Monika Johannsen

Solubilities of the xanthines caffeine, theophylline and theobromine in supercritical carbon dioxide

Abstract Johannsen, M. and Brunner, G., 1994. Solubilities of the xanthines caffeine, theophylline and theobromine in supercritical carbon dioxide. Fluid Phase Equilibria, 95: 215-226. An apparatus for the experimental determination of the equilibrium solubilities of solids in dense gases is described. Determination of solubilities has been performed by using a static analytical method with direct coupling of an equilibrium cell to a supercritical fluid Chromatographic (SFC) system. The solubilities of caffeine, theophylline and theobromine in supercritical carbon dioxide were measured at different temperatures (313, 333 and 353 K) and over a pressure range of 20–35 MPa. Although the chemical structures of the xanthines are very similar, their solubilities in supercritical carbon dioxide vary substantially. The solubilities of caffeine in CO2 are one order of magnitude higher than those of theophylline and two orders of magnitude higher than those of theobromine. Solubility values obtained in this work are compared with published data. Reasons for observed differences are discussed.

Supercritical-fluid extraction of oil-palm components

Abstract Residue from the mechanical processing of palm oil was treated with supercritical-fluid extraction (SFE) to extract carotenes. This was done at different extraction conditions. Also, leaves of palm oil trees were extracted using supercritical fluid to gain high concentrations of tocopherols in the extract. The aim of these SFE experiments was to evaluate whether either the carotene or tocopherol contents of the extracts were sufficiently high enough to allow downstream processing of these waste products. In addition, solubility data for α-tocopherol in supercritical carbon dioxide in a density range of 220–930 kg m −3 were measured.

Separation of stereoisomers in a simulated moving bed-supercritical fluid chromatography plant

The combination of two techniques, simulated moving bed (SMB) and supercritical fluid chromatography (SFC), leads to an apparatus with unique features. Besides the known advantages of the SMB process, like reduced solvent consumption and its continuity, the use of supercritical carbon dioxide as the mobile phase offers an easy product recovery by depressurizing the supercritical fluid. Details of a SMB-SFC plant are presented for the first time. Due to the large number of process parameters a simulation of the SMB process is necessary to achieve optimal operating conditions. The most important thermodynamic information for a SMB process is the adsorption isotherms. Therefore, isotherms for two phytol isomers are measured and correlated. A fast dynamic model for the simulation of SMB is used to calculate the region of complete separation taking different column configurations and the compressibility of the mobile phase into account.

Separation of ibuprofen enantiomers by supercritical fluid simulated moving bed chromatography

The continuous separation of R(−)-ibuprofen and S(+)-ibuprofen by supercritical fluid simulated moving bed chromatography has been developed. First, experiments were performed at a low concentration level. Therefore, a starting set of operating parameters was calculated using the “triangle theory,” which has been developed in the frame of equilibrium theory. Subsequently, the feed concentration was increased. A dynamic simulation program, based on a plug flow model with axial dispersion and linear mass transfer resistance, was used to predict the effect of operating variables on the process performance. Adsorption isotherms were determined with the elution by a characteristic point method. The experimental results were compared both with the model predictions based on the triangle theory and with the results of simulations.

Separation of enantiomers of ibuprofen on chiral stationary phases by packed column supercritical fluid chromatography

A packed column supercritical fluid chromatography (SFC) method for the separation of ibuprofen enantiomers on a chiral stationary phase and CO2 with modifier as mobile phase has been developed at an analytical scale. Among 11 different stationary phases the Kromasil CHI-TBB phase showed by far the best separation properties. The influence of different modifiers, injection solvents, temperature, and pressure, and density of the fluid, respectively, on the separation behavior has been studied. It was found that the separation behavior strongly depends on the type of modifier and the modifier content. Temperature and pressure are of less influence.

Simulated moving bed chromatography with supercritical fluids for the resolution of bi-naphthol enantiomers and phytol isomers

The combination of the simulated moving bed (SMB) technique with supercritical fluid chromatography (SFC) leads to a process with unique features. Besides the known advantages of the SMB process, the use of supercritical carbon dioxide as the mobile phase offers the advantages of reduction in organic solvents and an easy eluent/solute separation. Because of the low viscosity and high diffusion coefficients of supercritical fluids, a high efficiency is possible. The steps of process development for SMB SFC are presented using the separations of the bi-naphthol enantiomers and phytol isomers as examples. The development of a packed column SFC method at an analytical scale is shown for the separation of the bi-naphthol enantiomers on a chiral stationary phase and CO(2) with a modifier as the mobile phase. The influence of the modifier, modifier content, and column configuration on productivity of the SMB SFC process was investigated by simulation. The first set of experiments was performed in the SMB separation of phytol isomers at low concentration to test the feasibility of the SMB SFC high purity separation of the binary mixtures. In the second set of experiments, the productivity of the process was increased by increasing the feed concentration up to 54 grams feed per liter stationary phase (SP) and hour (g(feed)/l(SP) h).

Regeneration Methods for Caffeine-Loaded CO2

Abstract Supercritical gas extraction for the decaffeination of green coffee beans has become an established method in the last decade. However, because of the commercial aspects in this field, few research results on applications have been published. In this publication, three different methods for the regeneration of caffeineloaded CO2 are presented: depressurization, adsorption with activated carbon, and absorption with water. For all these methods, phase equilibrium experiments with pure caffeine were done. Furthermore, pilot-plant experiments were performed to decaffeinate green coffee beans.