| HS Code | 949138 |
| Chemical Name | Sodium hydroxide |
| Formula | NaOH |
| Cas Number | 1310-73-2 |
| Molecular Weight | 40.00 g/mol |
| Appearance | White solid flakes, pearls, or granules |
| Purity | 99% min |
| Melting Point | 318 °C |
| Boiling Point | 1388 °C |
| Density | 2.13 g/cm3 at 25 °C |
| Solubility In Water | 1110 g/L at 20 °C |
| Ph Of 1 Percent Solution | 13.5 |
| Hygroscopicity | Highly hygroscopic |
As an accredited Caustic Soda Solid | China Sodium Hydroxide Manufacturer factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25kg double-layer PP woven bags, moisture-proof lined, 24 metric tons per 20ft container, for solid caustic soda. |
| Container Loading (20′ FCL) | 20′ FCL container loading of Caustic Soda Solid: bagged, palletized, secured, with proper moisture protection and labeling for safe transport. |
| Shipping | Caustic soda solid is shipped in 25kg PP woven bags with PE liners, packed in 20ft containers, about 25 MT per load. Ensure moisture-proof storage, proper labeling, and compliance with hazardous cargo regulations. Reliable export logistics ensure safe, timely delivery worldwide from China. |
| Storage | Store caustic soda solid in a cool, dry, well-ventilated warehouse, away from moisture, acids, and incompatible chemicals. Keep containers tightly sealed and protected from physical damage. Use dry, clean, non-metal packaging—typically polyethylene-lined bags or drums—elevated on pallets to prevent water contact. Avoid aluminum, zinc, or tin containers. Ensure proper labeling and immediate spill containment procedures. |
| Shelf Life | Shelf life is approximately 2 years when stored sealed, dry, and protected from moisture and air. |
The dissolution of bauxite in circulating sodium aluminate liquor represents the primary global volume driver for solid caustic soda. In the Bayer circuit, ground and pre-desilicated bauxite is contacted with a hot, concentrated NaOH solution under controlled temperature-pressure profiles to selectively extract alumina as sodium aluminate, leaving behind insoluble iron oxides, titanium compounds, and silica residues. The caustic consumption per tonne of calcined alumina is not a fixed stoichiometric value but varies sharply with the mineralogical composition of the bauxite—gibbsitic ores require substantially less free NaOH than diasporic ores—and with the extent of reactive silica that sequesters sodium into desilication products. Operational compliance for alumina refineries is defined by the European Commission BAT Reference Document for the Non-Ferrous Metals Industries (2017) concerning spent liquor containment, caustic recovery via multiple-effect evaporation, and red mud disposal protocols compliant with national environmental discharge limits and, where applicable, the ISO 14001:2015 environmental management framework. Typical caustic dosage, expressed as 100% NaOH equivalent, ranges from 0.065 tonnes per tonne of alumina for high-grade tropical gibbsite to 0.100 tonnes or higher for Chinese domestic diasporic bauxites processed in high-pressure tube digesters. The process downstream involves a series of horizontal autoclaves or single-stream tube digestion units operating under turbulence to minimize scale formation, with residence times controlled between 20 and 60 minutes; post-digestion, the slurry is flash-cooled across multiple stages, sand and red mud are separated in thickeners and high-rate decanters, and the aluminate liquor is seeded with fine trihydrate crystals in the precipitation chain. The terminal product is smelter-grade alumina (SGA) with a -45 µm fraction typically above 95%, loss on ignition below 0.9%, and alpha-alumina content engineered to balance dissolution in molten cryolite for the Hall-Héroult process.
| Bauxite Mineralogy | Digestion Temperature Range | NaOH Concentration in Liquor (g/L Na₂O) | Autoclave Pressure Range (MPa) |
|---|---|---|---|
| Gibbsitic (trihydrate) | 105–150°C | 100–150 | atmospheric–0.5 |
| Boehmitic (monohydrate) | 200–240°C | 180–220 | 1.5–3.5 |
| Diasporic (monohydrate, high hardness) | 240–260°C | 200–300 | 3.5–4.8 |
Control of effective alkali (EA) charge in the kraft cook is dictated by wood species anatomy, chip thickness distribution, and the target kappa number. Sulfidity—the ratio of Na₂S to active alkali expressed as Na₂O—is held in a narrow window to accelerate delignification while preserving polysaccharide integrity; a deviation of even 1–1.5 sulfidity points can shift the H-factor trajectory and produce screenable rejects. The solid caustic soda is integrated into the white liquor preparation circuit, where it is dissolved together with recycled smelt to reconstitute the cooking liquor. Industrial compliance for bleachable-grade kraft pulp is governed by the Integrated Pollution Prevention and Control (IPPC) BREF for Pulp and Paper, mandating strict management of non-condensable gases, chemical recovery boiler emissions, and effluent adsorbable organic halides (AOX) under EU Directive 2010/75/EU. In a continuous Kamyr digester producing northern bleached softwood pulp, the EA charge is typically set between 18 and 22% Na₂O on oven-dry wood, while for short-fiber eucalyptus the EA demand drops to 15–18%. The downstream process involves pre-steaming the chips, impregnation with hot black and white liquor in a co-current zone, then counter-current cooking at a peak temperature of 168–175°C, followed by in-line blow tank discharge where fiber separation is initiated. The pulp is then screened, oxygen-delignified, and bleached in a sequence such as D0-EOP-D1. The terminal product is fully bleached softwood or hardwood market pulp bales with ISO brightness >89%, stored as sheets with 10% moisture for paper, tissue, and board conversion.
| Wood Source | Effective Alkali (% Na₂O on dry wood) | Sulfidity (% Na₂O basis) | Typical H-Factor Range |
|---|---|---|---|
| Scandinavian Scots Pine | 18–22 | 30–35 | 1200–1700 |
| Brazilian Eucalyptus grandis | 15–18 | 25–30 | 600–1000 |
| Nordic Silver Birch | 16–20 | 25–32 | 500–800 |
Mercerization of cotton yarn and fabric under tension relies on the controlled swelling of the cellulose fiber in concentrated caustic soda below 20°C, which irreversibly converts the cellulose I lattice to cellulose II, increasing dye affinity, lustre, and dimensional stability. The lye strength is monitored continuously by density and refractive index; a concentration window of 220–300 g/L NaOH is maintained, with the lower end used for lightweight scoured knits and the upper end for heavy woven drills intended for vat-dyed uniform products. Process water hardness must be negligible—calcium and magnesium precipitates foul the squeeze rolls and create uneven alkali add-on that manifests as warp-direction dyeing streaks. Compliance for mercerized cotton goods destined for OEKO-TEX Standard 100 Annex 4 certification requires residual surface alkali to be below detectable limits after souring in acetic acid baths, and the entire wet-processing line must align with the ZDHC Manufacturing Restricted Substances List for effluent discharge, particularly ensuring that neutralized waste lye is recovered through multiple-effect evaporators operating at 5–7 bar steam pressure rather than discharged to drain. The fabric enters the mercerizing range via a J-box or accumulator, passes through a series of heavy nip rollers submerged in chilled caustic liquor for an optimum dwell of 45–70 seconds, is stretched widthways on a tenter frame under controlled tension corresponding to 3–5% overfeed depending on construction, and is then stabilized in a hot wash cascade. Terminal products include mercerized single-ply yarn on cheese for circular knitting, high-thread-count mercerized sheeting, and stabilized interlinings with residual shrinkage below 1.5% per ISO 6330:2012 washing protocols.
Saponification of triglycerides with sodium hydroxide follows a biphasic reaction sequence in which the rate-limiting step is the interfacial contact between the aqueous alkali phase and the molten fatty charge. In a full-boiled kettle operation, a 30–38 wt% NaOH solution is metered into the fat blend—typically a mixture of tallow and coconut oil—at a stoichiometric excess of 2–5% over the calculated saponification value to ensure complete splitting, after which the neat soap is agitated and boiled with salt brine to effect graining-out of the soap curd from the glycerine-rich spent lye. Over-saponification must be carefully avoided, because residual free alkali exceeding 0.05% in the dry soap destabilizes the waxy beta-phase polymorph during milling and causes skin irritation failures under the Draize test criteria embedded in EU Cosmetic Regulation EC 1223/2009. Compliance is demonstrated analytically through the free caustic alkali method of ISO 456:1973 and surfactant biodegradability testing per EU 648/2004 Annexes. The downstream process proceeds from neat soap through a vacuum spray drying tower to achieve moisture reduction to 9–13%, followed by amalgamation, roll milling over chilled drums, and continuous plodding into billets that are cut and pressed. Finished goods encompass framed laundry bars containing sodium stearate as the primary active, cosmetic toilet soaps with superfatting agents, and industrial soap noodles shipped in bulk to detergent formulators for blending with syndets.
In the chlorohydrin route to propylene oxide, aqueous NaOH serves as the dehydrochlorinating agent converting propylene chlorohydrin to the epoxide in a steam-stripping column where pH and residence time govern both yield and the formation of the major by-product, propylene glycol. The caustic soda is dissolved to a working concentration of approximately 10–12% w/w NaOH and dosed into the midpoint of the saponifier such that the effluent brine maintains a pH floor of 12.3–12.6, suppressing ring-opening hydrolysis but sufficiently basic to push the reaction to completion within a vapor-liquid contact time of less than 90 seconds. Process safety falls under the scope of the Seveso III Directive (2012/18/EU) for installations handling chlorine and flammable epoxides; product specification is aligned with ASTM D6865-17 for propylene oxide purity and aldehyde content. Material consumption approaches 1.10–1.25 tonnes NaOH (100% basis) per tonne of propylene oxide, substantially influenced by the extent of propylene dichloride formation in the preceding hypochlorination step and by the efficiency of the soda ash or lime supplementation used to recover caustic from the calcium chloride-rich effluent when a combined lime-soda process is employed. The unit operation integrates the saponifier tower, a partial condenser operating at 75–80°C overhead, and a rectification column where crude propylene oxide is separated from water and light ends. The terminal product is propylene oxide with a minimum purity of 99.95%, destined for polyether polyol production for flexible polyurethane slabstock foam and rigid insulation panels.
Drilling fluid systems designed for high-temperature, high-pressure (HTHP) horizons and those encountering carbon dioxide and anhydrite influx require precise alkalinity control to stabilize the rheological profile of bentonite suspensions and to mitigate hydrogen ion interference with organic thinners. Solid caustic soda is introduced directly into the active mud system through a chemical mixing hopper or jet eductor at a rate of 0.5 to 2.0 lb/bbl (1.4–5.7 kg/m³), adjusted continuously in response to Pf (phenolphthalein end-point) and Pm (methyl orange end-point) filtrate alkalinity measurements as defined by API 13B-1 for water-based fluids. Compliance with API 13A Section 9 and the ISO 13500:2008 specification for barite-laden fluids dictates that the excess lime or gypsum content in the mud must be balanced without inducing clay flocculation that would elevate yield point above 25 lb/100 ft² and compromise equivalent circulating density management. The material is added in micro-dose sacks through a high-shear mud hopper upstream of the shale shakers; localized pH spikes near the dosing point are mitigated by a premixing tank with a retention volume equivalent to 15–20 minutes of rig circulation rate. The terminal fluid is a dispersed lignosulfonate or polyanionic cellulose water-based mud with stable properties at bottomhole static temperatures up to 150°C, designed for horizontal and extended-reach sections where cement contamination or acid gas influx would otherwise degrade filter cake quality and cause differential sticking.
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Caustic Soda Solid, produced as anhydrous sodium hydroxide in flake, pearl, or cast block morphology, constitutes a core inorganic commodity with annual global production surpassing 80 million tonnes. Manufactured in the People’s Republic of China under the nationally codified standard GB/T 209-2018, industrial-grade solid NaOH delivers a minimum 99.0% assay with tightly bounded impurities of sodium carbonate (Na₂CO₃), sodium chloride (NaCl), and iron oxide (Fe₂O₃). Unlike the widely distributed 50% liquid caustic soda solution, the solid form eliminates the freight burden of water and circumvents the 12°C freezing point that complicates liquid storage in unheated tanks, establishing it as the alkali of choice for transcontinental supply chains, cold-climate job sites, and processes requiring precisely metered anhydrous alkalinity. The following sections examine product specification tiers, logistical differentiation, and insertion points across high-tonnage industrial applications.
Liquid caustic soda at 50% concentration carries an effective net weight of 1.0 tonne of NaOH per 2.0 tonnes of shipped solution, whereas solid flake with a bulk density of 1.1–1.3 g/cm³ delivers near-unit efficiency, lowering ocean freight mass by approximately 45–50% for equivalent delivered alkalinity. Freezing of the liquid form at temperatures below 12°C mandates insulated tank containers and recirculation heating loops, adding capital and energy costs not required for solid flake stored in ambient warehouses at relative humidity below 40%. Solid material also permits concentration flexibility at the point of use: make-down systems dissolve the anhydrous pellets or flakes in water to generate solutions from 5% to 50% by mass, whereas liquid deliveries are fixed at the nominal strength dictated by chlor-alkali membrane cell product specifications. The dissolution exotherm (ΔHsol ≈ −44.5 kJ/mol) requires controlled addition into agitated, jacketed vessels, particularly where final solution temperature must remain below the boiling point to avoid caustic aerosol release. These combined logistical and operational factors drive adoption at remote bauxite refineries, pulp mills lacking liquid terminal infrastructure, and export destinations in northern Europe or Central Asia.
| Parameter | Superior Grade IL | First Grade IL | Qualified Grade IL | Test Method |
|---|---|---|---|---|
| NaOH, % (m/m) ≥ | 99.0 | 98.5 | 98.0 | GB/T 4348.1-2013 |
| Na₂CO₃, % (m/m) ≤ | 0.5 | 0.8 | 1.0 | GB/T 7698-2014 |
| NaCl, % (m/m) ≤ | 0.03 | 0.05 | 0.08 | GB/T 4348.2-2014 |
| Fe₂O₃, % (m/m) ≤ | 0.005 | 0.008 | 0.01 | GB/T 4348.3-2012 |
Membrane-cell grades, distinguishable from diaphragm-cell products by significantly lower chloride content, routinely achieve NaCl ≤ 0.005% and iron ≤ 3 ppm. These low-residual specifications are critical for viscose fiber production, electronic-grade cleaning chemistries, and applications where transition metal carry-over accelerates oxidative degradation of organic substrates. Chinese producers typically supply solid forms sized for specific dissolution kinetics: flake (0.5–5.0 mm) for medium-rate make-down and pearl (0.3–1.5 mm) for high-speed automated dosing systems.
When selecting an alkali for a greenfield process plant or retrofitting an existing chemical feed system, the choice among solid NaOH, 50% liquid NaOH, and sodium carbonate (soda ash) hinges on freight structure, storage infrastructure, and process compatibility. The following table collapses the primary selection factors.
| Parameter | Solid NaOH (Flake/Pearl) | 50% Liquid NaOH | Soda Ash (Na₂CO₃) |
|---|---|---|---|
| Available alkalinity as Na₂O, % | 76.7 | 38.7 | 58.5 (after causticizing) |
| Freezing point | Not applicable (solid) | ≈ 12°C | Not applicable |
| Mass shipped per 1.0 tonne NaOH equivalent | ≈ 1.01 tonne | 2.0 tonnes | 1.58 tonnes |
| Heat of dissolution/causticizing, kJ/mol | −44.5 (exothermic) | Negligible | +28.1 (endothermic) |
| UN transport classification | UN 1823, Class 8, PG II | UN 1824, Class 8, PG II/III | Not regulated |
| Preferred application driver | Remote sites, cold climates, batch make-down | Adjacent to chlor-alkali plant, continuous feed | Glass manufacture, where hydroxide-free sodium is required |
Alumina refining via the Bayer process consumes roughly 55% of global caustic soda volume. In high-temperature tube digesters operating at 240–270°C and pressures exceeding 30 bar, bauxite is leached with a recycled sodium aluminate liquor containing 150–250 g/L Na₂O caustic. Chemical losses of 60–100 kg NaOH per tonne of alumina produced, caused by desilication product formation (sodalite and cancrinite), are replenished by feeding solid caustic soda through dedicated dissolvers into the spent liquor stream before re-heating. The direct addition of anhydrous NaOH bypasses the energy-intensive lime causticization step that would be required if sodium carbonate were used, eliminating process CO₂ emissions at the refinery. Low-carbonate solid feedstock (Na₂CO₃ ≤ 0.5%) is critical: carbonate anions increase lime consumption in desilication and promote scaling on tube walls, reducing heat transfer coefficients by as much as 30% over a 90-day campaign. Chinese membrane-grade solid NaOH with Fe₂O₃ ≤ 0.005% supports the production of smelter-grade alumina in which total iron must remain below 0.015% to preserve the electrical conductivity of the subsequent aluminum metal.
In sulfate pulping, white liquor composed of NaOH and Na₂S is regenerated in the recausticizing loop, yet continuous sodium losses from pulp washing, black liquor spills, and chemical recovery boiler electrostatic precipitator ash necessitate a makeup stream. Solid caustic soda flake is dissolved in mill water and fed directly to the white liquor storage tank or the digester extraction screens at a rate of 15–35 kg NaOH per air-dried metric ton of unbleached pulp, depending on chip species and kappa target. The advantage over soda ash makeup lies in the immediate availability of hydroxide ion without requiring additional lime kiln capacity for conversion. Soda ash addition would raise the deadload of sodium carbonate in the liquor cycle, consuming slaking and causticizing plant throughput. However, solid flake storage demands sealed silos with dehumidified air purge to maintain a dew point below −40°C; at 50% relative humidity, surface hydration initiates within 30 minutes, leading to agglomerate formation that bridges gravimetric screw feeders. Chinese suppliers offer low-chloride solid grades (NaCl ≤ 0.03%) to mitigate alkaline stress corrosion cracking of mild steel liquor tanks, a failure mode extensively documented when chloride ion concentration in white liquor exceeds 5 g/L.
Manufacture of viscose rayon requires mercerization of dissolving pulp with 18–22% NaOH solution to generate alkali cellulose, followed by xanthation and spinning. Chloride ion contamination profoundly affects the ripening kinetics of viscose dope; sodium chloride levels exceeding 0.05% in the dissolving NaOH can retard depolymerization, increase filter plugging values measured per the clogging constant Kw method, and necessitate spin bath adjustments that compromise filament tenacity. Diaphragm-cell caustic soda commonly retains NaCl at 0.5–1.0%, rendering it unsuitable for modern high-tenacity staple lines. In contrast, Chinese-manufactured membrane-cell solid NaOH with NaCl ≤ 0.005% and iron ≤ 3 ppm provides a chloride-poor feedstock that eliminates chromophore formation responsible for yellowing in the finished fiber. Mill qualification protocols for such grades frequently require a certificate of analysis demonstrating compliance with the textile auxiliaries criteria of OEKO-TEX® Standard 100, a documentation package routinely furnished by China’s larger chlor-alkali exporters.
Industrial water and wastewater pH correction presents a direct substitution case versus hydrated lime or soda ash. The addition of 1.0 kg of solid NaOH delivers 1.00 equivalent alkalinity without producing the calcium carbonate sludge characteristic of lime treatment—a byproduct generated at 0.8–1.2 kg dry solids per kg of CaO equivalent, requiring thickeners and filter presses. In a once-through cooling circuit handling 10,000 m³/h, raising pH from 6.5 to 8.0 with solid caustic soda demands approximately 2,000 kg/h of flake dissolved into a side stream, eliminating the polymer flocculant and dewatering costs embedded in lime systems. The exothermic dissolution, however, can cause localized boiling at the point of addition if make-down water volume is under-designed. Industry practice dictates a dilution to 10–15% NaOH in an agitated, 316L stainless steel tank before injection, keeping the adiabatic temperature rise below 40°C and preventing atmospheric caustic mist formation that would violate the ACGIH TLV-C of 2 mg/m³.
Solid NaOH serves as the stoichiometric base in the preparation of sodium phenolate from phenol, a key precursor for salicylic acid and diphenyl ether herbicides. The anhydrous nature of flake or pearl feedstock avoids water introduction that would shift the phenol‑phenolate equilibrium and reduce conversion. In the neutralization of linear alkylbenzene sulfonic acid (LABSA) to produce detergent-grade sodium alkylbenzene sulfonate, solid caustic is metered into a high-shear loop reactor to maintain a pH endpoint of 7.0–8.0 while restricting water input to the stoichiometric minimum. Excess water elevates the paste viscosity above the pumpable limit of 100,000 cP at 25°C, causing packaging line stoppages. A solid feedstock with Na₂CO₃ ≤ 0.5% limits carbon dioxide entrainment in the neutralization off-gas, a consideration relevant to OSHA 29 CFR 1910.1000 compliance in enclosed processing areas.
Deliquescence of solid NaOH initiates at relative humidity levels as low as 30–35% at 25°C; unsealed bags undergo weight gain exceeding 5% within 48 hours, accompanied by severe caking that renders the product un-meterable. Bulk silos equipped with desiccant dryers must deliver sweep air at a pressure dew point of −40°C or lower. Materials of construction for storage and dissolution are restricted: post-weld stress-relieved carbon steel is acceptable for concentration up to 50% at temperatures below 50°C, whereas 316L stainless steel is required for elevated processing temperatures or where iron leaching cannot be tolerated. Aluminum, zinc, tin, and galvanized coatings are chemically incompatible due to rapid hydrogen evolution. Solid caustic soda exported from China is packaged in UN-certified FIBCs with inner polyethylene liners and palletized to meet IMDG Code Class 8, PG II provisions, with full documentation including a Safety Data Sheet compliant with GHS Revision 8 and a REACH registration number for shipments entering the European Economic Area.
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