Process Integrated Membrane Separation with Application to the Removal
of CO2 from Natural Gas
Hilde K. Engelien
22. March 2004
Department of Chemical Engineering, NTNU
1
Definition of Given Title
Process integrated membranes:
– Membranes integrated into a process.
– Process integration techniques (process synthesis, modelling & optimisation).
CO2 removal from natural gas:
– Have mainly looked at natural gas sweetening.
– Other applications exists.
2
Overview of Presentation
• Membranes
– Principles of separation
– Material selection
– Types of membrane modules
• Membrane separation for CO2 removal from natural gas
– Applications for CO2 removal
– Natural gas
– Advantages/disadvantages
– Current solutions & some industrial examples
• Process integration
• Future trends & developments
• Concluding Remarks
3
Principles of Membrane Separation
Phase 1
(Feed)
Membrane module
Feed
Phase 2
(Permeate)
Retentate
Permeate
Membrane
- a physical barrier from
semi-permeable
material
that allows some component
to pass through while others
are held back.
4
Microfiltration
Ultrafiltration
Reverse Osmosis
Molecular sieving
Gas separation
Membrane contactors
Pervaporation
Driving
force
(C, P, T, E)
Flux
Selectivity
Different Membrane Structures
(Selective layer)
Porous membrane
5
Non-porous membrane
Carrier membranes
Size
Diffusion & solubility
Affinity
(microfiltration/ultrafiltration)
(gas separation/pervaporation)
(gases/liquids)
Ref: Mulder, Basic principles of separation technology)
Typical Membrane Structures
(Gas Separation)
Asymmetric membranes:
Composite membranes:
– very thin non-porous layer selective
– thick, highly porous layer mechanical support
– thin selective layer of one type
polymer
– mounted on asymmetric
membrane - support
Selective layer
Nonporous layer
(selectivity)
Porous layer
(stability)
6
Asymmetric membrane structure
(one type of material)
Asymmetric
membrane
Composite membrane structure
(two types of materials) Ref. Dortmundt, 1999
Membranes - Material Selection
Polymers: most common
Inorganic: more stable
Membrane
Materials
Biological
e.g. Lungs
Cell membranes
Synthetic
Organic
(polymeric)
Glassy
Monomer: ethene
Rubbery
hybrid
Ceramic
Polymer: poly(ethene)
7
Ref.: www.btinternet.com/~chemistry.diagrams/polymer.htm
Inorganic
Glass
Metallic
Zeolitic
Different Types of Membrane Modules
Membrane
Modules
Flat sheets
Plate-and-frame
Spiral modules
Tubular
Tubular
>10 mm
Capillary
0.5-10 mm
• Two main categories for industrial applications:
– Spiral wound modules
– Hollow fibre modules
8
Ref.: Filtration Solutions Inc.
Hollow fiber
Different Types of Membrane Modules
Membrane
Modules
Flat sheets
Plate-and-frame
Spiral modules
Tubular
Tubular
> 5 mm
Capillary
0.5-5 mm
Hollow fiber
< 0.5 mm
• Two main categories for industrial applications:
– Spiral wound modules
– Hollow fibre modules
9
Cross section of hollow fibre
Ref.: Aquilo Gas Separation
CO2 Removal from Natural Gas
10
Applications for CO2 Removal
• Separation of CO2 from gas streams are required in:
–
–
–
–
Purification of natural gas (gas sweetening).
Separation of CO2 in enhanced oil recovery processes (EOR).
Removal of CO2 from flue gas.
Removal of CO2 from biogas.
• Reasons for sour gas sweetening ?
–
–
–
–
Impurities (CO2, H2S, H2O)
Increase heating value of natural gas - pipeline quality gas.
Reduce corrosion.
Prevention of SO2 pollution (formed during combustion of natural gas).
• Methods used in gas sweetening (removal of CO2, H2S)
11
–
–
–
–
Absorption process using amine (conventional).
Cryogenic distillation.
Membranes.
Hybrid process where membrane is integrated with absorption unit.
Natural Gas
• Natural gas: Mainly methane (CH4), ethane, propane, butane.
• Impurities: H2O, CO2, N2 and H2S.
• Natural gas treatment is the largest application of industrial gas
separation. Membrane processes have < 1% of this market
large
potentials ! (Baker, 2002)
• “Disposal”: Compression & re-injection of CO2 in reservoir .
12
Ref.: Australian Petroleum Cooperative Research Centre
Typical Natural Gas Plant
- Possible Membrane Applications
13
Ref.: UOP
CO2 Separation Using Membranes
• Mechanism of separation: diffusion through a non-porous membrane
• A pressure driven process - the driving force is the partial pressure
difference of the gases in the feed and permeate.
l
CH4
+
CO2
CO2
– Selective removal of fast permeating
gases from slow permeating gases.
– The solution-diffusion process can
be approximated by Fick’s law:
P
14
•
•
•
•
Selectivity - separation factor,  (typical selectivity for CO2/CH4 is 5-30)
Permeability = solubility (k) x diffusivity (D)
Either high selectivity or high permeability - use highly selective thin membranes.
Commercial membranes: polymer based (cellulose acetate)
CO2 Removal from Natural Gas
Current Membrane Solutions
• Membranes (Baker, 2002):
– 8-9 polymer materials used for 90 % of total gas separation membranes.
– Several hundred new polymers reported (academia/patents) in the last few
years. Problem: maintaining properties during real operation.
– Most gas separation modules are hollow-fibre modules.
• Three markets:
– Low gas volumes (e.g. treatment of offgas) - better than conventional
amine absorption units.
– Moderate gas volumes - competitive with amine systems.
– Higher volumes - not competitive with current amine systems. Problem:
low selectivity and flux.
• Hybrid solution with conventional amine absorption technology.
• Feed treatment - extend membrane life (condensing liquids, particles
blockage and well additives can harm the membrane).
15
causing
CO2 Separation Using Membranes:
Advantages & Disadvantages
Advantages (compared with absorption units):
–
–
–
–
–
–
–
–
–
–
Simpler process solutions
Smaller & lighter systems (offshore)
Cleaner
A better environmental solution
Less chemical additives
than conventional absorption units
Lower energy consumption
Simultaneous removal of CO2, H2S and water vapour
No fire or explosion hazards
Less maintenance
Lower capital and operating costs (small to medium scale)
Ability to treat gas at wellhead
Disadvantages:
16
–
–
–
–
Low selectivity & flux - large scale systems not economically viable (yet).
Thermal stability of polymer membranes.
Degradation & lifetime of membrane.
Unmature technology (in industrial terms, compared with existing solutions)
Natural Gas Processing Plant
Qadirpur, Pakistan
• In 1999: Largest membrane based natural gas plant in the world
(Dortmundt, UOP, 1999).
• Design: 265 MMSCFD natural gas at 59 bar.
• CO2 content is reduced from 6.5 % to less than 2 % using a cellulose
acetate membrane.
• Feed treatment & feed heaters.
• Also designed for gas dehydration.
• Plant processes all available gas.
• Plans for expansion to 400 MMSCFD.
17
Membrane plant, Qadirpur, Pakistan
18
(Dortmundt, UOP, 1999)
Examples of Membranes In Gas Industry
Plants using membranes for CO2 removal:
• Kadanwari, Pakistan - 2 stage unit for treatment of 210 MMSCFD gas at 90 bars
• Taiwan (1999) - 30 MMSCFD at 42 bar.
• EOR facility, Mexico - processes 120 MMSCFD gas containing 70 % CO2
• Slalm & Tarek, Egypt - 3 two-stage units each treating 100 MMSCFD natural
gas at 65 bar.
• Texas, USA - 30 MMSCFD of gas containing 30% CO” at 42 bar.
Companies with membranes for CO2 removal:
• NATCO Group (Cyanara membranes)
•
•
•
19
Aker Kværner Process Systems
Air Liquid
UOP
Process Integrated Membranes
20
Process Integrated Membrane:
Membrane Gas/Liquid Contactors
• Process integrated membrane
and absorption unit (developed
by Kværner Process Systems).
• Membrane acts as barrier &
surface area.
• Increased mass transfer area.
• Used for natural gas treatment,
dehydration and removal of
CO2 from offgas.
Ref.: Aker Kværner Process Systems
• There are several tests sites for this system (Falk-Pedersen) :
– Large laboratory unit at SINTEF.
– Large scale pilot unit at Kårstø (exhaust gas treatment from gas engine)
– Pilot unit at gas terminal in Scotland - testing different membranes.
21
Membrane Gas/Liquid Contactors
Benefits:
–
–
–
–
Reduction of size and weight (important offshore).
Wide range of liquid and gas flows (separation of gas/liquid phase).
Lower capital costs compared with alternative schemes.
Reduction in energy (if membranes are integrated with the stripping
unit).
– Reduction in solvent losses.
– No entrainment, flooding or channelling.
– Performance is insensitive to motion.
Santos Gas Plant, Queensland, Australia
–
–
–
–
22
Australia's largest gas producer.
Novel polymide membrane facility for CO2 removal (installed Dec. 2003).
Uses the gas/liquid contactor.
Problem: benzene/toluene/xylene in gas stream - a dewpoint control
unit is installed to ensure that BTX are at acceptable levels.
Process Integration
for Membrane Applications
• Design.
• Modelling & optimisation.
• Superstructure approach for optimisation.
Process synthesis and optimisation methods are
important for development of efficient membrane
structures for specific separation tasks.
23
Process Integration Used
in Membrane Applications
• Design.
• Modelling & optimisation.
• Superstructure approach for optimisation.
• Design decisions for membrane systems:
– Operating conditions (temperature, pressure, flow).
– Module configuration (parallel, series, single stage, multiple stage, recyle).
– Membrane material (organic, inorganic, mixed, …).
24
Single stage scheme
Two-step scheme
Two-stage scheme
Process Integration
for Membrane Applications
• Design.
• Modelling & optimisation.
• Superstructure approach for optimisation.
• Modelling of membrane designs for gas (Pettersen, Lien, 1993, 1994, 1995) :
– Parametric study.
– Algebraic model (analogous with counter-current heat exchanger). Looked
at single stage and multiple stages, effects of recycle and bypass
configurations.
– Classification modules - suitable for recovery of fast or slow permeating
component.
• Common design approach: sequential procedures:
25
– Module configurations are selected a priory.
– Optimisation on selected module to determine the operating conditions.
– Resulting flowsheet may be sub-optimal.
Process Integration
for Membrane Applications
• Design
• Modelling & optimisation.
• Superstructure approach for optimisation.
Membrane system design for multicomponent
gas mixtures via MINLP (Qi, Henson, 2000):
• Superstructure
– Consists of: membrane units, compressors,
stream mixers and splitters.
– Used to represent the possible network
configurations of a membrane system.
26
• Case study: CO2 and H2S separation from
natural gas using spiral-wound membranes.
• Simultaneous optimisation of flowsheet in
terms of total annual process costs.
Ref: Kookos, I.K, 2002
Process Integration
for Membrane Applications
• Design
• Modelling & optimisation.
• Superstructure approach for optimisation.
Optimal design of membrane systems (Mariott, Sørensen, 2003):
• Detailed rigorous mathematical models for the membrane separation.
• Superstructure representation of the membrane system.
• Optimisation using generic optimisation algorithm for pervaporation
pilot plant (ethanol/water).
• Significant improvement in design.
• Favourable compared with conventional MINLP solution methods.
27
Generic algorithms can be a basis for an effective & powerful tool for
optimal design of membrane systems.
Process Integration
for Membrane Applications
• Design
• Optimisation
• Superstructure approach
A targeting approach to the synthesis of membrane networks for gas
separations (Kookos, 2002):
• Superstructure representation.
• Hollow-fibre membrane system.
• Uses the “upper bound” trade-off curve (relationship between
permeability and selectivity for membranes).
• Configuration and membrane properties are optimised together.
28
Find the optimal membrane permeability and selectivity and the
optimum structure.
Future Development
29
Problems/Challenges
• Increasing selectivity without productivity loss (flux) - larger volume
application will then be possible.
• Maintaining membrane properties under real conditions:
– Loss of stability & performance at high T and high P.
– Maintaining membrane properties in the presence of aggressive feeds.
– Condensing heavy hydrocarbons - can degrade the performance of the
membrane.
• Thermal stability (of polymer membranes) - inorganic membranes
would be better.
• Economic competitiveness for large scale systems.
• Improving lifetime of membrane.
• Commercialisation - getting the industry to accept membranes.
30
Future High Performance Membranes
Selectivity vs. Permeability: Upper Bound
• Upper bound for selectivity vs.
permeability.
• Current selectivity of CO2/CH4
membranes is typically 5-30.
• High performance membranes
will move the upper bound
upwards.
CO2/CH4 selectivity vs. CO2 permeability
30
Higher selectivity and permeability
will:
– reduce area (capital cost).
– reduce loss of methane in
permeate (profit).
31
Upper bound (1991)
(Ref Koros, 2000)
Future Trends and Developments
For improved thermal & chemical stability of polymer membranes:
– New polymers with different side-chains or different backbones .
– Cross-linked polymers.
– Plasma treatment.
New materials (move into large-scale gas separations):
– New polymer structures with higher selectivity & permeability.
– Facilitated transport membranes - high selectivity.
– Mixed matrix materials - blends of inorganic materials (e.g. molecular
sieving) domains in polymers.
– Combination of cross-linking and mixed matrix material.
– Membranes tailored for specific separation tasks.
– Inorganic materials.
Process Integration:
32
– Rigorous models.
– Optimisation of whole structure (module design).
Concluding Remarks
Looked at:
• Introduction to principles of membrane separation, material selection
& types of membrane modules.
• Membranes for the use of CO2 removal from natural gas.
– Small scale: better than conventional absorption process.
– Medium scale: Competitive with conventional absorption process.
– Large scale: future applications along with development of membranes.
•
•
•
•
•
Industrial examples.
Process integrated membrane gas/liquid contactor.
Optimisation of membrane structures (superstructure approach).
Problems and challenges.
Future trends and development.
Membrane technology and industrial applications is a growing industry !
33
Future CO2 Separation: Going to Mars ?
Ref. NASA Space Research
34
Acknowledgements
Taek-Joong Kim, Department of Chemical Engineering, NTNU
Jon A. Lie, Department of Chemical Engineering, NTNU
Arne Lindbråthen, Department of Chemical Engineering, NTNU
Olav Falk-Pedersen, Aker Kværner Process Systems, Norway
Mike Entwistle, Aker Kværner Australia
35
References
Textbooks
‘Basic Principles of Membrane Technology’, Mulder, M., 2nd. Edt., Kluwer Academic Publishers, 1996
‘Polymer gas separation membranes’, Paul, D.R., Yampol’skii, Y.P., CRC Press, 1994
36
General Papers
Baker, R.W., ‘Future directions of membrane gas separation technology’, Ind. Eng. Chem. Res., 2002, 41, 1393-1411
Koros, W.J., Mahajan, R., ‘Pusing the Limits on Possibilities for Large Scale Gas Separation: Which Strategies ?’, J.
Membrane Science, 175, 2000, 181-196
Tabe-Mohammadi, A., A Review of the Applications of Membrane Separation Technology in Natural Gas Treatment’,
Separation Science and technology, 34, 10,1999, 2095-2111
Dortmund,
D.,
Doshi,
K.,
‘Recent
Developments
in
CO2
Removal
Membrane
Technology,
http://www.uop.com/gasprocessing/TechPapers/CO2RemovalMembrane.pdf
Lee, A.L., Feldkirchner, H.L., Gamez, J.P., Meyer, H.,S., ‘Membrane process for CO2 removal tested at Texas plant’, Oil &
Gas Journal, 1994, 92, 5, 90-93
Leiknes, T.O., ‘Gas transfer and degassing using hollow fibre membranes, Dr. ing. thesis, Department of Hydraulic and
Environmental Engineering, NTNU, Norway, ISBN 82-471-5391-2.
Hagg, M.B., ‘Membrane purification of chlorine gas’, Dr. ing. thesis, Department of Chemical Engineering, NTNU,
Norway, ISBN
Ali, S., Boblak, P., Capili, E., Milidovich, S., ‘Membrane Separation and Ultrafiltration’,Laboratory for Process and
Product Design, University of Illinois, , http://vienna.che.uic.edu/teaching/che396/sepProj/FinalReport.pdf
Lindbråthen, A., Ottøy, M., ‘Natural Gas Dehydration and Purification by Membranes’, Report, 1999, Telemark Tekniske
Industrielle Utviklingssenter.
Drioli, E., Romano, M., ‘Progress and new perspectives on integrated membrane operation for sustainable industrial
growth’, Ind. Eng., Chem. Res., 2001, 40, 1277-1300
References
Lokhandwala, K.A., Jacobs, M.L., ‘Membranes for fuel gas conditioning’, Hydrocarbon Engineering, May 2000
Echt, W., Hybrid systems: combining technologies leads to more efficient gas conditioning’, 2002 Laurance Reid Gas
Conditioning Conference, http://www.uop.com/gasprocessing/TechPapers/HybridSystems.pdf
Koros., W.J., Fleming, G.K., ‘Review: Membrane-based gas separation’, J. Membrane Science, 83, 1993, 1-80
37
References
Membrane Gas/Liquid Contactor
Grønvold, M.S., ‘CO2 capture with membrane contactors’, presented at the Third Nordic Mini symposium on
Carbon Dioxide Capture and Storage, Trondheim, Norway, 2-3 Oct. 2003.
Herzog, H., Falk-Pedersen, O., ‘The Kvaerner Membrane Contactor: Lessons from a Case Study in How to Reduce Capture
Costs’, 5th International Conference on Greenhouse Gas Control Technologies, Cairns, Australia
13-16 August, 2000
Hoff, K.A., Svendsen, H., Juliussen, O., Falk-Pedersen, O., Grønnvold, M.S., Stuksrud, D.B., ‘The Kvaerner/Gore
Membrane Process for CO2 removal’, Presented at AIChE Annual Meeting, 2000, Los Angeles
Dannstrøm, H., Stuksrud, D.B., Svendsen, H., ‘Membrane Gas/Liquid Contactors for Natural Gas Sweetening’,
http://www.gasprocessors.com/GlobalDocuments/E00May_06.PDF
Falk-Pedersen, O., Grønnvold, M.S., Nøkleby, P., ‘Membrane gas/liquid contactors’, paper received from O. Falk-Pedersen.
38
Optimal Design and Optimisation
Pettersen, T., Lien, K.M., ‘Design studies of membrane permeator processes for gas separation’, Gas. Sep. Purif., 9, 3, 151169, 1995.
Pettersen, T., Lien, K.M., ‘Insights into the design of optimal separation systems using membrane permeators’, Computers
Chem. Eng., 18, Suppl. S319-S324, 1994.
Pettersen, T., Lien, K.M., ‘Design of complex ga separation processes’, Presented at the AIChE Annual Meeting, St. Louis,
Nov. 1993
Pettersen, T., Lien, K.M., ‘Synthesis of separation systems using membrane permeators’, Proceedings of PSE, 1994, 835842.
Lien, K.M., ‘Sizing and Costing of Gas Separating Membrane Modules - A shortcut method’, Report for a 2-week projeck
for SINTEF, Division of Applied Chemcistry, July 1990, Draft Version
Marriott, J., Sørensen, E., ‘The optimal design of membrane systems’,
References
Kookos, I.K., ‘A targeting approach to the synthesis of membrane network for gas separations’, j. Membrane Science, 208,
193-202, 2002
Qi., R., Henson, M.A., ‘Optimization-based design of spiral-wound membranes systems for CO2/CH4 separations’,
Separation and Purification Technology, 13, 209-225, 1998
Qi., R., Henson, M.A., ‘Membrane system design for multicomponent gas mixtures via mixed-integer nonlinear
programming’, Computers and Chemical Engineering, 24, 2719-2737, 2000
Company/Internet References
GE Water Technologies; http://www.gewater.com/index.jsp
Aquilo Gas Separation bv; http://www.aquilo.nl/products.htm
Australian Petroleum Cooperative Research Centre; http://www.co2crc.com.au/geodisc.htm
UOP, http://www.uop.com
Filtration Solutions Inc., http://www.filtsol.com/technology/super_hydrophilic.shtml
NASA Space Research, http://science.nasa.gov/headlines/y2003/03dec_membranes.htm
Aker Kværner Process Systems, http://www.kccprocess.com/
Air Liquide, http://www.medal.airliquide.com/en/membranes/carbon/natural/offshore.asp
NATCO Group, http://www.natcogroup.com/default.asp
Membrane Technology and Research Inc., http://www.mtrinc.com/
39
CO2 Removal from Flue Gas
Capture & Storage of CO2
• Natural gas fired power plant:
– natural gas is burnt to produce power - CO2 is created in the combustion
– CO2 is separated from flue gas - then stored or used
• Four possible methods for removal of CO2
40
–
–
–
–
Ref. IEA
conventional absorption
pressure swing absorption
cryogenic separation
membrane technology (e.g. Aker Kværner membrane gas/liquid contactor)