1,720,967 research outputs found
Thermochemical conversion of microalgae: challenges and opportunities
Full text linkResearch in Advanced Biofuels steadily developed during recent years. A number of highly innovative technologies have been explored at various scale: among these, lignocellulosic ethanol and CTO (Crude Tall Oil)-biofuel technologies already achieved the early-commercial status, while hydrotreating of vegetable oils (HVO, or HEFA) can be considered today fully commercial. However, despite the level of innovation in each specific technological process under consideration, the feedstock maintains a central role in making a biofuel chain really sustainable. In this context, microalgae grown in salt-water and arid areas offers a considerable opportunity for advanced biofuel production: at the same time, however, they also represent a considerable challenge. Processing microalgae in an economic way into a viable and sustainable liquid biofuel (a low-cost mass-produced product) is not trivial. So far, the main attention has been given to cultivating the microorganism, accumulating lipids, extracting the oil, valorising co-products, and treating the algae oil into biodiesel (through esterification) or HEFA (Hydrotreated Esthers and Fatty Acids), this second one representing a very high quality biofuels, almost a drop-in fuel (suitable either for road transport or for aviation), which production exceed 2 Mt y-1 today. However, extracting the algae oil at low cost and at industrial scale is not yet a full industrial mature process, and the still limited market size of algae-to-biofuels makes difficult the development of industrial-scale systems. Nevertheless, another option can be considered, i.e. processing the whole algae into dedicated thermochemical reactors, thus approaching the downstream processing of algae in a completely different way from separation. The present work examines the possible routes for thermochemical conversion of microalgae, distinguishing between dry-processes (namely pyrolysis and gasification) and wet-processes (near critical water hydrothermal liquefaction and hydrothermal gasification). Typical expected elementary composition of major products is given. Main peculiarities of batch versus continuous processing are also discussed from an engineering point of view. Major engineering advantages and challenges in thermochemically conversion of algae are identified and discussed, in view of the production of a transport biofuel. Finally, future perspectives for each route are given in terms of current and expected technological readiness level
Bio-Hydrocarbons through Catalytic Pyrolysis of Used Cooking Oils: towards sustainable jet and road fuels
Full text linkVegetable Oil (VO) is today the most used feedstock for transport biofuel production by transesterification to biodiesel. Other commercial technologies for renewable fuels production are mainly based either on Fischer-Tropsch (FT) synthesis from coal, natural gas and possibly biomass, or hydro treating of vegetable oil (Hydrotreated Vegetable Oil, HVO): this also includes Hydrotreated Renewable Jet fuel, HRJ, Used Cooking Oil (UCO) is a highly sustainable feedstock (based on EC-RED scheme): it is therefore considered as a possible alternative to VOs for greening of air transport and, under proper circumstances, for reducing the feedstock cost component. However, the use of UCO is not trivial in reactors, as catalysts are sensitive to impurities and contaminations, which are typical of waste oils. Moreover, the chemical composition of UCO is variable regionally as well as seasonally, because the type of base-vegetable oils vary with Country and period of the year. In the framework of the ITAKA EU FP7 project, (catalytic) thermochemical conversion of UCO has been considered to obtain an intermediate biofuel suitable for upgrading by hydrotreating. The catalytic conversion of UCO and Fatty Acids were investigated in a 1.5 kg/h pilot unit. UCO, properly filtered and conditioned, was characterized, and then converted in bio-oil by means of thermal and catalytic reactionsunder controlled conditions. The type of catalyst and the reaction conditions, including several parameters such as temperature, reactor geometry, heating rate and residence time, were evaluated, and selected combinations were tested. The bio-oil was characterized in terms of main constituents and hydrocarbons content, and GC-MS and GC-FID analyses were used to qualitatively and quantitatively assess the composition of the fuel
Isomerization of long-chain fatty acids and long-chain hydrocarbons: A review
No full textIsomerization of long-chain saturated fatty acids (LCSFAs) by catalytic conversion through zeolites is of great interest in cosmetics and biofuel production. This conversion pathway has received attention in the last two decades due to the increasing interest in renewable feedstock. A favorable policy framework and a larger availability of lipid wastes from industry promote new valorization practices like this one and open new opportunities for the near future. Moreover, the next decade is likely to witness a considerable rise in the research for improvement of isomerization yield by testing various bifunctional zeolites. Although this approach has enormous potential in terms of applicability, it currently suffers from low yields that stems from focus on only one type of zeolite. Despite limited number of studies in this field, there is a considerable amount of literature about isomerization of similar compounds, i.e., long-chain unsaturated fatty acids (LCUFAs) and long-chain linear alkanes (LCAs); where, past research has focused on increasing the isomerization yield by using different catalysts, co-catalysts and optimizing operating conditions. Among all types of isomerization catalysts, bifunctional metal loaded microporous solid acids catalysts, known as zeolites, have attracted extensive attention due to their sustainable, environmentally friendly nature, as well as recoverable features. The current challenges of isomerization of LCSFAs are about enhancing the yields towards isomerized products and lowering the long reaction times to scale-up towards industrialization. The innovative aspect of this work is about the identification of the most promising catalysts and co-catalysts for isomerization of LCSFAs and the comparison of isomerization of two similar compounds, LCUFAs and LCAs. It also provides a comprehensive overview of the current state of the art. Results show that the best yields for isomerization of LCUFAs and LCAs have been obtained by 1-dimensional and 2-dimensional zeolites; while, 3-dimensional zeolites have shown the lowest isomerization yields. It also indicates that, for isomerization of LCSFAs, 3-dimensioanl zeolites are the only category that have been tested. Thus, the present paper, highlights shortcomings and provides a blueprint for future research on isomerization of LCSFAs
Energy and environmental assessment of hydrogen from biomass sources: Challenges and perspectives
Full text linkHydrogen is considered as one of the pillars of the European decarbonisation strategy, boosting a novel concept of the energy system in line with the EU's commitment to achieve clean energy transition and reach the European Green Deal carbon neutrality goals by 2050. Hydrogen from biomass sources can significantly contribute to integrate the renewable hydrogen supply through electrolysis at large-scale production. Specifically, it can cover the non-continuous production of green hydrogen coming from solar and wind energy, to offer an alternative solution to such industrial sectors necessitating of stable supply. Biomass-derived hydrogen can be produced either from thermochemical pathways (i.e., pyrolysis, liquefaction, and gasification) or from biological routes (i.e., direct or indirect-biophotolysis, biological water–gas shift reaction, photo- and dark-fermentation). The paper reviews several production pathways to produce hydrogen from biomass or biomass-derived sources (biogas, liquid bio-intermediates, sugars) and provides an exhaustive review of the most promising technologies towards commercialisation. While some pathways are still at low technology readiness level, others such as the steam bio-methane reforming and biomass gasification are ready for an immediate market uptake. The various production pathways are evaluated in terms of energy and environmental performances, highlighting the limits and barriers of the available LCA studies. The paper shows that hydrogen production technologies from biomass appears today to be an interesting option, almost ready to constitute a complementing option to electrolysis
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
