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Energy

Cellulose alcohol

Bagasse and sugarcane straw are quoted to increase the production of ethanol

EDUARDO CESARWith the sugarcane straw left in the field it is also possible to produce fuel alcoholEDUARDO CESAR

The word “ethanol” has really entered the order of the day. Since the report on the climate of the planet was disclosed at the beginning of February, showing that there has to be a reduction in the emissions of gases arising from the burning of fossil fuels, the race has intensified to partly replace gasoline, a fossil fuel, with alcohol, a renewable and less pollutant source. A worldwide concern that Brazil has been taking into account for over 30 years. The country currently produces about 16 billion liters of fuel ethanol, which represents 35% of the world total. As today only one third of the biomass contained in the sugarcane plant is taken advantage of to produce sugar and alcohol, the great challenge is to transform the cellulose that is in the bagasse and sugarcane straw discarded in harvesting into fuel alcohol. “There is a study under way that indicates an increase in fuel ethanol from 15 to 20 billion or so liters a year currently produced to 200 billion liters in 20 years”, says chemical engineer Carlos Eduardo Vaz Rossell, a researcher from the Interdisciplinary Energy Planning Nucleus (Nipe) of the State University of Campinas (Unicamp). “It is possible to do this in a sustainable way, without advancing into forests and food crops.”

One of the studies that aims to make the production of alcohol viable via bagasse and straw, which the researcher refers to, is part of the Bioethenol Project, which has the objective of developing enzymatic hydrolysis in Brazil, one of the ways for getting ethanol. The researchers involved in the project, which has a two and a half year duration, which Rossell is taking part in, coordinated by Professor Rogério Cezar de Cerqueira Leite, from Nipe, and supported by the Financier of Studies and Projects (Finep), of the Ministry of Science and Technology, with the amount of R$ 3.7 million, hope to obtain ethanol by the enzymatic route using cellulases, enzymes produced by microorganisms capable of breaking up the sugar in the cellulose, which will be transformed into fuel alcohol after the process of fermentation. In parallel to the development of enzymatic hydrolysis, studies are also being done to evaluate the impacts from the increase in the production of ethanol, with researches about agricultural, economic, social and environmental targets, and of the industrial processes as well. The project brings together as well a national network of researchers from 15 universities and research institutes, such as Unicamp, the Federal University of Rio de Janeiro, the University of Brasilia, the University of São Paulo, the Federal University of Pernambuco, the Sugarcane Technology Center (CTC), an association maintained by sugarcane producers, and the Technological Research Institute, besides Lund University, in Sweden.

To reach the target of 200 billion liters a year, the production of fuel ethanol, which is today more focused on the Center-South of Brazil, would be extended to other regions, like the North and Northeast. With this, the country would be in a condition to supply part of the international ethanol market, and it could replace from 5% to 10% of the gasoline currently used in the world. In 2002, the world market for this fuel derived from petroleum was about 1.17 trillion liters. If Brazil produces 150 billion liters of ethanol, it may meet the demand for 10% of this market. Besides replacing part of the petroleum, ethanol has in its favor the fact that it does not contribute towards greenhouse gases, because the main gas in this phenomenon, carbon dioxide, released by the combustion of alcohol in one year is reabsorbed by the plants in the following crop.

Making good use of the biomass from sugarcane is going to contribute towards eliminating the problem of burning, because only a few mills today take advantage of part of the bagasse for generate electricity in specific generators. The straw, in mechanized harvesting, is chopped up and strewn as a cover on the soil, but the excess of it has caused serious problems of pests that proliferate in protected damp environments. The studies conducted under the auspices of the Bioethanol Project indicate that a distillery that currently produces 1 million liters of ethanol per day from the sugarcane juice could initially, with the hydrolysis technology, produce an additional 150 thousand liters of ethanol from the bagasse. In 2025, with the technique well optimized, the same production could see an increase of 400 thousand liters coming from the recovered bagasse.

Enzyme in the biomass
The estimate of future production may be expanded as new scientific and technological advances are incorporated into the processes of hydrolysis of the cellulose for obtaining ethanol. The development of efficient enzymes to process the bagasse and sugarcane straw is one of the routes for leaving the current level of production without needing to increase the planted area. It is possible to take full advantage of this residual biomass for the production of ethanol, both the cellulosic fraction and the hemicellulosic fraction, a compound of the chemical group of the sugars, present between the cellulose fibers. This was the way chosen by Professor Nei Pereira Jr., the coordinator for postgraduate studies in Chemical and Biochemical Process Technology of the Technology Center of the Federal University of Rio de Janeiro (UFRJ) and the coordinator of a project carried out in partnership with Petrobras to transform cellulose into sugar. “We are producing 198 liters of ethanol for each ton of bagasse”, Pereira Jr. says.

The technology under development adopts the model of the two currents, producing ethanol both from the acid hydrolysis of the hemicellulosic fraction and from the enzymatic hydrolysis of the cellulosic fraction. The results were obtained in the laboratory with reactors of up to 10 liters. A pilot plant with a capacity for processing 2 thousand tons of biomass a day in under construction at UFRJ for larger scale tests. “We expect to arrive at 260 liters of ethanol for each ton of sugarcane in the pilot plant”, the researcher says. The same process can be applied to other residual biomass, such as corn cobs and husk, leftovers of wood, paper thrown away and other materials. Production on an industrial scale depends on the results achieved at the pilot plant. This is the great challenge, to pass from the laboratory scale to commercial production. No country has so far arrived at an industrial scale in the employment of the technology for transforming cellulose into ethanol.

EDUARDO CESARStudies indicate that a distillery that produces 1 million liters of alcohol could generate 150 thousand liters from sugarcane bagasseEDUARDO CESAR

The United States, for example, is laying heavy bets on the route of transforming cellulose into ethanol. There, they hope to extract alcohol from corn cobs and husk, waste which is discarded after taking advantage of the grain used for getting ethanol, besides other products like straw from wheat, leftovers of wood and a grass called switchgrass. The most recent card to be played by the Americans was the announcement, at the end of February, of an investment by the Department of Energy of US$ 385 million, in four years, for the construction of six biorefineries to produce ethanol via cellulose. When they are ready, in 2012, operating in great measure with the enzymatic hydrolysis method, they should produce about 492 million liters of ethanol. The United States wants to reduce the consumption of gasoline by 20% by 2017, when the government’s plan foresees a production of 132 billion liters.

One of the difference between the American production and the Brazilian is that here the ethanol from cellulose is going to add millions or billions of liters to the alcohol produced from sucrose that is already distributed today in the company’s fuel stations. In the world’s existing projects for taking advantage of cellulose, there is no such increase brought about by sugarcane. One other difference in Brazil’s favor lies in the cost of producing ethanol in the two countries. While ethanol from the corn of the United States works out at US$ 0.39 a liter, the ethanol from sugarcane juice costs US$ 0.21.

Taking advantage of the sugarcane bagasse and straw still merits many studies. They are materials consisting of cellulose, a polymer of glucose made up of six carbons, the hexoses; of hemicellulose, made up of sugars of five carbons, called pentoses, still not out to use for the production of sugar; and of lignin, a structural material of the plant, associated with the plant cell wall, responsible for its rigidity, impermeability and resistance to microbiological and mechanical attacks on the plant tissues. For the biomasses to be used as raw materials for chemical and biological processes, they need to be submitted to a pre-treatment to disorganize the lignocellulosic complex. Lignin is the great obstacle in this whole process. Breaking down this component releases phenols and other chemical products that inhibit the fermentation process.

After the pre-treatment of the material has been done, one of the two routes for transforming cellulose into sugar to get ethanol is applied. The sugar obtained acts as building blocks (substrates) for the production of fuel alcohol and various chemical substances. “This makes it possible to replace the hydrocarbons derived from petroleum by carbohydrates coming from biomasses in various industrial transformation processes”, says Pereira Jr., the winner of the 2006 Abiquim Technology Award in the Researcher category, granted by the Brazilian Chemical Industry Association, with the paper “Biotechnology of lignocellulosic materials for chemical production”.

At the end of the process for getting ethanol from cellulose there is still the lignin left over, which can be used to produce energy. “The heat from the combustion of lignin is 3.5 times more than the heat from the very bagasse of the sugarcane”, says the researcher, who, since the end of the 1980’s has been studying the use of biomass from waste. This was the theme of his doctoral thesis defended in England in 1990. Since then, the subject has been present in 26 of the 63 master’s and doctor’s papers supervised by Pereira Jr. The technology developed in partnership has resulted in two patent requests. One is on the pre-treatment and fermentation of the hemicellulosic hydrolysate, and the other deals with the process of simultaneous saccharification and fermentation of the cellulosic fraction.

Pilot plant
Acid hydrolysis was also the path chosen by the Dedini industrial group, of Piracicaba, in the project carried out in partnership with the CTC, coordinated by Rossell (read Pesquisa Fapesp No. 77, of July 2002) and financed by FAPESP. Baptized as Dedini Rapid Hydrolysis (DHR), the process is in operation, at the test stage, at a demonstration pilot plant, with a capacity for 2 thousand kilos of bagasse an hour, installed in the city of Pirassununga (SP). “There are still operational problems and adjustments to the conception of the processes that are being corrected. But the results are heartening, not only as far as refers to the efficient conversion of the bagasse into ethanol, but also for the fact of operating on a scale that represents a commercial process, which will supply a very important experience for the design of future units”, says Rossell.

One of the largest Brazilian companies in the chemical sector, Oxiteno is in search of technological solutions for getting ethanol from cellulose, but not for use as fuel. The company is interested in mastering the hydrolysis process for bagasse and straw to make chemical products used in the pharmaceutical and chemical industries. They are substances currently obtained by the petrochemical route, and one of the main manufacturers of these products is Oxiteno. In November 2006, in partnership with FAPESP, the company launched a public call for proposals in 16 thematic research areas for cooperative projects in the area of technology for the production of sugars, alcohol and byproducts. At the end of January, the 23 projects approved in the first stage were disclosed.

The projects under way for getting ethanol from cellulose are an addition to others conducted in recent years by universities, research institutes and companies that have resulted in a great technological advance for the sector, such as the selection of new sugarcane varieties and the Sugarcane Genome Project (read the article on page 74). “Researches that seemed to be abstract are today beginning to be understood and can be used in another context”, says Rossell.

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