Effect of Aqueous Phase pH on the Dynamic Interfacial Tension of Acidic Crude Oils and Myristic Acid in Dodecane

Abstract

The time dependence of the interfacial tension between water-acidic crude oil and watersynthetic oil was investigated for aqueous phase pHs ranging from 2 to 9 using the du Noüy ring method at 20 C. Myristic acid in dodecane was selected as a model (synthetic oil) for acidic crude oil containing indigenous surfactants, and the similarities and differences between the dynamic interfacial tension behaviours of the natural and synthetic crude oil systems were compared. The initial interfacial tension and the relaxation of the interfacial tension are sensitive to the aqueous phase pH for both systems. The adsorption kinetics of the indigenous surfactants and myristic acid could be well fitted with the monoexponential model, and the time constants obtained in this manner indicates that reorganization of the indigenous surfactants and myristic acid at the w/o interface are pH dependent. The experimental results also indicate that indigenous surfactants in acidic crude oil and myristic acid in dodecane have similar film formation behaviours at the w/o interface for the range of pHs investigated.

Equilibrium partitioning of naphthenic acids and bases and their consequences on interfacial properties

“…Organic acids and bases can have an amphiphilic nature which allows them to adsorb and desorb at the oil-water interface and lower the interfacial tension. If the adsorption rate is larger than the desorption, then the interfacial tension decreases over time until the desorption rate matches the adsorption rate and the interfacial tension is at equilibrium [55]. Crude oil can contain both surface active acids and bases as shown by Buckley, Takamura and Morrow [56].…”

Role of Aqueous Phase Chemistry, Interfacial Film Properties, and Surface Coverage in Stabilizing Water-in-Bitumen Emulsions

“…where o  is the interfacial tension at time zero, e  is the equilibrium interfacial tension and  is a parameter with the same unit as time which signifies the relaxation time. This mono exponential model has been applied to find the equilibrium IFT for asphaltenes and crude oil systems (Kumar, 2012;Keleşoğlu et al, 2011;Buckley and Fan, 2007). In the example shown in Figure 3.5, the IFT appears to reach equilibrium within 2000 s (33 min) and the equilibrium IFT can be taken directly from the data after 100 s. However, in some cases at asphaltene concentrations of 2 g/L, equilibrium was not reached within two hours.…”

Dynamic Duo: Vibrational Sum Frequency Scattering Investigation of pH-Switchable Carboxylic Acid/Carboxylate Surfactants on Nanodroplet Surfaces

“…Carboxylic acid containing surfactants, or fatty acids, are ubiquitous in biological, industrial, and environmental systems. − They are building blocks for complex polar lipids such as triglycerides capable of storing energy for microbes, are found in many cleaning substances as a nontoxic soap, and are often used in remediation efforts due to the switchable nature of the headgroup . The reason these types of surfactants are found in so many processes is because of the diverse and complex chemical interactions of the headgroup. ,,− They have been shown to readily bind to metals, can easily be formed through hydrolysis reactions of more complex starting material, and can have varied functionality and adsorptive properties by simple protonation and deprotonation of the headgroup. , This last point has made carboxylic acids of particular interest in oil spill remediation efforts as the protonated headgroup is much less hydrophilic than its deprotonated counterpart . Furthermore, the pH switchability of the surfactant can be used to stabilize oil droplets when the headgroup is charged and destabilize the oil droplets when the headgroup is neutral. , This has allowed for enhanced ability in removing oil from contaminated sands, which is notoriously hard to remediate .…”