PERFORMANCE COMPARISON OF SYNGAS METHANATION ON FLUIDIZED AND FIXED BED REACTORS

The performance was compared on Syngas Completely Methanation at atmospheric pressure on fluidized and fixed bed reactors. From space-time yield of CH4, coke content and hot spots of bed temperature, fluidized bed technology was demonstrated to be more applicable to Syngas Completely Methanation. Characterization results showed that different carbon deposition forms were presented on the two operation modes

Modeling of a Catalytic Packed Bed Reactor and Gas Chromatograph Using COMSOL Multiphysics

This project\u27s purpose was to create a model using COMSOL that depicts the catalytic packed bed and gas chromatograph used in CHE4402. The reactor was run in order to collect data on the combustion of methane in air, and this data was used to create the COMSOL models that could be used as supplemental learning tools for the unit operations class

Steam reforming of isobutanol for the production of synthesis gas over Ni/g-Al2O3 catalysts

Bio-isobutanol has received widespread attention as a bio-fuel and a source of chemicals and synthesis gas as part of an integrated biorefinery approach. The production of synthesis gas by steam reforming (SR) of isobutanol was investigated in a down-flow stainless steel fixed-bed reactor (FBR) over Ni/g-Al2O3 catalysts in the temperature range of 723–923 K. The NiO/g-Al2O3 catalysts were prepared by the wet impregnation method and reduced in the FBR prior to the reaction. The surface area, metal dispersion, crystalline phase, and reducibility of the prepared catalysts were determined using BET, chemisorption, XRD and TPR, respectively. From the TPR studies, the maximum hydrogen consumption was observed in the temperature range of 748–823 K for all the catalysts. The presence of nickel species was confirmed through the characterization of the catalysts using powder XRD. The time-on-stream (TOS) studies showed that the catalysts remained fairly stable for more than 10 h of TOS. The conversion of carbon to gaseous products (CCGP) was increased by increasing the nickel loading on g-Al2O3 and the temperature and by decreasing the weight hourly space velocity (WHSV). The hydrogen yield was increased by increasing the nickel loading on g-Al2O3, the WHSV, the steam-to-carbon mole ratio (SCMR), and the temperature. The selectivity to methane decreased at high reaction temperatures and SCMRs. The selectivity to CO decreased with increasing SCMRs and decreasing temperatures. The work was further extended to the thermodynamic equilibrium analysis of the SR of isobutanol under experimental conditions using Aspen Plus, and the equilibrium results were then compared to the experimental results. A reasonably good agreement was observed between the trends in the equilibrium and the experimental results

Temperature control in a multi-tubular fixed bed Fischer-Tropsch reactor using encapsulated phase change materials

The Fischer-Tropsch synthesis is a highly exothermic, indirect, catalytic, gas (syngas) liquefaction chemical process. Temperature control is particularly critical to the process in order to ensure longevity of the catalyst, optimise the product distribution, and to ensure thermo-mechanical reliability of the entire process. This thesis proposes and models the use of encapsulated, phase change material, in conjunction with a supervisory temperature control mechanism, as diluents for the catalytic, multi-tubular fixed bed reactor in order to help mitigate the heat rejection challenges experienced in the process. The modelling was done using the Finite Element Analysis (FEA) software, COMSOL Multiphysics. In the main, three studies were considered in this thesis. In the first study, a two dimensional quasi-homogeneous, reactor model, without and with the dissipation of the enthalpy of reaction into a near isothermal phase change material (silica encapsulated tin metal) heat sink, in a wall-cooled, single-tube fixed bed reactor was implemented and the results were presented. The encapsulated phase change material was homogeneously mixed with the active catalyst pellets. The thermal buffering provided by the phase change material were found to induce up to 7% increase in selectivity towards the C5+ and a 2.5% reduction in selectivity towards CH4. Although there was a reduction in the conversion per pass of the limiting reactant and hydrocarbon productivity due to a reduction in reactor temperature, it was observed that for a unit molar reduction in the productivity of C5+, there was a corresponding 1.5 moles reduction in methane production. In the second study, a modified, one dimensional, α-model was derived which accounted for the heat sink effect of the phase change material diluent. The resulting, less computationally cumbersome, yet sufficiently accurate model was benchmarked against the more rigorous two-dimensional quasi-homogeneous model in order to check its fidelity in predicting the reactor performance. As in the first case study, a homogeneous distribution of the phase change material and active catalyst pellets was assumed. The α-model was able to approximate the reactor temperature profile of the 2D-quasi-homogeneous reactor model to within 4% error, and consistently, slightly over-predicted the limiting reactant conversion by about 3%. Based on these comparisons, the α-model was deemed sufficiently accurate to predict the reactor performance in place of the 2D model for the optimisation simulation in the third study. The third case study entailed simultaneously maximising the production of long chain hydrocarbon molecules and ensuring proper heat rejection from the reacting system, two desirable yet often conflicting operational requirements. The homogeneous distribution of the active catalyst pellets and the phase change material diluents was abandoned for a multi-zonal axial distribution in which, individual zones of the catalyst bed were diluted to varying extents. The best dilution and distribution “recipe” was determined using optimisation techniques and the previously derived modified α-model. The multi-zonal axial dilution of the catalyst bed brought about a marked increase (up to 19%) in the productivity of the long chain hydrocarbons, while ensuring a more judicious use of the catalyst bed in contrast to the homogeneous catalyst/phase change material arrangement in the previous two studies. The latent enthalpy of the metallic phase change material combined with its good thermal conductivity helped push the limits of the catalyst bed by increasing the conversion per pass beyond the typical 20-30% reported in literature, with less likelihood of either early catalyst deactivation or thermal unreliability of the reacting system. In the main, it was observed that the overall productivity of the desired C5+ could be enhanced by reducing the quantity of the catalyst pellets by a pre-defined reactor volume. In addition, the reactor productivity benefits from a highly active zone situated at the reactor entrance, immediately followed by a less reactive zone. This arrangement has the effect of ramping the reaction rate (and in effect the reactor temperature) early on, and this is kept in check by the less reactive zone immediately adjacent to the reactive one at the reactor entrance

Reactions of ethanol over CeO2 and Ru/CeO2 catalysts

The reaction of ethanol has been investigated on Ru/CeO2 in steady state conditions as well as with temperature programmed desorption (TPD). High resolution transmission electron microscopy (HRTEM) images indicated that the used catalyst contained Ru particles with a mean size of ca. 1.5 nm well dispersed on CeO2 (of about 12–15 nm in size). Surface uptake of ethanol was measured by changing exposure to ethanol followed by TPD. Saturation coverage is found to be between 0.25 and 0.33 of a monolayer for CeO2 that has been prior heated with O2 at 773 K. The main reactions of ethanol on CeO2 during TPD are: re-combinative desorption of ethanol; dehydrogenation to acetaldehyde; and dehydration to ethylene. The dehydration to ethylene occurs mainly in a small temperature window at about 700 K and it is attributed to ethoxides adsorbed on surface-oxygen defects. The presence of Ru considerably modified the reaction of ceria towards ethanol. It has switched the desorption products to CO, CO2, CH4 and H2. These latter products are typical reforming products. Ethanol steam reforming (ESR) conducted on Ru/CeO2 indicated that optimal reaction activity is at about 673 K above which CO2 production declines (together with that of H2) due to reverse water gas shift. This trend was well captured during ethanol TPD where CO2 desorbed about 50 K below than CO on both oxidized and reduced Ru/CeO2 catalysts.Peer ReviewedPostprint (author's final draft

Novel bifunctional double-layer catalysts for application in microreactors for direct DME synthesis

This thesis describes experimental research toward the selective and efficient DME production from syngas in microstructured reactors using bifunctional catalysts. Two catalysts, Cu/ZnO/Al2O3 and ZSM-5, catalyze syngas conversion to methanol and methanol conversion to DME, respectively. The catalysts were prepared and successfully introduced in microchannel reactor for direct DME synthesis