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Monthly Archives: November 2007

November 2007 News

The summer 2007 issue of The Bent, the magazine of Tau Beta Pi, had an interesting article on “Implementing the hydrogen economy with synfuels” by R. E. Uhrig et al. It deals with how to utilize hydrogen to gain energy independence, reduce the use of coal, reduce the output of CO2, and at the same time avoid the very volatile and hard to handle hydrogen itself by synthesizing it into conventional gasoline. This approach would allow continuation of the use of the present gasoline infrastructure, but would compensate the output of CO2 from burning conventional gasoline by using an equivalent amount of CO2 in the fuel synthesis, thus reducing the net output of CO2 from synfuel use to almost zero. This would be a considerable reduction of CO2 output compared to three other alternatives, such as burning crude, as we do now, producing synfuel from coal, or from coal and external hydrogen. Of course, synfuel decoupled from coal requires cheap and large amounts of energy to produce the right ingredients, and this energy would have to come from a non-coal source, such as nuclear, solar or wind. And here the buck could stop right away, because presently we know only coal and nuclear that could provide this amount of energy. But for the moment let’s assume such an energy source can be made available. To make gasoline, an organic compound of C and H, we need these two ingredients in the proper form. C would be in the form of CO2 and H in the form of H2O. Nature uses ultraviolet light to synthesize these two compounds into carbohydrates by the reaction nCO2 + nH2O -> (CH2O)n + nO2, where n is some integer number. All the world’s biomass is produced in this way. The Fischer- Tropsch synthesis looks quite similar: nCO + 2 nH2 -> (- CH2 -)n + nH2O, where the expression in parentheses is the methylen group, a building block of paraffins; a well-known member is CH4, methane. web security . While the plant synthesis uses inputs readily available in the environment, the fuel synthesis requires CO and H2, both of which consist of the most widely distributed elements on the planet, but not in usable compounds, which must be artificially produced. If water vapor is blown through red hot coke, one obtains water gas: C + H2O = CO + H2, both the ingredients for the Fischer-Tropsch synthesis, but this would involve coal. The idea proposed by the authors is to produce CO from CO2 + H2 -> CO + H2O, a process that also consumes hydrogen, but recycles available CO2 that is a pollutant in the stack gases of conventional fossil power plants. CO could be made from CO2 by heating it to 1000 C according to the reaction 2CO2 + heat -> 2CO + O2. The hydrogen must also be externally produced by an energy intensive process, such as electrolysis, in order to avoid coal. If this can be done, the synthetic gasoline can be obtained by the Fischer-Tropsch synthesis and used like conventional gasoline. It would be entirely home-made, with the added benefit of recycling an equivalent amount of CO2 that it produces when it is burned. Providing transportation fuel on this basis would also call for fuel efficient cars as such synfuel would be very energy and capital intensive. According to the authors, just to produce the hydrogen for all the gasoline used in US transportation by electrolysis would require a power source of 1400 GW, or about 45 times the TVA installed capacity of about 30 GW.

 
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Posted by on November 1, 2007 in News