Crude oils differ from one another in numerous chemical and physical properties, many of which play an important role in defining their quality and price. Generally, statistical analysis of price differentials has focused on two main properties: density and sulfur content. However, the growing significance of high total acid number (TAN) crude oils, especially from developing countries, has aroused the necessity for extending these models. Consequently, refineries must obtain real and exact information regarding crude oil quality to achieve optimal crude oil selection and processing decisions. This could be attained when a detailed molecular-level characterization is performed. The present work presents the combination of negative electrospray ionization [(−)­ESI] and positive atmospheric pressure photoionization [(+)­APPI] Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, as a prominent approach to semi-quantify the acid species comprised in crude oils. A novel polarity index is proposed that corrects the relative abundances of (−)­ESI classes, where mainly acid species are detected. By consideration of different indexes, it was possible to enhance the correlation coefficients (R 2) from 0.579 to 0.986 between the percentage of acid compounds and TAN of crude oils, where most of the samples stand close to a linear tendency. These results avoid the deviations observed in previous works on the correlations between relative abundances of the O2 class through (−)­ESI and TAN and could support achieving optimal crude oil selection and defining their quality and price.

In the present work the distribution of oxygen compounds in the total organic acid content of ten crude oils was assessed by means of negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry ((−) ESI FT-ICR-MS). As a first attempt, the relative abundance of the O2 class was related to the total acid number (TAN) for samples following the state of the art, and no positive correlation was achieved. Therefore, we performed the selective isolation of acidic compounds via solid phase extraction using amino-propyl silica (APS), finding an acceptable correlation (R 2 = 0.98) between acidic fraction percentage and TAN. Both the reliability and performance of the APS method were confirmed using a chosen sample as control. FT-IR spectroscopy was employed to validate the acidic nature of the isolated fraction. In the IR spectrum of the acidic fractions, characteristic signals of carboxylic acids, such as the sharp band around 1700 cm–1 and the wide band around 2300–3500 cm–1, were identified. Additionally in such fractions, oxygenated classes such as O2, NO2, O3, SO2, and O3S were detected through (−) ESI FT-ICR-MS. Nevertheless, it can be said that none of these classes exclusively belong to the acidic fraction since for instance, O2 and NO2 compounds were found in both nonacid and acid fractions. In this sense, some O2 compounds may be considered to be bifunctionalized alcohols, phenols, ketones, or ethers. Finally, by comparing the contour plots DBE vs carbon number of chosen samples, it was possible to infer that the contribution of the O2 class over the TAN is structure dependent for samples with TAN lower than 0.5 mg KOH/g. Thus, the DBE distribution within the acidic and nonacidic fractions must be carefully considered in order to estimate their relevance over the total acid content.

Petroleum sulfonates obtained from heavy vacuum gas oil (HVGO) were characterized by negative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry [(−) ESI FT-ICR MS] to better understand the chemical nature of their surface-active components. Electrospray ionization (ESI) analysis showed that sulfonates contain mainly O3S, O3S2, O4S, and NO3S classes, which means that the sulfonation reaction does not occur selectively for aromatic hydrocarbon (HC) class compounds because it also reacts with N, S, and O heteroatom classes. Because sulfonates were separated by solubility into lipophilic and hydrophilic categories, it was confirmed that the same classes compose hydrophilic and lipophilic sulfonates. Moreover, this procedure revealed that lipophilic sulfonate extracts contain organic acids (O2 class) that are related to the total acid number of the starting HVGO. However, selective isolation of the surface-active species using the “wet-silica” procedure allowed for detection that these compounds have a non-surface-active character because they do not interact with the water phase. The new structural information disclosed about petroleum sulfonates and their raw materials might encourage further studies on the rational design and synthesis of novel petroleum surfactants with the desired properties for industrial applications, such as chemical enhanced oil recovery (CEOR).

In situ combustion (ISC) is one of the highest potential enhanced oil recovery (EOR) processes for heavy oils. However, several operational issues, including the formation of highly stable emulsions, have limited its application. Disclosing the physicochemical proprieties of these emulsions, especially the chemical nature of the compounds involved in the stabilization process, has become relevant for the success of ISC projects. In the present work, the physicochemical changes at a laboratory-scale low-temperature oxidation (LTO) regimen performed over a Colombian heavy crude oil were followed by mass spectrometry. The compositional analyses were performed using both positive-ion atmospheric pressure photoionization ((+) APPI) and negative-ion electrospray ionization ((−) ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Further isolation of acidic compounds and surface-active species allowed us to determine that the process incorporates a wide variety of compounds to build up the O/W (oil/water) interface, thus increasing the stabilizing tendency of the emulsions. During the combustion, oxygen is chemically incorporated to the crude over hydrocarbon compounds, as well as over sulfur- and nitrogen-containing compounds, generating classes such as O, O2, O3, O4, OS, NO2, and NO3 that explain the high viscosity and high stability of the emulsions.