Synthesis and application of carbonated fatty acid esters from carbon dioxide including a life cycle analysis.

Carbon dioxide can be used in various ways as a cheap C1 source. However, the utilization of CO2 requires energy or energy-rich reagents, which leads to further emissions, and therefore, diminishes the CO2-saving potential. Therefore, life cycle assessment (LCA) is required for each process that uses CO2 to provide valid data for CO2 savings. Carbon dioxide can be incorporated into epoxidized fatty acid esters to provide the corresponding carbonates. A robust catalytic process was developed based on simple halide salts in combination with a phase-transfer catalyst. The CO2-saving potential was determined by comparing the carbonates as a plasticizer with an established phthalate-based plasticizer. Although CO2 savings of up to 80 % were achieved, most of the savings arose from indirect effects and not from CO2 utilization. Furthermore, other categories have been analyzed in the LCA. The use of biobased material has a variety of impacts on categories such as eutrophication and marine toxicity. Therefore, the benefits of biobased materials have to be evaluated carefully for each case. Finally, interesting properties as plasticizers were obtained with the carbonates. The volatility and water extraction could be improved relative to the epoxidized system.

Evaluation of industrially applied heat-transfer fluids as liquid organic hydrogen carrier systems.

Liquid organic hydrogen carrier (LOHC) systems offer a very attractive method for the decentralized storage of renewable excess energy. In this contribution, industrially well-established heat-transfer oils (typically sold under trade names, e.g., Marlotherm) are proposed as a new class of LOHC systems. It is demonstrated that the liquid mixture of isomeric dibenzyltoluenes (m.p. -39 to -34 °C, b.p. 390 °C) can be readily hydrogenated to the corresponding mixture of perhydrogenated analogues by binding 6.2 wt% of H2. The liquid H2 -rich form can be stored and transported similarly to diesel fuel. It readily undergoes catalytic dehydrogenation at temperatures above 260 °C, which proves its applicability as a reversible H2 carrier. The presented LOHC systems are further characterized by their excellent technical availability at comparably low prices, full registration of the H2 -lean forms, and excellent thermal stabilities.

Selection of stationary phase particle geometry using X-ray computed tomography and computational fluid dynamics simulations.

The X-ray computed tomography (CT) is used to determine local parameters related to the column packing homogeneity and hydrodynamics in columns packed with spherically and irregularly shaped particles of same size. The results showed that the variation of porosity and axial dispersion coefficient along the column axis is insignificant, compared to their radial distribution. The methodology of using the data attained by CT measurements to perform a CFD simulation of a batch separation of model binary mixtures, with different concentration and separation factors is demonstrated. The results of the CFD simulation study show that columns packed with spherically shaped particles provide higher yield in comparison to columns packed with irregularly shaped particles only below a certain value of the separation factor. The presented methodology can be used for selecting a suited packing material for a particular separation task.

Solvent system selection in counter-current chromatography using conductor-like screening model for real solvents.

The aim of this investigation was to minimize the experimental effort for solvent system selection in counter-current chromatography. The separation mechanism in counter-current chromatography is based exclusively on the partitioning of the solute between the two liquid phases. Therefore, a quantum chemical method combined with statistical thermodynamics (conductor-like screening model for real solvents, COSMO-RS) was used for the prediction of the partition coefficient. A comparison of the experimental and predicted data for five model solutes systems demonstrated the potential of the use of COSMO-RS as a screening tool for the solvent system selection.

COSMO-RS: an alternative to simulation for calculating thermodynamic properties of liquid mixtures.

The conductor-like screening model for realistic solvation (COSMO-RS) method has been established as a novel way to predict thermophysical data for liquid systems and has become a frequently used alternative to force field-based molecular simulation methods on one side and group contribution methods on the other. Through its unique combination of a quantum chemical treatment of solutes and solvents with an efficient statistical thermodynamics procedure for the molecular surface interactions, it enables the efficient calculation of many properties that other methods can barely predict. This review presents a short delineation of the theory, the application potential and limitations of COSMO-RS, and its most important application areas.

Hydrodynamic impact of particle shape in slurry packed liquid chromatography columns.

We report on a series of flow velocity and efficiency profiles, which were measured across the cross section of preparative chromatographic columns packed with different stationary phase materials using computed tomography. It is shown that this non-invasive technique is very useful for visualization of the inner part of a packed column and measurement of the spatial resolved column packing properties. For evaluation of the influence of the particle shape on the velocity distribution and column performance, irregular and spherical reversed phases were studied in detail. The results showed a decreasing velocity towards the column wall most certainly due to a lower permeability. This effect was much less pronounced in the case of spherical particles, indicating a more homogenous packing structure. The influence of the column packing pressure, as a possible measure for improvement of the packing homogeneity was also studied. It was shown that under the same packing conditions spherical particles always lead to a more homogeneous packing. The overall results of this work contribute to the origin of the fact that spherical material is superior to irregular one from the hydrodynamic point of view.

Model-based design of a pilot-scale simulated moving bed for purification of citric acid from fermentation broth.

One of the conventional processes used for the recovery of citric acid from its fermentation broth is environmentally harmful and cost intensive. In this work an innovative benign process, which comprises simulated moving bed (SMB) technology and use of a tailor-made tertiary poly(4-vinylpyridine) (PVP) resin as a stationary phase is proposed. This paper focuses on a model-based design of the operation conditions for an existing pilot-scale SMB plant. The SMB unit is modeled on the basis of experimentally determined hydrodynamics, thermodynamics and mass transfer characteristics in a single chromatographic column. Three mathematical models are applied and validated for the prediction of the experimentally attained breakthrough and elution profiles of citric acid and the main impurity component (glucose). The transport dispersive model was selected for the SMB simulation and design studies, since it gives a satisfactory prediction of the elution profiles within acceptable computational time. The equivalent true moving bed (TMB) and SMB models give a good prediction of the experimentally attained SMB separation performances, obtained with a real clarified and concentrated fermentation broth as a feed mixture. The SMB separation requirements are set to at least 99.8% citric acid purity and 90% citric acid recovery in the extract stream. The complete regeneration in sections 1 and 4 is unnecessary. Therefore the net flow rates in all four SMB sections have been considered in the unit design. The influences of the operating conditions (the flow rate in each section, switching time and unit configuration) on the SMB performances were investigated systematically. The resulting SMB design provides 99.8% citric acid purity and 97.2% citric acid recovery in the extract. In addition the citric acid concentration in the extract is a half of its concentration in the pretreated fermentation broth (feed).

Dissolution rate enhancement by adsorption of poorly soluble drugs on hydrophilic silica aerogels.

The aim of this work is to evaluate the feasibility of hydrophilic silica aerogels as drug carriers and to investigate the influence of the aerogels properties on the release rate of poorly water-soluble drugs. Hydrophilic silica aerogels of different densities were loaded with two model drugs, ketoprofen and griseofulvin, by adsorption from their solution in supercritical CO2. It is demonstrated that up to 30 wt% of ketoprofen and 5.4 wt% of griseofulvin can be deposited on hydrophilic aerogels through physical adsorption. The obtained drug-aerogel formulations were characterized by IR- and UV-spectroscopy, X-ray diffraction and scanning electron microscopy. Release kinetics of both drugs were studied in vitro. The release rate of ketoprofen from the drug-aerogel formulation is much faster than that of the corresponding crystalline drugs. The release rate of ketoprofen increases in 500% and that of griseofulvin in 450%, respectively. The reasons for the release enhancement are the enlarged specific surface area of drugs by adsorption on aerogels compared to their crystalline form and the immediate collapse of aerogel network in aqueous media. The dissolution rate of poorly water soluble drugs can be significantly enhanced by adsorption on highly porous hydrophilic silica aerogels.