The U.S. Navy's Office of Naval Research (ONR) is sponsoring advanced research in a variety of component areas, with the goal of obtaining a three to four time improvement in overall system power density. The technology development programs ongoing as part of the ONR advanced fuel cell program are addressing numerous areas of process improvements. One of the most critical is the ability to remove sulfur from F-76 and JP-5 Navy logistics fuel, in liquid phase at ambient temperature and pressure, with high regeneration capability over high numbers of cycles. Such removal of refractory sulfur compounds is a challenge due to the nature of the molecules themselves, as well as their high concentrations, up to 5000 ppm of sulfur. The ability to remove sulfur from fuel at such conditions is important, as it provides benefits in process simplification and system safety. Liquid-phase desulfurization allows systems to become far more compact, due to the removal of pressure vessels, large valve and actuator assemblies and high inventory reactors, which contain large amounts of vaporized fuel and other combustibles.

The goal of the sorbent development program is to create new and improved desulfurization sorbents which have ten or more times the capacity of current sorbents. The previous state-of-the-art sorbents at the start of the program exhibited capacities of approximately 0.5 mg S/g sorbent, when utilized at ambient conditions. As various materials may be especially well suited to specific types of sulfur compounds, the U.S. Navy is performing development work, while also partnering with Auburn University, the Pennsylvania State University and the University of Michigan, to explore a wide variety of novel sorbent types.

This paper describes the most current updates and results on efforts ongoing as part of the ONR advanced sorbent work. The paper describes new breakthroughs in capacity enhancement, as well as improvements in regenerative stability and capacity maintenance. Discussion is made regarding analysis of the affinity of various sorbent formulations for specific components found in typical logistics fuels, and also provided regarding the formulation of layered sorbent beds to optimize performance in high duty cycle applications. Additionally, this paper describes efforts being performed to analyze the effects of fractionated fuels on desulfurization sorbent performance, with the intent to determine means of dealing with inferior grades of fuel, or minimizing system size and complexity, in order to enable further variations of fuel processing equipment, suitable for shipboard and vehicle APU use.