Recent environmental regulations set the limits of sulfur in gasoline to 30 ppm and in diesel fuel to 15 ppm (2006). Even though in the off-road fuel 500 ppm of sulfur is still an acceptable level, the limits are set to be 15 ppm by 2010. Hydrodesulfurization (HDS) is a method, which is able to remove the majority of sulfur-containing compounds from fossil fuel. In spite of the high efficiency and established technological importance of HDS it is not able to remove completely dibenezothiophenes. Especially 4,6 - dimethyldibezothiophene is considered as resistant to any chemical reactions.
In the research program proposed here we seek to define the features of carbonaceous adsorbents that govern the deep desulfurization process and to develop efficient diesel fuel desulfurization media. The removal process we target is based on reactive adsorption of DBT and 4, 6-DMDBT from very low concentration of 20 ppm sulfur. In the "best case scenario", thiophenic molecules will first be specifically adsorbed on the catalytic metal center/ heteroatom containing groups and then the breaking of the carbon sulfur bond will occur with retention of sulfur on the surface and a return of the hydrocarbon molecule to the fuel stream. In the "worse case scenario", the DBT and 4,6-DMDBT molecules will be specifically adsorbed in the pore system on metal oxides, sulfides, sulfur, nitrogen, phosphorus or oxygen containing centers. Various scenarios of the in-between interactions can exist. We will provide the detailed experimental procedure for the preparation of the most efficient removal media (from the point of view of the capacity, selectivity and regeneration feasibility) along with the mechanism of the process. The performance of adsorbents in desulfurization from liquid phase will be linked to their surface features. This will open new routes for designing more efficient and cost effective adsorbents and catalysts.
Our review of the literature and research experience lead to the following research questions related to achieving our objectives and to the development of new technology: 1) Which temperature of carbonization does lead to the most effective adsorbent/catalyst? 2) Which heteroatoms do enhance the capacity and selectivity of adsorption? 3) Which metals/ surface groups or their combinations are the most effective desulfurization catalysts? 4) Which content of metal does result the highest capacity? 5) What are the products of surface reactions (if any)? 6) What is the mechanism of adsorption? 7) Can we efficiently regenerate the spent adsorbents? 8) Can we design an adsorbent (based on the commercial carbonaceous precursors) with the surface features leading to the effective deep desulfurization of diesel fuel?
The proposed research is directly relevant to developing new materials and improving technologies of desulfurization of diesel fuel and other heavy fuel fractions. Due to new environmental regulations, not only in the US but also worldwide, there is a great interest in petrochemical, chemical and power generating industries in new adsorbents and catalysts for withdrawal of sulfur from thiophenic species. The technology developed besides lowering the cost of future low sulfur level fuel, may also prove to be important for development of fuel cell, cutting edge of technology, where sulfur free hydrogen source is the first priority due to the poisoning of the reforming catalysts by sulfur compounds. The research will also lead to a new class of adsorbents and catalysts, which may find application in other scientific challenges where the separation of molecules is involved. Moreover, the broad spectrum of surface characterization methods applied will have an impact on better understanding the surface chemistry of carbon and carbonaceous adsorbents in general. The proposed research is relevant to environmental problems facing contemporary society. First, it will develop the relatively simple technology in compliance with environmental regulations to be commenced in the near future. By decreasing the level of sulfur in fuel, the emissions of SO2 will be reduced, which will lead to the reduction in acid rain incidents and their detrimental effects on the environments and human health. Moreover, the lifetime of the automobile exhaust expensive catalyst will be prolonged.
One graduate student and one undergraduate student will work on the project. Since CCNY is a minority serving institution there is a high probability that students from underrepresented groups will be involved in the research. This will have a positive effect on the development of environmental awareness in the minority group. Other important educational aspects are the development of new environ./phys. chemistry experiments by the undergraduate student involved in the research (independent research undergraduate project) and the graduate ?undergraduate teem working approach with all steps of research/problem solving including searching literature resources, familiarity with the principles of operation of scientific instruments and the ability to outline research theses and research plans.