Abstract: The separation efficiency of a representative sheet metal structured packing (Mellapak 350Y) in experimental columns (0.15m i.d.) is presented at high-pressure and total reflux distillation conditions. N -butane and n-pentane is used as the testing system.Pressures span the range of 0.7-1.9MPa.With the increase of F -factor,the HETP values decrease slightly in the loading area at all test pressure but increase before flooding point.By comparing the experiment data with the predictions of SRP model,it is found that SRP model performance deteriorates at a high pressure.