AN EXPERIMENTAL AND KINETIC MODELLING STUDY OF THE OXIDATION OF THE FOUR ISOMERS OF BUTANOL (original) (raw)

An Experimental and Kinetic Modeling Study of the Oxidation of the Four Isomers of Butanol

The Journal of Physical Chemistry A, 2008

Butanol, an alcohol which can be produced from biomass sources, has received recent interest as an alternative to gasoline for use in spark ignition engines and as a possible blending compound with fossil diesel or biodiesel. Therefore, the autoignition of the four isomers of butanol (1-butanol, 2-butanol, iso-butanol, and tert-butanol) has been experimentally studied at high temperatures in a shock tube, and a kinetic mechanism for description of their high-temperature oxidation has been developed. Ignition delay times for butanol/oxygen/argon mixtures have been measured behind reflected shock waves at temperatures and pressures ranging from approximately 1200 to 1800 K and 1 to 4 bar. Electronically excited OH emission and pressure measurements were used to determine ignition-delay times. The influence of temperature, pressure, and mixture composition on ignition delay has been characterized. A detailed kinetic mechanism has been developed to describe the oxidation of the butanol isomers and validated by comparison to the shock-tube measurements. Reaction flux and sensitivity analysis illustrates the relative importance of the three competing classes of consumption reactions during the oxidation of the four butanol isomers: dehydration, unimolecular decomposition, and H-atom abstraction. Kinetic modeling indicates that the consumption of 1-butanol and iso-butanol, the most reactive isomers, takes place primarily by H-atom abstraction resulting in the formation of radicals, the decomposition of which yields highly reactive branching agents, H atoms and OH radicals. Conversely, the consumption of tertbutanol and 2-butanol, the least reactive isomers, takes place primarily via dehydration, resulting in the formation of alkenes, which lead to resonance stabilized radicals with very low reactivity. To our knowledge, the ignitiondelay measurements and oxidation mechanism presented here for 2-butanol, iso-butanol, and tert-butanol are the first of their kind.

An experimental and kinetic modeling study of combustion of isomers of butanol

Combustion and Flame, 2010

A kinetic model is developed to describe combustion of isomers of butanol-n-butanol (n-C 4 H 9 OH), secbutanol (sec-C 4 H 9 OH), iso-butanol (iso-C 4 H 9 OH), and tert-butanol (tert-C 4 H 9 OH). A hierarchical approach is employed here. This approach was previously found to be useful for developing detailed and semidetailed mechanism of oxidation of various hydrocarbon fuels. This method starts from lower molecular weight compounds of a family of species and proceeds to higher molecular weight compounds. The pyrolysis and oxidation mechanisms of butanol isomers are similar to those for hydrocarbon fuels. Here, the development of the complete set of the primary propagation reactions for butanol isomers proceeds from the extension of the kinetic parameters for similar reactions already studied and recently revised for ethanol, n-propanol and iso-propanol. A detailed description leading to evaluation of rate constants for initiation reactions, metathesis reactions, decomposition reactions of alkoxy radicals, isomerization reactions, and four-center molecular dehydration reactions are given. Decomposition and oxidation of primary intermediate products are described using a previously developed semi-detailed kinetic model for hydrocarbon fuels. The kinetic mechanism is made up of more than 7000 reactions among 300 species. The model is validated by comparing predictions made using this kinetic model with previous and new experimental data on counterflow non-premixed flames of n-butanol and iso-butanol. The structures of these flames were measured by removing gas samples from the flame and analyzing them using a gas chromatograph. Temperature profiles were measured using coated thermocouples. The flame structures were measured under similar conditions for both fuels to elucidate the similarities and differences in combustion characteristics of the two isomers. The profiles measured include those of butanol, oxygen, carbon dioxide, water vapor, carbon monoxide, hydrogen, formaldehyde, acetaldehyde, and a number of C 1 -C 4 hydrocarbon compounds. The predictions of the kinetic model of flame structures of the two isomers were satisfactory. Validation of the kinetic model was also performed by comparing predictions with experimental data reported in the literature. These data were obtained in batch reactors, flow reactors, jet-stirred reactors, and shock tubes. In these configurations, combustion is not influenced by molecular transport. The agreement between the kinetic model and experimental data was satisfactory.

Combustion and pyrolysis of iso-butanol: Experimental and chemical kinetic modeling study

Combustion and Flame, 2013

The first reaction mechanism for iso-butanol (372 species and 8723 reversible elementary reactions) pyrolysis and combustion that includes pressure dependent kinetics and proposes reaction pathways to soot precursors has been automatically generated using the open-source software package RMG. High-pressure reaction rate coefficients for important hydrogen abstraction reactions from iso-butanol by hydrogen, methyl and HO 2 were calculated using quantum chemistry at the CBS-QB3 level. The mechanism was validated with recently published iso-butanol combustion experiments as well as new pyrolysis speciation data under diluted and undiluted conditions from 900 to 1100 K at 1.72 atm representative of fuel rich combustion conditions. Sensitivity and rate of production analysis revealed that the overall good agreement for the pyrolysis species, and in particular for the soot precursors like benzene, toluene and 1,3-cyclopentadiene, depends strongly on pressure dependent reactions involving the resonantly stabilized iso-butenyl radical. Laminar flame speed, opposed flow diffusion flame speciation profiles, and autoignition are also well-captured by the model. The agreement with speciation profiles for the jet-stirred reactor could be improved, in particular for temperatures lower than 850 K. Flux and sensitivity analysis for iso-butanol consumption revealed that this is primarily caused by uncertainty in iso-butanol + OH, iso-butanol + HO 2 and the low temperature peroxy chemistry rates. Further theoretical and quantum chemical studies are needed in understanding these rates to completely predict the combustion behavior of iso-butanol using detailed chemistry.

A shock tube and chemical kinetic modeling study of the pyrolysis and oxidation of butanols

Combustion and Flame, 2012

A detailed kinetic model describing the oxidation of 2,5dimethylfuran (DMF), a potential second-generation biofuel, is proposed. The kinetic model is based upon quantum chemical calculations for the initial DMF consumption reactions and important reactions of intermediates. The model is validated by comparison to new DMF shock tube ignition delay time measurements (over the temperature range 1300−1831 K and at nominal pressures of 1 and 4 bar) and the DMF pyrolysis speciation measurements of Lifshitz et al. [J. Phys. Chem. A 1998, 102 (52), 10655−10670]. Globally, modeling predictions are in good agreement with the considered experimental targets. In particular, ignition delay times are predicted well by the new model, with model−experiment deviations of at most a factor of 2, and DMF pyrolysis conversion is predicted well, to within experimental scatter of the Lifshitz et al. data. Additionally, comparisons of measured and model predicted pyrolysis speciation provides validation of theoretically calculated channels for the oxidation of DMF. Sensitivity and reaction flux analyses highlight important reactions as well as the primary reaction pathways responsible for the decomposition of DMF and formation and destruction of key intermediate and product species.

Autothermal partial oxidation of butanol isomers

Applied Catalysis A: General, 2012

The four isomers of butanol offer an interesting platform from which to study the reaction pathways of alcohols in an autothermal partial oxidation system, as they comprise one tertiary, one secondary, and two primary alcohols with the same number of carbon atoms. We demonstrate high yields of syngas or unsaturated molecules at contact times on the order of 10 ms, and investigate the reaction pathways of each isomer over Rh, RhCe, Pt, and PtCe catalysts for a range of carbon-to-oxygen (C/O) ratios.

Kinetic Modeling of the Low Temperature Reactivity of N-Butanol

The aim of this paper is to analyze and discuss a kinetic mechanism able to describe the low temperature reactivity of n-butanol. Using a lumped approach, already successfully adopted for the low temperature mechanism of n-alkanes, an existing mechanism of n-butanol pyrolysis and combustion is extended to include the low temperature reactivity. The model is validated in a wide range of conditions (P=1÷80 atm, T=500÷1500 K), using recent autoignition data measured in shock tubes and detailed species profiles measured in Jet Stirred Reactors (JSR). The comparisons between the experimental data and model predictions further confirm the validity and the broad applicability of the kinetic model.

Thermal Decomposition of 2-Butanol as a Potential Nonfossil Fuel: A Computational Study

The Journal of Physical Chemistry A, 2011

The thermochemistry and kinetics of the pyrolysis of 2-butanol have been conducted using ab initio methods (CBS-QB3 and CCSD(T)) and density functional theory (DFT). The enthalpies of formation and bond dissociation energies of some alcohols including 2-butanol and its derived radicals have been calculated. A variety of simple and complex dissociations have been examined. The results indicated that dehydration to 1-and 2-butene through four-center transition states is the most dominant channel at low to moderate temperatures (T e 700 K), where formation of butenes is kinetically and thermodynamically more favorable than other complex and simple bond scission reactions. Although the C-C bond fission channels require more energy than needed for some complex decomposition reactions, the former pathways predominate at higher temperatures (T g 800 K) due to the higher values of the pre-exponential factors. The progress of the complex decomposition reactions has been followed through intrinsic reaction coordinate (IRC) calculations to understand the mechanism of transformation of 2-butanol to different products.

On the Chemical Kinetics of n-Butanol: Ignition and Speciation Studies

Direct measurements of intermediates of ignition are challenging experimental objectives, yet such measurements are critical for understanding fuel decomposition and oxidation pathways. This work presents experimental results, obtained using the University of Michigan Rapid Compression Facility, of ignition delay times and intermediates formed during the ignition of n-butanol. Ignition delay times for stoichiometric nbutanol/O 2 mixtures with an inert/O 2 ratio of 5.64 were measured over a temperature range of 920À1040 K and a pressure range of 2.86À3.35 atm and were compared to those predicted by the recent reaction mechanism developed by Black et al. (Combust. Flame 2010, 157, 363À373). There is excellent agreement between the experimental results and model predictions for ignition delay time, within 20% over the entire temperature range tested. Further, high-speed gas sampling and gas chromatography techniques were used to acquire and analyze gas samples of intermediate species during the ignition delay of stoichiometric n-butanol/O 2 (χ(n-but) = 0.025, χ(O 2 ) = 0.147, χ(N 2 ) = 0.541, χ(Ar) = 0.288) mixtures at P = 3.25 atm and T = 975 K. Quantitative measurements of mole fraction time histories of methane, carbon monoxide, ethene, propene, acetaldehyde, n-butyraldehyde, 1-butene and n-butanol were compared with model predictions using the Black et al. mechanism. In general, the predicted trends for species concentrations are consistent with measurements. Sensitivity analyses and rate of production analyses were used to identify reactions important for predicting ignition delay time and the intermediate species time histories. Modifications to the mechanism by Black et al. were explored based on recent contributions to the literature on the rate constant for the key reaction, n-butanolþOH. The results improve the model agreement with some species; however, the comparison also indicates some reaction pathways, particularly those important to ethene formation and removal, are not well captured.

An Investigation of Combustion Properties of Butanol and Its Potential for Power Generation

Journal of Engineering for Gas Turbines and Power, 2018

Over the last years, global concerns about energy security and climate change have resulted in many efforts focusing on the potential utilization of nonpetroleum-based, i.e., bioderived, fuels. In this context, n-butanol has recently received high attention because it can be produced sustainably. A comprehensive knowledge about its combustion properties is inevitable to ensure an efficient and smart use of n-butanol if selected as a future energy carrier. In the present work, two major combustion characteristics, here laminar flame speeds applying the cone-angle method and ignition delay times applying the shock tube technique, have been studied, experimentally, and by modeling exploiting detailed chemical kinetic reaction models, at ambient and elevated pressures. The in-house reaction model was constructed applying the reaction model generation (RMG)-method. A linear transformation method recently developed, linTM, was exploited to generate a reduced reaction model needed for an e...

Thermal Decomposition of Methyl Butanoate: Ab Initio Study of a Biodiesel Fuel Surrogate

The Journal of Organic Chemistry, 2008

In this paper, we report a detailed analysis of the breakdown kinetic mechanism for methyl butanoate (MB) using theoretical approaches. Electronic structures and structure-related molecular properties of reactants, intermediates, products, and transition states were explored at the BH&HLYP/cc-pVTZ level of theory. Rate constants for the unimolecular and bimolecular reactions in the temperature range of 300-2500 K were calculated using Rice-Ramsperger-Kassel-Marcus and transition state theories, respectively. Thirteen pathways were identified leading to the formation of small compounds such as CH 3 , C 2 H 3 , CO, CO 2 , and H 2 CO. For the initial formation of MB radicals, H, CH 3 , and OH were considered as reactive radicals participating in hydrogen abstraction reactions. Kinetic simulation results for a high temperature pyrolysis environment show that MB radicals are mainly produced through hydrogen abstraction reactions by H atoms. In addition, the C(O)OCH 3 ) CO + CH 3 O reaction is found to be the main source of CO formation. The newly computed kinetic sub-model for MB breakdown is recommended as a core component to study the combustion of oxygenated species. * Corresponding author. Fax: (734) 647-9379. (1) Metcalfe, W. K.; Dooley, S.; Curran, H. J.; Simmie, J. M.; Al-Nahas, A. M.; Navarro, M. V. J. Phys. Chem. A 2007, 111, 4001. (2) Fisher, E. M.; Pits, W. J.; Curran, H. J.; Westbrook, C. K. Proc. Combust. Inst. 2000, 28, 1579-1586. (3) Gaïl, S.; Thomson, M. J.; Sarathy, S. M.; Syed, S. A.; P. Dagaut, B.; Dievart, P.; Marchese, A.