Energy-Efficient Design of Downstream Separation To Produce n

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Energy-efficient design of downstream separation to produce n-butanol by several heat integrated technologies Hui Xia, Qing Ye, Shenyao Feng, Jingxing Chen, and Tong Liu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b02077 • Publication Date (Web): 10 Sep 2018 Downloaded from http://pubs.acs.org on September 11, 2018

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Industrial & Engineering Chemistry Research

Energy-efficient design of downstream separation to produce n-butanol by several heat integrated technologies Hui Xia, Qing Ye*, Shenyao Feng, Jingxing Chen, and Tong Liu

Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, Jiangsu 213164, China

AUTHOR INFORMATION *Tel.: +86 519 86330355. Fax: +86 519 86330355. E-mail: [email protected].

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Bio-butanol is a widely used biofuels and it is traditionally produced mainly via the fermentation process of Acetone-Butanol-Ethanol (ABE). However, the separation of the ABE fermentation broth featured with low concentration of N-butanol in the presence of butyric acid and acetic acid consumes considerable energy. For the sake of reducing the capital cost as well as the energy consumption greatly, a novel DWC-SHR process was proposed in the paper to achieve further energy saving through the combination of dividing wall column technology and the self-heat recuperation technology. Moreover, the heat exchanger network (HEN) can be applied to design the HEN of the DWC-SHR process. The DWC-SHR process can be compared with the base process as well as the heat integrated processes (HI-A process and HI-B process) from the point of the energetic, economic as well as the environmental impact. The results illustrated that the DWC-SHR process can achieve 71.13%, 57.87% and 47.79% savings of energy consumption compared to that of the base process, HI-A process and the HI-B process, respectively. In addition, the DWC-SHR process exhibits great advantages in economic performance as well as the environmental performance. The thermodynamics efficiency of the DWC-SHR process is significantly improved compared to that in the base process as well as the heat integrated process (HI-A process and HI-B process).

Keywords:

ABE fermentation; Dividing wall column; Self-heat recuperation;

Energy saving


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Nomenclature ABE

Acetone–butanol–ethanol

AOC

Annual operating cost

CO2

Carbon dioxide

CCC

Cold composition curve

COP

Coefficient of performance

C%

Carbon content

[CO2]emissions

CO2 emissions

DWC

Dividing wall column

DWC-SHR

Dividing Wall Column - Self-Heat Recuperation

Ex

Exergy of the process

EXQ

Energy of an amount of heat

EXloss

Energy loss

GCC

Grand Composite Curve

HPC

High pressure column

HCC

Hot composition curve

HEN

Heat exchanger network

H

Enthalpy of stream

LPC

Low pressure column

NHV

Net heating value

PSD

Pressure swing distillation

PP0

Compression ratio

QFH

Hot utility requirements

QCW

Cold utility requirements

Qcon

Energy consumption

QComp

Compressor duty

QR

Reboiler duty

Qc

The condenser duty

RD

Reactive distillation

S

Entropy of stream

SHRT

Self-heat recuperation technology

T-H

Temperature-heat

TETB

Flame temperature



TR

Reboiler temperature

Tstack

Stack temperature

TAC

Total annual cost

T0

Environmental temperature

Tc

Condenser temperature

TIC

Total investment costs

WILS-NTH

‘Wilson/Nothnag el equation of state with Henry’s law’

Wmin

Ideal work of the process

α

Ratio of mass fraction of CO2 and C

λproc

Latent heat

µ

Thermodynamic Efficiency


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1. Introduction Recently, biofuels are receiving public concern as well as scientific attention, due to the depleted fossil fuel, tightening legislation and environmental impacts considering the overuse of fossil fuels and the greenhouse gases emissions in the air1–4. Among the biofuel alternatives, bio-butanol is a promising alternative biofuel. In comparison with other biofuels, bio-butanol has many advantages: bio-butanol can be blended with gasoline easily; the heat energy in bio-butanol is higher than the heat energy in ethanol. Bio-butanol is more environmental than ethanol5. The Acetone-Butanol-Ethanol (ABE) process is an efficient method to produce Bio-butanol6. However, in the conventional ABE fermentation process, the concentration of ABE fermentation broth is low, this is because of the concentration of solvents is restricted by its inhibitory results on the used microorganism in the ABE process

7,8

. Many published papers assumed that the minimum concentration of

butanol in the fermentation broth of 13 g/L and complete conversion from acidogenesis to solventogenesis for the assessment of the separation efficiency of the ABE fermentation broth. However, some experimental works show that the concentration of butanol in the fermentation broth is lower than 13 g/L, owing to the significant butyric acid as well as the acetic acid in the fermentation broth. This characterizes unsuccessful conversion from acidogenesis to solventogenesis which will affect the separation efficiency9,10. There are many separation methods that can be applied to separate the ABE fermentation broth. Distillation process , gas stripping process , liquid-liquid extraction process , adsorption process as well as the membrane distillation process are very effective methods that can be used to separate the ABE fermentation broth119,

12

,

13

,

14

,

15

. Amongst those separation technologies, as is

illustrated in the literature, gas stripping process is the most effective separation technology, because the gas stripping process can be operated easily and it can be scale up easily

16

. Aneke and Görgens

17

compared three different ABE separation

technologies based on the same feed conditions, including ABE separation using only distillation (Option A), ABE separation using gas stripping with distillation (Option B) and ABE separation liquid-liquid extraction with distillation (Option C). From the results in terms of separation efficiency and the energy consumption among the three processes. Option B is the most effective one, which exhibits advantages of highest separation efficiency and lowest energy consumption. In the process, a gas stripping



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and four distillation columns (Column I, II, III, IV) are used to separate the products and the by-products from the dilute fermentation broth. However, in the four distillation columns, the bottom stream is heated by the hot utilities in the reboiler and the top vapor stream is condensed through the cold utilities in the condenser, almost all the supplied heat to the reboiler is wasted in the condenser, thus, the four columns consumes a large amount of energy. To reduce the energy use of the process, Aneke and Görgens.

17

applied heat integration technology to the process, in the

heat-integrated process; the heat released of Column IV was used to satisfy the heat requirement in the reboilers for the Column I, II, III. The results showed that the energy consumption of ABE separation process with heat integration can be greatly reduced with that of ABE separation process without heat integration. In the heat-integrated process, due to the heat integration between the columns, the hot utility requirements for the reboilers of Column I, II, III can be greatly reduced. However, the reboiler of HPC still requires large amount of heat from the hot utility while and the condensers of the Column I, II, III also consumes cold utilities. Moreover, the capital cost of the process is still very expensive. An innovative method to reduce the energy consumption, greenhouse gas emissions as well as the capital cost of the process is to apply the advanced heat integrated methods to the process, dividing wall column (DWC) technology is a very efficient intensified technologies in the distillation process because it can not only reduce the energy consumption as well as the capital cost significantly but also reduce the CO2 emissions significantly18–20. Recent papers illustrated the application of a DWC to enhance the separation efficiency and reduce the CO2 emissions as well as the capital cost of the separation process. Aurangzeb et al.

21

investigated the

economic advantages of the application of a DWC to the separation of a ternary system, the results exhibit that the DWC process not only reached 23.23% in total annual cost (TAC) but also achieved 22.6% saving in energy consumption. Tututi-Avila et al. 22 proposed a dividing wall distillation column process for the BTX separation, the results showed that the DWC configuration is the best process with the highest energy efficiency. The DWC configuration can save 24.5% of energy compared with the conventional process and it also reduce the energy consumption by 11.8% compared with the Kaibel column. Kaur et al. 23 investigated the application of a reactive dividing wall column to the synthesis of ethyl tertiary butyl ether, the CO2 emissions of the reactive dividing wall column process were reduced by 74% and 43% ACS Paragon Plus Environment

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compared with the conventional process and the reactive distillation process, respectively. And the energy consumption of the reactive dividing wall column process is less than the energy consumption of the conventional process as well as the reactive distillation process. From the conclusions of their studies, DWC is a very efficient method in the distillation process while achieve great savings in energy saving and the capital cost. Thus, DWC can be applied to the ABE separation section with the function of achieving great savings in the energy consumption and the total capital cost. However, few researches have been studied in this area24,25. With the function of achieving further energy saving in the chemical process, Kansha et al.

26

proposed the self-heat recuperation technology (SHRT) which can be

applied to the chemical process in order to reduce the energy consumption as well as reduce the amount of the carbon dioxide emissions greatly. In the chemical process based on SHRT, both the latent heat and the sensible heat of the chemical process can be recycled by using compressors as well as the self-heat exchangers. Thence, both the latent heat and the sensible heat of the process can be recycled perfectly. The self-heat recuperation technology can be applied to the reaction part, separation part and drying section. Kansha applied the self-heat recuperation technology to the crude oil distillation for further energy saving27. In the novel process, the heat in the process can be perfect circulated without any further heat addition. Thus, the self-heat recuperative crude oil distillation process can avoid the usage of any hot utilities in the process. Van Duc Long applied the SHRT to the NGL recovery process28. The results demonstrated that the NGL recovery process based on SHRT can reduce the energy consumption greatly compared with the conventional process. Kansha applied SHRT to the methanol synthesis process to reduce the energy consumption of the process29. In the process, the whole heat in the process can be recycled within the process without any heat addition, thus the energy consumption of the process can be greatly reduced. Aziz et al. proposed a novel drying system based on SHRT for further energy saving30. The results demonstrates that the novel proposed drying process based on SHR technology could reduce the energy consumption greatly compared with the MVR-based drying technology. Based on the research results of their studies, SHRT can be applied to the chemical process to reduce the energy consumption greatly. Thus, SHRT can be applied to the ABE separation section with the function of reducing energy consumption. However, few studies have been published in the area31,32. ACS Paragon Plus Environment


Recently, heat exchanger network (HEN) technology is a very effective method which can be used to the chemical process to reduce the energy consumption. HEN integrates the networks of heat exchangers, condensers, reboilers as well as the furnaces for the best energy usage33,34. Brunet et al.

35

applied HEN to the biofuel

processes to achieve a heat integrated biofuel process. The results exhibited that the heat integrated process show great advantages in energetic, economic and environmental performance. Kravanja et al.

36

applied the HEN to the biochemical

ethanol production process from straw to propose a novel heat integrated biochemical ethanol production process. The results demonstrated that the improved process can reduce the utility targets by 15% compared to the base process. Poddar et al. 37 applied HEN to design the heat integration of the reactive distillation processes for biodiesel production. The results demonstrated that the novel heat-integrated process based on HEN can reduce the energy consumption greatly compared with the base process. Based on the studied processes, HEN can be applied to design the heat integrated process for further energy saving. Therefore, HEN can be utilized in the DWC-SHR process for further energy saving. However, few published papers have involved in this area few studies have studied in this area38. Although several published papers have demonstrated the energy saving advantages of the heat integrated technologies to the ABE separation process, no studies have addressed the combination of DWC and SHRT to the ABE separation process to achieve further energy saving. In order to reduce the energy consumption of the process, DWC as well as SHRT can be applied to the ABE separation process to propose a novel energy saving DWC-SHR process. Moreover, HEN can be applied to the process to optimize the heat integration of the process. The proposed DWC-SHR process is compared with the base process, HI-A process as well as the HI-B process in terms of energetic, economic and environmental performance.

2. Evaluation method of economic performance and CO2 emissions The four proposed processes are compared in terms of the energetic, economic as well as the environmental performance based on the same feed conditions as well as the same separation specifications. The energy consumption (Qcon) is a very important parameter which can be applied to conduct the energy analysis. The Qcon can be calculated as Eqa. 1 39.


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Eqa.1

QCons = QR + 3QComp

The CO2 emissions can be used to evaluate the environmental performance, the emission factor of steam is used at 224 kg CO2/t, and the emission factor of electrical is utilized as 51.1 kg CO2/GJ40,41. The calculation of the thermodynamic efficiency can be used to analyze the exergy analysis, the detailed calculation can be viewed as Eqa. 2-642,43:

Eqa.2

E X = H − T0S =

E XQ =

∑Q into system

R

(1 −

T0 )− TR

−

Eqa.3

∑Q

C

(1 −

outof system

T0 ) + Wcomp TC

E xloss = E XQ − Wmin

Eqa.4

Eqa.5

Eqa.6 Wmin Wmin + E xloss The economic evaluation can be conducted via calculating the total annual cost µ =

(TAC). Table S1 (Supporting Information) shows the basis of economics. TAC contains annual investment cost as well as the annual operating cost (AOC). And the AOC can be calculated via the total investment cost (TIC) divided by the payback period 44,45. AOC concludes the cost of annual cooling water, annual steam as well as the electricity, while TIC concludes the cost of plate, column vessel, heat exchangers as well as the compressors. The payback time is considered as 5 years in the process. TAC can be calculated as Eqa.7 46–48:

=

TIC + ( !"#$%&

Eqa.7

3. Problem statement Fig. 1 demonstrates the flowsheet of the ABE fermentation broth separation process utilizing gas stripping and distillation columns noted in the literature 17. As is shown from the flowsheet in the literature, the gas stream from the fermentation broth which contains most of H2 and CO2 is bubble via the fermentation broth utilizing a compressor. The gas stream strips off the lighter fractions from the fermentation broth leaving behind the bottom stream which contains water, arabinose as well as xylose. The top stream from the gas stripping unit is condensed to -5 ˚C and then flashed to



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create a vapor and a liquid stream. The gaseous fraction is then recycled back. Through the gas-stripping process, most of water, xylose and arabinose is removed through the bottom stream of Bioreaction. Thus, xylose and arabinose are not considered in our research work. In order to compare with the energy performance of the Aneke and Görgens’s process17, the quantities of the components from the fermentation broth of Aneke and Görgens’s

17

can be adopted here. The feed streams

of the Aneke and Görgens’s process can be calculated based on the material balance of the COLUMNI, COLUMN II, COLUMN III and COLUMN IV. The results of the material balance are involved in Table S2 (Supporting Information). Table 1 lists the Mass fraction of feed stream from the literature49. To fit for the practical production, we scale the production rate to 12500 kg/hr. From the operating parameters from the literature17, the HPC operates at 10 atm, the temperature of the bottom streams in HPC is above 212 ˚C, and the high pressure steam (254 ˚C)

45

is needed to heat the

bottom streams of HPC, and thus the energy cost of the HPC is very high. To reduce the energy cost of the HPC, the pressure of the HPC should be designed lower. Based on the energy data from the literature, the energy consumption of COLUMN III and COLUMN IV is extremely large, we re-simulated the base process based on the same feed conditions as the Aneke and Görgens’s proces. And the operating parameters of C1, C2, LPC and HPC should be optimized with the function of reducing the energy consumption as well as the capital cost. Owing to the existence of azeotrope between acetic acid and butanol, the distillation section in Fig 1 can be divided into the pre-separation section as well as the PSD section. DWC as well as SHRT can be applied to the distillation section to achieve an energy saving DWC-SHR process, whereas DWC can be used in the pre-separation section and the SHRT can be used in the PSD section. And the heat exchanger networks (HEN) is carried out to design the HEN of the DWC-SHR process.

Table 1. Mass fraction of feed stream from the literature Component

Mass fraction (%)

Butanol

0.2483

Acetone

0.1215

Ethanol

0.0252

Acetic acid

0.2782


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Butyric acid

0.3156

Water

0.0113

Fig 1. Fermentation broth separation using gas stripping and distillation process (option B)

4. Base process The Aspen plus is used to develop the all the processes in this paper. WILS-NTH is selected as the property method for the system due to the existence of the carboxylic acid in the mixture, where Wilson is used for the activity coefficient of the liquid phase while the Nothnagel is used for the vapor phase17,50. From the operating parameter of the literature, the LPC operates at 0.1 atm while HPC operates at 10 atm. Fig. 2(a) shows the T-xy diagram of the system at 10 atm, the temperature of the bottom streams in HPC is above 212 ˚C since the HPC operates at 10 atm, and thus the high-pressure steam (254 ˚C)

45

is needed to heat the bottom streams. Thus, the

energy cost of the HPC is very large. To reduce the energy cost in the HPC, the pressure of HPC should be designed lower thus the medium-pressure steam (184 ˚C) 45

can be used to heat the bottom streams of HPC. Therefore, we set the pressure of

HPC at 3.7 atm. Fig. 2 (b, c) show the T-xy diagram of the system at 3.7 atm and 0.1atm, respectively. The N-Butanol composition in the azeotrope changes from 70.57 mol% N-Butanol (BOH) at 0.1 atm to 23.35mol% BOH at 3.7 atm. The large shift of the composition in the azeotrope indicates the refluxed flow rate from HPC to LPC is relatively small. Thus, the operating pressure of HPC and LPC is considered as 3.7 atm and 0.1 atm, respectively.



（a））

214

（b））

P=10 atm

210

T-y Temperature/℃

Temperature/℃

206

64

T-x

165

T-x 208

P=0.1atm

66

T-y

166

T-y

（c））

67

P=3.7 atm

167

212

Temperature/℃

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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164 163 162

T-x 62

60

204 161 202 0.0

58

160 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Mole Fraction of N-Butanol

0.9

1.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


56 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9


Fig 2. T-xy diagram for BOH/ acetic acid at 0.1 atm, 3.7 atm and 10 atm 4.1. Process description Fig 3 shows the flow sheet of the base process. The concentrated fermentation broth at 37 ˚C is firstly heated in H1 and then fed to C1 where most of the lighter streams (acetone and ethanol) leaves as the distillate, and the distillate is cooled in Cooler 1. The flowsheet of the separation of acetone and ethanol is involved in Fig S1 (Supporting Information). The bottom product from C1 which contains BOH, acetic acid and butyric acid is fed to C2 where almost all the butyric acid leaves at the bottom. The bottom stream from C2 is cooled in Cooler 2. The distillate from C2 is fed to the PSD section with the function of separating the BOH and acetic acid using the PSD technology. The LPC operates at 0.1 atm while the HPC operates at 3.7 atm. The distillate of the LPC which contains high purity acetic acid is cooled in Cooler 3 while the bottom product with a composition close to the low-pressure azeotrope is pumped in P1 and then heated in H2. The effluent from H2 is fed to the HPC where high purity BOH is obtained at the top. The top product from HPC is cooled in Cooler4. The bottom product with a composition close to the high-pressure azeotrope from the HPC is cooled in Cooler 5 and then recycled to LPC. According to the optimized method suggested in the references 45, we optimized the base process based on the minimum TAC. Fig S2 shows the sequential iterative optimization procedure of the base process (Supporting Information). Table S2A shows the energy consumption of reboilers of Column I, Column II, Column III and Column IV in the literature. Fig S3 shows the optimal results of the base process. The process parameters of the base process can be observed in Table S3 (Supporting Information).


1.0

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D1=40.806kmol/h 50.74℃ BOH:0.002 mf Acetone:0.640 mf EOH:0.168 mf Acetic:0.004mf But-acid:0 mf Cooler 1 Water:0.186 mf 30℃

FFeed=12500kg/h 37℃ BOH:0.226 mf C1-C Acetone:0.141 mf EOH:0.037 mf Acetic:0.312 mf But-acid:0.242 mf H1 P=0.6 atm Water:0.042 mf 104.08℃ 12 Qc=-2481.69kW Qr=2489.88kW 560.41kW RR=5.2 D=1.454m

-25.90kW

C2-C

23 Steam C1-B

Cooler 5 70.86℃

D2=99.769kmol/h 65.00℃ BOH:0.418 mf Acetone:0 mf EOH:0 mf Acetic:0.578 mf But-acid:0.002 mf Water:0.002 mf

P=0.1 atm 14 Qc=-1804.51kW Qr=1502.18kW B1=144.679kmol/h RR=0.75 144.63℃ D=1.949m BOH:0.289 mf 27 Acetone:0 mf EOH:0 mf Steam Acetic:0.399mf C2-B But-acid:0.310 mf Cooler 2 Water:0.001 mf 30℃ B2=44.91kmol/h 99.76℃ BOH:0.002 mf Acetone:0 mf EOH:0 mf Acetic:0.002 mf But-acid:0.995 mf Water:0 mf

D3=57.869kmol/h 56.30℃ BOH:0.003 mf Acetone:0 mf EOH:0 mf Acetic:0.995 mf But-acid:0 mf -58.33kW Water:0.002 mf 30℃

LPC-C

-154.05kW

Cooler 3 11 13

P=0.1 atm Qc=-3422.97kW Qr=3391.46kW RR=7.9 D=2.763m

HPC-C

23 Steam

LPC-B

H2

159.9℃ 24

417.96kW B3=71.90kmol/h 65.76℃ BOH:0.700 mf Acetone:0 mf EOH:0 mf Acetic:0.291 mf But-acid:0 mf Water:0 mf

-130.93kW

D4=41.90kmol/h 160.00℃ BOH:0.995 mf Acetone:0 mf EOH:0 mf Acetic:0.005 mf But-acid:0 mf Water:0 mf

P=3.7 atm Qc=-6578.76kW Qr=6592.12kW RR=14 D=1.794m

37 HPC-B

Steam

B4=30kmol/h 167.41℃ BOH:0.289 mf Acetone:0 mf EOH:0 mf Acetic:0.690 mf But-acid:0.022 mf Water:0 mf

4. 2. Energy analysis The energetic analysis of chemical process can be conducted through the T-H diagram51. QFH stands for the total hot utility requirements of H1, H2, C1-B, C2-B, LPC-B and HPC-B while QCW stands for the total cold utility requirements of C1-C, Cooler 1, C2-C, Cooler 2, LPC-C, Cooler 3, HPC-C, Cooler 4 and Cooler 5. As is shown in Fig 4, there exists no overlap between CCC and HCC in Fig 4. Therefore, the QFH and QCW in the base process are 14954.01 kW and 15020.28 kW, respectively.

QCW

180

QFH

160 140 120 100 80 60 40 20 0

5000

10000

15000

20000

25000

Enthalpy (kW)

Fig 4. T-H diagram of the Base process

5. Heat integrated process ACS Paragon Plus Environment

30000

30℃

Cooler 4 -363.14kW

Fig 3. Flow sheet of the Base process

Temperature (℃ )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



The bottom temperature of C1 and C2 is 114.63 C ̊ and 99.76 ̊C, respectively, and the condenser temperature of the HPC is 160.00 ̊C. Since the condenser temperature of HPC is larger than the bottom temperature of C1and C2. Heat integration can be applied to save energy. Two types of heat integration were proposed to achieve a heat integrated A process (HI-A process) and a heat integrated B process (HI-B process).

5.1 Heat integrated A process (HI-A process) 5.1.1 Process description Fig. 5 shows the flow sheet of the HI-A process. The condenser duty of the HPC can be used to meet the heat requirements for H1, C1-B and C2-B. The design parameters of the base process are adopted here, such as feed conditions, total trays of C1, C2, LPC and HPC, feed locations, etc. The concentrated fermentation broth is firstly heated in E1 and then fed to C1 where most of the lighter streams leave as the distillate. The distillate from C1 is cooled in Cooler 1. The bottom products from C1 which contains BOH, acetic acid and butyric acid is fed to C2 where most all the butyric acid leaves at the bottom. The bottom stream from C2 is cooled in Cooler 2. The distillate from C2 which contains BOH and acetic acid is fed to the LPC. The top product from the LPC contains high purity acetic acid while the bottom product with a composition close to the low-pressure azeotrope is pumped in P1 and then heated in H2. The top product from LPC is cooled in Cooler 3. The effluent from H2 is fed to the HPC where the effluent from H2 is separated into the vapor stream that is high purity BOH and the bottom products with a composition close to the high-pressure azeotrope. The condenser duty of the vapor stream of HPC can be used to meet the heat requirements for E2, E1 and E3, respectively. The vapor stream is cooled to liquid stream in E2, E1 and E3 and then separated into two streams, one is refluxed to the top tray of HPC, and the other is cooled in cooler 4. The bottom products of HPC is cooled in Cooler 5 and then recycled to LPC. The Heat exchanger networks (HEN) of the HI-A process is shown in Fig S4. The process parameters of the HI-A process can be observed in Table S4 (Supporting Information).


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FFeed=12500kg/h 37℃ BOH:0.226 mf C1-C Acetone:0.141 mf EOH:0.037 mf Acetic:0.312 mf But-acid:0.242 mf E1 Water:0.042 mf 104.08℃ 12 P=0.6 atm Qc=-2481.69kW 560.41kW RR=5.2 D=1.454m

-25.90kW

C2-C

23 2489.88kW

70.86℃


B1=144.679kmol/h 144.63℃ BOH:0.289 mf Acetone:0 mf EOH:0 mf Acetic:0.399mf But-acid:0.310 mf Water:0.001 mf

P=0.1 atm 14 Qc=-1804.51kW RR=0.75 D=1.949m

D3=57.869kmol/h 56.30℃ BOH:0.003 mf Acetone:0 mf EOH:0 mf Acetic:0.995 mf But-acid:0 mf -58.33kW Water:0.002 mf 30℃

LPC-C

Cooler 3 11 13

E2

P=0.1 atm Qc=-3422.97kW Qr=3391.46kW RR=7.9 D=2.763m

HPC-C

23 Steam

LPC-B 27

E4 1502.18kW E3

B2=44.91kmol/h 99.76℃ BOH:0.002 mf Acetone:0 mf EOH:0 mf Acetic:0.002 mf But-acid:0.995 mf Water:0 mf

105.5℃

154.05kW

Cooler 2 30℃ -130.93kW

H2

159.9℃

24

263.91kW

B3=71.90kmol/h 65.76℃ BOH:0.700 mf Acetone:0 mf EOH:0 mf Acetic:0.291 mf But-acid:0 mf Water:0 mf


P=0-.3.7 atm Qc=-2026.29kW Qr=6592.12kW RR=14 D=1.794m

37 HPC-B

Steam

Fig 5. Flow sheet of the HI-A process

5.1.2 Energy analysis The T-H diagram of the HI-A process is shown as Fig 6. The shadow in Fig 6 shows the heat recovery zone. QFH presents the total hot utility requirements while QCW presents the total cold utility requirements. QFH concludes the total hot utility requirements of LPC-B, H2 and HPC-B while QCW comprises the total cold utility requirements of C1-C, C2-C, LPC-C, HPC-C, Cooler 1, Cooler 2, Cooler3 and Cooler 4. As is shown in Fig 6, the amount of heat recovery of the HI-A process in Fig 6 is 4552.47 kW. QFH and QCW of the HI-A process are 10247.49 kW and 10213.76 kW, respectively. The HI-A process can save 31.47% of QFH and 32.00% of QCW compared with the base process. 180

QCW

Heat recovery zone

QFH

160 140

Temperature (℃ )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


120 100 80 60 40 20 0

5000

10000

15000

Enthalpy (kW)


20000

24000

30℃

Cooler 4 -363.14kW B4=30kmol/h 167.41℃ BOH:0.289 mf Acetone:0 mf EOH:0 mf Acetic:0.690 mf But-acid:0.022 mf Water:0 mf


Fig 6. T-H diagram of the HI-A process

5.2 Full heat integrated process (HI-B process) 5.2.1 Process description Fig. 7 presented the flow sheet of the HI-B process. The condenser duty of the HPC can be used to meet the heat requirements for H1, C1-B, C2-B and LPC-B, respectively. To reach the expected configuration, the condenser output of HPC should be equal to the sum of the heat input for H1, C1-B, C2-B and LPC-B through regulating the reflux ratio of the HPC. The concentrated fermentation broth is firstly heated in E1 and then fed to C1 where almost all the lighter streams leave as the distillate. The distillate from C1 is cooled in Cooler 1. The bottom product from C1 containing BOH, acetic acid and butyric acid is fed to C2 where almost all the butyric acid leaves at the bottom while the distillate contains BOH and acetic acid. The bottom product from C2 is cooled in Cooler 2. The distillate from C2 is fed to LPC. The top product from the LPC which contains high purity acetic acid is further cooled in Cooler 3 while the bottom product with a composition close to the low-pressure azeotrope is pumped in P1 and then heated in H2. The effluent from H2 is fed to the HPC where the effluent from H2 is separated into the vapor stream that is the high purity BOH and the bottom products with a composition close to the high-pressure azeotrope. The condenser duty of the vapor stream of HPC can be used to meet the heat requirements for E2, E1, E3 and E4, respectively. The vapor stream is cooled to liquid stream in E2, E1, E3 and E4 and then separated into two streams: one that is refluxed to the top tray of HPC, and the other is cooled in cooler 4. The bottom products of HPC is cooled in Cooler 5 and then recycled to LPC. Finally, the distillate of C1 is cooled in Cooler 1, the bottom products of C2 is cooled in Cooler 2, and the distillate of LPC is cooled in Cooler 3. The heat exchanger network (HEN) of the HI-B process is shown in Fig S5. Table S5 shows the process parameters of the HI-B process.


Page 16 of 30

Page 17 of 30


FFeed=12500kg/h 37℃ BOH:0.226 mf C1-C Acetone:0.141 mf EOH:0.037 mf Acetic:0.312 mf But-acid:0.242 mf E1 P=0.6 atm Water:0.042 mf 104.08℃ 12 Qc=-2481.69kW 560.41kW RR=5.2 D=1.454m

-25.90kW

C2-C

23 2489.88kW

70.86℃


LPC-C

B1=144.679kmol/h 144.63℃ BOH:0.289 mf Acetone:0 mf EOH:0 mf Acetic:0.399mf But-acid:0.310 mf Water:0.001 mf

P=0.1 atm 14 Qc=-1804.51kW RR=0.75 D=1.949m

D3=57.869kmol/h 56.30℃ BOH:0.003 mf Acetone:0 mf EOH:0 mf Acetic:0.995 mf But-acid:0 mf -58.33kW Water:0.002 mf

30℃


Cooler 3 11 13

E2

P=0.1 atm Qc=-3422.97kW RR=7.9 D=2.763m

23 E4

3391.46kW H2 159.9℃ 24 105.5℃ 154.05kW 417.96kW

27

E5 1502.18kW E3

B2=44.91kmol/h 99.76℃ BOH:0.002 mf Acetone:0 mf EOH:0 mf Acetic:0.002 mf But-acid:0.995 mf Water:0 mf


Cooler 2 30℃ -130.93kW

37

30℃

Cooler 4 -363.14kW

P=3.7 atm Qr=7957.24kW RR=17.11 B4=30kmol/h D=1.986m 167.41℃ BOH:0.289 mf Acetone:0 mf EOH:0 mf Acetic:0.690 mf Steam HPC-B But-acid:0.022 mf Water:0 mf

Fig 7. Flow sheet of the HI-B process 5.2.2 Energy analysis The T-H diagram of the HI-B process is presented as Fig 8. The amount of heat recovery in the HI-B process is 8097.98kW. The QFH and QCW in the HI-B process are 8375.20kW and 8297.47kW, respectively. The HI-B process can save 43.99% of QH compared to that of the base process and the HI-B process can also save 44.76% of QCW compared to that of the base process.

180

QCW

QFH

Heat recovery zone

160 140

Temperature (℃ )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


120 100 80 60 40 20 0

5000

10000

15000

20000

25000

Enthalpy (kW)

Fig 8. T-H diagram of the HI-B process

6. DWC-SHR process Based on the energetic analysis of the HI-A process as well as the HI-B process, ACS Paragon Plus Environment


Page 18 of 30

the cold utility demand as well as the hot utility demand of the HI-A process and the HI-B process can be reduced greatly compared to that of the base process. The HI-A process and the HI-B process can achieve energy saving. However, in the HI-A process, LPC-B, H2 and the HPC-B also consumes the hot utilities. C1-C, C2-C, LPC-C, HPC-C and Coolers (1-5) also consumes large amount of cold utilities; in the HI-B process, H2 and the HPC-B also consumes the hot utilities. C1-C, C2-C, LPC-C and Coolers (1-5) also consumes large amount of cold utilities; Thus, the hot utility demand as well as the cold utility demand of the HI-A process and the HI-B process are still very high. In order to reduce the hot utility demand as well as the cold utility demand of the system, self-heat recuperation technology (SHRT) can be applied to the system for further energy saving26. From the results of the base process, the temperature difference between bottom stream and the top stream of C1, C2, LPC and HPC is 63.89 ˚C, 34.76 ˚C, 9.46 ˚C and 7.41 ˚C, respectively. SHRT can be utilized in LPC as well as HPC to achieve further energy saving since there is very small temperature difference between bottom stream and the top stream. However, if SHRT is applied to C1 and C2, the two compressors consume very large amount of compressor work due to the very large temperature difference between top stream and the bottom stream in C1 and C2, thus the capital cost as well as the operating cost of the compressors is very large. Therefore, the SHRT is uneconomical applied to C1 and C2. To reduce the capital cost as well as the energy consumption of C1 and C2, dividing wall column (DWC) is one of the intensified techniques in distillation because it can reduce the capital cost and operating cost significantly

19

. Therefore,

DWC can be used to instead of C1 and C2 with the function of reducing the capital cost and energy consumption. If we apply vapor recompression for DWC, the compressor consumes a very large amount of compressor work due to the very large temperature difference between bottom stream and the top stream in DWC. Thus, we didn’t consider the use of vapor recompression in DWC. Thus, a novel DWC-SHR process is proposed that a DWC is used instead of C1 and C2 while the SHRT is utilized to LPC as well as HPC to achieve further energy saving.

6.1 Process description The flowsheet of the DWC-SHR process is presented in Fig. 11. DWC is used instead of C1 and C2, whereas the SHRT is applied to the PSD section to reduce the capital cost as well as the energy consumption. We use a four-column module to


Page 19 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


design the DWC, Fig. S6 shows the four-column modules for the DWC. All the parameters of DWC is optimized based on the minimum of TAC. Fig. S7 shows the sequential iterative optimization procedure of DWC. Fig. S8 shows the optimal results of DWC. The basic operating parameters of the LPC as well as HPC are also utilized here. The concentrated fermentation broth is firstly heated by preheaters and then fed to the DWC, where most of the lighter streams leave as the distillate and almost all the butyric acid leave at the bottom. The distillate from DWC is cooled in Cooler 1 while the bottom product from DWC is cooled in Cooler 4. The sidestream from DWC is almost the mixture of BOH and acetic acid. The sidestream from DWC was sent to LPC as the feedstock, where the feed mixture can be separated into top vapor products containing high-purity acetic acid and the bottom streams, C1 can be used to compress the vapor stream from LPC to raise the temperature and pressure of the vapor stream. Thus, the vapor stream discharged from C1 can be applied to heat the bottom products of LPC in E4. The effluent stream from E4 is separated into two lines: one is refluxed to the top of LPC, and the other is cooled in Cooler 2. The bottom stream from LPC is pumped in P1 and then heated in HPC preheaters, the effluent from HPC preheaters is fed to HPC, where the feed stream is separated into top products with high-purity BOH and bottom stream with a composition close to the low-pressure azeotrope. The vapor stream is compressed in C2 to raise its energy grade. Thus, the latent heat of the discharged stream from C2 can be used to heat the bottom products of HPC in E6. The effluent stream from E6 is separated into two streams: one that is recycled back to the HPC as a reflux, and the other is used to preheat the HPC feed streams. And the bottom streams from HPC is used to heat the feed streams and then recycled to LPC. The bottom streams of HPC can be utilized to preheat the feed streams. According to the literature52,53, The minimum temperature difference of E4 and E6 are considered as 5 ℃. In order to reduce the hot utility demand as well as the cold utility demand of DWC-SHR process, heat integration can be applied to achieve further energy saving.

6.2 Energy analysis Fig 9 shows the T-H diagram of the DWC-SHR process. The shadow in Fig 9 shows the heat recovery zone. The QFH and QCW in the DWC-SHR process are 1667.27 kW and 3516.99 kW, respectively. The DWC-SHR process shows 88.86%



reduction of QFH compared to that of the base process while the DWC-SHR process can shows 76.59% reduction of QCW compared to that of the base process.

200

QCW

Heat recovery zone

QFH

180 160

Temperature (℃ )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 30

140 120 100 80 60 40 20 0

3000

6000

9000

12000

15000

Enthalpy (kW)

Fig 9. T-H diagram of the DWC-SHR process

6.3 HEN design Heat Exchanger Network (HEN) is a very effective tool to conduct the HEN of the DWC-SHR process

34

. Thus, the heat integrated DWC-SHR process can be

accomplished based on the HEN. All of the hot streams as well as the cold streams of the DWC-SHR process is shown in Table S7. The Aspen Energy analyzer software can be used to conduct the HEN design of the DWC-SHR process. Fig 10 presents the optimal HEN of the DWC-SHR process. The HEN concluded 13 heat exchangers. Among 13 heat exchangers, E1-6 are self-heat exchangers. DWC-B is the reboiler of the DWC, DWC-C is the condenser of the DWC, coolers 1-5 are coolers. As is shown in Fig 10, the heating demand in the HEN is 1667.27 kW, the cooling demand in the HEN is 3516.99 kW. Fig 11 presents the final flowsheet combined with the optimal HEN. The detailed parameters of the DWC-SHR process is shown as Table S6 (Supporting Information).


Page 21 of 30

25.2kW 131.1kW

Cooler3 29.7℃ ℃ 36.7kW

40℃ ℃

HPC Top

160℃ ℃

DWC Bot

160℃ ℃

E3

160℃ ℃

154kW E1

70.9℃ ℃ 30℃ ℃

E2 48.1℃ ℃

99.9℃ ℃

30℃ ℃ 265.75kW C1

72.4℃ ℃ LPC vapor

56.4℃ ℃ 56.4℃ ℃

℃ E4 71℃

30℃ ℃

56.4℃ ℃

LPC Top DWC Con DWC Top

25℃ ℃

0.31

E5 HPC Bot

617.52kW C2

0.69

6592.17kW ℃ E6 172.5℃ 167.4℃ ℃

58.3kW

Cooler5 306.5kW

186.4℃ ℃ HPC vapor

2959.19kW

Cooler4

Cooler2

50℃ ℃

49.9℃ ℃ DWC-C

49.9℃ ℃

30℃ ℃

Cooler1

167.4℃ ℃ E6 159.9℃ ℃

167℃ ℃ HPC Reb 66.1℃ ℃ HPC Pre

E5 417.9kW

99.9℃ ℃

99.6℃ ℃ DWC Reb

DWC-B

65.8℃ ℃

E4

65.7℃ ℃ 3391.50kW

0.28

108.9℃ ℃ E2 326.5kW

E3 186.2kW

0.49 E1

LPC Reb

37℃ ℃ Preheater

0.23 1667.27kW

LS

Fig 10. Heat exchangers network (HEN) of the DWC-SHR process

160.00℃

E2 154kW E1

15

DWC

28

Steam 1667.27kW -131.1kW

DWC-B

B2=44.91kmol/h 99.9 ℃ BOH:0.002 mf Acetone:0 mf EOH:0 mf Acetic:0.002 mf But-acid:0.995 mf Water:0 mf

11 P=0.1 atm 13 D=2.763m

23 E4

160.00℃ Cooler 5 -306.5kW

3391.50kW 30℃

Cooler4

172.5℃

C2

66.1℃


E5

159.9℃ 24 P=3.7 atm D=1.794m

417.9kW HPC 37 E6 6592.17kW 167.4℃

Fig 11. Optimal flowsheet of the DWC-SHR process


617.52kW

160.00℃ 160.00℃

160.00℃

326.5kW


172.5℃

5 186.2kW E3 108.9℃

186.4℃

DWC-C -2959.19kW

Cooler3

160.00℃

160.00℃ D3=57.869kmol/h BOH:0.003 mf Acetone:0 mf 56.4℃ EOH:0 mf Acetic:0.995 mf But-acid:0 mf C1 265.75kW Water:0.002 mf 30℃ 56.4℃ -58.3kW Cooler 2

D1=40.806kmol/h 49.90℃ BOH:0.002 mf Acetone:0.640 mf -25.2kW EOH:0.168 mf 30℃ Acetic:0.004mf Cooler2 But-acid:0 mf Water:0.186 mf

-36.7kW

160.00℃

FFeed=12500kg/h 37℃ BOH:0.226 mf Acetone:0.141 mf EOH:0.037 mf Acetic:0.312 mf But-acid:0.242 mf Water:0.042 mf

160.00℃ 172.5℃

72.4℃

D4=41.90kmol/h 30℃ BOH:0.995 mf Acetone:0 mf EOH:0 mf Acetic:0.005 mf But-acid:0 mf Water:0 mf

71.0℃

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



7

Comparisons

of

economic,

energetic

and

environmental

performance Fig. 12 (a) compares the energy consumption (Qcon) of the Aneke and Görgens’s process without heat integration as well as the Aneke and Görgens’s process with heat integration after scaling the production rate to 12500 kg/h. Fig. 11 (b) compares the Qcon of the base process, HI-A process, HI-B process as well as the DWC-SHR process. Compared with the Aneke and Görgens’s process without heat integration, the base process can reduce the Qcon from 860301.05 kW to 14954.01kW by optimizing the operating parameters of C1, C2, LPC and HPC. The base process can also show 97.02% potentials of Qcon compared with the Aneke and Görgens’s process with heat integration. It can be observed in Fig. 9(B) that the DWC-SHR process can reduce the energy consumption greatly by applying DWC as well as the SHRT to the process; the heat input in the DWC-SHR process is the reboiler of DWC and the compressor duty of C1 and C2 to motivate the heat cycling in the process. The DWC-SHR process can save 71.13% of Qcon compared to that of the base process. The DWC-SHR process can also reduce the Qcon of 57.87% compared to that of the HI-A process. The DWC-SHR process can also reduce the Qcon of 47.79% compared to that of the HI-B process. Through the comparison in terms of the energy consumption, DWC-SHR process show significant advantages in energy saving. (a)

(b) 910000

16000

860301.05

Energy consumption

800000

14954.01

Energy consumption

14000

Energy consumption (kW)

Energy consumption of Aneke's process (kW)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 30

600000

502115.83 400000

200000

12000

10247.49

10000

8221.15

8000 6000

4317.08 4000 2000

0

ion integrat out heat s's with d Gorgen an ke Ane

0

Aneke

gens's and Gor

at integr

with he

ation

Base process

HI-A process

HI-B process

DWC-SHR process

Item

Fig 12. Energetic comparisons ((a) Energetic comparisons of Aneke and Görgens ’s process with heat heat integration and without heat integration; (b) Energetic comparisons of the base process, heat integrated process and DWC-SHR process).


Page 23 of 30

The CO2 emissions ([CO2]emissions) of the base process, HI-A process, HI-B process as well as the DWC-SHR process is shown in Fig. 13. The [CO2]emissions of the base process, HI-A process, HI-B process and the DWC-SHR process is 2601.95kg/h, 1783.03kg/h,1430.45kg/h and 517.61 kg/h, respectively. Based on the comparisons in terms of the CO2 emissions, DWC-SHR process shows advantages in terms of reducing CO2 emissions.

2601.95

Carbon dioxide emissions (kg/h)

2500

Carbon dioxide emissions (kg/h)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2000

1783.03 1430.45

1500

1000

517.61

500

0 Base process

HI-A process

HI-B process

DWC-SHR process

Item

Fig 13. Environmental comparisons of the base process, heat integrated process and DWCSHR process

Fig.14 shows the economic assessments of the base process, heat integrated process as well as the DWC-SHR process. The TIC of the DWC-SHR process increases because two compressors are installed. However, the DWC-SHR process can reduce the annual operating cost (AOC) greatly. The DWC-SHR process can achieve 68.57% savings of AOC compared to the AOC of the base process, the DWC-SHR process can also show 54.72% potentials in reducing AOC compared to the AOC of the HI-A process, the DWC-SHR process can also show 44.44% potentials in reducing AOC compared with the HI-B process. In terms of TAC comparisons, the DWC-SHR process can save 47.61% of TAC compared to the TAC of the base process. The DWC-SHR process can achieve



reduction of TAC by 29.58% compared to the TAC of the HI-A process. The DWC-SHR process can achieve reduction of TAC by 17.36% compared to the TAC of the HI-B process. Thus, DWC-SHR process shows great economic advantages compared with the base process, HI-A process and the HI-B process.

6

TIC AOC TAC

5

5.45

4.18

Cost (×106$)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 30

4

3.39 3.50

3.32

3.11

3

3.34 2.65

2.44

2.19

1.98

2

1.10

1

0 Base proess

HI-A process

HI-B process

DWC-SHR process

Item

Fig 14.Economic assessments of the base process, HI-A process, HI-B process and DWC-SHR process

Fig.15 shows the comparisons of the base process, HI-A process, HI-B process as well as the DWC-SHR process in terms of thermodynamic efficiency. The thermodynamic efficiency of the base process, HI-A process, HI-B process as well as the DWC-SHR process is 18.6%, 20.4%, 22.1% and 24.4%, respectively.


Page 25 of 30

0.244

0.25

0.221 0.204

Thermodynamic efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.20

0.186

0.15

0.10

0.05

0.00 Base process

HI-A process

HI-B process

SHR-DWC process

Fig 15. Thermodynamic efficiency comparisons of the base process, HI-A process, HI-B process and DWC-SHR process

From the comparisons of the base process, HI-A process, HI-B process as well as the DWC-SHR process from the point of performance analysis, the DWC-SHR process can not only shows energy saving potentials, but also reduces the green gas emissions. Additionally, the DWC-SHR process exhibits good advantages in environmental performance.

8

Conclusions A DWC-SHR process was proposed in the paper with the function of reducing

the energy input of the ABE separation process. The energy demand of the base process, HI-A process, HI-B process as well as the DWC-SHR process can be analyzed through the T-H diagram. The cooling utility requirements as well as the heating utility requirements of the DWC-SHR process can be observed from the GCC diagram. Moreover, the heat integration of the DWC-SHR process can be designed based on the application of the HEN technology. Additionally, the base process, the HI-A process as well as the HI-B process are also proposed with the function of comparing the energetic performance, economic performance as well as the environmental performance of the DWC-SHR process. The DWC-SHR process can achieve 71.13% energy saving potentials compared with the base process, the DWC-SHR process can achieve 57.87% energy saving potentials compared with the



HI-A process, and the DWC-SHR process can also achieve 47.79% savings of energy consumption compared with the HI-B process. Moreover, the DWC-SHR process shows great advantages in economic performance and the environmental performance and improves the thermodynamic efficiency compared with the base process, heat integrated process.

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org/ Basis of economics; Stream results of stream 10; Flowsheet of separation of acetone and ethanol; Sequential iterative optimization procedure of the base process; Optimal results of the base process; Basic parameters of the Base process; Basic parameters of the HI-A process; Basic parameters of the HI-B process; Four-column modules for the DWC; Sequential iterative optimization procedure of DWC; Optimal results of DWC; Detailed parameters of the DWC-SHR process; Stream energy loads of the DWC-SHR process

Acknowledgment We are thankful for the assistance from the staff at the Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology from the School of Petrochemical Engineering (Changzhou University).

References (1) (2) (3) (4) (5) (6)

Drapcho, C. M.; Nhuan, N. P.; Walker, T. H. Biofuels Engineering Process Technology; McGraw-Hill: New York, 2008. Biofuel Technologies: Recent Developments; Gupta, V. K., Tuohy, M. G., Eds.; Springer: Heidelberg ; New York, 2013. Lee, S.; Shah, Y. T. Biofuels and Bioenergy: Processes and Technologies; Green chemistry and chemical engineering; Taylor & Francis: Boca Raton, FL, 2012. Handbook of Biofuels Production, 2nd edition.; Elsevier: Waltham, MA, 2016. Kumar, M.; Gayen, K. Developments in Biobutanol Production: New Insights. Applied Energy 2011, 88 (6), 1999–2012. Dürre, P. Biobutanol: An Attractive Biofuel. Biotechnology Journal 2007, 2 (12), 1525– 1534.


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(7) (8)

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TOC Graphic

41.90kmol/h BOH:0.995 mf Acetic:0.005 mf DWC-C FFeed=12500kg/h BOH:0.226 mf Acetone:0.141 mf EOH:0.037 mf Acetic:0.312 mf But-acid:0.242 mf Water:0.042 mf

40.806kmol/h BOH:0.002 mf Acetone:0.640 mf EOH:0.168 mf Acetic:0.004mf Water:0.186 mf

C1

57.869kmol/h BOH:0.003 mf Acetic:0.995 mf Water:0.002 mf

LPC C2 23 Steam DWC-B 44.91kmol/h BOH:0.002 mf Acetic:0.002 mf But-acid:0.995 mf

HPC

Fig 11. Optimal flowsheet of the DWC-SHR process


Energy-Efficient Design of Downstream Separation To Produce n

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