Oil from rapeseed or canola seed, the edible crop varieties, is used in biodiesel energy production. The oil has a low cloud point so it gels at lower temperatures than many other feedstocks.
Rapeseed — An Ancient Crop
Rapeseed is related to mustard and to other cabbage-family crops.
According to the Canola Council of Canada, rapeseed has been cultivated since the 20th century B.C. Because the plant can grow with less sunlight and at lower temperatures than other crops, it was cultivated in Europe as early as the 13th century A.D.
Rapeseed oil has been used for cooking, lighting, and industrial uses. However, traditional rapeseed contains high quantities of erucic acid and glucosinolates,which make the seed meal unpalatable and possibly dangerous to livestock if fed in large quantities.
Canola — An Edible Variety of Rapeseed
Canola is an edible variety of rapeseed with a low percentage of erucic acid and low levels of glucosinolates. It was developed by Canadian plant breeders in the 1970s.
The word “canola” was coined from “Canada” and from “oleo” (oil). According to the Canola Council of Canada, the term is no longer a trademark. “Canola” can be applied to varieties of rapeseed with 2% or less erucic acid and less than 30 micromoles of glucosinolates per gram of oil-free meal.
Much of the rapeseed grown in Europe is of canola quality but retains the name rapeseed probably because the word “rape” does not have the negative connotations in Europe that it does in English-speaking countries.
Current Potential for Use as Feedstock for Biofuel
Soybeans are the major oilseed used for biodiesel production in the United States. Edible rapeseed is the most common oilseed used for biodiesel in Europe.
Biodiesel made from canola or edible rapeseed gels at a lower temperature than biodiesel produced from other feedstocks, making canola biodiesel a more suitable fuel for colder regions. University of Idaho research showed that canola biodiesel had a “cloud point” of 1°C and a “pour point” of -9°C (Peterson et al., 1997).
The cloud point is the temperature of the fuel at which small, solid crystals can be observed as the fuel cools. These crystals will clog vehicle filters. The pour point refers to the lowest temperature at which there is movement of the fuel when the container is tipped. Because canola biodiesel has a slightly lower cloud point and pour point than soy biodiesel, and a much lower cloud point and pour point than biodiesel made from animal fats, canola biodiesel is useful in cold climates.
Canola and rapeseed contain about 40% oil and have a high yield of oil per acre: 127 to 160 gallons per acre, compared to 48 gallons per acre for soybeans (Pahl, 2008, pp. 40-42).
Canola oil is high in oleic acid, which makes it competitive with other cooking oils, a market in which it is well established. The oil is also a high-grade lubricant and fuel additive; conversion to biodiesel, therefore, is just one of its several potential end uses.
Canola meal (what’s left after the oil is extracted) is a good source of protein, containing 38 to 42% protein and a favorable balance of amino acids. It can be used as a feed additive for livestock rations.
Industrial rapeseed makes a biodiesel with very good low temperature performance. University of Idaho research showed that rapeseed biodiesel had a cloud point of 0°C and a pour point of -15°C . However, comparatively little of this crop is grown because the market for canola and edible rapeseed is much larger than the market for industrial rapeseed.
Industrial rapeseed contains more long-chain fatty acids than canola. Therefore, sometimes industrial rapeseed biodiesel turns out to be slightly more viscous (thicker) and may have a higher distillation temperature than the ASTM D6751 specification allows. In this case, the rapeseed biodiesel can be blended with other fuels (such as canola or soy biodiesel) in order to meet the specification.
Biology and Adaptation
Rapeseed and canola divide into two main species: Brassica rapa, known as “Polish type,” and Brassica napus, known as “Argentine.” Canadian breeders have also developed a low erucic acid, low glucosinolates variety of brown mustard (Brassica juncea).
There are both spring and winter (fall planting) types in canola and rapeseed species. The species differ in agronomic characteristics and yield. These differences must be evaluated when selecting a variety to grow.
In temperate climates such as the Pacific Northwest, canola/rapeseed can be planted either in the fall or spring. Fall-planted canola or rapeseed can develop more extensive root systems and is more drought hardy, but excessively cold winter weather or wet winter growing conditions can reduce yield potential, so the advantage may lie with spring planting dates. Canola must be planted in time to ensure maturity before the onset of hot weather. Winter canola must be planted in time to ensure significant plant development (six leaves or more) before hard freezing weather.
Most canola in the United States is produced in North Dakota.
Responses to fertilizer and soil fertility are similar to those for small grains; however, canola is a heavy user of sulfur. In a 2,000 lb/acre crop, for example, about 12 and 15 lb/acre of sulfur are in the straw and seed, respectively. Canola competes well with weeds, and herbicides are registered for use in the crop.
Seed size ranges from 80,000 to 135,000 seeds/lb, depending on variety. (Seed size can significantly affect seeding rate in pounds per acre.) Canola is handled and stored like flax; tight containers are necessary to avoid loss in transit.
Yields of oil per acre vary from about 75 gallons per acre to about 240 gallons per acre.
In Oregon canola trials, yields ranged from 1,900 to 4,800 pounds of seed per acre. Since canola is about 40% oil, and since a gallon of vegetable oil weighs about 8 pounds, this comes out to about 95 to 240 gallons of oil per acre.
The 2009 canola trials in North Dakota resulted in an average yield of 1,900 pounds of seed per acre, with an average oil content of 45%. This works out to about 107 gallons of oil per acre.
Recent trials in Maine (where the crop is relatively new) resulted in 75 to 100 gallons of oil per acre.
Trials in Minnesota resulted in an average of about 96 gallons of oil per acre. The average percentage of oil in the seeds was 46%.
Since it is a Brassica crop, canola can cross pollinate with other Brassicas such as rutabaga, Chinese cabbage, broccoli rabe, and turnip unless buffer distances are adequate. In addition, it is problematic to grow canola among infestations of mustard-family weeds.
Canola grows on most soil types but requires good drainage. The emerging crop is very susceptible to soil crusting; seedbed preparation is important. Canola is susceptible to blackleg and Sclerotinia stem rot. If not rotated with resistant crops, seed treatment may be necessary.
Seed shattering at harvest is a potential problem, so crops commonly are swathed or “pushed” (mechanically bent over without cutting the stem) when seed moisture is about 35%.