Process Improvements In Selective Ethylene Oligomerizations

Disclosed are processes, systems, and reaction systems for the oligomerization of ethylene to form an oligomer product in a reaction zone using a catalyst system having i) a chromium component comprising an N2-phosphinyl amidine chromium compound complex, an N2-phosphinyl formamidine chromium compound complex, an N2-phosphinyl guanidine chromium compound complex, or any combination thereof, and ii) an aluminoxane. Ethylene can be contacted with an organic reaction medium to form an ethylene feedstock mixture prior to contact with the catalyst system. The ethylene feedstock mixture can be contacted with the catalyst system inside or outside of the reaction zone.