Lignocellulosic biomasses are primarily composed of cellulose, hemicelluloses and lignin and these biopolymers are bonded together in a heterogeneous matrix that is highly recalcitrant to chemical or biological conversion processes. Thus, an efficient pretreatment technique must be selected and applied to this type of biomass in order to facilitate its utilization in biorefineries. Classical pretreatment methods tend to operate under severe conditions, leading to sugar losses by dehydration and to the release of inhibitory compounds such as furfural (2-furaldehyde), 5-hydroxy-2-methylfurfural (5-HMF), and organic acids. By contrast, supercritical fluids can pretreat lignocellulosic materials under relatively mild pretreatment conditions, resulting in high sugar yields, low production of fermentation inhibitors and high susceptibilities to enzymatic hydrolysis while reducing the consumption of chemicals, including solvents, reagents, and catalysts. This work presents a review of biomass pretreatment technologies, aiming to deliver a state-of-art compilation of methods and results with emphasis on supercritical processes.

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Recebido em 11/8/11; aceito em 13/4/12; publicado na web em 20/7/2012 EFFECT OF MOISTURE CONTENT IN THE STEAM TREATMENT AND ENZYMATIC HYDROLYSIS OF SUGARCANE BAGASSE. The effect of moisture content in the steam treatment and enzymatic hydrolysis of sugarcane bagasse was evaluated. Steam treatment was perfomed at 195-210 ºC for 4-8 min using cane bagasse with moisture contents in the range 16-100 wt% (dry basis). Increased moisture contents not only had a positive influence in recovery of main cane biomass components but also resulted in better substrates for enzymatic hydrolysis. As a result, drying is not required for optimal pretreatment and enzymatic hydrolysis of sugarcane bagasse, which can be processed into second generation ethanol immediately after crushing and hot water washing.Keywords: sugarcane bagasse; steam explosion; moisture content. INTRODUÇÃOO etanol é um dos principais combustíveis renováveis da atualidade e seu uso em grande escala contribui diretamente para a redução do uso extensivo de combustíveis fósseis no setor automotivo. Sua produção pode ser obtida a partir de diferentes matérias-primas e por diferentes tecnologias de conversão, que podem ser de primeira ou de segunda geração. Enquanto as tecnologias de primeira geração estão baseadas na fermentação alcoólica dos carboidratos presentes, por exemplo, no caldo de cana-de-açúcar (modelo brasileiro) ou em hidrolisados enzimáticos do amido de milho (modelo norte-americano), as tecnologias de segunda geração utilizam resíduos agrícolas e agroindustriais para este mesmo fim. 1-3 Neste caso, o processo fermentativo é baseado nos carboidratos liberados da biomassa vegetal por hidrólise da celulose e das hemiceluloses. 4 A produção de etanol a partir de resíduos agroindustriais representa uma das mais importantes alternativas à consolidação de um modelo sustentável para a produção de combustíveis renováveis. 5,6 Por esta razão, diferentes tecnologias de pré-tratamento, sacarificação (ou hidrólise) e fermentação vêm sendo estudadas em todo mundo para demonstrar a viabilidade comercial deste processo. 3,4,[7][8][9] Neste sentido, a maior parte destes estudos está orientada ao aumento da acessibilidade química da celulose, buscando reduzir a quantidade de enzima necessária para a conversão dos polissacarídeos em açúcares fermentescíveis. 7,10,11 A explosão a vapor tem sido proposta como um dos métodos mais promissores para separar os principais constituintes da biomassa vegetal e aumentar a sua susceptibilidade à bioconversão. 8,[12][13][14][15][16] Este processo, que atua tanto química como fisicamente na estrutura do material lignocelulósico, está baseado no contato direto da biomassa com vapor saturado à alta pressão por um determinado tempo de residência no reator, seguido de descompressão rápida à condição atmosférica (explosão). Ao longo deste processo, as ligações quími-cas que mantêm os componentes macromoleculares da fitobiomassa fortemente associados são em parte quebradas, de forma que, no momento da descompressão, o material é desfibr...

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Polymers derived from cyclodextrins show several biomedical applications. In this paper, six cross-linked polyurethane networks based on b-cyclodextrin (bCD) or hydroxypropyl-b-cyclodextrin (HPbCD) and polyethylene glycols (PEG 400, PEG 1500 or PEG 4000) were synthesized by the usual two-step polymerization method. The polymers were characterized by Fourier-transformed infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The inclusion capacity was evaluated by the discoloration method of a phenolphthalein solution. In order to explore their potential use as controlled drug delivery systems, dissolution profiles and release behavior of inclusion complexes between PUR/TDI/ bCD/PEG4000 or PUR/TDI/HPbCD/PEG1500 and nifedipine (NIF) were investigated. FTIR assignments confirmed the formation of urethane linkages. XRD patterns revealed that the crystallinity decreased mainly due to the crosslinking process. TGA showed three stages of mass loss attributed to water loss, cleavage of urethane bonds and volatilization of decomposition products. The inclusion capacity of cyclodextrins cross-linked with polyurethane was suitably maintained. Dissolution profiles demonstrated that the inclusion complexes PUR/TDI/bCD/PEG4000-NIF and PUR/TDI/HPbCD/PEG1500-NIF are feasible systems for controlling drug release, showing a biexponential release behavior.

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Statistical design and mathematical modeling were used to investigate the fed-batch enzymatic hydrolysis of steam-exploded sugarcane bagasse (195 °C, 7.5 min). First, a Box-Behnken experimental design was used to evaluate the effect of enzyme loading (8, 24, and 40 FPU g-1 glucans of Cellic CTec3®), stirring speed (100, 150, and 200 rpm), and substrate total solids (5, 12.5, and 20 wt%) on the release of glucose equivalents (GlcEq, mostly glucose) after hydrolysis for 48 h in batch mode. A simplified kinetic model was used to fit the experimental data, in which specific activities in Cellic CTec3 were not differentiated, enzyme adsorption was ignored, and end-product inhibition was only attributed to glucose accumulation. The adjusted kinetic model was used to predict the effects of substrate and enzyme intermittent feedings in fed-batch hydrolysis experiments. Compared with batch experiments at 20 wt%, the proposed fed-batch procedure was able to increase GlcEq productivity by nearly 68% using the same enzyme loading, producing substrate hydrolysates containing 91.8 g L-1 GlcEq.