Toward a comprehensive mechanism for methanol pyrolysis

Abstract

A single kinetic mechanism for methanol pyrolysis is tested against multiple sets of experimental data for the first time. Data are considered from static, flow, and shock tube reactors, covering temperatures of 973 to 2000 K and pressures of 0.3 to 1 atmosphere. The model results are highly sensitive to the rates of unimolecular fuel decomposition and of various chain termination reactions that remove CHzOH and H radicals, as well as to experimental temperature uncertainties. The secondary fuel decomposition reaction CH,OH = CH,OH + H. which has previously been included only in mechanisms for high temperature conditions, is found to have a significant effect a t low temperatures as well, through radical recombination. %'he reaction CH,O 4 C = CH3 + C 0 2 , rather than CHIOH + H = CH,? t H20, is found to be the dominant source of CH3 a t low temperatures. The reverse of CH, + OH = CH,OH T H is important to CHs production at high temperatures.

A comprehensive mechanism for methanol oxidation

“…The same authors expanded upon their previous work to develop a comprehensive model for methanol pyrolysis [2]. Although not an oxidation mechanism, many of the important reaction paths in high-temperature oxidation are identical to those found in pyrolysis studies as well.…”

“…Considerable importance was placed upon the dehydration reaction CH OH ϩ OH ϭ CH ϩ H O 3 3 2 as a source of methane and C 2 hydrocarbons. Later work [2] has indicated that this reaction route is negligible, and other sources are sufficient to account for experimental methane and C 2 species measurements. The effects of pressure-dependent reactions were not included in this early modeling effort.…”

On the Composition of Young, Directly Imaged Giant Planets

“…Note that we do not include the fast rate coefficient for H + CH 3 OH  CH 3 + H 2 O suggested by Hidaka et al (1989) that is controlling CO-CH 4 quenching in the Venot et al (2012) mechanism. As discussed by Norton & Dryer (1990), Lendvay et al (1997), and Moses et al (2011), this reaction actually possesses a very high energy barrier (>10,000 K) and is not expected to be important under either methanolcombustion conditions or in the deep atmospheres of hydrogen-rich exoplanets-in other words, the Hidaka et alrate coefficient greatly overestimates the rate of this reaction. Zahnle & Marley (2014) adopt the upper limit for this reaction as suggested by Norton & Dryer (1989) and find it to be important but not typically dominant in CO-CH 4 quenching, except for cooler brown dwarfs with weak mixing.…”

“…The rate-limiting step in the above scheme is the reaction CH OH 3 + M  CH 3 + OH + M, where the rate coefficient is derived from the reverse reaction from Jasper et al (2007). Our chemical model differs from some others in the literature (e.g., Venot et al 2012;Zahnle & Marley 2014) in that we adopt a slower rate coefficient for H + CH OH (1997), and the discussion of relevant experimental data in Norton & Dryer (1990). However, the rate coefficient for this reaction adopted by Zahnle & Marley (2014) and Zahnle et al (2016) is slow enough that CH OH 3 + M  CH 3 + OH + M is usually faster, and hence their quench results are not greatly different from those described here.…”

Implementation of a variational code for the calculation of rate constants and application to barrierless dissociation and radical recombination reactions: CH3OH = CH3 + OH

“…The use of alcohols as fuels for internal combustion engines has been considered a promising renewable energy resource and considerable attention has been given to methanol reactions as it is an important alternative fuel. Theoretical calculations and experimental works aiming for the thermal decomposition of CH 3 OH are available in the literature [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] although new investigations of the elementary reactions have been encouraged, specially the unimolecular dissociation (Reaction I), which appears as the main important step in the thermal decomposition kinetic model. [26] The main goal of this article is to evaluate the implementation of the canonical variational TST in the kcvt program, as well as to investigate the calculation of rate constants within different models for treating low vibrational frequencies and their contribution for the reaction dynamics.…”