Kinetics of the reaction of CH4 gas with liquid iron

In iron bath smelting and other processes that use coal, the effective use of volatile matter can improve the energy efficiency of the process. The reaction of simulated volatile (CH₄) with iron was studied. The rate of carburization of liquid iron by CH₄ gas was measured between 1400 °C and 1700 °C under conditions for which the effect of mass transfer can be corrected with reasonable accuracy. The rate was measured for partial pressures of CH₄ in Ar in the range of 0.02 to 0.06 atm and sulfur contents in the metal from 0.0006 to 0.5 mass pct. The results indicate that the rate of carburization may be controlled by the dissociation of CH₄ on the surface. Sulfur was found to decrease the rate, and the residual rate phenomenon was observed for high sulfur contents. The rate constant may be represented by the following equation: $$ k_C = \frac{{k^\circ }}{{1 + K_S a_S }} + \frac{{K_S a_S k_r }}{{1 + K_S a_S }}$$ wherek ^o ,k _r,K _s, anda _s are the bare surface rate constant, residual rate constant, adsorption coefficient for sulfur, and activity of sulfur in the metal, respectively. The second term in the rate equation represents the rate of dissociation on the adsorbed sulfur. The rate constants and adsorption coefficient were determined as functions of temperature to be $$\begin{gathered} log k^\circ = \frac{{ - 12,000}}{T} + 2.95 (mole/cm^2 s atm) \hfill \\ log k_r = \frac{{ - 14,000}}{T} + 3.45 (mole/cm^2 s atm) \hfill \\ log K_S = \frac{{ - 1800}}{T} + 1.04 \hfill \\ \end{gathered} $$