Biofuels From Canola Straw

A field of Canola in bloom is a sea of bright yellow flowers and a common enough sight in many corners of the world these days. This was not so sixty years ago.

Today’s Canola oil must be under 2% erucic acid, so it is alright for human consumption, while its meal must be suitable for livestock feed. Both traits separate it from rapeseed whose oil can be ~30% erucic acid.

This modification of rapeseed occurred around 1970 by researchers in Saskatoon and Winnipeg. Within a few years, Canola became a crop in a rapidly growing market. In 1978, Canola was officially adopted as the name for this new culinary vegetable oil, and the plants and seeds come from it; the name joins Canada and oil.   

Canola in the field and after

Canola does not ripen evenly, so many of the highest pods will harbour seeds that have not yet ripened, regardless of when they are cut. This makes it difficult to decide just when to cut the crop. Too soon, and you have many green seeds, but wait too long, and some of the pods may split open, scattering their seeds. These will be the ripest ones lower on the plant.

Such shattering may be due to the shock of forming a swath, or occur some days later as the swath is drying. The pods naturally split open when dry enough, though there are now cultivars in which this tendency is largely suppressed. Still, some degree of seed loss is inevitable when harvesting.

Clearly what is needed is a gathering machine specific to Canola, perhaps one making tied bundles of the standing crop, done above a solid platform so any seeds dropping down are saved. These bundles could then be stacked, either on the ground or on a trailer.

The bundles would best be moved to a yard where they may be heaped on a solid drying pad, again to retain any seeds dropping as they dry over the next few weeks. Since the tiny round seeds separate easily from the straw, threshing may be a matter of flailing and air separation. [see British Pat 2171 285]

The composition of the branches indicates they would be suitable for fermenting, having a good amount of cellulose and not much lignin. They could also be used for making paper. Researchers at a university in Iran about a dozen years ago showed that canola straw can make a strong paper suitable for corrugated cardboard boxes. This was laboratory-scale work.

Someone who worked on an industrial scale, turning straws of various plants into paper, was the Italian engineer Umberto Pomilio. His first factory was built in Napoli circa 1920, but it was not very successful.

Later, in Brazil, he had a workable design using gravity flow to prevent plugging. [USPat 1970 148]. He was lured to Chile by some businessmen to build a new plant using his latest designs. This he also patented in several countries. US Pat 2178 266 is particularly useful, issued in 1937, which includes five pages of detailed drawings.

This equipment could also be used to prepare straws for a ferment. Canola straw, which is to say its several branched stalks, is about 40% cellulose, 25% xylans, and 20% lignin. Mineral content may be relatively high, even over 10%, depending on the water and soil where grown.

Pomilio found that even a 1% sodium hydroxide [lye] can remove most of the xylans and about half the lignin within a few hours. Though the reaction is exothermic, the material moving through the apparatus never boils.

He also stated that sodium carbonate would work, though no doubt more of it would be needed, as would be true if potassium carbonate were used instead. Either sodium or potassium acetate would also work.

The watery extract could be filtered to obtain a mat of solids comprised mostly of lignin and xylans. Dried, these may be solid fuels, while liquids should contain most minerals. Alternatively, an acid could be used on the solids, to obtain xylose separate from the lignin.

Ferments

Several different ferments could be used to produce biofuels suitable for home furnaces or EC engines [external combustion], both of which are burning in the open air. Air quality would improve in urban areas once EC engines become common. Swapping the diesel in transit buses for EC engines would be a good start.

Bacteria, which produce 2,3 butanediol, can use a broad range of substrates, though if necessary, another which produces enzymes attacking cellulose could also be included. This diol converts to butanone readily enough in the presence of a solid acid catalyst. Butanone is the end product wanted, a well-known solvent also called MEK [methyl.ethyl.ketone]. As fuel for an EC engine or furnace, it could have dissolved in it something to increase its heating value per litre. Something derived from a wax or inedible vegetable oil might do.

Another likely ferment is to butanoic and acetic acids; the first stage of a ferment to propanone and butanol was done on an industrial scale circa 1920. Here the butanoic acid may be extracted, leaving a weak acetic acid solution. Through a bed of trapped suitable bacteria, it becomes propanone, which is a condensed vapour.    

The butanoic acid gets separated from the extractant to be made into dipropyl ketone [PPK], a fuel of many uses: EC engines, furnaces, even blended with gasoline. Now, butanoic acid comes together with both H2 and CO2, which suggests an interesting comparison.

 Many have touted ‘green’ methanol to be made from ‘captured’ CO2 and H2 made by water electrolysis. This is an expensive way to obtain eMethanol, as this route has been labelled.  

Here, however, both H2 from a ferment plus propanone may become 2-propanol by use of hydrogen. Thus, more energy-dense alcohol is obtained at a much lower expense. When zero CO2 emissions refer only to fossil fuels, it is as ‘green’ alcohol as the methanol so expensively made.

Very recently, researchers at the University of Nagoya in Japan applied electrolysis to an aqueous solution of lignin from bamboo or other grasses and got hydrogen at the cathodes and methanol at the anodes; it comes from the lignin. They even did this from the grass without any special alteration.

Essentially, this is splitting water with the OH-  ions that interact with the lignin, while the H+ ions form hydrogen gas. Of course, it will be many years before seeing this a commercial reality, should that ever happen.

Theo Hart