(222ao) Vapor-Liquid Equilibrium for Binary System of 2-Methyl-1,3-Propanediol(MPO)+Water, and MPO +1,4-Butandiol(BDO)

2-methyl-1,3-propanediol (MPO), as a new glycol synthesis of block, has been widely applied to saturated polyester, unsaturated polyester, coating, personal care products, plasticizer and so on due to its colorless, odorless, water-soluble, low toxic and environmentally benign. Vapor-liquid equilibrium (VLE) data are absolutely necessary to modeling separation process, analyzing the efficiency of chemical plant, and optimizing operation conditions of vapor-liquid mass transfer. However, to the best of our knowledge, there are few reports about thermodynamic properties of MPO, and the VLE data of MPO+H₂O and MPO+BDO systems so far. So, Vapor pressures of MPO and VLE data of the two systems were measured under atmospheric pressure with the static method and improved ROSE vapor-liquid equilibrium still respectively in this work, which intend to provide the preliminary data and fundamental information for various applications of MPO. The reliability of static device and improved ROSE still were calibrated before measuring. And the consistency of thermodynamics was also verified.

Materials: 2-methyl-1,3-propanediol (MPO, Darian Co. H₂O<0.08% ) was purified by distillation under reduced pressure after dried with 3A molecular sieve and analyzed by GC900 with a purity>99.6%. Chromaticity < 15 (APHA), carbonyl group ( by -CHO)<500ppm, Fe< 0.5ppm; 1,4-butanediol ( BDO) , double-distilled water.

Experimental devices: Analytical Balance (Mettler Toledo AB204-N with 0.1mg precision), isobaric gauge, improved ROSE equilibrium still, WZS-1 Abbe refractometer, GC900，micro-thermometer (1/10 precision, 150^oC-200^oC, 200^oC-250^oC); ZXZ-1 rotary-vane vacuum pump; potential transformer.

First, Vapor pressures of MPO at 100^oC and BDO at 140^oC and 180^oC under atmospheric pressure were measured to calibrate the purity of the reagents and the reliability of experimental methods. Compared with literature data, the average relative error was less than 0.04%. Then, vapor pressures of MPO were measured under normal pressure at 298.15K-484.95K with a static apparatus, which there is a linear relationship between lnp^sand 1/T (square of correlation coefficient R²=0.9984). And the average enthalpy of vaporization of MPO is 37.68KJ/mol at above temperature range.

Then, experimental VLE data of ethanol (1) + water (2) binary system were measured, and compared with the literature data to verify the reliability of the improved ROSE equilibrium still. A series of different concentrations of ethanol(1) + water(2) mixture were prepared as standard solutions. Refractive index in a corresponding concentration was measured by Abbe refractometer at 306.15K and the standard curve was obtained. Then, the solution to be tested was put into the improved ROSE equilibrium still. When the temperature of system was almost constant within 20 minutes, an equilibrium state was reached. Gas and liquid phase sample were taken from corresponding sample port, and equilibrium temperatures were recorded at the same time. The molar concentrations of gas and liquid phase were obtained in according to the standard curve.

Third, VLE data of MPO(1) + H₂O(2) were measured with the improved ROSE equilibrium still, which the measuring procedure was followed as stated above. The x-y-t diagram of MPO+H₂O system was done according to the experimental VLE data. The results showed that there was no azeotropic point of MPO+H₂O binary system and the larger area between gas and liquid phase curves meant the big difference of boiling point between pure 2-methly-1,3-propandiol and H₂O, which MPO+H₂O mixture can be completely separated by distillation easily.

VLE data of MPO(1) + BDO(2) were measured with the same ROSE still. Accurate concentration of prepared solutions was obtained by gas chromatography. The analysis of each sample was repeated three times. The x-y-t data of MPO+BDO system shown that an azeotropic point was found (x₁=0.9507; T=487.0K) at low concentration of BDO.

At last, the isobaric VLE data of MPO (1) + H₂O (2) and MPO(1) + BDO(2) binary systems were verified with the Herrington method of area test. The results showed that the experimental VLE data of two binary systems were in according with the consistency of thermodynamics.

 Acknowledgement: Thanks for the financial support from Henan Natural Science Foundation (511021100).