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* Rotary Rig Counts * Renewable Energy o Biofuels o Geothermal o Hydroelectric o Ocean, Tidal & Wave o Solar o Wind * Non-Renewable Energy o Coal o Nuclear o Oil & Natural Gas o Oil & Tar Sands o Oil Shale Researchers Develop Two-Stage Process For Optimal Biohydrogen Production Thursday, 17 July 2008 00:13:00 CDT Alternative-Energy-News.INFO - BioFuel News Researchers have combined the efforts of two kinds of bacteria to produce hydrogen in a bioreactor, with the product from one providing food for the other. According to an article [*.pdf] in the August issue of Microbiology Today , this technology has an added bonus: leftover enzymes can be used to scavenge precious metals from spent automotive catalysts to help make fuel cells that convert hydrogen into energy. Hydrogen has three times more potential energy by weight than petrol, making it the highest energy-content fuel available. Research into using bacteria to produce hydrogen from waste biomass has been revived thanks to the rising profile of energy issues. According to the researchers, the UK throws away a third of its food, wasting 7 million tonnes a year. The majority of this is currently sent to landfill where it produces gases like methane, which is a greenhouse gas 25 times more potent than carbon dioxide. Following some major advances in the technology used to make biohydrogen, this waste can now be turned into valuable energy. Two-stage process There are special and yet prevalent circumstances under which micro-organisms have no better way of gaining energy than to release hydrogen into their environment. Microbes such as heterotrophs, cyanobacteria, microalgae and purple bacteria all produce biohydrogen in different ways, says Dr Mark Redwood from the University of Birmingham. When there is no oxygen, fermentative bacteria use carbohydrates like sugar to produce hydrogen and

hydrogen

CO-shift The processes described above produce gas with a high content of carbon monoxide - CO. It is therefore necessary to put the gas through the CO-shift process to increase the content of hydrogen. The shift reaction (see sidebar) is a two-step process to achieve the most complete reaction between CO and steam. Initially steam is added in a high-temperature step (300-500ºC), followed by a a low-temperature step (200ºC), with different catalysts in the two steps. Separation of CO2 Each of the processes described above produces CO2 in addition to H2. To separate hydrogen and CO2, it is common to use amine based absorption processes. This is conventional technology. Methods based on selective membranes or sorbents are under development.

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Producing fuel alcohol via hydrolysis of lignocellulosic biomass leaves a considerable amount of residues waiting for treatment. A study was carried out on the preparation of hydrogen via catalytic gasification of residues from biomass hydrolysis with a novel Ni/modified dolomite binary catalyst, which was prepared by a two-step coprecipitation method and proved available for hydrogen production in terms of both activity and strength. The effects of four operation parameters, that is, the fluidized bed temperature, the catalytic fixed bed temperature, the particle size of the catalyst, and S/B (i.e., the mass ratio of steam to biomass material fed into the fluidized bed per unit time), on hydrogen yield were investigated. The results indicate that hydrogen yield increases with an increase in the temperature of either the fluidized bed or the downstream catalytic fixed bed or the S/B ratio or a reduction in the particle size of the catalyst. The optimum range for each of the four operation parameters from a comprehensive consideration is as follows: 800-850 °C for both the fluidized bed temperature and the catalytic fixed bed temperature, 1.5-2 for the S/B ratio, and 2.0-3.0 mm for the particle size of the catalyst. Furthermore, the gas product from catalytic gasification of residues from biomass hydrolysis contains less CO and CO2 and has a higher H2/CO ratio compared with that of the sawdust. The hydrogen yield of the former is also much higher than that of the latter. These suggest that residues from biomass hydrolysis are an even better gasification material than the original sawdust. This paper provides a novel effective method for modifying the calcined dolomite, which endows the catalyst with satisfactory strength while retaining high activity, and opens a new promising way for utilizing the residues from biomass hydrolysis. Download the full text: PDF | HTML

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