Phase diagrams of binary systems containing n-alkanes, or cyclohexane, or 1-alkanols and 2,3-pentanedione at atmospheric and high pressure

Abstract

Phase equilibria, for the binary systems { n-alkanes (tridecane, octadecane, or eicosane), or cyclohexane, or 1-alkanol (1-hexadecanol, or 1-octadecanol, or 1-eicosanol) + 2,3-pentanedione} have been determined using a cryometric dynamic method at atmospheric pressure. The influence of pressure on liquidus curve up to 800 MPa was determined for (tridecane, or cyclohexane + 2,3-pentanedione) systems. A thermostated apparatus for the measurements of transition pressures from the liquid to the solid state in two component isothermal solutions (pressometry) was used. The freezing and melting temperatures at a constant composition increase monotonously with pressure. The high-pressure experimental results obtained at isothermal conditions ( p– x) were interpolated to well known T– x diagrams. Immiscibility in the liquid phase was observed only for the n-alkanes mixtures. The solubility decreases with an increase of the number of carbon atoms in the n-alkane, or 1-alkanol chain. The higher intermolecular solute–solvent interaction was observed for the 1-alkanols. Experimental solubility results are compared with values calculated by means of the NRTL equation ( n-alkanes) and the NRTL and UNIQUAC ASM equations utilizing parameters derived from SLE and LLE results. The existence of a solid–solid first-order phase transition in tridecane, eicosane and 1-alkanols has been taken into consideration in the calculations. The correlation of the solubility data has been obtained with the average root-mean-square deviation of temperature σ < 1.0 K with both equations. The pressure–temperature–composition relation of the high-pressure (solid + liquid) phase equilibria, was satisfactorily presented by the polynomial.