High-Temperature Unimolecular Decomposition of Diethyl Ether: Shock-Tube and Theory Studies.

The unimolecular decomposition of diethyl ether (DEE; C2H5OC2H5) is considered to be initiated via a molecular elimination, a C-O, and a C-C bond fission step: C2H5OC2H5 → C2H4 + C2H5OH (1), C2H5OC2H5 → C2H5 + C2H5O (2), and C2H5OC2H5 → CH3 + C2H5OCH2 (3). In this work, two shock-tube facilities were used to investigate these reactions via (a) time-resolved H-atom concentration measurements by H-ARAS (Atomic-Resonance Absorption Spectrometry), (b) time-resolved DEE-concentration measurements by high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS), and (c) product-composition measurements via gas chromatography/mass spectrometry (GC/MS) after quenching the test gas. The experiments were conducted at temperatures ranging from 1054 to 1505 K and at pressures between 1.2 and 2.5 bar. Initial DEE mole fractions between 0.4-9300 ppm were used to perform the kinetics experiments by H-ARAS (0.4 ppm), GC/MS (200-500 ppm), and HRR-TOF-MS (7850-9300 ppm). The rate constants ktotal (ktotal = k1 + k2 + k3) derived from the GC/MS and HRR-TOF-MS experiments agree well with each other and can be described by the Arrhenius expression ktotal(1054-1467 K; 1.3-2.5 bar) = 1012.81±0.22 exp(-240.27±5.11 kJ mol-1/RT) s-1.From H-ARAS experiments, overall rate constants for the bond fission channels k2+3 = k2 + k3 have been extracted. The k2+3 data can be well described by the Arrhenius equation k2+3(1299-1505 K; 1.3-2.5 bar) = 1014.43±0.33 exp(-283.27±8.78 kJ mol-1/RT) s-1. A master-equation analysis was performed using CCSD(T)/aug-cc-pvtz//B3LYP/aug-cc-pvtz and CASPT2/aug-cc-pvtz//B3LYP/aug-cc-pvtz molecular properties and energies for the three primary thermal decomposition processes in DEE. The derived experimental data is very well reproduced by the simulations with the mechanism of this work. Regarding the branching ratios between bond fissions and elimination channels, uncertainties remain.

[1]  C. Schulz,et al.  Direct Measurement of High-Temperature Rate Constants of the Thermal Decomposition of Dimethoxymethane, a Shock Tube and Modeling Study. , 2018, The journal of physical chemistry. A.

[2]  C. Schulz,et al.  A quantum chemical and kinetics modeling study on the autoignition mechanism of diethyl ether , 2017 .

[3]  C. Schulz,et al.  A single-pulse shock tube coupled with high-repetition-rate time-of-flight mass spectrometry and gas chromatography for high-temperature gas-phase kinetics studies. , 2016, The Review of scientific instruments.

[4]  Ulrich Maas,et al.  Ignition delay times of diethyl ether measured in a high-pressure shock tube and a rapid compression machine , 2015 .

[5]  S. M. Sarathy,et al.  Alcohol combustion chemistry , 2014 .

[6]  C. D. Rakopoulos,et al.  Influence of properties of various common bio-fuels on the combustion and emission characteristics of high-speed DI (direct injection) diesel engine: Vegetable oil, bio-diesel, ethanol, n-butanol, diethyl ether , 2014 .

[7]  Gaurav Mittal,et al.  Autoignition of ethanol in a rapid compression machine , 2014 .

[8]  N. Labbe,et al.  Direct measurements of rate constants for the reactions of CH3 radicals with C2H6, C2H4, and C2H2 at high temperatures. , 2013, The journal of physical chemistry. A.

[9]  T. Balusamy,et al.  Effect of biodiesel and its blends with diethyl ether on the combustion, performance and emissions from a diesel engine , 2013 .

[10]  J. Troe,et al.  The dissociation/recombination reaction CH4 (+M) ⇔ CH3 + H (+M): a case study for unimolecular rate theory. , 2012, The Journal of chemical physics.

[11]  R. Sivaramakrishnan,et al.  High-temperature rate constants for H/D + C2H6 and C3H8 , 2012 .

[12]  C. Schulz,et al.  A shock tube with a high-repetition-rate time-of-flight mass spectrometer for investigations of complex reaction systems. , 2011, The Review of scientific instruments.

[13]  Hao Chen,et al.  Effect of diethyl ether and ethanol additives on the combustion and emission characteristics of biodiesel-diesel blended fuel engine. , 2011 .

[14]  H. Curran,et al.  A multiple shock tube and chemical kinetic modeling study of diethyl ether pyrolysis and oxidation. , 2010, The journal of physical chemistry. A.

[15]  Can Çinar,et al.  Effects of premixed diethyl ether (DEE) on combustion and exhaust emissions in a HCCI-DI diesel engine , 2010 .

[16]  R. Sivaramakrishnan,et al.  High temperature rate constants for OH+ alkanes ☆ , 2009 .

[17]  A. Boehman.  Developments in production and utilization of dimethyl ether for fuel applications , 2008 .

[18]  J. Kiefer,et al.  Shock tube/time-of-flight mass spectrometer for high temperature kinetic studies. , 2007, The Review of scientific instruments.

[19]  James A. Miller,et al.  Reaction of ethylene with hydroxyl radicals: a theoretical study. , 2006, The journal of physical chemistry. A.

[20]  Henry J. Curran,et al.  Rate constant estimation for C1 to C4 alkyl and alkoxyl radical decomposition , 2006 .

[21]  Weiyong Tang,et al.  Shock tube pyrolysis of 1,2,4,5-hexatetraene. , 2006, The journal of physical chemistry. A.

[22]  Robert W. Dibble,et al.  Investigation of HCCI combustion of diethyl ether and ethanol mixtures using carbon 14 tracing and numerical simulations , 2005 .

[23]  Stephen J. Klippenstein,et al.  Dissociation, relaxation, and incubation in the high-temperature pyrolysis of ethane, and a successful RRKM modeling , 2005 .

[24]  Angela K. Wilson,et al.  Harmonic Vibrational Frequencies: Scaling Factors for HF, B3LYP, and MP2 Methods in Combination with Correlation Consistent Basis Sets , 2004 .

[25]  I. A. Kirillov,et al.  Chemical Workbench––integrated environment for materials science , 2003 .

[26]  M. Su,et al.  Rate constants for H + CH4, CH3 + H2, and CH4 dissociation at high temperature , 2001 .

[27]  B. Viskolcz,et al.  The thermal unimolecular decomposition rate constants of ethoxy radicals , 1999 .

[28]  V. Knyazev,et al.  Density of States of One-Dimensional Hindered Internal Rotors and Separability of Rotational Degrees of Freedom , 1998 .

[29]  J. Michael,et al.  The thermal reactions of CH3 , 1994 .

[30]  Michael J. Pilling,et al.  Evaluated Kinetic Data for Combustion Modelling , 1992 .

[31]  P. Huhn,et al.  Radical steps in diethyl ether decomposition , 1986 .

[32]  B. C. Garrett,et al.  SEMICLASSICAL TUNNELING CALCULATIONS , 1979 .

[33]  J. P. Appleton,et al.  Shock tube studies of deuterium dissociation and oxidation by atomic resonance absorption spectrophotometry , 1975 .

[34]  K. Laidler,et al.  Kinetics and mechanisms of the pyrolysis of diethyl ether I. The uninhibited reaction , 1964, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[35]  K. Laidler,et al.  Kinetics and mechanisms of the pyrolysis of diethyl ether II. The reaction inhibited by nitric oxide , 1964, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[36]  E. Resler,et al.  Studies with a Single‐Pulse Shock Tube. I. The Cis—Trans Isomerization of Butene‐2 , 1963 .

[37]  Kenneth S. Pitzer,et al.  Energy Levels and Thermodynamic Functions for Molecules with Internal Rotation I. Rigid Frame with Attached Tops , 1942 .