In this study, we first report the development of a robust and efficient finite volume based adsorption process simulator, essential for rigorous optimization of a transient cyclic operation without resorting to any model reduction. We present a detailed algorithm for the common boundary conditions encountered in nonisothermal and nonisobaric adsorption process simulations. A comprehensive comparison of the high-resolution total variation diminishing (TVD) schemes, namely, van Leer and Superbee, with the weighted essentially nonoscillatory (WENO) finite volume scheme is performed, and trade-off plots are presented to identify the numerical scheme most suitable for attaining speed and accuracy at the same time. The simulator is then used to perform rigorous optimization of a four-step process for postcombustion CO2 capture from dry flue gas on zeolite 13X. The aim is to identify operating conditions at which the purity and recovery demands are met and to calculate corresponding energy consumption and process productivity. The purity–recovery and energy–productivity Paretos are generated using multiobjective optimization. It is shown that, for a strict vacuum swing adsorption (VSA) process, an evacuation pressure of 0.02 bar is required to satisfy regulatory demands of attaining a CO2 purity and recovery of 90%. It is also quantitatively shown that pressurizing the flue gas is detrimental to the energy consumption of process, although offering improvement in productivity.

Crystallization is a major separation process in the pharmaceutical industry. Most crystallizations are performed batchwise, but there is great incentive for converting them to continuous operations. This paper investigates the modeling, simulation, and optimization of a special antisolvent plug-flow crystallizer: the multisegmented, multiaddition plug-flow crystallizer (MSMA-PFC). The MSMA-PFC accepts multiple antisolvent flows along its length, permitting finer control of supersaturation. A steady-state population balance equation was applied for tracking the crystal size distribution, and a mass balance equation was used to track the depletion of dissolved solute (flufenamic acid). A multiobjective optimization framework was applied to determine the antisolvent flow rates into each segment that simultaneously maximize the average crystal size, and minimize the coefficient of variation. The set of coupled differential equations was solved, depending on circumstance, with either the method-of-moments (MOM), or the high-resolution finite-volume (FV) method. The significant nonconvexity in the objective functions motivated the use of the nondominated sorting genetic algorithm (NSGA-II) to calculate the Pareto frontiers for the two competing objectives. It was found that the optimal antisolvent profile provides better product crystals, compared to the cases with equal additions of antisolvent in 1−4 injection points by keeping the total amount of antisolvent the same. The sensitivity of the Pareto frontier to variation in the growth and nucleation kinetic parameters was investigated. In addition, a novel simultaneous design and control (SDC) approach was proposed, based on the optimization of the full crystallizer design, over not only antisolvent profile, but also the number of injections and total crystallizer length, providing the best crystallization design that can allow optimal product performance in conjunction with the multiaddition control approach.

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Encrustation, also known as fouling or scale formation, on the wall of plug flow crystallizers (PFC) can cause major operational and economic problems in pharmaceutical industries. These include increased energy requirements due to increment of thermal resistance and pressure drop, and clogging of the crystals due to reduction of flow area. In this work, a mathematical model for predicting the dynamic behavior of a PFC undergoing encrustation is presented. This model describes the formation of encrust layer by considering various mechanisms such as rate of solute transport from bulk to the wall, integration and removal due to shear stress induced by fluid turbulence. A population balance model for describing the crystallization process in the PFC is also coupled with the encrustation model in order to obtain the appropriate concentration profile in the PFC as well as product crystal size distribution (CSD). Based on this model, a mitigation strategy is proposed that relies on injection of pure solvent to dissolve the encrust layer.

. Multiimpurity adsorption model for modeling crystal purity and shape evolution during crystallization processes in impure media.Crystal Growth and Design, 16(2), pp. 555-568.Additional Information:•

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High-resolution (HR) finite-volume methods can provide an accurate numerical solution of population balance equations describing crystallization processes. To satisfy the stability requirements, the time step (Δt) for the available HR methods needs to be selected conservatively, rendering them computationally expensive for processes with size-dependent growth rates. In this paper, we propose a coordinate transformation scheme to improve the solution time of HR methods applied to batch crystallization processes with nucleation and size-dependent growth. The coordinate transform takes advantage of the functional form that is used to describe the size dependency of the growth rate. Using benchmark examples, we demonstrate that the proposed method provides a more significant reduction in the solution time than existing HR methods, while retaining the same level of accuracy.

The separation of enantiomers is of great importance due to their possible differences in therapeutic properties. Preferential crystallization in various configurations of coupled batch crystallizers is used as an attractive means to separate the conglomerate-forming enantiomers from racemic mixtures. However, the productivity of such batch processes can be limited by the nucleation of the counter enantiomer and consumption of the supersaturation. In this work, a recently proposed process configuration, which uses coupled mixed suspension mixed product removal (MSMPR) with liquid phase exchange, is investigated by simulation studies. A detailed study on the effect of process parameters (e.g., feed flow rate, seed mass, and liquid phase exchange) on the productivity and yield of the coupled MSMPR has been presented. Moreover, a comparison of various coupled crystallizer configurations is carried out. It is shown through simulation studies that the productivity of the enantiomeric separation can be significantly improved compared to the previously proposed batch modes when the continuous configuration is used. The effect of nucleation kinetic parameters on the performances of various crystallizer configurations is studied as well. A set of coupled population balance equations (PBEs) was used to describe the evolution of the crystal phase of the both enantiomers in each vessel. These equations were solved numerically using the quadrature method of moments. The insights obtained in this study will be useful in the process design of coupled crystallizer systems.