Abstract
The presence of water in the form of relative humidity (RH) may lead to deliquescence of crystalline components above a certain RH, the deliquescence RH (DRH). Knowing the DRH values is essential, e.g., for the agrochemical industry, food industry, and pharmaceutical industry to identify stability windows for their crystalline products. This work applies the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) to purely predict the DRH of single components (organic acids, sugars, artificial sweeteners, and amides) and multicomponent crystal mixtures thereof only based on aqueous solubility data of the pure components. The predicted DRH values very well agree with the experimental ones. In addition, the temperature influence on the DRH value could be successfully predicted with PC-SAFT. The DRH prediction also differentiates between formation of hydrates and anhydrates. PC-SAFT-predicted phase diagrams of hydrate-forming components illustrate the influence of additional components on the hydrate formation as a function of RH. The DRH prediction via PC-SAFT allows for the determining of the stability of crystals and crystal mixtures without the need for time-consuming experiments.
Highlights
Water is omnipresent in the atmosphere and might be potentially absorbed by any kind of product
The deliquescence relative humidity (DRH) was predicted by a coupled solubility/water-sorption calculation with Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), which explicitly considers intermolecular interactions between the components in the liquid phase
By comparing the DRH values predicted via PC-SAFT with those calculated by Raoult’s law, it was shown that thermodynamic activity coefficients are indispensable for a correct prediction of the deliquescence behavior
Summary
Water is omnipresent in the atmosphere and might be potentially absorbed by any kind of product. Deliquescence is a first-order phase transformation, where a crystalline solid is transformed into an aqueous saturated solution. This occurs abruptly as soon as a crystal is stored above its deliquescence relative humidity (DRH) [2]. The measurement of DRH is performed via gravimetric vapor-sorption measurements, equilibrium water-activity measurements of saturated solutions, or determining dynamic dew-point sorption profiles [10]. Predictions of the DRH values for single components have been performed via Raoult’s law This simplest approach neglects any solute–water interactions in the liquid phase, and results might significantly deviate from experimental data [13]. DRH values of single components and of multicomponent crystal mixtures were predicted using PC-SAFT only based on the single-component solubility data in water. The influence of temperature on the DRH was predicted and compared with measured DRH values from literature
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