Propylene, {HEAD ~ oxygen}, and hydrogen are preferably fed to {TAIL ~ the reactor} at or near the bottom of the reactor 
are preferably fed to
Propylene , { HEAD ~ oxygen } , and hydrogen are preferably fed to { TAIL ~ the reactor } at or near the bottom of the reactor
OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH