Thermal in Situ and System-Integrated Regeneration Strategy for Adsorptive On-Board Desulfurization Units

This work deals with the introduction and investigation of a novel system-integrated thermal regeneration strategy based on hot off-gas for on-board desulfurization units. A highly thermally stable Ag–Al₂O₃ material was used as the adsorbent because it has the advantage of being active in the oxidized form so that it requires no activation after regeneration in an oxidative atmosphere. Dibenzothiophene (DBT) was used as the representative polycyclic aromatic sulfur heterocycle (PASH) in Jet A-1 fuel with a total sulfur concentration of 900 ppmw. This PASH has a stronger adsorption energy and is significantly more stable than benzothiophene or thiophene. This is why oxidative thermal regeneration strategies had formerly been failing to fully regenerate any type of adsorbent after the adsorption of DBT. This work reports excellent regeneration results upon the use of the hot off-gas from a solid-oxide-fuel-cell- (SOFC-) driven auxiliary power unit (APU) as the regeneration medium. The highly thermally stable Ag–Al₂O₃ showed a high breakthrough adsorption capacity of 2.2 mg-S/g-adsorbent in the first desulfurization cycle that was fully recovered by regeneration with hot APU off-gas. This is the first time that 100% regeneration has been reported for thermal regeneration after the adsorption of DBT. Additional investigations were performed to gain deeper insight into the overall desorption mechanism. The H₂O content has an especially significant influence on the overall desorption mechanism of DBT. With a H₂O content of 12.4 mol %, full regeneration was also obtained by reducing the final regeneration temperature from 525 to 450 °C. The results reported herein show that this novel regeneration strategy requires no additional regeneration medium, no additional tanks, and no additional bulky equipment and is thus fully integrated into the concept of an SOFC-operated APU.