A mechanistic exploration of oil recovery via selective oil permeation

Oil-water separations are necessary for the reuse of oil-laden wastewater. For example, oil and gas produced water may have influent oil concentrations of up to 2,000 mg/L that must be reduced to <10–35 mg/L to meet regulatory requirements for non-industrial reuse. However, many conventional oil-water separation processes are unable to achieve these effluent concentrations. Selective oil permeation is a promising membrane-based oil-water separation approach that may be able to meet these treatment goals. The process differs from traditional membrane-based oil-water separations by permeating oil (instead of water) through the hydrophobic membrane. Exploitation of the preferential oil wetting of the membrane surface minimizes viscous fouling and generates an oil permeate stream. Previous investigation of selective oil permeation has demonstrated its ability to recover oil over extended durations. Researchers have hypothesized that mechanistic competition between coalescence and permeation controls oil recovery, results in the development of an oil film at the membrane surface, and leads to transport phenomena that deviate from traditional pore flow models. However, further verification is necessary to validate the existence of hypothesized mechanisms within the process and verify its applicability to produced water treatment. Few studies have investigated mechanistic interactions or process performance (i.e., oil flux, oil recovery, permeate quality) for oil concentrations less than 1%. Even fewer have probed relationships between process performance, operating conditions, and water quality characteristics. Understanding the answers to these outstanding questions is crucial to defining the opportunity space for selective oil permeation. This dissertation is the first set of studies to present results that (1) characterize and provide guidance for enhancing the membrane conditioning process, (2) identify how the operative mechanisms are impacted by system characteristics, operating conditions, and water quality characteristics within this lower oil concentration range, and (3) apply selective oil permeation to produced water. Achieving the outlined objectives will both expand our understanding of the role of the two key mechanisms underlying selective oil permeation (coalescence and permeation) and begin to define the opportunity space for oil recovery via selective oil permeation.