Browsing by Issue Date, starting with "2015"
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- Current pretreatment technologies for the development of cellulosic ethanol and biorefineriesPublication . Silveira, Marcos H. Luciano; Morais, Ana Rita C.; Lopes, André; Olekszyszen, Drielly Nayara; Lukasik, Rafal M.; Andreaus, Jurgen; Ramos, Luiz PereiraLignocellulosic materials, such as forest, agriculture, and agroindustrial residues, are among the most important resources for biorefineries to provide fuels, chemicals, and materials in such a way to substitute for, at least in part, the role of petrochemistry in modern society. Most of these sustainable biorefinery products can be produced from plant polysaccharides (glucans, hemicelluloses, starch, and pectic materials) and lignin. In this scenario, cellulosic ethanol has been considered for decades as one of the most promising alternatives to mitigate fossil fuel dependence and carbon dioxide accumulation in the atmosphere. However, a pretreatment method is required to overcome the physical and chemical barriers that exist in the lignin–carbohydrate composite and to render most, if not all, of the plant cell wall components easily available for conversion into valuable products, including the fuel ethanol. Hence, pretreatment is a key step for an economically viable biorefinery. Successful pretreatment method must lead to partial or total separation of the lignocellulosic components, increasing the accessibility of holocellulose to enzymatic hydrolysis with the least inhibitory compounds being released for subsequent steps of enzymatic hydrolysis and fermentation. Each pretreatment technology has a different specificity against both carbohydrates and lignin and may or may not be efficient for different types of biomasses. Furthermore, it is also desirable to develop pretreatment methods with chemicals that are greener and effluent streams that have a lower impact on the environment. This paper provides an overview of the most important pretreatment methods available, including those that are based on the use of green solvents (supercritical fluids and ionic liquids).
- Identificação do potencial renovável para produção de electricidade na perspectiva da microgeraçãoPublication . Simões, Teresa; Estanqueiro, Ana; Alves, Jorge MaiaNos últimos anos a preocupação das entidades governamentais com o aquecimento global conduziu ao lançamento de várias iniciativas europeias e nacionais visando a redução das emissões de gases de efeito de estufa para a atmosfera, bem como a redução da dependência em combustíveis fósseis. A preocupação em tornar mais eficiente o consumo de energia, tem conduzido nos últimos anos à procura de soluções alternativas para a geração de energia e à adopção de medidas com vista à sensibilização das sociedades para a utilização eficiente de recursos energéticos. Assim, surgiram nos anos mais recentes conceitos como, Cidades Inteligentes e Cidades Sustentáveis, os quais recorrem à utilização de sistemas de energias renováveis para produção de electricidade. O desenvolvimento do conceito Cidades Inteligentes não foi, contudo, acompanhado do necessário desenvolvimento de metodologias de caracterização e quantificação do potencial energético dos recursos renováveis das cidades, por forma a promover uma boa gestão dos recursos existentes e o desenvolvimento sustentável urbano. Apesar da caracterização do potencial solar poder actualmente ser efectuada com ferramentas inseridas em plataformas de informação geográfica, a sua quantificação à escala da cidade num contexto de sustentabilidade energética, carece ainda de metodologias estruturadas. A avaliação do potencial eólico urbano é um tema amplamente debatido entre os especialistas da área do vento urbano, tendo ainda um longo caminho a percorrer até se encontrar metodologias fiáveis e de utilização simples e pouco onerosa. Os custos associados à realização de campanhas experimentais do vento são elevados quando comparados com o custo das micro-turbinas eólicas, bem como o risco associado à sua instalação num local sem recurso energético suficiente para justificar o investimento. Este trabalho apresenta metodologias de aplicação simples e pouco onerosas de caracterização do potencial renovável urbano para a instalação de sistemas de produção de electricidade. Estas metodologias foram aplicadas a dois casos de estudo, onde se avaliou e quantificou o potencial renovável. Neste trabalho, são apresentadas as metodologias, ferramentas desenvolvidas, e resultados obtidos para cada área urbana. Estas metodologias podem ser replicadas a outras áreas urbanos, constituindo uma contribuição para o planeamento de energias renováveis em áreas urbanas e construídas num contexto de Cidades Inteligentes.
- The effects of tantalum addition on the microtexture and mechanical behaviour of tungsten for ITER applicationsPublication . Tejado, Elena; Carvalho, Patricia Almeida; Munoz, A.; Dias, Marta; Correia, J.B.; Mardolcar, U. V.; Pastor, Jose YgnacioTungsten (W) and its alloys are very promising materials for producing plasma-facing components (PFCs) in the fusion power reactors of the near future, even as a structural part in them. However, whereas the properties of pure tungsten are suitable for a PFC, its structural applications are still limited due to its low toughness, ductile to brittle transition temperature and recrystallization behaviour. Therefore, many efforts have been made to improve its performance by alloying tungsten with other elements. Hence, in this investigation, the thermo-mechanical performance of two new tungsten-tantalum materials has been evaluated. Materials with W–5wt.%Ta and W–15wt.%Ta were processed by mechanical alloying (MA) and later consolidation by hot isostatic pressing (HIP), with distinct settings for each composition. Thus, it was possible to determine the relationship between the microstructure and the addition of Ta with the macroscopic mechanical properties. These were measured by means of hardness, flexural strength and fracture toughness, in the temperature range of 300–1473 K. The microstructure and the fracture surfaces features of the tested materials were analysed by Field Emission Scanning Electron Microscopy (FESEM).
- PV systems linked to the grid: parameter identification with a heuristic procedurePublication . Fialho, L.; Melício, R.; Mendes, V. M. F.; Estanqueiro, Ana; Pereira, Manuel CollaresThis paper focuses on a PV system linked to the electric grid by power electronic converters, identification of the five parameters modeling for photovoltaic systems and the assessment of the shading effect. Normally, the technical information for photovoltaic panels is too restricted to identify the five parameters. An undemanding heuristic method is used to find the five parameters for photovoltaic systems, requiring only the open circuit, maximum power, and short circuit data. The I–V and the P–V curves for a monocrystalline, polycrystalline and amorphous photovoltaic systems are computed from the parameters identification and validated by comparison with experimental ones. Also, the I–V and the P–V curves under the effect of partial shading are obtained from those parameters. The modeling for the converters emulates the association of a DC–DC boost with a two-level power inverter in order to follow the performance of a testing commercial inverter employed on an experimental system.
- Hydrothermal pretreatment of several lignocellulosic mixtures containing wheat straw and two hardwood residues available in Southern EuropePublication . Silva-Fernandes, Talita; Duarte, Luís C.; Carvalheiro, Florbela; Loureiro-Dias, M. Conceição; Fonseca, César; Gírio, FranciscoThis work studied the processing of biomass mixtures containing three lignocellulosic materials largely available in Southern Europe, eucalyptus residues (ER), wheat straw (WS) and olive tree pruning (OP). The mixtures were chemically characterized, and their pretreatment, by autohydrolysis, evaluated within a severity factor (log R0) ranging from 1.73 up to 4.24. A simple modeling strategy was used to optimize the autohydrolysis conditions based on the chemical characterization of the liquid fraction. The solid fraction was characterized to quantify the polysaccharide and lignin content. The pretreatment conditions for maximal saccharides recovery in the liquid fraction were at a severity range (log R0) of 3.65–3.72, independently of the mixture tested, which suggests that autohydrolysis can effectively process mixtures of lignocellulosic materials for further biochemical conversion processes.
- Manufacture of furfural in biphasic media made up of an ionic liquid and a co-solventPublication . Peleteiro, Susana; Lopes, André; Garrote, Gil; Lukasik, Rafal M.; Parajó, J. C.Xylose was converted into furfural operating in a medium containing the acidic ionic liquid (AIL) 1-butyl-3-methylimidazolium hydrogen sulfate, in the presence of toluene as a co-solvent. No catalytic species different from the AIL were needed for furfural production from xylose. Operating at 100.140 .C for 15.480 min in media containing 10 g xylose/100 g AIL and 2.4 g toluene/g (AIL + xylose), most furfural generated in the AIL phase was transferred to the co-solvent, limiting the losses caused by undesired side reactions. Operating under optimal conditions (140 .C for 240 min using 4.4 g toluene/g initial AIL phase), xylose was almost completely consumed, and furfural was obtained at 73.8% of the stoichiometric yield.
- An integrated approach to energy production and nutrient recovery through anaerobic digestion of Vetiveria zizanoidesPublication . Crocamo, Angelo; Di Berardino, Santino; Di Giovanni, Raffaele; Fabbricino, Massimiliano; Martins-Dias, SuseteThis paper reports on experimental results used to verify the applicability of Vetiveria zizanoides (VZ) as a virtuous energetic crop. VZ produces biogas through its anaerobic digestion, and its nutrient content can be recovered through reuse, after digestion, as an agricultural amendment. Biomethanation tests were conducted with fresh and pretreated VZ, and the results of these tests were compared with those from the anaerobic degradation of common garden grass. Specific methane production was found to be around 650 Nm3 per ton of total organic carbon (TOC) for Vetiveria zizanoides, and around 510 Nm3 per ton of TOC for common grass, with no significant improvement after thermal pretreatment. Germination tests conducted with the digested VZ showed that the produced digestate fulfills the requirements of a fertilizer.
- Spatial diffusion and the formation of a technological innovation system in the receiving country: The case of wind energy in PortugalPublication . Bento, Nuno; Fontes, MargaridaThis paper investigates how energy technologies diffuse spatiallythrough the examination of wind growth in Denmark (core) andPortugal (follower). The research draws on the empirical his-torical scaling dynamics to compare patterns of diffusion, andproposes an explanation for these patterns with the help of thetechnological innovation systems (TIS) theoretical framework. Theanalysis uncovered an acceleration of diffusion when the technol-ogy attained the new market. The mechanisms that allowed rapidadoption were found to be, among others, transnational linkagesand an improved absorptive capacity. The latter benefited frompast investments in knowledge development, imports of state-of-the-art technology and construction of a local industry assemblingavailable competencies. Targeted policies (e.g. tender-based feed-in scheme) were effective to stimulate technology transfer andboost diffusion. The linkages with the global TIS and the conceptof absorptive capacity improve the understanding of the processesinvolved in the formation of a TIS in receiving countries.
- Direction, legitimacy and structuration in technological innovation systems upscaling-insights from roadmaps for deepwater offshore wind energyPublication . Bento, Nuno; Fontes, MargaridaThis research investigates strategies aiming to accelerate the up-scaling of low- carbon innovations. We adopt the technological innovation systems (TIS) perspective to focus on structuration or system building processes, including key innovative activities. We analyze national roadmaps that have been developed for offshore wind energy in deep waters - more than 50 meters deep where most of the potential is expected but whose technologyis more immature . in Europe. The roadmaps analysis not only reveals how actors expect the TIS grow but also enables the understanding about the critical functions at this stage, such as direction of search and legitimacy.
- New dual-stage pH control fed-batch cultivation strategy for the improvement of lipids and carotenoids production by the red yeast Rhodosporidium toruloides NCYC 921Publication . Dias, Carla; Sousa, Sofia; Caldeira, João; Reis, Alberto; Silva, Teresa Lopes daThe optimal medium pH to produce biomass and fatty acids by the red yeast Rhodosporidium toruloides NCYC 921 is 4.0, and to produce carotenoids is 5.0. Based on this difference, a dual-stage pH control fed-batch cultivation strategy for the enhancement of lipids and carotenoids production by this yeast was studied. The results showed that when the yeast growth phase was conducted at pH 4.0, and the products accumulation phase was conducted at pH 5.0, biomass, total fatty acid and total carotenoid productivities were significantly improved comparing with the yeast fed batch cultivations carried out at fixed medium pH (4 or 5). Under dual-stage pH control conditions, the biomass, carotenoids and lipids productivities attained 2.35 g/L h, 0.29 g/L h and 0.40 g/L h, respectively. It was also observed that the oxygen played a major role in the yeast carotenoid production.