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