therefore a shorter reactor than in the low recycle ratio case above the higher recycle ratio also provides the stability of operating clearly within the bubble flow regime throughout the length of the reactor thus the flow regime map can be used to optimize the hydrodynamic performance of a traditional fixed bed reactor with a recycle by plotting conditions for various values of key variables and selecting those with a suitable hydrodynamic performance in this example conditions have been selected to be within the bubble flow regime however in other examples it might be desirable to operate the process to be within another flow regime such as the pulsing flow regime or even at or near a regime boundary the desired flow regime will be selected based on the desired properties of the process and the map used to ensure that the process falls within the selected regime turning now to the tail section 2 the tail section 2 in fig1 comprises a single fixed bed reactor 31 operating in once through mode very high conversion in the tail reactor 31 can produce a product that can be marketed as u201c phthalate free u201d an adiabatic fixed bed reactor may be referred to as a plug flow reactor pfr a pfr operated in recycle mode is known to approximate a continuously stirred tank reactor cstr for high recycle rates see for example carberry jj chemical and catalytic reaction engineering 1976 mcgraw hill inc chap 3 pp 95 furthermore it is known that a once through pfr requires less volume to achieve the same conversion as.