Showing papers by "João G. Crespo published in 2007"
TL;DR: The features of the solid-liquid phase transition were analyzed, namely the glass transition temperature and the heat capacity jump associated with the transition from the non-equilibrium glass to the metastable supercooled liquid.
Abstract: More than 50 ionic liquids were prepared by using imidazolium, quaternary ammonium, and guanidinium cations and various anions. In these series, different cationic structures such as 1-benzyl-3-methylimidazolium [Bzmim]+, 1,3-dibenzylimidazolium [BzmiBz]+, 1-octyl-3-methylimidazolium [C8mim]+, 1-decyl-3-methylimidazolium [C10mim]+, tricapryl-methylammonium [Aliquat]+, benzyltriethylammonium [BzTEA]+, phenyltrimethylammonium [PhTMA]+, and dimethyldihexylguanidinium [DMG]+ were combined with anions, p-toluenesulfonate [TSA](-), dicyanoamide [DCA]-, saccharine (2-sulfobenzoic acid imide sodium salt) [SAC]-, trifluoroacetate [TFA]-, bis(trifluoromethanesulfonyl)imide [Tf2N]-, trifluoromethanesulfonate [TfO]-, and thiocyanate [SCN]-. Important physical data for these ionic liquids are collated, namely solubility in common solvents, viscosity, density, melting point and water content. Apart from the viscosity, the Newtonian and non-Newtonian behavior of these ionic liquids is also disclosed. Stability of these ionic liquids under thermal, basic, acidic, nucleophilic, and oxidative conditions was also studied. The features of the solid-liquid phase transition were analyzed, namely the glass transition temperature and the heat capacity jump associated with the transition from the non-equilibrium glass to the metastable supercooled liquid. A degradation temperature of each ionic liquid was also determined. Comparisons of the properties of various ionic liquids were made.
215 citations
TL;DR: In this paper, a modified friction factor was introduced to investigate the effect of the hydrodynamic conditions in the channel on the shear stress at the walls, and the experimental results showed that the transition between laminar and transitional flow regime could be rigorously determined for the spacers under study.
138 citations
TL;DR: In this paper, an optical technique was developed for studying the process of polymer swelling, which is able to produce highly reproducible data of swelling of dense polymeric membranes exposed to liquid mixtures.
103 citations
TL;DR: In this article, an enantio-selective extraction of propranolol, an amino-alcohol with proven efficacy in the treatment of hypertension, ischemic heart disease and arrhythmia, is presented.
81 citations
TL;DR: In this article, a set of alternative membrane and solvent descriptors was defined based on published studies, in order to improve the modelling of this system. But the relationship between the solvent flux and the new selected descriptors is currently not known or poorly known at the mechanistic level, alternative chemometric and hybrid chemometric-mechanistic modelling methodologies were adopted.
32 citations
TL;DR: These studies reveal that, in future, a task-specific ionic liquid can be prepared and used for specific solute capture from the vapor phase and a remarkable selectivity was observed for some ionic liquids towards a specific organic solute.
Abstract: A novel study on organic solute absorption from the vapor phase is reported. The organic solutes chosen for the absorption studies include 1,4-benzodioxane, biphenyl, xanthene, and menthol. A series of imidazolium, ammonium, and guanidinium-based ionic liquids (ILs) containing several types of anions were used as absorbents. Absorption of water vapor was also studied along with the organic solutes. Absorption studies of each organic solute were performed by using a specially devised glass apparatus at 50 degrees C. It was observed that the rate of absorption increases with time and is faster in the case of 1,4-benzodioxane (24 h). The absorption process for each organic solute with different classes of ionic liquids was studied and the results were compared with each other. Absorption values of more than 25,000 ppm were observed in some ionic liquids. Distribution ratios of organic solutes in an ionic liquid and in the vapor phase were measured and the selectivity was evaluated by using the distribution ratio values. A remarkable selectivity was observed for some ionic liquids towards a specific organic solute. Importantly, it was observed that the selectivity remained constant, even though a mixture of solute was used for the absorption study. Desorption of organic vapors from ionic liquids was successfully carried out by applying a vacuum. Further, it was observed that the same ionic liquid can be repeatedly reused several times for absorption. These studies reveal that, in future, a task-specific ionic liquid can be prepared and used for specific solute capture from the vapor phase.
30 citations
TL;DR: An improved method for deconvoluting complex spectral maps from bidimensional fluorescence monitoring is presented, relying on a combination of principal component analysis (PCA) and feedforward artificial neural networks (ANN).
22 citations
TL;DR: It is shown that the hydrodynamic feed flow conditions represent a further degree of freedom for tailoring the permeate composition, and hence the product quality, under defined conditions.
19 citations
TL;DR: In this article, successive batch steps of an osmium-catalyzed asymmetric dihydroxylation reaction using Sharpless conditions and nanofiltration of post-reaction mixture were coupled, allowing to enhance the cumulative catalyst turn over number to about 3.7 times over six cycles.
Abstract: In this paper, successive batch steps of an osmium-catalyzed asymmetric dihydroxylation reaction using Sharpless conditions and nanofiltration of post-reaction mixture were coupled, allowing us to enhance the cumulative catalyst turn over number to about 3.7 times over six cycles. The nanofiltration step provides for isolation of the chiral product, whereas the catalytic system (osmium and chiral ligand) is re-used in the following batch cycle. In this work the osmium average rejection through the selected nanofiltration membrane, Starmem™120, was 83%; this result may indicate the existence of free osmium in solution and implies residual product osmium contamination at an average value of 1.5 mg Os/g-product. Effective application of this methodology to the model reaction requires improvement of catalyst rejection, which calls for an effective complexation of osmium by the ligand. Nevertheless, the enantioselectivity of the reaction was maintained constant over the six cycles at a value of 69%.
17 citations
TL;DR: The fluorescence approach used allowed to identify irreversible losses of structural integrity of β-lactoglobulin in the permeates, while β- lactoglOBulin retentates seemed to be unaffected by the ultrafiltration process.
14 citations
TL;DR: In this paper, the chiral resolution of propranolol, an amino-alcohol with proven efficacy in the treatment of hypertension, ischemic heart disease and arrhythmia, was studied using a tubular module contactor.
01 Jan 2007
TL;DR: Membranes are semipermeable barriers that permit the separation of two compartments of different composition or even condition, with the transport of components from one compartment to another being controlled by the membrane barrier.
Abstract: Membranes are semipermeable barriers that permit the separation of two compartments of different composition or even condition, with the transport of components from one compartment to another being controlled by the membrane barrier. Ideally, this barrier is designed to let pass selectively only certain target compounds, while retaining all others—hence the denotation “semipermeable”. Membrane separations are particularly suitable for food applications because (1) they do not require any extraction aids such as solvents, which avoids secondary contamination and, hence, the necessity for subsequent purification; (2) transfer of components from one matrix to another is possible without direct contact and the risk of cross-contamination; (3) membrane processes can, in general, be operated under smooth conditions and therefore maintaining in principle the properties and quality of delicate foodstuff.