Determination and Estimation/Prediction of Some Properties of Biodiesel and Biodiesel- Diesel-Butanol Blends

Abstract

The demand for energy is increasing very rapidly and this has led to the depletion of fossil fuels. Biodiesel (a mixture of fatty acid alkyl esters or FAAEs) can be considered as a promising alternative to petroleum diesel. Critical properties and phase equilibrium properties are required for design and simulation of processes involving biodiesel. Density, viscosity and heat of vaporization of biodiesel are required for the modeling of combustion and fuel injection. Pour point and flash point are important for storage, handling and transport of fuel. Experimental determination of some properties like critical temperature, critical pressure, vapor pressure, cetane number and heat of vaporization is time-consuming and cumbersome. Methods for accurate estimation or prediction of above-mentioned properties are required. The objective of the present study was to propose most suitable model for a given property. For the study purpose, three biodiesels, jatropha, karanja, and palm which are of relevance to the Indian region were selected. Two types of blends, biodiesel-diesel and biodiesel-diesel-butanol were used. Study of butanol blends of these biodiesels is reported for the first time in this work. Density, viscosity, pour point and flash point of biodiesel, biodiesel-diesel and biodiesel-diesel-butanol blends were experimentally determined. Total of 112 experimental data points for density, 651 data points for viscosity, 48 data points each for pour point and flash point were used to correlate these properties with volume fraction of biodiesel and temperature of blends. Pour point and flash point could only be related to volume fraction of the biodiesel. % OARD for biodiesel-diesel blends was 0.673 for density, 5.23 for viscosity, 12.10 for pour point and 2.78 for flash point. % OARD for biodiesel-diesel-butanol blends was 0.249 for density, 4.42 for viscosity, 11.46 for pour point and 4.96 for flash point. For critical temperature method of Joback, for critical pressure method of Marrero and Pardillo and for acentric factor method of Constantinou and Gani is recommended. Critical properties of jatropha, karanja and palm biodiesel are reported for the first time in this work. A total of 244 experimental vapor pressure data points for FAMEs and 55 data points for FAEEs were used for the estimation of vapor pressure. For vapor pressure, method of Othmer and Yu was used for the first time in this study and is recommended for estimation of vapor pressure of FAMEs. For estimation of heat of vaporization, method of Ceriani is recommended. For prediction of VLE of biodiesel systems, three types of binary systems of FAAE+other FAAE, FAAE+Alcohol and FAAE+Alkane were studied. A total of 275 experimental VLE data points (197 P-T-x-y and 78 P-T-x data points) were obtained from the literature and tested for the study of VLE. Peng Robinson cubic equation of state (PR CEOS) and Soave-Redlich-Kwong cubic equation of state (SRK CEOS) could predict VLE of FAAE+ Other FAAE and FAAE+Alkane with reasonable accuracy. For FAAE+Alcohol systems, simple activity coefficient models of Margules 2 suffix, Margules 3 suffix and van Laar were used to fit experimental VLE data. Cetane number, density, viscosity, pour point and flash point of jatropha, karanja and palm biodiesels were predicted by various models based on composition, molecular structure and group contribution of FAMEs. For density prediction of biodiesels, model of Ramirez-Verduzco is recommended, for prediction of cetane number compositionbased model of Gopinath is recommended and for viscosity model of Ceriani is recommended. For flash point and pour point of biodiesels, models available in the literature could not give good prediction.