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  • In general accurate results for the

    2019-07-13

    In general, accurate results for the prediction of the solubility in scCO2 + cosolvents using the CPA-EoS were verified. ALD values for each solute (Table 1) varied from 0.04 to 1.5. Few solutes, such as lauric acid, myristic acid, hydroquinone and salicylic acid, presented the highest ALD values. According to Ting et al. [23], higher deviations for carboxylic acids with short chain can be associated to their lower melting temperatures. The melting temperatures for lauric (dodecanoic acid) and myristic (tetradecanoic acid) acids are 316.6 K and 326.5 K, respectively. These values are very close to the temperatures of solubility measurements, indicating that CPA model can not describe these systems at conditions close to the phase transition region. In this way, excluding the myristic 7ACC2 solubility data at 318 K, the ALD value decreased from 1.32 to 0.75 (at T = 308 K), i.e., when the difference between the melting temperature and the solubility temperature measurement, the CPA prediction significantly improves. The ALD value obtained by evaluating all the systems simultaneously was 0.47, and excluding lauric and myristic acids the ALD is decreased to 0.32. Both values are significantly lower than those reported by Ting et al. [23] (ALD = 0.64), when PR + COSMOSAC equation was used for prediction of the solubility of 23 solutes in scCO2 and cosolvents. Excluding trans-ferulic acid, all the solutes here evaluated were also investigated by Ting et al. [23] applying the SAFT model to predict solubility of naphthalene, phenanthrene, anthracene, pyrene and benzoic acid in scCO2 with cosolvents, Yang et al. [22] reported AARD values (between 4.7% and 48.5%) lower than those obtained with a cubic EoS (ranging from 15.0% to 70.8%). This difference was probably due to the fact that these authors have mainly evaluated systems containing non-associating compounds. For instance, to predict the solubility of caffeic acid, which has three association sites, the values estimated using a cubic EoS were more than 100 times lower than the actual experimental data [24]. In addition, the CPA EoS presented good accuracy when predicting the solubility of caffeic acid in scCO2 + ethanol, with ALD = 0.29 [24]. The dispersion between the experimental and calculated data can be visualized in Fig. 3. Fig. 3 divides the compounds in aromatic acids (●), aromatic alcohols (■), aliphatic acids (▲) and aliphatic alcohols ( × ). Underestimated prediction of the solubility data was observed in most cases. The solubility of hydroquinone was the only one significantly overestimated. No systematic deviations, by analyzing the different classes of compounds, was identified, since the highest differences between experimental and calculated data were observed for an aromatic acid (salicylic acid), an aliphatic acid (lauric acid) and an aromatic alcohol (hydroquinone). Experimental errors should be analyze since they could justify the deviation between predicted and experimental data. Error experimental for solubility data in ternary and quaternary systems were not reported in detail (for each point) in most solubility data sources used in our work. Excluding the ferulic acid data, the mean deviations values reported ranged from 3 to 15%. The maximum experimental error was verified for the paracetamol solubility [39]. In this way, the error values does not show relevant to justify the deviation between the experimental and calculated data for solubility of the solutes in the CO2 and cosolvent mixtures. Because the ternary solubilities of solids in systems containing cosolvents are complex functions of temperature, pressure and cosolvent/cosolute composition [13], it is essential to study the influence of variables, such as temperature, pressure, concentration and type of cosolvent, and number of associating sites of the solute, on the results.
    Conclusions
    Introduction Utilization of amino acid solutions is highly significant in many industrial and biological processes such as applicability of these substances as constituent of pharmaceutical products and food additives. Therefore, the investigations in biotechnology have obtained lots of attentions to develop a chemical process for separation and purification of amino acids which are the simplest structures among plenty of bio-chemicals, and are so similar with complex bio-chemicals [1]. Thus, an accurate explanation of thermodynamic properties of bio-products like amino acids is so essential for designing and scaling up the chemical and bio-separation processes, and is indispensable for getting knowledge of phase equilibria.