摘要:

The Molten-Caustic-Leaching (MCL) Process is quite effective in its ability to remove both organic and pyritic sulfur, mineral matter, and trace elements from coal. In recent years, the chemistry of various reactions taking place in the process has been examined in detail by several researchers. For example, Ames Laboratory of Iowa State University is actively studying the chemistry of MCL desulfurization and reagent regeneration reactions, and researchers at the U.S. Department of Energy's Pittsburgh Energy Technology Center are examining the reactions of molten caustic with the organosulfur compounds present in coal. As a result of these research efforts, reactions of mineral pyrite, benzothiophene, and minerals commonly found in coal (quartz, illite, etc.) with molten caustic are very well characterized. However, reactions of the organic components of coal with molten caustic are still difficult to understand because of the complexity of interaction between the various compounds present in coal and variations in the chemical composition of different coals. Also, considerable insight into the overall development of the process has been obtained as a result of these research efforts; and alternate, and probably more energy-effective, process development steps have been suggested. Various analytical techniques and methodologies that can remove some of the uncertainties associated with the characterization of coals have been developed.

ISSN:0734-9343    

DOI:10.1080/07349348908960538

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Coal model compounds, such as dibenzothiophene, its analogs and the hydroxylated derivatives of these compounds. were treated with molten hydroxides to evaluate the importance of nucleophilicity for the different alkali-metal hydroxides. The soluble hydroxylated model compounds were decomposed and desulfurized by RbOH or CsOH at lower temperatures and in less time than when decomposed by KOH or NaOH, indicating that molten hydroxides have varying degrees of nucleophilicity, the progression of nucleophilicity being CsOH > RbOH ≥ KOH > NaOH. The discrepancy of these results with previously published studies, suggesting NaOH is as effective as KOH in desulfurizing coal, is discussed. Increased solubility of the hydroxylated derivatives in molten hydroxide led to faster reaction rates under homogeneous reaction conditions. Aryl ethers decomposed more readily than did aryl sulfides. Sulfur-carbon bond cleavage was more facile in sulfur compounds with conformational mobility.

ISSN:0734-9343    

DOI:10.1080/07349348908960539

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Coal from two seams in Eastern Canada was pyrolysed at temperatures up to 532°C and at pressures of 50 torr or atmospheric. Selected sulphide occurrences in polished sections of the chars were examined for completeness of the transformation to “FeS” with the use of quantitative scanning electron microscopy. Results showed that porous framboidal aggregates reacted at temperatures 100°C lower than monolithic occurrences. In addition, low pressure pyrolysis reduced the reactivity of sulphide, and it is suggested that marcasite reacted more readily than pyrite. The relevance of these findings to the removal of sulphur from coal by magnetic beneficiation is discussed.

ISSN:0734-9343    

DOI:10.1080/07349348908960540

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The removal of sulfur from Mequinenza (Spanish) lignite was investigated by hydrodesulfurization reactions in microautoclaves. This lignite is of interest because of its very high sulfur content, 9.94% on a dry basis, of which about 90% is organic sulfur. The reaction variables investigated were temperature, hydrogen pressure, catalyst, and reaction time. The best total sulfur removal was about 77%, achieved at 350°C in 1000 psig H2with an impregnated sulfided molybdenum catalyst. In addition to total sulfur removal, the selectivity to H2S production was also investigated, to evaluate maximizing sulfur removal as H2S rather than as organosulfur compounds in by-product liquids. This work is the first study of sulfur removal using dispersed catalysts in the absence of added liquid vehicle.

ISSN:0734-9343    

DOI:10.1080/07349348908960541

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Trace elements in coal are detrimental from both an environmental and a technological perspective. Since most trace elements in coal are associated primarily with the mineral phases, they are often amenable to removal by conventional physical coal beneficiation methods. However, these methods generally are not adequate for removing those trace elements which are associated with the organic matrix or which are very finely disseminated. Thus, chemical treatments may be necessary for removal of these trace components. Data from a variety of studies indicate that cleaning by concentrating tables, jigs, heavy-media cyclones, hydrocyclones, froth flotation, and oil agglomeration could effectively remove many trace elements from some coals. However, trace element removal efficiencies varied widely between coals. Because cleaning efficiencies are strongly coal-dependent, conclusions regarding the relative effectiveness of various cleaning techniques are difficult to draw since different coals were used among studies.

ISSN:0734-9343    

DOI:10.1080/07349348908960542

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

This study investigated the generation of humic substances from the coal and the coal surface, and evaluated the effect of humic substances on the surface property of coal.

ISSN:0734-9343    

DOI:10.1080/07349348908960543

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A series of 10 reagents of known chemical structure, synthesized or obtained commercially, were evaluated for their ability to remove pyritic sulfur and ash from ultrafine coal by flotation processes. A correlation was made between the structure of these reagents and their coal cleaning effectiveness and efficiency, i.e., dosage versus weight and energy recovery, and ash and pyrite rejection, for two ultrafine samples, the Illinois No. 5 (hva) and Illinois No. 2 (hvc) coals. Within the series of structurally related surfactants, molecular size, symmetry, and geometry were found to be influential in determining coal cleanability. In general, thecis-1,2-dialkylethenesulfonate salts were more effective than the commercial surfactants which included an alkanesulfate salt, an alpha-olefin sulfonate salt, polyetheralkanesulfonate and sulfate salts, and some alcohols. In some cases, the dosage required to produce equivalent energy recoveries from the, synthesizedcis-1,2-dialkylethenesulfonate salt reagents was only one-third that of the commercial surfactants and one-seventh that of the alcohol frother MIBC.

ISSN:0734-9343    

DOI:10.1080/07349348908960544

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Improvement in the floatability and cleanability of ultrafine, lower rank bituminous coals - removal of pyritic sulfur and ash - has been achieved by employing mixtures composed of anionic surfactants and conventional frothing alcohols. In particular, of those surfactants studied, the lower molecular weightcis-dialkylethenesulfonate salts afforded the greatest improvement. Roughly half as much alcohol/surfactant mixture as conventional alcohol/kerosene blends produced equivalent energy recoveries. Ratios of surfactant to alcohol must be properly balanced to maximize ash and pyrite rejections. Such mixtures were also beneficial for floating and cleaning higher rank bituminous coals and for use in conventional fine size froth flotation feed.

ISSN:0734-9343    

DOI:10.1080/07349348908960545

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0734-9343    

DOI:10.1080/07349348908960546

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0734-9343    

DOI:10.1080/07349348908960537

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor