Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary mixture containing bioethanol

Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary mixture containing bioethanol

Accepted Manuscript Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary m...

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Accepted Manuscript Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary mixture containing bioethanol

Yongteng Zhao, Kang Ma, Wenting Bai, Deqing Du, Zhaoyou Zhu, Yinglong Wang, Jun Gao PII:

S0360-5442(18)30189-0

DOI:

10.1016/j.energy.2018.01.161

Reference:

EGY 12273

To appear in:

Energy

Received Date:

16 November 2017

Revised Date:

22 January 2018

Accepted Date:

29 January 2018

Please cite this article as: Yongteng Zhao, Kang Ma, Wenting Bai, Deqing Du, Zhaoyou Zhu, Yinglong Wang, Jun Gao, Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary mixture containing bioethanol, Energy (2018), doi: 10.1016/j.energy.2018.01.161

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ACCEPTED MANUSCRIPT Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary mixture containing bioethanol Yongteng Zhaoa, Kang Maa, Wenting Baia, Deqing Dub, Zhaoyou Zhua, Yinglong Wang a,*, Jun Gaoc a

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

266042, China b

ShanDong Xin Hua Pharmaceutical Company Limited, ZiBo, 255022, China

c

College of Chemical and Environmental Engineering, Shandong University of Science and

Technology, Qingdao, 266590, China Corresponding Author *E-mail: [email protected] Abstract The major intrinsic obstacle of extractive distillation is the high energy consumption. It is an actual problem for reducing energy consumption of extractive distillation processes. Two thermally coupled ternary extractive distillation processes were studied to separate the ternary azeotropic mixture tetrahydrofuran/ethanol/water using a single component solvent (dimethyl sulfoxide ) and a mixed solvent (dimethyl sulfoxide and ethylene glycol ) as entrainer. The optimal conditions of all ternary extractive distillation processes were obtained based on the minimal total annual cost. Thermodynamic efficiency and CO2 emissions index were also considered to evaluate the energy efficiency and environmental impact of alternative ternary extractive distillation processes. The results show that the use of mixed entrainer can result in reduction in both energy consumption and total annual cost for the same ternary extractive distillation configuration. Comparisons of the conventional ternary extractive distillation process and thermally coupled ternary extractive distillation process 1 (combining extractive distillation column with entrainer-recovery column) with mixed entrainer show that a thermally coupled extractive distillation sequence with a side rectifier present the best results. However, thermally coupled ternary extractive distillation process 2 (combining extractive distillation column with entrainer-recovery column) does not show good result due to existence of remixing effect. Keywords: extractive distillation; thermally coupled; total annual cost; azeotrope 1. Introduction 1

ACCEPTED MANUSCRIPT Tetrahydrofuran (THF) and ethanol are both excellent organic solvents. Ethanol, an important biomass energy source, can be obtained by the conversion of various biomasses through microbial fermentation. THF have the potential to become promising biofuel for internal combustion engines due to its high heating value [1]. There is an effluent containing THF, ethanol, and water in some chemical and pharmaceutical processes. Distillation is the most common method used to separate mixtures in the chemical and pharmaceutical industries. However, it is difficult to effectively separate the azeotropic or closeboiling mixtures by conventional distillation. Special distillation technologies such as pressureswing distillation [2-6], azeotropic distillation [7-10], and extractive distillation [11-14] are adopted to achieve the separation target. Pressure-swing distillation takes advantage of characteristic that the composition of azeotrope has a significant shift with pressure to achieve separation, so it is only applicable to the azeotropic mixture that is sensitive to pressure. Azeotropic distillation can separate the mixtures with the aid of an entrainer, nevertheless the azeotropic system also brings some challenges like multiple steady states and high energy requirement. Extractive distillation is an important technique and is widely used to separate binary or multiple azeotropes in chemical industry due to flexible selection of the possible entrainers. Gil et al. [15] studied the dehydration of ethanol by extractive distillation using glycerol as entrainer. Luyben

[16]

explored

the

ternary

extractive

distillation

for

the

separation

of

benzene/cyclohexane/toluene using dimethyl formamide as entrainer. Shen et al. [17] proposed a systematic approach to design a two-column extractive distillation process for separating azeotropes with heavy entrainers. Arifin and Chien [18] compared extractive distillation and heterogeneous azeotropic distillation for separating the azeotrope of isopropyl alcohol and water, and the results showed that the extractive distillation has better economy. Luyben [19] made a comparison of extractive distillation and pressure-swing distillation for separating acetone and methanol. The results indicated that the extractive distillation process has lower costs compared to the pressure-swing distillation. Although extractive distillation has been widely used for the separation of azeotropes, its major intrinsic obstacle is still the high energy consumption. It is an actual problem for reducing energy consumption of extractive distillation processes. The traditional energy-saving ways for extractive distillation are implemented by searching for high-selective entrainers [12, 20-22], determining 2

ACCEPTED MANUSCRIPT optimal distillation sequence [23-24], or optimizing operation parameters [25-26]. Dai et al. [21] explored the separation of ethanol/water using a mixture of organic solvent ethylene glycol (EG) and ionic liquids as entrainer, reducing energy and material consumption compared with the process using EG as entrainer. Luyben [24] studied direct and indirect extractive distillation separation sequences with an intermediate-boiling solvent triethylamine to separate methanol and toluene, and the results demonstrated that the indirect separation sequence is more energy efficient compared with direct sequence. You et al. [25] investigated lower pressure design to reduce energy consumption of extractive distillation for separating diisopropyl ether and isopropyl alcohol. Nowadays, some energy-saving technologies have been proposed to reduce the energy consumption of distillation processes based on process intensification, such as divided wall column [27-33], thermal coupling of columns [16, 34], heat-integrated distillation [35], heat pump-assisted distillation [36-37], which have been applied to the extractive distillation process. Sun et al. [38] investigated the application of the extractive dividing wall column to separate benzene/cyclohexane, which could achieve up to 22% saving of the total reboiler duties. Gordênia et al. [39] proposed a systematic procedure based on stage equilibrium for obtaining an optimized extractive dividing-wall column configuration in terms of operability and design. Salvador et al. [40] explored the design and control of an extractive dividing-wall distillation column for ethanol dehydration using ethylene glycol as entrainer, the results indicated the extractive dividing-wall distillation column can result in significant savings over the conventional process. Timoshenko et al. [41] introduced many extractive distillation flowsheets to separate ternary mixtures with azeotropes and evaluated the applicability of the extractive distillation flowsheets with the partially thermally coupled distillation columns for all types of vapor–liquid equilibrium diagram. Luyben [19] investigated the heat-integrated extractive distillation to separate acetone and methanol leading to 27% energy saving. Luo et al. [37] advocated a novel heat-pump-assisted extractive dividing wall column sequence for bioethanol purification, and the results showed that approximately 24% total annual cost (TAC) savings can be achieved for this innovative process. In our previous work [42], the ternary extractive distillation processes using two single component solvents (dimethyl sulfoxide (DMSO) and EG) and a mixed solvent (the mixture of DMSO and EG) as entrainers were explored for separating the ternary mixture of 3

ACCEPTED MANUSCRIPT THF/ethanol/water. Mixed entrainer was introducted to reduce TAC and energy consumption of the process by a tradeoff of entrainer performance between two extractive distillation columns. However, the ternary extractive distillation process combining mixed entrainer and process intensification technology is not investigated. The ternary extractive distillation process combining mixed entrainer with process intensification was explored in this work. Two thermally coupled ternary extractive distillation (TCTED) sequences using a single component solvent and a mixed solvent as entrainers for separating the ternary azeotropic mixture THF/ethanol/water were studied. The economical evaluations of the TCTED processes were carried out to estimate their feasibilities. Moreover, the thermodynamic efficiency and CO2 emissions of the TCTED processes were also calculated to evaluate their performance from the perspective of energy efficiency and environmental impact. 2. Performance evaluation methods of process design Three common criteria consisting of TAC, CO2 emissions, and thermodynamic efficiency were used for the evaluation of process design in this work. 2.1 Economic evaluation TAC includes annual capital costs and operating costs and is usually used for an economic evaluation criterion of process design. It can be described as eq 1, TAC ($/year) = annual operating costs + annual capital costs

(1)

Annual operating costs mainly include steam costs for reboilers and cooling water costs for condensers, Annual operating costs = steam costs

+ cooling water costs

(2)

The capital costs containing the costs of distillation column shell and heat exchangers are annualized over a period which is often referred to as plant life time, Annual capital costs = capital costs/plant life time

(3)

The plant life time of 3 years is assumed to calculate the annual capital costs. The basis of economics, equipment sizing, and corresponding prices are consistent with our previous work [42]. 2.2 Evaluation of CO2 emissions for process design CO2 emissions can be used to evaluate the environmental benefits of process design. CO2 emissions (kg/h) are calculated by the following model [43], 4

ACCEPTED MANUSCRIPT

[CO2]

QFuel C%

Emiss

(4)

= ( NHV )(100)α

where α (=3.67) is the molar masses ratio of CO2 and C, NHV is the net heating value of the fuel with a C% carbon content. Heavy fuel oil is assumed to supply stream heat in this study. Values for NHV and C% are 39771 kJ/kg and 86.5 for heavy fuel oil. QFuel is the amount of fuel burnt (kW) and depends on the heat duty (QProc) according to eq 5, QFuel =

Qproc

TFTB - To

λproc

FTB

(hproc - 419)T

(5)

- Tstack

where λProc (kJ/kg) and hProc(kJ/kg) are the latent heat and enthalpy of utility steam. TFTB, TStack and T0 are the flame temperature of the boiler flue gases, the stack temperature, and the ambient temperature, respectively. For the boiler feed water, input temperature and enthalpy values of 373.15 K and 419 kJ/kg were used. 2.3 Evaluation of thermodynamic efficiency for process design The thermodynamic efficiency (η) is the estimation criterion of the energy economy evaluation the process design. The thermodynamic efficiency reported by Seader et al. is shown in eq 6: Wmin

(6)

η = LW + W

min

where the Wmin [kJ/h] and LW [kJ/h] are the minimum work of separation and the lost work, respectively, which can be described as eqs 7 and 8: Wmin = ∑out of systemnb - ∑into systemnb

(7)

b is the availability function and is defined as b = h − T0s ,where n [kmol/s] is mole flow rate; h [kJ/kmol] is enthalpy; s [kJ/kmol K]is molar entropy; and T0 [K] is the surrounding temperature. Ex = Wmin + LW

( ) T0

= ∑into systemQR 1 - T

R

( ) T0

- ∑out systemQC 1 - T

C

- Ws

(8)

where Ex [kW] presents exergy consumption of the system; QR[kW] and TR[K] are heat duty and temperature of reboilers, respectively; QC[kW] and TC[K] are heat duty and temperature of condensers, respectively; and Ws [kW] is shaft work. The thermodynamic efficiency of the different configurations can be calculated on the basis of the simulation results using the above equations. 3. Process design of ternary extractive distillation In this paper, the commercial software Aspen Plus (V 8.4) was used to investigate the ternary 5

ACCEPTED MANUSCRIPT extractive distillation process for separating the ternary mixture of THF/ethanol/water based on Non-random two liquid (NRTL) model. The initial feed flow rate was set at 100 kmol/h with the composition of 30 mol% THF, 30 mol% ethanol, and 40 mol% water. The purities of three products were set at no less than 99.9 mol%, and the impurity of entrainer was specified at 0.001 mol%. Optimization of conventional ternary extractive distillation processes were explored in our previous work [42]. For thermally coupled ternary extractive distillation process 1 (TCTED 1), the design variables including total stages (NT1), fresh feed stage (NF1), entrainer feed stage (NFE1), and entrainer flow rate (EF1) of the first extractive distillation column, total stages (NT2), fresh feed stage (NF2), entrainer feed stage (NFE2), and entrainer flow rate (EF2) of the second second extractive distillation column, total stages (NT3), and fresh feed stage (NF3 )of the entrainer recovery column, the stage of sidestream (NS) and flowrate of sidestream (FS) need to be optimized. To promote optimization, sequential iterative optimization procedure was established as shown in Figure 1, in which reflux ratios were optimized based on the design spec inside Aspen Plus. For thermally coupled ternary extractive distillation process 2 (TCTED 2), the design variables including NT1, NF1, NFE1, and EF1 of the first extractive distillation column, NT2, fresh feed stage (NF2), NFE2, and EF2 of the second extractive distillation column, NT3 of the entrainer recovery column, NS and FS need to be optimized. The sequential iterative optimization procedure of TCTED 2 was established as shown in Figure 2. 3.1 Conventional ternary extractive distillation process (CTED) The CTED includes two extractive distillation columns and an entrainer-recovery column. The THF/ethanol/water mixture and the partial entrainer are fed into the first extractive distillation column (C1). The entrainer can alter the relative volatility of THF/ethanol and THF/water causing THF to move toward the top part and water along with ethanol to move toward the bottom part of C1. The bottom stream of C1 and another part of the entrainer are fed into the second extractive distillation column (C2) for separating ethanol and water. The entrainer can also alter the relative volatility of ethanol and water causing ethanol to move toward the top part and water to move toward the bottom part of C2. The bottom stream of C2 is fed into the entrainer recovery column (C3) to produce water in the distillate and entrainer in the column bottom. Entrainer is recycled back to two extractive distillation columns. To balance tiny entrainer losses in both distillate 6

ACCEPTED MANUSCRIPT streams, the small makeup stream of entrainer is added. The flowsheet of the CTED with single entrainer DMSO is shown in Figure 3, in which the optimal operating parameters were obtained by sequential iterative optimization procedure based on minimum TAC in our previous work [42]. There are some slight differences due to the different setting for impurity of entrainer in the bottom of C3. The liquid composition profile of the CTED with DMSO is shown in Figure 4. The composition of ethanol goes through a maximum in the middle of stripping and then decreases toward the column bottom in C1, which indicates that there is a remixing effect in C1. A prominent remixing effect also exhibits in the stripping section of C2 with the composition of water going through a rise and then decreasing toward the column bottom. For C3 with negligible THF and ethanol, the composition profile is normal and a light component (water) enriched toward the top of the column and a heavy component (DMSO) to the bottom. The optimal flowsheet of the CTED with mixed entrainer (60 mol% DMSO+40 mol% EG) based on minimum TAC is shown in Figure 5. The liquid composition profile of the CTED with mixed entrainer is shown in Figure 6. Remixing effect is broadly consistent with the CTED with single entrainer. Both the composition of ethanol in C1 and water in C2 also go through a maximum in the middle of stripping and then decreases toward the column bottom in corresponding column. 3.2 Thermally coupled ternary extractive distillation process 1 (TCTED 1) A coupled sequence of ternary extractive distillation is combining two extractive distillation columns. The TCTED 1 requires two distillation columns and a rectifier column, in which the vapor traffic of the rectifier column is provided by a sidedraw from the first extractive distillation column (C1). The bottom stream of C1 is fed into the entrainer recovery column to produce water in the distillate and entrainer in the column bottom. For thermally coupled process, the flowrate of vapor to rectifier column is a vital parameter. The effect of different flowrate of vapor to rectifier column on the total energy consumption of reboiler (Qtotal) and TAC for TCTED 1 with single entrainer and mixed entrainer were explored, which are plotted in Figures 7 and 8. As the flowrate of vapor to rectifier column increase, Qtotal and TAC have a sharp increase. So the flowrate of vapor to rectifier column should be as small as possible in the case of meeting the purity of the product. The optimal TCTED 1 using DMSO as entrainer based on minimum TAC is illustrated in Figure 9. It is observed that all the three product purities meet the specification. The Qtotal of TCTED 1 with DMSO reduces from 2386.2 kW for CTED process with DMSO (in Figure 3) to 7

ACCEPTED MANUSCRIPT 2335.7 kW. The reduction in the reboiler duties (2.12%) is not significant. The optimal TCTED 1 using mixed solvent as entrainer based on minimum TAC is shown in Figure 10. There is a greater reduction (9.11%) in the reboiler duties compared with TCTED 1 process with DMSO. The liquid composition profiles of the TCTED 1 with DMSO and mixed entrainer are shown in Figures 11 and 12. The remixing phenomenon of C2 is relieved in the TCTED 1. 3.3 Thermally coupled ternary extractive distillation process 2 (TCTED 2) Another coupled sequence of ternary extractive distillation is combining extractive distillation column with entrainer-recovery column. The TCTED 2 also requires two distillation columns and a rectifier column, in which the vapor traffic of the rectifier column is provided by a sidedraw from the second extractive distillation column (C2). Entrainer from the bottom stream of C2 is recycled back to two extractive distillation columns. The optimal TCTED 2 using DMSO as entrainer based on minimum TAC is illustrated in Figure 13. There is a slight increase in the reboiler duties compared with CTED process with DMSO. The optimal TCTED 2 using mixed solvent as entrainer based on minimum TAC is illustrated in Figure 14. The Qtotal for TCTED2 with mixed entrainer has a slight reduction compared with CTED process with DMSO. However, TCTED 2 with mixed entrainer do not show good results compared with CTED with mixed entrainer. The liquid composition profiles of the TCTED 2 with DMSO and mixed entrainer are shown in Figures 15 and 16. The remixing phenomenon of C2 is not relieved in the TCTED 2. 4. Results and discussion The processes of CTED, TCTED 1, and TCTED 2 with single entrainer (DMSO) and mixed entrainer (60 mol% DMSO+40 mol% EG) were compared and their performance with respect to TAC, CO2 emissions, and thermodynamic efficiency were discussed in this section. The TACs of all configurations were calculated and the corresponding results of economics and energy consumption were summarized in Table 1. TCED with mixed entrainer can decrease Qtotal by approximately 4.28% compared with the process with single entrainer. In comparison to TCTED 1 with single entrainer, this reduction in TCTED 1 with mixed entrainer is nearly 7.15% for Qtotal and 8.08% for TAC. For TCTED 2 with mixed entrainer, this reduction is nearly 3.22% for Qtotal and 1.71% for TAC compared with TCTED 2 using single entrainer. Thus, for the same ternary extractive distillation configuration, the use of mixed entrainer can result in reduction in both energy consumption and TAC. 8

ACCEPTED MANUSCRIPT TAC and Qtotal of TCTED 1 with mixed entrainer have a significant reduction when compared with other processes. The TCTED 1 with mixed entrainer can achieve more than 8.65% TAC savings compared with TCED with single entrainer, in which the Qtotal can reduce 9.11%. However, TAC and Qtotal of TCTED 1 with single entrainer only have a minor reduction compared with TCED with single entrainer. This is because the performance of single entrainer DMSO is relatively poor for the separation of ethanol and water [42], and a large vapor flowrate to rectifier column is required to meet product purity increasing the loading of C1. In addition, TCTED 2 does not show good result compared with CTED and TCTED 1 due to still existing remixing phenomenon. Table 2 lists the results of the thermodynamic efficiency and CO2 emissions of the all configurations. As shown in Table 2, the minimum work of separation for all process is approximate. In general, thermodynamic efficiency in distillation columns is low (around 10%), however, it is below 10% (around 6.5%) for all configurations in this work. The reason may be that the azeotropic system is difficult to separate and additional loss work (the work consumed by the recovery of the entrainer) is needed to achieve separation. There are three binary azeotropes in the THF/ethanol/water system, and it is necessary to add entrainer to achieve effective separation. However, the work consumed by the recovery of the entrainer is the loss of work rather than effective separation work, which increases the loss of work. Therefore, the thermodynamic efficiency of extractive distillation column is lower than convention distillation column. The thermodynamic efficiency of TCTED 1 with mixed entrainer is higher than other configurations, and it is minor improved from 6.37% to 6.70%. However, the thermodynamic efficiency of TCTED 2 with single entrainer and mixed entrainer is lower than other configurations. It demonstrates that the TCTED 2 is not an effective separation method for the low thermodynamic efficiency. The CO2 emissions for different sequences show a similar trend to their energy consumptions. As a result, TCED with mixed entrainer can decrease CO2 emissions by approximately 4.28% compared with the process with single entrainer. There is a slight decrease for TCTED 1 with single entrainer (reduced by 2.11%) and TCTED 2 with mixed entrainer (reduced by 2.15%), in comparison to TCED with single entrainer. However, TCTED 2 with single entrainer is higher than other configurations and increases by 1.11% for CO2 emissions compared with TCED with single entrainer, which demonstrates that the TCTED 2 is not an 9

ACCEPTED MANUSCRIPT effective separation method due to the high CO2 emissions. TCTED 1 with mixed entrainer presents the lowest CO2 emissions with 733.20 kg/h among configurations, and can reduce by 9.11% compared with CTED with single entrainer. Therefore, it can be concluded that the TCTED 1 with mixed entrainer has not only a high thermodynamic efficiency but also a greater advantage than other designs in the economic and environmental aspect. 5. Conclusion The ternary extractive distillation processes combining mixed entrainer with process intensification for the separation of tetrahydrofuran/ethanol/water were explored. The TAC, thermodynamic efficiency and CO2 emissions index of the thermally coupled ternary extractive distillation processes were calculated to evaluate their performance from the perspective of economic, energy efficiency and environmental impacts. Comparisons of same ternary extractive distillation configuration with single and mixed entrainer demonstrate that the mixed entrainer have the advantages on energy efficiency and economics. Remixing effect in two extractive distillation columns is main factors influencing energy consumption for conventional ternary extractive distillation processes. The thermally coupled ternary extractive distillation process 1 (combining two extractive distillation columns) with mixed entrainer is the most energy-saving process and also show apparent benefits on economics and environment aspects. The main reason is because the remixing effect is relieved and the good performance of mixed entrainer enhances the relative volatility of the original component. Moreover, comparisons of the conventional ternary extractive distillation process and thermally coupled ternary extractive distillation process 2 (combining extractive distillation column and entrainer-recovery column) show that a thermally coupled extractive distillation sequence with a side rectifier did not always present the best results due to still existing remixing.

Author information Corresponding Author E-mail: [email protected] The authors declare no competing financial interest.

Acknowledgements This work is supported by the National Natural Science Foundation of China (No. 21776145), National Natural Science Foundation of China (No. 21676152). 10

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ACCEPTED MANUSCRIPT Chemical Engineering 2018, 110, 93-105. [33] Kim, Y. H. Energy saving of benzene separation process for environmentally friendly gasoline using an extended DWC (divided wall column). Energy 2016, 100, 58-65. [34] Anokhina, E.; Timoshenko, A. Criterion of the energy effectiveness of extractive distillation in the partially thermally coupled columns. Chemical Engineering Research and Design 2015, 99, 165175. [35] Knapp, J. P.; Doherty, M. F. Thermal integration of homogeneous azeotropic distillation sequences. Aiche Journal 2010, 36 (7), 969-984. [36] You, X.; Rodriguez-Donis, I.; Gerbaud, V. Reducing process cost and CO2 emissions for extractive distillation by double-effect heat integration and mechanical heat pump. Applied Energy 2016, 166, 128-140. [37] Luo, H.; Bildea, C. S.; Kiss, A. A. Novel Heat-Pump-Assisted Extractive Distillation for Bioethanol Purification. Industrial & Engineering Chemistry Research 2015, 54 (7), 2208-2213. [38] Sun, L.; Wang, Q.; Li, L.; Zhai, J.; Liu, Y. Design and Control of Extractive Dividing Wall Column for Separating Benzene/Cyclohexane Mixtures. Industrial & Engineering Chemistry Research 2014, 53 (19), 8120-8131. [39] Cordeiro, G. M.; de Figueirêdo, M. F.; Ramos, W. B.; Sales, F. A.; Brito, K. D.; Brito, R. P. Systematic Strategy for Obtaining a Dividing-Wall Column Applied to an Extractive Distillation Process. Industrial & Engineering Chemistry Research 2017, 56 (14), 4083-4094. [40] Tututi-Avila, S.; Jiménez-Gutiérrez, A.; Hahn, J. Control analysis of an extractive dividing-wall column used for ethanol dehydration. Chemical Engineering and Processing: Process Intensification 2014, 82, 88-100. [41] Timoshenko, A. V.; Anokhina, E. A.; Morgunov, A. V.; Rudakov, D. G. Application of the partially thermally coupled distillation flowsheets for the extractive distillation of ternary azeotropic mixtures. Chemical Engineering Research and Design 2015, 104, 139-155. [42] Zhao, Y.; Zhao, T.; Jia, H.; Li, X.; Zhu, Z.; Wang, Y. Optimization of the composition of mixed entrainer for economic extractive distillation process in view of the separation of tetrahydrofuran/ethanol/water

ternary

azeotrope.

Journal

of

Chemical

Technology

&

Biotechnology 2017, 92 (9), 2433-2444. [43] Gadalla, M.; Olujic, Z.; Derijke, A.; Jansens, P. Reducing CO2 emissions of internally heatintegrated distillation columns for separation of close boiling mixtures. Energy 2006, 31 (13), 2409-2417.

13

ACCEPTED MANUSCRIPT Table 1. Results of economics and energy consumption for all configurations. TCED

TCTCD1

TCTCD2

single entrainer

mixed entrainer

single entrainer

mixed entrainer

single entrainer

mixed entrainer

QR1 (kW)

761.8

840.2

1696.7

1579.4

761.8

840.1

QR2 (kW)

971.5

791.1

-

-

1650.8

1494.7

QR3 (kW)

652.9

652.8

629.7

589.4

-

-

Qtotal (kW)

2386.2

2284.1

2335.7

2168.8

2412.6

2334.8

Qtotal saving

-

4.28%

2.12%

9.11%

-1.11%

2.15%

TIC (105$)

10.178

9.121

10.283

9.315

10.239

10.599

5.512

5.274

5.423

5.030

5.723

5.524

TAC (105$/year)

8.905

8.315

8.850

8.135

9.136

9.057

TAC saving

-

6.63%

0.62%

8.65%

-2.59%

-1.71%

operation cost (105$/year)

14

ACCEPTED MANUSCRIPT Table 2. Results of the thermodynamic efficiency (η) and CO2 emissions of the all configurations. TCED

TCTCD1

TCTCD2

single entrainer

mixed entrainer

single entrainer

mixed entrainer

single entrainer

mixed entrainer

Wmin (kW)

48.20

48.06

47.56

46.14

47.82

48.05

LW(kW)

709.02

725.86

707.99

641.98

753.88

724.02

η

6.37%

6.62%

6.23%

6.70%

5.96%

6.22%

806.65

772.16

789.67

733.20

815.63

789.33

-

4.28%

2.11%

9.11%

-1.11%

2.15%

CO2 emissions (kg/h) CO2 emissions saving

15

ACCEPTED MANUSCRIPT Figure 1. Sequential iterative optimization procedure of TCTED 1.

16

ACCEPTED MANUSCRIPT Figure 2. Sequential iterative optimization procedure of TCTED 2.

17

ACCEPTED MANUSCRIPT Figure 3. Optimal flowsheet of the CTED process with single entrainer DMSO.

18

ACCEPTED MANUSCRIPT Figure 4. Liquid composition profile in the CTED with single entrainer DMSO

19

ACCEPTED MANUSCRIPT Figure 5. Optimal flowsheet of the CTED process with mixed entrainer of DMSO and EG.

20

ACCEPTED MANUSCRIPT Figure 6. Liquid composition profile in the CTED mixed entrainer of DMSO and EG.

21

ACCEPTED MANUSCRIPT Figure 7. The effect of different flowrate of vapor to rectifier column on Qtotal and TAC for TCTED1 with single entrainer.

22

ACCEPTED MANUSCRIPT Figure 8. The effect of different flowrate of vapor to rectifier column on Qtotal and TAC for TCTED1 with mixed entrainer.

23

ACCEPTED MANUSCRIPT Figure 9. Optimal flowsheet of the TCTED1 process with single entrainer DMSO.

24

ACCEPTED MANUSCRIPT Figure 10. Optimal flowsheet of the TCTED1 process with mixed entrainer of DMSO and EG.

25

ACCEPTED MANUSCRIPT Figure 11. Liquid composition profile in the TCTED1 with single entrainer DMSO.

26

ACCEPTED MANUSCRIPT Figure 12. Liquid composition profile in the TCTED1 with mixed entrainer of DMSO and EG.

27

ACCEPTED MANUSCRIPT Figure 13. Optimal flowsheet of the TCTED2 process with single entrainer DMSO.

28

ACCEPTED MANUSCRIPT Figure14. Optimal flowsheet of the TCTED2 process with mixed entrainer of DMSO and EG.

29

ACCEPTED MANUSCRIPT Figure 15. Liquid composition profile in the TCTED2 with single entrainer DMSO

30

ACCEPTED MANUSCRIPT Figure 16. Liquid composition profile in the TCTED2 with mixed entrainer of DMSO and EG.

31

ACCEPTED MANUSCRIPT 1. The strategy of mixed entrainer and thermally coupled technology are combined. 2. Mixed entrainer can reduce TAC for the same ternary extractive distillation process. 3. The TCTED1 with mixed entrainer could achieve more than 8.65% TAC savings.