Crystallization and precipitation engineering
Introduction
Crystallization from solution is a core technology in major sectors of the chemical process and allied industries. Crystals are produced in varying sizes ranging from as small as a few tens of nanometres to several millimetres or more, both as discrete particles and as structured agglomerates. Well-established examples include bulk and fine chemicals and their intermediates, such as common salt, sodium carbonate, zeolite catalysts and absorbents, ceramic and polyester precursors, detergents, fertilisers, foodstuffs, pharmaceuticals and pigments. Applications that are more recent include crystalline materials and substances for electronics devices, healthcare products and a wide variety of speciality applications.
Thus, the tonnage and variety of particulate crystal products worldwide is enormous, amounting to possibly more than half the product of the modern chemical industry. The economic value, social benefit and technical sophistication of crystal products and processes are ever increasing, particularly in the newer high added value sectors of global markets. This places yet greater demands on the skill and ingenuity of the scientist and engineer to form novel materials of the required product characteristics and devise viable process engineering schemes for their manufacture (Jones, 2002).
Previously, a largely empirical art, the design of process systems for manufacturing particulate crystals has now begun to be put on a rational basis, and the more complex precipitation processes whereby crystallization follows fast chemical reactions have also been analysed more deeply. This progress has been aided by the growing power of the population balance and kinetic models, computational fluid dynamics and mixing theory. This not only increases understanding of existing processes but also enhances the possibility of innovative product and process designs, and speedier times to market.
The process engineering goal for crystallization systems is to develop generic scale-up methodologies to integrate across the length scales—from the formation of primary crystals to industrial scale plant operation. In this selective review, particular attention is paid both to the fundamental mechanisms of mixing and the formulation of computer aided mathematical methods for scale-up, whilst emphasising throughout the continuing need for careful yet efficient practical experimentation to collect basic data; the latter being essential in order to discriminate between competing theories, to inform and validate process models, and to discover the unexpected. Substantial progress has been made in integrating computational fluid dynamics (CFD) with particulate process models but because of the extra dimensionality, however, there remain substantial challenges (Bezzo et al., 2004).
Section snippets
Particulate crystal characteristics
Crystallization is an important separation process that purifies fluids by forming solids. Crystallization is also a particle formation process by which molecules in solution or vapour are transformed into a solid phase of regular lattice structure, which is reflected on the external faces. Crystallization may be further described as a self-assembly molecular building process. Crystallographic and molecular factors are thus very important in affecting the shape (habit), purity and structure of
Fluid-particle transport processes
The formation and subsequent solid–liquid separation of particulate crystals from solution normally involves alternate periods of suspension and sedimentation during which they experience relative fluid-particle motion. Similarly, solid matter may change phase from liquid to solid or vice versa. New particles may be generated or existing ones lost, e.g. in crystallizers or mills. They may be separated from fluids by flow through vessels, e.g. settlers, thickeners or filters. Thus, both the
Conclusion
Combined population balance and kinetic models, computational fluid dynamics and mixing theory enable prediction and scale-up of crystallization and precipitation systems. Though these hybrid approaches represent essentially a compromise, their lifetime is likely to be quite long, as the full CFD solution at each node awaits a radical breakthrough in computer software and hardware technology. Simultaneously, alternatives to conventional agitated vessels for crystallization and precipitation
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2021, Chemical Engineering JournalCitation Excerpt :Several authors [4,8–10] distributed the reactor into different mixing zones to avoid the computational effort of CFD-simulations. A comparable approach was proposed by the group around Zauner and Jones [11–15], who developed the segregated feed model, which is a zone-model approach for precipitation in STRs. Furthermore, several authors [16–18] conducted experiments to enable further insights into the process and the correlation between the STR’s parameters and the final product PSD.
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2020, Computers and Chemical EngineeringCitation Excerpt :Seminal work was conducted by Gradl et al. (2006), Marchisio et al. (2002, 2006), Schwarzer (2004a, 2004b, 2005, 2006), Schwarzer et al. (2006), Veroli and Rigopoulos (2009) and Metzger and Kind (2015) by combining computational fluid dynamics (CFD) with population balance equations (PBEs). Most of the publications dealing explicitly with the simulation of STRs investigate the process on a high-level spatial resolution (Fig. 2a), resulting in numerically expensive multiscale models (Barrett et al., 2011; Jaworski and Nienow, 2003; Jones et al., 2005; Vicum and Mazzotti, 2007; Vicum et al., 2004; Wang et al., 2006; Wang et al., 2007; Zauner and Jones, 2000; Zhang et al., 2009). Together with several experimental studies on precipitation in STRs (Matynia et al., 2005; Steyer and Sundmacher, 2009; Torbacke and Rasmuson, 2001), these studies provided further insights into the complex coupling between fluid dynamics and solids formation during precipitation.
LBM for separation processes
2020, Advances in Chemical EngineeringCitation Excerpt :They can also be both as discrete particles and as structured agglomerates. The large variety of crystalline products contribute possibly to more than half of the products of the modern chemical industry (Jones et al., 2005). Some examples of crystal product include bulk and fine chemicals and their intermediates, such as sodium chloride (table salt), sodium carbonate, detergents, fertilizers, pharmaceuticals, and sugar.
- 1
Present address: Department of Mechanical Engineering, Imperial College London, SW7 2BX, UK.
- 2
Present address: Austrian Research Centers, A-2444 Seibersdorf, Austria.