Sorption of Naphthenic Acids using β-Cyclodextrin-based Polyurethanes
Date
2010-11-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Degree Level
Doctoral
Abstract
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 ɣ-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.
Description
Keywords
sorption, complexation, naphthenic acids, cylclodextrin, polymer, isotherms
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Chemistry
Program
Chemistry