Os componentes do conjunto membrana/eletrodos (MEA) das células a combustível de membrana de eletrólito polimérico/Polymer Electrolyte Membrane Fuel Cells (PEMFC) são sensíveis a impurezas, as quais podem vir do ar, do gás combustível e/ou da degradação dos componentes do módulo. Amônia, sulfeto de hidrogênio e monóxido de carbono são juntos os três principais subprodutos cotaminadores nos processos de geração de hidrogênio por reforma de combustíveis. Estes contaminadores afetam negativamente o desempenho das PEMFCs, assim é importante o entendimento destes efeitos para mitigá-los e introduzir a tecnologia das PEMFCs no mercado consumidor. Desta forma experimentos foram realizados visando diagnosticar os efeitos da amônia e do sulfeto de hidrogênio sobre os componentes do MEA das PEMFCs. Para a contaminação por sulfeto de hidrogênio foi provado, utilizando-se da técnica de cromatografia gasosa e de stripping, que a contaminação ocorre através da interação química e eletroquímica do contaminador com a superfície do catalisador de platina, e que estas interações ocorrem via um processo dissociativo e um processo oxidativos respectivamente. Estes processos de interação geram enxofre adsorvido sobre a superfície da platina, a qual é bloqueada para posterior oxidação de hidrogênio, gerando sobrepotenciais que reduzem a diferença de potencial da célula. Utilizando-se da técnica de cromatografia gasosa e agora de voltametria cíclica foi mostrado na PEMFC, que durante o processo de remoção do enxofre adsorvido a platina dióxido de enxofre é gerado. Ainda na PEMFC, foi mostrado utilizando-se da técnica de \"air bleed\" que maiores tolerâncias ao sulfeto de hidrogênio podem ser alcançadas, apesar de ser insignificante. Para o caso da contaminação da PEMFC por amônia, indiretamente foi mostrado, utilizando-se técnicas eletroquímicas solução de ácido perclórico, que amônia pode afetar a reação de redução de oxigênio pela sua adsorção sobre a superfície do catalisador, ou pelo bloqueio da mesma para posterior adsorção/redução de oxigênio. Em estudos de absorção de água e condutividade de membranas de NafionTM, sob diferentes frações catiônicas (prótons/amônio), em contato com água na fase vapor sob diferentes atividades, foi mostrado que quanto maior a concentração de íons contaminadores no eletrólito menor a quantidade de água absorvida e menor a condutividade da membrana. Também foi mostrado que se tais membranas fossem usadas como eletrólito em PEMFCs, o desempenho da célula seria afetado drasticamente por perdas ôhmicas. Também foi mostrado que sob contaminação por amônia, PEMFCs sofrem aumentos em resistências ôhmicas devido a reduções na condutividade do eletrólito, contudo foi provado que esta representa menos de dez por cento do total de perdas observadas no desempenho da célula. Desde estudo foi concluído que amônia afeta o desempenho das PEMFCs principalmente pela redução na atividade dos prótons na camada catalítica catódica, que causa reduções no potencial misto de equilíbrio da reação de redução de oxigênio, e portanto na diferença de potencial da célula. Finalmente foi provado indiretamente que amônia deixa a célula através do equilíbrio de amônio com água, o qual deslocado gera amônia, a qual deixa a célula junto com o fluxo de gás cotódico. / The Membrane Electrode Assembly components of a PEMFC are sensitive to impurities, which can came with the air or hydrogen stream, or from the degradation of the stack components. Ammonia, hydrogen sulfide and carbon monoxide are together the main sub-products of fuel reforming processes for generating hydrogen. These contaminants negatively affect the PEMFC performance, so it is important to understand what those effects are in order to mitigate them and introduce PEMFC technology in the mass market. Therefore, experiments were carried out to diagnose the effects hydrogen sulfide and ammonia have on the MEA components of PEMFCs. For contamination by hydrogen sulfide it was proved utilizing EMS and stripping techniques that the poisoning process happens by chemical and electrochemical interactions of the contaminant with the Platinum catalyst surface, and that these interactions happen by a dissociative and oxidative process, respectively. Those processes generate sulfur adsorbed on the Platinum surface, which blocks it for further hydrogen oxidation, generating overpotentials, which reduce the cell potential. Utilizing the EMS and now the cyclic voltammetry technique it was shown that during the process of removing sulfur from the Platinum surface one generates sulfur dioxide. Using the Air Bleed technique it was shown that higher tolerances of the PEMFC against hydrogen sulfide can be reached, despite being insignificant. For contamination of the cell by ammonia it was indirectly proved utilizing electrochemical techniques in perchloric acid solutions that ammonia can affect the oxygen reduction reaction by adsorbing on the catalyst surface, or by blocking the surface for further oxygen adsorption/reduction. Studying water uptake and ionic conductivity of Nafion membranes under many different cation fractions (proton/ammonium) in contact with water vapor at different temperatures and water activities, it was proved that the more ammonium one has in the membrane the less will be the water uptake and ionic conductivity of it. It was also shown that if those membranes were used as electrolyte in PEMFC the cell performance would be severely affected by ohmic losses. It was also shown that under ammonia exposure PEMFCs suffer by ohmic resistance increases due to the lowering in the ionic conductivity of the electrolyte, however it was proved that it represent less than ten percent of the observed losses in the cell performance. From this study it was concluded that ammonia mainly affect the PEMFC performance by lowering the cathode catalyst layer proton activity, which lowers the oxygen reduction reaction equilibrium potential, and then the cell potential. Finally it was indirectly proved that ammonia leaves the cell by the equilibrium of ammonium and water, which dislocated generates ammonia that leaves the cell together with the cathode gas stream.

As respostas termorregulatórias ao lipopolissacarídeo (LPS) são influenciadas por moduladores que aumentam (febrigênicos) ou diminuem (criogênicos) a temperatura corporal (Tb). Entre eles, o neurotransmissor gasoso sulfeto de hidrogênio (H2S) modula a inflamação sistêmica induzida por endotoxina em ratos, agindo como uma molécula anti-inflamatória e criogênica, embora os mecanismos subjacentes ainda sejam pouco compreendidos. Considerando que a endotoxina é um ligando para o Toll-like receptor 4 (TLR4) e que evidências recentes revelam um cross-talk entre a via de sinalização TLR e fosfo-Akt (p-Akt), o objetivo do presente estudo foi investigar se o H2S atua como um mediador antiinflamatório e antipirético durante as fases termorregulatórias que ocorrem no choque endotoxêmico (hipotermia e febre) induzido por lipopolissacarídeo bacteriano (LPS, 2,5 mg / kg intraperitoneal (ip)) através da modulação sobre a produção de prostaglandina D2 (PGD2) e a ativação de Akt na área pré-óptica ântero-ventral do hipotálamo (AVPO). A Tb profunda de ratos mantidos a uma temperatura ambiente de 25 °C foi registrada antes e depois da inibição farmacológica da enzima cistationina ?-sintase (CBS - responsável pela produção endógena de H2S no cérebro) usando aminooxiacetato (AOA, 100 pmol, intracerebroventricular (icv)), combinado ou não com administração de LPS. Para esclarecer os mecanismos responsáveis por esses ajustes da resposta imune, foram determinados na AVPO os níveis de H2S, a produção de PGD2 e o perfil de expressão das proteínas CBS, p-Akt e p-CREB. Além disso, foi analisada a concentração de citocinas plasmáticas (IL-1?, IL-6, IL-10, TNF?, IFN-? , E IL-4). A injeção ip de LPS causou hipotermia típica seguida de febre. Os níveis de AVPO H2S aumentaram significativamente durante a hipotermia quando comparado com ratos eutérmicos e febris. A microinjeção icv de AOA não causou nenhuma alteração na Tb nem na produção basal de PGD2 durante a eutermia. Em ratos tratados com LPS, o AOA causou uma atenuação na queda da Tb durante a fase de hipotermia e uma febre exacerbada, simultaneamente com o aumento na produção de PGD2 e abolição do aumento induzido pela endotoxina na atividade de Akt. Durante a fase de febre, a expressão relativa de CBS esteve significativamente diminuída enquanto a expressão relativa de p-Akt esteve aumentada, quando comparado com ratos eutérmicos e hipotérmicos. As citocinas plasmáticas aumentaram durante a inflamação sistêmica, mas apenas a IL-4 mostrou um padrão semelhante em relação à Akt. Estes dados são consistentes com a noção de que o neurotransmissor gasoso H2S modula as fases de hipotermia e febre durante o choque endotoxêmico, atuando como uma molécula criogênica. Este papel anti-inflamatório durante a inflamação sistémica envolve uma regulação positiva da PGD2, de Akt e da IL-4 plasmática. / Thermoregulatory responses to lipopolysaccharide (LPS) are affected by modulators that increase (pro-pyretic) or decrease (cryogenic) body temperature (Tb). Among them, the gaseous messenger hydrogen sulfide (H2S) modulates endotoxin-induced systemic inflammation being an anti-inflammatory and cryogenic molecule, although the underlying mechanisms are still poorly understood. Since endotoxin is a Toll-like receptor 4 (TLR4) ligand and recent evidence indicates that there is a possible a cross-talk between the TLR and phospho-Akt (p-Akt) signaling pathway, the current study aimed to investigate whether H2S acts as an anti-inflammatory and anti-pyretic mediator during thermoregulatory phases of endotoxic shock (hypothermia and fever) induced by bacterial lipopolysaccharide (LPS, 2.5 mg/kg intraperitoneal (ip)) through the modulation of prostaglandin D2 (PGD2) production and activation of Akt in the anteroventral preoptic region of the hypothalamus (AVPO). Deep Tb in rats kept at an ambient temperature of 25 °C, was recorded before and after pharmacological inhibition of the enzyme cystathionine ?-synthase (CBS - responsible for H 2S endogenous production in the brain) using aminooxyacetate (AOA; 100 pmol/1 ?l intracerebroventricular (icv)) combined or not with endotoxin administration. To clarify the mechanisms responsible for these adjustments on immune response were verified in the AVPO H 2S levels, PGD2 production and expression profiles of CBS, p-Akt and p-CREB. In addition, plasma cytokines concentration (IL-1?, IL-6, IL-10, TNF?, IFN-?, and IL-4) was analyzed. Intraperitoneal injection of LPS caused typical hypothermia followed by fever. Intracerebroventricular microinjection of AOA neither affected Tb nor basal PGD2 production during euthermia. Levels of AVPO H2S were significantly increased during hypothermia when compared to both euthermic and febrile rats. In LPS-treated rats, AOA increased Tb values during hypothermia and fever, along with enhanced PGD2 production and abolition of endotoxin-induced increase in Akt activity. During fever, CBS relative expression was significantly decreased whereas p-Akt was significantly increased when compared to both euthermic and hypothermic rats. Plasma cytokines were increased during systemic inflammation, but only IL-4 showed a similar pattern in relation to Akt. These data are consistent with the notion that the gaseous messenger H2S modulates hypothermia and fever during endotoxic shock, acting as a cryogenic molecule. This anti-inflammatory role during systemic inflammation involves a H2S-induced up-modulation of PGD2, Akt and plasma IL-4.

Les composés traces présents dans les biogaz sont un frein à leur valorisation énergétique. Trois familles ont été identifiées comme particulièrement nocives pour les catalyseurs des reformeurs externes et pour l’anode des piles à combustible de type SOFC : les composés soufrés, siliciés et chlorés. Un traitement poussé du biogaz est donc indispensable pour une telle application. Ce travail à caractère expérimental s’intéresse au développement d’un système de traitement d’affinage destiné à l’adsorption de ces composés. Des matériaux adsorbants ont été sélectionnés pour leur efficacité dans l’élimination du sulfure d’hydrogène (H2S – composé soufré), de l’octaméthylcyclotétrasiloxane (D4 – composé silicié) et du cis-1,2-dichloroéthène (C2H2Cl2 – composé chloré), molécules cibles représentatives des trois familles préjudiciables. La zéolithe étudiée présente la meilleure efficacité d’élimination de l’H2S, tandis que le gel de silice est plus adapté à l’adsorption du D4. Une étude paramétrique a mis en évidence l’influence de la hauteur de lit d’adsorbant, de la concentration en polluant, du débit de gaz, de la présence de composés traces en mélange et de l’humidité sur les performances épuratoires. Des essais sur un biogaz brut d’installation de stockage de déchets non dangereux ont montré qu’il est possible de maintenir une concentration en H2S sous le seuil de tolérance de 1 ppmvH2S du reformeur. En s’appuyant sur des caractérisations physico-chimiques des adsorbants, des hypothèses concernant les mécanismes de rétention ont été proposées pour les couples zéolithe + H2S et gel de silice + D4. L’H2S est adsorbé puis oxydé en soufre élémentaire à la surface de la zéolithe. Lors de l’adsorption sur gel de silice, le D4 semble polymériser en surface. Ces deux phénomènes empêchent la régénération des adsorbants. Une première approche de modélisation des phénomènes d’adsorption pour le couple gel de silice + D4 a permis de déterminer le coefficient global de transfert de masse. Les courbes de percée obtenues expérimentalement pour différentes masses d’adsorbant ont été simulées avec succès. Des « règles de dimensionnement » ont été proposées pour un dimensionnement industriel d’un traitement d’affinage pour une valorisation en SOFC. L’analyse technico-économique a montré que la filière SOFC envisagée est viable techniquement, mais pas économiquement, la technologie SOFC étant encore trop coûteuse par rapport aux techniques de valorisation conventionnelles. Toutefois, la solution semble prometteuse d’un point de vue environnemental. / Biogas energy use is hampered by the presence of trace compounds. Three contaminant families are particularly detrimental for external reforming catalysts and solid oxide fuel cell (SOFC) anodes: sulfur-containing compounds, volatile organic silicon compounds (VOSiC) and chlorinated compounds. Therefore, a thorough biogas treatment is necessary for such an application. This experimental work deals with the development of a polishing treatment for the adsorption of these contaminants. Adsorbents were selected for their efficiency to remove hydrogen sulfide (H2S – sulfur-containing compound), octamethylcyclotetrasiloxane (D4 – VOSiC) and cis-1,2-dichloroéthene (C2H2Cl2 – chlorinated compound), molecules representative of the three harmful families. The studied zeolite showed the best efficiency for H2S removal whereas silica gel performed best for D4 adsorption. A parametric study highlighted the influence of adsorbent bed height, contaminant concentration, gas flow rate, the presence of contaminants in mixture and humidity on purification performance. Adsorption tests with a raw landfill biogas showed that it is possible to guarantee an H2S concentration below the 1 ppmvH2S tolerance limit of the reformer. Using adsorbent physicochemical characterizations, hypothesis about retention mechanisms were proposed for the couples zeolite + H2S and silica gel + D4. H2S is adsorbed and then oxidized into elemental sulfur at the surface of the zeolite. During the adsorption on silica gel, D4 seems to polymerize on the surface. These two phenomena prevent the regeneration of the adsorbents. A first modeling approach of the adsorption phenomena involved for the couple silica gel + D4 allowed the determination of the global mass transfer coefficient. Experimental breakthrough curves obtained for different masses of adsorbent were successfully simulated. Some “dimensioning rules” were proposed for the industrial design of a polishing treatment able to produce a biogas with the quality required to feed an SOFC. The techno-economic analysis showed that the SOFC solution is technically feasible but not economically viable because SOFC technology is still too costly compared to conventional conversion devices. However, the solution seems promising from an environmental point of view.

Les résidus miniers représentent les sous-produits minéraux finement broyés issus des procédés de traitement et d’enrichissement des minerais. Durant l’exploitation d’une mine, ces rejets sont habituellement transportés sous formes de pulpes et entreposés en surface dans des aires d’accumulation appelées parcs à résidus. Ces derniers sont des ouvrages, le plus souvent, difficiles à gérer et coûteux à restaurer. Ils sont à l’origine d’une multitude d’impacts environnementaux qui dépendent principalement de leur potentiel polluant, de leur mode de gestion, de la stabilité physique des infrastructures de confinement et des conditions climatiques spécifiques au site d’entreposage. Dans ce contexte, plusieurs études ont été entreprises afin de développer de nouvelles techniques qui permettraient une gestion effective et durable de ces sous-produits minéraux. Des voies de valorisation dans le domaine du BTP ont ainsi été explorées. Les résultats ont montré la possibilité de réutilisation de certains rejets miniers comme matériaux cimentaires et additifs pour mortiers ou béton. Toutefois, la majorité des formulations proposées n’ont pas dépassé le stade du laboratoire. De plus, l’utilisation des rejets miniers comme matériaux de construction est encore sujet à des difficultés en matière d’acceptabilité sociale et à d’innombrables préoccupations, notamment leur stabilité physico-chimique et leur éco-compatibilité. En parallèle, l’utilisation artisanale et non contrôlée des rejets miniers à faibles teneurs en sulfures comme matériaux de construction est en pleine croissance dans quelques pays tel que le Maroc. En effet, à proximité de quelques sites miniers abandonnés, ces rejets sont considérés comme des sables naturels et sont utilisés pour la confection de mortier de finition et de surfaçage des murs d’habitations. Ce recyclage artisanal peut constituer des risques mécaniques et environnementaux liés surtout à la non-conformité mécanique de ces matériaux et à la présence de concentrations non négligeables de métaux résiduels dans les rejets miniers. L’objectif de ce travail de recherche est donc d’évaluer l’impact de l’utilisation actuelle de deux rejets miniers marocains (Zeida et Mibladen), communément utilisés comme agrégats dans la région de la haute-Moulouya, sur les propriétés physico-chimiques des mortiers de finition et d’étudier, sur le long terme, le relargage des métaux lourds en scénario de lixiviation. Ce travail se donne aussi comme objectif spécifique, d’étudier la faisabilité technique d’utilisation des rejets miniers à faible teneur en sulfures comme substituant au sable conventionnel pour la confection de mortiers d’enduit et de maçonnerie. / Mine tailings represent the finely ground industrial by products generated throw beneficiation of ore minerals. During mine exploitation, these tailings are generally transported in slurry form to large storage facilities, called tailings ponds or impoundments. These facilities are, in most cases, difficult to manage and expensive to rehabilitate. They are responsible for the generation of important environmental impacts and significant ecological disruptions, depending on their pollution potential, management technique, physical stability and the climate conditions. In this context, numerous studies have been conducted to develop new techniques for a sustainable management of mine tailings. The feasibility of reusing some tailings in the construction sector as cementing materials and additives for mortars or concretes were successfully achieved. However, the majority of the conducted studies are still at laboratory stages. Moreover the reuse of tailings as construction material is yet subject of numerous difficulties in term of social acceptance. Various parameters are also of concern, especially the physical and chemical stability of tailings as well as their eco-compatibility. In parallel, the uncontrolled reuse of low sulfide tailings as construction material is increasing in some developing countries (e.g. Morocco). In fact, nearby some abandoned mine sites, these tailings are considered as natural sands and are used for the manufacture of surface finishing mortars. This traditional recycling may constitute mechanical and environmental risks, principally related to tailings mechanical unconformity and to their non-negligible residual metal concentrations. Therefore, the aim of the current research is to evaluate the actual impact of two Moroccan mine tailings (named Zeida and Mibladen), commonly used as aggregates in the Upper-Moulouya region, on the mechanical properties of mortars and on their long term environmental behavior. This work has also as specific aim, to study the technical feasibility of using low sulfide tailings as sand substitute for the manufacture of rendering and masonry mortars. To attain this aim, a thorough characterization of the physical, chemical and mineralogical properties as well as the geochemical behavior of mine tailings was carried out. Mechanical properties of tailings-based mortars were then measured and compared to reference samples (sand-based mortars) using different tests such as setting time, entrained air volume and compressive strength. In parallel, mortars durability and hydration products were evaluated by mean of durability tests (wetting drying cycles, sulfate attack and acid rain simulation) and analytical methods (scanning electron microscopy, X-ray diffraction and thermo-gravimetric analysis). Finally, mortar samples were submitted to various leaching tests to evaluate the pollution potential of these matrices.

Le méthanethiol (MeSH) est un intermédiaire important dans la synthèse de la méthionine, un acide aminé largement utilisé dans l'industrie agro-alimentaire. Le marché étant en constante augmentation, il est indispensable d'optimiser la formation de MeSH à partir de méthanol (MeOH) et de sulfure d'hydrogène (H2S) en présence de K2WO4/Al2O3 (10,5 % massique). L'impact de paramètres clés, tels la conversion du méthanol, la température ou le rapport molaire H2S/MeOH a été étudié dans des conditions proches de celles du procédé. Un fort effet inhibiteur de l'eau, co-produit de la réaction, a été mis en évidence, aussi bien sur l'activité catalytique que sur les sélectivités des différents produits. En revanche, le dioxyde de carbone (CO2) et le monoxyde de carbone (CO), produits non valorisables, n'ont aucun impact sur les performances du catalyseur. Un schéma réactionnel complet a été établi rendant compte de la formation des différents produits de réaction. Un modèle cinétique faisant intervenir le formalisme de Langmuir-Hinshelwood, en accord avec les résultats expérimentaux, a été développé.La caractérisation du catalyseur K2WO4/Al2O3 a confirmé que le site actif est une paire acide-base, l'acidité étant apporté par le tungstène alors que le potassium génèrerait une basicité à la surface du matériau. A partir de ces observations, la mesure des performances catalytiques de solides à base de terres rares, présentant une acidité et une basicité plus fortes, montre que ceux-ci sont plus actifs que le catalyseur K2WO4/Al2O3, tout en conservant une sélectivité en MeSH similaire. / Methanethiol (MeSH) is a key intermediate involved in the synthesis of methionine, an essential amino acid widely used in food-processing industry. Given that methionine market is constantly growing, optimizing MeSH production from methanol (MeOH) and hydrogen sulfide (H2S) is of paramount importance. The impact of key parameters, such as MeOH conversion, temperature, or H2S/MeOH molar ratio has been studied in a range consistent with industrial conditions. A strong inhibiting effect of water (which is the co-product of the reaction) has been highlighted, both on catalytic activity and selectivities towards the different products. However, carbon dioxide (CO2) and carbon monoxide (CO), which are non-recoverable products, have no influence on catalytic performances. A complete reaction scheme accounting for the formation of the different reaction products has been proposed. A kinetic model using Langmuir-Hinshelwood formalism was developed, which affords precise estimation of experimental data.Characterization of K2WO4/Al2O3 catalyst confirmed that acid-base dual sites were the active sites responsible for MeSH formation. Acidity is mainly brought by tungsten species whereas potassium addition allows increasing the basicity of the catalyst. Based on these observations, the catalytic performances of rare-earth based oxides, which possess stronger acidity and basicity, have been measured. These materials exhibit significantly higher activity than K2WO4/Al2O3 catalyst, with similar MeSH selectivity.

Gegenstand dieser Arbeit ist die wissensbasierte Untersuchung verschiedener Eisenoxid/-hydroxid-Modifikationen für die alternierende Entfernung von Schwefelwasserstoff und Sauerstoff aus regenerativ erzeugten Gasen. Dafür wurden 37 Eisenoxide/-hydroxide systematisch auf ihre H2S- und O2-Adsorption hin untersucht und in Kombination mit deren physikalisch-chemischen Eigenschaften Struktur-Aktivitäts-Korrelationen abgeleitet. Die Aufklärung der ablaufenden Reaktionsmechanismen erfolgte mit spektroskopischen Analysenmethoden (DRIFTS Raman). Relevante Betriebsparameter wurden an einem α-FeOOH systematisch im Labormaßstab ermittelt. Daneben steht die Übertragbarkeit der Laborergebnisse in die technische Anwendung im größeren Maßstab (Upscaling) und mit Realgas im Fokus. Zudem wurde eine Wirtschaftlichkeitsbetrachtung inklusive eines Vergleiches mit Konkurrenzverfahren durchgeführt.

This diploma thesis is focused on comparison of results from simulations programs ProMax and PRO/II. Both simulation models were based on a sour water stripping unit according to a project of CBI Lummus s.r.o. The thesis also includes a theroretical part deals with technology of sour water stripping.

In ariden Gebieten tritt Schwefelwasserstoff häufig im Grundwasser auf, wodurch dessen Nutzung für die Trinkwassergewinnung aufgrund des störenden Geruchs und Geschmacks stark beeinträchtigt wird. Die in der Praxis oft eingesetzte Belüftung erweist sich zumeist als ineffizient und führt zu Geruchsbelästigungen in der Umgebungsluft. Das Ziel der Arbeit, die im Rahmen eines deutsch-israelischen Forschungsprojekts angefertigt wurde, bestand darin, einen wirksamen und für den praktischen Einsatz bei der Wasseraufbereitung geeigneten Katalysator zur Entfernung von Schwefelwasserstoff zu entwickeln, hinsichtlich verschiedener Verfahrensparameter und relevanter Randbedingungen durch systematische Batch- und Säulenversuche zu erproben und zu optimieren. Wichtige Kriterien zur Charakterisierung der Katalysatoren waren die Kinetik des Sulfidumsatzes, die Langzeitstabilität und die Zusammensetzung der Reaktionsprodukte. Die Nachahmung natürlich vorkommender Strukturen (z. B. Häm-Gruppe) und deren Anpassung an eine katalytische Sulfidoxidation war der Grundgedanke am Anfang der Arbeit. Entsprechende Materialien, organische Metallkomplexe (Porphyrine) auf Kohlenstoffträgern (Acetylen Black), wurden bereits erfolgreich bei der Sauerstoffreduktion in Brennstoffzellen eingesetzt. Cobalttetraphenylporphyrin (CoTPP) zeigte von allen getesteten Materialien die beste katalytische Wirksamkeit zur Sulfidoxidation. Die Sulfidumsetzung lief sowohl bei höheren pH-Werten als auch mit zunehmender Temperatur schneller ab. Anhand von Untersuchungen zum Einfluss des pH-Werts konnte bestätigt werden, dass eine katalytische Wirksamkeit nur für die Oxidation der Sulfid-Spezies HS- und S2- besteht. Mit Aktivkohle konnte ebenfalls eine katalytische Sulfidumsetzung erzielt werden, jedoch lag die Aktivität hier im Vergleich zum CoTPP deutlich niedriger. Bei allen getesteten katalytisch wirksamen Materialien entstand als vorrangiges Reaktionsprodukt Schwefel, gebildete Schwefel-Sauerstoff-Verbindungen wie Sulfat und Thiosulfat waren von untergeordneter Bedeutung. Die Untersuchungen zeigten, dass Acetylen Black aufgrund der sehr geringen Teilchengröße technisch kaum einsetzbar ist, weshalb weitere Trägermaterialien erprobt wurden. Im Gegensatz zu Aktivkohle oder Anthrazit erwiesen sich Weichfilze, insbesondere der Sigratherm Kohlenstoff-Weichfilz (KFA-Filz), als sehr gut geeignete Trägermaterialien. Beim Einsatz von Aktivkohle lagerte sich der gebildete Schwefel in den Porenräumen ab, was zu einer erheblichen Verringerung der katalytischen Aktivität führte. Dagegen wurde unter Verwendung des modifizierten Filzmaterials auch bei sehr langen Laufzeiten (bis 3000 Stunden) keine Abnahme der katalytischen Wirksamkeit beobachtet. Durch diese Katalysatormatrix konnte somit die Deaktivierung des Katalysators durch elementaren Schwefel verhindert werden. Bei abschließenden Versuchen unter Verwendung einer kleintechnischen Versuchsanlage konnte gezeigt werden, dass der Katalysator für den großtechnischen Einsatz geeignet ist. Im Vergleich zur Aktivkohle sind zwar größere Investitionskosten notwendig, andererseits können mit dem CoTPP-Material deutlich längere Laufzeiten realisiert werden. Aufgrund seiner guten technischen Handhabbarkeit ist der modifizierte KFA-Filz sowohl in kleinen dezentralen Anlagen (ländliche Siedlungen) als auch in größeren Wasserwerken einsetzbar. Zusätzliche Chemikalien sind für den Betrieb eines solchen Filters nicht erforderlich. Eine weitere Verbesserung der Sulfidentfernung wird bei langen Filterlaufzeiten durch sulfidoxidierende Bakterien bewirkt. Das Ziel, einen effizienten, technisch einsetzbaren Katalysator zur oxidativen Sulfidentfernung aus Wässern zu entwickeln, wurde somit erreicht. / Hydrogen sulfide often occurs in groundwater of arid areas. Because of its malodour, H2S containing water cannot be used as drinking water without treatment. Aeration as the most common treatment technique is less effective and leads to nasty odour of ambient air. Catalytic oxidation could be an alternative. The aim of this work was to develop and to optimize a technically applicable oxidation catalyst as well as to test its applicability under practical conditions. Various N4-chelates (e. g. porphyrins), which are frequently used for the reduction of oxygen in fuel cells, were evaluated for catalytic oxidation of sulfide at selected boundary conditions and process parameters using batch and column experiments. The new catalysts should be characterized in comparison with other materials. The oxidation kinetics, the long-time stability of the catalyst and the composition of oxidation products were the main criteria used for catalyst assessment. Cobalt tetraphenylporphyrin (CoTPP) showed the highest catalytic activity of all tested materials. The rate of sulfide transformation increased significantly with increasing temperature and at pH values higher than 6. A catalyst suitable for technical use in fixed-bed reactors was obtained by coating of a supporting material (carbon felt KFA) with the active substance. For all investigated materials, sulfur was found to be the main reaction product of the sulfide oxidation. In contrast to activated carbon, which showed catalytic activity for sulfide oxidation too, modified KFA felt materials were not blocked and deactivated by formed sulfur, even after long-term use. The new catalyst is well qualified for a stable oxidation of sulfide in water. In comparison to activated carbon, higher investment costs are required, but the carbon felt supported porphyrin has a significant longer lifetime. Because of its easy use, modified KFA felt is applicable both in small local plants and in large waterworks. There is no necessity to add chemicals or to install complex control equipment. As a positive side-effect, further improvement of sulfide elimination caused by sulfide-oxidizing bacteria was found during long filter run times.

<div>Conventional soybean oil and high-oleic soybean oil offer opportunities as bio-solvents for sweetening sour natural gas, adding value to the soybean oil industry and the natural gas industry. The rise of fracking in the United States and changing economics in the energy industry have increased use of natural gas, which is often rendered sour by high concentrations of hydrogen sulfide (H2S), a toxic and corrosive impurity. The present work evaluates the viability of both conventional and high-oleic soybean oil to act as bio-solvents for removing gaseous H2S. Predictive in silico methods, experimental validation, and economic feasibility analysis are included to draw conclusions regarding the overall capability and feasibility of using soybean oils as bio-solvents for gas sweetening.</div><div><br></div><div>In silico predictive methods for sweetening were implemented to assess the relationship between fatty acid composition in the soybean oils and the ability to effectively partition H2S from methane or nitrogen gases. The Conductor-like Screening Model for Real Solvents (COSMO-RS) was used to predict the partition coefficient (K) of H2S in a bi-phasic liquid-vapor system made up of fatty acids in the liquid phase and methane or nitrogen gas in the vapor phase. The fatty acid mass fractions represented those found in soybean or high-oleic soybean oil. Methane represented gas and nitrogen was considered in order to compare to experimental conditions. This proof of concept work predicted K values for H2S below 0.0005 at temperatures from 10 to 100 °C at atmospheric pressure; K values near zero indicate near-complete removal of H2S from the gas phase.</div><div><br></div><div>Experimental validation included equilibrium extraction experiments as well as data collection for isotherm model development. Experimental equilibrium studies were carried out at residence times ranging from 0 – 60 minutes with mixing at ambient conditions. Experiments resulted in K values below 0.1 for H2S in soybean oil and high-oleic soybean oil at 25 °C with residence times less than 15 minutes and a 2:1 gas to oil ratio. More than 90% of the H2S was removed from the gas phase within 15 minutes. Isotherm models demonstrated the saturation limits of the soybean oils and compared them to saturation limits in water and heptane. </div><div><br></div><div>Economic feasibility experiments used graphical and algebraic methods to determine the number of equilibrium stages needed to remove 99.9% of H2S from feed gas with H2S concentrations ranging from 40 – 400 ppm. A gas flow rate equivalent to industrial levels was used to design an extraction column. Capital costs and operating costs were estimated, along with the revenues to be gained from selling methane and selling recovered elemental sulfur as a secondary product. Solvent regeneration would need to exceed 98% in order to keep the cost of treating a unit of natural gas equal to or less than existing industrial methods. Suggestions for cutting costs and improving process viability are made.</div><div><br></div>

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