Research from SRI International has identified a promising new way to produce liquid transportation fuels from coal without consuming water or generating carbon dioxide. Based on data from bench-scale tests, SRI engineers estimate that the capital cost for a full-scale plant using SRI’s process would be less than half that of a conventional coal-to-liquids (CTL) plant that uses a process called Fischer-Tropsch synthesis (FTS). FTS produces only a small fraction of the hydrocarbons needed for fuel and requires extensive recycling.
SRI’s new process uses natural gas to provide the hydrogen needed to convert coal to syngas (a mixture of carbon monoxide and hydrogen). Syngas is first converted into methanol, which can then be efficiently processed to make transportation fuels.
Using natural gas eliminates the need to add water as a source of hydrogen, reduces the need to add energy to drive the gasification reaction, and results in the use of a smaller gasifier. In conventional CTL approaches, energy is supplied by burning a portion of the coal feed, which then produces carbon dioxide. SRI’s approach makes it economical to use carbon neutral electricity, such as nuclear, hydro, or solar as a source of additional energy.
“The implications of this research are expansive, including enhancing US energy security through the use of domestic carbon sources,” said Robert Wilson, Ph.D., director, Chemical Science and Technology Laboratory, SRI International. “The process can also dramatically reduce the environmental footprint associated with alternative transportation fuels.”
If nuclear power, hydro or solar power is used then the new fuel would be cleaner than diesel
The SRI CTL plant design offers a lower CO2-emitting fuel then conventional diesel; a lifecycle analysis by SRI put conventional diesel at 389 gCO2/mile, conventional F-T coal-to-liquids diesel at 830 gCO2/mile; and the SRI synthetic fuel at 326 gCO2/mile (when using carbon-neutral electricity. If biogas is substituted for conventional natural gas, total GHG emissions can further significantly reduced (190 gCO2/mile).
DARPA solicitation. The DARPA solicitation set goals for a coal-to-liquids process for JP-8 of:
Process scalable to 100,000 bbl/day
Production cost of JP8 less than $3.00/gallon
No CO2 emissions during process
Water consumption less than 235 kg/barrel
Capital cost less than $15,000/daily barrel
(The availability of CO2-free electricity was assumed.)