Process improvements in selective ethylene oligomerizations

A process comprising:

• introducing a catalyst system to a reaction zone, the catalyst system comprising 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;
• introducing an ethylene feedstock mixture to the reaction zone separately from the catalyst system, the ethylene feedstock mixture comprising ethylene and at least a portion of an organic reaction medium, wherein the ethylene feedstock mixture is substantially free of the catalyst system;
• optionally introducing hydrogen to the reaction zone;
• and
• contacting the catalyst system and the ethylene feedstock mixture in the reaction zone to form an oligomer product,
• wherein:
• A) a mass of polymer per mass of oligomer in the reaction zone is less than a mass of polymer per mass of oligomer in the reaction zone of an otherwise similar process which does not:
• i) contact ethylene with the at least a portion of the organic reaction medium prior to contact of ethylene with the catalyst system, and ii) introduce or feed the ethylene feedstock mixture into the reaction zone separately from the catalyst system,
• or
• B) the process has a productivity greater than a productivity in an otherwise similar process which does not:
• i) contact ethylene with the at lea a portion of the organic reaction medium prior to contact of ethylene with the catalyst system, and ii) introduce or feed the ethylene feedstock mixture into the reaction zone separately from the catalyst system.