Comparison of Alternative Control Structures for an Ideal Two-Product Reactive Distillation Column

Abstract

Although steady-state design and open-loop dynamics of reactive distillation columns have been explored in many papers, very few papers have dealt with closed-loop control. Most of these control papers consider reactive distillation columns in which there is only one product, and an excess of one of the reactants is sometimes assumed. This paper explores the closed-loop control of a reactive distillation column in which two products are produced in a single column and stoichiometric amounts of fresh feeds are desired. The reversible reaction is A + B h C + B. The relative volatilities are favorable for reactive distillation; i.e., the reactants are intermediate boilers between the light product C and the heavy product D. Simple ideal physical properties, kinetics, and vapor-liquid equilibrium are assumed so that the basic control issues of reactive distillation can be explored without being clouded by complexities of a specific chemical system. Six alternative control structures are evaluated via rigorous dynamic simulation. All of the schemes use a composition analyzer in the reactive zone of the column to detect the inventory of one of the reactants so that fresh feed can be manipulated to satisfy the reaction stoichiometry. Therefore, the use of excess reactant is not required. The interaction between design and control is illustrated by the impact of holdup in the reactive zone: increasing holdup (catalyst) improves the dynamic controllability of the process. Single-end temperature control can keep both products at or above specified purity values, even for large disturbances, if reactive-zone holdup is sufficiently large.

Systematic integrated process design and control of binary element reactive distillation processes

“…(21). When x 1 =1 (pure isobutene), and x 2 =x 3 =0, then, Daza et al 24 have extended this method to also include reactive binary distillation columns (systems which can be represented by two elements, A and B).…”

Plantwide control for TAME production using reactive distillation

“…The literature with respect to the control of reactive distillation is not as abundant as in other areas such as analysis of the steady state. In our recent publication (Al-Arfaj and Luyben, 2000) we reviewed some of the literature in this area. We studied the control of different classes of reactive distillation in previously reported studies:…”

Reactive Distillation: Control Structure and Process Design for Robustness

“…The rectifying and stripping trays recycle the reactants escaping the reactive zone and prevent their exit in the product streams. This hypothetical ideal RD column was originally proposed by Luyben (2000) as a test-bed for studying various control structures (Al-Arfaj & Luyben, 2000). In terms of its design configuration, the methyl acetate column is similar to the ideal RD column with light methanol being fed immediately below and heavy acetic acid being fed immediately above the reactive section.…”