A Comparative Study on Adsorption Desulfurization of Liquid Transportation Fuels Over Different Sorbents for Fuel Cell Applications

Open Access
Author:
Reed, Nicole J.
Graduate Program:
Energy and Geo-Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 03, 2008
Committee Members:
  • Chunshan Song, Thesis Advisor
  • Yaw D Yeboah, Thesis Advisor
  • Yongsheng Chen, Thesis Advisor
Keywords:
  • fuels
  • adsorption
  • desulfurization
Abstract:
This study examines the performance of different materials for adsorption desulfurization of liquid transportation fuels for fuel cell applications. Fixed-bed, continuous flow experiments were performed on eight different materials treating six different fuel mixtures representing gasoline, diesel, and jet fuel. Adsorbents are compared according to the 1 ppmw sulfur breakthrough capacity and capacity at saturation. Results indicate that for the same fuel, different adsorbents perform differently, and for the same adsorbent, different fuels interact differently. Comparisons are made on the basis of adsorbent weight, volume, and surface area. Nickel-based adsorbents have the highest overall sulfur capacity. Supported nickel (A-5) is significantly better than NiAl (A-2) for all fuels except model jet fuel, even when comparing on a surface area basis. The breakthrough capacity per surface area for nickel-based adsorbent materials is about ten times greater than for metal oxides, which are about twice as active as activated carbon. The activated carbon adsorptive capacity is greater on a weight basis than on a volume or surface area basis due to the high surface are of this material. Although typical sulfur compounds are the same, the breakthrough capacity is lower for real fuels than for model fuels, possibly due to fuel additives and additional compounds in real fuels such as olefins and aromatic compounds present in higher concentrations than sulfur. Among the real fuels used in this study, diesel is the most difficult fuel to treat, probably due to the presence of sterically hindered refractory sulfur compounds, which are not suitable for adsorbents that act through a direct sulfur-metal interaction such as the nickel-based adsorbents. No significant difference in performance between the metal oxide adsorbents A-8 and A-9 is observed, indicating that these adsorbents function through similar mechanisms. The impact of temperature and liquid hourly space velocity (LHSV) on the desulfurization performance of nickel-based adsorbents is also reported. The sulfur capacity of nickel-based adsorbents is higher at 200 °C than room temperature, indicating that adsorption proceeds via a surface reaction for these adsorbents. The breakthrough and saturation capacity increases at lower space velocities of 1.2 h-1 LHSV versus 4.8 h-1 LHSV. The results of this study help to assess the potential for using different adsorbents with different liquid fuels for portable fuel cell applications.