1,720,969 research outputs found
Analysis of a bio-plasticizer production unit from biodiesel
No full textPhtalates constitutes the 70 % of the overall plasticizer production. Despite their unique physicochemical properties, most of the esters of phthalic acid pose health concerns and lead the European Union to restrict their amount in plastic to a level below the 0.1 % by weight in June 2017. Toxic phthalates may be substituted by epoxidized soybean biodiesel (ESB). Although ESB are comparable to commercial bioplasticizers in terms of oxygen content, no information is available for the cost of a unit operation to produce ESB. In this work, we model the epoxidation reaction of soybean biodiesel and we simulate a unit operation that produces ESB. A Python script calls iteratively a PRO/II 9.3 simulation file that numerically solves the mass balances. A MATLAB 2017b script solves the kinetic equations. We estimate the operative and capital costs, and we identify the best techno-economic ESB production conditions for the explored range of reaction parameters
Studio sperimentale e conseguente analisi dei costi di processo per la produzione di bioplasticizzanti a partire da biodiesel
Get PDFNel 2016 il mercato globale dei plastificanti è stato pari a 8,4 milioni di tonnellate, di cui il 70% ricoperto dalla produzione di ftalati. L’utilizzo di questi ultimi, nonostante le loro ottime proprietà chimico-fisiche (elevata solubilità nella matrice polimerica, bassa volatilità e bassi costi di produzione), pone problemi di salute e ha indotto l'Unione Europea nel Giugno 2017 a limitarne la percentuale nei prodotti plastici ad un livello inferiore allo 0,1% in peso.
Gli oli vegetali epossidati (EVO) sono buoni candidati come sostituenti degli ftalati, specialmente quando applicati al cloruro di polivinile (PVC). Tali molecole possono venire prodotte grazie alla reazione, catalizzata da acido solforico, tra la frazione insatura di un olio vegetale e l'acido perossiacetico, che funge da vettore attivo di ossigeno e viene ottenuto dalla reazione di acido acetico e perossido di idrogeno. Tuttavia, la solubilità degli EVO in PVC è bassa, il che rende questi prodotti solo parzialmente idonei come sostituti degli ftalati, la cui concentrazione tipica nel polimero varia dallo 0,5 al 45% in peso. Il biodiesel di soia epossidato (ESB) può essere proposto come alternativa agli EVO. Il biodiesel è una miscela di esteri metilici di acidi grassi, il cui peso molecolare è circa un terzo rispetto agli oli vegetali. Tale prodotto può essere portato alla forma epossidata e può così fungere da plastificante primario e quindi essere considerato adatto come sostituto degli ftalati.
Nel presente lavoro si propone una strategia per la produzione di ESB a partire da biodiesel ricavato da olio di soia, tramite un’operazione di distillazione seguita da reazione di epossidazione. L’obiettivo di tale processo è la massimizzazione del contenuto di ossirano nel prodotto finale, grazie alla concentrazione delle molecole insature ottenute a valle della colonna di distillazione a seguito della rimozione della parte satura del biodiesel di partenza. Tale strategia permette di ottenere sperimentalmente prodotti che, dopo l’ottimizzatione di specifici parametri operativi, risultano chimicamente idonei all’utilizzo come bioplastificanti primari.
Per potere stimare i costi di processo, è stata simulata la colonna di distillazione e il reattore di epossidazione usando un codice Python 3.0 che si interfaccia in modo autonomo con il software di simulazione PRO / II 9.3 (SimSci Schneider Electrics by AVEVA). Le equazioni cinetiche e lo stato di equilibrio liquido-liquido sono state risolte numericamente ad ogni istante temporale della reazione (la reazione avviene in un sistema bifasico liquido) tramite un codice MATLAB. I coefficienti di attività di ciascun componente sono stati calcolati utilizzando il modello UNIFAC.
La stima dei costi di investimento ed operativi ha permesso, in ultimo, di definire le migliori condizioni tecno-economiche di produzione di ESB
Attitude Responses in Coupled Orbit-Attitude Dynamical Model in Earth–Moon Lyapunov Orbits
Get PDFThe attitude motion of a rigid spacecraft in fully nonlinear reference orbits is explored in this investigation, within the context of the planar circular restricted three-body problem. The reference trajectories originate from the Lyapunov families about the Lagrangian points L1 and L2 in the Earth–Moon system. Kane’s method is employed to derive the equations of motion, which are numerically solved. The capability to reproduce the dynamic response is leveraged to understand the attitude behavior across the Lyapunov families. The problem formulation and the simulation environment are detailed. The inertia properties of the spacecraft are varied across the periodic family of orbits. Finally, attitude maps are introduced to summarize the results and identify the regions, in terms of the orbit size and inertia properties, where the spacecraft maintains the initial orientation with respect to the rotating frame in the circular restricted three-body problem
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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