| HS Code | 347207 |
| Product Name | Tianjin Bohua Caustic Soda |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Appearance | White flakes or pearls |
| Purity | 99% |
| Melting Point | 318°C |
| Boiling Point | 1388°C |
| Density | 2.13 g/cm³ |
| Solubility In Water | 1090 g/L at 20°C |
As an accredited Tianjin Bohua Caustic Soda factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Tianjin Bohua Caustic Soda is packaged in 25 kg PP woven bags with PE inner liner, moisture-proof and sealed. |
| Container Loading (20′ FCL) | 20′ FCL container loading of Tianjin Bohua caustic soda: bagged, palletized, secured, fully loaded for safe transport. |
| Shipping | Tianjin Bohua Caustic Soda ships as hazardous material, UN 1824 (solution) or UN 1823 (solid), Class 8 corrosive. It requires corrosion-resistant or lined containers, leak-proof packaging, and secure ventilation. Avoid moisture and incompatible acids; handle with PPE and emergency spill response protocols. |
| Storage | Store Tianjin Bohua Caustic Soda in a cool, dry, well-ventilated area, away from moisture, acids, and incompatible organics. Keep containers tightly sealed and protected from physical damage. Use corrosion-resistant materials like polyethylene or lined drums. Avoid water contact, as dissolution generates heat. Ensure proper labeling and secondary containment to prevent spills. |
| Shelf Life | Shelf life is typically 2 years when stored sealed, dry, and away from moisture and acids. |
In Bayer-process alumina refining, Tianjin Bohua sodium hydroxide, supplied as membrane-cell 50 wt% liquid or anhydrous solid, functions as the caustic aluminate extraction agent rather than a simple pH buffer. Spent liquor containing 140–280 g/L Na₂O and an alumina-to-caustic weight ratio of 0.60–0.75 is contacted with bauxite in multi-pass tubular digesters or stirred autoclaves. Gibbsite-bearing bauxite digests at 140–160 °C, boehmite at 200–240 °C, and diasporic bauxite requires 240–270 °C. Residence time ranges from 10 min for some gibbsitic feeds to 120 min for refractory diasporic ores. Caustic consumption per tonne of alumina ranges from approximately 30 kg NaOH/t Al₂O₃ for low-silica gibbsite to 120 kg NaOH/t Al₂O₃ for high-silica diasporic ore, with the upper limit driven by chemical combination with reactive silica, not by evaporative losses. Flash-cooling trains depressurize the slurry through 8–12 stages, reducing temperature to 100–110 °C before atmospheric settlers.
| Bauxite mineralogy | Digestion temperature | Caustic concentration as Na₂O | Residence time |
|---|---|---|---|
| Gibbsite | 140–160 °C | 150–200 g/L | 10–60 min |
| Boehmite | 200–240 °C | 200–250 g/L | 30–90 min |
| Diaspore | 240–270 °C | 220–280 g/L | 60–120 min |
Desilication product is the dominant chemical sink for sodium hydroxide in high-silica bauxite circuits. Digested liquor with reactive silica above 6–8 g/L SiO₂ precipitates sodium aluminosilicate on heat-exchanger surfaces and in downstream pipes, reducing heat transfer coefficient and forcing acid washes every 30–90 days. Red mud separation uses high-rate thickeners followed by countercurrent decantation washers; underflow solids are maintained at 35–50 wt% and wash water ratios of 2.0–4.0 m³/t dry mud recover sodium hydroxide. Final washer overflow containing 5–10 g/L Na₂O is returned to the process; published data for a specific Bohua-linked bauxite source is limited, but the loss mechanism is chemically characterized. Organic contamination in Bayer liquor forms sodium oxalate, which co-precipitates and lowers caustic activity; evaporator scaling requires controlled oxalate removal via side-stream crystallization. Precipitation of gibbsite from clarified pregnant liquor is not a caustic-heavy step, but the spent liquor is regenerated by evaporation to 250–280 g/L Na₂O for recycle. Calcined smelter-grade alumina typically meets 98.5–99.5 wt% Al₂O₃ with particle size measured by ISO 13320:2020 and alpha-phase content by X-ray diffraction. The downstream terminal product is alumina consumed in Hall-Héroult reduction cells, where residual sodium oxide is specified at 0.3–0.5 wt% Na₂O to control electrolyte chemistry.
Across the kraft fibreline, sodium hydroxide is consumed as white liquor in the digester and as extraction-stage alkali in bleaching. In recausticizing, green liquor sodium carbonate reacts with calcium hydroxide in a slaker-causticizer train at 90–105 °C; causticizing efficiency is held at 78–85% because residual sodium carbonate above 15–20 g/L reduces digester alkali availability. Clarified white liquor carries total titratable alkali of 120–170 g/L NaOH+Na₂S, effective alkali of 80–115 g/L, and sulfidity of 25–35%. Softwood cooks at 155–170 °C receive an effective alkali charge of 16–22% on oven-dried wood; hardwood cooks at 150–160 °C use 13–18%. The H-factor is maintained between 800 and 2000 to achieve target Kappa numbers of 18–25 for linerboard and 25–35 for unbleached market pulp, measured by ISO 302:2015.
Following oxygen delignification, the peroxide-reinforced alkaline extraction stage consumes sodium hydroxide at 1.5–3.5 wt% on oven-dried pulp. The extraction tower operates at 70–90 °C, retention 60–90 min, and pH 10.5–11.5. Caustic soda saponifies chlorinated lignin fragments and neutralizes acidic oxidation products; the Kappa reduction across the extraction stage is monitored by ISO 302:2015. In cold caustic extraction for dissolving pulp, the sodium hydroxide concentration is raised to 5–9 wt% at 20–40 °C; this converts hemicellulose to soluble form and lifts alpha-cellulose above 90% for acetylation-grade dissolving pulp. Final brightness of bleached hardwood kraft is measured by ISO 2470-1:2016 and typically exceeds 88% ISO; dirt count is assessed against TAPPI visual dirt standards. Terminal products include kraftliner, bleached softwood market pulp, and dissolving pulp for viscose staple fibre.
Mercerizing with 18–25 wt% NaOH at 15–25 °C alters cellulosic crystalline structure only when width-controlled tension is applied. Tianjin Bohua liquid caustic soda at 50 wt% is diluted to the saturator concentration and the fabric enters a chain mercerizer or slasher mercerizer for 30–45 s; load cells govern the tension at the width-control section, not a generic high-tension setting. Hot wash water at 70–85 °C then removes caustic from the fabric, and countercurrent rinsing recovers 95–98% of the alkali as weak lye at 8–12 wt% NaOH. This weak lye is concentrated in a caustic recovery evaporator and returned to the saturator; the concentration loop prevents discharge of high-COD alkali to effluent. Tensile strength and elongation are measured by ISO 13934-1:2013; dye uptake change is determined by ΔE colorimetry after controlled dyeing, not by visual assessment. Residual alkali on processed fabric is determined by AATCC TM 81-2016.
At caustic concentration below 18 wt% the cellulose I to cellulose II transition is incomplete, and above 25 wt% the swelling increment diminishes while wash-water caustic loading increases. Mercerization is therefore operated inside a narrow window of 18–25 wt% NaOH. Residual alkali on greige fabric must be neutralized with acetic acid buffer before drying because cellulose at pH above 9 undergoes yellowing during high-temperature stenter finishing. Terminal products include high-density cotton shirting, denim, sewing thread, and industrial filter fabric where dimensional stability and higher wet modulus are specified.
For full-boiled kettle saponification, the caustic soda charge is fixed by the saponification value of the fat blend rather than by a single generic alkali addition. Tallow with a saponification value of 190–205 mg KOH/g requires 13.5–15.0 wt% NaOH on fat basis; coconut oil with a saponification value near 250–260 mg KOH/g requires 18–20 wt% NaOH on fat basis. The 50 wt% membrane-cell liquid is diluted to 25–30 wt% before injection into the open kettle or continuous saponification column, where the fat charge is preheated to 75–95 °C. Agitation is maintained at a rate sufficient to disperse the aqueous caustic phase without forming a stable emulsion; the reaction is continued until free alkali in neat soap falls to 0.05–0.15%.
Excess sodium hydroxide above approximately 0.3 wt% of fat charge promotes glycerol darkening and can gel the neat soap phase, so the caustic feed is trimmed by sampling free alkali every 15–30 min in batch kettles. The wet soap is washed with sodium chloride brine to remove glycerol and then dried under vacuum in a spray dryer or wiped-film evaporator to total fatty matter 76–82%. Total alkali and moisture are determined by ISO 684:1974, and aqueous pH is measured by ASTM D1172-15. Terminal products include toilet soap bars, laundry bars, soap noodles, and soap flakes for industrial cleaning.
In municipal water treatment, liquid sodium hydroxide is selected over lime where alkalinity correction must avoid adding calcium hardness. The 25 wt% or 50 wt% solution is metered by positive-displacement diaphragm pumps into a flash mixer operating at velocity gradient 300–1000 s⁻¹ and hydraulic residence time 1–5 s. Finished drinking water is held at pH 7.8–8.4 and total alkalinity 20–50 mg/L as CaCO₃ to reduce lead and copper corrosion. The dose is determined by jar testing and online pH analyzers calibrated to ISO 10523:2008; a universal mg/L hydroxide dose is not used because source alkalinity, temperature, and carbon dioxide content shift the titration curve. Storage of 50 wt% NaOH requires heat tracing because its freezing point is near 12 °C; 25 wt% remains pumpable at lower temperatures.
For acidic industrial wastewater, sodium hydroxide raises pH from 2–4 to permitted discharge limits of 6.5–8.5 in a neutralization tank with retention 2–5 min. In-line static mixers are avoided when hardness exceeds 150 mg/L as CaCO₃ because rapid hydroxide addition precipitates calcium carbonate scale; instead, flash mixing is followed by a reaction basin. The terminal product is corrosion-stable potable water or neutralized effluent that meets receiving-water pH limits. Compliance is documented against AWWA B501-19 for sodium hydroxide quality and NSF/ANSI/CAN 60 for potable use.
| Standard | Scope | Specified indicator |
|---|---|---|
| AWWA B501-19 | Liquid sodium hydroxide for potable water | Heavy metals and strength conforming to purchase specification |
| NSF/ANSI/CAN 60 | Drinking water treatment chemicals | Single-product health effects criteria |
| ISO 10523:2008 | pH measurement in water | Measurement uncertainty ≤ 0.05 pH |
Sodium hydroxide enters biodiesel synthesis as a methoxide precursor, not as a direct solid addition to raw oil. Catalyst loading ranges from 0.3–1.0 wt% NaOH on oil basis, and methanol:oil molar ratio is held at 6:1. The methoxide solution is prepared with anhydrous sodium hydroxide and dry methanol containing less than 0.1 wt% water, then transferred through closed stainless steel piping to prevent moisture pickup. Transesterification runs at 60–65 °C for 60–120 min in a conical-bottom reactor with two-stage turbine agitation. When free fatty acid content exceeds 2 wt%, hydroxide is diverted to soap formation; the process must use acid pre-esterification or reduce the base catalyst, otherwise phase separation slows and glycerine purity drops.
Soap in crude glycerine raises viscosity and stabilizes methyl ester-glycerol emulsions. Separation is performed by settling at 55–60 °C or by disc-stack centrifugation; soap content in crude FAME above 0.05 wt% increases water washing demand. Water washing is carried out at 50–55 °C with 3–10 vol% water, followed by vacuum drying at 90–110 °C and filtration through 1–5 μm media. Final B100 must meet ASTM D6751-23a or EN 14214; free glycerin is specified below 0.02 wt% and total glycerin below 0.25 wt% by ASTM D6584-17. The terminal product is fatty acid methyl ester blendstock for diesel engines.
Lye peeling in tomato and stone-fruit canning uses food-grade sodium hydroxide under controlled time-temperature-soda concentration windows. Peeling solutions of 1–3 wt% NaOH at 75–95 °C contact product for 30–120 s; loosened skin is removed by rotary rubber disc or water-spray peelers. A citric acid dip neutralizes residual surface alkali. Food-grade sodium hydroxide conforms to 21 CFR 184.1763 current good manufacturing practice and Food Chemicals Codex identity and impurity specifications. Published data for specific Tianjin Bohua food-grade lot residual values is limited; processors verify by rinse-water pH and titration, not by a universal residual limit. Terminal products include canned whole peeled tomatoes, peeled peaches, and frozen root vegetable products.
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Tianjin Bohua Caustic Soda designates industrial sodium hydroxide manufactured by chlor-alkali electrolysis at Tianjin Bohua Chemical Industry Co., Ltd. The product is placed on the market as liquid caustic soda at 32% and 50% NaOH by mass, and as solid anhydrous flake or pearl with NaOH content at or above 99.0%. Certificates of analysis reference GB/T 209-2018, Sodium hydroxide for industrial use, and the substance is identified by CAS 1310-73-2. Membrane-grade liquid produced at the Bohua site typically reports sodium chloride as NaCl at or below 0.005% for the 32% liquid, sodium carbonate at or below 0.1%, and iron as Fe₂O₃ at or below 0.0005%. The solid grades are hygroscopic and are specified with low carbonate pickup after drying. Applications include Bayer alumina digestion, Kraft and sulfite pulping, cotton mercerization, sulfonation neutralization, soap and detergent saponification, water treatment, and chemical synthesis where a low-chloride, low-transition-metal strong alkali is required.
The distinction between Tianjin Bohua membrane-grade caustic soda and diaphragm or mercury cell products is best resolved through the impurity spectrum carried into the finished solution. Membrane electrolysis uses a perfluorosulfonic or perfluorocarboxylic acid cation-exchange membrane that blocks chloride ion transport while allowing sodium ion migration. The resulting 32% NaOH catholyte contains substantially lower sodium chloride than diaphragm-cell catholyte, where a porous diaphragm separates anolyte and catholyte without preventing chloride migration. Mercury cell caustic soda can achieve low chloride, but the process has been largely phased out in China under mercury emission restrictions and may retain trace mercury. The following table summarizes typical reported impurity ranges in 50% NaOH across the three routes; actual lot values on a certificate of analysis govern acceptance.
| Parameter | Membrane | Diaphragm | Mercury |
|---|---|---|---|
| NaCl | ≤ 50 mg/kg | 5,000–12,000 mg/kg | ≤ 50 mg/kg |
| NaClO₃ | ≤ 10 mg/kg | 100–500 mg/kg | ≤ 5 mg/kg |
| Fe₂O₃ | ≤ 5 mg/kg | 50–200 mg/kg | ≤ 10 mg/kg |
The practical consequence is that membrane-grade Bohua material can be used in rayon spinning baths, food-contact cleaning, and pharmaceutical intermediate neutralization without downstream filtration to remove chloride or iron. Diaphragm-grade caustic soda, by contrast, may carry 0.5–1.2% NaCl and is generally restricted to pulp digesters, petroleum neutralization, or bulk pH adjustment where chloride tolerances are wider. Published data for this specific configuration is limited with respect to lot-to-lot variance, but the listed ranges reflect chlor-alkali process literature. Chlorate accumulation is also lower in membrane-grade product because chlorate formed in the anolyte cannot readily migrate through the cation-exchange membrane. Sulfate carryover is controlled by brine sulfate purge and membrane nanofiltration before electrolysis, so the product certificate often reports sulfate as Na₂SO₄ at or below 0.002% in liquid grades.
The Bohua production route employs ion-exchange membrane electrolyzers with coated titanium anodes and nickel cathodes. Brine purification before the membrane cell includes primary settling, filtration, and secondary ion-exchange polishing to reduce hardness below 0.02 mg/L as Ca+Mg before entering the anode compartment. Depleted brine is dechlorinated and resaturated, minimizing chlorate accumulation in the final product. Because no asbestos diaphragm or mercury cathode is present, the product stream does not carry related fibers or mercury residues. The cathode-side evaporation train concentrates membrane cell liquor to 50% NaOH and may include a falling-film evaporator where liquor is recirculated under vacuum at approximately 90–120°C. Solid flake or pearl is produced by further concentration in nickel or nickel-alloy evaporators and flaking or prilling equipment. The resulting anhydrous solid is characterized by low water content, typically ≤ 1.0% loss on drying, and low sodium carbonate. Oxygen and carbon dioxide ingress during packaging are controlled by heat sealing and stacking limits.
| Form | NaOH (% by mass) | Na₂CO₃ (% by mass) | NaCl (% by mass) | Fe₂O₃ (% by mass) |
|---|---|---|---|---|
| Liquid 32% membrane grade | ≥ 32.0 | ≤ 0.10 | ≤ 0.005 | ≤ 0.0005 |
| Liquid 50% membrane grade | ≥ 50.0 | ≤ 0.15 | ≤ 0.008 | ≤ 0.0008 |
| Solid flake or pearl | ≥ 99.0 | ≤ 0.50 | ≤ 0.03 | ≤ 0.005 |
At liquid concentrations of 32% and 50%, bulk shipment is carried out in FRP or lined carbon steel tank trucks with unloading pumps rated for pH 14 corrosive service. Crystallization onset is observed near 15 °C for 32% NaOH and near 12 °C for 50% NaOH; storage tanks should therefore be insulated or heat traced where site ambient temperatures drop below those thresholds. Dissolution of solid flake or pearl in water is exothermic with an enthalpy of solution of approximately −44.5 kJ/mol; the recommended addition sequence is solid into agitated cool water, never water onto a static bed of solid. The solid grades are supplied in 25 kg multiwall paper/PE or PP/PE bags and should be stored at relative humidity below 60% to limit moisture and carbon dioxide uptake. Avoid contact with aluminum, zinc, tin, brass, and galvanized surfaces because hydrogen evolution and corrosion are immediate; use stainless steel, PTFE-lined, or high-density polyethylene wetted parts.
In Bayer alumina digestion, 50% NaOH is let down into process streams to maintain caustic concentrations of 100–250 g/L as Na₂CO₃-corrected Na₂O at digestion temperatures of 150–250°C. Low chloride in membrane-grade material reduces chloride accumulation in Bayer liquor and downstream aluminum hydroxide washing circuits. In linear alkylbenzene sulfonic acid neutralization for anionic surfactants, 32% or 50% NaOH is metered to maintain a final paste pH of 5.5–7.0, with the low iron and chloride content preventing off-color bodies and salt excursions in the dried surfactant. For batch neutralization, a jacketed stainless steel reactor with high-shear dispersion at 60–80°C is used; localized overtreatment above pH 9 is avoided because it can hydrolyze sulfonate esters and liberate unsulfonated oil. In Kraft pulping, caustic soda is used to fortify white liquor to effective alkali of 15–25% Na₂O on oven-dry wood, with sulfidity maintained at 25–35% and cooking temperatures between 155°C and 170°C. Cotton mercerization uses 18–24% NaOH at 15–25°C under tension; low iron content avoids fabric yellowing, while low chloride reduces corrosion of mercerizing frames and washing baths. For municipal water treatment, caustic soda is dosed to maintain pH 8.5–9.5 for corrosion control in distribution systems; the applicable reference is AWWA B501 for sodium hydroxide.
In dairy, beverage, and brewery cleaning-in-place lines, Tianjin Bohua liquid caustic soda is diluted to 2–3% NaOH and circulated at 70–80°C for 20–30 min to remove proteinaceous and fatty soil. For food-contact use, the product must satisfy the applicable purity requirements of GB 1886.20-2016 or an equivalent food chemical codex monograph when designated as food grade; the manufacturer’s certificate should be evaluated before use. Transition-metal content is controlled because residual iron catalyzes oxidative degradation of unsaturated oils and can discolor bottle-wash caustic. Chloride levels are kept low because chloride promotes stress-corrosion cracking in austenitic stainless steel at elevated temperatures, particularly in the presence of residual tensile stress. Operational boundaries include avoiding the use of potable water containing high temporary hardness for final rinse, since saponification of fatty soils can form calcium soaps and scale. In rayon production, low transition metals and low chloride in 18–20% NaOH steeping liquor preserve cellulose color and protect spinnerette alloys; the steeping operation typically runs at 45–55°C to form alkali cellulose before xanthation. Solid flake and pearl grades are preferred in small and medium-scale neutralization, drilling fluid alkalinity, and laboratory reagent make-down where liquid bulk receipt is impractical. Batch dissolvers constructed of carbon steel with steam jackets are used, with temperature maintained below 80°C to limit aerosol carryover. Published data for this specific configuration is limited with respect to long-term storage stability of dilute working solutions, so each user should validate in-house dilution protocols against the certificate of analysis and corrosion-monitoring records.
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