1,720,969 research outputs found
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
Fossil vs. Renewable Sources for Chemicals Production: A new Process for the Production of Acetonitrile from Bioethanol
No full textA new fully integrated ethanol-to-acetonitrile production plant has been designed here from the grass roots on a pilot scale (10 kg/h) from ethanol, ammonia and air. Besides the reaction section, the full separation train for pure acetonitrile recovery (> 99%) has been optimized and integrated with the recovery of all the byproducts (CO2, HCN) and unreacted NH3. The recovery and valorisation of the marketable byproducts (cyanide salts and NH4HCO3) is also discussed. Finally, the process consumes more CO2 than what constitutes the reactor byproduct, allowing the further sequestration of this greenhouse gas
Fossil vs. Renewable Sources for Chemicals Production: A new Process for the Production of Acetonitrile from Bioethanol Compared with the Sohio Process
No full textA new fully integrated ethanol-to-acetonitrile production plant has been designed here from the grass roots on a pilot scale (10 kg/h) from ethanol, ammonia and air. Besides the reaction section, the full separation train for pure acetonitrile recovery (> 99%) has been optimized and integrated with the recovery of all the byproducts (CO2, HCN) and unreacted NH3. The recovery and valorisation of the marketable byproducts (cyanide salts and NH4HCO3) is also discussed. Finally, the process consumes more CO2 than what constitutes the reactor byproduct, allowing the further sequestration of this greenhouse gas
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
A newly designed process for the production of acetonitrile from renewable sources
No full text1. Introduction
The chemical importance of acetonitrile comes from its very particular polarity, affinity with both organic liquids and water and relatively high boiling point. Its main use is as a solvent for pharmaceutical and laboratory applications (nearly 70%) [1], but is also used in the extractive separation of butadiene from C4 alkanes and in other similar processes.
Acetonitrile is mainly a byproduct of the acrylonitrile synthesis (6 Mton in 2010) and its yield depends on how the main process is operated. This intrinsic dependence is the underlying reason for the recognized mismatch between its demand and availability worldwide.
More recently, routes to acetonitrile as the main reaction product have been sought [1] and an efficient atom-economy could be achieved by using C2 substrates, such as ethanol, ethane and ethylene. In brief, all these reactions are characterized by the alkylation of ammonia. Ethanol as a reactant is a promising alternative being a renewable resource, readily available from established fermentation processes and usable for this process without particular purification requirements.
A new fully integrated ethanol-to-acetonitrile production plant has been designed here from the grass roots. The system is designed to produce acetonitrile on a pilot scale (10 kg/h) from ethanol, ammonia and air (ammoxidation). Besides the reaction section, the full separation train for pure acetonitrile recovery (> 99%) has been optimized and integrated with the recovery of all the byproducts (CO2, HCN) and unreacted NH3. The recovery and valorisation of the marketable byproducts (cyanide salts and NH4HCO3) is also discussed. Finally, the process consumes more CO2 than what constitutes the reactor byproduct, allowing the further sequestration of this greenhouse gas.
2. Methods
The overall process design has been carried out using the software Aspen PLUS® V 8.8, with the APV88 and NISTV88 components databanks for components properties. The thermodynamic system used is the ENRTL (Electrolyte Non Random Two Liquids) to compute the non-ideality in the liquid phase. It was chosen since salts are present overall the process and it allows to model their thermodynamic properties in a more reliable way than NRTL. The Redlich-Kwong equation of state was used to model non-ideality for the gaseous phase. Some species were also treated as Henry components (properties from the same databases) to account for their solubility.
3. Results and discussion
After selecting the most appropriate thermodynamic package to correctly compute phase equilibria and the relative duties, a new integrated process has been designed as conceptually sketched in the Figure. Basically, ethanol, ammonia and air are mixed in the reactor, which operates according to the specifications experimentally derived in a previous work [2]. The product mixture is composed of unreacted and newly formed N2, NH3, HCN, CO2, CH3CN and H2O. All the byproducts are separated by washing and precipitation as marketable NH4HCO3 (even using additional CO2 as external input) and NaCN. The separation of the former salt is accomplished straigforwardly by using ethanol, which recovered in the drier, thus achieving preheating and partial vaporisation of the reactant and its mixing with air. Further heat recovery is allowed between the reactor fedd/products lines (not drawn). Finally, the separation of pure acetonitrile is accomplished by pressure swing distillation, for intensified resolution of the azeotrope [3]. 92% recovery of the produced acetonitrile (99.5% purity) is the final yield of the process, which includes marketable byproducts, heat recovery options and further CO2 sequestration.
4. Conclusions
A process for acetonitrile production through ethanol ammoxidation has been designed on a pilot-plant scale. This represents a fully new process, with complete materials recovery, that allows the independent production of acetonitrile exploiting renewable sources. We consider the relatively low ammonia consumption, the full byproducts recovery and marketability and the close connection between the process sections as the most promising features of this newly designed plant.
In order to evaluate the potential benefits of the bio-based synthesis of acetonitrile a Life Cycle Assessment (LCA) approach was applied by comparing the environmental scores of the renewable route with those achieved by the traditional fossil-based pathway. A cradle to gate perspective, from raw material extraction up to the acetonitrile production, has confirmed the lower impacts in terms of resources depletion and environmental burdens for the innovative and renewable synthetic process.
References
[1] I.F. Mcconvey, D. Woods, M. Lewis, Q. Gan, P. Nancarrow, Org. Process Res. Dev. 16 (2012) 612-624.
[2] F. Folco, J.V. Ochoa, F. Cavani, L. Ott, M. Janssen, Catal. Sci. Technol. 7 (2017) 200–212.
[3] A. Tripodi, M. Compagnoni, G. Ramis, I. Rossetti, Chem. Eng. Res. Des., in press.
Keywords
Acetonitrile; Life cycle assessment; Pressure swing distillation; Plant design
A new renewable route to acetonitrile: process design and life-cycle analysis
No full textThe research for new routes to acetonitrile developed of catalysts active for the ammoxidation of various substrates. Among these ethanol represents a good substrate in terms of atom economy and, being renewable, in principle can improve the sustainability of the process. A fully integrated process has been designed ex novo for the production of acetonitrile from bioethanol, with 10 kg/h of acetonitrile set as unit of production for calculations. The reactants are ethanol, ammonia and air, but in the separation train, further CO2 is consumed, besides all that produced in the process. All the byproducts, mainly ammonium bicarbonate and sodium cyanide, are recovered as marketable chemicals. In principle, all the carbon atoms and 90% of the nitrogen atoms are turned into reaction products, the main loss being gaseous N2. The Aspen Plus® process simulator has been used for process design and, further, a life cycle analysis was carried out including all the stages involved in the bioacetonitrile production (from raw materials extraction up to the gate plant). The results were then compared with those achieved for the traditional fossil route (SOHIO process), showing a sensible decrease of the environmental burdens in terms of non-renewable resources and damage to ecosystems (e.g., toxicity, climate change, etc.).
Finally, a simplified sensitivity analysis was carried out by substituting the starting raw material for the production of bioethanol (corn) with other materials conventionally used worldwide, such as sugar cane and wood. The latter option seems to make the system more competitive in terms of carbon neutrality, thanks to the usage of the residual lignocellulosic fraction available on the market.
The basic scheme of the process is reported in the following Figure
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