Mitigation of Fouling from Vinyl Acetate Recycle to Ethylene Plant

摘要

Equistar Chemical Company’s ethylene plant located in Clinton, Iowa, receives apurge stream from the adjacent polyethylene unit. This purge stream, which is returned tothe quench tower, contains vinyl acetate (VA). The VA, which is used as a comonomer in thepolyethylene unit, polymerizes in the presence of excess caustic to form aldol polymer thatcontributes to fouling in the caustic tower. In addition, there is the energy cost associatedwith reprocessing the ethylene in the purge stream. A VA recovery system in the polyethyleneunit, which was not performing as expected, and a chemical (antipolymerant) injection systemin the ethylene unit were in place to treat the fouling problem.In order to reduce the operating cost of the fouling problem, the VA recovery system wasmodified. The demisters in the knockout drums in the VA recovery system were replaced witha more efficient material, reducing the amount of VA being returned to the caustic tower byapproximately two thirds, and therefore allowing a considerable drop in chemical usage.Implemented in April, 2009, this change is realizing a reduction in chemical treatment costbased on the lower amount of VA contained in the recycle stream, which paid for the projectafter one month.