Analysis of Steady-State Multiplicity in Reactive Distillation Columns

We propose a relatively simple method to identify multiplicity in reactive distillation due to the interaction of reaction and distillation. The nonlinear generation term and linear removal term, for both material and energy, are isolated from the conservation equations and evaluated at different values of suitable parameters such as product ratios (distillate to bottoms). The plot thus obtained is used to identify the presence of multiplicity and the cause for the same. The method presented here is inspired by the thermal stability analysis of nonisothermal CSTRs. Using the proposed method, the occurrences of multiple steady states in reactive distillation columns with the hypothetical ternary reaction a + b ⇔ c (with inerts) and quaternary reaction a + b ⇔ c + d with ideal vapor–liquid equilibrium (VLE) are predicted. The predictions of steady-state multiplicity obtained by the proposed method are in agreement with the results of bifurcation analysis using the arc-length continuation method. The method is further extended to the industrially relevant reactive distillation processes for the synthesis of methyl acetate and methyl tert -butyl ether (MTBE). The proposed method, as compared to the bifurcation technique, makes the analysis simpler and provides more insight into the influence of different factors on the multiplicity behavior.