Desulfurization of transportation fuels by π-complexation sorbents: Cu(I)-, Ni(II)-, and Zn(II)-zeolites

New π-complexation-based sorbents were studied for desulfurization of diesel, gasoline, and jet fuels. The sorbents were obtained by ion exchanging faujasite type zeolites with Cu⁺, Ni²⁺ or Zn²⁺ cations using different techniques, including liquid phase ion exchange (LPIE). Hydrolysis of the cations in aqueous solutions should be avoided in order to increase the ion exchange level when aqueous solutions are used. Cation hydrolysis limitation could be avoided when vapor phase (VPIE) and solid-state (SSIE) ion exchange techniques are used instead. The deep-desulfurization (sulfur levels of <1 ppmw) tests were performed using fixed-bed adsorption techniques. The treated and untreated fuels were fully characterized using the latest generation of FPD detectors in our laboratory, which are capable of eliminating quenching effects. After proper optimization and calibration of the detector non-linear response, as done in all our previous work, it was possible to detect sulfur concentration as low as 20 ppbw S. The data was verified using total sulfur analyzers. The π-complexation sorbents desulfurization performance decreases as follows: Cu(I)-Y(VPIE) > Ni(II)-Y(SSIE) > Ni(II)-X(LPIE) > Zn(II)-X(LPIE) > Zn(II)-Y(LPIE). Molecular orbital calculations indicate the sorbents performance decreases as follows: Cu ⁺ > Ni²⁺ > Zn²⁺. This agrees well with the experimental results. The best sorbent, Cu(I)-Y(VPIE), has breakthrough adsorption capacities of 0.395 and 0.278 mmol S/g of sorbent for commercial jet fuel (364.1 ppmw S) and diesel (297.2 ppmw S), respectively.