No abstract

An extraction and distillation hybrid process using a novel mixed solvent was proposed for enhancing acetic acid recovery during terephthalic acid production. Feasible hybrid extraction− distillation schemes were designed, simulated, and optimized for two mixed solvents, p-xylene + methyl acetate, and p-xylene + ethyl acetate, based on liquid−liquid equilibrium data for a quaternary system containing methyl acetate or ethyl acetate with p-xylene, acetic acid, and water. A hybrid process using the p-xylene + methyl acetate mixed solvent was found to generate the desired purity of acetic acid with a lower energy consumption and higher product yield than conventional extraction processes. Results showed that the proposed hybrid extraction−distillation process improves the process economics remarkably: the hybrid process using the p-xylene + methyl acetate and p-xylene + ethyl acetate mixed solvent reduced a total annual cost by 14% and 6%, respectively, compared with the conventional hybrid process using the ethyl acetate single solvent. With the important advantage of p-xylene and methyl acetate as internally existing components, the proposed mixed solvent is promising for safe and cost-effective recovery of acetic acid, particularly during terephthalic acid production.

The liquid−liquid equilibria (LLE) data for the quaternary system, acetic acid, water, p-xylene, and ethyl acetate, was obtained at 313.15 K under atmospheric pressure. The composition distribution of each component on the aqueous phase and organic phase were investigated. To examine the effects of the solvent, the LLE phase diagrams at different p-xylene to ethyl acetate ratios are presented for this quaternary system. The reliability of the tie-line data of this study was also confirmed using the Othmer−Tobias and Hand equation. The distribution ratio and separation factors for the extraction of acetic acid from the aqueous solutions were obtained. Furthermore, the equilibrium data of this study was analyzed using the quasichemical activity coefficient (UNI-QUAC) and nonrandom two liquid (NRTL) models. The experimental data was correlated successfully with both the activity coefficient models that were extended with each binary interaction parameter. To determine the accuracy of each activity model, the root-mean-square deviations (RMSDs) and average absolute deviation (AAD) resulting from these models were also calculated. The RMSDs and AAD of the NRTL models were 0.0196 and 0.0213, respectively, whereas those of the UNIQUAC model were 0.0166 and 0.0114, respectively. These values showed that the UNIQUAC model is superior to the NRTL model.

A novel active vapor distributor (AVD) was proposed to address the need for vapor split control during dividing wall column (DWC) design and operation. A DWC's energy efficiency can be significantly reduced by a small deviation in the vapor split ratio; therefore, the vapor split ratio needs to be regulated during operation. In the proposed AVD, vapor splitting was implemented by a modified chimney tray with a specially designed cap. The liquid level of the chimney tray on each end side of the dividing wall section could be adjusted to control the vapor flow split. As the proposed AVD adjusts the friction of the vapor flow path efficiently without any mechanical moving parts, it can realize a more reliable operation of a DWC. The performance of the proposed AVD was evaluated, and the results demonstrated its easy implementation and superior ability to regulate vapor flow split during DWC operation.

No abstract