METAL ORGANIC FRAMEWORKS FOR THE SELECTIVE CAPTURE OF VOLATIL ORGANIC COMPOUNDS COMPRISING CARBOXYLIC ACID FUNCTIONAL GROUP(S) AND/OR VOLATILE ALCOHOLS

Abstract

The present invention relates, inter alia, to the use of porous crystalline solids constituted of a metal-organic framework (MOF) for the selective capture of volatile organic compounds (VOCs) comprising carboxylic acid functional group(s) and/or volatile organic compounds (VOCs) comprising an hydroxyl functional group.

The MOF solids of the present invention can be used for the purification of air, for example for the selective capture of VOCs comprising carboxylic acid functional group(s) and/or volatile organic compounds (VOCs) comprising an hydroxyl functional group from outdoor air. It may be used for art preservation, such as the conservation of cellulose derivate films, for indoor air purification systems such as HEPA air filters, adsorbent purifiers, kettle filters, fette filters, honeycomb filters or air conditioning filters, for outdoor air purification systems such as gas mask, nose filter, adsorption columns or chimney filters, and in cosmetic applications such as deodorants, anti-odor shampoo, hygienic protection products, wipes or diapers.

Claims

1. A method for selective adsorption of volatile organic compounds from a gaseous environment, comprising contacting at least one porous Metal-Organic Framework (MOF) material with a gaseous environment volume comprising volatile organic compounds, wherein said volatile organic compound comprises at least one carboxylic acid group and/or said volatile organic compound comprises a hydroxyl group, and wherein said MOF material comprises at least 1 mmol/g of Lewis acid sites built up from trimers of metal octahedra and interconnected by organic polycarboxylate linkers.

2. The method according to claim 1, wherein the MOF, in terms of water adsorption isotherm at 30 C., adsorbs more than 50% of the said MOF total adsorption capacity at p/p.sub.0 relative pressure of less than 0.4.

3. The method according to claim 1, wherein the MOF material comprises metallic centers and the metallic centers are selected from the group consisting of Fe, Al, Ti, Mn, V, Sc, Mn, Cr and mixtures thereof.

4. The method according to claim 1, wherein the MOF material comprises Lewis acid sites, built up from trimers of metal octahedra and interconnected by organic polycarboxylate linkers, at a concentration of at least 1.5 mmol/g.

5. The method according to claim 1, wherein the MOF material has a specific surface area of more than 50 m.sup.2/g, said specific surface area being evaluated with the BET model from a N.sub.2 isotherm at 77K of the said MOF material.

6. The method according to claim 1, wherein the MOF material has an average pore size of more than 0.5 nm.

7. The method according to claim 1, wherein the organic polycarboxylate linkers are selected from di-, tri- or tetra-carboxylic acids.

8. The method according to claim 7, wherein the organic polycarboxylate linkers are C.sub.6 to C.sub.24 aromatic polycarboxylate linkers selected from the group consisting of terephtalate, 1H-pyrazole-3,5-dicarboxylate, 2,5-furandicarboxylate, naphtalene-2,6-dicarboxylate, biphenyl-4,4-dicarboxylate, benzene-1,2,4-tricarboxylate, benzene-1,3,5-tricarboxylate, benzene-1,3,5-tribenzoate, benzene-1,2,4,5-tetracarboxylate, 3,3,5,5-tetracarboxylatediphenylmethane, naphtalene-2,3,6,7-tetracarboxylate, naphtalene-1,4,5,8-tetracarboxylate, biphenyl-3,5,3,5-tetracarboxylate, 2-chloroterephthalate, 2-bromoterephthalate, azobenzene dicarboxylate, azobenzene tetracarboxylate, 2,5-thiophenedicarboxylate, 2-aminoterephthalate, 2-nitroterephthalate, 2,5-dihydroxyterephthalate, 2,5-pyrazine dicarboxylate, azobenzene-4,4dicarboxylate, 3,3-dichloro-azobenzene-4,4-dicarboxylate, 3,3-dihydroxy-azobenzene-4,4-dicarboxylate, 3,5,3,5-azobenzene tetracarboxylate and mixtures thereof.

9. The method according to claim 7, wherein the organic polycarboxylate linkers are C.sub.4 to C.sub.16 polycarboxylate alkyl linkers selected from the group consisting of fumarate, succinate, glutarate, muconate, adipate and mixtures thereof.

10. The method according to claim 1, wherein MOF material is selected from the group consisting of MIL-88A(Fe), MIL-88B(X)(Fe) in which X is selected from Br, NH.sub.2, Cl, NO.sub.2, 2OH and COOH, and mixtures thereof.

11. The method according to claim 1, wherein the method is for air quality applications, art preservation, indoor air purification, outdoor air purification, or cosmetic application.

12. The method according to claim 1, wherein the gaseous environment is air.

13. The method according to claim 1, wherein the volatile organic compounds comprise carboxylic acid functional group(s).

14. The use according to claim 1, wherein the volatile organic compounds comprise hydroxyl functional group(s).

15. The method according to claim 1, wherein the concentration of the volatile organic compound in the gaseous environment is of at least 40 ppb.

16. The method according to claim 1, wherein the at least one MOF material is in the form of a powder, a granule, a pellet, an extrudate, a monolith, a composite embedded in the form of a foam material, a polymer or a fiber, or coated on a surface of a polymer material, of a paper sheet, of a fiber or of a metal.

17. The method according to claim 1, wherein the at least one MOF material is comprised in a device selected from air purifiers, sensors, adsorption columns, filters, respiration masks, adsorption towers, hygienic protection products, wipes or diapers.

18. The method according to claim 1, wherein the organic polycarboxylate linkers are: C.sub.6 to C.sub.24 aromatic polycarboxylate linkers, optionally bearing one or more substituents selected from a halo group, OH, NH.sub.2 and NO.sub.2, or C.sub.4 to C.sub.16 polycarboxylate aliphatic linkers, optionally bearing one or more substituents selected from a halo group, OH, NH.sub.2 and NO.sub.2.

19. The method according to claim 1, wherein the gaseous environment has a relative humidity from 20% to 80%, and a temperature from 10 to 180 C.

20. The method according to claim 1, wherein the volatile organic compounds are (a) acetic acid, formic acid, acrylic acid, propionic acid, isovaleric acid, propiolic acid, butyric acid, isobutyric acid, crotonic acid, methacrylic acid, diacetic acid, butynedioic acid, valeric acid, 2-methylbutanoic acid, pivalic acid, hexanoic acid, 2,3-trimethylbutanoic acid, 3-methylhexanoic acid, 2-ethyl-2-methylbutanoic acid, 3-ethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,4-dimethylpentanoic acid, 2,3-dimethylpentanoic acid, 2-methylbutanoic acid or mixtures thereof; or (b) monoalcohols, linear, branched or cyclic C.sub.1 to C.sub.10 monalcohols or mixtures thereof, methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, pentanol, isopentanol, hexanol, isohexanol, or mixtures thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG. 1 represents a metal trimer. Each metal is six-coordinated by six oxygen atoms forming an octahedral environment (four oxygen atoms from the building ligand, one central p3-oxo and one oxygen atom from a terminal ligand). Three coordinated metals share one central p3-oxo forming a trimer with three terminal ligands, one HO.sup. and two water molecules (Hydrogen atoms are omitted for clarity). The Lewis acid sites are effective upon removal of terminal water ligands. In this invention, the carboxylate from the VOCs will replace the terminal water ligands which results in stronger Lewis acid sites-VOC interactions.

[0059] FIG. 2A represents a nitrogen adsorption isotherm obtained from MIL-100(Fe) (Evacuated under primary vacuum at 150 C. for 15 h). The Surface area obtained is 1850 m.sup.2.Math.g.sup.1 (evaluated using the BET model).

[0060] FIG. 2B represents a nitrogen adsorption isotherm obtained from MIL-100(Al) (Evacuated under primary vacuum at 150 C. for 15 h). The Surface area obtained is 1000 m.sup.2.Math.g.sup.1 (evaluated using the BET model).

[0061] FIG. 2C represents a nitrogen adsorption isotherm obtained from MIL-127(Fe) (Evacuated under primary vacuum at 200 C. for 3 h). The Surface area obtained is 1400 m.sup.2.Math.g.sup.1 (evaluated using the BET model).

[0062] FIG. 2D represents a nitrogen adsorption isotherm obtained from MIL-101(Cr) (Evacuated under primary vacuum at 220 C. for 15 h). The Surface area obtained is around 2700 m.sup.2.Math.g.sup.1 (evaluated using the BET model).

[0063] FIG. 3A represents acetic acid adsorption isotherms at T=25 C. of activated (open circles) and non-activated (full squares) MIL-100(Fe).

[0064] FIG. 3B represents acetic acid adsorption isotherms at T=25 C. of activated MIL-127(Fe).

[0065] FIG. 4 represents propionic acid adsorption isotherms of at T=25 C. of activated MIL-100(Fe).

[0066] FIG. 5 represents water adsorption isotherms at 25 C. of activated (open circles) and non-activated (full squares) MIL-100(Fe).

[0067] FIG. 6A represents acetic acid concentration profiles inside a closed chamber at 40% R.Math.H without any adsorbent.

[0068] FIG. 6B represents acetic acid concentration profiles inside a closed chamber at 40% R.Math.H for different MOFs.

[0069] FIG. 7 represents TPD spectra of acetic acid and water (50/50% volume) mixture on MIL-100(Fe).

[0070] FIG. 8 represents TPD spectra of proponic acid and water (50/50% volume) mixture on MIL-100(Fe).

[0071] FIG. 9A represents P-XRD patterns of the experimental MIL-100(Fe) in 2e range 1.6-30 compared with the calculated pattern from the literature. [37]

[0072] FIG. 9B represents P-XRD patterns of the experimental MIL-100(Al) in 2e range 1.6-30 compared with the calculated pattern from the literature. [37]

[0073] FIG. 9C represents P-XRD patterns of the experimental MIL-127(Fe) in 2e range 5-30 compared with the calculated pattern from the literature. [38,39]

[0074] FIG. 9D represents P-XRD patterns of the experimental MIL-101(Cr) in 2 range 1.6-30 compared with the calculated pattern from the literature. [40]

[0075] FIG. 10A represents thermogravimetric analysis of MIL-100(Fe). Conducted under O.sub.2 (heating rate of 5 C. per minute). The thermogravimetric analysis (performed under O.sub.2 at 5 C./min) shows two weight losses: the first one from 25 C. to 250 C. corresponds to the loss of water within the pores of the solid; the second weight loss is attributed to the degradation of the MOF at around 300 C. From this, it can be seen that the expected losses are well within the expected ranges from literature.

[0076] FIG. 10B represents thermogravimetric analysis of MIL-100(Al). Conducted under O.sub.2 (heating rate of 5 C. per minute). Thermogravimetric analysis (performed under O.sub.2 at 5 C./min) shows two weight losses: the first one until 200 C. corresponds to the loss of water trapped in the micropores; the second weight loss is attributed to the degradation of the MOF at around 300 C. From this, it can be seen that the expected losses are well within the expected ranges from literature.

[0077] FIG. 10C represents thermogravimetric analysis of MIL-127(Fe). Conducted under O.sub.2 (heating rate of 5 C. per minute). Thermogravimetric analysis (performed under O.sub.2 at 5 C./min) shows two weight losses: the first one until 200 C. corresponds to the loss of water trapped in the micropores; the second weight loss is attributed to the degradation of the MOF at around 300 C. From this, it can be seen that the expected losses are well within the expected ranges from literature.

[0078] FIG. 10D represents thermogravimetric analysis of MIL-101(Cr). Conducted under O.sub.2 (heating rate of 5 C. per minute). Thermogravimetric analysis (performed under O.sub.2 at 5 C./min) shows two weight losses: the first one until 200 C. corresponds to the loss of water trapped in the pores; the second weight is attributed to the degradation of the MOF at around 300 C. From this, it can be seen that the expected losses are well within the expected ranges from literature.

[0079] FIG. 11 represents the TPD spectra of formic acid and water (50/50% volume) mixture on MIL-100(Fe).

[0080] FIG. 12 represents formic acid adsorption isotherms at 25 C. of activated (open circles) and non-activated (full squares) MIL-100(Fe).

[0081] FIG. 13 represents a) the breakthrough curve for acetic acid (concentration 500 ppm in N2) on powder MIL-100(Fe) under 60% relative humidity and (b) respective isotherm in black with the value obtained from the breakthrough indicated in red.

EXAMPLES

[0082] According to the present invention, the usable MOFs materials and their preparation can be understood further by the examples that illustrate some of the processes by which these materials are prepared or used. It will be appreciated, however, that these examples should not be construed to limit the invention. Variations of the invention, now known or further developed, are considered to fall within the scope of the present invention as described herein and as hereinafter claimed.

Example 1: Materials Synthesis

[0083] 1.1. MIL-100(Fe) a MOF with 3.6 mmol/g [31] of iron(III) Lewis acid sites was obtained via ambient pressure synthesis with 0.96 mol of 1,3,5-benzene tricarboxylic acid and 1.42 mol of iron(III) nitrate nonahydrated and 18 L of deionised water, adapted from the conditions referred in Nouar et al., EP3357929A1, 2018 [15]. The mixture is stirred for 62 hours using a magnetic stirrer at a temperature of from 60 C. The brown mixture is then filtered to obtain a brown solid which is washed several times with absolute water and ethanol, to remove the unreacted 1,3,5-benzene tricarboxylic acid. Then the powder is dried at room temperature.

[0084] 1.2. MIL-100(Al) a MOF with 2.2 mmol/g [32] of aluminum(III) Lewis acid sites 6 mmol of 1,3,5-benzene tricarboxylic acid and 4 mmol of aluminium(III) nitrate nonahydrated are introduced in a 100 mL autoclave; 25 mL of deionised water are then added and the mixture is stirred for 10 minutes using a magnetic stirrer, as disclosed in the literature by Merquez et al. Eur J Inorg Chem., 2012, 100(32) [16]. The suspension is then placed in a microwave oven and heated until 210 C. (ramp of 1 min). The temperature is kept stable for 5 minutes with power at 1400 W. The mixture is then centrifuged and is washed several times with absolute water and ethanol and dried at room temperature.

[0085] 1.3. MII-127(Fe) a MOF with 2.7 mmol/g [33] of iron(III) Lewis acid sites was synthetisized by adding 2 mmol of NaOH to 4 mL of water and then stirring it. Then this solution is added to 1 mmol of 3,3,5,5-azobenzenetetracarboxylic acid and 22 mL of isopropanol solution that was previously stirred, as disclosed in Chevreau et al., Cryst Eng Comm. 2016, 18(22), 4094-4101 [17]. A solution of 2 mmol of iron(III) chloride hexahydrated that was prepared with 17 mL of isopropanol, was finally added to the previous solution. The mixture is stirred and heated gradually until 130 C. for 24 hours. The reaction mixture is then filtered to obtain a yellow solid which is washed several times with absolute ethanol and dried at room temperature.

[0086] 1.4. MIL-101(Cr) (counter-example) a MOF with <1 mmol/g [34] of chromium(III) Lewis acid sites was synthesized by adding 12 mmol of benzene-1,4-dicarboxylic acid and 2 mmol of chromium nitrate nonahydrate to a 100 mL autoclave; 25 mL of deionised water are then added and the mixture is stirred for 10 minutes using a magnetic stirrer. The suspension is placed in a microwave oven and heated until 200 C. (ramp of 4 minutes). The protocol followed was adapted from Jhung et al, Adv. Mater. 2007 [41]. The temperature is kept stable for 30 min with power at 1200 W. The mixture is then centrifuged and is washed several times with absolute water and ethanol and dried at room temperature.

Example 2: Materials Characterization

[0087] Three series of analysis have been carried out to confirm the obtention of the various materials synthetized in the above Example 1: [0088] Nitrogen adsorption at 196 C.; [0089] PXRD of the synthesized materials; and [0090] Thermogravimetric analysis of the synthesized materials.

[0091] 2.1 Nitrogen adsorption at 196 C.: Nitrogen (Air Liquid, 99.999%) adsorption-desorption isotherms were measured at 196 C. using a liquid nitrogen cryogenic bath, in a volumetric automatic apparatus (Micromeritics, ASAP 2010). Prior to the measurement the samples were outgassed under primary vacuum. All results of these analysis confirm the porosity of the various materials synthetized in example 1 and are presented in FIG. 2A to 2D.

[0092] 2.2 PXRD patterns of the synthesized materials: The powder X-ray diffraction patterns were obtained with a Bruker D8-Advance Diffractometer with Cu K radiation (=1.5418 ). Diffraction patterns were recorded across a 2 range of 5-70, with a step size of 0.02 and 0.1 s per step. All results of these analysis confirm the obtention of the various crystalline materials synthetized in example 1 and are presented in FIG. 9A to 9D.

[0093] 2.3 Thermogravimetric analysis of the synthesized materials: In order to obtain the TGA profile of each material synthesized, the samples (about 10 mg) were analysed with a gravimetric analyser (Mettler Toledo TGA/DSC 2, STAR system) under air at a constant rate of 5 C./min. All results of these analyses confirm the purity of the various materials synthetized in example 1 and are presented in FIG. 10A to 10D.

Example 3: Experiments on Adsorption Capacity of the Different Materials

3.1. Protocol Used for Water Adsorption Measurements

[0094] Water adsorption isotherms were measured by the gravimetric method at relative pressures, up to 1.0 p/p.sub.0, on about approximately 50 mg of the materials synthetized in example 1. The measurements were performed in a microbalance (CI Electronics) equipped with a pressure sensor (MKS a-BARATRON capacitance manometer of 100 Torr-range). The adsorption temperature was maintained with a water bath (VMR, VWB2 series, temperature stability 0.2 C.) at 25 C. Prior to the experiments the materials were activated at the desired temperature under high vacuum (10.sup.6 mbar).

3.2. Protocol Used for Acidic Vapors Adsorption Measurements

[0095] Adsorption isotherms were measured by the gravimetric method at low relative pressure, up to 0.06 p/p.sub.0, on about 50 mg different samples of the materials synthetized in example 1. The measurements were performed in a microbalance (CI Electronics) equipped with a pressure sensor (MKS a-BARATRON capacitance manometer of 100 Torr-range). The adsorption temperature was maintained with a water bath (VMR, VWB2 series, temperature stability 0.2 C.) at 25 C. Prior to the measurements the materials were activated at the desired temperature under high vacuum (10.sup.6 mbar).

3.3. Protocol Used for Acetic Acid Adsorption in a Controlled Relative Humidity Environment

[0096] Around 100 mg of materials were placed inside 10 cm.sup.3 glass vials and kept in an oven at 100 C. overnight. The vials were removed and closed tightly with polyethylene caps until being used in the experiments. 50 mg of adsorbent material was weighted (Mettler AE240) in a watch glass and immediately placed inside a glass chamber (2.9 dm.sup.3) with controlled humidity. The humidity was controlled to about 40% relative humidity by means of a saturated solution of potassium carbonate (BDH Prolabo, 99.6%). The chamber was flushed with nitrogen flow for 1 hour, where the gas passes through the saturated solution, to equilibrate in a humid environment. After this time, a syringe (Hamilton 7001 KH) was used to inject 1 L of acetic acid (Riedel-de Hasn, 99.8%) inside the chamber trough a rubber septum injection port. The total volatile organic compounds (TVOC) concentration, temperature and relative humidity inside the chamber were measured (Graywolf TG-502 TVOC ppb) and were recorded at fixed time interval (15 s) for one hour using computer software (Wolfsense LAP). During experiments, the temperature was 22.80.8 C. and the relative humidity was 43.53.5%. A blank experiment with no injection of acetic acid was preformed and a control experiment was performed with injection of acetic acid without any MOF to demonstrate the tightness of the chamber during the experiments time frame and ascertain the TVOC signal response obtained by 1 L injection.

3.4. Protocol used for Temperature-Programmed Desorption (TPD):

[0097] The protocol used for TPD was adapted from a dynamic adsorption system published by Sayari's group [42]. The flow of gases was controlled using mass flow meters (Stainless Steel Gas Thermal Mass Flo-Controller, McMillan 80SD), and the path of gases was controlled by 4-way valves. All the experiments were performed at a pressure slightly higher than the atmospheric pressure (103 kPa). Around 90 mg of activated sample (T=150 C., D=15 h) was loaded inside a stainless steel column of inner diameter of 6.4 mm. The material was regenerated at 200 C. for a duration of 2 hours under a flow of 44 cm.sup.3/min of He. The injection of vapors was enabled through a 6-way-valve. Liquid mixtures 50% V/V organic vapor and water were injected to the system with the help of a 10-L-volume loop connected to the 6-way-valve. The injected solution was evaporated using a heating element kept at 105 C. and carried out/diluted by He at flowrate of 44 cm.sup.3/min. Adsorption occurred at room temperature. The column was then heated from room temperature to T=200 C. with a heating ramp of 2 C./min. The composition of the column output was recorded as function of time with a mass spectrometer.

Example 4: Results of the Analysis

4.1 Nitrogen Adsorption

[0098] FIG. 2 shows the obtained nitrogen adsorption isotherms, at 196 C., on on a) MIL-100(Fe), b) MIL-100(Al), c) MIL-127(Fe), d) MIL-101(Cr).

4.2 Acetic Acid Adsorption

[0099] FIG. 3 shows, acetic acid adsorption isotherms, at 25 C., expressed as amount adsorbed per mass of a) MIL-100(Fe), b) MIL-127(Fe).

4.3 Propionic Acid Adsorption

[0100] FIG. 4 shows, propionic acid adsorption isotherms, at 25 C., expressed as amount adsorbed per mass of MIL-100(Fe). The steepness of the isotherms indicates that propionic acid strongly binds to the MOF in both activated and non activated samples. This is in agreement with the TPD results.

4.4 Water Adsorption

[0101] The water adsorption isotherms are represented on FIG. 5. This figure shows water adsorption isotherms, at 25 C., on activated and non-activatedMIL-100(Fe). In MIL-100(Fe) the water isotherms displays an initial step below 0.1 p/p.sub.0 attributed to the adsorption of water in the open metal sites. A second inflection is observed between 0.20 to 0.50 p/p.sub.0 attributed to capillary condensation in the mesopores (type IV isotherm). The total water capacities at relative pressures of 0.9 are around 35 mmol/g. Half the total water capacity of the MOF is attained at p/p.sub.0<0.4 (for 0.35 p/p.sub.0, around 17.5 mmol/g is reached). This confirms the MOF adsorbs more than 50% of the said MOF total adsorption capacity at p/p.sub.0 relative pressure of less than 0.4.

4.5 Removal of Acetic Acid with MOFs in the Presence of 40% RH

[0102] FIG. 6 shows: a) Blank experiments with no injection of acetic acid (baseline) and the injection of acetic acid without the presence of adsorbents. b) Acetic acid concentration profiles inside a closed chamber after the injection of 1 L of acetic acid with 40% RH, in the presence of 50 mg of MIL-100(Fe), MIL-100(Al), MIL-127(Fe), and MIL-101(Cr). Regarding both iron base MOFs and aluminum base MOFs, which present Lewis acid sites concentration higher than 2 mmol/g, it is seen a comparable efficiency of removal of acetic acid since the concentration inside the chamber after one hour is similar. Therefore, even in the presence of humidity, the named MOFs adsorbed remarkably high amounts of acetic acid. Conversely, for the chromium base MOF, MIL-101(Cr), the number of Lewis acid sites is lower than 1 mmol/g, and consequently the removal of acetic acid from the chamber environment is poorer.

4.6 Temperature-Programmed Desorption (TPD) Spectra of Acetic Acid and Water Mixture on MIL-100(Fe)

[0103] FIG. 7 shows the TPD of water and acetic acid from MIL-100(Fe). The first peak of water appears at around 66 C., a smaller peak appears at around 196 C. and a shoulder appears upon dwelling at 200 C. corresponding to more strongly bound water. An acetic acid peak appears at 196 C., which is 130 C. after the first peak of water, indicating the higher affinity towards the first. Therefore, it is clear that acetic acid adsorbs preferentially to the MOF.

4.7 Temperature-Programmed Desorption (TPD) Spectra of Propionic Acid and Water Mixture on MIL-100(Fe)

[0104] FIG. 8 shows the TPD of water and propionic acid from MIL-100(Fe). The first peak of water appears upon dwelling at around 95 C., a smaller peak appears at around 200 C. The peak of propionic acid only appears upon dwelling at 200 C. This indicates the higher affinity towards the latter. Therefore, it is clear that propionic acid adsorbs preferentially to the MOF.

Example 5: Results

[0105] The removal of low concentrations of acetic acid from indoor air at museums and archives poses serious conservation problems that current adsorbents cannot easily solve due to the competitive adsorption of water. In these examples, trimers based MOFs with different pore sizes, topologies and metal centers have been studied to demonstrate that the use of trimer based MOFs can present performant selective adsorbents in the adsorption of carboxylic acids. This is a result of the presence of Lewis acid sites in these structures than can interact strongly with the acid vapors without showing necessarily a hydrophobic character.

Example 6: Formic Acid Adsorption

[0106] The TPD analysis where repeated with formic acid instead of propionic acid.

[0107] FIG. 11 shows the TPD of water and formic acid (in a 50/50% volume) on MIL-100(Fe). The first peak of water appears at around 85 C., a smaller peak appears at around 200 C. The peak of formic acid only appears upon dwelling at 200 C. This indicates the higher affinity towards the latter.

[0108] FIG. 12 shows, formic acid adsorption isotherms, at 25 C., expressed as amount adsorbed per mass of MIL-100(Fe). The steepness of the isotherms indicates that formic acid strongly binds to the MOF in both activated and non-activated samples. This is in agreement with the TPD results.

[0109] The same protocol with formic acid lead to similar results than with propionic acid. The adsorption isotherm has indeed shown a steep increase at low pressures. The TPD evidenced a first peak related to water at lower temperatures, and a second peak at higher temperatures related to the formic acid, which indicates a stronger formic acid-MOF affinity.

Example 7: Acetic Acid Breakthrough 60% Relative Humidity

[0110] Protocol: Dynamic adsorption characterization of acetic acid of powder MIL-100(Fe) in a packed bed was tested in a setup similar to the one shown in Figure S7 from a paper published by Sayari's group [42]. Where, a flow of gases was controlled using mass flow meters (Stainless Steel Gas Thermal Mass Flow-Controller, McMillan 80SD), and the path of gases was controlled by 4-way valves. Around 25 mg of activated sample (T=150 C. t=15 hours) was loaded inside a stainless-steel column of inner diameter of 6.4 mm. The sample was activated in-situ using a flow of nitrogen of 40 cm.sup.3 min.sup.1 for 1 hour under temperature of 150 C. (lab-made electric oven equipped with Eurotherm controller, PV accuracy <0.25%, heating ramp 5 C. min.sup.1). During the adsorption experiments, the column was immersed in a water bath at temperature of 25 C. (water bath, accuracy 0.1 C.). The pressure of the column as well as the vent pressure were monitored using pressure sensors from MKS (AA08A Micro-Baratron, 100 PSI) and were maintained at equal pressure close to atmospheric pressure. The sample was then left to equilibrate with moisture controlled at around 60% by passing the flow of nitrogen through a bubbler of water kept at 16.5 C. (water bath VWR, accuracy 0.1 C.). The flow of gas was switched to the acetic acid mixture while the output of the column (column downstream) is recorded by the mass spectrometer (Prismapro, Pfeiffer).

[0111] Results: The dynamic separation performance was tested with MIL-100(Fe) as shown in FIG. 13 (a). The breakthrough system was at atmospheric pressure and room temperature (25 C.). The acetic acid mixture corresponds to 498.8 ppm in N2:

[00001]$\begin{array}{cc}C=\frac{C\left(\mathrm{ppm}\right)}{V_M{10}^6}=2.07833{10}^{-8}\left(\mathrm{mol}/{\mathrm{cm}}^3\right)& \left(1\right)\end{array}$

Where v.sub.M=24000 cm.sup.3 is the molar volume at T=25 C. and atmospheric pressure. The adsorbed volume (cm.sup.3) was calculated by:

[00002]$\begin{array}{cc}{V}_{\mathrm{ads}}=V_{\mathrm{sample}}-V_{\mathrm{background}}& \left(2\right)\end{array}$

Where V.sub.sample is obtained by integrating the area under the curve, of the signal acquired by the mass spectrometer as function of time, upon setting the maximum signal to the flowrate used (52 cm.sup.3/min). V.sub.background is obtained upon repeating the same procedure for the background measurement (with an empty column). The calculated adsorbed volume corresponding to the measurement shown in FIG. 13(a) is 7.0210.sup.3 cm.sup.3. The dynamic adsorbed quantity is obtained upon multiplying the adsorbed volume by the concentration. Taking into consideration the mass of the sample used of 28.5 mg:

[00003]$\begin{array}{cc}{n}_{\mathrm{ads}}=\frac{V_{\mathrm{ads}}C}{m_{\mathrm{sample}}}=5.13\mathrm{mmol}/g& \left(3\right)\end{array}$

[0112] To compare the amount dynamically adsorbed in the presence of moisture with the amount adsorbed in equilibrium for a clean sample, the concentration of acetic acid needs to be converted to partial pressure. This can be achieved by using the non-ideal gas law:

[00004]$\begin{array}{cc}p=\left(\frac{n}{V}\right)\mathrm{ZRT}& \left(4\right)\end{array}$

[0113] With p the pressure, the concentration, R the gas constant and T the temperature in K and Z the gas compressibility factor Z, expressed as function of p (in Pa) as:

[00005]$\begin{array}{cc}Z=0.351+0.729p^{-0.176}& \left(5\right)\end{array}$

[0114] The calculated pressure for the used concentration using the ideal gas law is p.sub.ideal=51.5 Pa. This gives Z=0.715 and p=Zp.sub.ideal=36.83 Pa. The saturation pressure of acetic acid at 25 C. and atmospheric pressure is 2118.36 Pa, thus, p/p.sub.0=0.0174. In the current experiment the flowrate of 52 cm.sup.3/min was not reached and the amount adsorbed was calculated till a flowrate of 39 cm.sup.3/min. This implies p/p.sub.0=0.0174*39/52=0.0131 is to be considered.

[0115] The amount adsorbed in equilibrium, corresponding to a partial pressure of 0.0131, is around 5.13 mmol g.sup.1 (acetic acid adsorption isotherm for MIL-100(Fe)), which is perfect alignment with the value obtained by the breakthrough experiment (FIG. 13 (b)).

[0116] This means that the presence of water in the gas mixture did not affect the acetic acid adsorption. This further supports the previously established conclusion that the acetic acid is able to replace the adsorbed water molecules, where the presence of water did not impair the dynamic adsorption of acetic acid.

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