<p>A flow distribution apparatus located above the top-most bed of solid particles in an adsorbent vessel of a simulated moving bed adsorptive separation process having a vertical axis having a lower boundary substantially perpendicular to the vertical vessel axis. A top grid plate defines a lower volume between the top grid plate and a lower fluid distributing boundary. A passageway having walls through the top grid plate provides fluid communication between (a) an inlet pipe having a diameter and a central axis parallel to the vertical vessel axis and (b) the lower volume. A perforate distribution plate provides fluid communication between the inlet pipe and the lower volume, has an imperforate area to reduce vertical momentum of the fluid, and has perforations sized and spaced apart to achieve a pressure drop across the distribution plate sufficient to adequately diffuse the incoming flow from the inlet pipe.</p>
