Chemical Engineering & Technology
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Every month, the Editors select two papers referring to current discussions in the scientific, public and economic communities and in view of the potential for further developments. The papers are freely accessible for one month.
Purification of Phosphoric Acid
July 12, 2016
Phosphoric acid is widely used in chemical, food, fertilizer, and electronic industries. It is mainly produced by the furnace process. However, many impurities such as iron, aluminum, magnesium, fluorine, and sulfate remain in the found products. Crystallization, as a highly efficient, low-cost, and environmental friendly method, is considered as potential purification step. Furthermore, an efficient post crystallization treatment such as washing or sweating is needed to further separate the crystalline products from the residual melt which is enriched with impurities. H. Tang and J. Ulrich combined the washing step and the solid-liquid separation in a hydraulic wash column. To evaluate the possibility of its application, a certain crystal permeability range is needed. The permeability of phosphoric acid hemihydrate crystal beds which result from different crystal sizes as well as crystal yield and crystal purity were studied. The key parameters were the width of the crystals, the supersaturation, and the stirring speed. The results show that a crystal bed which contains larger crystals gives a higher permeability. A higher supersaturation leads to a higher crystal yield but more impurity inclusions in crystals. A higher stirring speed causes more impurity inclusions, as well.
H. Tang, J. Ulrich
Permeability, Purity, and Yield in Crystal Beds
Chem. Eng. Technol. 2016, 39 (7), 1263–1267.
Continuous Tubular Cooling Crystallizer
July 12, 2016
The manufacturing of small lot size products, e.g., fine chemicals, life science products, and pharmaceuticals, is conventionally carried out in batch mode, but continuous processing would offer multiple advantages to improve product quality, cost efficiency, safety, and reduce time to market. Typically, the syntheses of those products are carried out in the liquid phase. Thus, cooling crystallization from solution is an important unit operation for purification and product isolation, when, e.g., distillation is not applicable. L. Hohmann et al. developed a continuously operated scalable tubular cooling crystallizer for lab-scale application, based on the coiled flow inverter design. Cooling crystallization experiments with a binary mixture of L-alanine and water as test system were carried out both in batch and in continuous mode. Experimental characterization proved a narrow residence time distribution of the liquid phase close to ideal plug flow. Counter-current air cooling allows for adjusting linear and curved temperature profiles. Unseeded operation with the test system demonstrated that nucleation has to be actively controlled to successfully apply intensified continuous cooling crystallization processes.
L. Hohmann, R. Gorny, O. Klaas, J. Ahlert, K. Wohlgemuth, N. Kockmann
Design of a Continuous Tubular Cooling Crystallizer for Process Development on Lab-Scale
Chem. Eng. Technol. 2016, 39 (7), 1268–1280.