The catalyst, water and {HEAD ~ unreacted methanol} can be recovered and recycled back to {TAIL ~ the reaction zones} 
recovered back to
The catalyst , water and { HEAD ~ unreacted methanol } can be recovered and recycled back to { TAIL ~ the reaction zones }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL