{HEAD ~ The H2} is separated and recycled to {TAIL ~ the alcohol synthesis zone} as a second source of H2 
is separated to
{ HEAD ~ The H2 } is separated and recycled to { TAIL ~ the alcohol synthesis zone } as a second source of H2
HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH