Process control system

In a process for the continuous production of polymer according to which the molten polymer flows continuously in a cascade system of successive polymerizer vessels from an outlet of a lower polymerizer vessel to the inlet for a higher polymerizer vessel, the improvement of controlling intrinsic viscosity of the polymer comprising the steps of:

• establishing as a set point a magnitude of a meaningful operating condition within the lower polymerizer vessel so as to achieve an optimum value of viscosity of the polymer at the outlet from the vessel;
• continuously measuring a first value of melt viscosity of the polymer at the outlet from the lower polymerizer vessel;
• periodically adjusting the magnitude of the meaningful operating condition within the lower polymerizer vessel about the set point according to short discrete time interval deviations occurring in the first value of melt viscosity;
• periodically measuring deviations occurring during an extended time interval in second values of melt viscosity of the polymer at a location distance from the immediately preceding vessel and adjacent the inlet to the next succeeding higher polymerizer vessel;
• and
• periodically resetting the set point when the second values of melt viscosity continue to deviate from the set point by a predetermined amount.

In a process for the continuous production of polymer according to which the molten polymer flows continuously from an outlet of a polymerization zone to an operating station downstream from the vessel, the improvement of controlling intrinsic viscosity of the polymer comprising the steps of:

• establishing as a set point a magnitude of a meaningful operating condition within the polymerization zone so as to achieve an optimum value of viscosity of the polymer at the outlet from the vessel;
• continuously measuring a first value of melt viscosity of the polymer at the outlet from the polymerization zone;
• periodically adjusting the magnitude of the meaningful operating condition within the polymerization zone about the set point according to short discrete time interval deviations occurring in the first value of melt viscosity;
• periodically measuring deviations occurring during an extended time interval in second values of melt viscosity of the polymer at a location adjacent to the operating station;
• and
• periodically resetting the set point when the second values of melt viscosity continue to deviate from the set point by a predetermined amount.