we do single pass bottom flooding and it works great...we utilize the pressure of a 125# room temp tank pushed thru a heat exchanger and generally do 3x the initial flood time then dump....best way to get a -40c bottom flood for 4" ers to flow. With tank pressure assist it takes about 60-90 seconds to fill a 4" column
So you flood / soak for 6 mins from the time the column is completely filled, then dump the column and reclaim, for a total exposure time of 7.5 minutes of solvent and material?
Does your yield change if you allow for a longer single pass?