title: Fractionation of oil sands-process affected water using pH-dependent extractions: a study of dissociation constants for naphthenic acids species.
abstract: The fractionation of oil sands process-affected water (OSPW) via pH-dependent extractions was performed to quantitatively investigate naphthenic acids (NAs, CnH2n+ZO2) and oxidized NAs (Ox-NAs) species (CnH2n+ZO3 and CnH2n+ZO4) using ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOFMS). A mathematical model was also developed to estimate the dissociation constant pKa for NAs species, considering the liquid-liquid extraction process and the aqueous layer acid-base equilibrium. This model provides estimated dissociation constants for compounds in water samples based on fractionation extraction and relative quantification. Overall, the sum of O2-, O3-, and O4-NAs species accounted for 33.6% of total extracted organic matter. Accumulative extracted masses at different pHs revealed that every oxygen atom added to NAs increases the pKa (i.e., O2-NAs<O3-NAs<O4-NAs), indicating that the additional O atoms exist as -OH in O3- and O4-NAs. Molecule electron-withdrawing groups such as double bonds and aromatic groups, as indicated by higher carbon and -Z number, may be responsible for the lower pKa of O2-, O3-, and O4-NAs. The model obtained estimated pKa values of 3.5 for O2-NAs, 4.8 for O3-NAs, and 6.8 for O4-NAs via nonlinear regression curve fittings. These pKa values are valuable physicochemical parameters for environmental engineering applications targeting OSPW NAs treatment.
authors.affiliation: Department of Civil and Environmental Engineering, 3-133 Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta T6G 2W2, Canada.
authors.forename: Rongfu
authors.initials: R
authors.lastname: Huang
authors.affiliation: Department of Civil and Environmental Engineering, 3-133 Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta T6G 2W2, Canada.
authors.forename: Nian
authors.initials: N
authors.lastname: Sun
authors.affiliation: Department of Civil and Environmental Engineering, 3-133 Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta T6G 2W2, Canada.
authors.forename: Pamela
authors.initials: P
authors.lastname: Chelme-Ayala
authors.affiliation: Department of Civil and Environmental Engineering, 3-133 Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta T6G 2W2, Canada.
authors.forename: Kerry N
authors.initials: KN
authors.lastname: McPhedran
authors.affiliation: Department of Civil and Environmental Engineering, 3-133 Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta T6G 2W2, Canada.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Changalov
authors.affiliation: Department of Civil and Environmental Engineering, 3-133 Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta T6G 2W2, Canada. Electronic address: mgamalel-din@ualberta.ca.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Gamal El-Din
mesh_terms: D002170:Canada; D002264:Carboxylic Acids / Q000032:analysis*; D005591:Chemical Fractionation; D002853:Chromatography, Liquid; D006863:Hydrogen-Ion Concentration; D059625:Liquid-Liquid Extraction; D013058:Mass Spectrometry; D061329:Oil and Gas Fields; D062065:Wastewater / Q000032:analysis* / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification / Q000379:methods*
chemical_list: D002264:Carboxylic Acids; D062065:Wastewater; D014874:Water Pollutants, Chemical; C046170:naphthenic acid
keywords: Dissociation constant; Naphthenic acids; Oil sands process-affected water; Ultra-performance liquid chromatography time-of-flight mass spectrometry; pH fractionation