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), [DOI: /science ] Group 14 Marcela HERNANDEZ Matt TRAHAN Clemence CHAPEAUX Christian MORENO Source:

Summary Introduction Olefin-Paraffin Mixture Cryogenic Distillation Fe 2 (dobdc) Tests for Analysis of Fe 2 (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 Fe 2 (dobdc) molecule Source:

Introduction Separation of Olefin-Paraffin mixtures is performed via cryogenic distillation New material to perform the separation would save time, money, and energy Fe 2 (dobdc) provides an active metal-organic framework for separation of hydrocarbons Source: Metal Framework isolating different hydrocarbon molecules

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:,,,

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:

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:

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: Cracking

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

Solution 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 Source:

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

Test 1: Hydrocarbon Adsorption Purpose: Determine the ability of Fe 2 (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 Results: Conclusion: Fe 2 (dobdc) has a strong affinity for unsaturated hydrocarbons (acetylene, ethylene, propylene) at 1 bar Graph that determines Fe 2 (dobdc)'s affinity from different hydrocarbons at 318K Source:

Test 2: Neutron Powder Diffraction Purpose: Determine nature of the interactions of the hydrocarbons with Fe 2 (dobdc) Fe 2 (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 Results: Provided structural models for Fe 2 (dobdc) All these hydrocarbons have an orientational disorder Conclusion Fe 2 (dobdc) has one adsorption site where unsaturated hydrocarbons have a predisposition to bind to Fe 2 (dobdc) maintains a high spin electron configuration when bond to these unsaturated gases Molecules obtained during neutron powder diffraction Source:

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:

Test 3: Variable-Temperature Magnetic Susceptibility (cont.d) Figure 3. Variable –temperature magnetic susceptibility Data Source: 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

Test 4: Binding Strength of Hydrocarbons with Fe 2 (dobdc) Determine the strength of hydrocarbon binding within Fe 2 (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 Fe 2 (dobdc) Source:

Binding Strength cont' Results: 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 Conclusion: Fe 2 (dobdc) binds strongly to the light hydrocarbons tested Hydrocarbon bonding with Fe 2 (dodbc) Source: A D00031.png

After determining that hydrocarbons bond strongly with Fe 2 (dobdc), the next test was to compare the adsorption of hydrocarbons to Fe 2 (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 Fe 2 (dobdc) and a number of other porous materials with analogous gas uptake properties Test 5: Adsorption Selectivities Source:

Adsorption Selectivities cont' Results: The adsorption selectivities obtained for Fe 2 (dobdc) are significantly greater than those calculated for either zeolite NaX or the isostructural metal- organic framework Mg 2 (dobdc) Conclusion: Fe 2 (dobdc) is a better choice for adsorbing hydrocarbons than Mg 2 (dobdc) or zeolite NaX Associating Binding Sites with Increased Enthalpy of Adsorption Source:

Test 6: Fe 2 (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 Fe 2 (dobdc) Breakthrough experiments were performed over a packed bed with equimolar mixtures of ethylene/ethane and propylene/propane Small Scale Packed Bed Reactor Source:

Fe 2 (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 (Fe 2 (dobdc)) retained the olefin Source: Flame Ionization Detector

Fe 2 (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: Feed

Fe 2 (dobdc) Performance Results Breakthrough simulations indicated Fe 2 (dobdc) with greater production capacities than Mg 2 (dobdc) and zeolite NaX Fe 2 (dobdc) proved to be effective with purifications of at least 99% for both ethane/ethylene and propane/propylene mixtures Mg 2 (dobdc) Source: Fe 2 (dobdc) Source: Zeolite NaX Source:

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, Fe 2 (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. Source: Overall Process of Gas Separation

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 Fe 2 (dobdc) bed is used to separate the ethane and ethylene components Source: Overall Process of Gas Separation

Conclusion The advantage of switching from current process technologies to the metal-organic framework of Fe 2 (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 Fe 2 (dobdc) Molecule Source: Source: :

Assessment Fe 2 (dobdc) is a good material to use for the separation of light hydrocarbon gases Fe 2 (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, Fe 2 (dodbc) Source:

Comparing To Other Research Other research includes using Fe 2+ 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 Source: (Top Left), (Right) Smog and Pollution from Greenhouse Gases Carbon Dioxide Molecule

Further research suggestions Removal of acetylene from ethylene produced in naphtha cracker using Fe 2 (dobdc) Investigate the use of Fe 2 (dobdc) in membrane based technology Full scale testing of Fe 2 (dobdc) in swing absorber Large Scale Swing Adsorber Unit Source: Membrane made of Fe 2 (dobdc)

References Bloch, E.D.; Brown, C.M.; Krishna, R.; Long, J.R.; Queen,W.L.; Zadrozny, J.M., Science 2012, Vol 335, full 6.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, df df