Optical properties as a tool for the biodiesel industry: A review

Abstract

Optical properties analysis is not included in biodiesel quality standards. However, it provides valuable information about biodiesel and its feedstocks. In particular, very accurate refractive index measurements can be carried out using low-cost (less than 1000 USD) and fast (a few seconds) equipment. Therefore, the most urgent question is to determine if the optical properties are a suitable tool for the biodiesel industry and in which applications they can currently be implemented. This work provides a comprehensive and systematic analysis of literature dealing with applications of refractive index measurements of biodiesel, its feedstocks and its blends with other fuels. Experimental data, typical ranges of values and mathematical models of refractive index are systematically presented and discussed, emphasizing biodiesel mixtures with diesel fossil fuel. Other applications, like transesterification monitoring, combustion, atomization and aging are also reviewed. At the present state of knowledge, measurements of refractive index can be used to determine the proportion of diesel and biodiesel blends and monitor the transesterification reaction.