Binder-free granular carbon molecular sieve and application thereof in C4 olefin mixture separation

Abstract

The invention discloses a binder-free granular carbon molecular sieve and application thereof in C4 olefin mixture separation, and belongs to the technical field of C4 olefin adsorption and separation. The granular carbon molecular sieve for C4 olefin mixture component separation is obtained by crushing a precursor, screening particles with a proper particle size as a carbon source, and then performing carbonization and pyrolysis in a tubular furnace. The granular carbon molecular sieve disclosed by the invention is high in adsorption capacity, high in selectivity, good in stability, high in particle strength and easy to recycle and regenerate, and can be directly used for industrial devices. Compared with the traditional solvent absorption, extractive distillation and low-temperature distillation technologies, the separation method provided by the invention has the advantages of low energy consumption, small equipment investment, environmental friendliness and the like, and has a wide application prospect in the field of C4 olefin component separation.

Description

Technical Field

[0001] The present invention relates to the technical field of C4 olefin separation and purification, and in particular to a binder-free granular carbon molecular sieve material and its application in the separation and purification of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8). Background Art

[0002] C4 components primarily consist of a mixture of diolefins, olefins, and alkanes consisting of four carbon atoms. They are important petrochemical raw materials and a crucial component of China's petrochemical and organic chemical development, possessing extremely high utilization value. They are primarily derived from catalytic cracking (FCC), the methanol-to-olefins (MTO) process, and steam cracking. Among them, 1,3-butadiene, n-butene, and isobutylene are crucial chemical raw materials with significant industrial and commercial value. Their value is greatly enhanced when their polymer-grade purity reaches 99.5% or higher. However, due to their similar molecular size and physical properties, complete separation and purification using conventional separation methods is difficult. Currently, C4 olefins are primarily separated by extractive distillation. Depending on the extractant used, extractive distillation methods are mainly categorized into the acetonitrile method (ACN), the N-methylpyrrolidone method (NMP), and the N,N-dimethylpyrrolidone method (DMF). However, extractive distillation technology has problems such as high energy consumption, large recycling of extractants, severe high-temperature polymerization of C4 olefins, and a large number of required plates (>110). Therefore, it is of great significance to use efficient, low-energy, and environmentally friendly separation methods.

[0003] Adsorption separation technology operates gently at atmospheric pressure, requires simple equipment, and offers great operational flexibility, making it an economical and efficient separation technique. Compared to current distillation techniques, it requires less energy (only one-third of rectification) and can separate mixed gases under mild conditions, making it a promising low-carbon hydrocarbon separation technology. The key lies in the preparation of highly selective adsorbents with high adsorption capacity.

[0004] In recent years, Chinese patent application publication number CN104030874A has disclosed a process for separating n-isobutene by adsorption using carbon molecular sieves. Using a pore-adjusted carbon molecular sieve as the adsorbent, it achieves high-purity separation of n-isobutene using a three- or multi-tower pressure swing adsorption system. Chinese patent application publication number CN102351630A also utilizes X or Y zeolite molecular sieves modified with barium or potassium to selectively adsorb 1-butene from liquid C4 feeds. These conventional adsorbents are only capable of partially separating C4 components and struggle to produce high-purity butadiene. Chinese patent application publication number CN118059541A reports a pillared anionic MOF adsorbent that can achieve molecular recognition and separation based on the three-dimensional size differences and surface electrostatic potential of C4 molecules, specifically capturing 1,3-butadiene. However, the adsorbent's complex preparation and high ligand costs have limited its large-scale industrial application. Chinese patent application CN108440235A reports a MOFs adsorbent with the molecular formula M(C7O5H4)·2H2O. However, the adsorbent is in powder form and requires additional molding, which often leads to pore clogging and performance degradation. Therefore, developing a novel granular carbon molecular sieve with both adsorption and separation properties and a green, efficient preparation method to separate C4 components remains of great industrial value. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, the present invention provides a binder-free granular carbon molecular sieve and its application in the separation of C4 olefin mixtures. This invention utilizes naturally formed biomass as a carbon source. Through crushing, screening, and pretreatment, and then controlled carbonization and pyrolysis, the granular carbon molecular sieve is produced with a specific pore size distribution, achieving efficient separation of C4 olefin components.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] A binder-free granular carbon molecular sieve, wherein the preparation method of the granular carbon molecular sieve comprises the following steps:

[0008] (1) Immersing the carbon source in a solution;

[0009] (2) carbonizing the solution-treated carbon source and then pyrolyzing it to obtain a granular carbon molecular sieve;

[0010] The carbonization process has a heating rate of 2-10°C / min, a carbonization temperature of 150-300°C, and a carbonization time of 0.5-1.5h;

[0011] The heating rate of the pyrolysis process is 2-10°C / min, the pyrolysis temperature is 400-1000°C, and the pyrolysis time is 0-2.5h.

[0012] Preferably, the carbon source in step (1) includes but is not limited to one of pine wood, bamboo, palm shell, walnut shell, corn cob, and macadamia nut shell.

[0013] Preferably, the particle size of the carbon source in step (1) is 8-30 mesh.

[0014] Preferably, in step (1), the carbon source is impregnated, then washed, filtered, and dried.

[0015] Preferably, the solution in step (1) comprises water, a metal salt solution, an acidic solution, an alkaline solution or a mixture of the above solutions.

[0016] Further preferably, the metal salt solution is mainly iron salt, zinc salt or a mixture of metal salts; the acidic solution is mainly phosphoric acid solution, nitric acid solution or a mixture of the two; the alkaline solution is mainly ammonia solution, sodium hydroxide solution, sodium bicarbonate solution or a mixture thereof.

[0017] Further preferably, the concentration of the metal salt solution is 0-0.2 mol / L, the immersion time is 0.5-12 h, and the immersion temperature is 15-60 ° C; the concentration of the acidic solution is 0-0.12 mol / L, the immersion time is 0.2-10 h, and the immersion temperature is 20-60 ° C; the concentration of the alkaline solution is 0-0.15 mol / L, the immersion time is 0.2-12 h, and the immersion temperature is 20-60 ° C.

[0018] Preferably, in step (2), the solution-treated carbon source is placed in a tubular furnace, carbonized at a suitable heating rate and in a specific gas atmosphere, and then pyrolyzed in the specific gas atmosphere to obtain a binder-free granular carbon molecular sieve.

[0019] Preferably, the gas atmosphere for carbonization and pyrolysis in step (2) is any one or a combination of nitrogen, argon, and carbon dioxide.

[0020] The above-mentioned binder-free granular carbon molecular sieve is used in the separation and purification of a C4 olefin mixture; the C4 olefin mixture includes at least two of butadiene, n-butene and isobutylene.

[0021] Preferably, the C4 olefin mixture is a butadiene / isobutylene mixture or a n-butene / isobutylene mixture.

[0022] In summary, the present invention provides a binder-free granular carbon molecular sieve for use in the separation of C4 olefin mixtures, which can separate and purify C4 olefin components at room temperature and pressure. The granular carbon molecular sieve of the present invention has a natural particle morphology and high particle strength, and can be directly used in a C4 olefin purification device. The present invention uses agricultural waste from a wide range of sources as a carbon source, which reduces the economic cost of adsorbent preparation. The preparation method is simple, green and low-consumption. Isobutylene is separated and purified by pore screening, butadiene and n-butene are separated by kinetic differences, and efficient separation and purification of C4 components are achieved by combining screening and kinetics.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] (1) The room-temperature rapid synthesis material of the present invention exhibits excellent butadiene adsorption at 298K, enabling the separation of C4H6 / i-C4H8 and n-C4H8 / i-C4H8, thereby obtaining high-purity isobutylene. The separation of butadiene and n-butene is achieved by the difference in kinetic diffusion rates between butadiene and n-butene. Notably, the energy consumption of this operation is significantly lower than that of the NMP technology developed by BASF, which has an initial energy consumption of 4.2 tons of steam per ton of 1,3-butadiene, about twice the typical industrial range (1.5-2.5 tons of steam per ton of 1,3-butadiene).

[0025] (2) The granular carbon molecular sieve of the present invention has a stable structure, high granular strength and low cost; the carbon molecular sieve of the present invention is granular and does not need to be formed, and can be directly loaded into an adsorption column separation device, and has the characteristics of being directly applicable to engineering applications.

[0026] (3) The present invention selects biomass from a wide range of sources as the carbon precursor and optimizes the preparation process to achieve one-time pyrolysis pore formation, thereby reducing the economic cost of adsorbent preparation.

[0027] (4) The present invention does not use adhesives and highly polluting pyrolysis agents, and is green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0029] Figure 1 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) in the granular carbon molecular sieve prepared in Example 1 of the present invention are shown.

[0030] Figure 2The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) in the granular carbon molecular sieve prepared in Example 2 of the present invention are shown.

[0031] Figure 3 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) in the granular carbon molecular sieve prepared in Example 3 of the present invention are shown.

[0032] Figure 4 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) in the granular carbon molecular sieve prepared in Example 4 of the present invention were obtained.

[0033] Figure 5 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) in the granular carbon molecular sieve prepared in Example 5 of the present invention are shown.

[0034] Figure 6 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) of the granular carbon molecular sieve were prepared for comparative example 1 of the present invention.

[0035] Figure 7 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) of the granular carbon molecular sieve were prepared for comparative example 2 of the present invention.

[0036] Figure 8 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) of the granular carbon molecular sieve were prepared for comparative example 3 of the present invention.

[0037] Figure 9 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) of the granular carbon molecular sieve were prepared for comparative example 4 of the present invention.

[0038] Figure 10 The single-component adsorption isotherms of butadiene (C4H6), n-butene (n-C4H8) and isobutylene (i-C4H8) of the granular carbon molecular sieve were prepared for comparative example 5 of the present invention. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present invention will be described clearly and completely below. The present invention will be further described in detail below in conjunction with the embodiments and drawings, but the implementation manner of the present invention is not limited thereto.

[0040] In the examples of the present invention, if the specific conditions are not specified, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. All raw materials and reagents used without specifying the manufacturer are conventional products that can be purchased from the market.

[0041] Example 1

[0042] A certain amount of walnut shells were crushed, and 10-20 mesh particles were screened out and soaked in deionized water for 2 hours, filtered and dried. The dried walnut shells were placed in a tube furnace and heated to 150°C at 5°C / min in a N2 atmosphere for carbonization for 1.5 hours. The temperature was then increased to 700°C at 7°C / min for pyrolysis for 1 hour. After cooling, the product was obtained and marked as Example 1.

[0043] Example 2

[0044] A certain amount of pine wood was crushed, and particles of 10-20 mesh were screened out and soaked in a 0.2 mol / L ZnCl2 solution at 15°C for 12 hours, filtered and dried. The dried pine wood was placed in a tubular furnace and heated to 300°C at a rate of 10°C / min in a N2 atmosphere for carbonization for 0.5 hours. The temperature was then increased to 400°C at a rate of 10°C / min for pyrolysis for 1 hour. After cooling, the product was obtained and marked as Example 2.

[0045] Example 3

[0046] A certain amount of bamboo was crushed, and bamboo particles of 8-10 mesh were screened out. The bamboo was then soaked in a 0.005 mol / L NaHCO3 solution at 60°C for 0.2 hour, filtered and dried. The dried bamboo was placed in a tube furnace and heated to 200°C at a rate of 3°C / min in a N2 atmosphere for carbonization for 1 hour. The bamboo was then heated to 500°C at a rate of 10°C / min for pyrolysis for 1 hour. After cooling, the product was obtained, which is labeled as Example 3.

[0047] Example 4

[0048] A certain amount of corn cobs were crushed, and particles of 20-30 mesh were screened out. The corn cobs were soaked in a 0.12 mol / L H3PO4 solution at 20°C for 10 hours, filtered and dried, and the dried corn cobs were placed in a tube furnace and heated to 250°C at a rate of 2°C / min in a N2 atmosphere for carbonization for 0.5 hour. The corn cobs were then heated to 400°C at a rate of 2°C / min for pyrolysis for 2.5 hours. The product obtained after cooling was marked as Example 4.

[0049] Example 5

[0050] A certain amount of corn cobs were crushed and 20-30 mesh particles were screened out. The corn cobs were soaked in a 0.15 mol / L NaHCO3 solution at 60°C for 0.2 hours, filtered and dried, and the dried corn cobs were placed in a tube furnace and heated to 250°C at a rate of 2°C / min in a N2 atmosphere for carbonization for 0.5 hours. The corn cobs were then heated to 1000°C at a rate of 10°C / min for pyrolysis for 0 hours. After cooling, the product was obtained and marked as Example 5.

[0051] Comparative Example 1

[0052] The soybeans were crushed, first passed through a 20-mesh filter sieve, and then through a 10-mesh filter sieve, and particles with a size of 1-2 mm between the two were screened out as a carbon precursor; the precursor was soaked in a 0.04 mol / L FeCl3 solution at 80°C for 12 h; after soaking, it was filtered, dried, and transferred to a tubular furnace, and heated to 900°C at a rate of 10°C / min in an Ar atmosphere and maintained for 60 min, and then cooled to obtain a granular carbon molecular sieve, which was recorded as Comparative Example 1.

[0053] Comparative Example 2

[0054] A certain amount of walnut shells were crushed, and particles of 10-20 mesh were screened out. The particles were soaked in a 0.5 mol / L KOH solution for 2 hours, filtered and dried, and the dried walnut shells were placed in a tube furnace and heated to 100°C at 5°C / min in a N2 atmosphere for carbonization for 2 hours. The temperature was then increased to 600°C at 5°C / min for pyrolysis for 3 hours. The product obtained after cooling was marked as Comparative Example 2.

[0055] Comparative Example 3

[0056] 3 g of rice was added to 40 mL of 7 wt % phosphoric acid solution and immersed in ultrasound for 1 hour, then filtered, placed in a watch glass and dried in a 60 ° C oven. The rice obtained after immersion and drying was placed in a porcelain boat and transferred to a tube furnace. Under a nitrogen atmosphere, programmed temperature heating was performed at a heating rate of 10 ° C / min. After heating to 500 ° C, carbonization was maintained for 1 hour, and then the temperature was continued to be raised to 850 ° C. Switch to CO2 atmosphere for pyrolysis for 0.5 hours, and then switch to nitrogen atmosphere and cool to room temperature to obtain a new granular carbon material marked as Comparative Example 3.

[0057] Comparative Example 4

[0058] A certain amount of rice was crushed, and particles of 10-40 mesh were screened out. The rice was washed with clean water, filtered, and then soaked in a 0.001 mol / L ferric chloride / copper chloride mixed solution (wherein the molar ratio of ferric chloride:copper chloride = 1:1) for 3 hours, filtered and dried. The dried rice was placed in a tubular furnace, and the tubular furnace was heated to 300°C at 5°C / min in a N2 atmosphere for pyrolysis and carbonization for 1 hour, and then heated to 800°C at 5°C / min for pyrolysis and carbonization for 1 hour. After cooling, microporous carbon materials were obtained; these microporous carbon materials were placed in a sealed container, evacuated, and filled with 1 bar of 1,3-butadiene gas. After static adsorption for 5 hours, the reactor was heated to 100°C and maintained for 1 hour, and then cooled to room temperature to obtain a product marked as Comparative Example 4.

[0059] Comparative Example 5

[0060] A certain amount of walnut shells were crushed and 10-20 mesh particles were screened out to obtain a product marked as Comparative Example 5.

[0061] The static single-component adsorption isotherms at 298 K were measured for the products obtained in Examples 1-5 and Comparative Examples 1-5. The results of the adsorption isotherms were used to determine whether they could be used in the separation and purification of C4 olefin mixtures.

[0062] Figure 1 The single-component static adsorption isotherms of the product obtained in Example 1 for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8 at 298K are shown. At a pressure of 1 bar, the adsorption amounts for C4H6 and n-C4H8 reached 2.17 mmol / g and 0.63 mmol / g, respectively. There was almost no adsorption of iso-C4H8. Sieving separation of iso-C4H8 was possible, achieving C4H6 / iso-C4H8 and n-C4H8 / iso-C4H8 separations, demonstrating excellent separation of C4 olefin mixtures.

[0063] Figure 2 The single-component static adsorption isotherms of the product obtained in Example 2 for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8 at 298K are shown. At a pressure of 1 bar, the adsorption amounts for C4H6 and n-C4H8 reached 1.63 mmol / g and 0.36 mmol / g, respectively. There was almost no adsorption of iso-C4H8, and iso-C4H8 could be separated by sieving, achieving C4H6 / iso-C4H8 and n-C4H8 / iso-C4H8 separations, demonstrating excellent separation of C4 olefin mixtures.

[0064] Figure 3The single-component static adsorption isotherms of the product obtained in Example 3 for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8 at 298K. At a pressure of 1 bar, the adsorption amounts for C4H6 and n-C4H8 reached 1.48 mmol / g and 0.38 mmol / g, respectively. There was almost no adsorption of iso-C4H8. Sieving separation of iso-C4H8 was possible, achieving C4H6 / iso-C4H8 and n-C4H8 / iso-C4H8 separations, demonstrating excellent separation of C4 olefin mixtures.

[0065] Figure 4 The single-component static adsorption isotherms of the product obtained in Example 4 for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8 at 298K are shown. At a pressure of 1 bar, the adsorption capacities for C4H6 and n-C4H8 reached 1.62 mmol / g and 0.54 mmol / g, respectively. The adsorption capacity for iso-C4H8 was lower at 0.2 mmol / g. Sieving separation of iso-C4H8 allowed for the separation of C4H6 / iso-C4H8 and n-C4H8 / iso-C4H8, demonstrating excellent separation of C4 olefin mixtures.

[0066] Figure 5 The single-component static adsorption isotherms of the product obtained in Example 5 for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8 at 298K. At a pressure of 1 bar, the adsorption amounts for C4H6 and n-C4H8 reached 1.38 mmol / g and 0.49 mmol / g, respectively. There was almost no adsorption of iso-C4H8. Sieving separation of iso-C4H8 was possible, achieving C4H6 / iso-C4H8 and n-C4H8 / iso-C4H8 separations, demonstrating excellent separation of C4 olefin mixtures.

[0067] By controlling the activation method, carbonization and pyrolysis temperature, and time, the material obtained by the present invention exhibits virtually no adsorption of iso-C₄H₂, demonstrating excellent separation performance for C₄ olefin mixtures. Example 1 exhibits high adsorption capacities for C₄H₂ and n-C₄H₂, namely 2.17 mmol / g and 0.63 mmol / g, respectively. Example 15 exhibits a Type I isotherm for C₄H₂ adsorption, demonstrating strong adsorption of small molecules and confirming its well-developed microporous structure.

[0068] Figure 6The single-component static adsorption isotherm for the product obtained in Comparative Example 1 at 298K for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8. At a pressure of 1 bar, the adsorption capacity for C4H6 is 1.24 mmol / g, while n-C4H8 and iso-C4H8 are almost non-adsorbed, resulting in the separation of only C4H6 from the C4 mixture.

[0069] Figure 7 Figure 2 shows the single-component static adsorption isotherms of the product obtained in Comparative Example 2 for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8 at 298K. At a pressure of 1 bar, the adsorption capacity for C4H6 is 2.75 mmol / g, the adsorption capacity for n-C4H8 is 2.25 mmol / g, and the adsorption capacity for iso-C4H8 is 2.00 mmol / g. The adsorption capacities of the three components are similar, making separation of the C4 mixture components impossible.

[0070] Figure 8 The single-component static adsorption isotherms for the product obtained in Comparative Example 3 at 298 K for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8. At a pressure of 1 bar, the adsorption capacity for C4H6 is 2.76 mmol / g, while the adsorption capacities for n-C4H8 and iso-C4H8 are close to 2.24 mmol / g. The similar adsorption capacities of the three components make it impossible to separate the components of the C4 mixture.

[0071] Figure 9 The single-component static adsorption isotherms for the product obtained in Comparative Example 4 for the C4 olefin mixture components C4H6, n-C4H8, and iso-C4H8 at 298K are shown. At a pressure of 1 bar, the adsorption capacity for C4H6 is 0.58 mmol / g, while n-C4H8 and iso-C4H8 are hardly adsorbed. The adsorption capacity for C4H6 is relatively low, and only a single component of the C4 mixture can be separated.

[0072] Figure 10 The single-component static adsorption isotherms of the product obtained in Comparative Example 5 for C4 olefin mixture components C4H6, n-C4H8 and iso-C4H8 at 298 K. The untreated carbon material hardly adsorbs the C4 olefin mixture components and cannot be separated.

Claims

1. A binder-free granular carbon molecular sieve, characterized in that: The preparation method of the granular carbon molecular sieve comprises the following steps: (1) Immersing the carbon source in the solution; (2) carbonizing the solution-treated carbon source and then pyrolyzing it to obtain a granular carbon molecular sieve; The carbonization process has a heating rate of 2-10°C / min, a carbonization temperature of 150-300°C, and a carbonization time of 0.5-1.5h; The heating rate of the pyrolysis process is 2-10°C / min, the pyrolysis temperature is 400-1000°C, and the pyrolysis time is 0-2.5h.

2. The binder-free granular carbon molecular sieve according to claim 1, characterized in that: The carbon source in step (1) comprises one of bamboo, pine wood, palm shell, walnut shell, corn cob, and macadamia nut shell.

3. The binder-free granular carbon molecular sieve according to claim 1, characterized in that: The particle size of the carbon source in step (1) is 8-30 mesh.

4. The binder-free granular carbon molecular sieve according to claim 1, characterized in that: The solution in step (1) is water, a metal salt solution, an acidic solution, an alkaline solution or a mixture of the above solutions.

5. The binder-free granular carbon molecular sieve according to claim 4, characterized in that: The metal salt solution is an iron salt, a zinc salt or a mixture of metal salts; the acidic solution is a phosphoric acid solution, a nitric acid solution or a mixture of the two; the alkaline solution is an ammonia solution, a sodium hydroxide solution, a sodium bicarbonate solution or a mixture thereof.

6. The binder-free granular carbon molecular sieve according to claim 5, characterized in that: The iron salt of the metal salt solution includes ferric chloride, ferric sulfate or ferric nitrate; the zinc salt includes zinc chloride or zinc acetate.

7. The binder-free granular carbon molecular sieve according to claim 4, characterized in that: The salt concentration in the metal salt solution is 0-0.2 mol / L, the immersion time is 0.5-12 hours, and the immersion temperature is 15-60°C; the concentration of the acidic solution is 0-0.12 mol / L, the immersion time is 0.2-10 hours, and the immersion temperature is 20-60°C; the concentration of the alkaline solution is 0-0.15 mol / L, the immersion time is 0.2-12 hours, and the immersion temperature is 20-60°C.

8. The binder-free granular carbon molecular sieve according to claim 1, characterized in that: The gas atmosphere for carbonization and pyrolysis in step (2) is any one or a combination of nitrogen, argon, and carbon dioxide.

9. Use of a binder-free granular carbon molecular sieve according to any one of claims 1 to 8, characterized in that: Application in separation and purification of C4 olefin mixture; the C4 olefin mixture comprises at least two of butadiene, n-butene and isobutene.

10. The use of a binder-free granular carbon molecular sieve according to claim 9, characterized in that: The C4 olefin mixture is a butadiene / isobutylene mixture or a n-butene / isobutylene mixture.

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