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This study presents a comprehensive comparison of the batch cooling crystallization performance of aqueous solutions containing sugars and sugar alcohols, namely, erythritol, glucose, xylitol, and xylose. Erythritol and xylitol are commonly used alternative sweeteners to replace sucrose. They can be obtained by fermentation-based bioprocesses, where glucose and xylose are typical raw materials. These model compounds were selected based on their differing rheological nature: saturated erythritol solution has a viscosity lower than 3 mPa·s, whereas xylitol has the highest viscosity: greater than 90 mPa·s in the studied temperature range. Viscosities and densities of saturated solutions as well as apparent viscosities of crystal-mother liquor suspensions were measured. The purpose was to evaluate their crystallization behavior within a specific temperature range from 40 to 20 °C and batch time of 2 h, with the aim of understanding the influence of viscosity on the process more comprehensively. The comparison within the selected compound systems was carried out in terms of the physical properties of the mother liquor and the crystalline product. In addition to empirical laboratory-scale (0.1 and 1 L) studies, larger-scale simulations (1 and 100 m 3 ) were performed with the experimental data obtained on average particle size, density, and viscosity for mother liquor and crystal-mother liquor suspensions. Mixing characteristics, such as the dissipation energy, mass transfer coefficient, energy of collisions, and micromixing time, were calculated with VisiMix software when using a single or dual impeller mixer. Furthermore, the scaling up of erythritol, xylitol, glucose, and xylose batch cooling crystallization from 40 to 20 °C based on the scaling-up rule of constant tip speed and energy of dissipation was done with VisiMix to obtain overall data on mixing conditions with crystallizers of 1 and 100 m 3 in volume. Furthermore, ANSYS CFD software was used to determine the strain rates close to the impeller tip and velocity profiles on various crystallizer scales., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The efficiency of layer melt crystallization for the selective separation of glycerol from a glycerol-diethylene glycol mixture containing 4 wt % of diethylene glycol was evaluated using solvent-free and solvent-aided approaches. The effect of 1-butanol and the binary solvent of 1-butanol and acetone with a total molar composition of 25 mol % on the crystal growth kinetics and the purity of the final product was studied at different undercooling degrees and crystallization yields. The melting point temperature of the mixtures was predicted by using the modified UNIFAC Dortmund model. The addition of both a single and binary solvents significantly increased the crystal growth rate and purity of the final product compared to crystallization from the solvent-free mixture. Additionally, higher crystal growth rates and product purity were observed in the binary solvent system compared to those in the single solvent system at the same degree of undercooling. The second stage of solvent-aided crystallization resulted in glycerol with a purity above 99.5 wt %, depending on the type of solvent used and the rate of crystal growth., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Four different techniques for xylitol crystallization, namely cooling, evaporative, antisolvent, and combined antisolvent and cooling crystallization, were investigated regarding their influence on the product crystal properties. Various batch times and mixing intensities were studied, and the antisolvent used was ethanol. Real-time monitoring of the count rates of various chord length fractions and distributions using focused beam reflectance measurement was conducted. Several solid characterization methods were used for studying the crystal size and shape, such as scanning electron microscopy and laser diffraction-based crystal size distribution analysis. Crystals ranging in size from 200 to 700 μm were obtained based on the analysis results by laser diffraction. The dynamic viscosity of saturated and undersaturated xylitol solution samples was measured; the density and refraction index were measured to determine the xylitol concentration in the mother liquor. Saturated xylitol solutions were found to have relatively high viscosities up to 129 mPa s in the studied temperature range. Viscosity can have a key role in crystallization kinetics, especially in cooling and evaporative crystallization. Mixing speed had a great influence, mainly on the secondary nucleation mechanism. The addition of ethanol decreased the viscosity, resulting in more uniform crystal shape and better filterability., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Liquid-liquidphase separation (LLPS) or dense liquid intermediates during the crystallization of pharmaceutical molecules is common; however, their role in alternative nucleation mechanisms is less understood. Herein, we report the formation of a dense liquid intermediate followed by a core-shell structure of ibuprofen crystals via nonclassical crystallization. The Raman and SAXS results of the dense phase uncover the molecular structural ordering and its role in nucleation. In addition to the dimer formation of ibuprofen, which is commonly observed in the solution phase, methyl group vibrations in the Raman spectra show intermolecular interactions similar to those in the solid phase. The SAXS data validate the cluster size differences in the supersaturated solution and dense phase. The focused-ion beam cut image shows the attachment of nanoparticles, and we proposed a possible mechanism for the transformation from the dense phase into a core-shell structure. The unstable phase or polycrystalline core and its subsequent dissolution from inside to outside or recrystallization by reversed crystal growth produces the core-shell structure. The LLPS intermediate followed by the core-shell structure and its dissolution enhancement unfold a new perspective of ibuprofen crystallization., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Luminescent materials have many interesting applications, but it remains difficult to control the luminescence of organic materials and in particular to retain the same luminescence in solution and in the solid state, a property of interest for various imaging applications. In the present work, the fluorescent properties of the salt of 2,6-diaminopyridinium with dihydrogen phosphate have been explored. As a result of proton transfer from phosphoric acid to the pyridine nitrogen and the stabilizing effect of the two primary amines at the positions ortho to the pyridine nitrogen, the band gap between the HOMO and the LUMO is considerably diminished in comparison with that in 2,6-diaminopyridine. This is confirmed by a red shift in its absorption spectrum. Because protonation is retained in aqueous solution, the dissolved 2,6-diaminopyridinium dihydrogen phosphate salt retains a similar fluorescent spectrum as in the solid state. The crystals have been studied by single-crystal X-ray diffraction; FTIR, Raman, UV-vis-NIR, and luminescence spectroscopy; HOMO-LUMO calculations using DFT; and thermal analysis. The compound provides an example of a supramolecular motif that controls the crystal structure and the luminescence properties. In addition, the crystal exhibits negligible thermal expansion over a temperature interval of 150 °C. In short, 2,6-diaminopyridinium dihydrogen phosphate is an interesting compound for the design of luminescent devices.