Design and Control of Acetic Acid Dehydration Process Containing p-xylene Impurity
Date Issued
2012
Date
2012
Author(s)
Chia, Min-Tse
Abstract
Acetic acid dehydration and recycle is an important process in purified terephthalic acid (PTA) production. The feed contains water (H2O), acetic acid (HAC) and some impurities, such as methyl acetate (MA) and p-xylene (PX). Acetic acetate is commonly used as entrainer in acetic acid dehydration, but it is an additional component which will cause unexpected reactions in the PTA process.
The reactant (PX) in PTA process also can be used as the entrainer. In this work, the heterogeneous azeotropic distillation will be used to separate high purity acetic acid and water and the optimum design with minimal total annual cost (TAC) will be investigated. In the process design, effect of side-draw to the process will be discussed. Using PX as entrainer not only can save the cost of entrainer makeup but also prevent the effect of acetic acetate remaining in the recycled acetic acid in the PTA process. It is found that the side-draw design can avoid entrainer loss from recycled acetic acid, but need higher TAC and cannot provide obvious advantage.
Some feasible control strategies for no side-draw design are then investigated subsequently. The open-loop and closed-loop sensitivity analyses techniques are adopted to develop the single-point as well as the dual-point temperature control strategies, where the manipulated variables are reboiler duty and aqueous reflux ratio. These strategies can reject feed composition disturbance and throughput change effectively.
Subjects
purified p-phthalic acid production
acetic acid dehydration
heterogeneous azeotropic distillation
p-Xylene
optimization
Type
thesis
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