Equilibrium of the simultaneous etherification ofisobutene and isoamylenes with ethanol inliquid-phase

The simultaneous etherification of isobutene and isoamylenes with ethanol has been studied using macroreticu-lar acid ion-exchange resins as catalyst. Most of the experiments were carried out over Amberlyst-35. In addition,Amberlyst-15 and Purolite CT-275 were also tested. Chemical equilibrium of four chemical reactions was studied:ethyl tert-butyl ether formation, tert-amyl ethyl ether formation from isoamylenes (2-methyl-1-butene and 2-methyl-2-butene) and isomerization reaction between both isoamylenes. Equilibrium data were obtained in a batchwisestirred tank reactor operated at 2.0 MPa and within the temperature range from 323 to 353 K. Experimental molarstandard enthalpy and entropy changes of reaction were determined for each reaction. From these data, the molarenthalpy change of formation of ethyl tert-butyl ether and tert-amyl ethyl ether were estimated. Besides, the chemical equilibrium between both diisobutene dimers, 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, wasevaluated. A good agreement between thermodynamic results for the simultaneous etherification carried out in thiswork and those obtained for the isolated ethyl tert-butyl ether and tert-amyl ethyl ether systems was obtained.

Influence of the temperature and type of salt on the phase equilibrium of peg 1500 + potassium phosphate and peg 1500 + sodium citrate aqueous two-phase systems

The present work analyzed the effect of the temperature and type of salt on the phase equilibrium of aqueous two-phase systems (ATPS) formed by poly (ethylene glycol) (PEG) 1500 + potassium phosphate, from (278.15 to 318.15) K, and PEG 1500 + sodium citrate, from (278.15 to 298.15) K. The rise of the temperature normally increased the slope of the tie line (STL). With respect to the influence of the type of salt, sodium citrate showed better capability to induce phase separation, when compared to potassium phosphate.

THE GENERALIZED MAXIMUM LIKELIHOOD METHOD APPLIED TO HIGH PRESSURE PHASE EQUILIBRIUM

The generalized maximum likelihood method was used to determine binary interaction parameters between carbon dioxide and components of orange essential oil. Vapor-liquid equilibrium was modeled with Peng-Robinson and Soave-Redlich-Kwong equations, using a methodology proposed in 1979 by Asselineau, Bogdanic and Vidal. Experimental vapor-liquid equilibrium data on binary mixtures formed with carbon dioxide and compounds usually found in orange essential oil were used to test the model. These systems were chosen to demonstrate that the maximum likelihood method produces binary interaction parameters for cubic equations of state capable of satisfactorily describing phase equilibrium, even for a binary such as ethanol/CO2. Results corroborate that the Peng-Robinson, as well as the Soave-Redlich-Kwong, equation can be used to describe phase equilibrium for the following systems: components of essential oil of orange/CO2.

Fractionation of lemon essential oil by solvent extraction: Phase equilibrium for model systems at T=298.2 K

The fractioning of lemon essential oil can be performed by liquid-liquid extraction using hydrous ethanol as a solvent. A quaternary mixture composed of limonene, gamma-terpinene, beta-pinene, and citral was used to simulate lemon essential oil. In this paper, we present (liquid + liquid) equilibrium data that were experimentally determined for systems containing essential oil compounds, ethanol, and water at T = 298.2 K. The experimental data were correlated using the NRTL and UNIQUAC models, and the mean deviations between calculated and experimental data were less than 0.0053 in all systems, indicating the accuracy of these molecular models in describing our systems. The results show that as the water content in the solvent phase increased, the values of the distribution coefficients decreased, regardless of the type of compound studied. However, the oxygenated compound always showed the highest distribution coefficient among the components of the essential oil, thus making deterpenation of the lemon essential oil a feasible process. (C) 2012 Elsevier Ltd. All rights reserved.

Geometrical study of the three-dimensional temperature–composition diagrams. An important aid to understand the behavior of the liquid–vapour equilibrium in ternary systems

In this work the usefulness of qualitatively studying and drawing three-dimensional temperature–composition diagrams for ternary systems is pointed out to understand and interpret the particular behavior of the liquid–vapour equilibrium of non-ideal ternary systems. Several examples have been used in order to highlight the interest and the possibilities of this tool, which should be an interesting support not only for lecturers, but also for researchers interested in experimental equilibrium data determination.

Isobaric vapor–liquid–liquid–solid equilibrium of the water + NaCl + 1-butanol system at 101.3 kPa

A mixture of water + NaCl + 1-butanol at 101.3 kPa is studied in order to determine the influence of salt on its experimental vapor–liquid–liquid–solid equilibrium. A detailed analysis of the evolution with temperature of the different equilibrium regions is carried out. The study is conducted at a constant pressure of 101.3 kPa in a recirculating still that has been modified by our research group. The changes in the 1-butanol/water composition ratio in the vapor phase that are provoked by the salt are studied as a function of equilibrium region. In addition, the mutual solubility of 1-butanol and water is assessed in the liquid–liquid and solid–liquid regions.

Negative second virial coefficients as predictors of protein crystal growth: Evidence from sedimentation equilibrium studies that refutes the designation of those light scattering parameters as osmotic virial coefficients

The effects of ammonium sulphate concentration on the osmotic second virial coefficient (B-AA/M-A) for equine serum albumin (pH 5.6, 20 degrees C) have been examined by sedimentation equilibrium. After an initial steep decrease with increasing ammonium sulphate concentration, B-AA/M-A assumes an essentially concentration-independent magnitude of 8-9 ml/g. Such behaviour conforms with the statistical-mechanical prediction that a sufficient increase in ionic strength should effectively eliminate the contributions of charge interactions to B-AA/M-A but have no effect on the covolume contribution (8.4 ml/g for serum albumin). A similar situation is shown to apply to published sedimentation equilibrium data for lysozyme (pH 4.5). Although termed osmotic second virial coefficients and designated as such (B-22), the negative values obtained in published light scattering studies of both systems have been described incorrectly because of the concomitant inclusion of the protein-salt contribution to thermodynamic nonideality of the protein. Those negative values are still valid predictors of conditions conducive to crystal growth inasmuch as they do reflect situations in which there is net attraction between protein molecules. However, the source of attraction responsible for the negative virial coefficient stems from the protein-salt rather than the protein-protein contribution, which is necessarily positive. (c) 2005 Elsevier B.V. All rights reserved.

Vapour-liquid equilibrium studies at atmospheric to moderate pressures

A study of vapour-liquid equilibria is presented together with current developments. The theory of vapour-liquid equilibria is discussed. Both experimental and prediction methods for obtaining vapour-liquid equilibria data are critically reviewed. The development of a new family of equilibrium stills to measure experimental VLE data from sub-atmosphere to 35 bar pressure is described. Existing experimental techniques are reviewed, to highlight the needs for these new apparati and their major attributes. Details are provided of how apparatus may be further improved and how computer control may be implemented. To provide a rigorous test of the apparatus the stills have been commissioned using acetic acid-water mixture at one atmosphere pressure. A Barker-type consistency test computer program, which allows for association in both phases has been applied to the data generated and clearly shows that the stills produce data of a very high quality. Two high quality data sets, for the mixture acetone-chloroform, have been generated at one atmosphere and 64.3oC. These data are used to investigate the ability of the new novel technique, based on molecular parameters, to predict VLE data for highly polar mixtures. Eight, vapour-liquid equilibrium data sets have been produced for the cyclohexane-ethanol mixture at one atmosphere, 2, 4, 6, 8 and 11 bar, 90.9oC and 132.8oC. These data sets have been tested for thermodynamic consistency using a Barker-type fitting package and shown to be of high quality. The data have been used to investigate the dependence of UNIQUAC parameters with temperature. The data have in addition been used to compare directly the performance of the predictive methods - Original UNIFAC, a modified version of UNIFAC, and the new novel technique, based on molecular parameters developed from generalised London's potential (GLP) theory.

Phase equilibrium studies at normal pressures

A total pressure apparatus has been developed to measure vapour-liquid equilibrium data on binary mixtures at atmospheric and sub-atmospheric pressures. The method gives isothermal data which can be obtained rapidly. Only measurements of total pressure are made as a direct function of composition of synthetic liquid phase composition, the vapour phase composition being deduced through the Gibbs-Duhem relationship. The need to analyse either of the phases is eliminated. As such the errors introduced by sampling and analysis are removed. The essential requirements are that the pure components be degassed completely since any deficiency in degassing would introduce errors into the measured pressures. A similarly essential requirement was that the central apparatus would have to be absolutely leak-tight as any leakage of air either in or out of the apparatus would introduce erroneous pressure readings. The apparatus was commissioned by measuring the saturated vapour pressures of both degassed water and ethanol as a function of temperature. The pressure-temperature data on degassed water measured were directly compared with data in the literature, with good agreement. Similarly the pressure-temperature data were measured for ethanol, methanol and cyclohexane and where possible a direct comparison made with the literature data. Good agreement between the pure component data of this work and those available in the literature demonstrates firstly that a satisfactory degassing procedure has been achieved and that secondly the measurements of pressure-temperature are consistent for any one component; since this is true for a number of components, the measurements of both temperature and pressure are both self-consistent and of sufficient accuracy, with an observed compatibility between the precision/accuracy of the separate means of measuring pressure and temperature. The liquid mixtures studied were of ethanol-water, methanol-water and ethanol-cyclohexane. The total pressure was measured as the composition inside the equilibrium cell was varied at a set temperature. This gave P-T-x data sets for each mixture at a range of temperatures. A standard fitting-package from the literature was used to reduce the raw data to yield y-values to complete the x-y-P-T data sets. A consistency test could not be applied to the P-T-x data set as no y-values were obtained during the experimental measurements. In general satisfactory agreement was found between the data of this work and those available in the literature. For some runs discrepancies were observed, and further work recommended to eliminate the problems identified.

Phase equilibrium studies at moderate pressures

The theory of vapour-liquid equilibria is reviewed, as is the present status or prediction methods in this field. After discussion of the experimental methods available, development of a recirculating equilibrium still based on a previously successful design (the modified Raal, Code and Best still of O'Donnell and Jenkins) is described. This novel still is designed to work at pressures up to 35 bar and for the measurement of both isothermal and isobaric vapour-liquid equilibrium data. The equilibrium still was first commissioned by measuring the saturated vapour pressures of pure ethanol and cyclohexane in the temperature range 77-124°C and 80-142°C respectively. The data obtained were compared with available literature experimental values and with values derived from an extended form of the Antoine equation for which parameters were given in the literature. Commissioning continued with the study of the phase behaviour of mixtures of the two pure components as such mixtures are strongly non-ideal, showing azeotopic behaviour. Existing data did not exist above one atmosphere pressure. Isothermal measurements were made at 83.29°C and 106.54°C, whilst isobaric measurements were made at pressures of 1 bar, 3 bar and 5 bar respectively. The experimental vapour-liquid equilibrium data obtained are assessed by a standard literature method incorporating a themodynamic consistency test that minimises the errors in all the measured variables. This assessment showed that reasonable x-P-T data-sets had been measured, from which y-values could be deduced, but that the experimental y-values indicated the need for improvements in the design of the still. The final discussion sets out the improvements required and outlines how they might be attained.

Equilibrium Sorption Studies of Hg (II) Ions from Aqueous Solution using Powdered Swamp Arum ( Lasimorpha senegalensis ) Seeds.

The potential of swamp arum ( Lasimorpha senegalensis ) seeds as a low-cost adsorbent for the removal of Hg (II) ions from aqueous solution was investigated in this study. The influence of initial metal concentration on the percent adsorption of Hg (II) ions onto powdered swamp arum seeds was studied in a batch system and the filtrate was analyzed using Atomic Absorption Spectrometry (AAS). The percent adsorbed for 10, 20, 40, 60 and 80 mg/L of the aqueous solution were 97.7, 98.9, 99.3, 99.7, and 96.5% respectively. Three isotherms; Langmuir, Freundlich, and BET were used to model the equilibrium sorption of Hg (II) ions onto powdered swamp arum seeds, with a correlation coefficient of 0.998, 0.784 and0.842 respectively. The Langmuir model fitted the equilibrium data best, with a correlation coefficient of 0.998 and a maximum adsorption capacity qm, of 5.917 mg/g. Thus, indicating monolayer coverage on the adsorbent. The results showed that swamp arum seed have the potential to be applied as alternative lowcost biosorbent in the remediation of heavy metal contamination in waste water.

An investigation of phosphate adsorption from aqueous solution onto hydrous niobium oxide prepared by co-precipitation method

The synthetic hydrous niobium oxide has been used for phosphate removal from the aqueous solutions. The kinetic data correspond very well to the pseudo second-order equation The phosphate removal tended. to increase with a decrease of pH. The equilibrium data describe very well the Langmuir isotherm. The peak appearing at 1050 cm(-1) in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The adsorption capacities are high, and increased with increasing temperature. The evaluated Delta G degrees and Delta H degrees indicate the spontaneous and endothermic nature of the reactions. The adsorptions occur with increase in entropy (Delta S positive) value suggest increase in randomness at the solid-liquid interface during the adsorption. A phosphate desorbability of approximately 60% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. (C) 2008 Elsevier B.V. All rights reserved.

An extension of the Pitzer equation for the excess Gibbs energy of aqueous electrolyte systems to aqueous polyelectrolyte solutions

Pitzer`s equation for the excess Gibbs energy of aqueous solutions of low-molecular electrolytes is extended to aqueous solutions of polyelectrolytes. The model retains the original form of Pitzer`s model (combining a long-range term, based on the Debye-Huckel equation, with a short-range term similar to the virial equation where the second osmotic virial coefficient depends on the ionic strength). The extension consists of two parts: at first, it is assumed that a constant fraction of the monomer units of the polyelectrolyte is dissociated, i.e., that fraction does not depend on the concentration of the polyelectrolyte, and at second, a modified expression for the ionic strength (wherein each charged monomer group is taken into account individually) is introduced. This modification is to account for the presence of charged polyelectrolyte chains, which cannot be regarded as punctual charges. The resulting equation was used to correlate osmotic coefficient data of aqueous solutions of a single polyelectrolyte as well as of binary mixtures of a single polyelectrolyte and a salt with low-molecular weight. It was additionally applied to correlate liquid-liquid equilibrium data of some aqueous two-phase systems that might form when a polyelectrolyte and another hydrophilic but neutral polymer are simultaneously dissolved in water. A good agreement between the experimental data and the correlation result is observed for all investigated systems. (c) 2008 Elsevier B.V. All rights reserved.

Modeling volatile organic compounds (voc`s) adsorption onto cup-stacked carbon nanotubes (cscnt) using the linear driving force model

Modeling volatile organic compounds (voc`s) adsorption onto cup-stacked carbon nanotubes (cscnt) using the linear driving force model. Volatile organic compounds (VOC`s) are an important category of air pollutants and adsorption has been employed in the treatment (or simply concentration) of these compounds. The current study used an ordinary analytical methodology to evaluate the properties of a cup-stacked nanotube (CSCNT), a stacking morphology of truncated conical graphene, with large amounts of open edges on the outer surface and empty central channels. This work used a Carbotrap bearing a cup-stacked structure (composite); for comparison, Carbotrap was used as reference (without the nanotube). The retention and saturation capacities of both adsorbents to each concentration used (1, 5, 20 and 35 ppm of toluene and phenol) were evaluated. The composite performance was greater than Carbotrap; the saturation capacities for the composite was 67% higher than Carbotrap (average values). The Langmuir isotherm model was used to fit equilibrium data for both adsorbents, and a linear driving force model (LDF) was used to quantify intraparticle adsorption kinetics. LDF was suitable to describe the curves.

High-pressure phase diagram of the drug mitotane in compressed and/or supercritical CO(2)

This work provides experimental phase diagram of mitotane, a drug used in the chemotherapy treatment of adrenocortical carcinoma, in compressed and/or supercritical CO(2). The synthetic-static method in a high-pressure variable-volume view cell coupled with a transmitted-light intensity probe was used to measure the solid-fluid (SF) equilibrium data. The phase equilibrium experiments were determined in temperature ranging from (298.2 to 333.1) K and pressure up to 22 MPa. Peng-Robinson equation of state (PR-EoS) with classical mixing rule was used to correlate the experimental data. Excellent agreement was found between experimental and calculated values. (C) 2009 Elsevier Ltd. All rights reserved.