1,721,020 research outputs found
Amberlyst A-70: A surprisingly active catalyst for the MW-assisted dehydration of fructose and inulin to HMF in water
Full text link5-Hydroxymethyl-2-furaldehyde (HMF) is a biomass-derived intermediate for the sustainable production of monomers and biofuels. However, most of its syntheses are performed under not environmentally and/or economically green conditions. In this work, the dehydration of fructose/inulin to HMF was optimized, employing aqueous medium, high substrate concentrations (10 and 20 wt%), low loading of commercial acid resin (Amberlyst-70) and microwave heating. The influence of substrate/catalyst ratio, time and temperature on the products yields was investigated. Amberlyst-70 resulted a very active and recyclable system: HMF yields up to 46 mol% were ascertained, the best result up to now reached under these reaction conditions
Della biomassa lignocellulosica non si butta via niente: esempi di valorizzazione integrale di biomasse diverse
No full textNegli ultimi anni è stata studiata la valorizzazione integrale di diversi tipi di biomasse, quali le erbacee da colture dedicate ed anche di biomasse per uso alimentare quali il mais, gli agrumi e la nocciola. Le biomasse erbacee, quali canna comune (Arundo Donax L.), miscanto (Miscanthus x Giganteus) e sorgo (Sorghum Bicolor), sono abbondanti nel nostro territorio, facilmente coltivabili e a basso costo di produzione. Per la loro idrolisi è stata utilizzata acqua come solvente di reazione, in modo tale da avere un approccio verde e sostenibile, e acido cloridrico come catalizzatore. Il residuo solido proveniente dall’idrolisi è stato caratterizzato ed impiegato per la sintesi di schiume poliuretaniche flessibili. La valorizzazione integrale è stata perseguita anche per le biomasse parzialmente edibili, come la nocciola e la buccia esausta degli agrumi. Dalla cuticola della nocciola sono stati estratti in alta resa e caratterizzati importantissimi agenti antiossidanti polifenolici. Il guscio e la buccia esausta degli agrumi sono stati idrolizzati ad acido levulinico ed il residuo di idrolisi convertito in carboni attivi che si sono dimostrati molto efficienti in processi di adsorbimento in fase liquida ed in fase gas
Phytotoxicity assessment of conventional and biodegradable plastic bags using seed germination test
Full text linkA large fraction of plastic litter found in natural environments is constituted by conventional not biodegradable plastic bags, and their adverse effects via ingestion or entanglement on terrestrial and marine organisms are largely documented. Biodegradable and compostable shoppers have been recently developed as alternative to traditional ones. These bags are specifically designed to degrade in composting facilities and generate a product devoid of toxicity to soils and crops. However, very little is known on the effects of bag leaching, i.e. the transfer of chemicals from plastic into natural environments, on vegetation. Some plant species are highly sensitive to a variety of chemicals, and seedling growth is generally the most affected life history stage. In this study we assessed the potential effects of conventional (high-density polyethylene, HDPE) and compostable (Mater-bi®, MB) bags, when left in natural environments, on water quality and plant development. To this end, seeds of Lepidium sativum L., a terrestrial plant commonly used in phytotoxicity standard tests, were exposed to leachates obtained from different amount of HDPE and MB bags, simulating various pollution degrees occurring in nature, for 72 h. Both not-exposed (or virgin) bags and natural weathering exposed bags were used. Variations of chemical-physical characteristics of extracts were used as indicative of water quality deterioration, while alterations of seed gemination and seedling radicle and hypocotyl length were considered as indicative of phytotoxicity. A chemical qualitative screening of the leachates was also performed to identify the compounds with potential phytotoxicity. Both types of bags affected water characteristics (pH, salinity and total dissolved solids) relevant to plants, and released into water intentionally added chemicals, such as the noxious bisphenol A, and other phytotoxic substances probably generated during bag manufacturing. Leachates from both bag types did not affect seed germination. But, a significant number of seedlings showed developmental abnormalities or reduced seedling growth. The hypocotyl was the most sensible seedling organ to HDPE bag leachates while the radicle was the most vulnerable to MB ones. These findings indicate that plastic bags, including those that meet biodegradability and compostability standards, represent a potential threat to plants, if left in natural environments. Therefore, people and managers should be adequately informed about the potential environmental impact of an incorrect bag disposal. Simple, rapid standard phytotoxicity tests, such as the L. sativum bioassay, applied to bag leachates could be used in the future to select not noxious additives so to develop more eco-friendly bags
Sustainable synthesis of 5-hydroxymethyl-2-furaldehyde and analytical study of the solid by-products
No full textIn the last years environmental problems such as pollution, greenhouse effect and lack of fossil materials have driven the interest of scientific community towards the catalytic valorisation of lignocellulosic biomass. In this scenario 5-hydroxymethylfurfural (HMF) represents a key molecule and it has been evaluated by US Department of Energy as one of the most important bio-based compounds. In fact HMF could be obtained starting from renewable materials and it represents a platform chemicals for several monomers and bio-fuels that result competitive with those originated from fossil resources. In this work the synthesis of HMF starting from both monosaccharide and polysaccharide has been studied with the aim of identifying as sustainable as possible reaction conditions. Moreover, in this work an analytical study has been conducted on the solid by-product in order to clarify its chemical structure and prove if the substrate could affect it
Heterogeneous catalysis for the production of 5-hydroxymethyl-2-furfural and of 2,5-bis(hydroxymethyl)furan from fructose and inulin
No full textToday, the sustainable growth of the chemical and energy industries has become an indispensable benchmark of our society and the current development of the industrial sector based on fossil resources must be replaced by an alternative one, linked to renewable resources. Therefore, the catalytic conversion of renewables is a promising and important topic, in particular for the synthesis of 5-hydroxymeththylfurfural (HMF) and of 2,5- bis(hydroxymethyl)furan (BHMF) which find several applications in many strategic fields. Consequently, from the point of view of sustainability and of an integrate approach based on the biorefinery concept, the conversion of fructose and inulin to HMF has been studied in the respect of green chemistry principles. The obtained aqueous solutions containing HMF, after removing the acid catalyst have been directly hydrogenated to BHMF
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
New Frontiers in the Catalytic Synthesis of Levulinic Acid: From Sugars to Raw and Waste Biomass as Starting Feedstock
Full text linkLevulinic acid (LA) is one of the top bio-based platform molecules that can be converted into many valuable chemicals. It can be produced by acid catalysis from renewable resources, such as sugars, lignocellulosic biomass and waste materials, attractive candidates due to their abundance and environmentally benign nature. The LA transition from niche product to mass-produced chemical, however, requires its production from sustainable biomass feedstocks at low costs, adopting environment-friendly techniques. This review is an up-to-date discussion of the literature on the several catalytic systems that have been developed to produce LA from the different substrates. Special attention has been paid to the recent advancements on starting materials, moving from simple sugars to raw and waste biomasses. This aspect is of paramount importance from a sustainability point of view, transforming wastes needing to be disposed into starting materials for value-added products. This review also discusses the strategies to exploit the solid residues always obtained in the LA production processes, in order to attain a circular economy approac
Multivariate approach for the optimization of sucrose ethanolysis: Paving the way to the exploitation of sucrose-rich by-products
No full textThe depletion of fossil resources is making the synthesis of renewable compounds urgent. Ethyl levulinate (EL) represents a strategic compound within the biorefinery process, being a valuable intermediate, solvent and biofuel additive of renewable origin. The one-pot ethanolysis is the preferred route for its synthesis, but the proper optimization of the reaction conditions to maximize the EL yield and minimize the critical by-products formation, diethyl ether (DEE) and humins, is still a challenge. In this regard, the present work aims at the optimization of sucrose ethanolysis through the multivariate approach, adopting H2SO4 as catalyst and following the high gravity approach (10.5 wt% sucrose loading), which allows the obtaining of concentrated EL streams, increasing productivity and making downstream operations easier and cheaper. The optimization allowed a compromise between the highest EL yield and the lowest DEE production, thus simplifying EL purification and consuming less solvent that can be recycled in the following run. Under these conditions, the humins formation was also kept low and, for the first time, not only the solid humins were characterized, proving to be suitable as solid fuel turning into a co-product of the process, but also the chemical structure of the soluble ones was investigated. For the first time, a preliminary study regarding the ethanolysis of thick juice was also performed, thus opening the way to the employment of low-cost sucrose-rich feedstocks as substrate for the synthesis of EL. Thus, this work contributes to making the synthesis of a strategic renewable compound as EL more sustainable
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
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