Metal oxide modified tubular ceramic membrane for the separation of oil-in-water emulsion.

Aisueni, Florence Anem

Abstract

Separating lower concentrations of oil-in-water (O/W) emulsion (< 250 mg/l) and smaller oil droplet size (< 20 μm) has been an industry challenge using conventional methods, including adsorption, electrocoagulation, flocculation, bioremediation, centrifugation, membranes, etc. This is mostly due to the oil droplet size falling in the emulsified range or nano range, which is easily stabilised with surfactant present in the O/W. Recently, membrane technology has been the most researched approach for the separation of O/W emulsion. This springs from the massive potential of its usage for future water purification and effluent treatment, with it being environmentally friendly and facilitating a high permeate rate, high percentage oil rejection, and low-cost separation processes. This study, therefore, focuses on modifying microporous asymmetric Aluminium Oxide (Al2O3) tubular ceramic membranes with metal oxides nanoparticles for surface wettability to improve hydrophilicity and increase O/W emulsion separation efficiency. A novelty material – Magnesium Oxide (MgO) - nanoparticles modified tubular ceramic membrane was investigated and discovered to have a high hydrophilicity and O/W emulsion separation efficiency in this study. This investigation, which includes modification of MgO nanoparticles on commercial Al2O3 tubular ceramic membrane using a deep coating method of membrane modification, was also applied to other naturally hydrophilic nanoparticle compounds (Manganese Oxide (MnO2) and Chromium Oxide (Cr2O3)), where MgO nanoparticles emerged as the most hydrophilic on tubular ceramic membranes measured using contact angle measurement. The MgO-modified tubular ceramic membrane was characterized to determine morphology, elemental composition, hydrophilicity, porosity and pore size, and was compared with unmodified an Al2O3 tubular ceramic membrane using various analytical instruments and methods. A novelty method of testing MgO-modified tubular ceramic membranes for the separation of lower concentration (< 500 mg/l) of synthesized O/W emulsion was investigated and achieved using an in-house rig set up. The MgO-modified tubular ceramic membrane test for O/W emulsion included test parameters for percentage oil rejection, flux, and flux recovery ratio. Where results from these tests were compared to results from unmodified Al2O3 tubular ceramic membrane, the MgO-modified membrane displayed a higher percentage oil rejection efficiency of 98%, leaving behind an O/W emulsion concentration of 11.63 mg/l from the 500 mg/l initial O/W emulsion concentration. Meanwhile, an Al2O3 unmodified ceramic membrane shows 69% oil rejection, leaving behind 156.25 mg/l from 500 mg/l O/W emulsion. This generated over 30% difference in the percentage of oil rejection between Al2O3 unmodified and MgO-modified ceramic membranes. This MgO-modified ceramic membrane percentage oil rejection concentration of only 11.63 mg/l falls within the OSPAR regulatory limit. Compared to Al2O3 unmodified ceramic membrane, the MgO-modified tubular ceramic membrane demonstrated a lesser performance in terms of permeate flux, with a higher flux decline due to quick concentration polarization and smaller pores sizes during O/W emulsion cross-filtration analysis. With this result, an MgO-modified ceramic membrane can be an alternative to other metal oxide ceramic membranes to improve separation efficiency of more than 90%. The success of this MgO-modified ceramic membrane can tackle the lower oil concentrations (250 mg/l) and oil droplet size (< 20 um) challenges that arise from unmodified ceramic membranes and conventional methods of O/W emulsion separation.

Citation

AISUENI, F.A. 2024. Metal oxide modified tubular ceramic membrane for the separation of oil-in-water emulsion. Robert Gordon University, PhD thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-2445693

• Thesis Type: Thesis
• Deposit Date: Aug 26, 2024
• Publicly Available Date: Aug 26, 2024
• DOI: https://doi.org/10.48526/rgu-wt-2445693
• Keywords: Ceramic membranes; Membranes; Emulsion separation; Oil separation; Flux; Magnesium oxide
• Public URL: https://rgu-repository.worktribe.com/output/2445693
• Award Date: Mar 31, 2024