Biodiesel cold flow properties

However, one of the limitations of using biodiesel fuel for diesel engines is higher cold flow properties compared with petroleum diesel fuel (4). Cold properties consist of cloud point, pour point, and cold filter plugging point. The cloud point is a temperature at which the fuel starts to thicken and cloud, the pour point is a temperature at which the fuel thickens and no longer pours, and the cold filter plugging point is the lowest temperature at which fuel still flows through a specific filter. These... 

Cold properties of biodiesel are highly correlated to the fatty acid composition. Biodiesel with a high content of saturated fatty acids, such as that from palm oil and coconut oil, possesses poor cold flow properties. On the other hand, biodiesel with a high content of unsaturated fatty acids possesses better flow properties at lower temperatures. However, biodiesel from highly unsaturated fatty acids with more than two double bonds has combustion problems. Therefore, in some countries, the content of highly unsaturated fatty acid methyl esters in biodiesel is kept low (5). 

Biodiesel made from feedstocks containing large concentrations of long-chain saturated fatty acids will have very poor cold flow properties. Less expensive feedstocks such as palm oil or tallow (see Table 1.3) may not be feasible in moderate temperature climates. In contrast, feedstocks with lower concentrations of long-chain saturated fatty acids yield biodiesel with more attractive cold flow properties. For example, biodiesel from canola, linseed, olive, rape-seed, and safflower oils have CP and PP close to or below 0°C (Table 1.3). 

Nearly linear correlations for CFPP versus CP and LTFT versus CP were reported for neat biodiesel and its blends with petrodiesel (Dunn and Bagby, 1995,1996 Dunn et al., 1996). For LTFT, the correlation was essentially LIFT CP, suggesting the labor- and time-intensive LTFT test could be spared by simply measuring CP. A major conclusion from these studies was that development of approaches to improve cold flow properties of biodiesel should focus on technologies that decrease CP. 

TABLE 1.3. Cold flow properties of biodiesel (B100) derived from various feedstock lipids and alcohols.2... 

Improving Cold Flow Properties, Operability and Performance of Biodiesel... 

Many approaches for improving the cold flow properties of biodiesel have been explored. These include blending with petrodiesel, transesterification with medium or branched-chain alcohols instead of methanol or ethanol, crystallization fractionation, and treatment with cold flow improver (CFI) additives. 

TABLE 1.5. Cold flow properties of fractionated biodiesel."... 

Despite its many advantages as a renewable alternative fuel, biodiesel presents a number of problems that must be resolved for it to be attractive for more widespread applications. These problems include improving relatively poor cold flow properties, monitoring and maintaining fuel quality... 

Shrestha, D. S., Van Gerpen, J., Thompson, J., and Zawadzki, A. 2005. Cold Flow Properties of Biodiesel and Effect of Commercial Additives. In Proc., ASAE Annual International Meeting. Warrendale PA Society of Automotive Engineers (Paper No. 056121). 

Waynick, J. A. 1997. Evaluation of the Stability, Lubricity, and Cold Flow Properties of Biodiesel Fuel. In Proc., 6th International Conference on Stability and Handling of Liquid Fuels. Atlanta GA IASH. 

Cold flow properties are of major importance in winter diesel. Cold performance limits are set to guarantee lack of crystallization. These are expressed as Cloud Point (CP), Pour Point (PP), or as Cold Filter Plugging Point (CFPP). For B100 biodiesel these have to be fully met with the biodiesel, and, if needed, with extra crystal retardation additives. In B2-B30 blends, though, the tendency is rather towards two types of Biodiesel, one for summertime (for example with CFPP of 0°C), and one for wintertime (for example with CFPP -10 °C). 

Dr Adam Harvey at Newcastle University (Harvey, 2006) is examining the use of oscillatory baffle reactors as components to intensify the production of biodiesel fuels. The research at Newcastle University uses rapeseed oil as the feedstock, the atfiaction being generally that it is a renewable energy source, it reduces CO2 emissions and pollution and it attracts tax relief in the UK at present. The range of PI projects in this area include a portable plant, solid catalysts (which allow a reduced number of process steps compared to liquid catalysts), the development of a reactive extraction process direct from the oilseeds, examination of cold flow properties and the production of biodiesel from algae. 

Esters of levulinic acid produced from either methanol or ethanol are under active development as blend components in diesel formulations. These esters are similar to the biodiesel fatty acid methyl esters (FAME) now used in European low emission diesel formulations. FAME has certain disadvantages as automotive fuel components in diesel due to cold flow properties (24) and gum... 

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