Sorption of Naphthenic Acids using β-Cyclodextrin-based Polyurethanes
Mohamed, Mohamed Hamid
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In general, the research focuses on sequestration of naphthenic acids (NAs) from simulated oil sands process water (OSPW) conditions using engineered copolymers known as β-cyclodextrin-based polyurethanes. The thesis research is divided into two main parts; i) synthesis and characterization of β-cyclodextrin-based polyurethanes, and ii) sorption studies of the copolymer materials with NAs from aqueous solutions. In the first part, β-cyclodextrin (β-CD) was crosslinked with five types of linker molecules, respectively, under various synthetic conditions. The various diisocyanates investigated as linkers include the following: 1,6-hexamethylene diisocyanate (HDI), 4,4'-dicyclohexylmethane diisocyanate (CDI), 4,4'-diphenylmethane diisocyanate (MDI), 1,4-phenylene diisocyanate (PDI) and 1,5-naphthalene diisocyanate (NDI). The polyurethanes (PUs) were systematically designed at different mole ratios of monomers by maintaining β-CD and varying the relative mole ratio of diisocyanate monomer from unity to greater values. Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTS), solid state 13C CP-MAS NMR, solution state 1H/13C NMR spectroscopy, thermogravimetric analysis (TGA), elemental analysis (CHN), nitrogen porosimetry, and a dye-based (p-nitrophenol; PNP, and phenolphthalein; phth) sorption method were used to characterize the copolymer materials. In general, the β-CD PUs were insoluble in water except for β-CD crosslinked with HDI at the 1:1 mole ratio which was moderately water soluble. All techniques show complementary results about the structural and compositional characterization, particularly for the estimation of the ratios between the co-monomers. The optimal preparation of copolymer materials for sorption-based applications occurs for β-CD/linker monomer mole ratios from 1:1 to 1:3. There is a maximum limit of the crosslinking density which is ~ 1:7 (β-CD:linker) according to the steric effects of the substituents in the annular region of β-CD. Also, the copolymers were generally found to be mesoporous with relatively low surface area (BET; ~101 m2/g) and they appear to exhibit swelling in aqueous solution due to hydration as observed from the estimation of the dye-based surface areas using PNP. The surface accessibilities of the β-CD inclusion sites ranged between 1-100%, as evidenced by the decolourization of phenolphthalein (phth) due to the formation of 1:1 β-CD/phth inclusion complexes. In the second part, the inclusion of NAs and its surrogates with three well known types of cyclodextrin (α-, β-, and γ-CD) was confirmed using negative ion mode electrospray ionization (ESI). The CDs were found to form well-defined 1:1 inclusion complexes. The binding constant (K2) of NAs and its surrogates inclusion with β-CD was determined indirectly using the spectral displacement technique and were found to be 103-104 M-1 (surrogates) and ~ 104 M-1 (NAs), respectively. Furthermore, the binding constants were found to increase with an increase of the lipophilic surface area (LSA) of the surrogates. The sorption results of NAs with three different types of β-CD materials (i.e. β-CD PU, β-CD crosslinked with epichlorohydrin (EP) and a silica-based mesoporous material containing β-CD), showed β-CD PU had a greater affinity. The sorption capacity (~ 0 - 75.5 mg NAs/g copolymer) and binding affinity (~103 - 104 M-1) of β-CD PUs varied due to the nature of linker monomer and the mole ratio of the co-monomers. Aromatic-based copolymers showed high sorption binding affinity while aliphatic-based copolymers showed a relatively high sorption capacity at the co-monomer ratio. Finally, Syncrude-Derived NAs showed fluorescent characteristics which contradict the classic definition of NAs. Further studies using UV-Vis and fluorescence emission spectroscopy showed potential development of an analytical method that can be used to quantify NAs in OSPW for in-situ field applications.
DegreeDoctor of Philosophy (Ph.D.)
Supervisorjohn headley; lee wilson
Committeedale ward; stephen urquhart; julian zhu; paul jones; ian burgess
Copyright DateNovember 2010