Search

The kinetics of chemical reactions in the liquid phase are often strongly determined by the reaction solvent. Consequently, the choice of the optimal solvent is an important task in chemical proces...

This work focuses on the ionic liquid (IL) synthesis starting from dimethyl carbonate and 1-ethylimidazole in methanol. In-situ IR-spectroscopy is used to gain time-dependent concentrations for kinetic analysis. The reaction is found to be self-accelerating, since the solvent polarity increases with the formation of the ionic product. This corresponds to a salting-out effect. Since the reaction rate is increasing in the beginning, pre-dosing of the product is proposed to enhance the overall productivity. Therefore, the space-time-yield is calculated as the arithmetic mean of the reaction rate with a varying starting point. It turns out that pre-dosing does not enhance the productivity here, since the space-time-yield of the complete reaction progress is below the initial reaction rate. Beyond that, two sharp bends can be observed in the progress of the reaction rate coefficient that point towards sudden changes in the reaction environment. The first bend can be assigned to a phase separation of the ionic liquid on a microscopical scale. The second bend takes place when the IL concentration surpasses roughly one sixth of the methanol concentration. Above that threshold, the whole amount of methanol is captured in the solvation shell of the anion monomethyl carbonate, as quantum chemical calculations suggest. Finally, the reaction rate coefficients were calculated using quantum chemical methods with respect to the solvent environment. The theoretical results show a good accordance with experimental values for the starting compositions. Thus, theoretical calculations help to estimate productive reaction mixtures.

Sustainable solvents are crucial for chemical processes and can be tailored to applications by computer-aided molecular and process design (CAMPD). Recent CAMPD methods consider not only economics but also environmental hazards and impacts. However, holistic environmental assessment needs to address the complete life cycle of solvents. Here, we propose a CAMPD framework integrating Life Cycle Assessment (LCA) of solvents from cradle-to-grave: COSMO-susCAMPD. The framework builds on the COSMO-CAMPD method for predictive design of solvents using COSMO-RS and pinch-based process models. Cradle-to-grave LCA is enabled by combining predictive LCA from cradle-to-gate using an Artificial Neural Network with gate-to-grave Life Cycle Inventory data from the process models. The framework is applied to design solvents in a hybrid extraction-distillation process. The results highlight the need for cradle-to-grave LCA as objective function: Heuristics, economics, or cradle-to-gate LCA lead to suboptimal solvent choices. COSMO-susCAMPD thus enables the holistic environmental design of solvents using cradle-to-grave LCA., Chemical Engineering Science, 245, ISSN:0009-2509

Molecular systems design & engineering 3(4), 645-657 (2018). doi:10.1039/C7ME00125H, Published by Royal Society of Chemistry, Cambridge

Property predictions are essential when dealing with molecules that have not been investigated experimentally yet. The accuracy of current predictive models like predictive perturbed-chain polar statistical associating fluid theory (PCP-SAFT) and conductor-like screening model for real solvents (COSMO-RS) is limited. We propose a combination of predictive models in order to yield a higher accuracy. Information from both predictive models are combined in PCP-SAFT parameter space using a log-likelihood function. Experimental vapor pressures, enthalpies of vaporization, and liquid densities over a wide temperature range are used to evaluate the predictions. The average error in the combined property prediction is lower than the error of the individual models. In addition, the maximum error is considerably lowered.

Chemical engineering science 159, 84-92 (2017). doi:10.1016/j.ces.2016.05.038 special issue: "iCAMD – Integrating Computer-Aided Molecular Design into Product and Process Design / Edited by Claire Adjiman and André Bardow", Published by Elsevier Science, Amsterdam [u.a.]

We present a hybrid modeling strategy for the prediction of octanol/water partition coefficients for alcohol ethoxylate surfactants of varying chain lengths. The strategy makes use of molecular dynamics (MD) simulations for the generation of molecular conformations in the presence of a solvent. A clustering of the conformations from the MD trajectories was carried out based on principal component analysis of their dihedral angles. Representative conformations thus selected were then used in the conductor-like screening model for realistic solvents (COSMO-RS). Each conformation has been assigned a weight using an equation derived on the basis of its probability of occurrence in the MD trajectory. Experimental partition coefficients were reproduced within conformation-independent accuracy of COSMO-RS despite the size and flexibility of the ethoxy chain otherwise posing a challenge on their solvation modeling.

The COSMO-SAC model for the calculation of activity coefficients has been improved by incorporating three-dimensional geometric information on molecules. This information is added to the model by means of the effective contact area of the molecules. We define a procedure to compute this contact area by using a probing sphere. The probing sphere rolls around the COSMO surfaces of two contacting atoms to define a spherical cap on each atom. The segments of the COSMO surfaces within the spherical caps are marked, and the summation of their areas defines the contact area for a pair of contacting molecules. The effective contact areas are used to compute the σ-profiles and the Onsager screening energies in the calculation of the surface activity coefficients, allowing us to remove one parameter from the COSMO-SAC model. The σ-profiles and effective areas need to be calculated only once and can be stored in a database. We show that the new model, named COSMO-3D because some three-dimensional information (the po...

This work describes the application of a hybrid two-step enantioselective separation process. As a first step, pertraction using supported liquid membranes provides an initial enrichment, while the following preferential crystallization delivers the enantiopure crystals as final product. Mandelic acid in water was studied as a model system. Using a suitable chiral selector, pertraction provides enrichments exceeding 10% and reaching up to 20% in the permeate phase, which was sufficient to allow for subsequent selective preferential crystallization. Based on the individual performances of pertraction and crystallization, overall yields and productivities are estimated. The calculated productivities are compared with values achievable in alternatively applicable chromatographic separation processes using chiral stationary phases. The realized hybrid pertraction-crystallization process is in its present state for the example considered still inferior to preparative chromatography. Strategies for further improvement are suggested.

Integrierter Prozess zur Trennung chiraler Systeme mit Verbindungsbildung Dipl.-Ing. (FH) L. Gou (E-Mail: gou@mpi-magdeburg.mpg.de), Dr. H. Lorenz, Dipl.-Ing. S. Robl, Dr. K. Leonhard, Prof. K. Schaber, Prof. A. Seidel-Morgenstern Max-Planck-Institut fur Dynamik komplexer technischer Systeme, Sandtorstrase 1, D-39106 Magdeburg, Germany Universitat Karlsruhe, Institut fur Technische Thermodynamik und Kaltetechnik, Engler-Bunte-Ring 21, D-76131 Karlsruhe, Germany RWTH Aachen, Lehrstuhl fur Technische Thermodynamik, Schinkelstrase 8, D-52062 Aachen, Germany Otto-von-Guericke-Universitat Magdeburg, Institut fur Verfahrenstechnik, Universitatsplatz 2, D-39106 Magdeburg, Germany DOI: 10.1002/cite.201050380