Monday, June 06, 2005

[Power plants] Dirty Kilowatts: America's Most Polluting Power Plants Power Plants--Pollution Source: Environmental Integrity Project Dirty Kilowatts: America's Most Polluting Power Plants "A handful of the nation's largest coal-fired power plants account for a disproportionately large share of sulfur dioxide, nitrogen oxides, carbon dioxide, and mercury pollution. The report lists the top 50 most polluting power plants based on both total tons and emission rates." (via A.T.) Full report (PDF; 742 KB) [ResourceShelf's DocuTicker] 3:12:23 PM Google It!    [Energy] Energy: A 21st Century Perspective Energy--Conference Presentations Source: National Academy of Engineering Energy: A 21st Century Perspective "Energy: A 21st Century Perspective addresses technological opportunities and the associated economics of various forms of energy. Few fields of critical social importance are more dependent on science and technology than those associated with the various methods of delivering energy in its different forms.... Speakers include prominent engineers, scientists, and economists, who will discuss the broad picture of energy technologies and economics, and specific topics including carbon-based fuels, the nuclear enterprise, the hydrogen economy, and alternative energy sources." Presentations available in PowerPoint. [ResourceShelf's DocuTicker] 3:11:51 PM Google It!    [Biofuels] Converting Biomass to Biodiesel The conversion of the oxygenated hydrocarbons in biomass to saturated alkanes could provide a route to cleaner fuels from renewable sources. Recently, such conversions were demonstrated that produced volatile alkanes, such as hexane, from simple sugars. Huber et al. (p. 1446; see the Perspective by Rostrup-Nielsen) have now converted biomass-derived oxygenated hydrocarbons to liquid alkanes ranging from n-C7 to C15, which are in the range needed for diesel fuel and have the advantage of being sulfur-free. In this process, glucose or xylose is dehydrated over acid catalysts to aldehydes. These products, which may also be first cross-coupled to other aldehydes, are then hydrogenated and subjected to aldol condensations over solid base catalysts. Subsequent dehydration and hydrogenation reactions over bifunctional catalysts that contain acid and metal sites lead to the formation of alkanes. [This Week in Science] 3:10:56 PM Google It!    [Climate change] A Lag in Global Warming Earth's climate is thermally stable only when the amount of radiation it absorbs from the Sun is balanced by the amount emitted back into space. Hansen et al. (p. 1431, published online 28 April 2005) report results from a climate model and validate them with measurements of recent changes in the heat content of the ocean, which show that Earth now is absorbing 0.85 ± 0.15 watts per square meter more energy from the Sun than it is emitting to space. Their findings confirm that there is a lag in response of the climate system relative to the radiative forcing that drives it, and they predict that climate will continue to warm by more than half a degree Celsius even without further increases in atmospheric greenhouse gas concentrations because of the thermal inertia of the climate system.  [This Week in Science] 3:10:19 PM Google It!    [Fuel cells] CHEMISTRY: Cleaning Up CO For use in fuel cells, hydrogen (H2) can be produced by reacting alcohols or hydrocarbons with steam or oxygen, yielding byproducts that include CO and CO2. Although CO can be removed or converted through the water-gas-shift reaction to CO2 and additional H2, even small amounts of residual CO inhibit reactions at the Pt anode of polymer electrolyte fuel cells (PEFCs). Onboard H2 production would likely need to remove CO in the presence of its oxidation product, CO2, and to do so without oxidizing the H2 to water. Landon et al. report the selective oxidation of CO to CO2 in the presence of H2, water vapor, and CO2 at 80C, which is below the operating temperature of PEFCs, with a single-stage reactor. They report that a gold catalyst on an Fe2O3 support, prepared in a two-step heating process up to 550C, created a catalyst with high CO oxidation activity but no H2 oxidation activity under typical PEFC conditions. -- PDS Chem. Commun. 10.1039/b505295p (2005). [Editors' Choice] 3:07:56 PM Google It!    [Climate change] CLIMATE SCIENCE: Urban Air Quality The oxidation of volatile organic compounds (VOCs) is an important step in the formation of photochemical smog in urban areas, but the rate at which VOCs are oxidized has been difficult to quantify. A reliable way to measure this rate would lead to improved prediction of smoke/fog events. Volkamer et al. used differential optical absorption spectroscopy (DOAS) to make direct measurements of atmospheric glyoxal concentrations over Mexico City in the spring of 2003. They show that VOC oxidation, of which glyoxal is a product, begins about an hour after sunrise and continues throughout the day. These observations allow a lower limit to be placed on the rate of VOC oxidation and reveal that VOC chemistry is active throughout sunlit hours. On the basis of these results, satellite measurements of glyoxal appear to be feasible, which would support the identification of photochemical hot spots in the atmosphere. -- HJS Geophysical Research Letters. 32, 10.1029/2005GL022616 (2005). [Editors' Choice] 3:06:42 PM Google It!

© Copyright 2005 Laura L. Barnes. Last update: 10/25/2005; 12:10:44 PM.