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New materials

Valuable ash

Products with high added value use waste from burnt sugarcane bagasse

SILVIO RAINHO TEIXEIRA / UNESPPreparation of frit, a raw material used in ceramics finishing process SILVIO RAINHO TEIXEIRA / UNESP

The quick growth of Brazil’s sugar and alcohol industry in the last few years has elevated the country to an outstanding position among the world’s producers of alternative fuels. The country’s mills make some 27 billion liters of ethanol a year. This growing activity has caused the volume of sugarcane bagasse, the production waste, to grow. Almost all this material, a subproduct of added value, is burnt in boilers, the steam of which generates power for turbines and generators. With this burning, another waste product arose: bagasse ash, with an annual volume estimated at four million tonnes. Several studies are proposing environmentally viable, economic solutions for this product, as is shown by the work of the physicist Silvio Rainho Teixeira, from the School of Science and Technology at Paulista State University (FCT/Unesp), in the city of Presidente Prudente, in western São Paulo state. He has developed at least three uses for the product: the production of briquettes, a product made from compressed dust from charcoal ash and is an alternative to regular charcoal;  frit, used in the final finish of ceramics; and  vitroceramic, produced by means of the controlled crystallization of vitreous materials. Pans and the “glass” tops of electric cookers are examples of transparent vitroceramic utensils. One of the first uses of bagasse ash was to sprinkle it over crops as a complementary fertilizer. Later, tests showed good results when it was included in the manufacturing of concrete (see Pesquisa FAPESP issue 171).

Teixeira explains that the first step to formulate these new products is to separate the organic fraction of the bagasse ash from the inorganic one. The briquettes are made from the organic portion, whereas the frit and the vitroceramics use the inorganic portion, which is rich silicon dioxide (SiOs), the raw material of the most common types of glass. The charcoal in the ash appears in two forms: small pieces, greater than one millimeter, that at first float and can be mechanically separated, and a fine powder, which forms a sediment along with the inorganic material. The thicker portion is removed with a sieve, whereas the finer one can be separated with a hydrocyclone, equipment that separates particles suspended in a liquid based on their density. After separation, the charcoal powder is mixed with a binder – a sort of glue – and pressed into small cylinders or bars, the most common briquette shape. Briquettes have greater density and calorific power that is equal or greater than that of charcoal and can be used in industrial or domestic applications. “As it is difficult to compact pure charcoal and give it a definitive shape without it breaking up, we use a binding agent,” says Teixeira. This part of the study is under the coordination of professor Algel Fidel Peña, from Unesp.

Floor and wall tiles
Frit and vitroceramic production is slightly more complex, requiring a great deal of energy, because the material has to be melted at a high temperature. The basic raw material for the formulation of such products is the silica found in bagasse ash, which accounts for more than 80% of its weight, and other oxides – of iron, aluminum, potassium, titanium and phosphorus – also found in the residue. As the silica melting point is very high, it must be mixed with calcium carbonates and potassium or sodium carbonates to allow the melting of the mixture to take place at a lower temperature, between 1,300 and 1,450 degrees Celsius. One molten, the mixture, in liquid form, is poured into a vessel full of water at room temperature. The result is a solid with the atomic structure typical of a liquid, because the fast chilling “freezes” the material, making it impossible for the atoms to organize into a crystalline solid. The material thus formed is a type of glass that is then broken into very small pieces, the frit. This is used to make the vitreous layer of ceramic pieces such as floor and wall tiles and vases, among other products. Teixeira estimates that for every kilogram of waste one can make almost one kilogram of frit.

The frit is then used to make vitroceramic pieces, a finer product with greater added value. To this end, the frit is first ground into an extremely fine powder and slowly heated, using a thermal analysis device. “This device monitors the reactions of the glass during the process. When we heat something up, we provide energy for the atoms to organize and to turn into a crystalline material, with a symmetrical pattern of organization. This is a well-known and well used process. In our case, the novelty is using sugarcane bagasse ash as the raw material,” states Teixeira. “Depending on the mixture used (the type and quantity of carbonates), different ceramic materials are produced, with different properties. We’re trying to get surfacing materials such as flooring, wall tiles and others that can be used in construction.” Vitroceramics have important properties, such as greater hardness than natural stone, zero water absorption and lower density. Therefore, they are used to line buildings both inside and outside. Another major advantage of this material relative to natural stone is that it enables the production of large plates, that can be flat, curved or in any shape needed to line columns.

EDUARDO CESARAbove, portions of bagasse, residual ash, and carbon black. EDUARDO CESAR

The development of vitroceramics made from bagasse ash included the collaboration of the Spanish researchers Jesús María Rincón López and Maximina Romero Pérez, who are glass and waste crystallization experts from the Eduardo Torroja Institute of Construction Sciences in Madrid. For the time being neither the process nor the new products (briquettes, frit and vitroceramics) have been patented, but Teixeira is evaluating this possibility. The research results were presented at domestic and international events, such as the Brazilian Ceramics Congress, and were also published in scientific journals. According to the researchers, following the good laboratory results, it will be necessary to set up a pilot production process and assess the costs of setting up a company for a precise evaluation of the financial viability of the innovations. Although there are no negotiations under way with private-sector firms to transfer this technology, Teixeira says that he has been approached by consulting companies and businessmen from the sector that are interested in learning about these innovations.

Carbon black
The possibility of using bagasse ash also concerns the production of an important product for the chemical industry, carbon black, a raw material found in paint, varnish, tires, rubber articles and fertilizers, among other products. An organic solution of this material made with bagasse ash was created by Leonardo Glidiz, a chemical engineer from São Paulo state. He says that he developed the material when he was researching bagasse ash and some carbon compounds on his own, in order to develop a possible fertilizer, when, by accident, he knocked over some solid compounds on the ground, his clothes and study material. “Annoyed, I went off to have some coffee and when I came back to clean up the mess, I saw that the compound had left dirty marks that were hard to remove,” he recalls. “I noticed that the outcome of what had looked like a disaster was actually a new product. With the help of two friends, I took samples to a company for initial trials and, to my satisfaction, found that organic carbon black had been invented.”

Glidiz does not reveal who his friends are and much less what were the solid compounds used in the experience. It is all part of the formulation’s secret. The patent request for the product, the process and the trademark “Bio Carbon Black,” was submitted in 2007 to INPI, the National Institute of Industrial Property. Glidiz actually spent some time in the projects hotel of Supera, the Incubator of Technology-based Companies in Ribeirão Preto, to open a company, but gave this up and decided to set up a scientific and socio-environmental organization called the Advanced Center for Research and Development of Bionanotechnology, a non-profit institution for the development of organic carbon black and other products. Still lacking permanent headquarters, the center is awaiting the opening of the Ribeirão Technological Center to request a vacancy.

“The organic carbon black that we developed is the only alternative for replacing the current petroleum-derived product,” assures Glidiz, who ranked second in the biotechnology field in the Olympics of the Innovation Agency at the University of São Paulo (USP) in 2008. Through a project of the Coordinating Office for the Training of Personnel with Higher Education (Capes), approved under a public notice released by MEC/MCT/MDIC (the ministries of Education, Science and Technology, and Industry and Trade), Glidiz conducted his project at the campus of the School of Philosophy, Sciences and Literature of USP in Ribeirão Preto. Also known as lampblack, carbon black is a black powder whose chief feature is that it is a chemical form of carbon that is free of impurities. It first started being manufactured on an industrial scale in 1870 and was initially used in paint. In the early decades of the twentieth century, it became important thanks to the discovery of its resistance properties, when it was mixed in with rubber in the vulcanizing process developed by Charles Goodyear, an American, to make tires. However, carbon black cannot be found in the wild and its production process affects the environment. The industrial substance is made by means of pyrolysis, a decomposition reaction that occurs using high temperatures or incomplete burning of oil products. The residual gases of the process include carbon monoxide and methane. According to Glidiz, estimates indicate that Brazil produces some 500 thousand tonnes of carbon black a year. The world market is thought to be 11.7 million tonnes, with average annual growth greater than 4%.

“The innovation that we proposed is to transform the ash from burning sugarcane bagasse into organic carbon black, an alternative product with environmental, economic and social advantages.” The initial stage to make this product, according to Glidiz, consists of a prior study of the residual ash of sugarcane bagasse in partnering mills, to develop a collection system. Later, this waste has to be transported to the company licensed to process it, where the impurities must be separated and the size of the particles selected in vibrating sieves. The final material should then be put in mixers with reagents to form the alternative form of carbon black.

The researcher’s aim is to license the technology to interested enterprises rather than to set up his own plant to make the product and sell it to third parties. “I already have companies in four different industrial segments – construction and ceramics, automotive products, plastics and polymers – that are interested in setting up this process,” says Glidiz. The investment to set up a processing unit with a production capacity of one thousand tonnes a year is some R$500 thousand, including the cost of the land, the machinery and the purchase of ash. The financial viability study prepared by the researcher indicates that the financial returns will materialize after two years. As part of the “industrial secret,” a reagent compound is to be supplied to the licensed companies, to be used in the process.

The materials engineering tests and analyses conducted to date on the product, according to the researcher, have been promising and yielded positive results. “The placement of organic carbon black in the market is immediate, to make products that do not depend on certification. For some industrial applications, such as tires, however, one must develop and test prototypes for three to five years, according to the law,” says Glidiz.

The project
Development of vitroceramic material through vitrification and crystallization of sugarcane bagasse ash (nº 08/04368-4); Type Regular Research Awards; Coordinator Silvio Rainho Teixeira – Unesp; Investment R$5,566.00 and US$37,892.50 (FAPESP)

Scientific articles
TEIXEIRA, S.R. et al. Briquetting of charcoal from sugar-cane bagasse fly ash (scbfa) as na alternative fuel. Waste Management. v.30, n.5, p. 804-07. mai. 2010.
TEIXEIRA, S.R. et al. Sugar-cane bagasse ash as a potential quartz replacement in red ceramic. Journal of the American Ceramic Society. v. 91, n. 6, p.1.883-87. 2008.