On the potential of absorption and reactive adsorption for desulfurization of ultra low-sulfur commercial diesel in the liquid phase in the presence of fuel additive and bio-diesel

Abstract

Sorption of sulfur components in the liquid phase was used to desulfurize ultra low sulfur diesel (ULSD) to below 1ppmw S. Several concepts of sorption were considered by using both physisorption and chemisorption materials and conditions. Adsorption assisted by reaction with Ni sorbent was found to be most successful. Using a pre-commercial diesel representing a mature diesel on all aspects except for the absence of fuel stabilizers and bio-diesel, a sulfur breakthrough capacity of 2mgS/g could be achieved using a Ni-sorbent at an acceptable LHSV of 0.7h−1 on average. However, successive experiments indicated that the desulfurization capacity depended strongly on the presence of fuel-additive and bio-diesel in commercial ULSD. The presence of the cetane improver 2-ethylhexylnitrate (2­EHN) was shown to decrease the sulfur capacity by roughly 50%. The presence of bio-diesel (fatty acid methyl ester, abbreviated to FAME) was shown to completely disable the desulfurization process. This was confirmed by comparing BP Ultimate diesel with FAME (obtained in 2008) and without FAME (obtained in 2006). From this evaluation it turned out that the targeted breakthrough capacity of 1mgS/g sorbent was within reach for commercial ULSD until late 2006 when adding bio-diesel to ULSD became common practice in Europe. Several attempts to remove the additives prior to desulfurization by using copper loaded zeolites, active carbon and silica gel proved unsuccessful to bring the sulfur adsorption capacity for current diesel to the level observed for 2­EHN and FAME-free diesel. It is concluded that sorption in the liquid phase does not yet represent a viable desulfurization technology for ultra-low sulfur diesel.