the batch figure, not the nominal grade. |
| Sodium carbonate | Forms when caustic soda absorbs CO₂; it is a weaker alkali, so carbonated material under-neutralises and can cause fizzing. |
| Sodium chloride | Salt changes the viscosity of liquid detergents, which are often thickened with salt to a target. |
| Iron | Iron traces darken pale and clear liquids. Ask for the figure in ppm. |
Membrane grade. All the caustic soda we supply is membrane-cell material, which carries markedly less chloride than older diaphragm-cell caustic and none of the mercury-cell legacy. Full grade data: types and grades of caustic soda.
Neutralising LABSA Safely in the Plant
Both raw materials are corrosive — caustic soda is UN 1823 / UN 1824, Class 8, and LABSA is UN 2586, Class 8 — and the neutralisation releases heat. Follow your plant procedure and the safety data sheets.
- Prepare the caustic solution firstAdd caustic soda slowly to cold water, never water onto caustic soda, and let the solution cool before use.
- Add LABSA graduallyFeed the acid in stages with continuous stirring and cooling so the temperature stays under control.
- Approach the end point slowlypH rises steeply near neutrality. Make the last additions small and check pH on a dilute sample each time.
- Protect the operatorsSplash goggles and face shield, nitrile or neoprene gloves, chemical-resistant apron and boots; eyewash and safety shower within about ten seconds.
- Store apartKeep caustic soda and LABSA in separate bunded areas, away from aluminium and zinc. Storage detail: how to store caustic soda safely.
On skin or in the eyes
Flush with running water for at least 30 minutes, remove contaminated clothing and get medical help. Never try to neutralise a chemical burn.
Caustic Soda and LABSA From One Supplier
SUHA International Trading supplies membrane-grade caustic soda — flakes 98–99%, pearls 99% and liquid — together with LABSA 96%, SLES 70% and soda ash, loading from Mersin (Türkiye) and Jebel Ali (UAE). One supplier for the alkali and the surfactant means one order cycle and one set of documents. Comparing surfactants? See LABSA vs SLES.
No prices are published on this page. Send the list below by email or WhatsApp and a firm quotation comes back, normally within 24 hours on working days.
- Products: caustic soda form and grade; LABSA, SLES or soda ash if needed
- Quantity: tonnes per shipment and per year
- Packing: 25 kg bags or ISO tank for caustic soda
- Destination: port and country
- Incoterm: FOB, CFR or CIF
- Payment: T/T or L/C at sight
- FormsFlakes 98–99% · pearls 99% · liquid 32–50%
- Production routeMembrane cell
- GradesIndustrial · food grade
- DocumentsCOA per lot · SDS · TDS
- Packing25 kg bags, palletised or in jumbo bags · ISO tank
- Minimum order1 FCL, 20ft or 40ft
- IncotermsFOB · CFR · CIF
- LoadingMersin · Jebel Ali · road from Türkiye
Caustic Soda in Soap and Detergent: FAQ
Related Guides and Products
References
- US EPA, AP-42 Chapter 6.8 — Soap and Detergents
- Regulation (EC) No 648/2004 on detergents
- PubChem CID 14798 — Sodium hydroxide
- NIOSH Pocket Guide — Sodium hydroxide
Reviewed by the SUHA International Trading technical desk, Dubai and Ankara. Figures are stoichiometric and indicative; always work from the certificates of analysis for your own raw materials and confirm with plant trials.