The nucleation kinetics of ice were investigated with four different types of aqueous solutions. The studied aqueous solutions, i.e., sucrose solution, ionic liquid (IL) solution, pyrolysis oil extract (PO) solution, and acetone‐1‐butanol‐ethanol (ABE) solution, were concentrated by batch suspension freeze crystallization. The nucleation kinetics were investigated using a temperature response method which results in data on nucleation rate per crystal. The obtained nucleation rate per crystal value can be used when dimensioning continuous crystallization processes: the nucleation rate per crystal is inversely proportional to the residence time in continuous crystallization. The subcooling degrees for different solutions were in the range of 0.33 °C to 1.89 °C. Aqueous sucrose solutions had the fastest nucleation kinetics. Ice crystallization from non‐ideal aqueous [DBNH][OAc] ionic liquid solutions required higher subcooling degrees and the nucleation rates per crystal were higher as well. Nucleation of ice formed from aqueous pyrolysis oil extract and aqueous ABE solutions occurred at a lower subcooling degree and the obtained nucleation rate per crystal values were lower.

: The suspension freeze crystallization of aqueous 1-butanol solutions, synthetic acetone-butanol-ethanol (ABE) solutions, and ABE fermentation broth was studied as a novel concentration method that requires less energy than evaporation for water removal. The equimolar aqueous ABE solutions in a total molality range of 0 − 5.05 mol/kg (water) were proven to be ideal solutions based on the freezing point depression obtained. An aqueous solution of 8 wt % 1-butanol and three different types of aqueous ABE solutions (3:8:1:88 ABEW, 6:16:2:76 ABEW, and 10:17:2:71 ABEW (wt %)) were concentrated for 80 min by suspension freeze crystallization in a subcooling range from 0.24 to 1.15 ° C. Freeze crystallization enabled 1-butanol separation from the generated mother liquor, which split into two liquid phases after ice separation, i.e., a water-enriched phase and a 1-butanol-enriched phase. Ice yield values were higher for higher subcooling degrees and higher initial water content in the feed solutions. 1-Butanol yields separated from the mother liquors were 9.85%, 59.46%, and 22.46% for 3:8:1:88 ABEW, 6:16:2:76 ABEW, and 10:17:2:71 ABEW, respectively, whereas two-stage freeze crystallization of the fermentation broths resulted in water removal with a maximum relative percentage of 29.5%.

In the present work, freeze crystallization studies, as a novel concentration method for aqueous 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) ionic liquid solution, were conducted. In order to find the appropriate temperature and composition range for freeze crystallization, the solid–liquid equilibrium of a binary [DBNH][OAc]–water compound system was investigated with differential scanning calorimetry (DSC). Results of this analysis showed that the melting temperature of the pure ionic liquid was 58 ℃, whereas the eutectic temperature of the binary compound system was found to be −73 ℃. The activity coefficient of water was determined based on the freezing point depression data obtained in this study. In this study, the lowest freezing point was −1.28 ℃ for the aqueous 6 wt.% [DBNH][OAc] solution. Ice crystal yield and distribution coefficient were obtained for two types of aqueous solutions (3 wt.% and 6 wt.% [DBNH][OAc]), and two freezing times (40 min and 60 min) were used as the main parameters to compare the two melt crystallization methods: static layer freeze and suspension freeze crystallization. Single-step suspension freeze crystallization resulted in higher ice crystal yields and higher ice purities when compared with the single-step static layer freeze crystallization. The distribution coefficient values obtained showed that the impurity ratios in ice and in the initial solution for suspension freeze crystallization were between 0.11 and 0.36, whereas for static layer freeze crystallization these were between 0.28 and 0.46. Consequently, suspension freeze crystallization is a more efficient low-energy separation method than layer freeze crystallization for the aqueous-ionic liquid solutions studied and, therefore, this technique can be applied as a concentration method for aqueous-ionic liquid solutions.