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My work to be added to carbon dioxide scrubber article, under technologies headline:

MOFs

Metal-organic frameworks are one of the most promising materials for carbon dioxide capture and separation in adsorption processes. Although no large-scale commercial technology exists nowadays, several research findings have indicated the great potential that MOFs have for CO₂ removal. Their characteristics such as pore structure and surface functions can be easily tuned to improve CO₂ adsorption selectivity over other gases.

A MOF could be specifically designed as a CO₂ removal agent in post-combustion power plants. In this scenario, the flue gas would pass through a bed packed with a MOF material, where CO₂ would be adsorbed. After saturation is reached, CO₂ could be desorbed by doing a pressure or temperature swing. Carbon dioxide could then be compressed to supercritical conditions in order to be stored underground or utilized in enhanced oil recovery processes. However, this is not possible in large scale yet due to several difficulties, one of those being the production of MOFs in great quantities.

Another problem is the availability of metals necessary to synthesize MOFs. In a hypothetical scenario where these materials are used to capture all CO₂ needed to avoid global warming issues, such as temperature rise above 2^oC from pre-industrial average temperature, we would need more metals than it's available on Earth. For example, to synthesize all MOFs using Vanadium, we would need 1620% of 2010 global reserves. Even if using Magnesium-based MOFs, which have demonstrated a great capacity to adsorb CO₂, we would need 14% of 2010 global reserves, which is a considerably amount. Also, extensive mining would be necessary, leading to more potential environmental problems.

In a project sponsored by the DOE and operated by UOP LLC in collaboration with faculty of four different universities, MOFs were tested as possible carbon dioxide removal agents in post-combustion flue gas. They were able to separate 90% of the CO₂ from the flue gas stream using a vacuum pressure swing process. From extensive investigation, they found out that the best MOF to be used was a Mg/DOBDC one, which has a 21.7 wt% CO₂ loading capacity. Estimations showed that, if a similar system would be applied to a large scale power plant, the cost of energy would increase by 65%, while a NETL baseline amine based system would cause an increase of 81% (the DOE goal is 35%). Also, each ton of CO₂ avoided would cost $57, while for the amine system this cost is estimated to be $72. The project ended in 2010,estimating that the total capital required to implement such project in a 580 MW power plant was 354 million dollars.

Maude work to be added to Carbon capture and storage article:

Capturing CO2 is most effective at point sources, such as large fossil fuel or biomass energy facilities, industries with major CO2 emissions, natural gas processing, synthetic fuel plants and fossil fuel-based hydrogen production plants. Extracting CO2 from air is also possible, but not very practical because the CO2 is not concentrated.[9]

Concentrated CO2 from the combustion of coal in oxygen is relatively pure, and could be directly processed. Impurities in CO2 streams could have a significant effect on their phase behaviour and could pose a significant threat of increased corrosion of pipeline and well materials.[10] In instances where CO2 impurities exist and especially with air capture, a scrubbing separation process would be needed.[11] According to the Wallula Energy Resource Center in Washington state, by gasifying coal, it is possible to capture approximately 65% of carbon dioxide embedded in it and sequester it in a solid form.[12]

CO2 can be separated, or captured, out of flue gas post-combustion with various technologies, namely  absorption (or scrubbing), adsorption, or membrane separation processes. Currently, amine scrubbing is the dominant technology for capture capture. Metal-organic frameworks (MOFs) are a novel, promising carbon capture technology alternative to amine scrubbing. MOFs are used to ___ carbon dioxide. They can be use pre-combustion, post-combustion, or in oxy-fuel combustion in the process of burning fossil fuels to reduce carbon dioxide emissions.

Organisms that produce ethanol by fermentation generate cool, essentially pure CO2 that can be pumped underground.[13] Fermentation produces slightly less CO2 than ethanol by weight.

Broadly, three different types of technologies for scrubbing exist: post-combustion, pre-combustion, and oxyfuel combustion:

An alternate method under development is chemical looping combustion (CLC). Chemical looping uses a metal oxide as a solid oxygen carrier. Metal oxide particles react with a solid, liquid or gaseous fuel in a fluidized bed combustor, producing solid metal particles and a mixture of carbon dioxide and water vapor. The water vapor is condensed, leaving pure carbon dioxide, which can then be sequestered. The solid metal particles are circulated to another fluidized bed where they react with air, producing heat and regenerating metal oxide particles that are recirculated to the fluidized bed combustor. A variant of chemical looping is calcium looping, which uses the alternating carbonation and then calcination of a calcium oxide based carrier as a means of capturing CO2.[20]

A few engineering proposals have been made for the more difficult task of removing CO2 from the atmosphere – a form of climate engineering – but work in this area is still in its infancy. Capture costs are estimated to be higher than from point sources, but may be feasible for dealing with emissions from diffuse sources such as automobiles and aircraft.[21] The theoretically required energy for air capture is only slightly more than for capture from point sources. The additional costs come from the devices that use the natural air flow. Global Research Technologies demonstrated a pre-prototype of air capture technology in 2007.[22]

Jesika work to be added to Metal-organic framework article:

Because of their small, tunable pore sizes and high void fractions, MOFs are a promising potential material for use as an adsorbent to capture CO₂.  MOFs could provide a more efficient alternative to traditional amine solvent-based methods in CO2 capture from coal-fired power plants.^[1]

MOFs could be employed in each of the main three carbon capture configurations for coal-fired power plants: pre-combustion, post-combusiton, and oxy-combustion.^[2] However, since the post-combustion configuration is the only one that can be retrofitted to existing plants, it garners the most interest and research. In post-combustion carbon capture, the flue gas from the power plant would be fed through a MOF in a packed-bed reactor setup. Flue gas is generally 40 to 60 °C with a partial pressure of CO2 at 0.13 - 0.16 bar. The main component CO2 must be separated from is nitrogen, but there are small amounts of other gasses as well. A typical flue gas composition is: 73-77% N2, 15-16% CO2, 5-7% H2O, 3-4% O2, 800 ppm SO2, 10 ppm SO3, 500 ppm NOx, 100 ppm HCl, 20 ppm CO, 10 ppm hydrocarbons, 1ppb Hg.^[2]

CO2 can bind to the MOF surface through either physisorption or chemisorption, where physisorption occurs through van der Waals interactions and chemisorption occurs through covalent bonds being formed between the CO2 and MOF surface.^[3] Once the MOF is saturated with CO2, the MOF would then be regenerated (CO2 is removed from the MOF to be transported elsewhere for sequestration or enhanced oil recovery) through either a temperature swing or a pressure swing. In a temperature swing, the MOF would be heated up until CO2 desorbs; temperature swing regeneration is usually used in post-combustion configurations where the heat is supplied from heat exchangers with the power plant. To achieve working capacities comparable to the amine solvent process, the MOF must be heated up to around 200 C. In a pressure swing, the pressure would be decreased until CO2 desorbs; this would usually be used in a pre-combustion carbon capture configuration.^[4]

The Yaghi group tested various MOFs for their performance in absorbing CO₂ and found their highest CO₂ capacity achieved of 33.5 mmol CO₂ / g MOF at ambient temperature and 35 bar, using MOF-177.  For comparison, zeolite 13X has a CO₂ capacity of 7.4 mmol/g at 32 bar and ambient temperature, and MAXSORB has a capacity of 25 mmol/g at 35 bar and ambient temperature.  MOF-177 has pore sizes of 11 and 17 Angstroms and is comprised of zinc complexes connected by benzene rings, with the repeating structure being Zn₄O(1,3,5-benzenetribenzoate)_2.  ^[5]

In addition to their tunable selectivities for different molecules, another property of MOFs that makes them a good candidate for carbon capture is their low heat capacities.  Monoethanolamine (MEA) solutions, the leading method for capturing CO₂ from flue gas, have a heat capacity between 3-4 J/g K since they are mostly water.  This is one of the main factors contributing to the energy penalty in the solvent regeneration step— when the absorbed CO₂ is removed from the MEA solution so that it can be reused.  MOF-177, on the other hand, has a heat capacity of 0.5 J/g K at ambient temperature.  The low heat capacities of MOFs could significantly reduce the energy penalty of carbon capture, which is currently around 30% of plant power for MEA solution-based methods.^[2]

In a project sponsored by the DOE and operated by UOP LLC in collaboration with faculty of four different universities, MOFs were tested as possible carbon dioxide removal agents in post-combustion flue gas. They were able to separate 90% of the CO₂ from the flue gas stream using a vacuum pressure swing process. From extensive investigation, they found out that the best MOF to be used was Mg(dobdc), which has a 21.7 wt% CO₂ loading capacity. Estimations showed that, if a similar system would be applied to a large scale power plant, the cost of energy would increase by 65%, while a NETL baseline amine based system would cause an increase of 81% (the DOE goal is 35%). The cost of capturing CO₂  would be $57 / ton CO2 captured, while for the amine system the cost is estimated to be $72 / ton CO2 captured. The project estimated that the total capital required to implement such project in a 580 MW power plant would be $354 million.^[6]