Nitrate modified flexible porous coordination polymer, preparation method and propylene-propane separation method

Abstract

The invention relates to a nitrate modified flexible porous coordination polymer, a preparation method and a propylene-propane separation method, and belongs to the technical field of coordination polymers used in the separation process. According to the invention, a flexible porous crystal is designed, and an electronegative nitrate acceptor is introduced into a dynamic skeleton. The material shows unprecedented reverse selectivity, the absorption amount of C3H8 is twice that of C3H6, and crystallography, theory and in-situ researches show that only C3H8 triggers pore expansion and secondary adsorption through nitrate-mediated recognition. Comparative studies with hydroxyl and methyl functionalized analogs prove an important role in receptor electronegativity. The polymer grade C3H6 can be directly produced through a one-step method, and the method has the advantages of breakthrough selectivity, excellent structural adaptability and large-scale synthesis.

Description

Technical Field

[0001] This invention relates to a nitrate-modified flexible porous coordination polymer, its preparation method, and a method for separating propylene and propane, belonging to the field of coordination polymer technology for separation processes. Background Technology

[0002] Adsorption separation using porous adsorbents is becoming a key technology for environmental remediation, energy-efficient industrial processes, and decarbonization, with applications ranging from water treatment to carbon capture. Despite this promising outlook, critical industrial separation remains energy-intensive and expensive. A notable example is the separation of propylene (C3H6) from propane (C3H8), which currently still relies on cryogenic distillation, consuming approximately 12.9 GJ of energy to produce 1 ton of C3H6, representing about 80% of the total production cost. Porous coordination polymers (PCPs), also known as metal-organic frameworks (MOFs), offer a versatile platform for adsorption-based separation due to their tunable pore structure and chemical functionality, achieved through the systematic design of organic ligands and metal nodes. However, C3H6 / C3H8 separation lags far behind because the nearly identical molecular size and polarizability of these gases, coupled with weak adsorbate-adsorbent interactions in conventional PCPs, hinder selective differentiation and limit progress in this crucial area.

[0003] Recent advances in rigid PCPs utilize open metal sites, functional organic groups, and / or precisely tailored pore size / shape selective adsorption of C3H6, while simultaneously weakening or excluding C3H8 adsorption through π-complexation, electrostatic interactions, and other supramolecular interactions. However, achieving high purity C3H6 in these systems typically requires at least two adsorption-desorption cycles, which significantly increases energy consumption and operational complexity. To achieve efficient one-step purification, research is increasingly focusing on reversing the adsorption sequence of these two gases.

[0004] Flexible porous coordination polymers (PCPs) have become one of the most promising materials in the field of gas separation in recent years due to their controllable structural dynamics. Early examples, such as the ethane-selective "gating" behavior of ZIF-7 and the different "gating" opening pressures exhibited by its isomorphic analog CdIF-1330 for propane (C3H8, threshold pressure 0.30 bar) and propylene (C3H6, threshold pressure 0.70 bar), demonstrate that this family of flexible materials is a potential candidate for achieving C3H8 / C3H6 separation. However, although the "gating" pressure can be optimized through node modification, it is difficult to effectively increase the adsorption capacity difference between the two gases. Summary of the Invention

[0005] This invention amplifies the dipole interaction between the pore surface and the more polarizable C3H8 molecule by enhancing the electronegativity of the pore surface, and designs and synthesizes a novel flexible porous crystal NTU-99-NO2, whose framework is modified by electronegative nitro functional groups.

[0006] A nitrate-modified flexible porous coordination polymer has the chemical formula [CuL1 L2]·xSolvent, where L1 is the ligand 4,4'-dipyridylamine, L2 is the ligand 5-nitroisophthalic acid, x refers to the number of molecules, and Solvent refers to the adsorbed solvent. After the solvent is removed, the Cu nodes of the flexible porous coordination polymer assemble with the two linkers to form a 4,4'-csql topological layer. Within the monolayer, L1 forms two different micropores, and adjacent larger and smaller pore structures are formed between the layers.

[0007] The sizes of the two different micropores are and

[0008] The size of larger pore structures is Smaller pore structure

[0009] The preparation method of the above-mentioned flexible porous coordination polymer includes the following steps:

[0010] L1 ligand, L2 ligand, copper salt and acid were dissolved in an organic solvent and subjected to coordination polymerization. The product crystals were washed to obtain a flexible porous coordination polymer.

[0011] The copper salt mentioned is copper nitrate.

[0012] The acid mentioned is nitric acid.

[0013] The organic solvent is obtained by mixing DMF, ethanol and water in a volume ratio of 2-2.5:0.5-1:0.5-1.

[0014] The coordination polymerization reaction conditions are 300-400K for 200-400 minutes.

[0015] The flexible porous coordination polymer is also activated by immersion in methanol followed by vacuum removal of methanol.

[0016] The conditions for vacuum methanol removal are 300-400K for 20-200 minutes.

[0017] The selective adsorption separation method for C3H6 and C3H8 employs the aforementioned flexible porous coordination polymer.

[0018] In the adsorption separation method described above, the flexible porous coordination polymer preferentially adsorbs C3H8.

[0019] The beneficial effects of this invention are:

[0020] Given that these two gases are in the presence of partially positively charged hydrogen atoms (H δ+ The difference in quantity leads us to speculate that a flexible PCP with an electronegative acceptor (functional group) can "sensor" this subtle difference, thereby inducing a multi-step phase transition (including pore expansion associated with the second or third adsorption step) only when adsorbing C3H8, while C3H6 cannot trigger this process, thus achieving a significant increase in the C3H8 / C3H6 adsorption ratio.

[0021] Under conditions of 298 K and 1 bar, NTU-99-NO2 adsorbed twice the amount of C3H8 as C3H6, thus reversing the conventional adsorption selectivity. Figure 1 Crystallographic analysis and computational simulations show that the nitro acceptor in the material can interact with hydrogen-rich C3H8 molecules, inducing cooperative layered expansion and thus promoting secondary adsorption; this process does not occur in the adsorption of C3H6. Through systematic comparison with analogs containing electron-donating groups (-OH) or neutral groups (-CH3), we confirm that the electronegativity of the framework is the key factor dominating this cooperative adsorption behavior.

[0022] In addition, NTU-99-NO2 has good stability and can be prepared on a large scale. It selectively adsorbs C3H8 under mixed component conditions, and when used in combination with a co-adsorbent, it can directly obtain polymer-grade C3H6. Attached Figure Description

[0023] Figure 1 Molecular recognition is achieved through adaptive skeleton dynamic changes.

[0024] Figure 2 Schematic diagram of the structural evolution of NTU-99-NO2 in synthetic and activated states; (a, e) Planar coordination configuration view of copper (Cu); (b, f) Stacked bilayer structure; (c, g) Accessible space of the spherical neck channel, in which the two NO2 groups define the size of the spherical space; (d, h) The narrow neck is formed by pyridine ring hydrogen (H pyridine ) and benzene ring hydrogen (H benzene The molecular radius of the probe used to analyze pore structure is limited by [specific parameters].

[0025] Figure 3Schematic diagram of reverse gas adsorption and phase transition in NTU-99-NO2; (a) Single-component adsorption isotherms of C3H6 and C3H8; (b) Adsorption ratio of C3H8 / C3H6 (100 kPa); (c) Comparison of in-situ PXRD spectra of C3H8 and (d) C3H6 under loading conditions. Dashed lines trace peak shifts and correlate them with structural kinetics. All measurements were performed at 298 K.

[0026] Figure 4 Schematic diagram of structural evolution and phase transition during gas adsorption: The diagram shows the interlayer spacing (a, d, g), narrow neck view (b, e, h), and spherical cavity width (c, f, i) of the NTU-99-NO2 structures loaded with C3H6 (100 kPa), C3H8 (17 kPa), and C3H8 (100 kPa), respectively. di represents the distance between adjacent layers, in units of... The probe radius used for pore analysis is

[0027] Figure 5 : Graphs showing the results of gas adsorption tests regulated by functional groups in the isomorphic framework; (a) Synthetic routes of isomers NTU-99-OH and NTU-99-CH3; (b) The ball-neck channel in NTU-99-OH and (c) the adsorption isotherms of C3H6 and C3H8 at 298 K; (d) The ball-neck channel in NTU-99-CH3 and (e) the adsorption isotherms of C3H6 and C3H8 at 298 K.

[0028] Figure 6 Transmission separation experimental results: (a, b) Transmission curves of a single NTU-99-NO2 packed column at different feed ratios (C3H8 / C3H6, v / v): (a) 50 / 50, (b) 80 / 20. (c, d) Transmission curves of a tandem column system of NTU-99-NO2 and ZIF-8 at different feed ratios: (c) 50 / 50, (d) 80 / 20. All experiments were conducted at 298 K and 1 bar. Detailed Implementation

[0029] NTU-99-NO2 utilizes the electronegativity of nitro groups and the dynamic self-adaptation of soft crystals to achieve the inversion of C3H8 / C3H6 selectivity at room temperature and pressure. This material not only achieves record-breaking selectivity but also enables the high-efficiency one-step purification of polymerization-grade C3H6. (Illustration) Figure 1 Molecular recognition is achieved through adaptive skeletal dynamic changes: electronegative nitro acceptors and C3H6 (containing 6 H atoms) δ+ The interaction between the hydrogen-rich C3H8 (containing 8 H atoms) and the hydrogen-rich C3H8 (containing 8 H atoms) is relatively weak, resulting in almost no adaptive structural change and a low adsorption capacity. δ+This can trigger a strong host-guest recognition process, driving synergistic pore expansion and doubling the adsorption capacity. This differentiated response allows the material to selectively adsorb C3H8, thus facilitating the direct acquisition of polymerization-grade C3H6 from mixed feed gases.

[0030] Example 1: Synthesis of NTU-99-NO2

[0031] The structure of ligand L1 is as follows:

[0032]

[0033] 4,4'-Dipyridylamine (L1, 4 mg, 0.023 mmol), 5-nitroisophthalic acid (L2, 4 mg, 0.019 mmol), Cu(NO3)2·6H2O (10 mg, 0.034 mmol), and HNO3 (20 μL) were dissolved in a mixed solvent of N,N'-dimethylformamide (DMF) / ethanol (EtOH) / water (H2O) (2.25 / 0.75 / 0.25, v / v / v, 3.25 mL). The solution was then sealed in a glass bottle (10 mL) and reacted at 363 K for 300 min. After cooling, purple flaky crystals were obtained and washed three times with fresh DMF solvent (yield: approximately 51% based on L1).

[0034] Synthesis of Comparative Example 1 NTU-99-OH

[0035] L1 (4 mg, 0.023 mmol), 5-hydroxyisophthalic acid (4 mg, 0.022 mmol), and Cu(NO3) were added. v • 6H2O (10 mg, 0.034 mmol) was dissolved in a mixed solvent of DMF / H2O (1.25 / 0.75, v / v / v, 2 mL). After cooling, the reaction solution yielded purple flaky crystals, which were washed three times with fresh DMF solvent (yield: approximately 42% based on L1).

[0036] Synthesis of 2NTU-99-CH3 (Comparative Example)

[0037] L1 (4 mg, 0.023 mmol), 5-methyl-1,3-phthalic acid (4 mg, 0.022 mmol), CuCl2 (10 mg, 0.074 mmol), and HNO3 (20 μL) were dissolved in a mixed solvent of N,N'-dimethylacetamide (DMA) / H2O (2.25 / 1.75, v / v / v, 4 mL). The solution was then sealed in a 10 mL glass container and reacted at 363 K for 2000 min. After cooling, purple flaky crystals were obtained and washed three times with fresh DMA solvent (yield: approximately 45.0% based on L1).

[0038] The activation process for the samples in the above examples and comparative examples involved immersing the newly synthesized NTU-99 series samples in anhydrous methanol for 3 days, replacing the methanol with fresh methanol every 8 hours to achieve activation. Afterward, the crystals were subjected to dynamic vacuum treatment at room temperature for 60 minutes. Subsequently, under dynamic vacuum conditions, the samples were treated for 20 hours at their respective activation temperatures (NTU-99-NO2: 353 K, NTU-99-OH: 333 K, NTU-99-CH3: 333 K).

[0039] Crystal structure characterization

[0040] Single-crystal X-ray diffraction analysis showed that it crystallized in space group P-1, with the chemical formula [CuL1 L2]·xSolvent(NTU-99-NO2). 2+ The ion exhibits a planar four-coordinate configuration, with its coordinating atoms originating from two pyridine nitrogen atoms (Npyridine) of two L1 ligands and two carboxyl oxygen atoms (OCOO) of two L2 ligands. Figure 2 (a) The Cu node and two connectors assemble to form a 4,4-c sql topology layer. The bending conformation of L1 induces two distinct micropores (characterized by a size of...) within the monolayer. and ()( Figure 2 b). Interlayer stacking (interlayer distance: It consists of multiple hydrogen bonds (NH··O distance: ) and the π-π interaction between the relative L2 benzene ring Stable. These interactions result in a 40.94° tilt along the a-axis, partially blocking smaller pores and shrinking larger pores into one-dimensional ball-neck channels. The "ball" region is defined by head-to-head aligned NO2 groups, with a size of... Due to the spatial confinement of pyridine and aromatic hydrogens, the "neck" narrows to... ( Figure 2 (cd). After solvent removal, the activated phase (NTU-99-NO2-α) underwent significant structural rearrangement. The dihedral angle between the L1 pyridine rings decreased from 27.41° to 16.53°, indicating that the pyridine rings underwent rotation (cd). Figure 2 (e). This behavior is similar to the rotation of the pyridine ring observed in NTU-88, which was prepared with an L1 ligand during C3H4 adsorption. Simultaneously, the distance of NHL1…OCOO increases slightly to (from 1.955 in NTU-99-NO2), while the interlayer spacing shrinks to These changes flattened the ball area and widened the neck of the passage. ( Figure 2 Powder X-ray diffraction (PXRD) analysis confirmed the phase purity of the synthesized phase. However, some diffraction peaks, such as those corresponding to the (001) and (100) crystal planes, shifted to higher angles after activation, exhibiting structural shrinkage. Thermogravimetric analysis (TGA) showed that the synthesized material and its activated phase remained stable at temperatures up to 300 °C.

[0041] Single-component gas adsorption determination and in-situ PXRD

[0042] Gas adsorption measurements were performed using a volumetric adsorption analyzer. Ultra-high purity C3H8, C3H6, N2, CO2, C2H4, and C2H6 gases were used in the adsorption experiments. The permanent porosity of NTU-99-NO2-α was investigated using adsorption isotherms of N2 (77 K) and CO2 (195 K). NTU-99-NO2-α exhibited a typical Type I N2 adsorption isotherm, with a BET surface area of ​​350 m². 2 ·g -1 The pore volume is 0.1341 cm³. 3 ·g -1 The CO2 isotherm shows a two-step absorption: rapid initial adsorption (56.2 cm⁻¹). 3 ·g -1 Then, when P / P0 = 0.65 or higher, proceed to the second step (99.4cm). 3 ·g -l The adsorption of C3H6 and C3H8 exhibits a reversible hysteresis loop upon desorption. This behavior confirms the framework's flexibility and stimuli-responsiveness. Single-component adsorption isotherms of C3H6 and C3H8 were collected. Figure 3 (a) At 298 K, NTU-99-NO2-α exhibits a typical type I adsorption isotherm for C3H6, with a maximum absorbance of 1.26 mmol·g⁻¹. -1 In contrast, the C3H8 isotherm exhibits a step-like profile. Initially (P < 23 kPa), the adsorption of C3H8 is very similar to that of C3H6. A rapid adsorption step then occurs, quickly reaching saturation with a maximum absorbance of 2.20 mmol·g⁻¹. -1 These unprecedented isotherms indicate the occurrence of reverse adsorption, with a maximum absorbance of 1.75 at 1 bar, which is the highest absorbance reported for porous materials. Figure 3 (b). Given the narrow neck of NTU-99-NO2-α and and Given its molecular size, initial adsorption is likely triggered by the rotation of the pyridine ring to widen the neck, allowing entry into the nanosphere cavity. Crucially, only C3H8 can trigger further channel expansion, enabling secondary adsorption, presumably due to its enhanced dipole interaction with the electronegative nitrate group.

[0043] In-situ powder X-ray diffraction (PXRD) analysis during C3H8 adsorption revealed a pressure-dependent phase transition in NTU-99-NO2-α. Below 40 kPa, the

[001] peak shifted to a lower angle, marking the transition to the mesophase (NTU-99-NO2-β), accompanied by pyridine ring rotation and initial pore expansion. Above 40 kPa, a doublet appeared, indicating the coexistence of NTU-99-NO2-β and the third phase (NTU-99-NO2-γ). The pure NTU-99-NO2-γ phase was clearly observed at 100 kPa. The lower angle shift of the [1 1 1] and [2 -1 0] peaks confirmed the gradual interlayer expansion. After desorption, the peaks corresponding to the [0 0 1] plane gradually shifted to relatively higher angles, eventually recovering to the characteristic peaks of NTU-99-NO2-α. This behavior highlights the reversibility of the three-phase structural transformation in the C3H8 adsorption-desorption cycle, characterized by the rotation of the pyridine ring followed by layer expansion. In contrast, C3H6 only induced an α→β phase transition (20→100 kPa) without undergoing a secondary expansion to the γ phase. Figure 3 (cd). Similarly, C2H6 can drive a three-phase transition (α→β→γ), while the phase transition of C2H4 terminates at the β phase. These structural kinetic behaviors are consistent with the characteristics of gas adsorption curves, in which alkanes (C3H8, C2H6) initiate multi-step adsorption through cooperative framework flexibility, while alkenes (C3H6, C2H4) initiate limited reactions.

[0044] To elucidate its structural dynamics and nitrate-mediated recognition mechanism at the atomic scale, three gas-loaded single-crystal structures were resolved at 298 K: and The structures loaded with C3H6 and those loaded with C3H8 under low pressure exhibit almost identical cell parameters and interlayer spacing. and channel dimensions ( Figure 4 (af). In contrast, loading C3H8 under high pressure induces a significant phase transition, characterized by lattice contraction along the a-axis. And elongate along the c-axis This structural rearrangement causes the interlayer spacing to... Expand to The nanosphere cavity also from Expansion to ( Figure 4Therefore, it is reasonable to classify the first two crystals as the β phase, while the third is the γ phase of NTU-99-NO2, a fact confirmed by gas-loaded PXRD analysis. The ligand rearrangement yielded crucial insights: the dihedral angle between pyridine rings in L1 increased from 12.96° (β phase of C3H6) to 17.13° (low-pressure C3H8 β phase), and then to 30.48° (high-pressure C3H8 γ phase). This stepwise rotation highlights the pressure- and guest molecule-dependent structural flexibility of the structure, allowing for tuning of the channel neck size. The static, closed conformational framework observed under these loading states reveals a mechanism: host-guest interactions stabilize specific skeletal conformations, which may contribute to enhanced gas storage capacity.

[0045] To investigate the unique role of the electronegative NO2 group in recognizing C3H6 and C3H8 molecules, we replaced L2 with L3 (5-hydroxyisophthalic acid) or L4 (5-methylisophthalic acid) during the synthesis of NTU-99-NO2, synthesizing two isomers, NTU-99-OH and NTU-99-CH3. Figure 5 They share almost identical topological stacking patterns and therefore also possess a spherical-neck channel structure. The difference lies in the boundary of the nanosphere cavities in NTU-99-OH and NTU-99-CH3, which is composed of electron-donating -OH groups and electronegative -CH3 groups, respectively. Adsorption studies revealed a clear functional group dependence. At 298 K, NTU-99-OH exhibited a Type I isotherm for C3H6, but for C3H8, the adsorption was negligible below 27.7 kPa, followed by a rapid and gradual increase in adsorption. In-situ PXRD patterns confirmed that NTU-99-OH undergoes a structural change earlier upon contact with C3H6 compared to C3H8. In contrast, NTU-99-CH3 showed almost identical Type I isotherms for both gas and in-situ PXRD patterns. Figure 5 (c, e). Furthermore, the maximum adsorption capacities for both gases in these two porous coordination polymers (PCPs) are very close to the C3H6 adsorption capacity (298 K) observed in NTU-99-NO2. These systematic comparisons confirm that the skeletal electronegativity, regulated by the type of functional group, determines the material's structural adaptability to specific gases. Only the nitro group in NTU-99-NO2 can trigger synergistic structural expansion, thereby achieving selective adsorption of C3H8, highlighting its unique role in alkane / olefin recognition.

[0046] Penetration test

[0047] All gas flow rates were regulated by a mass flow controller. The activated crystals were tightly packed into a stainless steel column (φ = 3 mm). The sample was activated under dynamic high vacuum to remove impurities. When no signal was detected, He was introduced into the system for pressure compensation, and then the inlet gas was switched to a C3H8 / C3H6 mixture. The breakthrough point was determined by gas chromatography. Regeneration was achieved by treating the cyclic experimental chamber with a high vacuum of 353 K for half an hour. In this work, the breakthrough gas pressure was 1.0 bar. The activated sample weights used for testing were: NTU-99-NO2 4.08 g and ZIF-8 2.50 g.

[0048] Based on the anomalous adsorption behavior of C3H8 / C3H6, its potential for one-step purification of polymerization-grade C3H6 was evaluated. Breakthrough experiments using an equimolar gas mixture showed that both gases elute simultaneously, a "slip effect" common in flexible framework materials such as ELM-1143 and CdIF-13.30. However, the effluent gas concentrations showed significant differences, reflecting the material's preferential adsorption of C3H8 (selectivity 2.17), slightly higher than the selectivity calculated based on the ratio of adsorption amounts of the individual components (1.75). To mitigate the slip effect, a tandem column system was employed: the first column was NTU-99-NO2 for selectively capturing C3H8, and the second column was ZIF-8 with nearly identical adsorption capacities for both gases. Even with different feed gas ratios, this method still yielded polymerization-grade C3H6 (≥99.5%) at 298 K and 1 bar. Figure 6 (cd). To verify the composition of the adsorbed gas in each packed column, we performed desorption analysis on two packed columns that reached saturation after a breakthrough experiment with equimolar feed gas. The calculated adsorption selectivity of NTU-99-NO2 for C3H8 / C3H6 was 2.39, while in ZIF-8 this value decreased to 1.38. Although the performance of this dual-column system differs from the evaluation metrics of a single column, the adaptive pore dynamics of NTU-99-NO2 remains the core of achieving efficient separation, highlighting its application value in solving challenging alkane / olefin purification problems. The practical application of porous crystalline materials usually depends on their ability to be synthesized on a large scale and the stability of the framework. Rapid synthesis of NTU-99-NO2 was achieved by adding ammonia (NH3·H2O, 4 mL) to a stirred solution (400 mL) of the reactants, yielding 10.3 g of product within 1 minute, with a space-time yield of approximately 37 t·m⁻¹. -3 ·d -1The mass-produced material retains its original phase purity, porosity, and gas-selective adsorption capacity. Crucially, NTU-99-NO2 exhibits excellent water and chemical stability in cyclic breakthrough experiments without performance degradation, making it a promising candidate material for industrial applications.

Claims

1. A nitrate-modified flexible porous coordination polymer, characterized in that, It has the chemical formula [CuL1 L2]·xSolvent, where L1 is the ligand 4,4′-dipyridylamine, L2 is the ligand 5-nitroisophthalic acid; x refers to the number of molecules, and Solvent refers to the adsorbed solvent. After the solvent is removed, the flexible porous coordination polymer Cu nodes and the two linkers are assembled to form a 4,4-c sql topological layer. Within the single layer, L1 forms two different micropores, and adjacent larger pore structures and smaller pore structures are formed between the layers.

2. The nitrate-modified flexible porous coordination polymer according to claim 1, characterized in that, The sizes of the two different micropores are and 3. The nitrate-modified flexible porous coordination polymer according to claim 1, characterized in that, The size of larger pore structures is Smaller pore structure 4. The method for preparing the flexible porous coordination polymer according to claim 1, characterized in that, Includes the following steps: L1 ligand, L2 ligand, copper salt and acid were dissolved in an organic solvent and subjected to coordination polymerization. The product crystals were washed to obtain a flexible porous coordination polymer.

5. The preparation method according to claim 4, characterized in that, The copper salt is copper nitrate, and the acid is nitric acid.

6. The preparation method according to claim 4, characterized in that, The organic solvent is obtained by mixing DMF, ethanol and water in a volume ratio of 2-2.5:0.5-1:0.5-1.

7. The preparation method according to claim 4, characterized in that, The coordination polymerization reaction conditions are 300-400K for 200-400 minutes.

8. The preparation method according to claim 4, characterized in that, The flexible porous coordination polymer is also activated by immersion in methanol followed by vacuum removal of methanol.

9. A method for the selective adsorption separation of C3H6 and C3H8, characterized in that, The flexible porous coordination polymer described in any one of claims 1-3 is used.

10. The selective adsorption separation method according to claim 9, characterized in that, In the adsorption separation method described above, the flexible porous coordination polymer preferentially adsorbs C3H8.

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