No abstract

Surfactant–oil–water (SOW) systems are important for numerous applications, including hard surface cleaning, detergency, and enhanced oil-recovery applications. There is limited literature on the wettability of solid–liquid–liquid (SLL) systems around the surfactant phase inversion point (PIP), and the few references that exist point to wettability inversion accompanying the microemulsion (μE) phase inversion. Despite the significance of this phenomenon and the extreme changes in contact angles, there are no models to predict SLL wettability as a function of proximity to the PIP. Recent works on SLL wettability in surfactant-free systems suggest that SLL contact angles can be predicted with an extension of Neumann’s equation of state (e-EQS) if the interfacial tension (IFT or γo–w) is known and if there is a good estimate for the interfacial energy between the wetting phase and the surface (γS–wetting liquid). In this work, IFT predictions for SOW systems around the PIP were obtained via the combined hydrophilic–lipophilic difference (HLD) and net-average-curvature (NAC) framework. To test the hypothesis that the combined HLD–NAC + e-EQS can predict wettability inversion around the PIP, with a given γS−μE, the contact angles (measured through the light oil phase, θO) for the μE of sodium dihexyl sulfosuccinate–toluene–saline water system were measured on high surface free energy (SFE) materials (glass, stainless steel, and mica) and on polytetrafluoroethylene (low SFE) around the PIP. Considering that at the PIP, most systems have a contact angle of 90°, an estimated γS−μE = 1/4γo–w@PIP was found to be suitable for the systems considered in this work and for systems presented in the literature. The largest deviations between the predictions and the experimental values were found in the positive HLD range (surfactant in the light oil phase). Although there is room for improvement, this framework can estimate the wetting behavior of SOW systems starting solely from formulation parameters.

Bitumen froth is a water-in-bitumen emulsion (∼30 wt % water, 60 wt % bitumen, and 10 wt % of solids) stream obtained during the water-based extraction process of mined oil sands. The separation of water (to 2 wt % or less) and solids (to 0.5 wt % or less) from the froth is necessary to prevent corrosion, catalyst deactivation, and fouling in downstream processes. In naphthenic froth treatment (NFT), aromatic naphtha is added to reduce the density and viscosity of bitumen to aid in this separation, which often requires the addition of demulsifiers and centrifugation. This work looks at simulating the dewatering of froth using a bench-scale mixer and heptol 80/20 (80 vol % heptane; 20 vol % toluene) as a simulated naphtha solvent. Power dissipation during mixing, water contents, image analysis of micrographs, and acoustic spectroscopy were used to examine the dewatering process as a function of time for three froth samples with different compositions. Gravity drainage, in the absence of additives, led to a residual water content, after 2 h, ranging from 1.7 to 3.7 wt % for the three different samples, consistent with the typical residual water reported for these systems. Micrographs of the diluted froth show the eventual disappearance of large water drops and the prevalence of smaller emulsified drops (<10 μm) in the residual water. An examination of this residual water using acoustic spectroscopy showed that up to 0.8 wt % water is in the form of ∼0.3 μm submicron drops that cannot be removed by gravity or centrifugation. A dewatering model using an initial drop size distribution (DSD) of water drops also supports the existence of a substantial amount of submicron drops. A low-shear dewatering test suggests that most of this submicron water was in the froth before simulated froth treatment, formed potentially during bitumen extraction and transportation, prior to solvent dilution and dewatering. Cryo-SEM imaging further supports this hypothesis. Studies of water solubilization in toluene–asphaltene and toluene–naphthenic acid systems suggest that up to 0.5 wt % of this submicron water could be originated from water–asphaltene association. The presence of high solid contents in the froth correlated with high residual water and submicron water contents, pointing to the potential role of solids in the formation of submicron drops.

During froth treatment, a water-in-diluted bitumen emulsion is obtained. The emulsified water contains chloride ions that form hydrochloric acid in downstream oil processing, leading to catalyst deactivation and equipment corrosion. Emulsified water, drops smaller than 10 μm, cannot be effectively removed by gravity settling and centrifugation to below 2 wt %. In this work, a filter-coalescer was used to promote the coalescence and separation of water-inbitumen emulsion. The larger water drops (>300 μm) exiting the coalescer undergo gravity settling, reducing the water content in diluted bitumen emulsions to values lower than 0.1 vol %. The performance of the coalescer was interpreted via the colloid filtration theory of Rajagopalan and Tien (RT), improved in this work with a coalescence probability (CP) prefactor. This new RTCP framework was able to reproduce the experimental data, allowing its potential use as a predictive model for emulsion filtration and the operation of filter-coalescers. A capillary number analysis was used to account for the detachment of coalesced drops and interpret the drop sizes with different superficial velocities and bed porosities.

To build awareness in second-year chemical engineering undergraduate students on runaway reaction dynamics and associated safety concerns, and to help students better identify crossovers between two different courses, a combined team project between the Heat and Mass Transfer and Applied Differential Equations courses at the University of Toronto has been implemented. To evaluate the effectiveness of this combined project on students learning, a survey was conducted around four different perspectives: (A) Contribution to learning, (B) Motivation and awareness, (C) Project structure and support, and (D) Personal experience and skills development. The results of the survey demonstrated that the project was effective at bringing awareness about safety issues and the role of students as future professional engineers. It helped them better learn the concepts seen in both courses and develop their team skills. A critical analysis of these results helped to provide guidance for improvement in future years are discussed.