M. Nunes da Ponte

A detailed thermodynamic analysis of [C4mim][BF4]+ water as a case study to model ionic liquid aqueous solutions

Since determining experimentally a wide variety of thermophysical properties—even for a very small portion of the already known room temperature ionic liquids (and their mixtures and solutions)—is an impossible goal, it is imperative that reliable predictive methods be developed. In turn, these methods might offer us clues to understanding the underlying ion–ion and ion–molecule interactions. 1-Butyl-3-methylimidazolium tetrafluoroborate, one of the most thoroughly investigated ionic liquids, together with water, the greenest of the solvents, have been chosen in this work in order to use their mixtures as a case study to model other, greener, ionic liquid aqueous solutions. We focus our attention both on very simple methodologies that permit one to calculate accurately the mixtures molar volumes and heat capacities as well as more sophisticated theories to predict excess properties, pressure and isotope effects in the phase diagrams, and anomalies in some response functions to criticality, with a minimum of information. In regard to experimental work, we have determined: (a) densities as a function of temperature (278.15 < T/K < 333.15), pressure (1 < p/bar < 600), and composition (0 < xIL < 1), thus also excess molar volumes; (b) heat capacities and excess molar enthalpies as a function of temperature (278.15 < T/K < 333.15) and composition (0 < xIL < 1); and (c) liquid–liquid phase diagrams and their pressure (1 < p/bar < 700) and isotopic (H2O/D2O) dependences. The evolution of some of the aforementioned properties in their approach to the critical region has deserved particular attention.

On the application of supercritical fluid extraction to the deacidification of olive oils

A recent suggestion on the applicability of supercritical fluid extraction to the deacidification of olive oils of high acid content was based on solubility data in clear disagreement with the results of other authors. In this work, we measured the solubilities of substances chosen for their importance in that extraction process, namely pure glycerol trioleate, the most abundant triglyceride in olive oil, and of a husk oil with a high acid content. Our results agree well with some of the previous reports on this subject. These seem to be a trustworthy data base, but more results are needed for a definite conclusion about the technical feasibility of the process.

Study on selectivity of β-myrcene hydrogenation in high-pressure carbon dioxide catalysed by noble metal catalysts

Hydrogenation of monoterpenes, such as β-myrcene, in high-density carbon dioxide over 0.5 wt.% Pd, or Rh, or Ru supported on alumina was investigated. Hydrogenation catalysed by Rh and Ru is generally faster in a single supercritical (sc) phase (gaseous reagents and solid catalyst) than in a biphasic system (liquid + gas reactants + solid catalyst). The reaction catalysed by Pd occurs faster in two phases. The final composition of the reaction mixture is strongly dependent on the noble metal catalyst used for the reaction. Palladium gives mainly 2,6-dimethyloctane (≈95%), rhodium produces 2,6-dimethyloctane with a yield higher than 40%, and around 40% of 2,6-dimethyloct-2-ene, while ruthenium gives around 10% of 2,6-dimethyloctane and 50% of 2,6-dimethyloct-2-ene leaving the highest amount of unreacted β-myrcene. The Pd catalyst is highly active with an excellent selectivity in enabling the one-pot synthesis of 2,6-dimethyloctane through β-myrcene hydrogenation in the presence of scCO2. The overall activity of the noble metal catalysts decreased in the order Pd > Rh > Ru. The problem of leaching of the active metal from the catalyst rod was also investigated.

Two ways of looking at Prigogine and Defay's equation

In the search for understanding of several types of abnormal thermodynamic behaviour in the vicinity of critical lines of binary liquid mixtures, we have revisited an apparently forgotten relationship between the pressure dependence of the critical temperature and the second derivatives with respect to the composition of the volumetric and enthalpic properties of the mixture. We refer to an equation originally developed in the fifties by Prigogine and Defay and soon afterwards analysed by others. Under some restrictive assumptions, the T–p slope of the critical locus can simply be inferred from the ratio between vE and hE. The interest and usefulness of this approximate relation is self-evident. Values for any one of the three properties involved,(dT/dp)c, vE or hE, can be assessed based on the availability of the other two. Moreover, the amplitude of the divergence of thermodynamic response functions to criticality are intimately associated with the slope of the critical locus. A link between critical behaviour and solution excess properties is thus established. For instance, double critical points tend to occur if one of the excess properties changes its sign as the temperature or pressure is varied. In this work, we have started a detailed study of the practical limits of validity of the approximate relation. Five binary liquid mixtures were tested, all of them sharing a UCST/LCSP-type of phase transition. Although, from a theoretical perspective, the original second-derivatives approach should perform better, in practice, the direct ratio of the excess properties constitutes a superior strategy for obtaining (dT/dp)c values. The underlying reasons for this are discussed in detail. The T–p critical slope is normally found to play a secondary role in assessing the critical amplitudes of diverging thermodynamic functions.

THE EXCESS THERMODYNAMIC PROPERTIES OF LIQUID (CH4+CD4)

The vapor pressure differences between a mixture of (CH4+CD4) and CH4 and between CD4 and CH4 were measured simultaneously with the CH4 vapor pressure. This was done at 29 temperatures between 97 and 122 K, and for six different mixtures, of compositions 0.150, 0.250, 0.375, 0.500, 0.625, and 0.750 mole fraction in CD4. These mixtures exhibit very small positive deviations from Raoult’s law. Calculated excess Gibbs energies for equimolar mixtures were 0.60 J mol−1 at 100 K and 0.42 J mol−1 at 120 K. These values of GE are 2 to 3 orders of magnitude smaller than those typically found in binary mixtures of simple nonisotopic species. The molar excess enthalpy, calculated from the temperature dependence of GE, is HE(x=0.5)=(1.5±0.2) J mol−1. The experimental results were used to test three theoretical models: the vdW‐1 fluid theory, 1cLJ perturbation theory, and the theory of isotope effects in mixtures. While the first two proved to be inadequate, the isotope effect theory agrees well with experiment.

Scale-up of a supercritical extraction unit for the deacidification of olive oil

Publisher Summary Olive oils with large quantities of free fatty acids must be refined to get a salable product. Deacidification is currently done by physical or chemical processes that may alter the organoleptic profile of the oil. Supercritical fluid deacidification of these oils has been suggested as a potential ecological alternative process, because it uses nontoxic solvents and low operating temperatures. The use of supercritical carbondioxide as a solvent for the deacidification of olive oils has shown the selective preference of carbon dioxide toward the free fatty acids (FFA) fraction and at the same time retaining the nutritional constituents of the oil. This chapter reviews a study carried out to evaluate the best operational conditions for the deacidification of olive oils by supercritical extraction (SCE) and to evaluate the design of an extraction unit. To assess the feasibility of the olive oil deacidification plant, an economical study that is described in the chapter was performed by simulating all the debits and credits involved in the industrial plant. The analysis was performed at constant prices instead of real prices and the units are in Portuguese escudos (PTE).

Evidence for nonideality in the fundamental liquid mixture (36Ar+40Ar)

Positive excess molar Gibbs energies were detected in liquid mixtures of (36Ar+40Ar) using a high-accuracy double differential manometric technique. The vapor pressure differences between a mixture of (36Ar+40Ar) and 40Ar and between 36Ar and 40Ar were measured simultaneously with the vapor pressure of 40Ar. Four different mixtures were selected and 80 temperatures were chosen in the 85–96 K temperature range. The results show that the vapor pressure of an equimolar liquid mixture is greater than what would be expected if the solution were strictly ideal, by approximately 2.5 Pa in the 85–96 K temperature range. The calculated excess Gibbs energy for the equimolar mixture at 85 K is G1/2E=(0.021±0.004) J mol−1. For the excess molar enthalpy a value of H1/2E=(0.12±0.04) J mol−1 was found. The corresponding deviations from Raoult’s law are therefore extremely small (3 to 4 orders of magnitude smaller than those typically found in binary mixtures of nonisotopic constituents). The evidence of nonideal behavio...

Vapor pressure of partially deuterated methanes (CH3D, CH2D2, and CHD3)

The difference between the vapor pressure of completely protiated or deuterated methane (CH4 or CD4) and partially deuterated methanes (CH3D, CH2D2, or CHD3) has been measured over the 96–121 K temperature range. The vapor pressure data obtained were fitted to equations of the type T ln(p/p)=A/T+B, where the prime always refers to the lighter molecule. Within the studied temperature range, the vapor pressure isotope effect was found to be “inverse” (p>p) for all the systems, except in the low-temperature range of the (CH4/CH3D) system. Our data agrees with other results found in the literature, both experimental and theoretical. Differences in the enthalpy of vaporization were calculated from the experimental results. In the case of the (CH4/CHD3) system, our vapor pressure isotope effect (VPIE) results were also compared with liquid–vapor isotope fractionation factor (LVIFF) data from other authors.

Thermodynamics of binary liquid mixtures of partially deuterated methanes with CH4 or CD4

The vapor pressure isotope effect of samples of isotopically substituted methane and their mixtures was measured as a function of temperature and mixture composition: The differential vapor pressure between CHiD4−i (with i=0 or 4) and CHjD4−j (with j=1, 2, or 3), the differential vapor pressure between mixtures of (CHiD4−i+CHjD4−j) and CH4 (if i=4) or CHjD4−j (if i=0) and the absolute vapor pressure of CH4 (if i=4) or CHjD4−j (if i=0), were measured simultaneously between 96 and 121 K for mixtures of nominal composition 0.25, 0.50, and 0.75 mole fraction in the reference methane species. The p(x,T) data were used to calculate the excess molar Gibbs energy function, GE(x,T) and the excess molar enthalpy HE(x), assuming that this last function is independent of temperature in the experimental range. The deviations from ideal behavior are very small, GE being only some tenths of J/mol for equimolar mixtures. The experimental GE values compare well with estimated results based on a modified version of the sta...

Using assistive robots to promote inclusive education

Abstract Purpose: This paper describes the development and test of physical and virtual integrated augmentative manipulation and communication assistive technologies (IAMCATs) that enable children with motor and speech impairments to manipulate educational items by controlling a robot with a gripper, while communicating through a speech generating device. Method: Nine children with disabilities, nine regular and nine special education teachers participated in the study. Teachers adapted academic activities so they could also be performed by the children with disabilities using the IAMCAT. An inductive content analysis of the teachers’ interviews before and after the intervention was performed. Results: Teachers considered the IAMCAT to be a useful resource that can be integrated into the regular class dynamics respecting their curricular planning. It had a positive impact on children with disabilities and on the educational community. However, teachers pointed out the difficulties in managing the class, even with another adult present, due to the extra time required by children with disabilities to complete the activities. Conclusions: The developed assistive technologies enable children with disabilities to participate in academic activities but full inclusion would require another adult in class and strategies to deal with the additional time required by children to complete the activities. Implications for Rehabilitation Integrated augmentative manipulation and communication assistive technologies are useful resources to promote the participation of children with motor and speech impairments in classroom activities. Virtual tools, running on a computer screen, may be easier to use but further research is needed in order to evaluate its effectiveness when compared to physical tools. Full participation of children with motor and speech impairments in academic activities using these technologies requires another adult in class and adequate strategies to manage the extra time the child with disabilities may require to complete the activities.