Marco J. Castaldi

Aromatic and polycyclic aromatic hydrocarbon formation in a laminar premixed n-butane flame

Experimental and detailed chemical kinetic modeling work has been performed to investigate aromatic and polycyclic aromatic hydrocarbon (PAH) formation pathways in a premixed, rich, sooting, n-butane–oxygen–argon burner stabilized flame. An atmospheric pressure, laminar flat flame operated at an equivalence ratio of 2.6 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 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 n-butane flame. Reaction flux analysis showed the propargyl recombination reaction was the dominant pathway to benzene formation. The consumption of propargyl by H atoms was shown to limit propargyl, benzene, and naphthalene formation in flames as exhibited by the large negative sensitivity coefficients. Naphthalene and phenanthrene production was shown to be plausibly formed through reactions involving resonantly stabilized cyclopentadienyl and indenyl radicals. Many of the low molecular weight aliphatics, combustion by-products, aromatics, branched aromatics, and PAHs were fairly well simulated by the model. Additional work is required to understand the formation mechanisms of phenyl acetylene, pyrene, and fluoranthene in the n-butane flame.

Modeling of Aromatic and Polycyclic Aromatic Hydrocarbon Formation in Premixed Methane and Ethane Flames

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 f...

Aromatic and polycyclic aromatic hydrocarbon formation in a premixed propane flame

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 of 2.6 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 ...

Experimental and modeling investigation of aromatic and polycyclic aromatic hydrocarbon formation in a premixed ethylene flame

Experimental and detailed chemical kinetic modeling has been performed to investigate aromatic and polyaromatic hydrocarbon formation pathways in a rich, sooting, ethylene-oxygen-argon premixed flame. 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 (GC/MS) 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 growth involve the combination of resonantly stabilized radicals. In particular, propargyl and 1-methylallenyl combination reactions lead to benzene and methyl substituted benzene formation, while polycyclic aromatics are formed from cyclopentadienyl radicals and fused rings that have a shared C{sub 5} 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 O{sub 2} leading to cyclopentadienyl formation is expected to play a pivotal role in the PAH or soot precursor growth process under fuel-rich oxidation conditions.

CO2 as a Carbon Neutral Fuel Source via Enhanced Biomass Gasification

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.

Formation of polycyclic aromatic hydrocarbons (PAH) in methane combustion: Comparative new results from premixed flames

Direct sampling and GC/MS analysis of fuel-rich, laminar, premixed flames of methane indicates the production of higher in-flame peak concentrations of benzene and polycyclic aromatic hydrocarbons (PAH) than in the flames of ethane under similar combustion conditions. These findings are surprising and significant because the methane flame not only had a higher H/C ratio and lower carbon density, but also produced less acetylene and soot than the ethane flame. These results suggest the significance of species containing an odd number of carbon atoms in PAH formation processes in the methane flame, as well as the importance of soot surface reactions. Although aromatic and polyaromatic intermediates constitute trace by-products of combustion, their formation is of practical concern due to their potential adverse health effects.

Real-time quantitative analysis of combustion-generated polycyclic aromatic hydrocarbons by resonance-enhanced multiphoton ionization time-of-flight mass spectrometry

We have combined resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry with on-line flame sampling to determine the centerline concentrations of naphthalene, fluorene, and anthracene in a pure methane + oxygen/argon (1:5) diffusion flame. Naphthalene concentrations between 100 parts per billion by volume (ppbV) and 6 parts per million by volume (ppmV) and fluorene concentrations below 50 ppbV are determined using one-color REMPI on jet-cooled samples extracted from the flame; anthracene concentrations in the 5-40 ppbV range are determined using two-color REMPI. The REMPI ion signals are converted to absolute concentrations in real time by performing gas-phase standard additions to the flame sample. Isomer-selective detection of larger polycyclic aromatic hydrocarbons, such as perylene and benzo[a]pyrene, is possible using the two-color REMPI approach.

Effect of carbon dioxide on the thermal degradation of lignocellulosic biomass.

Using biomass as a renewable energy source via currently available thermochemical processes (i.e., pyrolysis and gasification) is environmentally advantageous owing to its intrinsic carbon neutrality. Developing methodologies to enhance the thermal efficiency of these proven technologies is therefore imperative. This study aimed to investigate the use of CO2 as a reaction medium to increase not only thermal efficiency but also environmental benefit. The influence of CO2 on thermochemical processes at a fundamental level was experimentally validated with the main constituents of biomass (i.e., cellulose and xylan) to avoid complexities arising from the heterogeneous matrix of biomass. For instance, gaseous products including H2, CH4, and CO were substantially enhanced in the presence of CO2 because CO2 expedited thermal cracking behavior (i.e., 200-1000%). This behavior was then universally observed in our case study with real biomass (i.e., corn stover) during pyrolysis and steam gasification. However, further study is urgently needed to optimize these experimental findings.

Micro-structures of premixed hydrocarbon flames : methane

ABSTRACT The micro-structure of a premixed, atmospheric-pressure, fuel-rich (equivalence ratio 2.6 ), flat flame of methane has been determined experimentally using a heated micro-probe coupled to on-line gas chromatography/mass spectrometry (GC/MS ). The identities and absolute concentrations of over 40 major and minor species have been established, including a large number of aromatics, substituted aromatics and polycyclic aromatic hydrocarbons (PAH ) by the direct analysis of samples withdrawn from the flame without pre-concentration. Mole fractions of the species quantified were in the range 0.45—2.0 × 10−9. The largest PAHs detected were the family of C20H12s (molecular weight 252 ), that include benzo (a )pyrene, perylene and benz (e )-acephenanthrylene, with peak concentrations reaching 1 ppmv. The results show the preferential formation of fused PAHs with even number of aromatic rings over PAHs with odd number of rings. The PAHs detected also suggest that they can be formed by at least 3 parallel ...

Utilizing Carbon Dioxide as a Reaction Medium to Mitigate Production of Polycyclic Aromatic Hydrocarbons from the Thermal Decomposition of Styrene Butadiene Rubber

The CO(2) cofeed impact on the pyrolysis of styrene butadiene rubber (SBR) was investigated using thermogravimetric analysis (TGA) coupled to online gas chromatography/mass spectroscopy (GC/MS). The direct comparison of the chemical species evolved from the thermal degradation of SBR in N(2) and CO(2) led to a preliminary mechanistic understanding of the formation and relationship of light hydrocarbons (C(1-4)), aromatic derivatives, and polycyclic aromatic hydrocarbons (PAHs), clarifying the role of CO(2) in the thermal degradation of SBR. The identification and quantification of over 50 major and minor chemical species from hydrogen and benzo[ghi]perylene were carried out experimentally in the temperature regime between 300 and 500 °C in N(2) and CO(2). The significant amounts of benzene derivatives from the direct bond dissociation of the backbone of SBR, induced by thermal degradation, provided favorable conditions for PAHs by the gas-phase addition reaction at a relatively low temperature compared to that with conventional fuels such as coal and petroleum-derived fuels. However, the formation of PAHs in a CO(2) atmosphere was decreased considerably (i.e., ∼50%) by the enhanced thermal cracking behavior, and the ultimate fates of these species were determined by different pathways in CO(2) and N(2) atmospheres. Consequently, this work has provided a new approach to mitigate PAHs by utilizing CO(2) as a reaction medium in thermochemical processes.