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Optimization of Selective Oxidation of Renewable Raw Materials in Presence of Alumina as Heterogeneous Catalyst
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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
Epoxidation of Methyloleate by Hydrogen Peroxide catalyzed on supported Niobia
No full textDuring the last decade, niobium-based materials have attracted an increasing attention especially in the field of the catalysis1. Many niobium-based catalysts have been synthesised wih different preparation methods (such as impregnation, sol-gel, chemical vapour deposition) obtaining materials characterized by very different properties, in terms of specific area, nature (Brønsted and Lewis) and strength of the active sites1,2. Therefore, they have been applied in a lot of different processes, in particular involving water in the reaction medium(such as hydrogenation, selective oxidation, condensation and esterification reactions), due to their acidity and high water tolerance3,4.Niobium pentoxide (also known as niobia or niobic acidwhen fully hydrated) represents the most studied niobium oxide; for catalytic purposes, it can also be supported on different materials. Different species (isolated or bulk) may be formed depending on the nature and properties of the support material, niobium precursors, niobium content and synthesis method. For example,acid supports react via hydroxyl groups (Brønsted sites) and basic supports react preferentially on the Lewis sites2,3: in this way, specific catalytic properties are generated.
The aim of this work is to comparethe activity between silica and alumina supported niobia catalysts in the epoxidation of methyloleate with hydrogen peroxide.Epoxidized soybean oil and epoxidized methyl esters derived by oils play an important role as building blocks for the preparation of a wide variety of consumer products, such as plasticizers and stabilizers for PVC, and components of lubricants. On the industrial scale, the epoxidation reaction is currently carried out with peroxocarboxylic acids, obtained in situ by using mineral acids as catalysts, according to the Prileshajew method4. The use of hydrogen peroxide as oxidant and heterogeneous catalysts could be an interesting answer to more sustainable and green processes.For this purpose, the main goal of this work is to produce suitable catalysts for the methyloleate epoxidation reaction with hydrogen peroxide
SELECTIVE EPOXIDATION OF SOYBEAN OIL WITH ACID ZEOLITES
No full textEpoxidation of vegetable oils is a commercially important reaction, because the epoxides obtained from these renewable raw materials have wide applications as plasticizers and polymer stabilizers, such as PVC. Epoxidized oils are natural, non toxic, non corrosive and biodegradable, for these reasons they are useful as substitutes of phthalates, plasticizers derived from petroleum recently banned by EU in many countries due to their toxicity. Moreover, considering the high reactivity of epoxide groups, the epoxidized plant oils also acts as raw materials for the production of a variety of chemicals such as polyols, alkanolamines, and polymers like polyesters and polyurethane. Today, one of the most important epoxidized oil is soybean oil and its production is about of 200000 tons/year.
On industrial scale the vegetable oils epoxidation is currently performed in batch reactors, with peracids, generated in situ through the acid catalyzed oxidation of the respective organic acid with hydrogen peroxide. Soluble mineral acids are usually used as catalyst. However, the latter promotes also the side reactions of oxirane ring opening with a dramatic decrease of the selectivity1,2. The use of a heterogeneous catalyst, in alternative to a soluble mineral acids, could allow the suppression of the side degradation reactions, improving the selectivity. An ideal catalyst would be characterized by the presence of Brønsted acid sites, and of a porous structure having a size smaller than that of the natural unsaturated triglycerides molecules. This catalyst would be a porous acid solid characterized by a surface having a hydrophilic character, and by acid sites located inside the pore, that is, accessible only to the components dissolved in the aqueous phase. In this case, the catalyst would promote only the formation of performic acid; this migrates in the oil phase where it spontaneously reacts giving the desired product, while, the undesired ring opening reactions are prevented.
The use of acidic ionic exchange resins (AIER) as heterogeneous catalysts was found to minimize the side reactions and improve the selectivity, in addition of an easier recovery of the catalyst at end of the process. Acidic resins allow the isolation of stronger sites inside the pore structure thus the oxirane ring can be protected from the attack of the acid protons. Several polystyrene sulphonic resins, with different amount of divinylbenzene as cross-linking agent, were tested in the epoxidation of vegetable oils 3. Unfortunately, the use of these resins in continuous packed bed reactors is a difficult operation because their strong osmotic swelling, especially with gel-type resins causing a mechanical stress with the consequence of both the breakage of the resin and the increase of the pressure drop. The use of a more dimensionally stable heterogeneous catalyst, that could improve the selectivity allowing the shift from batch to continuous reactor, represents the key point to increase the productivity of the process.
High specific area, strong acidity, remarkable (hydro) thermal stability, and the presence of pores of adequate size, comparable with the molecular dimension, should predict that zeolites could be good catalysts for the epoxidation with percaboxylic acids. The use of this type of catalysts in epoxidation is new, although the use of zeolites in acid catalyzed reaction was consolidated.
The aim of this work is to evaluate the possibility of using zeolites as heterogeneous catalysts for promoting vegetable oils epoxidation.
For this purpose, a preliminary screening of different zeolites was performed considering the diameter size of principal channels. A very high yield than classical process was reached using zeolite Y as solid catalyst. Therefore, different reaction parameters, such as temperature, catalyst and reagent amounts, were investigated, in order to find the optimal conditions to obtain a product that answer to the market requirements. The stability of the catalyst zeolite Y was also studied with reuses runs with satisfactory results
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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