Befar Group Caustic Soda Flakes

What Caustic Charge Is Required for Effective Kraft Delignification?

White liquor preparation in a kraft mill uses flake NaOH as make-up alkalinity after recausticizing losses and recovery boiler reduction inefficiencies. The effective alkali (EA) charge, expressed as equivalent Na₂O on oven-dry wood, is set between 16 wt% and 22 wt% for softwood pine and 12 wt% to 18 wt% for mixed hardwood, with sulfidity controlled at 28–35%. Flake NaOH is added to the smelt dissolving tank or weak black liquor storage to raise the EA of white liquor from the recovery loop to target values; typical make-up is 8–25 kg NaOH (100%) per oven-dry metric tonne of unbleached pulp, dependent on brown stock washing soda loss and lime kiln recausticizing efficiency.

Inside a continuous downflow digester such as a Kamyr two-vessel hydraulic system or Lo-Solids downflow loop, impregnated chips are heated with direct steam from 115 °C to 150–170 °C, and H-factor is maintained between 800 and 1,800 depending on target kappa number. Residual effective alkali at the digester outlet is held at 3–6 g/L Na₂O; below 2 g/L, lignin reprecipitation raises kappa variability by 4–6 units and increases bleach chemical demand. Kappa number is measured by the method in ISO 302:2015. The recovery furnace, causticizing plant, and lime kiln are operated to comply with the EU BAT Reference Document for Production of Pulp, Paper and Board (2015), which sets emission and closed-loop recovery limits for sulfur species; low-carbonate flake NaOH (≤0.4 wt%) reduces dead load on the lime cycle. Brown stock washing uses pressure diffusion washers or DD washers at dilution factor 1.5–3.0 m³/ODt, with carryover of dissolved lignin to the bleach plant maintained below 10 kg COD/ODt.

Washed brown stock is oxygen-delignified and bleached in short-sequence ECF lines. Terminal grades include unbleached kraft paper for cement bags and linerboard, bleached kraft for printing and writing papers, and dissolving pulp for viscose staple fiber.

Befar Group flake caustic soda with NaOH mass fraction ≥98.5 wt% and sodium carbonate content ≤0.4 wt% is reintroduced into Bayer liquor cycles where post-precipitation spent liquor correction is required. In refineries processing bauxite with reactive silica content between 1.0 wt% and 6.0 wt%, the Na₂O balance requires caustic make-up of 40 kg to 120 kg NaOH (100% basis) per metric ton of alumina produced, depending on the kaolinite-to-gibbsite ratio and the extent of pre-desilication. The flake is dissolved in a dedicated lixiviant preparation tank fabricated from stress-relieved carbon steel, or in low-pressure steam-jacketed 304L stainless steel mixers where chloride accumulation from recycled liquor exceeds 10 g/L; dissolution exotherm is controlled by feedback throttling of flake screw feeders to maintain 70–80 °C in the dissolver. The clarified caustic solution is metered into the recirculating spent liquor header ahead of the slurry preheater; feedforward mass flow controllers adjust flake feed based on online conductivity and density measurement to maintain a target Na₂O/Al₂O₃ molar ratio of 1.35–1.55 in the feed slurry.

Digestion liquor is held at 140–250 g/L Na₂O and sent to high-pressure autoclaves operating at 145–270 °C and 1.0–5.5 MPa, depending on whether the bauxite is gibbsitic, boehmitic, or diasporic. After multistage flash cooling to 100–105 °C, the slurry enters high-rate thickeners and countercurrent red mud washing in 6–8 stages. Security-filtered pregnant liquor is then seeded with alumina trihydrate in air-lift precipitation vessels; the caustic-to-alumina molar ratio is raised to 1.6–1.8 to initiate supersaturation, with precipitation residence times of 20–36 h yielding gibbsite crystals of 45–120 µm mean diameter after classification.

Flake quality follows GB/T 209-2018 for solid ion-exchange membrane grade, with chloride mass fraction ≤0.05 wt% and iron oxide ≤0.004 wt%. Red mud and effluent control are aligned with the IFC Environmental, Health, and Safety Guidelines for Aluminum Manufacturing (2007), requiring pH after neutralization in the range 6–9 and TSS limits before discharge. Terminal products include smelter-grade alumina with α-Al₂O₃ content ≥98.3 wt% and loss on ignition 0.6–1.0 wt%, chemical-grade alumina for ceramics, and fine alumina trihydrate for flame-retardant fillers.

Batch saponification of palm stearin or tallow with 32–36 wt% NaOH solution proceeds at a stoichiometric ratio of 0.95–1.00 mol NaOH per mol esterified fatty acid, with free residual alkali in the resultant neat soap limited to 0.05–0.15 wt% Na₂O before drying. The flake is dissolved in softened water within a jacketed dissolver and filtered through 5 µm polypropylene bag filters to remove carbonate haze; addition to the oil charge is carried out under high-shear mixing at 80–95 °C to prevent localized saponification and gel formation. The reaction vessel is a 20–50 t stainless steel kettle with counter-rotating scraped-surface agitators, and saponification is completed in 2–4 h.

The neat soap is washed with sodium chloride brine at 8–12% NaCl to remove glycerol and excess alkali; spent lye is sent to glycerin recovery, where it is acidulated and evaporated to 80% crude glycerin. Vacuum spray drying at 60–70 °C and 2.7–5.3 kPa absolute pressure reduces moisture to 10–13 wt%, after which the dried soap is blended with builders, extruded through twin-screw plodders, and stamped into finished bars. Free caustic alkalinity is measured in accordance with ASTM D460-91, and the finished detergent product meets the biodegradability and labeling requirements of EC No 648/2004. Terminal product grades include toilet soap bars with moisture ≤13 wt%, industrial laundry soap chips, and sodium-based greases produced by in situ reaction of fatty acids with NaOH during hot processing.

When Caustic Soda Flakes Are Dissolved to 280–300 g/L for Slack Mercerization

Slack mercerization of cotton knitted fabric is performed in open-width or rope form with NaOH concentration in the impregnation bath of 220–300 g/L, typically 280–300 g/L, corresponding to 18–25 °Bé, at a well-controlled temperature of 15–25 °C. The flake NaOH is predissolved in a chilled water circuit with plate heat exchanger cooling to counteract the heat of solution; without cooling, bath temperature rises above 40 °C and the degree of swelling drops sharply. A wetting agent concentration of 25–50 g/L, selected from cresol-free sulfated alcohol or phosphate ester types, is required for uniform wetting because pure NaOH solution above 200 g/L has poor fiber penetration.

Fabric after scouring and bleaching is passed through the mercerizing bath with a dwell time of 30–60 s, then stretched on a chain frame to impose 2–5% width extension while the caustic is washed off countercurrently at 70–80 °C. Residual alkali is neutralized in a final sour bath with acetic acid to pH 5.5–6.5. The degree of mercerization is assessed by the barium activity number method specified in AATCC TM89-2019; acceptable values for yarn mercerization are 150–170, while values below 130 indicate incomplete swelling. NaOH concentration below 180 g/L produces only surface luster without full fiber modification, and concentrations above 300 g/L combined with dwell times over 90 s can cause 2–4% weight loss and pilling. Published data for the interaction of slack mercerization with cellulosic certification schemes is limited. Tensile strength retention is monitored per ISO 13934-1:2013 to ensure the caustic treatment does not reduce fabric strength below the buyer specification. Caustic recovery from weak wash water using evaporation to 300 g/L for reuse reduces fresh flake consumption in integrated knit finishing.

Terminal outputs include high-luster mercerized cotton jersey, dyed or printed apparel fabric, and mercerized sewing thread with increased strength and dye affinity.

Continuous sodium hypochlorite generators produce bleach solution by reacting 18–20 wt% NaOH with compressed chlorine gas at a molar ratio of 1.98–2.05 mol NaOH per mol Cl₂, with the absorber operating at 25–35 °C and pH 12.5–13.0. Flake NaOH is first dissolved in demineralized water and cooled by a plate-and-frame heat exchanger to remove the heat of dilution; final NaOH concentration must not exceed 20 wt% to avoid chlorate formation and product decomposition. The reactor is constructed of titanium or lined carbon steel because hypochlorous acid attacks stainless steel above 40 °C. Chlorine gas is sparged through a packed column or venturi absorber at 0.1–0.3 MPa, and the resulting sodium hypochlorite is withdrawn at 10–15 wt% available chlorine with residual NaOH at 0.5–1.5 wt%.

Compliance for the incoming caustic follows AWWA B501-19, and the finished hypochlorite product is controlled under AWWA B300-18 with additional certification to NSF/ANSI/CAN 60 where the solution is dosed into municipal water systems. Storage is in fiberglass-reinforced plastic tanks with UV-stabilized exteriors at ≤20 °C to limit chlorate formation. Terminal product types are 12.5% trade percent sodium hypochlorite for municipal disinfection, industrial sanitizing bleach, and wastewater cyanide oxidation.

Free Fatty Acid Neutralisation in Soybean and Palm Oil Streams

Refining of crude soybean and palm oil uses NaOH flakes dissolved to 16–20 °Bé (11–14 wt% NaOH) for neutralisation of free fatty acids in degummed oil. The caustic dosage is calculated as 0.13–0.15 kg NaOH (100% basis) per kg of FFA plus an empirical excess of 10–20%, depending on phospholipid carryover after enzymatic degumming. Excess NaOH beyond this window saponifies neutral triglycerides; oil loss is observed to rise from approximately 1.2 to 2.5 times the FFA content. The oil and alkali are mixed in a high-shear disc contactor or centrifugal mixer at 60–80 °C, with a contact time of 15–30 s before entering a disc-stack centrifuge at 6,500–7,200 rpm to separate soapstock from neutralized oil.

After primary separation, the neutralized oil is water-washed with 10–20% hot soft water, centrifuged again, and vacuum-dried at 85–90 °C and 4–6 kPa absolute pressure. Bleaching follows with acid-activated clay at 0.5–1.5 wt% on oil, then steam deodorization at 240–250 °C and 0.3–0.6 kPa for 60–120 min. Soapstock from the separator is acidulated with sulfuric acid to produce acid oil for oleochemical or animal feed use. Food-grade compliance for sodium hydroxide is established under 21 CFR 184.1763 and the corresponding Food Chemicals Codex monograph. Terminal products include RBD soybean oil for packaged frying oil, RBD palm olein for margarine, and specialty oil fractions for infant formula bases.

A 5–10 kg NaOH Make-Up per 1000 m² of Extruded Profile

Anodising pretreatment for extruded aluminium profiles uses a caustic etch bath with 40–60 g/L NaOH, 10–20 g/L dissolved aluminium, and 2–5 g/L sodium gluconate as a complexing agent to suppress aluminium hydroxide scale on tank walls. The bath operates at 50–60 °C; immersion time of 8–20 min removes 3–10 µm of surface metal. Below 10 g/L dissolved Al, etch rate accelerates and matte finish becomes uneven, while above 20 g/L the etch rate falls and sludge generation increases. Bath start-up and steady-state make-up addition are controlled at 5–10 kg NaOH flakes per 1000 m² of extruded profile surface, as determined by drag-out measurement and weekly bath analysis. Etch bath sludge is dewatered in a plate-and-frame filter press, and dissolved aluminium is reduced by cooling crystallization to maintain the working range.

After etching, the profiles are rinsed in double counterflow tanks and de-smuted in 10–20 vol% nitric acid at ambient temperature for 1–3 min to remove intermetallic smut. The anodizing stage is carried out in 15–20 wt% sulfuric acid electrolyte at 18–22 °C, with current density 1.2–1.8 A/dm². Final coating thickness conforms to ISO 7599:2018 for architectural anodic coatings or MIL-A-8625F for military-specification coatings, and sealing quality is assessed by the mass-loss method of ISO 3210:2017. Terminal products are anodized aluminium window and curtain-wall profiles, automotive trim, and extruded heat sinks.