Caustic Soda Dose Calculator

How the calculation works

Step 1 is free fatty acid mass: FFA (kg) = oil (kg) × FFA % ÷ 100. Step 2 is stoichiometric sodium hydroxide. One mole of NaOH (39.997 g) neutralises one mole of oleic acid (282.46 g), so NaOH (kg) = FFA (kg) × 39.997 ÷ 282.46 = FFA (kg) × 0.1416. Stoichiometric NaOH (kg) = oil mass (kg) × FFA % ÷ 100 × 0.1416, when FFA is expressed as oleic acid.

Step 3 adds excess: total NaOH = stoichiometric × (1 + excess % ÷ 100). Typical batch practice uses 10–25 % excess; more for dark or high-FFA oils, less when neutral-oil loss matters most. Step 4 converts that alkali into a lye solution: solution mass (kg) = total NaOH ÷ (strength % ÷ 100); volume (L) = solution mass ÷ solution density. If you enter degrees Baumé, the tool interpolates the table below; the handbook density approximation is 145 ÷ (145 − °Bé). Step 5 estimates soapstock / refining loss as FFA mass × refining factor. The factor (total loss ÷ FFA) is commonly 1.3–3.0 for batch chemical neutralisation; the default is 2.0 and is a planning figure, not a plant guarantee. The treat line is total NaOH as a percentage of oil mass — the number refiners quote.

Measure FFA first with the FFA titration calculator. The meaning of a given FFA is on the free fatty acid specification. The process narrative is how shea butter is refined to N-RBD. Lye for soap making is a different calculation — use the shea saponification lye calculator. Convert pounds or short tons to kilograms with the oils and fats unit converter before entering a batch mass.

Assumptions and limits

FFA is expressed as oleic acid (M = 282.46). For palm (palmitic) or lauric oils the factor changes — this tool is fixed to oleic and says so. Convert the FFA basis first if your certificate uses another acid. Excess depends on oil type, colour, phosphatide content and the refiner's equipment; the 10–25 % band is a starting point, not a recommendation for a specific batch. Colour and settling are discussed on colour grading and unsaponifiable matter. Shea's high unsaponifiable matter (4–11 %) does not change the stoichiometry but does affect colour and settling.

The sodium hydroxide solution table is at 15.6 °C. Soapstock estimate is a planning figure; real loss depends on centrifuge or settling efficiency and emulsion losses. The calculator does not cover degumming, bleaching or deodorising, and it does not cover potassium hydroxide or sodium carbonate neutralisation. The definition of the step is in the neutralisation glossary.

Sodium hydroxide is corrosive. Add caustic to water, never water to caustic. Use eye and face protection, gloves and ventilation. Keep lye away from aluminium. This calculator does not replace a process safety review.

What your result means for shea butter

At FFA at or below 1 % — the published Grade A / ECOWAS Grade 1 band — chemical neutralisation is rarely economic; the butter is already in the range buyers specify for unrefined cosmetic use. See shea butter grades. Between 1 and 5 % is typical neutralisation territory, with estimated loss often 2–10 % of the batch. Above 5 % consider two-stage neutralisation or physical refining; soapstock becomes large. The process choice is explained in the N-RBD refining guide.

EMI Agro supplies refined N-RBD shea butter already neutralised, bleached and deodorised to a stated FFA, so a buyer does not have to run this calculation on unrefined stock. Request that grade on the refined N-RBD product page. Test methods for FFA are listed under AOCS Ca 5a-40.