CAREER: Revolutionizing sulfur removal in transportation fuels via adsorption in ion exchanged zeolites

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Mandatory government- and industry-issued standards require the reduction of sulfur in transportation fuels (e.g., gasoline, diesel, and jet fuels) to near-zero levels. Hydrodesulfurization (HDS) is the widely-accepted commercial refinery technology used for the removal of sulfur in fuels. Although HDS is effective for this purpose, it is also energy intensive, particularly as refineries attempt to meet tighter regulatory standards of sulfur. This project will establish a new technological platform and associated fundamental science enabling the development of environment-friendly "filters" for the efficient and cost-effective adsorptive desulfurization (ADS) of liquid hydrocarbon fuels at ambient conditions. Such "filters" will be portable, compact, and regenerable and may eventually be integrated into vehicle engines or gas stations. Successful design of these desulfurization "filters" will transform the fuel processing industry by reducing combustion-based sulfur emissions, the energy requirements, and the cost of fuel desulfurization. Achieving sulfur-free fuels has widespread human health and environmental implications; thus, the results of this research also have the potential to benefit national health and prosperity. The proposed ADS process will be based on porous minerals, called ion-exchanged zeolites. It is expected that the ADS process will be combined with existing HDS processes to specifically target the sulfur-containing molecules that are particularly difficult to degrade. Through this approach, ultra-low sulfur levels in fuels can be reached. This project will focus on developing an integrated experimental and modeling methodology to investigate correlation of the intrinsic properties of the ion-exchanged zeolites and their performance as a sulfur molecule "filter." Research and education are integrated in the project through the development of an innovative class that will train the students to become community-engaged scholars and even policy makers through a service learning pedagogy. The PI's long-term career goal is to create novel materials and processes for clean fuels production. Toward this goal, the overarching research objective for this project is to advance the fundamental science of ion-exchanged zeolites for use in the ADS process. Zeolites are excellent molecular sieves due to their active sites, high surface area, and porous structure. However, to transform zeolites into effective sulfur sorbents, the following research challenges need to be addressed: (1) diffusion - zeolite pores need to be large enough to accommodate the sterically hindered sulfur molecules; (2) capacity and selectivity - zeolite active sites need to have high capacity and adsorb sulfur molecules selectively (leaving the rest of the aromatic molecules in the hydrocarbons intact); and (3) feasibility and lifetime - the process should be spontaneous, and the zeolites regenerative and reusable. To address these challenges, a dynamic-learning methodology will be developed that integrates materials tailoring and characterization, ADS testing using sulfur model compounds in model fuels, and data science. This methodology will be an iterative process between experiments and modeling and will create fundamental knowledge on how the properties of metal and bimetal-exchanged Y zeolites, such as pore size, metals properties, location, oxidation state and interaction, affect the ADS process. The outcome of the study will be fundamental knowledge leading to the prediction and design of optimum zeolites for ADS. The optimum zeolite will then be tested using real fuels, namely gasoline, jet fuel, and diesel.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.