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