Application of Carbonaceous Material for Remediation of Oil Sands Process Water: Adsorption and Development of Nanocomposite Membranes with Enhanced Properties

  • Author / Creator
    Benally, Chelsea
  • Oil sands process water (OSPW) is a highly complex mixture that contains sand, silt, clay, dissolved salts, heavy metals and a wide range of organic compounds such as naphthenic acids (NAs) and polyaromatic hydrocarbons (PAHs). To effectively manage water during operations and support reclamation efforts, there is a need to release the treated OSPW back into the environment. This thesis presents the results of two different treatment options for OSPW: membrane filtration and adsorption.
    Ultrafiltration nanocomposite polysulfone (PSU) membranes containing 0 to 5 wt.% carboxyl (-COOH) modified multiwalled carbon nanotubes (mMWNT) were fabricated and used to treat OSPW. Addition of mMWNT to PSU resulted in increased membrane surface hydrophilicity. Small additions of mMWNT (up to 1 wt.%) resulted in decreased average pore size on the selective membrane surface. Pure water and OSPW flux followed the same trend, decreasing with small mMWNT additions (up to 0.5 wt. %), followed by an increasing flux with higher mMWNT additions. All nanocomposite membranes had a higher rejection of polyethylene glycol (PEG) (76.5%-92.3%) than plain PSU membranes (65.5%). Membranes containing 2 wt.% mMWNT had the highest polyethylene glycol (PEG) flux and rejection of 83.1%. Addition of mMWNT reduced the tendency for membrane fouling to occur, indicated by a decrease in fouling ratios and increased flux recovery ratios for nanocomposite membranes as compared with those obtained for plain PSU. The dominant fouling mechanisms during OSPW filtration were standard blocking and cake filtration. Additions of 0.2 wt.% and 2 wt.% mMWNT resulted in permeates with SDI15 values lower than 1.0 and increased acid-extractable fraction (AEF) removal (11.9% and 13.9%, respectively) as compared with AEF removal by plain PSU membrane.
    Adsorption results demonstrated that mesoporous carbonaceous material can successfully be used to adsorb persistent and toxic organic contaminants from OSPW. Carbon xerogel (CX) made at pH 5.5 removed a larger amount of AEF than CX made at pH 6.9. The adsorption equilibrium was reached by about 12 hours for both AEF and total classical naphthenic acids (NAs). 74.6% of AEF was removed and 88.8% of total classical NAs were removed during 24 hours adsorption. With respect to classical NAs removal, a larger carbon number resulted in higher NAs removal. Carbon number had more influence on NAs removal when compared with hydrogen deficiency resulting from rings or unsaturated bonding formation (–Z number). For a 3 g/L dose of CX 5.5, the equilibrium adsorption capacity was found to be 15 mg AEF/g CX5.5 and 7.8 mg NAs/g CX5.5. Adsorption of AEF and total classical NAs onto CX5.5 followed pseudo-second order kinetics. With respect to diffusion of AEF and NAs, there were three distinct regions: bulk diffusion, film diffusion and pore diffusion. Pore diffusion had the lowest rate constant in all cases analyzed and was thus the rate limiting diffusion step. The results of this study showed that a mesoporous carbonaceous material such as CX may have the potential to be utilized in a fixed bed adsorption column for continuous treatment of OSPW or as a semi-passive treatment method in pit lakes for the removal of organic constituents from OSPW.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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