## 1 Introduction
Secondly, we propose a few energy-saving methods by heat integration. In the first proposed flowsheet, we come up with the idea of valuing the sensible heat of the solvent with a high temperature, starting from the base of the SRC, to preheat the EDC feed flow first and then, after additional cooling, to recirculate at the top of the EDC. In addition, in the same flowsheet proposed by us, we identify two more hot streams, namely, the water flow from the base of PC and the water flow from the top of SRC. Our original idea is to use their sensible heat to preheat the PC feed together. Moreover, the water cost for cooling the solvent before recirculating it at the top of the EDC column is also reduced to some extent. For an even better use of the sensible heat of the warm solvent, we propose another flowsheet in which it (hot solvent) is used after preheating the feed flow of the EDC to further use the remaining sensible heat and preheat the feed flow of PC. In addition to the fact that the feed flow of the PC can also be preheated by hot water flows (as in the first proposed flowsheet), it will benefit from another preheating with the sensible heat of the solvent. In addition, it further reduces the consumption of cooling water for the solvent before being recirculated to the top of the EDC. The purpose of these two flowsheets is to demonstrate that by simply preheating the feed flows, the thermal duties of the heat exchangers from the EDC and PC can be reduced and, implicitly, the cost of the saturated steam associated with them. The following other two proposed flowsheets are based on the idea that the PC is operated in a vacuum and the SRC is still operating under atmospheric pressure. Therefore, in the proposed third flowsheet, the vapors from the top of the SRC, with a high temperature, will be able to replace some of the saturated steam at the PC reboiler. To replace the required amount of saturated steam at the PC reboiler, it will use some of the sensible heat of the hot solvent stream from the base of the SRC. Further, the solvent with still enough sensible heat will be able to preheat the feed flow of the EDC and, after supplementary cooling, it will be able to recirculate at the top of the EDC. The fourth proposed flowsheet aims to exploit the sensible heat of the hot solvent. First, it will be able to replace some of the saturated steam from the EDC reboiler, then it will use another part of the sensible heat to the PC reboiler, and it will finally preheat the feed of the EDC. Thus, is not necessary for any supplementary cooling of the solvent and it can be recirculated at the top of the EDC. The lack of an SRC condenser and solvent cooler will decrease the investment costs, but these benefits are somewhat mitigated by the introduction of several heat exchangers into the process flowsheet diagrams. The energy saving, utilities cost saving and TAC saving of each heat-integrated flowsheet have been systematically analyzed and compared to the conventional TCED design. In all the proposed flowsheet diagrams, the same target regarding the purity of the IPA product is maintained as, respectively, at least 99.92 mol.%. Thus, the process of separating the water-IPA mixture in the presence of PG becomes a \"greener\" process due the energy savings that can be obtained through the proposed thermally integrated process schemes.