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