Louw J. Florusse

Triggered Self-Assembly of Simple Dynamic Covalent Surfactants

A prototype surfactant system was developed with the unique feature that it can be switched between an aggregated, amphiphilic state and a nonaggregated, nonamphiphilic state using external stimuli. This switchable surfactant system uses the reversible formation of a dynamic covalent bond for pH- and temperature-triggered on/off self-assembly of micellar aggregates by reversible displacement of the equilibrium between nonamphiphilic building blocks and their amphiphilic counterparts. The potential for application in controlled-release systems is shown by reversible uptake and release of an organic dye in aqueous media.

Crystallization of an organic compound from an ionic liquid using carbon dioxide as anti-solvent

In this paper the anti-solvency behavior of supercritical carbon dioxide (CO2) as a way to recover an organic compound from an ionic liquid by crystallization is explored. As an example, the conditions for crystallization of the organic compound methyl-(Z)-α-acetamido cinnamate (MAAC) from the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim+][BF4−]) using supercritical CO2 as anti-solvent are studied experimentally by measuring the phase behavior of the ternary system [bmim+][BF4−] + CO2 + MAAC. MAAC can be recovered from [bmim+][BF4−] by either using a shift to higher CO2 concentrations at constant temperature (anti-solvent crystallization) or by using a shift to lower temperatures at constant CO2 concentration (thermal shift).

Fluid multiphase equilibria and critical phenomena in binary and ternary mixtures of carbon dioxide, certain n-alkanols and tetradecane

Abstract Experimental results of fluid multiphase equilibria occurring in ternary mixtures of near-critical carbon dioxide, certain n-alkanols and tetradecane are presented. The following n-alkanols were used in this investigation: decanol, octanol, heptanol, hexanol and pentanol. In the ternary systems with decanol, octanol or heptanol a closed loop liquid-vapor two-phase region in the three-phase surface liquid-liquid-vapor was found. As far as the ternary system with decanol is concerned, this phenomenon is in agreement with an earlier and unexpected finding of Patton et al. (1993). In addition, it was also found in this study that the phase diagrams of the ternary mixtures with hexanol or pentanol as the n-alkanol show further complications.

Experimental and Computational Investigation of the sII Binary He−THF Hydrate

The objective of this work is to study the binary He-THF hydrate with both experimental and theoretical approaches. Experimental data for the hydrate equilibrium at pressures up to 12.6 MPa are reported for the binary He-THF hydrate with stoichiometric THF composition (i.e., 5.56 mol % THF). These data are used to calibrate a thermodynamic model [J. Phys. Chem. C2009, 113, 422] for the prediction of hydrate equilibrium that is based on the van der Waals-Platteeuw statistical thermodynamic theory. Then this model is used to extrapolate the obtained experimental data to much higher pressures, and good agreement is observed with other available experimental data at pressures up to 150 MPa. This model is also capable of estimating the cavity occupancies for He and THF. The results show that the large cavities are completely occupied by THF molecules, whereas the small ones are partially occupied by He atoms. The He occupancy of the small cavities is less than 60%, even at high pressures (100 MPa). The occupancies predicted from this model are in close agreement with similar results from molecular simulations and a previously reported thermodynamic approach.

Prediction of phase equilibria for binary systems of hydrogen chloride with ethane, propane and n-dodecane

Abstract In many industrially important processes hydrogen chloride occurs as one of the major constituents. Due to its corrosive nature, hydrogen chloride is not an easy substance to handle in industrial or experimental facilities and, as a consequence, accurate basic data of its mixtures is scarce. In this study, we examine the ability of two theoretical approaches, PACT (perturbed anisotropic chain theory), and SAFT (statistical associating fluid theory), to predict the phase behaviour of three binary mixtures of hydrogen chloride with n -alkanes. In the PACT approach, the molecules are modelled with Lennard–Jones spherical segments with a contribution to describe the dipole of the hydrogen chloride molecule. The non-sphericity of the n -alkane molecules is accounted for via Prigogines approximation for the external degrees of freedom. In the SAFT approach, the molecules are represented by chains of spherical repulsive segments with attractive short-range sites. Hydrogen chloride is represented by a single sphere, with two attractive sites to model the dipole of the molecule. Chain molecules, such as the n -alkanes, are modelled fusing together a number of spherical segments. No attractive sites are included as these molecules are non-polar. We treat the long-range dispersion forces via variable-range square-well potentials; with the SAFT-VR approach. We find that both approaches accurately reproduce the experimental phase behaviour of the three mixtures for wide ranges of temperature and pressure. In the case of the SAFT-VR approach, both the critical region and the low temperature region are well represented with one set of parameters. However, the PACT approach requires two different sets of parameters: one for the critical region and one for lower temperature regions.

Influence of the enzyme concentration on the phase behaviour for developing a homogeneous enzymatic reaction in ionic liquid–CO2 media

A homogeneous enzymatic reaction in an ionic liquid (IL)–CO2 medium integrated with the separation of the product is proposed. It takes advantage of the miscibility switch phenomenon using CO2, which is able to force two immiscible phases to form one homogeneous phase to perform the reaction. After completion of the reaction the homogeneous fluid phase is split in two or three phases upon pressure decrease in order to facilitate the product recovery. For this purpose the enzymeCandida antarctica lipase B (CaL B) and the IL 1-hydroxy-1-propyl-3-methyl imidazolium nitrate (HOPMImNO3) are used. In this study the solubility of CO2 in solutions of CaL B in HOPMImNO3 was experimentally determined using the Cailletet apparatus, which operates according to the synthetic method. Concentrations of the enzyme vary from 3 to 12% by weight, and concentrations of CO2 from 5 to 20 mol% were investigated in a temperature range from 30 to 75 °C and pressures up to 12 MPa were applied. No precipitation of the enzyme was observed when dissolving CO2 in the IL. At constant CO2/IL ratios the pressure of the bubble points remained almost unchanged with the enzyme concentration. Triacetin tests showed that the reduction of the activity of the enzyme after storage for three months in liquid HOPMImNO3 was only of the order of 20%. Recovery and purification of the IL was possible by precipitation of the enzyme using isopropanol (IPA) as an anti-solvent.

Phase and Interfacial Tension Behavior of Certain Model Gas Condensates: Measurements and Modeling

This contribution reports on the phase and interfacial tension behavior of some model high-temperature–high-pressure gas condensates. On the one hand these types of gas condensate are becoming a subject of major interest for the oil industry, while on the other their phase and interfacial tension behavior have not been very well studied. For two different model gas condensates, both composed of the three n-alkanes, methane, butane, and decane, experimental results on their fluid phase behavior have been obtained in the temperature region 270 < T (K) < 490 and up to pressures as high as 24 MPa. Also, critical points of the two mixtures have been determined experimentally. Both mixtures show an extended retrograde region. Using the Peng–Robinson equation of state, the phase behavior of the two mixtures was modeled. In addition, the interfacial tension behavior of the model gas condensates was modeled. For that purpose, the Cahn–Hilliard theory was applied in combination with the Peng–Robinson equation of state. Satisfactory results were obtained.

Measurements on fluid multiphase equilibria in ternary mixtures of carbon dioxide, tetradecane, and certain N-alkanols

Abstract Certain ternary mixtures of near-critical carbon dioxide + n -alkanols + tetradecane have been found to display unexpected fluid multiphase equilibria. For instance, it was found that in the systems with decanol, octanol, or heptanol the three-phase liquid-liquid-vapor surface contains a two-phase liquid-vapor region which is completely bounded by a closed loop critical endpoint locus of the type liquid = liquid + vapor ( l 1 = l 2 + g ). The occurrence of such “holes” indicate that at conditions encountered in supercritical fluid operations, the phase behavior might be more complex than expected, and may have consequences in process design.

Phase behavior of the binary system near-critical dimethylether and tripalmitin: measurements and thermodynamic modeling

Abstract This contribution reports new experimental data on the phase behavior of the binary system dimethylether (DME)+tripalmitin (PPP). The experimental work covers a temperature region between 275 and 450 K and pressures up to 12 MPa were applied. Near the critical point of pure DME a three-phase region liquid–liquid–vapor (l1l2g) was established. Although only an upper critical endpoint of this three-phase equilibrium could be determined experimentally, it is most likely that the system DME+PPP belongs to type-V fluid phase behavior in the classification of Van Konynenburg and Scott. Besides the fluid phase behavior of the system, also phase equilibria in the presence of solid PPP were measured. From earlier work it became apparent that a Group Contribution Equation of State is capable to model the vapor–liquid and liquid–liquid equilibria in related systems. Therefore, this equation also was chosen to model the fluid phase behavior of the system DME+PPP.

Classification of and transformations between types of fluid phase behavior in selected ternary systems

Abstract Experimental results of multiphase fluid equilibria occurring in ternary mixtures of near-critical carbon dioxide + dodecane + o-nitrophenol and near-critical carbon dioxide + octanol + o-nitrophenol are presented. According to the classification of Van Konynenburg and Scott, the binary subsystems of carbon dioxide with dodecane and octanol show type-II and type-III fluid phase behavior respectively, whereas the binary subsystem of carbon dioxide with o-nitrophenol shows type-V fluid phase behavior. Starting with one of the binary subsystems with its characteristic type of fluid phase behavior, the transformation into the fluid phase behavior of the second binary subsystem can be investigated by gradually exchanging the first solute with the second. This study focuses on the transformations of type-V fluid phase behavior into type-II or type-III respectively. Surprisingly, from this study it became apparent that there is a strong indication that the binary subsystem carbon dioxide + o-nitrophenol does not have the accepted type-V fluid phase behavior but type-IV. Additional research is underway to prove that the latter phenomenon applies in general.