Portrait | Kyriacos Zygouakis

Kyriacos Zygourakis

Chemical and Biomolecular Engineering

Adsorptive Desulfurization of Liquid Fuels

Overcoming a Competition

for Active Sites

Organosulfur compounds form a direct S-Metal (S-Me) bond

Zeolite sulfur-removal capacity from JP-8 at 180 oC increased by 14X over that at 30 oC

Desulfurization has two stages: chemisorption first followed by surface catalytic reactions. 

    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 oC. 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 oC and strong chemisorption (S-Cu bonding) at 130 or 180 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 2,230 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-S/g-adsorbent at 30 °C to 36 mg-S/g-adsorbent at 180 °C. 

    The feasibility of high-temperature adsorptive desulfurization was assessed using a continuous flow adsorber column packed with zeolite pellets.  JP-8 fuel with 2,230 ppm of sulfur by weight was treated using CuNa-Y zeolite pellets at 180 °C and 200 psig at three different flow rates: 0.2, 1, and  5 mL/min.  Our flow-through adsorber operating at these conditions reduced the sulfur content of JP-8 to ultra-low values (1-10 ppmw) over a broad range of liquid hourly space velocities with the expected strong dependence on flow rate.  We also showed that desulfurization has two stages.  Sulfur is initially removed via chemisorption on the active sites of the zeolite.  As the adsorbent becomes saturated, however, surface chemical reactions start e formation of polymerization products and hydrogen sulfide, and the deposition of carbon residue on the zeolite. However, the spent adsorbent can be regenerated and treatment with air at 550 or 600 °C restored its adsorption capacity to about 90% of its initial value.

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