Prediction of Crude Oil Properties and Chemical Composition by Means of Steady-State and Time-Resolved Fluorescence

Abstract

Steady-state and time-resolved fluorescence measurements are reported for several crude oils and their saturates, aromatics, resins, and asphaltenes (SARA) fractions (saturates, aromatics and resins), isolated from maltene after pentane precipitation of the asphaltenes. There is a clear relationship between the American Petroleum Institute (API) grade of the crude oils and their fluorescence emission intensity and maxima. Dilution of the crude oil samples with cyclohexane results in a significant increase of emission intensity and a blue shift, which is a clear indication of the presence of energy-transfer processes between the emissive chromophores present in the crude oil. Both the fluorescence spectra and the mean fluorescence lifetimes of the three SARA fractions and their mixtures indicate that the aromatics and resins are the major contributors to the emission of crude oils. Total synchronous fluorescence scan (TSFS) spectral maps are preferable to steady-state fluorescence spectra for discriminating between the fractions, making TSFS maps a particularly interesting choice for the development of fluorescence-based methods for the characterization and classification of crude oils. More detailed studies, using a much wider range of excitation and emission wavelengths, are necessary to determine the utility of time-resolved fluorescence (TRF) data for this purpose. Preliminary models constructed using TSFS spectra from 21 crude oil samples show a very good correlation (R 2 > 0.88) between the calculated and measured values of API and the SARA fraction concentrations. The use of models based on a fast fluorescence measurement may thus be an alternative to tedious and time-consuming chemical analysis in refineries. ' INTRODUCTIONOnline remote characterization and real-time classification of crude petroleum are the most important current challenges faced by the petrochemical industry and environmental agencies. A rapid and inexpensive method for the remote analysis and classification of petroleum prior to distillation of the crude would provide chemical information of great importance for real-time adjustment of the critical operational parameters of a refinery, permitting an optimization of the process and resulting in economic and environmental benefits.A variety of spectroscopic techniques have been used over the last few decades for the analysis, characterization, and classification of crude oil in drilling fields, for the analysis of petroleum products, and for the detection of oil spills. The advantages of using such techniques include rapid response, the requirement of minimal sample preparation, and relatively inexpensive equipment costs. Of all of the optical spectroscopic techniques employed, vibrational [infrared (IR) and Raman] 1,2 and electronic [ultravioletÀvisible (UVÀvis) and fluorescence] spectroscopies have shown the highest potential in the field. Fluorescence is a more complex phenomenon than absorption (UVÀvis or IR), and effects such as quenching and energy transfer have to be considered. 3,...

Contribution of mass spectrometry in assessing quality of petroleum fractions

“…Bulk properties, such as API gravity, boiling points, flash points, metal content, etc., are measured by a succession of physical testing methods (Hsu et al, 2011). More sophisticated analytical instruments, such as near-infrared spectroscopy and fluorescence spectroscopy (López-Gejo et al, 2008;Pantoja et al, 2011), have been used to determine the functionality and gross structure of the mixture. Furthermore, crude oil can be classified according to its oxidation characteristics.…”

Recent Applications of First- and Second-Order Multivariate Calibration to Analytical Chemistry

“…Additional determinations of industrial relevance are the total acid number (128), quality (129), and sulfur content (130) of crude oil, glucose and ethanol in bioethanol (131), butene in ethylene/ propylene/1-butene terpolymers (132) by MIR spectroscopy, saturates, aromatics, resins, and asphaltenes in crude oil by fluorescence spectroscopy (133), nickel and chromium in steel by laser UV spectroscopy (134), and 11 pesticides in agrochemical formulations by a NIR spectroscopy/PLS-based QC with results comparable to HPLC (135). In a typical realtime NIR spectroscopy/PLS application, the natural antimalarial artemisinin was determined in dried leaves of Artemisia annua L. using a hand-held device (136).…”

Rethinking Petroleum Products Certification

“…Efforts have been made to address the control problem, but the in-line instrumentation performance has seldom been compared to the off-line standard test ones for the sake of product certification (using repeatability and reprodutibility); correlation measures are provided instead [4,13,14]. In this sense, data validation is the key to assure the measurement precision, enhancing the signals of the sensors.…”

“…In a scenario in which the world economic growth slowed down and demand for petroleum products flattened or even decreased, it becomes clear that flexibility is the keyword for everybody involved in the oil sector [3]. In this sense, online remote characterization and real-time optimization of petroleum products emerge as instrumental technologies for competitive refineries [4]. Such technologies may have a Journal of Petroleum Engineering special impact on refining profitability with environmental benefits when considered to provide chemical information of great importance for real-time adjustment of short-term scheduling decisions concerned with product formulation and refinery dispatch logistics.…”