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A full-vector mode solver for bending waveguides is described based on the finite-difference frequency-domain method in a local cylindrical coordinate system in which the formulas are directly derived from Maxwell's equations with the help of Yee's mesh. The perfectly matched layer absorbing boundary conditions are incorporated into the present approach in order to effectively demonstrate the leaky nature of bending waveguides. A typical bending rib waveguide is considered as a numerical example to show the effectiveness of the established method.

Supercritical CO2 flooding has been considered as a promising enhanced oil recovery (EOR) method because it can effectively improve the oil recovery and promote greenhouse gas sequestration. However, the solubility of different petroleum components in supercritical carbon dioxide (SC-CO2) has not been well investigated. This paper presents the molecular selectivity of SC-CO2 extraction on crude oil under different pressures and temperatures. The crude oils were loaded on the surface of kieselguhr and extracted by SC-CO2. The extracts and residues from SC-CO2 extraction were analyzed by gas chromatography–mass spectrometry and Fourier transform ion cyclotron resonance mass spectrometry. Our results showed that the operating pressure (20–30 MPa) affected the extraction yields more than the temperature (50–70 °C). SC-CO2 preferentially extracted small molecules with relatively low aromaticity and polarity. Compound classes containing multiple heteroatoms had lower extraction yields than hydrocarbons. The carbon number distribution ranges of various compound classes in the residues were largely different. Carboxylic acids and phenolic compounds were found to have poor solubility in SC-CO2. The risk of asphaltene precipitation in CO2 EOR is also discussed.

We have investigated and established a preparative method of using a solid-phase extraction cartridge containing Ag + -exchange resin (Ag + -SPE) for separating olefins and paraffins in the saturate fractions of coal tar and petroleum coker oil. The successful separation of paraffins and olefins was confirmed by gas chromatography coupled with mass spectrometry (GC− MS). Proton nuclear magnetic resonance ( 1 H NMR) spectroscopy was applied to determine the olefin structures for olefin-type distributions. None or negligible amounts of iso-α-olefins were detected by 1 H NMR in the coal tar but were found significant in the coker oil. Gas chromatography coupled field ionization time-of-flight mass spectrometry (GC−FI-TOF MS) was employed to determine the molecular distribution of paraffins and olefins. With separate paraffin and olefin fractions, the differentiation between isomers, such as monocycloparaffins versus monoolefins, can be made.

A low-temperature coal tar was subject to a three-stage catalytic hydrotreating reactor. The raw coal tar and its hydrotreating products from each reactor section were characterized by electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The removal efficiencies of sulfur, nitrogen, and oxygen were 99.4%, 88.4%, and 78.1%, respectively. The molecular transformation routes of each heteroatomic species are different. Sulfur species were removed from low double bond equivalence (DBE) values to higher values through the whole hydrotreating process. Furanic compounds and basic nitrogen compounds carried out the saturation of aromatic rings before the hydrogenation of low DBE species. Neutral nitrogen compounds were resistant in the processing and cannot be removed completely in the end of the hydroprocessing. The phenolic compounds were the most resistant to hydrotreating during the whole process. The transformation capabilities of heteroatom compounds in the processing were as follows: phenolic compounds > neutral nitrogen compounds > furanic compounds > basic nitrogen compounds > sulfur compounds.

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N-Methyl-2-pyrrolidinone (NMP) is a capable solvent which could extract more substance from coals than any other solvents. However, the molecular composition of the extract was still unclear. In this study, a lignite was subjected to Soxhlet extraction using pyridine followed by NMP. The NMP extract and its hydrolyzed product were characterized by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The results showed that the NMP extract and its hydrolyzed product had very high nitrogen contents and N x O y class species with multiple nitrogen and oxygen atoms dominant in the detected species. Relative abundance of 15N isotope and the molecular composition of extracts obtained from different extraction conditions indicated that the NMP involved into the extracts. Both self-polymerization of NMP and chemical reactions between NMP and coals occurred in the thermal extraction.

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