Ab initio calculations and kinetic modeling of thermal conversion of methyl chloride: implications for gasification of biomass

Abstract

Limitations in current hot gas cleaning methods for chlorine species from biomass gasification may be a challenge for end use such as gas turbines, engines, and fuel cells, all requiring very low levels of chlorine. During devolatilization of biomass, chlorine is released partly as methyl chloride. In the present work, the thermal conversion of CH3Cl under gasification conditions was investigated. A detailed chemical kinetic model for pyrolysis and oxidation of methyl chloride was developed and validated against selected experimental data from the literature. Key reactions of CH2Cl with O2 and C2H4 for which data are scarce were studied by ab initio methods. The model was used to analyze the fate of methyl chloride in gasification processes. The results indicate that CH3Cl emissions will be negligible for most gasification technologies, but could be a concern for fluidized bed gasifiers, in particular in low-temperature gasification. The present work illustrates how ab initio theory and chemical kinetic modeling can help to resolve emission issues for thermal processes in industrial scale.

Theoretical and kinetic modeling study of chloromethane (CH3Cl) pyrolysis and oxidation

“…The mechanism thus obtained was tested against a wide set of experimental data, providing good agreement and improving the performances reported in Ref. 13. The model was used to highlight the chemical reasons behind the promoting effect of CH 3 Cl on methane ignition, and its inhibition effects on laminar flame speeds.…”

“…Differently from previous theoretical studies, both spin‐orbit corrections and pressure dependence where explicitly accounted for, allowing satisfactory agreement with fundamental rate constant measurements. In addition, the rate constants of 13 H‐abstraction reactions that were highlighted to be relevant in our preliminary model 13 were computed using AI‐TST‐ME methods. Even in this case our determinations agree very well with the available experimental data, with maximum deviations of a factor of 2.5.…”

“…The kinetic mechanism and thermodynamic and transport properties in CHEMKIN format are attached in the Supporting Information. Detailed references 10,55,64–91 to the source of the kinetic parameters that have not been determined in the current nor in our previous study on CH 3 Cl 13 are provided alongside the kinetic mechanism.…”

“…presented a state‐of‐the‐art kinetic model of the high‐temperature chemistry of HCl and Cl 2 and analyzed the effect of chlorine species on laminar, premixed hydrogen, and syngas flames. The underlying HCl/Cl 2 chemistry was adopted recently for the development of a preliminary CH 3 Cl model for specific application to biomass gasification processes 13 . In this previous work, the role of key reactions steps such as ĊH 2 Cl + O 2 and ĊH 2 Cl + C 2 H 4 was highlighted, and rate coefficients determined with ab initio methods.…”

“…The underlying HCl/Cl 2 chemistry was adopted recently for the development of a preliminary CH 3 Cl model for specific application to biomass gasification processes. 13 In this previous work, the role of key reactions steps such asĊH 2 Cl + O 2 andĊH 2 Cl + C 2 H 4 was highlighted, and rate coefficients determined with ab initio methods.…”