Thermal Decomposition and Oxidation of CH₃OH

Abstract

Thermal decomposition of CH(3)OH diluted in Ar has been studied by monitoring H atoms behind reflected shock waves of 100 ppm CH(3)OH + Ar. The total decomposition rate k(1) for CH(3)OH + M → products obtained in this study is expressed as, ln(k(1)/cm(3) molecule(-1) s(-1)) = -(14.81 ± 1.22) - (38.86 ± 1.82) × 10(3)/T, over 1359-1644 K. The present result on k(1) is indicated to be substantially smaller than the extrapolation of the most of the previous experimental data but consistent with the published theoretical results [Faraday Discuss. 2002, 119, 191-205 and J. Phys. Chem. A 2007, 111, 3932-3950]. Oxidation of CH(3)OH has been studied also by monitoring H atoms behind shock waves of (0.35-100) ppm CH(3)OH + (100-400) ppm O(2) + Ar. For the low concentration CH(3)OH (below 10 ppm) + O(2) mixtures, the initial concentration of CH(3)OH is evaluated by comparing evolutions of H atoms in the same concentration of CH(3)OH with addition of 300 ppm H(2) diluted in Ar. The branching fraction for CH(3)OH + Ar → (1)CH(2) + H(2)O + Ar has been quantitatively evaluated from this comparative measurements with using recent experimental result on the yield of H atoms in the reaction of (1,3)CH(2) + O(2) [J. Phys. Chem. A 2012, 116, 9245-9254]; i.e., the branching fraction for the above reaction is evaluated as, φ(1a) = 0.20 ± 0.04 at T = 1880-2050 K, in the 1.3 and 3.5 ppm CH(3)OH + 100 ppm O(2) samples. An extended reaction mechanism for the pyrolysis and oxidation of CH(3)OH is constructed based on the results of the present study combined with the oxidation mechanism of natural gas [GRI-Mech 3.0]; evolution of H atoms can be predicted very well with this new reaction scheme over a wide concentration range for the pyrolysis (0.36-100 ppm CH(3)OH), and oxidation (0.36-100 ppm CH(3)OH + 100/400 ppm O(2)) of methanol.

Experimental and theoretical studies on the reaction of H atom with C3H6

“…Details have been described in our previous papers, 21,[36][37][38] Briefly, the evolution of H atom was monitored by using an atomic-resonance absorption-spectrometry (ARAS) system at transition 2 P 1/2 -2 S 1/2 of H at 121.6 nm generated in a microwave discharge lamp using a flowing gas mixture of 1% H 2 diluted in He. Experiment was conducted behind reflected shock waves in a diaphragm-less shock tube (length 5.9 m and internal diameter 76 mm; remarks of diaphragm-less shock tube are shown in ESI).…”

­­Chemical reaction mechanisms accompanying pulsed electrical discharges in liquid methanol

“…The primary chemical reactions in methanol plasmas responsible for these products are assumed to take place via electron excitation and electron impact dissociation both of which require energies below 10 eV and result in the dissociation of CH, OH, and CO bonds. Concurrently, very high temperatures (1000 K and higher) that are characteristic of streamer‐like plasmas enable thermal decomposition of molecules . Regardless of the driving force, both thermal and electronic processes undergo identical initial methanol decomposition channels …”

“…Concurrently, very high temperatures (1000 K and higher) that are characteristic of streamer‐like plasmas enable thermal decomposition of molecules . Regardless of the driving force, both thermal and electronic processes undergo identical initial methanol decomposition channels …”

Theoretical study on the reactions of C2H5 with CnH2n+1OH (n = 1 - 4): Predicted rate constants and branching ratios

“…The favorable characteristics of C n H 2n+1 OH (n = 1-4) have led to an increasing number of studies investigating theirs use as a transportation fuel. Speci cally, there are many papers concerned C n H 2n+1 OH (n = 1-4) such as determining the structure of the molecules, vibrational frequencies, and heats of formation [10][11][12]; both experimental and theoretical papers concerning thermal decompositions of C n H 2n+1 OH (n = 1-4) at high-temperatures in the internal engines via combustion [13][14][15][16][17][18][19], or their reactions with various atoms and radicals existed in combustion gas, such as H, OH, CH 3 , etc [20][21][22][23][24][25][26][27][28][29][30][31]. The experimental studies by different techniques report their branching ratio and total rate constants at some speci c conditions while the theoretical studies proposed the mechanisms and kinetics results at wide-range conditions, especially experimental di culty in evaluating the branching fractions mainly arises from the contributions of the secondary reactions.…”