The role of kinetics and hydrocarbon distribution in the multiplicities of a two-bed catalytic distillation column for deep hydrodesulfurization

The Damköhler number (Da) is used to research the physical mechanisms leading to multiplicities and the effect of the hydrocarbon distribution on a light gasoil (LGO) deep hydrodesulfurization (HDS) two-bed catalytic distillation column. In doing so, three hydrocarbon mixtures are studied: a real LGO fraction, a synthetic gas oil mixture (SGO), and hexadecane (n-C16). The parametric planes, Da(RR) and Da(B), were obtained for the three mixtures as a function of the reflux ratio, RR, and the bottom flow rate, B. The total sulfur regions (Cs) with respect to Da and RR, and Da and B, were also obtained. RR and B were chosen as bifurcation parameters, since they are frequently used for column operation.Results show that this system is controlled kinetically because the operating point and the multiplicity region lay on the kinetically controlled region (Da ≪ 1). Results also show that the hydrocarbon distribution plays an important role in the occurrence of multiplicities, as well as exhibiting the importance of choosing a realistic gasoil fraction during process design and lab scale experiments.

Research highlights▶ Multiplicity and total sulfur regions are given as a function of the reflux rate and bottom flow rate. ▶ The hydrodesulfurization via catalytic distillation is controlled kinetically. ▶ Hydrocarbon distribution plays an important role in the occurrence of multiplicities.▶ The importance of choosing a realistic gasoil mixture during design and lab experiments is shown.