Detection and Impact of Carboxylic Acids at the Crude Oil–Water Interface

Abstract

The impact of surface active indigenous components on interfacial tension (IFT) of crude oil–water systems is an important parameter in many aspects of crude oil production such as emulsion stability, reservoir wettability, and capillary number calculations. These components may affect productivity across the reservoir due to variations in concentrations. In most cases simulation of IFT is not taking interfacial activity into account and is purely based on oil bulk properties. In this paper we examine two crude oils and their subfractions such as maltenes, deacidified crude, and natural acidic components. Films were prepared at the toluene–water interface with crude oil and its various fractions and studied for interfacial activity and chemical compositions. The chemical analysis of the interfacial active material indicated that carboxylic acids are preferentially adsorbed or concentrated at the oil/water interface. Infrared spectroscopic analysis of the interfacial films clearly demonstrates that carboxylic acids species (e.g., fatty acids, resins, or asphaltenes with a −COOH functionality) are concentrated at the interface. The GC-MS analysis of the interfacial film revealed the presence of a homologous series of linear chain carboxylic acids ranging from C10–C25+. 2D GC-MS analysis showed that heteroacids are also present. Acid free crude was prepared and back mixed with the original crude oil in different proportions confirming the role of the acids in decreasing IFT. The removal of these relatively small amounts of acids leads to a decrease in IFT between 1.3 and 2.2 mN/m. The results also indicate that acids can be preferentially removed by ion exchange resins without affecting the overall composition of the oil as is shown by back-mixing deacidified oil into the original oil.

Physical and chemical aspects of “precursor films” spreading on water from natural bitumen

“…Using a more rigorous analysis than we have adopted for the present study, these workers observed very similar heteroatom class speciation, enabling their conclusion that the interfacial material obtained from Athabasca bitumen contains a higher abundance of acidic oxygen-, nitrogen-, and sulfur-containing species compared to the parent bitumen. The ubiquitous presence of carboxylic acids found in the present study is also consistent with results obtained elsewhere [50][51][52]. Using the same bitumen sample, we also extracted material directly from a toluene-diluted bitumen/water interface, from which we identified similar species distributions to those shown in Fig.…”

“…In a hydrocarbon environment, polar species contained in heavy fractions, such as asphaltenes and resins, will exhibit surface activity [21]. Unsurprisingly, therefore, interfacial materials are enriched in polar species, and chemical analysis has identified numerous species classes, including carboxylic and hetero-acids [22]. Such species are associated with operational problems, including corrosion, catalyst poisoning, deposit formation and emulsion stabilization [22], which has led to research into their isolation and characterization [23,24].…”

“…Unsurprisingly, therefore, interfacial materials are enriched in polar species, and chemical analysis has identified numerous species classes, including carboxylic and hetero-acids [22]. Such species are associated with operational problems, including corrosion, catalyst poisoning, deposit formation and emulsion stabilization [22], which has led to research into their isolation and characterization [23,24]. Isolated acid fractions (generically referred to as "naphthenic acids") frequently contain phenols but are principally complex mixtures of carboxylic acids [1].…”

Components of Paraffin-Base and Naphthenic-Base Crude Oil and Their Effects on Interfacial Performance

“…By comparison, HB resin has lower interfacial activity. This is because the active molecules with high molecule weights of resin separated from extra heavy oil preferentially adsorbe and enrich on the side of oil phase in the O/W interface [28].…”

“…Acidic components rich in resin as a well-known strong interfacial active species play a major role in reducing O/W IFT [24] [25] [26] [27] [28]. Cao et al [26] suggested that the mixed adsorption of positive synergistic effect between acidic components and linear betaine molecule on the interface of oil and solution might cause densification of interfacial film and reduction of O/W IFT.…”