The corrosion behaviour of NiAl in Molten Carbonate at 650°C

In Molten Carbonate Fuel Cells (MCFC) the separator plates in a stack are exposed to severe conditions. The normal operating temperature of a MCFC is 650°C, while the electrolyte consists of an eutectic mixture of 62/38 Li₂CO₃/K₂CO₃. On one side the separator plate material is in contact with a reducing atmosphere and on the other side it is an oxidising atmosphere. Due to the application of a wet seal the material is also in contact with the molten carbonate. A wide range of materials is therefore being investigated to enable a justified materials selection either as base material or as coating. NiAl is one of the investigated materials, which has promising properties, due to the possible formation of a protective oxide LiAlO₂ layer. A comparison will be made with data available for pure Ni, with special emphasis on the protective character of the oxide layer based on quasi-stationary polarisation curves, exposure tests at open circuit potential and quenching experiments, incorporating earlier published results obtained on Ni with impedance measurements. All experiments were performed in molten carbonate, while the gas composition over the melt was 64% H₂, 16% CO₂, and 20% H₂O.     

Electrodeionisation 3: The removal of nickel ions from dilute solutions

The removal of nickel ions from dilute solutions using a process that combines an ion-exchange bed with electrodialysis has been studied. The main aspects include: the concentration of nickel ions in the diluate, the voltage over the cell and the current density distribution along the ion-exchange bed. The current density distribution provides insight into the state of the bed as it is simultaneously loaded with Ni²⁺ and regenerated with an electric potential difference applied perpendicular to it. A simple model is used to describe the state of the bed and the quantity of nickel removed from it as a function of time. Under specific conditions the precipitation of metal hydroxides is observed in the compartment containing the ion-exchange bed. The results show that hydroxide precipitation is related to the nickel concentration in solution and the electric potential gradient across the bed.     

Molecular dynamics simulations as a tool for improving protein stability

Haloalkane dehalogenase (DhlA) was used as a model protein toexplore the possibility to use molecular dynamics (MD) simulationsas a tool to identify flexible regions in proteins that canserve as a target for stability enhancement by introductionof a disulfide bond. DhlA consists of two domains: an     

CO oxidation and CO2 reduction on carbon supported PtWO3 catalyst

The activity of a carbon supported PtWO₃ (PtWO₃/C) catalyst in the CO oxidation and CO₂ reduction reactions was evaluated in sulfuric acid solution at room temperature.Cyclic voltammetry combined with on-line mass spectrometry shows that the oxidation of both saturated CO adlayer and dissolved CO on PtWO₃/C material commences at rather low potentials, ca. 0.18 and 0.12 V vs. RHE, respectively. However, the low-potential process seems to involve only a minor fraction of the CO adlayer, the major part of the adsorbed CO layer being oxidised at the potentials as high as those for pure Pt catalysts—ca. 0.7 V vs. RHE. PtWO₃/C material was found to reversibly de-activate upon a prolonged exposure to the CO-saturated solution due to the inhibition of the hydrogen tungsten bronze formation.The reduction of CO₂ on PtWO₃/C leads to the formation of an adsorbate - presumably CO - on the Pt sites of the catalyst. Although the rate of the adsorbate build-up on PtWO₃/C at 0.1 V is lower than that on pure Pt/C, our results indicate that upon a prolonged exposure of the PtWO₃/C electrode to a CO₂-saturated solution a complete poisoning of the Pt sites with the adsorbate is likely to occur at room temperature.     

Catalytic role of the active site histidine of porcine pancreatic phospholipase A2 probed by the variants H48Q, H48N and H48K

The catalytic contribution of His48 in the active site of porcinepancreatic phospholipase A2 was examined using site-directedmutagenesis. Replacement of His48 by lysine (H48K) gives riseto a protein having a distorted lipid binding pocket. Activityof this variant drops below the detection limit which is 10⁷-foldlower than that of the wild-type enzyme. On the other hand,the presence of glutamine (H48Q) or asparagine (H48N) at thisposition does not affect the structural integrity of the enzymeas can be derived from the preserved lipid binding propertiesof these variants. However, the substitutions H48Q and H48Nstrongly reduce the turnover number, i.e. by a factor of 10⁵.Residual activity is totally lost after addition of a competitiveinhibitor. We conclude that proper lipid binding on its ownaccelerates ester bond hydrolysis by a factor of 10². With theselected variants, we were also able to dissect the contributionof the hydrogen bond between Asp99 and His48 on conformationalstability, being 5.2 kJ/mol. Another hydrogen bond with His48is formed when the competitive inhibitor (R)-2-dodecanoylamino-hexanol-1-phosphoglycolinteracts with the enzyme. Its contribution to binding of theinhibitor in the presence of an interface was found to be 5.7kJ/mol.     

From coal to biomass gasification: Comparison of thermodynamic efficiency

The effect of fuel composition on the thermodynamic efficiency of gasifiers and gasification systems is studied. A chemical equilibrium model is used to describe the gasifier. It is shown that the equilibrium model presents the highest gasification efficiency that can be possibly attained for a given fuel. Gasification of fuels with varying composition of organic matter, in terms of O/C and H/C ratio as illustrated in a Van Krevelen diagram, is compared. It was found that exergy losses in gasifying wood (O/C ratio around 0.6) are larger than those for coal (O/C ratio around 0.2). At a gasification temperature of 927 °C, a fuel with O/C ratio below 0.4 is recommended, which corresponds to a lower heating value above 23 MJ/kg. For gasification at 1227 °C, a fuel with O/C ratio below 0.3 and lower heating value above 26 MJ/kg is preferred. It could thus be attractive to modify the properties of highly oxygenated biofuels prior to gasification, e.g. by separation of wood into its components and gasification of the lignin component, thermal pre-treatment, and/or mixing with coal in order to enhance the heating value of the gasifier fuel.     

Derivation of an aquatic predicted no-effect concentration for the synthetic hormone, 17 alpha-ethinyl estradiol

17alpha-Ethinyl estradiol (EE2) is a synthetic estrogen widely used in combination with other steroid hormones in oral contraceptives and in the contraceptive patch. EE2 has been detected in sewage treatment plant effluents in the low nanogram -per-liter range and occasionally in surface waters in the U.S., U.K., Canada, Brazil, Germany, and elsewhere. The mode of action is receptor-mediated, and estrogen receptors exist in mammals and other vertebrates. A large number of studies on the effects of EE2 on aquatic organisms exist. One hundred English language studies published between 1994 and 2007, one as yet unpublished study, and findings published in conference proceedings (in German) were compared to published data quality criteria to identify the most relevant studies for deriving a predicted no-effect concentration (PNEC). Reproduction in fish was identified as the most sensitive end point in aquatic species. A species sensitivity distribution was constructed using no observed effect concentrations (NOECs) for reproductive effects from 39 papers in 26 species, resulting in a median hazardous concentration at which 5% of the species tested are affected (HC5,50) of 0.35 ng/L. After comparing this HC5,50 to all of the laboratory and field-derived toxicity information available for EE2, we recommend using 0.35 ng/L as the PNEC for EE2 in surface water. This PNEC is below 95% of the existing NOECs for effects on reproduction and is also below virtually all of the NOECs for vitellogenin induction in the key fish reproduction studies.     

Sustainability of biofuels in Latin America: Risks and opportunities

Several Latin American countries are setting up biofuel programmes to establish alternative markets for agricultural commodities. This is mainly triggered by the current success of Brazilian bioethanol production for the domestic market and for export. Furthermore, the global biofuel market is expected to increase due to ambitious biofuel programmes in the EU and in the USA. Colombia, Venezuela, Costa Rica and Guatemala are focusing on bioethanol production from sugarcane whereas biofuel production in Argentina is based on soy biodiesel. Recent developments of the biofuel sector take place extremely rapid especially in Argentina, which became one of the five largest biodiesel producers in the world in 2008. Till date no specific biofuel sustainability certification systems have been implemented in Latin American, as well as on global level. This fact and the predominant use of food crops for biofuel production raise concerns about the sustainability of biofuel production related to environmental and social aspects. This paper provides an overview of the hotspots of conflicts in biofuel production in Latin America. It investigates presently available sustainability tools and initiatives to ensure sustainable biofuel production in Latin America. Finally, it provides an outlook on how to integrate sustainability in the Latin American biofuel sector.