Abstract: The pressure dependence of partial molar volumes was calculated in detail by RK equation of state for the dehydrogenation of dodecane to internal dodecane.The results showed that clustering between supercritical medium and internal dodecane and hydrogen was much stronger in supercritical phase than in gas phase,and that,clustering between supercritical medium and the reaction products was more remarkable.This provided a quantitative description of the change in cluster size resulted by an increase in solutesolvent attraction force.

Key words: Supercritical phase, Partial molar volume, Clustering