Caustic soda guide · Membrane-grade supply from Türkiye & Dubai
Types and Grades of Caustic Soda: Flakes, Pearls, Liquid and Purity Grades Explained
The chemical is the same in every form. What changes is how much water it carries, how it is handled, and how much salt, iron and carbonate it contains. Those differences decide which product a soap plant, a viscose mill, a refinery or a food processor should buy. This guide explains each type and grade of caustic soda with typical specification values. It then shows how to match them to your process and how to order them in container loads from SUHA International. For the basics of the chemical, see our caustic soda supplier overview.
Short answer
Caustic soda (sodium hydroxide, NaOH) comes in three physical types: flakes, pearls (also called prills or beads) and liquid solution, usually 32% or 50%. Its grade is set by purity and production route: technical/industrial, rayon (high purity), food grade E524 and reagent grade. Membrane-cell material is the cleanest of the bulk grades.
Other trade names: lye, sodium hydrate, soda lye (liquid) and anhydrous caustic soda (the solid forms, which contain almost no water). Reviewed 25 October 2026 by the SUHA International technical and export desk.
Physical form
Types of Caustic Soda: Flakes, Pearls and Liquid
Every type of caustic soda starts as the same solution leaving a chlor-alkali plant. Producers then either sell it as liquid, or boil off the water to make a molten, anhydrous product that is cooled into flakes or sprayed into pearls. The full production route is explained in how caustic soda is made.
Caustic Soda Flakes
Thin, white, brittle flakes made by cooling molten NaOH on a rotating drum flaker. They are the default choice for importers and distributors because they ship the most NaOH per container at the lowest freight per tonne.
Caustic Soda Pearls (Prills)
Small round granules, typically 0.5–2.0 mm, formed when molten NaOH is sprayed down a prilling tower. They flow freely, raise very little dust and dose accurately by weight, which suits automated feeders, detergent plants and food use.
Liquid Caustic Soda (Lye)
A clear, colourless water solution, sold mainly as 50% NaOH and in some markets as 32%. It needs no dissolving and is pumped straight into the process, but you pay freight on the water as well as the NaOH.
| Criterion | Flakes | Pearls / prills | Liquid 50% |
|---|---|---|---|
| NaOH content | 98% or 99% | ≥ 99% | 50 ± 0.5% |
| Shape | Irregular flakes, ≈ 0.3–1 cm³ | Spheres, 0.5–2.0 mm | Solution |
| Dust | Moderate | Very low | None |
| Flow and dosing | Good; can bridge in hoppers | Free-flowing, precise by weight | Pumped, metered by volume |
| Dissolving | Fast, strongly exothermic | Fast and even | Already dissolved |
| Caking risk | Moderate if the liner is damaged | Low | None (but freezes when cold) |
| Freight per tonne of NaOH | Lowest | Lowest | About double: half the cargo is water |
| Export packing | 25 kg bags, palletised or inside jumbo bags | 25 kg bags, palletised or inside jumbo bags | ISO tank |
| Best for | Cost-driven bulk users, distributors | Auto-dosing, detergents, food, fine chemicals | Large continuous plants with storage tanks |
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Comparison
Caustic Soda Flakes vs Pearls: Which Is Better?
Neither is chemically stronger in any meaningful way. A 99% flake and a 99% pearl deliver the same alkali. The choice is about handling, dust and cost per tonne.
Choose caustic soda pearls when…
- You dose automatically by screw feeder or weigh hopper
- Operator dust exposure is a concern
- You dissolve small, frequent batches and need even dissolving
- You need food grade (E524) or cosmetic-grade material
Choose caustic soda flakes when…
- You dissolve in bulk tanks and want the lowest cost per tonne
- You resell to distributors who expect the most traded form
- You make soap, paper, textiles or treat water at volume
- Your market is import-led: Africa, South Asia, the Middle East
If you are deciding between a solid and a solution instead, our caustic soda flakes vs liquid caustic soda comparison works through the cost per tonne of NaOH.
Liquid grades
Liquid Caustic Soda: 32% vs 50% Solution
Membrane cells produce a solution of roughly 32–33% NaOH. Many plants sell it at that strength to nearby customers, and evaporate the rest to 50% for longer journeys. The 50% grade carries far less water per tonne of NaOH, so it is the standard for export. Its weakness is temperature: 50% caustic soda starts to freeze at about 12 °C (54 °F) and becomes very viscous as it cools, so storage tanks and lines need heating in cold climates.
| Property | 32% solution | 50% solution |
|---|---|---|
| Density at 20 °C | ≈ 1.35 g/cm³ | ≈ 1.53 g/cm³ |
| NaOH per tonne of liquid | ≈ 320 kg | ≈ 500 kg |
| Cold weather | Lower freezing risk | Freezes at ≈ 12 °C; heated tanks needed |
| Typical market | Local and regional deliveries | Export and long-distance supply |
SUHA exports the 50% membrane grade in ISO tanks. Other strengths can be quoted on enquiry.
Production route
Membrane Grade vs Diaphragm Grade Caustic Soda: How the Process Defines Purity
All caustic soda is made by electrolysing salt brine, which yields chlorine, hydrogen and sodium hydroxide together. The type of electrolytic cell is the biggest single factor in how pure the final caustic soda is. That is why specifications and tenders often name it as a grade: membrane grade or diaphragm grade.
| Factor | Membrane cell | Diaphragm cell | Mercury cell |
|---|---|---|---|
| NaOH leaving the cell | ≈ 32–33% | ≈ 12%, mixed with salt | ≈ 50% directly |
| Salt (NaCl) in 50% product | Very low: our liquid spec is ≤ 0.005% (50 ppm) | High, around 1%, because salt carries through evaporation | Very low |
| Main contaminant risk | Minimal | Chloride and chlorate | Trace mercury |
| Status today | Modern standard; most new capacity | Still operated in some older plants | Phased out under the Minamata Convention (deadline 2025) |
| Suitable for | Rayon, food, pharma, textiles, electronics and every general use | General industrial use where chloride is tolerated | Legacy supply only |
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Membrane cells keep the brine separated from the caustic side, so the product needs no salt removal and arrives with very low chloride, chlorate and iron. Low chloride matters in several places:
- Wherever caustic soda contacts stainless steel at high temperature, because chloride causes stress-corrosion cracking
- In viscose fibre spinning
- In food and pharmaceutical use
- In battery recycling and other hydrometallurgical circuits
All SUHA caustic soda is membrane grade. Flakes, pearls and liquid are sourced from membrane-cell producers. We do not supply diaphragm or mercury-cell material.
Ask for a membrane-grade COAPurity grades
Grades of Caustic Soda by Purity and Use
Caustic soda grades are not fully standardised across countries. These are the grades buyers actually ask for, what defines each one, and whether we supply it.
Technical / Industrial Grade
The workhorse of the chemical industry and most of the caustic soda traded worldwide. Standards such as IS 252 allow technical grade down to 95% NaOH. In membrane-grade flakes, the main impurity is sodium carbonate, which forms when the product absorbs CO₂ from air. We supply technical-grade flakes at 98% and 99%.
Rayon Grade (Pure Grade)
Viscose production steeps cellulose pulp in caustic soda. Iron or manganese in that liquor degrades the cellulose and discolours the fibre. India's IS 252 calls this the "pure" grade: 99.5% minimum NaOH, iron ≤ 20 ppm, NaCl ≤ 0.10% and chlorate ≤ 10 ppm on the solid. Send your mill's specification and we will confirm what can be guaranteed per batch.
Food Grade Caustic Soda (E524)
Sodium hydroxide is the permitted food additive E524, used as an acidity regulator and processing aid. Food grade is defined by contaminant limits, not by a higher NaOH number alone. It must meet the rules of the market it enters, such as EU Regulation 231/2012 or the Food Chemicals Codex. See caustic soda in food production and olive curing.
Laboratory / Reagent Grade
Tested against pharmacopoeia monographs and sold in small sealed containers for laboratories and analysis. It is not a bulk trade product. Buy it from laboratory-chemical distributors.
Specialty Low-Impurity Grades
Tightened limits on one impurity for electronics, battery materials and high-temperature stainless systems. Membrane-grade caustic soda meets most low-chloride and mercury-free requirements as standard.
Is 99% caustic soda better than 98%?
Only if your process needs it. The extra 1% is mostly a smaller carbonate and moisture fraction. For soap, detergent, water treatment and pulp, 98% flakes perform the same once you adjust the dose for the assay. Food, cosmetic, rayon and automated-dosing users usually specify 99% pearls or 99% flakes. Compare cost per tonne of active NaOH, not per tonne of product. Current FOB levels for each grade are on the caustic soda price and caustic soda flakes price pages.
Specifications
Caustic Soda Specifications: Technical Data by Type and Grade
Typical values for SUHA membrane-grade caustic soda. Each shipment carries its own Certificate of Analysis, and the batch COA is the contractual document.
| Parameter | Test method | Flakes 98% (typical) | Pearls 99% industrial | Liquid 50% membrane | Food grade E524 pearls |
|---|---|---|---|---|---|
| NaOH (assay) | Titrimetric (ASTM E291) | 98 ± 1 % | ≥ 99.0 % | 50 ± 0.5 % | ≥ 99.0 % |
| Na₂CO₃ | Titrimetric | 0.43 % | ≤ 0.8 % | ≤ 0.5 % | ≤ 0.5 % |
| NaCl | Argentometric | 0.0085 % | ≤ 0.1 % | ≤ 0.005 % | ≤ 0.03 % |
| Fe | ICP-OES / AAS | 10 ppm | ≤ 50 ppm | ≤ 5 ppm | ≤ 20 ppm |
| Na₂SO₄ | Gravimetric | 0.0047 % | Per COA | Per COA | Per COA |
| SiO₂ | Spectrophotometric | 0.0019 % | Per COA | Per COA | Per COA |
| Heavy metals (as Pb) | ICP-OES / AAS | max 2 ppm | Per COA | Per COA | Pb ≤ 0.5 mg/kg |
| Arsenic (As) | ICP-OES / AAS | — | Per COA | — | ≤ 3 mg/kg |
| Mercury (Hg) | ICP-OES / AAS | — | Per COA | — | ≤ 0.1 mg/kg |
| Form / size | Visual / sieve | White flakes | 0.5–2.0 mm pearls | Clear, colourless | 0.5–2.0 mm pearls |
| Density | Hydrometer | ≈ 2.13 g/cm³ (true density, solid) | 1.525–1.535 g/cm³ | ≈ 2.13 g/cm³ | |
Swipe the table sideways to compare all four products.
| Property | Value |
|---|---|
| Melting point (solid) | 318 °C (604 °F) |
| Freezing point, 50% liquid | ≈ 12 °C (54 °F) |
| Solubility in water | ≈ 111 g / 100 mL at 20 °C, strongly exothermic |
| pH (1% solution) | ≈ 13–14 |
| Hygroscopic | Yes. Absorbs water and CO₂ from air |
Download the technical documents
Selection
Which Type and Grade of Caustic Soda Does Your Industry Need?
Use the finder or the table as a starting point, then confirm against your process specification. Each industry links to a detailed guide.
Caustic Soda Grade Finder
Choose your industry. The finder shows the type and grade most buyers start from, the impurity to watch, and the packing that usually fits.
| Industry | Usual type | Usual grade | Why |
|---|---|---|---|
| Soap making | Flakes or pearls | Technical 98–99% | Saponification needs a known assay, not ultra-purity |
| Detergents | Pearls or flakes | Technical 99% | Pearls suit automated powder and paste lines |
| Textile processing | Liquid 50% or flakes | Membrane, low iron | Iron stains cotton during mercerising and scouring |
| Viscose rayon | Liquid or flakes | Rayon / pure | Iron and manganese degrade cellulose |
| Pulp and paper | Liquid 50% | Membrane technical | Large continuous demand; low chloride protects equipment |
| Water treatment | Liquid 50% or flakes | Technical, low heavy metals | pH correction and metal precipitation |
| Mining and alumina | Liquid 50% or flakes | Technical | Bauxite digestion, gold leaching circuits, pH control |
| Oil refining | Liquid 50% | Membrane technical | Removing H₂S and mercaptans; chloride harms units |
| Food processing | Pearls | Food grade E524 | Contaminant limits are a legal requirement |
| Sugar industry | Liquid or flakes | Technical or food | Juice pH control and evaporator cleaning |
| Cosmetics | Pearls | Food or high purity | Product safety and consistent dosing |
| Biodiesel | Flakes or pearls | Technical 99% | Low water helps transesterification |
| Chemical manufacturing | All types | Technical, membrane | Depends on the downstream product |
| Metal processing | Flakes or liquid | Technical | Degreasing, etching and anodising lines |
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Procurement
Caustic Soda Packaging and Container Loading by Type
| Packaging | Products | Construction | Best for |
|---|---|---|---|
| 25 kg bags, palletised | Flakes, pearls | Woven PP bag with PE inner liner, shrink-wrapped on pallets | Fast forklift discharge and clean warehouse stacking |
| 25 kg bags inside jumbo bags | Flakes, pearls | The same 25 kg bags packed inside jumbo bags | Crane and forklift handling, with 25 kg units kept intact for resale |
| ISO tank | Liquid 50% only | Stainless ISO tank container | Plants with bulk storage; heat at destination if the product cools towards 12 °C |
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Minimum order is one full container load (1 FCL, 20ft or 40ft). The net tonnage depends on product and packing. We load FOB Mersin (Türkiye) and FOB Jebel Ali (UAE), with CFR and CIF to your port, and ship overland by truck from Türkiye to neighbouring markets.
Safety
Handling and Storage Differences Between Caustic Soda Types
- Flakes and pearls are hygroscopic. Keep them dry, under cover and in sealed bags. Moisture causes caking, and contact with air slowly turns NaOH into sodium carbonate, which lowers the assay.
- Liquid 50% is stored in carbon-steel, stainless-steel or lined tanks. Fit heating and insulation wherever ambient temperature can fall below about 15 °C.
- Metals to avoid: aluminium, zinc (including galvanised steel), tin, brass and bronze. Caustic soda attacks them and releases flammable hydrogen gas. Carbon steel and stainless steel are standard construction materials.
- Dissolving solids: always add flakes or pearls slowly to water, never water to caustic. The reaction is strongly exothermic and can boil and spatter.
- Transport class: UN 1823 (solid) or UN 1824 (solution), Class 8 corrosive, packing group II. GHS hazard statements H290 and H314.
Safety: caustic soda causes severe skin burns and permanent eye damage. Wear chemical goggles with a face shield, alkali-resistant gloves and protective clothing. Keep an eyewash station and safety shower near the handling area.
Storage guideQuality control
How to Check the Caustic Soda Grade Before You Buy
- Ask for the production route. Membrane grade should be stated on the COA or on the producer's specification sheet.
- Compare the full COA, not just the assay. Check Na₂CO₃, NaCl and Fe against your specification. For food use, also check Pb, As and Hg.
- Request a pre-shipment sample or third-party inspection. SGS or Bureau Veritas can draw samples at loading and verify quantity, packing and quality.
- Test on arrival. A simple acid titration confirms NaOH content. Our guide on how to check caustic soda quality walks through the method.
Supplier
Caustic Soda Supplier for Every Type and Grade, with Offices in Türkiye and Dubai
SUHA International Trading L.L.C. has exported caustic soda and industrial chemicals since 2018. We are an exporter, not a manufacturer. We source membrane-grade flakes, pearls and liquid from established chlor-alkali producers. Then we manage quality, documents and logistics for importers, distributors, traders and manufacturers in 139 countries. More about our company
Every type, one supplier
Flakes 98% and 99%, pearls 99% and liquid 50%. Industrial and food grade (E524) on one contract.
Membrane grade only
Low chloride, low iron and mercury-free, as standard on every type we ship.
Two loading hubs
FOB Mersin for Europe, the Black Sea, North Africa and the Mediterranean. FOB Jebel Ali for the Gulf, East Africa and South Asia.
Batch-level COA
Every cargo ships with its own COA, SDS, commercial invoice, packing list, B/L and certificate of origin. SGS or BV inspection on request.
Local and export reach
All 7 UAE emirates, all 81 Turkish provinces, and export by sea and by road from Türkiye.
Clear terms
MOQ 1 FCL (20ft or 40ft). Lead time 7–15 days to loading. Payment by T/T, L/C at sight or D/P.
Dubai Office
Office 2305, Burlington Tower,Business Bay, Dubai, United Arab Emirates Open in Google Maps
Ankara Office
Karşıyaka District, 749 Street, No 30,Gölbaşı, Ankara 06830, Türkiye Open in Google Maps
Caustic soda supply by region and price
FAQ
Types and Grades of Caustic Soda: Frequently Asked Questions
What are the main types of caustic soda?
There are three main types: caustic soda flakes, caustic soda pearls (also called prills or beads) and liquid caustic soda, usually sold as a 50% or 32% solution. Flakes and pearls are anhydrous solids of 98–99% NaOH, while the liquid is NaOH dissolved in water.
What are the different grades of caustic soda?
The main grades are technical or industrial grade, rayon or pure grade, food grade (E524) and reagent or pharmacopoeia grade. Caustic soda is also graded by production process: membrane grade, diaphragm grade and mercury-cell grade, with membrane grade the purest bulk product.
Which caustic soda is best?
The best caustic soda is the one that matches your process. Membrane-grade product is the cleanest bulk option. Pearls 99% suit automated dosing, food and detergents. Flakes 98% give the lowest cost per tonne for soap, paper and water treatment. Liquid 50% suits large plants with heated storage tanks.
What is the difference between membrane grade and diaphragm grade caustic soda?
Membrane grade is made in cells where an ion-exchange membrane separates the brine from the caustic, so the 50% product contains very little salt, typically under 100 ppm NaCl. Diaphragm grade starts as a weak caustic and salt mixture and still contains around 1% salt after evaporation, which makes it unsuitable for rayon, food and many stainless-steel systems.
Are caustic soda flakes or pearls better?
Chemically they are the same. Pearls are less dusty, flow freely and dose more accurately, which suits automated feeders and food use. Flakes are cheaper per tonne and dissolve quickly in bulk tanks, so most importers and distributors buy flakes.
What is food grade caustic soda?
Food grade caustic soda is sodium hydroxide that meets food-additive purity criteria, such as EU Regulation 231/2012 for E524 or the Food Chemicals Codex, with strict limits on lead, arsenic and mercury. It is used for olive curing, cocoa alkalisation, fruit peeling and pH control.
What is rayon grade caustic soda?
Rayon grade is a high-purity caustic soda with very low iron, manganese, copper, silica and chlorate, used to make viscose rayon fibre. India's IS 252 defines it as the pure grade with at least 99.5% NaOH and no more than 20 ppm iron on the solid.
What is the difference between 32% and 50% liquid caustic soda?
32% is close to the strength that leaves a membrane cell and is used for nearby deliveries. 50% is evaporated further so less water is shipped, which makes it the standard export grade. The 50% solution freezes at about 12 °C, so it needs heated storage in cold climates.
Is 99% caustic soda better than 98%?
99% contains slightly less carbonate and moisture. For soap, detergent, water treatment and pulp, 98% performs the same once the dose is adjusted for assay. Food, cosmetic, rayon and auto-dosing users usually specify 99%.
Are caustic soda and sodium hydroxide the same thing?
Yes. Caustic soda is the common trade name for sodium hydroxide, NaOH, CAS 1310-73-2. It is also called lye, and the anhydrous solid forms are sometimes sold as anhydrous caustic soda.
What are the HS codes for caustic soda types?
Solid caustic soda, including flakes and pearls, is classified under HS 2815.11. Caustic soda in aqueous solution (liquid or lye) is classified under HS 2815.12. National tariffs add further digits.
How is caustic soda packed for export?
SUHA packs flakes and pearls in 25 kg PP bags with a PE liner, either palletised or packed inside jumbo bags. Liquid caustic soda 50% ships in ISO tanks. The minimum order is one full container load, 20ft or 40ft.
Where are your offices?
SUHA International Trading has its head office at Office 2305, Burlington Tower, Business Bay, Dubai, UAE, and a Türkiye office at Karşıyaka District, 749 Street, No 30, Gölbaşı, Ankara 06830. Meetings at both offices are by appointment.
Standards and references used in this guide
- Bureau of Indian Standards, IS 252:1991 Sodium Hydroxide — Specification (pure and technical grades)
- Commission Regulation (EU) No 231/2012: specifications for food additive E 524 sodium hydroxide
- Food Chemicals Codex monograph: Sodium Hydroxide
- Minamata Convention on Mercury, Annex B Part I: phase-out of mercury-cell chlor-alkali production by 2025
- PubChem: Sodium hydroxide (CID 14798)
- SUHA International technical data sheets and COAs for flakes, pearls and liquid caustic soda (linked above)
Request a Quote for the Right Caustic Soda Grade
Send us five details. Our desk in Dubai or Ankara will reply with the matching type and grade, a recent batch COA, and a FOB Mersin or Jebel Ali offer.
- Type (flakes, pearls, liquid)
- Grade (technical, food, rayon)
- Packing (pallet, jumbo bag, ISO tank)
- Monthly tonnage
- Destination port or city