Vapor Liquid Equilibria of Binary and Ternary Systems with Water, 1,3-Propanediol, and Glycerol Maria Teresa Sanz, Beatriz Blanco, Sagrario Beltra ´ n,* and Jose Luis Cabezas Department of Chemical Engineering, University of Burgos, 09001 Burgos, Spain Jose ´ Coca Department of Chemical Engineering and Environmental Technology, University of Oviedo, 33071 Oviedo, Spain Isobaric vapor-liquid equilibrium data for the binary system water + 1,3-propanediol and for the ternary system water + 1,3-propanediol + glycerol were determined at 30 kPa. All the experimental data reported were thermodynamically consistent. The activity coefficients were correlated with the Wilson, NRTL, and UNIQUAC equations. A distillation column was simulated to study the removal of water from a fermentation broth containing 1,3-propanediol and glycerol. Introduction 1,3-Propanediol is commonly used in the synthesis of polyesters, refrigeration applications, paints, plastic in- dustries, and so forth. Presently, 1,3-propanediol is being manufactured by two chemical processes and a biochemical one for a share of a 30 million lb per year market. 1 1,3-Propanediol (1,3-PD) may be obtained by fermenta- tion of renewable substrates such as glycerol and sugars. 2-4 The recovery of 1,3-PD from the fermentation broth can be carried out by distillation, as this technique is the most widely used for separation of alcohol-water mixtures. 5 Other alternatives to recover 1,3-PD from fermentation broths by converting it into a substance without hydroxyl groups have been studied by Malinowski et al. 6 This study was undertaken to obtain the necessary VLE data to carry out the recovery of 1,3-PD, obtained by fermentation of glycerol, by distillation. Previous data on VLE were only found for the binary system water + glycerol. 7-9 In this work, VLE data for the binary system water + 1,3-propanediol are reported. Accurate data for the system 1,3-propanediol + glycerol could not be obtained with the available still due to an unstable boiling of this system. Therefore, to obtain the necessary parameters of the activity coefficient equations for computer simulation of the distillation process, the VLE of the ternary system, water + 1,3-propanediol + glycerol, was determined. The results obtained were used for the simulation of a distil- lation column for removal of the solvent, water. Experimental Section Chemicals. 1,3-Propanediol (97 wt %) and glycerol (99.5 wt %) were purchased from Fluka. 1,3-Propanediol was purified by vacuum distillation, and the final purity was 99.9 wt %, as determined by gas chromatography (GC) that failed to show any significant impurities other than water. Glycerol and 1,3-propanediol are very hygroscopic; glycerol may absorb water up to 50 wt %. Both products were stored over activated 3 Å molecular sieves in order to keep them dried. The water content of glycerol and 1,3-propanediol was determined, before being used, with a Karl-Fisher apparatus (Mitsubishi Kasei CA-20) and was found to be below 0.005 and 0.003 wt %, respectively. Ultrapure water, with a resistivity of 18.2 MΩ‚cm, obtained with a Milli-Q system (Millipore), was used. As an additional purity check, some physical properties of the pure components were measured and compared with values reported in the literature. The results are reported in Table 1. Apparatus and Procedure. An all-glass circulation still of the Gillespie 10 type modified by Ro ¨ ck and Sieg 11 was used in this work. This apparatus has been previously described and used in our laboratory to obtain VLE data. 12,13 The still was operated under a nitrogen atmo- sphere, to avoid decomposition of glycerol due to the presence of air. The total pressure of the system was monitored with a digital manometer ((0.1 kPa) and controlled at 30 kPa. Atmospheric pressure was measured with a Lambrecht type barometer. The boiling point temperature in the equilibrium still was measured with a mercury-in-glass thermometer with an accuracy of (0.05 K. The still was silanized prior to operation in order to avoid recirculation problems of the condensed vapor phase through the parts of the still with small internal diameter due to the high surface tension of some of the components. The high viscosity of the mixture may lead to uneven boiling. To minimize this effect, a very low flow of nitrogen was allowed in the liquid phase through the bottom of the still. This nitrogen current was dispersed with a magnetic stirrer to form small bubbles that promoted even boiling. Slow heating also avoided bumping of the liquid during boiling. Sample Analysis. The liquid and vapor phases of the binary and ternary systems were analyzed using a Hewlett- * To whom correspondence should be addressed. E-mail: beltran@ubu.es. Table 1. Physical Properties of Pure Compounds F (298.15 K)/kg‚m -3 n(D, 298.15 K) Tb(30 kPa)/K compound exp lit. a exp lit. a exp lit. water 997.05 997.047 1.3325 1.3325 342.31 342.25 b 1,3-propanediol 1049.65 1050 1.4387 1.4386 451.65 451.36 b glycerol 1257.76 1255.12 1.4730 1.4730 519.86 c a Riddick et al. 23 b Daubert and Danner. 24 c (PRO/II) Library. 25 635 J. Chem. Eng. Data 2001, 46, 635-639 10.1021/je000118v CCC: $20.00 © 2001 American Chemical Society Published on Web 03/22/2001