FIELD OF THE INVENTION

The invention generally relates to methods of analyzing crude oil.

BACKGROUND

Pipelines are generally the most economical way to transport large quantities of crude oil, refined oil products or natural gas over land. Steel pipes are commonly used, which can be subject to both internal and external corrosion. Corrosion protection is a critical process to ensure continuous pipeline operation.

Corrosion of oil transmission pipelines can result in leakage and large scale oil spills that are destructive of the ecosystem and pollute drinking water supplies (Sastri, Corrosion Inhibitors: Principles and applications, J. Wiley & Sons, New York, 2001, Ch 1, pp 5-30; Sacher, et al., J. Chromatogr, A, 1997, 764, 85-93; Zhao et al. Materials and Corrosion, 2004, 55, 684-688; Son, NACE International Corrosion Conference Series, 2007, 07618; Valentine, et al., Science, 2010, 330 208-211; Kujawinski, et al., Science & Technology, 2011, 45, 1298-1306; Thibodeaux, et al., Environmental Engineering Science, 2011, 28, 87-93; Bjorndal, et al., Science, 2011, 331, 537-538; and Atlas et al., Environmental Science & Technology, 2011, 45, 6709-6715). Corrosion is typically inhibited through addition to crude petroleum of oil-soluble heterocyclic compounds, such as quaternary ammonium salts and ionic liquids (Quraishi et al., Am. Oil Chem. Soc., 2000, 77, 1107-1111, Treybig et al., U.S. Pat. No. 4,957,640; Derek et al., U.S. Pat. No. 4,235,838; and Young et al., U.S. Pat. No. 6,645,399). Successful inhibition depends on the amount of inhibitor, and so measurement of inhibitor levels in crude oil is of great interest, especially in long-distance transfer pipelines (Nyborg et al., NACE-International, Corrosion Conference Series, 2012, 6, 4582-4590; Kvarekvål, NACE-International Corrosion, Conference Series, 2012, 6, 4329-4352; and Dugstad et al., NACE-International, Corrosion Conference Series, 2012, 5, 3573-3586).

Currently, no standard method exists for direct in-field monitoring of residual levels of corrosion inhibitors. Gas chromatography or high performance liquid chromatography combined with mass spectrometry (GC-MS or HPLC-MS) is the most widely adopted method for ex-situ quantification of residual corrosion inhibitors and other oil constituents. (Sacher et al., J. Chromatogr, A, 1997, 764, 85-93; Son, NACE International Corrosion Conference Series, 2007, 07618; Huhn et al., J. Anal. Chem., 1995, 351, 563-566; Gough et al., NACE-International, Corrosion, 98 paper, No 33; Schwartz et al., Anal. Chem., 1990, 62, 1809-1818; Chiang et al., Chemistry of Materials, 1992, 4, 245-247; Hsu, Anal. Chem., 1993, 65, 767-771; March, J. Mass Spectrom., 1997, 32, 351-369; and He et al., Energy Fuels., 2011, 25, 4770-4775). Although highly sensitive and specific, these methods are time consuming, requiring numerous sample purification and preparation steps prior to analysis. Due to the sample work-up required prior to analysis, samples need to be taken to the laboratory for analysis.

SUMMARY

The invention provides methods for analyzing a crude oil sample by mass spectrometry in an unmodified form from which it was obtained. Accordingly, methods of the invention may be performed without any sample pre-purification steps. Aspects of the invention are accomplished using wetted porous material as a substrate for the mass spectrometry analysis. An unmodified crude oil sample, such as that extracted from an oil transmission pipeline, is directly introduced to a porous substrate. Solvent and voltage is applied to the substrate to generate ions of an analyte in the sample. Those ions are directed into and analyzed by a mass spectrometer. In that manner, methods of the invention provide rapid and efficient in-field mass spectrometry techniques for the analysis of crude oil, such as monitoring corrosion inhibitors in the crude oil in transmission pipelines.

In certain aspects, the invention provides methods for analyzing a crude oil sample that involve obtaining a crude oil sample, and subjecting the crude oil sample to mass spectrometry analysis. The methods of the invention may be performed without any sample pre-purification steps, i.e., the sample is taken directly from its source and is directly analyzed by mass spectrometry without any additional modification to the sample. In certain embodiments, the mass spectrometry analysis is performed in an ambient environment.

In certain embodiments, the mass spectrometry analysis involves introducing the crude oil sample to a porous substrate, applying solvent (e.g., a mixture of methanol and acetonitrile) and voltage to the substrate to generate ions of an analyte in the crude oil sample, and analyzing the ions using a mass spectrometer. Numerous different types of porous substrates may be used with methods of the invention, and such substrates are described in greater detail below. An exemplary porous substrate is paper, such as filter paper. The mass spectrometer may be a bench-top mass spectrometer or a miniature mass spectrometer. In certain embodiments, the mass spectrometer or miniature mass spectrometer is coupled to a discontinuous atmospheric pressure interface.

Methods of the invention may be used to analyze numerous different types of analytes in crude oil. In certain embodiments, the analyte in the crude oil is a corrosion inhibitor. The corrosion inhibitor may include at least one alkyl ammonium salt, such as tetradodecylammonium bromide, benzylhexadecyldimethylammonium chloride, or a combination thereof.

Other aspects of the invention provide methods for quantifying a corrosion inhibitor in crude oil. The methods involve obtaining a crude oil sample including a corrosion inhibitor, subjecting the crude oil sample to mass spectrometry analysis, and quantifying the corrosion inhibitor in the crude oil sample based on results of the mass spectrometry analysis, in which the method is performed without any sample pre-purification steps.

