Measurement and Modeling of Emulsion Layer Growth in Continuous Oil-Water Separations

Water-in-crude oil emulsions present considerable challenges to the petroleum industry both during upstream production and downstream treatment of crude oil, especially in the case of oil sands separation processes, where these emulsions contribute to the formation of rag layers. A rag layer is the material that accumulates and persists at the oil/water interface and it consists of emulsified water and/or oil, clays, and solids. Sometimes, under poor processing conditions, rag layers grow large enough to cause a process upset.;The time dependent coalescence rates were determined from the change in heights of the emulsion and free oil layer over time. Continuous experiments were also performed where the emulsion was continuously fed to the separator until a steady state condition was reached. Then, the feed was shut off and the decrease in emulsion layer height was measured over time and this part was called as the decay experiment. The decay experiments were also modeled to find the coalescence rates.;The coalescence rate was found to decrease exponentially with time. The decrease was not caused by a change in drop size distribution which remained invariant over time. The decrease in coalescence rate was found to correlate with the thinning of the continuous aqueous phase film between the oil droplets. It was speculated that the surfactant released from prior coalescence remained trapped in the film and enhanced the stability of the emulsion. Gentle mixing of the emulsion layer to liberate trapped surfactant caused a lasting increase in the coalescence rate.;It was found that the initial coalescence rate determined from a decay experiment could be used to predict the steady state emulsion layer height measured in continuous experiments. To check the predictive capability of the model, experiments were performed at different flow rates and model was able to predict emulsion layer growth using the known coalescence rate.;This thesis is part of a study with an overall objective to understand the factors that trigger rag layer growth. In this thesis, the relationship between emulsion stability and rag layer growth was investigated using model emulsion systems. The model was developed based on the coalescence of the emulsified droplets. The methodology was first developed with relatively straightforward oil-in-water emulsions and then tested on the more challenging water-in-oil emulsions stabilized by asphaltenes which exhibit aging effects. To determine the coalescence rates of the model oil-in-water emulsions, batch experiments were performed with emulsions prepared from an aqueous phase consisting of reverse osmosis water with NEO-10 surfactant and an organic phase as 50_heptol (50 vol% toluene, and 50 vol% heptane) at the temperature of 45°C and with a mixer speed of 800 rpm. After mixing, the emulsion was allowed to coalesce and the heights of the emulsion, free oil and water layers were measured over time.;The effect of separator geometry was also studied by changing the separator diameter and volume. It was observed that coalescence is faster in the larger diameter separator than in the smaller diameter separator. The difference in coalescence rate was attributed to wall effects. A series of batch experiments were performed to assess the wall effect and it was found that as the surface area/volume (SA/V) ratio increased, the coalescence rate decreased; that is, the smaller the diameter, the lower the coalescence rate.;This study provides the first step to understand the rag layer growth and presents a methodology for relating rag layer growth to coalescence rates. Some experiments on asphaltene stabilized water-in-oil emulsions were also performed and were modeled with this methodology. These experiments were preliminary studies on water-in-oil emulsions which provide a base line for future studies on the role of precipitated asphaltenes and inorganic solids in rag layer growth in oil sands separation.