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Hydrocarbon Separation via Metal–Organic Frameworks. Article: Hydrocarbon Separations in a Metal-Organic Framework with Open Iron(II) Coordination Sites. Eric D. Bloch. Science: 335 (6076), 1606-1610. [DOI:10.1126/science.1217544] Group 14 Marcela HERNANDEZ Matt TRAHAN Clemence CHAPEAUX

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hydrocarbon separation via metal organic frameworks

Hydrocarbon Separation via Metal–Organic Frameworks

Article: Hydrocarbon Separations in a Metal-Organic Framework with Open Iron(II) Coordination Sites. Eric D. Bloch. Science: 335 (6076), 1606-1610. [DOI:10.1126/science.1217544]

Group 14




Christian MORENO

Source: <http://www.sulzer.com/en/Industries/Hydrocarbon-Processing/Gas-Processing>

  • Introduction
  • Olefin-Paraffin Mixture
  • Cryogenic Distillation
  • Fe2(dobdc)
  • Tests for Analysis of Fe2(dobdc)
    • Hydrocarbon Adsorption
    • Neutron Powder Diffraction
    • Variable Temperature Magnetic Susceptibility
    • Binding strength of Hyrdocarbons
    • Absorption Selectivities
    • Fe2(dobdc) Performance
  • Overall Separation Process
  • Conclusion
  • Assessment
  • Comparing to other research
  • Further research suggestions

Fe2(dobdc) molecule

Source: http://www.sciencemag.org/content/335/6076/1606.full

  • Separation of Olefin-Paraffin mixtures is performed via cryogenic distillation
  • New material to perform the separation would save time, money, and energy
  • Fe2(dobdc) provides an active metal-organic framework for separation of hydrocarbons

Metal Framework isolating different hydrocarbon molecules

Source: http://www.nature.com/srep/2013/130128/srep01149/full/srep01149.html?WT.ec_id=SREP-639-20130201

what is an olefin paraffin mixture
What is an Olefin-Paraffin Mixture?
  • Olefin: Unsaturated carbon molecule
  • Paraffin: Saturated carbon molecule
  • Definition of Saturation: A saturated compound has no double or triple bonds
  • Example of Mixture includes: ethylene/ethane and propylene/propane

Ethylene Ethane Propylene Propane

Source: <http://en.wikipedia.org/wiki/Propylene>, <http://en.wikipedia.org/wiki/Propane>, <http://en.wikipedia.org/wiki/Ethylene>, <http://en.wikipedia.org/wiki/Ethane>

olefin paraffin mixture
Olefin-Paraffin Mixture
  • Due to similar size and volatilities, separation requires cryogenic distillation
  • Molecular Weight of Ethane: 30.07 g/mol
  • Molecular Weight of Ethylene: 28.05 g/mol
  • Molecular Weight of Propane: 44.10 g/mol
  • Molecular Weight of Propylene: 42.08 g/mol

Various Hydrocarbon Boiling Points

Source: <http://www.google.com/patents/EP1515790A2?cl=en>

cryogenic distillation
Cryogenic Distillation
  • Olefin-Paraffin mixture stream is compressed to cold temperatures and high pressures
  • These cold temperatures and high pressures allow for the distillation of the olefin-paraffin mixture
  • The process is very energy-intensive

Cryogenic Distillation Tower

Source: <http://www.polarisengineering.com/polaris/technologies/cryogenic-distillation/>

the problem with distillation
The Problem with Distillation
  • Olefin-Paraffin mixtures are created by "cracking" long chain hydrocarbons at high temperatures
  • Cracking: cracking is the process where heavy, large hydrocarbons are broken down into simpler molecules such as light hydrocarbons by the breaking of carbon-carbon bonds

Long Chain Hydrocarbon


Olefin-Paraffin Mixture

Source: <http://www.educationquizzes.com/gcse/chemistry/crude-oil-2/>

problem with distillation
Problem with Distillation
  • Substantial energy cost arises from cooling these hot gases to the low temperatures required for cryogenic distillation

Source: <www.prometheusenergy.com>

  • Use new material to enable efficient separation at higher temperatures and atmospheric pressure
  • Process would include a Packed Bed Reactor using Swing Adsorption
  • Distillation not required
  • Result would be huge energy savings

Packed Bed Adsorption Pellets


material fe 2 dobdc
Material: Fe2(dobdc)
  • Metal organic Framework
  • Exposed iron (II) coordination sites
  • May be capable of fractionating a methane/ethane/ethylene/acetylene mixture into its pure components

Fe2(dobdc) Molecule

Source: <http://www.sciencemag.org/content/335/6076/1606.full>

test 1 hydrocarbon adsorption
Test 1: Hydrocarbon Adsorption
  • Purpose: Determine the ability of Fe2(dobdc) to adsorb light hydrocarbons
  • Use pure component equilibrium isotherms for methane, ethane, ethylene, acetylene, propane and propylene
  • These isotherms were measured at 318, 333 and 353K

Diagram demonstrating adsorption

Source: commons.wikimedia.org

hydrocarbon absorption results
Hydrocarbon Absorption Results


Conclusion: Fe2(dobdc) has a strong affinity for unsaturated hydrocarbons (acetylene, ethylene, propylene) at 1 bar

Graph that determines Fe2(dobdc)'s affinity from different hydrocarbons at 318K

Source: http://www.sciencemag.org/content/335/6076/1606.full

test 2 neutron powder diffraction
Test 2: Neutron Powder Diffraction
  • Purpose: Determine nature of the interactions of the hydrocarbons with Fe2(dobdc)
  • Fe2(dobdc) is dosed with deuterated gas at 300K and cooled

at 4K to collect data

  • Rietveld refinements (computational model to obtain the characterization of crystalline materials) were performed against this data to acquire structural models

Diagram of the Neutron Powder Diffraction process

Source: neutrons.ornl.gov

neutron powder diffraction results
Neutron Powder Diffraction Results


  • Provided structural models for Fe2(dobdc)
  • All these hydrocarbons have an orientational disorder


  • Fe2(dobdc) has one adsorption site where unsaturated hydrocarbons

have a predisposition to bind to

  • Fe2(dobdc) maintains a high spin electron configuration when bond to these unsaturated gases

Molecules obtained during neutron powder diffraction

Source: http://www.sciencemag.org/content/335/6076/1606.full


test 3 variable temperature magnetic susceptibility
Test 3: Variable-Temperature Magnetic Susceptibility
  • Purpose: To probe the electronic state of the iron centers upon gas binding
  • On its own, Iron(II) exhibits weak ferromagnetic coupling along the oxo-bridged chains, and weaker antiferromagnetic coupling between chains.

Image of Oxo-Bridge Chain of Lead

Source: http://origin-ars.els-cdn.com/content/image/1-s2.0-S1387700308003341-gr3.jpg

test 3 variable temperature magnetic susceptibility cont d
Test 3: Variable-Temperature Magnetic Susceptibility (cont.d)
  • Figure 3. Weak interacting adsorbates (alkanes) only slightly diminished the strength of ferromagnetic exchange. Strong interacting (alkenes) had a stronger effect on the iron centers, enough to make intrachain coupling from ferro to antiferromagnetic.
  • Conclusions: Strength of iron-hydrocarbon interactions increase as such: methane < ethane < propane < propylene < acetylene < ethylene

Figure 3. Variable –temperature magnetic susceptibility Data

Source: http://www.sciencemag.org/content/335/6076/1606.full

test 4 binding s trength of hydrocarbon s with fe 2 dobdc
Test 4: Binding Strength of Hydrocarbons withFe2(dobdc)
  • Determine the

strength of hydrocarbon

binding within Fe2(dobdc) through the analysis of adsorption data

  • Calculate isosteric heats of adsorption to compare the binding enthalpies of the gases

Hydrocarbons tested for bonding strength with Fe2(dobdc)

Source: http://sijieluo.files.wordpress.com/2012/09/mof.png

binding s trength cont
Binding Strength cont'


  • Heats of adsorption for the gasses show a significant reduction as the loading approaches the value corresponding to one gas molecule per iron(II) center presenting the strongest adsorption sites in the material


  • Fe2(dobdc) binds strongly to the light hydrocarbons tested

Hydrocarbon bonding with Fe2(dodbc)


test 5 adsorption selectivities
Test 5: Adsorption Selectivities
  • After determining that hydrocarbons bond strongly with Fe2(dobdc), the next test was to compare the adsorption of hydrocarbons to Fe2(dobdc) with other metal organic frameworks to determine which would be the most effective at separation
  • Calculate adsorption selectivities using ideal adsorbed solution theory
  • Compare adsorption select of Fe2(dobdc) and a number of other porous materials with analogous gas uptake properties

Source: http://chemistry.st-andrews.ac.uk/staff/rem/group/?page_id=4

adsorption selectivities cont
Adsorption Selectivities cont'

Results:The adsorption selectivities obtained for Fe2(dobdc) are significantly greater thanthose calculated for either zeolite NaX or the isostructural metal-organic framework Mg2(dobdc)

Conclusion: Fe2(dobdc) is a better choicefor adsorbing hydrocarbons than Mg2(dobdc) or zeolite NaX

Associating Binding Sites with Increased Enthalpy of Adsorption

Source: http://www.ncnr.nist.gov/staff/craig/

test 6 fe 2 dobdc performance
Test 6: Fe2(dobdc) Performance
  • Material performance was evaluated in an experimental packed bed reactor with an adsorption based process
  • Packed Bed: a packed bed is vessel that is filled with a packing material that could contain catalyst particles or adsorbents
  • Adsorption: the adhesion of molecules from a gas or liquid to an adsorbent surface such as Fe2(dobdc)
  • Breakthrough experiments were performed over a packed bed with equimolar mixtures of ethylene/ethane and propylene/propane

Small Scale Packed Bed Reactor

Source: <http://seat.massey.ac.nz/projects/yearbook/yearbook12/project.asp?id=09084363363>

fe 2 dobdc performance cont d
Fe2(dobdc) Performance cont'd
  • Outlet gas was monitored by gas chromatograph equipped with flame ionization detector to detect purity of each component of the gas mixture
  • As expected, alkane was first to elute from the packed bed while the solid adsorbent (Fe2(dobdc)) retained the olefin

Flame Ionization Detector

Source: <http://www.cambustion.com/products/hfr500/fast-fid-principles>

fe 2 dobdc performance results
Fe2(dobdc) Performance Results
  • Outlet Propane was 100% pure
  • Outlet Propylene during desorption was 99% pure
  • Outlet ethane was 99.5% pure
  • Outlet ethylene during desorption was 99% pure
  • Desorption: process where a substance is released from the adsorbent. The process is the opposite of adsorption

Packed Beds of Fe2(dobdc) Adsorbent

Purified Outlet Propane or Ethane


Outlet Propylene or Ethylene During Desorption

Source: <http://www.sciencedirect.com/science/article/pii/S1383586602002083>

fe 2 dobdc performance results1
Fe2(dobdc) Performance Results
  • Breakthrough simulations indicated Fe2(dobdc) with greater production capacities than Mg2(dobdc) and zeolite NaX
  • Fe2(dobdc) proved to be effective with purifications of at least 99% for both ethane/ethylene and propane/propylene mixtures


Source: <http://www.sciencemag.org/content/335/6076/1606.full>


Source: <http://www.cchem.berkeley.edu/co2efrc/publications/2011/selective-binding-of-o2.html>

Zeolite NaX

Source: <http://en.wikipedia.org/wiki/Zeolite>

overall separation process
Overall Separation Process

How would this process potentially work in place of cryogenic distillation?

1) A gas mixture of methane, ethane, ethylene, and acetylene are fed into the first of 3, Fe2(dobdc) beds.

2) The first fraction, methane, breaks through first because it has the lowest adsorptivity. Thus pure methane can be collected.

3) Pure methane can be collected until ethane breaks through.

Overall Process of Gas Separation

Source: http://www.sciencemag.org/content/335/6076/1606.full

overall separation process cont d
Overall Separation Process (cont.d)

4a) Gas flow is diverted to a second iron bed, from which more pure methane is collected.

4b) A mixture of ethane and ethylene are desorbed from this second bed.

5) The third Fe2(dobdc) bed is used to separate the ethane and ethylene components

Overall Process of Gas Separation

Source: http://www.sciencemag.org/content/335/6076/1606.full

  • The advantage of switching from current process technologies to the metal-organic framework of Fe2(dobdc) is to save money and energy
  • The prospects of using this material as a solid adsorbent through:
    • pressure/temperature swing adsorption
    • membrane-based applications

Fe2(dobdc) Molecule

Source: <http://www.sciencemag.org/content/335/6076/1606.full>

Source: <http://www.gtresearchnews.gatech.edu/energy-efficient-separations/l>


  • Fe2(dobdc) is a good material to use for the separation of light hydrocarbon gases
  • Fe2(dobdc) effectively separates hydrocarbons at a reduced cost compared to the current methods

The multistage separation is illustrated above where different Hydrocarbons are represented by each shape. Shows how each one can be separated out individually as it passes through the metal organic framework, Fe2(dodbc)

Source: http://www.cchem.berkeley.edu/co2efrc/publications/2012/co2ch4-ch4h2-and-co2ch4h2.html

comparing to other research
Comparing To Other Research
  • Other research includes using Fe2+ to store hydrogen and absorb carbon dioxide
  • Iron has a metal organic framework useful in capturing most gases
  • Gases could also include harmful greenhouse gases

Smog and Pollution from Greenhouse Gases

Carbon Dioxide Molecule

Source: (Top Left)<http://scholarsinida.blogspot.com/, (Bottom Left)<http://commons.wikimedia.org/wiki/File:CO2.png>, (Right)<http://www.deathandtaxesmag.com/190932/scientists-convert-greenhouse-gases-to-energy/>

further research suggestions
Further research suggestions
  • Removal of acetylene from ethylene produced in naphtha cracker using Fe2(dobdc)
  • Investigate the use of Fe2(dobdc) in membrane based technology
  • Full scale testing of Fe2(dobdc) in swing absorber

Membrane made of Fe2(dobdc)

Source: <http://www.beilstein-journals.org/bjoc/single/articleFullText.htm?publicId=1860-5397-6-86>

Large Scale Swing Adsorber Unit

Source: <http://www.gongtongmachinery.com/2-4-adsorption-plant.html>

  • Bloch, E.D.; Brown, C.M.; Krishna, R.; Long, J.R.; Queen,W.L.; Zadrozny, J.M., Science 2012, Vol 335, 1606-1610. http://www.sciencemag.org/content/335/6076/1606.full
  • Brown, C.M.; Dailly, A.; Grandjean, F.; Herm, Z.R.; Horike, S.; Kaye, S.S.; Long, G.J.; Long, J.R.; Queen, W.L.; Sumida, K., Chemical Science 2010, Vol 1, 184-191. http://alchemy.cchem.berkeley.edu/jeff/paper112.pdf