## 3 Results and Discussions
### Design of the Conventional TCED Process
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Parameters**} & \multicolumn{2}{c}{**EDC with PG**} & \multicolumn{2}{c}{**EDC with**} & \multicolumn{2}{c}{**EDC with**} \\  & & **Solvent \({}^{\star}\)** & **EG Solvent** & **DMSO Solvent** \\ \hline D2 flowrate & kmol/h & 109.07 & 108.79 & 108.76 \\  & kg/h & 6551.47 & 6534.05 & 6533.55 \\ \hline D2 composition & molar & IPA & 99.92 & 99.93 & 99.94 \\  & molar & Water & 807 ppm & 706.4 ppm & 600 ppm \\  & & Solvent & 5.5 ppm & 0.47 ppm & 1.57 ppm \\ \hline B2 flowrate & \multicolumn{2}{c}{kmol/h} & 628.32 & 267.43 & 192.21 \\ \cline{2-5}  & kg/h & 44,416.12 & 14,037.31 & 11,517.24 \\ \hline B2 composition & molar & Solvent & 90.69 & 78.15 & 69.59 \\  & molar & Water & 9.30 & 21.74 & 30.25 \\  & & IPA & 97.7 ppm & 1121 ppm & 1560 ppm \\ \hline NT2 & & & 30 & 22 & 23 \\ NF2 & & & 20 & 17 & 17 \\ NS2 & & & 5 & 5 & 6 \\ RR2 & & & 1.5 & 1.1 & 1.2 \\ \hline Condenser 2, duty & kWh & 2999 & 2512 & 2631 \\ Condenser 2, area & m\({}^{2}\) & 86.70 & 72.30 & 76.02 \\ Water consumption to condenser 2 (a) & kg/h & 128,899.085 & 107.979.57 & 113,108.26 \\ Reboiler 2, duty & kWh & 6639 & 3431 & 3205 \\ Reboiler 2, area & m\({}^{2}\) & 344.55 & 120 & 111.71 \\ Steam consumption to reboiler 2 (b) & kg/h & 12,118 & 6262 & 5849 \\ Diameter & m & 1.524 & 1.219 & 1.219 \\ \hline \hline \end{tabular}  
* All data are from previous work [18]. (a) Inlet water temperature of 305.15 K, exit water temperature of 325.15 K. (b) Saturated steam at 1300 kPa.  
\end{table} 
Table 1: Detailed design parameters of the EDCs. Figure 6: Effect of reflux ratio in EDC (RR2) over (**a**) IPA concentration in D2 and (**b**) solvent concentration in D2. Following the iterative optimization of the EDC and the selection of the optimal parameters, one can continue the work on optimizing the solvent regeneration columns. In the next step of our study, many variants were simulated for each solvent in order to depict the optimal design and operation parameters of the SRC. The target of the simulations of these columns is that in the D3 distillate, the solvent concentration should be a maximum of 2 ppm, but also the IPA concentration should be as low as possible. These specifications are desired because the D3 distillate is predominantly water. It is recommended that the D3 stream, together with the B1 stream, after cooling, be sent to a wastewater treatment plant [21]. Moreover, it is very important to find design and operating parameters with which to obtain very well-regenerated solvents, i.e., with a maximum water concentration of 5 ppm. This is because, after cooling, the solvent is recirculated to the top zone of the EDC. The SRC pressure is 101.3 kPa (in reflux drum) and 370.7 K, and the column pressure drop is 5 kPa. An iterative procedure for obtaining the optimal design and operation parameters and the SRC was developed, which is as follows:  
1. The feed tray (NF3) was fixed at 7, and the reflux molar ratio (RR3) was fixed at 1.5 for the SRCs. The number of trays in the SRCs was changed from 13 to 17 trays in the EDC for both EG and DMSO solvents. The results of the changing effect of the number of trays (NT3) over the IPA and solvent concentration in D3 are reported in Figure 7. The increase in NT3 leads to a significant reduction in the solvent concentration in the D3 water stream. The reduction is substantial in the case of DMSO, from 383,000 ppm (38.30 mol%) for 13 trays in the SRC to only 0.008 ppm for 17 trays in the SRC. Regarding the EG concentration in D3, it is 0.53 ppm for 13 trays and 0.0022 ppm for 17 trays in the SRC. It is observed that the number of trays in the SRC has minimal impact on IPA concentration in D3, which reaches a maximum of 0.51 mol% in both cases studied. The optimum number of trays for the EG recovery column was selected to be 15, and for the DMSO recovery column, it was selected to be 16. 2. The position of the feed tray on the composition of the D3 distillate is not notable. For these reasons, NF3 remains at 7.