Tunable Polymeric Sorbent Materials for Fractionation of Model Naphthenates Mohamed H. Mohamed, † Lee D. Wilson,* ,‡ and John V. Headley † † Water Science and Technology Directorate, Environment Canada, 11 Innovation Boulevard, Saskatoon, Saskatchewan, S7N 3H5, Canada ‡ Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan, S7N 5C9, Canada ABSTRACT: The sorption properties are reported for several examples of single- component carboxylic acids representing naphthenic acids (NAs) with β- cyclodextrin (β-CD) based polyurethane sorbents. Seven single-component examples of NAs were chosen with variable z values, carbon number, and chemical structure as follows: 2-hexyldecanoic acid (z = 0 and C = 16; S1), n- caprylic acid (z = 0 and C = 8; S2), trans-4-pentylcyclohexanecarboxylic acid (z = -2 and C = 12; S3), 4-methylcyclohexanecarboxylic acid (z = -2 and C = 8; S4), dicyclohexylacetic acid (z = -4; C = 14; S5), 4-pentylbicyclo[2.2.2]octane-1- carboxylic acid (z = -4; C = 14; S6), and lithocholic acid (z = -6; C = 24; S7). The copolymer sorbents were synthesized at three relative β-CD:diisocyanate mole ratios (i.e., 1:1, 1:2, and 1:3) using 4,4′-dicyclohexylmethane diisocyanate (CDI) and 4,4′-diphenylmethane diisocyanate (MDI). The sorption properties of the copolymer sorbents were characterized using equilibrium sorption isotherms in aqueous solution at pH 9.00 with electrospray ionization mass spectrometry. The equilibrium fraction of the unbound carboxylate anions was monitored in the aqueous phase. The sorption properties of the copolymer sorbents (i.e., Q m ) were obtained from the Sips isotherm model. The Q m values generally decrease as the number of accessible β-CD inclusion sites in the copolymer framework decreases. The chemical structure of the adsorbates played an important role in their relative uptake, as evidenced by the adsorbate lipophilic surface area (LSA) and the involvement of hydrophobic effects. The copolymers exhibit molecular selective sorption of the single-component carboxylates in mixtures which suggests their application as sorbents for fractionation of mixtures of NAs. By comparison, granular activated carbon (GAC) and chitosan sorbents did not exhibit any significant molecular selective sorption relative to the copolymer materials; however, evidence of variable sorption capacity was observed among the sorbents investigated. 1. INTRODUCTION Canadian oil sands deposits are vast and represent the second largest source of crude oil after Saudi Arabia for the North American economy. 1 The oil sands industry in Northern Alberta, Canada, employs a caustic warm water process, the Clark hot water extraction, 2 to extract oil sands. The resulting oil sands process water (OSPW) is saline and contains a complex mixture of organic compounds dominated by a class of naturally occurring naphthenic acids (NAs). The alkaline conditions solubilize NAs (cf. Scheme 1) as their naphthenate forms in aqueous solutions which are known to be toxic to aquatic organisms, algae, and mammals. 3-9 NAs are also suspected as endocrine-disrupting substances, however; the toxicology of the various component fractions of NAs is poorly understood at the present time. NAs are recognized among the various toxic components in OSPW as a potential threat to human and ecosystem health, as outlined above. The structural formulas of NAs may be described by the conventional definition C n H 2n+z O 2 , 3,10-13 where “z” is referred to as the “hydrogen deficiency” and is a negative, even integer value. More than one isomer may exist for a given z value, with variable molecular weight, and the carboxylic acid group is generally attached to a side chain, rather than directly to the alicyclic ring. 9,10 The molecular weights differ by 14 amu (CH 2 ) between n-series and by 2 amu (2H) between z-series. 14 However, the term NAs has been widened recently to include other species containing multiple heteroatoms (i.e., O, N, and S), in addition to the traditional NAs (cf. Scheme 1). For example, OSPW is known to contain other components containing two or more carboxylic acids. Furthermore, O x (x =1-6) containing species along with NAs containing S- and N-heteroatoms are also present in the OSPW acid extractable fractions. 15 The oil sands industry operates with a zero discharge policy where the OSPW is retained in vast tailing ponds. Given the estimated crude oil reserves (ca. 174 billion barrels bitumen) in the Athabasca oil sands and the significant water consumption (ca. 2-4 barrels of water per 1 barrel bitumen) for the extractive processing, there is growing interest to reclaim the OSPW to lower the industrial water footprint. 1 The estimated Received: October 25, 2012 Revised: March 4, 2013 Published: March 7, 2013 Article pubs.acs.org/JPCB © 2013 American Chemical Society 3659 dx.doi.org/10.1021/jp310593p | J. Phys. Chem. B 2013, 117, 3659-3666