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Detailed chemical kinetic modeling has been performed to investigate aromatic and polyaromatic hydrocarbon formation pathways in rich, sooting, methane and ethane premixed flames. An atmospheric pressure, laminar flat flame operated at an equivalence ratio of 2.5 was used to acquire experimental data for model validation. Gas composition analysis was conducted by an on-line gas chromatograph / mass spectrometer technique. Measurements were made in the flame and post-flame zone for a number of low molecular weight species, aliphatics, aromatics, and polycyclic aromatic hydrocarbons (PAHs) ranging from two to five-aromatic fused rings.The modeling results show the key reaction sequences leading to aromatic and polycyclic aromatic hydrocarbon formation primarily involve the combination of resonantly stabilized radicals. In particular, propargyl and I-methylallenyl combination reactions lead to benzene and methyl substituted benzene formation, while polycyclic aromatics are formed from cyclopentadienyl and fused rings that have a shared C, side structure. Naphthalene production through the reaction step of cyclopentadienyl self-combination, and phenanthrene formation from indenyl and cyclopentadienyl combination were shown to be important in the flame modeling study. The removal of phenyl by Ozleading to cyclopentadienyl formation isexpccted to playa pivotal role in the PAH or soot precursor growth process under fuel-rich oxidation conditions.

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Experimental and detailed chemical kinetic modeling has been performed to investigate aromatic and polycyclic aromatic hydrocarbon (PAH) formation pathways in a premixed, rich, sooting, propane-oxygen-argon burner stabilized flame. An atmospheric pressure, laminar flat flame operated at an equivalence ratio of2.6 was used to acquire experimental data for model validation. Gas composition analysis was conducted by an on-line gas chromatograph/mass spectrometer (GC/MS) technique. Measurements were made in the main reaction and post-reaction zones for a number of low molecular weight species, aliphatics, aromatics, and polycyclic aromatic hydrocarbons (PAHs) ranging from two to five-fused aromatic rings.Reaction flux and sensitivity analysis were used to help identify the important reaction sequences leading to aromatic and PAH growth and destruction in the propane flame. Benzene formation was shown to be dominated by the propargyl recombination reaction. A secondary benzene formation pathway occurred from the reaction sequence of allyl plus propargylleading to fulvenc and H-atoms whereupon the fulvene is converted to benzene by H-atom catalysis.Large negative sensitivity coefficients were calculated for the H,CCCH + H-CJH, + H, reaction in the propargyl, benzene, and naphthalene sensitivity analysis study. This result implicates propargyl consumption by H-atoms as an important reaction step that limits aromatic and PAH growth.Naphthalene formation through the reaction step of cyclopentadienyl self-combination and phenanthrene formation from indenyl and cyclopentadienyl combination were shown to be plausible global reaction steps for PAH production.

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The gas evolution, mass decay behavior and energy content of several woods, grasses, and agricultural residues were examined with steam and CO(2) gasification using thermogravimetric analysis and gas chromatography. CO(2) concentrations were varied between 0 and 100% with steam as a coreactant. Carbon conversion was complete with 25% CO(2)/75% steam compared to 90% conversion with pure steam in the temperature range of 800-1000 degrees C. The largest effect was from 0-5% CO(2) introduction where CO concentration increased by a factor of 10 and H(2) decreased by a factor of 3.3 at 900 degrees C. Increasing CO(2) from 5 to 50% resulted in continued CO increases and H(2) decrease by a factor of 3 at 900 degrees C. This yielded a H(2)/CO ratio that could be adjusted from 5.5 at a 0% CO(2) to 0.25 at a 50% CO(2) concentration. Selection of the gasification parameters, such as heating rate, also enabled greater control in the separation of cellulose from lignin via thermal treatment. 100% CO(2) concentration enabled near complete separation of cellulose from lignin at 380 degrees C using a 1 degrees C min(-1) heating rate. Similar trends were observed with coal and municipal solid waste (MSW) as feedstock. The likely mechanism is the ability for CO(2) to enhance the pore structure, particularly the micropores, of the residual carbon skeleton after drying and devolatilization providing access for CO(2) to efficiently gasify the solid.

This research investigates the catalytic properties of char which was recovered directly from a biomass gasifier. Poplar wood was gasified in steam and CO 2 environments in a fluidized bed reactor at temperatures ranging from 550 to 920°C. Char was composed of 85% carbon with concentrations of N, H, and S between 0.3% and 3%, depending on gasification conditions. The inorganics (Ca, K, Na, P, Si, Mg) were quantified, revealing that Ca was present in the highest concentration (0.5-1%), followed by K, ranging from 0.1% to 0.8%. The char had catalytic activity for decomposition of methane, which was used as a model molecule. The quantity of inorganics in the char was modified by acid washing in 16% aqueous HCl, which removed >95% of Ca, K, P, and Mg from the char. This resulted in an 18% decrease in the quantity of methane reacted compared to the original char sample, demonstrating that inorganics, which only make up approximately 2% of the char, play a significant role in its catalytic activity for methane cracking reactions. In addition, carbon was found to play an important role in the catalytic activity of the char, both as a catalyst and a support on which the inorganics were dispersed. The activity of carbon free ash was approximately 90% lower than that of char, and deactivated to have no measurable activity after 45 min on stream, demonstrating the importance of carbon and dispersed inorganics for catalytic activity. When char was heated to 1000°C in N 2 , inorganics and oxygen migrated to the surface of the char, covering the carbon surface in a metal oxide layer. This decreased the catalytic activity by approximately 40%. Acidic (e.g. carboxylic, lactones) and basic (e.g. carbonyl, pyrone) oxygen functional groups were identified on the char surface. However, acidic oxygen groups desorbed at reaction temperatures, so these groups likely do not participate in cracking reactions.

Gasification provides a mechanism to convert solids, such as biomass, coal, or waste, into fuels that can be easily integrated into current infrastructure. This paper discusses the use of residual char from a biomass gasifier as a catalyst for tar decomposition and presents an investigation of the catalytic properties of the char. Poplar wood was gasified in a fluidized bed reactor at temperatures ranging from 550 to 920°C in reaction environments of 90% steam/10% N 2 and 90% N 2 /10% CO 2 . The properties of the char recovered from the process were analyzed, and the catalytic performance for hydrocarbon cracking reactions was tested. Brunauer−Emmett−Teller (BET) measurements showed that the surface area of the char was higher than conventional catalyst carriers. The surface area, which ranged from 429 to 687 m 2 g −1 , increased with temperature and reaction time. The catalytic activity of the char was demonstrated through testing the catalytic decomposition of methane and propane to produce H 2 and solid carbon. Higher char surface area resulted in increased performance, but pore size distribution also affected the activity of the catalyst, and evidence of diffusion limitations in microporous char was observed. Clusters of iron were present on the surface of the char. After being used for catalytic applications, carbon deposition was observed on the iron cluster and on the pores of the char, indicating that these sites may influence the reaction. When the char was heated to 800°C in an inert (N 2 ), atmosphere mass loss was observed, which varied based on the type of char and the time. ESEM/EDX showed that when char was heated to 1000°C under N 2 , oxygen and metals migrated to the surface of the char, which may impact its catalytic activity. Through investigating the properties and performance of biomass gasification char, this paper demonstrates its potential to replace expensive tar decomposition catalysts with char catalysts, which are continuously produced on-site in the gasification process.