## 3 Results and Discussions
### Design of the Conventional TCED Process  
The feed flow rate of the PC was assumed at 200 kmol/h at 313.15 K and 113.48 kPa. The feed composition was defined as 54.5 mol% IPA and 45.5 mol% water, as reported in the literature [16,21]. All operating data of the PC reported in our previous work were kept the same [18]. From the beginning, for the design process of the PC, the distillate (D1) composition was specified at 65.19 mol% IPA (meaning a near-azeotropic composition mixture of IPA/water) at 111.46 kPa and 355.86 K. To reduce the IPA loss, the bottom composition was specified to be 99.997 mol% water, at 131.72 kPa and 380.7 K.  
Distillate flow D1 (IPA/water minimum-boiling azeotrope mixture) feeds EDC. The EDC design is much more complicated because the solvent flow rate is an important design variable without which we cannot obtain the desired purity of the D2 distillate, meaning at least 99.92 mol% IPA. But other variables must also be optimized: the number of stages, the position of the feed stage, the position of the solvent feed stage, and the column reflux ratio. The solvent feed temperature to the EDC is maintained constant at 348.15 K, as suggested by [PERSON] and [PERSON] [22]. The EDC operated at a 101.3 kPa condenser pressure and a column pressure drop of 20.3 kPa. The iterative procedure for obtaining the optimal design and operation parameters of the EDC is the following:  
1. The number of trays in the EDC, labeled as NT2, was set at 20, following AVEVA PRO/II's notation of numbering from top to bottom. The feed tray, referred to as NF2, was fixed at 16, while the feed tray for the extractive solvent, labeled NFE, was fixed at 5. Additionally, the reflux molar ratio (RR2) was set at 0.9. The molar ratio of the extractive solvent to feed (E/D1) was varied from 0.5:1.0 to 2.0:1.0 for the EG solvent and from 0.25:1.0 to 1.0:1.0 for the DMSO solvent. The results of the changing effect of the E/D1 ratio over the IPA and solvent concentration in D2 are reported in Figure 3a,b. The increase in the solvent ratio significantly impacts the purity of the D2 product from the top of the column. While it raises the IPA concentration in the D2 stream, which is desired, it also results in a higher concentration of solvent in that stream. Therefore, selecting the optimal solvent ratio involves balancing the IPA concentration with the solvent concentration. We will also examine additional parameters to ensure the overall quality of the D2 distilled product. In the case of EG solvent, the most proper IPA concentration in D2 is only 99.8 mol% but with a very small loss of EG in D2 (i.e., 0.74 ppm), which was depicted for the E/D1 value of 1.25/1, and in the case of DMSO solvent, there was an IPA concentration in D2 over the target (i.e., 99.93 mol%) but with an unacceptable loss of DMSO (i.e., 30.98 ppm) in D2, which was depicted for the E/D1 value of 0.8/1. Figure 3: Effect of solvent ratio E/D1 over (**a**) IPA concentration in D2 and (**b**) solvent concentration in D2. At an optimal solvent ratio (i.e., E/D1 at 1.25/1.0 for EG and E/D1 value of 0.8/1 for DMSO), the number of trays in EDCs changes from 20 to 26 trays in the EDC with EG and from 19 to 24 trays in the EDC with DMSO. All the other parameters remain unchanged. The number of trays in the EDCs affects both the height of the column and the investment costs. Generally, columns with fewer trays require a lower initial investment. However, the choice of the optimal number of trays should primarily focus on ensuring the quality of the D2 distilled product. Figure 4a,b show that at 22 optimal trays in the EDC with EG solvent, the IPA concentration in D2 was 99.91 mol% (very close to the target of 99.92 mol%) and with a very small loss of EG in D2 (i.e., 0.74 ppm). In the case of DMSO solvent, the optimal number of trays in the EDC was established at 23 because the loss of solvent was a little bit lower (i.e., 30.84 ppm), while the IPA concentration was 99.94 mol%. The number of trays in the EDC has minimal impact on the DMSO concentration in D2. 3.