I have pretty much focused in on rapeseed as my favoured biodiesel temperate-climate crop. Its yields are significantly above that of Soya, Safflower, and other North America oil crops. Unsurprisingly rapeseed is the primary crop used in Europe as a biodiesel source. I further examined the physical properties (namely viscosity) of the derived vegetable oils.
Generally speaking in we want the oil with the lowest surface tension so that it will flow through the fuel injection system easily and atomize in the combustion chamber well. This means we want to use unsaturated, short chain fatty acid. If we compared oleic acid with its saturated version, stearic acid, we can the difference in viscosity and melting temperature. Also we could compare oleic acid, with 18 carbon atoms, to erucic acid with 22 carbon atoms. Actual distributions of fatty acids in crop types can be seen in this table from Iowa State University. The table shows that Soya has a 8-15 % saturate content, versus 5.6 % for Canola or 11.2 % for traditional rapeseed.
Canola is a cultivar of rapeseed developed in Canada in the 1970s. It specifically bred out eruric acid (long-chain) content and increased the content of 18-chain unsaturated oils. This turns out to be to an advantage for the production of clean burning biodiesel. Canola also bred out glucosinolate content which may lower the pest resistance of the crop. On the other hand, the glucosinolate molecule contains sulfur and nitrogen. Canola has been genetically engineering by firms like Monsato to be herbicide resistant in an effort to increase crop yields. Unfortunately canola cross-pollinates between fields so issues with so called monster food aren't avoided in biodiesel production.
The check variety of Canola (to which other types are compared) is 46A65. It has an average yield of 49 bushels/acre which using this conversion table works out to 2.746 tonnes of biomass per hectare in middle and short growing zones. The longer growing system zones (mostly in Manitoba) can show yields up to 28 % higher. The highest yielding variety from Canola Council trials appears to be a set of Bayer CropScience varieties (5020, 5030, 5070) all running approximately 125 % yields. This is a herbicide resistant crop running the Liberty system. The yield would then be 3.432 tonnes/hectare.
The next step is to examine the composition of Canola. Government statistics show that the oil content is approximately 43 %. There are a variety of ways of extracting the oil from the plant which I will probably discuss at a later date. The remaining biomass (canola seedcake) has a number of potential applications. It can be composted and reapplied to the field but this does not take advantage of the energy stored in the biomass material. It can be sold as high-protein animal feed. It can be burned as biomass to produce heat and electricity as an alternative to coal. It can be fermented into alcohol fuels but the energy return on fermentation is poor. My alternative is to compost the biomass anerobically in water to gather methane from the biomass while retaining the nutrient content that would go up in smoke if the material was burned.
The overall composition of the canola harvest can be estimated by looking at the composition of canola meal and working back from about 40 % oil removal.
Much of leftover seedcake can be digested into biogas and the rest turns into liquid sludge that can be used as fertilizer. I am actively looking to improve the quality of my data; since I don't have an agronomy degree I am learning a new vocabulary. In future posts I'll be looking to talk about my methane/sluge bioreactor concept, methanol and methyl ester (biodiesel) production, and of course the system analysis and results.
As an aside, here's the NREL algae biodiesel study link if anyone was looking for it.