When I wrote my post about green diesel last week, I neglected to mention one other very useful attribute of green diesel: it has a much lower pour point than biodiesel. According to an articlein NREL’s 2005 research review,
“Green diesel consists of paraffin molecules produced by hydrogenating triglycerides by means of a conventional petroleum refining process. Green diesel has a very high cetane number, so it ignites fairly quickly after injection, and a low pour point—the lowest temperature at which a fuel will pour. Thus, it is a high-quality diesel fuel and is totally compatible with petroleum diesel.”
This is in contrast to biodiesel, which is produced by trans-esterifying triglycerides with methanol, and has a much higher pour point… which is why I can only use B20 (20% biodiesel) most of the year here in Colorado. At temperatures below about 50F, biodiesel begins to “cloud” and will clog fuel filters, preventing the fuel from getting to the engine. Since I don’t like my car stalling on me, I only use B100 during the hottest summer months.
The closest source of biodiesel to me is a truck stop without a heated storage tank, and so in the winter they only have B5 available, while they have B20 in the summer (which means I make sure to fill up with B20 whenever I’m near one of the greater Denver areas 3 other biodiesel stationsI know about.) The availability of green diesel would mean I could use 100% all the time, not just in the summer.
I did some more searching and found this presentationon the subject from Michael J. McCall, T.L. Marker, J. Petri, and D. Mackowiak at UOP, a division of Honeywell, in collaboration with D. Elliot at PNNL, SCzernik at NREL, and David Shonnardat Michigan Tech. According to their lifecycle analysis, Green Gasoline and Green Diesel produced from oils in refineries would actually have lower lifecycle CO2 emissions.
In short, the economics, environmental characteristics, and physical properties of green diesel/gas/jet fuel blow biodiesel out of the water (just as biodiesel is much better than ethanol from corn.) The downside: limited feedstocks. Avialable oil and grease from conventional sources is could only supply a tiny fraction of our liqid fuels; we will need to turn to nonconventional sources of oils to make a real dent in our liquid fuel needs (as well as invest massively in the efficiency of our transportation fleet.)
Non-traditional sources of oil to look into: algae and pyrolysisoil. I plan to write more about pyrolosys in another blog; it is a quick way of converting all sorts of biomass into useful syngas, and has some useful byproducts as well, and pyrolysis a a relatively omnivorous process, able to process everything from old tires to corn stover to forest trimmings, there is a lot of potential pyrolysis oil out there.