Preparation method of biomass-based carbon molecular sieve and application of biomass-based carbon molecular sieve in separation of refinery dry gas

Abstract

The invention provides a preparation method of a biomass-based carbon molecular sieve and application of the biomass-based carbon molecular sieve in separation of refinery dry gas. The preparation method comprises the following steps: mixing and dipping biomass and an organic solution, drying and carbonizing to obtain a carbon molecular sieve; the solute of the organic solution comprises one or more of a benzene compound, a phenol compound and an aldehyde compound, and the obtained carbon molecular sieve realizes aperture adjustment under a sub-nanometer scale and realizes different screening effects of mixed gas of hydrogen, methane, ethylene and ethane; wherein ethylene or ethylene and ethane mixed gas in the low-concentration refinery dry gas can be desorbed and purified to 80% or above in one step. According to the method, biomass with wide sources is selected as a precursor carbon source, a high-pollution adhesive and an activating agent are not used, one-time pore creation and pore size fine adjustment are achieved, and the economic cost and environmental pollution of material preparation are reduced. The carbon molecular sieve obtained by the method has good industrial application potential in the field of refinery dry gas separation and purification, especially ethylene recovery.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of carbon molecular sieves, and relates to a preparation method of biomass-based carbon molecular sieves and their application in separating refinery dry gas. Background Art

[0002] Refinery dry gas is a non-condensable gas containing hydrogen, methane, ethane, ethylene, etc. generated during the secondary processing of crude oil. Hydrogen, ethane, ethylene, etc. in the dry gas are all very important resources. With the rapid development of the refining industry, a large amount of dry gas is produced as a by-product during the processing, and the ethylene potential content exceeds one million tons. However, due to the complex composition of refinery dry gas, its separation and purification are difficult and energy-consuming. Therefore, dry gas is usually used as a gas fuel or even directly vented into the flare and burned, resulting in great waste of resources. Recycling and utilizing various components in dry gas is of great significance for enterprises to reduce costs and increase efficiency and environmental protection.

[0003] At present, there are many technologies for separating and recovering hydrogen and hydrocarbon resources from dry gas, mainly including cryogenic separation, absorption separation, adsorption separation, etc. Among them, physical adsorption separation technology has the advantages of reusable adsorbents, simple device and process flow, and lower energy consumption compared with other technologies, making it an ideal separation method. However, to obtain high-purity product gas, the adsorbent needs to have sub-nanometer-level adjustable micropores and a suitable chemical surface, which increases the preparation difficulty of the adsorbent. Carbon molecular sieves have the advantages of wide sources, high specific surface area, adjustable pore structure and surface chemistry, and excellent water vapor stability, and are often used for gas adsorption separation in different scenarios.

[0004] The conventional preparation method of carbon molecular sieves is complex, usually including activation pore formation and carbon deposition steps (CN103349973A). The cumbersome preparation process not only increases the cost of the adsorbent, but also the highly polluting active pore-forming agents (such as potassium hydroxide, zinc chloride, etc.) used will inevitably cause a large amount of environmental pollution. In addition, to meet the actual application needs, the powder adsorbent needs to be granulated to reduce the pressure drop of the adsorption bed layer. During this process, the use of binders will block the pore structure of the adsorbent and thus reduce the separation performance. For the complex gas components (hydrogen, methane, ethylene, ethane, etc.) in refinery dry gas, the existing carbon molecular sieves are difficult to achieve precise pore structure regulation and cannot achieve the separation and purification of specific gases.

[0005] In summary, there is still a lack of high-performance adsorbents in the field of refinery dry gas separation and purification. Carbon molecular sieves have great application potential due to their advantages of low cost and high customization. Developing granular carbon molecular sieves with a simple preparation method and adjustable pore structure to achieve efficient separation and purification among hydrogen, methane, ethylene, and ethane will open up a new technical route for the recovery and utilization of refinery dry gas resources, improve resource utilization rate and reduce environmental pollution. Summary of the Invention

[0006] To solve the problems of poor separation effect of existing adsorbents for multi-component mixed gas, complex preparation and large pollution, etc., the present invention uses biomass with a wide source as the precursor carbon source, without using binders and highly polluting activators, realizing one-time pore preparation and size fine-tuning, and reducing the economic cost and environmental pollution of material preparation. The finally prepared carbon molecular sieve can achieve different screening effects for the mixed gas of hydrogen, methane, ethylene and ethane by adjusting the pore structure, such as purifying ethylene or purifying the mixed gas of ethylene and ethane, etc.

[0007] To achieve the above invention purpose, the technical scheme adopted by the present invention is as follows:

[0008] A preparation method of a biomass-based carbon molecular sieve, comprising mixing and impregnating biomass with an organic solution, and obtaining the carbon molecular sieve through drying and carbonization; the solute of the organic solution includes one or more of benzene compounds, phenol compounds and aldehyde compounds.

[0009] The biomass includes one or more of coconut shell, macadamia nut shell, walnut shell, olive shell and apricot shell.

[0010] Among the solutes of the organic solution, the benzene compounds include one or more of benzene, toluene, ethylbenzene and xylene; the phenol compounds include one or more of phenol, o-cresol, m-cresol, p-cresol, catechol, resorcinol and hydroquinone; the aldehyde compounds include one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and isobutyraldehyde.

[0011] The solvent of the organic solution includes one or more of water, methanol and ethanol.

[0012] The concentration of the organic solution is 0.1 - 5 mol / L.

[0013] The mass ratio of the biomass to the organic solution for impregnation is biomass:organic solution = (1 - 5):(1 - 20).

[0014] The impregnation temperature is 10 - 100 °C, and the impregnation time is 1 - 40 h.

[0015] The drying temperature is 0 - 150 °C, and the drying time is 2 - 96 h.

[0016] The carbonization temperature is 600 - 1000 °C.

[0017] The carbonization process is to rise the temperature from room temperature to 50 - 150 °C at a rate of 0.5 - 5 °C / min and stay for 0.5 - 4 h, and then rise the temperature to 600 - 1000 °C at a rate of 1 - 10 °C / min and stay for 0.5 - 4 h. -1 and stay for 0.5 - 4 h, and then rise the temperature to 600 - 1000 °C at a rate of 1 - 10 °C / min -1 and stay for 0.5 - 4 h.

[0018] It also includes crushing pretreatment and / or cleaning pretreatment of biomass. The particle size of the crushed biomass is 10-100 mesh. The cleaning pretreatment includes soaking the biomass in a cleaning solvent for cleaning, repeating this process twice or more, and then drying; the cleaning agent includes one or several of water, methanol, and ethanol.

[0019] The micropore aperture of the obtained carbon molecular sieve is concentrated in the range of 0.30-1 nm.

[0020] The present invention also provides an application of the carbon molecular sieve obtained by the above method in separating refinery dry gas.

[0021] The adsorption temperature is 0-50 °C, and the adsorption pressure is 1-8 bar.

[0022] The adsorption separation adopts a fixed-bed process, and the carbon molecular sieve is subjected to activation treatment before adsorption.

[0023] The volume ratio of gas components treated by the carbon molecular sieve is hydrogen:methane:ethylene:ethane = (40-60):(20-40):(1-20):(1-20). Preferably, the volume ratio of gas components is hydrogen:methane:ethylene:ethane = (45-55):(25-35):(5-15):(5-15).

[0024] The activation treatment is carried out under a vacuum condition with an absolute pressure ≤ 0.05 bar at 20-100 °C for 0.5-5 h.

[0025] The regeneration method of the carbon molecular sieve includes, after adsorption is completed, purging and regenerating with an inert gas for 0.5-5 h under normal pressure (1 bar) at 20-100 °C or regenerating under a vacuum condition with an absolute pressure ≤ 0.05 bar at 20-100 °C for 0.5-5 h, and the separation performance can be completely restored.

[0026] The inert gas includes Ar or N2.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. By controlling conditions such as impregnation time, temperature, solute type, and carbonization temperature in the preparation process of the carbon molecular sieve prepared by the present invention, the structure of the ultramicropores of the final carbon molecular sieve is changed, so that it has slit-shaped micropores mainly in the range of 0.30-1 nm, realizing pore size adjustment at the sub-nanometer scale. By using carbon molecular sieves with different pore structures, different separation effects for refinery dry gas can be achieved. For example, ethylene or a mixture of ethylene and ethane can be purified to more than 80% in one step.

[0029] 2. During the preparation process of the carbon molecular sieve of the present invention, there is no need for activation pore formation and carbon deposition steps, avoiding environmental pollution caused by active pore-forming agents such as potassium hydroxide and organic deposits such as benzene during use.

[0030] 3. The carbon molecular sieve of the present invention can be completely regenerated by purging with an inert gas (such as Ar or N2) at normal pressure (1 bar) for 0.5 - 5 h or under a vacuum condition with an absolute pressure ≤ 0.05 bar at 20 - 100 °C for 0.5 - 5 h. At the same time, particulate adsorbents of different sizes in the range of 10 - 100 mesh can be obtained, reducing the bed pressure drop in the fixed adsorption bed. Description of the Drawings

[0031] Figure 1 It is the breakthrough curve of the simulated refinery dry gas separation and recovery of the carbon molecular sieve in Example 1.

[0032] Figure 2 It is the ethylene static adsorption isotherm of the carbon molecular sieve in Example 1 at 298 K.

[0033] Figure 3 It is the ethane static adsorption isotherm of the carbon molecular sieve in Example 1 at 298 K.

[0034] Figure 4 It is the breakthrough curve of the simulated refinery dry gas separation and recovery of the carbon molecular sieve in Example 11.

[0035] Figure 5 It is the micropore size distribution of the carbon molecular sieve in Example 6 and the carbon molecular sieve in Example 11.

[0036] Figure 6 It is the breakthrough curve of the simulated refinery dry gas separation and recovery of the carbon molecular sieve in Comparative Example 1.

[0037] Figure 7 It is the micropore size distribution diagram of the carbon molecular sieve in Example 1 and the carbon molecular sieve in Comparative Example 1. Specific Embodiments

[0038] The present invention is described in detail below through some representative examples. It should be understood that some of the following examples are only for exemplary display and should not be construed as a limitation on the protection of the invention. All technical solutions implemented based on the content described in the present invention should be covered within the protection scope of the present invention.

[0039] ① Preparation of biomass-based carbon molecular sieve for efficient separation of refinery dry gas

[0040] After crushing the biomass to 4 - 10 mesh, the biomass was soaked in water for cleaning according to the volume ratio of biomass: water = 1:5. This process was repeated twice and then dried at 100 °C for 24 h. Subsequently, impregnation treatment was carried out in an organic solution with each solute concentration of 1 mol / L and water as the solvent, and the mass ratio of biomass to solution was biomass: organic solution = 1:10. Finally, it was dried at 50 °C and carbonized to obtain carbon molecular sieve. The preparation conditions and pore size data of each example are shown in Table 1, and carbon molecular sieves with different micropore sizes were obtained.

[0041] ② Carbon molecular sieve separation performance test

[0042] Penetration test: The carbon molecular sieve activated under vacuum conditions at 200 °C and an absolute pressure lower than 0.01 bar for 5 h was filled in the adsorption column. A gas mixture with a volume fraction of hydrogen: methane: ethylene: ethane = 5:3:1:1 was passed into the adsorption column at a rate of 10 mL / min. The size of the adsorption column was 100 mm * 80 mm, and a gas chromatograph - mass spectrometer was connected to the end of the adsorption column. The gas composition passing through the adsorption column was detected, and when the gas concentration reached 0.5% of the saturation concentration, it was regarded as penetration. Subsequently, the separation performance of the adsorbent was evaluated and the gas adsorption capacity of each gas was calculated. After one round of gas separation, the carbon molecular sieve can recover its separation performance by purging and regenerating with Ar at a flow rate of 40 ml / min for 1 h under atmospheric pressure (1 bar) at 100 °C or by desorbing and regenerating under vacuum conditions with an absolute pressure of 0.05 bar at 50 °C for 0.5 h. The specific test results are as Figure 1 、 Figure 4 and Table 2 show that carbon molecular sieves with different micropore sizes achieved different separation effects for refinery dry gas.

[0043] ③ Adsorbent static isotherm and pore size distribution test

[0044] Weigh 50 ± 2 mg of carbon molecular sieve and load it into the sample tube of the physical adsorption instrument VSTAR, and activate and degas it at 200 °C for 5 h. The sample tube was placed in a constant temperature water bath or a heat - insulating jacket, and high - purity ethane or ethylene was filled into the sample tube to measure the gas adsorption capacity at different equilibrium pressures to obtain the adsorption isotherm.

[0045] Table 1 Preparation methods and properties of biomass - based carbon molecular sieves

[0046]

[0047] Table 2 Dynamic gas adsorption performance of biomass - based carbon molecular sieves

[0048]

[0049] The prepared carbon molecular sieves of the examples were characterized by multi - component dynamic gas penetration test and static adsorption after activation: Figure 1For the multi-component dynamic gas penetration test of the carbon molecular sieve in Example 1, the mixed gas atmosphere is a mixture of hydrogen: methane: ethylene: ethane = 5:3:1:1, and the gas velocity is 10 mL / min. From Figure 1 It can be seen that at the initial stage of the test, hydrogen, methane, and ethane penetrated rapidly and reached equilibrium. Ethylene penetrated at 6.2 min and reached adsorption equilibrium at 21.8 min. Example 1 showed good screening effect for the mixed gas and achieved selective adsorption and recovery of ethylene. Table 3 shows the desorbed gas components of the carbon molecular sieve in Example 1 after the above penetration test, where the proportion of hydrogen is 1.6%, the proportion of methane is 9.5%, the proportion of ethane is 4.8%, and the proportion of ethylene is 84.1%. Further, a static adsorption test of ethylene and ethane gases was carried out on Example 1. Figure 2 Figure is the ethylene static adsorption isotherm of Example 1 at 298K. It can be seen from the figure that this carbon molecular sieve showed a relatively high ethylene adsorption capacity at low pressure, and a large hysteresis appeared in the desorption curve, proving the strong adsorption force of the carbon molecular sieve on ethylene. Figure 3 Figure is the ethane static adsorption isotherm of Example 1 at 298K. It can be seen from the figure that this carbon molecular sieve had a relatively low adsorption capacity for ethane at low pressure. Comprehensive Figure 2 and Figure 3 It can be seen that Example 1 can achieve the directional recovery and purification of ethylene under low ethylene partial pressure. Figure 4 For the multi-component dynamic gas penetration test of the carbon molecular sieve in Example 11, the mixed gas atmosphere is a mixture of hydrogen: methane: ethylene: ethane = 5:3:1:1, and the gas velocity is 10 mL / min. From Figure 4 It can be seen that at the initial stage of the test, hydrogen and methane penetrated rapidly and reached equilibrium, while ethylene and ethane penetrated at 20.3 min. Example 11 showed good screening effect for the mixed gas and achieved selective adsorption and recovery of ethylene and ethane. Table 4 shows the desorbed gas components of the carbon molecular sieve in Example 11 after the above penetration test, where the proportion of hydrogen is 0.5%, the proportion of methane is 18.5%, the proportion of ethane is 40.5%, and the proportion of ethylene is 40.5%. Comprehensive Figure 4 and Table 4, it can be seen that Example 11 can achieve the directional recovery and purification of the ethylene-ethane mixed gas under low ethane and ethylene partial pressures. Figure 5 Figure is the micropore size distribution of Example 6 and Example 11. It can be seen from the figure that after being treated with different organic solutions and impregnation conditions during the preparation process, the micropores of Example 6 were rich and concentrated at 0.70 nm, while the micropores of Example 11 were concentrated at 0.80 nm.

[0050] Table 3 Desorbed gas components of the carbon molecular sieve in Example 1 after the above penetration test

[0051] Hydrogen Methane Ethylene Ethane <![CDATA[Desorption amount / mmol g -1 > 0.01 0.06 0.53 0.03 Proportion of desorbed gas / % 1.6 9.5 84.1 4.8

[0052] Table 4 Composition of the desorbed gas of the carbon molecular sieve in Example 11 after the above breakthrough test

[0053] Hydrogen Methane Ethylene Ethane <![CDATA[Desorption amount / mmol g -1 > 0.01 0.35 0.77 0.77 Proportion of desorbed gas / % 0.5 18.5 40.5 40.5

[0054] Comparative Example 1

[0055] The preparation method was similar to that of Example 1, but did not include the organic liquid impregnation step. The specific steps were as follows: after washing the biomass, it was crushed to 4-10 mesh, and the biomass was soaked in water for cleaning according to the volume ratio of biomass: water = 1:5. This process was repeated twice and then dried at 50 °C. After carbonization at 900 °C, the carbon molecular sieve of Comparative Example 1 was obtained. The multi-component dynamic gas breakthrough test and static adsorption characterization were carried out on the prepared carbon molecular sieve of Comparative Example 1 after degassing activation: Figure 6 For the multi-component dynamic gas breakthrough test of the carbon molecular sieve of Comparative Example 1, the mixed gas atmosphere was a mixture of hydrogen: methane: ethylene: ethane = 5:3:1:1, and the gas velocity was 10 mL / min. It can be seen from Figure 6 that in the initial stage of the test, the four gases of hydrogen, methane, ethane and ethylene all penetrated rapidly and reached equilibrium, proving that Comparative Example 1 has no screening ability for this mixed gas and cannot achieve selective ethylene recovery and purification. Figure 7 For the micropore size distribution of Example 1 and Comparative Example 1, Example 1 has abundant micropores and is concentrated at 0.45 nm, while Comparative Example 1 has few micropores and its micropore size is widely distributed at 0.3-0.8 nm. Therefore, it cannot play the role of gas screening.

Claims

1. A method for preparing a biomass-based carbon molecular sieve, characterized in that: The method comprises the steps of mixing and impregnating biomass with an organic solution, drying and carbonizing the solution to obtain a carbon molecular sieve; the solute of the organic solution comprises one or more of benzene compounds, phenol compounds and aldehyde compounds.

2. The method for preparing a biomass-based carbon molecular sieve according to claim 1, characterized in that: The biomass comprises one or more of coconut shells, macadamia shells, walnut shells, olive shells and apricot shells.

3. The method for preparing a biomass-based carbon molecular sieve according to claim 1, characterized in that: The benzene compounds include one or more of benzene, toluene, ethylbenzene and xylene; the phenol compounds include one or more of phenol, o-cresol, m-cresol, p-cresol, catechol, resorcinol and hydroquinone; the aldehyde compounds include one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and isobutyraldehyde; and / or, The solvent of the organic solution includes one or more of water, methanol and ethanol; and / or, The concentration of the organic solution is 0.1-5 mol / L.

4. The method for preparing a biomass-based carbon molecular sieve according to claim 1, characterized in that: The mass ratio of the biomass to the organic solution is (1-5):(1-20).

5. The method for preparing a biomass-based carbon molecular sieve according to claim 1, characterized in that: The immersion temperature is 10-100° C. and the immersion time is 1-40 hours; and / or, The carbonization temperature is 600-1000°C; and / or, The method also includes subjecting the biomass to crushing pretreatment and / or cleaning pretreatment.

6. Use of the carbon molecular sieve obtained by the method of claim 1 in separating refinery dry gas.

7. Use of the carbon molecular sieve according to claim 6 in separation of refinery dry gas, characterized in that: The adsorption temperature is 0-50°C and the adsorption pressure is 1-8 bar; and / or, Using fixed bed technology, the carbon molecular sieve is activated before adsorption.

8. Use of the carbon molecular sieve according to claim 6 in separation of refinery dry gas, characterized in that: The volume ratio of the gas components treated by the carbon molecular sieve is hydrogen: methane: ethylene: ethane = (40-60): (20-40): (1-20): (1-20).

9. Use of the carbon molecular sieve according to claim 8 in separation of refinery dry gas, characterized in that: The volume ratio of the gas components treated by the carbon molecular sieve is hydrogen: methane: ethylene: ethane = (45-55): (25-35): (5-15): (5-15).

10. A method for regenerating the carbon molecular sieve obtained by the method of claim 1, comprising: after the adsorption is completed, regenerating with inert gas under normal pressure conditions at 20-100°C for 0.5-5h or regenerating under vacuum conditions at 20-100°C with an absolute pressure of ≤0.05 bar for 0.5-5h.

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