Published: July 15, 2011 r2011 American Chemical Society 3712 dx.doi.org/10.1021/ef200669k | Energy Fuels 2011, 25, 3712–3717 ARTICLE pubs.acs.org/EF Prediction of Viscosities of Fatty Compounds and Biodiesel by Group Contribution Roberta Ceriani,* ,† Cintia B. Gonc -alves, ‡ and Jo ~ ao A. P. Coutinho § † Departamento de Processos Químicos, Faculdade de Engenharia Química, Universidade Estadual de Campinas, 13083-852 Campinas, Brazil ‡ Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de S ~ ao Paulo, 13635-900 Pirassununga, Brazil § Departamento de Química, Centro de Investigac - ~ ao em Materiais Cer ^ amicos e Comp ositos (CICECO), Universidade de Aveiro, Campus Universit  ario de Santiago, 3810-193 Aveiro, Portugal ABSTRACT: In the present work, a group contribution method is proposed for the estimation of viscosity of fatty compounds and biodiesel esters as a function of the temperature. The databank used for regression of the group contribution parameters (1070 values for 65 types of substances) included fatty compounds, such as fatty acids, methyl and ethyl esters and alcohols, tri- and diacylglycerols, and glycerol. The inclusion of new experimental data for fatty esters, a partial acylglycerol, and glycerol allowed for a further refinement in the performance of this methodology in comparison to a prior group contribution equation (Ceriani, R.; Gonc -alves, C. B.; Rabelo, J.; Caruso, M.; Cunha, A. C. C.; Cavaleri, F. W.; Batista, E. A. C.; Meirelles, A. J. A. Group contribution model for predicting viscosity of fatty compounds. J. Chem. Eng. Data 2007, 52, 965À972) for all classes of fatty compounds. Besides, the influence of small concentrations of partial acylglycerols, intermediate compounds in the transesterification reaction, in the viscosity of biodiesels was also investigated. 1. INTRODUCTION The industries dealing with vegetable and animal fats and oils are of increasing importance nowadays mainly because of the growth in the biodiesel production in the past few years. However, the models for the prediction of physical properties of fatty compounds, required for the design and evaluation of transport and separation processes involved, are still wanting. 1À3 This situation results in part from the lack of accurate experi- mental data, which has encouraged researchers to measure new experimental data for these systems, trying to map the behavior of fatty compounds under a variety of processing conditions. 4,5 Among physical properties, viscosity has been under attention in this area of research, especially for biodiesel compounds (mainly fatty esters), because of the influence of this transport property during fuel injection and combustion. Recently, Su et al. 1 and Díaz-Tovar et al. 6 presented a systematic development of com- puter-aided methods and tools related to the prediction of physical properties of fatty compounds. Because of the nature of fatty compounds, the concept of group contribution is suitable and has been used extensively for the prediction of thermodynamic and transport properties, 1 as vapor pressure, 7 viscosity, 8 heat capacity, 9 critical properties, 6 and surface tension. 6 Zong et al. 10 developed a chemical constituent fragment approach for some thermophysical properties of partial acylglycer- ols rather than a function group approach, but their methodology is not extendable for the other classes of fatty compounds. The release of new experimental data for viscosities of pure fatty esters 4 and the incapability of the model by Ceriani et al. 8 of dealing with the prediction of viscosities of partial acylglycerols (mono- and diacylglycerols), as pointed out by Freitas et al. 2 and Díaz-Tovar et al., 6 encouraged us to develop a refined methodology for the prediction of this relevant transport property in the oil and fat industry. This paper aims to develop a flexible group contribution method for estimating the viscosity of fatty compounds using the same set of functional groups as proposed by Ceriani et al. 8 but with a different temperature dependence. In fact, Freitas et al. 2 pointed out that the temperature-dependency behavior of the model by Ceriani et al. 8 in the prediction of viscosities of biodiesels could be related to the poor description of the viscosity of pure unsaturated fatty acid esters. To overcome the limitations mentioned above, the experimental data used for regression considered the recent values published by Pratas et al. 4 for methyl and ethyl fatty esters and also values for diacylglycerol 11 and glycerol 12 in conjunction with the databank gathered by Ceriani et al. 8 The predictive capability of the proposed model was tested against experimental data from Freitas et al. 2 for biodiesel from sunflower, soybean, palm, and rapeseed oils considering not only the presence of methyl esters but also partial acylglycerols, intermediate compounds in the transesterification reaction, following information given by the authors. Experimental data measured in this work for fairly good conversion transesterification reactions, i.e., biodiesel (from rapeseed, soybean, and palm oils) with the presence of considerable amounts of partial acylglycerols, was also used as a test databank. 2. EXPERIMENTAL SECTION 2.1. Samples. In this work, three biodiesel samples were synthe- sized in our laboratory (CICECO) by transesterification reactions of rapeseed, soybean, and palm oils, using the same procedure described by Received: May 2, 2011 Revised: July 14, 2011