Adsorptive Desulfurization of Liquid Fuels at Elevated Temperatures Using Metal Exchanged Zeolite Y

It has long been known that the ability of adsorptive methods to remove sulfur from transportation fuels at room temperature is limited by the competition of aromatic hydrocarbons and organosulfur compounds for the active sites of the adsorbent. In an effort to overcome these limitations, we studied adsorptive desulfurization at temperatures substantially higher than those considered by previous investigators. Na-Y and Cu-exchanged Na-Y (CuNa-Y) zeolites were used to remove sulfur from model fuels and a JP-8 fuel at temperatures up to 180 degrees C. Batch desulfurization and temperature-programmed desorption experiments with model fuels containing 3-methyl-benzothiophene (3-MBT) and dodecane showed that 3-MBT removal was strongly dependent on treatment temperature and involved weak physisorption bonds with Na, weak interactions with Cu sites at 30 or 80 degrees C, and strong chemisorption (S-Cu bonding) at 130 or 180 degrees C. Overcoming the competition that favors the adsorption of aromatics at low temperatures, the formation of strong S-Cu bonds at high temperatures shifted the balance and allowed significant 3-MBT removal even at high toluene concentrations. Desulfurization tests with a JP-8 fuel containing 2230 parts per million weight (ppmw) of total sulfur revealed that elevated temperatures dramatically improved the efficacy of the CuNa-Y zeolite, increasing its sulfur-removal capacity from 2.6 mg of S per gram of adsorbent at 30 degrees C to 36 mg of S per gram of adsorbent at 180 degrees C. Sequential desulfurization experiments showed that the total JP-8 sulfur content can be lowered by 95% after four treatments and that CuNa-Y removed the least refractory organosulfur compounds first. Our results suggest that ultradeep desulfurization of JP-8 fuel is achievable using zeolitic adsorbents at elevated temperatures.