Experimental and Numerical Study of Low Temperature Methane Steam Reforming for Hydrogen Production

Low temperature methane steam reforming for hydrogen production, using experimental developed Ni/Al2O3 catalysts is studied both experimentally and numerically. The catalytic activity measurements were performed at a temperature range of 500–700 °C with steam to carbon ratio (S/C) of 2 and 3 under atmospheric pressure conditions. A mathematical analysis to evaluate the reaction feasibility at all different conditions that have been applied by using chemical equilibrium with applications (CEA) software and in addition, a mathematical model focused on the kinetics and the thermodynamics of the reforming reaction is introduced and applied using a commercial finite element analysis software (COMSOL Multiphysics 5.0). The experimental results were employed to validate the extracted simulation data based on the yields of the produced H2, CO2 and CO at different temperatures. A maximum hydrogen yield of 2.7 mol/mol-CH4 is achieved at 700 °C and S/C of 2 and 3. The stability of the 10%Ni/Al2O3 catalyst shows that the catalyst is prone to deactivation as supported by Thermogravimetric Analysis TGA results

The application of inelastic neutron scattering to investigate the ‘dry’ reforming of methane over an alumina-supported nickel catalyst operating under conditions where filamentous carbon formation is prevalent

The use of CO2 in reforming methane to produce the industrial feedstock syngas is an economically and environmentally attractive reaction. An alumina-supported nickel catalyst active for this reaction additionally forms filamentous carbon. The catalyst is investigated by inelastic neutron scattering as well as elemental analysis, temperature-programmed oxidation, temperature-programmed hydrogenation, X-ray diffraction, transmission electron microscopy and Raman scattering. Isotopic substitution experiments, using 13CO2 for 12CO2, show the oxidant to contribute to the carbon retention evident with this sample. At steady-state operation, a carbon mass balance of 95 % is observed. A kinetic scheme is proposed to account for the trends observed

New Chiral Auxiliaries For The [3+2]-Cycloaddition Of Nonstabilised Azomethine Ylides

The [3+2]-cycloaddition reaction of nonstabilised azomethine ylides to alkenes is a valuable synthetic method for the assembly of functionalised pyrrolidines. However, there are only a few examples of such eye lo add it ions being successfully performed with an unstabilised azomethine ylide that has been tethered to a removable chiral auxiliary. Most of the reactions studied so far have exhibited only modest levels of diastereoselectivity (ca. 60 % d.e.), and in every case, destruction of the chiral auxiliary has proven necessary before the newly fashioned chiral pyrrolidine cycloadduct could be liberated. In the first part of this thesis, the potential utility of optically pure 1,1-dialkylhydrazines as chiral auxiliaries for nonstabilised azomethine ylide cycloadditions to alkenes has been investigated. While the preparation of several chiral 1,1-dialkylhydrazines was carried out successfully, the formation of the N-amino azomethine ylide precursors from these hydrazines failed, occasionally giving interesting unwanted and unexpected by-products. The second part of this thesis focuses on the evaluation of several new chiral auxiliaries as stereochemical control elements for 1,3-dipolar cycloadditions of azomethine ylides to alkenes. This work failed with some auxiliaries and was partially successful with others. The successful [3+2]-cycloaddition reactions were all performed with dimethyl fumarate as the dipolarophile, but afforded little or no stereoselectivity. The cleavage of the newly-created pyrrolidine systems from these auxiliaries under various conditions also proved to be unsuccessful. During this work a new method for the preparation of 1,1-dialkyIhydrazines by the reduction of N-nitroso precursors was discovered. The potential utility of this method has been evaluated, and the results are discussed in Chapter 4

A fast and accurate algorithm for computing radial transonic flows

AbstractAn efficient algorithm is described for calculating stationary one-dimensional transonic outflow solutions of the compressible Euler equations with gravity and heat source terms. The stationary equations are solved directly by exploiting their dynamical system form. Transonic expansions are the stable manifolds of saddle-point-type critical points, and can be obtained efficiently and accurately by adaptive integration outward from the critical points. The particular transonic solution and critical point that match the inflow boundary conditions are obtained by a two-by-two Newton iteration which allows the critical point to vary within the manifold of possible critical points. The proposed Newton Critical Point (NCP) method typically converges in a small number of Newton steps, and the adaptively calculated solution trajectories are highly accurate. A sample application area for this method is the calculation of transonic hydrodynamic escape flows from extrasolar planets and the early Earth. The method is also illustrated for an example flow problem that models accretion onto a black hole with a shock

Statistical models of diffusion and aggregation for coke formation in a catalyst pore

We simulated models of diffusion and aggregation in long pores of small widths in order to represent the basic mechanisms of coke deposition in catalysts' pores. Coke precursors are represented by particles injected at the pore entrance. Knudsen diffusion, which is usually expected inside the pores, is modeled by ballistic motion of those particles. The regime of molecular diffusion is also analyzed via models of lattice random walks biased along the pores. The aggregation at the surface or near previously aggregated particles was modeled by different probabilistic rules, accounting for the possibilities of more compact or more ramified deposits. In the model of Knudsen diffusion and in some cases of molecular diffusion, there is an initial regime of uniform deposition along the pore, after which the deposits acquire an approximately wedge shape, with the pore plugging near its entrance. After the regime of uniform deposition and before that of critical pore plugging, the average aggregation position slowly decreases with the number N of deposited particles approximately as N^{-0.25}. The apparently universal features of deposits generated by microscopic models are compared with those currently adopted in continuum models.Comment: 14 pages (figures included), to appear in Physica

Volatility Managed Short Duration Premium

This thesis investigates if the short duration premium of the equity duration strategy can be improved by managing its volatility. Based on estimates by Gonçalves (2021), we replicate equity duration sorted portfolios of U.S. stocks from 1973 to 2019, and identify a 9.3% premium for a strategy buying short duration firms, and selling long duration firms. These findings support literature suggesting the existence of a downward-sloping equity term structure. Managing the volatility of the equity duration strategy results in a reduction of 4.2% annualized risk-adjusted return, suggesting that volatility management does not lead to an improvement of the short duration premium. In contrast to strategies for which volatility management increases premiums, we note that the original equity duration strategy has a high positive skewness of 0.64, which is completely diminished. We argue that volatility management is not suitable for the equity duration strategy as strategy returns are generally high in periods of high volatility, and returns are generally low in periods of low volatility. We finalize our exploration of the short duration premium by testing its merits in a multi-factor environment. We show that combining the equity duration strategy with traditional asset pricing models in Markowitz’s (1952) portfolio optimization model increases Sharpe ratios significantly. Our findings underscore the viability of the equity duration investment strategy but warn investors of scaling investments to its volatility.nhhma

Ethane steam reforming over a platinum/alumina catalyst: effect of sulphur poisoning

In this study we have examined the adsorption of hydrogen sulfide and methanethiol over platinum catalysts and examined the effect of these poisons on the steam reforming of ethane. Adsorption of hydrogen sulfide was measured at 293 and 873 K. At 873 K the adsorbed state of hydrogen sulfide in the presence of hydrogen was SH rather than S, even though the Pt:S ratio was unity. The effect of 11.2 ppm hydrogen sulfide or methanethiol on the steam reforming of ethane was studied at 873 K and 20 barg. Both poisons deactivated the catalyst over a number of hours, but methanethiol was found to be more deleterious, reducing the conversion by almost an order of magnitude, possibly due to the co-deposition of sulfur and carbon. Changes in the selectivity revealed that the effect of sulfur was not uniform on the reactions occurring, with the production of methane reduced proportionally more than the other products, due to the surface sensitivity of the hydrogenolysis and methanation reactions. The water-gas shift reaction was affected to a lesser extent. No regeneration was observed when hydrogen sulfide was removed from the feedstream in agreement with adsorption studies. A slight regeneration was observed when methanethiol was removed from the feed, but this was believed to be due to the removal of carbon rather than sulfur. The overall effect of sulfur poisoning was to reduce activity and enhance hydrogen selectivity

Oversigt over de i 1884 indløbne Forespørgsler angaaende Sygdomme hos Kulturplanter.

Oversigt over de i 1884 indløbne Forespørgsler angaaende Sygdomme hos Kulturplanter