Óxidos à base de titânio são estudados por suas diversas aplicações. Dentre eles, compostos com estrutura cristalina de perovskita apresentam propriedades elétricas diferenciadas. Ademais, os recém-descobertos nanotubos derivados de TiO2 por método hidrotérmico têm chamado a atenção dos pesquisadores por sua alta área superficial e fácil obtenção, embora ainda haja controvérsias sobre sua estrutura cristalina e a influência das condições de síntese. Com o desenvolvimento tecnológico, tornou-se fundamental a obtenção de materiais mais puros e com propriedades controladas, o que vem sendo alcançado através de rotas brandas, relacionadas à Química Doce. Simultaneamente, a preocupação ambiental vem influenciando as metodologias sintéticas através das diretrizes da Química Verde. Esta pesquisa visa: 1. caracterização de SrTiO3 obtido por rotas brandas - sal fundido, hidrotérmica, precipitação do sol e combustão. Os produtos foram caracterizados por análise de sorção de N2, DRX e termogravimetria, para a comparação de área superficial (BET), perfil de porosidade (DFT), composição cristalina e cristalinidade, tamanho de partículas e composição química. 2. exploração do sistema de nanotubos derivados de TiO2 pelo método hidrotérmico em NaOH 10 mol.L-1. Foram comparados quatro precursores (TiO2 amorfo, anatase e rutilo obtidos via precipitação de alcóxido, e o comercial P25), dois tempos de reação (24h e 72h), e o efeito de lavagem posterior com HCl. As amostras foram caracterizadas por DRX, área superficial (BET), perfil de porosidade (BJH), MEV e MET, além de espectroscopia Raman e TG e o efeito da temperatura na composição cristalina das amostras. A rota de precipitação do sol produziu SrTiO3 com maior grau de cristalinidade e de impurezas, sendo que sua área superficial diminuiu após tratamento a 400°C. Todos os produtos continham SrCO3, eliminado após 900°C. O método da combustão não formou o titanato. Nanotubos de comprimentos variados foram obtidos de todos os precursores cristalinos, sendo que rutilo não gerou outros tipos de nanoestruturas e os nanotubos mais longos. Além disso, foi o polimorfo que reagiu mais lentamente. O precursor amorfo gerou nanoestruturas semelhantes a nanofios. Foi observado que os nanotubos são compostos de titanatos de sódio lamelares, sendo esses cátions trocados por H+ pela lavagem dos pós com HCl. Essa troca iônica promove a diminuição da região interlamelar e o aumento da área superficial das amostras. / Titanium based oxides are studied for their wide range of applications. Among them, perovskite-like oxides show especial electrical properties. Furthermore, the recently discovered TiO2-derived nanotubes through hydrothermal process have been drawing researchers\' attention for their high surface area and because they can be easily obtained, although their crystal structure and the influence of condition synthesis still being point of controversy. Due to technological advances, the production of property-controlled, composition and phase pure materials has become crucial. These aims have been achieved by the employment of soft routes, related to Soft Chemistry synthesis. Simultaneously, environmental concerns have influenced synthetic methodologies through the Green Chemistry guidelines. This research aims: 1. characterizing of SrTiO3 synthesized by soft routes, namely molten salt synthesis, hydrothermal method, sol-precipitation process and combustion synthesis. The products were characterized by N2 sorption analysis, XRD and thermogravimetry in order to compare their surface area (BET), porous structure (DTF), chemical and crystal phase composition, crystallinity and particle size. 2. exploring the system of nanotubes hydrothermally derived from TiO2 in NaOH 10 mol.L-1. The effects of precursor type (amorphous TiO2, anatase and rutile obtained by alcoxide hydrolysis, and commercial P25), reaction time (24h and 72h), and acid washing treatment were compared. The samples were characterized by XRD, surface area (BET), porous structure (BJH), SEM and TEM, besides Raman spectroscopy, TG and temperature effect on the crystal composition. The sol-precipitation route produced the SrTiO3 sample with higher crystallinity and amount of impurities, while its surface area decreased on 400°C heat-treatment. All products showed SrCO3 presence up to 900°C. Combustion synthesis did not lead to the strontium titanate. Varied-length nanotubes and other nanostructures were obtained from all crystalline precursors, although rutile-derived samples showed only nanotubes, and the longest ones. On the other hand, this precursor reacted more slowly than the others. Amorphous TiO2 produced wire-like nanostructures. It has been observed that nanotubes are composed of lamellar sodium titanate, and that HCl washing promotes Na+ exchange for H+ ions. This ion-exchange leads to a decrease in the interlamellar spacing and an increase in the surface area of the samples.

Óxidos à base de titânio são estudados por suas diversas aplicações. Dentre eles, compostos com estrutura cristalina de perovskita apresentam propriedades elétricas diferenciadas. Ademais, os recém-descobertos nanotubos derivados de TiO2 por método hidrotérmico têm chamado a atenção dos pesquisadores por sua alta área superficial e fácil obtenção, embora ainda haja controvérsias sobre sua estrutura cristalina e a influência das condições de síntese. Com o desenvolvimento tecnológico, tornou-se fundamental a obtenção de materiais mais puros e com propriedades controladas, o que vem sendo alcançado através de rotas brandas, relacionadas à Química Doce. Simultaneamente, a preocupação ambiental vem influenciando as metodologias sintéticas através das diretrizes da Química Verde. Esta pesquisa visa: 1. caracterização de SrTiO3 obtido por rotas brandas - sal fundido, hidrotérmica, precipitação do sol e combustão. Os produtos foram caracterizados por análise de sorção de N2, DRX e termogravimetria, para a comparação de área superficial (BET), perfil de porosidade (DFT), composição cristalina e cristalinidade, tamanho de partículas e composição química. 2. exploração do sistema de nanotubos derivados de TiO2 pelo método hidrotérmico em NaOH 10 mol.L-1. Foram comparados quatro precursores (TiO2 amorfo, anatase e rutilo obtidos via precipitação de alcóxido, e o comercial P25), dois tempos de reação (24h e 72h), e o efeito de lavagem posterior com HCl. As amostras foram caracterizadas por DRX, área superficial (BET), perfil de porosidade (BJH), MEV e MET, além de espectroscopia Raman e TG e o efeito da temperatura na composição cristalina das amostras. A rota de precipitação do sol produziu SrTiO3 com maior grau de cristalinidade e de impurezas, sendo que sua área superficial diminuiu após tratamento a 400°C. Todos os produtos continham SrCO3, eliminado após 900°C. O método da combustão não formou o titanato. Nanotubos de comprimentos variados foram obtidos de todos os precursores cristalinos, sendo que rutilo não gerou outros tipos de nanoestruturas e os nanotubos mais longos. Além disso, foi o polimorfo que reagiu mais lentamente. O precursor amorfo gerou nanoestruturas semelhantes a nanofios. Foi observado que os nanotubos são compostos de titanatos de sódio lamelares, sendo esses cátions trocados por H+ pela lavagem dos pós com HCl. Essa troca iônica promove a diminuição da região interlamelar e o aumento da área superficial das amostras. / Titanium based oxides are studied for their wide range of applications. Among them, perovskite-like oxides show especial electrical properties. Furthermore, the recently discovered TiO2-derived nanotubes through hydrothermal process have been drawing researchers\' attention for their high surface area and because they can be easily obtained, although their crystal structure and the influence of condition synthesis still being point of controversy. Due to technological advances, the production of property-controlled, composition and phase pure materials has become crucial. These aims have been achieved by the employment of soft routes, related to Soft Chemistry synthesis. Simultaneously, environmental concerns have influenced synthetic methodologies through the Green Chemistry guidelines. This research aims: 1. characterizing of SrTiO3 synthesized by soft routes, namely molten salt synthesis, hydrothermal method, sol-precipitation process and combustion synthesis. The products were characterized by N2 sorption analysis, XRD and thermogravimetry in order to compare their surface area (BET), porous structure (DTF), chemical and crystal phase composition, crystallinity and particle size. 2. exploring the system of nanotubes hydrothermally derived from TiO2 in NaOH 10 mol.L-1. The effects of precursor type (amorphous TiO2, anatase and rutile obtained by alcoxide hydrolysis, and commercial P25), reaction time (24h and 72h), and acid washing treatment were compared. The samples were characterized by XRD, surface area (BET), porous structure (BJH), SEM and TEM, besides Raman spectroscopy, TG and temperature effect on the crystal composition. The sol-precipitation route produced the SrTiO3 sample with higher crystallinity and amount of impurities, while its surface area decreased on 400°C heat-treatment. All products showed SrCO3 presence up to 900°C. Combustion synthesis did not lead to the strontium titanate. Varied-length nanotubes and other nanostructures were obtained from all crystalline precursors, although rutile-derived samples showed only nanotubes, and the longest ones. On the other hand, this precursor reacted more slowly than the others. Amorphous TiO2 produced wire-like nanostructures. It has been observed that nanotubes are composed of lamellar sodium titanate, and that HCl washing promotes Na+ exchange for H+ ions. This ion-exchange leads to a decrease in the interlamellar spacing and an increase in the surface area of the samples.

Plastic waste is accumulated in landfills and the environment at an exponentially increasing rate. Currently, about 350 million tons of plastic waste is generated annually while only 9% is recycled. Plastic waste and its degradation products, microplastics, pose a severe threat to the ecosystem and eventually human health. Polyolefin (Polyethylene (PE) and Polypropylene (PP)) waste is 63% of the total plastic waste. Converting polyolefin waste into useful products including clean gasoline, diesel, wax, and monomers, via hydrothermal processing (HTP) can help reduce the plastic waste accumulation. In this study, sorted PE waste was converted via supercritical water liquefaction (SWL) into gasoline blendstock, No.1 ultra-low-sulfur diesel, and clean waxes with high yields and high purities. Comprehensive reaction pathways for PE conversion were proposed based on detailed GC×GC analyses. Furthermore, a new low-pressure (~2 MPa) hydrothermal processing (LP-HTP) method was developed to convert mixed polyolefin waste. This new LP-HTP method can save 90% of the capital cost and energy compared to SWL. The oil products were distilled into clean gasoline and No.1 ultra-low-sulfur diesel. The reaction pathways of PE and PP were independent while the synergistic effects improved the fuel qualities. With this LP-HTP method, polyolefin waste can be converted into up to 190 million tons of fuels globally, while 92% of the energy and 71% of the GHG emissions can be saved compared to conventional methods for producing fuels. Overall, this method is robust, flexible, energy-efficient, and environmental-friendly. It has a great potential for reducing the polyolefin waste accumulation in the environment and associated risks to human health.<br>

The mining, processing, and use of finite natural resources is associated with significant interventions in the natural environment. Thus, these and other negative consequences make it necessary to reduce resource consumption. An important field of action is the more efficient use of biogenic residues as secondary raw materials. However, high water containing biomasses are still a problem since they need an energy- and cost-intensive pre-treatment for many conversion processes, which can make their use uneconomical. Hydrothermal processes (HTP) seem to be promising, since they require an aqueous environment for optimal processing anyway. Although technological progress within the industry is recognisable, however, to date HTP have not been established in industrial continuous operation in Germany. The core of this work is identifying reasons for this sluggish development and deriving appropriate recommendations for action. Based on the hypothesis that HTP can contribute to the efficient utilisation of biogenic residues in the future, potentials and obstacles for the development of HTP in Germany are identified using a literature review, expert survey, expert workshop, and SWOT analysis. To estimate the future potential of HTP in a systematic and structured way, a multi-criteria technology assessment approach is developed based on the results. To this end, assessment criteria for HTP are derived, weighted by expert judgment, and integrated into a transparent and structured procedure. In addition, mainly based on a Delphi-survey key factors of HTP development by 2030 in Germany are identified and three development alternatives for HTP in Germany by 2030 are derived. Using a system analysis and a comparative multi-criteria analysis at plant level, these scenarios are analysed for their possible future impact. Based on this methodology, the work shows that the production costs for the end products, the energy efficiency of the process, and the proportion of recycled phosphorus are of high relevance to the techno-economic success of HTP compared to reference systems, and they are therefore of high importance for its future development on the plant level. In addition, further key factors for the future development of HTP in Germany on the system level are found to be mainly in the political-legal (e.g. legal waste status of products from HTP) and techno-economic (e.g. cost-effective process water treatment) areas. According to this, important fields of action are the identification and use of cost reduction potentials (e.g. heat waste use), the development of system integrated decentralised plant concepts with integrated nutrient recycling (e.g. phosphorus), and the development of cost-effective ways to treat process water. System integration, cost-effective process water treatment, and nutrient recycling are all closely linked to production costs, investment costs, and potential revenues, and can contribute to improved process economics. For these areas, there is promising future potential to achieve higher competitiveness with reference technologies that are currently more economical.:Bibliographic description Curriculum Vitae Selbstständigkeitserklärung Danksagung List of Publications Contribution to the Publications Contents List of Acronyms List of Tables List of Figures Part I Introductory Chapters 1 Introduction and Background Hydrothermal processes: Introduction and status quo State of the art in the research field and knowledge gaps Objective and research framework Expected value added of this work 2 Materials and methods Derivation of HTP evaluation metrics and technology assessment tool Derivation of key HTP development factors and scenarios Performing the system-level scenario analysis Plant-level scenario analysis and test application of the assessment tool Derivation of core recommendations 3 Results and discussion Key development factors for HTP in Germany and scenarios System-level scenario analysis Test application of the assessment tool on plant level scenarios Recommendations Discussion 4 Conclusion and outlook Future research Further fields for the application of the developed methods 5 References Part II Appended Articles Paper I Paper II Paper III Paper IV Paper V Paper VI / Der Abbau, die Verarbeitung und die Nutzung endlicher natürlicher Ressourcen sind mit erheblichen Eingriffen in die natürliche Umwelt verbunden. Diese und andere negative Folgen machen es daher erforderlich, den Ressourcenverbrauch zu senken. Ein wichtiges Handlungsfeld ist die effizientere Nutzung biogener Reststoffe als Sekundärrohstoffe. Stark wasserhaltige Biomassen sind jedoch ein Problem, da sie für viele Umwandlungsprozesse eine energie- und kostenintensive Vorbehandlung benötigen, was ihre Verwendung unwirtschaftlich machen kann. Hydrothermale Prozesse (HTP) scheinen für diese Reststoffe allerdings vielversprechend zu sein, da sie ohnehin eine wässrige Umgebung für eine optimale Verarbeitung benötigen. Obwohl der technologische Fortschritt innerhalb der Branche erkennbar ist, wurde HTP in Deutschland bisher nicht im industriellen Dauerbetrieb etabliert. Der Kern dieser Arbeit besteht darin, Gründe für diese schleppende Entwicklung zu ermitteln und geeignete Handlungsempfehlungen abzuleiten. Basierend auf der Hypothese, dass HTP in Zukunft zur effizienten Nutzung biogener Reststoffe beitragen können, werden Potenziale und Hindernisse für deren Entwicklung in Deutschland anhand einer Literaturrecherche, einer Expertenumfrage, eines Expertenworkshops und einer SWOT-Analyse ermittelt. Um das zukünftige Potenzial von HTP systematisch und strukturiert abzuschätzen, wird basierend auf den Ergebnissen ein multi-kriterieller Technologiebewertungsansatz entwickelt. Zu diesem Zweck werden Bewertungskriterien für HTP abgeleitet, nach Expertenmeinung gewichtet und in ein transparentes und strukturiertes Verfahren integriert. Darüber hinaus werden hauptsächlich auf der Grundlage einer Delphi-Umfrage Schlüsselfaktoren für die HTP-Entwicklung bis 2030 in Deutschland identifiziert und drei Entwicklungsalternativen für HTP in Deutschland bis 2030 abgeleitet. Mithilfe einer Systemanalyse und einer vergleichenden multi-kriteriellen Analyse auf Anlagenebene werden diese Szenarien auf ihre möglichen zukünftigen Auswirkungen hin analysiert. Basierend auf dieser Methodik zeigen sich als Ergebnisse, dass die Produktionskosten für die Endprodukte, die Energieeffizienz der Prozesse und der Anteil an recyceltem Phosphor für den techno-ökonomischen Erfolg von HTP im Vergleich zu Referenzsystemen von hoher Relevanz und daher auch von hoher Bedeutung für die zukünftige Entwicklung auf Anlagenebene sind. Darüber hinaus liegen weitere Schlüsselfaktoren für die künftige Entwicklung von HTP in Deutschland auf Systemebene hauptsächlich im politisch-rechtlichen (z. B. legalen Abfallstatus von Produkten aus HTP) und techno-ökonomischen (z. B. kostengünstige Prozesswasseraufbereitung)) Bereichen. Wichtige Handlungsfelder sind demnach die Ermittlung und Nutzung von Kostensenkungspotentialen (zB Abwärmenutzung), die Entwicklung systemintegrierter dezentraler Anlagenkonzepte mit integriertem Nährstoffrecycling (z.B. Phosphor) und die Entwicklung kostengünstiger Wege zur Prozesswasserbehandlung. Systemintegration, kostengünstige Prozesswasseraufbereitung und Nährstoffrecycling hängen eng mit Produktionskosten, Investitionskosten und potenziellen Einnahmen zusammen und können zu einer verbesserten Wirtschaftlichkeit der Prozesse beitragen. Für diese Bereiche besteht ein vielversprechendes Zukunftspotenzial für eine höhere Wettbewerbsfähigkeit zu Referenztechnologien, die derzeit noch wirtschaftlicher sind.:Bibliographic description Curriculum Vitae Selbstständigkeitserklärung Danksagung List of Publications Contribution to the Publications Contents List of Acronyms List of Tables List of Figures Part I Introductory Chapters 1 Introduction and Background Hydrothermal processes: Introduction and status quo State of the art in the research field and knowledge gaps Objective and research framework Expected value added of this work 2 Materials and methods Derivation of HTP evaluation metrics and technology assessment tool Derivation of key HTP development factors and scenarios Performing the system-level scenario analysis Plant-level scenario analysis and test application of the assessment tool Derivation of core recommendations 3 Results and discussion Key development factors for HTP in Germany and scenarios System-level scenario analysis Test application of the assessment tool on plant level scenarios Recommendations Discussion 4 Conclusion and outlook Future research Further fields for the application of the developed methods 5 References Part II Appended Articles Paper I Paper II Paper III Paper IV Paper V Paper VI