Browsing by Issue Date, starting with "2009-09-02"
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- Hydrothermal processing of hardwoods and agro-industrial residues :evaluation of xylo-oligosaccharides productionPublication . Carvalheiro, Florbela; Fernandes, Talita Silva; Duarte, Luís C.; Lopes, Sónia; Moura, Patrícia; Pereira, Helena; Gírio, FranciscoAutohydrolysis was used as a pre-treatment method for the selective hydrolysis of hemicelluloses of four lignocellulosic materials: eucalypt wood chips (EWC), corn cobs (CC), wheat straw (WS) and brewery’s spent grain (BSG), and the process was optimized towards the production of xylo-oligosaccharides (XOS). The effects of temperature, both at isothermal (150-190ºC), and non-isothermal (up to 240ºC) conditions, and liquid-to-solid ratio (LSR), 8 or 10 g/g, on the composition of both the liquid and solid phases were studied. The operational conditions leading to the maximal recovery of XOS for each raw material were established and discussed based on the severity factor (log R0). The higher yields obtained were in the range of 43–65% of the feedstock (arabino)xylan, with the highest value attained for CC for log R0 =3.75. Under the optimised conditions for XOS production, glucan was only slightly solubilised, enabling an enrichment of the solid phase (up to 67% of glucan for EWC). Delignification was also not extensive reaching utmost 18%, in the case of CC. cosmetic industries.
- Biological upgrading of wastes from the pulp and paper industryPublication . Marques, Susana; Alves, Luís; Gírio, Francisco; Santos, J. A. L.; Roseiro, J. CarlosA process for biological upgrading of recycled paper sludge (RPS) was developed based on the enzymatic hydrolysis of major sludge components (cellulose and xylan) with commercial enzymes and fermentation of the resulting sugars into ethanol or lactic acid with adequate microbial strains. The process was implemented performing both steps sequentially (SHF) or simultaneously (SSF). Cellulosic and hemicellulosic fractions of RPS were completely converted by enzymatic hydrolysis (using Celluclast®1.5L with Novozym®188) into the constitutive glucose and xylose. Ethanol was produced from the RPS hydrolysate by the yeast Pichia stipitis CBS 5773. A slightly higher conversion yield was attained on SHF process, corresponding to an ethanol concentration of 19.6 g L-1, but 179 hours were needed. The SSF process was completed after 48 hours of incubation allowing the production of 18.6 g L-1 of ethanol from 178.6 g L-1 of dried RPS, corresponding to an overall conversion yield of 51% of the available carbohydrates on the initial substrate. Maximum production of lactic acid (LA) with Lactobacillus rhamnosus ATCC 7469 was obtained by performing the SSF process: 73 g L-1 of LA was achieved, corresponding to a maximum productivity of 2.9 g L-1 h-1, with 0.97 g LA produced per g of carbohydrates on initial sludge. The present results demonstrate the feasibility of the biological conversion of the ultimate waste obtained in the paper recycling loop into a biofuel (bioethanol) or an important chemical intermediate (LA, precursor of bioplastics), under the concept of a multi-purpose biorefinery.
- Hydrothermal processing of corn residues:process optimisation and products characterisationPublication . Moniz, Patricia; Gírio, Francisco; Carvalheiro, Florbela; Pereira, HelenaHydrothermal processing was used as pre-treatment method for the selective solubilisation of hemicellulose from corn residues (leaves and stalks). The raw material was treated at a liquidto- solid ratio of 10 g/g, under non-isothermal conditions (150-240ºC) and the effect of treatment on the composition of both liquid and solid phases was evaluated. The yields of solid residue and soluble products, e.g., oligosaccharides, monosaccharides, acetic acid and degradation compounds, such as furfural, hydroxymethylfurfural are presented and interpreted using the severity factor (log R0). The operational conditions leading to the maximum recovery of XOS (53% of initial (arabino)xylan) and for highest glucan content of the solid residue (64%) were established for log R0 of 3.75 and 4.21, respectively. Under the severest condition 95% of xylan was selectively solubilised and 90% of initial glucan was recovered on the solid residue, making it very attractive for further processing in a biorefinery framework.