Surface Active and Thermodynamic Properties in Relation to the Demulsification Efficiency for Some Ethoxylated Derivatives of Alkyldiamines and Polyalkylenepolyamines

In this work, nine monostearic esters of ethoxylated dialkyle-amine (group I) and ethoxylated polyalkylenepolyamine (group II) nonionic surfactants were prepared and characterized by FTIR spectroscopy and nitrogen content. The 1,4-diaminobutane (DAB), 1,6 diamino hexane (DAH), 1,8-diamino-octane (DAO), diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA) were ethoxylated at 50, 100, 150 ethylene oxide units individually. The ethoxylated products of (group I) reacted with stearic acid to give the monostearate products. The surface tension of the prepared compounds were measured at 25°C and 60°C. The thermodynamic parameters of micellization and adsorption were also calculated. The surface active properties, such as critical micelle concentration (CMC), maximum surface excess concentration (Γ_max), effectiveness of surface tension reduction (π_cmc), and minimum area per molecule at the aqueous solution-air interface (A_min), have been calculated. The surface active and thermodynamic properties of the prepared compounds were correlated to their chemical structure. It was found that CMC decreases when increasing the molecular weight of polyethylene oxide units. Furthermore, the data show that the synthesized surfactants favor adsorption than micellization, so that they can be used as demulsifiers for waxy crude oil emulsion (BSW 18%). In this respect, the demulsification test was carried out and the results of demulsification efficiency were correlated to the chemical composition of the investigated compounds. Some factors that affect the demulsification efficiency were also considered such HLB, concentration and time. The maximum demulsification efficiency (100%) was obtained by DAOE_150-M and TEPAE₁₅₀ at 60 and 45 minutes (300 ppm), respectively.