Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: With worldwide emissions standards becoming more stringent over the last decade, the South African market seems set to follow suit. Older technology engines are however unable to attain these stringent standards and will require cleaner burning fuels. Biofuels like biodiesel and bioethanol-diesel blends are an attractive option as a result of their inherently oxygenated nature and renewable, low carbon footprint. Oxygenated fuels have been found to lower particulate and soot emissions without any significant increase in NOx, thus alleviating the usual particulate-NOx trade-off. In this study an existing diesel engine test facility has been upgraded to include emission equipment, and a low cost pressure indicating system. Fuel-to-fuel comparative testing was done with pump diesel and splash blended fuels consisting of pump diesel blended with varying amounts of ethanol and also biodiesel without including any cetane enhancing or blend stability additives. Emission analysis of the blended fuels showed a marked reduction in soot emission with little to no increase in NOx emission for all oxygenated fuels. This type of soot reduction without NOx increase is difficult to obtain through any other method. Blend stability was however a problem with the 15% ethanol-diesel blends. / AFRIKAANSE OPSOMMING: Met wêreldwye uitlaatgas standaarde wat al hoe strenger geword het oor die laaste dekade, lyk dit asof dit net ‘n kwessie van tyd is voor Suid-Afrika dieselfde roete volg. Ouer tegnologie binnebrandenjins kan egter nie hierdie streng standaarde handhaaf nie en sal dus vereis dat die brandstof skoner brand. Biobrandstowwe, soos biodiesel en bio-etanol-diesel mengsels, blyk ‘n aantreklike opsie te wees vanweë hul natuurlike inhoud van suurstof en as hernubare hulpbron. Wanneer suurstof houdende brandstowwe soos hierdie verbrand word, word daar gevind dat daar ‘n daadwerklike afname in rook uitlaat is sonder enige merkbare toename in NOx uitlaatgasse. Dit is teenstrydig met die gewoonlike wisselwerking wat daar tussen hierdie twee uitlaatgas produkte is. In hierdie studie word die bestaande diesel enjin toetssel opgegradeer om uitlaatgas analiese toerusting asook ‘n lae-koste silinderdruk meettoestel te bevat. Brandstof-tot-brandstof vergelykings toetse word gedoen met gewone diesel asook toets diesel wat gemengde konsentrasies biodiesel of bio-etanol bevat. Die toets diesel bevat egter geen aanvullings om mengselstabiliteit of cetaan te verbeter nie. Toetsresultate toon dat daar merkbare vermindering in rook uitlaat is met min tot geen toename in NOx. Hierdie tipe van resultaat met produkte van ontbranding is moeilik om op enige ander manier te bewerkstellig. Daar word ook gevind dat diesel met 15 % bio-etanol nie ‘n stabiele mengsel is nie en dat fase skeiding plaasvind.

The modern concept of "biorefinery" is dominantly based on chemical pulp mills to create more value than cellulose pulp fibres, and energy from the dissolved lignins and hemicelluloses. This concept is characterized by the conversion of biomass into various biobased products. It includes thermochemical processes such as gasification and fast pyrolysis. In mechanical pulp mills, the feedstock available to the gasification-based biorefinery is significant, including logging residues, bark, fibre material rejects, biosludges and other available fuels such as peat, recycled wood, and paper products. This work is to study co-production of bio-automotive fuels, biopower, and steam via gasification in the context of the mechanical pulp industry.   Biomass gasification with steam in a dual-fluidized bed gasifier (DFBG) was simulated with ASPEN Plus. From the model, the yield and composition of the syngas and the contents of tar and char can be calculated. The model has been evaluated against the experimental results measured on a 150 KWth Mid Sweden University (MIUN) DFBG. The model predicts that the content of char transferred from the gasifier to the combustor decreases from 22.5 wt.% of the dry and ash-free biomass at gasification temperature 750 ℃ to 11.5 wt.% at 950 ℃, but is insensitive to the mass ratio of steam to biomass (S/B). The H2 concentration is higher than that of CO under normal DFBG operating conditions, but they will change positions when the gasification temperature is too high above about 950 ℃, or the S/B ratio is too far below about 0.15. The biomass moisture content is a key parameter for a DFBG to be operated and maintained at a high gasification temperature. The model suggests that it is difficult to keep the gasification temperature above 850 ℃ when the biomass moisture content is higher than 15.0 wt.%. Thus, a certain amount of biomass needs to be added in the combustor to provide sufficient heat for biomass devolatilization and steam reforming. Tar content in the syngas can also be predicted from the model, which shows a decreasing trend of the tar with the gasification temperature and the S/B ratio. The tar content in the syngas decreases significantly with gasification residence time which is a key parameter.   Mechanical pulping processes, as Thermomechanical pulp (TMP), Groundwood (SGW and PGW), and Chemithermomechanical pulp (CTMP) processes have very high wood-to-pulp yields. Producing pulp products by means of these processes is a prerequisite for the production of printing paper and paperboard products due especially to their important functional properties such as printability and stiffness. However, mechanical pulping processes consume a great amount of electricity, which may account for up to 40% of the total pulp production cost. In mechanical pulping mills, wood (biomass) residues are commonly utilized for electricity production through an associated combined heat and power (CHP) plant. This techno-economic evaluation deals with the possibility of utilizing a biomass integrated gasification combined cycle (BIGCC) plant in place of the CHP plant. Integration of a BIGCC plant into a mechanical pulp production line might greatly improve the overall energy efficiency and cost-effectiveness, especially when the flow of biomass (such as branches and tree tops) from the forest is increased. When the fibre material that negatively affects pulp properties is utilized as a bioenergy resource, the overall efficiency of the system is further improved. A TMP+BIGCC mathematic model is developed based on ASPEN Plus. By means of this model, three cases are studied:   1) adding more forest biomass logging residues in the gasifier, 2) adding a reject fraction of low quality pulp fibers to the gasifier, and 3) decreasing the TMP-specific electricity consumption (SEC) by up to 50%.   For the TMP+BIGCC mill, the energy supply and consumption are analyzed in comparison with a TMP+CHP mill. The production profit and the internal rate of return (IRR) are calculated. The results quantify the economic benefit from the TMP+BIGCC mill.   Bio-ethanol has received considerable attention as a basic chemical and fuel additive. It is currently produced from sugar/starch materials, but can also be produced from lignocellulosic biomass via a hydrolysis--fermentation or thermo-chemical route. In terms of the thermo-chemical route, a few pilot plants ranging from 0.3 to 67 MW have been built and operated for alcohols synthesis. However, commercial success has not been achieved. In order to realize cost-competitive commercial ethanol production from lignocellulosic biomass through a thermo-chemical pathway, a techno-economic analysis needs to be done.   In this work, a thermo-chemical process is designed, simulated, and optimized mainly with ASPEN Plus. The techno-economic assessment is made in terms of ethanol yield, synthesis selectivity, carbon and CO conversion efficiencies, and ethanol production cost.   Calculated results show that major contributions to the production cost are from biomass feedstock and syngas cleaning. A biomass-to-ethanol plant should be built at around 200 MW. Cost-competitive ethanol production can be realized with efficient equipments, optimized operation, cost-effective syngas cleaning technology, inexpensive raw material with low pretreatment cost, high-performance catalysts, off-gas and methanol recycling, optimal systematic configuration and heat integration, and a high-value byproduct.

abstract: The project aims at utilization of hydrothermal liquefaction (HTL) byproducts like biochar to grow microalgae. HTL is a promising method to convert wet algal biomasses into biofuels. The initial microalgae liquefaction at a temperature of 300 °C for 30 minute, converted 31.22 % of the Galdieria sulphuraria and 41.00 % of the Kirchneriella cornutum into biocrude. Upon changing the reactor from a 100 ml to a 250 ml reactor, the yield in biocrude increased to 31.48 % for G. sulphuraria and dropped to 38.05 % for K. cornutum. Further, energy recoveries based on calorific values of HTL products were seen to drop by about 5 % of the 100 ml calculated values in the larger reactor. Biochar from HTL of G. sulphuraria at 300 °C showed 15.98 and 5.27 % of phosphorous and nitrogen, respectively. HTL products from the biomass were analyzed for major elements through ICP-OES and CHNS/O. N and P are macronutrients that can be utilized in growing microalgae. This could reduce the operational demands in growing algae like, phosphorous mined to meet annual national demand for aviation fuel. Acidic leaching of these elements as phosphates and ammoniacal nitrogen was studied. Improved leaching of 49.49 % phosphorous and 95.71 % nitrogen was observed at 40 °C and pH 2.5 over a period of 7 days into the growth media. These conditions being ideal for growth of G. sulphuraria, leaching can be done in-situ to reduce overhead cost. Growth potential of G. sulphuraria in leached media was compared to a standard cyanidium media produced from inorganic chemicals. Initial inhibition studies were done in the leached media at 40 °C and 2-3 vol. % CO2 to observe a positive growth rate of 0.273 g L-1 day-1. Further, growth was compared to standard media with similar composition in a 96 well plate 50 μL microplate assay for 5 days. The growth rates in both media were comparable. Additionally, growth was confirmed in a 240 times larger tubular reactor in a Tissue Culture Roller drum apparatus. A better growth was observed in the leached cyanidium media as compared to the standard variant. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2017

This diploma thesis "Reasons why there was a food crisis in 2007 and 2008" summarizes and analyzes to what extent contributed particular factors to food crises all around the world in 2007 and 2008. Media and some well known international organizations believed that the main factors that caused last food crises were bio-fuels and significantly increased demand from China and India. This diploma thesis summarizes all main factors and comes to conclusion that the main factor that should be eliminated as soon as possoble is the problem with global climatic changes. Several international organizations have discussed this issue on international and global level for several years so let us hope we will not only discuss but we will do some active and concrete steps to solve this global problem. Of course the other factors need to be eliminated or at least moderated in the future as well. None of the crises occurs because of some concrete factor. It is always set of reasons that have caused some global problem.

Development of civilization faces a challenge of developing the resources of energy demand for the modern life. Extensive use of conventional fuel resources like crude oil and coal rise up a serious problem of increasing CO2 emission. New records levels of CO2 were registered during the early beginning of industrial revolution (http://climate.nasa.gov/evidence). Now a day’s more attention is oriented towards developing of biomass power stations owing to the increasing of conventional fuel prices and due to the potential to be CO2 neutral. One of the essential issues to successfully simulate and design efficient equipment for best utilization of the bio-fuel is to have better understanding of the interaction of bio-particles and the carrier gas. Almost, all two-phase flow system dealing with bio-mass power is turbulent flow. A unifying theory of turbulence does not yet exist. When particles are suspended into such a flow the flow becomes even more complicated and the resulting interactions between the particles and turbulent structures are not fully understood. For non-spherical particles, like most of the bio-mass particles found in cyclone filters and biomass gasification and combustion, the interactions of the particles and the fluid in turbulent flow are extremely complex while theories exists for low Reynolds number flow. The carrier phase turbulence alters the dispersed phase translational and rotational motion and the particles influence the detailed and overall flow of the carrier phase. The presence of the particles may also modify the turbulence of the fluid.To achieve my objective, to study the interaction of bio-particles with the carrier phase, and because of the complexity of the mechanisms related to such flow, it was essential to start to develop the knowledge on the possible mechanisms for the interactions and the importance of each of these interactions, see Paper A. Also, the controlling parameter which may have qualitative and/or quantitative influence of the flow interaction is covered by Paper A. To enable different types of experiments with PIV and LDA, a horizontal rectangular duct was designed and constructed. Design details and test is presented in Paper B. An introductory experimental series was performed in the current set-up using a high spatial resolution PIV system and the results can be found in Paper C.

The current societal needs for fuels and chemical commodities strongly depend on fossil resources. This dependence can lead to economic instabilities, political problems and insecurity of supplies. Moreover, global warming, which is associated with the massive use of fossil resources, is a dramatic “collateral damage” that endangers the future of the planet. Biomass is the main renewable source available today that can, produce various liquid, gaseous and solid products. Due to their lignocellulosic origin are considered CO2 neutral and thus can generate CO2 credits. Biomass processing can meet to the challenge of reducing of fossil resources by producing a liquid feedstock that can lessen the “fossil dependence” and /or meet the increased demand via a rapidly emerging thermochemical technology: pyrolysis. The ultimate goal of this process is to produce liquid with improved properties that could directly be used as liquid fuel, fuel additive and/or feedstock in modern oil refineries and petrochemical complexes. However, the liquids derived from biomass thermal processing are problematic with respect to their handling and end use applications. Thus, alternative routes of advanced liquid feedstock production are needed. Heterogeneous catalysis has long served the oil refining and petrochemical industries to produce a wide range of fuels and products. The combination of biomass pyrolysis and heterogeneous catalysis (by bringing in contact the produced vapours/liquids with suitable catalysts) is a very promising route. In this dissertation, the exploitation of biomass to produce of liquid feedstock via pyrolysis over a multifunctional catalyst and in a steam atmosphere is investigated.  Steam pyrolysis in a fixed bed reactor demonstrated that steam can be considered a reactive agent even at lower temperatures affecting the yields and the composition of all the products. The devolatilisation accelerates and the amount of final volatile matter in the char. Fast pyrolysis in the presence of steam results in improved and controlled thermal decomposition of the biomass; higher liquid yields and slightly deoxygenated liquid products are also obtained. Steam pyrolysis over a bi-metallic Ni-V catalyst can produce liquids of improved quality (lower O content) and also provide routes for selective deoxygenation. However, a decrease in liquid yield was observed. The combination of metal and acid catalysts (Ni-V/HZSM5) shows enhanced deoxygenation activity and increased H preservation in the produced liquid. The final O content in the liquid was 12.83wt% at a zeolite (HZSM5) loading of~75wt%; however, the yield of the obtained liquid was substantially decreased. Moreover, increased coke formation on the catalyst was observed at highest zeolite rate. The increased catalyst space time (τ) results in a lower liquid yield with reduced oxygen (7.79 wt% at τ =2h) and increased aromatic content. The coke deposited per unit mass of catalyst is lower for longer catalyst space times, while the char yield seems to be unaffected. The evaluation of the stability of the hybrid catalyst showed no significant structural defects and activity loss when the catalyst was regenerated at a low temperature (550οC). / Det nuvarande samhällets behov av bränslen och kemiska produkter är starkt knutet till fossila resurser. Detta beroende kan leda till ekonomisk instabilititet, politiska svårigheter och osäker leveranssäkerhet. Dessutom riskeras allvarliga skador i framtiden på grund av global uppvärmning, vilket är relaterat till det ökande och massiva användandet av fossila bränslen.   Biomassa är en förnybar resurs som är tillgänglig idag, möjlig att utnyttja för produktion av diverse flytande, gasformiga och fasta produkter. Dessa produkter, beroende på biogeniskt ursprung, betraktas som koldioxidneutrala och kan därför generera koldioxidkrediter. Processande av biomassa kan möta utmaningen av minskad fossilbränsleanvändning, genom produktion av flytande råvara som kan reducera beroendet och/eller möta ökad efterfrågan, via en snabbt expanderande termokemisk teknik - pyrolys.    Det slutgiltiga målet med en sådan process är att producera en flytande produkt med förbättrade egenskaper som direkt skulle kunna användas som flytande bränslen, bränsleadditiv och/eller som råmaterial i moderna oljeraffinaderier och petrokemiska komplex. Vätskor som utvinns från termiska processer är problematiska med avseende på hantering och slutanvändningen i olika applikationer, därmed behövs olika spår för produktion av avancerade flytande råvaror. Heterogena katalysen har länge tjänat raffinaderi- och petrokemisk industri, som producerar ett brett utbud av bränslen och produkter, lämpliga för säker användning. Kombinationen av biomassapyrolys och heterogen katalys  (genom att bringa pyrolysångorna i kontakt med en lämplig katalysator) är ett väldigt lovande spår. I denna avhandling undersöks användningen av biomassa för produktion av flytande råvara, via pyrolys över en flerfunktionel katalysator i ångatmosfär. Ångpyrolys i en fastbäddsreaktor visade att ånga kan betraktas som ett reaktivt medium,  även vid låga temperaturer, som påverkar utbyten och sammansättning av alla produkter. Avgasningen sker snabbare och den slutliga flykthalten i kolresterna blir lägren vid användning av ånga. Snabbpyrolys i ångatmosfär resulterar i förbättrad och mer kontrollerad termisk nedbrytning av biomassa, vilket ger ett högre vätskeutbyte och en något deoxygenerad flytande produkten. ångpyrolys i kombination med bimetalliska NiV-katalysatorer, ger upphov till en flytande råvara med förbättrad kvalitet och selektiv deoxygenering. Dock med ett minskande utbyte som följd. Kombinationen av metall och en sur katalysator (Ni-V/HZSM5) visade förstärkt deoxygenering med bibehållen vätehalt i den flytande produkten. Den slutliga syrehalten i vätskan var 12.83 vikt% vid en zeolithalt (HZSM5) på 75 vikt%, dock med ett kraftigt minskande vätskeutbyte. Dessutom noterades ökad koksbildning på katalysatormaterialet med den högsta zeolithalten. Ökad rymd-tid  för katalysatorn (τ) ger ett lägre vätskeutbyte med reducerad syrehalt (7.79 vikt% vid τ=2h) och ökad aromathalt. Koksbildning på ytan, per massenhet katalysatormaterial, minskade vid längre rymd-tider medan utbytet av kolrester förblev opåverkat.  Undersökningen av stabiliteten hos hybridkatalysatorn visade inga strukturella defekter och ingen signifikant minskad aktivitet efter regenerering vid låg temperatur (550οC). / Οι σύγχρονες ανάγκες της κοινωνίας για παραγωγή υγρών καυσίμων και χημικών προϊόντων εξαρτώνται από τους ορυκτούς πόρους. Αυτή η εξάρτηση μπορεί να οδηγήσει σε οικονομικά προβλήματα, πολιτκή αστάθεια, όπως επίσης και αβεβαιότητα στις προμήθειες της ενεργειακής εφοδιαστικής αλυσίδας. Επιπροσθέτως, μια δραματική «παράπλευρη απώλεια» η οποία θέτει σε κίνδυνο το μέλλον του πλανήτη είναι η υπερθέρμανσή του, η οποία έχει συσχετισθεί με την εκτεταμένη χρήση ορυκτών πόρων. Σήμερα, η βιομάζα είναι η μόνη ανανεώσιμη πηγή από την οποία μπορούν να παραχθούν υγρά, αέρια και στερεά προϊόντα, που λόγω της λιγνοκυταρρινικής τους προελεύσεως, η συνεισφορά τους στις εκομπές CO2 θεώρειται μηδενική. Η θερμοχημική επεξεργασία της βιομάζας συνεισφέρει στον περιορισμό της χρήσης ορυκτών πόρων, με την παραγωγή υγρών προϊόντων, τα οποία μπορούν να μειώσουν την εξάρτηση ή /και την αυξημένη ζήτηση μέσω μιας ταχέως αναπτυσόμενης τεχνολογίας, της πυρόλυσης. Στόχος της διεργασίας είναι η παραγωγή υγρών προϊόντων με ιδιότητες, που επιτρέπουν την απευθείας χρήση τους ως υγρά καύσιμα ή ως πρώτη ύλη, για την παραγώγη χημικών προϊόντων σε συγχρονες μονάδες διύλισης πετρελαίου και σε πετροχημικά συγκτροτήματα. Εν τούτοις, τα υγρά προϊόντα της θερμικής διάσπασης (πυρόλυση) είναι προβληματικά στη διαχείρηση και στις τελικές τους εφαρμογές, λόγω της σύστασής τους. Ως εκ τούτου, απαιτούνται νέες τεχνικές για παραγωγή προηγμένων υγρών προοϊόντων. Η ετερογενής κατάλυση έχει επιτυχώς εφαρμοσθεί στην πετρελαϊκή και χημική βιομηχανία, παράγοντας ένα μεγάλο εύρος προϊόντων. Ο συνδυασμός της με την πυρόλυση (φέρνοντας σε επαφη τα υγρά/ατμούς με κατάλληλο καταλύτη) αποτελεί μια πολλά υποσχόμενη ενναλακτική. Στην παρούσα διατριβή μελετάται η αξιοποίηση βιομάζας για παραγωγή υγρών προϊόντων μέσω καταλυτικής πυρόλυσης, με χρήση πολυλειτουρικού καταλύτη (multi-functional catalyst) υπό την παρουσία ατμού. Η χρήση ατμου κατά τη διαρκειά πυρόλυσης βιομαζας σε αντιδραστήρα σταθερής κλίνης, μεταβάλει τη σύσταση των επιμέρους προϊόντων. Η παρουσία ατμού έχει ως αποτέλεσμα την ταχύτερη αποπτητικοποίηση του υλικού, ενώ παράλληλα η περιεκτικότητα του υπολειπόμενου εξανθρακώματος σε πτητικά είναι μικρότερη. Τα πειραματικά αποτελέσματα ταχείας πυρόλυσης σε αντιδραστήρα ρευστοστερεάς κλίνης δείχνουν ό,τι η χρήση ατμού βελτιώνει την θερμική διάσπαση της βιομαζας, αυξάνοντας την απόδοση σε υγρά προϊοντά, ενώ παράλληλα βοηθάει στην αποξυγόνωσή τους. Ο συνδυασμός της πυρόλυσης υπό την παρουσία ατμού και διμεταλλικού καταλύτη νικελίου–βαναδίου μπορεί να  βελτιώσει την ποιότητα των παραγόμενων υγρών (αποξυγόνωση) με παραλλήλη μείωση της απόδοσής τους, ενώ μπορεί να  παράγει προϊόντα εκλεκτικής αποξυγόνωσης. Συνδυασμός μεταλλικών και ζεολιθικών καταλυτών (Ni-V/HZSM5) εμφανίζει βελτιωμένη δραστικότητα στις αντιδράσεις αποξυγόνωσης, με παράλληλη συγκράτηση υδρογόνου (Η) στα υγρά προϊόντα. Η τελική περιεκτικότητα των υγρών προϊόντων σε οξυγόνου (Ο) μετά από 90 min αντίδρασης είναι 12.83 wt%, με περιεκτικότητα ζεόλιθου (ΗZSΜ5) ~75 wt% στον καταλύτη. Ωστόσο, η αυξηση της περεικτικότητας σε ζεόλιθο έχει ως αποτέλεσμα την αύξηση των επικαθήσεων άνθρακα επάνω στον κατάλυτη, καθώς και την σημαντική μειώση της απόδοσης των υγρών προϊόντων (24.35wt% επι ξηρής βιομάζας).  Η αύξηση του χώρου χρόνου του καταλύτη (τ) έχει ως αποτέλεσμα: τη μείωση των υγρών προϊόντων, τη μείωση του περιεχόμενου Ο στα υγρά προϊόντα (7.79 wt% at τ =2h), την αύξηση των αρωματικών υδρογονανθράκων και τη μείωση του επικαθήμενου κωκ ανά μονάδα μάζας καταλύτη. Η απόδοση του εξανθρακώματος παρέμεινε πρακτικά αμετάβλητη. Η αναγέννηση του υβριδικού καταλύτη σε χαμηλές θερμοκρασιές (550οC) δεν επέφερε σημαντικές δομικές αλλαγές και απώλεια δραστικότητας. / <p>QC 20140306</p>

[ES] El presente trabajo de investigación está centrado en la valorización y la mejora del bioetanol, empleando catalizadores heterogéneos, en un reactor de flujo continuo a escala de laboratorio. En primer lugar, en los laboratorios del Departamento de Química Industrial de la Universidad de Bolonia (Unibo), se ha estudiado la conversión catalítica del etanol en fase gaseosa sobre catalizadores basados en hidroxiapatitas (HAP). Los ensayos catalíticos se llevaron a cabo alimentando un reactor de lecho fijo a escala de laboratorio, empleando el catalizador en forma de pellets y una mezcla de etanol/He, en el rango de temperatura de 300-600 ºC. El interés se focalizó en la formación de productos de alta condensación, con el fin de obtener una mezcla orgánica que pueda ser empleada como bio-combustible. Tras seleccionar las condiciones de reacción, se sintetizaron y probaron diferentes hidroxiapatitas con capacidad de intercambio iónico que poseen metales de transición (Fe, Cu) y metales alcalinotérreos (Sr) en su composición. Mientras que las HAP conteniendo metales de transición actúan esencialmente como catalizadores ácidos, produciendo principalmente el producto de la deshidratación del etanol, el etileno, el catalizador de Sr-HAP permite la formación de una mezcla de reacción compleja, la cual necesita de una mayor optimización para cumplir con los requisitos adecuados para su posterior empleo como biofuel. A continuación, en los laboratorios del Instituto de Tecnología Química (ITQ) de la Universidad Politécnica de Valencia (UPV), el estudio se centró en dos materiales catalíticos diferentes, el óxido de zirconio y la sepiolita, una arcilla natural abundante en España. Ambos materiales se han probados para la transformación de etanol, en el rango de temperatura de 300-450 ºC, empleando un reactor de lecho fijo a escala laboratorio, con el catalizador en forma de pellets, y usando una mezcla de etanol/N2. Los catalizadores con óxido de zirconio se prepararon mediante dos métodos diferentes, precipitación e hidrotermal, variando algunos de los parámetros de síntesis (pH, naturaleza de la base), y empleando algunos metales de transición como elementos dopantes (Ti, Y). La presencia de un elemento dopante en la estructura de la zirconia favorece la estabilización de las fases tetragonal y cúbica frente a fase monoclínica. Todas las muestras exhibieron un comportamiento ácido. Resulta interesante que la zirconia dopada con 5%mol de Ti exhibe un comportamiento catalítico diferente, produciendo el dietiléter como principal producto a 300ºC, mientras que los otros catalizadores producen principalmente etileno, ambos, productos de la deshidratación del etanol. Por otra parte, se ha estudiado el efecto de las propiedades ácido-base de la sepiolita, modificada con metales alcalinos (Na, K, Cs) y cargas de metal variables (2, 4, 5, 7, 14 wt%), y de las propiedades redox de la sepiolita, como soporte de CuO o NiO, sobre la conversión catalítica de etanol a n-butanol. Las sepiolitas tratadas térmicamente actúan principalmente como catalizadores ácidos, produciendo preferentemente productos de deshidratación del etanol (etileno y dietiléter). Mientras que la presencia de un metal de transición no favorece la producción de n-butanol, la presencia de un metal alcalino en el sistema catalítico parece ser crucial para la formación de n-butanol. Los mejores resultados en términos de actividad (conversión de etanol, 59%) y selectividad (30%) de n-butanol se han obtenido a 400 ºC y un tiempo de contacto, W/F, de 2 g/mL·s, con el catalizador basado en sepiolita calcinada a 500 ºC, y modificada con 7 wt% de cesio, mediante impregnación en fase acuosa. / [CA] El present treball de recerca està centrat en la valorització i la millora del bioetanol, emprant catalitzadors heterogenis, en un reactor de flux continu a escala de laboratori. En primer lloc, en els laboratoris del Departament de Química Industrial de la Universitat de Bolonya (Unibo), s'ha estudiat la conversió catalítica de l'etanol en fase gasosa sobre catalitzadors basats en hidroxiapatitas (HAP). Els assajos catalítics es van dur a terme alimentant un reactor de llit fix, a escala de laboratori, contenint el catalitzador en forma de pèl·lets amb una mescla d'etanol/He, en el rang de temperatura de 300-600 °C. L'interés es va focalitzar en la formació de productes d'alta condensació, amb la finalitat d'obtindre una mescla orgànica que puga ser emprada com a bio-combustible. Després de seleccionar les condicions de reacció, es van sintetitzar i van provar diferents hidroxiapatitas amb capacitat d'intercanvi iònic que posseeixen metalls de transició (Fe, Cu) i metalls alcalinotérreos (Sr) en la seua composició. Mentre que les HAP contenint metalls de transició actuen essencialment com a catalitzadors àcids produint principalment el producte de la deshidratació de l'etanol, l'etilé, el catalitzador de Sr-HAP permet la formació d'una mescla de reacció complexa, la qual necessita d'una major optimització per a complir amb els requisits adequats per a la seua posterior ocupació com biofuel. A continuació, en els laboratoris de l'Institut de Tecnologia Química (ITQ) de la Universitat Politècnica de València (UPV), l'estudi es va centrar en dos materials catalítics diferents, l'òxid de zirconio i sepiolita, una argila natural abundant a Espanya. Tots dos materials s'han provats per a la transformació d'etanol en el rang de temperatura de 300-450 °C, emprant un reactor de llit fix a escala laboratori, contenint el catalitzador en forma de pèl·lets, i usant una mescla d'etanol/N2 Els catalitzadors amb òxid de zirconio es van preparar mitjançant dos mètodes diferents, precipitació i hidrotermal, variant alguns dels paràmetres de síntesis (pH, naturalesa de la base), i emprant alguns metalls de transició com a elements dopants (Ti, Y). La presència d'un element dopant en l'estructura de la zircònia afavoreix l'estabilització de les fases tetragonal i cúbica enfront de fase monoclínica Totes les mostres van exhibir un comportament àcid. Resulta interessant que la zircònia dopada amb 5%mol de Ti exhibisca un comportament catalític diferent, produint el dietiléter com a principal producte a 300 °C, mentre que les altres mostres produeixen principalment etilé, tots dos, productes de la deshidratació de l'etanol. D'altra banda s'ha estudiat l'efecte de les propietats àcid-base de la sepiolita, modificada amb metalls alcalins (Na, K, Cs) i càrregues de metall variables (2, 4, 5, 7, 14 wt%), i de les propietats redox de la sepiolita, com a suport de CuO o NiO, sobre la conversió catalítica d'etanol a n-butanol. Les sepiolites tractades tèrmicament actuen principalment com a catalitzadors àcids, produint principalment productes de deshidratació de l'etanol (etilé i dietiléter). Mentre que la presència d'un metall de transició no afavoreix la producció de n-butanol, la presència d'un metall alcalí en el sistema catalític sembla ser crucial per a la formació del n-butanol. Els millors resultats en termes d'activitat (conversió d'etanol, 59%) i selectivitat (30%) de n-butanol s'han obtingut a 400°C i un temps de contacte, W/F, de 2 g/ml·s amb el catalitzador compost de sepiolita calcinada a 500 °C, i modificada amb 7 wt% de Cs. / [EN] The present research work focused on the valorisation and upgrading of bio-ethanol over heterogeneous catalysts in a lab-scale continuous gas-flow system. Firstly, in the laboratories of the Department of Industrial Chemistry of the University of Bologna (Unibo), the catalytic ethanol gas-phase conversion was studied over hydroxyapatite (HAP) based catalysts. Catalytic tests have been carried out in the temperature range 300-600°C by feeding an ethanol/He mixture into a quartz lab-scale fixed bed reactor of pelletized catalyst. The focus was placed on enhancing the formation of higher condensation products in order to obtain an organic mixture with application as bio-fuel. After choosing the reaction conditions, ion-exchanged hydroxyapatite with transition metals (i.e., Fe, Cu) and alkaline earth metal (i.e., Sr) have been synthesized and tested. While the transition metal-exchanged HAP acted essentially as acid catalysts, yielding mainly the dehydration product of ethanol, ethylene, the Sr-HAP catalyst led to the formation of a complex reaction mixture the composition of which need further optimization in order to fill the requisite to be used as fuel-blend. Then, in the laboratories of the Institute of Chemical Technology (ITQ) of the Polytechnic University of Valencia (UPV), the study focused on two different catalytic materials, zirconium oxide and the natural clay sepiolite. Both the materials have been tested into the ethanol transformation carrying out the catalytic tests in the temperature range 300-450 °C by feeding an ethanol/N2 mixture into a quartz lab-scale fixed bed reactor of pelletized catalyst. Zirconium-oxide based catalysts have been prepared through two different methods, precipitation and hydrothermal, by varying some synthetic parameters (i.e., pH, the nature of the base) and by adding a transition metal as dopant agent (i.e., Ti and Y). The presence of a dopant into the zirconia structure favoured the stabilization of the tetragonal or cubic phase against the monoclinic one. All samples exhibited acidic behaviour. Interestingly, 5%mol Ti-doped zirconia exhibited a different catalytic behaviour yielding diethyl ether as major product at 300°C, while all the others samples produced mainly ethylene, both dehydration products of ethanol. The effect of acid-base properties of sepiolite, using alkali metals (i.e., Na, K, Cs) with different metal loading (i.e., 2, 4, 5, 7, 14 wt%) as promoters, and of the redox properties of sepiolite-supported CuO or NiO, on the catalytic conversion of ethanol into n-butanol has been investigated. Thermal treated sepiolite samples mainly acted as acid catalyst, yielding preferentially the dehydration products of ethanol (ethylene and diethyl ether). While the presence of a transition metal did not favour n-butanol production, the presence of an alkali metal into the catalytic system appeared to be crucial for n-butanol formation. Best results in terms of activity (ethanol conversion, 59%) and n-butanol selectivity (30%) where obtained at 400ºC and a contact time, W/F, of 2 g/mL·s over the catalyst consisting of sepiolite calcined at 500ºC modified with 7 wt% of cesium. / Balestra, G. (2022). Valorization of Bio-Alcohols into Added Value Chemicals [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/184991 / TESIS

L'épuisement des réserves pétrolières et l'augmentation de la concentration du gaz à effet de serre CO2 sont les deux principaux problèmes connus liés à l'utilisation des carburants fossiles. Les biocarburants apparaissent comme un des moyens permettant à la fois une diminution de la dépendance au pétrole et une réduction de l'impact néfaste des moteurs automobiles sur l'environnement. Les biocarburants sont en effet considérés comme une source d'énergie renouvelable. L'objectif de cette thèse était de développer et valider les modèles cinétiques de combustion des composés oxygénés de biocarburants : l'éthanol, les biocarburants de deuxième-génération des familles du furane (furane, 2-méthylfurane, 2,5-diméthylfurane), du tétrahydrofurane (tétrahydrofurane, 2-méthyltétrahydrofurane) et le tétrahydropyrane, en utilisant les nouvelles données obtenues en flamme laminaire pré-mélangée à basse pression. De 20 à 60 produits ont été quantifiés par chromatographie en phase gazeuse et identifiés par couplage avec la spectrométrie de masse. Les résultats obtenus ont ensuite été utilisés pour analyser les voies de consommation des réactifs et de formation des produits, surtout pour les polluants, dans le but de mieux comprendre la chimie de la combustion de ces biocarburants. Ce rapport comprend 5 chapitres et une conclusion. Le premier chapitre présente une revue bibliographique des travaux antérieurs sur l'oxydation de l'éthanol et des éthers cycliques. Dans le second chapitre, le dispositif expérimental est décrit, en détaillant en particulier les nouveaux développements. Enfin les chapitres 3, 4, 5 présentent les résultats de l'étude de la combustion des composés étudiés / The decrease of petroleum reserves and the increase of concentration of greenhouse gas CO2 are the two major known problems related to the use of fossil fuels. Bio-fuels appear as a means allowing a decrease of the dependence on fossil fuels and a reduction of the harmful impact of engine on the environment. Bio fuels are considered as a source of renewable energy. The aim of this thesis was to develop and validate experimentally the high temperature kinetic models for the combustion of oxygenated compounds of bio-fuels: ethanol, second-generation bio-fuels of families of furan (furan, 2-methylfuran, 2,5-dimethylfuran), of tetrahydrofuran (tetrahydrofuran, 2 methyltetrahydrofuran), and tetrahydropyran, using new data obtained in laminar premixed low-pressure flame. About 20-60 products were quantified by gas chromatography and identified using mass spectrometry. The results obtained were then used to analyze the consumption pathways of fuels and the formation pathways of products, especially for pollutants, in order to better understand the combustion chemistry of these bio-fuels. This thesis report includes 5 chapters and a conclusion. The first chapter presents a review of the major works already published in the literature for the oxidation of ethanol and cyclic ethers. In the second chapter, the experimental setup of laminar premixed flame with the analytical techniques is described, detailing in particular new developments. Eventually, chapters 3, 4, 5 present the experimental and modeling results of the study of the combustion chemistry of the compounds studied

<p>The main accomplishments of this research are </p> <p>(1) developed a high fidelity computational methodology based on large eddy simulation to capture lean blowout (LBO) behaviors of different fuels; </p> <p>(2) developed fundamental insights into the combustion processes leading to the flame blowout and fuel composition effects on the lean blowout limits; </p> <p>(3) developed artificial intelligence-based models for early detection of the onset of the lean blowout in a realistic complex combustor. </p> <p>The methodologies are demonstrated by performing the lean blowout (LBO) calculations and statistical analysis for a conventional (A-2) and an alternative bio-jet fuel (C-1).</p> <p>High-performance computing methodology is developed based on the large eddy simulation (LES) turbulence models, detailed chemistry and flamelet based combustion models. This methodology is employed for predicting the combustion characteristics of the conventional fuels and bio-derived alternative jet fuels in a realistic gas turbine engine. The uniqueness of this methodology is the inclusion of as-it-is combustor hardware details such as complex hybrid-airblast fuel injector, thousands of tiny effusion holes, primary and secondary dilution holes on the liners, and the use of highly automated on the fly meshing with adaptive mesh refinement. The flow split and mesh sensitivity study are performed under non-reacting conditions. The reacting LES simulations are performed with two combustion models (finite rate chemistry and flamelet generated manifold models) and four different chemical kinetic mechanisms. The reacting spray characteristics and flame shape are compared with the experiment at the near lean blowout stable condition for both the combustion models. The LES simulations are performed by a gradual reduction in the fuel flow rate in a stepwise manner until a lean blowout is reached. The computational methodology has predicted the fuel sensitivity to lean blowout accurately with correct trends between the conventional and alternative bio-jet fuels. The flamelet generated manifold (FGM) model showed 60% reduction in the computational time compared to the finite rate chemistry model. </p> <p>The statistical analyses of the results from the high fidelity LES simulations are performed to gain fundamental insights into the LBO process and identify the key markers to predict the incipient LBO condition in swirl-stabilized spray combustion. The bio-jet fuel (C-1) exhibits significantly larger CH₂O concentrations in the fuel-rich regions compared to the conventional petroleum fuel (A-2) at the same equivalence ratio. It is observed from the analysis that the concentration of formaldehyde increases significantly in the primary zone indicating partial oxidation as we approach the LBO limit. The analysis also showed that the temperature of the recirculating hot gases is also an important parameter for maintaining a stable flame. If this temperature falls below a certain threshold value for a given fuel, the evaporation rates and heat release rated decreases significantly and consequently leading to the global extinction phenomena called lean blowout. The present study established the minimum recirculating gas temperature needed to maintain a stable flame for the A-2 and C-1 fuels. </p> The artificial intelligence (AI) models are developed based on high fidelity LES data for early identification of the incipient LBO condition in a realistic gas turbine combustor under engine relevant conditions. The first approach is based on the sensor-based monitoring at the optimal probe locations within a realistic gas turbine engine combustor for quantities of interest using the Support Vector Machine (SVM). Optimal sensor locations are found to be in the flame root region and were effective in detecting the onset of LBO ~20ms ahead of the event. The second approach is based on the spatiotemporal features in the primary zone of the combustor. A convolutional autoencoder is trained for feature extraction from the mass fraction of the OH ( data for all time-steps resulting in significant dimensionality reduction. The extracted features along with the ground truth labels are used to train the support vector machine (SVM) model for binary classification. The LBO indicator is defined as the output of the SVM model, 1 for unstable and 0 for stable. The LBO indicator stabilized to the value of 1 approximately 30 ms before complete blowout.