Thermodynamic analysis of precipitation conditions of anionic surfactants by calcium and magnesium ions
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2024-02-10 20:15
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544.013:66.01 (1)
Substanțe și sisteme chimice. Origine. Stare naturală. Faze (7)
Tehnologie chimică. Industrii chimice și înrudite (1496)
SM ISO690:2012
POVAR, Igor, SPATARU, Petru, SHEPEL, Diana, SPINU, Oxana, PINTILIE, Boris, VIȘNEVSCHI, Alexandru. Thermodynamic analysis of precipitation conditions of anionic surfactants by calcium and magnesium ions. In: Ecological and environmental chemistry : - 2022, Ed. 7, 3-4 martie 2022, Chișinău. Chisinau: Centrul Editorial-Poligrafic al USM, 2022, Ediția 7, Vol.1, p. 53. ISBN 978-9975-159-07-4.. 10.19261/eec.2022.v1
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Ecological and environmental chemistry
Ediția 7, Vol.1, 2022
Conferința "Ecological and environmental chemistry 2022"
7, Chișinău, Moldova, 3-4 martie 2022

Thermodynamic analysis of precipitation conditions of anionic surfactants by calcium and magnesium ions

CZU: 544.013:66.01

Pag. 53-53

Povar Igor, Spataru Petru, Shepel Diana, Spinu Oxana, Pintilie Boris, Vișnevschi Alexandru
 
Institute of Chemistry
 
Proiecte:
 
Disponibil în IBN: 3 martie 2022


Rezumat

Sodium dodecyl sulfate (SDS) is an anionic surfactant that has found application in personal care products, detergents, in cosmetics and cleaning products. An obvious disadvantage of using anionic surfactants as detergents is the formation of the precipitate with calcium (Ca2+) and magnesium (Mg2+) ions contained in hard water. Below the CMC level, the solubility of SDS as a function of Ca2+ or Mg2+ concentration is governed by the solubility product (KS) and decreases with increasing its concentration. Information on the solubility of surfactant salts, determined by the dissolution of pure substances, is of limited utility. Apparent KS may be exceeded by orders of magnitude without the appearance of the solid phase, due to the surfactant association, the ion pairs formation, the complexation of the solutions, etc. In the paper, the equations for calculating the variation of the global Gibbs energy of the precipitation processes – dissolution of lauric acid and alkaline earth metal dodecyl sulfate have been deduced. The elaborated ΔG(pH) diagrams offer the possibility to determine the areas of thermodynamic stability of the solid phases depending on the chemical composition and acidity of the system. If ΔG > 0, then the compound precipitates and the system is biphasic, while for the values of ΔG < 0, all components are soluble in water, i.e. there is a homogeneous, single-phase system. It has been shown that as the concentrations of the surfactant and the metal ion increase, the range of precipitate formation, either slightly soluble salt or slightly soluble acid, expands, in all cases by some pH units. Thus, the conditions can be established when the formation of precipitates is avoided. Using the developed thermodynamic model, the areas in which the solid phase is formed at the interaction of the anionic surfactant with the calcium and magnesium ions have been determined.