Continuous processing gains importance in the fine chemical and pharmaceutical industries where crystallization is an important downstream operation. Seeded cooling crystallization of the L-alanine/water system was investigated under similar conditions, i.e., temperature interval, cooling rate, and seed material, both in a stirred batch vessel and in a continuous plug flow crystallizer in the coiled flow inverter (CFI) design with horizontal helical tube coils (ID = 4 mm) and frequent 90°bends of the coils. Short-cut calculations based on characteristic time scales and the Damkoḧler number allow for comparing the batch and continuous crystallization processes. The experimental results reveal crystal growth and growth rate dispersion to be dominating on the product crystal size distribution (CSD). However, at low flow rates of approximately 31 g min −1 , a moving sediment flow of the slurry was present in the CFI crystallizer, resulting in further size dispersion effects. Elevated flow rates of approximately 40 g min −1 resulted in a more homogeneous suspension flow and a product CSD comparable to batch quality. Simulation studies based on a population balance equation model strengthen the hypothesis of the solid phase residence time distribution (RTD S ) to be more spread in the moving sediment flow regime, leading to a wider product CSD.

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Furan compounds are of mounting global interest due to their biorenewable nature and their potential to replace petroleum-based compounds as feedstocks in manufacturing. In this work the solubilities of furfural and the furancarboxylic acids 2-furoic acid (FA), 5-formyl-2-furancarboxylic acid (FFA), and 2,5-furandicarboxylic acid (FDCA) in aqueous solutions and organic solvents were investigated experimentally and by modeling with perturbed-chain statistical associating fluid theory (PC-SAFT). The PC-SAFT pure-component parameters of the solutes FA, FFA, and FDCA and one binary parameter between each solute and each solvent were adjusted to fit experimentally determined solubilities of each solute in each organic solvent or in water. Pure-component parameters of furfural were fitted to experimental density data and vapor-pressure data, and a binary interaction parameter was fitted to capture the solubility behavior of furfural in water. Modeling of pH effects enhanced predictions of the mutual influences of the acids on their solubilities in ternary aqueous systems. Mutual solubility influences of furfural and the furancarboxylic acids were accurately modeled with one constant binary parameter for the acid–furfural mixtures. All PC-SAFT modeling results were validated with new experimental solubility data at 35 °C, which were measured by HPLC analysis of equilibrated saturated solutions.

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Succinic acid (SA) was esterified with ethanol using Candida antarctica lipase B immobilized on acrylic resin at 40 and 50 °C. Enzyme activity in the reaction medium was assured prior to reaction experiments. Reaction-equilibrium experiments were performed for varying initial molalities of SA and water in the reaction mixtures. This allowed calculating the molality-based apparent equilibrium constant K as function of concentration and temperature. K was shown to depend strongly on the molality of water and SA as well as on temperature. It could be concluded that increasing the molality of SA shifted the reaction equilibrium towards the products. Water had a strong effect on the activity of the enzyme and on K . The concentration dependence of K values was explained by the activity coefficients of the reacting agents. These were predicted with the thermodynamic models Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), NRTL, and Universal Quasichemical Functional Group Activity Coefficients (UNIFAC), yielding the ratio of activity coefficients of products and reactants K . All model parameters were taken from literature. The models yielded K values between 25 and 115. Thus, activity coefficients have a huge impact on the consistent determination of the thermodynamic equilibrium constants K . Combining K and PC-SAFT-predicted K allowed determining K and the standard Gibbs energy of reaction as function of temperature. This value was shown to be in very good agreement with results obtained from group contribution methods for Gibbs energy of formation. In contrast, inconsistencies were observed for K using K values from the classical g-models UNIFAC and NRTL. The importance of activity coefficients opens the door for an optimized reaction setup for enzymatic esterifications.