Lignin-rich biomass derived carbon material, preparation method thereof and hydrogen isotope separation method

Abstract

The invention discloses a lignin-rich biomass derived carbon material, a preparation method thereof and a hydrogen isotope separation method, and belongs to the technical field of porous materials. The ratio of ultramicropores of the carbon material is larger than or equal to 70%, the porosity is 0.35-0.45, the surface characteristic is that the sp3 / sp2 carbon hybridization ratio is 0.4-0.8, and the ultramicropores are formed by interweaving cellulose derived carbon layers and lignin derived fragments. The method is obtained through a synergistic regulation strategy of pre-oxidation-pyrolysis of biomass rich in lignin content. The carbon material realizes the selective enrichment of D2, the adsorption capacity reaches 4.76 mmol g <-1 >, in a 77K dynamic penetration experiment, the penetration time of D2 is delayed by 30% compared with that of H2, and the dynamic selectivity reaches 1.4. The carbon material is stable in performance after being pickled and has no obvious attenuation after being recycled, and a low-cost and large-scale solution is provided for hydrogen isotope separation. In addition, the carbon material is suitable for deuterium fuel purification, isotopic tracing and low-temperature adsorption separation processes in the nuclear energy field, and has the characteristics of cheap and easily available raw materials, simple process, high separation efficiency and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of porous carbon materials, and relates to a lignin-rich biomass-derived carbon material, a preparation method thereof, and a hydrogen isotope separation method. Specifically, it relates to the preparation of a carbon material with hybrid nanopores having quantum sieving characteristics from lignin-rich biomass to achieve efficient separation of hydrogen isotopes. Background Art

[0002] The separation of hydrogen isotopes (D2 / H2) is a core requirement in fields such as nuclear energy development, isotope tracing, and neutron scattering. The neutron scattering cross-section of deuterium is much smaller than that of hydrogen, so deuterium is widely used to label molecules and trace reaction paths. For example, deuterium labeling technology traces the enzyme-catalyzed path through isotope kinetic effects, and deuterated samples can reduce the background noise of neutron scattering experiments by 90%, providing a key means for analyzing polymer structures and protein dynamics. However, due to the similar molecular sizes and extremely small boiling point differences between hydrogen and deuterium molecules, the separation is extremely difficult. Currently, the mainstream separation method is cryogenic distillation. Separation is achieved based on the boiling point difference, but the separation coefficient is low, and multi-stage series equipment is required, resulting in a distillation tower height of dozens of meters, high investment costs, and huge energy consumption to maintain the temperature of liquid hydrogen. In recent years, porous materials such as MOFs have become a research hotspot due to their high specific surface area and adjustable pore size. For example, Cu-based MOF materials (such as Cu(I)Cu(II)-BTC) improve selectivity through the synergistic effect of chemical affinity and quantum sieving, but their performance significantly decreases at and above a temperature close to liquid nitrogen temperature (77K), and their test conditions are based on static tests, making it difficult to reflect industrial application conditions. FJI-Y11 MOF developed by Fujian Institute of Research on the Structure of Matter has good selectivity in the D2 / H2 dynamic breakthrough experiment, but MOF materials are complex to synthesize, have high costs, and have great room for improvement in stability, making it difficult to be applied on a large scale. Currently, most performance tests of hydrogen isotope separation adsorbents are based on static conditions. Although they can provide us with new perspectives and ideas, the test performance under dynamic conditions can provide a basis for the industrial separation of hydrogen isotopes. At the same time, dynamic tests are often restricted by the contradiction between selectivity and adsorption capacity, and the adsorbents used for D 2 / H2 separation are relatively expensive, and adsorbents with high efficiency and low cost need to be developed. Summary of the Invention

[0003] To solve the above technical problems, the present invention proposes a lignin-rich biomass-derived carbon material, its preparation method, and a hydrogen isotope separation method. With the lignin-rich biomass-derived carbon material as the core, the pore structure is regulated through a pre-oxidation pyrolysis process, and efficient hydrogen isotope separation is achieved by combining the kinetic quantum sieving (KQS) effect. During the pyrolysis of biomass rich in lignin and cellulose, a hybrid nanopore with quantum sieving characteristics formed by the interweaving of cellulose-derived carbon layers and lignin-derived fragments is formed, including ultramicropores (pore diameter < 0.7 nm), accounting for ≥ 70%, and the hybrid nanopores and defect sites can differentiate the diffusion rates of D2 / H2, while avoiding the use of precious metals and significantly reducing costs. Experiments show that the lignin-rich biomass-derived carbon material has a dynamic breakthrough selectivity of 1.41 at 77 K and a kinetic selectivity of 1.8, and has both high capacity (D2 adsorption capacity of 4.76 mmol g -1 ), and stability (the performance does not decay after pickling), providing new ideas for industrial applications.

[0004] The technical solution of the present invention is as follows:

[0005] A lignin-rich biomass-derived carbon material, the ultramicropores (< 0.7 nm) account for ≥ 70%, the porosity is 0.35 - 0.45, and the surface characteristics: sp 3 / sp 2 The carbon hybridization ratio is 0.4 - 0.8; the ultramicropores are formed by the interweaving of cellulose-derived carbon layers and lignin-derived fragments.

[0006] The present invention also provides a preparation method of the carbon material, including the following steps:

[0007] S1 Pre-oxidation treatment: Heat-treat the lignin-rich biomass raw material in an oxygen-containing atmosphere at 150 - 450 °C to obtain a pre-oxidized intermediate; the lignin content in the biomass raw material is ≥ 35 wt%; the pre-oxidation rate is 1 - 3 °C / min;

[0008] S2 Carbonization treatment: Pyrolyze the pre-oxidized intermediate under inert gas protection at 500 - 900 °C to obtain the carbon material.

[0009] Perform pre-oxidation treatment on lignin-rich biomass in an air atmosphere at 150 - 450 °C to directionally break lignin ether bonds and generate small molecule fragments; pyrolyze at 500 - 900 °C in an inert atmosphere, and use the difference in the pyrolysis behavior of cellulose and lignin to form a hybrid nanopore structure with quantum sieving characteristics formed by the interweaving of cellulose-derived carbon layers and lignin-derived fragments, thereby obtaining a carbon material mainly composed of ultramicropores (< 0.7 nm), with a surface rich in sp 3 Carbon hybridization defects and controllable pore size.

[0010] The biomass raw material is one or several of almond shells, walnut shells, or bamboo fibers.

[0011] The heat treatment time is 1 - 5 h.

[0012] The pyrolysis temperature is 500 - 800 °C.

[0013] The pyrolysis time is 1 - 3 h.

[0014] The present invention also provides a method for hydrogen isotope separation. Using the carbon material as an adsorbent, adsorbing and separating the D2 / H2 mixed gas to achieve efficient separation of hydrogen isotopes.

[0015] The adsorption temperature is 40 - 100 K, and the adsorption pressure is 0.1 - 1 bar.

[0016] The total gas flow rate is 5 - 15 mL / min.

[0017] The volume percentage of H2 or D2 in the mixed gas is 5 - 15%.

[0018] The adsorbent is activated before adsorption.

[0019] The activation treatment is to treat under vacuum conditions with an absolute pressure ≤ 0.05 bar at 20 - 100 °C for 0.5 - 5 h.

[0020] The regeneration method of the carbon material includes, after adsorption is completed, purging and regenerating with an inert gas under normal pressure (1 bar) at 20 - 100 °C for 0.5 - 5 h or regenerating under vacuum conditions with an absolute pressure ≤ 0.05 bar at 20 - 100 °C for 0.5 - 5 h, and the separation performance can be completely restored.

[0021] Compared with the existing technology, the beneficial effects of the present invention are as follows:

[0022] 1. The lignin-rich biomass-derived carbon material of the present invention has a specific surface area of ultra-micropores (< 0.7 nm) ≥ 70%, a porosity of 0.35 - 0.45, and surface characteristics: sp 3 / sp 2 The carbon hybridization ratio is 0.4 - 0.8. In hydrogen isotope separation, through the quantum sieving effect, it shows good separation performance. As its adsorption material, D2 selective enrichment is achieved, and the adsorption capacity reaches 4.76 mmol g -1 and a separation time of 4.37 min g -1 is achieved, and the separation selectivity reaches 1.41. And it has a short co-adsorption time and can achieve rapid cycling. In addition, the obtained carbon material is applicable to deuterium fuel purification, isotope tracing, and low-temperature adsorption separation processes in the nuclear energy field, and has the characteristics of cheap and easily available raw materials, simple process, and high separation efficiency.

[0023] 2. The carbon material is obtained by a co - regulation strategy of pre - oxidation - pyrolysis of lignin - rich biomass. Biomass carbon with a high lignin content (≥35 wt%) is a prerequisite for ensuring the number of ultra - micropores and a high defect density. By pre - oxidizing to regulate the lignin fragment size and the cellulose - derived carbon layer structure, the connectivity and porosity of the pores are improved. Combining low - temperature carbonization can retain the high defect density sp 3 / sp 2 hybrid ratio. It is still competitive when considering key scalability factors. The production cost of biomass carbon is low, the structure is stable, it remains stable after acid leaching tests, and it is easy to produce on a large scale, showing good industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow chart of the adsorption separation process.

[0025] Figure 2 It is the CO2 adsorption isotherm of the lignin - rich biomass - derived carbon material in Example 7.

[0026] Figure 3 It is the gray - scale value distribution map of the lignin - rich biomass - derived carbon material in Example 7.

[0027] Figure 4 It is the proportion of ultra - micropores of the lignin - rich biomass - derived carbon material in Example 7.

[0028] Figure 5 It is the XPS C1s spectrum of the lignin - rich biomass - derived carbon material in Example 7.

[0029] Figure 6 It is the D2 / H2 adsorption kinetic curve of the lignin - rich biomass - derived carbon material in Example 7.

[0030] Figure 7 It is the separation performance diagram of the lignin - rich biomass - derived carbon material in Example 7 for hydrogen isotopes.

[0031] Figure 8 It is the separation performance diagram of the lignin - rich biomass - derived carbon material in Example 7 and Example 7 after acid washing for hydrogen isotopes.

[0032] Figure 9 It is the D2 adsorption isotherm of the lignin - rich biomass - derived carbon material in Example 7.

[0033] Figure 10 It is the separation performance diagram of the hydrogen isotopes of the carbon materials in Comparative Examples 1 and 2.

[0034] Figure 11 It is the proportion of ultra - micropores of the carbon materials in Comparative Examples 1 and 2.

[0035] Figure 12 XPS C1s spectrum of the carbon material in Comparative Example 1 Specific embodiments

[0036] The following embodiments are provided to better further understand the present invention. They are not limited to the best mode of implementation, and do not constitute a limitation to the content and protection scope of the present invention. Any meaningless changes or polishing made on the theme design concept and spirit of the present invention, as long as the technical problems solved are still the same as those of the present invention, shall be included within the protection scope of the present invention.

[0037] For those embodiments where specific experimental steps or conditions are not specified, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For reagents or instruments whose manufacturers are not specified, they are all conventional reagent products that can be obtained through commercial purchase.

[0038] ① Synthesis of lignin-rich biomass-derived carbon materials with mixed nanopores

[0039] Wash the apricot shells with deionized water, dry them at 90 °C for 12 h, and crush them into particles with a size of 40 - 60 mesh. Air-preoxidize the biomass particles in a muffle furnace with a heating rate of 1.5 °C / min, and then transfer them to a tube furnace for carbonization under an argon atmosphere with a carbonization heating rate of 3 °C / min to obtain lignin-rich biomass-derived carbon materials. The preparation parameters for each embodiment are shown in Table 1.

[0040] ② Use of lignin-rich biomass-derived carbon materials for the adsorption and separation of hydrogen isotopes

[0041] The adsorption and separation process flow is as Figure 1 shown, with a mass spectrometer as the detector. Pack the lignin-rich biomass-derived carbon materials into a copper fixed-bed adsorption column with an inner diameter of 4 mm and a length of 70 mm. This adsorption column is fixed above the cold head of a He compression refrigerator, and the test temperature of 77 K is achieved by controlling the refrigerator (tested using the system disclosed in Application No. 2024110965372).

[0042] The test steps are as follows:

[0043] S1 Before the test, treat the lignin-rich biomass-derived carbon materials at 100 °C and an absolute pressure of <0.05 mbar for 2 h to remove possible adsorbed water and other impurity gases on the surface and in the pores of the carbon materials;

[0044] S2 Load the adsorbent into the adsorption column and continuously purge with Ne for more than 60 min to avoid the nitrogen in the air during loading from being adsorbed into the material at low temperature;

[0045] S3 reduces the temperature of the adsorption column to 77 K, and a mixed gas of H2:D2:Ne at a ratio of 1:1:8 and a total flow rate of 10 mL / min is continuously introduced into the adsorption column. A gas chromatograph-mass spectrometer is connected to the tail end of the adsorption column. The gas composition passing through the adsorption column is detected, and when the gas concentration reaches 0.5% of the saturation concentration, it is regarded as breakthrough. The test results are shown in Table 1.

[0046] ③Enhanced desorption performance of lignin-rich biomass-derived carbon materials by purge process

[0047] After the adsorbent adsorbs the saturated gas, Ne (20 mL / min) is used as the purge gas to blow the adsorbent and the residual H2 / D2 in the pipeline for 1 h. This process desorbs the adsorbate with weak adsorption on the surface of the adsorbent.

[0048] ④Programmed temperature desorption and enrichment of D2 of lignin-rich biomass-derived carbon materials

[0049] The adsorption column is heated in situ, and the carrier gas Ne (20 mL / min) is maintained to carry the desorbed D2. The heating rate is maintained at 3 °C / min, and complete desorption of D2 can be achieved when the temperature is raised to 140 K.

[0050] Table 1 Preparation methods and hydrogen isotope separation performance of lignin-rich biomass-derived carbon materials in examples

[0051]

[0052]

[0053] Specifically, Figure 2 Figure [X] shows the carbon dioxide adsorption isotherm of the lignin-rich biomass-derived carbon material adsorbent in Example 7. It belongs to a microporous material, and the cellulose-derived carbon layer and lignin-derived fragment intertwined nanopores in it are as Figure 3 (Based on XRM quantitative analysis by gray threshold segmentation, the gray value corresponds to the density of different phases in the material) shown. It shows two different gray value phases. The cumulative pore volume of micropores for CO2 testing is 0.16 cm 3 g -1 , and the porosity is 40.4%, as Figure 4 shown. The proportion of ultra-micropores (<0.7 nm) is 72%, as Figure 5 shown. The surface structure information sp 3 / sp 2 = 0.48. Figure 6 Figure [X] shows the kinetic selectivity of the single-component D 2 / H2 adsorbed on the biomass carbon at 77 K reaching 1.8 based on the curve of the adsorption amount changing with time. Its hydrogen isotope breakthrough velocity performance is as Figure 7, the D2 / H2 selectivity reached 1.41, and the separation time at 77K reached 4.31 min, showing excellent separation performance for hydrogen isotopes, and the performance did not decay after pickling, as Figure 8 shown. By measuring its adsorption isotherm at 77K, the D2 adsorption capacity reached 4.76 mmol g -1 , as Figure 9 shown.

[0054] Comparative Example 1

[0055] The preparation method was the same as that of Example 7, but biomass rice husk with a lignin content of 18% wt was selected, and the preparation parameters are shown in Table 1.

[0056] Comparative Example 2

[0057] The preparation method was the same as that of Example 7, but the pre-oxidation heating rate was 0.1 °C / min, and the preparation parameters are shown in Table 1.

[0058] The carbon materials obtained in Comparative Examples 1 and 2 were subjected to a dynamic gas penetration test, and the test method was the same as ② above. As Figure 10 and Table 2 show, although Comparative Example 1 had a longer adsorption time, its separation performance decreased significantly, with only 1.18 min g -1 of separation time. In Comparative Example 2, its adsorption capacity decreased significantly, and it had almost no separation time. Figure 11 shows the micropore size distribution of Comparative Examples 1 and 2 by CO2 adsorption isotherm test. In Comparative Example 1, the micropores were abundant but the number of ultramicropores (<0.7 nm) was small, only 50%, and there were more larger micropores. In Comparative Example 2, the proportion of ultramicropores was 65%, the micropore volume was small, and the cumulative pore volume of CO2 test was only 0.14 cm 3 g -1 , resulting in insufficient adsorption capacity. Figure 5 and Figure 12 are the XPS C1s spectra of Example 7 and Comparative Example 1 respectively, in which Example 7 shows a higher sp 3 / sp 2 ratio.

[0059] Table 2 Preparation methods of carbon materials in Comparative Examples 1 and 2 and hydrogen isotope and separation performance

[0060]

Claims

1. A lignin-rich biomass-derived carbon material, characterized in that: The proportion of ultra-micropores is ≥70%, the porosity is 0.35 - 0.45, surface characteristics: sp 3 / sp 2 The carbon hybridization ratio is 0.4 - 0.8; the ultra-micropores are formed by the interweaving of cellulose-derived carbon layers and lignin-derived fragments.

2. The preparation method of the carbon material according to claim 1, characterized in that: It includes the following steps: S1 Pre-oxidation treatment: Heat-treat the lignin-rich biomass raw material in an oxygen atmosphere at 150 - 450 °C to obtain a pre-oxidation intermediate; the lignin content in the biomass raw material is ≥ 35 wt%; the pre-oxidation rate is 1 - 3 °C / min; S2 Carbonization treatment: Pyrolyze the pre-oxidation intermediate under inert gas protection at 500 - 900 °C to obtain the carbon material.

3. The preparation method of the carbon material according to claim 2, wherein: The biomass raw material is one or several of apricot shells, walnut shells or bamboo fibers.

4. The preparation method of the carbon material according to claim 2, wherein: The heat-treatment time is 1 - 5 h; and / or, The pyrolysis time is 1 - 3 h.

5. A method for separating hydrogen isotopes, characterized in that: Using the carbon material described in claim 1 as an adsorbent, adsorb and separate the D2 / H2 mixed gas.

6. The method for separating hydrogen isotopes according to claim 5, characterized in that: The adsorption temperature is 40 - 100 K, and the adsorption pressure is 0.1 - 1 bar.

7. The method for separating hydrogen isotopes according to claim 5, characterized in that: The total gas flow rate is 5 - 15 mL / min.

8. The method for separating hydrogen isotopes according to claim 5, characterized in that: The volume percentage of H2 or D2 in the mixed gas is 5 - 15%.

9. The method for separating hydrogen isotopes according to claim 5, wherein: The adsorbent is activated before adsorption.

10. A regeneration method for the carbon material according to claim 1, characterized in that: It includes that after adsorption is completed, purge and regenerate with an inert gas at normal pressure of 20 - 100 °C for 0.5 - 5 h or regenerate under a vacuum condition of 20 - 100 °C with an absolute pressure ≤ 0.05 bar for 0.5 - 5 h.

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