A utilização dos pellets de madeira para a geração de energia térmica está se difundindo no Brasil e a análise termogravimétrica tem sido amplamente aplicada para o estudo da decomposição da madeira e seus principais componentes como a celulose, as hemiceluloses e a lignina. O objetivo deste trabalho foi investigar o comportamento térmico de quatro diferentes amostras de pellets de madeira, em condições não isotérmicas, por meio das análises termogravimétricas TGA. Os ensaios foram conduzidos desde a temperatura ambiente até 500C, com taxa de aquecimento de 20C/min, em atmosfera inerte de gás nitrogênio, com fluxo de 100 mL/min. Os termogramas mostraram três estágios de decomposição: o primeiro, atribuído à evaporação da água e dos materiais voláteis; o segundo, refere-se à decomposição da holocelulose na pirólise ativa; e o terceiro, atribuído a decomposição da lignina na pirólise passiva. Além disso, conclui-se que a maior decomposição térmica ocorreu na faixa de temperatura compreendida entre 250C e 400C, com perdas superiores a 60,8% da massa inicial do biocombustível. PALAVRAS-CHAVE:Pellets de Madeira, Biomassa, Pirólise da Madeira, Termogravimetria por TGA. THERMAL DECOMPOSITION OF WOOD PELLETS BY TGA ABSTRACTThe use of wood pellets for generating thermal energy is spreading in Brazil and thermogravimetric analysis has been widely applied to study the decomposition of wood and its main components such as cellulose, hemicellulose and lignin. The objective of this study was to investigate the thermal behavior of four different samples of wood pellets in non-isothermal conditions by means of thermogravimetric analysis TGA. Assays were performed from room temperature to 500°C with a heating rate of 20°C/min in an inert atmosphere of nitrogen gas with a flow of 100 mL/min. The thermograms showed three decomposition stages: first, assigned to the evaporation of water and volatile materials; the second, refers to the decomposition of the active holocellulose pyrolysis; and third, attributed to the decomposition of lignin pyrolysis passive. Furthermore, it is concluded that most decomposed in the temperature range between 250°C and 400°C, with greater than 60.8 % of the initial mass of the biofuels losses.
Wood pellets are biofuels produced from agroforestry waste such as sugarcane bagasse, wood sawdust and shavings. They are compressed biofuels that have low moisture, allowing high combustion efficiency, especially because they are natural products of easily handling with high energy density. To explore pellets opportunities in Brazil (production and marketing), it is necessary to provide information about the chemical and energy characteristics, technologies, prices and prospects of this market. Thus, this article aims to organize and make this information available, enabling general knowledge on the subject and subsidize more investment in the biofuels sector; mostly by adding value to agroforestry waste, available in large volumes in this country. The results showed a young industry, with sixteen plants and production of 49.39 ktonnes of pellets in 2014, but using only 25.5% of its annual production capacity.
Torrefaction is a thermal process that improves the energy properties of plant biomass pellets, providing greater biofuel efficiency for gasification technologies, as well as replacing coal in thermoelectric plants. In Brazil, many agroforestry residues can be improved in value through this technological process, transforming them into modern solid biofuels. There are few studies comparing torrefied wood and elephant grass pellets, especially in relation to their energetic characteristics. This study analyzed the high heat value, energy density, ash content, fixed carbon, volatile materials, lignin, holocellulose, extractives, bulk density, and mechanical durability of these pellets. Due to the absence of Brazilian normative standards for these pellets, the international standard ISO 17225 (2014) was used for comparisons. The results revealed substantial differences among the samples, mainly regarding their moisture content, higher heating value, and energy density in torrefied pellets. It was concluded that these torrefied pellets are biofuels having lower water adsorption, higher heating value, and higher energy density than the pine and elephant grass pellets.
Recebido em 26/3/08; aceito em 8/10/08; publicado na web em 2/2/09 THE INFLUENCE OF HEXENURONIC ACIDS IN YIELD AND BLEACHABILITY OF PULP KRAFT. This study investigated the impact of pulp hexenuronic acids (HexAs) content on pulping yield by changing cooking reaction temperature. The bleachability of pulps containing variable amounts of HexAs was also investigated. The cooking at 170 o C produced pulp of kappa number, HexAs and screen yield of 16.2, 49.4 mmol/kg and 50.2%, respectively, whereas the cooking at 156 o C resulted pulp of kappa 17.0, 61.3 mmol/kg HexAs and 50.8% screened yield. The pulp produced at lower cooking temperature also showed better bleachability as evaluated by the total amount of active chlorine required to achieve 90% ISO. The sequence OA HT D(EP)DD showed the lowest bleaching performance among all.Keywords: hexenuronic acid; pulping kraft; ECF bleaching. introduÇÃoAs principais estruturas de ácido carboxílico que ocorrem nos polissa carídeos da madeira são os grupos de ácidos glicurônicos, usualmente na forma dos ácidos mono metil éter, 2-O-(4-metil-α-Dglicopiranosilurônico) e galacturônico.O conteúdo total de unidades de áci dos urônicos presentes na madeira está em torno de 4-5% da madeira seca.1 Enquanto as unidades de ácido glicurônico predo minam nas xilanas (hemiceluloses) presentes na madeira, as de ácido galacturônico são constituintes das pectinas. Como as substâncias pécticas estão localizadas, principalmente, na lamela média e na parede primária, são facilmente dissolvidas durante a deslignificação da madeira.1 Os ácidos hexenurônicos são formados durante a polpação alcalina pela modificação dos ácidos 4-O-metilglicurônicos, presentes nas xilanas.2,3 A Figura 1 mostra o mecanismo de formação dos ácidos hexenurônicos.As condições de polpação que mais influenciam o conteúdo de ácidos hexenurônicos na polpa são álcali ativo, sulfidez e temperatura.4,5 A Figura 2 mostra o mecanismo da degradação dos ácidos hexenurônicos em meio alcalino. A concentração de ácido hexenurônico em polpas de diversas madeiras de folhosas em diferentes condições de cozimento kraft e, também, a sua concentração na polpa depende de vários fatores, como tempo de cozimento, temperatura e carga de álcali. 6 Os mesmos autores verificaram, ainda, que dois mecanismos afetam o decréscimo do teor de ácidos hexenurônicos, a hidrólise alcalina e conseqüente separação dos grupamentos de ácidos hexenurônicos das cadeias de xilana e a dissolução das xilanas, provocando decréscimo no rendimento. 5,6 Há indicações de que podem proteger as xilanas contra as reações de despolimerização terminal; portanto, sua presença na polpa preserva o rendimento em etapas alcalinas. Os ácidos hexenurônicos não são desejáveis nos processos de branqueamento pois, além de consumirem os reagentes químicos do branqueamento, causam um aumento na sua habilidade de quelar metais, comparado com seu precursor, o ácido 4-O-metil glicurônico e, conseqüentemente, uma maior reversão de alvura. 7Os ácidos hexenurônicos não são reativos no branqueamen...
One hundred different 5.5-year-old Eucalyptus grandis x Eucalyptus urophylla wood clones were cooked to kappa number 15-17.5 and the resulting kraft pulps oxygen-delignified to kappa 9.5-11.5 under fixed conditions, except for chemical charges. Thirteen samples showing large variations in effective alkali requirement, pulp yield and O-stage efficiency and selectivity were selected for brightness reversion studies. These samples were bleached to 90-91% ISO by DEDD and DEDP sequences and their brightness stability and chemical characteristics determined. Heat reversion of the eucalyptus kraft pulps was strongly influenced by the wood supply, with brightness loss varying in the range of 2.1-3.6 and 0.8-1.7 %ISO for ODEDD and ODEDP bleached pulps, respectively. Pulps bleached by the ODEDP sequence showed reversion values 1.3-1.9 % ISO lower than those bleached by the ODEDD sequence. Pulp carbonyl content decreased by 35-40% during the final peroxide bleaching stage. Carbonyl and carboxyl groups correlated positively with brightness reversion, as did permanganate number and acid soluble lignin. Pulp final viscosity and metal and DCM extractives contents showed no significant correlation with brightness reversion. Pulping, oxygen delignification and ECF bleaching performances also showed no correlation with brightness reversion.
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