KR101554325B1 - Method for Separating MethaneNitrogen Using Nanoporous materials - Google Patents

Abstract

The present invention using a CH ₄ / N relates to a method of separating _2, more specifically a metal organic structure _{(Metal-Organic Framework, Cu 3} BTC 2) having a hydrophilic pores and hydrophobic pores with nano-porous material (Nanoporous materials) And a method for separating CH ₄ / N ₂ .
According to the present invention, a nanoporous metal organic structure (Cu ₃ BTC ₂ ) having hydrophobic and hydrophilic properties is used to form CH ₄ / N ₂ It is possible to selectively separate CH ₄ from the mixed gas.

Description

[0001] METHOD FOR SEPARATING METHANE / NITROGEN WITH NANO POROUS MATERIALS [0002]

The present invention relates to a separation method of the CH ₄ / N _2, more particularly the separation of CH ₄ / N ₂ using a nanoporous material having a hydrophilic pores and hydrophobic pores method using a nano-porous materials (Nanoporous materials) .

International energy agenct has reported that with the development of China, India and the Middle East, there will be a 35% increase in energy demand worldwide after 2035. Natural gas, a part of global energy supply, is an important energy source and accounted for 21.4% in 2010. Low quality natural gas containing CO ₂ (> 2%), N ₂ (> 4%) and H ₂ S (> 4 ppm) is not well used for high production costs, . Untapped natural gas, such as shale gas and natural gas hydra, is also being extensively analyzed and investigated. However, they contain nitrogen and nitrogen requires additional processes that must be separated to meet the pipeline and liquefied natural gas standards.

Industrial standard CH ₄ / N ₂ separation techniques are essential and important to increase the quality of natural gas. CH ₄ / N ₂ separation is now used only fulfill the liquefied distillation this week, this has the disadvantage that a lot of energy for cooling the CH ₄ required. Methods of absorbing, adsorbing or using membranes have been proposed to solve these energy and cost problems, but are limited to industrial use due to low performance and gas selectivity. Among them, the method using a membrane has attracted attention as a high performance and simple method, but has a problem of low selectivity due to the similar properties (dynamic diameter and permeability) of N ₂ and CH ₄ .

On the other hand, metal organic frameworks (MOFs), which are nanoporous materials, are porous coordination polymer networks composed of metal ions, clusters and organic materials. At present, the gas separation using MOFs is mainly made by the functional difference of the interaction with the adsorbent material, so the focus is on introducing the functionality by using an open metal site or changing the functional group, CO ₂ separation. However, CH ₄ / N ₂ using MOFs No separation has been reported.

Thus, the present inventors have found that effective CH ₄ / N ₂ Manners to develop a separating method sought results, making the hydrophilic pores and hydrophobic metal organic structure pore nanoporous material having a (Metal organic frameworks, MOFs), and by using this, CH ₄ / N ₂ effectively remove the CH ₄ in a mixed gas And the present invention has been completed.

An object of the present invention is to provide a method for separating CH ₄ / N ₂ using a nanoporous material having hydrophilic pores and hydrophobic pores.

In order to achieve the above object, the present invention provides a method of manufacturing a nanoporous material, comprising the steps of: (a) saturating a nanoporous material having hydrophilic pores and hydrophobic pores with a hydrophilic solvent; (b) the step of selectively storing the hydrophobic pores of the nanoporous material CH ₄ / N ₂ into contact with the CH ₄ the nanoporous material in saturated with the hydrophilic solvent; And (c) provides a separation of CH ₄ / N ₂ method using a nano-porous material, including the step of recovering the CH ₄ in the nanoporous material is stored in the CH _4.

According to the present invention, a nanoporous material having hydrophobic and hydrophilic properties can be used to form CH ₄ / N ₂ It is possible to selectively separate CH ₄ from the mixed gas.

Figure 1 shows X-ray diffraction of synthesized Cu ₃ BTC ₂ .
Figure 2 shows the surface saturation pattern of Cu ₃ BTC ₂ .
FIG. 3 is an analysis of gas storage and separation capacity of Cu ₃ BTC ₂ saturated with water. [(A): Storage of CH ₄ and N _2, respectively, according to pressure; (B): Composition of the stored gas after contacting the equimolar binary mixture of CH ₄ / N _{2 with} the substance at various pressures].
Figure 4 is a saturated Cu ₃ BTC water ₂ CH ₄ This is the result of high resolution powder deffraction (HRPD) after contact.
Figure 5 is a graph showing the effect of Cu ₃ BTC ₂ (A) Raman and (B) NMR spectra of CH ₄ .
FIG. 6 shows the structural change of Cu ₃ BTC ₂ saturated with water after CH ₄ contact ((A) and (B): structure before and after water saturation for large hydrophilic pores; (C): structure of hydrophobic small pores; (D): Grid structure].
Figure 7 shows the Raman spectrum of Cu ₃ BTC ₂ saturated with water or THF.
Figure 8 shows the effect of temperature on the dissociation of the stored CH ₄ [(A): Raman spectra; (B): XRD].

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is well known and commonly used in the art.

(A) saturating a nanoporous material having hydrophilic pores and hydrophobic pores with a hydrophilic solvent; And (b) a step of contacting a CH ₄ / N ₂ in a nano-porous material impregnated with the hydrophilic solvent, optionally stored in the hydrophobic pores of the nanoporous material for the CH _4; And (c) the separation of CH ₄ / N ₂ method using a nano-porous material, including the step of recovering the CH ₄ in the nanoporous material is stored in the CH _4.

In the present invention, the nanoporous material may be a metal organic structure, and the metal organic structure may be Cu ₃ BTC _2. However, the present invention is not limited thereto. For example, nanostructures having both hydrophobic pores and hydrophilic pores can be used without limitation.

In the present invention, a metal organic structure composed of hydrophilic and hydrophobic pores was fabricated by the idea of including a molecule and changing the internal pore structure of the metal organic structure. This structure not only changes the pore structure but also controls the gas affinity with the material. In the present invention Cu ₃ BTC ₂ (BTC: 1,3,5-benzenetricarboxylate) was used to demonstrate how effective this method is, which is one of the characterized metal organic structures and is commonly referred to as HKUST-1.

In one embodiment of the present invention, Cu ₃ BTC ₂ having hydrophilic pores and hydrophobic pores was synthesized by a known solvent thermal synthesis method. Hydrophilic pores were saturated by vapor treatment to separate the mixed gas of CH ₄ / N ₂ using the synthesized Cu ₃ BTC _{2. As} a result of observation of the saturation pattern, 1 g of Cu ₃ BTC ₂ was added with 0.58 g of water (36.7 %) Were included.

As the hydrophilic solvent, besides water, alcohols such as tetrahydrofuran (THF), ethanol, methanol, propanol, and ethylene glycol can be used.

In the present invention, the contact pressure of the CH ₄ / N ₂ mixed gas to the nanoporous material of step (b) is preferably 2 to 100 bar, more preferably 80 bar.

In another embodiment of the present invention, water-saturated Cu ₃ BTC ₂ was used to confirm gas storage capacity. As a result of analyzing the contents of CH ₄ and N ₂ contained in 1 g of Cu ₃ BTC ₂ after the CH ₄ / N ₂ mixed gas was contacted at different pressures, the storage amount of CH ₄ rapidly increased to 50 bar, , The saturation stagnation was reached at about 1.5 mmol / g and N ₂ was 0.13 mmol / g at 100 bar. As a result of checking the constituents of the gas molecules in the material, CH ₄ increased from 50 mol% to 96 mol% at 80 bar, and showed selectivity of 22.8 at 80 bar.

On the other hand, when the CH ₄ is Cu ₃ BTC ₂ , Cu ₃ BTC ₂ was saturated with tetrahydrofuran (THF), which may exist only in large pores with a size that is not suitable for small pores but has polar functional groups. Chem. Phys ., 11: 10331, 2009) reported that the benzene rings constituting the hydrophobic pores exhibit a tetrahedral arrangement at the center. According to Gkionis et al . (Platts, JA and Gkionis, K., Phys . The interaction between the π of the benzene ring is strong, which makes it suitable for the storage of CH ₄ . As a result of Raman analysis after decompressing Cu ₃ BTC ₂ saturated with THF at 100 bar with CH ₄ , the intensity of the peak was maintained. However, by observing that the wavenumber of CH ₄ changed to high frequency, It was confirmed that CH ₄ was stored in the hydrophobic pores.

In the present invention, the CH ₄ recovery in the step (c) is performed at -40 ° C to 50 ° C, preferably -40 ° C to 0 ° C, more preferably -40 ° C to -20 ° C In the first embodiment.

In another embodiment of the present invention, in order to separate the stored CH ₄ from Cu ₃ BTC ₂ , the pattern of the stored gas according to the temperature was analyzed using XRD and Raman. As a result, it was found that a peak was observed between -40 ° C. and -20 ° C. And the XRD analysis showed a structural change between -60 ° C and -40 ° C due to the release of water and gas. The difference between the two results was that the injected pressure was different during the observation, and as a result, the stored gas was recovered above -40 ° C.

The synthesis of the metal organic frameworks (MOFs) follows a well-known conventional method and is prepared by the reaction of a metal ion compound and an organic ligand in a first solvent. The metal ion of the metal ion compounds used comprises from Group 1 to Group ^{16, Li +, Na +, K} +, Rb +, Be 2 +, Mg 2 +, Ca 2 +, Sr 2 +, Ba 2 + ^{, Sc 3 +, Y 3 +} , Ti 4 +, Zr 4 +, Hf +, V 4 +, V 3 +, V 2 +, Nb 3 +, Ta 3 +, Cr 3 +, Mo 3 +, W 3 ^+, Mn ^{+ 3,} Mn ^{+ 2, 3 +} Re, Re ^{+ 2,} Fe ^{+ 3,} Fe ^{+ 2,} Ru ^3+, Ru ^{+ 2,} Os ^{+ 3,} Os ^{+ 2,} Co ^{+ 3,} Co ^{+ 2, Rh 2 +, Rh +, Ir} 2 +, Ir +, Ni 2 +, Ni +, Pd 2 +, Pd +, Pt 2 +, Pt +, Cu 2 +, Cu +, Ag +, Au +, Zn 2 ^+, Cd ^{+ 2,} Hg ^{+ 2,} Al ^{+ 3,} Ga ^{+ 3,} In ^{+ 3,} Tl ^{+ 3,} Si ^{+ 4,} Si ^{2 +,} Ge ^{+ 4,} Ge ^2+, Sn ^{+ 4,} Sn ^{+ 2, Pb 4 +, Pb 2 +,} As 5 +, As 3 +, As +, Sb 5 +, Sb 3 +, Sb +, Bi 5 +, Bi 3 + , and one or more selected from the Bi ⁺ a They must participate in the reaction.

In the present invention, the synthesis of the metal organic frameworks (MOFs) is carried out by using at least one selected from the group consisting of at least one benzene ring known in the art and at least one kind of organic substance composed of two or more carboxylic acids Participate in the reaction. Trimersic acid is preferably used.

The first solvent may be at least one selected from the group consisting of acetone, acetonitrile, benzene, butanol, carbon tetrachloride, chloroform, methylene chloride, cyclohexane, Dimethylformamide, diethylformamide, dioxane, methanol, ethanol, ether, ethyl acetate, and the like. (Ethylene glycol), glycerin, pentane, hexane, heptane, methyl tertiary butyl ether (MTBE), propanol, xylene xylene, t-butyl alcohol, tetrahydrofuran, toluene and water may be used. Preferably, ethanol can be used. have.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are only for illustrating the present invention and that the scope of the present invention is not construed as being limited by these embodiments. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Example  One: Cu ₃ BTC ₂ Synthesis of

Cu ₃ BTC ₂ was synthesized by slightly modifying a known solvent thermal method (Kusgens, P. et al., Micropor. Mesopor. Mat., 20: 325, 2009). Copper nitrate trihydrate _{(Copper nitrate trihydrate, CuN 2 O} 6 · 3H 2 O) 4.35g and tree magic acid (Trimesic acid) 2.1g was dissolved in a solvent consisting of 60ml of ethanol and 60ml of deionized water. The mixture was mixed for 12 hours, sonicated for 30 minutes, transferred to a stainless steel reactor, and reacted at 120 DEG C for 12 hours. The crystalline solid synthesized by the above method was rinsed with ethanol twice a day for 2 days, dried at room temperature for 12 hours, and then placed at 200 ° C for 12 hours.

As a result, the synthesized Cu ₃ BTC ₂ is composed of three types of pores and has void channels of 1 nm in the [100] direction. The small pores are hydrophobic and the longest distance between the opposite copper ions is 13.3 ANGSTROM and one of the larger pores strongly interacts with water due to the strong hydrophilic nature of the exposed uncoated copper ions. The longest distance between molecules is 18.6 Å. The other large pores are less hydrophilic but contain water molecules, and the distance between atoms is 18.8 Å. Structure and pore properties were first reported by Williams et al. (Chui, SS et al ., Science , 283: 1148,1999)

The high crystallinity and curvature area (1091 m ² / g) of the synthesized Cu ₃ BTC ₂ was analyzed by XRD and BET and confirmed to be successfully synthesized (FIG. 1).

Example  2: with water Saturated Cu ₃ BTC ₂

Cu ₃ BTC ₂ synthesized in Example 1 was prepared by being saturated with water by vapor treatment. The dehydrated Cu ₃ BTC ₂ was placed in a vacuum dryer with a beaker containing water, vacuum-treated at 4 torr, and then the vacuum dryer was closed. The relative humidity was close to 100% and the evaporated water was diffused into the pores of the MOFs and held for about 5 hours until saturated. As a result, it was confirmed that 1 g of Cu ₃ BTC ₂ contained 0.58 g of water (36.7%) (FIG. 2).

Example  3: Gas storage capacity

Carried out according to Example 2, the pressure of ₂ Cu ₃ BTC saturated with water in the ready-CH ₄ And storage capacity of N ₂ were measured. Cu ₃ BTC ₂ was contacted with an equimolar binary mixture of CH ₄ / N ₂ at 15 ° C., maintained at -30 ° C., and 1 g of CH ₃ contained in Cu ₃ BTC ₂ And N ₂ were analyzed. As a result, as shown in FIG. 3 (a), the storage amount of CH ₄ rapidly increased to 50 bar, but the increase tendency decreased at a high pressure to reach a saturated stagnation state at about 1.5 mmol / g. N ₂ was 0.13 mmol / g at 100 bar. Considering that the amount of CH ₄ stored in dried Cu ₃ BTC ₂ is up to 9.4 mmol g, the storage capacity is lowered because the hydrophilic pores are saturated with water to prevent gas storage.

Considering the difference in gas storage amount, it can be expected that this material would be applicable for separating CH ₄ from a mixed gas such as natural gas, so Cu ₃ BTC ₂ is mixed with CH ₄ / N ₂ mixed gas (50: 50 and 90:10) and then subjected to a separation test by analyzing the constituents of the gas molecules in the material.

As a result, as shown in FIG. 3 (b) and Table 1, it was confirmed that the CH ₄ was increased from 50 mmol% to 95.8 mmol% at 80 bar, and the equilibrium selectivity was measured based on the following equation (1).

[Equation 1]

( _YCH4 / _XN2 ) / ( _YN2 / _XCH4 )

X and Y denote the gas constituents in the feed stream and the material, respectively, and the selectivity is expressed as 22.8 at 80 bar.

Example  4: CH ₄ Origin and Selectivity

CH ₄ In order to explain the origin and high selectivity of storage, structural analysis using high resolution powder diffraction (HRPD) of synchrotron radiation was carried out in the Pohang Accelerator Laboratory. HRPD analysis was performed using a synchrotron of the Pohang Accelerator Laboratory at -180 DEG C (lambda = 1.54950 ANGSTROM), stepwise with a fixed time of 3.5 seconds at a step size of 0.01 per hydrated sample, saturation with water The results of the diffraction of Cu ₃ BTC ₂ saturated with water contacted with CH ₄ at a pressure of Cu ₃ BTC ₂ and 100 bar were compared.

As a result, FIG. 4, the structure I CH ₄ hydrate was confirmed (hydrate) of 320 and 321, a new peak at 27.2 and 28.3 corresponding to diffraction as shown in. This is because the partial water present on the surface of Cu ₃ BTC ₂ and in the large pore has migrated to the guest molecule, CH ₄ hydrate, which occupies the vacant space of the hydrogen-bonded water cage. Also, there was no noticeable peak intensity change in the lattice expansion of Cu ₃ BTC ₂ after contact with CH ₄ , and the lattice parameter of Cu ₃ BTC ₂ was determined on the basis of the high intensity (222) peak As a result, it was increased from 26.2974 Å to 26.3333 Å. These results indicate that the expansion of the structure and the presence of CH ₄ in pores of Cu ₃ BTC ₂ saturated with water.

Example  5: Raman , ¹³ C CP / MAS NMR  And HRPD  analysis

5 -1: Raman analysis

Raman analysis was performed using a high-resolution dispersive Raman microscope (Horiba Jobin YvonLabRAM HR UV / Vis / NIR) at 514.53 nm light emitted from an Ar-ion laser (30 mW) at -180 ° C. (measurement conditions: 1800 grating, D1 filter, 100 holes). All gases containing the sample were placed in a 77K.XRD analytical sample holder and quenched with liquid nitrogen. Powder X-ray diffraction was performed using a low temperature XRD (D / MAX, Rigaku) of CuK radiation (λ = 1.5406 Å) in a 40 kV generator and a 300 mA AC generator. The XRD measurement was performed in the range of 3 ° to 40 ° (2θ) in 0.05 step, and the reaction temperature was -180 ° C. When examining the change in the sample according to the temperature, the temperature rose step by step at a rate of 5 [deg.] C per minute, and had a waiting time of 5 minutes before the measurement to stabilize the temperature.

The results, as shown in (A) of Figure 5, from the free CH ₄ molecule to move as much as 2896.8 -20.2, -14.2, and -3.2, at 2902.8 and 2913.8cm ^-1 CH symmetric stretching vibration mode (stretching vibration mode) Were identified. Peak appeared in the 2902.8cm ^-1 and 2913.8cm ^-1 is Cu ₃ BTC ₂ represents a CH ₄ in the gas hydrate structure I It was expected that a deviation of wavenumber of -1 to 2 would be seen from the bulk gas hydrate due to the influence of the surroundings. CH _{4 in} various metal organic structures (MOFs) According to the previous data for the Raman absorption, high mobility is to mean a strong interaction with the structure, the movement of the moving -20.2cm ^-1 (Siberio-Perez between 7.6 ~ 10.1cm ^-1 claimed in IRMOFs series, DY meat al ., Chem . Mater ., 19 : 3681, 2007 ) .

5-2: NMR analysis

NMR analysis was performed using a 400 MHz solid FT-NMR spectrometer (Bruker) at -40 ° C at 4 KHz rotation rate and all samples were sufficiently treated with ¹³ C methane to remove the carbon peaks of the MOFs themselves.

As a result, Cu ₃ BTC ₂ saturated with water contacted with CH ₄ at 100 bar showed four peaks at -4.3, -6.7, -11.2 and -12.7 ppm as shown in FIG. 5 (B) Considering the CH ₄ partly separated from the material and the -11.2 ppm peak resulting from the gas during the Raman data, the three peaks corresponding to the Raman data result represent different inclusion states of CH ₄ . The small deshielded peaks at -4.3 pm and -6.7 pm represent CH ₄ in the small, large cage of the structure I hydrate and the carbon nuclei of CH ₄ molecules contained in Cu ₃ BTC ₂ saturated with water Showed a shift from -11.2 ppm to -12.7 ppm, confirming the interaction of the structure with CH ₄ .

According to the interaction between Gkionis such as reported by CH ₄ and benzene cross between (Platts, JA and Gkionis, K. , Phys Chem Chem Phys, 11.... 10331, 2009), CH of benzene ring and π Action is said to reduce the strong shielding effect of CH ₄ on carbon. Also, the area ratio of each peak gives information on the quantitative ratio of CH ₄ , although it is difficult to know the exact ratio of CH ₄ in each step because the contained CH ₄ partly escapes, but the CH in Cu ₃ BTC _{2 4} was found to be larger than that of hydrate as shown in the Raman spectrum shown in Fig. 5 (A).

5 -3: HRPD analysis

(A) and (B) of Cu ₃ BTC ₂ having three different kinds of pores (Fig. 6 (A) and (B)) can not be used for gas storage because they are saturated with water and filled with pores, Small pores (Figure 6 (B)), which are surrounded by four benzene rings and are highly hydrophobic, block the inflow of water. A negligible small change in the HRPD results (FIG. 4) means that the included CH ₄ does not interfere with the placement of water clogged in all directions, and it is difficult to include CH ₄ in large pores filled with water 6 (D)).

Example NMR result, a sharp peak of 5-2 means that the CH ₄ present, and must be included in the status small hydrophobic pores, as shown in (C) of FIG. Interestingly, the benzene rings constituting the hydrophobic pores show a tetrahedral arrangement with respect to the center, and a strong interaction between 4π and 4C-H is suitable for CH ₄ , and nuclear shielding and high Raman migration In the United States.

To demonstrate this, while having a polar functional group can be present only in larger pore size that is not appropriate for the small pores to form the hydrate structure II CH ₄ from SI hydrate Tetrahydrofuran (THF) was used to prevent the peak from appearing. Cu ₃ BTC ₂ was added to the THF solution, excess solution outside the crystal was removed with filter paper, and Raman analysis was performed by depressurizing at 100 bar with CH ₄ (FIG. 7). The strength was maintained by the addition of THF, but it was found that the number of waves of CH ₄ slightly changed to high frequencies, indicating that CH ₄ was stored in the hydrophobic pores without interfering with THF.

Example  6: Stored gas separation

Gas separation was analyzed by using XRD and Raman for the aspect of gas stored at -180 ℃ to 0 ℃. As a result, as shown in Fig. 8 (A), the dissociation of the stored gas quickly disappeared between -40 ° C and -20 ° C of the Raman peak of CH ₄ , and the XRD result showed that at -60 ° C And showed an impressive structural change between -40 ° C (FIG. 8 (B)). This result means that the stored gas is recovered above -40 ° C. The difference in dissociation temperature between Raman (1 bar) and XRD (vacuum) is due to the different injected pressures during the observation.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereto will be. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (6)

A method for separating CH ₄ / N ₂ using a metal organic structure comprising the steps of:
(a) saturating hydrophilic pores of a metal organic structure having hydrophilic pores and hydrophobic pores with water;
(b) bringing CH ₄ / N ₂ into contact with the water-saturated metal organic structure to selectively move only CH ₄ through water-saturated pores, and transferring the transferred CH ₄ to the hydrophobic pores of the empty metal organic structure ; And
(c) recovering the metal from the organic structure that the CH ₄ CH ₄ are stored.
delete The method of claim 1, wherein the metal organic structure separation method of the CH ₄ / N _2, characterized in that Cu _{2 3} BTC.
delete The method of claim 1 wherein the (b) step is the separation of CH ₄ / N _2, characterized in that is carried out in 2 ~ 100bar.
The method of claim 1, wherein the step (c) separation method of the CH ₄ / N _2, characterized in that is carried out at -40 ℃ to 50 ℃.

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