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