Environmental and energy assessment of new vehicle technologies in the greater Athens area

The transport sector in Greece has the largest share in the final energy consumption and the resulting emissions are one of the main sources of atmospheric pollution. This situation is worse in the region of Attica, where nearly half of the country’s private cars circulate in an area equal to 3% of the total country area; the region’s climatic and geomorphological characteristics further aggravate the environmental problem. This paper examines energy saving and environmental impacts reduction from the penetration of eco-friendly technology passenger cars in this region. Three vehicle technologies are considered: (i) conventional hybrid electric vehicles, (ii) battery electric vehicles and (iii) fuel cell electric vehicles. The influence of the driving cycle is examined through the comparison of two different cycles, the New European Driving Cycle (a regulatory driving cycle) and the Athens Driving Cycle, based on actual driving data. Two alternative scenarios are formulated. The first involves the substitution of all the passenger cars that were registered during the last year (2010) with hybrid and battery electric vehicles that already exist in the Greek market. The second scenario examines the penetration of fuel cell electric vehicles. Both scenarios are evaluated on the basis of their expected energy savings and greenhouse gas emissions reduction. A 7.5% to 9% reduction of the CO2 emissions is expected, for the Athens Driving Cycle, if these measures are applied in a five year period

Attrition-enhanced deracemization of NaClO3 : comparison between ultrasonic and abrasive grinding

Ultrasound-enhanced grinding is a more practical alternative to glass bead-enhanced grinding for performing attrition-enhanced deracemization at large scale or in continuous flow. In this work, both ultrasound-enhanced grinding (41.2 kHz) and glass bead-enhanced grinding were applied to induce Viedma deracemization of sodium chlorate (NaClO3) crystals in isothermal conditions. The results demonstrate that high intensity, low frequency ultrasound can achieve efficient grinding of enantiomorphous NaClO3 crystals, producing small crystal size and narrow size distribution, both being highly desirable final product properties. Monitoring the width of the crystal size distribution reveals its crucial role and offers further insight into the underlying phenomena in the deracemization process. Compared to glass bead-enhanced grinding, ultrasound-enhanced grinding resulted in faster crystal size reduction and rapid initial deracemization. However, a further increase in the enantiomeric excess was hindered after prolonged times of ultrasonication. This ensues probably due to the absence of crystal size-induced solubility gradients, owing to the existence of close to monodispersed sized crystals after the initial stage in the ultrasound-enhanced grinding process. We show that this can be overcome by combining (a) ultrasound with glass beads or (b) ultrasound with seeding, both of which led to enantiopurity

Coupling Viedma ripening with racemic crystal transformations : mechanism of deracemization

It has been recently observed that coupling Viedma ripening with a seeded in situ metastable racemic crystal to conglomerate transformation leads to accelerated and complete deracemization: crystal transformation-enhanced deracemization. By means of a simple kinetic model, we show that the mechanistic pathway of this new process depends profoundly on the interplay between the crystal transformation and racemization processes, which in turn influence the nucleation process of the counter enantiomer. If the nucleation of the counter enantiomer is suppressed (e.g., by sufficiently fast racemization, low amount of racemic compound or gradual feed, low relative solubility between racemic compound and conglomerate), deracemization proceeds via a second order asymmetric transformation (SOAT) and is limited primarily by the dissolution rate of the racemic crystals and the growth rate of the preferred enantiomer crystals. Breakage and agglomeration accelerate the process, but contrary to conventional Viedma ripening, they are not essential ingredients to explain the observed enantiomeric enrichment. If the nucleation process of the counter enantiomer is not sufficiently suppressed, deracemization is initially controlled by the dissolution rate of the racemic crystals, but Viedma ripening is subsequently required to convert the conglomerate crystals of the counter enantiomer formed by nucleation, resulting in slower deracemization kinetics. In both cases, the combined process leads to faster deracemization kinetics compared to conventional Viedma ripening, while it autocorrects for the main disadvantage of SOAT, i.e., the accidental nucleation of the counter enantiomer. In addition, crystal transformation-enhanced deracemization extends the range of applicability of solid-state deracemization processes to compounds that form metastable racemic crystals

On the effect of secondary nucleation on deracemization through temperature cycles

Herein, the pivotal role of secondary nucleation in a crystallization-enhanced deracemization process is reported. During this process, complete and rapid deracemization of chiral conglomerate crystals of an isoindolinone is attained through fast microwave-assisted temperature cycling. A parametric study of the main factors that affect the occurrence of secondary nucleation in this process, namely agitation rate, suspension density, and solute supersaturation, confirms that an enhanced stereoselective secondary nucleation rate maximizes the deracemization rate. Analysis of the system during a single temperature cycle showed that, although stereoselective particle production during the crystallization stage leads to enantiomeric enrichment, undesired kinetic dissolution of smaller particles of the preferred enantiomer occurs during the dissolution step. Therefore, secondary nucleation is crucial for the enhancement of deracemization through temperature cycles and as such should be considered in further design and optimization of this process, as well as in other temperature cycling processes commonly applied in particle engineering

Towards deracemization in the absence of grinding through crystal transformation, ripening, and racemization

New insights into the obscure mechanisms of solid-state deracemization phenomena are obtained by crystal ripening experiments that, contrary to standard techniques, exclude attrition enhancement (grinding). The results point out that small particles and an initial size imbalance between the two enantiomeric crystal populations can intensify the rate of solidstate enantiomeric enrichment even in the absence of intermediate actions (e.g., grinding or thermal cycling). On this ground, a new process that creates such initial conditions is designed and exemplified for the proteinogenic glutamic acid. As a first step, racemic compound solvate (DL-glutamic acid monohydrate) crystals are completely converted to small-sized conglomerate anhydrate crystals, in the presence of larger seeds of a single chirality. After the transformation is complete and the racemization catalyst is added, the suspension contains an equal number of small-sized conglomerate crystals of both enantiomers together with the larger seeds of the preferred enantiomer. Over time, the large crystals of the preferred enantiomer tend to grow at the expense of smaller ones, which dissolve. This, combined with the fast racemization, leads to enantiomeric enrichment. The possible occurrence of enantioselective agglomeration between small and seed crystals speeds up this process by removing small crystals of the preferred enantiomer. Since most amino acids and several other pharmaceutical compounds are known to form metastable racemic hydrate crystals, it is expected that this new method is readily applicable to a variety of compounds. In addition, the process provides a technically simpler and more scalable route to enantiomeric enrichment compared to attritionenhanced deracemization, and its applicability extends to the wider pool of compounds that crystallize as racemic crystals

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

Towards continuous deracemization via racemic crystal transformation monitored by in-situ Raman spectroscopy

In this work, we demonstrate a semi-batch solid-state deracemization process for N-(2- chlorobenzylidene)-phenylglycine amide (NCPA), a complex chiral polymorphic system that involves three types of crystalline racemates (racemic compound and conglomerate forms I and II). In this process, gradually fed metastable racemic compound crystals are converted in situ to crystals of the preferred (seeded) enantiomer under grinding conditions through a series of solvent- mediated transformations in a racemizing solution. The phase diagram for this system shows that while conglomerate form II is stable at the conditions examined (acetonitrile at 21°C), form I crystals of a single enantiomer (used as seeds) are unstable at (nearly) racemic compositions and convert to the racemic compound upon addition of the racemization catalyst. Thus, care needs to be exercised in order to fully convert form I to form II before addition of the racemization catalyst in order to prevent the undesired crystallization of the racemic compound. This can be achieved by adding a small amount of water, which is found to enhance the nucleation and growth kinetics of the most stable conglomerate form II, eventually leading to complete deracemization. Importantly, we show that this special deracemization process can be easily monitored online by Raman spectroscopy, which gives access to the evolution of the solid phase composition. For the studied system, this information can in turn be used to directly estimate the solid-phase enantiomeric excess online throughout the process, as long as conglomerate crystals of the counter enantiomer do not form

Intensified Crystallization Processes for the Separation of Enantiomers

Molecular chirality is an important geometrical property with far-reaching implications in the pharmaceutical, food and agrochemical industries. Chiral molecules can exist in two non-superimposable mirror-image forms called enantiomers, which often possess substantially different biological effects. Since most chemical synthetic processes of chiral molecules result in an equimolar mixture of both enantiomers, referred to as a racemic mixture, there is high demand for developing downstream separation processes for enantiomers. Solid-state deracemization processes are a new class of crystallization-based methods that achieve such task by completely converting a racemic suspension of conglomerate crystals into a single chirality, simply by applying mechanical (Viedma ripening) or thermal treatments (temperature cycling-enhanced deracemization) to the crystals in contact with a racemizing solution. Compared to other methods applied for chiral resolution, they are advantageous, as they operate without the need for expensive chiral auxiliaries or extensive kinetic and thermodynamic information. However, they suffer from several limitations, most notably long processing times, limited applicability and challenging scalability. On top of that, the interplay between the mechanisms underlying the phenomena is not sufficiently understood, which hinders their effective application. The aim of this doctoral project is to address these limitations by using various experimental and theoretical approaches. With regards to enhancing the rates of these processes and improving their productivity, ultrasound-enhanced grinding and microwave heating are used to intensify the particle breakage mechanism in Viedma ripening and the heating/cooling steps in temperature cycling-enhanced deracemization, respectively. The experimental results reveal that ultrasound-enhanced grinding combined with seeding can effectively replace the conventional bead grinding in Viedma ripening. Furthermore, a comparison between different types of grinding in deracemization processes sheds significant mechanistic insight into the role of abrasion and fracture of crystalline particles in attrition-enhanced deracemization. Similarly, microwave heating coupled with rapid cooling, allows accessing novel operating windows for temperature cycling, with an order of magnitude higher heating/cooling rates than conventionally applied. This results not only in faster deracemization due to a reduction in the cycle duration, but also in higher selectivity due to the minimization of side reactions that lower productivity. Solid-state deracemization methods are only applicable when the enantiomers crystallize as a racemic conglomerate, in which each enantiomer forms individual crystals. However, the majority of racemic mixtures (~90%) form a racemic compound, in which single crystals contain both enantiomers. Consequently, extending deracemization to those compounds is highly desired. By exploiting conditions (temperature, solvent) where the (solvated) racemic compound becomes metastable with respect to the conglomerate, a new process that combines a solvent-mediated crystal transformation of the racemic compound to conglomerate with deracemization is designed and exemplified. The process is then applied to deracemize two chiral model compounds and the results show that it allows for much faster rate compared to the conventional deracemization of conglomerates, to such extent that grinding can be minimized. Besides, the new process extends deracemization to the wider pool of compounds that crystallize as racemic compounds and may undergo such transformations. Finally, in view of better understanding the mechanisms involved in deracemization phenomena, a simplified kinetic model is developed and validated to account for the physicochemical phenomena thought to occur in Viedma ripening, namely crystal growth/dissolution subject to the size-dependence of solubility, racemization, breakage and enantioselective agglomeration. The model results explain recent experimental observations and confirm that the aforementioned mechanisms combined could explain the deracemization process. Subsequently, the model is extended to account for the combined crystal transformation/deracemization process. For the latter case, it is shown that breakage and agglomeration are not essential ingredients, provided that the racemization reaction converts the counter enantiomer molecules faster than they nucleate, leading to a more direct conversion route for the counter enantiomer. The results presented in this work help increase the understanding of deracemization phenomena and may pave the way towards their industrial application.status: publishe

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

Intensified deracemization <i>via</i> rapid microwave-assisted temperature cycling

Rapid cooling and microwave heating substantially speed up temperature cycling-enhanced deracemization, while limiting the concomitant side reactions. During fast cooling, secondary nucleation is shown to enable deracemization.</p