Improving cold flow properties of biodiesel

Biodiesel is becoming increasingly popular as diesel and heating oil extender, as it has substantially similar physical and chemical properties. With respect to the cold flow properties, however, it can be sufficiently different enough to cause potential problems. Diesel and heating oils have been routinely "winterized" using chemical additives or blending with lower pour point petroleum stock such as kerosene. While some of these methods could work to some extent with blends of biodiesel in diesel or heating oil, they are not always successful. Also, the blending process itself becomes difficult in cold weather, unless stringent precautionary measures are taken. For all these reasons, the improvement of the cold flow properties of biodiesel remains an important research topic. It is known that the presence of saturates in the fatty acid composition of the plant oil which is transesterified to produce biodiesel is a major reason for the "poor" cold flow characteristics. This suggests several approaches to change the fundamental characteristic of the biodiesel starting at the source. Firstly, the distribution of the fatty acid composition of the oil from the plant source can be modified through biological alteration of the plant. Secondly, the transesterification process can be modified through choice of the catalyst, esterifying alcohol, operating conditions etc. to transform the unsaturates preferentially or obtain more desirable esters. Thirdly, the mixture of fatty acid esters can be "winterized" by physico-chemical separation (freezing out the fine crystals etc.), with the separated product being utilized in other processes. Some of the suggested methods are in various research phases (including incipient) and some have been studied or are in progress. The status and potential of these will be reviewed in this study.