Investigation of storage stability of diesel fuels containing biodiesel produced from waste cooking oil

Nowadays, the biodiesel is the biofuel which is blended into the diesel gas oil with the highest amount. Biodiesel can be produced from even waste-derived triglycerides (with the so-called transesterification process), but due to its adverse properties (even when produced from “clean” triglycerides like pure rapeseed oil) the storage stability of biodiesel/diesel blends containing biodiesel produced from waste have to be examined in detail. In our experimental work the changes in the quality of biodiesels produced from vegetable oil which contained various amount (10, 30, 50%) of used cooking oil (waste-derived component), and its 7 and 10% blends with gas oil in case of long-term (more than 150 weeks) storage were studied. It was found that with the increasing the proportion of used cooking oil in the vegetable oil used as raw material for biodiesel the oxidation reactions took place in greater amount during the storage of the biodiesel product. Biodiesel made from vegetable oils containing only 10% used cooking oil was the most applicable for blending; in case of the other biodiesels it is very necessary to use further amount of antioxidant additives to minimize the degradation. Furthermore, mathematical relationships were established which describe well the connection between the Rancimat induction period and the kinematic viscosity and acid number especially in case of the investigated BD-3 biodiesel. In the frame of further investigations post-additivation experiments were made with the stored biodiesels and its blends, and the results were positive: quality of the biodiesels improved, as well as the quality of the blends. However, more increased size experiments are needed to verify the blending possibility of this improved quality biodiesel into gas oil.