A very large area in Brasil is covered with sugarcane to be made into biofuel. The sugary juice of the cane is what gets fermented, something many microbes readily do. However, ethanol is their choice despite its several weaknesses as an engine fuel. For one thing, it must be made anhydrous in order for it to blend with other engine fuels. But distilled ethanol carries with it some water, and its removal is an expensive extra step.
That this ferment is very well-known technique evidently mattered more when raising capital. Also, selling the yeast as a protein for livestock feed helps. And depleted cane stalks, called bagasse, are typically burnt to provide heat for the distilling, plus electricity from a gas turbine generator, with excess electricity sold. It all adds up financially.
The Caribbean
Historically, several Caribbean islands were notable for producing sugar from sugarcane, which was very lucrative for a long time. One indication of this is the 1763 Treaty of Paris, by which France ceded to Britain its colony of New France (Quebec in Canada) but regained control of the sugar isles of Martinique and Guadeloupe, which the Brits had recently taken over. Evidently, having sugar was more valued.
But times change: the scale of sugar produced by a mill grew larger; sugar was cheaper; and smaller mills were no longer so profitable. Several of the islands which once had mills no longer do and sugarcane is no longer grown on them in quantity. However, if the juice itself is fermented to a biofuel other than ethanol, something easier to separate from the ferment, cane production may be revived.
Butanoic acid is a likely choice, as it may be isolated from the ferment in several ways. The cellulose of the bagasse can also be fermented to butanoic acid. The acid’s vapour sent over hot catalyst forms dipropyl ketone [PPK] which is superior to ethanol as an engine fuel, blending better with gasoline and being more energy dense. Doubtless in many markets it would soon displace ethanol as a gasoline additive.
The ferment may be continuous with the acid being removed by a solvent such as hexane, or perhaps the ketone PPK. Alternatively, if instead a batch ferment has calcium present to form calcium butanoate, gassing with CO2 with solvent present will remove the acid into a top layer of solvent while calcium carbonate forms and drops out.
Irrigation
Sugarcane is a thirsty crop, and the more water it gets the more it grows, so irrigation is beneficial. Many of the islands are rather dry, and about seventy desalination plants of various sizes, all using reverse osmosis, have been built over the last twenty years. This process uses quite a bit of electricity, which typically in the Caribbean is expensive.
Of the seawater entering such a plant, less than half becomes drinkable water, while the rest, now saltier, is rejected and sent back into the sea. It could instead have its sodium removed and then used for irrigation. The key to this is the low solubility of sodium bicarbonate, which will drop out when sufficient potassium bicarbonate is added, leaving a solution of potassium chloride [KCl]. It is likely to be about 12% by weight, which is too high and needs to be reduced.
One way is letting plants take the potassium ions out of the water and store them in their leaves. A preliminary step may be to mix in water already low in potassium ions and so lower their concentration. A good candidate for such removal is water hyacinth (Eichornia crassipes), which floats and grows rapidly. However, it is generally thought a weed difficult to control, so caution might dictate some other plant be selected.
Whichever plant it is, flowing water slowly past them in a lengthy canal should result in the exit water being low in potassium and thus well-suited for irrigation use. These plants get lifted from the canal to be sun dried, then compacted into pellets or wafers, and marketed as an organic fertiliser that provides much nitrogen and potassium in particular.
But it is the leaves that mostly do, and the dried leaves may be separated from the rest — by pin milling and air sorting, as example — to become the fertiliser, while the rest is otherwise made use of. Making furfural is a likely option since bagasse can also be used, as can sargassum gathered from the sea, so enough material for a furfural plant would be available.
Furfural is only made from vegetation, and the two largest plants in the world, in South Africa and the Dominican Republic, are based on bagasse. The numerous smaller makers, who are mostly Chinese, use maize cobs. An annual output of 5000 tonnes of furfural is usually profitable. Acetic acid is a byproduct.
Making Potassium Bicarbonate
From ordinary potash fertiliser (KCl) can come the potassium bicarbonate needed. [1] The first step is mixing the dry KCl or slurry with a strong solution of sodium acetate, and then using ethanol to extract potassium acetate leaving NaCl behind. It could be evaporated to obtain crystal salt. Else sent into the sea.
[2] Next: gas the alcoholic extract with CO2 to drop out potassium carbonate, which is not soluble in ethanol. Neither is the bicarbonate, which will be made if any water is present. About half the potassium reacts this way, while the rest gets an acetic acid molecule somewhat firmly attached. This rather surprising result was disclosed in an old British patent [521 202], according to which heat will drive off the acid. But here instead, simply contacting it with sodium bicarbonate will provide the sodium acetate wanted in the first step, in this case together with potassium acetate.
A stand alone plant is conceivable, buying potash fertiliser and soda, then selling potassium bicarbonate. Acetic acid would simply circulate, but a source of CO2 would be needed. Some quantity buyers of this bicarbonate could be mixing it with ordinary salt to get sodium bicarbonate (and soda also if they want), plus KCl, the usual potash fertiliser. Exports of potassium bicarbonate to several countries would be likely, where some local businessperson could supply the local market with washing soda.
Fiji
For many years now the value of refined sugar has often been too low for Fijian growers to get a decent price, let alone a good price, for sugarcane. Turning cane into refined sugar simply is no longer viable. Something different is clearly needed. Making a biofuel from the sugary juice would allow cane growers to get a better price.
To put this in context, Fiji has a large negative balance of trade, and prominent among its imports are fuels refined from petroleum. Reducing these imports considerably through use of biofuels would be very beneficial financially. Another financial aspect will be gone into farther on.
Sugar has been a major part of Fiji’s economy for a long time. Many aspects of its production are regulated by government, who also own and run the three old mills still operating. More than eleven thousand small farmers in Fiji still grow sugarcane, though few have more than 20 hectares in it. Most have less than five. A majority of all growers are over fifty years old.
Producing biofuels would be more profitable, in part because the bagasse would also provide significant revenues. It has three major components: cellulose, xylan and lignin polymers. A high-value chemical called furfural is made only from various plant materials, bagasse being one of these. Though it is the xylan which becomes furfural, it is typically not isolated first. Yet, it should be in order to have the cellulose fermented to a biofuel as well.
Many ways of making furfural exist, but low capital cost would indicate operation with little or no pressure, using a non-volatile catalyst in a salt slurry with a suitable solvent to capture the furfural as soon as it forms. A low amount of xylan present and continuous operation using a pipe converter is likely best.
Commodity Bonds
Financing is always an issue in any development project. When the currency of a small country is involved, and particularly if it has fluctuated in value relative to such major currencies as the Japanese Yen, US Dollar and the Euro, then raising money by its government issuing bonds may be iffy.
One way around this would be to issue ‘Commodity Bonds’ which don’t pay interest in any currency, but instead in stated amounts of a well-known standard commodity, to be sold at auction at regular intervals with the proceeds going to bondholders. The auction could, as example, be for delivery at Singapore.
In this way, in years to come, it is the value at auction that the bondholder receives, paid in whatever currency they wish, heedless of what value the issuer’s currency might then be trading at. So currency exchange risk for bondholders is absent for the interest payments.
Furfural could certainly be the commodity, as it has been a standard commercial product for over a century. Were the government of Fiji to issue such bonds, it would need to acquire each year the amount of furfural needed to sell at auction. What price it offers to local suppliers of furfural is arbitrary. These should be multi-year contracts at a set price for the furfural, or at least with a set minimum price.
Of course, what biofuel is being made and its value is another consideration. Butanoic acid, to be made into its ketone [PPK] is a likely choice — see above.
Such Commodity Bonds have not yet appeared, but they do make good sense for a development situation. Once anyone does it, the example will be set that others may follow.