Abstract
Summary A state-of-the-art portable dispersion characterization rig (P-DCR) is applied to study emulsions with Exxsol™ mineral oil (ExxonMobil Chemical Company, Houston, Texas, USA), commercial distilled water, and hydrophobic silica nanoparticles (NPs) as emulsifiers. The emulsion is prepared in the P-DCR batch-separator vessel, whereby the separation kinetics are observed and recorded. In this study, emulsion breakup by the integration of oil extraction/water addition and a stirring process is investigated, which is formed with 25% water cut (WC) and 0.01% w/w hydrophobic NPs (dispersed in the oil phase). The experimental data are divided into three data sets: oil extraction only, oil-extraction/pure-water addition, and oil-extraction/water with hydrophilic NP addition. For oil extraction only (Data Set 1), the WC of the fluid mixture increases, and for a sufficient volume extraction, phase inversion occurs that results in a complete separation of the oil and water. The minimum final required NP concentration for a fast separation, defined as the minimum concentration of NP required to begin the phase separation of the emulsion, is approximately 0.0045%. The acquired data for oil-extraction/pure-water-addition (Data Set 2) result in a faster breakup of the emulsion, as compared with oil extraction only. The oil-extraction/pure-water-addition process increases the system WC faster, reaching the phase-inversion point sooner. For the oil-extraction/pure-water-addition, the final lowest WC and NP concentrations are approximately 37% and 0.006% w/w, respectively, for fast separation. Thus, it can be concluded that the NP concentration and the WC are related. Repetitive oil-extraction/pure-water-addition cycles enable determination of the combined effects of the WC and NP on the separation process. A relatively stable emulsion is reached after approximately 2 minutes from the beginning of each cycle, which enables determining whether a quick separation occurs at the current cycle. Data Set 3 (oil-extraction/water with hydrophilic NP addition) results reveal that dispersing hydrophilic NPs in water does not promote emulsion breakup. On the contrary, the NPs produce a slightly more stable emulsion. The separation process, however, does not differ significantly even for high hydrophilic NP concentrations, emphasizing the dominant role of the hydrophobic particles (dispersed in the base-case emulsion).
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