N. Ghadipasha

First Steps towards Online Optimal Control of Molecular Weight in Batch and Semi-batch Free-Radical Polymerization Reactors

Abstract This paper discusses the first steps towards the formulation and implementation of a generic and flexible model centric framework for integrated simulation, estimation, optimization and feedback control of polymerization systems. Off-line capabilities of the framework were fully tested experimentally for model validations, parameter estimation as well as for process optimization using the Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP). A brief analysis on the controllability of the system under feedback conditions was also performed through a combination of simulation and experimental runs. Results are provided for free radical solution polymerization of methyl methacrylate system (MMA).

A real time particle size control framework in non-isothermal antisolvent crystallization processes

Abstract This paper focuses on the design and implementation of on-line optimal control strategies of crystal properties for non-isothermal antisolvent crystallization processes. The one-dimensional Fokker-Planck equation (FPE) is used to represent the dynamic characteristics of the crystal growth and to generate iso-mean and iso-standard deviation curves. Using controllability tools it is shown that the system is ill conditioned in the operational range, posing limitations on the achievable control performance. A novel digital image texturing analysis approach is implemented to track crystal’s size distribution along the experiment, thus providing the on-line information for further feedback control action. Subsequently, alternative control strategies are implemented and tested to achieve a desired crystal size distribution (CSD).

Online DEKF for State Estimation in Semi-Batch Free-Radical Polymerization Reactors

Abstract In this work, a dynamic filter for nonlinear systems is implemented for on-line sate estimation, dynamic data reconciliation, molar mass distribution (MMD) monitoring, and feedback control of polymerization processes. A discrete-time extended Kalman filter (DEKF) is designed for a free-radical polymerization reaction that synthetizes polyacrylamide using potassium persulfate as initiator in a semi-batch reactor. For improving the performance of the filter, its free parameters are tuned using a metaheuristic technique. The Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) is used for obtaining online measurement values in various experiments. Total moles of monomer, initiator and solvent and the corresponding moments of the dead polymers are estimated by the DEKF using weight average molecular weight, monomer concentration and reactor volume as real-time measurements. State estimation permits to estimate polymer properties that cannot be measured directly while reconciling measured values. A tailor made filter/controller module is formulated and implemented in Python environment supporting multiple programming paradigms such as object-oriented and functional programming styles.

A deterministic formulation and on-line monitoring technique for the measurement of salt concentration in non-isothermal antisolvent crystallization processes

A complete framework to measure and anticipate the salt concentration during crystallization process is presented. On-line monitoring of the solute concentration based on conductivity of the solution is implemented. The conductivity of the dissolved compound is dependent on its concentration in the solvent and temperature. Therefore, a calibration test is applied and an experimental exponential model of concentration as a function of conductivity is developed in the whole operating range of antisolvent feed rate and temperature. A deterministic model which can predict the behaviour of the amount of salt with respect to the crystal growth parameter is introduced. To validate the model and assess the merits of the proposed strategy, the crystallization of sodium chloride in water using ethanol as antisolvent is performed in an experimental bench-scale semi-batch crystallizer.