Characterization of naphthenic acids in crude oil samples-A literature review

Given the ill-defined term "naphthenic acids" (NAs), we will classify NAs as the carboxylic acids found naturally in crude oil, which include both classic NAs (c-NAs, monoacids) and ox-NAs (polyacids). Resulting from the biodegradation mainly of saturated hydrocarbons, we briefly present the probable formation mechanisms of these acids. Throughout the text, we will revisit the classification of NAs by highlighting the challenges to the petrochemical industry in the processing of acidic petroleum, related phenomena, metal corrosion, and the formation of naphthenates, which can stabilize emulsions or even precipitate to obstruct surface installation systems. An exploratory bibliometric review highlights the expansion in the number of publications about NAs from the 2000s to present. Advances in chemical characterization analyses contributed to the discovery a specific group of high molecular weight tetrameric NAs, sometimes called ARN, that will receive special attention. Here, we present the primary extraction and characterization techniques used in the elucidation of NAs. We highlight characterization efforts by infrared spectrometry, nuclear magnetic resonance spectroscopy, liquid and gas chromatography, and mass spectrometry. Of note, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) excels in the characterization of NAs and belongs to ultra-high resolution mass spectrometry (UHRMS) techniques, which redefined the analysis of the composition of crude oil and its fractions.