Dissertations / Theses on the topic 'Aqueous Phase Reforming'

Il processo di aqueous phase reforming (APR) consente la produzione di idrogeno e prodotti ad elevato valore aggiunto in soluzione acquosa a partire da zuccheri e altre biomasse. Nel presente lavoro è stato approfondito l’APR di glucosio dapprima studiando l’influenza dei parametri di reazione con l’obiettivo di massimizzare le rese e minimizzare la decomposizione termica del reagente con un catalizzatore modello (Pt/TiO2). In secondo luogo si è passato all’ottimizzazione del catalizzatore. Dapprima è stato analizzato l’effetto delle proprietà acide e basiche del supporto catalitico variando il contenuto di Mg ed Al e verificandone l’effetto sulla distribuzione dei prodotti. Successivamente è stata studiata la possibilità di sostituire Pt come fase attiva analizzando metalli del gruppo VIII più economici. Dallo screening effettuato sono stati scelti Fe, Co e Ni e ne sono state testate le proprietà in combinazione prima come fase depositata e in un secondo momento come catalizzatori bulk, più semplici ed economici da produrre rispetto ai catalizzatori supportati.

Aqueous-phase reforming (APR) is reported for the first time for the production of H2 from actual biomass. The experiments are carried out in batch using a 100mL Parr microreactor heated to 225C. In this one-pot, two-step process, acid hydrolysis is used to break down the polymeric constituents of biomass to smaller soluble molecules and these species are reformed using a Pt/Al2O3 catalyst. The experiments show that increasing the acid concentration from 1% to 5% causes more than a twelve-fold increase in H2 concentration, with hydrogen a minor product accounting for 18% of the non-condensable gas phase and CO2 as the major product. In the presence of the Pt/Al2O3 reforming catalyst, both the selectivity and yield of hydrogen in the gas phase increase. This is accompanied by a noticeable decrease in carbon monoxide production. Comparison with other feeds such as glucose, wastepaper and ethylene glycol showed that the amount of hydrogen produced from biomass is of a comparable magnitude per gram of feed, although biomass yields more hydrogen per gram of carbohydrate than either glucose or wastepaper. Baseline experiments with only the catalysts in the absence of any biomass show no increase in the reactor system pressure when only water and helium are present, indicating that the observed hydrogen produced is sourced form the biomass.

This thesis presents a feasibility study on the conversion of biomass-derived pyrolysis oils to hydrogen gas via the advanced steam reforming processes of chemical looping reforming (CLR) and sorption enhanced steam reforming (SESR). According to thermodynamic equilibrium, the optimum conditions of steam reforming of model pyrolysis oils compounds were around 600°C and molar steam to carbon ratio (S/C) of 3, to save raising excess steam in the process. Palm empty fruit bunches (PEFB) pyrolysis oil and pine pyrolysis oil were investigated as renewable feedstock for H2 production. The experiments were carried out in a down-flow packed bed micro reactor using commercial Ni catalyst at 1 atm. The SIC of 1.89 (moist fuel) was found to provide the best operating conditions for steam reforming of both pyrolysis oils. In the SESR experiments, dolomite was mixed in the reactor bed to capture C02 produced from the steam reforming of pyrolysis oils. High sorption enhancement effects were demonstrated in particular for pine oil. Short CLR experiments were performed tor both oils using the same Ni catalyst acting as oxygen transfer material. The oils were able to reduce the catalyst close to 90% despite high O-content, and undergo CLR. The feasibility of steam reforming of aqueous fraction of pyrolysis oils was performed with co-reforming of ethanol using two catalysts: 'A' with a NiO loading of 18 wt% on α-alumina, and 'B' with 25 wt% NiO on γ-alumina. The aqueous phase was derived from water phase separation of the pine oil at a 1: 10 oil :water mass ratio. Both catalysts demonstrated high fuel conversion and H2 yield for S/C ratios between 2.4 and 4.8. Chemical looping reforming performed at S/C of 3.66 resulted in almost 90% reduction of catalyst A and around 20% reduction of catalyst B whilst maintaining nearly complete fuel conversion.

There are many problems associated with the use of fossil fuels to produce fuels and chemicals, and lignocellulosic biomass stands as a promising alternative fuel/chemical feedstock. Large scale processing of biomass will likely take place in high temperature liquid water due to the low vapor pressure and polar nature of carbohydrates. However, little is known about the material stability of these catalysts in high temperature aqueous phase environments. This dissertation aims to investigate the structural integrity of some common catalytic materials under typical biomass reforming conditions. There are 3 main objectives of this study: 1) identify potentially stable candidates from commonly used materials, 2) understand the mechanism(s) by which these catalysts degrade, 3) design/modify catalysts in an effort to increase their hydrothermal stability. The two main materials investigated in this work are zeolites (faujasite, ZSM-5) and γ-Al2O3 as these are commonly used as catalysts and catalyst supports. A number of physicochemical techniques were used to characterize the materials as a function of treatment time at conditions relevant for biomass reforming. For zeolites, the major findings are that ZSM-5 framework is highly stable whereas faujasite stability depends on the Si/Al ratio, where silicon rich materials are less stable. For γ-Al2O3 based catalysts, it was found that the alumina support hydrates and undergoes a phase transformation to form crystalline boehmite (AlOOH) with a subsequent loss in surface area and Lewis acid sites. When metal particles are present on the support, the phase change kinetics are slowed. The role of metal precursor on the stability of γ-Al2O3 supported catalysts was also explored, and it was found that the precursor used in catalyst synthesis changes the boehmite formation kinetics and also affects alumina support dissolution. The final thrust aims to stabilize a Pt/γ-Al2O3 catalyst by depositing silicon on the catalyst surface. The silicon modification is effective in protecting the catalyst from boehmite formation upon exposure to hot liquid water while also stabilizing metal particles against sintering. Additionally, an increase in turnover number for hydrogen production via aqueous phase reforming of sorbitol was observed.

The current problem of the depletion of fossil-fuel reserves, call for new energy systems based on renewable fuels. Hydrogen, a clean fuel, is in growing demand due to the technological advancements made in the fuel cell industry. The ultimate objective of this project is to be able to feed the H2 rich and CO free gas directly to PEM fuel cell, without the expense of intermediate gas cleaning or upgrading (CO removing), which was approached by the development of efficient and low cost catalysts. Firstly, a series of Pt catalysts supported on alumina that was doped with different amounts of CeO2 were developed, characterized and tested in the aqueous-phase reforming (APR) of glycerol to H2. Several parameters like pressure, temperature, feed concentration and feed flow rate were optimized. No CO could be detected (< 100 ppm) in the product gas, meaning that the product may be directly useable in a PEM fuel cell. Secondly, bimetallic Pt-Ni supported on 3 wt% CeO2-doped Al2O3 (3CeAl) and multi-walled carbon nanotubes (MWNT) were studied. XRD, XPS and STEM-EDS analysis shows the evidence of Pt–Ni interaction which is thought to be responsible for their higher activity and selectivity in APR. A bimetallic catalyst – 1 wt% Pt and 3 wt% Ni supported on MWNT was then identified the best one compared to commercial Pt/Al2O3 Lastly, amongst the non-noble based Cu-Ni alloy catalysts tested, bimetallic 1Cu–12Ni/MWNT catalyst gave the higher H2 selectivity (86%) and glycerol conversion (84%). Though 1Cu–12Ni/MWNT catalyst showed slightly lower H2 selectivity (86%) than the 1Pt-3Ni/MWNT catalyst (H2 selectivity 91%), but the former is much cheaper compare to highly expensive Pt catalyst. This measure is crucial to the competitiveness of a catalyst in large-scale H2 production.

Biomass is one of the most promising replacements for fossil fuels as a feedstock for chemical and transportation fuel production. The combination of low vapor pressure and high polarity of most biomass derived molecules makes water the ideal solvent for biomass upgrading reaction schemes. Metal oxide and metal oxide supported catalysts are heavily used in oil refining and petrochemical production, and are capable of upgrading biomass molecules as well. However, the surface chemistries that dictate the behavior of aqueous phase biomass upgrading reactions over metal oxide catalysts are not nearly as well understood as in the case of gas phase hydrocarbon refining systems. This dissertation aims to investigate the surface chemistries of biomass derived oxygenate molecules on metal oxide and metal oxide supported metal catalysts. There are three main objectives in this dissertation: to understand how two and three carbon polyols interact with metal oxide surfaces, to elucidate the role of various surface sites on polyol-metal oxide interactions, and to discover the surface species of kinetic importance in aqueous phase reforming reactions of biomass molecules. Transmission infrared spectroscopy and density functional theory modeling were the major techniques used to demonstrate that polyols with alcohol groups on the first and third carbons, 1,3-propanediol and glycerol, form a multidentate surface species with a bridging alkoxide bond and an acid/base interaction through their two primary alcohol groups with Lewis acid sites of g-Al₂O₃. These interactions occur in the presence of bulk water. Polyols with alcohol groups only on the first and second carbons, ethylene glycol and 1,2-propanediol, only formed alkoxy bonds with the g-Al₂O₃ surface when bulk water was not coadsorbed, and these bonds were removed by re-adsorbing water. Glycerol also forms the same surface species on other metal oxides with strong Lewis acidic character: TiO₂ anatase, ZrO₂, and CeO₂. Glycerol only forms hydrogen bonds with MgO, which lacks strongly Lewis acidic sites. Basic surface hydroxyls and surface oxygen atoms of the metal oxides only played a minor role in interacting with the adsorbed glycerol. In-situ attenuated total reflectance infrared spectroscopy demonstrated that the aqueous phase reforming of glycerol over a 5 wt% Pt on g-Al₂O₃ catalyst is hindered by residual platinum bound hydrogen or oxygen atoms from commonly utilized catalyst reduction or cleaning procedures, respectively. A pretreatment consisting of multiple iterations of dissolved oxygen, dissolved hydrogen, and dissolved helium in water flow periods provides the cleanest Pt surface for monitoring carbon monoxide formation dynamics, and allows for observing the rate limiting step of the aqueous phase reforming reactions water-gas shift removal of Pt bound carbon monoxide. The bridging bound carbon monoxide is preferentially removed over the linearly bound species via water gas shift reactions even at room temperature.

Dramatic increases in the price of crude oil, and consequently, transportation fuels, coupled with increased environmental concerns have resulted in rapid growth in biodiesel production. Thus, so does production of the primary coproduct, glycerol, which has become a worrying factor because for every ton of biodiesel produced, are generated 100 Kg of glycerol. Because this reality research has been developed to search alternatives for the use of glycerol. So, an application for this alcohol is the search for value-added chemicals such as propylene glycol and others. Reactions of aqueous phase reforming of glycerol were performed without the addition of hydrogen and streaming using monometallic catalysts of Re and Pt and bimetallic Pt-Re all supported on carbon Black . We used an aqueous solution of glycerol feeding 80% m / m, temperature of 275°C and 30 bar pressure. WHSV was varied and the content thus evaluating Re, its influence on the Pt catalysts, the stability and activity. The catalysts was characterized for temperature-programmed reduction (TPR); chemisorption of CO studies; temperature-programmed desorption-CO (TPD-CO); temperature-programmed desorption-isopropylamine (TPD-IPA). Studies of RTP for the bimetallic catalysts Pt-Re showed that rhenium interacts strongly with the platinum and possibly, precursor species are formed bimetallic alloy. CO chemisorption experiments resulted in the formation of the alloys of Pt-Re / C. The results of TPD-CO demonstrated that the addition of Re to the catalyst Pt / C changes the surface of Pt and collaborates with the weakening of bond strength of the CO molecule to the sites involved. Through the catalytic reactions studied and a qualitative analysis of chromatograms from high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GCMS) was possible to verify from the reaction of aqueous phase reforming of glycerol, the formation 1,2-propanediol and other products.<br>O grande aumento no preço do petróleo e conseqüentemente o transporte de combustíveis, juntamente com as preocupações ambientais resultaram em um rápido crescimento na produção de biodiesel. Assim, o mesmo acontece com a produção do subproduto, o glicerol, o qual se tornou um fator preocupante já que para cada tonelada de biodiesel obtido, são gerados 100 Kg de glicerol. Devido a esta realidade pesquisas vem sendo desenvolvidas para buscar alternativas para a utilização deste excedente. Dentro deste contexto, uma aplicação para este álcool é a busca de produtos químicos de valor agregado como o propanodiol e outros. Reações de reforma líquida do glicerol foram realizadas sem a adição de hidrogênio e em fluxo contínuo utilizando catalisadores monometálicos de Re e Pt e bimetálicos Pt-Re todos suportados em carbono Black . Foi utilizada uma solução aquosa de alimentação de glicerol 80 % m/m, temperatura de 275ºC, e pressão 30 bar. Variou-se o WHSV e teor de Re avaliando, portanto a influência deste sobre os catalisadores de Pt, a estabilidade e atividade. Os catalisadores foram caracterizados por redução à temperatura programada (RTP) quimissorção de CO, dessorção de CO à temperatura programada (DTP-CO) e dessorção de isopropilamina à temperatura programada (DTP-IPA). Os estudos de RTP para os catalisadores bimetálicos de Pt-Re demonstraram que o rênio interage fortemente com a platina e que possivelmente, espécies precursoras de ligas bimetálicas são formadas. Experimentos de quimissorção de CO resultaram na formação de ligas para os catalisadores de Pt-Re/C. Os resultados de DTP-CO demonstraram que a adição de Re ao catalisador de Pt/C altera a superfície da Pt e colabora com o enfraquecimento da força de ligação da molécula do CO aos sítios envolvidos. Através dos testes catalíticos estudados e uma análise qualitativa dos cromatogramas de cromatografia líquida de alta eficiência (CLAE) e cromatografia gasosa acoplada ao espectrômetro de massas (CG/MS), foi possível verificar a partir da reação de reforma líquida do glicerol, a formação 1,2-propanodiol e outros produtos.<br>Mestre em Química

碩士<br>逢甲大學<br>化學工程學所<br>97<br>A hydrothermal-chemical process for the biomass hydrolysis and the formation of bio-hydrogen was proposed in this study. We utilized diluted acid to hydrolysis biomass by aqueous phase reforming to product reduce sugar. During the hydrolysis process, hydrogen was found in the case of adding sulfuric acid. Therefore, we utilized duilted sulfuric acid and biomass to hydrogen produced by the aqueous phase reforming by Pt/Al2O3 at 195℃~225℃. The Ru-Pt bimetallic catalysts were prepared by wetness impregnation, and compare the effect in aqueous phase reforming process. Study results revealed that a maximum reduced sugar concentration was at 26,010ppm by diluted hydrochloric acid hydrolysis at 170℃, at the same reaction the yield of reduced sugar was 0.51g/g-biomass. The yield of bio-hydrogen at 225℃ 0.88mmole/g-biomass was attained with Pt/Al2O3 catalyst and 0.101mmole/g-biomass with Ru/Pt/Al2O3 in this study. This study provided a potential route for the bio-hydrogen and reduced sugar production simultaneously in a one-pot reaction process using the energy crops or the agriculture wastes as the substrate.

Wasserstoff wird als Energieträger der Zukunft bezeichnet. Er kann in reiner Form direkt als Brennstoff oder zur Erzeugung von elektrischer Energie in Brennstoffzellen genutzt werden. Der Vorteil gegenüber fossilen Brennstoffen besteht darin, dass bei der Umsetzung mit Sauerstoff nur Wasser als Abfallprodukt entsteht. Dadurch kann die Emission an CO2, einem Treibhausgas, verringert werden. Die heutige Erzeugung von Wasserstoff erfolgt hauptsächlich aus fossilen Energieträgern, wie Erdöl oder Erdgas. Da deren Reichweite zeitlich begrenzt ist, sind erneuerbare Energiequellen in den letzten Jahren stark in den Mittelpunkt des Forschungsinteresses gerückt. Ein Beispiel dafür ist das Glycerol, welches als Koppelprodukt der Biodieselproduktion entsteht. Neben der herkömmlichen Gasphasenreformierung bietet das Aqueous-Phase Reforming (APR) eine energieeffizientere Alternative, da bei moderaten Temperaturen (200-250°C) und Drücken (20-25 bar) gearbeitet werden kann Im Rahmen dieser Arbeit wurde die katalytische Umsetzung von Glycerol zu Wasserstoff durch Aqueous-Phase-Reforming an verschiedenen Platinkatalysatoren untersucht. Dabei sollte die Auswirkung einer Modifizierung des Katalysators hinsichtlich Träger, Beladung, Metalldispersität und Zusammensetzung sowie der Einfluss der Reaktionsbedingungen auf die Wasserstoffausbeute untersucht werden. Weiterhin wurden Untersuchungen zum Einfluss von Stofftransportprozessen durchgeführt. Zur Katalysatorpräparation wurde eine Reihe von Platinsalzen verwendet. Mit Hilfe der Incipient Wetness Methode konnten hoch disperse Platinkatalysatoren mit Massenbeladungen zwischen 1 und 10 Ma.-% reproduzierbar hergestellt werden. Unter den eingesetzten Trägermaterialien (Polyanilin, verschiedene Metalloxide) wurde Aluminiumoxid als Träger der Wahl für die APR-Reaktion mit Glycerol identifiziert. Auch die Struktur des eingesetzten Aluminiumoxids spielt eine wichtige Rolle, da sie sich auf die Eigenschaften der Poren auswirkt. Dabei zeigte der Einsatz von Puralox, einer Mischung aus γ-, δ- und Θ-Aluminiumoxiden, die höchste Aktivität und Selektivität zu Wasserstoff gegenüber Katalysatoren auf Boehmit oder reinem γ-Aluminiumoxid. Durch die Anwendung unterschiedlicher Calcinierungstemperaturen gelang eine Variierung der Partikelgröße (1,7-3,2 nm). Die Katalysatoren zeigten unter den gewählten Reaktionsbedingungen mit einem Glycerolumsatz von 20 % die gleiche Aktivität, allerdings stieg die Selektivität zu Wasserstoff mit steigender Partikelgröße von auf 78 auf 96 % an. Somit kann die APR-Reaktion im untersuchten Bereich als struktursensitiv bezeichnet werden.