Comprehensive Characterization of Petroleum Acids by Distillation, Solid Phase Extraction Separation, and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

Crude acids or petroleum acids are considered to be one of the prime contributors to corrosion, emulsion, and fouling issues across upstream, downstream, and chemical operations. Thus, the composition of crude acids has been extensively studied in the last several decades. To achieve molecular level characterization, mass spectrometry is typically applied. However, one of the challenges in mass spectrometry characterization is that the dynamic range of the technique can severely limit the compositions observed. Here, we employ multiple separations before analyzing crude oil acid fractions to overcome this limitation. First, a whole crude (WC) oil was distilled into boiling point fractions including vacuum gas oil (VGO) and vacuum residue (VR). Acids were then collectively isolated from the VGO and VR fractions as well as the starting WC using a solid phase extraction (SPE) method. Isolated acids were also further separated by molecular weight (MW) using a similar SPE technique. The acid fractions were then characterized by negative-ion (−) electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). This combined analytical approach produced a comprehensive acid composition of the crude oil and a more accurate distribution of the acids as a function of boiling point. A comparison of the WC acid fractions to the VGO and VR acid fractions reveals that direct analysis of the WC fractions does not cover the full composition as exhibited through the combined analysis of the VGO and VR fractions. Thus, further fractionation of the crude oil, such as through distillation, aids in overcoming dynamic range limitations associated with FT-ICR MS.

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“…Broadband FT-ICR MS is uniquely suited for molecular-level characterization of ultra-complex mixtures because it can resolve and identify tens of thousands of elemental compositions in a single analysis in a matter of minutes, irrespective of the boiling point. − When combined with separations, FT-ICR MS constitutes a powerful tool to assess petroleum molecular composition and understand the compositional trends responsible for petroleum phase behavior, fouling, and refining. ,− …”

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“…The high molecular weight species will not be detected if the sample is analyzed "as is" due to dynamic range limitations as shown in Figure 2. 48 Clingenpeel et al 49 further combined physical distillation and MAPS to determine full acid composition for whole crude oils. The work demonstrated that a single FT-ICR measurement only provides a fingerprint of the petroleum acids.…”

Recent Advances in Petroleum Analysis by Mass Spectrometry

“…(−) MALDI allowed the detection of highly oxidized O x species ( x = 1–9, 11) that were not observed in the (−) ESI mass spectra. More recently, Clingenpeel et al utilized multiple separation methods followed by analysis using (−) ESI 15 T FTICR MS to increase the dynamic range of the analysis of NAs in crude oil . The crude oil was first distilled into fractions that included vacuum gas oil (VGO) and vacuum residue (VR).…”

“…More recently, Clingenpeel et al utilized multiple separation methods followed by analysis using (−) ESI 15 T FTICR MS to increase the dynamic range of the analysis of NAs in crude oil. 125 The crude oil was first distilled into fractions that included vacuum gas oil (VGO) and vacuum residue (VR). The NAs were then isolated from VGO, VR, and the original crude oil by using SPE and fractionated based on their MW by using the SPE method discussed above, followed by analysis using (−) ESI 15 T FTICR MS. Mass spectra measured for the VGO and VR fractions revealed small acidic compounds with two to four oxygens that were not detected in the original crude oil.…”