The military is exploring the field use of hydrogen fuel cells to power electronic gadgets and facilitate communications, thereby avoiding use of generators that are noisy and create heat signatures. One barrier to that approach, however, is the source of the hydrogen.
The military has no current plants to add hydrogen to the strategic and tactical operations logistics burden, and therefore the challenge is the on-board reforming of the existing prevalent JP-8 military fuel to produce hydrogen. JP-8, however, can be high in sulfur—specifications allow it to contain up to 3,000 ppm. Neither catalysts used in reforming nor fuel cells are tolerant of sulfur.
Researchers at Pacific Northwest National Laboratory (PNNL) are developing a compact microchannel distillation unit to create a light fraction of JP-8. The JP-8 light fraction is then reacted in a catalytic process called hydrodesulfurization (HDS) to remove the sulfur from the fuel—similar to the approach refineries take to produce low-sulfur fuel.
Conventional technology utilizes hydrogen as the co-reactant with JP-8 to power the process, but, again, hydrogen is not available in the field. Instead, the PNNL process uses syngas generated by the steam reforming of the de-sulfurized JP-8 to drive the process.
Most of the syngas is further purified for use by the fuel cell, but a fraction of it is diverted to the hydrodesulfurization unit. The use of syngas creates some challenges, but it appears that they have been mostly overcome in the PNNL process, and syngas performs almost as well as pure hydrogen.
The HDS process is operated in the gas phase at low or moderate pressure and high space velocity, in contrast to the conventional operation in a three-phase trickle bed reactor under high pressure.
The research team was able to reduce the JP-8 sulfur content to 5ppm or less when starting with 320 ppm sulfur fuel, using several different catalysts. (Samples of JP-8 in use in Iraq in 2004 found sulfur concentrations ranging from 2,000 ppm to 200 ppm, with 67% of the sample ranging from 1,500 ppm to 500 ppm.)
David L King and Xiwen Huang form PNNL presented the work at the 231st American Chemical Society National Meeting in Atlanta.