## 3 Results and Discussions
### Design of the Conventional TCED Process
The next step in our simulations was to study the effect of the feed tray (NF2) position on the target concentrations. All the other parameters remain unchanged. For the EDC with EG, the range of the feed tray position was in the range of 15 to 19, and for the EDC with DMSO, in the range of 14 to 18. The position of NF2 has very little influence on the concentrations of IPA and/or solvents in D2, as illustrated in Figure 5. Lowering the feed from tray 16 to tray 17 leads to an increase in the IPA concentration in D2 from 99.91 mol% to 99.93 mol% in the EDC with EG and from 99.94 mol% to 99.96 mol% in the EDC with DMSO. A significant decrease in DMSO concentration in D2 was not expected. Figure 4: Effect of tray number on EDC (NT2) over (**a**) IPA concentration in D2 and (**b**) solvent concentration in D2. 4. We expect the reflux ratio (RR2) to have a significant contribution to the separation. Also, the reflux ratio plays a crucial role in the overall TCED process, affecting both the diameter and investment costs of the EDCs. It also impacts the thermal duty of the condensers and reboilers, along with their associated utility consumption. Ideally, the reflux ratio should be kept as low as possible to minimize both investment and operating costs. However, the most important factor in determining the optimal ratio is the quality of the D2 distilled product. The investigation range of RR2 was 0.6 to 1.1 in the EDC with EG and in the range of 0.7 to 1.2 in the EDC with DMSO. As can be seen from Figure 6a,b, the increase in RR2 values leads to a slight increase in IPA concentration but also to an expected decrease in DMSO concentration. So, in taking into account the targets of concentrations in D2, it can be concluded that an RR2 value of 1.1 provides an IPA concentration of 99.93 mol% and an EG concentration of 0.47 ppm. In the case of DMSO solvent, for an RR2 of 1.2, the IPA concentration of 99.96 mol% is very satisfactory, but the DMSO at 16.5 ppm is still very high. 5. The last step in our iterative procedure refers to the feed ray position of solvent (NFE). This investigation was conducted only for the case of an EDC with DMSO. Lowering the NFE for DMSO by a single tray (from 5 to 6) has a pronounced impact on the decrease in DMSO concentration from 16.5 ppm to below 2 ppm (i.e., 1.57 ppm). A small decrease in IPA concentration was depicted (i.e., from 99.96 mol% to 99.94 mol%). The iterative procedure led to the identification of the most favorable operating parameters of the EDC: For the EG solvent, set the solvent ratio E/D1 at 1.25/1.0, NT2 at 22, NF2 at 17, NFE = 5, and RR2 = 1.1. For the DMSO solvent, set the solvent ratio E/D1 at 0.8/1.0, NT2 at 23, NF2 at 17, NFE = 6, and RR2 = 1.2. The detailed parameters of the EDC for the EG and DMSO solvents investigated in this work in comparison with the PG solvent investigated in our previous work are shown in Table 1. For all solvents investigated, it is observed that the IPA purity in the D2 distillate is at least 99.92 mol%, but this is achieved with a much higher PG flow rate than in the case of the other two solvents. This results in an increase in the reflux ratio and column diameter, as well as higher reboiler and condenser duties and larger heat exchanger areas. Figure 5: The influence of NF2 over IPA concentration in D2.