Chemical Process Engineering and Forest Products Research Centre

Thermodynamics and Thermophysical Properties

Low temperature vapor-liquid equilibria VLE.  The VLE of binary and ternary mixtures at cryogenic temperatures (≈ 100 K) in systems formed by simple polar and nonpolar molecules are measured in a complex measurement device assembled at the low temperature laboratory.  Among the systems studied, the H2S + C2H6, C3H8 + H2S + and H2S+n-C4H10 at 182 K are of high practical interest in the oil industry. From measurements of VLE the values ​​of GE can be determined. The VLE data  of H2S + hydrocarbons mixtures were treated with equations of state. The equilibrium pressure of ternary mixtures of {CH3F + HCl + N2O} covering the entire composition range has been measured at temperature of 182.33 K by a static method. The (p,x,y) surface for the ternary system and the corresponding curves for the three constituent binary mixtures were correlated with  cubic  EoS.

Gas-liquid solubility of hydrofluorocarbons (HFCs) in alcohols, aromatic solvents and ionic liquids (ILs). The effect of association between solute/solvent molecules in the solubility is studied, at least in a semiquantitative way. There are few systematic studies of the effect of chemical forces on gas solubility, primarily because of the inherent difficulty of characterize these forces in a quantitative way. An automated apparatus was used to measure the solubilities of HFCs, (CH3F, CH2F2, CHF3) in lower alcohols (= methanol, ethanol, 1-propanol, 1-butanol), in aromatic solvents (=benzene, chlorobenzene, toluene, benzotrifluoride, m-xylene and mesitylene), and in ionic liquids (ILs=1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, (trihexyl)tetradecyl-phosphonium bis(trifluoro-methylsulfonyl)imide, and N-methyl-2-hydroxyethylammoniumpropionate  and pentanoate within the temperature range ≈ (285, 310]) K, at atmospheric pressure. The experimental data is treated by the chemical solution theory which accounts for the additional chemical equilibrium in the liquid phase to the conventional vapour-liquid equilibrium. Correlations between Henry´s constants and some chemical characteristic of the solvent are developed. For solubility in ILs, the cubic plus association equation of state (CPA EoS) is used as a predictive model to estimate the solubilities using only pure components physical properties. The regular-solution theory is the basis to build an empirical model whose parameters are obtained through least-squares fitting of experimental values.

Ionic liquids: Thermophysical properties measurement and applications. The design of industrial processes and new products based on ILs can only be achieved when their thermophysical properties, such as density, viscosity, surface tension, speed of sound, termal conductivity and heat capacity are adequately characterized.
Thermophysical properties measurement. The density of different ILs (imidazolium, phosphonium and ammonium) have been measured at temperatures up to 360 K and up to pressures of 30 MPa by means of a vibrating tube densimeter, model DMA 512P from Anton Paar. The dynamic viscosities were measured with a digital rotational viscometer Brookfield DV-II+ (model LVDV-11) with the small sample adapter specially adapted for measurements. Also an Ubbelohde viscometer with a Schott–Gerate automatic measuring unit (Model AVS-470) has been used. The surface tension was measured using a tensiometer KSV Sigma 70 in extended ranges of temperature. We have constructed a facility which uses a non-intrusive method for sound speed measurement over wide ranges of temperature and pressure. ILs (imidazolium, phosphonium and ammonium) and biodiesel fuels have been measured. The thermal conductivity of different phosphonium based ILs were measured using the hotwire method. The thermal stability and the heat capacity of phosphonium and ammonium ILs were measured. Thermal stability was measured by High Resolution Thermogravimetric Analysis by using a TA Instruments Q500 thermogravimetric analyzer (thermobalance sensitivity: 0.1 lg) and heat capacity using a modulated differential scanning calorimetry (MDSC) equipment from TA Instruments (Q100 model). Applications: (a) Ionanofluids. The ability ionic liquids to disperse and chemically modify CNTs has raised great interest because the resulting suspensions are expected to be stable and homogeneous, leading to (CNT + IL) hybrids (or IoNanofluids) with exceptional properties and potential use in a wide range of applications fields. Therefore it will be important to collect information on transport and thermal properties of stable suspensions made of ILs (base fluids) and carbon nanotubes. In our studies, we have used phosphonium as base fluids and MWCNTs as nano-additives to fabricate IoNanofluids suspensions with small loadings of carbon nanotubes. (b) Wood processing. The wood pre-treatment is the most important step in the successful production of biofuels from cellulosic biomass, since the pretreatment is directly related to the extent and the cost of converting polysaccharides present in biomass into bioethanol. ILs are potencial solvents for the pretreatment of cellulose for hydrolysis employing different cellulosic substrates, and enzyme cellulase preparations. Some studies show that cellulose is dissolved in IL and thereafter regenerated by precipitating it by the addition of an anti-solvent, such as water or alcohol, yielding a regenerated cellulose, which is more amorphous than the starting material. This regenerated cellulose showed much better hydrolysis kinetics. Some ionic liquids (1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride and 1-allyl-3-methylimidazolium chloride) were tested in dissolution of wood. The process variables investigated were wood / ionic liquid ratio, type of agitation, dissolution time, and temperature. The 1-ethyl-3-methylimidazolium acetate seems promising. With appropriate working conditions (pretreatment of wood with [EMIM] OAc at 120 °C and with mechanical stirring) dissolution of  biomass with yields superior of 95% were achieved. (c) Membranes. The special properties of ionic liquids, specially its high thermal and chemical stability, low vapour pressure, non-flammability and tuneable physicochemical properties, make them ideal for the replacement of organic solvents in liquid membranes and hence for the realization of environmentally sound and economical membrane separation processes. Although the industrial application of supported ionic liquid membranes is still under study, laboratory and pilot plant applications have been studied in the last three decades. We expect to contribute in the development of supported ionic liquids membranes for separation of metals (here less toxic phosphonium and ammonium ILs can be used) and recovery of organic chemicals from aqueous solutions. (d) Gas-liquid solubility (see before).

Biodiesel production and monitoring.  Biodiesel (fatty acid methyl or ethyl esters) has become a good alternative for the large-scale substitution of petroleum-based fuels. Ultrasonic methods and density measurement can be made on line with the reactional mixture and they are non-evasive, robust and rapid providing suitable for automation. A new biodiesel reactor monitored via speed of sound and density has been tested. This work is done in collaboration with the Departamento de Engenharia Electrotécnica of FCTUC.