Control of polymer molecular weight using near infrared spectroscopy

Near Infrared spectroscopy is used to control a polymerization reactor in order to produce solution polymers with well-defined molecular weight. A model for the monitoring of both the average polymer molecular weight, and the concentration of monomer in the reactor is developed with the partial least-squares calibration technique applied to the NIR spectra. On the basis of a process model, a nonlinear input-output linearizing geometric approach is then applied to control the polymer molecular weight by manipulating the inlet flow rate of the monomer. The control strategy is then validated on-line during the solution polymerization of acrylic acid in an industrial pilot scale reactor. (C) 2004 American Institute of Chemical Engineers.