| HS Code | 236295 |
| Product Name | Formosa Caustic Soda Flakes |
| Chemical Name | Sodium hydroxide |
| Molecular Formula | NaOH |
| Cas Number | 1310-73-2 |
| Appearance | White solid flakes |
| Odor | Odorless |
| Assay Naoh | 99% min |
| Sodium Carbonate Na2co3 | 0.3% max |
| Sodium Chloride Nacl | 0.05% max |
| Iron Fe | 0.005% max |
| Solubility In Water | 109 g/100 mL at 20°C |
| Melting Point | 318°C |
| Boiling Point | 1388°C |
| Density | 2.13 g/cm3 |
| Ph 1 Percent Solution | 13-14 |
| Hygroscopic | Yes, absorbs moisture and carbon dioxide |
As an accredited Formosa Caustic Soda Flakes factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in 25kg sealed, plastic-lined woven bags to prevent moisture absorption and ensure safe handling. |
| Container Loading (20′ FCL) | 20′ FCL: dry container loaded with Formosa Caustic Soda Flakes in sealed bags on pallets, secured, moisture-protected. |
| Shipping | Formosa Caustic Soda Flakes ship as a hazardous, corrosive solid (UN1823). Pack in sealed, moisture-proof polypropylene bags inside ventilated containers, or IBCs/drums. Ensure proper Class 8 labeling, segregation from acids, waterproofing, and dry conditions to prevent caking and chemical reaction during transit. |
| Storage | Store Formosa Caustic Soda Flakes in a cool, dry, well-ventilated area, away from moisture, humidity, and direct sunlight. Keep containers tightly sealed and elevated on pallets to prevent water contact. Segregate from acids, metals, and incompatible chemicals. Ensure spill containment and use corrosion-resistant materials. Always wear appropriate PPE when handling stored material. |
| Shelf Life | Shelf life is indefinite if stored tightly sealed in a dry, cool area away from moisture and air. |
In Bayer-process alumina refining, Formosa caustic soda flakes are normally dissolved in low-carbonate process condensate to a concentration of 50 wt% NaOH before injection into the digestion liquor. The finished pregnant digestion liquor typically carries 180–250 g/L Na₂O caustic, an alumina-to-caustic ratio of 0.55–0.75, and 120–180 g/L Al₂O₃ depending on bauxite reactive silica and digestion temperature. Boehmite-rich monohydrate bauxites are processed in double-flow digestion vessels at 240–260 °C and 35–45 bar; gibbsite-rich trihydrate bauxites are digested at 140–160 °C. Heat recovery flash trains with 8–10 stages cool the slurry before red mud separation in high-rate thickeners and security filtration. Caustic loss to desilication products is monitored by measuring soda-to-silica ratio in washed red mud, commonly maintained below 0.25 kg Na₂O per tonne dry mud. Carbonate, sulfate, and chloride impurities introduced through flake and process water must be purged through evaporative crystallization or causticization; otherwise carbonate exceeds 25 g/L Na₂CO₃ and reduces digestion efficiency. Terminal product is smelter-grade alumina with residual Na₂O below 0.5 wt%. Batch-to-batch variance in flake dissolution heat can be managed by feed-rate control on a continuous dissolver with forced circulation and a tube-and-shell cooler, because dissolution of NaOH in water releases approximately 44.5 kJ/mol. The slurry should never be reverse-charged into solid flake. Published operational data for liquor productivity in high-temperature tube digesters sometimes does not separate flake soda from cell liquor soda, but the flake is used mainly to trim caustic losses and maintain molar ratios.
A kraft mill’s recausticizing loop uses flake caustic soda as makeup alkali to compensate sodium losses in dissolving tank vents, lime mud, and bleach plant effluent when the purchased flake assay is confirmed at ≥98 wt% NaOH and carbonate below 0.8 wt%. The flake is dissolved to 20–25 wt% NaOH in a dedicated dissolver equipped with a bag dump hopper, wet-scrubber dust extraction, and a magnetic separator for tramp metal. White liquor for softwood linerboard digesters is maintained at 85–110 g/L effective alkali as Na₂O, 25–30% sulfidity, and 1.5–2.1 molar hydroxide-to-hydrosulfide ratio. Continuous digesters with Lo-Solids or MCC cooking require caustic concentration trim at the high-heat washing section to maintain 12.5–13.5 pH and avoid lignin re-precipitation. In batch digesters, caustic charge is expressed as 15–18% active alkali on oven-dry wood, and H-factor is controlled at 1700–2000 for southern pine. Flake stored in unheated silos above 60% relative humidity forms a surface hydrate crust that clogs rotary feeders; a desiccant wheel dehumidifier set to ≤40% RH at the transfer bin is required. White liquor active alkali is determined by TAPPI T 624, and sulfidity titration follows TAPPI T 625. The terminal fibre is unbleached kraft pulp with kappa number 20–30 for linerboard or 10–15 for bleachable grades. The recausticizing loop must maintain causticity of lime mud above 80%, otherwise dead-load carbonate rises and increases consumption of flake caustic.
The liquid-liquid extractor in an LPG sweetening train is charged with caustic soda flakes reconstituted to 3–6 wt% NaOH in demineralized water. The caustic reacts with hydrogen sulfide, thiols, and carbonyl sulfide in a packed or trayed contactor with a caustic-to-hydrocarbon volume ratio between 0.05:1 and 0.15:1, contact temperature 35–45 °C, and pressure held above the vapor pressure of the hydrocarbon, typically 12–18 bar for C3/C4 streams. Spent sulfidic caustic leaving the bottom of the extractor contains sulfide concentrations that may exceed 1000 mg/L S²⁻ and mercaptide concentrations above 5000 mg/L as sulfur; this stream requires wet air oxidation or chemical oxidation before biotreatment. The oxidation unit operates at 180–220 °C and 20–35 bar air pressure, with residence time 60–120 min. Caustic carryover into the treated hydrocarbon is limited to 5 ppm Na⁺ by water-wash coalescing filters. The treated C3/C4 stream must meet ASTM D2420 for hydrogen sulfide and ASTM D3227 for total mercaptans, typically below 1 ppm H₂S and 30 ppm thiol sulfur. The flake product must be low in iron (≤10 ppm) because iron catalyzes phenolic caustic emulsion stabilization, and low carbonate is required to avoid scaling in the spent caustic oxidation heat exchanger. Each mole of H₂S consumes 2 mol NaOH and each mole of methyl mercaptan consumes 1 mol NaOH. Published data for spent caustic oxidation of highly phenolic FCC-derived naphtha streams is limited, and pilot-scale verification is required before scale-up to a fixed-bed or bubble column reactor.
| Hydrocarbon stream | NaOH strength | Extractor temperature | Extractor pressure | Spent sulfidic caustic S²⁻ | Product control method |
|---|---|---|---|---|---|
| C3/C4 LPG | 3–6 wt% | 35–45 °C | 12–18 bar | 1000–5000 mg/L | ASTM D2420, ASTM D3227 |
| Light straight-run naphtha | 5–10 wt% | 40–50 °C | 2–5 bar | 2000–8000 mg/L | ASTM D3227 |
Cotton mercerizing relies on a recirculated caustic trough under closed-loop conductivity and density analyzer control. Cold tension mercerizing of ring-spun cotton yarn uses NaOH strength of 20–25°Bé, corresponding to 14–19 wt% NaOH, at a trough temperature of 15–18 °C; dwell time in the caustic padder is 45–75 s and fabric tension during shrinkage compensation is maintained within ±2% of original width by a clip stenter. Slack mercerizing for knitted goods may run at 28–32°Bé (22–26 wt% NaOH) at 10–25 °C and 10–30 s immersion, followed by steeping in a J-box for 2–5 min to complete crystallite conversion from cellulose I to cellulose II. The recovered weak caustic is concentrated in a multi-effect evaporator to 32–36°Bé and returned to the main bath; only losses through cloth carry-out and neutralization are replenished with flake caustic. Washing must reduce residual fabric pH below 7.5 before drying because residual alkali above 0.05 wt% NaOH on the fibre causes yellowing during curing at 150–180 °C. Dye uptake after mercerizing is measured by AATCC 89 or the barium activity number; acceptable mercerization is indicated by barium activity number ≥115 for cotton. A production-scale limitation arises when flake-derived caustic contains high carbonate because sodium carbonate competes for water and lowers effective NaOH activity; carbonate in the bath above 2 wt% Na₂CO₃ reduces equilibrium swelling and creates fabric stiffness after drying. The terminal products are dimensionally stable woven fabrics, high-lustre sewing thread, and print cloth.
| Mercerizing route | NaOH concentration | Temperature | Dwell time | Width tension | Barium activity number |
|---|---|---|---|---|---|
| Cold tension woven cotton | 20–25°Bé | 15–18 °C | 45–75 s | ±2% of original width | ≥115 |
| Slack knitted cotton | 28–32°Bé | 10–25 °C | 2–5 min steeping | No tension | ≥110 |
The saponification kettle charge in full-boiled soap manufacture is calculated from the saponification value of the blended vegetable oil or tallow fraction. For a tallow-coconut blend with a saponification value of 210–220 mg KOH/g, the stoichiometric NaOH requirement is approximately 15–16 wt% of the oil charge; the controller sets a final free caustic concentration of 0.08–0.12 wt% NaOH in the neat soap to avoid rancidity while limiting excess alkali that would produce brittle, dull bars. The flake caustic is dissolved to 25–30 wt% NaOH and metered into the kettle at 80–90 °C under a slow-pitched gate agitator rotating at 35–50 rpm. After saponification, the soap is salted out with dry sodium chloride to separate neat soap from glycerol-rich lye; the glycerol concentration in spent lye is typically 8–12 wt%. The neat soap is then fitted and washed to reduce glycerin below 0.5 wt% and chloride below 0.2 wt% to prevent hygroscopic sweating in the final stamped bar. The use of flake rather than diaphragm cell caustic introduces low chloride, which is critical because residual sodium chloride in the soap base depresses the Kraft point of liquid soap formulations; the specification for flake chloride is ≤0.05 wt% NaCl. Equipment in continuous saponification includes a high-pressure saponification loop at 110–130 °C and 2–3 bar, a static mixer with 10–20 mixing elements, and a multistage neutralization column to remove free fatty acid odors. Total free alkali is determined using ISO 8212, and unsaponified fat is controlled below 0.2 wt% by hot extraction with petroleum ether. High carbonate in the flake reacts with fatty acids to release carbon dioxide, causing foam and kettle overflow; the feed tank should be vented and the recirculating pump should be interlocked with a foam detector.
Municipal water treatment plants predilute caustic soda flakes in a fiberglass-reinforced plastic dissolver to 20–25 wt% NaOH and meter the solution by positive displacement diaphragm pumps into rapid mix basins. The dose is determined by total alkalinity and dissolved carbon dioxide; a water with 50 mg/L CO₂ and 80 mg/L calcium carbonate alkalinity may require approximately 35 mg/L NaOH on a 100% basis to shift pH from 6.8 to 7.6 and precipitate excess hardness as calcium carbonate in the clarification sludge. Ferric chloride coagulation consumes caustic depending on water alkalinity, with a stoichiometric demand of approximately 2.0–2.2 mg NaOH per mg Fe³⁺ dosed; plant operators use jar-test pH curves and a streaming current detector to maintain coagulation pH at 6.9–7.2 for organics removal. In lime-soda softening, flake caustic is used as a supplement to lime when non-carbonate hardness must be removed; magnesium hardness expressed as 1 mg/L as CaCO₃ requires 0.8 mg/L NaOH for hydroxide precipitation. Safety interlocks prevent overfeed because a pH above 8.5 in the distribution system increases the potential for cement-mortar lining leaching and siderite scaling. The final treated water must meet ISO 9963-1 for total alkalinity and ASTM D1293-18 for pH; sodium levels are kept below 20 mg/L for low-sodium consumer requirements. The lime sludge dewatering centrifuge performance deteriorates when calcite fines contain residual magnesium hydroxide from over-causticization, so the softening basin pH is controlled within ±0.1 pH units by a cascade loop. Carbon dioxide sparging or sulfuric acid trim can be used downstream for final pH correction, but sodium-to-calcium ratio in the finished water should not exceed 3:1 to avoid corrosion control issues. The terminal product is finished drinking water meeting pH 7.2–7.8, turbidity below 0.1 NTU, and a Langelier saturation index of ±0.3.
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Formosa Caustic Soda Flakes are a solid sodium hydroxide product, CAS 1310-73-2, EINECS 215-185-5, molecular weight 40.00 g/mol, supplied as white deliquescent flakes with a nominal sodium hydroxide content not less than 98.0 wt% at packaging. The material is hygroscopic and reacts with atmospheric carbon dioxide to form surface sodium carbonate; unopened moisture-barrier multi-wall paper sacks with polyethylene liners limit this migration, but opened sacks should be reclosed under dry-air purge or consumed within a shift to avoid assay drift. The product is classified as corrosive under GHS and is transported as UN 1823, Packing Group II. The technical role of the flakes is not simply to deliver alkalinity; because the solid form removes approximately 50 wt% of water from the logistics stream relative to standard membrane-grade liquid caustic soda, it changes the energy balance of reconstitution and the design requirements for dosing equipment.
Lot acceptance should be based on the supplier certificate of analysis because the product is not a single-molecule entity; sodium carbonate and sodium chloride are the principal process-derived impurities, with iron and other metals present at trace levels. The typical values below are drawn from membrane-grade flaked caustic soda data and are not a substitute for the lot-specific CoA.
| Parameter | Typical value or limit | Test method |
|---|---|---|
| NaOH assay | 98.0 wt% minimum; 98.5–99.0 wt% typical | acid-base titration after sample dissolution; ISO 979:1974 |
| Na2CO3 | ≤0.5 wt% | titration; ISO 3196:1975 |
| NaCl | ≤0.03 wt% | mercurimetric titration; ISO 981:1973 |
| Fe2O3 | ≤0.001 wt% | photometric/ICP after acid dissolution |
| Water-insoluble matter | ≤0.005 wt% | filtration/drying after aqueous dissolution |
Carbonate content is not a fixed product property; it increases with storage duration and exposure to air, particularly at relative humidity above 60%. In high-purity applications such as controlled alkalinity dosing for boiler feed or demineralized water conditioning, this drift may require pre-dissolved filtration through 10 µm polypropylene depth media or use of fresh stock. Flakes should not be allowed to sit in open hoppers under humid conditions because deliquescence forms a concentrated surface brine that corrodes carbon steel and attacks aluminum.
Dissolution of solid NaOH in water is strongly exothermic. The integral heat of solution to dilute aqueous concentrations is approximately −44.5 kJ/mol, which corresponds to roughly 1.1 MJ per kg NaOH. When a 50 wt% solution is produced by adding flakes to water at 25 °C, the adiabatic temperature rise exceeds 80 K; the actual peak temperature depends on solution heat capacity, addition rate, and heat losses. Equipment for reconstitution therefore requires jacketed stainless vessels, a recirculation loop through a plate-and-frame or shell-and-tube heat exchanger, and a caustic-resistant pump with mechanical seals suitable for hot 50% NaOH. Addition must be controlled by a rotary valve or screw feeder to prevent localized boiling and violent bumping. Vents should be routed through a demister because water vapor and aerosolized caustic form a corrosive plume that can blind ductwork.
Materials of construction for continuous service with 50% NaOH at 90 °C include austenitic stainless steels such as 316L and 304L only if stress-corrosion cracking is managed by stress relief and low chloride control; nickel alloys such as Alloy 200 and Alloy 400 are preferred where temperature or chloride is elevated. Carbon steel is acceptable for ambient concentrated caustic due to passivation but must be stress-relieved to avoid caustic stress-corrosion cracking. Unsuitable materials include aluminum, zinc, tin, galvanized steel, and bronzes; aluminum reacts with NaOH to release hydrogen and form soluble aluminate. Borosilicate glass, ceramic fibers, and some glass-reinforced plastics degrade in hot caustic through silicate leaching. Elastomer seals should be EPDM, PTFE, or FFKM; NBR is avoided in hot caustic service.
In municipal and industrial water treatment, caustic soda flakes are reconstituted to a 10–25 wt% NaOH solution and dosed through diaphragm metering pumps into raw water or wastewater to raise pH, enhance coagulation, and precipitate dissolved metals. For ferric iron removal, the solubility of Fe(OH)3 is minimized at roughly pH 4–6; copper precipitation is typically optimized at pH 8–9; zinc removal is commonly achieved at pH 9–10. These ranges are equilibrium approximations and must be confirmed by jar tests because complexing agents, temperature, and redox state shift the precipitation envelope. The product's low chloride content relative to industrial-grade caustic is relevant in closed-loop cooling towers and boiler feed conditioning, where chloride can accelerate pitting in austenitic stainless steel. Injection quills fabricated from PVDF or 316L stainless steel are used to prevent corrosion at the point of high pH. On-line pH is measured per ASTM D1293-18, with grab-sample verification using a calibrated glass electrode.
The selection of flakes rather than 50 wt% liquid caustic soda shifts the mass balance of a chemical dosing system. A 1000 kg batch of flake caustic with 98.0 wt% NaOH delivers approximately 980 kg dry NaOH; the equivalent mass of 50% liquid is 1960 kg. This difference reduces inbound freight mass by roughly 49% if water is available at the site. However, the downstream operation gains a dissolving duty not required with liquid supply: storage silos must be kept dry, conveying lines must be designed for a cohesive deliquescent solid, and dust collection must use wet scrubbers rather than dry bag filters because caustic dust from bag media is difficult to clean and creates a chemical exposure risk. For sites with existing liquid storage and no steam or waste heat for reconstitution, the flakes may be less attractive because the dissolution exotherm must be removed and the solution cooled before transfer.
In cotton mercerizing, the material is dissolved to a caustic concentration of 20–25 wt% NaOH and applied at controlled tension to increase fiber lustre, dye uptake, and tensile strength. The working solution is maintained at 15–25 °C because higher temperatures reduce fiber swelling and lower the mercerizing effect. Carbonate accumulation from flake storage or atmospheric CO2 absorption must be monitored; excessive sodium carbonate can produce crusting on rolls and reduce alkali penetration. Filtration of the mercerizing bath through a 10–20 µm screen or depth media is typical. The product's sodium chloride level matters less in mercerizing than in rayon viscose production, where chloride can influence spin-bath coagulation rates and salt content in the spin bath is controlled separately.
In Bayer process alumina refining, concentrated sodium hydroxide is used to digest bauxite at elevated temperature and pressure. Spent liquor entering digestion is commonly maintained at 150–250 g/L Na2O caustic, depending on bauxite composition and plant design; flakes are reconstituted to make up caustic lost to sodium aluminosilicate desilication product and red mud washing losses. The addition point is typically the spent-liquor surge tank or lime mixing circuit, before heat exchangers and digestion. Control of free caustic and the alumina-to-caustic ratio is more critical than the physical form of the alkali; use of flakes requires the same security filtration and sand removal steps used for liquid caustic to prevent insoluble carbonate and iron particulates from fouling heat exchanger surfaces. Published data for this specific configuration is limited because Bayer plant caustic balances are site-specific and are not disclosed in the open literature.
In batch chemical neutralization, the flakes are metered into acidic organic or aqueous reaction masses to neutralize spent acids before phase separation or distillation. The dry solid avoids adding water that would otherwise dilute a reaction mass and increase downstream evaporation load. The addition rate is controlled by solution conductivity or pH, and the temperature of the reaction mass is held below the boiling point of the solvent. For neutralization of concentrated sulfuric acid, local boiling at the liquid surface must be prevented by subsurface injection of the flake slurry or by slow flake addition into a circulating loop. The use of flakes rather than liquid caustic in this service can reduce reaction volume and wastewater generation but increases the need for dust control and mechanical feeding.
In industrial cleaning and bottle washing, caustic solutions are maintained at 2–5 wt% NaOH for soaker or spray washers. Flakes are reconstituted to a concentrated stock solution and diluted with softened water; hardness salts can form carbonate and precipitate scale on heating coils. Use of softened or demineralized water for reconstitution reduces scale and maintains heat transfer. Bath alkalinity is monitored by titration and replenished based on caustic consumption rather than visual appearance.
In biodiesel production, sodium hydroxide is used to prepare sodium methoxide when dissolved in methanol; this application requires very low water content because water hydrolyzes triglycerides to free fatty acids and consumes alkali, forming soaps. Flakes with a low water specification are preferred over 50% liquid caustic because the liquid introduces water into the methanolic catalyst. The dissolution of NaOH in methanol is exothermic and requires cooling and methanol-resistant seals; the resulting sodium methoxide solution is flammable and must be handled under nitrogen.
Compared with potassium hydroxide flakes, Formosa Caustic Soda Flakes deliver higher neutralization equivalent per unit mass: 1 kg of 98% NaOH contains approximately 24.5 mol of hydroxide equivalents, whereas 1 kg of 90% KOH flake contains approximately 16.1 mol. Sodium hydroxide is selected where the cation is not functionally relevant because the cost per hydroxide equivalent is typically lower. Potassium hydroxide is preferred in certain saponification and liquid-soap processes where potassium carboxylates have lower melt point and higher water clarity than sodium carboxylates. The choice is governed by downstream cation effects, not by alkalinity as such.
| Property | Formosa Caustic Soda Flakes | Caustic soda prills/pearls | 50 wt% membrane-grade liquid |
|---|---|---|---|
| Nominal NaOH | 98.0 wt% minimum | 98.0 wt% minimum | 50.0 wt% |
| Water content | ≤2.0 wt% | ≤2.0 wt% | ≈50 wt% |
| Solution freezing risk | None in dry solid storage | None in dry solid storage | 50% liquid freezes below approximately 12 °C |
| Dissolution rate | High; fines can increase surface area | Moderate; better flow and lower dust | Immediate dilution |
| Dusting | Moderate | Lower | No dust |
| Freight mass per dry NaOH | Higher efficiency | Higher efficiency | Lower efficiency |
Conversion from liquid to dry flake feed requires dry storage with relative humidity below 60% and dust extraction through a wet scrubber; mechanical conveying should avoid aluminum transfer lines and use rotary valves with abrasion-resistant coatings because flake fines are abrasive and hygroscopic. Regulatory status depends on intended use: industrial flakes should not be used in food contact or potable water treatment unless certified against applicable standards such as 21 CFR 184.1763 for food-grade sodium hydroxide and relevant national drinking-water additives standards.
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