And, after the first catalytic bed, {TAIL ~ the reaction mixture} passes through {HEAD ~ at least one subsequent bed} to promote the other hydroconversion reactions 
And , after the first catalytic bed , { TAIL ~ the reaction mixture } passes through { HEAD ~ at least one subsequent bed } to promote the other hydroconversion reactions
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH