(46f) Multiple Steady States in Catalytic Distillation for Deep Hydrodesulfurization of Diesel

Catalytic distillation (CD) is a technology that has the potential to reduce the capital and operational costs of the oil fraction deep hydrodesulfurization (DHDS) process. However, integrating the reaction and separation in-situ within a single unit leads to complex nonlinear interactions. As a result, multiple steady states (MSS) and complex dynamics may arise. Thus, MSS must be taken into consideration during design, operation, and control. This work deals with the steady state multiplicities for the DHDS via catalytic distillation of a real light gas oil (LGO) fraction. First a CD cost optimal design is obtained, then bifurcation plots for both the DBT and 4,6-DMDBT conversions are presented against the reboiler duty, boil-up ratio, bottom flow rate, reflux ratio, and catalyst loading. The classical S-shape is obtained for the reboiler duty, boil-up ratio, reflux ratio, and catalyst loading for the DBT conversion but not for the 4,6-DMDBT conversion. When the bottom flow rate is the continuation parameter, isola branches arise for both the DBT and 4,6-DMDBT conversions. Input-output multiplicities exist for both DBT and 4,6-DMDBT when the bottom flow rate is the continuation parameter. A process with input-output multiplicities may have a zero gain which makes it uncontrollable, while isolas may lead to a region were the zero dynamics is unstable. To facilitate operation and control, the operation point must be in a region characterized by high total sulfur conversion and no multiplicity.