Benzene Formation Research Articles

Effect of Fe and Zn promoters on Mo/HZSM-5 catalyst for methane dehydroaromatization

The promotional effect of Fe in the presence and absence of Zn was studied over Mo/HZSM-5 catalysts for the methane dehydroaromatization reaction. The reaction was conducted at 700°C, 3000scc/g/h and atmospheric pressure. Adding Fe as the only promoter increased the benzene formation rate by 35% compared to unpromoted Mo after 12h of reaction time. With Zn as the only promoter the benzene formation rate was initially slightly higher (up to 10%); however, after 3h it performed similarly to the unpromoted Mo catalyst. When Mo/HZSM-5 was promoted with both Fe and Zn a significant drop (31%) in benzene formation was observed. Temperature programmed oxidation of the spent catalysts suggested that unhydrogenated, high-temperature carbon plays a role in catalyst deactivation of Fe–Zn promoted Mo/HZSM-5 catalyst. Further, Zn-loaded catalysts had a higher formation rate of ethylene, with and without Fe, compared to MoFe catalyst, possibly due to coke formation associated with Zn. Characterization of the catalysts suggested the presence of two types of Zn species. The first type is likely a loosely bound, unstable ZnO, which was reduced and vaporized during the reaction. This was supported by elemental microanalysis of spent catalysts, which showed that more than 50% of Zn was lost during the reaction testing. The second type of Zn is more strongly bound to HZSM-5. This is consistent with the NH3-TPD results, where significantly fewer Bronsted acid sites were observed after Zn addition to Mo catalyst. The catalysts were also characterized by XRD, SEM, surface area and micropore analysis, and the correlation between performance and catalyst properties is discussed.

Metallic Sn- and SnO2-doped SAPO-34 as Model Catalysts for Investigating the Effect of Oxidation States on Bio- Ethanol Dehydration Products

Over the last decade, due to the increase of energy demand and lower cost of bio-ethanol production, the conversion of bio-ethanol to valuable products such as light olefins, paraffins and aromatics have been received considerable attention. From the previous result, it was found that tin oxide doped on SAPO-34 was discovered to have properties that enhance the formation of cooking gas and larger hydrocarbons. However, during the preparation, tin oxide doped on SAPO-34 cannot be made pure as a single oxide of tin; therefore, the outcomes from bio-ethanol were influenced by the oxidation states of tin. The aim of this work was therefore to examine the oxidation states of tin oxide doped on previously-tested SAPO-34support, and study their effects on products. Metallic Sn- and SnO2- doped on SAPO-34 were employed as model catalysts in order to investigate the influences of Sn0 and Sn+4 oxidation states on the products from bio-ethanol dehydration. The results were compared with those obtained from the tin-oxide-doped SAPO-34 catalyst previously tested. The loading percentage of tin oxides was fixed at 7 wt%, and the catalysts were characterized by using SAA, XRD, XRF and, mainly, XPS. The reaction was carried out in an isothermal fixed bed reactor at atmospheric pressure 400 °C and at WHSV of 0.5 h-1. The product sampling was taken at 1 hour of time-on-stream. The gaseous products were analyzed by using an online- GC while the liquid products needed a SIMDIST-GC and a GC-TOFMS to identify petroleum fractions and hydrocarbon species, respectively. It was found that from XPS spectra, tin oxides on the previously-testedcatalyst were found to be in the form of Sn–OH and SnO2. After the catalytic test, tin oxide doped on SAPO-34 contained mixed valences of Sn0 and Sn+4, which affect the product distribution of both gas and liquid. The liquid product was distributed in gasoline range, and comprised, mainly, of benzene andoxygenate compounds. From the result, it was also observed that Sn+4 seems to contribute in the production of oxygenate compounds; whereas, metallic tin contributes on benzene formation.

Highly selective formation of benzene upon toluene transformation on CsY zeolite

Gas-phase transformation of toluene is carried out on Cs-exchanged NaY zeolite in a fixed-bed tubular reactor and it is observed that toluene can transform through dealkylation, producing benzene and a small amount of hydrogen under the experimental conditions. After a definite activation period, the transformation of toluene can achieve its steady state with the yield of benzene above 25 % for a relatively long continuous time at low space velocity. Combining the results of characterization and catalytic performances, it can be concluded that benzene is the steadiest product except the carbonaceous residues within the CsY zeolite pores. The in situ carbonaceous deposition experiment shows a similar trend of the carbonaceous forming process and the yield of benzene, indicating the important role of carbonaceous species in the formation of benzene, i.e., it is necessary for the accumulation of carbonaceous species in the initial stage of reaction. The discovery in the current work sheds light on new strategies for the transformation of other similar compounds.

Experimental and modelling study of speciation and benzene formation pathways in premixed 1-hexene flames

An existing detailed and broadly validated kinetic scheme is augmented to capture the flame chemistry of 1-hexene under stoichiometric and fuel rich conditions including benzene formation pathways. In addition, the speciation in a premixed stoichiometric 1-hexene flame (flat-flame McKenna-type burner) has been studied under a reduced pressure of 20–30mbar applying flame-sampling molecular-beam time-of-flight mass spectrometry and photoionization by tunable vacuum-ultraviolet synchrotron radiation. Mole fraction profiles of 40 different species have been measured and validated against the new detailed chemical reaction model consisting of 275 species and 3047 reversible elementary reactions. A good agreement of modelling results with the experimentally observed mole fraction profiles has been found under both stoichiometric and fuel rich conditions providing a sound basis for analyzing benzene formation pathways during 1-hexene combustion. The analysis clearly shows that benzene formation via the fulvene intermediate is a very important pathway for 1-hexene.

Origin of carbon in aromatic and olefin products derived from HZSM-5 catalyzed co-pyrolysis of cellulose and plastics via isotopic labeling

Catalytic pyrolysis over HZSM-5 is an effective method for the conversion of biomass to aromatic hydrocarbons, albeit with low yield and short catalyst lifetimes. Addition of co-reactants rich in carbon and hydrogen can enhance yield and possibly increase catalyst lifetimes by reducing coke formation. Particularly, the catalytic co-pyrolysis of plastic and biomass has been shown to enhance conversion to aromatic hydrocarbons, and also offers a method for productive disposal of waste agricultural plastics. In an effort to determine the origin of the carbon (plastic or biomass) in the products from this catalytic co-pyrolysis, mixtures of uniformly labeled 13C cellulose and non-labeled plastic including polyethylene terephthalate, polypropylene, high density polyethylene, low density polyethylene and polystyrene were subjected to catalytic fast pyrolysis (CFP) at 650°C in the presence of HZSM-5. A micro pyrolyzer coupled with GC/MS (py-GC/MS) advised product distributions and mass spectral data was used to determine the distribution of biogenic carbon and plastic derived carbon in the products. The results demonstrate that aromatic hydrocarbon products formed from the CFP of mixtures of cellulose and plastic are composed mostly of molecules containing carbon of mixed origin. Data on the distribution of 13Cx12Cy from the products followed in this study show that polyolefin mixtures with cellulose favor the formation of alkyl benzenes that incorporate carbon from both sources. Utilization of aromatic polymers (polystyrene or polyethylene terephthalate) is more selective for formation of naphthalenes with carbon derived from both products. The distribution of various13Cx12Cy products is used to suggest active mechanisms that result in the formation of the observed products.

Experimental and kinetic modeling study of laminar coflow diffusion methane flames doped with 2-butanol

In order to understand the interactions between 2-butanol and hydrocarbon fuels in combustion chemistry, experimental and kinetic modeling investigations were performed to study laminar coflow diffusion methane flames doped with two inlet mole fractions of 2-butanol (1.95% and 3.90%) in this work. Mole fractions of flame species along the flame centerline, particularly unsaturated C2–C5 hydrocarbons, C6–C16 aromatics and some free radicals, were measured using synchrotron vacuum ultraviolet photoionization mass spectrometry. A detailed kinetic model was developed to simulate the fuel decomposition and the formation of benzene and PAHs in the investigated flames. The simulated results can reproduce the observed effects of 2-butanol addition. The reaction pathway analysis reveals that resonantly stabilized radicals, such as propargyl, cyclopentadienyl, phenyl, and benzyl radicals, are major precursors of indene and naphthalene. With the increasing inlet mole fraction of 2-butanol, the formation of these resonantly stabilized radicals increases significantly. PAHs with more carbon atoms, including acenaphthylene, phenanthrene, pyrene, and fluoranthene, are dominantly derived from indenyl and naphthyl radicals.

Negative charge induced dissociation: fragmentation of deprotonated N-benzylidene-2-hydroxylanilines in electrospray ionization mass spectrometry.

Unimolecular reactivities of different N-benzylidene-2-hydroxylaniline anions were investigated in gas phase by electrospray ionization tandem mass spectrometry. All the collision-induced dissociation spectra of N-benzylidene-2-hydroxylaniline anions show similar ions at phenyl anions, neutral loss of benzonitrile and benzoxazole anions, respectively. The possible fragmentation pathway was probed through deuterium labeling and various group substituents experiments. Computational results were applied to shed light on the mechanism of fragmentation patterns. The proton in the CH=N is reactive in the formation of the concerned ions. Its direct transfer to the oxygen results in 2-hydroxyphenyl anion. Proton abstraction between benzoxazole and phenyl anion leads to the formation of benzene and benzoxazole anion.

Formation of a new benzene-ethane co-crystalline structure under cryogenic conditions.

We report the first experimental finding of a solid molecular complex between benzene and ethane, two small apolar hydrocarbons, at atmospheric pressure and cryogenic temperatures. Considerable amounts of ethane are found to be incorporated inside the benzene lattice upon the addition of liquid ethane onto solid benzene at 90-150 K, resulting in formation of a distinctive co-crystalline structure that can be detected via micro-Raman spectroscopy. Two new features characteristic of these co-crystals are observed in the Raman spectra at 2873 and 1455 cm(-1), which are red-shifted by 12 cm(-1) from the υ1 (a1g) and υ11 (eg) stretching modes of liquid ethane, respectively. Analysis of benzene and ethane vibrational bands combined with quantum mechanical modeling of isolated molecular dimers reveal an interaction between the aromatic ring of benzene and the hydrogen atoms of ethane in a C-H···π fashion. The most favored configuration for the benzene-ethane dimer is the monodentate-contact structure, with a calculated interaction energy of 9.33 kJ/mol and an equilibrium bonding distance of 2.66 Å. These parameters are comparable to those for a T-shaped co-crystalline complex between benzene and acetylene that has been previously reported in the literature. These results are relevant for understanding the hydrocarbon cycle of Titan, where benzene and similar organics may act as potential hydrocarbon reservoirs due to this incorporation mechanism.

Photochemical degradation of atenolol, carbamazepine, meprobamate, phenytoin and primidone in wastewater effluents

The photochemical degradation of five pharmaceuticals was examined in two secondary wastewater effluents. The compounds, which included atenolol, carbamazepine, meprobamate, phenytoin and primidone, were evaluated for both direct and sensitized photolysis. In the two wastewaters, direct photolysis did not lead to significant compound degradation; however, sensitized photolysis was an important removal pathway for the five pharmaceuticals. Upon solar irradiation, hydroxyl radical (HO) was quantified using the hydroxylation of benzene and singlet oxygen (1O2) formation was monitored following the degradation of furfuryl alcohol. Degradation via sensitized photolysis was observed following five-day exposures for atenolol (69–91%), carbamazepine (67–98%), meprobamate (16–52%), phenytoin (44–85%), and primidone (34–88%). Varying removal is likely a result of the differences in reactivity with transient oxidants. Averaged steady state HO concentrations ranged from 1.2 to 4.0×10−16M, whereas the concentrations of 1O2 were 6.0–7.6×10−14M. Partial removal due to presence of HO indicates it was not the major sink for most compounds examined. Other transient oxidants, such as 1O2 and triplet state effluent organic matter, are likely to play important roles in fates of these compounds.

Isomer-Specific Product Detection of Gas-Phase Xylyl Radical Rearrangement and Decomposition Using VUV Synchrotron Photoionization

Xylyl radicals are intermediates in combustion processes since their parent molecules, xylenes, are present as fuel additives. In this study we report on the photoelectron spectra of the three isomeric xylyl radicals and the subsequent decomposition reactions of the o-xylyl radical, generated in a tubular reactor and probed by mass selected threshold photoelectron spectroscopy and VUV synchrotron radiation. Franck-Condon simulations are applied to augment the assignment of elusive species. Below 1000 K, o-xylyl radicals decompose by hydrogen atom loss to form closed-shell o-xylylene, which equilibrates with benzocyclobutene. At higher temperatures relevant to combustion engines, o-xylylene generates styrene in a multistep rearrangement, whereas the p-xylylene isomer is thermally stable, a key point of difference in the combustion of these two isomeric fuels. Another striking result is that all three xylyl isomers can generate p-xylylene upon decomposition. In addition to C8H8 isomers, phenylacetylene and traces of benzocyclobutadiene are observed and identified as further reaction products of o-xylylene, while there is also some preliminary evidence for benzene and benzyne formation. The experimental results reported here are complemented by a comprehensive theoretical C8H8 potential energy surface, which together with the spectroscopic assignments can explain the complex high-temperature chemistry of o-xylyl radicals.

Dynamics simulation and reaction pathway analysis of characteristics of soot particles in ethylene oxidation at high temperature

Soot particles characteristics were investigated numerically for high temperature oxidation of C2H4/O2/N2 (C/O ratio of 2.2) in a closed jet-stirred/plug-flow reactor (JSR/PFR) system. Based on the growth mechanism of polycyclic aromatic hydrocarbons (PAHs), two mechanisms were used to explore the formation pathways of soot precursors and soot. Numerical results were compared with the experimental and reference data. The simulation results show that the value predicted for small molecule intermediates within A1 gives a strong regularity, consistent trend with reference data. However, with the hydrogen-abstraction-carbon-addition (HACA) growth mechanism, the predicted value for beyond-A1 PAH macromolecules and soot volume fraction are smaller than the experimental data. The results also show that the predicted soot volume fraction is in good agreement with experimental data when a combination of the HACA and PAHs condensation (HACA + PAH-PAH) growth mechanisms is used. Analyses of the A1 sensitivity and reaction pathway elucidated that A1 are mainly formed from C2H3, C2H2, C3H3, C6H5OH, A1C2H and A1-. The reaction 2C3H3 → A1 is the dominant route of benzene formation. The prediction results and an analysis of the A3 reaction pathway indicate that the growth process from benzene to larger aromatic hydrocarbons (beyond two-ring polycyclic aromatic hydrocarbons [PAHs]) goes by two pathways, i.e., HACA combined with the PAH-PAH radical recombination and addition reaction growth mechanisms.

Structure and Composition of Au–Cu and Pd–Cu Bimetallic Catalysts Affecting Acetylene Reactivity

Au–Cu and Pd–Cu bimetallic model catalysts were prepared on native SiO2/Si(100) substrate under ultra high vacuum (UHV) by employing buffer layer assisted growth procedure with amorphous solid water as the buffer material. The effect of the bimetallic nanoclusters (NCs) surface composition and morphology on their chemical reactivity has been studied with acetylene decomposition and conversion to ethylene and benzene as the chemical probe. It was found that among the Au–Cu NCs compositions, Au0.5Cu3 NCs revealed outstanding catalytic selectivity towards ethylene formation. These NCs were further characterized by employing TEM, XPS and HAADF-STEM coupled EDX analysis. With CO molecule as a probe, CO temperature programmed desorption has been used to investigate the distribution of gold on the top-most surface of the supported clusters. Surface segregation at high relative elemental fraction of gold leads to a decreased activity of the Au–Cu NCs towards ethylene formation. In contrast to the Au–Cu NCs, the Pd–Cu bimetallic system reveals reduced sensitivity to the relative elemental composition with respect to selectivity of the acetylene transformation toward ethylene formation. On the other hand, remarkable activity towards benzene formation has been observed at elemental composition of Cu3Pd, at comparable rates to those for ethylene formation on clean Pd NCs.

Effect of hydrogen and helium addition to fuel on soot formation in an axisymmetric coflow laminar methane/air diffusion flame

A detailed numerical study was conducted to investigate the effects of hydrogen and helium addition to fuel on soot formation in atmospheric axisymmetric coflow laminar methane/air diffusion flame. Detailed gas-phase chemistry and thermal and transport properties were employed in the numerical calculations. Soot was modeled using a PAH based inception model and the HACA mechanism for surface growth and oxidation. Numerical results were compared with available experimental data. Both experimental and numerical results show that helium addition is more effective than hydrogen addition in reducing soot loading in the methane/air diffusion flame. These results are different from the previous investigations in ethylene/air diffusion flames. Hydrogen chemically enhances soot formation when added to methane. The different chemical effects of hydrogen addition to ethylene and methane on soot formation are explained in terms of the different effects of hydrogen addition on propargyl, benzene, and pyrene formation low in the flames.

Catalytic aromatization of methane

Recent developments in natural gas production technology have led to lower prices for methane and renewed interest in converting methane to higher value products. Processes such as those based on syngas from methane reforming are being investigated. Another option is methane aromatization, which produces benzene and hydrogen: 6CH4(g) → C6H6(g) + 9H2(g) ΔG°(r) = +433 kJ mol(-1) ΔH°(r) = +531 kJ mol(-1). Thermodynamic calculations for this reaction show that benzene formation is insignificant below ∼600 °C, and that the formation of solid carbon [C(s)] is thermodynamically favored at temperatures above ∼300 °C. Benzene formation is insignificant at all temperatures up to 1000 °C when C(s) is included in the calculation of equilibrium composition. Interestingly, the thermodynamic limitation on benzene formation can be minimized by the addition of alkanes/alkenes to the methane feed. By far the most widely studied catalysts for this reaction are Mo/HZSM-5 and Mo/MCM-22. Benzene selectivities are generally between 60 and 80% at methane conversions of ∼10%, corresponding to net benzene yields of less than 10%. Major byproducts include lower molecular weight hydrocarbons and higher molecular weight substituted aromatics. However, carbon formation is inevitable, but the experimental findings show this can be kinetically limited by the use of H2 or oxidants in the feed, including CO2 or steam. A number of reactor configurations involving regeneration of the carbon-containing catalyst have been developed with the goal of minimizing the cost of regeneration of the catalyst once deactivated by carbon deposition. In this tutorial review we discuss the thermodynamics of this process, the catalysts used and the potential reactor configurations that can be applied.

Investigation of the Deactivation Phenomena Occurring in the Cyclohexane Photocatalytic Oxidative Dehydrogenation on MoOx/TiO2 through Gas Phase and in situ DRIFTS Analyses

In this work, the results of gas phase cyclohexane photocatalytic oxidative dehydrogenation on MoOx/SO4/TiO2 catalysts with DRIFTS analysis are presented. Analysis of products in the gas-phase discharge of a fixed bed photoreactor was coupled with in situ monitoring of the photocatalyst surface during irradiation with an IR probe. An interaction between cyclohexane and surface sulfates was found by DRIFTS analysis in the absence of UV irradiation, showing evidence of the formation of an organo-sulfur compound. In particular, in the absence of irradiation, sulfate species initiate a redox reaction through hydrogen abstraction of cyclohexane and formation of sulfate (IV) species. In previous studies, it was concluded that reduction of the sulfate (IV) species via hydrogen abstraction during UV irradiation may produce gas phase SO2 and thereby loss of surface sulfur species. Gas phase analysis showed that the presence of MoOx species, at same sulfate loading, changes the selectivity of the photoreaction, promoting the formation of benzene. The amount of surface sulfate influenced benzene yield, which decreases when the sulfate coverage is lower. During irradiation, a strong deactivation was observed due to the poisoning of the surface by carbon deposits strongly adsorbed on catalyst surface.

Anisole hydrodeoxygenation over Ni–Cu bimetallic catalysts: The effect of Ni/Cu ratio on selectivity

The activity and selectivity of model NiCu–SiO2 catalysts with the high metal loading (90%) and various Ni content was studied in anisole hydrotreatment at 280°C and a hydrogen pressure of 6MPa in a batch reactor. To obtain the alloys with the homogeneous phase composition, the catalysts were prepared by simultaneous decomposition of metal salts with the subsequent stabilization with 10wt% SiO2. The composition of the NiyCu1−y alloy surface was estimated from the combination of XPS and XRD data. On the basis of obtained kinetic data, a reaction scheme of anisole conversion was proposed. The scheme includes two parallel routes, one of which leads to CarO bond cleavage with the formation of benzene, which is then converted to cyclohexane (HDO route), while the second route leads to hydrogenation of the aromatic ring of anisole with the formation of methoxycyclohexane and cyclohexanol (HYD route). The experimental dependence of anisole conversion was described by the first-order kinetics with respect to the reagents. The effect of the surface composition of the active phase NiyCu1−y on the specific catalytic activity was examined. According to the proposed reaction scheme, the dependence of the first-order rate constants for both routes on the nickel content in the active component of the catalysts was determined. The selectivities of both reaction routes of anisole conversion (HDO and HYD) were found to be independent of the Ni content except for the nickel-rich and copper-rich sides. The specific catalytic activity in the HDO route rises with an increase in the nickel content in the whole range of Ni loading.

Experimental and kinetic modeling study of PAH formation in methane coflow diffusion flames doped with n-butanol

In order to understand the interactions between butanol and hydrocarbon fuels in the PAH formation, experimental and kinetic modeling investigations were combined to study methane laminar coflow diffusion flames doped with two inlet mole fractions of n-butanol (1.95% and 3.90%) in this work. Mole fractions of flame species along the flame centerline were measured using synchrotron VUV photoionization mass spectrometry. A detailed kinetic model of n-butanol combustion, extended from a recent published n-butanol model, was provided in this work to reproduce the fuel decomposition and the formation of benzene and PAHs in the investigated flames. Numerical simulations were performed with laminarSMOKE code, a CFD code specifically conceived to handle large kinetic mechanisms. The simulation results were able to follow the observed effects of n-butanol addition from the experimental results. In particular, unsaturated hydrocarbons, especially C6–C16 aromatics, were predicted satisfactorily. The reaction flux analysis revealed that benzene precursors, especially C3 radicals, increase significantly with increasing inlet mole fraction of n-butanol. This enhances the formation of phenyl and benzyl radicals, which are important PAH precursors. Reactions of benzyl, phenyl radicals and benzene with C2–C3 species are the major formation pathways for indene and naphthalene. And PAHs with more carbon atoms are dominantly formed from naphthyl and indenyl radicals.

Effect of cofeeding n-butane with methanol on aromatization performance and coke formation over a Zn loaded ZSM-5/ZSM-11 zeolite

The aromatization performance of cofeeding n-butane with methanol was investigated in a fixed bed reactor over a Zn loaded ZSM-5/ZSM-11 zeolite. Coke deposited on the catalyst was characterized by TG, TPO, FTIR and Raman technique. During the 48h life-test under the conditions of 510°C, 0.4MPa, WHSV (CH2)=2h−1, pure n-butane reaction performance of the catalyst changes little, but high LPG and low aromatics yields are obtained. Only under the suitable n-butane/methanol ratio, the relatively good aromatics selectivity can be obtained and maintained during the reaction process. Compared with methanol aromatization, the integrated process exhibits a much slower rate of deactivation. Addition of methanol in n-butane inhibits the dry gas production while promotes the LPG production. Water generated from methanol dehydration may occupy the catalytic active sites for olefins aromatization over the catalyst and thus suppress the production of total aromatics. In fact, water mainly suppresses benzene formation and this inhibiting effect increases with n-butane content in the feed, in contrast to its promoting effect on formation of C8 and C9 aromatics. Increasing methanol content in the feed, a simultaneous increase in coke content of the spent catalyst and preference for coke deposition in micropore is observed. Furthermore, the fraction of aliphatics in coke decreases, while those of less-condensed aromatics and polyaromatics incease, which is associated with the increased deactivation of catalyst.

Experimental and kinetic modeling study on methylcyclohexane pyrolysis and combustion

Methylcyclohexane is the simplest alkylated cyclohexane, and has been broadly used as the representative cycloalkane component in fuel surrogates. Understanding its combustion chemistry is crucial for developing kinetic models of larger cycloalkanes and practical fuels. In this work, the synchrotron vacuum ultraviolet photoionization mass spectrometry combined with molecular-beam sampling was used to investigate the species formed during the pyrolysis of methylcyclohexane and in premixed flame of methylcyclohexane. A number of pyrolysis and flame intermediates were identified and quantified, especially including radicals (e.g. CH3, C3H3, C3H5 and C5H5) and cyclic C6- and C7-intermediates (benzene, 1,3-cyclohexadiene, cyclohexene, toluene, C7H10 and C7H12, etc.). In particular, the observation of cyclic C6- and C7-intermediates provides important experimental evidence to clarify the special formation channels of toluene and benzene which were observed with high concentrations in both pyrolysis and flame of methylcyclohexane. Furthermore, the rate constants of H-abstraction of methylcyclohexane via H attack, and the isomerization and decomposition of the formed cyclic C7H13 radicals were calculated in this work. A kinetic model of methylcyclohexane combustion with 249 species and 1570 reactions was developed including a new sub-mechanism of MCH. The rate of production and sensitivity analysis were carried out to elucidate methylcyclohexane consumption, and toluene and benzene formation under various pyrolytic and flame conditions. Furthermore, the present kinetic model was also validated by experimental data from literatures on speciation in premixed flames, ignition delays and laminar flame speeds.

Applied kinetics for modeling of reactive hot gas filters

First order kinetics were developed based on experimental results of a noble metal catalyst. Activation energies and pre-exponential factors were determined by parameter estimation for steam reforming of tars, sulfur tars and ethene. The formation of ethane and benzene was assumed to be at constant rate depending on the decomposition of ethene and toluene respectively. Further, for steam reforming of methane and water gas shift reaction, the kinetic parameters of Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate laws including equilibrium term and adsorption of sulfur could be determined.With the applied kinetics, catalytic tar conversion of producer gas from biomass gasification was simulated. Simulation results at operating temperatures of 850°C showed significantly higher conversions rates for sulfur free tars, ethene and methane than at 600°C or 750°C while the conversion of sulfur tars was less temperature dependent and high at all temperatures.The simulation results were used to evaluate different possibilities regarding the integration of catalytic material into hot gas filter units with vertical and horizontal filter design. The option of catalytic active filter elements, additional catalytic foam type packing at the inside of the filter element and a monolith at the exit of the filter vessel are feasible assuming the same catalyst material as applied in the reforming catalyst used in this study. These three options can be applied independently of the horizontal or vertical filter design. Placing a catalytic monolith or foam structure at the filter candle exit of a horizontal filter design was found to be unrealistic because the monolith or foam structure would be too long to reach sulfur tar concentrations below 1ppmV.