CN116532082A - Porous carbon foam/metal organic framework composite adsorbent for separating C6 alkane isomer and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of adsorption separation materials, and discloses a porous carbon foam/metal organic framework composite adsorbent for separating C6 alkane isomers, which is used for realizing the selective adsorption separation of normal hexane and branched alkane with high octane number. Foaming a carbon source by adopting metal salt, and anchoring metal oxide on the porous carbon foam; combining metal ions with metal oxides to form a porous carbon foam intermediate containing hydroxy bimetallic salt; under the action of an organic ligand, the metal-organic framework material is loaded on the porous carbon foam in situ, and the porous carbon foam and the metal-organic framework composite material endow the porous carbon foam with multiple functions of adsorption separation and the like. The porous carbon foam and metal-organic framework composite adsorbent prepared by the invention has excellent gas mixture separation capability, can be used for high-efficiency separation of gas mixtures, and has good industrial application prospect.

Description

A porous carbon foam/metal-organic framework complex for the separation of C6 alkane isomers Composite adsorbent and its preparation method and application

technical field

The invention belongs to the technical field of adsorption and separation materials, and in particular relates to a porous carbon foam and metal organic framework composite adsorbent for separating C6 alkane isomers, a preparation method and application thereof.

Background technique

Refined separation of gas mixtures is an indispensable core technology in energy and chemical systems, and the key to further improving oil quality, conversion efficiency, and reducing pollutant emissions. For example, as the main component of gasoline, C6 has a large difference in the octane number of its isomers, and its content is also crucial to the quality of gasoline. Therefore, it is necessary to extract straight-chain n-hexane with a low octane number from the mixture separate from. At present, the traditional heat-driven separation process (such as rectification separation) has the defects of high energy consumption and low economic benefit, but the use of non-heat-driven separation (such as adsorption separation) can greatly reduce energy consumption. Among them, the adsorption separation material is the core of the adsorption separation technology, and its structural properties play a decisive role in the quality of the adsorption separation effect.

Among many adsorption and separation materials, metal-organic framework (Metal-Organic Framework, MOF) materials have high porosity (50%-90% free volume), large specific surface area (100-10000m ² /g), highly scalable The regulated pore size (0.3-10nm) and exposed active sites have shown great application potential in the field of gas adsorption and separation. However, intrinsic MOF materials have the problem of having both adsorption capacity and separation selectivity when separating mixtures.

To improve the separation performance of intrinsic MOF materials, carbon-based porous materials with excellent hydrophobicity and structural stability are widely used as functional composite substrates, thus endowing MOF materials with rich pore structures. However, intrinsic carbon-based porous materials (such as activated carbon AC, carbon nanotubes CNTs, graphene GR, etc.) are difficult to form effective composites with MOF materials due to their hydrophobicity and lack of binding sites. In recent years, pre-acidification or hydroxyl functionalization strategies of carbon-based porous materials have been widely adopted. For example, Shang et al [Yaxin Shang, Qing Xu, Zhixiao Gao, et al. Enhanced phosphate removal from practical waste water via in situ assembled dimension-engineered MOF@carbonheterostructures [J]. Chemical Engineering Journal, 2022, 428: 132536.] put the intrinsic C NTs pre After hydroxylation and dispersion in organic solvents, ZIF-8@CNT-OH composites with excellent properties were obtained to effectively remove phosphate from polluted water bodies. Sun Zhaoxing [Sun Zhaoxing. Research on the preparation and performance of MOF-porous carbon composite materials [D]. Beijing, China University of Petroleum, 2018.] also acidified carbon-based porous materials (activated carbon, graphene foam) and synthesized Thermally stable and adsorbable MOF-porous carbon composites are used for sewage treatment and methane adsorption. However, the acidification pretreatment does not conform to the preparation concept of green chemistry, and the preparation process is complicated. SUN et al. IES [J] .industric & Engineering Chemistry Research, 2020,59: 13744-13754.] On the surface Driven by the active agent (sodium dodecylbenzenesulfonate), the ZIF-8/3DGR composite material was synthesized, but the preparation process of 3DGR was complicated, and the specific surface area was reduced after the composite, the crystal distribution was uneven, and the loading rate was low. How to efficiently synthesize composites of MOF and porous carbon materials and endow them with excellent selective adsorption and separation performance is an urgent problem to be solved.

Contents of the invention

For the above problems, one of the objects of the present invention is to provide a kind of porous carbon foam (Porous Carbon Foam, PCF)/metal-organic framework (Metal-Organic Framework, MOF) composite adsorbent for separating C6 alkane isomers, with It is used to adsorb n-hexane to realize the separation of n-hexane and high-octane branched alkanes. The high-octane branched alkanes in the present invention are 3-methylpentane, 2-methylpentane, 2,3-dimethylbutane and 2,2-dimethylbutane.

The porous carbon foam/metal-organic framework composite adsorbent used for separating C6 alkane isomers according to the present invention is to form a hydroxyl double metal salt (HDS) by first anchoring a metal oxide on the porous carbon foam, and then combining with a metal salt , and finally adding organic ligands to synthesize the metal-organic framework material on the porous carbon foam in situ; the average pore diameter of the porous carbon foam/metal-organic framework composite adsorbent is 1.25-1.75nm.

Further, the metal element in the metal oxide is zinc or copper; the metal ion in the metal salt is one of zinc ion, cobalt ion and copper ion.

The second object of the present invention is to provide the above-mentioned preparation method for the porous carbon foam/metal-organic framework composite adsorbent used for separating C6 alkane isomers, the specific steps are:

(1) Preparation of porous carbon foam containing metal oxide: mix carbon source and metal salt solution, stir evenly, and pyrolyze and foam under inert atmosphere to obtain porous carbon foam/metal oxide substrate;

(2) Preparation of porous carbon foam containing hydroxy bimetallic salt: prepare an aqueous metal salt solution, add it to the porous carbon foam/metal oxide substrate in step (1), and stir to fully react to obtain porous carbon foam/hydroxy bimetallic Salt;

(3) Preparation of porous carbon foam containing metal-organic framework: prepare an aqueous solution of organic ligand, add it to the porous carbon foam/hydroxyl double metal salt in step (2), and stir evenly, then carry out solvothermal synthesis, and the obtained precipitate The material was centrifuged, washed, and dried to obtain a porous carbon foam/metal-organic framework composite adsorbent.

Further, the molar ratio of the metal salt of the step (1) of the present invention: the metal salt of the step (2): the organic ligand of the step (3) is 1:1:2～20; further, the metal salt of the step (1) Metal salt: the metal salt in step (2): the molar ratio of the organic ligand in step (3) is 1:1:10-16.

Further, the carbon source in step (1) is one of polymers, asphalt, and biomass.

Further, the metal salt described in step (1) is selected from any one of metal acetate, metal nitrate, metal sulfate, and basic carbonate; further; in the metal salt of step (1) The metal ion is zinc ion or copper ion.

Further, the pyrolysis temperature in step (1) is 300-900°C, and the time is 1-3h; further, the pyrolysis temperature is 600-700°C, and the time is 2h. If the pyrolysis temperature is greater than 900 degrees, a redox reaction will occur, and the metal oxide will be reduced to metal by carbon.

Further, the metal salt described in step (2) is selected from any one of metal acetate, metal nitrate, metal sulfate, basic carbonate; further, in the metal salt of step (2) The metal ion is one of zinc ion, cobalt ion and copper ion.

Further, the organic ligand described in step (3) is imidazole, 2-methylimidazole, 2-formyl imidazole, 2-aminobenzimidazole, terephthalic acid, aminoterephthalic acid, hydroxyterephthalic acid One or more of formic acid, fluoroterephthalic acid, trimesic acid, pyrazine, aminopyrazine, bipyridine, and azopyridine.

Further, the solvothermal synthesis condition in step (3) is 100-150° C. for 1-3 hours.

The third object of the present invention is to provide the above-mentioned porous carbon foam/metal organic framework composite adsorbent for separating C6 alkane isomers in the separation of normal hexane/2-methylpentane, normal hexane/2,3-dimethyl Butane, n-hexane/2,2-dimethylbutane, n-hexane/3-methylpentane, n-hexane/cyclohexane, methane/nitrogen, carbon dioxide/nitrogen, acetylene/ethylene, ethylene/ethane , Application in propylene/propane.

The present invention has following advantage and effect:

(1) The present invention adopts metal salt as foaming agent, not only obtains the functionalized PCF containing metal oxide, but the metal oxide anchored on its surface improves the bonding fastness of PCF and MOF materials; also endows it with porous structural properties , with excellent adsorption properties.

(2) The present invention adopts metal oxide post-modification (Post Metal-Oxide Modification, PMOM) method, utilizes metal ions to combine with metal oxides on the surface of PCF to form hydroxyl double metal salts, and replace metal salts or organic ligands to Realize in-situ synthesis of functionalized PCF/MOF composite adsorbent with high adsorption capacity and high separation selectivity.

(3) In the present invention, the functionalized MOF material is uniformly distributed on PCF with low price and wide source, which not only reduces the agglomeration of MOF material, but also endows PCF with higher gas adsorption and separation performance.

(4) The present invention has the characteristics of simple operation and high loading rate, and is convenient for large-scale preparation.

Description of drawings:

Fig. 1 is the SEM figure of comparative example 1 (PCF/ZnO) and embodiment 1 (PCF/ZIF-8) and embodiment 2 (PCF/ZIF-8-Co) composite adsorbent;

Fig. 2 is the _N adsorption-desorption of comparative example 1 (PCF/ZnO), comparative example 2 (ZIF-8), comparative example 3 (PCF/mIm) and embodiment 1 (PCF/ZIF-8) composite adsorbent Isotherm;

Fig. 3 is the pore size distribution figure of comparative example 1 (PCF/ZnO), comparative example 2 (ZIF-8), comparative example 3 (PCF/mIm) and embodiment 1 (PCF/ZIF-8) composite adsorbent;

Fig. 4 is the XRD pattern of comparative example 1 (PCF/ZnO), comparative example 2 (ZIF-8) and embodiment 1 (PCF/ZIF-8) composite adsorbent;

Fig. 5 is the normal hexane/3-methanol of comparative example 1 (PCF/ZnO), comparative example 2 (ZIF-8), comparative example 3 (PCF/mIm) and embodiment 1 (PCF/ZIF-8) composite adsorbent Vapor adsorption isotherm of pentane;

Fig. 6 is the n-hexane/3-methylpentane vapor adsorption isotherm of embodiment 2 (PCF/ZIF-8-Co) and embodiment 3 (PCF/ZIF-8-NH ₂ ) composite adsorbent;

Fig. 7 is the ratio of the n-hexane adsorption amount and the n-hexane/3-methylpentane adsorption amount of the PCF/MOF composite adsorbent synthesized by the present invention and the reported MOF material.

Detailed ways

In order to make the purpose of the present invention, the technical scheme is clearer, the present invention will be further described below in conjunction with accompanying drawing and embodiment, obviously, described embodiment is only a part embodiment of the present invention, rather than all embodiment, but the present invention The scope of the claimed protection is not limited thereto.

Example 1

Stir 0.5mmol sucrose and 1mmol zinc nitrate evenly, then transfer to 600°C for 2h to obtain PCF/ZnO substrate; add 1mmol zinc acetate aqueous solution to PCF/ZnO substrate, stir at room temperature for 24h to obtain PCF/HDS (Zn, Zn) intermediate; add 16 mmol of 2-methylimidazole, react at 120° C. for 2 h, wash and dry the resulting precipitate to obtain PCF/ZIF-8 composite adsorbent.

Example 2

Stir 0.5mmol sucrose and 1mmol zinc acetate evenly, then transfer to 600°C for 2h to obtain PCF/ZnO substrate; add 1mmol cobalt acetate aqueous solution to PCF/ZnO substrate, stir at room temperature for 24h to obtain PCF/HDS (Zn, Co) intermediate; add 16mmol of 2-methylimidazole, react at 120°C for 2h, and finally wash and dry the precipitate to obtain PCF/ZIF-8-Co composite adsorbent.

Example 3

Stir 0.5mmol sucrose and 1mmol zinc nitrate evenly, then transfer to 600°C for 2h to obtain PCF/ZnO substrate; add 1mmol zinc acetate aqueous solution to PCF/ZnO substrate, stir at room temperature for 24h to obtain PCF/HDS (Zn, Zn) intermediate; add 12mmol of 2-methylimidazole and 4mmol of 2-aminobenzimidazole, react at 120°C for 2h, and finally wash and dry the resulting precipitate to obtain PCF/ZIF-8-NH ₂ composite adsorbent.

Example 4

Stir 0.5mmol of glucose and 1mmol of zinc sulfate evenly, then transfer to 900 ℃ high temperature environment for 2h to obtain PCF/ZnO substrate; add 1mmol of zinc acetate aqueous solution to PCF/ZnO substrate, stir at room temperature for 24h to obtain PCF/HDS (Zn, Zn) intermediate; add 6 mmol of 2-methylimidazole, react at 100° C. for 2 h, and finally wash and dry the obtained precipitate to obtain PCF/ZIF-8 composite adsorbent.

Example 5

Stir 0.5mmol of polydopamine and 1mmol of zinc nitrate evenly, and then transfer to 600°C for 2 hours of pyrolysis to obtain PCF/ZnO substrate; HDS (Zn, Cu) intermediate; add 10 mmol of terephthalic acid (BDC), react at 150°C for 2 hours, and finally wash and dry the resulting precipitate to obtain PCF/Cu-BDC composite adsorbent.

Example 6

Stir 0.5mmol of sucrose and 1mmol of copper nitrate evenly, then transfer to 700°C for 1.5h of pyrolysis to obtain PCF/CuO substrate; HDS (Cu, Zn) intermediate; add 12 mmol of trimesic acid (BTC), react at 130°C for 2 hours, and finally wash and dry the resulting precipitate to obtain PCF/Cu-BTC composite adsorbent.

Comparative example 1

0.5mmol sucrose and 1mmol zinc nitrate were stirred evenly, and then transferred to a high temperature environment of 600°C for 2h for pyrolysis to obtain a PCF/ZnO substrate.

Comparative example 2

Stir 1mmol of zinc nitrate and 1mmol of zinc acetate aqueous solution at room temperature for 24h to obtain (Zn, Zn)HDS intermediate, add 16mmol of 2-methylimidazole, react at 120°C for 2h, and finally wash and dry the obtained precipitate to obtain ZIF-8 material.

Comparative example 3

Stir 0.5mmol of sucrose and 1mmol of zinc nitrate evenly, then transfer to 600°C for 2 hours of pyrolysis to obtain PCF/ZnO substrate; add 16mmol of 2-methylimidazole, react at 120°C for 2h, and finally remove the After washing and drying, a PCF/mIm composite adsorbent is obtained.

(1) SEM images of PCF/ZnO, PCF/ZIF-8 and PCF/ZIF-8-Co composite adsorbents

Scanning electron microscopy (SEM) was used to analyze the microscopic morphology of the intrinsic PCF/ZnO and PCF/ZIF-8, PCF/ZIF-8-Co composite adsorbent prepared by the present invention, and the test results are shown in Figure 1. The results showed that a large number of ZnO nanoparticles were anchored on the chemically foamed PCF, and after adding an organic ligand (2-methylimidazole), ZnO was transformed into ZIF-8 material, realizing the original principle of PCF/ZIF-8 composite adsorbent. The ZIF-8 particles on the surface are uniform and dispersed, the crystal surface is smooth, and more adsorption sites are exposed. After adding Co metal source, PCF/ZnO was transformed into bimetallic PCF/ZIF-8-Co composite adsorbent, realizing the in situ synthesis of PCF/ZIF-8-Co composite adsorbent, and the ZIF-8-Co particles on the surface Uniform and dispersed, the crystal surface is smooth, and more adsorption sites are exposed.

(2) _N2 adsorption-desorption isotherms of PCF/ZnO, ZIF-8, PCF/mIm and PCF/ZIF-8 composite adsorbents

PCF/ZnO, ZIF-8, PCF/mIm and PCF/ZIF-8 composite adsorbent prepared by the present invention are carried out by using Autosorb- _IQ Adsorber N Adsorption-desorption isothermal measurement, analysis of its _specific surface area and adsorption capacity The test results are shown in Figure 2. The results showed that when only organic ligand (2-methylimidazole) was added, the specific surface area of PCF/mIm of the sample increased by 439%, but it was still lower than that of ZIF-8 material, which may be because only a part of ZIF-8 crystal was synthesized. After adding the bridging agent Zn ²⁺ , the specific surface area of the PCF/ZIF-8 composite adsorbent was further improved, which was 501% and 26% higher than the intrinsic material PCF/ZnO and ZIF-8, respectively, indicating that the addition of external Zn ²⁺ It can provide more metal ions for the growth of ZIF-8 crystals, and then promote the uniform and dispersed loading of ZIF-8 crystals on the surface of PCF.

The PCF/ZnO, ZIF-8, PCF/mIm and PCF/ZIF-8 composite adsorbents prepared by the present invention were analyzed for pore size distribution, and the test results are shown in Table 1 and Figure 3. The results showed that the micropore volume of PCF/ZnO was relatively small (<2nm), lower than that of ZIF-8. Directly adding the organic ligand mIm, the micropore of PCF/mIm has been greatly improved, far superior to the intrinsic materials PCF/ZnO and ZIF-8. Subsequently, the micropore volume of PCF/ZIF-8 transformed by hydroxyl double salt HDS increased most obviously, which was better than that of PCF/mIm directly transformed by ZnO, further demonstrating the advantages of the method of the present invention, which is beneficial to the adsorption and separation of hexane.

(3) XRD patterns of PCF/ZnO, ZIF-8 and PCF/ZIF-8 composite adsorbents

The crystal structure of the PCF/ZnO, ZIF-8 and PCF/ZIF-8 composite adsorbents prepared by the present invention was determined by X-ray powder diffractometer (XRD). The test results are shown in FIG. 4 . The results showed that the characteristic peaks of PCF/ZnO after chemical foaming were consistent with those of simulated ZnO, indicating that the product contained metal source ZnO. After adding the metal salt bridging agent and organic ligand (2-methylimidazole), the characteristic peaks of ZnO have basically disappeared, and the characteristic peaks of the synthesized sample PCF/ZIF-8 are basically consistent with the characteristic peaks of the ZIF-8 sample. It is proved that ZnO has been completely converted to ZIF-8. The above results also confirmed that PCF/ZnO can be used as a metal source, which can be converted into PCF/ZIF-8 composite adsorbent in situ under the action of organic ligands.

(4) C6 vapor adsorption isotherms of PCF/ZnO, ZIF-8, PCF/mIm and PCF/ZIF-8 composite adsorbents

PCF/ZnO, ZIF-8, PCF/mIm and PCF/ZIF-8 composite adsorbents prepared by the present invention are carried out by using Autosorb-IQ ₂ adsorption instrument to measure the hexane vapor adsorption isotherm, and explore its effect on C6 isomers The separation performance, the test results are shown in Figure 5. The results show that the intrinsic material PCF/ZnO has a considerable amount of adsorption capacity for n-hexane vapor and 3-methylpentane vapor, and preferentially adsorbs linear n-hexane vapor. For the intrinsic ZIF-8 material, due to its special pore size range, it shows a strong n-hexane/3-methylpentane separation effect at low pressure. After adding organic ligand (2-methylimidazole) and bridging agent Zn ²⁺ , due to the synergistic effect of PCF and ZIF-8, the composite sample PCF/ZIF-8 has both adsorption capacity and separation selectivity, not only achieving low High-efficiency adsorption of straight-chain n-hexane vapor with octane number, and separation of branched-chain 3-methylpentane vapor with high octane number, the effect is obviously better than PCF/mIm, which helps to improve gasoline quality.

(5) C6 vapor adsorption isotherms of bimetallic PCF/ZIF-8-Co and dual-ligand PCF/ZIF-8- _NH composite adsorbents

Based on the excellent adsorption and separation characteristics of PCF/ZIF-8, the C6 adsorption and separation performance of the bimetallic PCF/ZIF-8-Co and double ligand PCF/ZIF-8-NH prepared in Examples 2 and ₃ were further analyzed, The result is shown in Figure 6. The results show that the bimetallic PCF/ZIF-8-Co and double ligand PCF/ZIF-8-NH ₂ can have good adsorption capacity and separation selectivity, almost no adsorption of high-octane branched-chain 3-formazan Pentane further demonstrates the superiority and universality of the present invention, providing support for the in situ synthesis of functionalized PCF/MOF.

(6) The ratio of the normal hexane adsorption capacity of the synthesized PCF/MOF composite adsorbent of the present invention and the reported MOF material and normal hexane/3-methylpentane adsorption capacity

In order to highlight the advancement of the technology of the present invention, the PCF/MOF composite adsorbent synthesized by the present invention is compared with the ratio of n-hexane adsorption capacity and n-hexane/3-methylpentane adsorption capacity of the reported MOF material, the results are shown in Fig. 7. The results show that PCF/ZIF-8-Co (Example 2) and PCF/ZIF-8-NH ₂ (Example 3) synthesized by double metals and double ligands have both adsorption capacity and separation selectivity, and the separation effect more significant. It further demonstrates the advancement and applicability of the technology of the present invention, which can realize the in-situ synthesis of more functional materials, thereby realizing the efficient adsorption separation of the mixture.

The performance comparison of the material prepared by table 1 comparative example 1-3 and embodiment 1-3

Claims (10)

1. A porous carbon foam/metal-organic framework composite adsorbent for separating C6 alkane isomers, characterized in that, the porous carbon foam/metal-organic framework composite adsorbent is used for adsorbing normal hexane, to realize normal hexane and 3-methylpentane, 2-methylpentane, 2,3-dimethylbutane, 2,2-dimethylbutane separation; the porous carbon foam/metal organic framework composite adsorbent is It is prepared by first anchoring metal oxides on porous carbon foams, then combining with metal salts to form hydroxyl double metal salts, and finally adding organic ligands to make metal-organic framework materials synthesized in situ on porous carbon foams; the porous carbon foams The average pore diameter of the metal-organic framework composite adsorbent is 1.25-1.75 nm. 2. the porous carbon foam/metal-organic framework composite adsorbent for separating C6 alkane isomers according to claim 1, is characterized in that, the metal element in the metal oxide is zinc or copper; The metal ion in the salt is one of zinc ion, cobalt ion and copper ion. 3. the preparation method of the porous carbon foam/metal-organic framework composite adsorbent that is used to separate C6 alkane isomers as claimed in claim 1, is characterized in that, concrete steps are as follows: (1) Preparation of porous carbon foams containing metal oxides: mixing carbon sources and metal salt solutions, stirring evenly, foaming and pyrolyzing under an inert atmosphere to obtain porous carbon foams/metal oxide substrates; (2) Preparation of porous carbon foam containing hydroxy bimetallic salt: prepare an aqueous metal salt solution, add it to the porous carbon foam/metal oxide substrate in step (1), and stir to fully react to obtain porous carbon foam/hydroxy bimetallic Salt; (3) Preparation of porous carbon foam containing metal-organic framework: prepare an aqueous solution of organic ligand, add it to the porous carbon foam/hydroxyl double metal salt in step (2), and stir evenly, then perform solvothermal synthesis, and centrifuge the precipitate , washing and drying to obtain a porous carbon foam/metal organic framework composite adsorbent. 4. the preparation method of the porous carbon foam/metal-organic framework composite adsorbent that is used to separate C6 alkane isomers according to claim 3 is characterized in that, metal salt in step (1): metal in step (2) Salt: the molar ratio of the organic ligand in step (3) is 1:1:2-20. 5. the preparation method of the porous carbon foam/metal-organic framework composite adsorbent that is used to separate C6 alkane isomers according to claim 3 is characterized in that, the metal salt of step (1) is selected from metal acetate, A kind of in metal nitrate, metal sulfate, basic carbonate; The metal salt of step (2) is selected from the one in metal acetate, metal nitrate, metal sulfate, basic carbonate. 6. the preparation method of the porous carbon foam/metal-organic framework composite adsorbent that is used to separate C6 alkane isomers according to claim 3 is characterized in that, the carbon source described in step (1) is polymer, asphalt , any of the biomass. 7. the preparation method of the porous carbon foam/metal-organic framework composite adsorbent that is used to separate C6 alkane isomers according to claim 3 is characterized in that, the pyrolysis temperature described in step (1) is 300-900 ℃, the time is 1-3h. 8. the preparation method of the porous carbon foam/metal-organic framework composite adsorbent that is used to separate C6 alkane isomers according to claim 3 is characterized in that, the organic ligand described in step (3) is imidazole, 2 -Methylimidazole, 2-formylimidazole, 2-aminobenzimidazole, terephthalic acid, aminoterephthalic acid, hydroxyterephthalic acid, fluoroterephthalic acid, trimesic acid, pyrazine, One or more of aminopyrazine, bipyridine and azopyridine. 9. the preparation method for separating the porous carbon foam/metal-organic framework composite adsorbent of C6 alkane isomers according to claim 3, is characterized in that, the solvothermal synthesis condition described in step (3) is 100- Reaction at 150°C for 1-3h. 10. The application of the porous carbon foam/metal organic framework composite adsorbent for separating C6 alkane isomers as claimed in claim 1, characterized in that, the porous carbon foam/metal organic framework for separating C6 alkane isomers The composite adsorbent is used in the separation of n-hexane/2-methylpentane, n-hexane/2,3-dimethylbutane, n-hexane/2,2-dimethylbutane, n-hexane/3-methylpentane , n-hexane/cyclohexane, methane/nitrogen, carbon dioxide/nitrogen, acetylene/ethylene, ethylene/ethane, propylene/propane.