The present disclosure provides methods and systems for introducing an activator to a polymerization reactor. The methods may include introducing liquid activator to a mixing vessel or an inline mixer and mixing aliphatic hydrocarbon solvent to form an activator solution which is introduced to a polymerization reactor. The systems may include a storage vessel, a mixing vessel or inline mixer configured to mix a liquid activator with a hydrocarbon solvent, and a polymerization reactor. The present disclosure also provides a process for producing a polyolefin. The process may include introducing liquid activator to an inline mixer and mixing an aliphatic hydrocarbon solvent with the liquid activator to form an activator solution. The process may include introducing the activator solution, a catalyst, and an olefin feed to a polymerization reactor.