Phenylacetylene (PA) damages the quality of styrene. There are small amounts of PA in styrene which comes from extraction of C 8 distillate in or ethylene plant and from dehydration of ethylbenzene. There is about 34 mol/m(3) of PA in C 8 distillate in the former process and we have to reduce the concentration of PA lower than 0.10 mol/m(3) by hydrogenation over a Pd catalyst. But severe hydrogenation would convert styrene to ethylbenzene. We proposed a kinetic model for the gas and liquid upflow fixed bed differential reactor. The mass transfer coefficent of PA between the solid-liquid interface, which was observed in the experiments of the differential reactor, agreed well with the theoretical one. According to this model, larger K-phi favored higher ST selectivity. Experimental results of an integral reactor were in good accordance with the proposed model., if we introduced a backmixing model.