Design and Control of Reactive Distillation for Parallel Reactions System--Methanol and Mixed Acids
Date Issued
2007
Date
2007
Author(s)
Wu, Yen-Yi
DOI
zh-TW
Abstract
This work presents a complete design for converting mixed acetic (HAc) and propionic (HPr) acids, into methyl acetate (MeAc) and methyl propionate (MePr) esters. The two esters are produced via a reactive distillation process using Amberlyst 36 as heterogeneous catalyst. Methanol (100 mol% MeOH) and mixed Acids (88 mol% HAc and 12 mol% HPr) are used as feeds, which are waste acids from a plant of China Petrochemical Development Corporation (CPDC). In the VLE calculations, UNIQUAC model is used to predict the compositions and temperatures for the five azeotropes in the system. The vapor association of acetic acid and propionic acid due to dimerization and trimerization has been considered as well. By the boiling point ranking of the system, a complete flowrsheet is proposed. It includes one reactive distillation column followed by a conventional distillation column. In the reactive distillation column, the by-product water (98 mole%) can be separated from the bottoms. To reach industrial specification, the conventional distillation column is used to purify the MeAc to 98 wt% and the MePr to 99 mol%. It is difficult to procure higher purity of MeAc by using this reactive distillation process, because of the existence of MeAc-H2O azeotrope on the MePr-MeAc-H2O RCM path. A systematic design procedure to optimize the flowsheet based on the total annual cost (TAC) is conducted. Finally, the control structure design for plant-wide control is proposed. Two possible quality control structures are considered---three-point temperature control, and four-point temperature control. Dynamic simulation results show that reasonable control can be achieved using these two control schemes. Moreover, steady-state composition offset can be mitigated using feedforward and cascade compensation for temperature set points.
Subjects
混合酸
乙酸
丙酸
反應蒸餾
mixed acids
acetic acid
propionic acid
reactive distillation
Type
thesis
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