Particle breakage kinetics and mechanisms in attrition-enhanced deracemization

In this study, we report on experiments designed to deconvolute the particle breakage kinetics and mechanism from the parallel phenomena (growth-dissolution, agglomeration) in attrition-enhanced deracemization processes. Through such experiments, we derived the specific breakage rates and cumulative breakage distribution functions for three grinding methods typically used in deracemization experiments: (a) bead grinding, (b) ultrasound grinding, and (c) the combination of bead and ultrasound grinding. Subsequently, we tested these methods on their ability to induce deracemization. We show that in the conventional bead grinding process, breakage occurs mostly by fracture. This results in slow deracemization rates due to the delayed formation of submicron particles that are essential to the process. Conversely, ultrasound grinding very efficiently breaks particles by abrasion. This leads to fast generation of an abundance of submicron fragments resulting in fast deracemization. However, using ultrasound, large crystals fracture rates are an order of magnitude lower than those using bead grinding, which results in an insufficient size decrease of the large counter enantiomer crystals and eventually to incomplete deracemization. Remarkably, the simultaneous application of bead and ultrasound grinding leads, due to synergistic effects of both fracture and abrasion, to 2-fold higher total deracemization rates compared to bead grinding alone. The present work offers new insights into the key role of particle breakage in attrition-enhanced deracemization, together with a basis for decoupling the individual phenomena involved in the process

Environmental and energy assessment of new vehicle technologies in Greater Athens Area

85 σ.Ο τομέας των μεταφορών στην Ελλάδα καταλαμβάνει το μεγαλύτερο μέρος της τελικής κατανάλωσης ενέργειας και συνεπώς αποτελεί τεράστιο πεδίο μελετών εξοικονόμησης ενέργειας. Οι επακόλουθες εκπομπές αποτελούν επίσης μια από τις κύριες πηγές ατμοσφαιρικής ρύπανσης. Η κατάσταση επιβαρύνεται σημαντικά στο Λεκανοπέδιο της Αττικής, όπου περίπου τα μισά ιδιωτικά αυτοκίνητα της χώρας, κυκλοφορούν σε μία έκταση ίση με το 3% της συνολικής έκτασης της χώρας. Επιπρόσθετα, ο στόλος των επιβατικών αυτοκινήτων αποτελείται σχεδόν εξ’ ολοκλήρου από οχήματα εσωτερικής καύσης, που χρησιμοποιούν ως καύσιμο βενζίνη ή πετρέλαιο κίνησης. Η χαμηλή ενεργειακή απόδοση των οχημάτων αυτών καθώς και η ανάγκη περιορισμού της χρήσης των πετρελαϊκών παραγώγων, απαιτούν την ανάπτυξη και την εφαρμογή νέων τεχνολογιών οχημάτων και εναλλακτικών καυσίμων. Η παρούσα εργασία εξετάζει την ενεργειακή εξοικονόμηση, και τον περιορισμό των περιβαλλοντικών προβλημάτων, μέσω της εισαγωγής νέων, φιλικότερων προς το περιβάλλον επιβατικών οχημάτων στην ευρύτερη περιοχή της Αθήνας. Τρείς τεχνολογίες οχημάτων εξετάζονται: (α) υβριδικά οχήματα, (β) ηλεκτρικά οχήματα και (γ) οχήματα κυψελών καυσίμου. Ο περιορισμός της κατανάλωσης βενζίνης, εξαρτάται σε μεγάλο βαθμό, από το ποσοστό διείσδυσης των νέων τεχνολογιών οχημάτων στη σύνθεση του στόλου. Τα υβριδικά και ηλεκτρικά οχήματα έχουν ήδη εισαχθεί στην ελληνική αγορά, αλλά το μερίδιο τους είναι ακόμη πολύ χαμηλό. Αντίθετα, τα οχήματα κυψελών καυσίμου χρειάζονται ακόμη βελτιώσεις πριν την εμπορευματοποίηση τους. Για τους λόγους αυτούς, δύο εναλλακτικά σενάρια σχεδιάζονται. Το πρώτο, περιλαμβάνει την αντικατάσταση όλων των επιβατικών αυτοκινήτων που καταχωρήθηκαν κατά τη διάρκεια της περασμένης χρονιάς (2010), με ηλεκτρικά και υβριδικά οχήματα, διαθέσιμα στην ελληνική αγορά. Το δεύτερο εξετάζει τη διείσδυση οχημάτων κυψελών καυσίμου. Για τους σκοπούς της ανάλυσης ένας αριθμός οχημάτων κυψελών καυσίμου σχεδιάζεται, με σκοπούς να ικανοποιούν κοινά κριτήρια επιδόσεων παρόμοια με τα συμβατικά αυτοκίνητα που κυκλοφορούν. Για τους σκοπούς της ανάλυσης χρησιμοποιείται παραμετρικό μοντέλο υπολογισμού ενεργειακής κατανάλωσης. Το μερίδιο των καταχωρημένων διαφόρων τεχνολογιών οχημάτων καθώς και τα ετήσια οχηματοχιλίομετρα, για τη περιοχή μελέτης, βασίζονται σε βιβλιογραφικές πηγές. Δύο διαφορετικοί κύκλοι οδήγησης χρησιμοποιούνται, ο Ευρωπαϊκός Κύκλος Οδήγησης (NEDC), και ο Αθηναϊκός Κύκλος Οδήγησης (ADC), και τα αποτελέσματα συγκρίνονται. Η διαστασιολόγηση των μερών των οχημάτων κυψελών καυσίμου επιτυγχάνεται μέσω σχεδιαστικού μοντέλου, βάσει δεδομένων κριτηρίων επιδόσεων. Τα δύο σενάρια αξιολογούνται βάσει της εξοικονόμησης ενέργειας και εκπομπών που επιτυγχάνουν. Σύμφωνα με τα αποτελέσματα η μείωση των εκπομπών CO2 μπορεί να φτάσει από 5,5% - 9% εάν τα μέτρα εφαρμοστούν σε πενταετή ορίζοντα.The transport sector in Greece has the largest share of final energy consumption and thus is an enormous scope for energy saving studies. The resulting emissions are also a major source of air pollution. The situation is aggravated significantly in Attica, where almost half of the total country cars circulate in an area equal to 3% of the total country area. Additionally, the fleet of passenger cars consists almost entirely of internal combustion vehicles, fueled with gasoline or diesel. The low efficiency of these vehicles and the need to limit the use of oil derivatives, require the development and implementation of new vehicle technologies and alternative fuels. This paper examines the energy savings and CO2 emissions reduction by introducing new, environmentally friendly passenger cars in the Greater Athens Area. Three vehicle technologies are examined: (a) hybrid vehicles, (b) electric vehicles and (c) fuel cell vehicles. The reduction of gasoline consumption depends, to a large extent, on the penetration of new vehicle technologies in the composition of the fleet. Hybrid and electric vehicles have been introduced in Greek market but their share is still very low. In contrast, fuel cell vehicles still need improvements before launching them in the market. For these reasons, two alternative scenarios are plotted. The first includes the replacement of all passenger cars registered during the past year (2010), with electric and hybrid vehicles, available in Greek market. The second examines the penetration of fuel cell vehicles. For the purposes of the analysis, a number of fuel cell vehicles is designed in order to meet common performance criteria similar to conventional cars in circulation. For the purposes of the analysis a parametric model is used for estimating energy consumption of different vehicle technologies. The share of registered vehicles of different technologies and the annual vehicle-kilometers for the study area are based on literature data sources. Two different driving cycles are used in the analysis, the European Driving Cycle (NEDC), the Athens Driving Cycle (ADC), and the results are compared. The component sizing of fuel cell vehicles is achieved through a design model, based on data performance criteria. The two scenarios are evaluated on the basis of energy savings and emissions reduction. According to the results a 5.5% - 9% CO2 emissions reduction could be achieved if the measures were to be implemented in a five year horizon.Χρήστος Α. Ξιούρα

A Population Balance Model for Temperature Cycling-Enhanced Deracemization (Retracted article. See vol. 19, pg. 520, 2019)

© 2018 American Chemical Society. It has been recently observed that a suspension of conglomerate crystals of both chiralities in contact with a solution where racemization takes place can undergo symmetry breaking due to periodic fluctuations in temperature. The interplay between the mechanisms behind this process is still a matter of debate, although there is consensus that growth/dissolution of crystals and racemization in the solution phase play a crucial role. In this work, we present a population balance model (PBM), based on temperature-size dependent solubility, which simulates a system of enantiomeric crystals of both chiralities subjected to Ostwald ripening under periodic temperature fluctuations, in the presence of a liquid-phase racemization reaction. Our simulations reveal that for a racemic system with small initial size asymmetries between the enantiomers complete deracemization is achieved due to temperature fluctuations, whereas isothermal Ostwald ripening only leads to partial enantiomeric enrichment. This implies that size-temperature dependence of solubility is an essential mechanism in temperature cycling-enhanced deracemization. Although enantiopurity is achieved with only growth, dissolution and temperature cycling, other mechanisms, such as breakage, could also be included. While our model qualitatively reproduces many of the experimental observations in temperature cycling-enhanced deracemization, the autocatalytic nature of the process is not captured and, similarly to Viedma ripening, some sort of chiral feedback mechanism (e.g., agglomeration or secondary nucleation) seems to be required to fully describe the process dynamics. The results presented here offer further insight into temperature cycling-enhanced deracemization and help pinpoint the influence of the various mechanisms in the process.This article has been retractedstatus: Unpublishe

A Population Balance Model for Temperature Cycling-Enhanced Deracemization (Retraction of Vol 18, Pg 6547, 2018)

© 2018 American Chemical Society. The authors retract this article because of a technical mathematical error in the mass balance of the nonisothermal model. After correcting the model and having rerun all simulations in section 4.2, we see that the results in section 4.2 are quantitatively affected. Given that extensive correction of the manuscript would be needed (all graphs in section 4.2), we have requested that the article be retracted. The original article was published on the web on October 2, 2018 and retracted on December 4, 2018.This article has been retractedstatus: Unpublishe