PLS models for determination of SARA analysis of Colombian vacuum residues and molecular distillation fractions using MIR-ATR

Modelos PLS para determinación del Análisis SARA en residuos de vacío y fracciones de destilación molecular usando MIR-ATR PLS modelos para determinação da análise SARA em resíduos de vácuo e frações de destilação molecular utilizando MIR-ATR    Abstract In this work, prediction models of Saturates, Aromatics, Resins and Asphaltenes fractions (SARA) from thirty-seven vacuum residues of representative Colombian crudes and eighteen fractions of molecular distillation process were obtained. Mid-Infrared (MIR) Attenuated Total Reflection (ATR) spectroscopy in combination with partial least squares (PLS) regression analysis was used to estimate accurately SARA analysis in these kind of samples. Calibration coefficients of prediction models were for saturates, aromatics, resins and asphaltenes fractions, 0.99, 0.96, 0.97 and 0.99, respectively. This methodology permits to control the molecular distillation process since small differences in chemical composition can be detected. Total time elapsed to give the SARA analysis per sample is 10 minutes. Keywords: MIR-ATR, PLS, SARA analysis, molecular distillation, vacuum residue.  Resumen En este trabajo se obtuvieron modelos predictivos para la determinación de la fracción de saturados, aromáticos, resinas y asfáltenos (SARA) en fondos de vacío y sus fracciones, a partir del análisis de treinta siete muestras de dichos fondos. Se utilizó espectroscopia infrarroja en el modo de reflectancia total atenuada en combinación con regresión de mínimos cuadrados parciales para predecir de manera relativamente exacta el análisis SARA. Los coeficientes de regresión para la calibración fueron de 0,99, 0,96, 0,97 y 0,99 para los modelos predictivos de saturados, aromáticos, resinas y asfáltenos, respectivamente. El tiempo requerido para el análisis SARA por muestra fue de 10 minutos. Palabras claves: MIR-ATR, PLS, análisis SARA, destilación molecular, fondos de vacío.  Resumo Neste trabalho, os modelos preditivos para determinar a fração de saturados, aromáticos, resinas e asfaltenos (SARA) em fundos de vácuo e suas frações foram obtidas a partir da análise de trinta e sete amostras de fundos. A espectroscopia de infravermelho foi utilizada em modo de reflectância total atenuada em combinação com regressão parcial para prever com precisão relativamente à SARA análise dos mínimos quadrados. Os coeficientes de regressão para calibração foram de 0,99, 0,96, 0,97 e 0,99 para os modelos preditivos saturados, aromáticos, resinas e asfaltenos, respectivamente. O tempo necessário para a análise SARA por amostra foi de 10 minutos. Palavras-chave:MIR-ATR, PLS, análise SARA, a destilação molecular, fundos de vácuo.   Orrego-Ruiz JA, Cabanzo R, Mejía-Ospino E. PLS models for determination of SARA analysis of Colombian vacuum residues and molecular distillation fractions using MIR-ATR. 2014;27(1):43-48

PLS models for determination of SARA analysis of Colombian vacuum residues and molecular distillation fractions using MIR-ATR

Modelos PLS para determinación del Análisis SARA en residuos de vacío y fracciones de destilación molecular usando MIR-ATR PLS modelos para determinação da análise SARA em resíduos de vácuo e frações de destilação molecular utilizando MIR-ATR    Abstract In this work, prediction models of Saturates, Aromatics, Resins and Asphaltenes fractions (SARA) from thirty-seven vacuum residues of representative Colombian crudes and eighteen fractions of molecular distillation process were obtained. Mid-Infrared (MIR) Attenuated Total Reflection (ATR) spectroscopy in combination with partial least squares (PLS) regression analysis was used to estimate accurately SARA analysis in these kind of samples. Calibration coefficients of prediction models were for saturates, aromatics, resins and asphaltenes fractions, 0.99, 0.96, 0.97 and 0.99, respectively. This methodology permits to control the molecular distillation process since small differences in chemical composition can be detected. Total time elapsed to give the SARA analysis per sample is 10 minutes. Keywords: MIR-ATR, PLS, SARA analysis, molecular distillation, vacuum residue.  Resumen En este trabajo se obtuvieron modelos predictivos para la determinación de la fracción de saturados, aromáticos, resinas y asfáltenos (SARA) en fondos de vacío y sus fracciones, a partir del análisis de treinta siete muestras de dichos fondos. Se utilizó espectroscopia infrarroja en el modo de reflectancia total atenuada en combinación con regresión de mínimos cuadrados parciales para predecir de manera relativamente exacta el análisis SARA. Los coeficientes de regresión para la calibración fueron de 0,99, 0,96, 0,97 y 0,99 para los modelos predictivos de saturados, aromáticos, resinas y asfáltenos, respectivamente. El tiempo requerido para el análisis SARA por muestra fue de 10 minutos. Palabras claves: MIR-ATR, PLS, análisis SARA, destilación molecular, fondos de vacío.  Resumo Neste trabalho, os modelos preditivos para determinar a fração de saturados, aromáticos, resinas e asfaltenos (SARA) em fundos de vácuo e suas frações foram obtidas a partir da análise de trinta e sete amostras de fundos. A espectroscopia de infravermelho foi utilizada em modo de reflectância total atenuada em combinação com regressão parcial para prever com precisão relativamente à SARA análise dos mínimos quadrados. Os coeficientes de regressão para calibração foram de 0,99, 0,96, 0,97 e 0,99 para os modelos preditivos saturados, aromáticos, resinas e asfaltenos, respectivamente. O tempo necessário para a análise SARA por amostra foi de 10 minutos. Palavras-chave:MIR-ATR, PLS, análise SARA, a destilação molecular, fundos de vácuo.   Orrego-Ruiz JA, Cabanzo R, Mejía-Ospino E. PLS models for determination of SARA analysis of Colombian vacuum residues and molecular distillation fractions using MIR-ATR. 2014;27(1):43-48

Finding a relationship between the composition and the emulsifying character of asphaltenes through FTICR-MS

ABSTRACT In this work, n-heptane insoluble fractions (asphaltenes) from six crude oils were analyzed by means of Fourier-transform ion cyclotron resonance mass spectrometry (FTICR MS) using both positive Atmospheric Pressure Photo Ionization (+) APPI and negative Electro-Spray Ionization (-) ESI in order to understand their water-oil emulsion stabilization capability on a molecular level basis. Through (+) APPI it was possible to obtain an overview of samples composition. By sorting as nitrogen sulfur and oxygen containing compounds, it was possible to compositionally distinguish the asphaltenes. Through (-) ESI, several differences were also observed by grouping the classes as oxygen (NxOy+NxOySz+Oy+OySz) and non oxygen containing classes (Nx+NxSz). The interactions of these two groups of compounds must be considered in order to understand the water-oil emulsion stability. It implies that the cores where nitrogen and sulfur are part may interact via n-n stacking, while the oxygen containing compounds may interact either via hydrogen bonding or via dipole forces with the aromatic aggregates (highly polarizable), forming potentially surface active aggregates. Thus, the rate between these two families of compounds may determine the surfactant character of asphaltenes at the water-oil interface. Bearing this in mind, an emulsion stability coefficient was proposed based on the relative abundances of some families of compounds detected by (-) ESI-FTICR-MS to explain the crude oils' tendency to form emulsions.RESUMEN En el presente trabajo, las fracciones iiinsolubles en n-heptano (asfaltenos) de seis crudos fueron analizadas por espectrometría de masas de resonancia Ion-Ciclotrón con transformada de Fourier (FT-ICR MS) utilizando ionización de presión atmosférica en modo positivo (+) APPI e ionización electro-spray en modo negativo, con el fin de comprender a nivel molecular su capacidad de estabilización de emulsiones agua-aceite. A través de (+) APPI, fue posible obtener una visión general de la composición de las muestras. Al ordenar los compuestos como azufrados-nitrogenados, y oxigenados fue posible distinguir composicionalmente los asfaltenos. A través de (-) ESI también se observaron varias diferencias, al agrupar los compuestos detectados como los que contienen oxígeno (NxOy + NxOySz + Oy + OySz) y los que no contienen oxígeno (Nx + NxSz). Las interacciones de estos dos grupos de compuestos deben considerarse para comprender la estabilidad de la emulsión agua-aceite. Esto implica que los núcleos donde el nitrógeno y el azufre son parte pueden interactuar mediante apilamiento n-n, mientras que los compuestos que contienen oxígeno pueden interactuar mediante enlaces de hidrógeno o mediante fuerzas dipolo con los agregados aromáticos (altamente polarizables) formando agregados superficialmente activos. Es decir, la relación entre estas dos familias de compuestos puede determinar el carácter tensioactivo de los asfaltenos en la interfaz agua-aceite. Teniendo esto en cuenta, se propuso un coeficiente de estabilidad de emulsiones basado en las abundancias relativas de algunas familias de compuestos detectadas por (-) ESI-FT-ICR.MS que permita luego explicar la tendencia de los aceites crudos a formar emulsiones

Distribution of Oxygen-Containing Compounds and Its Significance on Total Organic Acid Content in Crude Oils by ESI Negative Ion FT-ICR MS

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 (<i>R</i>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

Combination of Negative Electrospray Ionization and Positive Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry as a Quantitative Approach of Acid Species in Crude Oils

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 (<i>R</i>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

Characterization of Acid Species in Asphaltenic Fractions by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Infrared Spectroscopy

Despite significant advances in the characterization of asphaltenes, the study of this fraction of crude oil remains challenging for the scientific community and oil companies. It is well-known that asphaltenes are responsible for many of the difficulties found in the extraction, production, transportation, storage, and refining of petroleum. Although they are defined as the fraction of crude oil that is insoluble in paraffinic solvents of low-molecular-weight-type n-heptane (C7) or n-pentane (C5), asphaltenes present a great compositional variety, concentrate a variety of elements (among which nitrogen, oxygen, sulfur, vanadium, and nickel stand out), apart from hydrogen and carbon, and are distinguished by grouping the molecules with greater aromaticity of crude oil. Given its high compositional and structural complexity, associating operational problems with specific characteristics of asphaltenes is a task that is still in force. Asphaltenes, in addition to being distinguished by their high aromaticity, are also known for their acid–base properties. The acid character varies according to the origin of the asphaltenes and is related to the presence of carboxylic acids, phenols, carbazoles, and indoles. The basic character can be attributed to the presence of amines, amides, and other nitrogen-containing compounds. Progressing in the detailed compositional characterization of the polar compounds comprising the n-heptane-insoluble fraction (asphaltenes) is still a necessary task toward the understanding of asphaltene aggregation phenomena and the relationship with crude oil properties, such as interfacial tension and viscosity. In the present work, the naphthenic acids of the insoluble fractions of five Colombian crude oils were characterized. The n-heptane-insoluble fraction was subjected to a washing process affording four subfractions, named as extractable 48 h, extractable 72 h, and extractable 96 h, which correspond to the heptane-soluble fractions that were recovered after each indicated time, and asphaltene 96 h, which corresponds to the remaining heptane-insoluble compounds after 96 h of washing. The samples were chosen so that they had a wide range of asphaltene content that varied from 3.0 to 19.2%. The acid fraction was obtained from each sample by solid-phase extraction using aminopropyl silica as an adsorbent material

Exploring Compositional Changes along In Situ Combustion and Their Implications on Emulsion Stabilization via Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)

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

Detailed Characterization of Petroleum Sulfonates by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

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)

Identification of Refractory Weakly Basic Nitrogen Compounds in a Deeply Hydrotreated Vacuum Gas Oil and Assessment of the Effect of Some Representative Species over the Performance of a Ni–MoS₂/Y-Zeolite–Alumina Catalyst in Phenanthrene Hydrocracking

Heavy crude oil processing leads the way in current refining. These crudes yield larger amounts of distillable heavy fractions such as vacuum gas oil (VGO). VGO must be treated in at least two refining units: a hydrotreating unit where sulfur, nitrogen, and other heteroatoms are removed, and a hydrocracking unit where suitable fuels are obtained. Removal of heteroatoms during hydrotreating, particularly, nitrogen, dictates the efficiency of hydrocracking. In the first part of this work, the nature of refractory nitrogen-containing compounds on the performance of a hydrotreating catalyst was evaluated. To achieve this goal, both a VGO and its hydrotreated counterpart were studied using electrospray ionization with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Weakly basic N-containing compounds, namely, heavy pyrrolic-like compounds and their partially hydrogenated derivatives, were found to be the most refractory to hydrotreating. These compounds are weakly basic compared to most nitrogen compounds present in VGO. Considering this finding, the second part of the work was devoted to assessing the effect of pyrroles on the reactivity of phenanthrene over a Ni–MoS₂/Y-zeolite–alumina two-stage hydrocracking catalyst. Tests were carried out in a fixed-bed reactor using mixtures of carbazole and tetrahydrocarbazole. Results showed that these compounds can affect the catalytic performance of Ni–MoS₂/Y-zeolite–alumina by reducing its activity and inhibiting its selectivity to hydrocracking products. These findings draw attention to the possible role of weakly basic nitrogen compounds in the catalytic performance of materials employed for two-stage hydrocracking units