Special Issue "Recent Progress in Industrial Crystallization"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Industrial Crystallization".

Deadline for manuscript submissions: 30 June 2022 | Viewed by 6439

Special Issue Editors

Prof. Dr. Heike Lorenz
E-Mail Website
Guest Editor
Max Planck Institute for Dynamics of Complex Technical Systems, 39106 Magdeburg, Germany
Interests: phase equilibria; crystallization kinetics; process monitoring & design; separation of fine chemicals, large scale industrial products and renewable resources; innovative crystallization-based separation concepts; enantiomers; natural products; multi-component mixtures
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Alison Emslie Lewis
E-Mail Website
Guest Editor
Department of Chemical Engineering, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
Interests: industrial crystallization; freeze crystallization; water treatment
Dr. Erik Temmel
E-Mail Website
Guest Editor
Sulzer Chemtech Ltd., Basel, Switzerland
Interests: melt crystallization; crystallizer design; fractional crystallization; phase equilibria; crystallization kinetics; continuous crystallization; process monitoring; process design; applied population balance and process modelling; process intensification and combination; process optimization; novel measurement techniques
Prof. Dr. Jens-Petter Andreassen
E-Mail Website
Guest Editor
Department of Chemical Engineering, Norwegian University of Science and Technology, Trondheim, Norway
Interests: industrial crystallization; crystal growt mechanisms; hydrometallurgy; biomineralization; resource recovery

Special Issue Information

Crystallization is an important industrial process, a purification technique, a separation process and a branch of particle technology. It also encompasses several key areas of chemical and process engineering. Industrial crystalline products include bulk chemicals, such as sodium chloride and sucrose, fertilizer chemicals such as potassium chloride and urea and, high-price products such as pharmaceuticals, platinum group metal salts, high-grade materials for battery production and organic fine chemicals such as food additives. Industrial crystallization further plays a role in the new and rapidly expanding field of engineered nanoparticles and the production of crystals for the electronics industry and biotechnology. Other prominent industrial application domains comprise the use of crystallization in water and effluent treatment, reflecting the waste-to-resource movement that is becoming increasingly important and relevant in the field.

The overall theme of this Special Issue is how theoretical concepts are adapted in industrial crystallization, and how practical understanding in the field is enhanced through applied research. The latter covers a wide range of subjects, such as crystallization fundamentals, analytical tools for process analysis and monitoring, crystallization process and product design, as well as the integration of crystallization in industrial process chains for, for example, solving environmental and sustainability issues. These topics are also the focus of the 21st International Symposium on Industrial Crystallization (ISIC 21) held from 31 August to 2 September this year (https://dechema.de/en/ISIC_2021), seen as the most important international conference in the field.

This Special Issue is dedicated to Professor Gerda van Rosmalen (27 May 1936–18 January 2021), who was a pioneer in this field. She developed the field of industrial crystallization research through her original courses developed over many decades and given to industrial partners and postgraduate students. Professor van Rosmalen spent 20 years as the Professor of Industrial Crystallization and Clean Technology at the Laboratory for Process Equipment at TU Delft in the Netherlands, and her distinguished positions include being a Board Member of the Working Party on the Industrial Crystallization of the European Federation of Chemical Engineers. She was regarded globally as a pre-eminent figure in industrial crystallization.

The keywords given below encompass examples addressed in the Special Issue, but papers concerning other innovative and novel subjects in industrial crystallization are also welcome.

Prof. Dr. Heike Lorenz
Prof. Dr. Alison Emslie Lewis
Dr. Erik Temmel
Prof. Dr. Jens-Petter Andreassen
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Nucleation
  • Crystal growth
  • Polymorphism, solvates, co-crystals and solid solutions
  • Crystallization
  • Precipitation
  • Monitoring of crystallization
  • Crystallization hybrid processes
  • Application in large-scale, fine chemical, specialty and life science industries
  • Sustainability: circular economy, resource recovery

Related Special Issue

Published Papers (10 papers)

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Article
Gypsum Seeding to Prevent Scaling
Crystals 2022, 12(3), 342; https://doi.org/10.3390/cryst12030342 - 02 Mar 2022
Viewed by 435
Abstract
Eutectic freeze crystallization (EFC) is a novel separation technique that can be applied to treat brine solutions such as reverse osmosis retentates. These are often a mixture of different inorganic solutes. The treatment of calcium sulphate-rich brines using EFC often results in gypsum [...] Read more.
Eutectic freeze crystallization (EFC) is a novel separation technique that can be applied to treat brine solutions such as reverse osmosis retentates. These are often a mixture of different inorganic solutes. The treatment of calcium sulphate-rich brines using EFC often results in gypsum crystallization before any other species. This results in gypsum scaling on the cooled surfaces of the crystallizer, which is undesirable as it retards heat transfer rates and hence reduces the yield of other products. The aim of this study was to investigate and understand gypsum crystallization and gypsum scaling in the presence of gypsum seeds. Synthetic brine solutions were used in this research because they allowed an in-depth understanding of the gypsum bulk crystallization process and scaling tendency without the complexity of industrial brines. A cooled, U-shaped stainless-steel tube suspended in the saturated solution was employed as the scaling surface. This was because a tube-shaped surface enabled the introduction of a constant temperature cold surface in the saturated solution and most industrial EFC crystallizers are constructed from stainless steel. Gypsum seeding was effective in decreasing the mass of scale formed on the heat transfer surface. The most effective seed loading was 0.25 g/L, which reduced scale growth rate by 43%. Importantly, this seed loading is six times the theoretical critical seed loading. The seeding strategy also increased the gypsum crystallization kinetics in the bulk solution, which resulted in an increase in the mass of gypsum product. These findings are relevant for the operability and control of EFC processes, which suffer from scaling problems. By using an appropriate seeding strategy, two problems can be alleviated. Firstly, scaling on the heat transfer surface is minimised and, secondly, seeding increases the crystallization kinetics in the bulk solution, which is advantageous for product yield and recovery. It was also recommended that the use of silica as a seed material to prevent gypsum scaling should be investigated in future studies. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Article
Continuous Isolation of Particles with Varying Aspect Ratios up to Thin Needles Achieving Free-Flowing Products
Crystals 2022, 12(2), 137; https://doi.org/10.3390/cryst12020137 - 19 Jan 2022
Viewed by 292
Abstract
The continuous vacuum screw filter (CVSF) for small-scale continuous product isolation of suspensions was operated for the first time with cuboid-shaped and needle-shaped particles. These high aspect ratio particles are very common in pharmaceutical manufacturing processes and provide challenges in filtration, washing, and [...] Read more.
The continuous vacuum screw filter (CVSF) for small-scale continuous product isolation of suspensions was operated for the first time with cuboid-shaped and needle-shaped particles. These high aspect ratio particles are very common in pharmaceutical manufacturing processes and provide challenges in filtration, washing, and drying processes. Moreover, the flowability decreases and undesired secondary processes of attrition, breakage, and agglomeration may occur intensively. Nevertheless, in this study, it is shown that even cuboid and needle-shaped particles (l-alanine) can be processed within the CVSF preserving the product quality in terms of particle size distribution (PSD) and preventing breakage or attrition effects. A dynamic image analysis-based approach combining axis length distributions (ALDs) with a kernel-density estimator was used for evaluation. This approach was extended with a quantification of the center of mass of the density-weighted ALDs, providing a measure to analyze the preservation of the inlet PSD statistically. Moreover, a targeted residual moisture below 1% could be achieved by adding a drying module (Tdry = 60 °C) to the modular setup of the CVSF. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Article
Reactive Crystallization Kinetics of K2SO4 from Picromerite-Based MgSO4 and KCl
Crystals 2021, 11(12), 1558; https://doi.org/10.3390/cryst11121558 - 14 Dec 2021
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Abstract
In this work, the kinetic parameters, the degrees of initial supersaturation (S0) and the profiles of supersaturation (S) were determined for the reactive crystallization of K2SO4 from picromerite (K2SO4.MgSO4.6H2 [...] Read more.
In this work, the kinetic parameters, the degrees of initial supersaturation (S0) and the profiles of supersaturation (S) were determined for the reactive crystallization of K2SO4 from picromerite (K2SO4.MgSO4.6H2O) and KCl. Different reaction temperatures between 5 and 45 °C were considered, and several process analytical techniques were applied. Along with the solution temperature, the crystal chord length distribution (CLD) was continuously followed by an FBRM probe, images of nucleation and growth events as well as the crystal morphology were captured, and the absorbance of the solution was measured via ATR-FTIR spectroscopy. In addition, the ion concentrations were analyzed. It was found that S0 is inversely proportional to the reactive crystallization temperature in the K+, Mg2+/Cl, SO42−//H2O system at 25 °C, where S0 promotes nucleation and crystal growth of K2SO4 leading to a bimodal CLD. The CLD was converted to square-weighted chord lengths for each S0 to determine the secondary nucleation rate (B), crystal growth rate (G), and suspension density (MT). By correlation, from primary nucleation rate (Bb) and G with S0, the empirical parameters b = 3.61 and g = 4.61 were obtained as the order of primary nucleation and growth, respectively. B versus G and MT were correlated to the reaction temperature providing the rate constants of B and respective activation energy, E = 69.83 kJ∙mol−1. Finally, a general Equation was derived that describes B with parameters KR = 13,810.8, i = 0.75 and j = 0.71. The K2SO4 crystals produced were of high purity, containing maximal 0.51 wt% Mg impurity, and were received with ~73% yield at 5 °C. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Article
Solubility and Crystallization of Piroxicam from Different Solvents in Evaporative and Cooling Crystallization
Crystals 2021, 11(12), 1552; https://doi.org/10.3390/cryst11121552 - 11 Dec 2021
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Abstract
In this work, the solubility of a non-steroidal anti-inflammatory drug (NSAID), piroxicam, is investigated. The polymorphic form II, which is the most stable form at room temperature, was investigated in seven different solvents with various polarities. It has been found that the solubility [...] Read more.
In this work, the solubility of a non-steroidal anti-inflammatory drug (NSAID), piroxicam, is investigated. The polymorphic form II, which is the most stable form at room temperature, was investigated in seven different solvents with various polarities. It has been found that the solubility of piroxicam in the solvents is in the following order: chloroform > dichloromethane > acetone > ethyl acetate > acetonitrile > acetic acid > methanol > hexane. Crystallization of piroxicam from different solvents has been performed with evaporative crystallization and cooling crystallization; the effects of solvent evaporation rate and solute concentration have also been studied. Both form I and form II could be produced in cooling and evaporative crystallization, and no simple link can be identified between the operating parameters and the polymorphic outcome. Results obtained in the present work showed the stochastic nature of the nucleation of different polymorphs as well as the complexity of the crystallization of a polymorphic system. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Article
The Effect of Reaction Conditions and Presence of Magnesium on the Crystallization of Nickel Sulfate
Crystals 2021, 11(12), 1485; https://doi.org/10.3390/cryst11121485 - 30 Nov 2021
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Abstract
Recycling of valuable metals such as nickel is instrumental to meet the need from the dramatic increase in electric vehicle battery production and to improve its sustainability. Nickel required in the battery manufacture can be recovered from the hydrometallurgical industrial process streams by [...] Read more.
Recycling of valuable metals such as nickel is instrumental to meet the need from the dramatic increase in electric vehicle battery production and to improve its sustainability. Nickel required in the battery manufacture can be recovered from the hydrometallurgical industrial process streams by crystallization of nickel sulfate. Here, crystallization of nickel sulfate is studied from an industrial point of view, investigating the effects of temperature, seeding and presence of magnesium on the formation of various solid phases for the evaluation of their potential influence on the process design. Results showed that the precipitating phase was dictated both by seed amount and reaction temperature. Transformation of metastable phases both in suspension and in a dry state was observed over time. Presence of magnesium was shown to promote formation of NiSO4·7H2O in solution and increased its stability in a dry form. In their dry state, nickel sulfate that was formed in the absence of magnesium transformed towards α-NiSO4·6H2O, whereas those precipitated in the presence of high magnesium concentrations transformed towards β-NiSO4·6H2O, indicating that magnesium inhibited the phase transformation towards α-NiSO4·6H2O. Knowledge about various solid phases of varying crystal morphology and stability can be used as input to decisions for the best suited solid product type and how this relates to the initial conditions of the sidestreams. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Article
Contact-Mediated Nucleation of Subcooled Droplets in Melt Emulsions: A Microfluidic Approach
Crystals 2021, 11(12), 1471; https://doi.org/10.3390/cryst11121471 - 26 Nov 2021
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Abstract
The production of melt emulsions is mainly influenced by the crystallization step, as every single droplet needs to crystallize to obtain a stable product with a long shelf life. However, the crystallization of dispersed droplets requires high subcooling, resulting in a time, energy [...] Read more.
The production of melt emulsions is mainly influenced by the crystallization step, as every single droplet needs to crystallize to obtain a stable product with a long shelf life. However, the crystallization of dispersed droplets requires high subcooling, resulting in a time, energy and cost intensive production processes. Contact-mediated nucleation (CMN) may be used to intensify the nucleation process, enabling crystallization at higher temperatures. It describes the successful inoculation of a subcooled liquid droplet by a crystalline particle. Surfactants are added to emulsions/suspensions for their stabilization against coalescence or aggregation. They cover the interface, lower the specific interfacial energy and form micelles in the continuous phase. It may be assumed that micelles and high concentrations of surfactant monomers in the continuous phase delay or even hinder CMN as the two reaction partners cannot get in touch. Experiments were carried out in a microfluidic chip, allowing for the controlled contact between a single subcooled liquid droplet and a single crystallized droplet. We were able to demonstrate the impact of the surfactant concentration on the CMN. Following an increase in the aqueous micelle concentrations, the time needed to inoculate the liquid droplet increased or CMN was prevented entirely. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Article
Flow Map for Hydrodynamics and Suspension Behavior in a Continuous Archimedes Tube Crystallizer
Crystals 2021, 11(12), 1466; https://doi.org/10.3390/cryst11121466 - 26 Nov 2021
Viewed by 478
Abstract
The Archimedes Tube Crystallizer (ATC) is a small-scale coiled tubular crystallizer operated with air-segmented flow. As individual liquid segments are moved through the apparatus by rotation, the ATC operates as a pump. Thus, the ATC overcomes pressure drop limitations of other continuous crystallizers, [...] Read more.
The Archimedes Tube Crystallizer (ATC) is a small-scale coiled tubular crystallizer operated with air-segmented flow. As individual liquid segments are moved through the apparatus by rotation, the ATC operates as a pump. Thus, the ATC overcomes pressure drop limitations of other continuous crystallizers, allowing for longer residence times and crystal growth phases. Understanding continuous crystallizer phenomena is the basis for a well-designed crystallization process, especially for small-scale applications in the pharmaceutical and fine chemical industry. Hydrodynamics and suspension behavior, for example, affect agglomeration, breakage, attrition, and ultimately crystallizer blockage. In practice, however, it is time-consuming to investigate these phenomena experimentally for each new material system. In this contribution, a flow map is developed in five steps through a combination of experiments, CFD simulations, and dimensionless numbers. Accordingly, operating parameters can be specified depending on ATC design and material system used, where suspension behavior is suitable for high-quality crystalline products. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Article
Comparison of the Nucleation Parameters of Aqueous l-glycine Solutions in the Presence of l-arginine from Induction Time and Metastable-Zone-Width Data
Crystals 2021, 11(10), 1226; https://doi.org/10.3390/cryst11101226 - 12 Oct 2021
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Abstract
Induction time and metastable-zone-width (MSZW) data for aqueous l-glycine solutions in the presence of l-arginine impurity were experimentally measured using a turbidity probe in this study. The nucleation parameters, including the interfacial free energy and pre-exponential nucleation factor, obtained from induction [...] Read more.
Induction time and metastable-zone-width (MSZW) data for aqueous l-glycine solutions in the presence of l-arginine impurity were experimentally measured using a turbidity probe in this study. The nucleation parameters, including the interfacial free energy and pre-exponential nucleation factor, obtained from induction time data, were compared with those obtained from MSZW data. The influences of lag time on the nucleation parameters were examined for the induction time data. The effects of l-arginine impurity concentration on the nucleation parameters based on both the induction time and MSZW data were investigated in detail. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Article
Thermal Deformations of Crystal Structures in the L-Aspartic Acid/L-Glutamic Acid System and DL-Aspartic Acid
Crystals 2021, 11(9), 1102; https://doi.org/10.3390/cryst11091102 - 10 Sep 2021
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Abstract
The method of temperature-resolved powder X-ray diffraction (TRPXRD) was used to determine the elevated temperature behavior of L-aspartic acid (L-asp), DL-aspartic acid (DL-asp), L-glutamic acid (L-glu), and an L-asp0.25,L-glu0.75 solid solution. These amino acids were not found to undergo any [...] Read more.
The method of temperature-resolved powder X-ray diffraction (TRPXRD) was used to determine the elevated temperature behavior of L-aspartic acid (L-asp), DL-aspartic acid (DL-asp), L-glutamic acid (L-glu), and an L-asp0.25,L-glu0.75 solid solution. These amino acids were not found to undergo any solid-phase (polymorph) transformations. When heated, they all experienced only thermal deformations. The corresponding parameters of the monoclinic cells of L-asp and DL-asp, and the orthorhombic cells of L-glu and L-asp0.25,L-glu0.75, were calculated for the entire range of studied temperatures (up to 220 °C). The data obtained were used to calculate the parameters of the thermal deformation tensors, and to plot the figures of their thermal expansion coefficients. A correlation between the maximum and minimum values of thermal expansion coefficients and the length, type, direction, and number of hydrogen bonds in the crystal structures of the investigated amino acids was established. The observed negative thermal expansion (contraction) of crystal structures of L-asp and DL-asp along the ac plane can be explained as a result of shear deformations occurring in monoclinic crystals with a non-fixed angle β. The studies were related to the presence of amino acids in various natural and technological processes occurring at different temperatures. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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Obituary
In Memoriam—Gerda van Rosmalen
Crystals 2022, 12(2), 177; https://doi.org/10.3390/cryst12020177 - 26 Jan 2022
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Abstract
This Special Issue is in memory and in honor of Professor Gerda van Rosmalen, who saddened the crystallization community with her departure and left us with the wide and deep heritage of her work and most pleasant personal memories[...] Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1. Tentative title: *Thermal Deformations of Crystal Structures Formed in the L-Aspartic Acid /**L-Glutamic Acid Enantiomer System*

Authors: *Roman Sadovnichii1, Elena Kotelnikova1 and Heike Lorenz2*
1 Department of Crystallography, St. Petersburg State University, St. Petersburg, Russia
2 Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany

 

2.Tentative title: Purification of Styrene from Waste Plastics

Authors: Temmel1, M. Stepanski1, P. Cramers1, J. Ulrich2

1 Sulzer Chemtech Ltd, Sulzerallee 48, CH-8404 Winterthur, Switzerland

2 Martin Luther University, Halle-Wittenberg, Center of Engineering Science, Process Engineering/ TVT, D-06099 Halle, Germany

Abstract: Recycling of waste plastics is nowadays a major challenge for environmental protection and sustainability, as long as oil-based polymers are still as widely applied as today. Pyrolysis is a common process in that context to break down the polymer chains utilizing heat and catalysts, which facilitates the recovery of the main polymer educts. As a result, a complex reaction mixture is created, which varies with the waste feed composition and needs to be separated in several steps to produce single components in the required purity for further usage. Multi-column distillation is usually the first choice for such mixtures due to its excellent separation efficiency, its continuous operation and the long-term experience with this technology in almost every company. For certain tasks, involving separating of close- and/ or co-boiling substances, distillation requires, however, large installations, significant energy input or the intended separation is even not possible. In these cases, a combination with melt crystallization can be reasonable since operational and maybe also the investment costs can be reduced.

The advantages of such process combinations are illustrated on the example of styrene recovery from polystyrene pyrolysis oils. The standalone separation efficiencies of both technologies are demonstrated, at first, based on recent experimental findings in lab- and pilot-scale and the basics of the separation problem are explained. A typical example of a pyrolysis oil serves then as the benchmark to quantify the expenses for a common distillation process designed with the relevant VLE. Subsequently, different scenarios are derived for oil compositions containing substances boiling together or close to styrene, which represent different pyrolysis products from different waste plastic sources. Finally, the benefits of a distillation-crystallization process to produce ultra-pure styrene (Purity > 99.95%) are quantified based on these scenarios to simplify future evaluations of such process combinations.

3. Title: Solubility and crystallization of piroxicam from different solvents in evaporative and cooling crystallizations
Authors: Iben Ostergaard and Haiyan Qu
*Abstract:* Piroxicam is a non-steroidal anti-inflammatory drug (NSAID) and it can form 4 anhydrous polymorphs and one monohydrate. In this work, the solubility of the polymorphic form II, which is the most stable form at room temperature, was investigated in seven different solvents with various polarities; It has been found that the solubility of piroxicam in the solvents is in the following order: chloroform > dichloromethane > acetone > ethyl acetate > acetonitrile > acetic acid > methanol > hexane. Crystallization of piroxicam from different solvents has been performed with evaporative crystallization and cooling crystallization, the effects of solvent evaporation rate and solute concentration have been studied. Both form I and form II could be produced in cooling and evaporative crystallization, and no simple link can be identified between the operation parameters and the polymorphic outcome. Results obtained in the present work showed the stochastic nature of nucleation of different polymorphs as well as the complexity of the crystallization of a polymorphic system.

4. Title: Crystallization in fluidized bed reactors: from fundamental knowledge to full scale applications

Author: Seckler, Marcelo Martins

Department of Chemical Engineering of the Polytechnic School, University of São Paulo, Brazil

Abstract: A review is presented on fifty years of research on crystallization in fluidized bed reactors (FBR). FBR´s are suitable for recovery of slightly soluble compounds from aqueous solutions, as it yields large (centimeter-sized) particles that are easily processed for reuse and permits liquid residence times of only a few minutes. Full scale application for water softening has been applied since the years 1980´s, for phosphate removal since the years 2000 and new applications have been developed or are in development since then, involving crystallization of a wide range of metals, as well as carbonates, phosphates, chromates, sulfides and sulfates.

Besides, process integration with other unit operations have been proposed to address a number sustainability demands, as shown in the following examples. In desalination and in water treatment for reuse with zero liquid discharge, metals precipitation in FBR are combined with membrane processes to reduce scaling upon membrane surfaces, thereby reducing energy demand. In carbon capture from air, calcium carbonate precipitation in FBR combined with absorption and calcination units offer an efficient closed system. In remediation of contaminated areas due to acid mine drainage, metals sulfide precipitation in FBR´s are integrated with biogenically produced H2S and HCO3 with low energy and chemicals consumption. Wastewater treatment using FBR combined with adsorption, membrane filtration, membrane distillation, electrochemical systems, among others, have been applied to reduce and concentrate waste materials or to valorize them as products.

Further, novel FRB concepts have been proposed, such as an aerated FBR for chemical-free precipitation of calcium carbonate, a FBR where the seeds and target compound are of the same material to yield a pure particulate product, FBR´s in series to selective separation of pure metals from multicomponent mixtures and a circulating FBR for improved recovery of the target compound.

Intensified processes have been proposed to yield core-shell products with desired performance, such as an integrated supercritical antisolvent-fluidized bed process for pharmaceutical formulations. A novel FBR – microbial electrochemical cell allows simultaneous removal of organics and of mineral particulate. A modified Fenton process for organics removal consists of a FBR where undesirable iron hydroxide sludge is removed by aggregation upon active carbon seeds.

Fundamental studies have elucidated the elementary steps of crystallization in FBR´s. For example, crystal growth has been found to be the dominant process for the formation of calcium carbonate and struvite particles, whereas agglomeration is important for calcium phosphate and metal sulfides.  Fluid dynamics has also received attention, as FBR´s are populated with particles with varying density and size, which tend to segregate to minimize the potential energy, but they also mix due to turbulence.  These phenomena have been incorporated in population, mass and energy balances to describe certain experimental systems. Consequently, mathematical models have been extensively used for process optimization and control at bench, pilot and full-scale units.

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