Caustic Soda in Soap Making: Complete Guide to Saponification, Safety & Bulk Supply

Caustic Soda in Soap Making
Table of Content
Technical & procurement guide ·

Caustic Soda in Soap Making
Grades, dosage and bulk supply for soap manufacturers

Caustic soda in soap making is the alkali that converts oil into soap, and roughly 121 kg of it on a 100% basis goes into every tonne of 78% TFM soap you produce. This guide covers the reaction, the SAP arithmetic, which NaOH grade and form each soap type needs, what the finished-product standards demand, and exactly what to specify when you buy caustic soda for soap manufacturing in bulk from an exporter.

Product
NaOH · CAS 1310-73-2
Forms supplied
Flakes 98% · Pearls 99% · Liquid
Typical dosage
≈121 kg/MT of soap
HS codes
2815.11 · 2815.12
MOQ
25 MT — 1 × 20ft FCL
Loading
Mersin · Jebel Ali
Calculate my NaOH tonnage How to get a price
  • ≈121 kgNaOH per MT of soap
  • 98–99%flake & pearl assay
  • UN 1823Class 8 · PG II
  • 25 MTMOQ, one 20ft FCL
Sizing tool

How much caustic soda per tonne of soap?

Set your oil blend, your finished-product TFM and your monthly output, and this returns the sodium hydroxide you actually have to buy — in kilograms, in 25 kg bags and in containers. The arithmetic is the real stoichiometry, shown in full below the result, not a rule of thumb.

Finished soap TFM
MT of finished soap

Assumes 98% assay flakes and the 1–2% alkali excess plants normally charge, with 2% used here. Recalculate against the saponification value stated on your own oil certificate of analysis — SAP values are ranges, not constants.

Caustic soda flakes to purchase 25.3 MT
Per tonne of finished soap 126 kg
NaOH on a 100% basis 24.3 MT
Oil and fat charged 163.7 MT
Crude glycerol released 18.6 MT
25 kg bags 1,011
20ft containers at 25 MT 2 (1.01 FCL)

Indicative sizing, not a specification. Actual consumption shifts with free fatty acid in the oil, alkali losses, whether part of the alkali is substituted with soda ash on a fatty-acid route, and your own excess policy. Use it to size an enquiry, then confirm against a plant trial.

Why this matters commercially: caustic soda is usually the second-largest raw material line in a soap plant after the oil itself. Getting the tonnage right is what lets you buy a full container instead of paying part-load freight, and what tells you whether an annual contract or spot buying suits your production plan.
The reaction

What caustic soda does in soap making

Caustic soda in soap making supplies the hydroxide ion that splits a triglyceride and converts the released fatty acids into their sodium salts — and a sodium salt of a fatty acid is what soap physically is.

Saponification, step by step

A fat or oil is a triglyceride: three fatty acid chains held on a glycerol backbone by ester bonds. Hydroxide attacks each ester carbon, the bond breaks, and the fatty acid leaves as a carboxylate ion which pairs with sodium.

1 triglyceride + 3 NaOH → 3 sodium soap + 1 glycerol

Three points follow from the stoichiometry and they drive everything else on this page. First, the alkali requirement is fixed by the number of ester bonds in the oil, which is what a saponification value measures. Second, the reaction is exothermic — dissolving the caustic soda releases heat, and so does the saponification itself, which is why lye preparation and reaction vessels need cooling and controlled addition. Third, the hydroxide is fully consumed when the dose is correct, which is why correctly made soap contains no free caustic soda.

Glycerol is the co-product, not a waste stream. Around 93 kg of glycerol on a 100% basis is released per tonne of 78% TFM soap, about 11% of the oil charged. On the saponification route it is recovered from the spent lye and refined; in cold-process bars it stays in the soap and is sold as a feature.

Why sodium hydroxide and not another alkali

Because the sodium ion packs the fatty acid chains into a hard crystal. Swap sodium for potassium and the same fatty acids give a soft, water-soluble paste instead of a bar. That single difference divides the industry: caustic soda for solid bar soap and soap noodles, potassium hydroxide for liquid hand soap, soft soap and shaving products.

Two consequences for dosing. Potassium hydroxide SAP values are 1.403 times the sodium hydroxide values for the same oil, because KOH is the heavier molecule. And technical KOH flake is normally supplied at 90% rather than the 98–99% of caustic soda, so the charged weight has to be divided by the purity — a correction of about 11% against roughly 2% for NaOH.

What caustic soda is not doing

It is not a catalyst, though it is often described as one. A catalyst is recovered unchanged; the hydroxide here is a stoichiometric reagent that is consumed and ends up as part of the soap molecule. That distinction is why you buy it by the tonne against output, and why the calculator above works at all.

Where the ≈121 kg per tonne figure comes from

For a standard 80:20 palm / palm kernel blend making soap at 78% total fatty matter:

Blend SV = 0.80 × 199.5 + 0.20 × 242 = 208.0 mg KOH/g NaOH per g oil = 208.0 × 0.71289 / 1000 = 0.1483 g/g Fatty acid yield = 1 − (208.0 × 2.26074e-4) = 0.9530 g FA per g oil Oil per MT soap = 780 / 0.9530 = 818.5 kg NaOH (100%) = 818.5 × 0.1483 = 121.4 kg

Cross-checked against the fatty-acid neutralisation route, which must give the same answer: 780 kg fatty acid × 39.997 ÷ 257.1 average fatty acid molecular weight = 121.4 kg. The mass balance closes — 818.5 kg oil plus 121.4 kg NaOH minus 93.1 kg glycerol gives 846.7 kg of anhydrous soap, which back-calculates to exactly 78.0% TFM.

Add the 1–2% alkali excess normally charged, and buy 98% flakes rather than pure NaOH, and the practical purchase figure is roughly 124 to 127 kg per tonne of soap — about five 25 kg bags. Figures quoted as high as 140 kg per tonne imply about 15% alkali loss and are not defensible as a general number.

One qualification worth knowing before you size a contract: plants running the fat-splitting route, where the oil is hydrolysed to fatty acids first and the acids are then neutralised, often substitute part of the sodium hydroxide with soda ash. That lowers NaOH consumption below the figures above and changes your raw material mix.

Formulation data

SAP values for soap-making oils and fats

The saponification value is the mass of alkali needed to saponify one unit mass of a given oil. The NaOH figures below are derived from the Codex Alimentarius saponification value ranges for named vegetable oils and animal fats,[1][2] converted to the sodium hydroxide basis. They are ranges, not constants — fatty acid composition moves with cultivar, origin, harvest and refining, which is exactly why Codex publishes ranges in the first place.

NaOH saponification values for common soap-making oils, derived from Codex saponification value ranges
Oil or fat Codex SV, mg KOH/g NaOH SAP range, g/g Midpoint What it contributes
Coconut oil248–2650.1768–0.18890.183Hardness and fast, dense lather from lauric acid; usually capped in skin bars
Palm kernel oil230–2540.1640–0.18110.173The lower-cost lauric oil; the foaming half of a standard 80:20 noodle
Palm oil190–2090.1354–0.14900.142The industry's structural hard oil; creamy stable lather, predictable supply
Beef tallow190–2020.1354–0.14400.140Chemically close to palm; hard, long-lasting bars where tallow is cheap locally
Lard192–2030.1369–0.14470.141White, hard, mild bars; regionally constrained by market acceptance
Cottonseed oil189–1980.1347–0.14120.138A soft-oil filler where locally milled and priced below palm
Soybean oil189–1950.1347–0.13900.137Soft oil; conditioning but slows hardening and shortens shelf life
Sunflower oil187–1940.1333–0.13830.136Soft oil, mild; high-oleic grades keep better than commodity grades
Olive oil184–1960.1312–0.13970.135Defines Castile soap; mild and conditioning, needs a long cure
Rice bran oil180–1990.1283–0.14190.135Regional soft oil; the wide SV range makes a batch COA essential
Castor oil176–1850.1255–0.13190.129Small additions only; lather booster and humectant
Shea butter160–1950.1141–0.13900.127Premium positioning; the SV range spans ±14%, so never dose from a table

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Using a SAP value correctly

Multiply each oil weight by its NaOH SAP value, add the results, then multiply by one minus the superfat fraction:

NaOH = Σ (oil weight × SAP) × (1 − superfat)

If your figure is published as mg KOH per gram — which is how oil suppliers and Codex state it — divide by 1.403 to convert to the sodium hydroxide basis before using it. Getting this wrong in either direction is the single most common dosing error, and it is a 40% error, not a rounding one.

Superfatting, also called a lye discount, means charging slightly less alkali than the theoretical requirement so that a little oil stays unsaponified. Craft cold-process practice generally runs a 5–10% lye discount,[3] both for skin feel and as a hedge against SAP-value uncertainty. Industrial noodle production works to a specified free fatty acid figure instead, so the superfat concept translates differently and should be set from your own finished-product specification rather than copied from a craft formula.

Dose against the certificate of analysis, not the table

Every number in the table above is a published range for a named oil, not a property of the drum in your warehouse. Rice bran spans 180–199 and shea spans 160–195; at the extremes of those ranges the alkali requirement moves by more than 10%.

Reputable oil suppliers state the actual saponification value on the batch certificate of analysis. Use that figure. Where it is missing, ask for it before contracting — an oil supplier who will not state a saponification value is asking you to guess at your largest process variable.

The same discipline applies on the alkali side: dose from the assay on the caustic soda COA, not the nominal grade on the offer sheet. A batch running 97.6% against a 98% nominal is perfectly normal and perfectly saleable, but it is a 0.4% shortfall in every batch you make from it.

Sizing a caustic soda contract for your soap plant?

Send your monthly soap output and the grade you need, and a firm quotation comes back with the specification, a batch certificate of analysis format, the safety data sheet, packing and container loading options, MOQ and lead time — loading FOB Mersin or FOB Jebel Ali, or CFR, CIF and DAP to a named destination.

Email info@causticsodaco.com WhatsApp +971 50 720 9246
Specification

Best caustic soda for soap making: which grade to specify

For most soap manufacturers the answer is 98–99% membrane-grade caustic soda in flake or pearl form, and the parameter that separates a good batch from a problem batch is iron, not assay. Assay tells you how much alkali you are paying for. Iron tells you what the bar will look like in six months.

Caustic soda grade selection by soap product type
Soap product Grade to specify Form Critical parameter Why
Laundry bar soap98% industrialFlakesAssay, Na₂CO₃High volume, lean formulation, colour tolerance is wide — cost per unit of active alkali decides
Soap noodles for onward sale98–99%Flakes or pearlsAssay consistencyYour customer reformulates around your TFM; batch drift in alkali shows up as drift in their product
Toilet soap & bath bars99% membranePearlsIron, chlorideIron traces catalyse oxidation of the fat phase — discolouration and rancid odour over shelf life
Transparent / glycerin soap99% membranePearlsIron, colourEvery impurity is visible by definition; the product's whole claim is optical clarity
Antibacterial & medicated bars99% membranePearlsHeavy metalsActive-ingredient claims usually bring a tighter raw-material dossier with them
Industrial & institutional soap98% industrialFlakes or liquidAssay, logisticsConcentrate strength dominates; liquid caustic works where the plant has tank capability
Liquid & soft soapPotassium hydroxideFlakes, 90%KOH purityA different alkali entirely — NaOH gives a bar, not a liquid. Dose at 1.403 × the NaOH SAP value

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The four impurities that matter

  • Iron (Fe) — the one that shows in the finished bar. Iron traces catalyse oxidation of the fatty phase, producing yellowing and rancid odour over shelf life. Premium toilet soap buyers specify a low-iron membrane grade for exactly this reason. Ask for the figure in ppm, not a "low iron" adjective.
  • Sodium carbonate (Na₂CO₃) — formed when caustic soda meets atmospheric carbon dioxide. It is a weaker alkali than NaOH, so a carbonated batch under-doses your saponification even though the bag weight is unchanged. It is also the reason opened bags degrade.
  • Sodium chloride (NaCl) — a residue of the electrolysis. It affects electrolyte balance, and in liquid systems it moves viscosity in ways you did not ask for. Membrane-grade material carries less of it than diaphragm-grade.
  • Heavy metals — arsenic, lead, mercury. Only decisive where the finished product carries a cosmetic, food-contact or pharmaceutical claim, but where it applies it is a pass-or-fail dossier item rather than a preference.

What "membrane grade" actually means

Caustic soda is a co-product of chlorine manufacture, and three cell technologies have been used: mercury cell, diaphragm cell and membrane cell. Membrane cell material carries markedly lower chloride and sulfate than diaphragm material and none of the mercury-cell legacy, which is why it has become the reference grade for anything with a purity-sensitive end use.

For a soap manufacturer the practical question is not the cell technology name on the offer but whether the COA carries the numbers. A supplier who writes "membrane grade, 99% min" and stops has told you the marketing; a supplier who states assay, carbonate, chloride and iron per batch has told you what you are buying.

Do you need food or pharmaceutical grade?

Almost never for soap. Food-grade FCC and pharmacopoeial caustic soda exist and carry tighter heavy-metal limits, but soap is a rinse-off product and the finished-product standards that govern it — free caustic alkali, TFM, moisture — are met comfortably with good industrial material. Specify a higher grade only where your own customer's dossier or a specific market registration demands it, and expect to pay for it. Speciality grades are quoted on enquiry.

Physical form

Caustic soda flakes, pearls or liquid for soap manufacturing

Assay decides soap quality; physical form decides how your plant runs and what your landed cost per unit of active alkali actually is. These three are the same chemical in three delivery formats, and the right one is a function of your handling equipment, your climate and your distance from supply.

Caustic soda flakes, pearls and liquid compared for soap manufacturing
Property Flakes 98% Pearls 99% Liquid 30–50%
Typical assay98% min, 96% and 99% traded99% min30–50% w/w, 50% standard merchant
Active alkali per unit costBestGoodLowest — you freight the water
Dust generationModerate — enclosed transfer and PPE neededLow — the main reason plants switchNone
Flow in feedersIrregular shape, can bridge in screw conveyorsFree-flowing — suits automated dosingPumped; metering is the simplest of the three
DissolutionFast; exothermic, needs cooling and controlled additionFast and evenAlready dissolved — no lye-making step
Storage requirementDry, sealed, ambient warehouseDry, sealed, ambient warehouseCorrosion-resistant tank; heated in cool climates
Cold-weather issueNone — solids are unaffectedNoneCrystallises near 12 °C; minimum unloading temperature about 21 °C[4]
Packing25 kg bags · 500/1,000 kg FIBC25 kg bags · FIBCISO tank · tank truck · 1,000 L IBC
Shelf life sealed12–24 months12–24 monthsLong, but carbonates on air contact
Dangerous goodsUN 1823, Class 8, PG IIUN 1823, Class 8, PG IIUN 1824, Class 8, PG II or III by concentration
Best fitMost soap plants; laundry and general bar productionToilet soap, transparent soap, automated linesContinuous plants close to the supply point

← Swipe the table sideways to see all three columns.

The comparison buyers get wrong: comparing a quotation for 50% liquid against a quotation for 98% flakes on a per-tonne basis. Normalise to active alkali first — one tonne of 50% liquid delivers about 500 kg of NaOH against about 980 kg from a tonne of flakes, so the liquid has to be roughly half the price before it is even level, and that is before freight, tank capital and heating.
In the plant

How industrial soap is made with caustic soda

Two routes dominate, and which one you run changes what you buy. The saponification route reacts oil directly with caustic soda. The fat-splitting route hydrolyses the oil to fatty acids first, then neutralises them — often with soda ash substituting part of the caustic soda, which lowers your NaOH tonnage.

Lye preparationCaustic soda is dissolved to a working strength. Batch practice commonly runs 30–35% NaOH, with published practice spanning roughly 25–38%;[14] continuous plants generally work stronger, with patent practice specifying 30–40%. Dissolution is strongly exothermic — always add caustic to water, never water to caustic, control the rate, and cool to the working temperature before the lye meets the oil.
Oil phase preparationOils and fats are melted, blended to the target ratio and brought to temperature. Free fatty acid content is the variable to watch: high-FFA or partly oxidised oil consumes alkali unpredictably and carries colour into the bar. Check the FFA and the saponification value on the oil COA before the batch, not after.
SaponificationLye and oil are combined under agitation. The traditional full-boil kettle process brings the mass to a brisk boil at around 100 °C and takes days;[5] continuous plants complete the same conversion in minutes to hours in plug-flow or stirred reactors with residence time and pH under instrument control. Alkali is normally charged at a 1–2% excess over theoretical.
Separation and washingOn the kettle and continuous saponification routes the neat soap is separated from the spent lye by salting out with sodium chloride. The spent lye carries the glycerol, which is concentrated and refined into crude glycerine — a genuine co-product revenue line, not a waste stream. Cold-process production skips this entirely and keeps the glycerol in the bar.
Drying to noodlesNeat soap at around 30% water is vacuum spray-dried to soap noodles at the target moisture. Noodles are the traded intermediate: many manufacturers buy noodles rather than saponifying, and many saponifiers sell noodles to finishers. If you sell noodles, your caustic soda consistency becomes your customer's process variable.
Milling, plodding, stampingNoodles are milled with fragrance, colour, preservative and any actives, extruded through a plodder into a continuous billet, cut and stamped. Nothing here touches caustic soda, but everything here shows up any colour or odour defect that a high-iron alkali introduced upstream.
Quality controlFinished soap is tested for total fatty matter, total alkali, free caustic alkali, moisture, matter insoluble in alcohol and chlorides. These are the numbers your customer and your regulator read, and they are set by international method standards rather than house practice.

Where cold process sits in a commercial conversation

Cold process combines lye and oils without external heat, moulds the batch, and lets saponification finish in place. It takes roughly 18–24 hours to complete the reaction and a further 3–4 weeks to cure.[6] It retains the glycerol, accommodates heat-sensitive additives, and needs almost no capital equipment.

It also cannot be verified complete before the bar is wrapped, which is precisely why the SAP arithmetic has to be right the first time and why the alkali assay has to be trustworthy. For a manufacturer choosing a route, the honest framing is that cold process is a premium positioning and low-capital decision, not a throughput or consistency one — and either way the caustic soda specification matters more, not less.

Standards

What the finished soap standards actually require

Two numbers connect your caustic soda purchase to your finished-product compliance: total fatty matter, which sets how much alkali you consume per tonne, and free caustic alkali, which proves you dosed correctly. Both are governed by published method standards, not house practice.

Free caustic alkali — the limit that proves your dosing

Free caustic alkali is unreacted sodium hydroxide left in the finished bar. It is a skin-irritation and product-safety parameter, and the limits are tight:

  • IS 2888:2004 — toilet soap, all three grades: 0.05% by mass maximum[7]
  • IS 13498:1997 — bathing bars: 0.05% by mass maximum[8]
  • EAS 186:2011 — East African toilet soap: 0.1% by mass maximum[9]

Note the factor of two between the Indian and East African limits — cite the standard your destination market actually applies rather than assuming a global figure. The measurement method is ISO 456 or the equivalent national method.

The practical link back to procurement: free caustic alkali failures come from over-dosing, and over-dosing usually comes from working off a nominal grade instead of a batch assay, or from a partly carbonated bag that read as full-strength on the label.

TFM — the grade your soap is traded on

Total fatty matter is the proportion of the soap that is fatty acid, determined by splitting the soap with dilute acid, extracting the fatty matter with ether, evaporating and weighing.[10]

Soap noodles are benchmarked in trade at 78% TFM, and the standard blend designation 80:20 means 80% palm oil and 20% palm kernel or coconut oil, with 90:10, 70:30 and 60:40 also traded.[11] Regulatory floors sit below the trading benchmark: IS 2888:2004 requires 76% minimum for Grade 1 toilet soap, 70% for Grade 2 and 60% for Grade 3, and EAS 186:2011 requires 76% minimum.

Why a caustic soda buyer cares: alkali consumption is proportional to fatty matter. Moving a product from 70% to 78% TFM raises your caustic soda requirement per tonne of output by roughly the same proportion — which is a real line in the raw-material budget and a real change in how many containers you book a year.

International method standards for soap analysis
Standard What it determines Why it matters to your alkali purchase
ISO 685:2020[15]Total alkali content and total fatty matter, simultaneously, in soaps including liquid soaps, excluding compounded productsThe single method behind both of your headline finished-product numbers
ISO 684:1974Total free alkaliCatches over-dosing before it becomes a customer complaint
ISO 456:1973Free caustic alkaliThe specific test against the 0.05% and 0.1% regulatory limits
ISO 672:1978Moisture and volatile matter, oven methodMoisture dilutes TFM; a wet bar fails a grade it should have passed
ISO 673:1981Ethanol-insoluble matterPicks up inorganic carry-over, including excess salt from the wash
ISO 8212Sampling techniques during manufactureA COA is only as good as the sample behind it — this is the method that makes it defensible

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Safe handling

Handling caustic soda safely in a soap plant

Solid caustic soda is a Class 8 corrosive. The hazard is not exotic and it is entirely manageable, but it is the one raw material in a soap plant that will cause a serious injury from a single careless minute — and the exposure limits are widely misquoted, so they are set out precisely below.

Occupational exposure limits for sodium hydroxide
Limit Value Form — this is the part usually misstated
OSHA PEL2 mg/m³8-hour time-weighted average, not a ceiling — 29 CFR 1910.1000 Table Z-1[12]
NIOSH REL2 mg/m³Ceiling — must not be exceeded at any time[13]
ACGIH TLV2 mg/m³Ceiling
NIOSH IDLH10 mg/m³Immediately dangerous to life or health

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Personal protective equipment

  • Eyes — chemical splash goggles as the minimum. Safety glasses alone are not sufficient. A full face shield is worn over goggles for dissolving, decanting and open-vessel work.
  • Hands — chemically resistant gloves in nitrile, neoprene or butyl rubber, inspected before each use. Not latex.
  • Body — resistant apron or suit, long sleeves, rubber or PVC boots. Caustic soda destroys leather footwear, so leather boots are not protective equipment here.
  • Respiratory — a NIOSH-approved particulate respirator where flake dust is generated in an enclosed area, or during large-scale dissolving. Enclosed transfer beats respirators wherever it is achievable.
  • Facilities — an eyewash station and safety shower within ten seconds of the work area, tested on a schedule, with a clear unobstructed path.

First aid and storage

Skin contact — remove contaminated clothing at once and flush with cool running water for at least 20 minutes. Do not attempt to neutralise with acid: that generates additional heat in an already burned tissue. Seek medical attention for any burn larger than a palm.

Eye contact — a medical emergency. Flush at the eyewash station holding the eyelids open for 20–30 minutes and arrange transport to an ophthalmologist. Alkali burns to the eye progress after the exposure ends, which is why the flushing time is so long.

Ingestion — do not induce vomiting; contact poison control immediately.

Storage in the warehouse

Sealed, moisture-proof packaging in a cool, dry, ventilated store. Caustic soda is hygroscopic and reacts with carbon dioxide, so open or damaged bags cake and convert progressively to sodium carbonate. Segregate from acids — including any sulfuric acid or hydrochloric acid held for splitting or cleaning — and from aluminium, zinc and tin, which liberate hydrogen on contact. Bund spill containment to 110% of the largest single container.

The rule that has to survive staff turnover: caustic into water, never water into caustic. Adding water to solid caustic soda concentrates the heat of solution at the surface and can boil and spatter alkali out of the vessel. Post it in the local language at the lye station, not only in the SDS binder.
Bulk procurement

Buying caustic soda for soap manufacturing: the checklist

These are the parameters to verify on the batch certificate of analysis and fix in the contract — not target values. Specifications vary by producer, grade and batch, and no published figure, ours included, substitutes for the documentation travelling with your own cargo.

On the certificate of analysis

what to read before you accept

  • NaOH assay — the actual batch figure, not the nominal grade. This is what you dose against.
  • Sodium carbonate — carbonated material under-doses your saponification at unchanged bag weight.
  • Sodium chloride — electrolyte carry-over; matters most in liquid and transparent systems.
  • Iron, in ppm — the parameter that decides whether a premium bar yellows on the shelf. Ask for a number, not an adjective.
  • Heavy metals — where a cosmetic or food-contact dossier applies.
  • Batch spread — ask for COAs from several recent batches. Judge the spread, not whether each one merely sits inside specification. Drift is what forces you to reformulate.
  • Traceability — batch numbers that connect the bag in your warehouse to a COA and a production date.
  • Production date and shelf life — typically 12–24 months sealed. Confirm you are not being offered aged stock.

On the contract and the cargo

what to fix before you sign

  • Packing and net weight — 25 kg bags, 500 or 1,000 kg FIBC, or pallets. Confirm net weight per unit rather than assuming it.
  • Bag quality — multi-layer with an inner liner, closure integrity, palletisation and shrink wrap. Bagged caustic soda that gets wet in transit arrives as a solid block.
  • Container loading — 25 MT of bagged material in a 20ft is the standard load. Confirm stuffing pattern and dunnage.
  • Dangerous goods documentation — UN 1823 Class 8 PG II for solid, UN 1824 for solution with the packing group assigned by concentration. Confirm marking and labelling meet destination requirements.
  • SDS language — in the language your destination authority requires, not only English.
  • Incoterm — EXW, FOB, CFR, CIF or DAP, and who arranges and pays for inland transport, loading, documentation and destination handling.
  • Pre-shipment inspection — whether SGS, Intertek or Bureau Veritas is accepted at your cost.
  • Payment terms — T/T, L/C at sight or D/P, matched to the trade history between you.

Container loading and what actually fits

A 20ft container takes 25 metric tons of bagged caustic soda as a standard load — 1,000 bags of 25 kg. That is also our minimum order quantity, and it is not an arbitrary number: it is one full container, which is the point below which the freight cost per tonne rises sharply and the documentation cost stops being proportionate.

Put that against the calculator at the top of this page. At roughly 125 kg of caustic soda per tonne of finished soap, one 25 MT container covers about 200 tonnes of soap production. A plant making 50 tonnes of soap a month is buying roughly one container a quarter; a plant making 500 tonnes a month is on a monthly or contract programme and should be pricing it that way.

Buyers who also take soda ash light for the fatty-acid route, stearic acid for bar hardness, or LABSA and SLES for a detergent line alongside the soap plant can consolidate several products into one shipment rather than booking part-loads separately.

Pricing

How to get a price for caustic soda for soap making

No price is published on this page. Caustic soda is a traded commodity whose level moves with chlor-alkali operating rates, energy cost, freight and regional supply, and a figure written today would be wrong within weeks and misleading in any market other than the one it was quoted for. Every enquiry is answered individually — by email or on WhatsApp. Indicative current levels for reference grades are maintained on our caustic soda price page.

Grade and formFlakes 98%, pearls 99% or liquid, plus any specification limit your own customer names — an iron figure in ppm above all, if you make toilet or transparent soap.
QuantityTonnage per shipment and expected annual volume. Both, not one — a single container and a twelve-month programme are quoted differently.
Packaging25 kg bags, 500 or 1,000 kg FIBC, ISO tank for liquid — and whether your warehouse unloads by forklift or by hand.
Destination portNamed discharge port, plus the inland destination if you want a door-to-door comparison.
IncotermEXW, FOB, CFR, CIF or DAP. Unsure which? Say what you want the number to include and we will suggest the right term.
Schedule and termsShipment window, spot or repeating, whether SGS or BV inspection is required, and preferred payment — T/T, L/C at sight or D/P.
What comes back: a firm, contractable offer with its own stated validity period, the technical data sheet, the certificate-of-analysis format and the full document set — normally within 24 hours on working days.

Ask for a price directly

Send the six lines above and you will have a quotation for caustic soda flakes, pearls or liquid, loading FOB Mersin or FOB Jebel Ali. Soap manufacturers sourcing several raw materials for one production line can consolidate the enquiry into a single shipment.

WhatsApp: +971 50 720 9246 Email: info@causticsodaco.com Contact form
Three sourcing patterns

How soap manufacturers actually structure caustic soda supply

What changes between these is your working capital, your exposure to a price move, and how much warehouse space the alkali occupies.

Spot, container by container

Under ~50 MT of soap a month
Lowest commitmentOne 25 MT container ordered as stock runs down, quoted fresh each time.
  • No contract exposure to a falling market
  • Minimal warehouse space tied up
  • Fully exposed to a rising market and to lead-time gaps
  • Highest cost per tonne over a year

Scheduled programme

~50–500 MT of soap a month
The usual answerAn agreed annual tonnage drawn down on a shipment schedule, priced per lifting.
  • Supply security without pre-paying for the year
  • Volume pricing against committed tonnage
  • Predictable warehouse and cash planning
  • Specification locked once, applied to every lifting

Annual contract

Above ~500 MT of soap a month
Maximum securityCommitted annual volume with agreed pricing mechanism and a fixed specification.
  • Best pricing and priority on allocation
  • Dedicated batch reservation where required
  • Needs a reliable production forecast to sign
  • Suits plants selling noodles onward under their own spec
Sourcing

How to choose a caustic soda supplier or exporter for soap manufacturing

For a commodity alkali, supplier selection comes down to consistency and documentation. A supplier who delivers variable assay does far more damage — through reformulation, off-spec batches and customer complaints — than any apparent saving elsewhere recovers.

Batch-to-batch consistencyAsk for COAs from several recent batches, not one flattering sample. Look at the spread, not just whether each result sits inside specification.
Complete documentationCOA per batch, a current SDS in the language your destination requires, technical data sheet, and correct UN 1823 dangerous goods documentation.
TraceabilityBatch numbers that connect the material in the bag to the COA and to a production date.
Packaging qualityBag gauge, inner liner, closure integrity, palletisation and labelling. Caustic soda that takes on water in transit arrives caked and short on assay.
Export experience on your routeA supplier who has shipped to your destination before knows its documentation, inspection and marking requirements — and the customs treatment of a Class 8 cargo.
Loading and logistics capabilityWhich ports, which container types, ISO tank availability for liquid, and realistic loading windows rather than optimistic ones.
Honest lead timesA supplier who quotes an achievable date and meets it is worth more than one who quotes what you want to hear.
Technical responsivenessHow fast a technical question gets a technical answer. It predicts how a shipment problem will be handled.
Terms and inspectionT/T, L/C at sight or D/P appropriate to the trade history, and willingness to accept third-party pre-shipment inspection at your cost.
Ability to support recurring supplyOne container is a transaction. A year of production needs a supplier who can hold specification and schedule.

SUHA International Trading — caustic soda supplier for soap manufacturers

SUHA International Trading L.L.C., trading as Caustic Soda Co, is a supplier and exporter of caustic soda flakes 98%, caustic soda pearls 99% and liquid caustic soda to soap manufacturers, distributors and traders internationally, loading from Mersin in Türkiye and Jebel Ali in the UAE, with a batch certificate of analysis and safety data sheet supplied for every shipment.

Two loading origins is a practical point rather than a slogan: when a route is disrupted, a port congested or a producer on turnaround, the enquiry moves to the other origin instead of stalling. For buyers in Europe, the Black Sea, North Africa and the eastern Mediterranean, Mersin usually lands cheaper; for the GCC, East and West Africa, South Asia and the Indian Ocean, Jebel Ali usually does.

Soap manufacturers sourcing more than one input can consolidate — soda ash light for the fatty-acid neutralisation route, stearic acid for bar hardness, and the detergent surfactants LABSA 96% and SLES 70% for a parallel liquid line — all come from the same source, on one set of documents. The full range is on our products page, and buyers importing into Türkiye specifically can start from the caustic soda supplier Türkiye page.

CAS
1310-73-2
HS codes
2815.11 · 2815.12
Dangerous goods
UN 1823 · Class 8 · PG II
Grades
Flakes 98% · Pearls 99% · Liquid
Packing
25 kg bags · FIBC · ISO tank
MOQ
25 MT — 1 × 20ft FCL
Loading
Mersin · Jebel Ali
Payment
T/T · L/C · D/P
Documents
COA · SDS · TDS · CO · B/L
Common questions

Caustic soda in soap making — FAQ

Buying, supply and logistics

About 121 kg of sodium hydroxide on a 100 percent basis per metric ton of finished soap at 78 percent total fatty matter, using a standard 80:20 palm and palm kernel oil blend. Allowing the 1 to 2 percent alkali excess plants normally charge, and buying 98 percent flakes rather than pure NaOH, the practical purchase figure is roughly 124 to 127 kg per tonne of soap, or about five 25 kg bags. Recalculate against the saponification value on your own oil certificate of analysis, because the figure moves with the blend.

Caustic soda flakes or pearls at 98 to 99 percent assay from the membrane process are the standard choice for soap manufacturing. For laundry bars and industrial cleaning soap, 98 percent flakes give the best cost per unit of active alkali. For toilet soap, premium bars and any product judged on colour, 99 percent pearls with low iron and low chloride are preferred, because iron traces promote discolouration and rancidity over shelf life. Ask for the iron figure on the batch certificate of analysis rather than relying on the assay alone.

Flakes are the usual choice for most soap plants: highest active alkali per unit cost, straightforward 25 kg bag handling, no heated storage. Pearls cost more but dust less, flow better in screw feeders and dose more accurately, which suits automated lines and premium toilet soap. Liquid caustic at 50 percent removes the dissolving step entirely but needs corrosion resistant tanks and, in cool climates, heating, because 50 percent solution begins to crystallise near 12 degrees Celsius. Liquid is economic only when the plant is close to the supply point, since you are paying freight on the water.

Our minimum order is 25 metric tons, which is one 20 foot full container load of 25 kg bags. At roughly 125 kg of caustic soda per tonne of finished soap, one container covers about 200 tonnes of soap production. Buyers running several products, or combining caustic soda with soda ash, sodium silicate or stearic acid, can consolidate into a single shipment. Smaller trial quantities are considered case by case where a longer term supply programme is being evaluated.

Every shipment carries a batch certificate of analysis stating NaOH assay, sodium carbonate, sodium chloride and iron, a GHS compliant safety data sheet, a technical data sheet, commercial invoice, packing list, bill of lading and certificate of origin. Because solid caustic soda is UN 1823 Class 8 Packing Group II, the dangerous goods declaration and correct package marking travel with the cargo. Pre shipment inspection by SGS, Intertek or Bureau Veritas is available at the buyer's cost.

Caustic soda flakes and pearls are packed in 25 kg multi layer polypropylene or polyethylene lined bags, in 500 kg or 1,000 kg FIBC jumbo bags, or on shrink wrapped pallets of 1,000 kg. A 20 foot container takes 25 metric tons of bagged material as a standard load, which is 1,000 bags of 25 kg. Liquid caustic soda moves in ISO tanks, tank trucks for regional delivery and 1,000 litre IBCs for smaller volumes.

Loading is from Mersin in Turkiye and from Jebel Ali in the UAE, and the choice normally follows the destination and the freight. Mersin generally suits Europe, the Black Sea, North Africa and the eastern Mediterranean; Jebel Ali suits the GCC, East and West Africa, South Asia and the Indian Ocean. Quotations are given FOB from either port, or CFR, CIF and DAP to a named destination on request.

No price is published on this page, because caustic soda is a traded commodity whose level moves with chlor alkali operating rates, energy cost, freight and regional supply, so a figure written today would be wrong within weeks. Send the grade, tonnage per shipment, packaging, destination port and preferred Incoterm and a firm quotation with its own stated validity period comes back, normally within 24 hours on working days.

Ask for certificates of analysis from several recent batches rather than one sample, and judge the spread rather than whether each result merely falls inside specification, because batch to batch drift in assay is what forces reformulation on your side. Confirm traceable batch numbering to a production date, a current safety data sheet in the language your destination requires, correct UN 1823 dangerous goods documentation, bag quality and palletisation, prior export experience on your specific trade lane, and willingness to accept third party pre shipment inspection at your cost.
Chemistry, formulation and quality

Caustic soda supplies the hydroxide ion that breaks the ester bonds in a triglyceride and converts the released fatty acids into their sodium salts, which are soap. The reaction, saponification, also frees glycerol. Sodium hydroxide is used rather than another alkali because the sodium salt of a fatty acid forms a hard crystalline solid, which is what a bar of soap physically is. Potassium hydroxide gives soft and liquid soaps instead.

One molecule of triglyceride reacts with three molecules of sodium hydroxide to give three molecules of sodium soap and one molecule of glycerol. Written simply: fat or oil plus sodium hydroxide gives soap plus glycerol. The reaction is exothermic and irreversible under normal soap making conditions, and the hydroxide is fully consumed when the formulation is correctly balanced, which is why properly made soap contains no free caustic soda.

The saponification value is the mass of alkali needed to saponify one unit mass of a given oil. Expressed as grams of NaOH per gram of oil it is used directly: multiply each oil weight by its SAP value, add the results, then multiply by one minus the superfat fraction. If your figure is published as mg KOH per gram, divide by 1.403 to convert to the NaOH basis. SAP values are ranges rather than constants because fatty acid composition varies with origin and refining, so dose against the saponification value on your oil supplier's certificate of analysis.

Sodium hydroxide makes hard bar soap and potassium hydroxide makes soft and liquid soap, because the sodium salt of a fatty acid packs into a tighter crystal than the potassium salt. On dosage, KOH saponification values are 1.403 times the NaOH values for the same oil, since KOH is the heavier molecule. Technical KOH flake is also normally supplied at 90 percent rather than 98 to 99 percent, so the charged weight has to be divided by the purity, a correction that is much larger than for caustic soda.

In correctly formulated and fully processed soap, no. The hydroxide is consumed by the reaction, and what remains is soap, water, glycerol if it has been retained, and any deliberately unsaponified oil. Finished product standards set a hard limit on what is left: Indian Standard IS 2888:2004 for toilet soap and IS 13498:1997 for bathing bars both cap free caustic alkali at 0.05 percent by mass, and the East African Standard EAS 186:2011 caps it at 0.1 percent. Free caustic alkali is measured by ISO 456 or the equivalent national method.

Batch soap making commonly runs a 30 to 35 percent sodium hydroxide solution, and published practice across the literature spans roughly 25 to 38 percent. Continuous industrial saponification usually works stronger, with patent practice specifying 30 to 40 percent. Dissolving caustic soda is strongly exothermic, so always add the caustic to the water and never the reverse, control the addition rate, and cool the solution to the working temperature before it meets the oil phase.

Total fatty matter is the proportion of a soap that is fatty acid, measured by splitting the soap with acid and weighing the extracted fatty matter. It is the grade that soap is traded and regulated on: soap noodles are benchmarked at 78 percent TFM, while Indian Standard IS 2888:2004 sets 76 percent minimum for Grade 1 toilet soap, 70 percent for Grade 2 and 60 percent for Grade 3. TFM matters to a caustic soda buyer because alkali consumption is proportional to the fatty matter in the product, so a higher TFM specification raises the caustic soda tonnage you need per tonne of output.

Iron is the one that shows in the finished bar, because iron traces catalyse oxidation of the fatty phase and cause discolouration and rancid odour over shelf life, which is why premium toilet soap buyers specify low iron membrane grade material. Sodium carbonate from carbonation of the caustic soda lowers effective alkali and shifts your dosing, sodium chloride affects electrolyte balance and can alter viscosity in liquid systems, and heavy metals matter where the finished product carries a cosmetic or food contact claim. Ask for all four on the batch certificate of analysis rather than the assay alone.

Sealed 25 kg bags stored in a cool, dry, well ventilated warehouse typically hold their assay for 12 to 24 months. Caustic soda is hygroscopic and reacts with atmospheric carbon dioxide, so once bags are opened or the packaging is compromised the material absorbs moisture, cakes, and converts progressively to sodium carbonate, which lowers the effective alkali and makes dosing inconsistent. Rotate stock first in first out and re seal opened bags.

Chemical splash goggles are the minimum for eye protection and safety glasses alone are not sufficient; a full face shield is worn over them for dissolving, pouring and open vessel work. Chemically resistant gloves in nitrile, neoprene or butyl rubber, a resistant apron or suit, and rubber or PVC boots are standard, since caustic soda destroys leather. For occupational exposure, the OSHA permissible exposure limit under 29 CFR 1910.1000 Table Z-1 is 2 mg per cubic metre as an 8 hour time weighted average, while the NIOSH recommended limit and the ACGIH threshold limit value are both 2 mg per cubic metre as a ceiling, and the NIOSH immediately dangerous to life or health value is 10 mg per cubic metre. Eyewash stations must be within ten seconds of the work area.

Not true soap. Soap is by definition the salt of a fatty acid, and forming that salt requires a strong alkali, whether the sodium hydroxide route for bars or potassium hydroxide for soft and liquid soaps. Cleansing bars sold without alkali are synthetic detergent bars, built from surfactants such as sodium cocoyl isethionate rather than saponified oils, and they are a chemically and commercially different product with different raw material sourcing.
The decision

Choosing caustic soda for your soap manufacturing operation

Specify 98–99% membrane-grade caustic soda, choose flakes or pearls on how your plant handles solids rather than on headline price, and buy against the batch assay and the iron figure rather than the nominal grade.

What decides the technical choice

Assay sets your dosing, iron sets your shelf life, and physical form sets your handling. Laundry and general bar production runs comfortably on 98% flakes. Toilet soap, transparent soap and anything judged on colour justifies 99% low-iron pearls, and the premium is small against the cost of a discoloured production run.

What decides the commercial choice

Consistency, documentation and lead time. A supplier whose assay drifts costs you reformulation and complaints; a supplier who cannot produce a batch COA, a current SDS in the right language and correct UN 1823 paperwork costs you at the port. Neither cost appears in the unit price you compared.

Caustic soda is the non-substitutable input of soap manufacturing — there is no soap without a strong alkali, and no bar soap without sodium hydroxide specifically. That makes it a supply-security question as much as a purchasing one, which is why two loading origins and an honest lead time are worth more to a running plant than a marginal saving on a single container.

The practical sequence is short. Work out your tonnage from your own oil blend and TFM using the calculator above, decide the grade and form from the tables, write the specification down including the iron limit, and put the same enquiry to more than one supplier so you are comparing like with like. Then verify what arrives against the COA rather than the offer sheet — every time, not only on the first shipment.

Send the specification. Get a firm offer back.

Grade, tonnage, packaging, destination port and Incoterm — that is all it takes. A quotation comes back with the technical data sheet and the certificate-of-analysis format attached, normally within 24 hours on working days, for caustic soda flakes 98%, pearls 99% or liquid caustic soda, loading from Türkiye and the UAE.

Email info@causticsodaco.com WhatsApp +971 50 720 9246
Sources

References

  1. FAO/WHO Codex Alimentarius, CXS 210-1999 — Standard for Named Vegetable Oils (saponification value ranges). fao.org/fao-who-codexalimentarius
  2. FAO/WHO Codex Alimentarius, CXS 211-1999 — Standard for Named Animal Fats. fao.org (PDF)
  3. Handcrafted Soap & Cosmetic Guild, Superfatting and the Lye Discount. soapguild.org
  4. Occidental Chemical Corporation, Caustic Soda Handbook (50% solution crystallisation and minimum unloading temperature). oxychem.com (PDF)
  5. US Environmental Protection Agency, AP-42, Chapter 6.8 — Soap and Detergents. epa.gov (PDF)
  6. Adawiyah Jamil et al., cold saponification and curing of handmade soap, PMC6225244. pmc.ncbi.nlm.nih.gov
  7. Bureau of Indian Standards, IS 2888:2004 — Toilet Soap Specification. law.resource.org (PDF)
  8. Bureau of Indian Standards, IS 13498:1997 — Bathing Bars Specification. law.resource.org (PDF)
  9. East African Community, EAS 186:2011 — Toilet Soap Specification. law.resource.org (PDF)
  10. Bureau of Indian Standards, IS 286:1978 — Methods of Sampling and Test for Soaps (total fatty matter definition and method). law.resource.org (PDF)
  11. ICIS, Soap Noodles Pricing Methodology (78% TFM benchmark; 80:20, 90:10, 70:30 and 60:40 blend designations). icis.com
  12. US Occupational Safety and Health Administration, 29 CFR 1910.1000 Table Z-1 — Limits for Air Contaminants. osha.gov
  13. US National Institute for Occupational Safety and Health, NIOSH Pocket Guide to Chemical Hazards — Sodium hydroxide. cdc.gov/niosh
  14. Handcrafted Soap & Cosmetic Guild, The Water Discount (published lye concentration practice). soapguild.org
  15. International Organization for Standardization, ISO 685:2020 — Analysis of soaps: determination of total alkali content and total fatty matter content. iso.org

Technical values on this page are general commercial ranges and published standard figures provided for orientation. Saponification values are ranges rather than constants and vary with the origin, cultivar and refining of the oil; caustic soda specifications vary by producer, grade and batch. Always verify against the certificate of analysis and safety data sheet supplied with your own material, confirm the finished-product standard that applies in your destination market, and validate any formulation change through your own bench and plant trials before production. Nothing on this page constitutes a specification, a warranty or a formulation recommendation for a specific product. Content reviewed .