1,720,973 research outputs found
Experimental and theoretical study of VOC removal by adsorption onto activated carbon in a fixed bed column.
No full textIn this work, an experimental and theoretical study on the adsorption of vapors of volatile organic compounds (VOCs) in a fixed bed column is presented and developed; the analyzed system is composed by three kinds of VOCs, that is dimethoxy-ethane (DME), isopropyl alcohol (IPA) and methyl-tertbutyl-ether (MTBE) and a commercial activated carbon as adsorbent material.
Nowadays VOC are widely used as dissolving and cleaning agents in many industrial processes such as printing, manufacturing of magnetic tapes, electronic chips, pharmaceutical and cosmetic synthesis and are therefore frequently present in the gaseous industrial effluents.
Unfortunately VOC are a class of hazardous pollutants, due to their harmful effects of human and animal health and the environments. It is well documented that VOC inhalation and longterm exposure can cause serious health effects; moreover they are included in the “ozone precursor substances”, that means substances which contribute to the formation of ground-level ozone. Therefore, control of VOC emission is mandatory for the industries, according to the environmental regulations issued world-wide.
Different techniques are available to destroy VOC by different types of thermal, catalytic or biological oxidation or to remove VOC from gaseous effluents by absorption, adsorption or membrane separation. Among the last type of technologies, adsorption is one of the most extensively used, because of the high selectivity and capacity of the adsorbent material, the ease of operation, the low capital and operating costs, and the compactness of equipment; due to its high separation efficiency even at low concentrations and at low operating costs, adsorption is also employed after one or more previous treatment processes, which operate a more gross separation to reduce pollutant’s concentrations to low levels. Furthermore, adsorption in fixed bed columns is suitable to treat effluents of variable composition and can tackle the problem of accidental increases of pollutant concentration without compromising the effluent quality, but at the expense of a reduction of the column’s useful life.
Several adsorbent materials can be used to adsorb VOCs: activated carbon, zeolite, silica gel, MOF, carbon molecular sieve. In particular, activated carbon is a good adsorbent with high adsorption capacities towards polar and non-polar compounds; it can be produced by a great variety of raw materials, such as hazelnut shell, rubber-seed shell, palm kernel shell, coconut shell, rice husk, wood; this large availability of waste material makes the activated carbon relatively cheap and available. However, its removal efficiency can be negatively affected by gas relative humidity, competitive adsorption of different contaminants and slow mass transfer rate. In particular, in the pharmaceutical industry in which the production is predominantly in batch mode, the gaseous streams contain several VOCs and competitive adsorption usually occurs. Furthermore, the gaseous composition can vary periodically in relation to the planning of production.
The effluent is treated in a fixed bed column packed with activated carbon before its release into the atmosphere; it is clear that it is difficult to study the column behavior, and hence, to predict its life time in such operating conditions. Indeed, as mentioned before, when a column is fed with a multicomponent stream, the competitive adsorption for the adsorbent sites usually occurs; moreover, because of the discontinuity nature of the feeding stream, the column is
subjected to adsorption and desorption phases which take place along the bed until its break occurs.
Therefore, the development of a fixed-bed mathematical model able to describe the complex system behavior is crucial if you want to predict the performance of such separation process; to this aim an adequate understanding of both equilibrium and kinetics of adsorption and desorption is essential. In order to obtain this information, the experimental response must be matched with the theoretical response, calculated from the dynamic model of the system. On
the other hand, from the perspective of the fixed-bed column design, the model can represent a useful tool to predict the dynamic behavior of the column in a wide range of operating conditions, without recourse to extensive experimentation.
Single VOC removal by adsorption process is widely analyzed in the literature, where a variety of VOCs as well as kinds of models to describe their adsorption in several adsorbent materials can be found; far fewer studies focusing on the adsorption of multicomponent mixtures in dynamic conditions are instead available and even fewer studies on the desorption phase have been carried out.
In this research work, adsorption and desorption of the three aforementioned organic solvents, widely used in pharmaceutical industries, on a commercial activated carbon are experimentally and theoretically studied in a fixed bed column
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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