High-pressure density of biodiesel: experimental measurements and modeling with the CPA EoS

M. Pratas1, M. Oliveira1,3, M. Piñeiro2, M. Gallego2, A. Queimada3 and J. Coutinho1

1CICECO, Chemistry Department, University of Aveiro, Aveiro, Portugal
2Facultade de Ciencias, Departamento de Fisica Aplicada, Universidad de Vigo, Vigo, Spain
3LSRE - Laboratory of Separation and Reaction Engineering, Faculdade de Engenharia, Universidade do Porto, Porto, Portugal

Keywords: high pressure, CPA, experimental, modelling
property: density
material: biodiesel

Biodiesel is a promising alternative energy resource for diesel fuel, consisting of alkyl monoesters of fatty acids, obtained from vegetable oils or animal fats combined with a short chain alcohol. It has properties similar to ordinary diesel fuel made from crude oil and can be used in conventional diesel engines without any transformation of motorization. The growing interest in vegetable oil and their derivatives as renewable fuels for diesel engines has been motivated by the predictable dwindling of fossil resources as well as by the environmental concerns associated with fossil CO2 emissions. Europe aims to replace 20% of fossil fuels for alternative renewable fuels such as biofuels until 2020. Density is one of the most important biodiesel properties, since injection systems (pumps and injectors) must deliver the amount of fuel precisely adjusted to provide a proper combustion. Nowadays, the pressure influence in the fuel density is particularly important for modern common rail systems where the pressure can reach 250MPa instead of 35 MPa. However, besides its importance, little attention has been given to high pressure densities of biodiesels. In fact, there are almost no reports in literature about experimental high pressure biodiesel density data. In this work, new experimental density measurements were carried out for fatty acid esters and biodiesels. Measurements from 283 to 333 K and from atmospheric pressure to 45MPa were performed for fatty acid esters as methyl laurate, methyl myristate and methyl oleate and biodiesels from palm, soybean and rapeseed oils. Following previous works, were the Cubic-Plus-Association equation of state (CPA EoS) was shown to be the most appropriate model to be applied to biodiesel production and purification processes, the new experimental data here reported was also successfully predicted with the CPA EoS. A discussion about the most appropriate CPA pure compound parameters for esters is also presented.

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