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The flotation agent is an important collector in the production of potassium chloride and is brought into the crystallization stage with the reflux of the mother liquor. Octadecylamine Hydrochloride (ODA), 1-Dodecylamine Hydrochloride (DAH) and Sodium 1-dodecanesulfonate (SDS) were selected to study their effect on the nucleation of potassium chloride. Focused Beam Reflectance Measurement was used to collect the nucleation-induced periods of KCl in the presence of flotation agents at different supersaturations. Then, empirical equations, classical nucleation theory and growth mechanism equations were employed for data analysis. It was found that the presence of flotation agents increased the nucleation sequence m, and m(ODA) > m(SDS) > m(DAH) > m(H2O). In addition, the interfacial energy data obtained using classical nucleation theory suggest that the flotation agents used in our paper promoted the homogeneous nucleation of KCl (reduced from 5.3934 mJ·m−2 to 5.1434 mJ·m−2) and inhibited the heterogeneous nucleation of KCl (increased from 2.8054 mJ·m−2 to 3.6004 mJ·m−2). This investigation also revealed that the growth of potassium chloride was consistent with the 2D nucleation-mediated growth mechanism, and the addition of flotation agent did not change the growth mechanism of potassium chloride. Finally, the particle size distribution results were exactly consistent with the order of nucleation order m. The study of nucleation kinetics and growth mechanisms of different flotation agents on potassium chloride can provide guidance for optimizing the production process of potassium chloride and developing new flotation agents. [ABSTRACT FROM AUTHOR]

The metastable zone width (MSZW) of p-methoxybenzoic acid (PMBA) in an ethanol-water system was measured using the polythermal method. The nucleation order m obtained by the Nývlt's model indicates the nucleation of PMBA following a progressive nucleation mechanism at low saturation temperature (m = 3.18–7.50) and an instantaneous nucleation mechanism at high saturation temperature (m = 1.46–2.55). Then, combined with the metastable zone experiment and the Sangwal model, we found that the MSZW and the interfacial energy reached the maximum when the mass fraction of ethanol was 0.8, which resulted in the smallest crystal product size. Meanwhile, the maximum r c r i t and Δ G c r i t obtained based on the modified Sangwal model indicating the PMBA needs to overcome a higher nucleation barrier in the ethanol mass fraction of 0.8. Finally, we proposed a preferential strategy for adjusting MSZW by correlating the interfacial energy with the change in ethanol mass fraction, saturation temperature, and cooling rate, respectively. [ABSTRACT FROM AUTHOR]

Levofloxacin is a fluoroquinolone and bears a broad-spectrum antibacterial effect. The polymorphism of levofloxacin was intensively studied, nevertheless, the landscape of polymorphs is not fully understood. Herein we reported for the first time the fully solved crystal structure of an anhydrous α form and three newly discovered solvates including n-propanol solvate, ethylene glycol solvate and acetic acid solvate. The successfully solved crystal structure of the anhydrous α form by single crystal X-ray diffraction was found to be in good agreement with the reported data by the SDPD (structure determination from powder X-ray diffraction data) method, but is significantly different from the one by the crystal structure prediction (CSP) approach. The comparison results suggest the wrong solved crystal structure of the α form using the CSP method. The newly reported n-propanol solvate, ethylene glycol solvate and acetic acid solvate of levofloxacin were fully characterized by powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and single crystal X-ray diffraction (except for the acetic acid solvate). It was found that the solvent molecules of the n-propanol solvate fill the channels and interact weakly with the active pharmaceutical ingredient (API) molecules, while they play crucial roles in the stability of the crystal structure. Further, the phase transformations among different solid-state crystal forms of levofloxacin were investigated in detail by variable-temperature powder X-ray diffraction. The results reveal that all of the newly discovered solvates can be directly dehydrated to an anhydrous γ form, which eventually converted into an anhydrous α form during subsequent heating. [ABSTRACT FROM AUTHOR]

Batch crystallization in acidic aqueous solution of cephalexin was conducted by reactive crystallization with or without seeding. Supersaturation was generated by mixing ammonia and acidic aqueous solution of cephalexin and controlled by solution feeding rate and seeding conditions. UV and Morphologi G3 were used to measure supersaturation and aspect ratio. Experimental results demonstrated that burst nucleation occurred and the products were needle-like at high supersaturation; meanwhile, the products were plate-like and had high aspect ratio at low supersaturation. Analysis of the measured supersaturation profiles and corresponding aspect ratio explained the mechanisms governing the aspect ratio. The optimized operating parameters were also proposed (seeding supersaturation is equal to 1.3, seed mass ratio 8% and feeding rate 368 μL/min). [ABSTRACT FROM AUTHOR]