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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 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...

Over the next decade there will be a renewed emphasis on the use of biomass as a fuel and the cofiring of coal and biomass materials. In view of the tremendous diversity of biomass feedstocks, a great need exists for a robust, comprehensive model that could be utilized to predict the composition and properties of pyrolysis products as a function of feedstock characteristics and process conditions. The objective of this work was to adapt an existing coal pyrolysis model, the Functional Group-Depolymerization, Vaporization Crosslinking (FG-DVC) model, and make it suitable for the pyrolysis of biomass. The soundness of this approach is based on numerous similarities between biomass and coal. However, there are important differences, which preclude direct application of the coal model. This work involved: (1) selection of a set of materials representing the main types of biomass, (2) development of a classification scheme, (3) development of a modeling approach based on an extension of a coal pyrolysis model, (4) calibration of the model for a set of standard materials against pyrolysis data taken over a range of heating rates, and (5) validation of the model against pyrolysis data taken under higher heating rate conditions. A streamlined version of the FG-DVC coal pyrolysis model was successfully developed for whole biomass samples and demonstrated to have predictive capability when extrapolated to high heating rate conditions (103 °C/sec). Improvements will be needed in the model to properly account for mineral effects and secondary reactions, and the model has not yet been tested under the very high heating rates that may exist in some combustion devices (104–105 °C/sec).

This paper continues previous work on pyrolysis processing of solid wastes for spacecraft and planetary surface applications. A prototype microwave pyrolyzer apparatus was designed, constructed and tested. Experiments were done with cellulose, wheat straw and two formulations of a feces simulant. A central microwave absorber was used consisting of a quartz tube filled with activated carbon. The pyrolyzer included a primary pyrolysis zone and a secondary cracking zone consisting of a SiC bed. The cracking zone temperature ranged from ~ 850 to 1000 °C. The sample was inserted into the (primary) microwave heating zone after the cracking bed temperature was stabilized to ~ 950 °C. Analysis of the gas products was performed by both FTIR spectroscopy and mass spectrometry. The sample sizes were 15-20 g for wheat straw, 40 g for cellulose and 100 g for the feces simulants. The cellulose sample was not run to completion, but was interrupted to provide photographic evidence that microwave heating using a central microwave absorber results in pyrolysis beginning near the center of the sample and proceeding in an outward fashion. For the wheat straw and feces simulant samples, it was found that, on a per-gram basis, the yields of ethylene, methane, and hydrogen were significantly higher than a previous pyrolyzer that was based on a modified domestic microwave oven. This result was mainly attributed to the presence of a separate cracking zone in the current pyrolyzer.

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.

There has recently been an increased interest in using pyrolysis of mixed solid wastes in space or on planetary surfaces to produce methane for applications in propulsion and for power generation using fuel cells. This paper involves a review of previous pyrolysis results collected at Advanced Fuel Research, Inc. (AFR) and elsewhere to determine how the pyrolysis conditions and feedstock composition affect methane yields. In general, the production of methane from primary pyrolysis of most biomass materials is pretty modest, 0.1 to 2.5 wt. % for a wide range of materials, with an average slightly above 1.2 wt. % (dry, ash-free basis). The primary pyrolysis yield variations for methane (and other species) with biomass sample type are well described using a simple Neural Network model. In pyrolysis experiments that include significant secondary reactions (e.g., tar cracking), the methane yield can be increased by a factor of 2-3. The methane yield can also be increased significantly by increasing the plastic component of the mixed waste stream (e.g., by the addition of polyethylene), but would be unlikely to exceed 15 wt. % by conventional, low-pressure pyrolysis of a typical mixed waste stream. The use of high pressure (>500 psig) pyrolysis in pure hydrogen is one approach that could be used to increase the methane yield even further. However, this approach would require a much heavier reactor unit, high pressures, and the associated safety concerns. An alternative pathway to higher methane yields would be to oxidize the waste completely to carbon dioxide and water and use the Sabatier reaction to convert the carbon dioxide to methane.

The desire to employ a range of pure fuels as surrogates for jet fuels has led to an increased need for detailed oxidation reaction mechanisms. These mechanisms require a good pyrolytic base mechanism. Furthermore, aircraft cooling requirements beyond those of conventional fuels has led to research into so called “endothermic” fuels. Unlike conventional fuels, whose heat sink capabilities are derived solely from sensible and latent enthalpies, endothermic fuels offer additional heat sink potential through endothermic chemical reaction. Endothermic fuels play an important role in cooling for hypersonic craft. To date, heavy iso-alkanes, an important hydrocarbon class present in logistical fuels, have not received much analysis with respect to their pyrolytic decomposition or endothermic potential. Yet such compounds are likely to be present in large fractions in future alternate fuels. This paper presents the development of computational suband supercritical pyrolysis mechanisms for iso-dodecane (i.e., 2,2,4,6,6-pentamethyl heptane). Both proposed mechanisms utilize Wang et al.’s small species (C4 and below) reactions and Curran et al.’s isooctane model for large species reactions. Utilizing fuel structure similarities, reactions involving iso-dodecane are patterned after those for iso-octane. Standard group additivity techniques are used to estimate associated kinetic rate parameters as necessary, and several parent fuel activation energies are compared with ab-initio (Gaussian) calculations. Reactions necessary to model supercritical environments are also presented. The sub-critical mechanism is benchmarked against several literature reactor data-sets, and the new supercritical mechanism is compared to newly acquired UTRC non-isothermal rig data.

Pyrolysis of lignin is one approach that has been investigated to upgrade this material into higher value products. However, there have been relatively few efforts to quantitatively model these reactions. This paper describes a methodology for modeling lignin pyrolysis which has been extensively developed for related materials like coal. The samples are characterized using pyrolysis experiments under a standard set of conditions, where the products are analyzed by Fourier Transform Infrared (FT-IR) Spectroscopy and Field Ionization Mass Spectrometry (FIMS). Solvent extraction experiments are done to determine the extractables yields and elemental analysis is done to further constrain the model. One lignin, produced from ethanol/water extraction of mixed hardwoods, was selected for the application of this modeling approach. The model was able to qualitatively predict the tar molecular weight distributions and quantitatively predict the variations of the gas and tar evolution rates and yields with heating rate for the calibration set of experiments. The model can be improved by more precise information on lignin structure, crosslinking chemistry, and tar transport mechanisms. It also needs to be validated by simulation of pyrolysis conditions at high heating rates and/or high pressures for which data is currently not available.

In this paper, results of further work on pyrolysis processing of mixed solid wastes for spacecraft applications are reported. A domestic microwave oven was modified for scoping studies in which the effects of sample size and the use of distributed versus central microwave absorbers were studied. Experiments were done with wheat straw and included those in which the sample was rotated during pyrolysis in order to improve heating uniformity. The experiments using central microwave absorbers of various compositions included a ferrite rod, a quartz tube filled with activated carbon, and silicon carbide. The ability to monitor the sample temperature and sample heating uniformity during microwave heating was demonstrated. A comparison was made with conventional pyrolysis experiments in an electrically heated furnace to a similar final temperature. In general, it was found that microwave heating reduced the energy demand by about 50% and increased the yield of gas products by about 100%, while reducing the char yield about 20%.

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

Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid, liquid and/or gaseous products. The pyrolysis processing of pure and mixed solid waste streams has been under investigation for several decades for terrestrial use and a few commercial units have been built for niche applications. The use of pyrolysis as a key step in solid waste processing in space has been under consideration by NASA for several years. A large component of the solid waste is from biomass sources (e.g., paper, food waste, human waste). A methodology has been developed to characterize a large number of biomass materials using a standard pyrolysis experiment in combination with a neural network model in order to classify the data. Such a methodology can be helpful in the design and operation of pyrolysis reactors for spacecraft applications.

We have developed a TG-FT-IR instrument which combines thermogravimetric analysis (TGA) with evolved product analysis by Fourier Transform Infrared (FT-IR) spectroscopy. FT-IR analysis of evolved products has an advantage over mass spectroscopy in allowing analysis of very heavy products, and over gas chromatography in speed. This paper describes the most recent improvements in the apparatus and presents its application in characterizing coal. The emphasis in this work is on employing the TG-FT-IR system to obtain kinetic rates for species evolution under easily obtained laboratory conditions. These rates can then be extrapolated to predict the conversion behavior of the hydrocarbon at higher heating rates and temperatures in practical conversion processes or at lower heating rates and temperatures in geological conversion processes. For several coal samples, a kinetic analysis was applied to species evolution data collected at several different heating rates. For coal, there is a systematic variation in rate with rank for almost all volatile species. Extrapolation to high temperatures shows excellent agreement with high temperature coal pyroloysis data. Extrapolation to low temperatures is consistent with the expected changes induced by bed temperatures over geological times.

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

Pyrolysis processing is one of several options for solid waste resource recovery in space. It has the advantage of being relatively simple and adaptable to a wide variety of feedstocks and it can produce several usable products from typical waste streams. The overall objective of this study was to produce a prototype mixed solid waste pyrolyzer for spacecraft applications. A twostage reactor system was developed which can process a maximum of about 0.5 kg of waste per cycle. The reactor includes a pyrolysis chamber where the waste is heated to temperatures above 600 °C for primary pyrolysis. The volatile products (liquids, gases) are transported by a N2 purge gas to a second chamber which contains a catalyst bed for cracking the tars at temperatures of about 1000-1100 °C. The tars are cracked into carbon and additional gases. Most of the deposited carbon is subsequently gasified by oxygenated volatiles (CO2, H2O) from the first stage. In a final step, the temperature of the first stage can be raised and the purge gas switched from N2 to CO2 and/or O2 in order to gasify the remaining char in the first stage and the remaining carbon deposits in the second stage. Alternatively, the char can be removed from the first stage and saved as a future source of CO2 or partially gasified to make activated carbon. This paper describes several improvements that were made in the original (First Generation) prototype pyrolyzer including: 1) replacement of stainless steel flanges with machineable ceramic in order to reduce weight; 2) construction of a new sample holder in order to make sample insertion and removal easier and sample heat-up more uniform; 3) replacement of a stainless steel outer shell with a double-wall quartz cylinder in order to significantly reduce weight and heat losses. In addition, experimental results are included for wheat straw and chicken manure feedstocks, primarily from the First Generation prototype.

Pyrolysis processing is one of several options for solid waste resource recovery in space. It has the advantage of being relatively simple and adaptable to a wide variety of feedstocks and it can produce several usable products from typical waste streams. The objective of this study is to produce a prototype mixed solid waste pyrolyzer for spacecraft applications. A two-stage reactor system was developed which can process about 1 kg of waste per cycle. The reactor includes a pyrolysis chamber where the waste is heated to temperatures above 600°C for primary pyrolysis. The volatile products (liquids, gases) are transported by a N2 purge gas to a second chamber which contains a catalyst bed for cracking the tars at temperatures of about 1000 °C – 1100 °C. The tars are cracked into carbon and additional gases. Most of the carbon is subsequently gasified by oxygenated volatiles (CO2, H2O) from the first stage. In a final step, the temperature of the first stage can be raised and the purge gas switched from N2 to CO2 in order to gasify the remaining char in the first stage and the remaining carbon deposits in the second stage. Alternatively, the char can be removed from the first stage and saved as a future source of CO2 or used to make activated carbon. The product gases from the pyrolyzer will be rich in CO and cannot be vented directly into the cabin. However, they can be processed in a shift reactor or sent to a high temperature fuel cell. A control system based on artificial neural networks (ANNs) is being developed for the reactor system. ANN models are well suited to describing the complicated relationships between the composition of the starting materials, the process conditions and the desired product yields.

The NASA objective of expanding the human experience into the far reaches of space will require the development of regenerable life support systems. A key element of these systems is a means for solid waste resource recovery. The objective of this work was to demonstrate the feasibility of pyrolysis processing as a method for the conversion of solid waste materials in a Controlled Ecological Life Support System (CELSS). A pyrolysis process will be useful to NASA in at least four respects: 1) it can be used as a pretreatment for a combustion process; 2) it can be used as a more efficient means of utilizing oxygen and recycling carbon and nitrogen; 3) it can be used to supply fuel gases to fuel cells for power generation; 4) it can be used as the basis for the production of chemicals and materials in space. A composite mixture was made consisting of 10% polyethylene, 15% urea, 25% cellulose, 25% wheat straw, 20% Gerepon TC-42 (space soap) and 5% methionine. Pyrolysis of the composite mixture produced light gases as the main products (CH4, H2, CO2, CO, H2O, NH3) and a reactive carbon-rich char as the main byproduct. Significant amounts of liquid products were formed under less severe pyrolysis conditions, but these were cracked almost completely to gases as the temperature was raised. A primary pyrolysis model was developed for the composite mixture based on an existing model for whole biomass materials. An artificial neural network model was also used successfully to model the changes in gas composition with the severity of pyrolysis conditions.

Publisher Summary This chapter discusses a study to examine the importance of key factors, such as oxygen functional group content, water content, and cation content, that are important in retrograde reactions that occur under pyrolysis conditions. Three coals from the Argonne premium sample bank were used. The results from various techniques suggested that nearly all the hydroxyls and carboxyls were methylated for each coal. The results of the X-ray analysis of the exchanged, demineralized, and methylated samples confirmed that the concentrations of exchangeable metal cations (Ca, Mg, Na, and K) were significantly reduced. The results of programmed pyrolysis in the TG-FTIR apparatus of the raw, ion-exchanged, demineralized, and methylated coals indicated significant increases in the yield of tar for the latter two modifications in the case of the two low rank coals. After the samples were characterized, experiments were done under coal liquefaction conditions in a microautoclave reactor, which allows for gas analysis. The extent of retrogressive reactions in pyrolysis and liquefaction for low rank coals (lignite, subbituminous) is significantly reduced by methylation and demineralization.

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.

A computer model was developed to relate pyrolysis and soot formation to fuel properties. A Fourier Transform-Infrared Spectrometer (FT-IR) was used to characterize the effect of temperature, pressure, reaction time, and hydrogen and oxygen concentration of fuels undergoing pyrolysis. The problem of how to identify and measure the hydrogen available for release during pyrolysis was investigated. A detailed data base of a variety of fuels undergoing pyrolysis was developed. The data base conditions included: temperature 800-1500 C; pressure 1-15 atm; and reaction time 100ms-1 sec. Experimental data results show that fuels decompose to form small hydrocarbon species prior to the onset of soot formation. A hydrocarbon model was extended to include Rice-Kossiakoff-Herzfeld mechanism to predict the decomposition of long chain aliphatics to small molecules. A free radical soot model was developed to predict the growth of soot precursors from the small molecules. Keywords: Combustion pyrolysis model; Soot formation; Fourier transform-infrared spectroscopy; Rice-Kossiakoff-Herzfeld mechanism; Free radical.