Search results for "Activity coefficient"
showing 10 items of 60 documents
Aqueous coefficient calculations for chemicals and drugs
1999
Aqueous functional group activity coefficients (AQUAFAC) is a group‐contribution method for estimating the aqueous coefficients. We have written a program for the calculation of these coefficients. The solubility S w of alkanes shows variation of 8 orders of magnitude. The comparison with experiment shows that AQUAFAC gives good S w estimations. For 4'‐substituted acetanilides, I‐, Br‐, nitro‐, Cl‐, F‐ and methoxy‐substituents decrease S w, while formyl‐ and amino‐substituents increase S w. For acetaminophen esters, S w decreases from the acetate to the decanoate. The S w of 29 barbiturates shows typical errors of 0.4 log S w units. For the cyclo‐alkane‐l’,5‐spirobarbituric acids, S w decre…
Polycarboxylic acids in sea water: acid–base properties, solubilities, activity coefficients, and complex formation constants at different salinities
2016
This paper reports the results of the investigations carried out in synthetic sea water at different salinities for different classes of polycarboxylic acids. The investigations can be summarized as follows: (a) Determination of the protonation constants in such multicomponent solution in a salinity range 15 ≤ S ≤ 45, at t = 25 °C, for the linear dicarboxylic acids HOOC-(CH2) n –COOH (0 ≤ n ≤ 8), and aromatic polycarboxylic acids (o-phthalic and 1,2,4-benzenetricarboxylic acids). For malonic, succinic, 1,2,3-benzenetricarboxylic, and 1,2,3,4-benzenetetracarboxylic acids, investigations were also carried out at t = 10 and 37 °C; (b) Determination of the total and intrinsic solubility (S T an…
Isobaric vapour–liquid equilibria for the binary systems 4-methyl-2-pentanone+1-butanol and+2-butanol at 20 and 101.3kPa
2009
Abstract Isobaric vapour–liquid equilibrium (VLE) measurements for the binary systems 4-methyl-2-pentanone + 1-butanol and 4-methyl-2-pentanone + 2-butanol are reported at 20 and 101.3 kPa. The system 4-methyl-2-pentanone + 1-butanol presents a minimum boiling point azeotrope at both pressures (20 and 101.3 kPa) and the system 4-methyl-2-pentanone + 2-butanol presents only a minimum boiling azeotrope at 20 kPa. In both systems, which deviate positively from ideal behaviour, the azeotropic composition is strongly dependent on pressure. The activity coefficients and boiling points of the solutions were correlated with its composition by the Wilson, UNIQUAC, and NRTL models for which the param…
Isobaric Vapor−Liquid Equilibria of the Water + 1-Propanol System at 30, 60, and 100 kPa
1996
Isobaric vapor−liquid equilibria for the water + 1-propanol system are reported at 30, 60, and 100 kPa. The results were found to be thermodynamically consistent according to Van Ness−Byer−Gibbs, Kojima, and Wisniak methods. The system shows a minimum boiling azeotrope, and the azeotropic composition is scarcely shifted with pressure. Results were compared with literature values. The data were correlated with Margules, Van Laar, Wilson, NRTL, and UNIQUAC liquid-phase activity coefficient models.
Potential of phosphonium-based ionic liquids to purify 1-propanol from water by liquid–liquid extraction at mild conditions
2022
Abstract In order to reduce the environmental of the separation of 1-propanol from water in a residual industry stream for its reuse, the capability as solvents of two different trihexyl(tetradecyl)phosphonium ionic liquids (ILs) – trihexyl(tetradecyl)phosphonium chloride ([TDTHP][Cl]) and trihexyl(tetradecyl)phosphonium bromide ([TDTHP][Br])-, was studied. The liquid–liquid equilibria data for both ternary systems, {water + 1-propanol + [TDTHP][Cl]} and {water + 1-propanol + [TDTHP][Br]} at different mild work temperatures, (283.2, 303.2 and 323.2) K, and atmospheric pressure were measured. The thermodynamic parameters for both ternary systems at different work conditions were obtained by …
Modeling S-carboxymethyl-L-cysteine protonation and activity coefficients in sodium and tetramethylammonium chloride aqueous solutions by SIT and Pit…
2007
Solubility and acid–base properties of S-carboxymethyl-l-cysteine (carbocysteine, ccys) in NaClaq and tetramethylammonium chloride, (CH3)4NClaq ,a tt =2 5 ◦ C and at different ionic strengths were investigated. Solubility was studied at 1.0 ≤ I (mol L −1 ) ≤ 5.0 for NaClaq and 1.0 ≤ I (mol L −1 ) ≤ 3.0 for (CH3)4NClaq, while potentiometric measurements (by ISE-H + , glass electrode) were performed at 0.1 ≤ I (mol L −1 ) ≤ 5.0 for NaClaq and 0.5 ≤ I (mol L −1 ) ≤ 3.0 for (CH3)4NClaq. Solubility data allowed us to determine Setschenow constants and activity coefficients of neutral carbocysteine (H2ccys). Dependence on ionic strength and ionic medium of protonation constants and activity coeff…
Solubility and acid-base properties and activity coefficients of chitosan in different ionic media and at different ionic strengths, at T=25°C
2009
Studies on the acid-base properties and solubility of a polyammonium polyelectrolyte (chitosan) with different molecular weights (MW 310 and 50 kDa), were performed at T=25 °C, in the pH range 2.5–7. The protonation of chitosan was investigated by potentiometry ([H+]-glass electrode) in NaCl, NaNO3 and mixed NaNO3+Na2SO4 ionic media, at different ionic strengths. Protonation constants were calculated as a function of dissociation degree α by means of two different models, namely, a simple linear model and the modified Henderson–Hasselbalch equation. Experimental data were also fitted using a model independent of α (Diprotic-like model), according to which the acid-base properties can be sim…
A fluorescence spectroscopy study of the interaction of monocationic quinine with phospholipid vesicles Effect of the ionic strength and lipid compos…
1997
Abstract The interaction of monocationic quinine with zwitterionic dimyristoyl phosphatidylcholine (DMPC) and mixed negatively-charged dimyristoylphosphatidyl glycerol (DMPG) DMPC small unilamellar vesicles in the liquid-crystalline phase was investigated by steady-state fluorescence spectroscopy at pH 7 and 37°C. The maximum fluorescence emission peak at 383 nm, upon excitation at 335 nm, shifts to lower wavelength and decreases its intensity as the ratio between the total lipid and quinine concentrations increases. This indicates that in the membrane-bound state quinine is in an environment of low polarity, more deeply buried when anionic DMPG is present in the vesicle. For monoprotonated…
Activity coefficients and Donnan coion exclusion in charged membranes with weak-acid fixed charge groups
1998
Abstract We have studied theoretically the effects that the dissociation equilibrium of weak-acid fixed charge groups (e.g. carboxyl groups) exerts on the mean activity coefficients in charged membranes using a Donnan formalism. The model calculations indicate that unless carbon dioxide is excluded from the external aqueous solution, the pH of the membrane solution can be low enough to affect significantly the effective fixed charge concentration and the coion exclusion when the membrane fixed charge concentration is high compared with the external solution salt concentration. Although this problem was already pointed out in previous studies, the possibility that the pH and salt concentrati…
Modelling of the ternary system H3PO4/H2O/TBP
2002
Abstract A thermodynamic model is presented for the extraction of phosphoric acid from water by tri-n-butylphosphate (TBP), from aqueous solutions containing 0–6 mol/kg phosphoric acid. The activity coefficient of phosphoric acid was calculated from experimental data using Pitzer’s equation, and those of the components in the organic phase were calculated by Sergievskii–Danus’s relationship. The proposed model gives a satisfactory description of the distribution of phosphoric acid and water, in the considered concentration range, by taking into account the formation of the following species: TBP, TBP·H2O, H3PO4·TBP and (TBP)2·H3PO4·H2O.