Methods and apparatus relate to processing of petroleum with a bed having a sorbent based diluent that the petroleum contacts upon passing through the bed. Magnetic properties of the sorbent and any other material, such as zeolite, used in the bed enable separation of such bed constituents based on a sulfided form of the sorbent being magnetic in contrast to a non-sulfided form of the sorbent being non-magnetic. Dividing the bed constituents into first and second portions by magnetic separation facilitates in selective replacing and/or regenerating the first portion independent of the second portion.