Transportation fuel from coal with low CO₂ emissions

This chapter explores a strategy for mitigating climate change for coal-derived synthetic fuels both by CCS and by choosing an energy carrier that facilitates a shift to more-efficient energy end-use technology. The focus is on dimethyl ether (DME). Its high cetane number makes DME a suitable candidate fuel for compression ignition engine vehicles, which are more energy efficient than spark-ignition engine vehicles. Compression ignition engine vehicles are not more widely used in part because of difficulties in realizing simultaneously low levels of emissions of both NO_x and particulate matter (PM), which are being sought in tightening air pollutant emission regulations throughout the world, driven by public health concerns. The tradeoffs that make simultaneous NO_x and PM control difficult for diesel fuel do not exist for DME, the combustion of which generates essentially no PM because of the absence of C-C bonds and of sulfur. Low NO_x emissions can be realized with much less complicated tailpipe emission control technologies. These pollution control advantages can facilitate a transition to fuel-efficient vehicles such as compression ignition engine/hybrid electric vehicles, although the pollution control advantages offered by DME are offset in part by the refueling infrastructure challenges that arise because at atmospheric pressure. DME is a gas that must be stored in mildly pressurized canisters. It also illustrates the potential DME offers for reducing emissions by facilitating a shift to more energy-efficient vehicles.