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Design of Divided Wall Reactive Distillation for Hydrolysis of Methyl Acetate

Hao-Yeh Lee, Hsiao-Ping Huang, and Chih-Chun Hsu. Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan

Because the price of the crude oil is arising constantly, the exploitation of energy saving becomes one of the recent focuses in research. Utilizing integrated multi-functional unit to replace some single function units is one effective approach toward this goal. Reactive distillation column (RD) and divided wall column (DWC) are examples of such integration. A further integration of RD and DWC is thus motivated and is called reactive divided wall column (RDWC). The methyl acetate hydrolysis process with RDWC design was first proposed by Sander (2007). However, their work was aimed to illustrate that the concept of RDWC could be physically feasible for industry. From their research, the major products (i.e. methanol and acetic acid) are not as pure as the industrial grade. To overcome this deficiency, the design of RDWC aimed to high quality products and the possible energy savings achievable are studied.

In this paper, a traditional RD configuration which contains one RD column and one sidedraw distillation column for methyl acetate hydrolysis is studied. In this configuration, RD top condenser contains 10 times catalyst than reactive tray and has total reflux to improve the methyl acetate conversion. Except the methyl acetate, the acetic acid, methanol, and excess reactant water are drawn from the RD bottom and fed into the second column. In the second column, top distillate with high pure methanol and bottom product with high purity acetic acid are obtained. The sidedraw of second column contains rich water which is fed as a recycle stream back to the RD column. It is found that although the above-mentioned configuration can achieve high product specifications, it needs much more reboiler duty and total annual cost. To decrease the energy consumption and capital cost reduction, the above process is integrated to a RDWC configuration. By simulation, it proves that this RDWC can be an effective design. Compared with the original configuration, the original RD reboiler is removed. From this RDWC design, all energy required is provided by the reboiler of the second column. The resulting RDWC can reduce 40 % energy demand and 25 % total annual cost. It is observed that, to make this major saving possible, this RDWC avoids the remixing effect that used to take place is the original RD bottom.