Diethanolamine (DEA) 99%: Personal Care Surfactants & Gas Treating

Diethanolamine (DEA) at 99% purity is a secondary alkanolamine with CAS registry number 111-42-2 and molecular mass 105.14 g/mol. The material is hygroscopic and has a melting range of 27–29 °C; ambient storage below this range requires heated drum rooms or low-temperature trace heating before transfer. Normal boiling point at 101.3 kPa is 268–270 °C, density at 20 °C is 1.09–1.10 g/cm³, and viscosity at 30 °C is typically 350–420 mPa·s. The molecule carries one secondary amine nitrogen and two terminal hydroxyl groups. This combination enables condensation with fatty acids or methyl esters to form alkanolamide surfactants and enables reversible acid gas absorption in aqueous solution. In personal care, 99% DEA serves primarily as a chemical intermediate for lauramide DEA, cocamide DEA, and oleamide DEA, which are used as foam stabilizers and viscosity builders in rinse-off formulations. In gas treating, 20–35 wt% aqueous DEA removes hydrogen sulfide and carbon dioxide from natural gas, refinery gas, and synthesis gas. The two application domains have distinct process windows, impurity profiles, and equipment constraints.

Why does residual free DEA govern nitrosamine control in personal care surfactant batches?

Residual free DEA in the condensation product is not an inert diluent. It raises the basicity of the surfactant, increases the ability to neutralise acidic formulation components, and alters foam structure in anionic-surfactant systems. More critically, secondary amines are recognised nitrosamine precursors. Cosmetic-grade alkanolamides often require residual free DEA below 5 wt%, with lower limits such as 0.5–1.0 wt% specified for leave-on or high-retention applications. Analytical detection of N-nitrosamines is performed according to ISO 15819:2014. Under the CLP Regulation (EC) No 1272/2008, DEA carries hazard statements H302, H312, H332, H315, H319, and H373; REACH Regulation (EC) No 1907/2006 exposure scenarios apply to industrial use in amidation and gas treating. The control strategy in personal care is therefore process-linked: minimise residual precursor at the reactor, avoid nitrite-donating preservatives, and monitor finished surfactant batch pH between 5.0 and 7.0 to maintain stability without shifting to alkaline hydrolysis.

Specification and test methods for Diethanolamine 99%

Parameter	Typical range/value	Test method
Purity	99.0–99.8 wt%	Neutralization titration with standard hydrochloric acid
Water	≤ 0.30 wt%	ASTM E203
Color	≤ 30 APHA	ASTM D1209
Density at 20 °C	1.09–1.10 g/cm³	ASTM D4052
Viscosity at 30 °C	350–420 mPa·s	ASTM D445 dynamic conversion
Melting range	27–29 °C	Capillary melting, internal QC

In production-scale amidation, the 99% DEA charge is heated in a jacketed 316L stainless steel reactor fitted with a pitched-blade turbine or anchor agitator. Typical cocamide DEA synthesis uses a 1:1 to 1.5:1 molar ratio of DEA to coconut fatty acid or methyl ester at 150–170 °C under nitrogen and vacuum of 20–50 kPa absolute. The agitator tip speed is kept below 3 m/s to avoid vortexing and oxidative colour development. Water of condensation is removed through a condenser and vacuum receiver, and the reaction endpoint is monitored by acid value; values between 5 and 15 mg KOH/g are common for cocamide DEA, while free DEA is then measured by gas chromatography or titration. High residual free DEA raises the 10% aqueous solution pH above 10.5 and can irritate skin in leave-on systems. Finished alkanolamide viscosity depends on fatty acid chain distribution; coconut-derived products typically fall between 500 and 1,200 mPa·s at 25 °C, but published data for specific chain distributions is limited. Direct formulation use of free DEA as a neutraliser in personal care is restricted in several regulatory frameworks; where used, it is kept below 0.5 wt% of the final product and is added slowly under low-shear sweep mixing to avoid pH overshoot and local secondary amine concentration.

Where DEA is carried into finished cosmetics via cocamide DEA, the INCI naming convention identifies the amide, not the free amine. Formulators using DEA-derived surfactants must account for free secondary amine content when selecting preservatives because sodium nitrite, 2-bromo-2-nitropropane-1,3-diol, and certain oxidising agents can create nitrosating conditions. For this reason, preservation systems often shift to phenoxyethanol, benzyl alcohol, or organic acids. The manufacturing line itself is subject to cleaning validation; residual DEA in transfer lines can be detected at 10–100 mg/kg by liquid chromatography coupled to triple quadrupole mass spectrometry. Published data for specific nitrosamine yields in finished matrices are limited, but the precursor-control approach is aligned with ISO 15819:2014 and regional nitrosamine limits.

When 99% DEA replaces MEA in high-pressure acid gas absorbers

Aqueous DEA is usually prepared by diluting the 99% product with low-chloride, low-alkali process water to 20–35 wt% amine concentration. In a high-pressure absorber, lean amine temperature is kept between 38 °C and 50 °C. The lower limit prevents hydrocarbon condensation and emulsion formation on trays or structured packing; the upper limit reduces foaming and maintains absorption driving force. Absorber pressure in natural gas service commonly ranges from 3.5 MPa to 9.0 MPa. Hydrogen sulfide reacts with the secondary amine by proton transfer to form the DEA hydrosulfide salt. Carbon dioxide forms DEA carbamate, consuming two DEA molecules per CO₂ molecule near lean conditions, so the CO₂-specific capacity is inherently lower than that of tertiary amines. DEA has lower vapour pressure than MEA, which reduces top-of-absorber amine losses, and its lower alkalinity produces a less corrosive rich solution at comparable loadings. The trade-off is higher solution viscosity and slower CO₂ mass transfer, which requires more structured packing surface area or additional tray residence time. Design guidance for equilibrium acid gas loadings is available in the GPSA Engineering Data Book, FPS Section 14; published data for low-pressure tail gas configurations is limited.

Heat-Stable Salt Accumulation, Lean Loading, and Reboiler Degradation Boundaries

Rich amine leaving the absorber is preheated in a shell-and-tube rich/lean exchanger with an approach temperature of 5–10 °C. Regenerator reboiler temperature is maintained at 115–126 °C. Thermal degradation of DEA accelerates above 126 °C and produces high-boiling nitrogen compounds, including piperazine derivatives, that raise solution viscosity and foaming. Steam rate is set to achieve lean acid gas loading of 0.08–0.15 mol acid gas per mole of DEA; rich loading is typically limited to 0.35–0.45 mol/mol. Exceeding 0.45 mol/mol increases carbon steel corrosion in rich amine piping, particularly at temperatures above 90 °C and in the presence of heat-stable salt anions such as chloride, sulfate, formate, acetate, and oxalate. Heat-stable salts bind protonated DEA and reduce reversible acid gas capacity. A side-stream anion exchange or soda ash addition followed by filtration is used to maintain heat-stable salt levels below 1.0 wt% of circulating solution; above this level, foaming and pump cavitation become significant. Antifoam dosing is limited to 2–10 mg/L to avoid fouling of heat exchanger surfaces. Carbon steel absorber vessels require post-weld heat treatment to minimise amine stress corrosion cracking; rich amine piping velocity is typically limited to 1.5 m/s at elbows and control valves to prevent erosion-corrosion. In refinery service, weldment controls are aligned with NACE SP0472.

Operating envelope for aqueous DEA gas treating

Parameter	Typical range	Process limit
DEA concentration	20–35 wt%	Viscosity and freezing constraints
Lean amine temperature	38–50 °C	Hydrocarbon condensation /foaming
Absorber pressure	3.5–9.0 MPa	Natural gas service
Regenerator reboiler temperature	115–126 °C	Thermal degradation above 126 °C
Lean acid gas loading	0.08–0.15 mol/mol	Steam rate and stripping efficiency
Rich acid gas loading	0.35–0.45 mol/mol	Corrosion and equilibrium pinch
Heat-stable salt content	≤ 1.0 wt%	Foaming and capacity loss
Antifoam dosage	2–10 mg/L	Heat exchanger fouling

During continuous circulation at 25–30 wt% amine concentration, the main production-scale failure modes are not equilibrium-driven but impurity-driven. Activated carbon side-stream filtration at 0.5–2.0 wt% of circulating inventory per day removes high-molecular-weight degradation products and reduces foaming. A DEA system with 99% purity feed may show colour increase from 15 to 70 APHA after 6–12 months of continuous operation; colour alone does not predict acid gas capacity, but it accompanies conductivity rise and heat-stable salt accumulation. Operators monitor amine assay by titration, water content by Karl Fischer ASTM E203, conductivity, and foaming tendency. Transfer piping for 99% DEA requires heat tracing or insulation because solidification occurs below 27 °C; diluted systems can tolerate lower ambient temperatures. Reclaimed DEA from vacuum distillation should be limited to 20–30 wt% of the circulating inventory until corrosion and foaming history are established. Operationally, the lean amine filter differential pressure is logged at 10–30 kPa; a rise above 50 kPa triggers filter changeout to prevent bypass of degradation solids into the absorber.