Overall efficiency Carbonate

Reasons for interest in the catalyzed reactions of NO, CO, and COz are many and varied. Nitric oxide, for example, is an odd electron, hetero-nuclear diatomic which is the parent member of the environmentally hazardous oxides of nitrogen. Its decomposition and reduction reactions, which occur only in the presence of catalysts, provide a stimulus to research in nitrosyl chemistry. From a different perspective, the catalyzed reactions of CO and COz have attracted attention because of the need to develop hydrocarbon sources that are alternatives to petroleum. Carbon dioxide is one of the most abundant sources of carbon available, but its utilization will require a cheap and plentiful source of hydrogen for reduction, and the development of catalysts that will permit reduction to take place under mild conditions. The use of carbon monoxide in the development of alternative hydrocarbon sources is better defined at this time, being directly linked to coal utilization. The conversion of coal to substitute natural gas (SNG), hydrocarbons, and organic chemicals is based on the hydrogen reduction of CO via methanation and the Fischer-Tropsch synthesis. Notable successes using heterogeneous catalysts have been achieved in this area, but most mechanistic proposals remain unproven, and overall efficiencies can still be improved. 

Well-established anode materials are Ni cermets such as Ni/YSZ composites. The presence of the second phase increases the contact area and prevents the catalytically active Ni particles from aggregating. The use of the composite becomes problematic if hydrocarbons are to be directly converted Ni catalyzes cracking, and the resulting carbon deposition deactivates the fuel cells. Therefore either pure H2 has to be used or the fuel has to be externally reformed. A third way is internal conversion of CHV with H20 to synthesis gas. The necessary steam addition, however, reduces the overall efficiency. Another problem of Ni cermets, if they are to be used at lower temperatures, is a potential oxidation of the Ni. Alternatives are Cu/Ce02 cermets in which Cu essentially provides the electronic conductivity and Ce02 the catalytic activity. Note that an efficient current collecting property of the electrode presupposes a metal concentration above the percolation threshold. 

Second, molten carbonate fuel cells have electric efficiencies of 47 to 50 percent or more, which significantly reduces their fuel costs for stationary applications compared with both phosphoric acid and pem fuel cells, whose overall efficiency when running on natural gas might not exceed 35 to 40 percent. Third, high temperatures allow relatively inexpensive nickel to be used as a catalyst rather than pricey platinum, which is required by the lower-temperature fuel cells. Fourth, these fuel cells are far more tolerant of carbon monoxide, which can poison the electrochemical reaction of pem... 

The use of a suppressor column is not without problems. Eventually the resin becomes exhausted and needs to be regenerated, which is inconvenient. Also, the slightly ionized carbonic acid produces a small continuous baseline conductance signal, so that the vacancy peak from the sample injection is detected and produces a negative peak that can interfere with other analytes eluting at that time. The use of a second column also results in some zone broadening, of course, which decreases the overall efficiency of the analysis. 

One way to improve carbon emissions and overall efficiency is to ensure that all furnace operations employ efficient heat recovery from the flue gas. Ideally the flue gas should be cooled in order to recover the heat of condensation of the water produced in the combustion process. 

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