Selective Sulfur Removal from Liquid Fuels Using Nanostructured Adsorbents

Abstract

In recent years, there has been an increasing pressure to develop strategies to reduce the level of sulfur in transportation fuels due to stringent environmental regulations. Currently, hydrodesulfurization (HDS) is the most mature (pre-FCC) technology to remove sulfur from gasoline and diesel. However, conventional HDS can hardly produce ultra-low sulfur fuels while maintaining important fuel requirements (i.e., oxygen content, overall aromatic content, olefin content for gasoline, and cetane number for diesel). As a consequence, improvement of existing HDS processes and development of new desulfurization technologies is needed. In this regard, selective adsorption removal of sulfur (SARS) is a promising emerging approach for ultra-deep desulfurization of refinery streams by means of solid adsorbents. Contrary to HDS, SARS is usually carried out at low temperatures and pressures with minimal hydrogen consumption, preventing olefin hydrogenation and thus maintaining the properties of the fuels. This chapter presents a general overview of SARS. Emphasis is given to the use of nanostructured materials as sulfur adsorbents. Section 5.1 introduces the chapter presenting a general description of HDS, SARS and other emerging desulfurization technologies. Section 5.2 describes the two main groups of SARS (adsorption desulfurization and reactive adsorption desulfurization). Subsequently, the three main mechanisms for sulfur adsorption (π-complexation, direct sulfur–adsorption site interactions, and bulk incorporation in reactive adsorption desulfurization) are reviewed. Section 5.3 gives an overview of relevant literature concerning the use of promising groups of nanostructured adsorbents for SARS including zeolites, MOFs, mesoporous silicas, and carbon-nanostructured adsorbents. Finally, Sect. 5.4 gives some concluding remarks.