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Thermogravimetric analysis (TGA) of the reduction of Fe2O3 in a continuous stream of 100% CO was conducted at temperatures ranging from 800 to 900 °C. X-ray diffraction analysis of solids identified the presence of iron, graphite and a carbide of iron as the products of reactions. A kinetic model based on the first-order irreversible rate kinetics was developed and fitted to the TGA data so as to estimate the rate constants for each reduction reaction. The reaction pathways considered in this analysis involved reduction of iron oxides, Boudouard reaction and iron-carbide formation. The rate parameters were calculated and compared with data reported in literature.

The desulfurization of selectively oxidized coals and unoxidized control coals was investigated using mild pyrolysis and various base treatments. Both an Illinois No. 6 and an Indiana No. 5 coal were selectively oxidized with peroxyacetic acid in the pretreatment step and then treated with various hydroxide and carbonate bases, using either water, methanol or ethanol as the solvent. Reaction variables investigated include reaction temperature, reaction time, pyrolysis pressure, and the level of oxidation in the pretreatment step. In general, it was found that selective oxidation, when combined with subsequent desulfurization reactions, always led to greater sulfur removal. In addition, the reactivity of the sulfur in the coal towards desulfurization was apparently enhanced by the selective oxidation pretreatment. Thus, the severity of desulfurization conditions can be reduced by employing this pretreatment. Sulfur removals of up to 95% were obtained in some cases. Usually the most effective treatments involved carbonate bases under supercritical alcohol conditions. The desulfurization of some selectively oxidized, sulfur containing model compounds was also observed under similar reaction conditions.

The peroxyacetic acid oxidation products from a series of coals of organic sulfur content 0.5–9.8 wt% were examined. The distributions of organic S and N compounds were determined by gas chromatography with sulfur-selective flame photometric and nitrogen-selective thermionic specific detection respectively. A selected sample was also examined in greater detail using low-voltage high-resolution mass spectrometry. The distribution of organic sulfur compounds in the oxidation products was remarkably similar for all the coals. The number of sulfur compounds detected was small compared with that of organic nitrogen compounds detected. This suggests that the sulfur chemistry of coal is considerably simpler than its nitrogen chemistry. Analysis of the m.s. data, together with a comparison of sulfur-selective and nitrogen-selective chromatograms, indicated that a significant proportion of the heteroatomic species present in coal contain more than one heteroatom. This is significant, because few models of coal structure incorporate such species.

The primary objective of this study is to investigate the removal of both mineral and organic sulfur from Illinois coals using low temperature selective oxidation. This overall objective is to develop new methods for either physical/chemical or physical/microbial cleaning of Illinois coal. Innovative approaches to achieve deep cleaned products, containing both ash and sulfur contents less than 0.5 percent, will be considered. Experiments focus on developing cost-effective methods for the removal of organic sulfur and finely disseminated mineral impurities, especially fine pyrite particles, from coal. Rates and mechanisms for organic sulfur removal will be studied. Chemical reagent recycling and/or reagent wastes will be studied. Chemical reagent recycling and/or reagent wastes handling are included. Bench scale studies are performed.

The overall objective of this project was to determine the combustion properties of separated single coal maceral fractions from a rank series of coals and then to try to predict the combustion behaviour of various whole coals on the basis of their maceral compositions and rank. The combustion properties studied were based on the burning profile in a TGA apparatus. The results of this study indicate that most of the reactivity and combustion profile parameters varied significantly with coal rank and that all of the rank trends observed were best defined in the data from the single maceral samples which were more reproducible, more linear, and less variable. The variations in the combustion profiles and reactivities in different macerals from the same sample are of the same order of magnitude as the variations due to rank. It also appears that there are some maceral interactions during combustion and gasification that significantly affect these processes.

The main objective of this study is to investigate the desulfurization behavior of individual coal macerals. The sporinite and vitrinite macerals which contain most of the organic sulfur in coal are more reactive toward desulfurization processes than any of the other materials that were studied. They also give the highest desulfurization levels. Since they are more reactive than whole coals or floated samples, the other constituents in the coal matrix must reduce sulfur removals. This phenomenon has not been reported previously. It implies that the inertinite macerals may behave in a manner similar to activated charcoal and chemically absorb copious amounts of sulfur during the desulfurization processes. The practical result of this phenomenon is that selection of coals on the basis of maceral composition could be necessary to optimize thermal-chemical desulfurization.

Gasification rates of a Texas lignite char, having calcium contents varying from 1.1 to 12.9 wt%, were measured in air, steam, CO 2 , and H 2 . Gasification rates increased rectilinearly with increase in calcium loading. The chemisorption of CO 2 at 298 K on the CaO present on the char surface was used to determine CaO particle dispersion. Knowing this dispersion, specific activities of calcium as a catalyst for the gasification reactions were calculated. The spread in specific activities in different atmospheres is large, it being a maximum when the char-air reaction is compared with the char -H 2 reaction.

Analytical data from a set of 66 coal samples, ranging in rank from lignitic to low-volatile bituminous, were used to define relationships between coal properties. Unusual care was taken in selecting, collecting, preparing and analysing this set of premium samples providing a high degree of confidence in the conclusions obtained. It was found that univariate relationships between properties, which might seem to convey useful information, are generally of limited operational value and can lead to erroneous conclusions. However, multivariate correlations can predict a number of properties. Specific energy, volatile matter yield, and density (by helium pycnometry) can be estimated from the elemental composition according to the following expressions: Btulb−1 = 145.9%C + 569.6%H − 53.89%O + 43.08%S − 6.3%Ash%VM = −0.408%C + 11.25%H + %O + 1.3%Sgml−1 = 0.01556%C − 0.04117%H + 0.02247%O + 0.02049%S + 0.0208%Ash The standard deviations of the residuals (estimated-experimental) for the above three correlations are 86 Btu lb−1, 1.5% VM and 0.013 g ml−1. The free-swelling index was found to correlate strongly with the oxygen content (for coals containing > 2 wt% oxygen, daf) and the petrographic composition according to the following expression: FSI = 5 + 4.68f(O) − 0.00395NPC2 + 0.0897NPC − 0.06LIP where f(O) = sin(0.2513Odaf + 0.9505)NPC = ashweight% + inertinite, volume% mineral-freeLIP = liptinite, volume%, mineral-free It is concluded that the elemental composition of coal can predict many physical properties and process responses. The petrographic composition must be considered when predicting plastic properties. Though petrographic composition influences other properties and process responses, microscopically obtained maceral percentages did not prove useful for quantitatively predicting properties or responses.

An investigation of the microscopic properties of residues produced from Illinois coal treated under various supercritical alcohol extraction conditions has been conducted. The objective of this investigation was to obtain a better understanding of the supercritical alcohol/coal desulfurization system. It was found that pyrite is converted progressively to pyrrhotite and then to troilite. Also, coal particles tended to become fluid and form coke. The degree of coke formation and size of anisotropic units (optical texture) were found to correspond to the extent of desulfurization. These correlations were found to be solvent dependent. Zoning effects were also observed in both the organic and inorganic phases. These effects appear to be mass or heat transfer limited and related to the operation of the batch reactors employed in obtaining samples for this study. The investigation is continuing, employing smaller reactors with improved heat and mass transport properties. Attempts will be made to determine if desulfurization is enhancing fluidity or if fluidity is enhancing desulfurization.

This paper describes a desulfurization process to remove both organic and inorganic sulfur from coal employing alcohols under supercritical conditions. The overall objective of this study was to gain a better understanding of the kinetics of the supercritical alcohol/coal desulfurization process. A microreactor system was developed to examine in detail the reaction kinetics of coal desulfurization under supercritical conditions. The microreactors provide a uniform temperature within the reactor and allow precise measurement of temperature. Desulfurization tests were conducted to obtain solid residues for sulfur analysis (% in product), as well as optical microscopic examination. The results of the analysis indicate that the desulfurization process is highly temperature dependent. Generally, with increased reaction temperature, desulfurization is increased. For all isothermal reactions there is at least one stage at which sulfur is reincorporated into the product. Pretreatment of coal with 5% KOH is desirable to prevent coke formation, but under the conditions studied, had little effect on ultimate desulfurization levels. Additions of KOH increased the rate at which ultimate desulfurization levels were reached.

Coal combustion experiments were carried out over the temperature range 25–900 °C using air at atmospheric pressure in a derivative thermogravimetric analysis system. Sixty-six coals high in vitrinite (> 80% mineral-matter-free basis) and low in inorganics (all but 12 samples < 10%) were examined as part of a coal characterization programme. The coals varied in rank from lignites (69% carbon on a dry, mineral-matter-free basis) to low-volatile bituminous (91% carbon). Combustion rates increased progressively with increasing temperature, passed through maxima and then declined. The rate data were fitted to an Arrhenius equation and plots showed four distinct regions of combustion. Apparent activation energies were calculated for each region and varied from ≈4 kJ mol−1 in the high-temperature, diffusion-controlled region to 290 kJ mol−1 in the chemical-reaction controlled, low-temperature region. The temperatures at which 50% of the sample had burned away (sol12-life) were rectilinearly related to oxygen and carbon contents (correlation coefficient squared values of 0.88 and 0.86, respectively).

Reactivities of sixteen 40 × 100 (U.S.) mesh U.S. coals charred to 1000 °C were measured in carbon dioxide at 900 °C. Chars derived from coals with less than 80% carbon, on a dry-ash-free basis, were the most reactive. These chars also gave the widest spread in reactivity. Plots of inorganic element content in the chars versus reactivity showed that magnesium and calcium are important to char reactivity. Six coals were acid-washed with hydrochloric acid and four coals were further demineralized with hydrofluoric acid. Most acid-treated coals showed a decrease in reactivity; but two coals of high rank increased in reactivity. This increase in reactivity is attributed to the creation of additional porosity as a result of mineral matter removal and thus a reduction in resistance to carbon dioxide diffusion to reactive sites. Two demineralized and two original coals were divided into four size ranges and chars were produced from each size of each coal. Gasification rates increased monotonically with decreasing particle size reacted.

Chars produced from lignites typically have much higher reactivities to gasification than those produced from bituminous coals. This has been attributed previously to the presence of carboxylate salts of inorganic constituents on the lignites. Upon charring of the lignites, the carboxylate salts decompose leaving behind well dispersed inorganic constituents which act as catalysts for gasification. In this study, a raw lignite has been treated with HCl and HF to demineralize it and to increase its carboxyl content prior to exchanging selected cations with the hydrogen on the carboxyl groups. Up to 2.14 mmol of calcium per g of coal could be added using this procedure. Addition of varying amounts of calcium to the lignite resulted in the production of chars containing calcium contents ranging from 1.1 to 12.9 wt %. Such addition resulted in a rectilinear increase in reactivity of the char to steam with increasing amount of calcium added. Maximum reactivity attained was over ten times the reactivity found for the char produced from the raw lignite. At comparable molar loadings of metal cations onto the acid-treated lignite, the chars subsequently produced had reactivities in steam in the order: K >Na ≈ Ca >Fe >Mg. Char reactivity could also be enhanced by the addition of cations to nitric acid-treated char which had been produced, in turn, from demineralized lignite.