High Pressure Oxidation of Dimethoxymethane

The Journal of Physical Chemistry A, 1997

The rate constant for the reaction of dimethoxymethane (DMM) with OH radicals was determined to be (4.6 (1.6) × 10-12 at 346 (3 K using a pulse radiolysis/transient UV absorption absolute rate technique and (5.3 (1.0) × 10-12 cm 3 molecule-1 s-1 at 295 (2 K using an FTIR-smog chamber relative rate technique. The reaction of OH radicals with DMM occurs via an H-atom abstraction mechanism with 76% of the attack occurring on the-CH 3 end groups and 24% on the central-CH 2-unit. The atmospheric fate of the alkoxy radicals CH 3 OCH 2 OCH 2 O(•) and CH 3 OCHO(•)OCH 3 at 296 K in 700 Torr of air was investigated using an FTIR-smog chamber technique. The sole atmospheric fate of CH 3 OCHO(•)OCH 3 radicals is reaction with O 2 to give dimethyl carbonate (CH 3 OC(O)OCH 3) and HO 2 radicals. At least three loss processes were identified for CH 3 OCH 2 OCH 2 O(•) radicals. In 1 atm of air at 295 K, 84 (4% of the CH 3 OCH 2 OCH 2 O(•) radicals react with O 2 while 7 (3% undergo H-atom elimination; the fate of the remaining 9% is unclear. OH radical-initiated oxidation of DMM in 1 atm of air at 296 K results in a yield of 24% dimethyl carbonate and 69% methoxymethyl formate; the oxidation mechanism of the remaining 7% of DMM is unclear. Relative rate techniques were used to measure rate constants for the reaction of Cl atoms with CH 3 OCH 2 OCH 3 and CH 3 OCH 2 OCHO of (1.4 (0.2) × 10-10 and (3.6 (0.6) × 10-11 cm 3 molecule-1 s-1 , respectively. Results are discussed in the context of the atmospheric chemistry of DMM.

Combustion and Flame

kinetic model for dimethyl ether and dimethoxymethane oxidation and NO interaction utilizing experimental laminar flame speed measurements at elevated pressure and temperature. Combustion and Flame, 218, 57-74.

Journal of Physical Chemistry A, 2015

The oxidation of dimethylether (DME) was studied using a jet-stirred reactor over a wide range of conditions: temperatures from 500 to 1100 K, equivalence ratios of 0.25, 1 and 2, residence time of 2 s, pressure of 106.7 kPa (close to the atmospheric pressure) and an inlet fuel mole fraction of 0.02 (with high dilution in helium). Reaction products were quantified using two analysis methods: gas chromatography and continuous wave cavity ring down spectroscopy (cw-CRDS). cw-CRDS enabled the quantification of formaldehyde which is one of the major product from DME oxidation as well as that of hydrogen peroxide which is an important branching agent in low-temperature oxidation chemistry. Experimental data were compared with data computed using models from the literature with important deviations being observed for the reactivity at low-temperature. A new detailed kinetic model for the oxidation of DME was developed in this study. Kinetic parameters used in this model were taken from literature or calculated in the present work using quantum calculations. This new model enables a better prediction of the reactivity in the low-temperature region. Under the present JSR conditions, error bar on predictions were given. Simulations were also successfully compared with experimental flow reactor, jet-stirred reactor, shock tube, rapid compression machine and flame data from literature. The kinetic analysis of the model enabled to highlight some specificities of the oxidation chemistry of DME: 1) the early reactivity which is observed at very low-temperature (e.g., compared to propane) is explained by the absence of inhibiting reaction of the radical directly obtained from the fuel (by H-atom abstraction) with oxygen yielding an olefin + HO2•; 2) the low-temperature reactivity is driven by the relative importance of the second addition to O2 (promoting the reactivity through branching chain) and the competitive decomposition reactions with an inhibiting effect.

Russian Chemical Bulletin, 1996

A decrease of the rate of high pressure oxidation of very rich methane-oxygen mixtures with increasing oxygen concentration was found. The results were confirmed by kinetic simulation of the process. A very distinct temperature dependence of the rate of oxygen conversion can be explained on the basis of a critical change in the reaction mechanism.

Chemosphere, 2001

The oxidation of dimethyl ether (DME, 340 ppm in 10% O 2) has been studied experimentally in an atmospheric pressure laminar¯ow reactor in the temperature range from 240°C to 700°C for residence times in the range 2±4 s. The in¯uence of nitric oxide additions up to 620 ppm to the feed gases has also been investigated. Products of reaction were determined by FTIR. In the absence of NO, reaction is ®rst detected at about 260°C. The products in the low-temperature region include formaldehyde (HCHO), and formic acid (HCOOH). The addition of NO leads to the appearance of methyl formate (CH 3 OCHO). While the overall behaviour of the system can be explained qualitatively in terms of typical low-temperature hydrocarbon ignition, recently published chemical kinetic models for DME ignition do not allow for the formation of these formate species. We ®nd no experimental evidence for the formation of hydroperoxymethyl formate (HPMF, HOOCH 2 OCHO) which is predicted by the models to be a signi®cant stable intermediate at temperatures below 350°C. Since both formic acid and methyl formate have potentially harmful health eects, these observations may have signi®cant implications for use of DME as a diesel fuel.

Chemical Physics Letters, 1999

Ž . The gas-phase reaction of OH X P radicals with di-n-butoxymethane DBM has been studied in the temperature range 298-710 K at total pressures between 50 and 100 Torr argon. OH radicals have been generated by excimer laser photolysis of H O at 248 nm and have been detected by laser-induced fluorescence. Within the investigated ranges, the reaction has 2 2 Ž been found to be independent of temperature and total pressure. The bimolecular rate coefficient is k s 3.21 "

International Journal of Chemical Kinetics, 1998

A detailed chemical kinetic model has been used to study dimethyl ether (DME) oxidation over a wide range of conditions. Experimental results obtained in a jet-stirred reactor (JSR) at 1 and and were modeled, in addition to 10 atm, 0.2 Յ Յ 2.5, 800 Յ T Յ 1300 K those generated in a shock tube at 13 and 40 bar, and The JSR ϭ 1.0 650 Յ T Յ 1300 K. results are particularly valuable as they include concentration profiles of reactants, intermediates, and products pertinent to the oxidation of DME. These data test the kinetic model severely, as it must be able to predict the correct distribution and concentrations of intermediate and final products formed in the oxidation process. Additionally, the shock-tube results are very useful, as they were taken at low temperatures and at high pressures, and thus undergo negative temperature dependence (NTC) behavior. This behavior is characteristic of the oxidation of saturated hydrocarbon fuels, (e.g., the primary reference fuels, n-heptane and iso-octane) under similar conditions. The numerical model consists of 78 chemical species and 336 chemical reactions. The thermodynamic properties of unknown species pertaining to DME oxidation were calculated using THERM.

Combustion and Flame, 2019

The pyrolysis and oxidation of dimethyl ether (DME) and its mixture with methane were investigated at high pressure (50 and 100 bar) and intermediate temperature (450-900 K). Mixtures highly diluted in nitrogen with different fuel-air equivalence ratios (Φ = ∞, 20, 1, 0.06) were studied in a laminar flow reactor. At 50 bar, the DME pyrolysis started at 825 K and the major products were CH 4 , CH 2 O, and CO. For the DME oxidation at 50 bar, the onset temperature of reaction was 525 K, independent of fuelair equivalence ratio. The DME oxidation was characterized by a negative temperature coefficient (NTC) zone which was found sensitive to changes in the mixture stoichiometry but always occurring at temperatures of 575-625 K. The oxidation of methane doped by DME was studied in the flow reactor at 100 bar. The fuel-air equivalence ratio (Φ) was varied from 0.06 to 20, and the DME to CH 4 ratio changed over 1.8-3.6%. Addition of DME had a considerable promoting effect on methane ignition as the onset of reaction shifted to lower temperatures by 25-150 K. A detailed chemical kinetic model was developed by adding a DME reaction subset to a model developed in previous highpressure work. The model was evaluated against the present data as well as data from literature. Additional work is required to reconcile experimental and theoretical work on reactions on the CH 3 OCH 2 OO PES with ignition delay measurements in the NTC region for DME.

Combustion and Flame, 2018

Despite the great interest in oxygenated methyl ethers as diesel fuel additives and as fuels themselves, the influence of their methylenedioxy group(s) (O-CH 2 -O) has never been quantified using ab initio methods. In this study we elucidate the kinetics and thermochemistry of dimethoxymethane using high-level ab initio (CCSD(T)/aug-cc-pV(D+T)Z//B2PLYPD3BJ/6-311++g(d,p)) and statistical mechanics methods. We model torsional modes as hindered rotors which has a large influence on the description of the thermal behavior. Rate constants for hydrogen abstraction by . . CH 3 are computed and show that abstraction from the methylenedioxy group is favored over abstraction from the terminal methyl groups. β-Scission and isomerization of the radicals is computed using master equations. The effect of rovibrationally excited radicals from preceding hydrogen abstraction reactions on subsequent hot β-scission is computed and has large influence on the decomposition of the formed dimethylether radical. In the second part of this study, the computed kinetics and thermochemistry is used in a detailed model. The quantification of the effect of the dominant methylenedioxy group using ab initio methods can guide modeling of oxygenated methyl ethers that contain that group several times.

Fuel

The oxidation of din -propyl-ether (DPE), was studied in a jet-stirred reactor. Fuel-lean, stoichiometric and fuel-rich mixtures ( = 0.5-4) were oxidized at a constant fuel mole fraction of 1000 ppm, at temperatures ranging from 470 to 1160 K, at 10 atm, and constant residence time of 700 ms. The mole fraction profiles obtained through sonic probe sampling, were analyzed by gas chromatography and Fourier Transform Infrared spectrometry. As was the case in our previous studies on ethers (diethyl ether and din -butyl ether), the carbon neighboring the ether group was found to be the most favorable site for H-abstraction reactions and the chemistry of the corresponding fuel radical drives the overall reactivity. The fuel concentration profiles indicated strong low-temperature chemistry. A kinetic submechanism is developed based on similar rules as the other two symmetric ethers investigated. The proposed mechanism shows good performances in representing the present experimental data, nevertheless, more data such as atmospheric pressure speciation will be needed in order to better interpret the kinetic behavior of DPE.