Investigation and improvement of the kinetic mechanism for methanol pyrolysis

Due to the shortage of fossil energy and its pollutants emission, the utilization of alcohol fuel by pyrolysis and combustion has attracted increasing attention. However, there is still a lack of good understanding of the kinetic mechanism for accurate prediction of its combustion and pyrolysis process. In the paper, to improve the kinetic mechanism of methanol pyrolysis and combustion, an experiment was conducted to investigate methanol decomposition using a plug flow reactor (with temperature of 873-1273 K and volume flow rate of 4.4-34.2 ml/s) with on-line gas detection system, the reaction paths were analyzed and the intrinsic reaction kinetics of methanol decomposition was calculated with CHEMKIN. Then, the process of methanol pyrolysis was optimized, and an improved kinetic mechanism was proposed by modified the rate constant of methanol decomposition reaction, hydrogen abstraction reaction of methanol and formaldehyde based on the experimental results, and verified by the combination of calculated and experimental data. The results show that methanol starts decomposing at 910 K and reaches complete conversion at 1150 K, with major products of hydrogen, methane and carbon monoxide. Also, formaldehyde is an important intermediate species, and two dominant paths for methanol decomposition have been proposed: CH3OH → CH2O → CO and CH3OH → CH3 → CH4, which are in good agreement with that proposed by previous studies. Meanwhile, the much accurate rate constant k of methanol decomposition can be expressed as k=8.323×103(s−1)exp[−64.05(Jmol−1)/RT]. Moreover, mechanism verification indicated that the calculated result with improved mechanism is highly consistent with that of experiment detected in shock tube, especially for predicting methanol consumption and carbon monoxide fraction.