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The issues regarding the design and implementation of on-line optimal control strategies of crystal properties in nonisothermal antisolvent crystallization processes to control particles' mean size and standard deviation are dealt. The one-dimensional Fokker-Planck equation is used to represent the dynamic characteristics of the crystal growth and generate iso-mean and iso-standard deviation curves. Using controllability tools it is demonstrated that the system is ill conditioned in the whole operational range, posing limitations on the achievable control performance. To circumvent the problem, a control strategy is formulated by pairing crystals' mean size with antisolvent feed rate and manipulating temperature to control the standard deviation. A novel digital image-texturing analysis approach is discussed and implemented to track crystals' size distribution along the experiment and 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. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2188-2201, 2015 [ABSTRACT FROM AUTHOR]

A new formulation of the recent stochastic approach for the description of the particle-size distribution (PSD) time evolution in antisolvent crystal-growth processes is presented. In this new approach, the crystals size is modeled as a random variable driven by a Gompertz growth term and the corresponding Fokker-Planck equation is carried out. This proposed formulation, allows an analytical solution to describe the time evolution of the PSD as a function of the model parameters. The analytical solution is obtained by exploiting the typical properties of linear partial differential equations with linear coefficients, and using the analogy with Kalman filter, in terms of the first two stochastic moments: mean and variance of the PSD. Furthermore, an alternative way for the parameters estimation based on the maximum likelihood estimation is also introduced. Validations against experimental data are provided for the NaCl-water-ethanol antisolvent crystallization system. © 2012 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

Abstract: A multi-variable model predictive control (MPC) was formulated to solve control problems associated with a combination of regulation and targeting desired set-points. We investigated the simultaneous control of key polymer properties: the particle size (PSD) and molecular weight distribution (MWD) by manipulating the flow rates of the monomers (styrene, MMA), surfactant, initiator and the temperature of the reactor. A multi-input–multi-output (MIMO) formulation was constructed for the constrained optimal control problem to maximize the width of the PSD (with at a constant set-point), and to maximize the average molar mass. The strategy developed within a gPROMS-API-DCS environment allowed real-time implementation of model-based control of the process. The optimal control problem was implemented via an interface to a dynamic optimization code. Major improvements in process operation and polymer property control resulted on the implementation of our multi-variable MPC algorithm. The manipulation of the four flow rates and the temperature increased the degree of freedom in the system and achieved tighter PSD and MWD control. The on-line performance of MPC for MWD and PSD control was found to be satisfactory. [Copyright &y& Elsevier]

Theeffect of the temperature on the Crystal Size Distribution(CSD) in antisolvent crystallization operation, for systems wherethe solubility is weakly dependent on the temperature, is analyzed.The hydrogen bonding properties of the solvents used that influencethe supersaturation of the solution and consequently the growth andthe nucleation dynamic can explain this effect on the CSD. To verifyand quantify these effects, experiments were conducted and the Fokker–Planckmodeling equations were used to obtain the quantifying parameters(growth velocity, the asymptotic mean size, and the diffusivity).Results are provided through investigations into the nonisothermalantisolvent crystallization of sodium chloride (NaCl), in which thesolubility is practically independent of temperature for the rangeof operating conditions considered. [ABSTRACT FROM AUTHOR]