Dedini's São Luiz Mill in São Paulo state began producing cellulose bioethanol from bagasse - the leftover cane stalk after the sucrose is pressed out - at about US$ 40 cents a liter in 2002. But production costs have now fallen with improvements in processing technologies to below €20/US$ 27 cents a liter (US$ 1.02 per gallon). "This means the fuel is cost-competitive with oil at US$42 a barrel," said Dedini Operations Vice President José Luiz Olivério at the seminar.
The technology is based on a combination of two processing steps that convert bagasse, the lignocellulose-rich byproduct from cane processing, into ethanol: (1) pretreatment of the biomass with organic solvents, and (2) dilute acid hydrolysis. The innovation consists of the pretreatment phase which allows the diluted acids to do their work much faster and more efficiently. The liquid hydrolyzates are then easily fermented and distilled into ethanol. Because of the speed of the process, the proprietary technique was dubbed 'Dedini Rapid Hydrolysis' (DHR) [*Portuguese, *.pdf] (see below).
Brazil has the world's most advanced biofuels market, with 30 years of experience in national ethanol production. The state-of-the-art ethanol mills can produce the biofuel from cane sucrose at or below €13/US$18 cents a liter (US$0.68/gallon), experts say. This makes the fuel competitive when oil is at around US$35-40 per barrel.
During the production of sugar cane ethanol, a large stream of bagasse is released. Bagasse is a fibrous, cellulose rich biomass material that is most often burned in co-generation electric power plants on site to run operations at the mill. Excess is sold as green and renewable electricity to nearby cities and industries. To cope with the bagasse residue, many of Brazil's cane mills have even installed out-of-date, inefficient blast furnaces so they would not be left with excess biomass, for which they would otherwise have to pay for disposal. But Dedini's breakthrough may now change all this.
Analysts have predicted that the efficiency and productivity of Brazil's ethanol sector may double within two decades (previous post). This would be a repeat of the achievements made over the past 25 years, when Brazilian producers achieved a 75% cost reduction in the production of the biofuel (earlier post). Sugar cane based ethanol is by far the most efficient biofuel available. One hectare of cane now yields an average of around 6000 liters of ethanol, but if bagasse were to be converted efficiently this could increase to 12,000 liters. Likewise, the average energy balance of cane ethanol currently stands at around 8 to 1 (compared to corn's 1.5 to 1) and would reach well into the ten-point mark with the advent of cellulosic ethanol. This would put the energy balance of this type of biofuel on a par with that of petroleum production.
Commenting on the efficiency and productivity leap, Oliverio said "this will be able to boost a mill's ethanol output by 30 percent without planting one more cane stalk". In short, a hectare of sugar cane will deliver a third more ethanol and now yield up to 9000 liters, three to four times more than corn. In other words: with the technique, less land is needed to obtain a similar amount of liquid biofuel.
The technology: rapid acid hydrolysis
Cellulosic ethanol production comes under three broad conversion pathways: a thermochemical route (gasification, pyrolysis) , a biochemical route and a purely chemical conversion known as dilute acid hydrolysis. The biochemical pathway makes use of special enzymes to break down the cellulose to release its sugars, whereas the chemical pathway relies on an hydrolyzing lignocellulosic biomass by means of acids. The liquid hydrolyzates are then fermented into ethanol. Dedini's breakthrough is based on this latter technique:
biofuels :: energy :: sustainability :: sugar cane :: bagasse :: biomass :: cellulose :: acid hydrolysis :: ethanol :: Brazil ::
The chemical acid wash (acid hydrolysis) of the biomass breaks up the protective lignin fibers in the cane stalk and allows a type of sugar cell to be washed out. "This type of acid method typically inhibits fermentation of the syrup that comes from the sugars in the bagasse, so mills will have to figure out how to overcome this," said Professor Carlos Rossell at the State University of Campinas, or UNICAMP. But Olivério says Dedini has overcome the problem as the company's system uses a very diluted acid to free the sugars in the cane. The trick is to use high dilution levels on a pretreated slurry of dissolved lignocellulose.
The process was dubbed 'DHR' - 'Dedini Hidrólise Rápida' - and was developed in collaboration with the Centro de Tecnologia Copersucar (CTC) and with the Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp). Carlos Rossel was the lead researcher who achieved the breakthrough.
The DHR technology relies on a combination of two steps: the acid hydrolysis and a pretreatment with organic solvents. The technique was developed specifically for the conversion of bagasse. By pretreating the biomass with organic solvents, the lignocellulose is decomposed, which allows for a much faster attack of the acids. The hydrolyzed fraction that is then to be turned into ethanol is easily fermentable because it consists of hexoses - a monosaccharide consisting of 6 carbon atoms.
Dedini's first large scale demonstration facility produced 5000 liters per day. The objective is now to optimize the technique by means of process integration, automatisation and by increasing the stability and safety of the sensitive conversion process. Olivério thinks it must be possible to go beyond the current 30% increase in sugar cane ethanol production per hectare, and achieve a doubling within a few years.
Enzyme research continues
Meawhile, many researchers in the area of cellulose technology believe enzymes, or natural proteins that accelerate the breakdown of the lignin fibers, will be used in future cellulose ethanol production too.
But Rossell and Professor Elba Bom at Rio de Janeiro's UFRJ University pointed at to two challenges: reducing the exorbitantly high cost of industrial production of enzymes and shortening the time required for the enzymes to act on the lignin.
Bom said her research team has been developing methods of leaving shredded bagasse outside in something like a large compost heap to allow naturally occurring enzymes to go to work in a pretreatment stage to loosen the lignin's hold on the sugar, but this requires as much as a week. "We've already identified the best brews of enzymes, the challenge is bringing down production costs which are currently two to three times the cost of conventional ethanol," Bom said. "We're shooting for 1.5 times the cost of standard ethanol."
FIESP: Etanol brasileiro: novas tecnologias, perspectivas e competitividade - May 15, 2007.
Dedini: Dedini Hidrólise Rápida [*Portuguese/*.pdf], overview of the process.