| HS Code | 335637 |
| Product Name | China National Salt Industry Group Caustic Soda |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Molecular Weight | 40.00 g/mol |
| Appearance | White flakes or pearls |
| Purity | 99% min |
| Grade | Industrial grade |
| Packaging | 25 kg PP woven bag |
| Solubility | Readily soluble in water |
| Melting Point | 318°C |
| Boiling Point | 1388°C |
| Density | 2.13 g/cm³ at 25°C |
| Ph | 13-14 (1% aqueous solution) |
| Hazard Class | 8 - Corrosive substance |
As an accredited China National Salt Industry Group Caustic Soda factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25kg net weight in multilayer woven bags with PE liner, sealed and labeled, ensuring dry, safe transport and storage. |
| Container Loading (20′ FCL) | 20′ FCL container loading of caustic soda from China National Salt Industry Group, ensuring secure, safe packaging and proper ventilation. |
| Shipping | Caustic soda from China National Salt Industry Group ships as solid flakes/pearls or liquid solution. It requires corrosion-resistant packaging, moisture-proof sealing, and proper hazardous material labeling. Transport must follow UN 1823 (solid) or UN 1824 (solution) regulations, ensuring segregation from acids and adequate ventilation to prevent dangerous reactions. |
| Storage | Store China National Salt Industry Group Caustic Soda in a cool, dry, well-ventilated area away from moisture, acids, and incompatible materials. Keep containers tightly sealed and clearly labeled. Use corrosion-resistant flooring and secondary containment to prevent leaks. Ensure proper PPE during handling and maintain easy access to emergency wash equipment. |
| Shelf Life | Shelf life is indefinite when stored sealed in a dry, cool area, away from moisture and air. |
In alumina refineries processing gibbsitic bauxite, 50 wt% membrane-grade liquid caustic soda supplied by China National Salt Industry Group is metered into predesilication tanks after density correction to 1.525 g/cm³ at 20 °C. Supplied liquor meets GB/T 209-2018 for membrane-grade industrial sodium hydroxide; typical sodium chloride is below 50 mg/kg and iron oxide below 5 mg/kg. The Bayer liquor charge is controlled to 180–240 g/L Na₂O, with a molar Al₂O₃-to-caustic ratio of 0.62–0.74 and a liquor-to-bauxite ratio of 3.5:1 to 5.5:1. Digestion of gibbsitic ore proceeds at 140–150 °C and 0.35–0.50 MPa in double-pipe or agitated autoclaves; boehmitic bauxite requires 200–230 °C, and diasporic ore demands 240–270 °C with 5.0–6.0 MPa. Caustic soda consumption typically ranges from 0.06 t to 0.12 t per tonne of smelter-grade alumina, depending on reactive silica and carbonate content. Reactive silica in bauxite consumes NaOH to form desilication products with a SiO₂-to-Al₂O₃ mass ratio near 0.32; crystallisation in continuous stirred-tank desilication units is held at 90–100 °C for 4–8 h to achieve a silica-to-alumina ratio below 0.02 in the liquor. Red mud separation uses high-rate thickeners with 0.5–2.0 m/h overflow rise rate and polyacrylamide flocculant at 30–80 g/t. Membrane-grade supply is specified because diaphragm-cell residual NaCl above 0.5 wt% raises liquor density and accelerates caustic embrittlement of carbon steel piping. Operational limits include preheating of 50 wt% caustic storage tanks to 20–25 °C to avoid crystallisation near 12 °C, and exclusion of mercury-cell caustic where refinery wastewater discharge is regulated. Final product is smelter-grade alumina with α-Al₂O₃ content above 98.5 wt% and controlled loss on ignition below 1.0 wt% for Hall-Héroult cell feeding.
Kraft white liquor make-up in softwood pulp mills is controlled through effective alkali charge measured as Na₂O equivalent. Membrane-grade 50 wt% liquid caustic soda from China National Salt Industry Group is added downstream of the causticizer to reach 16–20% effective alkali on oven-dry wood. White liquor total titratable alkali is held at 100–120 g/L as NaOH, active alkali at 85–110 g/L, and sulfidity at 28–32%. Digester temperature is ramped to 165–170 °C in continuous digesters with 3.5:1 to 4.5:1 liquor-to-wood ratio; H-factor for bleachable softwood grade is 1500–1800. The sodium hydroxide fortifies green liquor after smelt dissolution because recovered smelt contains sodium carbonate that must be converted to sodium hydroxide via lime in the slaker. TAPPI T 624 cm-00 is used to determine oxidised white liquor composition. Residual alkali at the blow valve is maintained above 4 g/L as NaOH to prevent dissolved lignin re-precipitation on fibre. Chloride accumulation above 6 g/L in closed-cycle mills accelerates digester screen corrosion in carbon steel, so low-chloride membrane-grade supply is used. Excessive caustic charge above 20% effective alkali can reduce pulp viscosity and increase black liquor caustic carryover; insufficient charge below 16% produces high kappa number and screen rejects. Final products include bleached softwood kraft pulp, sack kraft paper, white-top linerboard, and dissolving-grade cellulose after acid sulfite pre-treatment.
Mercerizing of carded cotton yarn is carried out with 28–30°Be sodium hydroxide at 15–20 °C under controlled warp tension. China National Salt caustic soda flake or 50 wt% liquid is diluted with recovered alkali. The bath is maintained at 20–24 wt% NaOH to achieve lattice conversion from cellulose I to cellulose II; lower concentration at 18°Be produces only partial swelling and non-uniform dye uptake. Tension control at 3–5% stretch is applied through a series of clip or roller mercerisers. Wetting agent addition of sulfonated fatty alcohol at 2–5 g/L lowers contact angle to below 30° and prevents alkali spotting. After steeping, the fabric passes through hot water recovery tanks at 60–80 °C, producing weak liquor of 6–8 wt% NaOH. This weak liquor is fed to a triple-effect evaporator with mechanical vapour recompression; if suspended lint exceeds 500 mg/L, tube fouling reduces overall heat transfer coefficient below 600 W/m²·K. The evaporator output is reconcentrated to 30–40 wt% NaOH, then blended with fresh 50 wt% liquor. Sodium chloride above 0.1 wt% in the bath reduces sodium hydroxide activity and raises yellowing after heat treatment. Batch-to-batch variation in recovered alkali sodium carbonate above 1.5 wt% must be purged by lime treatment at 85–90 °C. Final products are mercerised cotton yarn, denim, and woven fabrics with higher tensile strength, improved dye sorption, and reduced shrinkage.
For split palm fatty acid distillate or coconut oil, continuous saponification with 50 wt% sodium hydroxide from China National Salt Industry Group is carried out in a high-shear loop reactor at 80–90 °C. The dosing rate is calculated from the saponification value of the fat; for palm fat with SV 195–205 mg KOH/g, the stoichiometric dry NaOH requirement is 0.139–0.146 kg per kg fat. An excess of 0.02–0.05 wt% free caustic is maintained at the reactor outlet to ensure complete saponification. Mixing is performed in a rotor-stator homogenizer with tip speed 12–18 m/s and residence time 15–30 min. Sodium chloride in industrial-grade caustic above 0.5 wt% promotes soap curd formation and creates salt bloom on cut bars after stamping. Therefore membrane-grade liquor with NaCl content below 50 mg/kg is preferred. Temperature lower than 80 °C increases viscosity above 1500 mPa·s, causing vapour lock in the first heat exchanger; temperature above 95 °C accelerates glycerine colour development and oxidative degradation. The finished soap passes through a vacuum spray dryer at 80–85 °C and is milled to produce toilet soap noodles with moisture 8–12 wt% and total fatty matter 76–82 wt%. Final products include laundry bars, toilet soap, and soap noodles for synthetic detergent compounding.
In epichlorohydrin plants using propylene-based chlorohydrin feedstock, calcium-free sodium hydroxide is preferred because calcium salt fouling in dehydrochlorination columns raises reboiler backpressure. Dichloropropanol is mixed with 50 wt% caustic soda from China National Salt in a static mixer, then reactively distilled at 85–100 °C under 0.3–0.6 bar vacuum. The NaOH-to-dichloropropanol molar ratio is held at 1.02:1 to 1.05:1; lower ratios leave unconverted chlorohydrins, higher ratios promote glycidol and glycerol formation. The pH of the aqueous phase at the reactor outlet is maintained at 8.5–9.5. Sodium chloride byproduct is removed in a forced-circulation brine crystallizer; sulfate above 20 mg/kg in the caustic feed forms sodium sulfate scale on the calandria tubes. Epichlorohydrin is distilled to 99.9 wt% purity for epoxy resin synthesis. The use of membrane-grade caustic with sodium carbonate below 0.1 wt% keeps the organic layer free of sodium bicarbonate-derived haze. Caustic feed temperature below 15 °C increases viscosity to more than 70 cP, reducing static mixer mixing intensity. Final product is epichlorohydrin for liquid epoxy resin, epoxy flooring, and structural adhesives in wind turbine rotor blades.
Potable water softening trains maintain a pH of 9.2–9.8 in rapid mix basins using 25 wt% or 50 wt% certified caustic soda. Lime-soda softening combined with NaOH is applied to reduce hardness to 80–120 mg/L as CaCO₃. A dose of 1.0 mg/L as 100 wt% NaOH raises total alkalinity by approximately 1.25 mg/L as CaCO₃. The upper pH boundary is set at 10.2 because calcium carbonate precipitation shifts from settleable floc to scale on distribution pipe walls; the Langelier Saturation Index is maintained at +0.2 to +0.5. pH measurement follows ISO 10523:2008. The product must conform to NSF/ANSI/CAN 60 and AWWA B501-19 for drinking water treatment chemicals. China National Salt membrane-grade caustic soda meets the heavy metal and mercury limits of these standards. pH above 10.5 shifts chloramine speciation and may reduce disinfection contact time efficiency. Final product is finished drinking water with total hardness below 120 mg/L as CaCO₃ and alkalinity 80–140 mg/L to reduce lead and copper corrosion from household plumbing.
Chemical refining of crude soybean oil uses food-grade sodium hydroxide flake dissolved to 12–15°Be, equivalent to 9–11 wt% NaOH. The dosage is indexed to free fatty acid content determined by AOCS Cd 3d-63. For crude soybean oil with FFA 0.5 wt% as oleic acid, the theoretical dry NaOH requirement is 0.71 kg/t oil; at 2.0 wt% FFA, it is 2.84 kg/t oil. Plant practice adds 0.05–0.15 wt% excess caustic to ensure complete neutralisation. Mixing is carried out in a high-shear disc mixer at 70–80 °C for 20–30 min, followed by centrifugation in a disc-stack separator. After neutralisation, the oil is washed with 10–15% hot water at 85–90 °C to reduce soap residues below 50 mg/kg. Food-grade caustic soda must comply with GB 1886.20-2016 and the Food Chemicals Codex monograph; sodium carbonate above 3.0 wt% increases soap viscosity and lowers neutral oil yield. Sodium chloride above 0.3 wt% promotes emulsion in the separator. Final products are degummed and neutralised soybean oil for cooking oil, margarine base stock, and biodiesel feedstock.
| Crude oil FFA (% as oleic acid, AOCS Cd 3d-63) | Dry NaOH dosage (kg/t oil) | Excess NaOH after neutralisation (wt%) | High-shear mixer residence time (min) |
|---|---|---|---|
| 0.5 | 0.71 | 0.05–0.10 | 20–25 |
| 1.0 | 1.42 | 0.05–0.10 | 20–25 |
| 2.0 | 2.84 | 0.05–0.10 | 25–30 |
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China National Salt Industry Group (CNSIG) caustic soda is sodium hydroxide produced by ion-exchange membrane electrolysis of refined brine at integrated chlor-alkali facilities. The product is supplied as solid flake, solid pearl, and 50% liquid, with commercial grade codes aligned to GB/T 209-2018: IS-I, IS-II, IL-I, and IL-II. Solid IS-I material is specified with NaOH content not less than 99.0 wt%, sodium carbonate not more than 0.8 wt%, sodium chloride not more than 0.05 wt%, and iron oxide not more than 0.008 wt%. Solid IS-II permits NaOH at or above 98.0 wt% and sodium chloride at or below 0.08 wt%. The liquid IL-I grade is supplied at 50.0 wt% NaOH with sodium chloride not more than 0.03 wt%. Typical packaging includes 25 kg and 50 kg woven polymer bags with inner polyethylene liners for solid forms, and rubber-lined tank trucks, railcars, or 1 m³ intermediate bulk containers for liquid material.
The production route uses ion-exchange membrane electrolyzers. Feed brine is subjected to hardness removal, sulfate control, and fine filtration before entering the membrane cells. This upstream brine purification reduces multivalent cation carryover and is one factor differentiating membrane-cell caustic soda from diaphragm-cell and mercury-cell output. Sodium chloride content in membrane-cell product is consistently below 0.08 wt%, whereas diaphragm-cell caustic soda can exhibit sodium chloride in the range 1.0-3.0 wt% depending on cell operation. The reduced chloride and chlorate load lowers downstream equipment corrosion and extends catalyst life in chloride-sensitive chemical synthesis.
The distinguishing impurity profile is controlled primarily by chlorate, chloride, iron, and heavy-metal residuals. Diaphragm-cell material typically contains sodium chloride between 1.0 wt% and 3.0 wt%, with sodium chlorate frequently observed near 0.1-0.4 wt%. Mercury-cell caustic soda may show low chloride but can retain trace mercury, making it unacceptable for food, pharmaceutical, or catalytic applications requiring heavy-metal restraint. CNSIG membrane-cell material is specified with NaCl not more than 0.05-0.08 wt% in solid grades and not more than 0.03 wt% in 50% liquid. Iron oxide is held below 0.01 wt% across standard solid grades. These impurity ceilings are significant in rayon spinning, where multivalent cations influence fiber coagulation and tensile strength, and in chlor-alkali downstream catalysis, where chloride can poison supported metal active sites.
| Control parameter | IS-I solid | IS-II solid | IL-I liquid 50% |
|---|---|---|---|
| NaOH | ≥99.0 wt% | ≥98.0 wt% | ≥50.0 wt% |
| Na₂CO₃ | ≤0.8 wt% | ≤1.0 wt% | ≤0.5 wt% |
| NaCl | ≤0.05 wt% | ≤0.08 wt% | ≤0.03 wt% |
| Fe₂O₃ | ≤0.008 wt% | ≤0.01 wt% | ≤0.002 wt% |
Sodium hydroxide content is determined by acid-base titration using standardized hydrochloric acid; chloride is quantified by argentometric or potentiometric titration. Iron is measured by visible spectrophotometry after color development. Certificates of analysis for each production batch report these values along with lot number, production date, and net weight. For applications requiring food-grade caustic soda, the product is also controlled under GB 1886.20-2016 for heavy metals and arsenic. Published data for CNSIG-branded material in specific food-processing configurations is limited; however, the standard impurity ceilings provide a conservative basis for process qualification.
Liquid 50% sodium hydroxide has a density of approximately 1.525 g/cm³ at 20°C and a freezing point near 12°C. Viscosity is approximately 70-100 mPa·s at 20°C and rises sharply below 15°C, producing a narrow operating window for transfer and storage. Storage tanks and circulation lines are commonly heat-traced and insulated to maintain 20-30°C with a control deadband of ±5°C so that both freezing and excessive corrosion are avoided. Carbon steel is acceptable for ambient storage only if post-weld heat treatment reduces residual stress; austenitic stainless steel is not recommended above 60°C in concentrated caustic service because caustic stress corrosion cracking can develop at welds and stress concentrators. For pumping, sealless magnetic-drive pumps with PTFE/PFA wetted ends or air-operated double-diaphragm pumps with PTFE diaphragms are specified to prevent leakage and seal failures caused by intermittent crystallization. Atmospheric carbon dioxide ingress can increase carbonate content by 0.1-0.3 wt% during open storage, producing batch-to-batch carbonate drift observed at dosing skids.
Direct contact with aluminum, zinc, galvanized steel, tin, brass, and bronze is prohibited because caustic soda attacks these materials and generates hydrogen in the case of aluminum. Dilution is strongly exothermic. Solid flake or concentrated liquid must be added slowly to water under mechanical agitation with temperature monitoring to prevent localized boiling. Adding water to solid caustic can produce a highly concentrated hot surface layer and violent ejection; the reverse order is mandatory in operating procedures.
Solid flake and pearl grades are deliquescent and require closed storage below 60% RH. Pearl particle size typically ranges from 0.2-1.5 mm and flake thickness from 0.5-1.5 mm, depending on granulation and flaking equipment settings. Loss-in-weight feeders with stainless steel contact surfaces are used for metering; carbon steel contact surfaces should be avoided for prolonged dry storage because moisture-driven corrosion can contaminate the product with iron. Moisture pickup above 60% RH causes caking, bridging, and erratic screw feeder output. A drying step is required if packaging has been opened for more than 4 h in humid environments. Published data for CNSIG-specific solid handling in automatic feeding systems is limited, but deliquescent behavior of solid sodium hydroxide is well documented in process engineering literature.
In Bayer-process alumina refining, 50% liquid caustic is used to maintain digester liquor in the range 120-250 g/L Na₂O, with digestion temperatures of 140-240°C depending on bauxite mineralogy. Caustic consumption is governed by sodium aluminosilicate desilication product formation. Quartz and kaolinite reactivity, rather than caustic grade alone, typically controls losses. The low chloride specification of membrane-cell material is relevant because chloride accumulation in closed Bayer liquor can increase heat-exchanger corrosion rates. Published field data for CNSIG-specific Bayer operation is limited; the impurity ceiling provided by GB/T 209-2018 is a conservative input for mass-balance models.
In kraft pulp mills, makeup caustic is fed to white liquor to maintain effective alkali charge between 14-20% as Na₂O on oven-dry wood and sulfidity between 25-30%. Membrane-cell caustic is selected for oxygen delignification and extraction-stage pH control because chloride and iron impurities are lower. Elevated iron can disturb bleach performance and brightness stability. Dosing is typically automated with conductivity-based liquor analyzers and mass flow meters calibrated for 50% NaOH density.
Mercerization of cotton uses sodium hydroxide at 18-25 wt% and 15-30°C under controlled tension to convert cellulose I to cellulose II, increasing luster and dye uptake. The caustic is recovered by evaporating wash water to 25-50% NaOH in multi-effect evaporators. Low chloride in the caustic feed reduces scaling and chloride-induced corrosion on evaporator tubes and recovery piping.
In batch soap saponification, NaOH is charged according to the saponification value of the triglyceride, typically with 0.5-1.0% excess, at 80-100°C. The reaction is conducted under slow mixing to avoid excessive foaming from glycerin and soap formation. Excess caustic must be neutralized before finishing to control free alkali specification. Food-grade caustic soda is used where the final soap or glycerin product enters food or personal care supply chains.
For pH adjustment in demineralized water, typical dosing rates are 5-50 mg/L based on raw water alkalinity and dissolved carbon dioxide, with target pH 8.0-8.5 after reverse osmosis or deionization. The product must meet AWWA B501 where municipal plant specifications require controlled heavy metals and insolubles. In clean-in-place operations, sodium hydroxide is recirculated as a 2-5 wt% solution at 60-80°C for 10-30 min to saponify fats and denature protein films. Aluminum equipment must be excluded from the CIP loop because pitting and hydrogen evolution occur rapidly under these conditions.
| Standard or regulation | Scope | Typical application constraint |
|---|---|---|
| GB/T 209-2018 | Industrial sodium hydroxide classification | IS-I, IS-II, IL-I grade selection |
| GB 1886.20-2016 | Food additive sodium hydroxide | Heavy metal and arsenic control |
| FDA 21 CFR 184.1763 | GRAS pH control in food processing | Good manufacturing practice limit |
| AWWA B501 | Water treatment caustic soda | Impurity and sampling protocols |
| REACH (EC) No 1907/2006 | EU registration and safe use | Exposure scenario documentation |
In sodium hypochlorite generation, chlorine is absorbed into 15-20 wt% NaOH with final pH above 12.5 to minimize chlorate formation. Low chloride in the caustic feed reduces the chlorate burden in bleach and disinfectant products. Sodium silicate is produced by digesting silica sand in 25-50 wt% NaOH at 160-200°C in agitated pressure reactors. For sodium phosphate and detergent builder production, solid flake or pearl is dissolved to 30-50 wt% before metering into neutralization reactors equipped with pH, density, and temperature control.
In light hydrocarbon sweetening, 10-20 wt% caustic soda is contacted with LPG or gasoline in a static mixer or prewash column to extract hydrogen sulfide and mercaptans. The spent caustic contains sulfides and mercaptides and requires steam stripping, wet air oxidation, or biological treatment before disposal. Membrane-cell caustic with low chloride reduces chloride carryover to downstream amine units and refinery wastewater treatment.
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