Ultra-deep desulfurization of transportation fuels via charge-transfer complexes under ambient conditions
Résumé
Very stringent regulations on the max. sulfur content of gas oil have led to intense research into all aspects of desulfurization. Deep desulfurization of diesel fuels is particularly challenging due to the difficulty of removing refractory sulfur compds., particularly 4,6-dialkyldibenzothiophenes, using conventional hydrodesulfurization processes (HDS). A novel approach to the potential desulfurization of fuels such as diesel is proposed. It relies on the ability of 4,6-dialkyldibenzothiophene to form charge-transfer complexes (CTC) with pi-acceptor mols. We present the synthesis of a new Π-acceptor mol., 4,5-dicyano-2,7-dinitrofluorenone, soln. redox behavior and the crystal structure of the charge-transfer complex with the refractory 4,6-dimethyldibenzothiophene. This pi-acceptor compd. was then immobilized on a hydrophobic support (poly(styrene-co-divinylbenzene)). The selectivity of the CTC process was confirmed by the anal. of the sulfur compds. trapped from straight run Arabian Light (SR) contg. 13600 ppm S. The functionalized polymer can be used in multiple cycles for the removal of refractory S-contg. compds. from hydrotreated SR. It can also be regenerated with toluene. The high selectivity of this material permits diesel fuel to be desulfurized to a level that meets future regulatory requirements, i.e. less than 10 ppm S, at ambient temp. and without hydrogen consumption.