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The first objective of this work was to compare the pyrolysis behavior of coals coming from different geographic locations (South Africa, South America, Europe, Australia, and North America). This preliminary study was limited to the kinetics of methane and tar evolution, with data on additional species to be reported in a separate publication. The second objective was to examine the possible relationship between tar and methane evolution during pyrolysis. This study was done by employing a thermogravimetric analyzer coupled with a Fourier-transform infrared spectrometer (TG-FTIR). The evolution curves for 35 coals of different elemental compositions were measured at three different heating rates (10, 30, and 100 K/min). Pyrolysis kinetics were described using a simple first-order reaction model. The technique, first proposed by Kissinger, is based on the variation of the temperature at which a volatile species evolution rate is a maximum (Tmax) as a function of the heating rate. The TG-FTIR data for tar evolution reveal a generally consistent behavior for coals from different parts of the world, showing increasing activation energies with increasing coal rank. The same correlation is also true for methane, although the slope of the activation energy versus carbon content curve is rather flat, at least up to about 90% carbon content. The values of activation energies for methane evolution were found to be lower in the case of the Argonne coals, as compared with the non-US coals. A study of the temperatures at which the evolution of methane and tar begins (Tini), and the temperatures at which the evolution rates reach a maximum (Tmax), reveals a correlation between the Tini for methane and Tmax for tar. This may be due to the fact that both tar and methane evolve as a result of similar reactions involved in the breakup and recombination of the coal macromolecular network.

The desirable characteristics of activated carbons for gas-storage applica tions are: (1) high microporosity (pores smaller than 2 nm) ; and (2) high sorbent packing density, i.e., low voidage in the storage container (e.g., the use of mono lithic sorbent elements). A cyclic chemisorption-desorption char activation tech nique was used to maximize micropore formation and minimize mesoporosity. Several carbons were prepared at different degrees of burn-off, and the BET surface areas were found to be up to 2000 m2/g. The carbons were prepared in the form of powders and pellets to demonstrate that the future use of shaped mono lithic elements can lead to the reduction of voidage in the storage container by up to 40%. The adsorption isotherms of the produced carbons showed high microporosity and no appreciable mesoporosity, even at high burn-offs. The advantage of using the cyclic chemisorption-desorption char activation technique over the traditional steady-state gasification was experimentally demonstrated. The paper also discusses the evolution of sorbent microporosity as a function of carbon burn-off and the duration of the chemisorption step. Preliminary data on hydrogen-storage capacity are also reported.

The interest in utilizing biomass as a CO2 neutral fuel by combustion, gasification, or pyrolysis processes is increasing due to concern about the emission of greenhouse gases from fossil fuel combustion. In thermal fuel conversion, pyrolysis is an important step which determines the split of products into char, tar, and gas. In this work, a combination of thermogravimetry and evolved gas analysis by Fourier transform infrared analysis (TG-FTIR) has been applied to study the influence of potassium chloride (KCl) on wheat straw pyrolysis. Raw straw, washed straw, and washed straw impregnated with KCl have been investigated. To facilitate interpretation of the results, pyrolysis of biopolymers (cellulose, xylan, lignin) in the presence and absence of KCl was investigated as well. The raw straw decomposed in a single broad featureless peak. By washing, two peaks appeared in the derivative weight loss curve, corresponding to the decomposition of hemicellulose and cellulose components in the straw. Washing red...

A methodology to determine the chemistry and kinetics of the multiple reactions during geological maturation was developed, with a special emphasis on the representation of diagenesis and oil formation processes. The methodology combines a unique macromolecular and kinetic model for hydrocarbon pyrolysis, the FG-DVC (functional group-devolatilization, vaporization, cross-linking) model, with a method of analysis based on thermogravimetric analysis with Fourier transform infrared spectroscopy (TG-FTIR). TG-FTIR pyrolysis data from several natural maturation series of coals and kerogens were measured, systematic trends with the degree of maturation were identified, and empirical processes and reaction kinetics during maturation necessary to induce these trends were estimated. This approach eliminates potential inaccuracies when extrapolating kinetic parameters obtained from laboratory experiments to geological conditions. The FG-DVC pyrolysis model was modified to include these maturation processes, with aqueous chemistry providing a guide for such modifications. The resulting FG-DVC maturation model was then used to predict the maturation of several immature samples through the well-known time/temperature history of the basin. The FG-DVC pyrolysis model was subsequently used to predict the open-system pyrolysis decomposition of the predicted maturation residues, and the predictions were compared to TG-FTIR data of the corresponding naturally matured samples. For most of the series investigated, the model gave good predictions of the variations in oxygenated gas precursors, tar T max , and extractable yield with maturation. Kinetics derived from open-system pyrolysis for bridge breaking were found to be applicable during maturation. However, faster kinetics were necessary to describe the removal of oxygenated gas precursors. In addition, the removal of methane and tar was found to be too slow during maturation when using open-system pyrolysis kinetics. Artificial maturation experiments using confined pyrolysis were also performed for comparison. While the evolution rates, during subsequent pyrolysis of the maturation residues, of oxygenated gas species are different from those obtained from samples naturally matured, the yields compare favorably with model predictions. The trends for pyrolysis tar and methane from artificially matured samples are similar to those of natural samples but suggest different kinetics.

Landfilling used tires which are generated each year in the US is increasingly becoming an unacceptable solution. A better approach, from an environmental and economic standpoint, is to thermally reprocess the tires into valuable products such as activated carbon, other solid carbon forms (carbon black, graphite, and carbon fibers), and liquid fuels. In this study, high surface area activated carbons (> 800 m{sup 2}/g solid product) were produced in relatively high yields by pyrolysis of tires at up to 900 C, followed by activation in CO{sub 2} at the same temperature. The surface areas of these materials are comparable with those of commercial activated carbons. The efficiency of the activation process (gain in specific surface area/loss in mass) was greatest (up to 138 m{sup 2}/g original tire) when large pieces of tire material were used ({approximately} 170 mg). Oxygen pretreatment of tires was found to enhance both the yield and the surface area of the carbon product. High-pressure treatment of tires at low temperatures (< 400 C) is an alternative approach if the recovery of carbon black or fuel oils is the primary objective.

Sulfur and nitrogen evolution from the Argonne Premium coals has been studied using thermogravimetric analysis with measurement of evolved products by Fourier transform infrared spectroscopy (TG-FTIR). The method combines temperature-programmed pyrolysis and combustion. H 2 S and tar sulfur were monitored by measuring SO 2 after oxidation of volatile products. The SO 2 evolution curves produced with volatile oxidation erhibit two main evolution peaks and one smaller high-temperature evolution peak. For each peak, the temperature of the maximum evolution rate (T max ) increases with increasing rank. The individual evolution curves of the organic and pyritic sulfur were identified, and their evolution kinetics were derived

This paper considers the development of a predictive macromolecular network decomposition model for coal conversion which is based on a variety of modern analytical techniques for coal characterization. Six concepts which are the foundation of the functional group-depolymerization-vaporization-cross-linking (FG-DVC) model are considered: 1. (1) The decomposition of functional group sources in the coal yields the light gas species in thermal decomposition. The amount and evolution kinetics can be measured by t.g.-FT-i.r., the functional group changes by FT-i.r. and n.m.r. 2. (2) The decomposition of a macromolecular network yields tar and metaplast. The amount and kinetics of the tar evolution can be measured by t.g.-FT-i.r. and the molecular weight by f.i.m.s. The kinetics of metaplast formation and destruction can be determined by solvent extraction, by Gieseler plastometer measurements and by proton magnetic resonance thermal analysis (p.m.r.t.a.). 3. (3) The molecular weight distribution of the metaplast depends on the network coordination number (average number of attachments on aromatic ring clusters). The coordination number can be determined by solvent swelling and n.m.r. 4. (4) The network decomposition is controlled by bridge breaking. The number of bridges broken is limited by the available donatable hydrogen. 5. (5) The network solidification is controlled by cross-linking. The changing cross-link density can be measured by solvent swelling and n.m.r. Cross-linking appears to occur with evolution of both CO2 (before bridge breaking) and CH4 (after bridge breaking). Thus low-rank coals (which evolve much CO2) cross-link before bridge breaking and are thus thermosetting. High-volatile bituminous coals (which form little CO2) undergo significant bridge breaking before cross-linking and become highly fluid. Weathering, which increases the CO2 yield, causes increased cross-linking and lowers fluidity. 6. (6) The evolution of tar is controlled by mass transport in which the tar molecules evaporate into the light gas or tar species and are carried out of the coal at rates proportional to their vapour pressure and the volume of light species. High pressures reduce the volume of light species and hence reduce the yield of heavy molecules with low vapour pressures. These changes can be studied with f.i.m.s. The paper describes how the coal kinetic and composition parameters are obtained by t.g.-FT-i.r., solvent swelling, solvent extraction and Gieseler plastometer data. The model is compared with a variety of experimental data in which heating rate, temperature and pressure are all varied. There is good agreement with theory for most of the data available from the authors' laboratory and in the literature.

Several groups have considered statistical network fragmentation models to describe coal thermal decomposition. In these models, the coal macromolecule is viewed as a collection of fused aromatic rings (monomers) linked by bridges. During thermal decomposition, existing bridges break and new bridges are formed. The parameters of the models are the geometry of the network, which is expressed as the number of attachments per monomer (the coordination number, σ + 1), and the chemistry of bridge breaking and formation. Given σ + 1 and the instantaneous number of unbroken and formed bridges, the molecular weight distribution can be predicted. The different groups have employed both Monte Carlo methods and percolation theory to describe the network statistics. The former approach has advantages in terms of describing both the depolymerization and crosslinking processes in coal decomposition, since it does not require a constant coordination number. The latter method provides closed form solutions and is computationally less demanding. The models differ in the geometry of the network, the chemistry of bridge breaking and bridge formation (crosslinking) and the mass transport assumptions. This paper considers for three such models: the mathematical schemes; the assumed network geometries; the assumed bond breaking and bond formation chemistries; and the mass transport assumptions. The predictions of three models were compared by comparing the oligomer populations as a function of the number of unbroken bridges per ring cluster. This paper also presents results from a new model which combines the geometry, chemistry and mass transport assumptions of the FG-DVC model with the mathematics of a modified percolation theory.

This paper describes the most recent improvements in the apparatus and presents its application in characterizing the Argonne premium coal samples. The TG-FTIR apparatus for pyrolysis, oxidation of pyrolysis products, and oxidation of the sample is described. To analyze coal, a sequence of drying, pyrolysis, and combustion is employed to obtain proximate analysis, volatile composition, volatile kinetics, and relative char reactivity. Pyrolysis results are presented for the eight Argonne coals, several demineralized coals, and two oxidized samples of Pittsburgh Seam coal. A kinetic analysis was applied to species evolution data collected at several different heating rates. There is a systematic variation in rate with rank

During coal conversion, the breakup of the coal macromolecular network and resulting product formation are controlled by the relative rates of bond breaking, cross-linking, and mass transport. THe objective of this work was to systematically study the variations in cross-linking with several parameters (rank, temperature, heating rate, pretreatment, etc.), to identify the factors that control cross-linking rates. This paper describes a study of cross-linking behavior in which chars of a number of coals (including the Argonne premium coal samples) have been pyrolyzed under a variety of temperature histories and analyzed at intermediate extents of pyrolysis for solvent swelling behavior and functionnal group compositions

A new ignition phenomenon has been observed during studies of coal combustion. The experiment, which was described in a recent publication [1], injects coal particles suspended in a roomtemperature carrier gas as a jet into a flowing preheated air stream. The new phenomenon is shown in Fig. 1, which is a photograph of several ignited particles traveling upward. The particles of interest are at the edge of the cold particle stream and have first contact with the surrounding hot preheated gas stream. They ignite and appear to burn on the particle's surface, as indicated by the fact that the width of the luminosity is roughly that of the particle diameter. The particles become hotter with increasing distance. The new ignition phenomenon occurs after the particles have burned for a short time. Under these conditions there is often a secondary ignition event. To the unaided eye, it looks like a bright flash of light at the end of a long luminous trajectory. When viewed through a microscope, this event has the following characteristics.

Utilisation des donnees provenant de trois types de reacteur ayant differentes caracteristiques de chauffe afin de developper une serie de parametres cinetiques

The kinetics of vapor-phase secondary reactions of newly formed coal pyrolysis tars were studied at temperatures and residence times of 500-900/sup 0/C and 0.6-3.9 s, respectively. Tar vapors, generated by heating a helium-swept, shallow packed bed of Pittsburgh No. 8 bituminous coal from room temperature to 550/sup 0/C, at 3/sup 0/C/min, were either rapidly conveyed to collection traps for subsequent characterization or else passed through an adjacent reactor for controlled thermal treatment prior to trapping. Results are described. A multiple, independent, parallel, first-order reaction model also performed well but could not predict step-like behavior in conversion at 0.6-s residence time. A single-reaction first-order decomposition model correlated the conversion data poorly at 0.6- and 1.1-s residence times, and use of the resulting best fit parameters gave totally inadequate predictions of conversions measured at 2.5 and 3.9 s.

Considerable controversy exists concerning the rate of coal pyrolysis. At 800 °C, the reported rates derived using a single first-order process to define weight loss vary from