## 4 Conclusions  
This work investigated PG's suitability as an extractive solvent for IPA's separation from its azeotrope mixtures with water. A three-column extractive distillation conventional (TCED) process was selected. The extractive distillation separation target was used to obtain a distillate product with 99.92 mol.% IPA. The optimal design of each column of the TCED conventional extractive distillation process was presented.  
The energy-saving possibility of an extractive distillation system was investigated. This work successfully developed two directions of heat integration: heat integration by recovering the sensible heat from the hot streams and heat integration using both the latent heat of the SRC overhead vapor and the sensible heat of the hot solvent. Four new flowsheets were investigated to verify their energy and economic advantages compared to the conventional TCED flowsheet. The economic evaluation results show that the LH-SH1 process can bring a 15.57% total annual cost reduction and the LH-SH2 brings a 43.12% energy cost reduction compared to the conventional TCED process for separating the IPA-water binary azeotropic system. Both thermal integrated designs (LH-SH1 and LH-SH2) demonstrated economic benefits, but the final decision of a developer regarding the selection of the convenient design depends on the situation in the field.  
**Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app14209420/s1](https://www.mdpi.com/article/10.3390/app14209420/s1)]([https://www.mdpi.com/article/10.3390/app14209420/s1](https://www.mdpi.com/article/10.3390/app14209420/s1)), Table S1: Binary interaction parameters of the NRTL thermodynamic system, specific for the components implied in the IPA-water dehydration process by extractive distillation with 12 PG as a solvent; Table S2: Formulas and data utilized for the economic evaluation; Table S3: Design parameters for the conventional TCED; Table S4: Design parameters for the SH1; Table S5: Design parameters for the SH2; Table S6: Design parameters for the LH-SH1; Table S7: Design parameters for the LH-SH2.  
**Author Contributions:** Conceptualization, M.N. ([PERSON]); methodology, M.N. ([PERSON]) and M.N. ([PERSON]); software, M.N. ([PERSON]); validation, D.L.C.; formal analysis, D.L.C.; writing--original draft preparation, M.N. ([PERSON]) and M.N. ([PERSON]); writing--review and editing, M.N. ([PERSON]) and D.L.C.; supervision, M.N. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
**Funding:** The APC was funded by Petroleum-Gas University of Ploiesti, Romania.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Conflicts of Interest:** The authors declare no conflicts of interest.  
**Nomenclature**  
Abbreviations
DMSO dimethyl sulfoxide  
EG ethylene glycol  
ED extractive distillation  
IPA isopropanol  
PG propylene glycol  
PDFs process flowsheet diagrams  
TCED three-column extractive distillation  
LMTDs log-mean temperature differences  
SH flowsheet for energy-saving process by sensible heat recovery