The desorption of methanol from a copper catalyst surface at a temperature of T-sys = 523 K was investigated by the Monte Carlo simulation. The model took into account the effect of n-hexane density on the desorption of methanol adsorbed on the catalyst surface. The results indicated that the methanol desorption was directly proportional to the n-hexane density in the system and the desorption amount of methanol increased with increasing of n-hexane density. The desorption increased rapidly in a linear way before the critical density of n-hexane was achieved. However, when the density went beyond the critical point, the increase rate of methanol desorption began to step down. Furthermore, the methanol desorption amount increased slightly when the density increased far from the critical point. Through studying configurations of methanol-hexane under different conditions, it was found that the phenomena were related to the local density of n-hexane around methanol and n-hexane bulk density in the solution. (C) 2004 Elsevier B.V. All rights reserved.