Surfactant adsorption onto solid surfaces is a major issue during surfactant flooding in enhanced oil recovery applications; it decreases the effectiveness of the chemical injection making the process uneconomical. Therefore, it was hypothesized that the adsorption of surfactant onto solid surfaces could be inhibited using a surfactant delivery system based on the complexation between the hydrophobic tail of anionic surfactants and b-cyclodextrin (b-CD). Proton nuclear magnetic resonance spectroscopy was used to confirm the complexation of sodium dodecyl sulfate (SDS)/b-CD. Surface tension analysis was used to establish the stoichiometry of the complexation and the binding constant (K a ). Static adsorption testing was applied to determine the adsorption of surfactant onto different solids (sandstone, shale, and kaolinite). The release of the surfactant from the b-CD cavity was qualitatively evaluated through bottle testing. The formation of the inclusion complex SDS/b-CD with a 1:1 stoichiometry was confirmed. The K a of the complexations increases as salinity and hardness concentration increases. The encapsulation of the surfactant into the b-CD cavity decreases the adsorption of surfactant onto solid surfaces up to 79 %. Qualitative observations indicate that in the presence of solid adsorbents partially saturated with crude oil, the b-CD cavity releases surfactant molecules, which migrate towards the oil-water interface.

Surfactant adsorption onto solid surfaces is problematic in some industrial processes, such as in surfactant flooding for enhanced oil recovery. In this work, it was hypothesized that the use of a surfactant delivery system could prevent surfactant adsorption onto solid surfaces. Therefore, the encapsulation of sodium dodecyl sulfate (SDS) into the hydrophobic core of β-cyclodextrin (β-CD) to generate a surfactant delivery system (SDS/ β-CD) was evaluated in this work. This complexation was characterized using optical and scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). Dynamic adsorption evaluation was applied to determine the effectiveness of the complexation in inhibiting surfactant adsorption onto a variety of solid adsorbents including sand, and mixtures of sand-kaolin and sand-shale. Surfactant adsorption was also evaluated applying the quartz crystal microbalance technology (QCM-D). The formation and morphology of the complexation was confirmed by optical microscopy, SEM, and FT-IR. Dynamic adsorption tests demonstrated the effectiveness of the surfactant delivery approach in preventing the adsorption of surfactant (up to 74 % adsorption reduction). The QCM-D technology confirmed these observations. Several mechanisms were proposed to explain the inhibition of surfactant adsorption including steric hindrance, self-association of inclusion complexes, hydrophilicity increase, and disruption of hemimicelles formation.

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This proof of concept research evaluates the performance of a surfactant/b-cyclodextrin (b-CD) inclusion complex during chemical flooding for enhanced oil recovery. It was hypothesized that the encapsulated surfactant propagates well through the porous media. Sodium dodecyl sulfate (SDS) was used to study the surfactant/b-CD complexations. Phase behavior analysis was carried out to prepare the most favorable chemical slug formulation. A series of core flooding tests were conducted to determine the efficiency of the SDS/b-CD inclusion complex in displacing residual oil. Surfactant flooding was conducted as tertiary oil recovery mode (after mature water flooding) by injecting 0.3 pore volume (PV) of the optimum surfactant slug that was chased by 0.3 PV of a polymer slug; followed by continuous water flooding until oil production stopped. The experimental results indicate that the encapsulated surfactant propagates well through the sandpack system and consistently produces higher incremental oil recoveries that range from 40 to 82 % over the incremental oil recovery achieved by conventional surfactant flooding. KeywordsSurfactant delivery system Á Surfactant carrier system Á Surfactant/b-cyclodextrin complexation Á Surfactant/b-cyclodextrin inclusion complexes Á Surfactant adsorption Á Surfactant adsorption inhibition Á Surfactant flooding Á Enhanced oil recovery Á Surfactant encapsulation in b-cyclodextrin List of symbols k Permeability in md (millidarcy) S or Residual oil saturation in fraction t Time uFlux in cm/h V sm Surfactant volume in the microemulsion phase V wm Water volume in the microemulsion phase V om Oil volume in the microemulsion phase r mw Interfacial tension (IFT) between the microemulsion/water phases r mo Interfacial tension (IFT) between the microemulsion/oil phases / Porosity

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Cloud point extraction (CPE) has shown to be an effective technique to remove organic compounds from contaminated water using nonionic surfactant as a separating agent. To make this process more economically attractive, the spent nonionic surfactants should be recycled and reused. This work utilized a packed column operated under vacuum in co-current mode to remove the volatile organic compounds (VOCs) from the secondary alcohol ethoxylates, AEs, coacervate solution. The co-current operation can effectively avoid plugging, excessive foaming, and flooding. The selected volatile organic contaminants are aromatic hydrocarbons such as benzene, toluene, and ethylbenzene. The hydrophobic properties of the VOCs are described by an octanol-water partition coefficient (Kow). The results show that as the Kow increases, the Ks substantially increases while the Happ of the VOCs significantly decreases. The reduction of VOCs volatilization is possibly due to greater partitioning of the VOCs into surfactant micelles. The similar trend is also observed in the continuous operation. The results show that as the Kow increases, the percentage of VOCs removal and the Kxa decrease due to the VOCs’ hydrophobic effect. The removal percentages of the VOCs vary from 60 to 90%. The R2 of the log-log and semi-log relationships between Kow and studied parameters are observed in the range of 0.96-0.99.