Caustic Soda 10KG

For drinking water pH correction and process water alkalinity control, the 10 kg sodium hydroxide package is made down to a 20-25% w/w stock solution in a 100 L high-density polyethylene or 316L stainless steel make-down tank equipped with a side-entry mixer. The anhydrous pellets or flakes are added slowly to pre-chilled demineralised water at 15-35°C because dissolution releases 44.5 kJ/mol and can push the solution above 80°C if the addition rate is uncontrolled. The resulting solution is continuously metered by a diaphragm dosing pump through a static mixer into the treated stream, with a pH analyser setpoint of 7.4-8.0 and a control dead band of ±0.2 pH units. The stoichiometric neutralisation of dissolved carbon dioxide is 0.91 mg/L of 100% NaOH per 1.0 mg/L of free CO₂, and the typical dosage for soft surface water ranges from 1 mg/L to 30 mg/L as 100% NaOH depending on alkalinity and temperature. Compliance for drinking water application is provided by EN 896:2012, NSF/ANSI/CAN 60, and AWWA B501-19; pH verification follows ISO 10523:2008 or ASTM D1293-18. The terminal treated products are potable water, low-pressure boiler feedwater, and closed-loop cooling water. Field production-scale observation: diaphragm pump check valves and injection quills in carbon-dioxide-rich water accumulate calcite and sodium carbonate scale when the stock solution is exposed to atmospheric air, requiring routine acid descaling with 5% citric or hydrochloric acid. The solution must not be stored or injected through aluminium, zinc, tin, galvanised steel, or unlined carbon steel when the temperature exceeds 40°C, because hydrogen evolution and pitting occur.

How Does Sodium Hydroxide Dosage Separate Transesterification from Saponification in Low-FFA Oil Batches?

Transesterification of low-free-fatty-acid oils with sodium methoxide prepared from the 10 kg package is governed by the acid number and moisture content of the feedstock. When the acid value is below 2.0 mg KOH/g and moisture is below 0.25% w/w, catalyst addition is 0.3-0.5% w/w of oil as 100% NaOH; the solid sodium hydroxide is dissolved in anhydrous methanol at 20-40°C in a closed 316L stainless steel or carbon steel methoxide tank with nitrogen blanketing. The methoxide solution is transferred into a batch reactor holding oil at 55-60°C, with a methanol-to-oil molar ratio of 6:1-9:1 and reaction temperature maintained at 60-65°C for 60-120 min under a 200-500 rpm pitched-blade agitator. The downstream terminal product is fatty acid methyl ester meeting EN 14214:2012+A2:2019 and ASTM D6751-23a specifications, together with crude glycerol of 70-80% purity. Ester content is measured by EN 14103:2020, kinematic viscosity by ISO 3104:2020, acid number by ASTM D664-18e2, and flash point by ASTM D93-20. The process boundary is narrow: when NaOH exceeds 0.6% w/w, saponification of free fatty acids and triglycerides consumes catalyst and generates soap at the interface, increasing the polar phase viscosity and delaying phase separation beyond 8-12 h. At 0.8% w/w and moisture above 0.3%, the alkali reacts irreversibly to form soap gel; the downstream ester content can fall below the 96.5% minimum required by EN 14214:2012+A2:2019. For feedstocks with acid value above 2.0 mg KOH/g, the production sequence must include an upstream esterification stage with sulfuric acid and methanol, because direct sodium hydroxide neutralisation raises the catalyst demand by 0.713 kg 100% NaOH per 1,000 kg oil per 1.0 mg KOH/g FFA, equivalent to 0.071% w/w, and does not reduce the saponification risk proportionally.

Dairy evaporators, brewhouse fillers, and pharmaceutical mixing vessels are cleaned with 0.5-2.0% w/w sodium hydroxide at 60-85°C, made up from the 10 kg pack in a clean-in-place skid storage tank. The CIP circuit operates with a centrifugal pump delivering 1.5-2.5 m/s flow velocity in pipework and 2-4 bar pressure at spray balls, with a contact time of 20-45 min and a final potable-water rinse until the conductivity returns to within 10 µS/cm of the incoming water. Sodium gluconate or low-foam phosphonate at 0.05-0.2% w/w is added where water hardness exceeds 300 mg/L as CaCO₃, because caustic alone precipitates calcium and magnesium salts that block spray nozzles. Compliance for food-contact equipment cleanliness is validated under FDA 21 CFR Part 117 CGMP, EHEDG Doc 1, and ISO 14159:2002; no direct chemical residue standard applies to the cleaning agent itself, but rinse-water verification by conductivity and pH is recorded. The terminal products are cleaned stainless steel tanks, plate heat exchangers, filling lines, and pasteurisers. Process field data: after the first CIP cycle at 85°C, the sodium hydroxide concentration typically drops by 0.1-0.3% w/w because of soil neutralisation and drag-out, so conductivity-controlled dosing is required rather than fixed timer-based injection. EPDM gaskets exposed to 2.0% caustic at 85°C for more than 1,000 h show embrittlement; perfluoroelastomer or PTFE components are preferred for repeated cycles. Sodium hydroxide should not be circulated through aluminium, brass, or tin components, and it should not be mixed with sodium hypochlorite unless a controlled excess alkali of 0.5-1.5% is required for stable hypochlorite formation.

Saponification Kettle Free-Alkali Limits in Vegetable Oil and Tallow Charge Reconciliation

Vegetable-oil and tallow charge reconciliation begins with the saponification value of the fat. The stoichiometric sodium hydroxide requirement per 1,000 kg of oil is calculated as oil mass × saponification value × 40/56.1 × 1/1,000, giving 17.8-18.9% w/w NaOH for coconut oil with saponification value 250-264 mg KOH/g and 13.1-14.0% w/w for olive oil with saponification value 184-196 mg KOH/g. A lye discount of 5-8% is applied to leave a superfat fraction, and the 10 kg package is dissolved in 12-20 L of distilled water to produce a 33-50% w/w caustic solution. The saponification kettle is held at 70-90°C with high-shear dispersion at 500-1,500 rpm; trace development occurs within 20-90 min depending on the fatty acid composition and mixing intensity. The terminal products are cold-process bar soap, liquid soap base, and castile soap; free caustic alkalinity in the finished soap is measured by ASTM D460-18 or ISO 684:1974 and must not exceed 0.1% as NaOH in direct skin-contact bars. In the European Union, the cosmetic safety assessment is recorded under Regulation (EC) No 1223/2009. The operational boundary for sodium hydroxide overdosing is narrow: free alkali above 0.1% causes skin irritation and accelerates rancidity by attacking the triglyceride-derived glycerol backbone under trace moisture, whereas free alkali below 0.02% due to over-fatting can leave unreacted oil pockets, reducing bar hardness and increasing surface tack. Production records from jacketed kettles show that the temperature overshoot above 90°C during dissolution of solid NaOH into the hot oil-water phase is a more frequent cause of false trace than the actual saponification rate, because vapour bubbles mimic trace viscosity and lead to pouring before full neutralisation.

Fruit and vegetable peeling lines use sodium hydroxide as a controlled depolymerisation agent for pectic substances in the middle lamella. For peaches and tomatoes, the 10 kg material is made into a 1.5-5.0% w/w solution at 70-95°C and applied for 30-180 s; for Spanish-style green olives, the concentration is 2.0-3.5% w/w at 15-25°C with lye penetration checked until it reaches two-thirds of the flesh thickness; for pretzel dough, the pieces are immersed in 3-5% w/w caustic solution at 85-95°C for 5-20 s before salt application and baking. The downstream process equipment is a continuous lye peeler with spray manifolds, a dwell screw conveyor, rubber disc scrubbers, and a citric acid neutralisation bath at 0.5-1.0% w/w. Terminal processed products include canned peeled tomatoes, frozen peach dice, Spanish-style green olives, and dark pretzel bread. Regulatory status for food use is established by FDA 21 CFR 184.1763; table olives must meet CODEX STAN 66-1981, and product pH verification follows AOAC 981.12. The process boundary is defined by rinsing and neutralisation: residual surface pH above 8.0 after the final rinse indicates incomplete citric acid neutralisation and can cause off-flavours, while prolonged lye contact beyond 180 s in thin-skinned fruit increases peel loss by 2-4 percentage points and reduces drained weight. Sodium hydroxide peeling is not interchangeable with sodium carbonate in pretzel operations, because the Maillard browning response and dough surface alkalisation differ; published data for this specific substitution in industrial pretzel lines is limited.

When Mercerisation Caustic Concentration Falls Below 24°Bé, Fibre Swelling and Lustre Development Are Not Uniform

Cotton fibre swelling in sodium hydroxide solution is concentration- and temperature-dependent: below 24°Bé, approximately 18% w/w NaOH, the fibre cross-section does not decrease the lumen sharply enough to generate uniform lustre, while above 25% w/w the solution viscosity and air-contact carbonate hardening create handling constraints. The 10 kg package is made down to a mercerising bath of 18-25% w/w NaOH at 15-25°C, with a high-alkali stable wetting agent at 0.2-0.5 g/L. Fabric is processed in a chainless merceriser or clip stenter for 30-120 s under controlled tension, followed by recovery washing and neutralisation with 0.5-1.0% acetic acid. For caustic scouring prior to bleaching, the addition is 3-6% on weight of fabric sodium hydroxide in a kier or jigger at 95-100°C for 30-60 min. Compliance for residual fabric pH is tested by ISO 3071:2005 with a target of 5.5-8.0, and mercerisation process control is referenced to AATCC TM 89-2019; finished textiles are expected to satisfy Oeko-Tex Standard 100 limits for extractable formaldehyde and heavy metals, although sodium hydroxide itself is not the regulated residue. The terminal products are mercerised cotton yarn, shirting, denim, and bed linen. Operational boundary: if the bath temperature rises above 30°C, the swelling equilibrium shifts and the same fabric loses dimensional stability and lustre, while tension loss during dwell allows length shrinkage of 20-25%. Mercerisation under no tension after scouring is not equivalent to slack-mercerisation; the fabric enters a plastic state and must be held dimensionally until the first recovery wash.

Effective Alkali Charge in Laboratory Kraft Digesters and Kappa Number Control

Laboratory kraft digesters use sodium hydroxide as a make-up alkali to correct white liquor effective alkali to 16-22% Na₂O on oven-dry wood. The 10 kg package is dissolved to produce a make-up solution that is added to recirculated white liquor with sulfidity 25-35%; the resulting liquor-to-wood ratio is 3:1-4:1. Digestion proceeds at 150-170°C in an electrically heated rotating bomb, with H-factor controlled between 1200-2000 for softwood; the pressure vessel is rated for 8-10 bar and cools to 80°C before blowdown. The terminal product is unbleached softwood kraft pulp with kappa number 25-35 measured by ISO 302:2015, and the resulting pulp is used in linerboard, sack paper, and high-burst kraft grades. Compliance for caustic soda test methods in pulp mill laboratories is referenced to TAPPI T 624; black liquor residual active alkali is titrated against the effective alkali charge before discharge. Process boundary: effective alkali charges above 24% Na₂O degrade carbohydrate yield and increase black liquor solids without proportional kappa reduction; charges below 15% Na₂O leave shives and high kappa numbers above 40. Use of sodium hydroxide alone without sodium sulfide reduces delignification selectivity and is limited to oxygen pre-extraction or neutral sulfite pulping variations. Production-scale recovery boilers are downstream of the pilot digester, but the 10 kg quantity is insufficient for full-scale liquor make-up; published data for mill-scale conversion from kraft to soda process using this package size is limited.