Regions of attainable particle sizes in continuous and batch crystallization processes

Abstract

Process alternatives for continuous crystallization, i.e., cascades of mixed suspension, mixed product removal crystallizers (MSMPRCs) and plug flow crystallizers (PFCs), as well as batch crystallizers are discussed and modeled using population balance equations. The attainable region approach that has previously been used in the design of chemical reactor networks and separation systems is applied to the above-mentioned alternatives for crystallization processes in order to identify attainable regions in a diagram of mean product particle size vs. total process residence time. It is demonstrated that the boundaries of these attainable regions can be found numerically by solving appropriate optimization problems and that the region enclosed by these boundaries is fully accessible. Knowing the attainable region of particle sizes, it is possible to generate feasible process alternatives that allow specific particle sizes to be obtained in a given process configuration. The attainable regions presented in this article are useful to determine whether a desired mean particle size can be achieved in a specific crystallizer type. The concept of the attainable region is illustrated on three case studies: the cooling crystallization of paracetamol grown from ethanol, the anti-solvent crystallization of L-asparagine monohydrate from water using isopropanol as the anti-solvent and the combined cooling/anti-solvent crystallization of aspirin from ethanol using water as the anti-solvent.

Mathematical modelling and experimental validation of a novel periodic flow crystallization using MSMPR crystallizers

“…3,4 Generally, there are two types of continuous crystallizers that are most investigated, viz., the tubular and the stirred-tank designs. 5 Regardless of recycling, these two designs help to achieve idealised flow patterns, namely the plug-flow 6 and the mixed-suspension mixed-product removal (MSMPR)…”

Particle Size Distribution and yield control in continuous Plug Flow Crystallizers with recycle

“…Using a similar approach of Vetter et al (2014) to illustrate the attainable regions for the volume average size of crystals in continuous processes, it was possible to study the maximum yield and d 4,3 as a function of the overall residence time τ = L C /<u> x,0 inside the PFC. The yield and the volume average size of particles were studied by adjusting the extraction point for the recycle flow from 0 % to 100 % of the total length of the PFC and using a recycle ratio between 0 and 1, keeping constant the remaining operating parameters such as the feed concentration (C 0 ) and temperature.…”

Crystal shape and size control using a plug flow crystallization configuration

“…However, due to the presence of back-mixing, which is commonly modeled by employing the residence time mixing model, those crystals nucleated at a later stage during the crystallization process will reside a relatively short amount of time in the crystallizer and thus they will end up leaving the crystallizer with undesired size and shape distributions (Kwon et al, 2014). To this end, plug flow crystallizer (PFC) has been proposed to produce crystals with narrow size and shape distributions (Eder et al, 2011;Vetter et al, 2014).…”