WO2019202105A1

WO2019202105A1 - Selective adsorption of carbon dioxide by a metal-organic framework

Info

Publication number: WO2019202105A1
Application number: PCT/EP2019/060148
Authority: WO
Inventors: Kyriakos STYLIANOU; Berend Smit; Arunraj CHIDAMBARAM; Peter Boyd; Tom WOO
Original assignee: Ecole Polytechnique Federale De Lausanne (Epfl)
Priority date: 2018-04-20
Filing date: 2019-04-18
Publication date: 2019-10-24

Abstract

The present invention relates to the removal of carbon dioxide from gases. More particularly, the invention relates to the use of metal-organic frameworks for a selective adsorption of carbon dioxide from a gas. Further, the invention relates to a method for removing carbon dioxide from a gas, preferably at ambient pressure with a metal organic framework.

Description

Selective adsorption of carbon dioxide by a metal-organic framework

The present invention relates to the removal of carbon dioxide from gases. More particularly, the invention relates to the use of specific metal-organic frameworks for a selective adsorption of carbon dioxide from a gas. Further, the invention relates to a method for removing carbon dioxide from a gas, preferably at ambient pressure with a metal organic framework.

Background of the invention

Traditionally the separation of carbon dioxide (C0₂) has been especially important for the sweetening of natural gas, where the aim is to separate carbon dioxide from methane (CH₄). As this is a relatively expensive process, the conventional use was focussed on natural gas fields, where pipeline corrosion required the removal of carbon dioxide before the natural gas could be transported. Recently, there has been increasing attention to sources of natural gas with low carbon dioxide concentrations such as mining or biogas. In addition, the separation of carbon dioxide from flue gases has attracted a lot of attention owing to the alarming reports that links global warming and climate change with the steadily increasing concentration of carbon dioxide in the atmosphere. Since 1970, the annual global emissions of carbon dioxide have risen drastically by around 80% due to the increasing dependence on the combustion of fossil fuels (coal, petroleum and natural gas) such that the concentration of carbon dioxide in the atmosphere is at an all-time high. Thus, there is a need to reduce carbon dioxide.

The need for strategies to reduce global atmospheric concentrations of carbon dioxide has prompted a large number of projects to be implemented in order to tackle climate change through the development and application of different carbon capture and storage technologies. Carbon Capture, Utilization and Storage (CCUS) is currently being investigated intensively as a way of limiting future CO2 emissions from large, stationary sources such as fossil fuel-fired power plants, waste incineration, cement and steel production followed by compression, transport and permanent storage or the re-use of carbon dioxide as a source of carbon for the chemical industry. The slow deployment of fully-integrated commercial CCUS schemes is mainly due to the considerable cost of the capture phase, which represents approximately two thirds of total effort and the corresponding cost for CCUS.

One of the current technologies for post-combustion carbon capture is scrubbing with liquid amine -based solutions. Although amines are efficient materials for the capture of carbon dioxide from flue gas, there are numerous problems with this technology. For example, said technology reduces the efficiency of a power plant by as much as 30%. In addition, the amines and their solutions are reported to be viscous, toxic and corrosive and have mass transfer limitations deterring the solubility of carbon dioxide. In addition, amines are sensitive to oxidation and oxygen present in the flue gas oxidizes the amines and decreases their activity. Hence, a continuous supply of amines is required. Finally, this process requires significant amounts of water, which is not always available. In summary, this technology leads to a range of technical difficulties and these efforts motivated the research for alternative solutions.

An alternative is solid-based adsorption of carbon dioxide, wherein the liquid-amine is replaced by a solid material to prevent or at least significantly reduce many of the disadvantages such as corrosion, need for water dedicated to the above-mentioned amine solutions. The solid adsorption or membrane -based capture technologies involve the selective adsorption or permeation of carbon dioxide from gas such as flue gas through favorable intermolecular forces between carbon dioxide molecules and a selected type of (porous) solid. These techniques are promising as it is possible to tune/optimize the interactions that occur between the substrate and carbon dioxide.

One kind of solid material considered suitable for selective carbon dioxide adsorption is a carbon-based material such as carbon nanotubes and carbon molecular sieves. These materials exhibit a good selectivity of carbon dioxide over nitrogen (N₂). However, most of these carbon materials are amorphous, their capacity for carbon dioxide is quite low, thus a large amount of material would be needed to purify carbon dioxide and they can adsorb water, which deters the application of activated carbon for practical purposes as post combustion flue gas contains water. Another kind of solid material is a microporous, aluminosilicate mineral, also known as zeolites. However, these materials are reported to exhibit either a low carbon dioxide selectivity or, when having an enhanced selectivity, a strong affinity towards water

(H₂O). Further, amongst the several classes of porous materials, metal organic frameworks (usually abbreviated as MOFs) represent another possible class of materials for a selective capture of carbon dioxide. The range of potential structures encompassed by this class are vast, as different structures and properties can be obtained not only by the choice of metal and ligand but also by the connectivity of the structure, such as different pore sizes and shapes as well as the groups decorating their pore surface.

To enhance the interactions between a MOF and carbon dioxide in the presence of water, amino-based ligands within the MOF structure were incorporated (Couck S. et al., Journal of the American Chemical Society 2009, 131 , page 6326) and a high selectivity for carbon dioxide over nitrogen is achieved. The loading of MOF with amines, however, is reported not to be consistent and to vary considerably. In addition, the amines within the pores of the MOF can be washed out when the MOF, amino- appended Mg-dopbdc, comes into contact with water and the amines have low stability and react with oxygen.

An alternative strategy to enhance the interactions between a MOF and carbon dioxide is the provision of unsaturated metal sites (Casky S. et al, Journal of the American Chemical Society 2008, 130, page 10870). Liu J. et al., Langmuir 2010 describes HKST-l , which is a MOF material consisting of open Cu(II) sites which are ideal for carbon dioxide capture.

Mason et al., Journal of the American Chemical Society 2015, 137, page 4787, describe MOF-74, which is a stable material and can be synthesized with many transition metals.

Upon activation, it is possible to generate open metal sites which are found to be a key asset for carbon dioxide capture.

Johnson et al., Chemistry-a European Journal, 2014, 20, pg 7632, introduced a metal organic framework, UNLPF-2, which was designed to given an optimal metal-metal distance between the coordinatively unsaturated metal centers. These metal sites serve as binding sites for C0₂.

Nandi and Goldberg, Chemical Communications, 2014, 50, page 13612, describe a strategy to capture C02 by inserting metal ions inside a porphyrin host and placing two these metal-containing porphyrin rings at an optimal distance to bind C0₂ through a metal-CCL-metal complex.

Zhang and Zhao, Patent No. WO2017052474A1 , 2017, describe the synthesis of nanosheets of MOFs. These nanosheets might be used as membranes to capture CO2 but have limited use in adsorption studies which require three-dimensional crystals.

A property of these materials is that both the uptake capacity of carbon dioxide as well as the selective adsorption of carbon dioxide over other gases such as nitrogen is significantly affected in the presence of water. Thus, up to now such materials cannot reasonably be used for post-combustion separation

In view of the above, many promising materials for carbon dioxide separation have been reported but the large majority of these materials requires dry flue gasses. This implies the requirement of drying the flue gas stream before the separation, which adds further restrictions as well as a prohibitive cost to the process.

Thus, there is a need for a material which can be used for carbon dioxide adsorption, wherein said material has a high selective adsorption of carbon dioxide over further gases, in particular over the gases contained in flue gas.

Hence, it was an object of the present invention to overcome the above drawbacks.

It was an object of the present invention to provide a material which can be used for selectively adsorbing carbon dioxide from a mixture of gases such as flue gas or waste gas. In particular, said material should exhibit a high selectivity towards carbon dioxide over nitrogen. In addition, the material should provide a high uptake capacity of carbon dioxide. More particularly, neither the selectivity with regard to carbon dioxide nor the uptake capacity should be negatively affected by the presence of water. Moreover, the carbon dioxide adsorption should not compete with the adsorption of water.

Further, said material should be stable both at normal temperatures as well as at elevated temperatures of up to 90°C in the presence of air, i.e. the material should not be sensitive to oxygen at least until a temperature of 90°C.

In addition, the material should be non-corrosive and easy to prepare, preferably at low costs.

Moreover, the material should be reclaimable under mild conditions, i.e. at temperatures under l00°C for less than one hour.

Further, it was an object to provide a method in which carbon dioxide is selectively adsorbed from a gas stream such as flue gas. The method should provide a substantial removal of the carbon dioxide from said gas stream. The method inter alia should provide a carbon dioxide-free gas which is of particular interest for environmental reasons as well as for chemical reasons when conducting reactions with ambient air to prevent possible side reactions with the carbon dioxide generally contained therein.

Summary

The present invention has unexpectedly solved the above objectives by the use of a metal organic framework for the selective adsorption of carbon dioxide, wherein the metal organic framework comprises two or more parallel aromatic planes which have a specific distance to each other (Figure 1).

Thus, the subject of the present invention is the use of a metal organic framework for the selective adsorption of carbon dioxide, wherein the metal organic framework comprises an aromatic ligand and a metallic component, wherein the ligand forms parallel aromatic planes having a distance to each other of 0.65 nm to 0.75 nm.

Further, a method for selectively adsorbing carbon dioxide from a gas stream is provided, wherein the carbon dioxide is adsorbed by a metal organic framework, wherein the metal organic framework comprises an aromatic ligand and a metallic component, wherein the ligand forms parallel aromatic planes having a distance to each other of 0.65 nm to 0.75 nm.

Thus, another subject of the present invention is a method for removing carbon dioxide from a gas comprising the steps of

(i) providing a gas comprising carbon dioxide,

(ii) contacting the gas with a metal organic framework, wherein the metal organic framework comprises an aromatic ligand and a metallic component, wherein the ligand forms parallel aromatic planes having a distance to each other of 0.65 nm to 0.75 nm, and (iii) allowing the carbon dioxide to be adsorbed by the metal organic framework.

Gases or gas streams containing carbon dioxide are widely known. For example, the atmosphere of the earth can be regarded as a mixture of gases surrounding our planet and is commonly known as air. The carbon dioxide content is reported to be about 0.04% by volume. Further, carbon dioxide is obtained for example during the combustion of organic material. Examples for further gases containing carbon dioxide are waste gas from internal combustion machines, waste gas from energy plants, industrial waste gases such as flue gas or gases from fermentation processes. The latter named gases are reported to contain significantly higher carbon dioxide contents. Internal combustion machines for oil are reported to have carbon dioxide contents of more than 15% by volume. Further, carbon dioxide needs to be removed from various sources of natural gases such as

wet biogas being a mixture with a ratio of carbon dioxide : methane : water of about 3 : 6 : 1 ,

sour biogas being a mixture with a ratio of carbon dioxide : methane : hydrogen sulfide of about 3 : 7 : 0.2,

coal mine gas being a mixture with a ratio of carbon dioxide : methane : water of about 5 : 85 : 10, and

shale gas being a mixture with a ratio of carbon dioxide : methane :water of about 45 : 45 : 10.

Generally, metal-organic frameworks (herein also referred to as MOFs) are crystalline materials containing metallic components, such as metal ions and clusters, also referred to as so-called secondary building units (SBUs) and aromatic ligands, also referred to as linkers, as connection units between the metallic components, wherein preferably one, two, or three-dimensional structures are formed. Thus, a metal-organic framework can be regarded is a coordination network with aromatic ligands (sometimes also referred to as “struts”), optionally containing voids. Expressed differently, metal- organic frameworks can be regarded as a subclass of coordination polymers wherein the metal-organic frameworks are often porous.

The metal-organic framework for use according the present invention comprises two or more parallel aromatic planes which have a distance to each other of 0.65 nm to 0.75 nm, preferably a distance to each other of 0.65 nm, 0.66 nm, 0.67 nm, 0.68 nm, 0.69 nm, 0.70 nm, 0.71 nm. 0.72 nm, 0.73 nm, 0.74 nm and 0.75 nm.

Generally, the term“parallel” is used for lines or planes being present side by side and having the same distance continuously between them. Aromatic compounds are often not completely planar, but their atoms and/or substituents can be twisted from the plane. Thus, in line with the present application the term“parallel” should also apply to planes which are not completely parallel, but slightly twisted to each other, i.e. twisted to each other by not more than an angle of 30°, preferably by an angle of 5° to 25°, compared to planes being completely parallel.

An aromatic plane of the metal-organic framework comprises aromatic molecules (ligands), wherein said molecules are assembled such that they built an aromatic plane. An aromatic ligand is referred to as an organic compound comprising at least one aromatic residue. An aromatic ligand is a residue including at least one ring system predominately containing carbon, nitrogen, sulphur or oxygen atoms, wherein said ring system comprises, according to the Huckel-Rule, a number of 4n+2 (n=0, 1 , 2, ...) delocalized electrons in conjugated double bonds, free electron-pairs or unoccupied p- orbitals.

In a preferred embodiment of the invention an aromatic residue refers to a residue with an aromatic skeletal structure, wherein the ring atoms of the aromatic skeletal structure are carbon or nitrogen atoms. In an alternatively preferred embodiment the aromatic residue can be substituted with one or more substituents. Substituents can preferably be selected independently from one or more of the following substituents: alkyl groups with 1 to 4 carbon atoms, halogen, nitro, nitrile, carboxylic group, carboxylic esters and carboxylic amide, methoxy and ethoxy.

In a preferred embodiment the aromatic ligand is a molecule which comprises from 18 to 80 carbon atoms, preferably 20 to 70, more preferably 22 to 60 carbon atoms.

In a further preferred embodiment, the aromatic ligand is a molecule which comprises 1 , 2, 3 or 4 carboxylic group(s), preferably 3 or 4 carboxylic groups, in particular 4 carboxylic groups.

It is preferred that the aromatic ligand of the metal-organic framework is selected from the group consisting of 4,4',4",4"'-(porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid; 4,4',4",4"'-(l ,6-dihydropyrene-l ,3,6,8-tetrayl)tetrabenzoic acid; 4',5'-bis(4-carboxy- phenyl)-[l ,r:2',l"-terphenyl]-4,4"-dicarboxylic acid; 4,4',4",4"'-(anthracene-2,3,6,7- tetrayl)tetrabenzoic acid; 4,4',4",4"'-(pyrazino[2,3-g]quinoxaline-2,3,7,8-tetrayl)tetra- benzoic acid; 4,4',4",4"'-(perylene-2,5,8,l l-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'- (chrysene-l,3,7,9-tetrayl)tetrabenzoic acid; 4,4',4",4"'-(naphtho[7,8,l ,2,3-nopqr]tetra- phene-l ,3,7,9-tetrayl)tetrabenzoic acid; 4,4',4",4"'-(l ,10-dihydrodi- benzo[cd,lm]perylene-l ,3,8,l0-tetrayl)tetrabenzoic acid; 4,4',4",4"'-(l ,l 0-dihydrodi- benzo[bc,kl]coronene-l ,3,8,l0-tetrayl)tetrabenzoic acid; 4,4',4",4"'-(coronene- l ,4,7,l0-tetrayl)tetrabenzoic acid; 3,3',3",3"'-(l ,6-dihydropyrene-l ,3,6,8-tetrayl)tetra- propiolic acid; 3,3',3",3"'-(benzene-l ,2,4,5-tetrayl)tetrapropiolic acid; 3, 3', 3", 3"'- ( anthracene-2, 3, 6, 7-tetrayl)tetrapropiolic acid; 3,3',3",3"'-(pyrazino[2,3-g]quinoxaline- 2,3,7,8-tetrayl)tetrapropiolic acid; 3,3',3",3"'-(perylene-2,5,8,l l -tetrayl)tetrapropiolic acid; 3,3',3",3"'-(chrysene-l ,3,7,9-tetrayl)tetrapropiolic acid; 3, 3', 3", 3"'-

(naphtho[7,8,l ,2,3-nopqr]tetraphene-l,3,7,9-tetrayl)tetrapropiolic acid; 3,3’,3", 3"'- (l ,l0-dihydrodibenzo[cd,lm]perylene-l ,3,8,l0-tetrayl)tetrapropiolic acid; 3, 3', 3", 3"'- (l ,l0-dihydrodibenzo[bc,kl]coronene-l ,3,8,l0-tetrayl)tetrapropiolic acid; 3 ,3’,3", 3"'- (coronene-l ,4,7,10-tetrayl)tetrapropiolie acid; 3,3',3",3"'-(porphyrin-5,l0,l5,20- tetrayl)tetrapropiolic acid; 6',8'-bis(7-carboxypyren-2-yl)-[2,l':3',2"-terpyrene]-7,7"- dicarboxylic acid and 4,4',4",4"'-(benzo-porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid, more preferably 4,4',4",4"'-(porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid; 4,4',4",4"'-(l ,6-dihydropyrene-l ,3,6,8-tetrayl)tetrabenzoic acid; 4',5'-bis(4-carboxy- phenyl)-[l ,r:2',l"-terphenyl]-4,4"-dicarboxylic acid; 4,4',4",4"'-(anthracene-2,3,6,7- tetrayl)tetrabenzoic acid; 4,4',4",4"'-(pyrazino[2,3-g]quinoxaline-2,3,7,8-tetrayl)tetra- benzoic acid; 4,4',4",4"'-(perylene-2,5,8,l 1 -tetrayl)tetrabenzoic acid and 4, 4', 4", 4"'- (benzo-porphyrin-5,l 0,l5,20-tetrayl)tetrabenzoic acid, in particular 4, 4', 4", 4"'- (porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid, 4,4',4",4"'-(l,6-dihydropyrene-l ,3,6,8- tetrayl)tetrabenzoic acid and 4',5'-bis(4-carboxyphenyl)-[l ,l':2',l"-terphenyl]-4,4"- dicarboxylic acid.

In Figure 2 the formulae of 4,4',4",4"'-(porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid (also referred to as SION-66); 4,4',4",4"'-(l ,6-dihydropyrene-l ,3,6,8-tetrayl)tetra- benzoic acid (also referred to as SION-67); 4',5'-bis(4-carboxyphenyl)-[l ,l':2',l"- terphenyl]-4,4"-dicarboxylic acid (also referred to as SION-68);4,4',4",4"'-(anthracene- 2,3,6,7-tetrayl)tetrabenzoic acid (also referred to as SION-69); 4, 4', 4", 4"'-

(pyrazino[2,3-g]quinoxaline-2,3,7,8-tetrayl)tetrabenzoic acid (also referred to as SION-70); 4,4',4",4"'-(perylene-2,5,8,l l -tetrayl)tetrabenzoic acid (also referred to as SION-71) and 4,4',4",4"'-(benzo-porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid (also referred to as SION-89) are shown.

As mentioned above, apart from the aromatic ligand a metal organic framework comprises a metallic component, which can serve as metallic junction, such as metallic molecules, ions or clusters. A metal can be considered as a chemical element being in the periodic system left and below a line from boron and astat, i.e. the elements having the atomic numbers 3,4, 1 1, 12, 13, 19 to 32, 37 to 51 and 55 to 83.

In a preferred embodiment of the invention the metallic component is magnesium, aluminium, zinc, cadmium or a transition metal having an atomic number of 21 to 29 or 39 to 47, i.e. scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium molybdenum, technetium, ruthenium, rhodium, palladium silver, more preferably vanadium, copper, nickel, chromium, zinc and aluminium, in particular aluminium.

In an alternative preferred embodiment of the invention the metallic component is magnesium, aluminium, cadmium or a transition metal having an atomic number of 21 to 29 or 39 to 47, i.e. scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium molybdenum, technetium, ruthenium, rhodium, palladium silver, more preferably vanadium, copper, nickel, chromium, and aluminium, in particular aluminium. The distance between the aromatic planes can be adapted by the choice of the metallic component.

In a further alternative embodiment the metallic component is not zinc or not cobalt, preferably not zinc. In a preferred embodiment the metallic component is not zinc or cobalt, if the organic ligand is 4,4',4",4"'-(porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid.

In a preferred embodiment the MOF which is used for adsorbing carbon dioxide comprises aluminium as metallic component and 4,4',4",4"'-(porphyrin-5,l 0,15,20- tetrayl)tetrabenzoic acid; 4,4',4",4"'-(l ,6-dihydropyrene-l ,3,6,8-tetrayl)tetrabenzoic acid; 4',5'-bis(4-carboxyphenyl)-[l ,l':2',l"-terphenyl]-4,4"-dicarboxylic acid as aromatic ligand.

A MOF as described above, which comprises two parallel aromatic planes which have a distance to each other of 0.65 nm to 0.75 nm, can be considered as binding pocket (also referred to as “adsorbaphore” - Figure 1), which is especially suitable for adsorbing carbon dioxide, preferably a monolayer of carbon dioxide molecules. A preferred density of adsorbaphores is from 0.10 to 0.60 mmol/cm ³, more preferably from 0.14 to 0.55 mmol/cm ³, even more preferably from 0.16 to 0.45 mmol/cm ³. These parallel aromatic rings form an ideal adsorption site for C0₂ (see figure 9) as the distance between these rings is such that an optimal energetics (see figure 1). As these rings do not contain any metals these adsorbaphores have a low affinity for water.

In other words, in a preferred embodiment the metal organic framework of the present invention is used for the selective adsorption of carbon dioxide, wherein the CO2 binds without coordination with the metal of the metal organic framework. Contrary, the CO2 binds in a sandwich of two aromatic planes (e.g. two aromatic rings). In a preferred embodiment the adsorbed CO2 molecule has a distance within 0.5 nm (5 A) to the adsorbophore. This is a fundamentally different binding mode compared to the prior art, where metal sites serve as binding sites for CO2. Usually, in the prior art systems the adsorbed CO2 molecule has a distance of less than 0.5 nm (5 A) to the metal site.

In a preferred embodiment of the present invention the adsorbed CO2 molecule does not have a distance of less than 0.5 nm (5 A) to any metallic component of the MOF.

In a preferred embodiment the adsorbed CO2 molecule has a distance of more than 0.5 nm (5 A) to any metallic component of the MOF.

In an alternative preferred embodiment of the present invention the adsorbed CO2 molecule has a distance of at least 0.5 nm (5 A) to 5 nm (50 A), preferably 0.55 nm (5.5 A) to 4 nm (4 A), more preferably 0.6 nm (6 A) to 3 nm (30 A), in particular 0.7 nm (7 A) to 2.5 nm (25 A) to any metallic component of the MOF.

The distance is determined by using the crystallographic software Mercury, Version 3.6 as described below in the experimental part.

The different binding mode of the present invention leads to unexpected advantages, as the metal will make the material attractive for water. In the above context the term "coordination" non-covalently binding through van der Waals interactions, hydrogen bonds, or Coulombic interactions.

The above described mode of binding (without coordination with the metal) can be preferably achieved by the above-mentioned components, by the distances between the planes and/or by the preferred embodiments as described below.

In preferred embodiment a MOF as used according to the invention has a BET surface area of more than 750 m²/g, preferably from 800 m²/g to 2000 m²/g, in particular of 850 m²/g to 1500 m²/g. The BET surface is determined as described in the experimental section below.

In preferred embodiment a MOF as used according to the invention has a pore volume form 0.30 cm³/g to 0.75 cm³/g, preferably from 0.35 cm³/g to 0.70 cm³/g, in particular from 0.40 cm³/g to 0.60 cm³/g. The pore volume is determined as described in the experimental section below.

Further, the carbon dioxide isosteric heat of adsorption which indicates the binding energy of the adsorbed carbon dioxide to the MOF as used according to the present invention is from -15 kJ/mol to -50 kJ/mol, preferably from -18 kJ/mol to -45 kJ/mol, in particular from -20 kJ/mol to -40 kJ/mol. Carbon dioxide isosteric heat of adsorption is determined as described in the experimental section below.

Generally, MOFs can be obtained by solvothermal synthesis, wherein such synthesis can be carried out in closed vessels at high pressures and at temperatures above the boiling point of a solvent. Suitable routes of syntheses are illustrated in the experimental section below.

A further subject of the invention is the use of a metal organic framework for the selective adsorption of carbon dioxide, wherein the metal organic framework comprises an aromatic ligand and a metallic component, wherein the aromatic planes of the ligands are arranged such that until a relative humidity (RH) of 60% the adsorption of water essentially does not compete with the adsorption of carbon dioxide, i.e. as long as the relative humidity (RH) is less or equal than 60%, the water contained in gas stream is essentially not adsorbed such that the adsorption of carbon dioxide at the active site of a molecular organic framework takes place without any interference/competition of water at the same time.

As indicated above the present invention relates to a method for removing carbon dioxide from a gas comprising the steps of

(i) providing a gas comprising carbon dioxide,

(ii) contacting the gas with a metal organic framework, wherein the metal organic framework comprises an aromatic ligand and a metallic component, wherein the ligand forms parallel aromatic planes having a distance to each other of 0.65 nm to 0.75 nm, and

(iii) allowing the carbon dioxide to be adsorbed by the metal organic framework, wherein preferably the carbon dioxide is coordinated between two aromatic claims of the metal organic framework, and wherein preferably the carbon dioxide is not coordinated to the metallic component of the metal organic framework.

Step (i) of the present invention is the provision of a gas comprising carbon dioxide, preferably carbon dioxide at ambient pressure. In step (i) any gas comprising carbon dioxide can be used. Examples are gases comprising carbon dioxide which can for example be obtained by the combustion or fermentation of organic material. Examples for such gases containing carbon dioxide are waste gas from internal combustion machines, waste gas from energy plants, industrial waste gases, such as flue gas, or gases from fermentation processes. These gases are reported to contain significantly higher carbon dioxide contents than the air. Alternatively, also the atmosphere of the earth can be regarded as a mixture of gases surrounding our planet and commonly known as air. Air is reported to contain a certain content of carbon dioxide. It is often desirable, for example for an atmosphere in which reactions can be carried out, to have air with a significantly lower content of carbon dioxide as the one in normally accessible air (about 0.04 vol.%).

In a preferred embodiment in step (i) the gas comprising carbon dioxide is provided at ambient pressure. Ambient pressure can also be referred to as surrounding pressure. For example, in case the surrounding pressure is caused by the weight of air this is referred to as atmospheric pressure. Further, the atmospheric pressure varies with altitude, for example the atmospheric pressure of air at sea level is 101325 Pa (1 atmosphere), while the atmospheric pressure of air at an altitude of 5486.4 meters (18Ό00 feet) is 50663 Pa (1/2 atmosphere). In addition, the atmospheric pressure varies with weather conditions, such as high- and low-pressure areas.

In view of the above, ambient pressure depends on different conditions. In this application, providing a gas comprising carbon dioxide at ambient pressure excludes providing the gas under pressurized conditions.

In an alternative embodiment the gas can be provided under pressurized conditions. Pressurized conditions are conditions under which a gas is compressed to a smaller volume, thereby increasing its density. Examples are pressurized gases in high pressure containers, for example pressurized air.

Gases like air can further comprise water in vaporous form, which can be referred to as air moisture or humidity. One measurement of humidity is the relative humidity, which depends on the temperature. The relative humidity measures the current absolute humidity relative to the maximum humidity for a specific temperature. The relative humidity f is expressed in per cent and calculated by the following equation:

with

/being the current absolute humidity; and

fmax being the maximum humidity at that temperature.

The relative humidity can for example be determined by a hygrometer such as a hair hygrometer.

A very common value for relative humidity of ambient air at 20°C, for example in Germany, is about 50%.

In a preferred embodiment the gas comprising carbon dioxide provided in step (i) is substantially free of water. In this application a gas being substantially free of water can be referred to as having a relative humidity of less than 5%, preferably less than 2%, more preferably less than 0.5%. In a particularly preferred embodiment the relative humidity of the gas comprising carbon dioxide is 0%, i.e. the gas does not contain water. Gases having a relative humidity of less than 5% can be regarded as dry gases, wherein the conditions can be accordingly referred to as dry conditions. Drying of a gas can be conducted by contacting the gas with a desiccant. A desiccant is a substance able to bind water, for example either by physically adsorbing water or reacting with water. Drying can preferably be conducted by directing gas over or through a desiccant, such as a molecular sieve, bentonite, silica gel and or by reacting the water with a desiccant, such as concentrated sulfuric acid, for example by blubbing it through said acid.

In an alternatively preferred embodiment, the gas comprising carbon dioxide provided in step (i) can contain a humidity of more than 5% up to 100%, wherein the conditions can be accordingly referred to as humid conditions. A relative humidity of 100% means that the air contains as much moisture, for example in the form of vapor, as it can at a given temperature. It was unexpectedly found that the MOFs as described in the present invention can be used to selectively adsorb carbon dioxide under dry as well as under humid conditions.

In step (ii) of the present method the gas from step (i) is contacted with a metal organic framework comprising two or more parallel aromatic planes which have a distance to each other of 0.65 nm to 0.75 nm (6.5 A to 7.5 A). Bringing the gas from step (i) in contact with the metal organic framework is meant as conducting any method for contacting the gas from step (i) with at least the surface of the metal organic framework. Thus, contacting the gas from step (i) with the metal organic framework can for example be conducted by leading the gas through the crystalline, porous structure of the metal organic framework or sucking the gas into the metal organic framework.

In step (iii) the carbon dioxide is allowed to be adsorbed by the metal organic framework. It is preferred, that the carbon dioxide is coordinated between two aromatic claims of the metal organic framework. In other words, the carbon dioxide preferably binds between two aromatic planes of the metal organic framework. Further, the carbon dioxide is preferably not coordinated to the metallic component of the metal organic framework. In other words, the carbon dioxide preferably does not bind to the metallic component of the metal organic framework.

It is particularly preferred, that the carbon dioxide is selectively adsorbed. The term selectively means that the molar ratio of adsorbed C0₂ to non-C0₂-gases is greater than 5, preferably from 50 to 5, more preferably from 35 to 8. The other constituents of the gas, such as nitrogen or oxygen in ambient air, are not adsorbed under the above conditions, whereas carbon dioxide is adsorbed by the metal organic framework. Thus, step (iii) can preferably be regarded as a step in which the carbon dioxide is captured in the metal organic framework. By being captured the carbon dioxide is bound to a solid material and maintained there. Consequently, the remaining gas can be regarded as purified gas from which carbon has been removed, preferably completely. Step (ii) and step (iii) are preferably carried out simultaneously.

Further, step (ii) and/or (iii) are carried out at a temperature of -20°C to l00°C, preferably from 0° to 80°C, in particular from 20°C to 70°C.

Further, step (ii) and/or (iii) are carried out for 5 minutes to 5 hours.

In a preferred embodiment of the present method the gas is air, industrial waste gas or a natural gas selected from wet biogas, sour biogas, coal mine gas and shale gas. As far as their components are concerned the same applies as described above.

Further, if desired, the carbon dioxide adsorbed in the metal organic framework can be released therefrom by applying a temperature of about 80°C. The release of carbon dioxide from the metal organic framework can be considered as regeneration of the active side to adsorb carbon dioxide. It is preferred that the regeneration of the metal organic framework is carried out at a temperature between 80 and l00°C, more preferably at about 80°C.

It unexpectedly turned out that the method of the invention for removing carbon dioxide, preferably for selectively removing carbon dioxide, from a gas can be carried out independently of the relative humidity of the gas containing carbon dioxide, i.e. the selective adsorption is not negatively affected by the presence of water in the gas containing carbon dioxide. This enables the selective removal of carbon dioxide from a gas without the need of a preceding drying step of the gas and thus without the need of an extensive instrumental effort and complex equipment.

The invention will now be illustrated with reference to the following examples. Experimental part:

Reagents and solvents

4,4',4",4"'-(l ,6-dihydropyrene-l ,3,6,8-tetrayl)tetrabenzoic acid (TBAPy) was prepared according to the procedure described in Stylianou et al., Journal of the American chemical Society, 201 , 132, page 41 19. All further chemicals were purchased from commercial sources and used as received, i.e. without further purification.

X-ray Powder Diffraction

The powder X-ray diffraction (PXRD) shown herein was carried out on a Bruker D8 Advance with TWIN/TWIN optics and a LYNXEYE XE detector, equipped with a robotic sample changer. The samples were loaded on low background silicon crystal sample holders and the PXRD data was collected throughout a 2Q range of 2-20‘tising a copper (Cu) X-ray source. The background was subtracted for all the PXRD plots presented herein. The sample holders were rotated about their central axes during data collection to improve statistics. All measurements were performed at 23°C (room temperature).

Adsorption

The C0₂ (293 K, 303 K, and 313 K) and N₂ (77 K, 313 K) isotherms shown herein were collected by gravimetric method using an IGA system (Intelligent Gravimetric Analyser, Hiden Isochema Ltd., Warrington, ETC). The water vapour sorption isotherms (298 K, 313 K) were measured using the BELSORP aqua system (MicrotracBEL Corp., Osaka, Japan).

BET Surface Area

The internal surface areas were calculated based on the application of the Brunauer- Emmett-Teller (BET) model according to equation 1 to the N₂ isotherms collected at 77 K in the classical relative pressure range of 0.05-0.30. P 1 l C- i ! ?

VI ? .-? 1 v.. c v. C P ₁

Where V is the amount of adsorbed gas (N₂) quantity, V_m is the monolayer capacity and C is the BET constant exponentially related to the heat of adsorption of N₂ in the monolayer. The collected N2 physisorption isotherm was transformed to a BET plot based on equation 1 to calculate the monolayer capacity.

The plot of— - - vs relative pressure— gave the slope

- and intercept - .

From which V_m was obtained and the value of C resulting from the linear fit was positive. Further, from the calculated monolayer capacity, the BET surface area (m²g ^!) was obtained based on equation 2.

Avoga ro number x cmss sectional area of adsorption x monolayer capacity

BEI surface area = - - - - - - - ^: - —

molar volume of ps

Pore volume

The total pore volume (cm³g^_1) was determined from the N2 isotherm (77 K at P/Po = 0.9) based on Gurvich-rule equation 3:

Total pore volume Ns uptake at saturation pressure x Molecular weight of M2 x (density of Ns at 77

3

Isosteric Heat of Adsorption

The isosteric heat of adsorption (Q_st) representing the average binding energy of the adsorbing gas molecules at a specific surface coverage (n) were calculated based on the Clausius-Clayperon equation 4. The C0₂ adsorption isotherms collected at 293 K and 303 K were used for these calculations.

4 Single Component Adsorption Selectivity

The adsorptive selectivity for C0₂ over N₂ was determined by calculating the selectivity factor (equation 5). The ratio of number of moles of CO2 and N2 adsorbed (qi, qj) at the pressures of 0.15 bar and 0.75 bar, respectively, determined from the individual single component isotherms collected at 313 K yielded the adsorptive selectivity factors. The pressures were selected in relevance to the partial pressures (pi, pj) of CO2 and N2 in the post combustion flue gas mixture conditions.

Dynamic Column CO₂ Breakthrough Experiments

Figure 6 shows a diagram of the set up used for the breakthrough experiments. The mixed-gas breakthrough experiments (fixed-bed adsorption) cycle experiments were performed with the pre-activated MOF powder, approx. 300 mg of which was packed in a stainless steel chromatographic column with a length of 20 cm and an inner diameter of 0.5 cm. The ends of the column were sealed with glass wool. Subsequently, the column was loaded onto a home-made gas setup. The composition of the inlet gas stream comprising carbon dioxide (CO2) and nitrogen (N₂) was controlled by mass flow controllers. The composition of the outlet gas stream was monitored on a mass spectrometer gas analysis system (Pfeiffer Vacoon) detecting ion peaks at m/z 44 (CO2), 28 (N₂), 18 (H2O) and 4 (He).

Helium was used as the purging gas before and after the breakthrough experiments with a flow rate of 20 ml min l . The two valves labeled as VI and V2 shown in the above diagram enabled the flow of the gas mixture through the bypass line and thus the isolation of the column and preparation of the gas mixture was facilitated. Following the stabilization of the corresponding mass spectrometer signals, the valves were turned to direct the feed mixture into the column. Thus, the raw breakthrough profiles have the following appearance: The mass spectrometer detects the feed mixture before valve VI is turned. Once the valve is turned, it engenders the feed mixture to be directed towards the column thus pushing the helium out of the column. Consequentially, the concentration of the components of the gas mixture decreases and helium was the only component to be detected until the occurrence of the breakthrough of the first component (moisture laden N₂ or N₂). Following which, the breakthrough of C0₂ occurred. After the stabilization of the feed mixture signals to their corresponding inlet composition values, the cycle was considered to be completed. For regeneration, the column was activated at 353 K under helium at a flow rate of 20 ml min ¹. Thus, this adsorption and desorption procedure constituted 1 cycle and it was repeated consecutively for 10 cycles.

Dynamic Adsorption Selectivity

The dynamic adsorptive selectivity was calculated for each of the individual breakthrough cycles. The ratio of the adsorbed amounts of CO2 and N2 to their molar fraction in the bulk phase yielded the dynamic selectivity values from the breakthrough experiments (equation 6).

6

The adsorbed amount of the compound was determined with equation 7,

7

where qi is the adsorbed amount of component i from the gas feed mixture and Ci is the corresponding gas phase concentration, m_ads is the mass of the MOF packed in the column and V_coi is the volume of the column, V is the total volumetric flow rate and pa_ds is the density of the MOF. The first moment was integrated based on equation 8,

8 where C_t, Ci are the concentrations of the component at the outlet and inlet of the column, respectively.

Computational Details

Gas adsorption isotherms for CO2, N2, CH₄, and H2O were performed with an in-house developed grand canonical Monte Carlo (GCMC) software which determines the quantity of gas adsorbed at a given external gas pressure and temperature. For each structure studied in this report, electrostatic interactions between gas particles and the material were determined from point charges assigned to each atom. The charges were assigned using an algorithm called “REPEAT” known from Campana, C et al., Journal of chemical theory and computation, 2009, vol. 5, page 2866 that accurately reproduces charge interactions from density functional theory (DFT). Parameters that govern van der Waals interactions between the framework and gas were assigned to the MOF atoms based on a study that showed good their reproducibility of CO2, N2 and CH₄ adsorption and diffusivity (Wu X. et al., RSC Advances 2014, vol. 4, page 16503). Each gas was modeled with parameters accepted in the literature:

C0₂: a potential designed to accurately simulate isotherms in zeolite (Garcia- Sanchez, A. et al, The Journal of Physical Chemistry, C, 2009, v. 133, page 8814) ; N2: potential designed to reproduce the phase behavior of pure nitrogen (Potoff, J.J. et al., AIChE Journal 2001, vol. 47, page 1676);

CH₄: potential designed to reproduce the phase behavior of pure methane (Martin, M. G., et al., The Journal of Physical Chemistry, B, 1998, vol. 102, page 2569); and H2O: a potential designed to reproduce phase behavior of water, and also shown to yield accurate adsorption in nano-porous materials (Hans W. Horn et al., The Journal of chemical Physics, 2004, vol. 18, page 3777 Determination of the adsobaphore spacing

The distance between the parallel aromatic planes (= adsorbaphore spacing) is determined from the crystal structure.

To ensure that each of the structures have a similar basis for comparison we carry out a Density Functional Theory (DFT) optimization of both the atoms and cell dimensions using Vienna ab initio Simulation Package (VASP) v 5.3.5 was used for the energy calculations (attractive dispersion interactions were modelled with the vdW-DF2 correction with the optPBE functional. A Gamma-centered 1x4x2 k-point grid was used, along with a 1000 eV planewave energy cutoff. Projector augmented wave (PAW) pseudopotentials were used). Potential adsorbaphores were detected using maximum clique detection techniques. If a potential adsorbaphore was detected, two parallel planes were constructed. These two planes were positioned such that one plane is closest to the position six atoms of one aromatic ring of the adsorbaphore and the other plane closest the six atoms of the other ring. The distance between these two planes defines parallel aromatic planes, and is measured by the commercially available crystallographic software, Mercury (Crystal Structure Visualisation, Exploration and Analysis Made Easy, Version 3.6).

Examples:

Example 1: Preparation of SION-66

100 mg (0.126 mmol) 4,4',4",4"'-(porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid (also tetrakis-(4-carboxyphenyl) porphyrin or TCPP) and 60 mg (0.25 mmol) of A1O₃·6H₂0 were introduced into lO mL of deionized water. The suspension was stirred for 10 minutes at 23°C (room temperature), transferred in a hydrothermal reactor and heated in an oven at l 80°C for 16 hours with a heating rate of 3°C per minute. The solution was allowed to cool with a cooling rate of l .5°C per minute. The solid was recovered by filtration, washed 3 times with DMF (3 x 80 mL) and once with acetone (1 x 80 mL) in order to remove the unreacted porphyrin. After drying, the as made product was obtained as a reddish brown solid powder. The activation (removal of solvent molecules) was carried out at l 70°C under dynamic vacuum for 12 hours to get the activated (desolvated) product which has the same structure as the“non-activated” (non-desolvated, as made or as synthesised) product. The distance between two parallel aromatic planes to each other was 0.66 nm (6.6 A) as measured by the commercially available crystallographic software, Mercury (Crystal Structure Visualisation, Exploration and Analysis Made Easy, Version 3.6), (Figure 2), and preferably determined as described above.

Example 2: Preparation of SION-67

A mixture of 12 mg (0.03 mmol) of A1(N0₃)₃ ·9H₂0 and 10 mg (0.015 mmol) 4,4',4",4"'-(l ,6-dihydropyrene-l ,3,6,8-tetrayl)tetrabenzoic acid (TBAPy) was introduced into a solvent mixture of 4 ml. of DMF/dioxane/EbO in a ratio of 2: 1 : l and 10 /rL (0.1 16 mmol) of concentrated HC1 was added. The vial was heated at 85°C for 12 h with a heating rate of 0.1 °C per minute and then cooled to 23°C (room temperature) at a rate of 0.2°C per minute. The solid was recovered by filtration, washed with DMF (3 x 80 mL) in order to remove any recrystallized TBAPy. After drying, the product was obtained as a yellow solid powder. The activation (removal of solvent molecules) was carried out at l 70°C under dynamic vacuum for 12 hours to get the desolvated product (which has the same structure as the “non-desolvated (as made or as synthesised)” product). The distance between two parallel aromatic planes to each other was 0.73 nm (7.3 A) as measured by the commercially available crystallographic software Mercury (Crystal Structure Visualisation, Exploration and Analysis Made Easy, Version 3.6), (Figure 2), and preferably determined as described above.

Example 3: Preparation of SION-68

A mixture of 338.7 mg (65.6 mmol) of Al(N0₃)₃ 9H₂0 and 133.3 mg (23.89 mmol) 4',5'-bis(4-carboxyphenyl)-[l , l':2',l"-terphenyl]-4,4"-dicarboxylic acid (also referred to as l ,2,3,4-tetrakis(4-carboxyphenyl)benzene) was introduced into 3 mL of DMF and 1 mL of deionized water was added. The hydrothermal reactor was sealed carefully and heated at l50°C for 24 hours with a heating rate of 0.2°C per minute. The reactor was cooled down within 12 hours to 23°C (room temperature). The solid was recovered by filtration, washed with water. After drying, the product was obtained as a white solid powder. The activation (removal of solvent molecules) was carried out at l70°C under dynamic vacuum for 12 hours to get the desolvated product (which has the same structure as the“non-desolvated” product). The distance between two parallel aromatic planes to each other was 0.66 nm (6.6 A) as measured by the commercially available crystallographic software, Mercury (Crystal Structure Visualisation, Exploration and Analysis Made Easy, Version.3.6), (Figure 2), and preferably determined as described above.

Stability and purity

The compounds of Examples 1 to 3 ( SION-66 and SION-68) were treated under various conditions for various periods. Subsequently a XRP diffractogram of each sample was determined. As can be seen in Figure 3, the XRP diffractograms of the corresponding SION-66 samples are substantially identical. Thus, the crystalline integrity of SION-66 has been maintained, even after the exposure to moist and oxidative atmosphere (HNO₃- vapour). With reference to Figures 3 the same applies to SION-67 and SION-68.

Further properties:

BET surface area, pore volume and CO2 isosteric heat of adsorption Q_st of compounds SION-66 to SION-68 were determined as indicated above and summarized in Table 1 Table 1

As can be seen from Table 1 , the present compounds exhibit advantageous high BET surface areas and pore volumes. In addition, C0₂ isosteric heat of adsorption Q_st indicates a high binding energy of the adsorbed gas to the surface of the MOFs as used according to the present invention.

Adsorption

The compounds of Examples 1 to 3 ( SION-66 and SION-68 ) were exposed at 313 K to CO2, N2 and H2O at different pressures and the corresponding isotherms were determined. As can be seen from Figures 4a and 4b the present compounds significantly adsorb CO2, while hardly any N2 is adsorbed. Water vapor isotherms collected on these materials are type V and show low water uptake up to 60 % relative humidity (RH) indicating that until said humidity the water adsorption does not compete with carbon dioxide adsorption. Further, low uptake of water suggests that low regeneration energies can be achieved in CO2 separation (Figure 5), i.e. the regeneration of the active site within the molecular organic framework can easily be achieved.

Figure 9 shows synchrotron data plot (l=0.5008 A) of activated and in-situ He and CO2 loaded SION-66 (2 mbar at 400 mbar Helium).

Figure 10 shows the representation of the Rietveld refinements of the data in terms of the coordination of the CO2 in SION-66 (left is a top view, right is a side view). As it can be seen from this Figure 10 the carbon dioxide is coordinated between the two aromatic planes of the metal organic framework, but not bound to the metallic component of the metal organic framework.

Selective Adsorption of carbon dioxide over nitrogen

The CO2 breakthrough experiment was carried out with a gas comprising C02:N2:H20 in a ratio of 15:80:5 and a gas comprising C0₂:N_{2 i}n a ratio of 15:85, wherein the ratios can be regarded to correspond to the ratios of the corresponding compounds in flue gas under humid (normal) conditions and flue under dry conditions respectively (Figure 6). The experiments were performed at 313 K and 1 bar. Figure 7 and 8 show the comparison of the dynamic selective factors for C0₂ and N₂ under dry (1 cycle) and humid conditions from the repetitive 10 breakthrough cycle experiments, from which the average selectivity can be calculated. Table 2 shows the selectivity of C0₂/N₂ under dry and humid conditions at 313 K.

Table 2

As can be seen from Table 2, all of the present compounds exhibit excellent carbon dioxide (C0₂) selectivity over nitrogen (N₂) under dry conditions, wherein additionally the compounds show also very good C0₂ selectivity over N₂ under humid conditions. In fact, the corresponding C0₂ selectivity over N₂ of the present compounds is only slightly lower than the one under dry conditions, i.e. the presence of water (vapor) in a gas stream does not really negatively influence the C0₂ selectivity of the present compounds at all. Thus, these compounds can also be used for the selective adsorption of C0₂ of a humid gas, which enables their use under technical conditions without the need of a preceding cleaning/preparation step.

Claims

1. Use of a metal organic framework for the selective adsorption of carbon dioxide, wherein the metal organic framework comprises an aromatic ligand and a metallic component, wherein the ligand forms parallel aromatic planes having a distance to each other of 0.65 nm to 0.75 nm.

2. Use according to claim 1 , wherein the aromatic ligand is a molecule comprising from 18 to 80 carbon atoms.

3. Use according to claim 1 or 2, wherein the aromatic ligand comprises at least one carboxylic group.

4. Use according to any one of claims 1 to 3, wherein the aromatic ligand comprises at least one carboxylic group and at most four carboxylic groups, preferably 3 or 4 carboxylic groups.

5. Use according to any one of claim 1 to 4, wherein the aromatic ligand is selected from 4,4',4",4"'-(porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'- (l,6-dihydropyrene-l,3,6,8-tetrayl)tetrabenzoic acid; 4',5'-bis(4-carboxyphenyl)- [l,r:2',r'-terphenyl]-4,4"-dicarboxylic acid; 4,4',4'',4"'-(anthracene-2,3,6,7- tetrayl)tetrabenzoic acid; 4,4',4",4"'-(pyrazino[2,3-g]quinoxaline-2,3,7,8- tetrayl)tetrabenzoic acid; 4,4',4",4"'-(perylene-2,5,8,l l-tetrayl)tetrabenzoic acid; 4,4',4'',4'"-(chrysene-l,3,7,9-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'-

(naphtho[7,8,l,2,3-nopqr]tetraphene-l,3,7,9-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'- (l,l0-dihydrodibenzo[cd,lm]perylene-l,3,8,l0-tetrayl)tetrabenzoic acid; 4,4',4'',4 - (l,l0-dihydrodibenzo[bc,kl]coronene-l,3,8,l0-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'- (coronene-l,4,7,l0-tetrayl)tetrabenzoic acid; 3,3',3'',3"'-(l ,6-dihydropyrene- l,3,6,8-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(benzene-l,2,4,5-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(anthracene-2,3,6,7-tetrayl)tetrapropiolic acid; 3, 3', 3", 3"'- (pyrazino[2,3-g]quinoxaline-2,3,7,8-tetrayl)tetrapropiolic acid; 3, 3', 3", 3"'-

(perylene-2,5,8,l 1 -tetrayl)tetrapropiolic acid; 3,3',3",3"'-(chrysene-l,3,7,9- tetrayl)tetrapropiolic acid; 3,3',3",3"'-(naphtho[7,8,l,2,3-nopqr]tetraphene-l,3,7,9- tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(l ,lO-dihydrodibenzo[cd,lm]perylene- l,3,8,l0-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(l ,10- dihydrodibenzo[bc,kl]coronene-l,3,8,l0-tetrayl)tetrapropiolic acid; 3, 3', 3", 3"'- (coronene-l,4,7,l0-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(porphyrin-5,l0,l5,20- tetrayl)tetrapropiolic acid; 6',8'-bis(7-carboxypyren-2-yl)-[2,r:3',2''-terpyrene]- 7,7''-dicarboxylic acid and 4,4',4'',4"'-(benzo-porphyrin-5,l0,l5,20-tetrayl)tetra- benzoic acid.

6. Use according to any one of claims 1 to 5, wherein the aromatic ligand is selected from 4,4',4'',4"'-(porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'- (l,6-dihydropyrene-l,3,6,8-tetrayl)tetrabenzoic acid and 4',5'-bis(4-carboxy- phenyl)-[l,r:2',r'-terphenyl]-4,4''-dicarboxylic acid.

7. Use according to any one of claims 1 to 6, wherein the metallic component is selected from magnesium, aluminium, zinc, cadmium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium molybdenum, technetium, ruthenium, rhodium, palladium and silver.

8. Use of a metal organic framework for the selective adsorption of carbon dioxide, wherein the metal organic framework comprises an aromatic ligand and a metallic component, wherein the aromatic planes of the ligands are arranged such that until a relative humidity RH of 60% the adsorption of water essentially does not compete with the adsorption of carbon dioxide.

9. Method for selectively removing carbon dioxide from a gas comprising the steps of

i) providing a gas comprising carbon dioxide,

ii) contacting the gas with a metal organic framework, wherein the metal organic framework comprises an aromatic ligand and a metallic component, wherein the ligand forms parallel aromatic planes having a distance to each other of 0.65 nm to 0.75 nm, iii) allowing the carbon dioxide to be adsorbed by the metal organic framework.

10. Method according to claim 6, wherein the aromatic ligand is a molecule comprising from 18 to 80 carbon atoms.

1 1. Method according to claim 9 or 10, wherein the aromatic ligand is selected from 4,4',4",4"'-(porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid; 4,4',4'',4"'-(l,6- dihydropyrene-l,3,6,8-tetrayl)tetrabenzoic acid; 4',5'-bis(4-carboxyphenyl)- [l,r:2',r'-terphenyl]-4,4"-dicarboxylic acid; 4,4',4'',4"'-(anthracene-2,3,6,7- tetrayl)tetrabenzoic acid; 4,4',4",4"'-(pyrazino[2,3-g]quinoxaline-2,3,7,8- tetrayl)tetrabenzoic acid; 4,4',4",4"'-(perylene-2,5,8,l l-tetrayl)tetrabenzoic acid; 4,4',4'',4'"-(chrysene-l,3,7,9-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'-

(naphtho[7,8,l,2,3-nopqr]tetraphene-l,3,7,9-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'- (l,l0-dihydrodibenzo[cd,lm]perylene-l,3,8,l0-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'- (l,l0-dihydrodibenzo[bc,kl]coronene-l,3,8,l0-tetrayl)tetrabenzoic acid; 4, 4', 4", 4"'- (coronene-l,4,7,l0-tetrayl)tetrabenzoic acid; 3,3',3'',3"'-(l ,6-dihydropyrene- l,3,6,8-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(benzene-l,2,4,5-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(anthracene-2,3,6,7-tetrayl)tetrapropiolic acid; 3, 3', 3", 3"'- (pyrazino[2,3-g]quinoxaline-2,3,7,8-tetrayl)tetrapropiolic acid; 3, 3', 3", 3"'-

(perylene-2,5,8,l 1 -tetrayl)tetrapropiolic acid; 3,3',3",3"'-(chrysene-l,3,7,9- tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(naphtho[7,8,l,2,3-nopqr]tetraphene-l ,3,7,9- tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(l ,lO-dihydrodibenzo[cd,lm]perylene-

1.3.8.10-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(l,l0-dihydrodi- benzo[bc,kl]coronene-l,3,8,l0-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(coronene-

1.4.7.10-tetrayl)tetrapropiolic acid; 3,3',3'',3"'-(porphyrin-5,l0,l5,20-tetrayl)tetra- propiolic acid; 6',8'-bis(7-carboxypyren-2-yl)-[2,r:3',2''-terpyrene]-7,7"- dicarboxylic acid and 4,4',4'',4'"-(benzo-porphyrin-5,l0,l5,20-tetrayl)tetrabenzoic acid.

12. Method according to any one of claims 9 to 1 1, wherein the metallic component is selected from magnesium, aluminium, zinc, cadmium or scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium molybdenum, technetium, ruthenium, rhodium, palladium and silver.

13. Method according to to any one of claims 9 to 12, wherein step (ii) and/or step (iii) are carried out at a temperature of -20°C to l00°C and/or, wherein step (ii) and step (iii) are carried out simultaneously.

14. Method according to any one of claims 9 to 13, wherein the gas is air, industrial waste gas or a natural gas selected from wet biogas, sour biogas, coal mine gas and shale gas.

15. Use or method according to any of claims 1 to 14, wherein the carbon dioxide binds without coordination with the metallic component of the metal organic framework.