## 3 Results and Discussion
### Design of the Conventional TCED Process with PG as New Proposed Extractive-Solvent  
The feed flowrate of the PC was assumed at 200 kmol/h. The feed composition was defined as 54.5 mol.% IPA and 45.5 mol.% water, as reported in the literature [30; 31]. For the preconcentration column, first, a shortcut distillation column was used to found the number of theoretical trays and the optimum feed stage, having as its specifications (1) the purity of water in the bottoms, and (2) the composition of the water-IPA azeotrope at the operation pressure, in the top product. Usually, PRO/II provides more than one variant of operation, but we selected the variant with the lowest condenser and reboiler duties. Then, the rigorous distillation column was run, and a sensitivity analysis was conducted, in order to obtain the lowest duties for the condenser and reboiler, while the feed stage was varied and the reflux ratio was followed to be minimum. The PC feed was operated at 313 K and 113.48 kPa and fed on stage 10 of 19 stages (17 valve trays). The operating pressure of the PC was 111.46 kPa in the condenser, 121.59 kPa in the top, and the column had a pressure drop of 10.13 kPa. Thus, the PC gave top and bottom temperatures products of 355.86 K and 380.7 K, respectively. The reflux ratio was 0.637, the bottom product was 100 mol.% water, and the distillate was 65.1 mol.% IPA, which is the azeotropic composition at the operating pressure. QR1 as the reboiler duty of the PC was 3407 kW. Figure 4: The conventional TCED process for IPA–water binary separation with PG as a new extractive solvent proposed in this work. The next step in the process simulation is the EDC design. No literature was found for IPA-water system separation by extractive distillation process using PG as an extractive solvent. Therefore, our starting point for the EDC simulations was to establish the target of the EDC, meaning a minimum of 99.92 mol.% IPA and a maximum of 2 ppm PG concentration (the minimum purity necessary for IPA to be used in the chemical industry or as a biocomponent in ecological gasoline is 99.9 mol.%). Similarly, the proper QR2, as the reboiler duty, was evaluated according to these targets. First, without the appropriate extractive solvent flowrate (E) and then the reflux ratio (RR2), we cannot obtain the desired purity of the IPA product. A heat exchanger (labeled as Cooler) must be placed between the EDC and the SRC to decrease the temperature of the recirculated solvent. [PERSON] and [PERSON] [32] suggested that the solvent feed temperature to the EDC should be 278.15-288.15 K below the boiling temperature of the distillate product from the EDC. In this case, the temperature of the PG extractive agent was fixed at 348.18 K. The EDC was operated at 101.3 kPa condenser pressure and a column pressure drop of 20.3 kPa. .1.1 Effect of the Molar Extractive Solvent to Feed Ratio (E/D1) on the Performance of the ED Column  
We started our investigation with several simulations to study the effects of changing the molar extractive solvent to feed ratio (E/D1) on the molar product composition of the distillate stream from the EDC. The start of our simulations followed the subsequent input conditions: the number of trays in the EDC (labeled as NT2) was first stated as 20 (using the PRO/II notation of numbering from top to bottom), the feed tray (mentioned as NF2) was fixed at 16, the feed tray of the extractive solvent (labeled as NFE) was set at 5, and the reflux molar ratio (RR2) was stated at 0.9. The molar ratio of E/D1 was selected from 1/1 to 3.4/1. Figure 5 shows the effects of E/D1 over the desirable water content in IPA products, as well as on the reboiler duty of EDC. The behavior of Figure 5 is explained by the fact that increasing the E/D1 ratio promotes a decrease in the molar water concentration in the IPA distillate product. On the other hand, a direct proportionality is observed between the E/D1 ratio and the reboiler duty.