Improving controllability of reactive double dividing-wall distillation columns through an overdesign strategy

Abstract

In our previous work, reactive double dividing-wall distillation columns (R-DDWDCs) have been demonstrated to have significant potential for energy savings in the separation of reacting mixtures with the most unfavorable ranking of relative volatilities (A + B ⇌ C + D, with α_A > α_C > α_D > α_B). However, if its design process focuses solely on economic considerations, the resulting design is likely to suffer from poor controllability. This is primarily because the economically optimal design tends to use a relatively low reaction conversion rate to enhance contact between reactants. As a result, this leads to the excessive accumulation of unconverted reactants in the top and bottom product streams, thereby narrowing the control range for these product streams and decreasing control flexibility. To address this issue, an overdesign strategy was proposed. The specific measure of this strategy is to adjust the liquid or vapor split ratio near the reactive section on the basis of the economically optimal design to moderately increase the reaction conversion rate, thereby reducing the accumulation of unconverted reactants in the top and bottom product streams. Based on the designs of two typical R-DDWDC configurations for an ideal quaternary endothermic reversible reaction and the exothermic esterification system of methanol + lactic acid ⇌ water + methyl lactate, the feasibility and effectiveness of the proposed overdesign strategy were evaluated. The results showed that the overdesigned R-DDWDC exhibits a significant improvement in controllability, with an acceptable decrease in steady-state performance. This achievement offers insights into integrating steady-state and dynamic design, facilitating the practical application of R-DDWDCs in industry.