Fuel cells operate on a variety of fuels depending upon the specific fuel cell technology. Polymer electrode membrane (PEM, i.e., plastic) fuel cells use hydrogen as a fuel. Since hydrogen is relatively expensive to obtain and store, and dangerous to handle, much research has gone into development of other fuel cell technologies that that can use natural gas, synthesized gas from coal and landfill gas. Solid oxide and molten carbonate fuel cells have advantage in that they can use the carbon in hydrocarbon fuels to make electricity. Carbon is a poison to PEM fuel cells. All fuel cell are poisoned by sulfur. Although there has been some recent success in reducing the sensitivity of the various fuel cell types to their poisons, none are yet able to use the relatively less expensive and easier to use natural gas, syngas or landfill gas without treatment to remove sulfur.
The following Table lists typical chemical analysis of fuels and the level of contaminants assumed for design of a desulfurization system.
Dry Analysis, % | Molecular Weight | Natural Gas | Natural Gas | Natural Gas | Coal Derived |
Component | g / mol | USA | European | Japanese | Syngas |
Methane | 16.043 | 94.41 | 87 | 88 | 3.2 |
Ethane | 30.07 | 3.08 | 1.5 | 6 | 0 |
Propane | 44.097 | 0.56 | 1 | 4 | 0 |
Butane | 58.123 | 1.76 | 0.1 | 2 | 0 |
iso-Butane | 58.123 | 0 | 0 | 0 | 0 |
Pentane | 72.15 | 0 | 0.1 | 0 | 0 |
iso-Pentane | 72.15 | 0 | 0 | 0 | 0 |
Hexane | 86.177 | 0 | 0 | 0 | 0 |
Heptane | 100.204 | 0 | 0 | 0 | 0 |
Octane | 114.231 | 0 | 0 | 0 | 0 |
Nitrogen | 28.0134 | 0.19 | 10 | 0 | 1.8 |
Oxygen | 31.9988 | 0 | 0 | 0 | 0 |
Helium | 4.0026 | 0 | 0 | 0 | 0 |
Carbon Dioxide | 44.01 | 0 | 0.3 | 0 | 1.3 |
Carbon Monoxide | 28.1 | 0 | 0 | 0 | 2.2 |
Hydrogen | 2.016 | 0 | 0 | 0 | 91.4 |
Water | 18.016 | 0 | 0 | 0 | 0.2 |
Contaminant | Formula | ppmv | ppmv | ppmv | ppmv |
Hydrogen Sulfide | H2S | 0 | 0 | 0 | 22 |
Carbonyl Sulfide | COS | 0 | 2 | 0 | 12 |
Tetrahydrothiophene (THT) | C4H8S | 2 | 2 | 2 | 0 |
Dimethyl Sulfide (DMS) | (CH3)2S | 2 | 0 | 2 | 0 |
Mercaptans* | R-SH | 2 | 2 | 2 | 0 |
Carbon Disulfide | CS2 | 0 | 0 | 0 | 0 |
Phosphine | PH3 | 0 | 0 | 0 | 0 |
Hydrogen Selenide | H2Se | 0 | 0 | 0 | 0 |
Arsine | AsH3 | 0 | 0 | 0 | 0 |
Methyl Chloride | CH3Cl | 0 | 0 | 0 | 0 |
* Includes methyl mercaptan (MM), ethyl mercaptan (EM), n-propyl mercaptan (nPM), iso-propyl mercaptan (iPM) and tertiary butyl mercaptan (TBM)
