Disclosure of Invention
In view of the above, the present invention provides a novel carbon molecular sieve production process. Based on the complex production process of the carbon molecular sieve of carbonization-activation-carbon deposition commonly used in the market, the invention creatively uses polyhydroxy carbohydrate with low cost as raw materials, forms homogeneous carbonaceous microspheres by hydrothermal self-assembly, adjusts the microsphere structure by adjusting the concentration of hydrogen ions in a reaction system, and finally matches with corresponding temperature for controlled pyrolysis. The carbon molecular sieve obtained by the method has uniform aperture, can be regulated and controlled in sub-angstrom level, and is suitable for screening and separating small molecular gases. Meanwhile, the production process is simple, the synthesis cost is low, and the method is beneficial to large-scale industrial production.
The purpose of the invention is realized by the following technical scheme.
A preparation method of an angstrom-scale carbon molecular sieve material with controllable pore diameter by taking polyhydroxy carbohydrate as a raw material comprises the following steps:
(1) hydrothermal self-assembly reaction: adding an acidic substance into distilled water to prepare an acidic aqueous solution with hydrogen ion concentration of 0-6 mol/L, then adding a polyhydroxy carbohydrate compound carbon precursor into the acidic aqueous solution, wherein the mass ratio of the polyhydroxy carbohydrate compound precursor to the distilled water is a preset mass ratio, fully and uniformly stirring, transferring the solution into a reaction kettle, and carrying out hydrothermal self-assembly reaction at the temperature of 180-200 ℃ to form uniform carbonaceous hydrated microspheres;
(2) high-temperature controlled thermal reduction: and (2) washing and drying the carbonaceous hydrated microspheres obtained in the step (1), removing intermediate products which are not reacted on the surface, protecting by inert gas, raising the temperature to 600-900 ℃ by program, performing controlled high-temperature annealing, and cooling to normal temperature to obtain the micron-grade carbon molecular sieve material with the pore diameter, wherein the pore diameter of the micron-grade carbon molecular sieve material can be adjusted by the hydrogen ion concentration.
Preferably, in step (1), the polyhydroxy sugar compound is fructose or the fructose and one or more of galactose, sucrose, maltose and lactose.
Preferably, in step (1), the polyhydroxy sugar compound is one or more of galactose, sucrose, maltose and lactose.
Preferably, in the step (1), the polyhydroxy sugar compound is a chitosan nitrogen-containing compound.
Preferably, in the step (1), the acidic substance is one or more of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, and more preferably, the acidic substance is hydrochloric acid with a mass fraction of 36.5%.
Preferably, in the step (1), the hydrogen ion concentration of the acidic aqueous solution is 0.1-6 mol/L.
Preferably, in the step (1), the hydrogen ion concentration of the acidic aqueous solution is 0.1-2 mol/L.
Preferably, in the step (1), the temperature of the hydrothermal self-assembly reaction is 180-200 ℃ and the time is 6-20 h.
Preferably, in the step (2), the inert gas is argon, nitrogen or helium.
Preferably, in the step (2), the controlled high-temperature annealing temperature is 600-. Preferably, in the step (2), the controlled high-temperature annealing temperature is 700-.
Preferably, in the step (2), the controlled high temperature annealing time is 0.5 to 4 hours, and more preferably 0.5 to 3 hours.
Preferably, the preset mass ratio is 1: 10.
The application also provides an angstrom-scale carbon molecular sieve material, which is prepared by the method in any one of the above.
Preferably, the pore diameter of the Hermite-grade carbon molecular sieve material is 4.2-7.0 Hermite. Wherein the pore diameter of the angstrom-scale carbon molecular sieve material can be adjusted by the concentration of hydrogen ions.
The micron-grade carbon molecular sieve material with the controllable ultramicropore aperture, which is prepared by the method, can be used in the field of adsorption and separation of small molecule gases.
The invention provides a novel establishment concept of the micron-grade carbon molecular sieve with controllable aperture, which is different from the traditional preparation method of the carbon molecular sieve. The method has the advantages that cheap and reproducible polyhydroxy carbohydrate is used as a carbon source, the structure of the hydrated carbon microsphere is adjusted by regulating the concentration of hydrogen ions in a hydrothermal self-assembly reaction system, and finally, a high-temperature thermal reduction process is carried out to obtain the novel controllable carbon molecular sieve material with uniform aperture.
Compared with the prior art, the invention has the following advantages:
(1) according to the synthesis process of the Hermite-grade carbon molecular sieve, the selected carbon source belongs to renewable resources, the price is low, the carbon source is easy to obtain, the synthesis process is simple to operate, the energy consumption is low, an activating agent is not required to be added, and the large-scale industrial production is facilitated.
(2) The selected saccharides are easier to prepare and have higher yield than other polysaccharides. Meanwhile, compared with other saccharides, the selected nitrogen-containing saccharide compound of chitosan has higher gas adsorption capacity and is more suitable for industrial application, and the amino group in the compound brings different effects to the final product.
(3) The carbon molecular sieve prepared by the invention has extremely high quality, the aperture is in the Hermite level range, the aperture is uniform, and the carbon molecular sieve can be in the sub-Hermite level
The adjustment and control within the range solve the difficulty that the aperture of the traditional carbon molecular sieve is difficult to be accurately adjusted.
(4) The carbon molecular sieve prepared by the invention is not easy to deposit carbon, has long service life, and the aperture is close to the dynamic diameter of small molecular hydrocarbon, so the carbon molecular sieve is very suitable for the field of screening and separating application of small molecular gas.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
The method is characterized in that cheap and reproducible polyhydroxy carbohydrate is used as a carbon source, the structure of a hydrated carbon microsphere is adjusted by regulating the concentration of hydrogen ions in a hydrothermal self-assembly reaction system (as shown in figure 7), and finally, a high-temperature thermal reduction process is carried out to obtain the angstrom-level carbon molecular sieve material with uniform aperture and controllable diameter.
Example 1
(1) 0.833mL of concentrated hydrochloric acid (mass fraction: 36.5%) was added to 99.2mL of distilled water to prepare an aqueous solution having a hydrogen ion concentration of 0.1mol/L, and 10g of fructose was added thereto and sufficiently stirred for 30min to disperse the solution uniformly. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 16 hours at the constant temperature of 190 ℃, and then the obtained carbonaceous hydrated microspheres are washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (2) drying the carbonaceous hydrated microspheres in an oven at 100 ℃ overnight, then placing the dried carbonaceous hydrated microspheres in a high-temperature tube furnace, carrying out programmed heating to 800 ℃ for high-temperature pyrolysis for 2h at a heating rate of 5 ℃/min under the nitrogen atmosphere, and cooling to room temperature to obtain the No. 1 carbon molecular sieve material.
(3) The aperture of the obtained 1# carbon molecular sieve is mainly concentrated on
Wherein
The narrow aperture ratio of the range is more than 51 percent, the ethylene-ethane separation effect is good, the ethylene adsorption capacity reaches 1.80mmol/g and the ethane adsorption capacity is only 0.51mmol/g under normal temperature and normal pressure.
Example 2
(1) 0.0833mL of concentrated hydrochloric acid (mass fraction: 36.5%) was added to 99.9mL of distilled water to prepare an aqueous solution having a hydrogen ion concentration of 0.01mol/L, and 10g of fructose was added thereto and sufficiently stirred for 30min to disperse the solution uniformly. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 16 hours at the constant temperature of 190 ℃, and then the obtained carbonaceous hydrated microspheres are washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (2) drying the carbonaceous hydrated microspheres in an oven at 100 ℃ overnight, then placing the dried carbonaceous hydrated microspheres in a high-temperature tube furnace, carrying out programmed heating to 800 ℃ for high-temperature pyrolysis for 2h at a heating rate of 5 ℃/min under the nitrogen atmosphere, and cooling to room temperature to obtain the No. 2 carbon molecular sieve material.
(3) The pore diameter of the obtained 2# carbon molecular sieve is mainly concentrated on
Wherein
The narrow aperture ratio of the range is more than 59 percent, the device has the screening separation effect of only adsorbing propylene and not adsorbing propane, and the adsorption quantity of the device to the propylene reaches 2.22mmol/g at normal temperature and normal pressure.
Example 3
(1) 0.02633mL of concentrated hydrochloric acid (mass fraction: 36.5%) was added to 100mL of distilled water to prepare an aqueous solution having a hydrogen ion concentration of 0.0032mol/L, and 10g of fructose was added thereto and sufficiently stirred for 30min to disperse the mixture uniformly. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 16 hours at the constant temperature of 190 ℃, and then the obtained carbonaceous hydrated microspheres are washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (2) drying the carbonaceous hydrated microspheres in an oven at 100 ℃ overnight, then placing the dried carbonaceous hydrated microspheres in a high-temperature tube furnace, carrying out programmed heating to 800 ℃ for high-temperature pyrolysis for 2h at a heating rate of 5 ℃/min under the nitrogen atmosphere, and cooling to room temperature to obtain the No. 3 carbon molecular sieve material.
(3) The aperture of the obtained 3# carbon molecular sieve is mainly concentrated on
Wherein
The narrow pore diameter ratio of the range is more than 53%, and the adsorption capacity to propylene is 2.13mmol/g and the adsorption capacity to propane is less than 0.95mmol/g at normal temperature and normal pressure.
Example 4
(1) 0.0054mL of concentrated sulfuric acid (98% by mass) was added to 100mL of distilled water to prepare an aqueous solution having a hydrogen ion concentration of 0.001mol/L, and 10g of fructose was added thereto and sufficiently stirred for 30min to disperse the solution uniformly. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 16 hours at the constant temperature of 190 ℃, and then the obtained carbonaceous hydrated microspheres are washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (2) drying the carbonaceous hydrated microspheres in an oven at 100 ℃ overnight, then placing the dried carbonaceous hydrated microspheres in a high-temperature tube furnace, carrying out programmed heating to 800 ℃ for pyrolysis for 2 hours at a heating rate of 5 ℃/min under the nitrogen atmosphere, and cooling to room temperature to obtain the No. 4 carbon molecular sieve material.
(3) The aperture of the obtained 4# carbon molecular sieve is mainly concentrated on
Wherein
The narrow pore diameter ratio of the range is more than 50 percent, the molecular size of the catalyst is larger than that of propylene propane, the adsorption capacity to propylene at normal temperature and normal pressure reaches 2.53mmol/g, and the adsorption to propaneThe attached amount reaches 1.98 mmol/g.
Example 5
(1) 100mL of distilled water having a hydrogen ion concentration of about 0mol/L was added with 10g of fructose and the mixture was sufficiently stirred for 30min to disperse the fructose uniformly. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 16 hours at the constant temperature of 190 ℃, and then the obtained carbonaceous hydrated microspheres are washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (2) drying the carbonaceous hydrated microspheres in an oven at 100 ℃ overnight, then placing the dried carbonaceous hydrated microspheres in a high-temperature tube furnace, carrying out programmed heating to 800 ℃ for pyrolysis for 2 hours at a heating rate of 5 ℃/min under the nitrogen atmosphere, and cooling to room temperature to obtain the No. 5 carbon molecular sieve material.
(3) The aperture of the obtained 5# carbon molecular sieve is mainly concentrated on
Wherein
The narrow pore diameter ratio of the range is more than 51 percent, the narrow pore diameter ratio is larger than the molecular size of propylene propane, the adsorption capacity to propylene at normal temperature and normal pressure reaches 2.58mmol/g, and the adsorption capacity to propane is 2.02 mmol/g.
Example 6
(1) 8.33mL of concentrated hydrochloric acid (mass fraction: 36.5%) was added to 91.7mL of distilled water to prepare an aqueous solution having a hydrogen ion concentration of 1mol/L, and 10g of chitosan was added thereto and sufficiently stirred for 30min to disperse the mixture uniformly. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 20 hours at a constant temperature of 180 ℃, and then the obtained carbonaceous hydrated microspheres are washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (2) drying the carbonaceous hydrated microspheres in an oven at 100 ℃ overnight, then placing the dried carbonaceous hydrated microspheres in a high-temperature tube furnace, carrying out programmed heating to 700 ℃ at a heating rate of 5 ℃/min under the nitrogen atmosphere, carrying out high-temperature pyrolysis for 3h, and cooling to room temperature to obtain the No. 6 carbon molecular sieve material.
(3) The aperture of the obtained 6# carbon molecular sieve is mainly concentrated on
Wherein
The narrow pore diameter ratio of the range is more than 54 percent, the sieve separation effect of only adsorbing propylene and not adsorbing propane is realized, the adsorption capacity to the propylene is 2.58mmol/g and the adsorption capacity to the propane is less than 0.20mmol/g under normal temperature and pressure, and the adsorption capacity is higher than that of the nitrogen-free polyhydroxylated saccharide compound.
Example 7
(1) 0.054mL of concentrated sulfuric acid (mass fraction: 98%) is added into 99.9mL of distilled water to prepare an aqueous solution with hydrogen ion concentration of 0.01mol/L, 10g of galactose is added, and the mixture is fully stirred for 30min to be uniformly dispersed. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 16 hours at a constant temperature of 180 ℃, and then the obtained carbonaceous hydrated microspheres are washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (2) drying the carbonaceous hydrated microspheres in an oven at 100 ℃ overnight, then placing the dried carbonaceous hydrated microspheres in a high-temperature tube furnace, carrying out programmed heating to 900 ℃ for pyrolysis for 1h at a heating rate of 5 ℃/min under the nitrogen atmosphere, and cooling to room temperature to obtain the No. 7 carbon molecular sieve material.
(3) The aperture of the obtained 7# carbon molecular sieve is mainly concentrated on
Wherein
The narrow aperture ratio of the range is more than 50 percent, the device has the screening separation effect of only adsorbing propylene and not adsorbing propane, and the adsorption capacity to the propylene reaches 2.31mmol/g at normal temperature and normal pressure.
Example 8
(1) 0.0833mL of concentrated hydrochloric acid (mass fraction: 36.5%) was added to 99.9mL of distilled water to prepare an aqueous solution having a hydrogen ion concentration of 0.01mol/L, and 5g of fructose and 5g of sucrose were added thereto and sufficiently stirred for 30min to disperse them uniformly. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 16 hours at the constant temperature of 190 ℃, and then the obtained carbonaceous hydrated microspheres are washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (2) drying the carbonaceous hydrated microspheres in an oven at 100 ℃ overnight, then placing the dried carbonaceous hydrated microspheres in a high-temperature tube furnace, carrying out programmed heating to 800 ℃ for pyrolysis for 2 hours at a heating rate of 5 ℃/min under the nitrogen atmosphere, and cooling to room temperature to obtain the No. 8 carbon molecular sieve material.
(3) The aperture of the obtained 8# carbon molecular sieve is mainly concentrated on
Wherein
The narrow aperture ratio of the range is over 53 percent, the device has the screening separation effect of only adsorbing propylene and not adsorbing propane, and the adsorption capacity to the propylene reaches 2.16mmol/g at normal temperature and normal pressure.
Example 9
(1) 16.66mL of concentrated hydrochloric acid (mass fraction: 36.5%) was added to 83.34mL of distilled water to prepare an aqueous solution having a hydrogen ion concentration of 2mol/L, and 7g of maltose and 3g of lactose were added thereto and sufficiently stirred for 30min to disperse them uniformly. Then, the solution is subjected to hydrothermal self-assembly reaction in a closed environment of a reaction kettle, the reaction is carried out for 20 hours at a constant temperature of 180 ℃, and then the obtained hydrated carbon is washed by 500mL of distilled water to remove unreacted intermediate products.
(2) And (3) drying the hydrated carbon in an oven at 100 ℃ overnight, then placing the dried hydrated carbon in a high-temperature tube furnace, carrying out programmed heating to 700 ℃ at a heating rate of 5 ℃/min under the nitrogen atmosphere, carrying out high-temperature pyrolysis for 3h, and cooling to room temperature to obtain the No. 9 carbon molecular sieve material.
(3) The obtained No. 9 carbon molecular sieve material mainly focuses on the pore diameter
Wherein
The narrow pore diameter ratio of the range exceeds 50%, and propylene alone is adsorbed, and almost no propylene is adsorbedThe screening separation effect of the attached propane is that the adsorption capacity to the propylene is 1.89mmol/g and the adsorption capacity to the propane is less than 0.23mmol/g under normal temperature and normal pressure.
The method firstly adopts an ASAP2020 analyzer of American Micro company to characterize the pore structure of the material. The invention respectively uses carbon dioxide and nitrogen as molecular probes, and obtains the temperature less than or equal to 273K by testing the adsorption and desorption isotherm of carbon molecular sieve material to carbon dioxide
Pore size distribution of (2). Then utilizing the adsorption and desorption isotherm of the carbon molecular sieve material to nitrogen under 77K to obtain the micropores of the material
Mesopores
And large pores
So as to synthesize the overall aperture structure parameters of the material.
FIG. 1 is a plot of the pore size distribution of the carbon molecular sieve material of example 2, wherein (a) is the pore size obtained with carbon dioxide as the probe, and (b) is the pore size distribution of the micropore-mesopore-macropore obtained with nitrogen as the probe. The carbon molecular sieve prepared by the invention has the aperture mainly concentrated on the aperture analyzed from the figure 1
Wherein
The narrow pore diameter ratio of the range exceeds 59%, and the medium pore and the large pore are not contained, so that the high-quality glass has extremely high quality.
Fig. 2 is a diagram showing a pore size distribution of a carbon molecular sieve material obtained according to a conventional "carbonization-activation-carbon deposition" method, wherein (a) the diagram shows a pore size distribution of carbon dioxide as a molecular probe, and (b) the diagram shows a pore size distribution of micro-meso-macro pores as a molecular probe. From the analysis in the figure, the traditional carbon molecular sieve mainly has micropores, but still has wider pore size distribution in the micropore range, the pore size of the micropores is not easy to control in the specification, and the synthesis process is complex.
FIG. 3 is an adsorption isotherm of the carbon molecular sieve material of example 1 for ethylene ethane at 298K, with the pore size being primarily concentrated
In the narrow pore diameter range, the pore diameter of the micropores can be well controlled to be mainly between that of ethylene (kinetic diameter:
) And ethane (kinetic diameter:
) The molecular size is between the molecular size, so that the high-selectivity separation of ethylene and ethane bi-components can be realized, and the adsorption capacity of the ethylene reaches 1.80mmol/g under 1 bar.
FIG. 4 is an adsorption isotherm of a conventional carbon molecular sieve material for ethylene and ethane at 298K, which can simultaneously adsorb two components of ethylene and ethane due to its wide pore size distribution in the micropore range, and the adsorption capacity for ethylene reaches 2.31mmol/g at 1bar and the adsorption capacity for ethane reaches 1.97 mmol/g.
FIG. 5 is an adsorption isotherm of the carbon molecular sieve material of example 2 for propene propane at 298K, due to its predominantly concentrated pore size
In the narrow pore diameter range, the pore diameter of the micropores can be well controlled to be between the pore diameter of propylene (kinetic diameter:
) And propane (kinetic diameter:
) Between molecular sizes, and therefore can be performedThe propylene-propane bi-component is separated by sieving, and the adsorption capacity of the propylene reaches 2.22mmol/g under 1 bar.
FIG. 6 is an adsorption isotherm of a conventional carbon molecular sieve material for propylene propane at 298K, which can simultaneously adsorb two components of propylene propane due to its wide pore size distribution in the micropore range, and the adsorption capacity for propylene reaches 2.59mmol/g at 1bar and the adsorption capacity for propane reaches 1.82 mmol/g.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.