A lignin-rich biomass-derived carbon material, a preparation method thereof, and a hydrogen isotope separation method

Abstract

This invention discloses a lignin-rich biomass-derived char material, its preparation method, and a hydrogen isotope separation method, belonging to the field of porous materials technology. The char material has an ultra-micropore ratio ≥70%, a porosity of 0.35-0.45, and surface properties: sp 3 / sp 2 The carbon hybridization ratio is 0.4–0.8, and the ultrapores are composed of an interwoven layer of cellulose-derived carbon and lignin-derived fragments. This was achieved through a synergistic regulation strategy of pre-oxidation-pyrolysis of lignin-rich biomass. The char material achieved D2 selective enrichment, with an adsorption capacity of 4.76 mmol g. ‑1 In the 77K dynamic breakthrough experiment, the breakthrough time of D2 was 30% later than that of H2, and the dynamic selectivity reached 1.4. The carbon material exhibited stable performance after acid washing and showed no significant degradation during recycling, providing a low-cost, scalable solution for hydrogen isotope separation. Furthermore, the carbon material is suitable for deuterium fuel purification, isotope tracing, and low-temperature adsorption separation processes in the nuclear energy field, featuring readily available and inexpensive raw materials, simple processes, and high separation efficiency.

Description

Technical Field

[0001] This invention belongs to the field of porous carbon materials technology, and relates to a lignin-rich biomass-derived carbon material, its preparation method and hydrogen isotope separation method. Specifically, it relates to the preparation of a hybrid nanoporous carbon material with quantum sieving characteristics using lignin-rich biomass to achieve efficient separation of hydrogen isotopes. Background Technology

[0002] Separation of hydrogen isotopes (D2 / H2) is a core requirement in fields such as nuclear energy development, isotope tracing, and neutron scattering. Deuterium has a much smaller neutron scattering cross section than hydrogen, therefore it is widely used for labeling molecules and tracing reaction pathways. For example, deuteration labeling technology tracks enzyme catalytic pathways through isotope kinetics. Deuterated samples can reduce background noise in neutron scattering experiments by 90%, providing a crucial means for resolving polymer structures and protein dynamics. However, due to the similar molecular sizes and extremely small boiling point differences between hydrogen and deuterium, separation is extremely difficult. Currently, the mainstream separation method is cryogenic distillation. Separation is achieved based on boiling point differences, but the separation coefficient is low, requiring multi-stage series equipment, resulting in distillation columns reaching tens of meters in height, high investment costs, and enormous 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 tunable 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 temperatures close to liquid nitrogen (77K) and above. Furthermore, their testing conditions are based on static measurements, making it difficult to reflect industrial application conditions. The FJI-Y11 MOF developed by the Fujian Institute of Research on the Structure of Matter achieved good selectivity in D2 / H2 dynamic breakthrough experiments, but MOF materials are complex to synthesize, costly, and have significant room for improvement in stability, hindering large-scale application. Currently, most performance tests of hydrogen isotope separation adsorbents are based on static conditions. While this provides new perspectives and ideas, dynamic testing can provide a basis for industrial hydrogen isotope separation. However, dynamic testing is often constrained by the contradiction between selectivity and adsorption capacity, and is also limited for D2 / H2 applications. 2 / Adsorbents for H2 separation are expensive, so there is a need to develop high-efficiency and low-cost adsorbents. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a lignin-rich biomass-derived char material, its preparation method, and a hydrogen isotope separation method. Using the lignin-rich biomass-derived char material as the core, the pore structure is controlled through a pre-oxidation-pyrolysis process, combined with kinetic quantum sieving (KQS) to achieve efficient hydrogen isotope separation. During the pyrolysis of lignin- and cellulose-rich biomass, hybrid nanopores with quantum sieving properties are formed, consisting of an interwoven cellulose-derived carbon layer and lignin-derived fragments. These nanopores include ultramicropores (pore size <0.7 nm), accounting for ≥70%. The hybrid nanopores and defect sites can differentiate the D2 / H2 diffusion rate, while avoiding the use of precious metals and significantly reducing costs. Experiments show that the lignin-rich biomass-derived char material achieves a dynamic penetration selectivity of 1.41 and a kinetic selectivity of 1.8 at 77 K, while also exhibiting high capacity (D2 adsorption capacity 4.76 mmol g). -1 Its stability (no performance degradation after pickling) provides new ideas for industrial applications.

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

[0005] A lignin-rich biomass-derived char material, with an ultramicropore content (<0.7nm) ≥70%, a porosity of 0.35-0.45, and surface properties: sp 3 / sp 2 The carbon hybridization ratio is 0.4-0.8; the ultrapores are formed by the interweaving of cellulose-derived carbon layers and lignin-derived fragments.

[0006] The present invention also provides a method for preparing the carbon material, comprising the following steps:

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

[0008] S2 carbonization treatment: The pre-oxidized intermediate is pyrolyzed at 500-900℃ under inert gas protection to obtain the carbon material.

[0009] Lignin-rich biomass was pre-oxidized in air at 150-450℃ to directionally break lignin ether bonds, generating small molecular fragments. Then, it was pyrolyzed in an inert atmosphere at 500-900℃. Utilizing the difference in pyrolysis behavior between cellulose and lignin, a hybrid nanoporous structure with quantum sieving properties was formed, consisting of an interwoven cellulose-derived carbon layer and lignin-derived fragments. This resulted in a structure dominated by ultramicropores (<0.7nm) with a surface rich in sp... 3 Carbon hybridization defects, carbon materials with controllable pore size.

[0010] The biomass raw material is one or more of apricot shells, walnut shells, or bamboo fiber.

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

[0012] The pyrolysis temperature is 500-800℃.

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

[0014] The present invention also provides a method for hydrogen isotope separation, which uses the carbon material as an adsorbent to adsorb and separate a D2 / H2 mixed gas, thereby achieving efficient separation of hydrogen isotopes.

[0015] The adsorption temperature is 40-100K 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 gas mixture is 5-15%.

[0018] The adsorbent is activated before adsorption.

[0019] The activation treatment is performed under vacuum conditions of 20-100℃ and absolute pressure ≤0.05 bar for 0.5-5 hours.

[0020] The regeneration method of the carbon material includes regenerating it by purging with inert gas for 0.5-5 hours at atmospheric pressure (1 bar) at 20-100℃ for 0.5-5 hours after adsorption, or regenerating it under vacuum conditions at absolute pressure ≤0.05 bar at 20-100℃ for 0.5-5 hours, which can completely restore the separation performance.

[0021] Compared with existing technologies, the advantages of this invention are as follows:

[0022] 1. The lignin-rich biomass-derived char material of this invention has an ultramicropore content (<0.7nm) of ≥70%, a porosity of 0.35-0.45, and surface properties: sp 3 / sp 2 The carbon hybridization ratio is 0.4–0.8. In hydrogen isotope separation, it exhibits excellent separation performance through quantum sieving effect. As an adsorbent, it achieves selective enrichment of D2 with an adsorption capacity of 4.76 mmol g. -1 And achieved 4.37 min g -1 The separation time was short, and the separation selectivity reached 1.41. Furthermore, it exhibits a short co-adsorption time, enabling rapid recycling. In addition, the resulting carbon material is suitable for deuterium fuel purification, isotope tracing, and low-temperature adsorption separation processes in the nuclear energy field, featuring readily available and inexpensive raw materials, simple processes, and high separation efficiency.

[0023] 2. The char material was obtained through a pre-oxidation-pyrolysis lignin-rich biomass synergistic regulation strategy. High lignin content (≥35wt%) in biochar is a prerequisite for ensuring the number of micropores and high defect density. Pre-oxidation regulates the size of lignin fragments and the structure of the cellulose-derived carbon layer, improving pore connectivity and porosity. Combined with low-temperature carbonization, the high defect density sp generated by lignin enrichment can be preserved. 3 / sp 2 Hybridization ratio. Remaining competitive when considering key scalability factors, biochar has low production costs, structural stability, maintains stability after acid leaching tests, and is easy to mass-produce with good industrial prospects. Attached Figure Description

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

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

[0026] Figure 3 This is a grayscale distribution diagram of the lignin-rich biomass-derived char material in Example 7.

[0027] Figure 4 The percentage of micropores in the lignin-rich biomass-derived char material in Example 7.

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

[0029] Figure 6 The D2 / H2 adsorption kinetics curve of the lignin-rich biomass-derived char material in Example 7 is shown.

[0030] Figure 7 This is a graph showing the separation performance of hydrogen isotopes by the lignin-rich biomass-derived carbon material in Example 7.

[0031] Figure 8 The diagram shows the separation performance of hydrogen isotopes of the lignin-rich biomass-derived char material in Example 7 and the acid-washed material in Example 7.

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

[0033] Figure 10 The diagram shows the hydrogen isotope separation performance of the carbon materials in Comparative Examples 1 and 2.

[0034] Figure 11 The percentage of micropores in the carbon materials of Comparative Examples 1 and 2 is shown.

[0035] Figure 12 The XPS C1s spectrum of the carbon material in Comparative Example 1 is shown. Specific Implementation

[0036] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments. They do not constitute a limitation on the content and scope of protection of the present invention. Any modifications or refinements made to the subject matter and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

[0037] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

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

[0039] The apricot shells were washed with deionized water, dried at 90℃ for 12 hours, and crushed into 40-60 mesh particles. The biomass particles were pre-oxidized in a muffle furnace with an air heating rate of 1.5℃ / min, and then transferred to a tube furnace for carbonization under an argon atmosphere with a carbonization heating rate of 3℃ / min, yielding lignin-rich biomass-derived char material. The preparation parameters for each example are shown in Table 1.

[0040] ② Lignin-rich biomass-derived char materials are used for the adsorption and separation of hydrogen isotopes.

[0041] The adsorption separation process flow is as follows: Figure 1 As shown, mass spectrometry was used as the detector. Lignin-rich biomass-derived char material was packed into a copper fixed-bed adsorption column with an inner diameter of 4 mm and a length of 70 mm. This adsorption column was fixed above the cold head of a He compressor refrigerator, and a test temperature of 77 K was achieved by controlling the refrigerator (testing was performed using the system disclosed in application number 2024110965372).

[0042] The testing steps are as follows:

[0043] Before the S1 test, the lignin-rich biomass-derived char material was treated at 100℃ and absolute pressure <0.05mbar for 2 hours to remove water and other impurity gases that may be adsorbed on the surface and in the pores of the char material.

[0044] S2 The adsorbent is packed into the adsorption column and continuously purged with Ne for more than 60 minutes to prevent nitrogen in the air from being adsorbed into the material at low temperature during packing.

[0045] S3 lowered the adsorption column temperature to 77K and continuously introduced a mixed gas of H2:D2:Ne 1:1:8 at a rate of 10 mL / min into the adsorption column. A gas chromatograph-mass spectrometer was connected to the end of the adsorption column. The composition of the gas after passing through the adsorption column was detected. A gas concentration reaching 0.5% of the saturation concentration was considered breakthrough. The test results are shown in Table 1.

[0046] ③ The purging process of lignin-rich biomass-derived charcoal materials enhances desorption performance.

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

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

[0049] In-situ heating of the adsorption column, while maintaining the carrier gas Ne (20 mL / min) carrying the desorbed D2, with a heating rate of 3 °C / min, can achieve complete desorption of D2 by heating to 140 K.

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

[0051]

[0052]

[0053] Specifically, Figure 2 The carbon dioxide adsorption isotherm of the lignin-rich biomass-derived carbon material adsorbent in Example 7 is shown. This material is a microporous material, in which cellulose-derived carbon layers and lignin-derived fragments intertwine in nanopores, as shown in Example 7. Figure 3 (Based on XRM quantitative analysis using grayscale threshold segmentation, where grayscale values ​​correspond to the densities of different phases in the material), as shown, it reveals two phases with different grayscale values. The cumulative pore volume of the micropores in the CO2 test is 0.16 cm³. 3 g -1 The porosity is 40.4%, such as Figure 4 As shown, its ultramicropores (<0.7nm) account for 72%, such as Figure 5 As shown, its surface structure information sp 3 / sp 2 =0.48. Figure 6 It shows 77K, which passes through a single component D. 2 / The kinetic selectivity of H2 adsorption on biochar over time reached 1.8. Its performance in hydrogen isotope penetration rate measurement is as follows: Figure 7The D2 / H2 selectivity reached 1.41, and the separation time at 77K was 4.31 min, demonstrating excellent separation performance for hydrogen isotopes. Furthermore, the performance did not degrade after acid washing. Figure 8 As shown. By measuring its adsorption isotherm at 77 K, the adsorption capacity of D2 reached 4.76 mmol g. -1 ,like Figure 9 As shown.

[0054] Comparative Example 1

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

[0056] Comparative Example 2

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

[0058] The carbon materials obtained in Comparative Examples 1 and 2 were subjected to dynamic gas penetration testing, using the same method as described in ② above. Figure 10 As shown in Table 2, although Comparative Example 1 had a longer adsorption time, its separation performance decreased significantly, lasting only 1.18 min g. -1 The separation time of Comparative Example 2 was significantly reduced, and its adsorption capacity decreased significantly, with almost no separation time. Figure 11 The micropore size distribution of Comparative Examples 1 and 2 was measured using CO2 adsorption isotherms. Comparative Example 1 had abundant micropores, but only 50% were ultramicropores (<0.7 nm), and a large number of larger micropores. In contrast, Comparative Example 2 had 65% ultramicropores, a smaller micropore capacity, and a cumulative pore volume of only 0.14 cm³ during CO2 testing. 3 g -1 This results in insufficient adsorption capacity. Figure 5 and Figure 12 XPS C1s spectra of Example 7 and Comparative Example 1, respectively, with Example 7 showing a higher sp. 3 / sp 2 ratio.

[0059] Table 2 Comparative Examples 1 and 2: Carbon Material Preparation Methods, Hydrogen Isotope Analysis, and Separation Performance

[0060]

Claims

1. A method for the preparation of a lignin-rich biomass- derived carbon material, characterized by: Micropore content ≥ 70%, porosity 0.35-0.45, surface properties: sp 3 / sp 2 The carbon hybridization ratio is 0.4-0.8; the ultrapores are composed of cellulose-derived carbon layers and lignin-derived fragments interwoven; the preparation method includes the following steps: S1 Pre-oxidation treatment: The lignin-rich biomass raw material is heat-treated in an oxygen atmosphere at 150-450 ℃ to obtain a pre-oxidized intermediate; the lignin content of the biomass raw material is ≥ 35 wt%; the pre-oxidation rate is 1-3 ℃ / min; S2 Carbonization treatment: The pre-oxidized intermediate is pyrolyzed at 500-900 °C under inert gas protection to obtain the carbon material.

2. The method for producing a carbon material according to claim 1, characterized by: The biomass raw material is one or more of apricot shells, walnut shells, or bamboo fiber.

3. The method for preparing carbon materials as described in claim 1, characterized in that: The heat treatment time is 1-5 hours; and / or, The pyrolysis time is 1-3 h.

4. A method for separating hydrogen isotopes, characterized in that: The carbon material obtained by the preparation method described in claim 1 is used as an adsorbent to adsorb and separate D2 / H2 mixed gas.

5. The method of hydrogen isotope separation as claimed in claim 4, characterized in that: The adsorption temperature is 40-100 K and the adsorption pressure is 0.1-1 bar.

6. The method of hydrogen isotope separation as claimed in claim 4, characterized in that: The total gas flow rate is 5-15 mL / min.

7. The method of hydrogen isotope separation as claimed in claim 4, characterized in that: The volume percentage of H2 or D2 in the gas mixture is 5-15%.

8. The method for separating hydrogen isotopes as described in claim 4, characterized in that: The adsorbent is activated before adsorption.

9. A method for regenerating carbon material obtained by the preparation method of claim 1, characterized in that: This includes regeneration by purging with inert gas for 0.5-5 h at ambient pressure and 20-100 °C after adsorption, or regeneration under vacuum conditions with an absolute pressure ≤0.05 bar at 20-100 °C for 0.5-5 h.

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