CN118062825A - A granular carbon molecular sieve capable of screening ethylene/ethane and its preparation method and application - Google Patents

Abstract

The present invention discloses a granular carbon molecular sieve capable of screening ethylene/ethane, and a preparation method and application thereof. The preparation method comprises the following steps: (1) crushing biomass carbon source particles, screening particles of target particle size, impregnating with a salt solution of a certain concentration, filtering, and drying, and then preliminarily pyrolyzing and carbonizing the granular carbon in a _N2 atmosphere and at a certain temperature to obtain a carbon precursor with a certain structure and chemical composition, and cooling to room temperature; (2) placing the granular carbon obtained after pyrolysis and carbonization in a C4 olefin mixed gas for adsorption; and (3) heating the porous carbon material to obtain a granular carbon molecular sieve capable of molecular screening and separation of ethylene/ethane.

Description

A granular carbon molecular sieve capable of screening ethylene/ethane and its preparation method and application

Technical Field

The invention belongs to the field of preparation of granular carbon molecular sieves, and in particular relates to a granular carbon molecular sieve capable of molecularly sieving ethylene/ethane, and a preparation method and application thereof.

Background technique

Ethylene is the world's largest basic organic chemical. In 2022, the global ethylene production capacity will reach 218 million tons/year. my country is also the world's largest ethylene producer. Ethylene and its derivatives account for 70% of petrochemical products. The production and utilization level of ethylene is considered an important indicator of a country's petrochemical development level.

Ethylene needs to reach a certain purity for subsequent processing and production as a chemical raw material. Taking the production of polyethylene as an example, the raw material ethylene needs to reach a purity of more than 99.95%. Industrial production of ethylene is usually produced by high-temperature cracking of naphtha and steam. In the product, unreacted ethane impurities are inevitably produced, so further separation and purification are required to prepare polymerized pure ethylene. At present, the purification of ethylene mainly adopts high-pressure and low-temperature distillation process. Since the main impurity is ethane, and the physical properties of ethylene and ethane are similar, the high-pressure and low-temperature distillation separation process has high energy consumption, and the separation cost accounts for 70% of the total production cost. Therefore, it is urgent to develop an ethylene/ethane separation technology that can be efficient and energy-saving at room temperature.

Adsorption separation technology can achieve ethylene/ethane separation at room temperature and pressure. Compared with high-pressure and low-temperature distillation technology, separation energy consumption can be reduced by 75%. Adsorption materials are the key. However, the kinetic diameters of ethylene and ethane are and The difference between the two is only The difficulty of separation is significantly higher than that of separating propylene and propane (/> and ). Therefore, a narrower pore structure and a more concentrated pore size distribution are required for the screening and separation of ethylene/ethane. At present, several metal-organic frameworks (MOFs), silver-loaded zeolite molecular sieves and microporous carbon materials have been reported to have the performance of screening ethylene/ethane. However, to become an industrial adsorbent, the adsorbent material must simultaneously meet the requirements of good stability, excellent selectivity, high adsorption capacity, easy particle forming and low preparation cost. Most of the current MOFs materials are unstable and very expensive; zeolite molecular sieves are prone to carbon deposition when separating olefins and have poor cyclic stability; Du et al. used dopamine as a raw material to achieve complete screening and separation of ethylene/ethane by porous carbon materials (Du S, Huang J, Ryder M, et al. Probing sub-5Angstrom micropores in carbon for precise light olefin/paraffin separation [J]. Nat Commun, 2023, 14 (1): 1197.). However, this carbon molecular sieve mainly uses expensive dopamine as a carbon source, and the resulting sample is in powder form and does not have the characteristics of direct industrial application. If the crystalline nanoparticles are formed by adding a binder, the adsorption capacity will be reduced, and the secondary pores generated will lead to a decrease in selectivity.

Summary of the invention

In order to prepare a low-cost granular carbon molecular sieve that can be directly used to separate ethylene and ethane, the present invention proposes a universal preparation method for granular carbon molecular sieves for separating ethylene/ethane. The present invention selects natural granular biomass as a carbon source, and after crushing, screening and pretreatment, controllable pyrolysis and carbonization, obtains a microporous carbon material with a specific pore size distribution, and then uses butadiene and its mixed gas that match the size of ethane molecules to adsorb into part of the pores of the carbon material, and then heats it for carbon deposition reaction to block the pores that can originally adsorb ethane, thereby accurately controlling the pore structure, achieving selective adsorption of ethylene without adsorbing ethane, and obtaining a granular carbon molecular sieve that efficiently screens ethylene/ethane.

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

A method for preparing a granular carbon molecular sieve capable of screening ethylene/ethane comprises the following steps:

(1) crushing the biomass carbon source particles, sieving them, and then impregnating them with a salt solution, and then pyrolyzing and carbonizing the particle carbon precursor;

(2) placing the granular carbon treated in step (1) in an atmosphere containing C4 olefins for adsorption, and then heating to allow the C4 olefins to undergo a carbonization reaction on the surface of the carbon material pores, thereby obtaining a granular carbon molecular sieve capable of screening ethylene/ethane.

Preferably, the biomass carbon source particles in step (1) include but are not limited to one or more of coconut shells, coffee beans, palm shells, rice and millet; the particle size range of the biomass carbon source particles after crushing and screening is 10-40 mesh.

Preferably, the salt solution in step (1) is mainly Fe salt, Cu salt or a mixture of the two salts, the concentration of the salt solution is 0.001-0.1 mol/L, the molar ratio of the two salts is Fe:Cu=0.005-1:1, the immersion time is 1-8 hours, and the temperature is room temperature to 40°C.

Preferably, the pyrolysis and carbonization in step (1) is carried out in an atmosphere of _N2 and/or an inert gas, and the temperature for preliminary pyrolysis and carbonization of the granular carbon is 250-900°C and the time is 1-4 hours.

Preferably, the C4 olefin in step (2) includes but is not limited to 1,3-butadiene 1-Butene One or a mixture of two or more gases.

Preferably, in the atmosphere containing C4 olefins in step (2), the volume proportion of 1,3-butadiene is 1%-100%, and the rest is other C4 olefins and N ₂ .

Preferably, in the atmosphere containing C4 olefins in step (2), the total pressure is 0.1-2 bar, and the equilibrium adsorption time is 0.5-6 hours.

Preferably, the heating temperature in step (2) is 60-130° C., and the carbonization reaction time is 0.5-2 hours.

A granular carbon molecular sieve prepared by any of the preparation methods described above has molecular sieving separation performance for ethylene/ethane at room temperature and pressure, and the adsorption ratio of ethylene/ethane is greater than 8 (at 298K and 1 bar).

The above-mentioned granular carbon molecular sieve is used for the adsorption separation of ethylene/ethane.

The idea of the present invention is to select natural and renewable particulate biomass carbon sources, such as coconut shells, palm shells, rice and millet (which can reduce costs); the next problem is that biomass particulate carbon of different types, origins, growth years or parts has different initial structures and different paths of structural evolution after heating, which makes it difficult to control the pore size of carbon materials in batches with sub-angstrom accuracy using existing pyrolysis technology to prepare qualified carbon molecular sieves. To overcome this problem, the present invention crushes these biomass carbon source particles into a certain particle size, and then uses a pyrolysis carbonization method to make a carbon precursor with a certain porosity and controllable pore size distribution. Then, in an environment under certain negative pressure conditions, a certain amount of C4 olefin mixture is inserted into the pores of the material by adsorption, and heated to a certain temperature under closed conditions, so that these olefin compounds form polymerization carbonization on the pore surface of the porous carbon material, and the pores with a size larger than the molecular dynamics diameter of ethane are sealed, thereby achieving precise control of the size of the screening pores, so that ethane is repelled and only ethylene is adsorbed, thereby realizing the molecular screening separation of ethane and ethane.

The advantages of the present invention are as follows: since natural granular biomass is selected as the carbon source, the preparation cost is low; a trace amount of C4 olefin mixture is used and inserted into the pores of the material to control the pore size at one time, the operation is simple, the control can be precise, and the carbon molecular sieve is suitable for preparing carbon molecular sieves from biomass carbon sources of different sources. The problem of temperature sensitivity faced by the pyrolysis method causing the sieving pores of the carbon molecular sieve to be difficult to control is avoided, and the industrial preparation is easy; since natural granular biomass is selected as the carbon source, the prepared material is a granular carbon material, which does not require subsequent molding, and the particle size can be controlled between 10-60 meshes (can be screened as needed).

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

(1) The granular carbon molecular sieve prepared by the present invention can achieve molecular sieving of ethylene/ethane, and the ratio of ethylene/ethane adsorption capacity at room temperature and pressure is greater than 8, which can meet the needs of industrial separation and purification of ethylene.

(2) The granular carbon molecular sieve prepared by the present invention has a stable structure and low cost; the carbon molecular sieve prepared by the present invention is granular and can be directly loaded into an adsorption column separation device, and has the characteristic of being directly applicable to engineering.

(3) The present invention adopts a unique principle to prepare a granular carbon molecular sieve capable of molecular sieving ethylene/ethane. Its unique sieving pore control strategy enables people to more widely select natural granular carbon sources and prepare granular carbon molecular sieves with stable performance.

(4) The present invention does not use adhesives and highly polluting activators, and is green and environmentally friendly.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 to 5 are adsorption isotherms of the products obtained in Examples 1 to 5 for ethylene/ethane at 298K.

FIG. 6 is an adsorption isotherm diagram of ethylene/ethane for the products obtained in Example 1 and Comparative Example 1 at 298K.

FIG. 7 is an adsorption isotherm diagram of the product obtained in Comparative Example 2 for ethylene/ethane at 298K.

FIG8 is a comparison chart of the ratio of ethylene/ethane adsorption of the products obtained in Examples 1-5 at 298K and 1 bar.

FIG. 9 is a graph showing the carbon dioxide adsorption and desorption isotherms of the products obtained in Example 1 and Comparative Example 1 at 273K.

FIG. 10 is a pore size distribution diagram (GCMC model) of the products obtained in Example 1 and Comparative Example 1 calculated by carbon dioxide adsorption-desorption isotherms at 273 K.

Detailed ways

The present invention is further described in detail below in conjunction with examples and drawings, but the embodiments of the present invention are not limited thereto.

If no specific conditions are specified in the examples of the present invention, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. All raw materials, reagents, etc., whose manufacturers are not specified, are conventional products that can be purchased commercially.

Example 1

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 the temperature was increased to 800°C at 5°C/min for pyrolysis and carbonization for 1 hour, and then the temperature was cooled to obtain a microporous carbon material; the microporous carbon materials were placed in a closed container, evacuated and filled with 1 bar of 1,3-butadiene gas, and 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 CMC1#.

Example 2

A certain amount of coconut shell carbon that has undergone preliminary carbonization is crushed, and particles of 10-40 mesh are screened out. The particles are washed with clean water, filtered, and then immersed in a 0.1 mol/L ferric chloride/copper chloride mixed solution (wherein the molar ratio of ferric chloride:copper chloride = 0.5:1) for 5 hours, filtered and dried. The dried coconut shell particles are placed in a tubular furnace, and the tubular furnace is heated to 400°C at 5°C/min in a _N2 atmosphere for pyrolysis and carbonization for 1 hour, and then the temperature is increased to 700°C at 5°C/min for pyrolysis and carbonization for 3 hours, and microporous carbon materials are obtained after cooling; these microporous carbon materials are placed in a closed container, evacuated and filled with 0.5 bar of 1,3-butadiene gas, and after static adsorption for 2 hours, the reactor is heated to 120°C and maintained for 1 hour, and then cooled to room temperature to obtain a product marked as CMC2#.

Example 3

A certain amount of coffee beans that have undergone preliminary carbonization are crushed, and particles of 10-40 mesh are screened out. The particles are washed with clean water, filtered, and then immersed in a 0.01 mol/L ferric chloride/copper chloride mixed solution (wherein the molar ratio of ferric chloride:copper chloride=0.1:1) for 8 hours, filtered and dried. The dried coffee bean particles are placed in a tubular furnace, and the tubular furnace is heated to 850°C at 3°C/min in a _N2 atmosphere for pyrolysis and carbonization for 1.8 hours. After cooling, microporous carbon materials are obtained; these microporous carbon materials are placed in a sealed container, evacuated, and filled with a 1.5 bar mixed gas of 1,3-butadiene (2%) + 1-butene (2%) + _N2 (96%), and then allowed to stand for 6 hours and then heated at 60°C for 0.5 hour to obtain a product marked as CMC3#.

Example 4

A certain amount of palm shell carbon that has undergone preliminary carbonization is crushed, and particles of 10-40 mesh are screened out, washed with clean water, filtered, and then immersed in a 0.003 mol/L ferric chloride/copper chloride mixed solution (wherein the molar ratio of ferric chloride:copper chloride = 0.005:1) for 1 hour, filtered and dried, and the dried coconut shell particles are placed in a tubular furnace, and the tubular furnace is heated to 250°C at 5°C/min in a _N2 atmosphere for pyrolysis and carbonization for 1 hour, and then the temperature is increased to 700°C at 5°C/min for pyrolysis and carbonization for 2 hours, and microporous carbon materials are obtained after cooling; these microporous carbon materials are placed in a closed container, evacuated and filled with 0.1 bar of 1,3-butadiene gas, and after static adsorption for 1 hour, the reactor is heated to 80°C and maintained for 2 hours, and then cooled to room temperature to obtain a product marked as CMC4#.

Example 5

A certain amount of millet was screened to obtain particles of 10-40 mesh, washed with clean water, filtered, and then soaked in a 0.005 mol/L ferric chloride/copper chloride mixed solution (wherein the molar ratio of ferric chloride:copper chloride = 0.5:1) for 4 hours, filtered and dried, and 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 the temperature was increased to 750°C at 5°C/min for pyrolysis and carbonization for 1 hour, and then the temperature was cooled to obtain a microporous carbon material; these microporous carbon materials were placed in a closed container, evacuated and filled with 2 bar of 1,3-butadiene gas, and after static adsorption for 4 hours, the reactor was heated to 130°C and maintained for 1 hour, and then cooled to room temperature to obtain a product marked as CMC5#.

Comparative Example 1

A certain amount of rice was crushed, and particles of 10-40 mesh were screened out, 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, and the dried rice was placed in a tubular furnace, and the tubular furnace was heated to 300° C. at 5° C./min in a N ₂ atmosphere for pyrolysis and carbonization for 1 hour, and then the temperature was increased to 800° C. at 5° C./min for pyrolysis and carbonization for 1 hour, and the product obtained in Comparative Example 1 was obtained after cooling.

Comparative Example 2

A certain amount of commercial coconut shell activated carbon was placed in a sealed container, and after evacuation, 1 bar of 1,3-butadiene gas was filled in. After static adsorption for 5 hours, the reactor was heated to 100°C, maintained for 1 hour, and then cooled to room temperature to obtain the product obtained in Comparative Example 2.

Figures 1 to 5 are the adsorption isotherms of ethylene/ethane for the products obtained in Examples 1 to 5 at 298K. It can be seen that the granular carbon molecular sieve prepared by the present invention hardly adsorbs ethane (less than 0.2 mmol/g), showing excellent ethylene/ethane screening and separation effect. Among them, the product obtained in Example 3 has a higher ethylene adsorption capacity (1.38 mmol/g), the product obtained in Example 5 has an extremely low ethane adsorption amount (0.014 mmol/g), and the product obtained in Example 1 has both adsorption capacity and selectivity.

Fig. 6 is an adsorption isotherm diagram of ethylene/ethane for the products obtained in Example 1 and Comparative Example 1 at 298 K. It can be seen from the isotherm diagram that after the steps of standing and heating in a C4 olefin atmosphere, the adsorption capacity of ethylene for the product obtained in Example 1 decreased compared with the comparative example, but the adsorption amount of ethane decreased from 1.10 mmol/g to 0.069 mmol/g, which greatly improved its selectivity for ethylene/ethane.

7 is an adsorption isotherm diagram of ethylene/ethane at 298°C for the product obtained in Comparative Example 2. The product obtained in Comparative Example 2 has a certain ethylene/ethane separation performance, but does not achieve a screening effect.

Figure 8 is a comparison chart of the ratio of ethylene/ethane adsorption capacity of the products obtained in Examples 1-5 at 298K and 1 bar. At room temperature and pressure, the ratio of ethylene/ethane adsorption capacity of the products obtained in Examples 1-5 is greater than 8, among which the ratio of ethylene/ethane adsorption capacity of the product obtained in Example 5 is as high as 60.29, showing excellent ethylene/ethane screening performance.

Figures 9 and 10 are the carbon dioxide adsorption and desorption isotherms of the products obtained in Example 1 and Comparative Example 1 at 273K and the pore size distribution calculated by the GCMC model. It can be seen from the carbon dioxide adsorption and desorption isotherms that after standing and heating in a C4 olefin atmosphere, the adsorption of carbon dioxide by the product obtained in Example 1 decreases compared to the comparative example, which is due to the decrease in the pore volume of the material. It can be seen from the pore size distribution that the product obtained in Example 1 is located at The pore structure of the nanostructured carbon nanotubes fails, resulting in excellent ethylene/ethane screening performance.

The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims (10)

1. A process for the preparation of a granular carbon molecular sieve capable of sieving ethylene/ethane comprising the steps of:

(1) Crushing biomass carbon source particles, sieving, then impregnating with a salt solution, and carrying out pyrolysis and carbonization on the particle carbon precursor;

(2) And (3) placing the granular carbon treated in the step (1) in an atmosphere containing C4 olefin for adsorption, and heating to enable the C4 olefin to carry out carbonization reaction on the surface of a pore canal of a carbon material, thus obtaining the granular carbon molecular sieve capable of screening ethylene/ethane.

2. The method of preparing a granular carbon molecular sieve from ethylene/ethane according to claim 1, wherein the biomass carbon source of step (1) comprises one or more of coconut shell, coffee beans, palm shell, rice and millet; the preferred particle size range of the biomass carbon source after particle breakage is 10-40 mesh.

3. The method for preparing the granular carbon molecular sieve capable of screening ethylene/ethane according to claim 1, wherein the salt solution in the step (1) is mainly Fe salt, cu salt or a mixture of two salts, the concentration of the salt solution is 0.001-0.1mol/L, and the molar ratio of the two salts is Fe: cu=0.005-1:1, the time of impregnation is 1-8 hours, the temperature is room temperature to 40 ℃.

4. The method for preparing a granular carbon molecular sieve capable of screening ethylene/ethane according to claim 1, wherein the pyrolysis and carbonization in the step (1) is performed under the atmosphere of N ₂ and/or inert gas, the temperature of the granular carbon is 250-900 ℃ and the time is 1-4 hours.

5. The method for preparing a granular carbon molecular sieve capable of screening ethylene/ethane according to claim 1, wherein the C4 olefin in the step (2) comprises one or more of 1, 3-butadiene and 1-butene.

6. The method of preparing a granular carbon molecular sieve for ethylene/ethane screening according to claim 1, wherein in the atmosphere containing C4 olefins in step (2), the volume ratio of 1, 3-butadiene is 1% to 100%, and the balance is other C4 olefins and N ₂.

7. The method for preparing a granular carbon molecular sieve capable of screening ethylene/ethane according to claim 1, wherein the total pressure in the atmosphere containing C4 olefins in step (2) is 0.1 to 2bar and the adsorption time is 0.5 to 6 hours.

8. The method for preparing a granular carbon molecular sieve capable of screening ethylene/ethane according to claim 1, wherein the heating temperature in the step (2) is 60-130 ℃, and the carbonization reaction time is 0.5-2 hours.

9. A granular carbon molecular sieve produced by the method of any one of claims 1-8.

10. A granular carbon molecular sieve as claimed in claim 9 for use in the adsorptive separation of ethylene/ethane.