Surface hydrophilic modified ZSM-5 molecular sieve adsorbent as well as preparation method and application thereof

Abstract

The invention discloses a surface hydrophilic modified ZSM-5 molecular sieve adsorbent as well as a preparation method and application thereof, and belongs to the technical field of preparation of inorganic nano materials. The method comprises the following steps: mixing a medium-temperature coal tar pitch extract liquid as a surface hydrocarbon-philic modification liquid with ZSM-5 molecular sieves with different silica-alumina ratios according to a certain mass ratio, carrying out dipping treatment, filtering, and drying to obtain the surface hydrocarbon-philic modified ZSM-5 molecular sieve adsorbent. The ZSM-5 adsorbent prepared by the method has the characteristics of high CH4 adsorption capacity, high CH4 / N2 selectivity and high stability, the process only relates to impregnation of primary raw materials, and compared with a traditional ion exchange modification strategy, the operation is greatly simplified, and the ZSM-5 adsorbent has a wider application range and is suitable for concentration of ventilation air methane.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic nanomaterial preparation, and particularly relates to a surface hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent, its preparation method and application. This adsorbent can be used for the concentration of ventilation air methane (VAM). Background Art

[0002] The maximum pore diameter of ZSM-5 molecular sieve is 6.36 Å, and the maximum diffusion diameter is 4.70 Å. Due to its suitable pore structure and high specific surface area, it has received extensive attention in the adsorption field. Because the surface of ZSM-5 molecular sieve is highly polarized and easy to adsorb polar molecules, while CH 4 is a non-polar molecule with a regular tetrahedron structure. Therefore, in order to improve the adsorption capacity of CH 4 , the key to modifying ZSM-5 molecular sieve lies in reducing the framework polarity and making it show hydrocarbonophilic properties.

[0003] Ion exchange modification is a conventional modification strategy for molecular sieves and has received extensive attention in the adsorption field. For example, silver ion exchange (CN117884092A), ammonium ion exchange (CN103359760A), and rare earth ion exchange (CN113522207A) have achieved remarkable effects in the modification of molecular sieves with low silica-alumina ratio. However, the ion exchange modification strategy has complex operations, low exchange rates, and a narrow scope of application, which limits its application.

[0004] Coal tar pitch is the residue after extracting light components from coal tar. It is divided into low-temperature coal tar pitch, medium-temperature coal tar pitch, and high-temperature coal tar pitch, accounting for about 50% - 60% of tar. Its basic structural unit is polycyclic aromatic hydrocarbons and their derivatives, which are mainly applied in fields such as road construction, building materials, electrode manufacturing, carbon products, anticorrosive coatings, and fuels. Among them, medium-temperature coal tar pitch has the advantages of high carbon content, good fluidity, and easy graphitization. However, the complexity of its composition determines that component separation and other pretreatment are required when applying coal tar pitch. The components of coal tar pitch are enriched through the principle of similar solubility to obtain components with a narrow molecular weight distribution. After extraction, operations such as distillation separation, oxidation, and thermal polymerization are often required to achieve the enrichment of the product, and the post-treatment operation process is complex. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a surface hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent, its preparation method and application; it solves the problems of complex operations, low exchange rates, and narrow scope of application in the ion exchange modification of molecular sieves.

[0006] The present invention is realized through the following technical solutions: A preparation method of a surface hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent, comprising the following steps: S1. Use an organic extractant to extract medium-temperature coal tar pitch, and use the obtained extract as a surface hydrocarbonophilic modification liquid. S2. Mix and impregnate ZSM-5 zeolite with the surface hydrocarbonophilic modification liquid at room temperature, and then obtain a surface hydrocarbonophilic modified ZSM-5 zeolite adsorbent through filtration and drying; the mass ratio of ZSM-5 zeolite to the surface hydrocarbonophilic modification liquid is 1:1 to 1:10, and the impregnation time is 12 to 48 h; the silica-aluminum ratio of the ZSM-5 zeolite, that is, the molar ratio of SiO 2 to Al 2 O 3 is 25 to 100.

[0007] Preferably, the organic extractant is one or any combination of n-butanol, tetrahydrofuran, toluene, n-heptane, and quinoline.

[0008] Preferably, the mass ratio of medium-temperature coal tar pitch to the organic extractant is 1:5.

[0009] Preferably, the extraction is to put medium-temperature coal tar pitch into the organic extractant and stir.

[0010] Preferably, the temperature of the extraction is 50 to 70 o °C, the stirring speed is 350 to 450 r / min, and the stirring time is 2 - 3 h.

[0011] Preferably, after extraction, suction filtration is carried out to obtain the extract.

[0012] Preferably, the drying is carried out in an oven at 40 to 80 o °C for 12 to 48 h.

[0013] A surface hydrocarbonophilic modified ZSM-5 zeolite adsorbent is prepared by using the preparation method of the surface hydrocarbonophilic modified ZSM-5 zeolite adsorbent described above.

[0014] The surface hydrocarbonophilic modified ZSM-5 zeolite adsorbent described above is used for the concentration of exhausted air gas.

[0015] The beneficial effects of the present invention compared with the prior art are as follows: After extracting medium-temperature coal tar pitch, the present invention directly uses the extract of medium-temperature coal tar pitch for the surface hydrocarbonophilic modification of ZSM-5 zeolite, avoiding the separation, purification and other treatments of the extract, and realizing the high-value "one-step" utilization of medium-temperature coal tar pitch. The present invention uses the extract of medium-temperature coal tar pitch to carry out surface hydrocarbonophilic modification on ZSM-5 zeolite, which has the characteristics of simple operation and wide application range.

[0016] Specifically: 1. By taking advantage of the low polarity of organic substances, the polarity of the molecular sieve adsorbent framework is changed through simple impregnation, and the operation is simple; 2. Directly utilize medium-temperature coal tar pitch for resource utilization to increase its added value; 3. Compared with traditional ion exchange modification, the present invention has the advantages of simple operation, controllable and adjustable loading amount, and wide applicability; 4. As an adsorbent for enriched ventilation air methane, it has a high CH 4 adsorption capacity and CH 4 / N 2 selectivity. Description of the Drawings

[0017] Figure 1 This is the XRD pattern of the unmodified ZSM-5 adsorbent in Comparative Example 1 of the present invention.

[0018] Figure 2 This is the XRD pattern of the ZSM-5 adsorbent obtained by surface hydrocarbonophilic modification in Example 2 of the present invention.

[0019] Figure 3 This is the FT-IR spectrum of the unmodified ZSM-5 adsorbent in Comparative Example 1 of the present invention.

[0020] Figure 4 This is the FT-IR spectrum of the ZSM-5 adsorbent obtained by surface hydrocarbonophilic modification in Example 2 of the present invention.

[0021] Figure 5 This is the structural formula of the substance with the highest content in the extraction liquid of coal tar extracted by different solvents of the present invention.

[0022] Figure 6 This is the SEM image of the ZSM-5 adsorbent of the present invention; among them, (a) is the unmodified ZSM-5 adsorbent in Comparative Example 1, (b) is the enlarged view of (a), (c) is the ZSM-5 adsorbent with surface hydrocarbonophilic modification in Example 2, and (d) is the enlarged view of (c). Detailed Embodiments

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail in combination with embodiments and drawings. It should be understood that the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention. The technical solutions of the present invention will be described in detail below in combination with embodiments and drawings, but the protection scope is not limited by this.

[0024] Example 1 This example provides a surface hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; the specific steps are as follows: S1. Using n - heptane as the extraction solvent for medium - temperature coal tar pitch, the mass ratio of medium - temperature coal tar pitch to n - heptane is 1:5. Put the medium - temperature coal tar pitch into n - heptane, and stir evenly at 400 r / min for 2 h at 60 o °C. Then perform suction filtration to obtain an extraction liquid mainly composed of polycyclic aromatic hydrocarbons, with the highest content of pyrene. The suction filtration is to put the material into a filter flask lined with filter paper, connect the filter flask with a suction pump and perform vacuum filtration on the material in the filter flask to separate the extraction liquid.

[0025] S2. Mix the extraction liquid with ZSM - 5 zeolite with a silica - alumina ratio (molar ratio of SiO 2 to Al 2 O 3 of 25) according to a mass ratio of 1:1, and impregnate at room temperature. The impregnation time is 12 h, then filter, and then place it in an oven at 40 o °C for 24 h to obtain ZSM - 5 zeolite with surface hydrocarbon -ophilic modification. The impregnation operation is to mix and let stand the mixed extraction liquid and ZSM - 5 zeolite at room temperature. In this example, the room temperature is 25 o °C.

[0026] Example 2 This example presents a surface hydrocarbon -ophilic modified ZSM - 5 zeolite adsorbent and its preparation method. Compared with Example 1, the silica - alumina ratio of the zeolite is changed, and the other steps are the same.

[0027] In this example, the silica - alumina ratio (molar ratio of SiO 2 to Al 2 O 3 is 100.

[0028] Example 3 This example presents a surface hydrocarbon -ophilic modified ZSM - 5 zeolite adsorbent and its preparation method. Compared with Example 2, the mass ratio and drying time are changed, and the other steps are the same.

[0029] Specifically, in this example, the extraction liquid and ZSM - 5 zeolite with a silica - alumina ratio of 100 are mixed according to a mass ratio of 1:10, left to stand at room temperature for 12 h, then filtered, and then placed in an oven at 40 o °C for 48 h to obtain ZSM - 5 zeolite with surface hydrocarbon -ophilic modification.

[0030] Example 4 This example presents a surface hydrocarbon -ophilic modified ZSM - 5 zeolite adsorbent and its preparation method. Compared with Example 2, the impregnation time is changed, and the other steps are the same.

[0031] In this example, the impregnation time is 48 h.

[0032] Example 5 This example presents a surface hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; compared with Example 2, the type of extraction solvent and the parameters of drying are changed, and the remaining steps are the same.

[0033] Specifically, in this example, n-butanol is used as the extraction solvent for medium-temperature coal tar pitch, and an extraction liquid mainly composed of polycyclic aromatic hydrocarbons is obtained under the same extraction conditions as in Example 2, with the highest content of fluoranthene. The extraction liquid is mixed with ZSM-5 molecular sieve with a silica-aluminum ratio (molar ratio of SiO 2 to Al 2 O 3 of 100) in a mass ratio of 1:1, left standing at room temperature for 12 h, filtered, and dried in an oven at 60 o °C for 12 h to obtain a surface hydrocarbonophilic modified ZSM-5 molecular sieve.

[0034] Example 6 This example presents a surface hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; compared with Example 2, the type of extraction solvent and the parameters of drying are changed, and the remaining steps are the same.

[0035] Specifically, in this example, toluene is used as the extraction solvent for medium-temperature coal tar pitch, and an extraction liquid mainly composed of polycyclic aromatic hydrocarbons is obtained under the same extraction conditions as in Example 2, with the highest content of benzo[b]anthracene. The extraction liquid is mixed with ZSM-5 molecular sieve with a silica-aluminum ratio of 100 in a mass ratio of 1:1, left standing at room temperature for 12 h, filtered, and dried in an oven at 80 o °C for 24 h to obtain a surface hydrocarbonophilic modified ZSM-5 molecular sieve.

[0036] Example 7 This example presents a surface hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; compared with Example 2, the type of extraction solvent and the parameters of drying are changed, and the remaining steps are the same.

[0037] Specifically, in this example, tetrahydrofuran is used as the extraction solvent for medium-temperature coal tar pitch, and an extraction liquid mainly composed of polycyclic aromatic hydrocarbons is obtained under the same extraction conditions as in Example 2, with the highest content of quinoline. The extraction liquid is mixed with ZSM-5 molecular sieve with a silica-aluminum ratio (molar ratio of SiO 2 to Al 2 O 3 of 100) in a mass ratio of 1:1, left standing at room temperature for 12 h, filtered, and dried in an oven at 70 o °C for 48 h to obtain a surface hydrocarbonophilic modified ZSM-5 molecular sieve.

[0038] Example 8 This example presents a surface-hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; compared with Example 2, this example changes the type of extraction solvent and the parameters of drying, and the remaining steps are the same.

[0039] Specifically, in this example, quinoline is used as the extraction solvent for medium-temperature coal tar pitch, and an extraction liquid mainly composed of polycyclic aromatic hydrocarbons is obtained under the same extraction conditions as in Example 2, in which the content of 9,10-benzophenanthrene is the highest. The extraction liquid is mixed with ZSM-5 molecular sieve with a silica-alumina ratio (molar ratio of SiO 2 to Al 2 O 3 of 100) at a mass ratio of 1:1, left standing at room temperature for 12 h, filtered, and placed in an oven at 60 o °C for 48 h to obtain a surface-hydrocarbonophilic modified ZSM-5 molecular sieve.

[0040] Example 9 This example presents a surface-hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; compared with Example 2, this example changes the type of extraction solvent and the parameters of drying, and the remaining steps are the same.

[0041] Specifically, in this example, a mixed solution of 50% n-heptane and 50% n-butanol by volume is used as the extraction solvent for medium-temperature coal tar pitch, and an extraction liquid mainly composed of polycyclic aromatic hydrocarbons is obtained under the same extraction conditions as in Example 2. The extraction liquid is mixed with ZSM-5 molecular sieve with a silica-alumina ratio (molar ratio of SiO 2 to Al 2 O 3 of 100) at a mass ratio of 1:1, left standing at room temperature for 12 h, filtered, and placed in an oven at 60 o °C for 48 h to obtain a surface-hydrocarbonophilic modified ZSM-5 molecular sieve.

[0042] Example 10 This example presents a surface-hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; compared with Example 2, this example changes the type of extraction solvent and the parameters of drying, and the remaining steps are the same.

[0043] Specifically, in this example, a mixed solution of 33% toluene, 33% tetrahydrofuran, and 33% quinoline by volume is used as the extraction solvent for medium-temperature coal tar pitch, and an extraction liquid mainly composed of polycyclic aromatic hydrocarbons is obtained under the same extraction conditions. The extraction liquid is mixed with ZSM-5 molecular sieve with a silica-alumina ratio (molar ratio of SiO 2 to Al 2 O 3 of 100) at a mass ratio of 1:1, left standing at room temperature for 12 h, filtered, and placed in an oven at 70 o °C for 48 h to obtain a surface-hydrocarbonophilic modified ZSM-5 molecular sieve.

[0044] Example 11 This example presents a surface-hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; compared with Example 1, the extraction operation parameters are changed, and the remaining steps are the same.

[0045] Specifically, in this example, the extraction is carried out by uniformly stirring at 450 r / min for 3 h under the condition of 50 o °C.

[0046] Example 12 This example presents a surface-hydrocarbonophilic modified ZSM-5 molecular sieve adsorbent and its preparation method; compared with Example 1, the extraction operation parameters are changed, and the remaining steps are the same.

[0047] Specifically, in this example, the extraction is carried out by uniformly stirring at 350 r / min for 2.5 h under the condition of 70 o °C.

[0048] Comparative Example 1 Comparative Example 1 is a ZSM-5 molecular sieve with a silica-alumina ratio (molar ratio of SiO 2 to Al 2 O 3 ) of 100 without surface-hydrocarbonophilic modification treatment.

[0049] Comparative Example 2 A mixed solution of ethyl acetate and petroleum ether with a volume fraction of 10% is prepared into a surface-hydrocarbonophilic modification liquid, and is mixed with a ZSM-5 molecular sieve with a silica-alumina ratio (molar ratio of SiO 2 to Al 2 O 3 ) of 100 according to a mass ratio of 1:1, left to stand at room temperature for 12 h, filtered, and placed in an oven at 70 o °C for drying for 12 h to obtain a surface-hydrocarbonophilic modified ZSM-5 molecular sieve.

[0050] Comparative Example 3 The ZSM-5 molecular sieve with a silica-alumina ratio (molar ratio of SiO 2 to Al 2 O 3 ) of 100 is leached and activated with 0.1 mol / L nitric acid solution, a silver nitrate solution with a concentration of 1 mol / L is prepared, the activated ZSM-5 molecular sieve is added to the silver nitrate solution, and ion exchange is carried out by heating in a water bath at 80 o °C for 6 h. After that, it is centrifuged, washed, dried, and calcined in a nitrogen atmosphere at 550 o °C for 2 h to obtain the ion-exchanged ZSM-5 molecular sieve.

[0051] XRD tests were carried out on the samples obtained from Comparative Example 1 and Example 2 ( Figure 1 and Figure 2 ). By comparing the two figures, it was found that before and after the surface hydrocarbonophilic modification, the intensity of the crystal diffraction peaks of the molecular sieve remained basically the same, and the peak positions did not shift. The results proved that the crystal form of ZSM-5 molecular sieve did not change after the surface hydrocarbonophilic modification; Figure 3 is the FT-IR image of Comparative Example 1. The stretching vibration peaks of -OH of crystal water in ZSM-5 are at 1620 cm -1 and 3480 cm -1 , and the stretching vibration peak of SiO -1 tetrahedron is at 1000 cm 4 ; Figure 4 is the FT-IR image of Example 2. The additional stretching vibration peak at 1460 cm -1 is for -CH 2 -. The overtone peaks of substituted benzenes are at 1868 cm -1 and 2006 cm -1 . By comparing the two figures, it was found that for the molecular sieve after the surface hydrocarbonophilic modification, in addition to the original peaks of the molecular sieve, peaks at 2006, 1868, and 1460 were added, indicating the successful adsorption of aromatic hydrocarbons. Figure 5 is the structural formula of the substance with the highest content in the extraction liquid of coal tar extracted by different solvents. Figure 6 is the SEM image of the ZSM-5 adsorbent of the present invention; among them, (a) is the unmodified ZSM-5 adsorbent of Comparative Example 1, (b) is the enlarged view of (a), (c) is the ZSM-5 adsorbent with surface hydrocarbonophilic modification of Example 2, and (d) is the enlarged view of (c). As Figure 6 can be seen, the ZSM-5 molecular sieve of Comparative Example 1 presents a hexagonal structure, and the single particle structure is about 200 - 300 nm, with a certain degree of aggregation. The microscopic morphology of the ZSM-5 molecular sieve after surface hydrocarbonophilic modification in Example 2 has basically not changed.

[0052] Adsorption and desorption performance evaluation: The saturated adsorption amounts of N 2 and CH 4 of the adsorbents with surface hydrocarbonophilic modification in Examples 1 - 10 were measured. 0.2 g of the adsorbent was loaded into a quartz tube and vacuum desorbed at 120 o °C for 3 h, and then pure N 2 or pure CH 4 was introduced to measure the adsorption curve. The test temperature was 273 K, and the test pressure range was 2 - 100 kPa. After the test, the saturated adsorption amount of the adsorbent was calculated by fitting with the Langmuir equation, and the results are shown in Table 1:

[0053]

[0054] The results show that through surface hydrocarbonophilic modification of CH 4 the saturated adsorption capacity generally increases, while the saturated adsorption capacity of N 2 slightly decreases. Zeolites with a high silica-alumina ratio are more likely to adsorb aromatic substances, so the modification effect is more ideal. The adsorption of aromatics significantly reduces the framework polarity, and it is similar to CH 4 in terms of "like dissolves like", which is the reason for the increase in the adsorption capacity of CH 4 . The surface hydrocarbonophilic modification liquid obtained by extracting medium-temperature coal tar pitch with n-heptane shows the best modification effect, and both the mass ratio of the zeolite to the hydrocarbonophilic modification liquid and the impregnation time have an impact on the modification effect. A low mass ratio and a long impregnation time lead to excessive adsorption of aromatic hydrocarbons, resulting in pore blockage. Selecting a single long-chain alkane for impregnation modification has an unsatisfactory effect, and the ion exchange modification strategy also has an unsatisfactory effect due to the high silica-alumina ratio of the zeolite.

[0055] For the adsorbents with surface hydrocarbonophilic modification in Examples 1 to 10, a pressure swing adsorption test of diluted air methane was carried out. 50 g of the 20-40 mesh adsorbent after tabletting and granulation was loaded into the adsorption column, and vacuum desorption was carried out at room temperature for 10 min. Then, the diluted air methane raw gas CH 4 :N 2 (CH 4 with a volume fraction of 0.37%) was used for rapid backpressure operation. When the pressure reached 0.6 MPa, the gas supply was stopped. The adsorption pressure was 0.6 MPa, and the adsorption temperature was room temperature (25°C). After 10 min, the pressure was released and vacuum desorption was carried out. The desorbed gas was collected and analyzed for concentration using a methane concentration analyzer. The results are shown in Table 2:

[0056]

[0057] The results show that the ZSM-5 zeolite after surface hydrocarbonophilic modification can achieve the concentration of diluted air methane, corresponding to the results of the saturated adsorption capacity measurement. The surface hydrocarbonophilic modification liquid obtained by extracting medium-temperature coal tar pitch with n-heptane shows the best modification effect, and the modified ZSM-5 zeolite has the most excellent performance in concentrating diluted air methane.

[0058] For the adsorbents with surface hydrocarbonophilic modification in Examples 1 to 10, a stability test of pressure swing adsorption of diluted air methane was carried out. 5 g of the 20-40 mesh adsorbent was loaded into the adsorption column, and vacuum desorption was carried out at room temperature for 10 min. Then, the diluted air methane raw gas CH 4 :N 2 (CH 4Penetration experiments were carried out with a volume fraction of 0.37%, the adsorption pressure was atmospheric pressure, the adsorption temperature was room temperature, and the flow rate of the feed gas was 100 mL / min. After complete penetration, the above experimental operations were repeated for a total of ten cycles. The tail end of the adsorption device was connected to a methane concentration analyzer, and the recorded penetration time was the dead volume and the response time of the methane concentration analyzer deducted. The results are shown in Table 3:

[0059]

[0060] Obviously, the surface-hydrocarbon-modified ZSM-5 molecular sieve adsorbent has good cyclic stability, and the adsorption performance shows no obvious decline after ten cycles. Therefore, surface-hydrocarbon modification shows the advantages of simple operation and wide applicability compared with traditional ion-exchange modification measures.

[0061] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific embodiments of the present invention are limited to this. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the present invention, several simple deductions or substitutions can still be made, which should all be regarded as belonging to the patent protection scope determined by the claims submitted by the present invention.

Claims

1. A method for preparing a surface hydrocarbon-affinity-modified ZSM-5 molecular sieve adsorbent, characterized in that: The following steps are involved: S1. Using an organic extractant to extract the medium-temperature coal tar pitch, and using the obtained extract as a surface hydrocarbon-affinity modification liquid; S2. Mix and impregnate the ZSM-5 molecular sieve and the surface alkyl-affinity modification liquid at room temperature, and then filter and dry to obtain the surface alkyl-affinity modified ZSM-5 molecular sieve adsorbent; the mass ratio of the ZSM-5 molecular sieve to the surface alkyl-affinity modification liquid is 1:1~1:10, and the impregnation time is 12~48h; the silicon-aluminum ratio of the ZSM-5 molecular sieve, that is, the molar ratio of SiO2 to Al2O3 is 25~100.

2. The method for preparing a surface alkyl-affinity-modified ZSM-5 molecular sieve adsorbent according to claim 1, characterized in that: The organic extractant is one or any combination of n-butanol, tetrahydrofuran, toluene, n-heptane and quinoline.

3. The method for preparing a surface hydrocarbon-affinity-modified ZSM-5 molecular sieve adsorbent according to claim 1, characterized in that: The mass ratio of medium-temperature coal tar pitch to the organic extractant is 1:

5.

4. The method for preparing a surface hydrocarbon-affinity-modified ZSM-5 molecular sieve adsorbent according to claim 1, characterized in that: The extraction is to put the medium-temperature coal tar pitch into an organic extractant and stir it.

5. The method for preparing a surface hydrocarbon-affinity-modified ZSM-5 molecular sieve adsorbent according to claim 4, characterized in that: The extraction temperature is 50~70 o C, stirring speed is 350~450r / min, stirring time is 2-3h.

6. The method for preparing a surface hydrocarbon-affinity-modified ZSM-5 molecular sieve adsorbent according to claim 5, characterized in that: After extraction, the extract is filtered to obtain an extract.

7. The method for preparing a surface hydrocarbon-affinity-modified ZSM-5 molecular sieve adsorbent according to claim 1, characterized in that: The drying is carried out at 40 to 80 o C oven for 12 to 48 h.

8. A surface alkyl-affinity-modified ZSM-5 molecular sieve adsorbent, characterized in that: The adsorbent is prepared by the method for preparing a surface hydrocarbon-philic modified ZSM-5 molecular sieve adsorbent as described in any one of claims 1 to 7.

9. The surface hydrocarbon-affinity-modified ZSM-5 molecular sieve adsorbent as claimed in claim 8 is used for concentrating the exhaust gas.

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