Extractive distillation for ethanol dehydration using imidazolium-based ionic liquids as solvents

Extractive distillation for ethanol dehydration using imidazolium-based ionic liquids as solvents

Accepted Manuscript Title: Extractive distillation for ethanol dehydration using imidazolium-based ionic liquids as solvents Author: Zhaoyou Zhu Yongs...

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Accepted Manuscript Title: Extractive distillation for ethanol dehydration using imidazolium-based ionic liquids as solvents Author: Zhaoyou Zhu Yongsaeng Ri Min Li Hui Jia Yongkun Wang Yinglong Wang PII: DOI: Reference:

S0255-2701(16)30207-0 http://dx.doi.org/doi:10.1016/j.cep.2016.09.009 CEP 6865

To appear in:

Chemical Engineering and Processing

Received date: Revised date: Accepted date:

15-7-2016 7-9-2016 15-9-2016

Please cite this article as: Zhaoyou Zhu, Yongsaeng Ri, Min Li, Hui Jia, Yongkun Wang, Yinglong Wang, Extractive distillation for ethanol dehydration using imidazolium-based ionic liquids as solvents, Chemical Engineering and Processing http://dx.doi.org/10.1016/j.cep.2016.09.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Extractive distillation for ethanol dehydration using imidazolium-based ionic liquids as solvents Zhaoyou Zhua, Yongsaeng Ria, b, Min Lia, Hui Jiaa, Yongkun Wanga, Yinglong Wanga, * a

College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao

266042, China b

Faculty of Chemistry, Kim Il Sung University, Pyongyang 999093, DPR Korea

Corresponding Author *E-mail: [email protected] Graphical abstract

Highlights    

Feasibility of ionic liquid-based extractive distillation (ILED) was evaluated by Aspen Plus. [Emim][BF4] was selected as the promising solvent for dehydration of ethanol. Comparison with the extractive distillation using conventional solvents was implemented. The ILED process might become a potential separation technology.

1

Abstract An extractive distillation process was investigated, comparing the imidazolium-based ionic liquids [EMIM][BF4] and [BMIM][BF4] as solvents for ethanol dehydration. An Aspen Plus process simulator was used to simulate the feasibility of the ionic liquid-based extractive distillation (ILED) process and determine the main operating conditions of anhydrous ethanol production. User-defined ionic liquid components were created in Aspen Plus, with the required thermodynamic and physical property parameters. The NRTL model was used to calculate the thermodynamic properties. The proposed process and methodology using [EMIM][BF4] as the solvent was applied to evaluate the potential of extractive distillation for ethanol dehydration. The results show that the distillate purity of ethanol was higher than 99.9 mol % and revealed the advantage of decreased energy requirements compared with the extractive distillation process using conventional solvents. The ILED process design obtained from the sensitivity analysis for minimum energy consumption presented a lower total annual cost (TAC). Keywords: Ionic liquids; Extractive distillation; Simulation; Anhydrous ethanol Nomenclature [EMIM][BF4] = 1-ethyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] = 1-buthyl-3-methylimidazolium tetrafluoroborate [EMIM][Cl] = 1-ethyl-3-methylimidazolium chloride [BMIM][Cl] = 1-buthyl-3-methylimidazolium chloride [EMIM][OAc] = 1-ethyl-3-methylimidazolium acetate Azeo. Point = azeotropic point αVLE = relative volatility from VLE data xD, ethanol = molar composition of ethanol in distillate ID1 = diameter of extractive distillation column ID2 = diameter of flash tank QC = heat duty of condenser (kW) QR = heat duty of reboiler (kW) QH = heat duty of flash tank (kW) AC = heat transfer area of condenser (m2) AR = heat transfer area of reboiler (m2) T = temperature (℃) Td = temperature of decomposition (℃)

1. Introduction Ethanol is widely used as a raw material in the manufacturing process of esters and ethers and as a solvent in the production of paint, cosmetics, and perfumery. It is also a biofuel with a high 2

energy value and can be obtained from renewable sources [1]. However, in order to be used as a raw material in the chemical industry and a fuel in current engines, ethanol must have at least 99.5 wt % purity. Additionally, because ethanol forms an azeotrope with water at 95.5 wt %, its purification requires the use of special separation techniques, such as membranes, molecular sieves, azeotropic distillation, extraction, and extractive distillation [2-6]. Extractive distillation has been proven to be a promising ethanol-water separation technology because of its low energy consumption [7]. In this process, a new solvent is included to increase the relative volatility of the key components of the feed without forming a new azeotrope [8, 9]. The selected solvent must have certain characteristics that increase the feasibility of the process by reducing energy and solvent consumptions [10, 11]. The solvents currently used in extractive distillation for ethanol dehydration are glycols [6, 10-12], glycerol [12-14], and gasoline [15]. Recent studies on extractive distillation have focused on the use of ionic liquids (ILs) as solvents [16-20]. ILs have the advantages of liquid solvents in promoting high separation ability, and their particular use for ethanol dehydration has shown promising results. The use of ILs as azeotropic breakers in separation processes, including liquid-liquid extraction and extractive distillation, has been presented [21, 22]. The azeotrope-breaking potential and influence of the IL structure on its capability as a solvent have been compared for the design of extractive distillation processes using ILs. However, most of these studies on ILs as potential solvents in extractive distillation have been focused on vapor-liquid equilibrium (VLE) experiments and pilot plant scale experiments [23-25]. In 2003, Lei’s group [26] first proposed extractive distillation with ILs as entrainers, in order to combine the advantages of a liquid solvent (easy operation) and a solid salt (high separation ability). Since then, studies on extractive distillation with ILs have increased dramatically. Lei et al. [27] discussed the use of ILs in extractive distillation in detail and provided an in-depth explanation of the advantages of extractive distillation with ILs. Due to the great advantages of this process, such as easy recovery, high thermal and chemical stability, and negligible vapor pressure, we applied extractive distillation with ILs to separate ethanol and water. Technical and economic evaluation via process simulation is necessary for the design of the industrial-scale applications. Recently, Ramirez-Corona et al. [28] introduced the design methodology of an extractive distillation column using ILs in ethanol dehydration systems. Such simulations rely on mathematical models to determine the thermodynamic behavior and physical 3

properties of components and their mixtures. VLE experimental data of ethanol-water-ILs have been reported in the literature [18, 20, 29-31], and calculations of phase equilibria in mixtures involving ILs have been carried out to generate binary interaction parameters for the correlative NRTL [32] and UNIQUAC [33] models. ILs have not been included in the component databases of process simulators such as Aspen Plus due to their relative novelty and the shortage of experimental data or predictive methods required to enable the simulation of their physical and thermodynamic properties. Therefore, it is necessary to create a user-defined IL database in order to allow ILs to be selected as components within a process simulation. This work aims to establish user-defined ILs in Aspen Plus and simulate and optimize the ILED process to design an industrial-scale process for ethanol dehydration. From the primary ILED process design using [EMIM][BF4] and [BMIM][BF4] as solvents, [EMIM][BF4] was selected as the proposed solvent to evaluate the potential of the ILED process for anhydrous ethanol production compared to other extractive distillation processes with conventional solvents. The conditions and configuration for the ILED process using [EMIM][BF4] were determined by sensitivity analysis so that energy and solvent requirements were minimized. TAC was calculated for the different configurations producing ethanol with a purity higher than 99.9 mol % to confirm a novel ILED process configuration. 2. Screening of imidazolium-based ionic liquids as solvents The selection of a suitable IL solvent is an important factor in the ILED process design. The screening of ILs is based on the availability of data required for the ILED process simulation and validation purposes. Relative volatility and selectivity are the criteria for solvent selection. Pereiro et al. [22] reviewed the ILs used as azeotrope breakers to separate ethanol and water and determined the minimum molar fraction of IL required to break the azeotrope. They concluded that the most —

promising ILs are those containing [OAc]



and [Cl] , but no dramatic increase in relative volatility



was observed in comparison with [BF4] . The anion had a more significant influence on selectivity than the cations [34]. The selectivities at infinite dilution provide a useful index for the selection of a suitable IL solvent. The comparison of selectivities at infinite dilution of ethanol to water for 24 imidazolium-based ILs along with the results predicted by the UNIFAC-Lei model [35-37] are —

shown in Figure 1. It can be seen that selectivities at infinite dilution for ILs with [BF4]

as the

anion are relatively higher than those of other imidazolium-based ILs investigated in this work. 4

Other properties of ILs are also important from the perspective of industrial process design. These include viscosity, chemical stability, toxicity, flammability, ease of recovery, recyclability and cost. The IL viscosity is the main criterion for cation and anion selection because it determines the rate of heat- and mass-transport processes. It strongly affects the pumping, mixing, and agitation operations [38]. Thus, the selection of an IL with low viscosity is generally desirable since it improves mass transfer in the extractive and recovery units and reduces the energy required for —

moving and mixing the solvent. ILs containing the anion [Cl] possess a high viscosity and are thus not favorable for a continuous process. [EMIM][OAc] is not suitable as a solvent for the recycling ILED process because it is known to decompose at a lower temperature than other ILs [23]. The comparison between thermodynamic properties of several ILs is presented in Table 1. Due to their favorable physical and thermodynamic properties and relatively wide availability [39, 40], [EMIM][BF4] and [BMIM][BF4] were primarily chosen as suitable solvents in the process design for ethanol dehydration. The purchase cost of ILs can be offset via optimal design of the IL recovery and recycling process. 3. Design methodology The general methodology for designing an extractive distillation process with solvents that form no new azeotrope is related to the knowledge of residue curve maps, which depend on the choice of solvents. According to Serafimov’s classification scheme [41], the system ethanol + water + IL solvent belongs to class (1.0-1a). Knowledge of the residue curve maps can help to assess which product is removed in the distillate when using IL as the solvent. The concept of residue curve maps is also related to a simple distillation process in which the liquid mixture is vaporized in a column and the vapor formed at any instant is immediately removed [42]. The steady-state composition profile in a packed column at total reflux is identical to the residue curve in a simple distillation process[43]. Moreover, residue curves show the general behavior of continuous columns operating at finite reflux ratios [9]. Residue curves are computed by the following equation:

Dxi  ( xi  yi ) dh

i = 1, n components

(1)

where yi is the vapor composition in equilibrium with the liquid composition xi. For liquid-based systems, the activity coefficient model NRTL is typically chosen to calculate phase equilibria. The NRTL model is used to describe the nonideality of the liquid phase and the vapor is assumed to be ideal. The NRTL binary parameters were taken from the literature [18] for all the species involved 5

in this study and were used for residue curve calculations by Aspen Plus for the ILED process simulation (Appendix 1). Here, binary parameters for water and ethanol were fixed as the values retrieved from APV84 VLE-IG in the Aspen Plus database. Since the Aspen Plus database does not provide any thermodynamic data for the studied ionic liquids, additional model parameters for physical properties of these components, such as vapor pressure and heat capacity, need to be found. Some thermodynamic and physical properties, including critical properties and normal boiling points of the ILs, are required to implement process simulation in Aspen Plus. For the two imidazolium-based ILs selected, critical properties, (Tc, Pc and Vc), the normal boiling temperature (Tb), and the acentric factor (ω) were calculated by Valderrama et al. [44, 45] and are shown in Appendix 2. The simulation flowsheet for the ILED process in Aspen Plus is shown in Figure 2. The ILED process consists of two parts, namely, an extractive distillation column and a flash tank. The feed flowrate for all cases is 100 kmol/h, with the composition of 15 mol % of water and 85 mol % of ethanol, corresponding approximately to the composition at the azeotropic point. This stream enters the extractive distillation column at 30 ℃ and 1 atm. The solvent stream is added on a stage higher than the feed stage of the ethanol–water mixture. Ethanol is obtained at the top of the extractive distillation column, and the water + IL mixture removed at the bottom is sent to the flash tank. At the bottom of the flash tank, the solvent [EMIM][BF4] with some trace water is recycled back to the extractive distillation column. To establish the operating conditions for the extractive distillation column with ILs as solvents, a sensitivity analysis was performed in order to determine the main design variables, such as the number of stages (NT), reflux molar ratio (RR), feed stage (NF), solvent feed stage (NIL), and solvent-to-feed molar ratio (IL/F). 4. Results and discussion 4.1. Feasibility of the ILED process The separation of an ethanol-water mixture by adding an ionic liquid solvent behaves like any extractive distillation process using heavy solvents [42]. The components, i.e., the main feed ethanol and water, are the saddle points of the residue curves; the solvents [EMIM][BF4] and [BMIM][BF4] are the stable node; while the azeotropic point is an unstable node (Figure 3). For a detailed analysis of the (1.0-1a) class extractive distillation process, the influence of the operation parameters should 6

be investigated, e.g., reflux ratio, solvent-to-feed ratio, and tray numbers to achieve the intersection of the composition profiles of different column sections (rectifying, extractive, and stripping sections) joining the top and bottom products of the column [46]. Figure 4 displays the effect of the solvent-to-feed ratio (IL/F) on the VLE behavior and shows the comparison of values calculated by the NRTL model and those predicted by the UNIFAC-Lei model. It also indicates that both the correlative NRTL model and the predictive UNIFAC-Lei model yield similar results. To facilitate the analysis, all data are plotted on an IL-free basis. It can be observed that higher IL/F values favor the azeotrope breakup and simplify ethanol purification; however, the VLE maintains a non-ideal behavior at low IL/F values, showing an inflexion point in the high-ethanol-composition area, which limits the degree of separation. From these results, it can be noted that process simulations can provide a good approximation only when IL/F values are sufficiently high. The optimal operating parameters for extractive distillation of the ethanol-water system in the presence of [EMIM][BF4] and [BMIM][BF4] as solvents are summarized in Table 2. It can be seen the IL/F and energy consumed at the reboiler are lower for [EMIM][BF4], and minimum reflux ratios are higher for [BMIM][BF4]. This can also be explained by the fact that [EMIM][BF4] has a better selectivity than [BMIM][BF4]. Since [EMIM][BF4] has a shorter organic chain length, it exhibits better capability for azeotrope elimination compared to [BMIM][BF4], with a direct effect on the design parameters. Figures 5(a) and 5(b) show the liquid composition profiles of the ILED column obtained using [EMIM][BF4] and [BMIM][BF4] as solvents. It can be observed that in order to obtain the desired purity of ethanol in the distillate, the separation of ethanol-water in the presence of [EMIM][BF4] and [BMIM][BF4] as solvents requires more stages in the extractive section than in the rectifying and stripping sections, regardless of the total number of stages. Since [EMIM][BF4] and [BMIM][BF4] are nonvolatile due to their high boiling points, their concentration remains constant throughout the extractive section without moving to the top of the column. Figure 5(c) shows the temperature profiles of the extractive distillation columns obtained with different solvents. In the extractive section, the temperature regions are maintained close to the azeotropic point, while the values are slightly decreased in the rectifying section. From this, it can be inferred that the extraction of ethanol from water in the presence of ILs is successfully carried out in the extractive section. 7

According to these results, ILED processes for anhydrous ethanol production using [EMIM][BF4] and [BMIM][BF4] as solvents are feasible. Additionally, it is obvious that the separation of the azeotropic ethanol-water mixture with [EMIM][BF4] requires lower IL/F values than that with [BMIM][BF4] due to the higher selectivity of [EMIM][BF4] compared to [BMIM][BF4]. In addition, the energy consumption by the reboiler in the case of [Emim][BF4] is less than that in the case of [BMIM][BF4]. Hence, it can be concluded that [EMIM][BF4] is a promising solvent for the ILED process design for ethanol dehydration. 4.2. Sensitivity analysis results of ILED process using [EMIM][BF4] as solvent 4.2.1. Effect of feed stage and number of stages The effects of the feed stage and number of theoretical stages on the molar composition of ethanol in the distillate and the reboiler duties were analyzed. Figure 6 (a) shows the relationship between the ethanol purity in the distillate and the number of theoretical stages and feed stages for the case of [EMIM][BF4]. The results indicate that ethanol with a purity higher than 99.5 mol % in the overhead product can be obtained with a suitable stage number and feed stage. Thus, the ethanol purity is immediately decreased when the feed stage is close to the bottom, so the number of stages in the stripping section is inadequate for the extraction of ethanol. Figure 6 (b) shows the influence of the number of stages and the feed stage on reboiler duties. It is observed that the reboiler duties have a similar tendency as that of the molar composition of ethanol in the distillate. Although no significant differences between reboiler duties are observed, an increase in energy consumption takes place when a higher ethanol concentration is obtained in the distillate. 4.2.2. Effect of solvent feed stage and reflux ratio The influence of the solvent feed stage and the reflux ratio on the distillate composition and reboiler duties of the extractive distillation column are shown in Figures 6(c) and 6(d). Figure 6(c) shows that the ethanol concentration is higher at a greater reflux ratio. As the solvent feed stage approaches the bottom from 3 to 9, the ethanol concentration in the distillate reaches the composition requirement of 99.9 mol % but then decreases after the 9th solvent feed stage. As observed from Figure 6(d), decreasing the reflux ratio can allow for a significant decrease in the reboiler energy consumption, but the reboiler duties do not show any change for the solvent feed stages 3 to 9 at the specified reflux ratio. Thus, the reflux ratio of 1.0 and the 8th solvent feed stage for [EMIM][BF4] 8

can lead to an ethanol of purity higher than 99.9 mol % with lower energy consumption in the reboiler. 4.2.3. Effect of solvent to feed molar ratio The solvent-to-feed molar ratio is an important parameter for the improvement of purity in the anhydrous ethanol production. From the sensitivity analysis plotted in Figure 6(e), the solvent-tofeed ratio has a direct effect on the distillate purity without considerably affecting the energy consumption. Moreover, at a constant reflux ratio, there is no change in energy consumption for different values of IL/F within the interval 0.1-0.4. Similarly, at a constant IL/F ratio, the reflux ratio increases until a distillate composition equivalent to the one obtained in the previous variation is reached; the increase in energy consumption is 13.6% (Figure 6(f)). Consequently, the reflux ratio must be set to the lowest possible value so that the IL/F ratio can be manipulated to reach the distillate composition without high energy consumption. Thus, it must be kept in mind that high IL/F ratios increase the energy consumption in flash tank. From sections 4.2.2 and 4.2.3, the reboiler energy consumption in the ILED process is obviously related to the reflux ratio. The configuration and operating conditions of the ILED process for anhydrous ethanol production were established from the results obtained by the sensitivity analysis. Table 3 shows the operation parameters and simulation results of the extractive distillation column and flash tank, which satisfy all of the specifications for the purity of anhydrous ethanol and recycling without the loss of ILs. 4.3. Economic analysis In this section, the total energy consumption and modular cost were estimated to assess the process profitability. Energy consumption is one of the important factors by which the separation process is evaluated. Table 4 shows the comparison between total energy requirements with the ILED simulation studied in this paper and the conventional extractive distillation simulation results reported in the literature. The reboiler duties converting the energy consumption per kilogram of ethanol production were calculated for comparison with the conventional extractive distillation process. This comparison shows that the ILED process for anhydrous ethanol production in this paper is superior to other conventional extractive distillation processes due to decreased energy requirements.

9

TAC is the sum of the operating cost and the annual capital investment, and the annual capital investment is assumed to be the capital investment divided by a payback period (Eq. 2). TAC is adopted as the objective function to be minimized by adjusting the design parameters, including the number of trays in each column, the feed location in the column, etc. The cost of equipment and utilities is estimated by formulas adopted from the book by Luyben [47], as shown in Appendix 3.

TAC 

capital cost  operating cost payback period

(2)

TACs were calculated for the three cases of ILED using [EMIM][BF4] obtained from the objective value of ethanol purity higher than 99.9 mol %, and the results are shown in Table 5. The equipment cost was annualized considering 3 years as the time to recover the investment. In addition, 8400 hours of operation per year were considered. The energy cost represents the most significant contribution to the TAC [48]. The solvent is recovered for reuse, thus avoiding the continuous use of fresh solvent. Therefore, the cost of the solvent was not considered in the cost calculations. The proposed ILED design evaluated from the sensitivity analysis, which used objective values for minimum energy consumption and ethanol purity higher than 99.9 mol %, can reduce TAC by 13.1% and 29.1% for the two other cases, respectively. 5. Conclusion In this work, the extractive distillation process with imidazolium-based ionic liquids as solvents for ethanol dehydration was simulated and optimized via Aspen Plus. User-defined ILs for [EMIM][BF4] and [BMIM][BF4] were created in Aspen Plus, and NRTL model parameters taken from the literature were used to estimate thermodynamic properties for the simulation of the ILED process. The feasibility of the ILED process using [EMIM][BF4] and [BMIM][BF4] as solvents was analyzed by residue curve maps and relative volatilities. Consequently, [EMIM][BF4] was selected as the proposed solvent in the ILED process design. The molar composition of ethanol in the distillate at the top of the extractive distillation column for all cases of studied ILs was higher than 99.9 mol %. This paper not only offers the operating parameters of the ILED but also demonstrates that ILs present higher capabilities along with shorter organic chain lengths. The ILED process of anhydrous ethanol production requires less energy than the conventional extractive distillation sequence. It has been confirmed that the ILED process configuration obtained from the sensitivity analysis for minimum energy consumption was better than other configurations, as demonstrated 10

by the TAC value of $0.73×106. The results show that with further investigation for new ILs as solvents, the ILED process is a potential energy-saving separation technology that can allow efficient separation of azeotropes, such as the ethanol-water system. Acknowledgement Financial support from National Natural Science Foundation of China (Project 21306093) is gratefully acknowledged.

Appendix 1. NRTL binary parameters for [EMIM][BF4] and [BMIM][BF4] taken from Ge et al. [18].

i j

gij (J·mol-1)

gji (J·mol-1)

water (1) + ethanol (2) + [EMIM][BF4] (3) 1-3 5410.1 -4061.1 2-3 9092.0 -1624.6



0.3

water (1) + ethanol (2) + [BMIM][BF4] (3) 1-3 2-3

5406.9 8301.9

-3523.1 -2799.6

11

0.3

Appendix 2. Several parameters of [EMIM][BF4] and [BMIM][BF4] taken from Valderrama et al. [45]. IL

Mw

Tb(K)

Tc(K)

Pc(bar)

Vc(cm3/mol)

Zc

ω

[EMIM][BF4] [BMIM][BF4]

198 226

449.5 495.2

596.2 643.2

23.6 20.4

540.8 655

0.2573 0.2496

0.8087 0.8877

12

Appendix 3. Basis of economics and equipment sizing Length: L = 1.2 × 0.61 × (NT - 2) Vessel (diameter and length in meters) Capital cost = 17640 × (ID) 1.066 × (L) 0.802 Condensers (area in m2) Heat-transfer coefficient (KC) = 0.852kW/(K﹒m2) AC = QC / KC×⊿TC Capital cost = 7296 × (AC) 0.65 Reboilers (area in m2) Heat-transfer coefficient (KR) = 0.568kW/(K﹒m2) AR = QR/(KR×⊿TR) Capital cost = 7296 × (AR)0.65

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[31] A.V. Orchillés, P.J. Miguel, F.J. Llopis, E. Vercher, A. Martínez-Andreu, Isobaric vapor–liquid equilibria for the extractive distillation of ethanol+ water mixtures using 1-ethyl-3methylimidazolium dicyanamide, Journal of Chemical & Engineering Data 56 (2011) 4875-4880. [32] H. Renon, J.M. Prausnitz, Local compositions in thermodynamic excess functions for liquid mixtures, AIChE journal 14 (1968) 135-144. [33] D.S. Abrams, J.M. Prausnitz, Statistical thermodynamics of liquid mixtures: a new expression for the excess Gibbs energy of partly or completely miscible systems, AIChE Journal 21 (1975) 116-128. [34] J.P. Gutiérrez, G.W. Meindersma, A.B. de Haan, COSMO-RS-based ionic-liquid selection for extractive distillation processes, Industrial & Engineering Chemistry Research 51 (2012) 1151811529. [35] Z. Lei, C. Dai, W. Wang, B. Chen, UNIFAC model for ionic liquid-CO2 systems, Aiche Journal 60 (2014) 716–729. [36] Z. Lei, C. Dai, L. Xing, X. Li, B. Chen, Extension of the UNIFAC Model for Ionic Liquids, Industrial & Engineering Chemistry Research 51 (2012) 12135-12144. [37] Z. Lei, J. Zhang, Q. Li, B. Chen, UNIFAC Model for Ionic Liquids, Industrial & Engineering Chemistry Research 48 (2009) 2697-2704. [38] E. Kuhlmann, S. Himmler, H. Giebelhaus, P. Wasserscheid, Imidazolium dialkylphosphates— a class of versatile, halogen-free and hydrolytically stable ionic liquids, Green Chemistry 9 (2007) 233-242. [39] K. Hayamizu, Y. Aihara, H. Nakagawa, T. Nukuda, W.S. Price, Ionic conduction and ion diffusion in binary room-temperature ionic liquids composed of [emim][BF4] and LiBF4, The Journal of Physical Chemistry B 108 (2004) 19527-19532. [40] J. Wang, Y. Tian, Y. Zhao, K. Zhuo, A volumetric and viscosity study for the mixtures of 1-nbutyl-3-methylimidazolium tetrafluoroborate ionic liquid with acetonitrile, dichloromethane, 2butanone and N, N–dimethylformamide, Green Chemistry 5 (2003) 618-622. [41] V. Kiva, E. Hilmen, S. Skogestad, Azeotropic phase equilibrium diagrams: a survey, Chemical Engineering Science 58 (2003) 1903-1953. [42] V. Gerbaud, I. Rodriguez-Donis, Chapter 6–Extractive Distillation, Distillation Equipment & Processes (2014) 201-245. [43] D.B. Van Dongen, M.F. Doherty, Design and synthesis of homogeneous azeotropic distillations. 1. Problem formulation for a single column, Industrial & engineering chemistry fundamentals 24 (1985) 454-463. [44] J.O. Valderrama, P.A. Robles, Critical Properties, Normal Boiling Temperatures, and Acentric Factors of Fifty Ionic Liquids, Industrial & Engineering Chemistry Research 46 (2007) 1338-1344. [45] J.O. Valderrama, R.E. Rojas, Critical properties of ionic liquids. Revisited, Industrial & Engineering Chemistry Research 48 (2009) 6890-6900. [46] W.L. Luyben, I.-L. Chien, Design and control of distillation systems for separating azeotropes, John Wiley & Sons, 2011. [47] W.L. Luyben, Distillation design and control using Aspen simulation, John Wiley & Sons, 2013. [48] R. Smith, Chemical process design, Wiley Online Library, 2005. [49] X. Li, W. Sun, G. Wu, L. He, H. Li, H. Sui, Ionic Liquid Enhanced Solvent Extraction for Bitumen Recovery from Oil Sands, Energy & Fuels 25 (2011). [50] E. Choi, J.G. Mcdaniel, J.R. Schmidt, A. Yethiraj, First-Principles, Physically Motivated Force Field for the Ionic Liquid [BMIM][BF4], Journal of Physical Chemistry Letters 5 (2014) 2670-2674. 15

[51] L.D. Olmo, I. Lage-Estebanez, R. López, J.M.G.D.L. Vega, Alkyl substituent effect on density, viscosity and chemical behavior of 1-alkyl-3-methylimidazolium chloride, Journal of Molecular Modeling 20 (2014) 1-9. [52] E. Quijada-Maldonado, S.V.D. Boogaart, J.H. Lijbers, G.W. Meindersma, A.B.D. Haan, Experimental densities, dynamic viscosities and surface tensions of the ionic liquids series 1-ethyl3-methylimidazolium acetate and dicyanamide and their binary and ternary mixtures with water and ethanol at T = (298.15 to 343.15 K), Journal of Chemical Thermodynamics 51 (2012) 51-58. [53] Y. Cao, T. Mu, Comprehensive Investigation on the Thermal Stability of 66 Ionic Liquids by Thermogravimetric Analysis, Industrial & Engineering Chemistry Research 53 (2014) 8651-8664. [54] A. Efimova, L. Pfützner, P. Schmidt, Thermal stability and decomposition mechanism of 1ethyl-3-methylimidazolium halides, Thermochimica Acta 604 (2015) 129-136. [55] A. Avilés Martínez, J. Saucedo-Luna, J.G. Segovia-Hernandez, S. Hernandez, F.I. GomezCastro, A.J. Castro-Montoya, Dehydration of bioethanol by hybrid process liquid–liquid extraction/extractive distillation, Industrial & Engineering Chemistry Research 51 (2011) 58475855. [56] J. Fu, Simulation of salt-containing extractive distillation for the system of ethanol/water/ethanediol/KAc. 1. Calculation of the vapor-liquid equilibrium for the salt-containing system, Industrial & engineering chemistry research 43 (2004) 1274-1278.

16

Figure 1. Selectivities at infinite dilution of ethanol to water for ILs calculated by the UNIFACLei model at 30℃.

17

Figure 2. ILED process flowsheet for ethanol dehydration.

18

Figure 3. Residue curve maps of ethanol-water with different solvents: (a) [EMIM][BF4] and (b) [BMIM][BF4].

19

Figure 4. Effect of solvent-to-feed ratio on the ethanol-water VLE: (a) [EMIM][BF4] and (b) [BMIM][BF4]. Solid lines represent data calculated by the NRTL model, and dashed lines indicate data predicted by the UNIFAC-Lei model.

20

Figure 5. Composition profiles and temperature profiles of the extractive distillation column of the ethanol-water system with an IL solvent: (a) composition profiles for the case of [EMIM][BF4]; (b) composition profiles for the case of [BMIM][BF4]; (c) temperature profiles.

21

Figure 6. Effect of several operation parameters on distillate composition and reboiler duties: (a) effect of the number of theoretical stages and feed stage on the distillate composition; (b) effect of the number of theoretical stages and feed stage reboiler duties; (c) effect of the reflux ratio and solvent feed stage on distillate composition; (d) effect of the reflux ratio and solvent feed stage on reboiler duties; (e) effect of the reflux ratio and solvent-to-feed molar ratio on distillate composition; (f) effect of the reflux ratio and solvent-to-feed molar ratio on reboiler duties.

22

Table 1. Thermodynamic properties of several ILs ILs

[EMIM][BF4]

[BMIM][BF4]

[EMIM][Cl]

[BMIM][Cl]

[EMIM][OAc]

Viscosity (cp)

66.5 (20℃)a

93.0 (27℃)b

581.2 (25℃)c

1160.4 (25℃)c

132.9 (25℃)d

Td (℃)

413e

399e

242d

257e

221e

αVLE

1.37g

1.37g

1.68g

1.47g

1.63g

a Reference

[49]. b Reference [50]. c Reference [51]. d Reference [52]. e Reference [53]. f Reference [54].

Reference [22].

23

g

Table 2. Operating parameters of the extractive distillation column in the presence of [EMIM][BF4] and [BMIM][BF4] as solvents [EMIM][BF4]

[BMIM][BF4]

Parameter

Case 1

Case 2

Case 3

Case 1

Case 2

Case 3

NT

45

40

35

45

40

35

NIL

8

8

8

6

6

6

NF

39

36

29

39

36

29

IL/F

0.3

0.32

0.32

0.5

0.55

0.55

RR

1.4

1.0

2.2

3

2

2.6

xD, ethanol

0.9990

0.9993

0.9990

0.9986

0.9990

0.9980

QR (kJ/kg of ethanol)

2.2

1.9

2.7

3.4

2.7

3.1

24

Table 3. Configuration of the ILED process using [EMIM][BF4] as a solvent parameter

extractive column

flash tank

NT NF NIL IL/F distillate rate (kmol/h) RR pressure (kPa) temperature of bottoms (℃) temperature of top (℃) temperature of flash tank (℃) QR (kW) QH (kW) Mole fraction in distillate Ethanol Water [EMIM][BF4] Mole fraction in bottom Ethanol Water [EMIM][BF4]

40 34 8 0.32 85 1.0 101.35 133.30 77.98

15 10

109.96 2047.8 170.41 0.9993 0.0007 3.79 e-05

0.0044 0.9956 9.96 e-12

0.0013 0.2988 0.6999

3.68 e-14 0.0002 0.9998

25

Table 4. Energy consumption for ethanol dehydration technologies solvent type

xD, ethanol

MJ/kg of ethanol

[EMIM][BF4]this work glycerol[55] gasoline[15] ethylene glycol-potassium acetate[56] ehtylene glycol-calcium chloride[3]

0.9993 0.9999 0.9990 0.9990 0.9950

2.27 2.66 3.18 3.58 5.02

26

Table 5. TAC of ILED for anhydrous ethanol production extractive distillation column NT NIL NF ID1 (m) RR QC (kW) QR (kW) flash tank ID2 (m) QH (kW) economic analysis capital cost (×106 $) operating cost (×106 $) TAC (×106 $)

Case 1

Case 2

Case 3

45 8 39 1.07 1.4 2221.9 2413.1

40 8 34 0.98 1.0 1851.6 2047.8

35 8 29 1.25 2.2 2962.6 3158.3

1.6 171.22

1.6 170.41

1.6 171.32

0.71 0.60 0.84

0.63 0.52 0.73

0.75 0.78 1.03

27