Impact of residual glycerides on viscosity of biodiesel (waste and rapeseed oil blends)

Purpose: Biodiesel, mixture of fatty acid methyl esters is a biodegradable alternative fuel that is obtained from renewable sources as a vegetable oils or animal fats. Use of waste cooking oils reduce the cost of raw materials for biodiesel production and also reduces the environment pollution. Moreover, pure edible vegetable oils for biodiesel production have an ethical significance because food is used to produce fuel. The aim of this work is a presentation of effects that residual glycerides have on kinematic viscosity values of biodiesels produced from the various waste cooking oils with crude rapeseed oil blends. Kinematic viscosity is one of the most important property of biodiesel and it directly depend on raw material composition. Design/methodology/approach: This article includes analysis and estimation of the effect that residual mono-, di- and triglycerides which remain in the biodiesels after transesterification processes have on their kinematic viscosities. Results obtained for biodiesel produced from various percentages of waste cooking oils and crude rapeseed oil blends were presented. Findings: Investigation during biodiesels production showed that the biggest impact on biodiesel kinematic viscosity have monoglycerides, diglycerides, and then at the end triglycerides. From these follows that kinematic viscosity of biodiesel is not a function only of the conversion (transesterification process) but also of the residual incompletely reacted glycerides which amount depend of the waste cooking oils percentage in raw material blends used for biodiesels production. Research limitations/implications: These presented results are the closed solution considering the used raw materials. Quality and chemical composition of the used waste cooking oils are quite different from each other, which affects the quality of the produced biodiesels. Because of that these results should be an indicator for the further testing and improvements to achieve optimization of transesterification process which can reduce the amount of the residual glycerides in the biodiesel. Practical implications: The results presented in the paper can be applied in the industry for estimation and selection of the optimal percentages of waste cooking oils and crude rapeseed oil blends for the biodiesel production. Originality/value: This paper presents research of the influence of residual glycerides on kinematic viscosity of biodiesels produced from the various waste cooking oils and crude rapeseed oil blends. Application of these research can leads to the better kinematic viscosity value of produced biodiesel with optimization of the transesterification process.