Manuel Nunes da Ponte

Phase behaviour of room temperature ionic liquid solutions: an unusually large co-solvent effect in (water + ethanol)

A surprising mixed solvent effect, both in its magnitude and direction, has been found in the phase diagram of the ternary mixture of ([C4mim][PF6]+(water+ethanol)). For a molar ratio of 1∶1 of water to ethanol, the co-solvent effect in the near-critical demixing temperature can be as large as 80 K.

Phase equilibria of natural flavours and supercritical solvents

Abstract To study the possibility of separation of cineole from limonene (two of the main components of eucalyptus oil) we measured the vapour-liquid equilibrium of the systems containing either d-limonene or 1, 8-cineole in the supercritical solvents carbon dioxide (at 318.2 and 323.2 K) and an azeotropic mixture of ethane+carbon dioxide (at 303.2 K). The results obtained show that both solutes have similar solubilities in the supercritical solvents studied here.

Liquid–liquid behaviour of ionic liquid–1-butanol–water and high pressure CO2-induced phase changes

The liquid–liquid equilibrium of the [C4mim][NTf2]–1-butanol system presents upper critical solution temperature (UCST) behaviour. We report the influence of added water as well as the effect of hydrostatic pressure on the cloud points. Similarly to previously studied systems that involved RTILs in our laboratories, water is shown to be a very good co-solvent with alcohols. If a small amount of water is present in the [C4mim][NTf2]–1-butanol system it decreases the UCST as much as 1.5 K per mol% of water added to butanol. The hydrostatic pressure effect on cloud points is rather modest (≈−3.5 × 10−3 K bar−1). As for liquid–vapour equilibria, a new apparatus which employs a high-pressure variable-volume cell, was conceived and built. The apparatus was tested for the well-known system 1-butanol–CO2. Demixing pressures of the ternary and quaternary mixtures, (1-butanol–water–CO2) and ([C4mim][NTf2]–1-butanol–water–CO2), were determined for a few compositions and temperatures. The demixing pressure is strongly controlled by the water concentration.

Phase equilibria of CO2 + dl-α-tocopherol at temperatures from 292 K to 333 K and pressures up to 26 MPa

Abstract Phase equilibria for the system carbon dioxide + dl-α-tocopherol were studied, at temperatures from 292 K to 333 K and pressures up to 26 MPa. Pressure-composition isotherms were measured for the liquid and vapour phases in equilibrium, using the analytical method, from 9 MPa to 26 MPa, and at five temperatures between 298 K and 333 K. The projection of the liquid-liquid-vapour three phase equilibrium surface on the pressure-temperature plane has been followed from 292 K up to the critical end point, close to the critical temperature of CO2. The results were modelled using the Peng-Robinson equation of state and the composition-dependent mixing rules of Panagiotopoulos and Reid. Good agreement with experimental results was obtained.

Phase equilibrium-driven selective hydrogenation of limonene in high-pressure carbon dioxide

Pressure-tuning of selectivity in the hydrogenation of limonene in carbon dioxide was found in biphasic systems, close but below the critical conditions of the reaction mixture, where hydrogen solubility in the liquid is highly dependent on pressure. The subtle effects of pressure on the two-phase region in CO2 + H2 + a liquid reagent mixtures are essential factors in determining hydrogenation rates and selectivities in high-pressure carbon dioxide.

Biphasic hydrogenation of α-pinene in high-pressure carbon dioxide

Results on the kinetics of hydrogenation of α-pinene in high-pressure carbon dioxide, using Pt/C (1%) catalysts, are presented. Experiments were performed at different carbon dioxide pressures, so that the reaction mixture in contact with the solid catalyst would either be biphasic (liquid + gas) or a single supercritical phase. The technique involved the use of a high-pressure view cell, which allows direct visual observation of the number of phases in the reactor. The hydrogenations in biphasic conditions, at lower carbon dioxide pressures, are completed faster than in supercritical conditions. The results indicate that the pinene adsorption to the metal in the catalyst is the rate-controlling step.

High pressure phase equilibria for poly(ethylene glycol)s + CO2: experimental results and modelling

Phase equilibrium results for mixtures of three poly(ethylene glycol)s (PEGs) of molar mass 200, 400 and 600 g mol-1 with carbon dioxide over the temperature range 313.15–348.15 K and pressures up to 26 MPa are presented. A new static analytical apparatus was built to carry out these measurements. The precision of the method is better than 3% and the accuracy is estimated to be better than 5% of the mass fraction. The results are well correlated with the Sanchez–Lacombe equation of state, using a non-temperature dependent interaction parameter ζ. Negative hydroxy end-group effects on the CO2 solubility in the polymer are highlighted in the case of PEG 200. Data from other workers for CO2+heavier PEG (1500–8000 g mol-1) are also successfully included in the correlation. However, previously published values for PEG 400 to PEG 1000 differ substantially from our results and could not be simultaneously correlated by this model.

A Comparative Study of Naproxen – Beta Cyclodextrin Complexes Prepared by Conventional Methods and Using Supercritical Carbon Dioxide

Naproxen is a poorly soluble anti-inflammatorydrug, the solubility of which canbe enhanced by complexation withbeta-cyclodextrin. Besides that, the inclusioncomplex reduces the incidence of gastrointestinal side effects of the drug. The aim of this work was to compare the physicochemical characteristics of the solid complexes prepared by traditional methods (kneading, freeze-drying and spray-drying) and using a supercritical fluid technology. The unusual solvent properties of carbon dioxide above their critical temperature and pressure were exploited in order to prepare inclusion compounds. Complexes prepared using supercritical fluid technology showed similar properties to those of freeze-drying andspray-drying complexes as proved by DSC, FT-IRand UV.

Lipase catalysed mono and di-acylation of secondary alcohols with succinic anhydride in organic media and ionic liquids

The acylation of the model substrate (R,S)-2-octanol with succinic anhydride catalysed by immobilised Candida antarcticalipase B was studied in two water-miscible organic solvents, two water-immiscible ones, nine 1-alkyl-3-methylimidazolium ionic liquids (RTILs) and two quaternary ammonium RTILs. From previous reports, the reaction was expected to yield an acidic half ester (hemiester). However, it was found that the diester was also produced, in many cases at an even higher yield. The major reaction products were the (R)-hemiester and the (R,R)-diester. In some of the solvents, the amount of hemiester formed increased and then remained constant, whereas in others the amount of hemiester first peaked and then decayed. This behaviour could be explained by the coupling of two reaction pathways: the hydrolysis of the hemiester, and the esterification of the hemiester. The solubility limit of succinic acid, produced in the former pathway, was found to be a discriminating parameter, the precipitation of the acid acting as a driving force for the consumption of the hemiester formed. The impact of the choice of solvent on the outcome of the acylation with succinic anhydride was confirmed by conducting the reaction on a preparative scale: in acetonitrile, the reaction produced 32% (w/w) of (R)-hemiester and 68% (w/w) of (R,R)-diester, whereas in tetrahydrofuran 85% (w/w) of (R)-hemiester and 15% (w/w) of (R,R)-diester were obtained.

An apparatus for high-pressure VLe measurements using a static mixer. Results for (CO2 + limonene + citral) and (CO2 + limonene + linalool)

Abstract A new flow apparatus for high-pressure vapour–liquid equilibrium measurements was assembled. Its main feature is the use of a static mixer followed by a cyclone separator. Phase equilibrium ratios were determined, at 323.2 K and at pressures up to the vicinity of the mixture critical pressure, for the following systems: carbon dioxide+limonene, carbon dioxide+citral, carbon dioxide+linalool, carbon dioxide+limonene+citral and carbon dioxide+limonene+linalool. The results compare well with available literature data.