| HS Code | 523337 |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Appearance | White solid flakes, pearls, or lumps |
| Grade | Industrial Grade |
| Purity | 99% minimum |
| Molar Mass | 40.00 g/mol |
| Melting Point | 318 °C (604 °F) |
| Boiling Point | 1,388 °C (2,530 °F) |
| Density | 2.13 g/cm³ at 25 °C |
| Solubility In Water | 109 g/100 mL at 20 °C |
| Ph 1 Aqueous Solution | 13-14 |
| Hygroscopic Nature | Absorbs moisture and CO₂ from air |
As an accredited Industrial Grade Caustic Soda | Leading Caustic Soda Manufacturer & Chinese Supplier factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Industrial grade caustic soda supplied in 25kg PP woven bags with PE liner, palletized and shrink-wrapped for safe transport. |
| Container Loading (20′ FCL) | 20′ FCL container loading ensures safe, efficient transport of industrial-grade caustic soda, maximizing capacity and protecting product integrity throughout shipment. |
| Shipping | Our industrial-grade caustic soda is safely packaged in 25kg bags, IBC totes, or bulk containers, complying with international shipping standards. We handle global export via sea freight, air freight, or rail, ensuring efficient delivery. With proper hazardous material documentation and secure handling, your order arrives reliably worldwide. |
| Storage | Store industrial-grade caustic soda in a cool, dry, well-ventilated area, away from moisture, acids, and incompatible materials. Use sealed, corrosion-resistant containers, preferably with clear labeling. Ensure secondary containment and proper PPE during handling. Maintain stable temperatures and inspect regularly for leaks or degradation to preserve product quality and safety. |
| Shelf Life | Industrial grade caustic soda has a long shelf life—typically 2–3 years when stored sealed, dry, and away from moisture. |
Within high-temperature Bayer digestion circuits, industrial-grade caustic soda functions not as a minor additive but as the continuous reaction medium that dissolves gibbsite, boehmite, and diaspore fractions from milled bauxite. Digestion liquors are maintained at 140–250 g/L Na₂O caustic concentration across low-temperature gibbsitic circuits (145–155°C) and high-temperature boehmitic/diasporic circuits (240–265°C); sodium hydroxide consumption in published refinery operating data spans 0.3–1.2 t NaOH per tonne alumina, with the upper quartile associated with monohydrate bauxite feedstocks and high organic carbon carry-over. In production-scale equipment, caustic-bauxite slurry is passed through multi-stage stirred autoclave trains or tube digesters with live steam injection; after flash cooling, red mud is removed in high-rate thickeners and polishing filters using synthetic flocculants, then clarified sodium aluminate liquor is seeded in precipitation tanks classified by particle size before calcination. Operational control under ISO 14001:2015 Clause 8.1 and ISO 45001:2018 Clause 8.1.2 addresses caustic unloading, storage, and spill containment; the substance itself is registered under REACH (EC) No 1907/2006 with exposure scenarios for industrial worker and environmental release. Terminal product types from caustic liquor are smelter-grade alumina for electrolytic aluminium smelting and alumina trihydrate for flame-retardant filler or synthetic zeolite feedstock. The dominant bottleneck is heat exchanger fouling: when free caustic concentration falls below the plant-specific target for the bauxite type, sodium aluminosilicate desilication product precipitates on tube walls rather than remaining suspended for thickener removal, raising steam consumption and shortening descaling cycles.
At 150–170°C in batch and continuous digesters, caustic soda is combined with sodium sulphide as white liquor to cleave lignin-carbohydrate bonds, but the controlling variable is effective alkali, not total NaOH inventory. Softwood kraft operations typically apply effective alkali charge of 12–25% on oven-dry wood, with sulphidity 20–35% and residual effective alkali in black liquor between 6–10 g/L as NaOH; hardwood charges are lower, but the same residual alkali target prevents redeposition of dissolved lignin. In hydraulic continuous digesters with impregnation, co-current, counter-current, and wash zones, spent black liquor is evaporated and burned in the recovery boiler, and the smelt is dissolved and causticized with slaked lime to regenerate white liquor. Delignification is measured by ISO 302:2015 Kappa number, while pulp viscosity is checked by ISO 5351:2010 limiting viscosity in cupriethylenediamine solution; the EU Best Available Techniques Reference Document for Pulp and Paper (2014) governs integrated emission and chemical recovery limits under the Industrial Emissions Directive. Terminal products include unbleached kraft linerboard, sack paper, bleached softwood kraft for fluff pulp, and dissolving pulp for viscose. The process conflict is sharp: raising effective alkali above 25% accelerates alkaline peeling and reduces pulp viscosity and yield, while falling residual alkali below 6 g/L can increase screen rejects and force a rate reduction; batch-to-batch variance in chip moisture and bark content therefore requires alkali ratio adjustment based on digester kappa samples rather than a fixed dosing curve.
When cotton fabric enters a chain mercerizer or open-width tension station, caustic concentration determines whether the cellulose lattice transitions from cellulose I to cellulose II and whether the fibre will gain luster and dye uptake without excessive fabric handling damage. Dry caustic in textile preparation is used in two distinct doses: scouring operations run at 2–6% NaOH on weight of fabric together with 0.1–0.5% chelating agent at 100–130°C in kiers or continuous open-width scouring ranges, whereas mercerizing operates with 20–24 wt% NaOH solution at 15–20°C and controlled residence of 40–60 s. The fabric is impregnated in the caustic trough, stretched on tenter clips to prevent width shrinkage, washed in a counter-current steam/spray cascade, neutralized in an acid sour, and dried; weak lye is recovered by multi-effect evaporation and returned to the mercerizer after purification. Compliance is managed through ZDHC MRSL v3.1 for chemical inputs, which does not restrict sodium hydroxide under current listings, and ZDHC Wastewater Guidelines requiring discharge pH in the 6–9 range. Terminal product types include mercerized cotton shirting, satin weave fabrics, cotton sewing thread, and knit interlock with improved dimensional stability and dye yield. Below 20%, the cellulose I to cellulose II conversion is incomplete, and subsequent dye yield improvement is reduced; above 24%, the solution viscosity rises and cold bath control becomes more difficult, while tightly constructed selvedges can suffer crease marking during tenter entry.
Saponification kettle operations treat industrial-grade caustic soda as a stoichiometric co-reactant, where the dose is fixed by the saponification value of the oil blend rather than a blanket percentage. An oil blend with a saponification value of 200 mg KOH/g requires 0.143 kg NaOH per kilogram of oil after applying the 40.0/56.1 molar conversion; commercial hard-oil soap bases using palm stearin and tallow are dosed at 13.5–15.5 wt% NaOH on fat weight, while coconut-rich bases with saponification values near 250 mg KOH/g require approximately 0.178 kg NaOH per kilogram oil. The process is run in jacketed or open-steam batch kettles at 80–100°C with turbine agitation; after the saponification reaction reaches homogeneity, sodium chloride is added to salt out the neat soap from the glycerol-bearing spent lye, and the crude soap is passed through counter-current washing columns and vacuum drying to reduce free alkali and moisture. Compliance for the input substance follows REACH (EC) No 1907/2006 Annex II safety data sheet requirements, while the finished soap falls under EC 648/2004 detergents regulation and total alkali is determined by ISO 685 for soap analysis. Terminal finished product types include soap noodles for personal care extrusion, laundry soap bars, and industrial soap bases. The main batch failure mode is incomplete saponification when the kettle temperature drops below 70°C or when caustic is added faster than the agitator can disperse it; under alkaline splitting conditions, glycerol can darken and the neat soap may hold excess free alkali above specification, requiring additional washing.
In acid neutralization systems, alkalinity demand is established by titration against a target pH setpoint of 7.5–8.5, and 50% NaOH liquid is metered into a forced-flow pipeline using a diaphragm or peristaltic pump with a static mixer and retention tank of 2–5 min to complete neutralisation before discharge; dosing rates for mixed acid waste streams are commonly in the range of 10–500 mg/L, but the actual rate is set by influent strong-acid load and buffering rather than a fixed formulation. For boiler feed conditioning, caustic injection downstream of reverse osmosis displaces carbonate-equilibria, elevates feedwater pH to 8.8–9.2, and reduces free carbon dioxide corrosion in steel economizers and condensate lines. Industrial-grade product applied to wastewater or neutralization is specified under ANSI/AWWA B501-19 for liquid sodium hydroxide handling and storage; if the same network is used for drinking water treatment, the product must meet EN 896:2012 certification requirements, and pH measurement uses ISO 10523:2008 for verifying sensor calibration. Terminal outputs are neutralized industrial effluent discharged under local integrated permit limits, cation/anion demineralizer regenerant neutralization, and dealkalized boiler make-up water. The operational boundary is precipitation: when caustic is overdosed upstream of membrane softening or lime-soda ash clarifiers, calcium carbonate and magnesium hydroxide scale form rapidly, increasing pressure drop across downstream cartridge filters and lowering heat transfer in boiler tube circuits.
Because the chlorination reaction is exothermic, continuous hypochlorite generation demands simultaneous control of alkali strength, temperature, and gas-liquid contact to avoid decomposition into chlorate instead of sodium hypochlorite. Caustic soda is charged at 20–32 wt% NaOH into a recirculating loop with an eductor, packed tower, or falling-film reactor; chlorine gas is sparged under vacuum or low pressure, and the heat of reaction is removed through a titanium or PVDF plate-and-frame heat exchanger to keep the reaction liquor below 30°C, with excursions above 35°C strongly accelerating chlorate formation. Stoichiometric consumption is 1.07 t NaOH per tonne NaOCl; industrial production maintains 2–5 g/L excess NaOH in the final product to suppress decomposition, resulting in a clear sodium hypochlorite solution of 10–15% available chlorine depending on market specification. Product for drinking water disinfection is assessed under EN 901:2013, and the substance itself remains within REACH (EC) No 1907/2006 registration obligations. Terminal output types are bulk sodium hypochlorite for municipal water treatment, industrial sanitizer for food contact surfaces, and intermediate bleach for textile finishing or wastewater disinfection. The critical operating conflict occurs when localized pH falls below 10 in the gas-liquid contact zone; chlorine gas can bypass reaction as the sodium hydroxide feed is depleted, leading to off-gas release and rapid decomposition of the hypochlorite product.
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Industrial Grade Caustic Soda | Leading Caustic Soda Manufacturer & Chinese Supplier is supplied as a high-assay sodium hydroxide product in solid flake, solid pearl, solid 98%, liquid 50%, and liquid 32% forms. The product is sodium hydroxide, CAS 1310-73-2, with transport classification UN 1823 for solid material and UN 1824 for solution. Solid material is packaged in 25 kg woven bags with HDPE inner liners; bulk liquid is moved in ISO tank containers or 1000 L IBCs. Specification data are generated under GB/T 209-2018 for industrial sodium hydroxide. Assays are performed by GB/T 4348.1-2018 for sodium hydroxide content, GB/T 4348.2-2018 for carbonate, GB/T 4348.3-2018 for chloride, and GB/T 4348.4-2018 for iron. The harmonised system codes are 28151100 for solid sodium hydroxide and 28151200 for aqueous solution. Industrial-grade material is not intended for direct food contact or reagent-grade use; food-contact applications require an appropriate FCC or regional food-additive specification such as 21 CFR 184.1763.
| Form | NaOH content | Na₂CO₃ maximum | NaCl maximum | Fe₂O₃ maximum |
|---|---|---|---|---|
| Flake-99 | 99.0% minimum | 0.5% | 0.03% | 0.002% |
| Pearl-99 | 99.0% minimum | 0.5% | 0.03% | 0.002% |
| Solid-98 | 98.0% minimum | 0.8% | 0.05% | 0.005% |
| Liquid-50 | 50.0% ± 0.5% | 0.1% | 0.005% | 0.0005% |
The values above reflect typical membrane-cell production from a Chinese integrated chlor-alkali platform. Diaphragm-cell material may carry higher chloride because the separator is less selective than an ion-exchange membrane. In stainless-steel downstream systems such as textile mercerising frames, membrane-cell flake with chloride at or below 0.03% is specified to reduce pitting corrosion.
The manufacturing route influences impurity profile more than the physical form. Membrane-cell production begins with saturated brine purification using precipitation and ion-exchange softening to reduce calcium and magnesium below 10 μg L⁻¹. Electrolysis in an ion-exchange membrane cell produces 30–35% NaOH with low chloride. Diaphragm-cell liquor contains higher chloride and chlorate; later evaporation and settling do not reduce chloride to membrane-cell levels. The product is therefore supplied for chloride-sensitive downstream lines in rayon, engineering thermoplastics, and sodium hypochlorite production.
Purity is limited by ion-exchange membrane selectivity, evaporation train metallurgy, and post-drying exposure to carbon dioxide and moisture. Membrane electrolysis of saturated brine produces catholyte containing 30–35% NaOH; vacuum evaporation in nickel-based forced-circulation or falling-film evaporators concentrates the material to 50% and then to molten 98–99% solid feed for flaking. Chloride migration rises with aged membranes, low anolyte pH, and high current density; producers monitor cell voltage and anolyte chlorate concentration. Carbonate is not only a raw-material impurity but also accumulates when solid caustic is stored in unsealed bags at relative humidity above 60%. Iron enters from carbon-steel handling if the protective nickel or polymer lining is damaged in high-temperature zones. For chloride-sensitive applications, the specification ceiling is 0.03% NaCl in solid flake and 0.005% NaCl in 50% liquid.
On production-scale flaking units, molten caustic is distributed over water-cooled drum surfaces; flake thickness, scraper blade temperature, and conveying air dew point determine dust fraction and caking tendency. If conveying air dew point is not maintained below -15 °C, surface moisture creates a liquid film that subsequently carbonates and bonds particles. Closed-loop hoppers with dried-air purges and batch bagging under sealed conditions are used to limit this.
Flake-99 is produced by cooling molten caustic on a rotating flaker drum; pearl-99 is formed by prilling or granulation, resulting in a more free-flowing geometry with lower caking tendency under humid conditions. Liquid 50% is stored and shipped as the standard bulk product; its crystallisation point is approximately 12 °C, so uninsulated tanks in colder terminals are heat-traced. Liquid 32% is used mainly for integrated site transfer to effluent neutralisation because it has a lower NaOH mass per cubic metre and higher transport cost per dry tonne. The product form is selected by receiving system design: liquids require centrifugal pumps with PTFE or EPDM seals and carbon-steel tanks with stress-relieved welds for ambient 50% service; solids require screw feeders, hoppers, and dust collection.
In Bayer-process alumina refineries, the liquid 50% product is metered into digestion liquor to maintain free hydroxide concentration. Digestion occurs at 150–250 °C under saturated steam pressure, and the effective NaOH level is monitored through the molar ratio of Na₂O to Al₂O₃ in the pregnant liquor. Typical digestion molar ratios range from 1.3 to 1.8, depending on bauxite mineralogy and reactive silica. If the ratio falls below the target range, dissolved alumina species can hydrolyse and precipitate prematurely in flash tanks and thin-film spent-liquor evaporators, causing scale and production interruption. Silicon introduced with industrial caustic can contribute to desilication product and heat-exchanger scale; low-silica specifications are therefore requested for some refinery supply contracts. Published data for a single universal caustic consumption rate is limited because the charge is set by bauxite alumina content, reactive silica, liquor inventory, and evaporation capacity.
For kraft pulp cooking, caustic soda is added to white-liquor make-up and oxidative extraction stages. It supplies direct hydroxide alkalinity, unlike sodium carbonate, which must first be converted by lime slaking in the recausticising loop. The effective alkali charge is expressed as Na₂O equivalents per oven-dry tonne of wood, typically in the range 15–25% on wood mass. In textile mercerising, solid flake caustic is dissolved to 18–25% NaOH and applied at 15–20 °C under tension to convert cellulose I to cellulose II. Low chloride and low iron grades are selected because ferric iron precipitates on fabric surfaces and chloride can accelerate pitting of stainless-steel chains and clips. In soap and surfactant saponification, the stoichiometric NaOH charge is based on the saponification value of the triglyceride feed; a production excess of 0.5–1.0% by mass relative to stoichiometric demand is commonly maintained to drive glyceride splitting to completion, followed by brine washing.
In interfacial polycarbonate synthesis and epoxy resin manufacture, caustic is used as a condensation catalyst or scrubber alkali; low iron and chloride are monitored because chloride can affect catalyst stability and product colour. In sodium hypochlorite generation, chlorinated gas is contacted with 32% or 50% caustic under cooling, and excess caustic is maintained at 0.2–1.0% to stabilise the product. In demineraliser regeneration, 4% NaOH solution is used for anion-exchange resin regeneration. These applications use industrial-grade material but require controlled chloride and iron for equipment service life.
In wastewater acid neutralisation and flue-gas desulphurisation, caustic soda is selected over sodium carbonate or hydrated lime when rapid pH response and low sludge mass are required. The neutralising equivalent of NaOH is 40.00 g eq⁻¹, compared with 53.00 g eq⁻¹ for Na₂CO₃ and 37.05 g eq⁻¹ for Ca(OH)₂. At 20 °C, NaOH solubility is approximately 1090 g L⁻¹, whereas Ca(OH)₂ solubility is approximately 1.7 g L⁻¹; caustic soda dosing therefore eliminates lime slaking and slurry handling. The pH response curve is steep with a strong base, so metering pumps are controlled with set-point dead bands of ±0.2 pH units. In flue-gas desulphurisation, caustic soda initially reacts with SO₂ to form sodium sulfite and sodium sulfate, but continued caustic addition drives pH above 9 and increases CO₂ absorption to form carbonate, which may reduce acid-neutralising capacity per dry tonne. The dosing point and pH set point are therefore matched to the scrubber liquor residence time and oxidation air supply.
| Reagent | Equivalent mass | Neutralising capacity | Solubility in water at 20 °C |
|---|---|---|---|
| Sodium hydroxide, NaOH | 40.00 g eq⁻¹ | 25.00 eq kg⁻¹ | 1090 g L⁻¹ |
| Potassium hydroxide, KOH | 56.11 g eq⁻¹ | 17.82 eq kg⁻¹ | 1120 g L⁻¹ |
| Sodium carbonate, Na₂CO₃ | 53.00 g eq⁻¹ | 18.87 eq kg⁻¹ | 215 g L⁻¹ |
| Calcium hydroxide, Ca(OH)₂ | 37.05 g eq⁻¹ | 26.99 eq kg⁻¹ | 1.7 g L⁻¹ |
Industrial-grade caustic soda differs from reagent-grade and food-grade material primarily in controlled impurity profile, packaging, and documentation. ACS reagent-grade sodium hydroxide is specified with lower trace-metal ceilings and is supplied in smaller analytical packages, not in bulk flake or tanker quantities. Food-grade sodium hydroxide is controlled under 21 CFR 184.1763, FCC monograph, or EU E 524, with limits relevant to food processing such as peeling, pH adjustment, and olive curing. Industrial-grade caustic soda may contain trace carbonates and chloride that are acceptable in alumina, pulp, and neutralisation but are not appropriate for direct food contact without additional purification and certification. Similarly, industrial caustic soda differs from potassium hydroxide in cation identity and neutralising equivalent; KOH is used where potassium ion is desired, such as in certain liquid soaps and drilling fluids, but its equivalent mass is 56.11 g eq⁻¹ versus 40.00 g eq⁻¹ for NaOH.
For solid flake and pearl, closed storage below 60% relative humidity is required to control caking and carbonate film formation. Bulk silos are equipped with dried-air purges and bag filters; screw conveyors and rotary valves are specified for abrasive and hygroscopic solids. Liquid 50% sodium hydroxide should be maintained above its approximate 12 °C crystallisation point; below this temperature, the solution thickens, and crystals deposit at tank bottoms, plugging withdrawal lines. Dissolution is strongly exothermic, with heat of solution approximately -44.5 kJ mol⁻¹. When preparing 20% working solutions from solid flake, the temperature rise can exceed 60 °C; batch tanks should be constructed of heat-shock-resistant materials and equipped with slow-speed agitation. The product is incompatible with aluminium, zinc, tin, magnesium, and concentrated acids. Contact with amphoteric metals generates hydrogen, and corrosion of carbon steel at high temperature or with 73% caustic is controlled only if stress-relieved welded tanks and nickel alloy heat-transfer surfaces are used. Gaskets, pump seals, and hoses are specified in PTFE, EPDM, or CSM rated for hot caustic service above 80 °C.
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