Experimental Study of Short Chain Oils Viscosity as Biodiesel Additives

Abstract

An increasing use of chemicals from biomass instead of non-renewable petrol-based ones is expected. For instance, the anaerobic digestion of organic residual streams generates many useful chemicals for the industry, together with short chain fatty acids. Another example is the biodiesel who is a suitable substitute for the non-sustainable petro-diesel. The diesel industry is mature and the biodiesel one is still under development. Oils are too viscous to be used directly in the nowadays diesel engines, producing a bad combustion. A way to reduce the viscosity of oils is to convert them into biodiesel. Biodiesel production by transesterification of non-edible oils with alcohols generates glycerol as by-product and many nowadays studies focus on providing uses to it. There are many applications for glycerol but not enough for a high biodiesel production. A way to avoid the glycerol excess is to use it in the biodiesel formulation. For instance, glycerol reacts with short chain organic acids producing short chain oils that are useful biodiesel additives. The present study determines and correlates the viscosity of short chain fatty acids (triacetin, tripropionin and tributyrin) and compares it to the viscosity of methyl oleate and solketal (another feasible biodiesel additive). The results show that short chain oils present a low enough viscosity to be used in biodiesel formulation. The viscosity model obtained is used to evaluate the viscosity of the biodiesel that would result, considering several literature experiments related to acid-genesis stages using different residual streams. The results show that the short chain fatty acids mixture obtained from any anaerobic digestion is useful as biodiesel additive. Although the short chain oil triacetin is technically a good biodiesel additive, it cannot be used in European Union due to biodiesel legal limitations on the maximum amount of triglycerides; these limitations are not present in the equivalent USA regulations.