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Tuesday, March 28, 2017
- For nearly five hundred years, sugar cane was used almost exclusively for making sugar, with a handful of by-products like rum, alcohol and molasses. Now, in Brazil, it has become a source of multiple derivatives, and the focus of much scientific and technological research.
Ethanol, or fuel alcohol, has become a major product, rivalling sugar, over the last three decades. But recently, the waste materials, like bagasse (the fibrous residue after sugar cane is crushed), straw and vinasse have grown in importance.
Vinasse, the liquid residue left over from ethanol distillation, can be used to feed the growth of microscopic algae that can produce biodiesel, a process being developed over the next few years by researchers at the Agricultural Sciences Centre (CCA) of the Federal University of São Carlos in Araras, 170 kilometres from São Paulo, the largest city in Brazil.
The nutrients in the vinasse accelerate proliferation of the algae, which are rich in fatty acids that in turn can be used to produce biofuels.
Fertilisers will also be produced, as “the algae capture up to 64 percent of the potassium present in the vinasse,” the head of the CCA’s Department of Agro-Industrial Technology, Octavio Valsechi, told IPS.
Using algae to produce biodiesel has the advantage that it avoids the monoculture of oilseed crops on extensive areas of land. However, it is still not clear whether the cost of biodiesel made from algae will be higher than that made from vegetable oils.
Synthetic gas, or syngas, produced at this pilot plant will generate three times the electricity currently generated from bagasse, and can also be converted into liquid fuel or a precursor material for plastics, according to the Institute for Technological Research (IPT), the São Paulo state government agency that set the project in motion and forged partnerships with several public and private bodies to make it a reality.
Syngas is normally produced from coal, but the technology to gasify biomass is only now being tested on an industrial scale.
The potential for electricity generation from bagasse with current technology, by burning it directly in furnaces, is equivalent to “one Itaipú,” a reference to the 14,000 megawatt hydroelectric complex shared by Brazil and Paraguay, according to the Brazilian Sugarcane Industry Association (UNICA) which represents the largest companies.
But using this traditional method, “we are losing half the potential energy of the cane,” because of the humidity content of the bagasse when it is burned, Valsechi pointed out.
Increasing mechanisation of harvesting, which by 2014 will extend to the whole sugar cane crop in the state of São Paulo, that accounts for 60 percent of national production, will do away with the practice of burning the cane fields. Studies are still under way to determine the best way of collecting the straw.
“Anything that can be derived from oil can also be extracted from sugar cane,” Tadeu Andrade, head of the Centre for Sugarcane Technology (CTC) established in 1969 by Copersucar, a cooperative of São Paulo sugar mills that has expanded into other states, told IPS.
Sugar cane is the closest thing to “a perpetual motion machine, because there is so much recycling and feedback,” he said, pointing out that it has the capacity to produce its own fertiliser to grow it and energy to process it, and it yields more biomass than other major crops like maize or soybeans.
The potassium-rich vinasse, together with the residues trapped in industrial filters and the straw left on the ground, fertilise new crops, he said, although he acknowledged additional input of chemical fertiliser was also needed.
Unprocessed sugar cane juice is a good medium for growing microorganisms that are a source of countless substances, including polymers for bone regeneration, various foods, medicines and cosmetics, and even components for artificial blood plasma, Valsechi said, adding he regrets the scarcity of sugar cane researchers to fill the huge demand.
Sugar cane may also provide a pathway towards hydrogen-based energy, he said. Great strides have been taken in researching the chemistry of alcohol in Brazil, and a large petrochemical company is already producing “green”, or biodegradable, plastics.
Even aviation fuel can be made from sugar cane. EMBRAER, the Brazilian Aerospace company, one of the world’s largest manufacturers of small and medium-sized passenger planes and military aircraft, has announced that the first test flight fuelled by biokerosene made from sugar cane will take place in 2012.
Diversification of sugar cane products and scientific exploration of their potential arose from the National Alcohol Programme (PROALCOOL), launched in 1975 to find gasoline substitutes and reduce imports of oil during the 1970s oil crisis, when prices rose fourfold.
Since then, production of sugar cane increased sevenfold in Brazil, reducing demand for oil, but generating other problems. Vinasse, for example, caused an environmental disaster in the early days of the PROALCOOL programme in the 1980s, when it was discarded into rivers and killed millions of fish by starving them of oxygen.
The environmental threat receded when discovery of the high potassium content of vinasse led to its being used as a fertiliser.
Production of ethanol from sugar cane is still resisted in many Latin American countries where the soil already contains plenty of potassium, and shallow water tables are at risk of pollution from “fertigation” – irrigation with dissolved fertilisers – said Valsechi, an agronomist who has done research on sugar cane since his graduation in 1980.
For every litre of ethanol distilled, 10 litres of vinasse are produced, so its disposal can be costly. Algae that capture potassium could provide a solution.
In Argentina, where the soil has a lot of aluminium and the climate is less favourable than Brazil’s, it is particularly difficult to produce ethanol from sugar cane, said Marcos Vieira, another CCA professor and head of the Inter-University Network for the Development of the Sugar/Alcohol Sector (RIDESA), where researchers are funded by the national government to carry out genetic improvement of sugar cane.
The varieties developed by RIDESA, identified by the code RB, are planted on 60 percent of Brazil’s sugar cane area and have helped raise productivity to 85 tonnes per hectare, and in some cases 150 tonnes per hectare, Vieira said. Thirty-five years ago, the average yield was less than 50 tonnes per hectare.
RIDESA seeks out “eclectic varieties” that are adapted to the different climate and soil conditions in Brazil, produce good yields and are resistant to diseases and drought, Vieira said.
In contrast, CTC, which primarily serves the needs of the cooperative’s members, adopted the opposite approach, developing specific varieties for different soils and climates. “There are 25 soil and climate combinations,” and maps of them help farmers select the most productive variety for their lands, Andrade said.
But the advances in genetic engineering that give Brazil an advantage over other sugar cane producing countries “do not by themselves improve productivity in the field,” he said. Good agricultural practices, taught on many CTC courses, and mechanisation are also needed.
A policy adopted in the 1980s, setting the price for sugar cane according to its sucrose content, compelled farmers to use the best sugar cane varieties and cultivation techniques, Andrade said. University professor Roberto Rodrigues, a former agriculture minister, said the policy caused “a revolution.”
Large companies, like U.S. biotechnology company Amyris, have taken up research and development of new sugar cane products. Amyris is keen to secure supplies of Brazilian sugar cane for manufacturing farnesene, a molecular building block used to produce aviation fuel, lubricants, cosmetics and other derivatives.