Calculation of Average Molecular Parameters, Functional Groups, and a Surrogate Molecule for Heavy Fuel Oils Using ¹H and ¹³C Nuclear Magnetic Resonance Spectroscopy

Abstract

Heavy fuel oil (HFO) is primarily used as fuel in marine engines and in boilers to generate electricity. Nuclear Magnetic Resonance (NMR) is a powerful analytical tool for structure elucidation and in this study, 1 H NMR and 13 C NMR spectroscopy were used for the structural characterization of 2 HFO samples. The NMR data was combined with elemental analysis and average molecular weight to quantify average molecular parameters (AMPs), such as the number of paraffinic carbons, naphthenic carbons, aromatic hydrogens, olefinic hydrogens, etc.in the HFO samples. Recent formulae published in the literature were used for calculating various derived AMPs like aromaticity factor (݂ ), C/H ratio, average paraffinic chain length (݊), naphthenic ring number (ܴ ே ), aromatic ring number (ܴ ), total ring number (ܴ ் ), aromatic condensation index (߮) and aromatic condensation degree (Ω). These derived AMPs help in understanding the overall structure of the fuel. A total of 19 functional groups were defined to represent the HFO samples, and their respective concentrations were calculated by formulating

Heavy fuel oil pyrolysis and combustion: Kinetics and evolved gases investigated by TGA-FTIR

“…If necessary, lighter cuts, based on refinery availability, may be added to reduce its viscosity. The present HFO sample was sourced from a refinery in Saudi Arabia and its physical and chemical properties were studied in previous works [1,7] and are briefly presented in Table 1. HFO has a high viscosity of 746.5 (10 -6 m 2 /s) at 313 K, more than a thousand times the viscosity of water at the same temperature.…”

“…Their formation is known to depend more on the asphaltene chemistry than the asphaltene quantity in the HFO [34]. Abdul Jameel and coworkers [1] presented the composition of this HFO sample in terms of the average molecular fragments, the concentration of different functional groups present, and a surrogate molecule that represents the average structure of the entire fuel. The fuel has a high aromatic content of nearly 37 mass% including multiple fused aromatic and naphthenic rings.…”

“…It is characterized by its high viscosity, tar-like nature and high asphaltene (n-heptane insolubles) content that makes it difficult to burn. HFOs are also characterized by high sulfur contents of up to 4.5 mass % [1], which leads to SO2 emissions. Combustion of HFO in boiler furnaces leads to the emission of particulate matter comprised of cenospheres, smoke and ash residues, soot, sulfuric acid and organic materials [2][3][4].…”

“…The market price of HFO is estimated to be half the price of light oil [6]. Despite recent regulations [1] limiting the use of HFO, it can be seen from present trends that HFOs are here to stay for the foreseeable future. Therefore, there is a need to gain better understanding of HFO combustion due to their complex nature, so as to obtain improve combustion efficiency and emissions control.…”

“…HFOs have been characterized by various techniques like thermogravimetry [7,8], nuclear magnetic resonance (NMR) spectroscopy [1,7] and Fourier transform-ion cyclotron resonance (FT-ICR) mass spectroscopy [7] to gain insights into their complex molecular structure, because most of the conventional chromatographic techniques like GC-MS [9] are unable to handle such heavy fuels. However, these techniques cannot explain the real time evolution of gaseous pollutants or other hydrocarbon functional groups during their pyrolysis or combustion, i.e., information that could help understand and control their combustion characteristics.…”