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No description available.

No description available.

No description available.

Iron oxide catalyst have been used to perform high temperature water-gas shift reactions (HTWGSR). They have shown to be affective for application in a pyrolysis gas pre-conditioning step to create a hydrogen enriched gas and possibly removing the need for bio-crude condensation before further treatment or use. A small-scale experimental study of an iron oxide catalyst with additives provided by Topsoe, exposed to different H2O:CO ratios temperatures was conducted. The catalyst was first activated following steps given by the supplier. The different H2O:CO ratios tested on the catalyst were 2:1, 4:1 and 6:1 at 350 °C and 2:1, 4:1 and 6:1 at 450 °C. The space velocity was kept constant at 52500 L/(kgcat·h) for all the experiments. No significant deactivation was observed through the 18-hour experiment, based on Brunauer-Emmett-Teller (BET) results. The results show that the highest conversion of CO was achieved at 4:1 H2O:CO ratio at 450 °C, the best H2 selectivity was at 2:1 H2O:CO ratio at 350 °C, and the highest yield was obtained at 6:1 ratio at 450 °C. The initial condition (4:1 H2O:CO ratio at 350 °C) showed anomalous activity as it had a surprisingly low H2 selectivity (25%) and a comparatively high conversion of CO (20.8%). This could have been due to systematic error or possibly due to other side reactions (production of methane) happening. Literature on similar behaviour was not found. A two-way Analysis of Variance (ANOVA) test was conducted and concluded that all 3 noll hypotheses could be rejected, furthermore, have 3 separate 2x2 factorial design tests been done using MATLAB where the results show that all effects including interaction effects were active with the most significant effect being the change in temperature and the least significant being the change in H2O:CO ratio above 4:1. The results show that this particular iron oxide catalyst with additives provided by Topsoe operates best at temperatures around 450 °C at a H2O:CO ratio of 4:1 or above. It shows no signs of deactivation and may be able to perform WGSR for extended periods of time. / Järnoxidkatalysatorer har använts för att utföra reaktioner för vatten-gasskift vid höga temperaturer (HTWGSR). De har visat sig vara effektiva för tillämpning i ett pyrolysgasförberedningssteg för att skapa en väteberikad gas och eventuellt eliminera behovet av kondensering av biologisk råolja innan ytterligare behandling eller användning. En småskalig experimentell studie av en järnoxidkatalysator med tillsatser från leverantören Topsoe, utsatt för olika H2O:CO-förhållanden vid olika temperaturer, genomfördes. Katalysatorn aktiverades först enligt de anvisningar som lämnats av leverantören. De olika förhållandena som testades på katalysatorn var 2:1, 4:1 och 6:1 vid 350 °C samt 2:1, 4:1 och 6:1 vid 450 °C. Utrymmeshastigheten (space velocity) hölls konstant på 52500 L/(kgcat·h) för alla experiment. Ingen signifikant inaktivering observerades under det 18 timmar långa experimentet, baserat på Brunauer-Emmett-Teller (BET) resultat. Resultaten visar att den högsta konverteringen av CO uppnåddes vid 4:1 H2O:CO-förhållande vid 450 °C. Bästa H2-selektiviteten observerades vid 2:1 H2O:CO-förhållande vid 350 °C, medan högsta utbytet erhölls vid 6:1-förhållande vid 450 °C. Det initiala förhållandet (4:1 H2O:CO vid 350 °C) visade anomalt beteende med en låg H2-selektivitet (25%) och en jämförelsevis hög konvertering av CO (20,8%). Detta kan ha berott på systematiskt fel eller möjligen på andra sidoreaktioner (produktion av metan). Litteratur om liknande beteende hittades inte. En tvåvägs Analysis of Variance (ANOVA) test genomfördes och slutsatsen var att alla tre nollhypoteser kunde förkastas. Dessutom har tre separata 2x2-faktoriella designtester utförts med hjälp av MATLAB, där resultaten visar att alla effekter, inklusive interaktionseffekter, var aktiva. Den mest signifikanta effekten var förändringen i temperatur, medan den minst signifikanta var förändringen i H2O:CO-förhållandet över 4:1. Resultaten visar att den specifika järnoxidkatalysatorn med tillsatser från Topsoe fungerar bäst vid temperaturer runt 450 °C och vid ett H2O:CO-förhållande på 4:1 eller högre. Den visar inga tecken på inaktivering och kan möjligen utföra WGSR under förlängda tidsperioder.

La production de l'hydrogène à partir de biomasse est actuellement à l'étude mais la méthode de valorisation du biogaz (mélange H2/CO2) par réactions catalytiques, autres que la simple combustion, n'a pas encore été retenue. Par conséquent, le principal objectif de ce travail est d'explorer les autres voies. L'effet du CO2 sur le système catalytique est mal connu et seulement un effet négatif sur la dissociation de l'hydrogène a été mentionné. L'hydrogénation du toluène sur un catalyseur Pt a d'abord été étudiée sans CO2 pour suivre son comportement et éventuellement sa perte d'activité. En présence de CO2, l'inactivité complète du catalyseur pour l'hydrogénation du toluène a été mis en évidence. La modification de la surface du catalyseur par le CO2 est quantifiée par DRIFT et un mécanisme à deux sites a été montré. La réaction de Reverse Water Gas Shift produisant du CO se trouve être la principale cause de la désactivation de la surface de catalyseur avec le CO2. Donc la compétition d'adsorption entre le CO et des acides carboxyliques a été mise à profit pour favoriser sélectivement la conversion des acides. Pour l'alumine, elle est polluée par des carbonates complexes venant du CO2. La silice étant aussi connue pour promouvoir la décomposition, ces supports ont été rejetés. L'oxyde de titane a été utilisé pour catalyser une autre gamme de produits. Sur ce catalyseur, le changement de sélectivité entre le RWGS et la conversion de l'acide a été observé. Quant à l'oxyde de fer (catalyseur moins actif), il n’est pas capable de produire du CO à partir du CO2. La chimie de surface de l'oxyde de fer joue un rôle important sur la sélectivité du produit parmi les cétones et les aldéhydes. Un mécanisme à deux sites peut réutiliser pour l'oxyde de fer, montrant qu'un fonctionnement stable peut être trouvé si la réduction par l'hydrogène est continue. Si l'oxyde de fer est totalement oxydé par le CO2, produit de réaction, la production des cétones cesse. Énergiquement, le procédé de production d'acétone peut être autosuffisant et l'acétone peut être utilisée comme une molécule de stockage d'énergie. Le procédé va aussi compenser le nouveau procédé de production de phénol qui ne produit pas l'acétone / Hydrogen potential from biomass is currently being studied but ways of valorization of such biogas (H2/CO2 mix) via catalytic reaction, other than simply burning has not yet been considered. Thus the main objective of this work is the exploration of such methods. Effect of CO2 over catalytic system was not well known and only hydrogen dissociation inhibition is reported. Toluene hydrogenation over Pt catalyst is studied and activity loss transition behavior is observed with no CO2 where as complete catalyst inactivity for toluene hydrogenation is found in presence of CO2. Catalyst surface change by CO2 is quantified by DRIFT analysis and two-site mechanism is found to prevail. Reverse water gas shift reaction producing CO is found to be the main cause behind such catalyst surface response to CO2. Adsorption competition between CO and carboxylic acids is exploited for selectivity shift in favor of acids conversion. Alumina support is fouled by carbonates complexes with CO2 while silica is reported to promote decomposition, thus both were rejected and titanium oxide is used instead with a range of products produced. The required selectivity shift between reverse water gas shift and acid conversion is thus observed. Less active iron oxide catalyst further suppresses CO2 conversion. Iron oxide surface chemistry plays an important role over product selectivity among ketones and aldehydes. Two sites mechanism still prevails over iron and stable continuous operation requires simultaneous iron reduction via hydrogen, if totally oxidized by CO2–a reaction product, will cease to produce ketones. Energetically the process devised for acetone production is self sufficient and acetone not only act as an energy storage molecule but can also compensate new phenol production process producing no acetone

Sustainable energy sources are of great importance, and will become even more important in the future. Gasification of biomass is an important process for utilization of biomass, as a renewable energy carrier, to produce fuels and chemicals. Density functional theory (DFT) calculations were used to investigate i) the effect of co-adsorption of water and CO on the Ni(111) catalysed water splitting reaction, ii) water adsorption and dissociation on Ni(111), Ni(100) and Ni(110) surfaces, as well as iii) formyl oxidation and dissociation, iv) hydrocarbon combustion and synthesis, and v) the water gas shift (WGS) reaction on these surfaces. The results show that the structures of an adsorbed water molecule and its splitting transition state are significantly changed by co-adsorption of a CO molecule on the Ni(111) surface. This leads to less exothermic reaction energy and larger activation barrier in the presence of CO which means that far fewer water molecules will dissociate in the presence of CO. For the adsorption and dissociation of water on different Ni surfaces, the binding energies for H2O and OH decrease in the order Ni(110) > Ni(100) > Ni(111), and the binding energies for O and H atoms decrease in the order Ni(100) > Ni(111) > Ni(110). In total, the complete water dissociation reaction rate decreases in the order Ni(110) > Ni(100) > Ni(111). The reaction rates for both formyl dissociation to CH + O and to CO + H decrease in the order Ni(110) > Ni(111) > Ni(100). However, the dissociation to CO + H is kinetically favoured. The oxidation of formyl has the lowest activation energy on the Ni(111) surface. For combustion and synthesis of hydrocarbons, the Ni(110) surface shows a better catalytic activity for hydrocarbon combustion compared to the other surfaces. Calculations show that Ni is a better catalyst for the combustion reaction compared to the hydrocarbon synthesis, where the reaction rate constants are small. It was found that the WGS reaction occurs mainly via the direct pathway with the CO + O → CO2 reaction as the rate limiting step on all three surfaces. The activation barrier obtained for this rate limiting step decreases in the order Ni(110) > Ni(111) > Ni(100). Thus, the WGS reaction is fastest on the Ni(100) surface if O species are present on the surfaces. However, the barrier for desorption of water (as the source of the O species) is lower than its dissociation reaction on the Ni(111) and Ni(100) surfaces, but not on the Ni(110) surface. Therefore the direct pathway on the Ni(110) surface will dominate and will be the rate limiting step at low H2O(g) pressures. The calculations also reveal that the WGS reaction does not primarily occur via the formate pathway, since this species is a stable intermediate on all surfaces. All reactions studied in this work support the Brønsted-Evans-Polanyi (BEP) principles.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2 and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.

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Chemical reactions can have a staggering amount of molecular complexity. Reaction mechanisms have been proposed with over one hundred elementary reaction steps that occur in the same system simultaneously. While several methods exist to simplify and make sense of the pathways and kinetics via which these reactions proceed, e.g., reaction graphs, sensitivity or flux analysis, microkinetic analysis, and comparison of energy landscapes, etc., these methods all have limitations and are often not able to capture a comprehensive picture of the kinetics of system. It has been found useful to view these mechanisms as a network, i.e., a reaction graph. These graphs enable the visualization of the pathways of the reaction and can provide an analytical tool for pathway and kinetic analysis. However, many of the specific graph-theoretic approaches in the literature are not the most suitable for kinetic analysis of complex mechanisms; as they are simply not based on rules that are rigorous enough to fully enumerate all the pathways or provide quantitative analysis of the reaction rates. Our Reaction Route (RR) Graph approach is different in that it depicts the mechanism by a graph that is consistent with all physical and chemical laws associated with reaction networks, particularly being consistent with mass and energy conservation, i.e., Kirchoff’s Flux Law (KFL) and Kirchoff’s Potential Law (KPL). Because of their adherence to these laws, RR Graphs are able to provide an accurate graph-theoretical tool not only for depicting all reactions routes as walks (hence the name RR Graph) but also for pruning mechanisms and allowing a simplified but accurate quantitative description of reaction rates. This adherence to KFL and KPL does mean that the construction and implementation of these graphs can be prohibitively difficult for large mechanisms. For large reaction systems,especially nonlinear mechanisms, it is not realistic to generate these graphs by hand. And although there exists an analytical solution to find a determinant matrix for the RR Graph of a mechanism, the process involves an exhaustive search for a solution which experiences a combinatorial explosion as the number of steps gets very large. This leads to the idea of developing an algorithm for a computer program that can determine how to generate these graphs automatically. Unfortunately, the same combinatorial explosion is present such that for a moderately sized twenty step mechanism, it could take an average computational processor over a decade to find a solution. We have determined, however, that this brute force combinatorial approach can be avoided if heuristics could be developed to bridge gaps in our knowledge of how these graphs are constructed. Thus, developing a better analytical approach and/or a tighter set of heuristics for a computer algorithm are the overarching goals of this work. To make progress toward developing such heuristics, a set of microkinetic mechanisms were analyzed with the notion that the realization of the RR Graphs would highlight a better approach to their construction and usage. In particular, a very large linear reaction system, a smaller linear system and two non-linear reaction systems were analyzed to develop insights into how each graph is manually constructed and analyzed. Furthermore, kinetic analysis was done for these mechanisms and compared to experimental data and other analytical tools to prove not only the validity of the RR Graphs, but also how they are a significant improvement over more commonly used approaches for mechanistic and kinetic analysis. Based on the lessons learned through a consideration of these examples, a set of heuristics are established and enumerated with the ultimate goal of developing an intuitive algorithm that can help automate drawing and kinetic analysis via RR Graphs of complex mechanisms.