Suchergebnisse

According to the REACH regulation chemicals produced or imported to the European Union need to be assessed to manage the risk of potential hazard to human health and the environment. An increasing number of chemicals in commerce prompts the need for utilizing faster and cheaper alternative methods for this assessment, such as quantitative structure-activity or property relationships (QSARs or QSPRs). QSARs and QSPRs are models that seek correlation between data on chemicals molecular structure and a specific activity or property, such as environmental fate characteristics and (eco)toxicological effects. The aim of this thesis was to evaluate and develop models for the hazard assessment of industrial chemicals and the exposure assessment of pharmaceuticals. In focus were the identification of chemicals potentially demonstrating carcinogenic (C), mutagenic (M), or reprotoxic (R) effects, and endocrine disruption, the importance of metabolism in hazard identification, and the understanding of adsorption of ionisable chemicals to sludge with implications to the fate of pharmaceuticals in waste water treatment plants (WWTPs). Also, issues related to QSARs including consensus modelling, applicability domain, and ionisation of input structures were addressed. The main findings presented herein are as follows: QSARs were successful in identifying almost all carcinogens and most mutagens but worse in predicting chemicals toxic to reproduction. Metabolic activation is a key event in the identification of potentially hazardous chemicals, particularly for chemicals demonstrating estrogen (E) and transthyretin (T) related alterations of the endocrine system, but also for mutagens. The accuracy of currently available metabolism simulators is rather low for industrial chemicals. However, when combined with QSARs, the tool was found useful in identifying chemicals that demonstrated E- and T- related effects in vivo. We recommend using a consensus approach in final judgement about a compound's toxicity that is to combine QSAR derived data to reach a consensus prediction. That is particularly useful for models based on data of slightly different molecular events or species. QSAR models need to have well-defined applicability domains (AD) to ensure their reliability, which can be reached by e.g. the conformal prediction (CP) method. By providing confidence metrics CP allows a better control over predictive boundaries of QSAR models than other distance-based AD methods. Pharmaceuticals can interact with sewage sludge by different intermolecular forces for which also the ionisation state has an impact. Developed models showed that sorption of neutral and positively-charged pharmaceuticals was mainly hydrophobicity-driven but also impacted by Pi-Pi and dipole-dipole forces. In contrast, negatively-charged molecules predominantly interacted via covalent bonding and ion-ion, ion-dipole, and dipole-dipole forces. Using ionised structures in multivariate modelling of sorption to sludge did not improve the model performance for positively- and negatively charged species but we noted an improvement for neutral chemicals that may be due to a more correct description of zwitterions. Overall, the results provided insights on the current weaknesses and strengths of QSAR approaches in hazard and exposure assessment of chemicals. QSARs have a great potential to serve as commonly used tools in hazard identification to predict various responses demanded in chemical safety assessment. In combination with other tools they can provide fundaments for integrated testing strategies that gather and generate information about compound's toxicity and provide insights of its potential hazard. The obtained results also show that QSARs can be utilized for pattern recognition that facilitates a better understanding of phenomena related to fate of chemicals in WWTP. ; Enligt kemikalielagstiftningen REACH måste kemikalier som produceras i eller importeras till Europeiska unionen riskbedömas avseende hälso- och miljöfara. Den ökande mängden kemikalier som används i samhället kräver snabbare och billigare alternativa riskbedömningsmetoder, såsom kvantitativa struktur-aktivitets- eller egenskapssamband (QSARs eller QSPRs). QSARs och QSPRs är datamodeller där samband söks korrelationer mellan data för kemikaliers struktur-relaterade egenskaper och t.ex. kemikaliers persistens eller (eko)toxiska effekter. Målet med den här avhandlingen var att utvärdera och utveckla modeller för riskbedömning av industri kemikalier och läkemedel för att studera hur QSARs/QSPRs kan förbättra riskbedömningsprocessen. Fokus i avhandlingen var utveckling av metoder för identifiering av potentiellt cancerframkallande (C), mutagena (M), eller reproduktionstoxiska (R) kemikalier, och endokrint aktiva kemikalier, att studera betydelsen av metabolism vid riskbedömning och att öka vår förståelse för joniserbara kemikaliers adsorption till avloppsslam. Avhandlingen behandlar även konsensusmodellering, beskrivning av modellers giltighet och betydelsen av jonisering för kemiska deskriptorer. De huvudsakliga resultaten som presenteras i avhandlingen är: QSAR-modeller identifierade nästan alla cancerframkallande ämnen och de flesta mutagener men var sämre på att identifiera reproduktionstoxiska kemikalier. Metabolisk aktivering är av stor betydelse vid identifikationen av potentiellt toxiska kemikalier, speciellt för kemikalier som påvisar östrogen- (E) och sköldkörtel-relaterade (T) förändringar av det endokrina systemet men även för mutagener. Träffsäkerheten för de tillgängliga metabolismsimulatorerna är ganska låg för industriella kemikalier men i kombination med QSARs så var verktyget användbart för identifikation av kemikalier som påvisade E- och T-relaterade effekter in vivo. Vi rekommenderar att använda konsensusmodellering vid in silico baserad bedömning av kemikaliers toxicitet, d.v.s. att skapa en sammanvägd förutsägelse baserat på flera QSAR-modeller. Det är speciellt användbart för modeller som baseras på data från delvis olika mekanismer eller arter. QSAR-modeller måste ha ett väldefinierat giltighetsområde (AD) för att garantera dess pålitlighet vilket kan uppnås med t.ex. conformal prediction (CP)-metoden. CP-metoden ger en bättre kontroll över prediktiva gränser hos QSAR-modeller än andra distansbaserade AD-metoder. Läkemedel kan interagera med avloppsslam genom olika intermolekylära krafter som även påverkas av joniseringstillståndet. Modellerna visade att adsorptionen av neutrala och positivt laddade läkemedel var huvudsakligen hydrofobicitetsdrivna men också påverkade av Pi-Pi- och dipol-dipol-krafter. Negativt laddade molekyler interagerade huvudsakligen med slam via kovalent bindning och jon-jon-, jon-dipol-, och dipol-dipol-krafter. Kemiska deskriptorer baserade på joniserade molekyler förbättrade inte prestandan för adsorptionsmodeller för positiva och negativa joner men vi noterade en förbättring av modeller för neutrala substanser som kan bero på en mer korrekt beskrivning av zwitterjoner. Sammanfattningsvis visade resultaten på QSAR-modellers styrkor och svagheter för användning som verkyg vid risk- och exponeringsbedömning av kemikalier. QSARs har stor potential för bred användning vid riskidentifiering och för att förutsäga en mängd olika responser som krävs vid riskbedömning av kemikalier. I kombination med andra verktyg kan QSARs förse oss med data för användning vid integrerade bedömningar där data sammanvägs från olika metoder. De erhållna resultaten visar också att QSARs kan användas för att bedöma och ge en bättre förståelse för kemikaliers öde i vattenreningsverk.

Acellular nerve allografts (ANGs) represent a promising alternative in nerve repair. Our aim is to improve the structural and biomechanical properties of biocompatible Sondell (SD) and Roosens (RS) based ANGs using genipin (GP) as a crosslinker agent ex vivo. The impact of two concentrations of GP (0.10% and 0.25%) on Wistar rat sciatic nerve-derived ANGs was assessed at the histological, biomechanical, and biocompatibility levels. Histology confirmed the differences between SD and RS procedures, but not remarkable changes were induced by GP, which helped to preserve the nerve histological pattern. Tensile test revealed that GP enhanced the biomechanical properties of SD and RS ANGs, being the crosslinked RS ANGs more comparable to the native nerves used as control. The evaluation of the ANGs biocompatibility conducted with adipose-derived mesenchymal stem cells cultured within the ANGs confirmed a high degree of biocompatibility in all ANGs, especially in RS and RS-GP 0.10% ANGs. Finally, this study demonstrates that the use of GP could be an efficient alternative to improve the biomechanical properties of ANGs with a slight impact on the biocompatibility and histological pattern. For these reasons, we hypothesize that our novel crosslinked ANGs could be a suitable alternative for future in vivo preclinical studies. ; This research was funded by the Spanish "Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica, Ministerio de Economía y Competitividad (Instituto de Salud Carlos III), Grants No FIS PI14-1343, FIS PI17-0393, FIS PI20-0318 co-financed by the "Fondo Europeo de Desarrollo Regional ERDF-FEDER European Union"; Grant No P18-RT-5059 by "Plan Andaluz de Investigación, Desarrollo e Innovación (PAIDI 2020), Consejería de Transformación Económica, Industria, Conocimiento y Universidades, Junta de Andalucía, España"; and Grant A-CTS-498- UGR18 by "Programa Operativo FEDER Andalucía 2014–2020, Universidad de Granada, Junta de Andalucía, España", co-funded by ERDF-FEDER, the European Union. ; Yes

[SPA] Los dispositivos electrocrómicos de transmisión variable son capaces de modular la luz que pasa a través suyo, por medio del paso de una corriente eléctrica. Sus aplicaciones más importantes pasan por el diseño de ventanas inteligentes en arquitectura, espejos retrovisores antirreflectantes en automoción o sistemas de visión adaptables para uso deportivo, profesional o militar. Estos dispositivos son celdas electroquímicas compuestas por materiales para los que los procesos de reducción u oxidación provocan cambios de color: materiales electrocrómicos. Dentro de los materiales con estas características, los polímeros conductores orgánicos se presentan como excelentes candidatos frente a los metales de transición inorgánicos, debido a su gran versatilidad en cuanto a colores alcanzables, facilidad de procesado, y bajo coste. Una configuración de celda en la que los dos electrodos sean activos electrocrómicamente, configuración dual, se presenta como una buena opción de cara a mejorar el rendimiento del dispositivo. El trabajo desarrollado en esta tesis pretende hacer hincapié en las relaciones existentes entre procesos electroquímicos y cambios de color, sobre la base de dos aspectos: estudio individual de los materiales constituyentes, y estudio del sistema dual. El objetivo es la optimización, tanto de los procesos electroquímicos como ópticos, de sistemas duales de polímeros conductores, obteniendo metodologías experimentales capaces de caracterizar, predecir teóricamente, y finalmente diseñar dispositivos electrocrómicos duales óptimos. La primera parte del estudio se centra en el desarrollo de la metodología precisa para obtener la caracterización óptica de un material electrocrómico en función de sus características electroquímicas, como son la carga redox total consumida durante sus procesos de oxidación o reducción, y la ventana de potencial donde ocurren estos procesos. Los materiales empleados son los polímeros conductores poli-3,4-etilendioxitiofeno (PEDOT) y poli-3,6-bis(2-(3,4-etilendioxi)tienil)-N-metilcarbazol (PBEDOT-NMCz). El primero de ellos se colorea mediante la reducción, mientras que el segundo lo hace durante la oxidación, además presentando coloraciones complementarias, por lo que pueden ser utilizados en un dispositivo electrocrómico dual. En base a los resultados obtenidos, durante la segunda parte se realiza un estudio teórico, junto con su comprobación experimental, sobre las respuestas ópticas resultantes en un sistema que incluya varias capas electrocrómicas. Las relaciones obtenidas permiten predecir la configuración de máximo contraste para un sistema dual, en función de las características electroquímicas de cada componente individual. El sistema dual estudiado es PEDOT / PBEDOT-NMCz. En una tercera sección, se propone y desarrolla una metodología experimental capaz de registrar los estados de oxidación individuales en cada electrodo durante el funcionamiento de un dispositivo dual, obteniendo una información directa sobre el rendimiento del dispositivo. Esto permite el estudio de la influencia que varias variables, como son el ratio de carga redox entre las dos películas constituyentes, el potencial aplicado al dispositivo, y el estado de oxidación inicial de los polímeros, tienen sobre el rendimiento del dispositivo. El objetivo final es la construcción de dispositivos electrocrómicos que puedan ser empleados fuera del ámbito académico. Para ello, y por motivos de seguridad para el usuario final, es necesario utilizar medios electrolíticos sólidos en la celda. Asimismo, es necesario fabricar dispositivos de unas dimensiones adecuadas. En la siguiente sección, se estudia la construcción de este tipo de dispositivos para el sistema PEDOT/PBEDOT-NMCz. La información obtenida en las secciones anteriores se utiliza para determinar las combinaciones con el máximo contraste posible. Se discuten problemas relativos a la deposición de polímeros en grandes superficies (alrededor de 30 cm2), la optimización de la velocidad de cambio de color cuando se utiliza un medio sólido, así como la capacidad de ajuste y retención del color en ausencia de potencial aplicado. Se propone un método de ensamblado fácil y rápido consistente en la solidificación del gel por curado ultravioleta. Por último, se propone una técnica electroquímica sencilla y rápida para detectar posibles dispositivos defectuosos. Los dispositivos electrocrómicos construidos presentan una superficie activa de 30 cm2, con un contraste de 30 % y con una velocidad de cambio de color menor de 1 s. La última sección incorpora el estudio de dos nuevos polímeros, poli-dibencil-ProDOT (PDiBz-ProDOT) y poli-bifenilmetiloximetil-ProDOT (PBPMOM-ProDOT), coloreables catódicamente y que individualmente presentan mayores contrastes que el PEDOT. Por esta razón, se estudia el efecto de la sustitución de éste por los dos nuevos polímeros en sistemas duales con el PBEDOT-NMCz. Para ello se repiten las caracterizaciones individuales con la metodología utilizada para el sistema PEDOT/PBEDOT-NMCz. Asimismo, se realiza el estudio teórico para calcular el máximo contraste de cada sistema. Con la información obtenida se construyen dispositivos en estado sólido, y se comprueba que los dos sistemas PDiBz-ProDOT/ PBEDOT-NMCz y PBPMOM-ProDOT/PBEDOT-NMCz presentan mayores contrastes que el sistema PEDOT/PBEDOT-NMCz. Los valores obtenidos son 46 y 52 % para los sistemas PBPMOM-ProDOT/PBEDOT-NMCz y PDiBz-ProDOT/ PBEDOT-NMCz, respectivamente. Por último, durante todo el estudio se propone la utilización de magnitudes ópticas comparables para cualquier estudio electrocrómico. Para ello, se propone la utilización de valores fotópicos, en sustitución a los valores descritos en una sola longitud de onda. Las medidas fotópicas están estandarizadas por la Commission Internationale de l'Eclairage (CIE), y se corresponden con las sensaciones reales que percibe el ojo humano, cuya sensibilidad es diferente para cada longitud de onda. ; [ENG] Variable transmission electrochromic devices are able to modulate, by means of electrical current, light passing through them. Applications such as smart windows in architecture, antireflective rearview mirrors or adaptable vision systems for sport, professional or military use are being developed. These devices are electrochemical cells, constituted by materials for which oxidation or reduction processes promote reversible colour changes. Among electrochromic materials, organic conducting polymers appear as excellent candidates for the construction of devices, compared with inorganic transition metal oxides, because of their larger versatility of attainable colours, or their easier processing and low cost. A cell configuration in which both electrodes are active and complementary from an electrochromic point of view appears as a good option to improve the devices performance. The aim of this thesis is to emphasize the existing relations between electrochemical processes, or electrochemical magnitudes, and colour changes. The work is focused on two aspects: individual spectroelectrochemical characterization of the constituent materials followed by an electrochemical and optical study of the performance of the dual system constructed with those materials. The objective is the optimization of both electrochemical and optical processes in dual conducting polymer systems, obtaining experimental methodologies able to characterize, predict, and finally design optimal dual electrochromic devices. The first part of the study is focused on the development of the proper methodology to obtain an optical characterization of any electrochromic material as a function of its electrochemical properties. Materials used were poly((3,4-ethylenedioxy)thiophene) (PEDOT) and poly-(3,6-bis(2-(3,4-ethylenedioxy)thienyl)-N-methylcarbazole) (PBEDOT-NMCz). PEDOT films are coloured under reduction, while PBEDOT-NMCz are coloured under oxidation, showing complementary colouration, and so they can be used to construct a dual electrochromic device. Based on the obtained experimental results, a theoretical study was undertaken to establish the optical responses of a system comprising several electrochromic layers. The theoretically obtained relations were experimentally proved. Relations obtained allow the prediction of the maximum contrast configuration for a dual system, as a function of the individual electrochemical properties of each constituent material. The system studied was PEDOT/PBEDOT-NMCz. The third chapter deals with the proposal and development of a new experimental methodology able to register the individual oxidation states of each electrode during operation of a dual device, obtaining then direct information about device performance. This methodology allows the study of the influence of different physical and chemical variables, like ratio of redox charge between both constituent films, applied potential to the device and initial oxidation state of the constituent polymer films, on the device performance. The final objective of this work is the construction of electrochromic devices that can be use in real applications out of research or academic contexts. It is necessary then, for safety purposes, to use solid electrolytes in the cell. For final applications it is also required to construct devices of appropriate dimensions. In the fourth chapter, the construction and study of large dimensions and solid state devices for the system PEDOT/ PBEDOT-NMCz was carried out. The information obtained in previous sections was used to determine maximum contrast combinations. Problems related to electrodeposition of conducting polymers on large surfaces (around 30 cm2) are discussed, together with the optimization of switching speeds when a solid electrolyte is used. Finally the ability to tune colour states and retain them in the absence of an external potential applied was studied and discussed. A fast and straightforward assembling method is proposed, consisting of the UV crosslinking of the gel electrolyte. Finally, an easy and fast electrochemical technique is proposed to evaluate possible defective devices. As a result of the above mentioned studies, solid state electrochromic devices with an active area of 30 cm2, with 30 % contrast and switching speeds lower than 1 second were constructed. The last section deals with the study of two new cathodically colouring polymers, poly(3-(Biphenyl-4-ylmethoxymethyl)-3,4-dihydro-2H-thieno(3,4-b)-(1,2)dioxepine) (BPMOM-ProDOT) and poly-dibenzylProDOT (PDiBz-ProDOT), which have been reported to show larger contrasts than PEDOT. For this reason, dual cells were constructed and checked by combination of these two polymers with PBEDOT-NMCz. The methodology previously developed and used to characterize PEDOT and PBEDOT-NMCz was applied to these polymers. The developed theoretical equations were used to determine the maximum contrast for both systems. The obtained information was used to construct solid state devices, and it was shown that both PDiBz-ProDOT/PBEDOT-NMCz and PBPMOM-ProDOT/PBEDOT-NMCz systems achieve larger contrasts than PEDOT/PBEDOT-NMCz system. The values obtained were 46 % and 52 % for PBPMOM-ProDOT/PBEDOT-NMCz and PDiBz-ProDOT/ PBEDOT-NMCz systems, respectively. Finally, the use of standard optical magnitudes as photopic values is emphasized. Photopic values are standardized by the Commission Internationale de l'Eclairage (CIE), and correspond to real sensations perceived by the human eye, whose sensitivity is different for each wavelength. In this sense the use of photopic values, instead of values corresponding to a single wavelength, is encouraged. ; Universidad Politécnica de Cartagena ; Programa de doctorado en Electroquímica Ciencia y Tecnología

Las células presentan en su superficie oligosacáridos ramificados unidos de modo covalente a lípidos (glicolípidos) o proteínas (glicoproteínas). La porción glucídica de estos glicoconjugados codifica una información biológica específica determinada por su estructura tridimensional que puede ser reconocida por proteínas llamadas lectinas. Las interacciones entre los carbohidratos y las lectinas son de importancia fundamental para la comunicación celular. Están relacionadas con procesos biológicos como la defensa inmunológica, la replicación vírica, la adhesión celular, la inflamación, la transducción de señales bioquímicas y los procesos de adhesión de agentes microbianos a la superficie de las células huésped potenciales. La toma de conciencia de la función que desempeñan los carbohidratos como portadores de información biológica ha desencadenado un importante esfuerzo investigar dirigido a la elucidación de los mecanismos que intervienen en su reconocimiento por lectinas, tanto a nivel macromolecular como atómico. Las interacciones carbohidrato-proteína, en contraste con las interacciones proteína-proteína, presentan constantes de afinidad débiles en el rango milimolar o incluso micromolar y, en general, requieren la existencia de numerosos contactos entre carbohidratos que se encuentran agrupados en la superficie celular ("clusters") y receptores protéticos que contienen múltiples regiones de reconocimiento ("carbohydrate recognition domains; CRDs") para alcanzar afinidades biológicamente útiles. Esta situación da lugar a la aparición de fuerzas asociativas cooperativas que conducen a afinidades superiores a las que serían predecibles de la sima de las interacciones individuales. La importancia de este fenómeno, conocido como "efecto cluster", fue puesta de manifiesto por primera vez por Y.C. Lee en sus trabajos sobre el receptor Gal/GalNAc de la asialoglicoproteína de las células del hígado. Utilizando neoglicoconjugados sintéticos, demostró que un aumento lineal en el número de los motivos de reconocimiento monosacarídicos conducía a un incremento logarítmico en la eficacia de la asociación. Desde entonces el diseño y la síntesis de nuevos neoglicoconjugados multivalentes capaces de interferir con los procesos de reconocimiento carbohidrato-proteína a nivel celular es un campo muy activo en glicobiología con aplicaciones en la preparación de vacunas, inmunomoduladores, antiinflamatorios, agentes para inmunodiagnosis, transportadores de medicamentos dirigidos a células específicas, soportes de afinidad, inhibidores de la adhesión celular y bacteriana y sondas utilizadas en radioimagen. Los carbohidratos difieren de las otras clases de biomoléculas en el amplísimo repertorio estructural que puede generarse a partir de un número reducido de sus elementos constituyentes (monosacáridos), lo que les hace especialmente adecuados para la transferencia de información biológica. Para que la transmisión de esta información sea eficaz, el proceso de reconocimiento por receptores específicos debe tener un alto grado de precisión. El estudio de como los carbohidratos son reconocidos por lectinas y de cuales son los factores que determinan la especificidad y la afinidad de la asociación a nivel atómico, es consecuentemente, un tema de gran interés. Las informaciones más detalladas de que se dispone en este sentido proceden del estudio por difracción de rayos X de cristales de complejos de lectinas y carbohidratos. Estos trabajos ponen de manifiesto la existencia simultánea de interacciones por enlace de hidrógeno y fuerzas de van de Waals, incluyendo interacciones entre caras hidrófobas del azúcar y aminoácidos aromáticos. La espectroscopía de RMN ha permitido ampliar esta información a sistemas en disolución. En cualquier caso, los sistemas naturales resultan demasiado complejos para permitir extraer conclusiones sobre aspectos tales como la importancia relativa de los diferentes tipos de interacciones implicadas en el reconocimiento de carbohidratos o la identificación de motivos individuales de reconocimiento. Estas cuestiones se han abordado mediante el uso de receptores más sencillos que permitan estudiar las interacciones supramoleculares entre carbohidratos y moléculas orgánicas simples. Las ciclodextrinas (CDs), ciclooligosacáridos formados por unidades de glucosa unidas mediante enlaces glicosídicos α(1→4), han desempeñado un papel fundamental en este sentido. Los derivados que incorporan 6, 7 y 8 unidades de glucopiranosilo (α, β y γ-CD, respectivamente), son comercialmente asequibles y presentan una estructura tridimensional troncocónica toroidal, con una cavidad relativamente hidrófoba que permite la formación de complejos de inclusión con moléculas apolares en disolución acuosa. Su estructura ha inspirado el diseño y la síntesis de otros oligosacáridos como receptores artificiales para el estudio de interacciones supramoleculares. Alternativamente se han desarrollado receptores basados en estructuras aromáticas y peptídicas capaces de reconocer azúcares mediante enlaces no covalentes. Además de proporcionar información fundamental sobre los procesos de reconocimiento biológico, estos trabajos han desembocado en el desarrollo de nuevos biosensores, fármacos y sistemas de transporte. Los objetivos planteados en esta Tesis se enmarcan en este contexto general y persiguen, por una parte, profundizar en el conocimiento de las interacciones supramoleculares que implican carbohidratos y, por otra, combinar la posibilidad de interacción de estas biomoléculas con receptores celulares y con otras moléculas orgánicas en el diseño de sistemas de transporte específico de fármacos. En la primera parte de esta memoria se recogen los resultados relativos a la síntesis de neoglicoconjugados multivalentes derivados de la β-ciclodextrina, la determinación preliminar de su poder de solubilización de fármacos usando el anticanceroso Taxotère® como referencia y la evaluación de la capacidad de reconocimiento por una lectina específica (concanavalina A, Con A) para el caso de los conjugados que incorporan ligando derivados de manosa como marcador celular. En la segunda parte se describe la preparación de receptores artificiales de tipo podando que incorporan carbohidratos diseñados para el estudio de interacciones por enlace de hidrógeno, la influencia de los aspectos estructurales y conformacionales en su asociación con ligandos aceptores de tipo carboxilato y monosacarídico y la síntesis de una nueva familia de ciclooligosacáridos (ciclotrehalinas) adecuados para el estudio de interacciones en medio acuoso. CONCLUSIONES 1. La adición nucleófila de derivados de β-CD incorporando uno o siete grupos amino en posición primaria a glicosil isotiocianatos peracetilados proporciona una metodología eficiente de acceso a conjugados mono- y heptaantenados, respectivamente. La reacción de acoplamiento se completa, en general, en pocos minutos en piridina (conjugados monovalentes) o en acetona/agua a pH 8 (conjugados heptavalentes) y la purificación del aducto puede efectuarse mediante cromatografía en columna de gel de sílice incluso para el caso de estructuras 21-sacarídicas. La etapa subsiguiente de desacetilación transcurre con rendimiento cuantitativo. Además, el procedimiento es compatible con isotiocianatos unidos a grupos alquilo o arilo. Todos los neoglicoconjugados preparados mostraron una solubilidad en agua entre 25 y 40 veces superior a la de la β-ciclodextrina canónica, incrementan la solubilidad en agua del Taxotère, un potente antimitótico derivado del taxol y mostraron una significativa disminución (en torno al 75%) en su carácter hemolítico en comparación con la β-ciclodextrina comercial lo que los hace buenos candidatos como sistemas de transporte específico de medicamentos. 2. La anomerización parcial observada para las α- y β-D- manopiranosiltioureas bajo las condiciones básicas de desacetilación de Zemplén puede evitarse efectuando la desprotección a 0º C, lo que permite obtener compuestos desprotegidos configuracionalmente estables en ausencia de base. La aplicación de esta metodología a derivados aminados de β-ciclodextrina permite obtener los correspondientes conjugados manosa-(tiourea)-β-Cd, adecuados para estudios de asociación con la lectina Concanavalina A. 3. Los estudios de afinidad de los conjugados manosa-(tiourea)-β-CD mono y heptavalentes hacia la Concanavalina A, siguiendo el protocolo ELLA, indican que la lectina no muestra selectividad anomérica entre ligando de α- o β-D- manopiranosiltioureas lo que excluye una disminución en la afinidad debida a posibles procesos de anomerización. En cambio, los derivados con ligandos de manosa unidos a través de la posición primaria (C-6) presentan una afinidad mucho menor y no son adecuados para la vectorización de fármacos. Aunque la presencia del puente intersacarídicos de tiourea origina una ligera pérdida de afinidad por la lectina en comparación con los enlaces O-glicosídicos, este efecto queda compensando en los conjugados monovalentes por la existencia de interacciones estabilizantes debidas a la presencia del anillo de ciclodextrina. En el caso de los aductos persustituidos, a pesar del aumento de la densidad de ligando manosilado, se observa una pérdida de afinidad por la lectina debido, probablemente a un acceso más impedido al sitio activo. 4. Para la preparación de conjugados ciclodextrina-glicodendrímeros se han examinado las metodologías sintéticas convergente y divergente teniendo como etapa clave en ambos casos la formación de un grupo tiourea. Se han empleado como elementos de base la monoamina de β-CD, el cloruro de 6-azidohexanoilo como espaciador y el 2-amino-1,3-di-terc-butoxicarbonilaminopropano como elemento de ramificación. Como motivos de reconocimiento se han utilizado el 2,3,4,6-tetra-O-acetil-β-D-manopiranosil isotiocianato y un marcador manosilado trivalente. Con estas unidades de base hemos preparado una serie de neoglicoconjugados manosilados di, tri, tetra, y hexavalentes y hemos evaluado su afinidad por la Con A utilizando el protocolo ELLA. La afinidad por la lectina aumenta, en general, con la valencia. La presencia del anillo de ciclodextrina origina interacciones adicionales con la proteína que aumentan la afinidad. Es notable que la afinidad de la asociación ligando manosilado-Con A aumenta fuertemente con la presencia de grupos de tres subunidades de manosa. 5. SE ha optimizado la autocondensación de isotiocianato para obtener tioureas simétricas y se ha empleado esta metodología para la preparación de receptores bidentados por enlace de hidrógeno derivados de azúcar. El análisis de la capacidad de complejación de estos receptores frente a carboxilatos indica que esta es relativamente independiente de las propiedades conformacionales del receptor, es decir, de la proporción de confórmero activo, y parece depende más de la naturaleza de los sustituyentes en el sitio de unión y de las interacciones intramoleculares que puedan competir con la formación de enlaces de hidrógeno intermoleculares. 6. Se han estudiado las propiedades de complejación de receptores politioureidos derivados de carbohidrato frente a huéspedes aniónicos y neutros, tomando como modelos el anión glutarato y el octil β-D-glucopiranósido. Hemos escogido sistemas con simetría C2V para promover interacciones de tipo cooperativo y facilitar el análisis estructural. En el diseño se han empleado segmentos complementarios de ambos huéspedes (p-xililen bis(tiourea)) y se han incorporado otros segmentos (m-xililen bis(tioirea)) que favorezcan la creación de una cavidad más profunda. En el caso de ligando aniónico, donde las interacciones por enlace de hidrógeno son fuertes, la estequiometría las Kas de los complejos resultaron fuertemente dependientes de la disposición de los motivos de reconocimiento en el receptor. Sin embargo, en el caso de ligando glicosídicos, donde las interacciones son débiles, la contribución a la energía de complejación debida a una superficie de contacto máxima es muy superior a la asociada al cambio de conformación entre los estados libre y enlazado del receptor. 7. La autocondensación de diisotiocianatos, en combinación con el acoplamiento de diisotiocianatos y diaminas derivadas de la trehalosa, constituye una estrategia muy conveniente de síntesis de macrociclos híbridos de trehalosa y tiourea (ciclotrehalinas) de diferentes tamaños. Esta familia de pseudooligosacáridos conservan las características esenciales de las CDs (alta simetría, solubilidad en agua y una cavidad relativamente hidrófoba). Se ha comprobado que la capacidad de inclusión de moléculas apolares dentro de la cavidad se conserva, midiendo Kas del orden de las descritas para las CDs. Sin embargo, al contrario que en estas, es la cara β del azúcar la dispuesta hacia el interior de la cavidad por lo que constituyen herramientas complementarias para el estudio de eventos de reconocimiento molecular que impliquen carbohidratos.

1. Introduction Biodiesel (BD) is a liquid biofuel that is defined as a fatty acid methyl ester fulfilling standards such as the ones set by European (EN 14214) and the American (ASTM 6751) regulations. BD is obtained by the transesterification (Scheme 1.1) or alcoholysis of natural triglycerides contained in vegetable oils, animal fats, waste fats and greases, waste cooking oils (WCO) or side-stream products of refined edible oil production with short-chain alcohols, usually methanol or ethanol and using an alkaline homogeneous catalyst (Perego and Ricci, 2012). Scheme 1.1. Transesterification reaction. BD presents several advantages over petroleum-based diesel such as: biodegradability, lower particulate and common air pollutants (CO, SOx emissions, unburned hydrocarbons) emissions, absence of aromatics and a closed CO2 cycle. Refined, low acidity oilseeds (e.g. those derived from sunflower, soy, rapeseed, etc.) may be easily converted into BD, but their exploitation significantly raises the production costs, resulting in a biofuel that is uncompetitive with the petroleum-based diesel (Santori et al., 2012; Lotero et al., 2005). Moreover, the use of the aforementioned oils generated a hot debate about a possible food vs. fuel conflict, i.e. about the risk of diverting farmland or crops at the expense of food supply. It is so highly desirable to produce BD from crops specifically selected for their high productivity and low water requirements (Bianchi et al., 2011; Pirola et al., 2011), or from low-cost feedstock such as used frying oils (Boffito et al., 2012a) and animal fats (Bianchi et al., 2010). The value of these second generation biofuels, i.e. produced from crop and forest residues and from non-food energy crops, is acknowledged by the European Community, which states in its RED directive (European Union, RED Directive 2009/28/EC): ''For the purposes of demonstrating compliance with national renewable energy obligations […], the contribution made by biofuels produced from wastes, residues, non-food cellulosic material, and ligno-cellulosic material shall be considered to be twice that made by other biofuels''. However, the presence of free fatty acids in the feedstock, occurring in particular in the case of not refined oils, causes the formation of soaps as a consequence of the reaction with the alkaline catalyst. This hinders the contact between reagents and the catalyst and makes difficult the products separation. Many methods have been proposed to eliminate FFA during or prior to transesterification (Pirola et al., 2011; Santori et al., 2012). Among these the FFA pre-esterification method is a very interesting approach to lower the acidity since it allows to lower the acid value as well as to obtain methyl esters already in this preliminary step (Boffito et al., 2012a, 2012b; 2012c Bianchi et al., 2010, 2011; Pirola et al., 2010, 2011). Aims of the work The aims of this work are framed in the context of the entire biodiesel production chain, ranging from the choice of the raw material, through its standardization to the actual biodiesel production. The objectives can be therefore summarized as follows: Assessing the potential of some vegetable or waste oils for biodiesel production by their characterization, deacidification and final transformation into biodiesel; To test different ion exchange resins and sulphated inorganic systems as catalysts in the FFA esterification; To assess the use of ultrasound to assist the sol-gel synthesis of inorganic sulphated oxides to be used as catalysts in the FFA esterification reaction; To assess the use of sonochemical techniques such as ultrasound and microwave to promote both the FFA esterification and transesterification reaction. 2. Experimental details 2.1 Catalysts In this work, three kinds of acid ion exchange resins were used as catalysts for the FFA esterification: Amberlyst®15 (A15), Amberlyst®46 (A46) (Dow Chemical) and Purolite®D5081 (D5081). Their characteristic features are given in Tab. 2.1. Various sulphated inorganic catalysts, namely sulphated zirconia, sulphated zirconia+titania and sulphated tin oxide were synthesized using different techniques. Further details will be given as the results inherent to these catalysts will be presented. Catalyst A15 A46 D5081 Physical form opaque beads Type Macroreticular Matrix Styrene-DVB Cross-linking degree medium medium high Functional group -SO3H Functionalization internal external external external Form dry wet wet Surface area (m2 g-1) 53 75 514a Ave. Dp (Ǻ) 300 235 37a Total Vp (ccg-1) 0.40 0.15 0.47 Declared Acidity (meq H+g-1) 4.7 0.43 0.90-1.1 Measured acidity (meq H+g-1) 4.2 0.60 1.0 Moisture content (%wt) 1.6 26-36 55-59 Shipping weight (g l-1) 610 600 1310a Max. operating temp (K) 393 393 403 Tab. 2.1. Features of the ion exchange resins used as catalysts. The acidity of all the catalysts was determined by ion exchange followed by pH determination as described elsewhere (López et al., 2007; Boffito et al., 2012a; 2012b). Specific surface areas were determined by BET (Brunauer, Emmett and Teller, 1938) and pores sizes distribution with BJH method (Barrett, Joyner and Halenda, 1951). XRD, XPS SEM-EDX and HR-TEM analyses were performed in the case of catalysts obtained with the use of ultrasound (Boffito et al. 2012a). Qualitative analyses of Lewis and Brønsted acid sites by absorption of a basic probe followed by FTIR analyses was also carried out for this class of catalysts (Boffito et al, 2012a). 2.2 Characterization of the oils Oils were characterized for what concerns acidity (by acid-base titrations) as reported by Boffito et al. (2012a, 2012b; 2012c), iodine value (Hannus method (EN 14111:2003)), saponification value (ASTM D5558), peroxide value and composition by GC analyses of the methyl ester yielded by the esterification and transesterification. Cetane number and theoretical values of the same properties were determined using equations already reported elsewhere (Winayanuwattikun et al., 2008). 2.3 Esterification and transesterification reactions In Tab. 2.2, the conditions adopted in both the conventional and sonochemically-assisted esterification are reported. For all these experiments a temperature of 336 K was adopted. Vials were used to test the sulphated inorganic oxides, while Carberry reactor (confined catalyst) (Boffito et al., 201c) was used just for the FFA esterification of cooking oil. Rector oil (+ FFA) (g) MeOH (g) catalyst amount vial 21 3.4 5%wt/gFFA sulphated inorganic catalysts slurry 100 16 - 10 g ion exchange resins - 5%wt/gF FA sulphated inorganic catalysts Carberry 300 48 10 g (5 g in each basket) Tab. 2.2. Free fatty acids esterification reaction conditions for conventional and sonochemically-assisted experiments. All the sonochemically-assisted experiments were performed in a slurry reactor. FFA conversions were determined by acid-base titrations of oil samples withdrawn from the reactors at pre-established times and calculated as follows: "FFA conversion (%)=" (〖"FFA" 〗_"t=0" "-" 〖"FFA" 〗_"t" )/〖"FFA" 〗_"t=0" " x 100" In Tab. 2.3, the conditions of both the conventional and ultrasound (US)-assisted transesterification are reported. KOH and CH3ONa were used for conventional experiments, while just KOH for the US-assisted experiments. The BD yield was determined by GC (FID) analysis of the methyl esters. Method Reactor Step gMeOH/100 goil gKOH/100 goil Temp. (K) Time (min) traditional batch step 1 20 1.0 333 90 step 2 5.0 0.50 60 US-assisted batch step 1 20 1.0 313, 333 30 US-assisted continuos step 1 20 1.0 338 30 Tab. 2.3. Transesterification reaction conditions. 3. Results and Discussion 3.1 Characterization and deacidification of different oils by ion exchange resins: assessment of the potential for biodiesel production In Tab. 3.1 the results of the characterization of the oils utilized in this work are displayed. The value in parentheses indicate the theoretical value of the properties, calculated basing on the acidic composition. The acidity of all the oils exceeds 0.5%wt (~0.5 mgKOH/g), i.e. the acidity limit recommended by both the European normative (EN 14214) and American standard ASTM 6751 on biodiesel (BD). The iodine value (IV) is regulated by the EN 14214, which poses an upper limit of 120 gI2/100 g. The number of saturated fatty chains in the fuel determines its behaviour at low temperatures, influencing parameters such as the cloud point, the CFPP (cold filter plugging point) and the freezing point (Winayanuwattikun et al., 2008). The IV are in most of the cases similar to the ones calculated theoretically. When the experimental IV differs from the theoretical one, it is in most of the cases underestimated. This can be explained considering the peroxide numbers (PN), which indicates the concentration of O2 bound to the fatty alkyl chains and is therefore an index of the conservation state of oil. Oils with high IV usually have a high concentration of peroxides, whereas fats with low IV have a relatively low concentration of peroxides at the start of rancidity (King et al., 1933). Moreover, although PN is not specified in the current BD fuel standards, it may affect cetane number (CN), a parameter that is regulated by the standards concerning BD fuel. Increasing PN increases CN, altering the ignition delay time. Saponification number (SN) is an index of the number of the fatty alkyl chains that can be saponified. The long chain fatty acids have a low SN because they have a relatively fewer number of carboxylic functional groups per mass unit of fat compared to short chain fatty acids. In most of the cases the experimental SN are lower than the ones calculated theoretically. This can be explained always considering the PN, indicating a high concentration of oxygen bound to the fatty alkyl chains. Oil Acidity (%wt) IV1 (gI2/ 100 g) PN2 (meqO2 /kg) SN3 (mg KOH/g) CN4 Fatty acids composition (%wt) animal fat (lard)* 5.87 51 2.3 199 62.3 n.d. soybean* 5.24 138 3.8 201 42.4 n.d. tobacco1 1.68 143 (149) 21.9 199 (202) 41.6 (39.8) C14:0 (2.0) C16:0 (8.3) C18:0 (1.5) C18:1 (12.0) C18:2 (75.3) C18:3 (0.6) C20:0 (0.1) C22:0 (0.2) sunflower* 3.79 126 3.7 199 45.4 n.d. WSO5 0.50 118 (129) 71.3 187 (200) 48.9 (44.6) C16:0 (6.9) C18:0 (0.9) C18:1 (40.1) C18:2 (50.9) C18:3 (0,3) C20:0 (0.1) C20:1 (0.4) C22:0 (0.4) palm 2.71 54.0 (53.0) 12.3 201 (208) 61.3 (60.6) 16:0 (43.9) 18:0 (5.6) 18:1 (40.5) 18:2 (8.6) WCO6 2.10 53.9 (50.7) 11.0 212 (196) 59.9 (62.7) C16:0 (38.8) C18:0 (4.1) C18:1 (47.9) C18:2 (4.2) WCO:CRO =3:1 2.12 69.0 (75.5) 30.1 200 (212) 58.1 (55.1) C16:0 (30.1) C18:0 (3.1) C18:1 (51.9) C18:2 (12.0) C18:3 (2.%) C20:0 (0.2) C22:0 (0.1) WCO:CRO =1:1 2.19 76.8 (90.7) 51.3 188 (203) 58.1 (52.8) C16:0 (21.5) C18:0 (2.1) C18:1 (55.8) C18:2 (14.7) C18:3 (5.1) C20:0 (0.8) C22:0 (0.1) WCO:CRO =1:3 2.24 84.5 (104) 62.4 177 (202) 58.1 (49.9) 14:0 (0.1) 16:0 (14.7) 16:1 (0.7) 18:0 (6.85) 18:1 (40.0) 18:2 (37.0) 18:3 (0.25) 20:0 (0.25) 22:0 (0.15) rapeseed (CRO7) 2.20 118 (123) 71.6 165 (200) 52.8 (45.9) C16:0 (4.1) C18:0 (0.1) C18:1 (63.7) C18:2 (20.2) C18:3 (10.2) C20:0 (1.5) C22:0 (0.2) rapeseed* 4.17-5.12 108 (107) 3.5 203 (200) 48.9 (49.5) C16:0 (7.6) C18:0 (1.3) C18:1 (64.5) C18:2 (23.7) C18:3 (2.4) C20:0 (0.5) Brassica juncea 0.74 109 (110) 178 (185) 52.4 (51.1) C16:0 (2.4) C18:0 (1.1) C18:1 (19.9) C18:2 (19.2) C18:3 (10.9) C20:0 (7.2) C20:1 (1.7) C22:0 (0.9) C22:1 (34.8) 24:0 (1.9) safflower 1.75 139 48.9 170 47.1 n.d. WCO: tobacco2 =1:1 4.34 119 (112) 56.0 191 (203) 48.1 (48.0) C16:0 (22.5) C18:0 (3.2) C18:1 (32.0) C18:2 (42.1) C18:3 (0.2) tobacco2 6.17 141 (151) 33.4 183 (201) 44.4 (39.5) C16:0 (8.7) C18:0 (1.6) C18:1 (12.8) C18:2 (76.0) C18:3 (0.7) C20:0 (0.1) C22:0 (0.1) 1Iodine value; 2Peroxide number; 3Saponification number; 4Cetane number; 5Winterized sunflower oil, 6Waste cooking oil; 7Crude rapeseed oil; * refined, commercial oils acidified with pure oleic acid up to the indicated value. Tab. 3.1. Results of the characterization of the oils. The results of the FFA esterification performed on the different oils are given in Fig. 3.1. Fig. 3.1. Results of the FFA esterification reaction on different oils. The dotted line represents a FFA concentration equal to 0.5%wt, i.e. the limit required by both the European and American directives on BD fuel and to perform the transesterification reaction avoiding excessive soaps formation. The FFA esterification method is able to lower the acidity of most of the oils using the ion exchange resins A46 and D5081 as catalysts in the adopted reaction conditions. High conversion was obtained with A15 at the first use of the catalyst, but then its catalytic activity drastically drops after each cycle. The total loss of activity was estimated to be around 30% within the 5 cycles (results not shown for the sake of brevity). A possible explanation concerning this loss of activity may be related to the adsorption of the H2O yielded by the esterification on the internal active sites, which makes them unavailable for catalysis. When H2O molecules are formed inside the pores, they are unable to give internal retro-diffusion due to their strong interaction with H+ sites and form an aqueous phase inside the pores. The formation of this phase prevents FFA from reaching internal active sites due to repulsive effects. What appears to influence the FFA conversion is the refinement degree of the oil. WCO is in fact harder to process in comparison to refined oils (Bianchi et al., 2010; Boffito et al., 2012c), probably due to its higher viscosity which results in limitations to the mass transfer of the reagents towards the catalyst. Indeed, the required acidity limit is not achieved within 6 hours of reaction. A FFA concentration lower than 0.5%wt is not achieved also in the case of WCO mixture 3:1 with CRO and 1:1 with tobacco oil and in the case of the second stock of tobacco oil (tobacco2). This is attributable to the very low quality of these feedstocks due to the waste nature of the oil itself, in the case of WCO, or to the poor conservation conditions in the case of tobacco oilseed. In this latter case, the low FFA conversion was also ascribed to the presence of phospholipids, responsible for the deactivation of the catalyst. BD yields ranging from 90.0 to 95.0 and from 95.0 to 99.9% were obtained from deacidified raw oils using KOH and NaOCH3 as a catalyst, respectively. In Fig. 3.2, the comparison between A46 and D5081 at different temperatures and in absence of drying pretreatment (wet catalyst) is displayed. As expected, D5081 performs better than A46 in all the adopted conditions. Nevertheless, the maximum conversion within a reaction time of 6 hours is not achieved by any of the catalysts both operating at 318 K and in the absence of drying pretreatment. A more detailed study on the FFA esterification of WCO and its blends with rapeseed oil and gasoline was carried out. In Tab. 3.2 a list of all the experiments performed with WCO is reported together with the FFA conversion achieved in each case, while in Fig. 3.3 the influence of the viscosity of the blends of WCO is shown. Fig. 3.2. Comparison between the catalysts. D5081 and A46 at a) different catalysts amounts and b) temperatures and treatments. The results show that Carberry reactor is unsuitable for FFA esterification since a good contact between reagents and catalyst is not achieved due to its confinement. A15 deactivated very rapidly, while A46 and D5081 maintained their excellent performance during all the cycles of use due to the reasons already highlighted previously. The blends of WCO and CRO show an increase of the reaction rate proportional to the content of the CRO, that is attributable to the decreases viscosity (Fig. 3.3), being all the blend characterized by the same initial acidity. Also the use of diesel as a solvent resulted in a beneficial effect for the FFA esterification reaction, contributing to the higher reaction rate. Feedstock %wtFFAt=0 Reactor Cat. gcat/100 goil gcat/100 g feedstock Number of cat. re-uses FFA conv. (%), 1st use, 6 hr 1 WCO 2.10 Carberry A15 3.3 3.3 6 15.4 2 WCO 2.10 slurry A15 10 10 6 71.7 3 WCO 2.10 Carberry A46 3.3 3.3 6 7.7 4 WCO 2.10 slurry A46 10 10 6 62.0 5 WCO 2.10 slurry D5081 10 10 6 63.7 6 CRO 2.20 slurry A46 10 10 10 95.9 7 CRO 2.20 slurry D5081 10 10 10 93.7 8 WCO 2.10 slurry A46 10 10 0 62.0 9 WCO 75 CRO 25 2.12 7.5 71.3 10 WCO 50 CRO 50 2.19 5.0 79.9 11 WCO 25 CRO 75 2.24 2.5 86.1 12 CRO 2.20 10 95.9 13 WCO 75 DIESEL 25 1.74 7.5 76.8 14 WCO 50 DIESEL 50 1.17 5.0 58.7 15 WCO 25 DIESEL 75 0.65 2.5 40.4 16 WCO 25 DIESEL 75 (higher FFA input) 2.44 2.5 63.5 Tab. 3.2. Experiments performed with waste cooking oil. . Fig. 3.3. FFA conversions and viscosities of the blend of WCO with rapeseed oil. 3.2. Sulphated inorganic oxides as catalysts for the free fatty acid esterification: conventional and ultrasound assisted synthesis Conventional syntheses In Tab. 3.3, the list of all the catalyst synthesized with conventional techniques is reported together with the results of the characterization. Catalyst Composition Prep. method precursors T calc. SSA (m2g-1) Vp (cm3g-1) meq H+g-1 1 SZ1 SO42-/ZrO2 one-pot sol-gel ZTNP1, (NH4)2SO4 893 K O2 107 0.09 0.90 2a SZ2a SO42-/ZrO2 two-pots sol-gel ZTNP, H2SO4 893 K 102 0.10 0.11 2b SZ2b SO42-/ZrO2 two-pots sol-gel ZTNP, H2SO4 653 K 110 0.10 0.12 3 SZ3 SO42-/ZrO2 Physical mixing ZrOCl2.8H2O (NH4)2SO4 873 K 81 0.11 1.3 4 SZ4 Zr(SO4)2/SiO2 Impregnation Zr(SO4)2.4H2O SiO2 873 K 331 0.08 1.4 5 SZ5 Zr(SO4)2/Al2O3 Impregnation Zr(SO4)2.4H2O Al2O3 873 K 151 0.09 0.67 6 ZS Zr(SO4)2.4H2O (commercial) - - - 13 0.12 9.6 7 STTO_0 SO42-/SnO2 Physical mixing + impregnation SnO2 TiO2 P25 H2SO4 773 K 16.8 0.10 3.15 8 STTO_5 SO42-/95%SnO2-5%TiO2 773 K 15.9 0.11 3.43 9 STTO_10 SO42-/ 90%SnO2-10%TiO2 773 K 16.5 0.09 5.07 10 STTO_15 SO42-/ 85%SnO2-15%TiO2 773 K 14.9 0.11 7.13 11 STTO_20 SO42-/ 80%SnO2-20%TiO2 773 K 16.9 0.09 7.33 Tab. 3.3. Sulphated inorganic catalysts synthesized with conventional techniques. The FFA conversions of the sulphated Zr-based systems are provided in Fig. 3.4a and show that Zr-based sulphated systems do not provide a satisfactory performance in the FFA esterification, probably due to their low acid sites concentration related to their high SSA. Even if catalysts such as SZ3 and SZ4 exhibit higher acidity compared to other catalysts, it is essential that this acidity is located mainly on the catalyst surface to be effectively reached by the FFA molecules, as in the case of ZS. In Figure 3.4b, the results of the FFA esterification tests of the sulphated Sn-Ti systems are shown. Other conditions being equal, these catalysts perform better than the sulphated Zr-based systems just described. This is more likely due to the higher acidity along with a lower surface area. With increasing the TiO2 content, the acidity increases as well. This might be ascribable to the charge imbalance resulting from the heteroatoms linkage for the generation of acid centres, (Kataota and Dumesic, 1988). As a consequence, the activity increases with the TiO2 content along with the acidity of the samples. For the sake of clarity, in Fig. 3.4c the FFA esterification conversion is represented as a function of the number of active sites per unit of surface area of the samples. Ultrasound- assisted synthesis In Tab. 3.4, the list of all the catalyst synthesized with conventional techniques is reported together with the results of the characterization. Samples SZ and SZT refer to catalysts obtained with traditional sol-gel method, while samples termed USZT refer to US-obtained sulphated 80%ZrO2-20%TiO2. The name is followed by the US power, by the length of US pulses and by the molar ratio of water over precursors. For example, USZT_40_0.1_30 indicates a sample obtained with 40% of the maximum US power, on for 0.1 seconds (pulse length) and off for 0.9 seconds, using a water/ZTNP+TTIP molar ratio equal to 30. SZT was also calcined at 773 K for 6 hours, employing the same heating rate. This sample is reported as SZT_773_6h in entry 2a. Further details about the preparation can be found in a recent study (Boffito et al., 2012b). Entry Catalyst Acid capacity (meq H+/g) SSA (m2g-1) Vp (cm3g-1) Ave. BJH Dp (nm) Zr:Ti weight ratio S/(Zr+Ti) atomic ratio 1 SZ 0.30 107 0.20 6.0 100 0.090 2 SZT 0.79 152 0.19 5.0 79:21 0.085 2a SZT_773_6h 0.21 131 0.20 5.0 n.d.1 n.d 3 USZT_20_1_30 0.92 41.7 0.12 12.5 80:20 0.095 4 USZT_40_0.1_30 1.03 47.9 0.11 9.5 81:19 0.067 5 USZT_40_0.3_30 1.99 232 0.27 4.5 81:19 0.11 6 USZT_40_0.5_7.5 1.70 210 0.20 5.0 78:22 0.086 7 USZT_40_0.5_15 2.02 220 0.20 5.0 80:20 0.13 8 USZT_40_0.5_30 2.17 153 0.20 5.0 78:22 0.12 9 USZT_40_0.5_60 0.36 28.1 0.10 10 79:21 0.092 10 USZT_40_0.7_30 1.86 151 0.16 5.0 78:22 0.11 11 USZT_40_1_15 3.06 211 0.09 7.0 80:20 0.15 12 USZT_40_1_30 1.56 44.1 0.09 7.0 80:20 0.17 Tab. 3.4. Sulphated inorganic Zr-Ti systems synthesized with ultrasound-assisted sol-gel technique. Some of the results of the characterizations are displayed in Tab. 3.4. The results of the catalytic tests are shown in Fig. 3.5 a, b and c. In Fig. 3.5a and 3.5b the FFA conversions are reported for the samples synthesized using the same or different H2O/precursors ratio, respectively. Fig. 3.5. FFA conversions of sulphated inorganic Zr-Ti systems synthesized with ultrasound-assisted sol-gel for a) the same amount of H2O, b) different amount of H2O used in the sol-gel synthesis, c) in function of the meq of H+/g of catalyst Both the addition of TiO2 and the use of US during the synthesis are able to improve the properties of the catalysts and therefore the catalytic performance in the FFA esterification. The addition of TiO2 is able to increase the Brønsted acidity and, as a consequence, the catalytic activity (compare entries 1 and 2 in Tab. 3.4). The improvement in the properties of the catalysts due the use of US is probably caused by the effects generated by acoustic cavitation. Acoustic cavitation is the growth of bubble nuclei followed by the implosive collapse of bubbles in solution as a consequence of the applied sound field. This collapse generates transient hot-spots with local temperatures and pressures of several thousand K and hundreds of atmospheres, respectively (Sehgal et al., 1979). Very high speed jets (up to 100 m/s) are also formed. As documented by Suslick and Doktycz (Suslick and Doktycz, 1990), in the presence of an extended surface, such as the surface of a catalyst, the formation of the bubbles occurs at the liquid-solid interface and, as a consequence of their implosion, the high speed jets are directed towards the surface. The use of sonication in the synthesis of catalysts can therefore improve the nucleation production rate (i.e. sol-gel reaction production rate) and the production of surface defects and deformations with the formation of brittle powders (Suslick and Doktycz, 1990). For the samples obtained with the US pulses with on/off ratio from 0.3/0.7 on, the conversion does not increase much more compared to the one achieved with the sample obtained via traditional sol-gel synthesis. Their conversion is in fact comparable (see samples USZ_40_0.3_30, USZ_40_0.5_30, USZ_40_0.7_30 and SZT in Fig. 3.5a. The similarity in the catalytic performance of these catalysts may be ascribable to the fact that they are characterized by comparable values of SSA (entries 2, 5, 8, 10 in Tab. 3.4) and, in the case of the catalysts obtained with pulses, also by comparable acidities (entries 5, 8, 10 in Tab. 3.4). A high SSA may in fact be disadvantageous for the catalysis of the reaction here studied for the reasons already highlighted in the previous sections. The best catalytic performance is reached by the sample USZT_40_1_30, i.e. the one obtained using continuous US at higher power. This catalyst results in fact in a doubled catalytic activity with respect to the samples prepared either with the traditional synthesis or with the use of pulsed US. In spite the acidity of this catalyst is lower than that of the samples obtained with the US pulses, it is characterized by a rather low surface area (entry 12 in Tab. 3.4) that can be associated with a localization of the active sites mainly on its outer surface. As evidenced by the FTIR measurements (not reported for the sake of brevity), it is also important to highlight, that only in the case of the USZT_40_1_30 sample, a not negligible number of medium-strong Lewis acid sites is present at the surface, together with a high number of strong Brønsted acid centres. The XRD patterns of the samples were typical of amorphous systems, due to the low calcination temperatures. Samples calcined for a long time (SZT_773_6h) exhibit almost no catalytic activity (results not reported for the sake of brevity). This catalytic behaviour might be ascribable to the loss of part of the sulphates occurred during the calcinations step that result also in a very low acid capacity (see Tab. 3.4). For the sake of clarity, in Fig. 3.5c the FFA conversions as a function of the concentration of the acid sites normalized to the surface area are reported for the most significant samples. For what concerns how the water/precursors ratio affects the catalysts acidity, some general observations can be made: increasing it up to a certain amount increases the H+ concentration (compare entries from 6 to 9 and 11 to 12 in Tab. 3.4) because the rate of the hydrolysis and the number of H2O molecules that can be chemically bounded increases. Nevertheless, increasing the water/precursor ratio over a certain amount (30 for pulsed and 15 for continuous US, entries 8 and 11 in Tab. 3.4, respectively), seems to have a negative effect on the acidity concentration. In fact, the risk of the extraction of acid groups by the excess of water increases as well and the US power density decreases. 3.3 Sonochemically-assisted esterification and transesterification Esterification In Tab. 3.5 a list of the sonochemically-assisted esterification experiments is displayed together with the final acidities achieved after 4 hours of reaction. The reactor used for these experiments, provided with both an US horn (20 kHz) and a MW emitter (2450 MHz) is described elsewhere in detail (Ragaini et al., 2012). Standard calorimetric measurements were carried out to measure the actual emitted power (Suslick and Lorimer, 1989). Considering entries from 1 to 6 (rapeseed oil with high acidity), a final acidity lower than 0.5%wt is achieved within 4 hours operating at the conventional temperature of 336 K with all the methods, while this does not happen operating at lower temperatures. In particular, the lowest acidity is achieved at 336 K with MW. Considering entries from 7 to 12, inherent to the raw tobacco oilseed, final acidities lower than 0.5%wt are achieved only with the use of US. It is remarkable that at the temperature of 293 K the FFA esterification reaction rate results 6X faster than the conventional process at the same temperature. In the case of the rapeseed oil with low acidity (entries from 13 to 20), the use of MW increases the FFA conversion at 293 K and 313 K but not at 336 K. Moreover, the higher the applied power, the higher the FFA conversion. Oil Initial acidity (%wt) Cat. Technique Temp. (K) Emitted power (W) Tthermostat (K) Final acidity (%wt), 4 hr 1 Rapeseed oil (5)* 4.2-5.0 A46 conventional 313 - 315 1.18 2 336 338 0.50 3 ultrasound 313 38.5 293 0.55 4 336 313 0.48 5 microwaves 313 61.4 293 0.69 6 336 313 0.32 7 Tobacco 1.17 A46 conventional 293 - 293 0.97 8 313 315 0.55 9 336 338 0.45 10 ultrasound 293 38.5 277 0.48 11 313 293 0.46 12 336 313 0.30 13 Rapeseed oil (2)* 2.0-2.3 D5081 conventional 293 - 277 0.82 14 313 315 0.44 15 336 338 0.25 16 microwaves 293 31.7 277 0.73 17 313 31.7 293 0.34 18 61.4 293 0.37 19 336 31.7 313 0.29 20 61.4 313 0.25 Tab. 3.5. Sonochemically-assisted esterification experiments. The positive effects of acoustic-cavitation in liquid-solid systems are ascribable to the asymmetric collapse of the bubbles in the vicinity of the solid surface. When a cavitation bubble collapses violently near a solid surface, liquid jets are produced and high-speed jets of liquid are driven into the surface of a particle. These jets and shock waves improve both the liquid–solid and liquid-liquid mass transfer (Mason and Lorimer, 1988). MW is considered as a non-conventional heating system: when MW pass through a material with a dipole moment, the molecules composing the material try to align with the electric field (Mingos et al., 1997). Polar molecules have stronger interactions with the electric field. Polar ends of the molecules tend in fact to align themselves and oscillate in step with the oscillating electric field. Collisions and friction between the moving molecules results in heating (Toukoniitty et al., 2005). The increase of the FFA conversion as the power increases may be attributed to the fact that more power is delivered to the system and, therefore, the enhanced temperature effects caused by electromagnetic irradiation are increased with respect to lower powers. Differently the reason why a too high power was detrimental at the temperature of 336 K could be accounted for by two factors: i) the acoustic cavitation is enhanced at lower temperatures due to the higher amount of gas dissolved; ii) possible generation of too high temperatures inside the reaction medium that could have caused the removal of methanol from the system through constant evaporation or pyrolysis. Transesterification Transesterification experiments were performed on rapeseed oil both in batch and continuous mode. For the batch experiments two kinds of reactors were used: a traditional reaction vessel and a Rosett cell reactor, both with two ultrasound horns with different tip diameters (13 and 20 mm), and operating powers. A Rosett cell is a reactor designed to promote hydrodynamic cavitation through its typical loops placed at the bottom of vessel. Sonicators used in this work were provided by Synetude Company (Chambery, France). In Fig. 3.6, results from the conventional and the US-assisted batch experiments are compared. The US methods allows to attain very high yields in much shorter times than the traditional method and using less reagents (see Tab. 2.3) in just one step. The beneficial effects given by the US are attributable to the generation of acoustic cavitation inside the reaction medium leading to the phenomena already described in the case of esterification reaction. In particular, with the use of the Rosett cell reactor, BD yields of 96.5% (dotted lined) are achieved after 10 minutes of reaction. This is likely due to the combined approach exploiting acoustic cavitation along with hydrodynamic cavitation, which is able to provide a very efficient mixing inside the system. The use of the Rosett cell reactor provided transesterification reaction rates up to 15X faster than the conventional process. Continuous experiments were performed using two tubular reactors with different volumes (0.070 L at 35 KHz and 0.700 L at 20 kHz) and different US powers (19.3 and 68.3 W, respectively). The volume of the treated reagents was varied to obtain the same power density in both the reactors. Results are presented in Fig. 3.7. BD yields higher than 96.5% were obtained in the case of the small reactor within a reaction time of ~5 minutes. It is remarkable that BD yields higher than 90% were obtained using pulsed US (2 seconds on, 2 seconds off) after only 18 seconds, corresponding to just one passage in the reactor. In this case the transesterification reaction rate was 300X faster than the conventional process. The beneficial effects of pulses for the reactivity of the transesterification have been extensively reported (Chand et al., 2010; Kumar et al., 2010). In particular, as reported by Chand, when pulses are adopted, excessive heating of the reaction medium is not promoted, so preventing the loss of the gases dissolved in the system that are necessary for the acoustic cavitation to occur. Moreover, excessive heating during the transesterification reaction might lead to evaporation followed by pyrolysis of methanol and its subsequent removal from the reaction environment. 4. Conclusions As a conclusion to this work, some final remarks can be claimed: Feedstocks with a high potential for biodiesel (BD) production are Brassica juncea oilseed, which can be used as feedstock for BD100, Carthamus tinctorus, tobacco, animal fat and waste cooking oil to be used in BD blends with other oils or in diesel blends. However, blending different oils among them or with diesel already during the free fatty acids (FFA) esterification reaction may increase the reaction rate due to the lowered viscosity. Free fatty acids esterification over acid ion exchange resins in slurry reactors remains the preferred method of oils deacidification due to the optimal contact between the reagents and the catalyst and the good durability over time. The final high BD yields obtained for the oils de-acidified with the pre-esterification method over sulphonic ion exchange resins demonstrate its effectiveness in lowering the acidity and the possibility of obtaining high quality biodiesel from the selected feedstocks. Surface acidity and specific surface area of sulphated inorganic systems can be increased by both adding TiO2 and using ultrasound (US) in precise experimental conditions to assist the sol-gel synthesis of the catalysts. Changing the experimental conditions of US during the sol-gel synthesis makes also possible to tune the properties of the catalysts. In spite of not satisfying FFA conversions were obtained, US-assisted sol-gel synthesis turns out to be an extremely interesting method to obtain catalysts with high acidity and surface area. Both US and microwaves (MW) enhanced the FFA esterification reaction rate at temperatures lower than the one used conventionally (336 K). The positive effects of US are attributable to the phenomena generated inside the reaction medium by the acoustic cavitation, while MW are able to generate temperature effects localized in the proximity of the catalyst surface and to increase MeOH-oil solubility. US-assisted transesterification reaction is much faster than conventional transesterification: BD yields higher than 96.5% were achieved in most of the cases within 10 minutes of reaction, whereas the conventional method requires 150 minutes, besides higher reagents amount and higher temperatures. In particular, BD yields higher than 90% were obtained using a continuous reactor and pulsed US within 18 seconds, corresponding to just one passage in the reactor. In this case the transesterification reaction rate resulted to be 300X faster than the conventional process. Suggestions for the continuations of the work concern the further study of the synthesis of sulphated inorganic systems such as SO42-/ZrO2 or SnO2 or TiO2 with US and MW. Future work should also be devoted to the optimization of the experimental variables related to the use of MW and US to promote both FFA esterification and transesterification reactions. References Barrett E.P., Joyner L.G., Halenda P.P., "The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms", J. Am. Chem. Soc. 1951, 73, 373. Bianchi C.L., Boffito D.C., Pirola C., Ragaini V., "Low temperature de-acidification process of animal fat as a pre-step to biodiesel production", Catal. Lett., 2010, 134, 179. Bianchi C.L., Pirola C., Boffito D.C., Di Fronzo A., Carvoli G., Barnabè D., A. Rispoli, R. Bucchi, "Non edible oils: raw materials for sustainable biodiesel", in Stoytcheva M., Montero G. (Eds.): Biodiesel Feedstocks and Processing Technologies, Intech, 2011, pp. 3-22. Boffito D.C., Pirola C., Galli F., Di Michele A., Bianchi C.L., "Free Fatty Acids Esterification of Waste Cooking Oil and its mixtures with Rapeseed Oil and Diesel", Fuel, 2012a, accepted on 19th October 2012, DOI:10.1016/j.fuel.2012.10.069. Boffito D.C., Crocellà V., Pirola C., Neppolian B., Cerrato G., Ashokkumar M., Bianchi C.L., "Ultrasonic enhancement of the acidity, surface area and free fatty acids esterification catalytic activity of sulphated ZrO2-TiO2 systems", J. Catal., 2012b, http://dx.doi.org/10.1016/j.jcat.2012.09.013 Boffito D.C., Pirola C., Bianchi C.L., "Heterogeneous catalysis for free fatty acids esterification rea.ction as a first step towards biodiesel production", Chem, Today, 2012c, 30, 14. Brunauer S., Hemmett P., Teller E., "Adsorption of Gases in Multimolecular Layers", J. Am. Chem. Soc. 1938, 60, 309. López D. E., Suwannakarn K., Bruce D. A., Goodwin JG. "Esterification and transesterification on tungstated zirconia: Effect of calcination temperature", J Catal 2007, 247, 43. Mason T.J., Lorimer J.P., "Sonochemistry, Theory, Applications and Uses of Ultrasound in Chemistry", Efford, J. Wiley, New York, 1988. Mingos D.M.P.,Baghurst D.R., "Applications of Microwave Dielectric Heating Effects to Synthetic Problems in Chemistry", Microwave-Enhanced Chemistry, American Chemical Society,Washington, DC, USA, 1997. Perego C., Ricci, M., "Diesel fuel from biomass", Catal. Sci. Technol., 2012, 1, 1776. Pirola C., Boffito D.C., Carvoli G., Di Fronzo A., Ragaini V., Bianchi C.L., "Soybean oil deacidification as a first step towards biodiesel production", in D. Krezhova (Ed.): Recent Trends for Enhancing the Diversity and Quality of Soybean Products, Intech, 2011, pp. 321-44. Pirola C., Bianchi C.L., Boffito D.C., Carvoli G., Ragaini V., "Vegetable oil deacidification by Amberlyst : study of catalyst lifetime and a suitable reactor configuration", Ind. Eng. Chem. Res., 2010, 49, 4601. Ragaini V., Pirola C., Borrelli S., Ferrari C., Longo I., "Simultaneous ultrasound and microwave new reactor: Detailed description and energetic considerations", Ultrasonics Sonochemistry 2012, 19, 872 Sehgal C., Steer R.P., Sutherland R.G., Verrall R.E., "Sonoluminescence of argon saturated alkali metal salt solutions as a probe of acoustic cavitation", J. Chem. Phys., 1979, 70, 2242. Suslick K. S., Doktycz, S. J., "The Effects of Ultrasound on Solids" in Mason, T.J.: Advances in Sonochemistry, JAI Press: New York, 1990, vol.1, pp. 197-230. Toukoniitty B., Mikkola J.P., Murzin D.Yu., Salmi T., "Utilization of electromagnetic and acoustic irradiation in enhancing heterogeneous catalytic reactions", Appl. Catal. A 2005, 279, 1 Winayanuwattikun P., Kaewpiboon C., Piriyakananon K., Tantong S., Thakernkarnkit W., Chulalaksananukul W. et al. "Potential plant oil feedstock for lipase-catalyzed biodiesel production in Thailand", Biomass. and Bioen. 2008, 32, 1279.