Water / wastewater treatment
Process Role:
pH increase, neutralization, alkalinity control
Critical Procurement / Engineering Parameters:
Concentration; dosing accuracy; carbonate/iron limits
Caustic Soda (Sodium Hydroxide, NaOH)
Flakes and 32-50% Liquid Alkali for Water, Refining, Pulp, Detergent and Process Operations
Caustic soda is sodium hydroxide, a strong, highly corrosive alkali supplied as solid flakes/prills or aqueous solutions, commonly around 32-50 wt% NaOH. Form and concentration must be selected around storage temperature, dosing system, annual consumption, impurities and materials of construction. For 50% solution, crystallization/freezing begins near 12°C, making heat tracing or a lower-concentration grade important in cool logistics.
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Chemistry, Manufacturing Route & Material Behaviour
Modern caustic soda is manufactured primarily by chlor-alkali electrolysis of purified brine, producing NaOH together with chlorine and hydrogen. Membrane-cell material typically has a lower residual salt impurity profile than diaphragm-cell product. NaOH is strongly hygroscopic and absorbs atmospheric CO₂ to form sodium carbonate. Dissolution and dilution are strongly exothermic, so solution preparation requires controlled addition, cooling capacity and an approved operating procedure.
Process-Engineering & Grade-Selection Considerations
- Specify membrane/diaphragm grade when chloride and other impurity limits affect the process.
- For liquid storage, use the NaOH concentration-freezing curve, not ambient average temperature. 50% solution may crystallize around 12°C; tank/line heating and insulation can be required.
- Avoid aluminum, zinc, magnesium and other susceptible metals because strong caustic can attack them and may generate hydrogen. Materials selection must account for concentration, temperature and stress corrosion.
- For flakes, protect against moisture and CO₂ ingress to prevent caking and loss of assay through carbonate formation.
- For continuous dosing, verify density/viscosity at operating temperature for pump sizing and mass-flow calculations.
◎ Technical Specifications
| Property | Value |
|---|---|
Formula / CAS |
NaOH / 1310-73-2 |
Molar mass |
40.00 g/mol |
Solid appearance |
White, odorless flakes, beads or granules; deliquescent |
Solid density |
~2.13 g/cm³ |
Solid melting point |
~318°C |
50% solution density |
~1.50 g/cm³ at 20°C (typical) |
50% solution viscosity |
~79 mPa·s at 20°C (typical) |
50% freezing point |
~12°C (typical; concentration-dependent) |
Transport |
UN 1823 solid / UN 1824 solution; Class 8, commonly PG II |
Engineering note:
Values shown are reference or typical data, not a sales specification. Final acceptance must be based on the offered manufacturer grade, analytical method, COA, SDS and buyer specification.
Industrial Application
Refinery / petrochemical
Process Role:
Alkaline wash, neutralization, cleaning, pH control
Critical Procurement / Engineering Parameters:
Impurity profile; materials compatibility; delivery continuity
Pulp & paper
Process Role:
Pulping, extraction and process alkalinity
Critical Procurement / Engineering Parameters:
NaOH assay; salt/iron; bulk supply reliability
Soap & detergents
Process Role:
Saponification / alkalinity
Critical Procurement / Engineering Parameters:
Form; concentration; impurity control
Textile processing
Process Role:
Scouring, mercerization, dye preparation
Critical Procurement / Engineering Parameters:
Concentration; iron; process temperature
Chemical manufacture
Process Role:
Base, reactant, neutralization agent
Critical Procurement / Engineering Parameters:
Grade purity; NaCl/Na₂CO₃/Fe limits
Storage, Handling, Materials Compatibility & HSE
NaOH causes severe chemical burns and eye damage. The airborne concern is solid dust or corrosive mist rather than vapor. Provide splash protection, appropriate gloves/clothing, eyewash and emergency shower, controlled transfer, ventilation where mist/dust can form, and a current SDS. Dilution is strongly exothermic and can cause local boiling and splashing if performed incorrectly.
HSE control principle:
Use the current product-specific SDS, destination regulations, receiving-site risk assessment and applicable engineering standards. Website text must never substitute for an SDS, process safety review or site procedure.
Packaging, Transport & Supply Planning for GCC / MENA
Flakes are commonly supplied in 25 kg moisture-barrier bags and FIBCs. Liquid caustic may
be supplied in drums, IBCs, ISO tanks, road tankers or bulk vessels depending on destination
and concentration. Final packaging must match the offered grade and dangerous-goods rules.
RFQ Specification Checklist
- Solid flakes/prills or liquid concentration (32%, 45%, 48%, 50% etc.)
- Minimum NaOH and maximum Na₂CO₃, NaCl, NaClO₃, Fe and other critical impurities
- Membrane or diaphragm grade if relevant
- Storage minimum temperature and need for heat tracing/insulation
- Packaging / bulk delivery mode and unloading connection standard
- COA/SDS, batch traceability, food/NSF/other compliance only if required and documented
Quality Control, COA Parameters & Test Focus
- NaOH assay: Acid-base titration — confirms primary active concentration.
- Na₂CO₃: Titration — indicates CO₂ uptake and product ageing.
- NaCl: Ion analysis / producer method — controls membrane vs diaphragm purity and process impact.
- NaClO₃: Ion analysis — monitors chlor-alkali process impurity.
- Iron: ICP/AAS — controls colour and downstream quality impact.
- Density: Hydrometer / density meter — verifies concentration and dosing requirements.
- Appearance: Visual inspection — provides contamination screening.
Why Choose OGSCM?
Application-Driven Solutions
We match the right grade to your process needs.
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On-time delivery with strong regional & global logistics.
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Strict quality control and batch consistency.
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Technical & commercial support throughout your procurement journey.
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Frequently Asked Questions
A lower concentration can offer a lower crystallization risk in cool climates and easier pumping, but increases delivered water and storage volume.
No. A typical 50% solution begins to crystallize at about 12°C, so winter logistics can require heat management.
Generally no for strong caustic service. NaOH can attack aluminum and several other metals; final materials selection requires an engineering compatibility review.
Membrane-cell caustic generally has substantially lower residual sodium chloride and is selected where impurity control is more demanding.
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