de Ab André Haan

Complexation of phenols and thiophenol by phosphine oxides and phosphates. Extraction, isothermal titration calorimetry, and ab initio calculations

To develop a new solvent-impregnated resin system for the removal of phenols from water the complex formation of triisobutylphosphine sulfide (TIBPS), tributylphosphate (TBP), and tri-n-octylphosphine oxide (TOPO) with a series of phenols (phenol, thiophenol, 3-chlorophenol, 3,5-dichlorophenol, 4-cyanophenol, and pentachlorophenol) was studied. The investigation of complex formation between the extractants and the phenols in the solvent toluene was carried out using liquid-liquid extraction, isothermal titration calorimetry (ITC), and quantum chemical modeling (B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) and MP2/6-311++G(2d,2p)//B3LYP/6-311G(d,p)). The equilibrium constant (binding affinity, Kchem), enthalpy of complex formation (DeltaH), and stoichiometry (N) were directly measured with ITC, and the entropy of complexation (DeltaS) was derived from these results. A first screening of K chem toward phenol revealed a very high binding affinity for TOPO, and very low binding affinities for the other extractants. Modeling results showed that although 1:1 complexes were formed, the TIBPS and TBP do not form strong hydrogen bonds. Therefore, in the remainder of the research only TOPO was considered. Kchem of TOPO for the phenols in toluene increased from 1,000 to 10,000 M(-1) in the order phenol < pentachlorophenol < 3-chlorophenol < 4-cyanophenol approximately 3,5-dichlorophenol (in line with their pKa values, except for pentachlorophenol) in the absence of water, while the stoichiometric ratio remained 1:1. In water-saturated toluene, the binding affinities are lower due to co-complexation of water with the active site of the extractant. The increase in binding affinity for TOPO in the phenol series was confirmed by a detailed ab initio study, in which Delta H was calculated to range from -10.7 kcal/mol for phenol to -13.4 kcal/mol for 4-cyanophenol. Pentachlorophenol was found to behave quite differently, showing a DeltaH value of -10.5 kcal/mol. In addition, these calculations confirm the formation of 1:1 H-bonded complexes.

Binary and Ternary Vapor-Liquid Equilibrium Data of the System (Ethylbenzene+Styrene+4-Methyl-N-butylpyridinium Tetrafluoroborate) at Vacuum Conditions and Liquid-Liquid Equilibrium Data of Their Binary Systems

Ethylbenzene and styrene are currently separated by ordinary fractional distillation, which is challenging due the low relative volatility of this mixture of 1.3 to 1.4. Extractive distillation is a promising alternative to save capital and operational expenditures. Recently, ionic liquids (ILs) have been reported as a promising option to replace commonly used organic solvents like sulfolane. The IL 4-methyl-N-butylpyridinium tetrafluoroborate ([4-mebupy][BF4]) is an IL with a strong effect on the relative volatility of the ethylbenzene/styrene mixture. In this work, binary VLE data in the range of (3 to 30) kPa, ternary VLE data at (5, 10, and 15) kPa, and binary LLE data at (313.2, 333.2, and 353.2) K have been determined for the system (ethylbenzene + styrene + [4-mebupy][BF4]). The ternary VLE experiments show that [4-mebupy][BF4] can enhance the relative volatility up to 2.7 to 2.8, and thereby [4-mebupy][BF4] has a stronger effect on the relative volatility than the benchmark solvent sulfolane, which can increase the relative volatility up to 2.3. Therefore, [4-mebupy][BF4] is a promising solvent for use in extractive distillation to separate ethylbenzene from styrene. The binary and ternary VLE data were correlated separately with the NRTL model and were regressed both together with the binary LLE data. The NRTL model could describe both data sets properly. The ternary VLE data could not be properly calculated by the binary NRTL parameters determined solely from the binary systems

Extractant Screening for Liquid-Liquid Extraction in Environmentally Benign Production Routes

Fermentation processes offer a promising alternative for the production of chemicals by more environmentally benign routes. However, a major challenge in applying this technology remains the recovery of typically highly hydrophilic products from the complex broth. Here, we report the results of a study with the aim to enhance the separation of organic acids from fermentation broths by liquid-liquid extraction by improved design of the extractant. Based on extensive literature research supported by molecular modeling and isothermal titration calorimetry (ITC) experiments, different groups of extractants were evaluated, including amines, amides, superbases, guanidines and N-oxides. Octanol, 2-octyl-1-dodecanol and heptane were used as solvents. After extraction, a sample of the aqueous phase was analyzed with high performance liquid chromatography (HPLC) and the distribution coefficients were calculated. The obtained results showed that tertiary amines remain the state-of-the-art extractants for the recovery of organic acids. Highly basic compounds, like guanidines or superbases, as well as the N-oxides, were not able to outperform the tertiary amines. The performed work demonstrated that the applied molecular modeling tools were not sufficient to adequately assess the interactions observed between amines and organic acids.

Entrainer-based reactive distillation versus conventional reactive distillation for the synthesis of fatty acid esters

In this paper different reactive distillation configurations for the synthesis of isopropyl myristate were compared with the use of process models made in Aspen Plus. It can be concluded that the configurations in which an entrainer is added are more capable to reach the required conversion of 99.0%: the required reactive section and energy amount is significantly smaller than in the configurations without entrainer. The differences in design and operating parameters of the different entrainer-based reactive distillation configurations are small. Only at higher pressures a two column set-up is favourable due to the reduced amount of entrainer.

Modeling the liquid back mixing characteristics for a kinetically controlled reactive distillation process

The state of the art equilibrium model and the rate-based models for reactive distillation (RD) are well known and have been used since a couple of decades. However, these models are not sufficient to represent a slow reaction process that is kinetically controlled. This shortcoming is due to neglecting the effect of liquid back mixing on the whole process. This work starts with reviewing the modeling approach for the RD and then discusses the applicability of various models. The main focus is on the extension of the dynamic rate-based model to take into account the liquid back mixing. We also show how the axial dispersion is introduced into the RD model, without adopting the axial dispersion model. The results of the rate-based model were compared, with and without the axial dispersion. Remarkably, the extended model predicts more accurately the kinetically controlled process, as compared to the conventional rate-based model.

Enhanced configurations for polyesters synthesis by reactive distillation

Abstract This study explores the best suitable internals and various feed configurations of a reactive distillation process for unsaturated polyester synthesis. Multi-product simulations were performed to find the operational parameters for producing different grades of polyester in the same equipment. The product transition time during product changeover is determined for various configurations and product grades. The selection criteria for the best configuration are the minimum requirements of volume and energy to produce 100 ktpy polyesters. The results of the rigorous simulations carried out in Aspen Custom Modeler show that the best configurations employ the reactive stripping section as a packed or trayed bubble column, and the reactive rectifying section as a packed column. With respect to the feed configuration, the feeding of monoesters to the RD column significantly intensifies the polyester process as compared to an anhydrous reactant fed directly to the column. Moreover, the product transition time in this configuration is also significantly reduced as compared to the other configurations.