Energy-Saving Reduced-Pressure Extractive Distillation with Heat Integration for Separating the Biazeotropic Ternary Mixture Tetrahydrofuran–Methanol–Water Jinglian Gu, Xinqiang You, Changyuan Tao, Jun Li, Vincent Gerbaud To cite this version: Jinglian Gu, Xinqiang You, Changyuan Tao, Jun Li, Vincent Gerbaud. Energy-Saving Reduced- Pressure Extractive Distillation with Heat Integration for Separating the Biazeotropic Ternary Mixture Tetrahydrofuran–Methanol–Water. Industrial and engineering chemistry research, American Chemical Society, 2018, 57 (40), pp.13498-13510. 10.1021/acs.iecr.8b03123. hal-01957130 HAL Id: hal-01957130 https://hal.archives-ouvertes.fr/hal-01957130 Submitted on 17 Dec 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible This is an author’s version published in: http://oatao.univ-toulouse.fr/21066 Official URL: https://doi.org/10.1021/acs.iecr.8b03123 To cite this version: Gu, Jinglian and You, Xinqiang and Tao, Changyuan and Li, Jun and Gerbaud, Vincent Energy-Saving Reduced-Pressure Extractive Distillation with Heat Integration for Separating the Biazeotropic Ternary Mixture Tetrahydrofuran–Methanol–Water. (2018) Industrial & Engineering Chemistry Research, 57 (40). 13498-13510. ISSN 0888-5885 Any correspondence concerning this service should be sent to the repository administrator: [email protected] Energy-Saving Reduced-Pressure Extractive Distillation with Heat Integration for Separating the Biazeotropic Ternary Mixture Tetrahydrofuran−Methanol−Water Jinglian Gu,† Xinqiang You,*,‡ Changyuan Tao,† Jun Li,*,† and Vincent Gerbaud§ †School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China ‡Fujian Universities Engineering Research Center of Reactive Distillation Technology, College of Chemical Engineering, Fuzhou University, Fuzhou 350116, Fujian China §Université de Toulouse, INP, UPS, LGC (Laboratoire de Genié Chimique), 4 alleé Emile Monso, F-31432 Cedex 04, Toulouse, France ABSTRACT: There is rich literature on the separation of binary azeotropic mixtures, whereas few studies exist on the separation of biazeotropic ternary mixtures. In this work, we propose a systematic approach for energy-efficient extractive distillation processes for the separation of a biazeotropic mixture that involves thermodynamic insights via residue curve maps and the univolatility line to find the optimal entrainer and operating pressure, global optimization based on a proposed two-step optimization procedure, and double-effect heat integration to achieve further saving of energy consumption. An energy-saving reduced-pressure extractive distillation (RPED) with a heat integration flowsheet is then proposed to achieve the minimum total annual cost (TAC). The results show that the TAC, energy consumption, and exergy loss of the proposed RPED with heat integration are reduced by 75.2%, 80.5%, and 85.8% compared with literature designs. 1. INTRODUCTION energy consumption compared to the conventional ED fi Tetrahydrofuran (THF) and methanol are important organic process. The result reminds us that it is necessary to nd the solvents in chemical, pharmaceutical, and biochemical optimal conventional ED design before further considering energy-saving configurations. engineering, etc. The related processes produce large amounts 6 − − For the separation of ternary azeotropes, Timoshenko et al. of THF methanol water mixture, and economically separat- fi ing this mixture is an urgent mission in reducing energy cost proposed a set of comprehensive alternative ED con gurations 1−3 including both a conventional three-column flowsheet and a and CO2 emissions. However, it is impossible to separate fl THF−methanol−water mixture by simple distillation, due to partially thermally coupled owsheet for ternary mixtures of − different phase equilibriums. Luyben7 investigated the ED the presence of two binary azeotropes. At atmosphere, THF − − methanol forms a minimum azeotrope at 332.94 K with 50.79 process for the ternary mixture of benzene cyclohexane − toluene and explored the dynamic controllability of the mol % THF, and THF water gives another minimum 8 azeotrope at 336.58 K with 82.87 mol % THF. Therefore, a process. Zhao et al. compared the heterogeneous azeotropic − special technique like extractive distillation (ED) is needed. distillation and ED processes for the mixture of ethanol − ED is realized by feeding an additional entrainer, which toluene water and declared that ED is much more attractive could keep the relative volatility of the azeotrope components in terms of total annual cost (TAC). Further, mixed entrainers far away from unity. For the separation of binary azeotropes, are employed to reduce the energy cost for the separation of 4 THF−ethanol−water azeotropic mixture.9 Modla investigated conventional ED, thermally integrated 10 ED, and extractive dividing-wall columns for separating the Since distillation is still energy-intensive, from the view of minimum azeotropic mixture of methanol−toluene with the thermodynamic insight for extractive distillation, we propose intermediate entrainer trimethylamine and found that the extractive dividing-wall column could reduce the energy cost by 45%. However, Luyben5 improved Modla’s conventional ED process by largely reducing the entrainer flow rate and concluded that the improved process gives a 50% reduction in DOI: 10.1021/acs.iecr.8b03123 for the first time, as far as we know, a new three-step strategy to reduce the energy consumption and improve the perform- ance of the ED process. (1) Find a better entrainer. This includes a heuristic method (based on the literature, molecular classification,11 selectivity and capacity,12,13 thermodynamic insight,14 and computer-aided molecular design15,16). The issues of why one extractive column could break two biazeotropes and how to select a better entrainer without tedious optimization are solved. (2) Improve the design. This − refers to changing operating pressure17 19 and using different optimization methods, such as a sequential iterative optimization procedure,9,20 a two-step optimization proce- dure,21,22 mixed integer nonlinear programming,13,23 a genetic 24−27 28 algorithm, and an artificial neural network. How to find Figure 1. Simulation setup and optimal design of THF−methanol− the possible direction for reducing energy consumption is water extractive distillation with DMSO (the design of case 2). illustrated by a ternary map and univolatility line. (3) Integrate the heat. This covers product to feed stream heat integration (HI),29,30 double-effect HI,31,32 thermal coupling scheme and − entrainer loss in the three products and calculated by the dividing-wall column,33 38 heat pump,39,40 and so on. It fi calculator model built in Aspen Plus. involves how to choose the con gurations of heat integration, The flow rate of the ternary azeotropic mixture is 500 kmol/ which one is better, and if there is a potential advantage when h, with a content of 25 mol % THF, 37.5 mol % methanol, and changing operating pressure. 37.5 mol % water. The purity of product THF, methanol, and For a ternary mixture of THF−methanol−water, Raeva and − 2 water in the distillates are all set to be 99.9 mol %. The vapor Sazonova tried to use ethylene glycol (EG) as entrainer with liquid equilibrium of THF−methanol−water−DMSO is the aim of validating their entrainer selection rule, but no described by the nonrandom two liquid (NRTL) property further optimization and heat integration techniques were model with Aspen Plus built-in binary parameters (see Table considered. In this study, the above three aspects are fi fi S2 in the Supporting Information). systematically investigated: rst, DMSO is used for the rst 2.2. Energy Consumption, TAC, and Exergy Loss. time, as far as we know, as a better entrainer for the THF− − Energy consumption is one of the main criteria for comparing methanol water system, and the conventional three-column different designs of the extractive distillation. In order to extractive distillation process at atmospheric pressure is simultaneously take the three columns into account, we use a optimized by the two-step optimization procedure with total new objective function full energy consumption equation energy consumption per product unit (FEC) as an objective (FEC), which represents the energy cost per unit product (kJ/ function and TAC as the decision-determining criterion. The kmol) reason for selecting the specific flowsheet is given. Second, the conventional ED (CED) design is improved by considering min FEC= (MQR1 + mQ C1 + MQ R2 + mQ C2 + MQ R3 thermodynamic insight. The reason why reduced pressure ED +mQ + mQ )/(kD+ D ) (RPED) could save energy consumption for the studied system C3 cooler 1 2 is illustrated and the optimal pressure is obtained. Third, subject to double-effect HI (DEHI) is applied to the RPED process to further improve the energy efficiency and reduce TAC and