| HS Code | 605514 |
| Chemical Name | Sodium Hydroxide |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Molecular Weight | 40.00 g/mol |
| Appearance | White flakes |
| Purity | 99% min |
| Grade | Industrial Grade |
| Melting Point | 318 °C |
| Solubility | Soluble in water |
| Ph | 13-14 (1% solution) |
As an accredited Shaanxi Beiyuan Chemical Industry Group Co Ltd Caustic Soda Flakes factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25 kg net in double-layer PP woven bags with PE inner liner, sealed to protect from moisture. |
| Container Loading (20′ FCL) | 20′ FCL container loaded with Shaanxi Beiyuan caustic soda flakes, packed securely in bags for safe transport. |
| Shipping | Caustic soda flakes are shipped in 25kg PP woven bags with PE liners, palletized and shrink-wrapped for stability. Containers must be dry, clean, and well-ventilated to prevent moisture absorption. Keep away from acids and moisture; handle with protective gear. Standard export packaging ensures safe maritime transport. |
| Storage | Store caustic soda flakes in a cool, dry, well-ventilated area away from moisture, water, and incompatible substances like acids. Keep containers tightly sealed, preferably on raised pallets to prevent floor contact. Use corrosion-resistant materials and ensure proper labeling and spill containment. Protect from physical damage and direct sunlight. |
| Shelf Life | Store in a dry, sealed container away from moisture; shelf life is typically two years from manufacture. |
Caustic soda flakes supplied by Shaanxi Beiyuan Chemical Industry Group Co Ltd are typically converted to a 20–50% w/w solution before metering into downstream unit operations. The dissolution enthalpy of sodium hydroxide is approximately −44.5 kJ/mol, and a 5,000 L agitated tank producing 25% w/w caustic from flakes at 20°C can reach 65–75°C when the flake feed rate is controlled to avoid unmixed zones near the addition point. Production-scale dilution skids therefore use Hastelloy C276, PVDF-lined static mixers, or 316L stainless steel recirculation loops with a minimum line velocity of 1.2–1.8 m/s to prevent local boiling and stress corrosion cracking. Typical flake specifications relevant to downstream processing include sodium hydroxide assay ≥99.0% w/w by ASTM E291-18, sodium carbonate ≤0.5% w/w, sodium chloride ≤0.03% w/w, and iron as Fe₂O₃ ≤0.005% w/w; carbonate contributes to evaporator scaling, while chloride influences pitting corrosion in 304/316L stainless steel equipment. Flakes are hygroscopic, and storage in unsealed bags at relative humidity above 60% produces caking and local sodium carbonate formation. Aluminium, zinc, tin, and galvanized surfaces are incompatible with caustic solutions.
In the Bayer digestion circuit, flaked caustic is metered into spent wash liquor to achieve 180–240 g/L Na₂O in the digestion feed. Bauxite mineralogy dictates digestion temperature and caustic consumption: gibbsite dissolves at 140–150°C, boehmite at 220–250°C, and diasporic ore at 250–280°C, with caustic-to-alumina molar ratios of 1.45–1.85 in the blow-off liquor. The dissolution reaction converts gibbsite to sodium aluminate and is followed by solid-liquid separation in high-rate thickeners and plate-and-frame filters. Consumption of NaOH per tonne of alumina ranges from 0.35 t for low-silica gibbsite to more than 0.60 t for high-silica bauxite because reactive silica forms sodium silicate and subsequently precipitates as sodalite 3Na₂O·3Al₂O₃·2SiO₂·2H₂O, trapping Na₂O in red mud. Digestion residence time in a continuous pipe reactor or multi-compartment autoclave ranges from 15 min to 60 min, and the slurry is flashed through 2–10 pressure let-down stages to recover heat. A field-observed bottleneck occurs when flake dissolution upstream of the slurry heater is incomplete; undissolved particles entering the digestion train can cause local caustic depletion and diaspore conversion loss. The end product is smelter-grade alumina with ≥98.5% Al₂O₃, controlled particle size distribution, and low residual Na₂O for dry scrubber injection.
| Bauxite mineralogy | Digestion temperature (°C) | Caustic Na₂O in digestion liquor (g/L) | NaOH consumption (t NaOH/t Al₂O₃) |
|---|---|---|---|
| Gibbsite | 140–150 | 130–160 | 0.35–0.45 |
| Boehmite | 220–250 | 180–240 | 0.45–0.60 |
| Diaspore | 250–280 | 200–260 | 0.55–0.70 |
Under kraft pulping conditions, white liquor is prepared by dissolving flaked caustic and sodium sulfide to an effective alkali charge of 15–22% Na₂O on oven-dry wood, with sulfidity held at 25–35% for linerboard-grade softwood fibre. The flakes are converted into raw white liquor at a target total titratable alkali of 90–120 g/L NaOH-equivalent, then clarified through a disc filter before entering the digester. Cooking temperature in a continuous Kamyr digester is 155–170°C, corresponding to an H-factor of 800–1,500 for pine; hardwood furnish for bleachable grade is cooked at 150–160°C and H-factor 400–800. Caustic consumption varies with lignin content: southern pine may require 16–20% effective alkali, while eucalyptus kraft requires 12–15%. Pulp yield and kappa number respond to the caustic-to-wood ratio, not simply to liquor temperature. In batch digesters using flaked caustic, direct addition of flakes to the cold recirculation line can leave undissolved material in the chip chute, creating non-uniform alkali distribution and a kappa variation of ±3 across the cooked batch. End products include unbleached kraft pulp for linerboard, sack paper, and bleached market pulp. A 1,000 air-dry tonne/day pulp mill typically consumes 35,000–55,000 t/year of caustic soda depending on digester yield, washing efficiency, and chemical recovery boiler availability.
For cotton yarn and fabric mercerization, the alkali concentration window is the critical variable governing cellulose I to cellulose II conversion and uniform dye uptake. Tension mercerization operates at 20%–24% w/w NaOH and 15–20°C, while slack mercerization for stretch recovery uses 25%–30% w/w at 20–25°C. The process increases dye uptake by 10–20% and tensile strength by 15–25% in combed cotton yarn under controlled warp tension of 2–5 cN/tex. A production chainless mercerizer uses multiple bowl impregnation: the first bowl holds 190–230 g/L NaOH and the final rinse bowl holds 20–40 g/L NaOH before hot water displacement at 70–85°C. Caustic recovery from wash liquor via multiple-effect evaporators concentrates dilute wash to 28–30% w/w for reuse, reducing flake consumption to 0.15–0.25 kg NaOH per kg of treated fabric. The main processing conflict is temperature-dependent swelling: exceeding 25°C during tension mercerization reduces cellulose II conversion yield and produces uneven selvedge shrinkage in open-width fabric. Dwell time in the alkali zone is limited to 35–60 s for woven fabric; immersion beyond 90 s at 25% w/w NaOH causes fabric weight loss and strength degradation. End products are mercerized cotton shirting, poplin, sewing thread, and high-lustre knitted outerwear.
| Mercerization type | NaOH concentration (% w/w) | Temperature (°C) | Dwell time (s) | Warp tension (cN/tex) |
|---|---|---|---|---|
| Tension mercerization | 20–24 | 15–20 | 35–60 | 2–5 |
| Slack mercerization | 25–30 | 20–25 | 30–90 | 0–0.5 |
In a soap crutcher processing palm stearin, the sodium hydroxide charge is set at 1.45–1.55 kg NaOH per 10 kg of saponification-value units, a molar excess of 0.5–1.5% over the theoretical saponification value. The reaction is run in a 15,000–30,000 L crutcher at 80–90°C, with flakes fed through a screw feeder into 5–10% brine solution to control gel-phase viscosity. High-shear mixing at 1,200–1,500 rpm is maintained for 30–60 min until total fatty matter and electrolyte separation reaches a soap curd with 30–34% moisture. Excess NaOH remaining as free alkali in soap is controlled to 0.05–0.15% w/w as NaOH because skin compatibility and detergent standards such as ISO 456:1973 define the free caustic alkalinity limit. Flake purity directly affects soap texture: carbonate above 0.5% w/w neutralizes to sodium carbonate and produces brittle soap, while chloride above 0.03% w/w can accelerate pitting of 316L stainless steel crutchers. Process control is based on saponification value, free fatty acid content, and electrolyte curve rather than on fixed time alone. End products include toilet soap base, sodium stearate, industrial soap flakes, and laundry bars.
Light straight-run naphtha and LPG streams require caustic extraction when mercaptan sulfur exceeds 10–50 mg/kg or when kerosene total acid number is above 0.05 mg KOH/g. The caustic scrubber is a countercurrent packed column or jet-loop reactor in which 10–20% w/w NaOH solution contacts the hydrocarbon at a treat ratio of 0.5–2.0 vol% of hydrocarbon feed. In Merox extraction, the caustic phase containing naphthenates and mercaptides is regenerated with air and Merox catalyst, reducing flake caustic consumption to 0.05–0.15 kg NaOH per tonne of naphtha. Spent caustic bleed is routed to a wet air oxidation unit; mercaptan removal efficiency falls below 85% when sodium sulfide concentration in the recirculating caustic exceeds 2–5 wt%. Flake caustic is used in refineries without adjacent chlor-alkali supply to prepare 10%–15% solutions in a Hastelloy C276 dilution skid with a 10 min residence time and a diaphragm metering pump. Treated streams feed naphtha hydrotreating, isomerization, or gasoline blending, while naphthenic acid salts are separated for disposal or acidification to naphthenic acid byproducts. The main operational boundary is the incompatibility of concentrated caustic with aluminium internals in crude overhead systems and the exothermic reaction with acidic hydrocarbon entrainment.
When raw water pH falls below 6.5 and coagulant demand rises above 20–60 mg/L as alum or polyaluminium chloride product, flake caustic is injected to maintain a pH setpoint of 6.8–7.2 before flocculation. A 5–10% w/w NaOH solution is prepared in a 1,000–5,000 L day tank with HDPE or PVDF wetted parts and metered through a pulsation dampener into a static mixer downstream of the injection quill. Post-treatment pH is monitored by an online glass electrode calibrated to ±0.1 pH; underdosing below 6.5 allows coagulation failure with residual aluminium above 0.1 mg/L, while overdosing above 8.0 increases trihalomethane formation potential and calcium carbonate scaling on plate settler surfaces. Flake caustic is also used to adjust finished water pH after reverse osmosis to stabilize aggressive water with a Langelier Saturation Index target of 0.0 to +0.5, with a typical post-RO dose of 2–8 mg/L as NaOH. The product used in potable water applications should conform to ANSI/AWWA B501-19 and the final pH should remain within the WHO guideline range of 6.5–8.5. End products include corrosion-controlled potable water and cement-mortar-lined distribution main protection.
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Shaanxi Beiyuan Chemical Industry Group Co Ltd supplies caustic soda flakes as a solid sodium hydroxide product obtained from ion-exchange membrane electrolysis. The material is classified under CAS 1310-73-2, UN 1823, Class 8, Packing Group II, and is shipped as white flakes with a nominal NaOH mass fraction of 99.0% under the producer’s Grade I export specification. The flake is formed on a chilled drum flaker after forced-circulation evaporation of membrane-cell 50% sodium hydroxide liquor; typical flake thickness is 0.5–1.5 mm, and standard packaging is 25 kg multi-wall paper bags with an inner 0.06–0.10 mm low-density polyethylene liner. Where a model descriptor is required in export documentation, the product is identified as industrial-grade 99% caustic soda flakes rather than a proprietary resin-style model number; batch traceability is maintained by the producer’s lot code on each bag and pallet label. The selection of membrane-cell feedstock distinguishes this product from mercury-cell caustic, which may carry residual mercury requiring separate control in downstream supply chains.
The commercial specification for the 99% flake grade is controlled by the producer and is aligned to GB/T 209-2018 for industrial sodium hydroxide. Representative certificate-of-analysis limits are given in Table 1. Batch-specific values may be tighter, but users must verify each lot against the intended process limits.
| Parameter | Limit | Test method |
|---|---|---|
| NaOH mass fraction | ≥99.0% | GB/T 4348.1-2013 |
| Na₂CO₃ | ≤0.5% | GB/T 4348.1-2013 |
| NaCl | ≤0.03% | GB/T 4348.2-2014 |
| Fe₂O₃ | ≤0.005% | GB/T 4348.3-2012 |
| Water-insoluble matter | ≤0.01% | GB/T 209-2018 annex |
The chloride limit is operationally significant in closed-loop alumina and textile systems because residual sodium chloride can accumulate to concentrations that initiate pitting corrosion on 316L stainless steel digestion heaters and mercerizing frames. The carbonate limit is relevant in soap and viscose production, where sodium carbonate consumes acid in neutralization steps and can alter the alkali water mass balance during steeping. Iron oxide at the specified limit reduces the risk of visible iron staining in rayon spin baths and in white cotton mercerizing. Analytical verification is commonly performed by acid-base titration with 1 mol/L hydrochloric acid and a methyl orange indicator for total alkalinity, with sodium carbonate determined by barium chloride precipitation or ASTM E291-18 methods.
A 50% membrane-grade liquid has a freezing point near 12°C, which means unheated tank trucks and above-ground storage require trace heating in northern China, North America, and Northern Europe. Flake eliminates that phase-change risk because the dry solid can be stored below 0°C without freezing. For an equivalent 1,000 kg NaOH quantity, 50% liquid carries approximately 1,000 kg water, while 99% flake carries approximately 10 kg water plus packaging. This water mass difference lowers freight cost per unit alkalinity and simplifies site logistics where water availability for dilution is not the primary constraint. However, flake requires an on-site dissolution system with dust control, whereas liquid can be pumped directly into a process.
Bayer circuits use makeup sodium hydroxide to restore free caustic after red mud losses. Digestion liquors typically maintain total caustic concentration in the range 200–250 g/L Na₂O and a molar Na₂O/Al₂O₃ ratio of 1.2–1.6 depending on bauxite reactivity. The flake is dissolved in weak wash water in a carbon-steel or 316L agitated tank before being dosed into the digestion slurry. Direct addition of undissolved flake to bauxite slurry is not recommended because localized high-alkali regions can cause reprecipitation of sodium aluminosilicate scale on heat exchanger surfaces. Published data for this specific producer’s effect on scale composition is limited.
For saponification systems, the flake is first dissolved to a 25–30% NaOH solution and metered into the fat charge. The required caustic dose is calculated from the saponification value of the fat blend, with a typical free alkali excess of 0.5–1.0% of oil weight at the endpoint. Use of a low-carbonate flake avoids excessive soap clouding from sodium carbonate gel formation, while chloride below 0.03% limits corrosion in cast-iron or 316 saponification vessels.
In kraft mills, flake caustic is used to supplement white liquor effective alkali without increasing sulfidity from sodium sulfide. Typical effective alkali charges for softwood and hardwood pulping are 12–25% Na₂O on oven-dry wood, and a mill producing 1,000 t/d air-dried pulp may add several tonnes per day of flake to maintain white liquor titratable alkali. The dissolution tank is often constructed from 316L or nickel-clad steel; carbon steel is not recommended for continuous service above 60°C because caustic stress-corrosion cracking can initiate at welds and heat-affected zones. The flake must be added to water, not water to flake, to prevent rapid hydration and localized temperature excursions above 120°C in poorly mixed vessels.
Cotton mercerization employs sodium hydroxide concentrations of 20–24% by mass at 15–25°C to swell the cotton fiber and increase dye uptake. Flake addition allows a finishing plant to prepare mercerizing liquor from dry product without over-dilution. The dissolution vessel should have cooling coils sized for the heat of solution; manufacturing-scale tanks have been observed to exceed 80°C during rapid flake addition if cooling water flow is interrupted. In continuous mercerizing ranges, the caustic bath is titrated by conductivity and density, with density measured at 20°C using a 1.200–1.250 g/cm³ hydrometer range.
For viscose steeping, a steeping liquor of 18–20% NaOH is maintained at 45–55°C. Flake is dissolved in a jacketed, agitated nickel-clad vessel and then dosed into the steeping bath. The integral heat of solution of solid NaOH is approximately -44.5 kJ/mol; preparing 1,000 L of 20% NaOH from solid flake releases enough heat to raise the solution temperature by more than 35°C above the initial water temperature if no cooling is applied. Low-shear agitation below 100 rpm is common to reduce air entrainment, because entrained carbon dioxide reacts with sodium hydroxide to form sodium carbonate, which lowers the effective alkali and produces carbonate turbidity in the viscose spin bath.
The preparation of sodium hypochlorite from flake caustic begins with dissolution to a 15–20% NaOH solution, followed by chlorine contact in a packed column or eductor. The resulting product target is 12–15% available chlorine by mass, and excess caustic of 0.5–1.0% NaOH is maintained to minimize chlorate formation. Low chlorate content in membrane-cell flake is critical because chlorate carryover can accelerate decomposition of stored hypochlorite. In oilfield drilling fluids, NaOH is added at 0.1–0.5 lb/bbl to control calcium and alkalinity in bentonite mud systems, with pH maintained between 9.5–10.5.
Petroleum treating operations dissolve caustic soda flakes to 10–20% solution for sulfur removal from liquefied petroleum gas and light naphtha streams. The spent caustic stream is subsequently regenerated or oxidized; chloride control in the fresh caustic reduces chloride-related fouling in downstream incinerators and wet air oxidation systems. In water treatment, 0.5–5.0% NaOH solution is metered to raise pH and suppress lead and copper solubility, with dosing controlled by pH set points in the range 8.5–9.5 for potable water systems under ANSI/AWWA B501-2008 or equivalent national standards. The flakes must meet applicable drinking-water additive criteria where used in potable treatment.
Open-bag exposure at ambient relative humidity above 60% causes rapid moisture uptake, caking, and sodium carbonate formation within 30–60 min. The flakes are packaged in 25 kg and 1,000 kg bags with a polyethylene liner and should be resealed after withdrawal. Bulk storage silos should be kept under dried air with a dew point below -20°C and should not use carbon steel surfaces in direct product contact because of iron contamination and hydrogen embrittlement risk. At temperatures below 10°C, the product remains free-flowing if protected from condensation; at temperatures above 40°C and high humidity, caking accelerates due to surface dissolution and recrystallization. The difference from pearl caustic is primarily geometric: flakes have higher surface-to-volume ratio and may absorb moisture faster in an open hopper than compacted pearls, but flakes dissolve more rapidly in a stirred tank at equal agitation.
| Form | NaOH mass fraction | Water freight per 1,000 kg NaOH | Freezing point | Typical packaging |
|---|---|---|---|---|
| Flake | 99.0% | 10 kg | solid | 25 kg PE-lined bag |
| Pearl | 99.0% | 10 kg | solid | 25 kg PE-lined bag |
| Liquid | 50.0% | 1,000 kg | 12°C | stainless steel tank container |
| Solid block | 98–99% | 10–20 kg | solid | steel drum |
For continuous dissolution, a bag-dump hood with a dust extraction rate of 1,000–1,500 m³/h per dump station is used to capture fine particles during flake transfer. The flaker feed hopper and screw conveyor are often constructed from 304L or 316L stainless steel to prevent iron contamination; carbon steel is not suitable for wetted surfaces. The dissolution tank is fitted with a level transmitter, temperature transmitter, and a conductivity loop calibrated to 0–500 mS/cm; the solution is transferred by a centrifugal pump with a 50–80 m head and 316 stainless steel wetted parts to the day tank.
Compared with producers using diaphragm-cell technology, Shaanxi Beiyuan membrane-cell flakes typically contain lower sodium chloride in the raw liquor, which allows the solid product to meet the ≤0.03% NaCl specification without additional salt-removal steps. Compared with mercury-cell caustic, the flake does not carry mercury contamination, eliminating the need for a mercury exclusion clause in food-contact or pharmaceutical auxiliary use. Dissolution time in a stirred vessel at 25°C with 200 rpm is generally 3–6 min for flakes of 0.5–1.5 mm thickness and 2–5 min for compacted pearls of similar mass. Flake pieces can bridge in a hopper more readily than spherical pearls; hopper half-angle should be greater than 60° from horizontal for reliable mass flow.
Handling of Shaanxi Beiyuan caustic soda flakes requires splash goggles conforming to EN 166, long-cuffed neoprene or nitrile gloves conforming to EN 374, and a chemical-resistant suit where dust or spray is generated. Sodium hydroxide is corrosive to aluminum, zinc, tin, and magnesium, releasing hydrogen gas; the reaction with aluminum follows a stoichiometric release of 1.5 mol hydrogen per mol sodium hydroxide. In closed vessels, hydrogen generation from inadvertent contact with amphoteric metals can create an explosive atmosphere above 4% hydrogen by volume. The flakes must not be mixed with concentrated acids, chlorinated solvents, or reducing sugars in enclosed systems. In the event of spills, dry material should be collected without water flushing into confined sumps to avoid violent hydration and aerosol formation.
Occupational exposure limits for sodium hydroxide are 2 mg/m³ as a ceiling under ACGIH and OSHA guidance, requiring local exhaust ventilation during bag dumping and flake transfer. Emissions from the flake surface are not significant at ambient temperature, but fine dust generated by pneumatic conveying can be irritating at concentrations above the exposure limit. Dust suppression systems using water spray should not be used directly on the flake; dust collection should use dry cartridge filters with a 99% removal efficiency at 0.5 µm particle size. For export to the European Union, the REACH registration number for sodium hydroxide is 01-2119457892-27-0000 or equivalent, and the product is classified as Skin Corr. 1A, H314 under CLP Regulation (EC) No 1272/2008. For food-chemical use, sodium hydroxide is addressed by FDA 21 CFR 184.1763 and Food Chemicals Codex monographs. The Grade I industrial flake described here is not automatically food-grade; users must verify the batch-specific certificate and the producer’s compliance statement for the intended regulatory jurisdiction.
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