Most kinetic studies of catalytic steam reforming of individual hydrocarbons have shown that the reaction products are carbon monoxide

carbon -dioxide

methane and hydrogen only

and the conversion rate equation of different hydrocarbons can be expressed in the same form but the rate constants are different. In addition

the water gas shift reaction is assumed to be at equilibrium in the reaction processes. In order to simulate catalytic steam reforming of naphtha

a relative reaction rate constant a

which is the ratio of the rate constant of species i to that of the reference species

was proposed. The value of a is used to distinguish a species from the others. When many hydrocarbons have the same value of a

they may be lumped as a psudospecies. Two continuous distribution functions D (a) and yo(a) were defined for naphtha. D(a) is called as species distribution function and y0(a) is the composition distribution function of naphtha. In this paper gamma distribution function was applied to represent D(a) and yo(a). The parameters of these distribution functions were estimated by use of the experimental results. If the activation energies of the hydrocarbons are the same

both D(a) and yo(a) do not depend upon the reaction temperature. The lumped kinetic model suggested fits with the experimental results satisfactorily.