Investigation of the Chemical Composition of the Organic Material Associated with Inorganic Solids Found in Heat Exchanger Deposits: Possible Fouling Precursor in Refinery Operation

In the oil sand literature, the deposits containing organics associated with solids and insoluble in toluene are often referred to as toluene-insoluble organic material (TIOM). In this work, we call these materials toluene insolubles (TI) and clarify what TIOM means. Our focus in this work is to determine the chemical composition of the organic portion of the TI obtained from the extraction of fouling deposits collected from a heat exchanger unit of a refinery. Analysis of TI using thermogravimetric analysis (TGA), optical microscopy, inductive coupling plasma (ICP), and X-ray diffraction (XRD) showed that these materials are composed of both organic and inorganic solids/clay minerals. Using an accelerated solvent extraction (ASE) unit, the TI fraction was sequentially solvent-extracted using methylene chloride/methanol (9:1, at 110 °C/1000 psi) and acetonitrile CH₃CN (ACN, at 130 °C/1000 psi). The extracted fractions were then analyzed by using high-resolution mass spectrometry (HRMS) and Fourier transform infrared (FTIR). The results showed that the extracted materials were mainly organic polymers consisting of a variety of polyethers used as chemical additives in the oil industry. The analysis by atmospheric pressure photoionization (APPI) in positive ion mode and electrospray ionization (ESI) in positive and negative ion modes revealed that besides the predominant polyether polymer in the form of ethylene oxide (EO) and propylene oxide (PO), there are also condensed aromatics, pyridine, alkylpyridines, sulfonates, low-carbon low-double bond equivalent (DBE) species with one heteroatom, and acidic species. A subsequent analysis of the blank solvent obtained from the ASE unit by HRMS showed that no polyether polymers were present, indicating that these polymers are part of the foulant deposits. To obtain more structural information on the organic fraction, the TI sample was subjected to pyrolysis gas chromatography–mass spectrometry (GC-MS) between 300 and 600 °C. Compositional analysis revealed that the volatile organic fraction of the TI is composed mostly of polar components with oxygen and nitrogen functionality, including phenols, indoles, alkylpyrroles, aldehydes, and carboxylic acids. These products are most likely from the decomposition of polyethers as well as nonylphenols used as chemical additives. The presence of intact nonylphenol indicates the desorption of polar molecules from the surface of clays/minerals during pyrolysis. The results of this work have demonstrated that fouling deposits of a heat exchanger formed by organic molecules associated with inorganic solids are not only derived from the original oil but also derived from chemical additives that are used during oil production/processing.