Experimentation and thermodynamic representations of binaries containing compounds of low boiling points: Pentane and alkyl methanoates

Abstract

a b s t r a c tThis work presents experimental mixing properties, h E and v E , at several temperatures and the isobaric vapor-liquid equilibria (iso-p VLE) at 101.32 kPa for four binaries containing pentane and four alkyl (methyl to butyl) methanoates. Particular conditions are established to work with these solutions with highly volatile compounds, especially for the case of methyl methanoate + pentane system, for which a continuous feeding device is designed and constructed for measuring the densities. The mixing processes of the compounds chosen give rise to high values for the excess properties and also for the activity coefficients, since in addition to the known effects that arise in the binaries ester + alkane, in this case the associative effects caused by the HCOO-group, which diminish with increasing methanoate chain length are also relevant. The change in temperature produces slopes of opposite signs for the mixing properties, being ∂v E /∂T p < 0 and ∂h E /∂T p > 0. The systems comprised of methyl and ethyl methanoate with pentane present azeotropes with coordinates (x az ,T az /K) situated at (0.558, 293.9) and (0.218, 306.5), respectively. The estimation of these coordinates and the iso-p VLE by the UNIFAC method are acceptable but do not give good predictions of the h E even less so for the LLE of the methyl methanoate + pentane system. For this binary, experimental data of all the properties are correlated with a mathematical procedure described using two models, one developed by us, and an extended form of the NRTL model. The latter does not represent the LLE data but shows the properties of isobaric equilibria, with acceptable results, while the proposed model, in addition to representing the binodal curve, gives a good representation of the v E and of these properties derived from excess Gibbs function.

Solutions of alkyl methanoates and alkanes: Simultaneous modeling of phase equilibria and mixing properties. Estimation of behavior by UNIFAC with recalculation of parameters

“…Data correlation using the NRTL equation [14] is used to validate and compare the results obtained with the proposed model. Finally, the UNIFAC method [15] was applied, since in previous works [5][6][7] we have verified that the specific interaction HCOO/CH 2 produces values that become more distant from real values as the chain length of the saturated hydrocarbon increases. The database created with the 24 systems of the subset alkyl methanoates + alkanes can be used to recalculate the values for this interaction to improve theoretical predictions.…”

“…The four working temperatures were obtained by passing a water current from a Polyscience 1166D thermostatic bath into the measuring cell, verifying the stability of the temperature (T AE 0.01) K with a sensor connected to a DT-100 Anton Paar system, calibrated previously (ITS-90). The densimeter was calibrated with bidistilled water, degasified and purified in our laboratory (with a conductance lower than 1 mS) and nonane, following our standard practice [5][6][7][8][9]. Solutions were prepared by weighing and the average uncertainty of the compositions was (x AE 0.0002).…”

“…In spite of the scientific and technical interest in methanoates, there is only limited information in the literature about solutions of these compounds with aliphatic hydrocarbons, the best known solvents. Previous works have reported experimental data of isobaric vaporliquid equilibria [2][3][4][5][6][7] (iso-p VLE) and several mixing properties [3][4][5][6][7][8][9][10] (v E , h E ) at different temperatures for some of the binaries selected, empirically defined by: {HCOOC u H 2u+1 (1)+C n H 2n+2 (2) u = [1-4] n = [7][8][9]}. In other words, considering the matrix composed of 24 systems, recent studies were focused on the saturated hydrocarbons: pentane [7], hexane [5] and decane [6], leaving the 12 systems corresponding to heptane, octane and nonane, for a later study, which are now included in this work.…”

“…Previous works have reported experimental data of isobaric vaporliquid equilibria [2][3][4][5][6][7] (iso-p VLE) and several mixing properties [3][4][5][6][7][8][9][10] (v E , h E ) at different temperatures for some of the binaries selected, empirically defined by: {HCOOC u H 2u+1 (1)+C n H 2n+2 (2) u = [1-4] n = [7][8][9]}. In other words, considering the matrix composed of 24 systems, recent studies were focused on the saturated hydrocarbons: pentane [7], hexane [5] and decane [6], leaving the 12 systems corresponding to heptane, octane and nonane, for a later study, which are now included in this work. According to NIST information, in the ThermoLit database, only partial information is available (VLE, [2][3][4]; v E , [8]; h E , [9][10][11][12][13]; c E p , [11]) for some of the binaries we propose to study here.…”

“…To verify the broad capacity of the model used previously by the authors [5][6][7], all the thermodynamic quantities y E were correlated as a function of two variables y E = j(x,T), using an appropriate algorithm and a multivariate optimization method. Data correlation using the NRTL equation [14] is used to validate and compare the results obtained with the proposed model.…”