Systematic design of hybrid separation processes · 2019. 1. 31. · Identifying hybrid separation...

Systematic design of hybrid separation processes

PI &PSE

Meeting

Twente University

Enschede

13.04.2017

Mirko Skiborowski

Mirko Skiborowski | Twente | 13.04.2017

Conceptual design of separation processes

Process synthesis

Distillation as default choice

~ 95% of all fluid separations

> 40.000 columns in the US

> 10% of the energy demand in the

US (3% worldwide)

Humphry and Siebert, 1992, Chem. Eng. Progr., 88, 32-41

Wankat 2012, 3rd edition, Prentice Halll

Koeijer & Kjelstrup, 2010, Int. J. of Therm., 3, 105-110

2


Why to look for alternative/hybrid separation

processes?

High energy requirements

Low energy efficiency

thermodynamic efficiency of distillation is

in the range of 5-20%

Distillation boundaries

caused by azeotropes

Unfavorable operating conditions

Boiling temperatures vs. temperature stability

Koeijer & Kjelstrup, 2010, Int. J. of Therm.,

3, 105-110

Sholl & Lively, 2016, Nature, 532, 435–437

3


Thermodynamic efficiency

Definition thermodynamic efficiency 𝜂 =Δ𝐺 𝑢𝑛𝑚𝑖𝑥𝑖𝑛𝑔

𝑊+𝑄

E.g. seawater desalination with reverse osmosis

Thermodynmically reversible process = negative free energy of mixing

−𝑑 Δ𝐺𝑚𝑖𝑥 = −𝑅𝑇 ln 𝑎𝑤 𝑑𝑛𝑤 + ln 𝑎𝑠 𝑑𝑛𝑠 ⇒ 𝑊𝑟𝑒𝑣 = 1.15𝑘𝑊ℎ

𝑚3

Ideal RO process (𝑥𝑃,𝑊 = 1) at the pinch: 𝑊 = Δ𝑃 ⋅ 𝑄𝑃 ≡ ΔΠR c, T, Y ⋅ 𝑄𝑃

𝐹 38,000 ppm

𝑅 = 0.5𝐹

𝑃 = 0.5𝐹

In Anlehnung an: Semiat, 2008, Env. Sci. & Tech., 42 (22), 8193-9201

4

F

R

P

𝑊 = 1.69𝑘𝑊ℎ

𝑚3

𝜂 = 68%

F

R

P

𝑊 = 1.39𝑘𝑊ℎ

𝑚3

𝜂 = 83%


Thermodynamic efficiency

E.g. seawater desalination with reverse osmosis

Ideal separation includes 100% energy recovery

from the retentate (ERI systems >96%)

real energy demand 𝑊 ≈ 4.0𝑘𝑊ℎ

𝑚3 (incl. pretreatment)

MED plant (GOR=16) required 𝑊 ≈ 40𝑘𝑊ℎ

𝑚3

BUT: Transferability generally stands to question!

Elimelech & Philipp, SCIENCE, 333, 2011 Al-Karaghouni et al. Renewable and Sustainable Energy Reviews 24 (2013) 343–356

Utilize different separation techniques such that they

operate within the ranges they are most efficient.

• efficiency drops rapidly with recovery R

(𝑅 = 75% → 𝜂 ≈ 50%) • osmotic pressure limits recovery R

(𝑅 = 75% → Π ≈ 125 𝑏𝑎𝑟)

Cussler & Dutta, AIChE J., 2012, 58, 12, 3825-3831

5


How to design alternative/hybrid separation

processes?

Process synthesis

separation

process

A

B

C

A

B

C

Dis

tilla

tio

n c

olu

mn

Decanter

Adsorption

GP/VP RO/NF/UF PV

Crystallization

LL-E

xtr

actio

n

Hybrid processes

?

6


Identify potentially suitable separation

techniques.

Identification based on a thermodynamic analysis

Selection on the basis of limit values for binary system ratios

Separation technique is potentially suitable if 𝑟𝑗𝐴𝐵 =

𝑝𝑖𝐴

𝑝𝑗𝐵 ≥ 𝑟𝑗,𝑚𝑖𝑛

Selection of one or more techniques for a binary separation

Jaksland et al., Chem. Eng. Sci., 1995, 50 (3). 511-530

Separation Separation technique Chracteristic physical properties

Gas separation Absorption solubility

Gas membrane critical temperature, van der Waals volume

Liquid separation Micro/Ultrafiltration kinetic diameter, molecular volume

Nanofiltration solubility, molecular weight

Liquid-liquid

separation

LL-Extraction solubility

SC-Extraction solubility, critical temperature and pressure

Vapor-liquid

separation

Distillation Vapor pressure, heat of evaporation, boiling temperature

Pervaporation molecular volume, solubility, dipole moment

Solid-liquid

separation

Crystallization melting temperature and heat of fusion

Adsorption Solubility, kinetic diameter

7


Identifying hybrid separation processes

Hybrid separation process

are a “combination of at least two different unit operations in two different

apparatus, which contribute to the same separation task“.

an consequently be generated as combination of potentially suitable techniques.

E.g. ethanol/water separation

Franke, et al. Chem. Ing. Techn., 2004, 76, 199–210,.

Roth et al., Chem. Eng. Res. Des., 2013, 91, 1171–1185.

ethanol water

𝑀𝑊 (𝑔/𝑚𝑜𝑙) 46 18

𝑇𝐵(°𝐶) 78 100

𝑇𝑀(°𝐶) -114 0

𝜇 (𝐷) 1.69 1.85

𝜎 (𝑀𝑃𝑎12)

26.5 48

𝑑𝑘𝑖𝑛(Å) 4.46 2.25

distillation, PV/VP, … ,

crystallization, adsorption

> < >

<

>

8

- 30% energy duty


Determine suitable combinations

Driving force analysis in dependence of concentration ranges

Definition of a “general“ driving force 𝐷𝐹𝐴𝐵 = 𝑦𝐴/𝐵 − 𝑥𝐴/𝐵

E.g. ethanol/water separation

Alternatively: Analysis of the real driving force/thermodynamic efficiency!

Analysis of idealized separation processes without a specific model.

identify the maximal potential & according operating ranges

E.g. ethanol/water separation by ideal RO membrane

pmax = 200bar → 𝑥𝐸𝑡𝑂ℎ = 1 − exp −𝑉𝐻2𝑂Δ𝑝

𝑅𝑇 ≈ 0,135 → wEtOh = 0,286

Gani & Bek-Pedersen, AIChE J., 2000,46 (6), 1271-1274 & Bek-Pedersen et al., Comp. Chem. Eng., 2000, 24, 253–259, Chem. Eng. & Proc.: Proc. Int., 2004, 43, 251–262

𝐷𝐹

𝐸𝑊

𝑥𝑊

9


Multicomponent systems

Graphical or geometric methods

allows for the consideration of separating boundaries

Specifically important for the selection of suitable additives/MSA

ethanol 78°C

water

100°C

cyclohexane

81°C AZVLLE 69°C

AZVLLE 65°C

AZVLLE 62°C

𝑥𝐼

𝑥𝐼𝐼

D1

EW

E W

C

𝑥𝐼𝐼

𝑥𝐼 D1

10


Evaluation of process variants

Hybrid separation processes are characterized by

a high degree of integration (recycle streams are almost always included)

a high number of design degrees of freedom

Optimization-based process design

EW

E W

C

min𝑥,𝑦

𝑇𝐴𝐶

𝑠. 𝑡. ℎ 𝑥, 𝑦 = 0 𝑔 𝑥, 𝑦 ≤ 0

ETHANOL

WATERCYCLOHEX

VLE-azeotrope:78.15C

VLE-azeotrope:64.92C

VLLE-azeotrope:69.49C

VLLE-azeotrope:62.39C

78.31C

100.02C 80.78C

D1

B1

D2

B2

𝑥𝐶𝑜𝑙1

𝑥𝐶𝑜𝑙2

11


Design of solvent-based separation

processes

Selection of potentially suitable solvents (MSA)

Use of databases/expert knowledge or Computer Aided Molecular Design

taking into account thermodynamic constraints (𝑇𝐵 , 𝑇𝑀, 𝛾∞, 𝐾, … )

in combination with applied graphical/geometric analysis

Evaluation based on optimization-based process design

E.g. separation of acetone & methanol by extractive distillation

acetone

methanol

𝑝1 = 1atm 𝑝2 = 1atm

solvent

acetone

(methanol)

methanol

(acetone)

annualized capital cost 10𝑘€

𝑎

an

nu

al op

era

ting c

ost

10

𝑘€

𝑎

5 6 7 8 9 1012

14

16

18

20

22

24

26

cinv

co

p

CAMD

1 2 3 4 5 615

20

25

30

35

40

45

50

generation

CT

A

chlorobenzene

DMSO

ethanol

mesitylene

water

p-xylene

Skiborowski et al., Ind. Eng. Chem. Res. 2015, 54, 10054−10072

12


Potential suitable model reductions

Use of thermodynamically sound shortcut methods

Limitations of each separation technique have to be depicted “accurately“

E.g.: thermodynamically sound pinch-based shortcut methods

Analysis of ideal separation techniques to identify

the maximum potential Would a detailed analysis be worth the effort?

min. requirements Define targets for experimental investigations.

model-based

evaluation

of more than 1400

potential solvents

Scheffcyk et al., Chem. Eng. Res. Des., 2016, 115 (B), 433–442

13


Analysis of the potential impact

Simplified analysis of a membrane separation processes by

estimating expected costs based on

variable permeability

variable selectivity/rejection

Bsp.: analysis of the potential impact of an OSN-assisted distillation

14

𝑃, 𝑅, 𝛼 =? A,Q,P

TAC

𝑀𝑊 (𝑔/𝑚𝑜𝑙)

𝑇𝐵 (°𝐶)

𝐷𝑒𝑐𝑎𝑛 142 174

𝐷𝑜𝑑𝑒𝑐𝑎𝑛𝑎𝑙 198 250

𝐻𝑒𝑥𝑎𝑐𝑜𝑠𝑎𝑛𝑒 367 412

𝛼𝐷𝑒𝑐𝑎𝑛/𝐷𝑜𝑑𝑒𝑐𝑎𝑛 = 1.1

𝛼𝐷𝑒𝑐𝑎𝑛/𝐷𝑜𝑑𝑒𝑐𝑎𝑛 = 10

𝛼𝐷𝑒𝑐𝑎𝑛/𝐻𝑒𝑥𝑎𝑐𝑜𝑠𝑎𝑛 𝛼𝐷𝑒𝑐𝑎𝑛/𝐻𝑒𝑥𝑎𝑐𝑜𝑠𝑎𝑛

𝛼𝐷𝑒𝑐𝑎𝑛/𝐷𝑜𝑑𝑒𝑐𝑎𝑛 = 1.1

𝛼𝐷𝑒𝑐𝑎𝑛/𝐷𝑜𝑑𝑒𝑐𝑎𝑛 = 10

Micovic et al., Chem. Eng. Res. Des., 2014, 92 (11), 2131–2147


Final summarizing example (1)

Separation of mixture of acetone, isopropanol & water

thermodynamic analysis

Graphical analysis

acetone isopropanol water

𝑀𝑊 (𝑔/𝑚𝑜𝑙) 58 60 18

𝑇𝐵(°𝐶) 56 82 100

𝑇𝑀(°𝐶) -95 -89 0

𝜇 (𝐷) 2.9 1.7 1.85

𝜎 (𝑀𝑃𝑎12)

19.7 11.5 48

𝑑𝑘𝑖𝑛(Å) 4.6 4.7 2.25

< <

<

>

<

>

acetone (56°C)

isopropanol (82°C) azeotrope (80°C) water (100°C)

RC DB

sequential hybrid

15



Solvent-based process option

isopropanol + water

simple minimum boiling azeotrope

completely miscible

Variant screening

extractive distillation

AzIW

I

W

LM = ethylene glycole

1

2

3

1

2

3

4

1

2

3

4

1

2

4

3

1

43

2

Feed

Feed

Feed

Feed

Ac

Ac

AcAc

IPA

IPA

IPA

IPA

EG

EGEG

EG

H2O

H2O

H2O

H2O

H2O

H2O

H2O

- 684 kW

- 188 kW

- 424 kW

695 kW

175 kW

455 kW

67 kW

40 kW140 kW

695 kW

- 684 kW

- 122 kW

- 76 kW

- 26 kW

555 kW

689 kW

117 kW

57 kW

- 40 kW

- 134 kW

- 690 kW

- 525 kW

555 kW

- 525 kW

- 554 kW

- 630 kW

523 kW

630 kW

- 48 kW

77 kW

1

2

3

1

2

3

4

1

2

3

4

1

2

4

3

1

43

2

Feed

Feed

Feed

Feed

Ac

Ac

AcAc

IPA

IPA

IPA

IPA

EG

EGEG

EG

H2O

H2O

H2O

H2O

H2O

H2O

H2O

Minimum heat duty

determined with RBM*

∑𝑸𝑩 [𝒌𝑾] ∑𝑸𝑪 [𝒌𝑾]

Nr. 1 1325 -1296

Nr. 2 942 -908

Nr. 3 1418 -1389

Nr. 4 1786 -1757

Skiborowski et al., 2011, EPIC 2011, IChemE, pp. 37-45.

Bausa, et al., AIChE J., 1998, 44(10), 21812198.

Brüggemann et al., AIChE J., 2004, 50(6), 11291149.

Berg et al., US-Patent, 1992, Nr. 5,085,739

16



Ideal PV identifikation of max. benefit and operating conditions

experimental identification/characterization of a suitable membrane

selective separation of water in the side stream and recycle of

the retentate 𝑄𝐵𝑐𝑜𝑙 = 630𝑘𝑊

heat of evaporation (water) 𝑄𝑣𝑎𝑝𝐻2𝑂 = 426𝑘𝑊

permeate pressure: 𝑝𝑃 [𝑚𝑏𝑎𝑟] 10 30 50 100

𝑇𝐵 𝑝𝑝 [°𝐶] 7 24 33 46

1056𝑘𝑊 > 940𝑘𝑊

Koch & Górak, Chem. Eng. Sci., 2014, 115, 95–114

17



Optimization-based design

Extractive distillation process

> 695kW

VRC 130kW

col. 1 col. 2 col. 3 col. 4 process

invest [k€/a] 59.8 10.7 15.8 5.5 91.8

heating [k€/a] 148.8 22.3 29.7 14.4 214.8

cooling [k€/a] 15.8 2.1 2.7 0.6 21.2

solvent [k€/a] 0.7 0.7

TAC [k€/a] 224.0 35.1 48.9 20.5 328.5

18


Membrane-assisted distilaltion


Optimization-based design

Extractive distillation process

> 695kW

VRC 130kW

col. 1 col. 2 col. 3 col. 4 process

invest [k€/a] 59.8 10.7 15.8 5.5 91.8

heating [k€/a] 148.8 22.3 29.7 14.4 214.8

cooling [k€/a] 15.8 2.1 2.7 0.6 21.2

solvent [k€/a] 0.7 0.7

TAC [k€/a] 224.0 35.1 48.9 20.5 328.5

𝑝𝑃=30mbar

3-stage

invest [k€/a] 124

heating [k€/a] 216

cooling [k€/a] 732

solvent [k€/a] 53

TAC [k€/a] 1125

𝑝𝑃=50mbar

3-stage 4-stage 5-stage

130 125 123

219 218 217

38 38 38

73 53 43

460 434 420

19


Summary & Conclusions

Alternative/hybrid separation process

can provide significant improvements by exploiting synergies.

result automatically from (limited) suitability of different separation techniques

Process systems engineering provides the means

to determine suitable configurations by graphical/geometrical analysis

determine the max. potential benefit by evaluation of ideal separations

determine necessary efficiency material screening/optimization

determine a suitable range of operation reducing experimental effort

perform a comparison of competing process concepts

efficiently handling the high degree of integration and complexity

Nevertheless, the identification of “optimal” solutions still require that

systems engineering methods are based on appropriate process insight,

taking into account experimental validation and verification.

20


Thank you for your attention!

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Systematic design of hybrid separation processes · 2019. 1. 31. · Identifying hybrid separation...

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