Abstract: The present disclosure is directed to an improved mass-transfer column, the column comprising a plurality of trays and associated downcomers, wherein at least one of the downcomers comprises an upstream and downstream end, as defined by the direction of flow of liquid through the column, the upstream and downstream end each having an opening defined by a plurality of walls, wherein each of the walls extend substantially entirely between the upstream opening and the downstream opening, and wherein at least one of the walls has at least two sections, a first section of the wall forming an angle ? with a plane parallel to the associated tray, and a second section of the wall, which forms an angle ? with a plane parallel to the associated tray, wherein said second section is downstream from the first section, and ?<?.