This paper reports a thermodynamic-based study into the production of hydrogen via biogas decomposition for use in polymer electrolyte membrane fuel cells (PEMFC) and solid oxide fuel cells (SOFC). For biogas with a CO2/CH4 ratio of 40 : 60, it was necessary to separate carbon dioxide before supplying the biogas to the decomposition unit to achieve higher performance. However, the decomposition of biogas with CO2 capture under autothermal conditions was not compatible with PEMFCs because the CO concentration was higher than 10 mu mol/mol. For application in SOFCs, the highest H-2 yields were achieved by combusting the methane-rich gas split from the decomposition reactor feed stream to heat the system, while those obtained by combusting the gas split from the decomposition reactor product stream resulted in the highest carbon yields and lowest overall CO2 emissions.

Process simulation of sorption enhanced chemical-looping reforming for hydrogen production from biomass was investigated. Corn stover was converted to bio-oil via pyrolysis prior to sorption enhanced chemical-looping reforming (SE-CLR). NiO was used as a catalyst and oxidizing agent and CaO was used as a CO2 sorbent which are cycled between the reduction and oxidation reactors. Modification of the process to incorporate a step for catalyst and sorbent regeneration was examined and compared with conventional sorption enhanced chemical-looping reforming process. By modifying the SE-CLR process with the recirculating of solids from the air reactor directly to the reformer, a maximum bio-oil conversion rate of 92%, a maximum hydrogen production yield of 153.4 g H-2/kg corn stover, and a maximum hydrogen purity of 77% v/v can be obtained with a circulated NiO to bio-oil molar ratio (CNB) of 12.3; a circulated Cab to bio-oil molar ratio (CCB) of 125.2; and where the ratio of solids recovered by the air reactor from the calcination reactor (alpha) was set as 1, and the ratio of solids flowing directly from the air reactor to the reformer (beta) was set as 0.02. The split of a fraction of solids streams to feed directly back to the reformer offers a great impact process control as operating conditions can be broadened. (C) 2016 Elsevier B.V. All rights reserved.

Modified sorbents - produced by adding compounds of Mg2+, Sr2+ and Al3+ to calcium oxide - have been tested in terms of their CO2 sorption/desorption performance in a fixed bed reactor at high temperatures. In particular this study focuses on the stability of the sorbents as well as the sorption capacity, both of which are important factors when selecting sorbents. X-ray diffraction (XRD) and scanning electron microscope (SEM), coupled with energy dispersive X-ray spectroscopy (EDX), were used for characterization of the modified sorbents. XRD results indicated that samples produced using the wet mixing process and those produced using the hydration with wet mixing process, contained MgO-CaO, Ca0.2Sr0.80O-CaO and Ca12Al14O33-CaO phases, respectively.The operating conditions have been investigated and results showed that the CaO showed the highest sorption capacity (0.571g(CO2)/g(sorbent)) when compared with MgO, SrO and Al2O3 at temperature of 600 degrees C. In terms of sorption capacity performance for sorbents produced by the CaO hydration and wet mixing method, Mg-CaO-HW showed the best sorption/desorption stability for more than 10 cycles (CO2 sorption capacity of 0.259 for 1st cycle to 0.252g(CO2)/g(sorbent) for the 10th cycle). Al-CaO-HW and Sr-CaO-HW exhibited a decrease in sorption capacity due to the sintering as confirmed by SEM images (0.257 and 0.286g(CO2)/g(sorbent) for 1st cycle dropping to 0.243 and 0.251g(CO2)/g(sorbent) for 10th cycle resulting in decreasing approximately of 5.45% and 12.24%, respectively). (c) 2015 Elsevier B.V. All rights reserved.

The production of hydrogen from methane via two chemical looping reforming (CLR) processes was simulated and thermodynamically analysed, one process being the conventional CLR process, the other being a CO2 sorption enhanced process. The aim of the work was to identify suitable operating conditions for obtaining an optimum hydrogen gas purity and yield, whilst operating auto-thermally, at atmospheric pressure and with no carbon formation. In both simulations, the reactors were simulated using the Gibbs minimisation technique. NiO was used as the oxygen storing species, whilst CaO was used as the CO2 adsorbent. For conventional CLR, within the range of conditions tested, the optimum reactor operating conditions are a temperature of 800 °C, a H2O/CH4 ratio of 3, and a NiO/CH4 ratio of 1 resulting in an approximate hydrogen production yield of 2.5 mol of H2 per mole of CH4 and an approximate hydrogen purity of 75%. However, with the application of in situ CO2 adsorption, a hydrogen purity > 90% and a yield within the region of 3 mol of H2 per mole of CH4, can be achieved with a NiO/CH4 ratio ≈ 1, a CaO/CH4 ratio ≥ 1, a H2O/CH4 ratio ≥ 2 and a temperature between 500 °C and 600 °C. The results indicate that the implementation of in situ CO2 adsorption could potentially bring about significant improvements in both yield and purity of hydrogen.

Hydrogen gas is a clean and sustainable fuel/energy carrier considered to be a possible alternative to fossil fuels. Sorption enhanced biogas steam reforming is a process which combines a CO2 adsorption unit with a hydrogen production unit. In the CO2 sorption section, CaO was selected as the adsorbent due to its high stoichiometric adsorption capacity. From the adsorption test, the highest adsorption capacity (0.2849 gCO(2)/gCaO) was achieved at a temperature of 873 K. Four types of bed arrangement were investigated using a feed gas with a CH4/CO2 ratio of 1.5, an S/C ratio of 3, a temperature of 873 K and at atmospheric pressure. The results indicate that the Type II system (Catalyst physical mixed with sorbent system packed in fixed bed quartz reactor, 8.0 g of 12.5 wt.% Ni/Al2O3 mixed with 2 g of CaO) exhibits the highest improvement in CH4 conversion with the introduction of CO2 adsorption (93.0% and 81.7%, with and without CO2 sorption, respectively) and high purity hydrogen was produced (97.0 % v/v and 62.3 % v/v, with and without CO2 sorption respectively).

The rheological and flow behaviour of ceramic pastes with varying solids loadings (solids volume fraction) has been studied. The pastes were shown to exhibit power law slip flow at both low and high solids loadings, with no slip yield stress. As would be expected, the extrusion rheometry data showed an increase in the die entry extrusion pressures with solids loading, in a trend similar to that of the Dougherty–Krieger equation. The die land flow however was shown to exhibit, only within a narrow range of solids loadings of approximately 53 to 56 v/v %, a trend in the die land extrusion pressure that was relatively independent of solids loading. Outside of this range the die land extrusion pressures increased significantly with solids loading in a trend similar to that of the die entry pressures. Using the Mooney analysis method, this was shown to be due to the development of slip flow with solids loading, as is consistent with other studies into the flow behaviour of concentrated suspensions. The slip velocity was also shown to be related to the wall shear stress by way of power law relationship also consistent with results from previous studies of concentrated suspensions using shear thinning liquid phases. The results presented in this report show that by using paste formulations that lie within said range of solids loadings, improved plug flow can be achieved in the die land without a significant change in the die land extrusion pressure at a given flow rate. This offers an advantage in the co-extrusion of ceramic products such as micro-tubular solid oxide fuel cells, as a uniform velocity profile results in improved control of the laminate structure.

This study evaluates the use of cracking for the removal of carbon from fuels to be used in a power generation process. Unlike conventional power generation systems, the proposed system includes a cracking unit, the function of which is to convert primary fuels into H-2 rich syngas and solid carbon, thus avoiding the emission of CO2 and the need for carbon capture and storage (CCS) in the power generation system. Based on the thermodynamic analysis of equilibrium reactions in the cracker, it is demonstrated that the operating temperature has a significant influence on the carbon capture rate achieved and the composition of the syngas. Carbon in the fuel can be captured in solid form from hydrocarbon fuels when operating the cracker at sufficiently high temperatures; however, only a portion of carbon can be captured in a solid form from oxygenated hydrocarbon fuels, with the maximum carbon capture rate being achieved at an optimum temperature. An energy analysis, which takes into account the energy penalty of CCS for the conventional power generation system, reveals that the net available energy from the proposed system is still not as high as that of the conventional system with CCS; however, the solid carbon can be of high commercial value when appropriate technology is employed to convert the carbon byproduct into a high-added-value carbon product such as carbon black or carbon nanotubes (CNTs).

An ultra-large pore mesocellular foam silica (MCF) was employed as a support for preparation of supported Pd catalysts for the liquid-phase selective hydrogenation of phenylacetylene. The catalysts were prepared by three different routes: (i) incipient wetness impregnation using Pd(II)acetate solution (Pd/MCF-imp), (ii) impregnation of colloidal Pd nanoparticles obtained by the solvent reduction method (Pd/MCF-col), and (iii) in situ synthesis of MCF in the presence of the Pd colloid (Pd/MCF-ss). The conventional impregnation method resulted in more agglomeration of Pd particles and partial collapse of MCF structure, hence the Pd/MCF-imp exhibited the lowest selectivity towards styrene at total conversion of phenylacetylene. Only the Pd/MCF-ss, in which most of the Pd nanoparticles were encapsulated by the silica matrix, was found to retain high styrene selectivity (>80%) after complete conversion of phenylacetylene. Comparing to the other highly efficient Pd catalysts reported in the literature under similar reaction conditions, it can be emphasized that coverage of Pd surface by the support produces great beneficial effect for enhancing styrene selectivity, regardless of the type of supports used (i.e., TiO2, carbon nanotubes, or mesostructured silica).

Current methods to manufacture tubular solid oxide fuel cells (SOFCs) involve multiple steps of extrusion, layer deposition and sintering, leading to high manufacturing costs. The aim of the work presented in this paper is to reduce the cost of manufacturing SOFCs. This is achieved by developing a method for manufacturing a five-layered micro-tubular structure by a multi-billet co-extrusion process. With the implementation of continuous screw extrusion equipment, this co-extrusion process could easily be adapted into a fully continuous manufacturing process.The co-extrusion process presented initially involves rheologically unifying five pastes made up of individual powder compositions. It is shown that it is possible to formulate the pastes with in an optimum solids loading region where the die land rheological properties are relatively insensitive to small variations in solids loading, thus allowing for a more stable process.These pastes are then extruded as billets from separate extrusion barrels through a single nozzle. This uses a novel die design which does not require the use of a central mandrel to form the tubular structure. The sintered structure comprises four Ni/YSZ anode layers and a YSZ electrolyte layer, each layer being approximately 60 mu m thick, forming a tube with an outer diameter of 3 mm and an inner diameter of 2.4 mm. (C) 2010 Elsevier Ltd. All rights reserved.

Current methods used to manufacture solid oxide fuel cells (SOFCs) involve multiple steps, applying successive layers to produce laminated components associated with repeated sintering steps. This work aims to cut the number of processing steps involved by co-extruding a complete SOFC tube from pastes in a single step, which is then co-sintered. Several aspects must be overcome in order to co-extrude such a fuel cell. Crucially the co-extrusion process requires that the theological properties of the materials are well matched. This prevents the formation of flow defects and allows for the continuous operation of the co-extrusion process. This work has investigated the manipulation of the rheological parameters through design of the paste formulation as well as the manufacturing process.Two pastes, one made from a fine yttria stabilised zirconia (YSZ) and the other from a combination of a fine YSZ, a coarser nickel oxide and activated carbon, have been characterised using the Benbow/Bridgwater model and their parameters have been unified through adjustment of their solids loading. Using packing theory and the assumption that pastes will only flow when the powder void space has been filled with a slight excess of liquid to overcome inter-particulate friction, an intermediate paste has been designed to possess similar rheological properties. (c) 2008 Elsevier Ltd. All rights reserved.

Experimental measurements were made in a rotating-cavity rig with an axial throughflow of cooling air at the centre of the cavity, simulating the conditions that occur between corotating compressor discs of a gas-turbine engine. One of the discs in the rig was heated, and the other rotating surfaces were quasi-adiabatic; the temperature difference, between the heated disc and the cooling air was between 40 and 100 °C. Tests were conducted for axial Reynolds numbers, Rez, of the cooling air between 1.4 × 103 and 5 × 104, and for rotational Reynolds numbers, Reφ, between 4 × 105 and 3.2 × 106. Velocity measurements inside the rotating cavity were made using LDA, and temperatures and heat flux measurements on the heated disc were made using thermocouples and fluxmeters. The velocity measurements were consistent with a 3D, unsteady, buoyancy-induced flow in which there was a multicell structure comprising one, two or three pairs of cyclonic and anti-cyclonic vortices. The core of fluid between the boundary layers on the discs rotated at a slower speed than the discs, as found by other experimenters. At the smaller values of Rez, the radial distribution and magnitude of the local Nusselt numbers, Nu, were consistent with buoyancy-induced flow. At the larger values of Rez, the distribution of Nu changed, and its magnitude increased, suggesting the dominance of the axial throughflow.

Numerous indicators for disease progression have been described in the last decade. The purpose of this study was to examine, longitudinally, a large battery of clinical, microbiological, and immunological indicators, to try to determine whether the presence of one or a combination of these parameters at baseline, would correlate positively with increased attachment and or bone loss (true prognostic factors). Following initial screening, 79 patients with established periodontitis were monitored longitudinally for one year. Whole mouth clinical measurements, plaque gingival and calculus indices, together with pocket depth and attachment level measurements, were repeated every three months. Full mouth radiographic survey, performed at baseline and 12 months, served to determine changes in crestal bone height using an image enhancement technique. Subgingival plaque samples were taken at baseline and every 3 months. Immunofluorescence assays were performed for the a battery of target microorganisms. Serum and GCF samples for IgG subclasses analysis were obtained at each visit and assayed using ELISA techniques. Likewise blood, samples were also drawn at each visit for a quantitative analysis of serum cotinine level. The overall mean attachment loss (AL) and bone loss (BL) were almost identical(0.l59 mm and 0.164 mm, respectively). Individual patients variation was large (-0.733 to + 1.004 mm). An overall 6.89% of sites were active; individual patients' means ranged from 0-28.9%. Mean pocket depth (PD) showed minimal change over the study period (-0.033 mm) thus suggesting that most if not all the AL was accompanied by concomitant gingival recession. Smokers exhibited greater AL and radiographic BL compared to non-smokers. Likewise, patients' cotinine level showed direct correlation with outcomes of progressive periodontal breakdown. Past severity of periodontal involvement, as reflected in the patients baseline PD, AL and crestal bone height, showed good correlation with longitudinal changes in the periodontium. This correlation was higher for crestal BL as the outcome variable, while somewhat smaller for change in AL as the outcome variable. Bacteroides forsythus (Bf.), Prevotella intermedia (Pi.) and Porphyromonas gingivalis (Pg.) were frequently found in these patients. The presence of these microorganisms at baseline was associated with further disease progression. Subjects with mean baseline pocket depth equal or greater than 3.2 mm were at greater risk for future bone loss 1 year later (O.R. 2.97; C.I. 1.02-8.70). Smokers were at significantly greater risk for further attachment loss when compared to non-smokers (O.R. 5.41; C.I. 1.50-19.5). Subjects that harbored B. forsythus at baseline, were at seven times greater risk for increased pocket depth (O.R. 7.84; C.I.1.74-35.3). In conclusion, past periodontal destruction, smoking habits, BS., Pg., & Pi. are prognostic factors for further periodontal breakdown. When designing clinical trials, or when evaluating epidemiological data, it is most important to balance for these factors. Also, treatment strategies should attempt to eliminate or modify these factors.