Natural gas contactors operating on high-CO2 produced gas are frequently converted from primary amine solvents to diethanolamine-based aqueous blends when reboiler steam cost outranks acid-gas slip constraints. In a regeneration loop, a 25–30 wt% DEA solution is circulated at a lean loading of 0.10–0.15 mol acid gas/mol amine, while rich loading is capped at 0.35–0.45 mol/mol to avoid excessive carbon steel corrosion in rich-amine piping. The absorption column, typically a trayed or structured-packed vessel, operates at 35–50 °C and 20–70 bar(g) depending on feed-gas composition; the regenerator reboiler is held at 115–125 °C and 1.7–2.1 bar(a). Field operation shows that solvent loss is dominated by stripper-overhead vaporisation carryover and chemical degradation to heat-stable salts, not by pump leakage. A rich-amine flash drum, carbon filtration on a lean-amine slipstream, and a vacuum reclaimer are therefore specified when heat-stable salt concentration exceeds 0.5 wt% of the circulating solution. Post-weld heat treatment of carbon steel piping is required when rich loading exceeds 0.35 mol/mol and H2S partial pressure is above 0.5 bar. Product gas is checked for CO2 content by ASTM D1945-14 and for sulfur compounds by ISO 6974-1:2012 or ASTM D5504-20; pipeline gas commonly requires H2S below 4 ppmv, while LNG feed pretreatment targets CO2 below 50 ppmv. Terminal outputs are pipeline-quality sales gas, a Claus-plant acid-gas stream, and, where integrated, CO2 for enhanced oil recovery or sequestration. Regenerator reboiler duty in this service normally falls between 3.5 and 4.2 MJ/kg CO2 captured; higher duties indicate salt accumulation, tray fouling, or lean/rich exchanger bypassing.

In closed-circuit cement grinding circuits, diethanolamine is metered onto the mill feed belt or sprayed into the first compartment of the ball mill at a dosage of 0.02–0.05 wt% of clinker mass, with 150–400 g/t clinker being a common window for aqueous blends. The product is usually supplied as a 25–40 wt% aqueous formulation with triethanolamine and triisopropanolamine, because DEA alone at high dosage can cause pack-set variation and inconsistent separator efficiency. The amine adsorbs on clinker fines and grinding-media surfaces, reducing agglomeration, ball coating, and the cushioning effect inside the mill, which increases mill throughput and narrows the particle-size distribution at a given Blaine fineness. Production-scale ball mills with 2.4–4.6 m diameter and closed-circuit separators show that the benefit is more pronounced at high circulating loads, where separator oversize return is high and agglomeration is the throughput-limiting variable. Compressive strength development is measured according to ASTM C109/C109M-21, setting time according to ASTM C191-21, and air content by ASTM C185-20; the processing addition must meet the requirements of ASTM C465-23 for both early-age performance and 28-day compressive strength. Addition levels above 0.05 wt% are evaluated on a trial basis because DEA and triethanolamine can retard setting and reduce 1-day strength. Terminal products are Portland and blended cements under EN 197-1:2011 or ASTM C595-23, used in ready-mixed concrete, precast elements, and bagged mortar.

What Limits Borate Ester Stability in Water-Dilutable Cutting Fluid Concentrates?

Diethanolamine is condensed with boric acid to form a borate ester complex in the concentrate stage of water-dilutable metalworking fluids. A typical soluble-oil or semi-synthetic concentrate contains 1.0–2.5 wt% DEA and 0.5–1.2 wt% boric acid, producing a buffered pH of 8.8–9.5 after dilution to 5 vol% in water. The borate ester provides ferrous corrosion protection by forming a polar film on exposed cast iron and steel surfaces, and its stability depends on free alkanolamine content, water hardness, and top-up pH control. In production, the condensation is run under vacuum at 80–100 °C to remove water; residual free DEA is titrated by acid-base titration, and the concentrate is checked for clarity and pH. Metalworking fluid performance is evaluated by ASTM D4627-22 for iron chip corrosion, while dilution water hardness is measured by ASTM D1126-17. When sump water hardness exceeds 300 mg/L CaCO3, calcium and magnesium salts can compete with the amine-borate complex and produce haze or residue; chelating agents or deionized water are used to prevent this failure mode. In a central coolant system, tramp oil, bacterial contamination, and evaporation shift the pH upward; if pH exceeds 10.0, aluminum staining can occur on sensitive aerospace alloys, so pH is maintained by dosing fresh concentrate rather than adding neat DEA. Final products include high-lubricity soluble oils, semi-synthetic coolants for transfer lines, and grinding fluids for bearing steel.

Methanol-Stripped Condensation with Methyl Esters Yields Alkanolamides

Diethanolamine is reacted with fatty acid methyl esters, such as methyl laurate or methyl oleate, to produce diethanolamides for heavy-duty detergents, degreasers, and oilfield cleaning formulations. The reaction is performed at a methyl ester-to-DEA mole ratio of 1:1.0 to 1:1.05, with sodium methoxide added at 0.1–0.4 wt% as a catalyst, in a vacuum-rated stainless steel or glass-lined reactor equipped with an internal steam coil. The batch is heated to 90–110 °C and methanol is distilled overhead at 50–100 mbar(a) until the acid number falls below 3 mg KOH/g as measured by ASTM D664-18e2; free diethanolamine is controlled between 2 and 7 wt% because excess amine contributes to water-in-oil emulsification but may cause yellowing in certain solvent blends. Production-scale reactors are typically 5–20 m3 in volume, and the methyl ester feed is staged to avoid excessive foam from methanol evolution. Vacuum-pump vapor lines are fitted with chilled condensers to recover methanol, and the product is discharged through a filter to remove sodium methoxide residues. The resulting alkanolamide is used at 2–5 wt% in industrial hard-surface cleaners and solvent degreasers as a foam stabilizer, thickener, and low-temperature wetting agent. Use in leave-on personal-care products is restricted under EC 1223/2009 because secondary amine-derived amides may form nitrosamines; industrial cleaning formulations are evaluated under REACH 1907/2006 but fall outside the cosmetic restriction.

When Diethanolamine Replaces Triethylamine in Phenoxy Herbicide Salt Formation

Diethanolamine is used to neutralize phenoxyacetic acid herbicides, particularly 2,4-dichlorophenoxyacetic acid, to produce water-soluble amine salts for selective broadleaf control in cereals, pasture, and turf. The reaction is exothermic; process equipment consists of a jacketed stainless steel reactor with turbine agitation, where 2,4-D acid is slurried in water and DEA is added under cooling to hold the batch below 60 °C, with final pH adjusted to 7.0–8.0. A typical finished formulation may be expressed as 480 g/L acid equivalent 2,4-D, although concentration is adjusted to local registration requirements. The diethanolamine salt reduces the volatility and odor of the free acid, improves solubility in hard water, and is compatible with nonionic surfactant adjuvants and ammonium sulfate tank-mix systems. Formulation stability is checked by cold- and heat-cycle storage, with crystal growth absent after alternating storage at -10 °C and 45 °C; active content is determined by HPLC, and pH is measured in 1 vol% aqueous dilution. Regulatory compliance is jurisdiction-specific: residue tolerances for 2,4-D are listed under 40 CFR 180.142 in the United States and under EU Regulation 396/2005 Annex II; classification and labelling are assessed under CLP Regulation 1272/2008. The terminal product is a selective herbicide for broadleaf weeds, applied after dilution in water through conventional boom sprayers.

Polyether Triol Synthesis and Amine Autocatalysis in Rigid Foam Systems

Diethanolamine serves as a trifunctional initiator in propoxylation reactors because the secondary amine nitrogen and the two primary hydroxyl sites contain a total of three active hydrogens available for alkylene oxide addition. The reaction is carried out in a pressure-rated stainless steel reactor at 100–120 °C and 3–6 bar(g) using propylene oxide, with potassium hydroxide catalyst charged at 0.1–0.3 wt% based on final polyol mass. The propylene oxide feed is staged to maintain the unreacted oxide concentration in the headspace below 2 vol%, and the reactor is equipped with a rupture disc, safety relief valve, and interlocked cooling water because propoxylation is strongly exothermic. After digestion, the crude polyol is neutralized with acid, filtered to remove potassium salts, and stripped under vacuum to 0.5–1.0 wt% water. Hydroxyl number is measured by ASTM D4274-21 and viscosity by ASTM D4878-15; DEA-initiated polyols for rigid polyurethane foam commonly target a hydroxyl number between 350 and 650 mg KOH/g, although published data for this specific configuration is limited and product viscosity varies with propylene oxide chain length. The tertiary amine centre in the polyol backbone accelerates the isocyanate-hydroxyl reaction in polyurethane rigid foam, reducing the amount of external amine catalyst needed during pour-in-place insulation, appliance foam, and spray-applied foam applications.