ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInvestigation of Associated Structure of Upper Freeport Coal by Solvent SwellingToshimasa Takanohashi, Masashi Iino, and Masaharu NishiokaCite this: Energy Fuels 1995, 9, 5, 788–793Publication Date (Print):September 1, 1995Publication History Published online1 May 2002Published inissue 1 September 1995https://pubs.acs.org/doi/10.1021/ef00053a009https://doi.org/10.1021/ef00053a009research-articleACS PublicationsRequest reuse permissionsArticle Views257Altmetric-Citations60LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Coals were heat-treated at the heating rate of 3°C/min or 100°C/min in an autoclave at 200550°C under nitrogen, and then quenched rapidly to room temperature. The heat-treated coals were extracted with a carbon disulfide-N-methyl -2-pyrrolidinone mixed solvent at room temperature. At the heating rate of 3°C/min, the maximum extraction yields were obtained at around the initial stage of softening, and the maximum yields showed a good correlation with the maximum fluidity of the coals. While, ultimate analysis and FT-IR measurement for the heat-treated coals showed that significant structural changes did not occur before the initial stage of softening. In the stages of maximum fluidity and resolidification, the extraction yield rapidly decreased, especially for caking coals. An increase in heating rate to 100°C/min shifted the temperature which gives the maximum extraction yield to higher temperature and the yield was high compared to the low heating rate (3°C/min), suggesting that the fluidity is increased by increasing the heating rate. Softening mechanism of coal was discussed from various coal structure models including associate model.
Small-angle X-ray scattering (SAXS) analyses of an asphaltene (a heptane-insoluble fraction in Canadian oil sand bitumen (CaAs)) at various concentrations in bromobenzene (BB) were performed at a synchrotron facility. BB is the first trial medium in which the aggregation behavior of asphaltenes has been elucidated, and is considered to be one of the "best" pure solvents for CaAs when determining the Hansen solubility parameters (HSP). Although the aggregation behavior of the CaAs in toluene (TL) and toluene–pentane mixed solvent (TL-PT10, containing 10% pentane on a volume basis) was confirmed to be similar to that reported in previous SAXS studies, the behavior in BB was markedly different. The results indicated that aggregates with a soft boundary of ∼30–60 Å in the radius of gyration (Rg), which were observable in TL and TL-PT10, disappeared in BB and larger aggregates with a clear boundary appeared simultaneously. This phenomenon supported a colloidal aggregation model, with HSP analyses suggesting that BB dispersed the colloid surface fraction at the molecular level and isolated the colloid core fraction, which led to the formation of a rigid aggregation of the core fraction. The HSP analyses enabled us to evaluate the aggregation behavior quantitatively, and the results obtained by SAXS were consistent with those obtained by Rayleigh scattering that we reported previously.
The repression of coke precursor formation is key to heavy oil upgrading. Asphaltenes are known to form aggregates that may be responsible for coke precursor formation and the consequent deactivation of catalysts. A Supra-Molecular Asphaltene Relaxation Technology (SMART) is introduced herein and may be applied to asphaltene aggregates in order to reduce their detrimental effects. The nature of asphaltene aggregates was examined using molecular simulation methods. Molecular mechanics and molecular dynamics calculations on asphaltenes obtained from vacuum residues revealed that the most stable conformations of asphaltene aggregates were those held together by several noncovalent interactions. At 673 K, where decomposition reactions begin, aggregates formed of aromatic-aromatic stacking interactions were still stable. These stable aggregates likely comprised heavier oil fractions such as coke precursors. Changes induced in these aggregated structures by pretreatment with various solvents were investigated. Some stacking interactions could be disrupted in quinoline at 573 K but remained stable when the aggregates were pretreated in 1-methylnaphthalene. Autoclave experiments showed that the coke yield after pyrolysis at 713 K was significantly decreased when the asphaltene was presoaked in quinoline for 1 h. In contrast, pretreatment with 1-methylnaphthalene resulted in negligible changes in coke yield. The results of both simulations and autoclave experiments suggest that, when aggregates were presoaked in quinoline, some aromatic stacking interactions were disrupted and molecular mobility increased. This prevented the asphaltenes from polymerizing via condensation reactions between aromatic rings. Thus, coke yields after pretreatment in quinoline were relatively low. The contribution of each type of interaction (aromatic stacking, aliphatic ring entanglement, heteroatom interactions, and hydrogen bonding) to the overall aggregation energy of asphaltene was estimated using an imaginary simulation technique. Aromatic-aromatic interactions accounted for approximately 50 % of the total aggregate interactions. Contributions from aliphatic side-chain entanglement and heteroatom interactions were around 27 % and 20 %, respectively. The combination of these interactions stabilized the asphaltene aggregates.
"HyperCoal" (HPC) is the ashless coal produced by thermal solvent extraction; the extraction yield is a key factor in HPC production. The extraction yield varies depending upon the properties of the coals and the solvent used. For a wide range of coals, the extraction yields at 360 °C have been successfully estimated by a multiple regression analysis, using the values of ultimate and proximate analyses. The equation consists of volatile matter/O% (or O%), C/H, and a function of S%; a correlation coefficient of r = 0.790 was obtained for the extraction yield with 1-methyl-naphthalene (1-MN) for 76 coals. When the polarity of the extraction solvent was increased, the effects of O% decreased, while that of C/H did not change. With regard to coals with an O% less than 8.2, the extraction yield of 1-MN correlated only with the C/H value. These results suggest that the C/H value is the main factor for a high extraction yield.
Coke making is becoming more expensive because of the sudden rise in the price of caking coals due to the decreasing supply, and so a technology to manufacture good-quality coke from coal blends containing low-quality slightly caking or non-caking coals is strongly required. "HyperCoal" (ash-free coal, HPC) is produced by thermal extraction using cost-effective industrial solvents below 400 °C in an inert atmosphere. It has originally a wider temperature range of thermoplasticity during heating than ordinary caking coals. HPC can be produced from various ranks of coals including lignite and subbituminous coal, however, the chemical property of HPC is different depending on the coal rank. HPCs produced from low-rank coals such as lignite and subbituminous coal, showed a high thermoplasticity from lower temperature range than those from high-rank bituminous coals. In addition, HPCs from low-rank coals possess a higher permeability due to the lower viscosity in the thermoplastic region. As a result, the addition of HPCs from low-rank coals to a coal standard blend showed a higher effect on the tensile strength of cokes produced by carbonization of the HPC-blending coals at 1000 °C, than that of HPCs from caking coals.
