Conceptual design of a reactive distillation process for ultra-low sulfur diesel production

Based on a thermodynamic analysis in terms of reaction-separation feasibility, a conceptual design of a reactive distillation column for ultra-low sulfur diesel production has been developed. The thermodynamic analysis considers the computation of reactive and non-reactive residue curve maps for a mixture that models the sulfured diesel fuel. The visualization of the reactive residue curves is posed in terms of elements. From the reactive residue curve maps, it is found that there is a high temperature region where the vaporization of hydrogen sulfide favors the elimination of the heavier organo-sulfur compounds. Considering the differences in volatility and reactivity of the organo-sulfur compounds and the phase behavior through the residue curve maps, a conceptual reactive distillation column design was developed. The reactive distillation column considers two reactive zones: In reactive zone I, located above the hydrocarbon feed stream, thiophene and benzothiophene are preferentially eliminated. In reactive zone II, located below the feed stream, dibenzothiophene and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT) are mostly consumed. To validate the conceptual design, rigorous steady state simulations were performed. The design goal was stated to produce 4000 bbl/day of ultra-low sulfur diesel with a 99% conversion of 4,6-DMDBT. It is shown that reactive distillation may be considered a viable technological alternative for deep HDS of diesel.