Biodiesel winterization

Biodiesel is diesel fuel produced from vegetable oils and other renewable resources. Many different types of oils can he used, including animal fats, used cooking oils, and soybean oil. Biodiesel is miscible with petroleum diesels and can he used in biodiesel-diesel blends. Most often blends are 20 percent biodiesel and 80 percent traditional diesel. Soy diesel can be used neat (100%), hut many other types of biodiesel are too viscous, especially in winter, and must be used in blends to remain fluid. The properties of the fuel will vaiy depending on the raw material used. Typical values for biodiesel are shown in Table 1. 

Dunn, R. O. 1998. Effect of Winterization on Fuel Properties of Methyl Soyate. In Peterson, C. L. (Ed.), Proc., Commercialization of Biodiesel Producing a Quality Fuel (pp. 164-186). Moscow University of Idaho. 

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). 

The more pragmatic approach used in the Biodiesel Cost Optimizer (see below) is based on the work of Dr. Lee and colleagues (1996). Soy methyl esters were winterized on lab scale at -21.5°C, -25.0 °C and -28.4 °C. This yielded FAME olein with 11.2%, 7.4% respectively 6.0% saturated FAME (palmitic acid and stearic acid methyl esters), and FAME stearin with 46.6%, 42.2% respectively 33.1% saturated FAME. This simple lab test con-... 

Table 3.2 displays some examples for ternary blends of palm oil, soybean oil and rapeseed oil methyl esters. Under the price conditions given in the table, a typical winter formula would contain SQ-90% rapeseed methyl esters, with the balance mainly soy methyl esters and maybe a few percent of palm methyl esters. In summertime no rapeseed would be used. For Europe 70 to 80% soy methyl esters would combine with palm methyl esters as the balance. For Biodiesel in the U. S., the palm oil methyl ester content would be equally high, making the formula considerably cheaper than pure soy methyl esters. 

In temperate climates, diesel fuel must remain fluid at temperatures below the minimum expected temperature for the season. Through much of North America, winter diesel fuels have low temperature flow points below —30°C. Diesel fuels with low pour points have lower viscosity and often lack lubricity (110). These fuels typically provide little lubricity. For example, Noureddini (111) reports that biodiesel fuels that are simple esters of various vegetable oils have poor flow characteristics below a temperature of —2°C. To overcome this difficulty, a solvent consisting of mixed ethers of glycerol is added to the biodiesel. The resultant fluid has a low temperature cloud point below —32°F (—36°C). The pour point of this fluid is still above that necessary to effectively add to many winter diesels, as it may be necessary to pour the fuel component at temperatures as low as —45°C. 

P. B. Hertz, Winter Engine Wear Comparisons with a Canola Biodiesel Fuel Blend (1995). Available http //www.nbb.org/resources/reportsdatabase/reports/gen/gen-233. pdf. 

Biodiesel made with commodity soybean oil tends to crystallize when used at low temperature (-2°C). Biodiesel made from soybean oil with a low content of 16 0, together with branched chain alcohols, has a decreased crystallization temperature (-7°C) (Lee et al., 1995). In the same way, when methyl soyate made from low-l6 0 soybean oil was winterized to decrease its saturation, and thus its crystallization temperature, the yield of the process was better than that from winterization of methyl soyate from commodity soybean oil (Lee et al., 1996). 

Of course, biodiesel also has some serious drawbacks. The main one is that it costs about three times as much as regular diesel fuel. Biodiesel also produces more nitrogen oxides in the exhaust than conventional diesel fuel and is less stable in storage. Biodiesel also can leave more gummy deposits in engines and must be winterized by removing components that tend to solidify at low temperatures. 

Biodiesel performs similarly to diesel and is used in unmodified diesel engines of trucks, tractors, and other vehicles and is better for the environment. Biodiesel is often blended with petroleum diesel in ratios of 2, 5, or 20 percent. The most common blend is B20, or 20 percent biodiesel to 80 percent diesel fuel. Biodiesel can be used as a pure fuel (100 percent or BlOO), but pure fuel is a solvent that degrades the rubber hoses and gaskets of engines and cannot be used in winter because it thickens in cold temperatures. The energy content of biodiesel is less than that of diesel. In general, biodiesel is not used as widely as ethanol, and its users are mainly governmental and... 

Several approaches to the low-temperature problems of esters have been investigated including blending with conventional DF, winterization, additives, branched-chain esters, and bulky substituents in the chain. The latter approach may be considered a variation of the additive approach as the corresponding compounds have been investigated in biodiesel at additive levels. Blending of esters with conventional DF will not be discussed here. 

Dorn, K.M., Fankhauser, J.D., Wyse, D.L., Marks, M.D., 2013. De novo assembly of the pennycress (Thlaspi arvense) transcriptome provides tools for the development of a winter cover crop and biodiesel feedstock. Plant J. 75,1028-1038. 

Perez, A., Casas, A., et al., 2010. Winterization of peanut biodiesel to improve the cold flow properties. Bioresource Technology 101 (19), 7375—7381. 

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