The oxidation behaviour of sintered iron

The oxidation behaviour of porous, sintered iron was studied by thermo-gravimetric analysis (TGA), at temperatures between 300oC and 700oC, in a flowing atmosphere of 20% O2/80% N2. Samples for TGA tests were compacted from pure iron powder, at 150MPa to 550MPa, and vacuum sintered at 1120oC. The mass gain of samples during oxidation was recorded continuously for a period of 24 hours. It was found that the oxidation mass gain of PM samples depended on the permeability of the pore structure and the temperature. At low temperatures, the oxidising gas was able to permeate through the pore structure, causing the oxidation of a large active surface area. At high temperatures the active surface area was smaller, because oxygen diffusing into the pore structure, from the external atmosphere, was adsorbed by pore surfaces close to the external surface of the compact. Although the weight of the external oxide scale on compacts increased with increasing oxidation temperature, the absence of oxide in the core porosity in compacts oxidised at higher temperatures resulted in smaller mass gains than were observed for compacts oxidised at lower temperatures. The heat generated by the oxidation of the large active surface areas of porous samples was studied by thermo-calorimetric analysis (TCA). It was determined that this phenomenon could raise the core temperature of samples significantly above the ambient furnace temperature, and affecting the morphology of the oxide scale formed. The effects (on oxidation behaviour at 500oC) of small, elemental alloy additions of Al, Cu, P and Si to pure iron powder were studied. It was found that elements that promote pore rounding during sintering caused a significant reduction in the mass gain rate of the PM alloys, compared to the PM pure iron. The oxidation resistance due to these elements prevented pore closure by oxide growth, so that the active surface area of these PM alloys remained high. The PM alloys were also studied by thermo-mechanical analysis (TMA, dilatometry), to determine their dimensional stability during sintering and subsequent elevated temperature service. The oxidation experiment was augmented with optical and electron microscopy, and X-ray analysis of alloy and scale compositions.

Genetic and environmentally derived variation in the cell wall composition of miscanthus and implications for thermo-chemical conversion

Fifteen Miscanthus genotypes grown in five locations across Europe were analysed to investigate the influence of genetic and environmental factors on cell wall composition. Chemometric techniques combining near infrared reflectance spectroscopy and conventional chemical analyses were used to construct calibration models for determination of acid detergent lignin, acid detergent fibre, and neutral detergent fibre from sample spectra. The developed equations were shown to predict cell wall components with a good degree of accuracy and significant genetic and environmental variation was identified. The influence of nitrogen and potassium fertiliser on the dry matter yield and cell wall composition of M. x giganteus was investigated. A detrimental affect on feedstock quality was observed to result from application of these inputs which resulted in an overall reduction in concentrations of cell wall components and increased accumulation of ash within the biomass. Pyrolysis-gas chromatography-mass spectrometry and thermo-gravimetric analysis indicates that genotypes other than the commercially cultivated M. x giganteus have potential for use in energy conversion processes and in the bio-refining. The yields and quality parameters of the pyrolysis liquids produced from Miscanthus compared favourably with that produced from SRC willow and produced a more stable pyrolysis liquid with a higher lower heating value. Overall, genotype had a more significant effect on cell wall composition than environment. This indicates good potential for dissection of this trait by QTL analysis and also for plant breeding to produce new genotypes with improved feedstock characteristics for energy conversion.

Structure and thermal properties of yttrium alumino-phosphate glasses

The structure and thermal properties of yttrium alumino-phosphate glasses, of nominal composition (Y2O3)(0.31-z)(Al2O3)(z)(P2O5)(0.69) with 0 less than or similar to z less than or similar to 0.31, were studied by using a combination of neutron diffraction, Al-27 and P-31 magic angle spinning nuclear magnetic resonance, differential scanning calorimetry and thermal gravimetric analysis methods. The Vickers hardness of the glasses was also measured. The data are compared to those obtained for pseudo-binary Al2O3-P2O5 glasses and the structure of all these materials is rationalized in terms of a generic model for vitreous phosphate materials in which Y3+ and Al3+ act as modifying cations that bind only to the terminal (non-bridging) oxygen atoms of PO4 tetrahedra. The results are used to help elucidate the phenomenon of rare-earth clustering in phosphate glasses which can be reduced by substituting Al3+ ions for rare-earth R3+ ions at fixed modifier content.

The intermediate pyrolysis and catalytic steam reforming of brewers spent grain

Brewers spent grain (BSG) is a widely available feedstock representing approximately 85% of the total by-products generated in the brewing industry. This is currently either disposed of to landfill or used as cattle feed due to its high protein content. BSG has received little or no attention as a potential energy resource, but increasing disposal costs and environmental constraints are now prompting the consideration of this. One possibility for the utilisation of BSG for energy is via intermediate pyrolysis to produce gases, vapours and chars. Intermediate pyrolysis is characterised by indirect heating in the absence of oxygen for short solids residence times of a few minutes, at temperatures of 350-450 °C. In the present work BSG has been characterised by chemical, proximate, ultimate and thermo-gravimetric analysis. Intermediate pyrolysis of BSG at 450 °C was carried out using a twin coaxial screw reactor known as Pyroformer to give yields of char 29%, 51% of bio-oil and 19% of permanent gases. The bio-oil liquid was found to separate in to an aqueous phase and organic phase. The organic phase contained viscous compounds that could age over time leading to solid tars that can present problems in CHP application. The quality of the pyrolysis vapour products before quenching can be upgraded to achieve much improved suitability as a fuel by downstream catalytic reforming. A Bench Scale batch pyrolysis reactor has then been used to pyrolyse small samples of BSG under a range of conditions of heating rate and temperature simulating the Pyroformer. A small catalytic reformer has been added downstream of the reactor in which the pyrolysis vapours can be further cracked and reformed. A commercial reforming nickel catalyst was used at 500, 750 and 850 °C at a space velocity about 10,000 L/h with and without the addition of steam. Results are presented for the properties of BSG, and the products of the pyrolysis process both with and without catalytic post-processing. Results indicate that catalytic reforming produced a significant increase in permanent gases mainly (H2 and CO) with H2 content exceeding 50 vol% at higher reforming temperatures. Bio-oil yield decreased significantly as reforming temperature increased with char remaining the same as pyrolysis condition remained unchanged. The process shows an increase in heating value for the product gas ranging between 10.8-25.2 MJ/m as reforming temperature increased. © 2012 Elsevier B.V. All rights reserved.

Intermediate pyrolysis studies of aquatic biomass and potential applications in the BtVB-process

Aquatic biomass is seen as one of the major feedstocks to overcome difficulties associated with 1st generation biofuels, such as competition with food production, change of land use and further environmental issues. Although, this finding is widely accepted only little work has been carried out to investigate thermo-chemical conversion of algal specimen to produce biofuels, power and heat. This work aims at contributing fundamental knowledge for thermo-chemical processing of aquatic biomass via intermediate pyrolysis. Therefore, it was necessary to install and commission an analytical pyrolysis apparatus which facilitates intermediate pyrolysis process conditions as well as subsequent separation and detection of pyrolysates (Py- GC/MS). In addition, a methodology was established to analyse aquatic biomass under intermediate conditions by Thermo-Gravimetric Analysis (TGA). Several microalgae (e.g. Chlamydomonas reinhardtii, Chlorella vulgaris) and macroalgae specimen (e.g. Fucus vesiculosus) from main algal divisions and various natural habitats (fresh and saline water, temperate and polar climates) were chosen and their thermal degradation under intermediate pyrolysis conditions was studied. In addition, it was of interest to examine the contribution of biochemical constituents of algal biomass onto the chemical compounds contained in pyrolysates. Therefore, lipid and protein fractions were extracted from microalgae biomass and analysed separately. Furthermore, investigations of residual algal materials obtained by extraction of high valuable compounds (e.g. lipids, proteins, enzymes) were included to evaluate their potential for intermediate pyrolysis processing. On basis of these thermal degradation studies, possible applications of algal biomass and from there derived materials in the Bio-thermal Valorisation of Biomass-process (BtVB-process) are presented. It was of interest to evaluate the combination of the production of high valuable products and bioenergy generation derived by micro- and macro algal biomass.

The influence of surface functionalization of activated carbon on palladium dispersion and catalytic activity in hydrogen oxidation

Stone-fruit activated carbon (SAC) and modified versions containing acidic oxygen and basic nitrogen groups have been used to prepare palladium catalysts by wet impregnation. Carbon supports and catalysts are investigated by thermo-gravimetric analysis, TPD, oxygen chemisorption, TEM and XPS. The influence of the nature of the functional groups on the dispersion and oxidation state of palladium and its activity in hydrogen oxidation is investigated. Pd dispersion is found to increase with the basic strength of functional groups on the support. XPS reveals that introduction of amine groups in SAC results in an increased proportion of Pd0, resistant to re-oxidation. Palladium catalysts supported on activated carbon modified by diethylamine groups are found to exhibit the highest metal dispersion and greatest activity in hydrogen oxidation. © 2007 Elsevier B.V. All rights reserved.