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