Partial combustion of natural gas is of great popularity in coproducing acetylene and syngas. Instead of macrokinetics, detailed chemistry modeling is performed to describe fuel-rich methane and ethane flames by using two typical combustion mechanisms: GRI-Mech 3.0 and Curran mechanism. A large uncertainty is found in the rate coefficient of C2H2 + OH CH2CO + H in GRI-Mech 3.0. A more chemically sound rate coefficient expression is proposed and GRI-Mech 3.0 and Curran mechanism are optimized for predicting acetylene profiles in the laminar premixed flames. Major species profiles in the flames are also calculated and compared with experimental data in the literature. The industrial partial combustion process is reasonably predicted by using the new rate coefficient within the framework of GRI-Mech 3.0. The optimum equivalence ratio is determined for attaining the maximum acetylene yield.