Springtime Doesn't Make the Cold Flow Issue Go Away

By Ron Kotrba | May 11, 2009
It may seem odd to have two feature articles in a June issue covering the topic of cold flow or biodiesel low-temperature operability. Really it is not. We all here realize it is springtime even in North Dakota but one of the most repeated concerns I hear from lay people, especially from those in the North Country, is that "biodiesel would be great if it worked when it's cold." Well, as you all know, No. 2 petro-diesel doesn't work so great in cold weather either, which is why in places like Minnesota and North Dakota, No. 1 diesel fuel is blended 50/50 with No. 2.

Diesel fuels, and of course biodiesel, all have cloud point temperatures at which the fuel becomes, well, cloudy from crystallization. No diesel or biodiesel fuel is expected to perform below the cloud point, but with biodiesel a technical issue that is baffling the industry is the potential with biodiesel for operability problems at temperatures above the cloud point. As NREL principal engineer Robert McCormick says in a Q&A I conducted with him (page 42), "The problem with biodiesel from a low-temperature perspective is when you get fuel filter plugging in temperatures above the cloud point no one expects that." The Cold Soak Filtration Test was incorporated into ASTM D 6751 to curb this phenomenon.

Assistant editor Sue Retka Schill wrote an interesting feature article, on Page 36, "B100 to the Arctic Circle," which is about Purdue University's Permaflo process that uses urea to facilitate fractionation of the saturated and unsaturated methyl esters. The unsaturated fraction, Permaflo biodiesel as it's called, powered a contingent of Hoosiers and Alaskans north to the Arctic Circle and, while bottled water and canned foods were frozen solid, the Permaflo biodiesel kept performing.

So, while springtime does not make the cold flow issue go away, the warm weather is highly welcomed. Enjoy the weather!

Ron Kotrba
[email protected]
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