Development and intensification of a four-column hybrid process of heteroazeotropic distillation and pressure-swing distillation

Journal Pre-proof Development and intensification of a four-column hybrid process of heteroazeotropic distillation and pressure-swing distillation Chao Guang (Conceptualization) (Methodology) (Software) (Writing - original draft), Xiaojing Shi (Software) (Data curation), Xiaoxiao Zhao (Data curation) (Validation), Zhishan Zhang (Supervision) (Conceptualization) (Writing - review and editing), Guijie Li (Project administration) (Funding acquisition)

PII:

S0255-2701(20)30041-6

DOI:

https://doi.org/10.1016/j.cep.2020.107875

Reference:

CEP 107875

To appear in:

Chemical Engineering and Processing - Process Intensification

Received Date:

8 January 2020

Revised Date:

21 February 2020

Accepted Date:

25 February 2020

Please cite this article as: Guang C, Shi X, Zhao X, Zhang Z, Li G, Development and intensification of a four-column hybrid process of heteroazeotropic distillation and pressure-swing distillation, Chemical Engineering and Processing - Process Intensification (2020), doi: https://doi.org/10.1016/j.cep.2020.107875

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Development and intensification of a four-column hybrid process of heteroazeotropic distillation and pressure-swing distillation

Chao Guanga, Xiaojing Shia, Xiaoxiao Zhaoa, Zhishan Zhanga,*, Guijie Lib,* a

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

Technology, Qingdao 266590, China School of Materials Science and Engineering, Shandong University of Science and Technology,

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b

Qingdao 266590, China

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*Corresponding authors: Email: [email protected], [email protected]

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Graphical abstract

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TOC/Abstract graphic

Highlights

A heteroazeotropic and pressure-swing distillation hybrid process is developed.

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Intensified models by dividing-wall column and vapor recompression are explored.

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All proposed processes are economically viable compared to available treatments.

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Abstract

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1.

This article develops a four-column hybrid process of hetero-azeotropic distillation and

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pressure-swing distillation (HAD-PSD) for separating a ternary multi-azeotropic mixture i.e., an organic aqueous solution with a low concentration of isopropanol (IPA) and diisopropylether (DIPE). For improving its economic and energetic performances, an intensified process by heat pump and dividing wall column is proposed, namely HAD-DWC-VRC-PSD. The quantified performance improvement over the HAD-PSD process reveals that the annual energy cost is drastically reduced by 39.7% from 45.5 to 27.4 $ per tonne of IPA and DIPE while the total annual cost is cut by 11.7% from 92.0 to 81.3 $ per tonne of IPA and DIPE. Besides, the 2 / 34

thermodynamic efficiency is increased from 19.80% to 25.96%, and the carbon footprint as an indicator of unsustainable energy use is abated by 59%. Overall, the HAD-DWC-VRC-PSD process is economically viable and eco-sustainable in a way.

Keywords: Heteroazeotropic distillation; Pressure-swing distillation; Dividing wall column; Heat pump; Diisopropylether/isopropanol/water

1. Introduction Isopropanol (IPA) and diisopropylether (DIPE) are widely used in industry as important raw materials [1]. In IPA production, a large amount of organic aqueous solution containing IPA and

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DIPE at low concentrations is often generated and needs to be treated efficiently for acquiring more economic and environmental benefits [2]. However, it is very difficult to separate high-purity DIPE and IPA from the ternary mixture with multiple azeotropes (binary or ternary, homogenous or heterogeneous [3]) by regular distillation. Therefore, some special distillation

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methods have to be selected, such as pressure-swing distillation (PSD) and heterogeneous azeotropic distillation (HAD).

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PSD is an effective method of separating azeotropic mixtures when the composition of azeotrope varies greatly with the change of operating pressure [4,5]. HAD is an approach of

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separating azeotropic or close-boiling mixtures in which a heterogeneous azeotrope with a minimum boiling point needs to be formed and one independent or integrated decanter is used to

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separate dual-liquid phases [6,7]. Zhu et al. [8] studied different PSD sequences for separating an acetonitrile/methanol/benzene ternary mixture. Following this, Aurangzeb and Jana [9] conducted energy intensification on the above PSD sequences via a dividing wall column technique. Chen et

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al. [10] improved the energy performance of HAD through a self-heat recuperation technology in the separation of t-butanol/water/cyclohexane mixture. Shi et al. [11] presented a HAD process to

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separate 2,2,3,3-tetrafluoro-1-propanol/water binary azeotrope using chloroform as an entrainer. All the above-referred processes for azeotrope separation performed high efficiency in energy usage and economics. Distillation is the most common operation of separating liquid mixtures but requires a large amount of energy usage [12-17]. Many energy-saving measures for various special distillation processes have been attempted and developed in recent years, for example, ordinary heat 3 / 34

integration (HI), dividing-wall column (DWC) and vapor recompression (VRC). HI is the most effective method of reducing energy utilization in the distillation system and has been widely used [18-20]. DWC attempts to reduce the remixing effect with respect to some middle components and decrease equipment costs by combining several columns into one column with one or more partitions [11,21-25]. VRC aims to increase the energy efficiency of regular distillation by introducing a mechanical compressor for heat transfer from low-temperature to high temperature [9,14,26-29]. Qian et al. [30] studied a four-product Kaibel DWC for separating alkane and aromatic hydrocarbon quaternary systems, saving about 40% energy compared to the conventional

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distillation sequence. Wang et al. [31] suggested three PSDs with HI for ethylacetate/ethanol, methanol/chloroform, and ethylenediamine/water mixtures, leading to a great reduction of energy consumption and economic costs. Shi et al. [32] explored an energy-saving configuration of VRC

assisted HAD for separating binary azeotropic mixtures of isopropyl alcohol/water and

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pyridine/water using cyclohexane and toluene as the entrainers, respectively. The use of the above intensification technologies improved the thermodynamic driving force or facilitated column

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debottlenecking, thus resulting in the reduction in energy and capital costs and harmful emissions [18,27,33-35].

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This article aims to develop an economical and energy-efficient process for separating an aqueous mixture with a low concentration of IPA and DIPE. A new four-column hybrid process

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with HAD and PSD (HAD-PSD) is proposed by utilizing the features of heterogeneous and pressure-sensitive azeotropes in the system. Further, the HAD-PSD process is enhanced by the

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application of DWC and VRC into the HAD section, leading to two energy-saving processes— HAD-DWC-PSD and HAD-DWC-VRC-PSD. All the processes are rigorously simulated and

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optimized to minimize the total annual costs (TAC) and energy consumption. Simultaneously, the two indexes of exergy efficiency and CO2 emissions are also calculated for a more comprehensive evaluation of the proposed processes.

2. Methodology 2.1 Property analysis The property method of UNIQ-RK is chosen to simulate the DIPE/IPA/water system, in which the UNIQUAC activity coefficient model is used for the liquid phase and the RK equation of state 4 / 34

is used for the VRC process at a high pressure. The high consistency between the experimental and simulated phase equilibrium data has been demonstrated in our previous work [6]. All binary interaction parameters (BIP) derived from the Aspen database are shown in Table 1. The ternary diagram of the DIPE/IPA/water system at atmospheric pressure is shown in Fig. 1(a). It can be observed that the component composition space is divided into three distillation regions (I–III) by several simple-distillation boundaries and meanwhile has a large heterogeneous area that crosses different distillation regions. And the properties of all azeotropes and pure components at 1 atm and 5 atm are listed in Table 2. The composition of a ternary minimum azeotrope has a great

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change as the pressure increases, as shown in Fig. 1(b). The system’s characteristics above will be used to develop the separation processes in this study.

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Table 1. BIPs of the UNIQUAC model for the DIPE/IPA/water system at 1 atm.

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Fig.1. The DIPE/IPA/water system’s phase equilibrium assessment: (a) ternary diagram and (b)

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pressure sensitivity of a ternary azeotrope.

Table 2. The properties of all azeotropes and pure components at 1 atm and 5 atm.

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2.2 Conceptual design

According to the above property analysis, a four-column hybrid process of HAD and PSD

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(HAD-PSD) is developed and the corresponding material balances are displayed in the ternary diagram, as depicted in Fig.2. The section of HAD consists of two columns (C-1 and C-2) and one

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decanter. The fresh feed enters from the upper part of the C-1. All the water is taken out from the bottom of the C-1. The mixture of IPA and DIPE is obtained at the bottom of the C-2. Two overhead vapors are condensed and divided into the organic phase and the aqueous phase in the decanter, as the reflux of the C-1 and the C-2 respectively. The section of PSD constitutes the other two columns (C-3 and C-4) with different operating pressures. The IPA/DIPE mixture from the bottom of the C-2 goes into the C-3. The high-purity IPA and DIPE are obtained as bottom products of the C-3) and high-pressure column (C-4), respectively. 5 / 34

Fig. 2. Conceptual design of the HAD-PSD process.

Attractively, the conventional HAD process, as shown in Fig. 3(a), can be progressively enhanced by two technologies of DWC and VRC. Fig. 3(b) gives an intensified configuration with the DWC, called HAD-DWC. Regarding the construction of the DWC, a vertical dividing wall is placed in the middle section and a liquid collector is set at the left side of the wall in order to prohibit liquid from escaping and vapor from rising. Meantime, a condenser at the top and two

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reboilers at the bottom are collocated. The VRC as one of the heat pump technologies can recover the low-grade energy of overhead vapors in the case of a small top-to-bottom temperature difference. Fig. 3(c) gives a further intensified configuration with VRC, called HAD-DWC-VRC.

A part of vapor at the top of DWC is compressed to higher pressure and temperature. After

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supplying the required heat for the bottom kettle, it mixes with the other part of the vapor and

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enters the condenser.

2.3 Evaluation indexes

Specific energy requirement

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2.3.1

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Fig. 3. The intensification of HAD with DWC and VRC.

Specific energy requirement (EP) refers to the sum of various utilities consumed per unit valuable products, in which the price factor is used to represent the energy grade [36]. It can be

EP 

m1QCond +m2 QReb +m3 WComp FIPA +FDIPE

(1)

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calculated by Eq. (1)

where, Qreb (kW), Qcond (kW) and Wcomp (kW) are the heat duty of reboiler, condenser and compressor, respectively; m1(=0.036), m2(=1.0) and m3(=2.008) are respectively the cost ratios of cooling water, low pressure steam and electricity to low pressure steam; FIPA (kmol/h) and FDIPE (kmol/h) are the flowrate of IPA and DIPE, respectively. 2.3.2

TAC 6 / 34

TAC is the sum of the annualized capital costs and operating costs. The capital costs include the expenditures on column shell, column internals, condenser, reboiler and compressor. The costs of other equipment including pipe, valve, separator, reflux drum, and pump are ignored. The operating costs indicate the consumption of steam, cooling water and electricity. The annual operating time is set to 8000 hours. For the VRC process, isentropic efficiency, mechanical efficiency and motor efficiency are set to 0.8, 1.0, and 0.9, respectively. Its calculation procedure is consistent with our previous works [4,6]. 2.3.3

Thermodynamic efficiency

by Eq. (2) [37].

 F  H  T S   F  H  T S 0

=

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Thermodynamic efficiency generally means the usage efficiency of exergy. It can be determined

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 Q 1  T reb

0

TR    Qcond 1  T0 TC   Wcomp out

(2)

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in

0

feed

where, F (kmol/s), H (kJ/kmol) and S (kJ/(kmol·K)) is the flowrate, enthalpy and entropy of each

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stream, respectively; T0 (K), TR (K) and TC (K) is the temperature of surrounding, reboiler and

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condenser, respectively; Qreb (kW), Qcond (kW) and Wcomp (kW) is the heat duty of reboiler, condenser, and compressor, respectively. CO2 emission

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2.3.4

The CO2 emission is introduced in order to make an environmental assessment of the process.

[CO2 ]emissions 

Qfuel C%   NHV 100

(3)

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Its calculation is described as Eq. (3) [38].

where, α (=3.67) is the molar mass ratio of CO2 and C; NHV (=51600 kJ/kg) is the net heating value of natural gas; C% (=75.5%) the carbon content of natural gas; Qfuel (kW) is the heat released by burnt fuels, as calculated by Eq. (4).

Qfuel 

Qproc  proc

 (h proc  419) 

TFTB  T0 TFTB  Tstack

(4)

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where, λproc (kJ/kg) and hproc (kJ/kg) are the latent heat and enthalpy of stream, respectively; TFTB (=1800℃) and Tstack (=160 ℃) are the temperature of flame and stack in theory, respectively; The enthalpy of the boiler feedwater at 373.15K is set to 419 kJ/kg. 2.4 Optimization procedure Fig. 4 gives a dual-staged iterative optimization procedure. Generally, the computer time required to get the best solution grows exponentially as the number of optimized variables increases. So, the EP-based sensitivity analysis (SA) is used to identify some operational variables

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in the inner loop, which is accomplished by running the Aspen model analysis tool/sensitivity. The other variables in the outer loop are determined by minimizing the TAC, which is performed in

Microsoft Excel. In the HAD-PSD process, such variables as the number of trays (NT1, NT2, NT3,

and NT4), feed locations (NF, NB2, ND3, and ND4), reflux ratios (RR3 and RR4), vapor flow rate (FV),

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and vapor molar composition (XV, IPA and XV, DIPE) need to be optimized. As for the selection of operating pressures, the optimal processes under several different pressures are compared in terms

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of the TAC. Herein, all the design constraints are stated below.

(1) The pressure of the C-4 is estimated to be 5 atm because the greater pressure difference from

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the C-3 results in the greater azeotropic composition change and meanwhile the use of the low-pressure steam (433 K) is still guaranteed.

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(2) The temperature of the Dec-1 is set to 308.2 K for the formation of two liquid phases. (3) Overall mass balances of the components DIPE, IPA, and water are achieved by adjusting the flowrates of B1, B3, and B4.

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(4) The purities of IPA and DIPE are achieved by manipulating RR3 and RR4, respectively. (5) The amounts of IPA and DIPE in the discharge water are achieved by manipulating XV, IPA

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and XV, DIPE.

Fig. 4. The dual-staged iterative optimization procedure for the HAD-PSD process.

Regarding the optimization of the HAD-DWC-PSD process, fifteen independent parameters need to be determined. Among them, nine discrete variables are the number of trays (NT1, NT2, and NT3), the number of trays in the rectifying section (NR), the number of trays in the left stripping 8 / 34

section (NLS), and the number of trays in the feed stage (NF, ND3, NS1, and ND2). Six continuous variables are the liquid distribution ratio (LL/LR), the flow rate and composition of the overhead vapor (FV, XV, IPA, and XV, DIPE), and the reflux ratio (RR2 and RR3). On one hand, some variables are the same as those of the HAD-PSD process or chosen by a simple method. For instance, NT1 and NLS are, respectively, equal to the number of trays in C-2 and C-1 in HAD-PSD. NR is equal to the number of trays in the upper segment of C-2, in which a greater water composition (≥7.5 mol%) can be maintained to reduce the degree of back-mixing. Several design parameters of the PSD section (NT2, NT3, ND3, NS1, ND2, RR2, and RR3) remain unchanged. On the other hand, FV,

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XV, IPA, and XV, DIPE are sequentially optimized through implementing a set of SAs. LL/LR, as an adaptive variable, is adjusted to achieve the purity requirement of water

As far as the design of VRC is concerned, two key variables need to be optimized, i.e., the overhead vapor distributed ratio (V1/V) and the compression ratio (Rcomp). The compressed vapor

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is used to boil the reboiler liquid and itself becomes a saturated liquid. Compared with phase change heat, the change in enthalpy caused by vapor compression is negligible. The vapor

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throttling through the valve is considered an isenthalpic process. With this, the ratio of V1/V can be determined simply based on the fact that the condensation heat of the divided vapor (V1) is

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equal to the heat duty of reboiler. In determining the Rcomp, which is often limited to between 2.5 and 4 for high efficiency [39], the outlet temperature of the compressor must be more than 5K

3

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higher than the reboiler temperature for heat transfer.

Results and discussion

The dilute solution separated in this study comes from the production of IPA and contains a

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small amount of IPA and DIPE and most of the water. It is assumed to have a composition of 7 mol% IPA and 3 mol% DIPE and a flowrate of 100 kmol/h. The separation requirements are to

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obtain IPA and DIPE with purity greater than 99.9 mol% and water with less than 10 ppm of both DIPE and IPA.

3.1 Optimal flowsheets 3.1.1

HAD-PSD process

The optimized flowsheet of the HAD-PSD process is shown in Fig. 5. The fresh feed (F) at 298.2 K is fed into the top tray of the first column (C-1) while the high-purity water (B1) is 9 / 34

removed at the bottom. Two overhead vapors (V1, V2) are fully condensed in the condenser (Cond-1) and the resulting condensate enters a decanter (Dec-1) to obtain two liquid phases. The aqueous phase (Laq) returns to the top tray of the C-1 as reflux whereas the organic phase (Lorg) is fed into the second column (C-2) on the first tray. The mixture of IPA and DIPE that contains trace amounts of water (B2) flows out from the bottom of the C-2, and then into the middle tray of the third column (C-3). The high-purity IPA (B3) is obtained at the bottom of the C-3. The distillate (D3) of the C-3 is pumped into the upper tray of the fourth column (C-4) operating at 5 atm. The high-purity DIPE (B4) is received at the bottom of the C-4. The distillate (D4) of the C-4 is

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recycled to the upper tray of C-3.

Fig. 5. The optimized flowsheet of the HAD-PSD process.

HAD-DWC-PSD process

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3.1.2

Fig. 6 shows the optimized flowsheet of the HAD-DWC-PSD process, in which the HAD

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section is combined into the above-mentioned DWC while the PSD section remains unchanged. The high-purity water and IPA/DIPE mixture are removed as bottom products from the left and

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right stripping sections, respectively. The overhead vapor is condensed and fed into a decanter. The organic phase is fed into the top of the rectifying section. The aqueous phase along with the

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fresh feed is introduced into the left stripping section. In optimizing the DWC, the number of trays required for dehydration is increased from 8 to 12. Besides, most of the organic phase is allocated

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into the right side of the stripping section to ensure the purity of water.

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Fig. 6. The optimized flowsheet of the HAD-DWC-PSD process.

3.1.3

HAD-DWC-VRC-PSD process

Fig. 7 presents the optimized flowsheet of the HAD-DWC-VRC-PSD process, in which a

fraction of the overhead vapor (V1) is recompressed to supply the required heat for the Reb-2. The exhaust vapor is throttled and fed into the Cond-1. Simultaneously, some potential HIs between two columns are implemented and thus a reboiler (Reb-3b) and a feed-effluent heat exchanger 10 / 34

(FEHE) are added. The top vapor of the C-3 is used as the heat source of the Reb-3a. The water from the Reb-1 provides heat for the Reb-3b and then preheats the fresh feed in the FEHE.

Fig. 7. The optimized flowsheet of the HAD-DWC-VRC-PSD process.

3.2 Optimization variables With respect to the HAD-PSD process, Fig. 8 gives the effects of some optimization variables on energy consumption. From Fig. 8(a), the EP gradually decreases until FV decreases to a value

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lower than 65 kmol/h, where an infeasible separation situation is encountered. As the FV decreases, QReb-1 and QReb-2 show a significant decrease whereas QReb-3 and QReb-4 hardly change. From Fig. 8(b), EP is strongly affected by RR3 and RR4 and reaches a minimum value when RR3 = 0.537 and RR4 = 0.334. As shown in Fig. 9(a)-(f), the outer variable number of stages (NT1, NT2, NT3, and

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NT4) and vapor molar composition (XV, IPA and XV, DIPE) are determined by minimizing the TAC.

During this, the trays where the liquid composition closes to the feed composition are selected as

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the optimal feed stages (NF, NB2, ND3, and ND4) as such can effectively decrease the back-mixing and exergy loss in this stage. Also, Fig. 9(g) shows the change in the TAC when the C-4 is

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operated at other pressures and the other optimized parameters have remained.

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Fig. 8. (a) The effect of FV on EP and QReb, and (b) the effect of RR3 and RR4 on EP.

Fig. 9. The effects of optimization variables on the TAC for the HAD-PSD process: (a) NT1, (b)

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NT2, (c) NT3, (d) NT4, (e) XV, IPA, (f) XV, DIPE and (g) P4.

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As for the HAD-DWC-VRC-PSD process, Fig. 10 shows the effects of the compression ratio on

the compressor outlet temperature and electric power. As the compression ratio is lowered, the compressor outlet temperature and electric power are both monotonously decreasing. Thus, the compression ratio is set to 2.5 following the above-mentioned rules. Correspondingly, the outlet temperature is 363.5 K and the electric power is 53.7 kW. The heat transfer temperature difference of the Reb-2 is calculated to reach 17.2K. 11 / 34

Fig. 10. The effects of the compression ratio on the outlet temperature and the electric power.

3.3 Profiles of temperature and composition Fig. 11 provides a comparison of the temperature and liquid composition profiles between the DWC in the HAD-DWC-PSD process and the former two columns in the HAD-PSD process. From Fig. 11(a), the top-bottom temperature difference is 22.8 K for the C-1 and 28.8 K for the C-2. From Fig. 6(b), the two-side temperature difference of the DWC is between 11.0 and 33.2 K.

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Nevertheless, heat transfer between the two sides of the wall is neglected. There are two different temperatures at the bottom because of the use of double reboilers. In addition, the top-bottom temperature difference of the C-1 is 10.8 K. Fig. 11(c) presents the liquid composition profiles in the C-1 and the C-2. Fig. 11(d) gives the liquid composition on both sides of the dividing wall

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across plates 5 through 12. The high-purity water can be removed at the bottom of the left

stripping section. Meanwhile, the right stripping section is used to evaporate the residue water in

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heterogeneous mixture at the top.

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the bottom mixtures. The rectifying section of plates 1 through 4 is mainly used to obtain a

Fig. 11. Temperature profiles: (a) HAD-PSD; (b) HAD-DWC-PSD, and liquid composition

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profiles: (c) HAD-PSD; (d) HAD-DWC-PSD.

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3.4 Energy analysis

The composite curves are often used to analyze the energy use of a process. For the

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HAD-DWC-PSD process with partial HI between Cond-3 and Reb-2, as shown in Fig. 12(a), the energy targets of heating and cooling are 987.4 and 795.9 kW, respectively. The temperature difference at the pinch point is up to 46 K. This minor HI only reduces the energy requirement by 74.7 kW. For the HAD-DWC-VRC-PSD process with HI, as shown in Fig. 12(b), the energy targets of heating and cooling decrease to 473.8 and 438.1 kW respectively and the energy of 639.1 kW is saved because of the use of VRC technology (Q/W = 7.64). It is of note that the pinch temperature difference becomes 5.6 K, that is, the Reb-3b’s heat transfer temperature difference. 12 / 34

Nevertheless, the considerable increase in area requirements is still avoided because the heat load has only 39.1 kW.

Fig. 12. The composite curves of: (a) HAD-DWC-PSD and (b) HAD-DWC-VRC-PSD.

3.5 Comparison of schemes Table 3 gives a comprehensive comparison between the proposed processes. It is shown that the HAD-DWC-PSD process can reduce the energy cost by 8.97%, the capital cost by 4.96% and the

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TAC by 7.03% as compared to the HAD-PSD process. Moreover, the HAD-DWC-VRC-PSD process can save the energy cost by 39.7% and the TAC by 11.7%, but the expensive compressor

leads to a 15.7% increase in the capital cost. However, a longer payback period is allowed (i.e., 5

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years or more), the VRC-assisted process will be more competitive.

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Table 3. A comprehensive comparison between the proposed processes.

Regarding CO2 emissions, compared with the amount of 270.6 kg/h of the HAD-PSD process

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the HAD-DWC-PSD and the HAD-DWC-VRC-PSD reduces by 14.6% and 59.0%. This should be attributed to the reduction of energy consumption and the use of clean electricity.

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As for thermodynamic efficiency, both intensified processes have better performance (greater than 20%) than the HAD-PSD process (19.8%). The reason for the HAD-DWC-PSD is that the use of DWC reduces the amounts of cooling water and high-level steam. For the

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HAD-DWC-VRC-PSD process, a lot of steam can be saved by the use of heat pump driven with electricity, and the ratio of Q/W is up to 7.64. In summary, most of the indicators except for capital

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costs imply that the HAD-DWC-VRC-PSD process is the best scheme.

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Conclusions

This article developed a four-column hybrid process consisting of HAD and PSD (HAD-PSD)

and two intensified schemes (HAD-DWC-PSD, HAD-DWC-VRC-PSD) for handling a dilute solution of IPA, DIPE and water. The optimal conditions of these three processes were determined in an attempt to reduce the TAC and energy consumption. As compared to the HAD-PSD process, 13 / 34

the HAD-DWC-PSD process saved 4.96% capital costs, 8.97% energy costs and 14.6% CO2 emissions while the HAD-DWC-VRC-PSD process reduced 39.7% energy costs and 59.0% CO2 emissions but increased 15.7% capital costs. Besides, the thermodynamic efficiency of these three processes reached up to 19.8%, 23.14%, and 25.96%, respectively. It should be pointed out that the above-mentioned processes without mass separating agents deserve further study in terms of controllability and operability in practice.

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Author Statement

Chao Guang: Conceptualization, Methodology, Software, Writing-original draft.

Xiaoxiao Zhao: Data Curation, Validation.

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Xiaojing Shi: Software, Data Curation.

Zhishan Zhang: Supervision, Conceptualization, Writing-review & editing.

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Guijie Li: Project administration, Funding acquisition

Conflict of Interest statement:

References

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The authors declare no conflicts of interest to this work.

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[1] J. Qi, Q. Zhang, X. Han, Q. Wu, Y. Li, Q. Li, Vapor-liquid equilibrium experiment and process simulation of extractive distillation for separating diisopropyl ether-isopropyl alcohol using

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ionic liquid, J. Mol. Liq. 293 (2019) 111406. http://doi.org/10.1016/j.molliq.2019.111406

[2] L. Petrus, R.W. De Roo, E.J. Stamhuis, G.E.H. Joosten, Kinetics and equilibria of the hydration of propene over a strong acid ion exchange resin as catalyst, Chem. Eng. Sci. 39 (1984) 433-446. http://doi.org/10.1016/0009-2509(84)80041-x [3] M. Yorizane, S. Yoshimura, T. Yamamoto, Measurement of the ternary vapor-liquid equilibrium (isopropyl alcohol-water-isopropyl ether system), Kagaku Kogaku 31 (1967) 451-457. https://doi.org/10.1252/kakoronbunshu1953.31.451 14 / 34

[4] Y. Cui, X. Shi, C. Guang, Z. Zhang, C. Wang, C. Wang, Comparison of pressure-swing distillation and heterogeneous azeotropic distillation for recovering benzene and isopropanol from wastewater, Process Saf. Environ. Prot. 122 (2019) 1-12. https://doi.org/10.1016/j.psep. 2018.11.017 [5] C. Wang, Z. Zhang, X. Zhang, C. Guang, J. Gao, Comparison of pressure-swing distillation with or without crossing curved-boundary for separating a multiazeotropic ternary mixture, Sep. Purif. Technol. 220 (2019) 114-125. https://doi.org/10.1016/j.seppur.2019.03.047

azeotropic

and

pressure-swing

distillations

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[6] C. Guang, X. Shi, Z. Zhang, C. Wang, C. Wang, J. Gao, Comparison of heterogeneous for

separating

the

diisopropylether/isopropanol/water mixtures, Chem. Eng. Res. Des.143 (2019) 249-260. https://doi.org/10.1016/j.cherd.2019.01.021

-p

[7] Y. Fan, Q. Ye, J. Chen, X. Chen, T. Liu, H. Cen, A systematic method for optimum

heterogeneous azeotropic distillation systems with vapor recompression, Chem. Eng. Process

re

143 (2019) 107597. https://doi.org/10.1016/j.seppur.2016.06.009

[8] Z. Zhu, D. Xu, X. Liu, Z. Zhang, Y. Wang, Separation of acetonitrile/methanol/benzene ternary

lP

azeotrope via triple column pressure-swing distillation, Sep. Purif. Technol. 169 (2016) 66-77. http://doi.org/10.1016/j.seppur.2016.06.009

na

[9] M. Aurangzeb, A. K. Jana, Pressure-swing dividing wall column with multiple binary azeotropes: improving energy efficiency and cost savings through vapor recompression, Ind. Eng. Chem. Res. 57 (2018) 4019-4032. http://doi.org/10.1021/acs.iecr.7b03586

ur

[10] J.X. Chen, Q. Ye, T. Liu, H. Xia, S.Y. Feng, Improving the performance of heterogeneous azeotropic distillation via self-heat recuperation technology, Chem. Eng. Res. Des.141 (2019)

Jo

516-528. http://doi.org/10.1016/j.cherd.2018.11.022

[11] P. Shi, D. Xu, J. Ding, J. Wu, Y. Ma, J. Gao, Y. Wang, Separation of azeotrope (2,2,3,3-tetrafluoro-1-propanol + water) via heterogeneous azeotropic distillation by energy-saving dividing-wall column: Process design and control strategies, Chem. Eng. Res. Des.135 (2018) 52-66. http://doi.org/10.1016/j.cherd.2018.05.025

[12] Z.Y. Zhu, X.L. Geng, G.X. Li, X.P. Yu, Y.L. Wang, P.Z. Cui, G.W. Tang, J. Gao, Control 15 / 34

comparison of extractive distillation with two different solvents for separating acetone and tetrahydrofuran, Process Saf. Environ. Prot. 125 (2019) 16-30. http://doi.org/10.1016/j.psep.2 019.03.009 [13] C. Wang, C. Guang, Y. Cui, Z.S. Zhang, X.K. Zhang, Separation of a ternary mixture with multiple azeotropes via pressure-swing distillation, J. Chem. Technol. Biot. 94 (2019) 2023-2033. http://doi.org/10.1002/jctb.5988 [14] A. Singh, G.P. Rangaiah, Development and optimization of a novel process of double-effect distillation with vapor recompression for bioethanol recovery and vapor permeation for dehydration,

J.

Chem.

Technol.

Biot.

94

(2019)

1041-1056.

ro of

bioethanol

http://doi.org/10.1002/jctb.5851

[15] I. Patraşcu, C.S. Bîldea, A.A. Kiss, Eco-efficient butanol separation in the ABE fermentation process, Sep. Purif. Technol. 177 (2017) 49-61. http://doi.org/10.1016/j.seppur.2016.12.008

-p

[16] Z. Zhang, C. Wang, C. Guang, C. Wang, Separation of propylene oxide-methanol-water

mixture via enhanced extractive distillation: Design and control, Chem. Eng. Process. 144

re

(2019) 107651. http://doi.org/10.1016/j.cep.2019.107651

[17] V.H. Grisales Díaz, G. Olivar Tost, Energy efficiency of a new distillation process for

lP

isopropanol, butanol, and ethanol (IBE) dehydration, Chem. Eng. Process. 112 (2017) 56-61. http://doi.org/10.1016/j.cep.2017.01.005

na

[18] X. Li, X. Geng, P. Cui, J. Yang, Z. Zhu, Y. Wang, D. Xu, Thermodynamic efficiency enhancement of pressure-swing distillation process via heat integration and heat pump technology, Appl. Therm. Eng. 154 (2019) 519-529. http://doi.org/10.1016/j.applthermaleng.

ur

2019.03.118

[19] P.V. Mangili, D.M. Prata, Improvement of the butyl acetate process through heat integration: sustainability-based

Jo

A

assessment,

Chem.

Eng.

Process.

135

(2019)

93-107.

http://doi.org/10.1016/j.cep.2018.11.020

[20] J. Gu, X. You, C. Tao, J. Li, Analysis of heat integration, intermediate reboiler and vapor recompression for the extractive distillation of ternary mixture with two binary azeotropes, Chem. Eng. Process. 142 (2019) 107546. http://doi.org/10.1016/j.cep.2019.107546 [21] A.A. Kiss, D.J.P.C. Suszwalak, Enhanced bioethanol dehydration by extractive and 16 / 34

azeotropic distillation in dividing-wall columns, Sep. Purif. Technol. 86 (2012) 70-78. http://doi.org/10.1016/j.seppur.2011.10.022 [22] A. Yang, R. Wei, S. Sun, S. Wei, W. Shen, I.L. Chien, Energy-saving optimal design and effective control of heat integration-extractive dividing wall column for separating heterogeneous mixture methanol/toluene/water with multiazeotropes, Ind. Eng. Chem. Res. 57 (2018) 8036-8056. http://doi.org/10.1021/acs.iecr.8b00668 [23] E.A. Anokhina, A.V. Timoshenko, A.Y. Akishin, A.V. Remizova, Benzene purification from thiophene using dimethylformamide as an entrainer in thermally coupled extractive columns,

Chem.

Eng.

Res.

Des.146

(2019)

391-403.

ro of

distillation

https://doi.org/10.1016/j.cherd.2019.04.003

[24] A.V. Timoshenko, E.A. Anokhina, A.V. Morgunov, D.G. Rudakov, Application of the partially thermally coupled distillation flowsheets for the extractive distillation of ternary azeotropic

-p

mixtures, Chem. Eng. Res. Des. 104 (2015) 139-155. https://doi.org/10.1016/j.cherd.2015.07. 007

re

[25] A. Yang, S. Jin, W. Shen, P. Cui, I.L. Chien, J. Ren, Investigation of energy-saving azeotropic dividing wall column to achieve cleaner production via heat exchanger network and heat

lP

pump technique, J. Clean. Product. 234 (2019) 410-422. https://doi.org/10.1016/j.jclepro.201 9.06.224

na

[26] A. Yang, S. Sun, A. Eslamimanesh, S. Wei, W. Shen, Energy-saving investigation for diethyl carbonate synthesis through the reactive dividing wall column combining the vapor recompression heat pump or different pressure thermally coupled technique, Energy 172

ur

(2019) 320-332. https://doi.org/10.1016/j.energy.2019.01.126 [27] A. Yang, Y. Su, W. Shen, I.L. Chien, J. Ren, Multi-objective optimization of organic Rankine

Jo

cycle system for the waste heat recovery in the heat pump assisted reactive dividing wall column, Energ. Convers. Manage. 199 (2019) 112041. https://doi.org/10.1016/j.enconman.20 19.112041

[28] B. Kiran, A.K. Jana, Thermal integration of vapor recompression in a heat-integrated distillation: Impact of multiple intermediate reboilers, Chem. Eng. Res. Des.114 (2016) 171-179. https://doi.org/10.1016/j.cherd.2016.08.021 17 / 34

[29] M. Yang, X. Feng, G. Liu, Heat integration of heat pump assisted distillation into the overall process, Appl. Energy 162 (2016) 1-10. https://doi.org/10.1016/j.apenergy.2015.10.044 [30] X. Qian, K. Huang, H. Chen, Y. Yuan, L. Zhang, S. Wang, Intensifying Kaibel dividing-wall column via vapor recompression heat pump, Chem. Eng. Res. Des.142 (2019) 195-203. https://doi.org/10.1016/j.cherd.2018.12.015 [31] Y. Wang, K. Ma, M. Yu, Y. Dai, R. Yuan, Z. Zhu, J. Gao, An improvement scheme for pressure-swing distillation with and without heat integration through an intermediate connection to achieve energy savings, Comput. Chem. Eng. 119 (2018) 439-449.

ro of

https://doi.org/10.1016/j.compchemeng.2018.09.012 [32] L. Shi, K. Huang, S.-J. Wang, J. Yu, Y. Yuan, H. Chen, D.S.H. Wong, Application of vapor recompression to heterogeneous azeotropic dividing-wall distillation columns, Ind. Eng. Chem. Res. 54 (2015) 11592-11609. http://doi.org/10.1021/acs.iecr.5b02929

-p

[33] Y. Ma, X. Zhang, Z. Zhu, Y. Wang, J. Gao, P. Cui, Process intensification and waste

minimization for ibuprofen synthesis process, J. Clean. Product. 194 (2018) 396-405.

re

https://doi.org/10.1016/j.jclepro.2018.05.131

[34] C. Wang, C. Guang, Y. Cui, C. Wang, Z. Zhang, Compared novel thermally coupled distillation

sequences

for

separating

lP

extractive

acetonitrile/benzene/methanol,

Chem.

Eng.

Res.

multi-azeotropic Des.136

mixture

(2018)

of

513-528.

na

https://doi.org/10.1016/j.cherd.2018.06.017

[35] N. Van Duc Long, T.N. Pham, M. Lee, Optimal retrofit and debottlenecking using novel multi-effect

dividing

wall

column,

Chem.

Eng.

Process.

127

(2018)

65-71.

ur

https://doi.org/10.1016/j.cep.2018.03.021 [36] X. You, J. Gu, V. Gerbaud, C. Peng, H. Liu, Optimization of pre-concentration, entrainer

Jo

recycle and pressure selection for the extractive distillation of acetonitrile-water with ethylene

glycol,

Chem.

Eng.

Sci.

177

(2018)

354-368.

https://doi.org/10.1016/j.ces.2017.11.035

[37] M. Aurangzeb, A.K. Jana, Vapor recompression with interreboiler in a ternary dividing wall column: Improving energy efficiency and savings, and economic performance, Appl. Therm. Eng. 147 (2019) 1009-1023. https://doi.org/10.1016/j.applthermaleng.2018.11.008 18 / 34

[38] M.A. Gadalla, Z. Olujic, P.J. Jansens, M. Jobson, R. Smith, Reducing CO2 emissions and energy consumption of heat-integrated distillation systems, Environ. Sci Technol. 39 (2005) 6860-6870. https://doi.org/10.1021/es049795q [39] H. Luo, C.S. Bildea, A.A. Kiss, Novel heat-pump-assisted extractive distillation for bioethanol

purification,

Ind.

Eng.

Chem.

Res.

54

(2015)

2208-2213.

Jo

ur

na

lP

re

-p

ro of

http://doi.org/10.1021/ie504459c

19 / 34

(a)

ro of

(b)

Fig.1. The DIPE/IPA/water system’s phase equilibrium assessment: (a) ternary diagram and (b)

Jo

ur

na

lP

re

-p

pressure sensitivity of a ternary azeotrope.

20 / 34

ro of

Jo

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na

lP

re

-p

Fig. 2. Conceptual design of the HAD-PSD process.

21 / 34

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-p

ro of

Fig. 3. The intensification of HAD with DWC and VRC.

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Start

End

Fix P1, P2, P3=1atm, P4=5atm

Get the optimal variables Outer iterative loop

Yes

Is TAC minimal ?

Give NT1 No

Yes

No

Is TAC minimal with NT1?

No

Is TAC minimal with NT1 and NT2?

Give NT2

Yes

Give NT3

Give NT4 No

ro of

Yes Is TAC minimal with NT1, NT2 and NT3?

Yes Give XV, IPA and XV, DIPE

-p

No

Give NF, NB2, ND3, ND4, RR3, RR4 and FV.

Min EP

Subject to: XB1, IPA 10 ppb XB1, DIPE 10 ppb XB3, IPA 99.9 mol% XB4, DIPE 99.9 mol%

lP

SA(NB2) with optimal NF.

Calculate the TAC

re

SA(NF).

Is TAC minimal with NT1, NT2, NT3 and NT4?

na

SA(ND3) with optimal NF and NB2.

SA(ND4) with optimal NF, NB2 and ND3.

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ur

SA(RR3 and RR4) with optimal NF, NB2, ND3, and ND4.

SA(FV) optimal NF, NB2, ND3, ND4, RR3 and RR4.

Fig. 4. The dual-staged iterative optimization procedure for the HAD-PSD process.

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ro of

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re

-p

Fig. 5. The optimized flowsheet of the HAD-PSD process.

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re

-p

Fig. 6. The optimized flowsheet of the HAD-DWC-PSD process.

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ro of

Fig. 7. The optimized flowsheet of the HAD-DWC-VRC-PSD process.

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Fig. 8. (a) The effect of FV on EP and QReb, and (b) the effect of RR3 and RR4 on EP.

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ro of -p re lP na ur Jo Fig. 9. The effects of optimization variables on the TAC for the HAD-PSD process: (a) NT1, (b) NT2, (c) NT3, (d) NT4, (e) XV, IPA, (f) XV, DIPE and (g) P4. 28 / 34

Jo

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na

lP

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-p

ro of

Fig. 10. The effects of the compression ratio on the outlet temperature and the electric power.

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ro of -p

re

Fig. 11. Temperature profiles: (a) HAD-PSD; (b) HAD-DWC-PSD, and liquid composition

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na

lP

profiles: (c) HAD-PSD; (d) HAD-DWC-PSD.

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Fig. 12. The composite curves of: (a) HAD-DWC-PSD and (b) HAD-DWC-VRC-PSD.

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Table 1. BIPs of the UNIQUAC model for the DIPE/IPA/water system at 1 atm. Component, i-j

αij

αji

βij / K

βji / K

IPA-DIPE (VLE)

0

0

129.099

-353.648

2.923

-3.313

-1111.67

1045.58

DIPE-water

(VLE)

0

0

-774.712

-29.592

DIPE-water

(LLE)

-0.322

-1.049

-497.159

202.937

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IPA-water

(VLE)

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Table 2. The properties of all azeotropes and pure components at 1 atm and 5 atm. Component

1atm

5atm Temp (K)

Type

Composition

Temp (K)

Type

DIPE/IPA/water

0.705/0.087/0.208

334.8

Hetero

0.565/0.133/0.301

385.7

Hetero

DIPE/water

0.783/0.217

335.3

Hetero

0.678/0.322

387.2

Hetero

DIPE/IPA

0.773/0.227

339.1

Homo

0.577/0.423

391.8

Homo

DIPE

-

341.6

Homo

-

401.2

Homo

IPA/water

0.647/0.353

352.7

Homo

0.670/0.330

400.7

Homo

IPA

-

355.2

Homo

-

402.7

Homo

water

-

373.2

Homo

-

425.7

Homo

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Composition

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Table 3. A comprehensive comparison between the proposed processes. Performance item

HAD-PSD

HAD-DWC-PSD

HAD-DWC-VRC-PSD

81.16

76.20

93.93

Column vessels

19.68

22.39

22.39

Heat exchangers

61.48

53.81

40.14

Capital costs

(104$)

Compressors Energy costs

31.40

(104$/y)

26.47

24.36

15.95

LP steam

25.70

23.66

13.11

Colling water

0.770

0.699

0.440

Energy-costs-gain

-

-8.97%

-39.7%

Capital-cost-gain

-

-4.96%

+15.7%

53.52

49.76

47.26

TAC-gain

-

-7.03%

CO2 emission (kg/h)

270.6

231.2

Emission reduction

-

+14.6%

Thermodynamic efficiency

19.8%

23.14%

(104$/y)

-11.7% 110.9

+59.0% 25.96%

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TAC

2.40

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Electricity

34 / 34