| Summary: | 博士 === 國立臺灣科技大學 === 化學工程系 === 95 === The design and control of various reactive distillation systems were systematically studied for two categories of heterogeneous catalytic esterification over acidic ion-exchange resins. A series of one-stage esterification of acetic acid with five different alcohols, from methanol to amyl alcohol, was selected as model systems for the first category, while two-stage esterification of adipic acid with methanol was chosen as an illustrative example for the second category. In the process simulations, the kinetic models were taken from literature and the thermodynamic models have been verified with experimental phase equilibrium data before use. The total annual cost (TAC) was adopted as the objective function for process optimization.
Three types of flowsheets were developed for those five one-stage esterification systems. The process development was mainly based on the phase behavior of the related mixtures such as boiling point ranking, immiscibility, and residue curve map (RCM). For each system, the degree of process nonlinearity was evaluated with the fraction of “sign reversal” of tray temperatures and the index of Allgower’s nonlinearity. The multiple steady-state phenomena were also found in most of the studied processes. Both dual-temperature control and one-temperature-one- composition control were investigated for each type of flowsheet. It was found that simple decentralized control was effective for those highly nonlinear reactive distillation systems.
For accurately analyzing the operation of liquid-liquid separation unit in the processes of two-stage esterification of adipic acid with methanol, liquid-liquid equilibrium (LLE) data of two ternary systems containing water, methanol and esters were measured in the present study. These LLE data were correlated with the NRTL model to determine the optimal binary interaction parameters. Two types of reactive distillation flowsheets were developed for this two-stage esterification system. Similarly, the process nonlinearity was also evaluated. Three kinds of temperature control structures were tested in this work. Satisfactory control performances have been achieved regardless of the control structures, but using different control structures lead to substantial difference in energy demands.
It is concluded that analysis the system characteristics first and then selection of correct control stratagem are keys to success for development of an efficient reactive distillation process, regardless of complexity of the reaction systems. As demonstrated in this study, good operability and controllability have been achieved for the processes which consist of only one reactive distillation column or plantwide complex reactive distillation systems.
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