Atomic emission detection (AED) is a convenient method for the selective detection of oxygen-containing polycyclic aromatic compounds (O-PAC), especially furan derivatives, in the gas chromatographic (GC) analysis of coal-derived oils, although the specific response for oxygen compounds is much less than those of compounds detected from carbon emission. The use of very high purity helium as GC carrier gas is preferred, since interferences are fewer; sensitivity is improved by optimisation of cavity and transfer line temperatures. The variation of response factor with mass chromatographed is linear in the working range, but is not compound independent for O-PAC. Applications are shown of the use GC-AED in the analysis of benzo-, dibenzo- and benzonaphthofurans at low concentration in coal liquids.

This paper reviews the current state of molecular mass determination for fossil fuel materials by chromatographic methods and describes improvements which can be made to both the chromatographic separation and the detection of eluting material. Most significantly, N-methyl-2-pyrrolidinone (NMP) offers a number of advantages as a mobile phase in the size-exclusion chromatography (SEC) of coal derivatives. Much more coal-derived material dissolves in NMP and solute-column packing interactions common with SEC solvents such as tetrahydrofuran are much reduced. NMP is compatible with UV absorption and UV fluorescence detection

Fixed-bed hydropyrolysis tests have been conducted on a UK bituminous coal (Gedling), the Wyodak Argonne Premium coal sample and the high-sulfur Mequinenza lignite at a pressure of 15 MPa with heating rates of 5 and 300 K min−1. The tar yields and overall conversions increased markedly by ∼5–20 wt% daf coal as the heating rate was decreased from 300 to 5 K min−1 for final temperatures of 520 and 600°C, both with and without a sulfided molybdenum catalyst. Conversions of > 90 wt% were achieved with slow heating in catalytic hydropyrolysis for all three coals. The small increases in gas yield indicated that tar-forming as opposed to hydrogasification reactions are promoted by slow heating. These results demonstrate the value of slow heating for analytical applications of hydropyrolysis, which include the determination of organic sulfur forms and the covalently bound biomarker hydrocarbons in coals and petroleum source rocks.

For the well-swept fixed-bed reactors used in temperature-programmed reduction (TPR) to specify the organic sulfur forms present in coals and kerogens, calibrants must neither melt nor evaporate before the onset of thermal decomposition. In this respect, nonmelting silica-immobilized substrates are suitable with the Si-O-C linkage being stable up to ca. 500 degrees C. Silica-immobilized samples of dibenzothiophene, diphenyl sulfide, phenyl benzyl sulfide, and thioanisole have been synthesized and noncatalytic tests have been conducted in atmospheric and high-pressure TPR reactors. The characteristic reduction temperatures of the non-thiophenic compounds investigated are well resolved from that of dibenzothiophene for both techniques and the results have validated previous findings by TPR on coals. The use of high hydrogen pressure (150 bar) lowered the reduction temperatures substantially. The H2S recoveries from the atmospheric experiments are low suggesting that, for the non-thiophenic compounds, secondary reactions occur yielding refractory thiophenes which are not detected. Although sulfur recoveries are greatly improved, such reactions are still evident with 150 bar hydrogen pressure especially in the case of the phenyl benzyl sulfide, possibly as a consequence of the high surface coverages used. Insights into the retrogressive chemistry occurring for the immobilized phenyl benzyl sulfide have been provided from GC-MS analysis of hydrolyzed TPR residues obtained at different temperatures, and from vacuum pyrolysis experiments conducted as a function of surface coverage.

A complete knowledge and understanding of the thermal reactivety of sulphur forms in coal is crucial for the development of new, efficient desulphurisation techniques. This contribution reports on seven selective desulphurization treatments of a Bulgarian lignite. The impact of individual treatments on the sulphur distribution was monitored by AP-TPR and XANES techniques. Complementary data concerning the physical impact of the treatments was obtained by DTA and SEM-EDX.

A selection of low rank coals have been analysed by Atmospheric Pressure Temperature Programmed Reduction and the results are compared with those from the high pressure TPR technique. For purposes of comparison a relatively immature Type 1 kerogen has also been investigated.

Atmospheric and high pressure TPR profiles were obtained from initial and LiAlH{sub 4} treated coal samples: Illinois No 6, Wyodak-Anderson, Upper-Freeport, Gedling, Goynuk, Kimmeridge, Dorset-Cuddle, Rasa and Mequinenza. AP-TPR results indicated that LiAlH{sub 4} treatment not only removes pyrite, but also changes, removes and/or modified other sulphur functionalities. The different AP-TPR profiles are discussed in detail and assignments of the signals are based on previous model compound work. Both AP-TPR and HP-TPR results on the same sets of samples are compared with literature results obtained with other S-characterisation techniques.

Non-melting silica immobilised substrates have previously been used to investigate pyrolysis behaviour and were shown to be ideal calibrants for temperature programmed reduction (TPR), with the SiO-C linkage stable at temperatures above 500{degrees}C. An alternative class of materials that should prove equally suitable am phenol-formaldehyde resins which enable model moieties to be incorporated into a highly cross-linked matrix. A series of sulphur containing co-resites have been prepared using phenol with, as the second component, dibenzothiophene, diphenylsulphide, phenylbenzylsulphide and thioanisole. A mole ratio of 3:1 (phenol to sulphur-containing component) was adopted to ensure that a reasonably high degree of cross-linking was achieved in the initial preparation of the resoles. The formation of the resites by curing the resoles at 200{degrees}C was monitored by solid state {sup 13}C NMR. A resole has also been prepared from diphenyldisulphide but due to the comparable bond strengths of the S-S and C-O linkages, the curing temperature was reduced to 120{degrees}C to avoid cleavage of the disulphide bond. As well as being used as calibrants for TPR, the resites offer considerable potential for probing the influence of catalysts in hydropyrolysis and for investigating the effect of pyrolysis conditions on the interconversion of sulphides into thiophenes.

There is a growing interest in packed capillary columns in supercritical fluid chromatography (SFC) because of their larger sample volume loadability and differing selectivities as compared with capillary columns. Such columns are also more favorable because they provide higher efficiencies than conventional packed columns. In this paper, we evaluate the possibility of performing simulated distillation by SFC using packed capillary columns. The columns are packed with different types of commercially available bonded-silica packing materials using a supercritical carbon dioxide (CO 2 ) mobile phase. We compare the potential of each column to elute the highest molecular weight compound at the maximum available pressure

The principal inherent drawbacks associated with temperature-programmed reduction (TPR), for specifying the distribution of organic sulfur forms in solid fuels, in that first, thiophenic sulfur is largely undetectable and second, sulfides interconvert readily into thiophenes, have been overcome by the use of a well-swept, fixed-bed reactor, operating at relatively high hydrogen pressure (15 MPa). The high pressure technique was applied previously to two high sulfur lignites, Rasa (Croatia) and Mequinenza (Spain), and indicated that thiophenic forms account for ~ 70% of the total organic sulfur. The study has now been extended successfully to samples of varying organic sulfur content which include three of the Argonne Premium coals i.e. Wyodak-Anderson, Illinois No. 6 and Upper Freeport; a UK bituminous coal i.e. Gedling; two kerogens i.e. Goynuk (Type I, Turkey) and Kimmeridge Dorset-Cuddle (Type II, UK); and a liptinite concentrate of Mequinenza lignite. For those samples in which pyritic sulfur represents a significant proportion of the total sulfur, treatment with lithium aluminium hydride was necessary, in order to obtain any meaningful information on the organic sulfur forms present. From the subsequent H2S evolution profiles, the relative contributions from thiophenic and non-thiophenic forms have been resolved satisfactorily. In common with other pyrolysis techniques and X-ray techniques (XPS and XANES), high pressure TPR indicates that thiophenic sulfur increases with rank. However, the proportions of thiophenic sulfur derived from high pressure TPR are consistently higher than by other techniques.

Hydropyrolysis is potentially an attractive means for the production of synthetic fuels and chemical feedstocks from coals. It offers a simpler process configuration than traditional direct liquefaction with a higher throughput and avoids problems with liquid (tar)-solids (residue) separation. Recent evaluations of coal liquefaction processes have concluded that, provided 50% or more distillable liquids can be produced, hydropyrolysis will be a viable alternative to the traditional vehicle solvent-based processes. For low-rank coals, hydrogenation catalysts are much less effective than for their bituminous counterparts with the increases in tar yields being typically less than 10% daf coal{sup 6}. Nonetheless, without catalyst, the tar yields of 40--50% at 150 bar pressure are appreciably higher than for bituminous coals. In this investigation, tests have been conducted at temperatures up to 600{degrees}C and using an extremely low heating rate of 5{degrees}C/min on the Wyodak Argonne Premium Coal Sample (APCS) and the high-sulfur Mequinenza and Rasa lignites to ascertain whether tar yields could be further increased without catalyst. It was initially considered that the tar yields for low rank coals are limited by the fact that retrogressive reactions, particularly those involving phenolic and carboxylic moities, are more prevalent than for bituminous coals. Data obtained indicatesmore » that low heating rates do, in fact, improve the conversion for low-rank coals.« less

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSilica-immobilized compounds as models for probing coal pyrolysis and hydropyrolysis phenomenaS. C. Mitchell, C. J. Lafferty, R. Garcia, C. E. Snape, A. C. Buchanan, III, P. F. Britt, and E. KlavetterCite this: Energy Fuels 1993, 7, 2, 331–333Publication Date (Print):March 1, 1993Publication History Published online1 May 2002Published inissue 1 March 1993https://doi.org/10.1021/ef00038a027RIGHTS & PERMISSIONSArticle Views56Altmetric-Citations16LEARN 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 InReddit PDF (312 KB) Get e-Alertsclose Get e-Alerts

The temperature-programmed reduction procedure used thus far to investigate the distributions of organic sulphur forms in coals suffers from only a small proportion of thiophenic sulphur actually being observed and from the likelihood of secondary reactions which convert sulphides into thiophenes. These shortcomings have been largely overcome by using a well-swept fixed-bed reactor at relatively high hydrogen pressures (up to 15 MPa) in conjunction with an effective hydrodesulphurization catalyst, sulphided molybdenum. The technique has been applied to three high sulphur lignites, namely Mequinenza (Spain), Rasa (Yugoslavia) and Cayirhan (Turkey) and, for the first two samples, the results have been compared with those from X-ray and other pyrolysis techniques. For all three lignites, thiophenic sulphur is the dominant form with sulphides accounting for 20–35% of the total organic sulphur; the proportions of the latter are, in general, significantly lower than those recently obtained by X-ray techniques and fluidized-bed pyrolysis for the Mequinenza and Rasa samples.