Article pubs.acs.org/EF
Cite This: Energy Fuels XXXX, XXX, XXX-XXX
Thermal in Situ and System-Integrated Regeneration Strategy for Adsorptive On-Board Desulfurization Units Raphael Neubauer,*,† Norbert Kienzl,‡ Brigitte Bitschnau,§ Hartmuth Schroettner,∥ and Christoph Hochenauer† †
Institute of Thermal Engineering, Graz University of Technology, Inffeldgasse 25/B, 8010 Graz, Austria Bioenergy2020+ GmbH, Inffeldgasse 21/B, 8010 Graz, Austria § Institute of Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse 9/I, 8010 Graz, Austria ∥ Institute for Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria ‡
S Supporting Information *
ABSTRACT: 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.
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INTRODUCTION The desulfurization of fuels is necessary for operating sulfursensitive technologies with hydrocarbon base fuels and for fulfilling environmental regulations and protecting the environment. The sulfur levels of liquid fuels are in the range of 10− 5000 ppm and depend on the type of fuel and the correlated legal requirements.1 Hydrodesulfurization (HDS) is used for fuel desulfurization to achieve country-specific legal requirements. HDS is the most prevalent and industrially relevant desulfurization process, and it operates at high temperature (300−400 °C) and pressure (3−6 MPa) in the presence of H2.2,3 Fuel cells are one of the most effective tools for converting chemical to electrical energy. This technology is not only suitable for stationary approaches4 but is also a promising source of on-board electricity supplies for all kinds of vehicles, ships, and aircraft.5 The advantages of fuel cells are, in particular, higher efficiency, reduced emissions, and lower noise generation in comparison to conventional combustion engines.6,7 Fuel cell technology becomes especially attractive when on-board fuel is used to produce hydrogen-rich syngas by reforming that is subsequently fed to the fuel cell. However, the sulfur threshold limits for the reformer and the fuel cell are
