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The recent growing interest in biofuels is due to the continuous increase in crude oil prices, limited resources of fossil energies, and environmental concerns. In what concerns road transportation, biodiesel is being considered a good alternative to conventional diesels. It consists of a blend of fatty acid esters, and its production and formulation needs to be optimized to ensure that the fuel quality complies with the legal standards. Although in various aspects biodiesel is superior to conventional diesel, it also poses some problems such as its poor behavior at low temperatures and higher hygroscopicity than conventional diesel. Up to now, little information is available about the water solubility in fatty acid methyl and ethyl esters and commercial biodiesels. To overcome this lack of data, water solubility measurements were carried out for 11 pure esters and 6 biodiesels in the temperature range 288.15-323.15 K. This new experimental data was successfully modeled with the cubic-plus-association (CPA) equation of state with global average deviations inferior to 7% for the ester systems, and predictions with deviations of 16% for commercial biodiesels were achieved.

The understanding of the specific interactions between salt ions and ionic liquids (ILs) in aqueous solutions is relevant in multiple applications. The influence of a series of anions on the solubility of 1-butyl-3-methylimidazolium tricyanomethane in aqueous environment was here studied. This study aims at gathering further information to evaluate the recently proposed 1,2 mechanisms of salting-in-and salting-out-inducing ions in aqueous solutions of ILs and to provide insights at the molecular-level on the phenomena occurring in these systems. The observed effect of the inorganic species on the aqueous solubility of the ionic liquid qualitatively follows the Hofmeister series, and it is dependent on the nature and concentration of the anions. The liquid-liquid equilibrium data and 1 H NMR results here reported support a model according to which salting-in-and salting-out-inducing ions operate by essentially different mechanisms. While salting-out is an entropically driven effect resulting from the formation of hydration complexes and the increase of the surface tension of cavity formation, the salting-in phenomena is a consequence of the direct binding of the ions to the hydrophobic moieties of the IL. Further evidence here obtained suggests that the interactions of the inorganic ions are not only established with the cation of the IL, but also with the anion, with the observed solubility effect the result of a balance between those two types of interactions.

The solubilities of tetracycline hydrochloride, moxifloxacin hydrochloride, and ciprofloxacin hydrochloride were measured in several solvents, such as water, ethanol, 2-propanol, and acetone, in the temperature range of 293.15-323.15 K for ciprofloxacin.HCl and moxifloxacin.HCl and 288.15-310.15 K for tetracycline. All the antibiotics have the same solubility order; that is, they are more soluble in water than in ethanol, and more soluble in ethanol than in 2-propanol and acetone. The solubility in water is ∼3 orders of magnitude higher than that in acetone. The modeling of the experimental solid-liquid equilibria (SLE) data, using the NRTL and UNIQUAC models, proves that these models can correlate the solubility of studied antibiotics satisfactorily in the temperature range for which experimental data are available, with the UNIQUAC model generally being slightly superior to the NRTL model, when only two adjustable parameters are used for each binary system.

The aim of this work is to establish a comparison between the solubility of the hydrochloride and nonhydrochloride forms of ciprofloxacin and tetracycline in relevant solvents. For that purpose the solubilities of the non-hydrochloride forms of ciprofloxacin and tetracycline were measured in water, ethanol, 2-propanol, and acetone, in the temperature range between 293.15 and 323.15 K for ciprofloxacin and between 288.15 and 303.15 K for tetracycline. The obtained results were compared with those of part I of this study, published previously, where the solubilities of the respective hydrochloride forms of the antibiotics in the same solvents were investigated. The solubility of the hydrochloride forms in water is about 2 orders of magnitude higher than those of the respective base forms. In acetone, we see the opposite effect. For ethanol and 2-propanol the influence of the hydrochloride group of the antibiotic on the solubility in the alcohol is much smaller than for water and acetone. The experimental data was correlated with good results using two different activity coefficient models, NRTL and UNIQUAC, with UNIQUAC giving better results, particularly for ciprofloxacin. The performance of COSMO-RS model to describe the studied systems was also evaluated.

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Heat transfer fluids play an important role in many industrial sectors. However, the low heat transfer characteristics of conventional fluids obstruct the performance enhancement and the high compactness of heat exchangers. In order to improve thermal characteristics of the conventional fluids, nanofluids are prepared by adding multi walled carbon nanotubes (CNTs) with base fluids. Though different experimental studies on nanofluids are available, theoretical models are also needed to predict its thermal behaviour. This work intends to address dimensional analysis using the Buckingham Pi theorem to develop an empirical model for predicting thermal characteristics of nanofluids. The latter will be achieved through the use of operational variables and physical properties for the identification of detrimental factors which eventually lead to the thermal enhancement of nanofluids. It can be observed from this analysis that volume fraction and temperature of the nanofluids are the most influencing parameters on the nanofluids thermal conductivity. In what concerns heat transfer coefficient, it is the velocity of the nanofluid that plays a critical role apart from the afore mentioned two parameters. Therefore it is believed that by controlling these parameters, the thermal effectiveness of the nanofluids can be established.