On the mass transfer of CO2 in enzyme

enhanced solvents - comparison with

conventional solvent systems

Arne Gladis, Philip L. Fosbøl, John M. Woodley, Nicolas von Solms

Technical University of Denmark

1

2

-5

15

35

55

75

95

115

0 20 40 60 80 100

Te

mpera

ture

°C

Wt % Piperazine

ExtendedUNIQUAC

PIPH2·6H2O

PIPH2·½H2O

PIPH2

Ice

Experimental

• Physical Properties

• Equilibrium

• Kinetics

Modelling

• Energy consumption

• Heat of reaction

• Thermodynamics

• Kinetics

Simulation

• Variance analysis

• Optimization of energy use

• Optimization of packing

• Rate based approach

• Equilibrium approach

• Aspen Plus

• Cape-Open

Pilot tests

• Real life tests

• Solvent study

• Packing testing

• Energy requirements

• Mass transfer

DTU CO2

Research

2

Overview

Benchmarking overall mass transfer

Energy consumption

Benchmarking solvent capacity

3

4

Ideal solvent for postcombustion CCS

Low capital costs

High mass transfer rates

Low operational costs

High solvent capacity

Low energy demand for regeneration

5

Solvents

K2CO3

Alkanolamines are the most prominent group of solvents for CO2 capture

Carbonate salt

6

K2CO3PZ

Solvents in CCS

Primary amine Tertiary amine Carbonate salt

Absorption rate of CO2

Secondary amine

Carbonate salt solutions and tertiary amines are not even

considered as potential solvents because of slow absorption

kinetics

∆𝑯𝑹≈ 𝟖𝟎 − 𝟖𝟓 𝒌𝑱

𝒎𝒐𝒍 ∆𝑯𝑹≈ 𝟓𝟎 − 𝟔𝟓

𝒌𝑱

𝒎𝒐𝒍 ∆𝑯𝑹≈ 𝟏𝟓 − 𝟐𝟕

𝒌𝑱

𝒎𝒐𝒍 ∆𝑯𝑹≈ 𝟕𝟓 − 𝟖𝟓

𝒌𝑱

𝒎𝒐𝒍

7

K2CO3PZ

Primary amine Tertiary amine Carbonate salt

Absorption rate of CO2

Secondary amine

∆𝑯𝑹≈ 𝟖𝟎 − 𝟖𝟓 𝒌𝑱

𝒎𝒐𝒍 ∆𝑯𝑹≈ 𝟓𝟎 − 𝟔𝟓

𝒌𝑱

𝒎𝒐𝒍 ∆𝑯𝑹≈ 𝟏𝟓 − 𝟐𝟕

𝒌𝑱

𝒎𝒐𝒍 ∆𝑯𝑹≈ 𝟕𝟓 − 𝟖𝟓

𝒌𝑱

𝒎𝒐𝒍

The enzyme carbonic anhydrase (CA) can catalyze the reaction of

bicarbonate forming solvents and speed up the absorption rates

𝑪𝑶𝟐 + 𝑯𝟐𝑶𝑪𝑨

𝑯+ + 𝑯𝑪𝑶𝟑−

Solvents in CCS

WWC Experiments

8

Determine effect of:

• Temperature (298- 333 K)

• Solvent loading

Solvent Solvent type

30 wt% MDEA + 8.5 g/L CA Enzyme enhanced solvent

30 wt% MDEA + 5 wt% PZ Chemically promoted solvent

30 wt% MEA Primary amine

Comparison of absorption behavior of conventional solvents and

enzyme ehanced solvents on a wetted wall column

WWC – measurements

9

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0 10000 20000 30000Ab

sorb

ed f

lux

(m

ol/

m2/s

)

Driving force mean log pCO2 (Pa)

30 wt% MDEA, 313 K 0.02 ldg 3 g/l CA

0.02 ldg 1.5 g/l CA

0.35 ldg 3 g/l CA

0.35 ldg 1.5 g/l CA

Measurement of absorption kinetics

Comparison of different solvents

• Opposing trends for

conventional and enzyme

enhanced solvents

• Reaction kinetics increase for

conventional solvents

• Enzyme kinetics are not

increasing with temperature

10

0.0E+00

1.0E-06

2.0E-06

3.0E-06

4.0E-06

5.0E-06

290 300 310 320 330 340

kli

q (

mo

l p

a-1

m-2

s-1

)

Temperature (K)

MEA MDEA + PZ MDEA + CA 30 wt% MEA, unloaded

30 wt% MDEA 5 wt% PZ, unloaded

30 wt% MDEA + 8.5 g/L CA, unloaded

Effect of temperature on CO2 mass transfer

11

0.0E+00

1.0E-06

2.0E-06

3.0E-06

0 0.1 0.2 0.3 0.4 0.5 0.6

kli

q (

mo

l p

a-1

m-2

s-1

)

Loading (mol CO2/ mol solvent)

MEA MDEA + PZ MDEA + CA

• Rapid decline in mass

transfer upon loading for

conventional solvents

• Just slight deline in mass

transfer for enzyme

enhanced solvents

Effect of solvent loading on CO2 mass transfer

30 wt% MEA,

30 wt% MDEA 5 wt% PZ,

30 wt% MDEA + 8.5 g/L CA

12

0.0E+00

1.0E-06

2.0E-06

3.0E-06

0 0.1 0.2 0.3 0.4 0.5 0.6

kli

q (

mo

l p

a-1

m-2

s-1

)

Loading (mol CO2/ mol solvent)

MEA MDEA + PZ MDEA + CAReaction Rates:

Conventional solvents:

Dependent on active amine concentration

Enzyme enhanced solvents:

Independent on active amine concentration

Am

ov Am Amk k C

3

2

2

2

1

CA CACA

ov

HCO

MS CO

MP

HOC kk

CK

C

CK

Effect of solvent loading on CO2 mass transfer

Different reaction mechanism can explain the different mass transfer of conventional and

enzyme enhanced solvents.

Modelling results [1] [2] [3]

[1] G. F. Versteeg, L. A. J. . van Dijck, and W. P. M. van Swaaij, “On the Kinetics between CO2 and Alkanolamines

both in aqueous and non-aqueous solutions. An overview,” Chem. Eng. Commun., vol. 144, pp. 113–158, 1996.

[2] J. Gaspar and P. L. Fosbøl, “Practical Enhancement Factor Model based on GM for Multiple Parallel Reactions:

Piperazine (PZ) CO2 Capture,” Chem. Eng. Sci., 2016.

[3] A. Gladis, M. T. Gundersen, R. Nerup, P. L. Fosbøl, J. M. Woodley, N. von Solms, R. Neerup, P. L. Fosbøl, J. M.

Woodley, and N. Von Solms, “CO2 mass transfer model for carbonic anhydrase enhanced MDEA solutions,” Chem.

Eng. J., vol. 335, no. October 2017, pp. 197–208, 2018.

13

Benchmark of experiments

Comparison of the average liquid side mass transfer coefficient as well

as the cyclic capacity of the different solvents

Definition of average kliq by Li and Rochelle [4].

14

Benchmark of experiments

[4] L. Li, H. Li, O. Namjoshi, Y. Du, and G. T. Rochelle, “Absorption rates and CO 2 solubility in new

piperazine blends,” Energy Procedia, vol. 37, pp. 370–385, 2013.

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12

Cy

clic

ca

pa

city

(mo

l C

O2 /

kg

(so

lven

t +

wa

ter)

)

average kliq (*107 mol Pa-1 s-1 m-2)

30 wt% MEA

5/30 wt% PZ/MDEA

30 wt% MDEA 8.5 g/L CA

Comparison of the average liquid side mass transfer coefficient as well

as the cyclic capacity of the different solvents

𝑷𝑪𝑶𝟐𝒈𝒂𝒔

= 12 kPa

𝑷𝑪𝑶𝟐𝒈𝒂𝒔

= 1.2 kPa 𝑷𝑪𝑶𝟐𝒍𝒊𝒒∗

= 0.5 kPa

𝑷𝑪𝑶𝟐𝒍𝒊𝒒∗

= 5 kPa

Top

Bottom

DF=0.7 kPa

DF=7 kPa

Isothermal

at 40°C

15

Benchmark of experiments

40 wt% PZ

30 wt% PZ

30 wt% AMP

9/42 wt%

PZ/MDEA

21/29 wt%

PZ/MDEA

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12

Cy

clic

ca

pa

city

(mo

l C

O2 /

kg

(so

lven

t +

wa

ter)

)

average kliq (*107 mol Pa-1 s-1 m-2)

conventional amines

30 wt% MEA

5/30 wt% PZ/MDEA

30 wt% MDEA 8.5 g/L CA

Comparison of the average liquid side mass transfer coefficient as well

as the cyclic capacity of the different solvents

• Enzyme enhanced MDEA has

highest average kliq in own

experiments

• Just solvents with high PZ

concentration (>21%) have a higher

mass transfer

• MDEA+CA solvents have a

comparable cyclic capacity at 298 K

16

Benchmark of experiments

Comparison with literature values [5]

• Enzyme enhanced MDEA has

highest average kliq in own

experiments

• Just solvents with high PZ

concentration (>21%) have a higher

mass transfer

• MDEA+CA solvents have a

comparable cyclic capacity at 298 K

30 wt% MEA

5/30 wt%

PZ/MDEA

30 wt% MDEA

8.5 g/L CA

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12

Cy

clic

ca

pa

city

(mo

l C

O2 /

kg

(so

lven

t +

wa

ter)

)

average kliq (*107 mol Pa-1 s-1 m-2)

PZ PZ blends PZ derivates

Amino acids primary monoamines secondary monoamines

hindered monoamines Diamines

[5]: G. T. Rochelle, “Conventional amine scrubbing for CO 2 capture,”

in Absorption-Based Postcombustion Capture of Carbon Dioxide,

2016.

17

Benchmark of experiments

𝑷𝑪𝑶𝟐𝒈𝒂𝒔

= 12 kPa

𝑷𝑪𝑶𝟐𝒈𝒂𝒔

= 1.2 kPa 𝑷𝑪𝑶𝟐𝒍𝒊𝒒∗

= 0.5 kPa

𝑷𝑪𝑶𝟐𝒍𝒊𝒒∗

= 5 kPa

Top

Bottom

DF=0.7 kPa

DF=7 kPa

Isothermal

at 40°C

0.0E+00

1.0E-06

2.0E-06

3.0E-06

0 0.1 0.2 0.3 0.4 0.5 0.6

kli

q (

mo

l p

a-1

m-2

s-1

)

Loading (mol CO2/ mol solvent)

MEA MDEA + PZ MDEA + CA

Enzyme enhance solvents show a good performance compared to conventional solvents,

because of the high mass transfer at higher solvent loadings (higher driving forces in the

bottom of absorber)

• Reaction mechanism of enzymes different than amines

• Enzyme enhanced solvent have potential to utilize lower

absorption temperature to maximize cyclic capacity

• Enzyme enhanced solvents show comparable mass transfer

as well as cyclic capacity compared to conventional solvents

18

Conclusion

Need of precise process modelling for comparison and

benchmark of total systems

(See also our Poster: Process Model Validation of enzyme

enhanced CO2 capture)

Thank you for your attention

19