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