A method for the staged removal of lignin metal ions by hydrogen peroxide in conjunction with sodium ethylenediaminetetraacetate.

Abstract

The application provides a method for removing lignin metal ions in stages by hydrogen peroxide and sodium ethylenediaminetetraacetate, and relates to the technical field of new energy materials and high-value utilization of biomass. According to the method, active oxygen species (·OH) are selectively generated through controllable oxidation, lignin-metal bonds are pre-dissociated, and the metal ions are deeply removed by using the oxidation-chelation synergistic effect of hydrogen peroxide and sodium ethylenediaminetetraacetate, and low-metal-ion-content and high-purity lignin products are obtained through gradient acid precipitation.

Description

Technical Field

[0001] This invention relates to the field of new energy materials and high-value utilization of biomass, specifically to a method for the staged removal of lignin metal ions by hydrogen peroxide in conjunction with sodium ethylenediaminetetraacetate. Background Technology

[0002] Lignin is the second most abundant renewable organic resource in nature after cellulose, accounting for 15%-30% of plant biomass. As a natural high-molecular polymer, lignin has an aromatic structure, abundant functional groups (such as phenolic hydroxyl, methoxy, and carboxyl groups), as well as good thermal stability and chemical modifiability, making it promising for a wide range of applications in new energy, materials science, and chemical engineering.

[0003] However, industrial lignin (such as alkali lignin and sulfite lignin) usually contains a large number of metal ions (Fe, Mn, Ca, Mg, etc.), which come from the raw plant itself or the pulping process (such as the alkali process / sulfite process), which seriously limits the high-value utilization of lignin.

[0004] Traditional alkaline lignin removal processes generally suffer from two major defects: (1) Incomplete removal of metal ions: transition metal ions (Fe2+) 3+ Mn 2+ Cu 2+ (2) Poor product stability: Residual oxidants (such as H2O2) and residual metal ions catalyze the degradation of lignin, resulting in darker product color and decreased molecular weight. The existing technology adopts a one-step oxidation-chelation method. Due to the mismatch between oxidation activity and chelation timing, the metal ion removal rate is less than 60%, and the acid precipitation process is prone to metal ion re-adsorption.

[0005] To overcome the above limitations, this invention proposes a method for the staged removal of lignin metal ions by hydrogen peroxide in conjunction with sodium ethylenediaminetetraacetate. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the staged removal of metal ions from lignin using hydrogen peroxide and sodium ethylenediaminetetraacetate. This method utilizes the synergistic effect of oxidation-chelation between hydrogen peroxide and sodium ethylenediaminetetraacetate to deeply remove metal ions and obtains a lignin product with low metal ion content and high purity through gradient acid precipitation.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0008] A method for the staged removal of lignin metal ions by hydrogen peroxide in conjunction with sodium ethylenediaminetetraacetate, the method comprising the following steps.

[0009] (a) Controlled oxidation activation: Add hydrogen peroxide solution to lignin alkaline solution, the amount of hydrogen peroxide solution added being 5-10% of the volume of lignin alkaline solution; then, under an inert atmosphere, raise the temperature from room temperature (25°C) to 85-105°C at a rate of 2-4°C / min and hold for 20-40 min.

[0010] (b) EDTA-Na synergistic chelation: After completing step (a), maintain the temperature and add 2-4 wt% sodium ethylenediaminetetraacetate solution to the reaction system. Stir the reaction at 500-1200 rpm for 0.5-2 h. After the reaction is completed, cool, centrifuge, filter in stages, and take the filtrate for later use.

[0011] (c) Residual oxidant removal: Add ascorbic acid solution to the filtrate, the amount of ascorbic acid solution added being 1-3% of the filtrate volume; stir for 15-25 min under an inert atmosphere.

[0012] (d) Gradient acid precipitation purification: After stirring, take the liquid component and add acid at a rate of 10-30 mL / min to adjust the pH until the lignin no longer precipitates. Centrifuge to separate the solid lignin and wash until neutral. Then, vacuum dry.

[0013] In this invention, further, the concentration of the hydrogen peroxide solution in step (a) is 1-3 wt%.

[0014] In this invention, the lignin alkaline solution in step (a) is derived from industrial alkali lignin, sulfite lignin, biorefining residue lignin, or other lignin-rich biomass raw materials. The extraction reagent includes sodium hydroxide, potassium hydroxide, or ammonia water, with a concentration of 5-15 wt%. The inert atmosphere is a nitrogen or argon atmosphere.

[0015] In this invention, further, the sodium ethylenediaminetetraacetate in step (b) is selected from disodium ethylenediaminetetraacetate or tetrasodium ethylenediaminetetraacetate.

[0016] In this invention, further, step (b) of graded filtration specifically involves sequentially using 0.45 μm and 0.22 μm nylon filter membranes for filtration.

[0017] In this invention, further, the concentration of the ascorbic acid solution in step (c) is 5-10 wt%.

[0018] In this invention, further, in step (c), the inert atmosphere is nitrogen or argon, and the stirring speed is 500-700 rpm.

[0019] In this invention, the acid used in step (d) to adjust the pH is 0.1-1 mol / L hydrochloric acid, sulfuric acid, or phosphoric acid.

[0020] In this invention, further, step (d) vacuum drying involves placing the washed lignin into a vacuum drying oven and drying it at 40°C for 12-24 hours.

[0021] In summary, due to the adoption of the above technical solutions, the present invention has at least the following beneficial effects.

[0022] This invention achieves the following multiple breakthroughs by using hydrogen peroxide in conjunction with sodium ethylenediaminetetraacetate to remove metal ions from lignin in stages.

[0023] (1) Disruptive Breakthrough in Traditional Process Bottlenecks: This application pioneers a three-level synergistic mechanism of "controllable oxidation-targeted chelation-passivation purification," achieving for the first time the efficient stripping of the most difficult-to-dissociate metal ions (such as calcium ions and iron-manganese complexes) in lignin. It breaks through the inherent limitations of traditional one-step or disordered mixing processes, completely solving the industry problem of incomplete dissociation of metal-lignin stable complexes. In addition, it achieves dynamic blocking of the chain reaction of metal re-adsorption and oxidative degradation. Firstly, it terminates residual oxygen with ascorbic acid, eliminating the secondary binding channel of metal ions during acid precipitation. Secondly, it uses an inert atmosphere to synergistically gradient acid precipitation, inhibiting the oxidative condensation of phenolic hydroxyl groups and maintaining the integrity of the aromatic ring structure of lignin.

[0024] (2) Non-obvious synergistic effect: This application reveals the irreversible time sequence logic of oxidative activation → chelation capture → passivation protection. First, hydrogen peroxide is used to pre-oxidize and selectively break the lignin-metal coordination bond to open the ion release channel. Then, sodium EDTA is used to precisely chelate the free metal during the release window to avoid competitive consumption in the simultaneous treatment. Finally, ascorbic acid is used to simultaneously achieve residual oxygen removal and saturation of metal chelation sites, blocking the side reactions of the post-treatment.

[0025] (3) Pioneering expansion of downstream high-value applications: The lignin prepared in this application is used in electrode preparation. This derived carbon electrode breaks through the internal resistance-capacity-lifetime triangle constraint of energy storage devices, giving supercapacitors military-grade cycle stability and rate performance. Moreover, the method of this application is applicable to three types of industrial lignin waste (alkali process / sulfite process / biorefining residue), promoting the transformation of biorefining plants from "processing cost center" to "material value center", providing core raw material support for the billion-dollar bio-based new materials market.

[0026] In summary, the method of this application breaks the lignin-metal bond through the controlled oxidation of hydrogen peroxide and the synergistic effect of sodium EDTA, allowing sodium EDTA to chelate the dissociated metal ions, thus avoiding the competitive failure of oxidation and chelation in the traditional one-step method. Combined with ascorbic acid to eliminate residual H2O2, it blocks the metal ion-catalyzed degradation of lignin. At the same time, the acid precipitation purification method inhibits the re-adsorption of metal ions to the lignin surface during the acid precipitation process, significantly improving the demetallization efficiency and ensuring product stability. Finally, a lignin product with low metal ion content and high purity is obtained, providing a new path for the high-value utilization of biomass, which is of great significance. Detailed Implementation

[0027] The following embodiments can help those skilled in the art to more fully understand the present invention, but should not be construed as limiting the present invention in any way.

[0028] Example 1:

[0029] This application provides a method for removing lignin metal ions by using hydrogen peroxide in conjunction with sodium ethylenediaminetetraacetate. The specific preparation method includes the following steps.

[0030] a. Controlled oxidation of lignin: Industrial alkali lignin is dissolved in 5% NaOH alkaline solution, 5% H2O2 solution (volume ratio 2%) is added, nitrogen gas is introduced and the mixture is placed in a reaction vessel, and the temperature is increased from room temperature (25℃) to 90℃ at 2℃ / min and held for 40min.

[0031] b. Synergistic removal of metal ions by sodium ethylenediaminetetraacetate: After the incubation period, maintain the reaction temperature at 90℃, add 2.5% (w / v, mass-to-liquid ratio) disodium ethylenediaminetetraacetate, stir at 700 rpm, and incubate for 1.5 h. After the incubation period, cool to room temperature, centrifuge, and filter the supernatant through 0.45 μm and 0.22 μm nylon membranes in stages, retaining the filtrate.

[0032] c. Post-treatment purification: Add 1% (v / v, volume ratio) ascorbic acid solution (5wt% ascorbic acid concentration) to the filtrate and stir at 500 rpm for 20 min at room temperature and under inert gas protection. After stirring, add acid precipitation solution (0.5 mol / L hydrochloric acid) to the liquid component at 30 mL / min to adjust the pH until lignin no longer precipitates. Then centrifuge at 5000 rpm for 10 min to separate the solid lignin. Then wash the lignin with deionized water through multiple centrifugations (5000 rpm, 10 min) until neutral. Transfer the obtained lignin to a vacuum drying oven and dry at 40℃ for 24 h.

[0033] Example 2:

[0034] This application provides a method for removing lignin metal ions by using hydrogen peroxide in conjunction with sodium ethylenediaminetetraacetate. The specific preparation method includes the following steps.

[0035] a. Controlled oxidation of lignin: Sulfite lignin is dissolved in 10% KOH alkaline solution, 10% H2O2 solution (volume ratio 1%) is added, argon gas is introduced and the mixture is placed in a reaction vessel, heated to 100℃ at 3℃ / min and kept at that temperature for 1 h.

[0036] b. Synergistic removal of metal ions by sodium ethylenediaminetetraacetate: After the incubation period, maintain the reaction temperature at 90℃, add 2.5% (w / v, mass-to-liquid ratio) sodium ethylenediaminetetraacetate, stir at 700 rpm, and incubate for 1.5 h. After the incubation period, cool to room temperature, centrifuge, and filter the supernatant through 0.45 μm and 0.22 μm nylon membranes in stages, retaining the filtrate.

[0037] c. Post-treatment purification: Add 3% (v / v, volume ratio) ascorbic acid solution (7wt% ascorbic acid concentration) to the filtrate and stir at 600 rpm for 25 min at room temperature and under inert gas protection. After stirring, add acid precipitation solution (0.8 mol / L sulfuric acid) to the liquid component at 15 mL / min to adjust the pH until lignin no longer precipitates. Centrifuge at 5000 rpm for 10 min to separate solid lignin. Wash the lignin with deionized water until neutral by multiple centrifugations (5000 rpm, 10 min). Transfer the obtained lignin to a vacuum drying oven and dry at 40℃ for 18 h.

[0038] Example 3:

[0039] This application provides a method for removing lignin metal ions by using hydrogen peroxide in conjunction with sodium ethylenediaminetetraacetate. The specific preparation method includes the following steps.

[0040] a. Controlled oxidation of lignin: The lignin residue after ethanol fermentation of biomass raw materials is dissolved in 15% NaOH alkaline solution, 5% H2O2 solution with a volume ratio of 1% is added, nitrogen gas is introduced and the mixture is placed in a reaction vessel, the temperature is increased to 80℃ at 2℃ / min and kept at this temperature for 1 h.

[0041] b. Synergistic removal of metal ions by sodium ethylenediaminetetraacetate: After the incubation period, maintain the reaction temperature at 80℃, add 4% (w / v, mass-to-liquid ratio) sodium ethylenediaminetetraacetate, stir at 1000 rpm, and incubate for 2 h. After the incubation period, cool to room temperature, centrifuge, and filter the supernatant through 0.45μm and 0.22μm nylon membranes for fractional filtration, retaining the filtrate.

[0042] c. Post-treatment purification: Add 1% (v / v, volume ratio) ascorbic acid solution (5wt% ascorbic acid concentration) to the filtrate and stir at 500 rpm for 15 min at room temperature and under inert gas protection. After stirring, add acid precipitation solution (0.3 mol / L phosphoric acid) to the liquid component at 10 mL / min to adjust the pH until lignin no longer precipitates. Centrifuge at 5000 rpm for 10 min to separate solid lignin. Wash the lignin with deionized water until neutral by multiple centrifugations (5000 rpm, 10 min). Transfer the obtained lignin to a vacuum drying oven and dry at 40℃ for 24 h.

[0043] Comparative Example 1: Removal of hydrogen peroxide.

[0044] The comparative method for removing hydrogen peroxide in this application includes the following steps.

[0045] a. Lignin dissolution: Industrial alkali lignin is dissolved in 10% KOH alkaline solution, argon gas is introduced and the mixture is placed in a reaction vessel, and the temperature is increased to 100℃ at 3℃ / min and held for 1 h.

[0046] b. Co-removal of metal ions by sodium ethylenediaminetetraacetate: consistent with step b in Example 1.

[0047] c. Post-processing purification: Follow the same procedure as step c in Example 1.

[0048] Comparative Example 2: Removal of EDTA-Na.

[0049] The comparative method for removing sodium ethylenediaminetetraacetate includes the following steps.

[0050] a. Controlled oxidation of lignin: Sulfite-process lignin was dissolved in 10% KOH alkaline solution, and 10% (v / v) of 1% H2O2 solution was added. Argon gas was introduced and the mixture was placed in a reaction vessel. The temperature was increased to 100℃ at 3℃ / min and held for 1 h. After the holding time was completed, the mixture was cooled to room temperature, centrifuged, and the upper liquid was filtered through 0.45μm and 0.22μm nylon filter membranes for fractional filtration. The filtrate was retained.

[0051] b. Post-processing purification: consistent with step c in Example 2.

[0052] Comparative Example 3: Simultaneous removal of H2O2 and EDTA-Na.

[0053] The comparative method for removing hydrogen peroxide and sodium ethylenediaminetetraacetate includes the following steps.

[0054] a. Lignin dissolution: The lignin residue after ethanol fermentation of biomass raw materials is dissolved in 15% NaOH alkaline solution, nitrogen gas is introduced and the mixture is placed in a reaction vessel, and the temperature is increased to 80℃ at 2℃ / min and kept at this temperature for 1 h.

[0055] b. Post-processing purification: consistent with step c in Example 3.

[0056] Comparative Example 4: H2O2 and EDTA-Na were added simultaneously (one-step method).

[0057] This comparative verification of the failure of simultaneously adding oxidants and chelating agents includes the following steps.

[0058] a. Simultaneous treatment of lignin: Industrial alkali lignin is dissolved in 10% NaOH alkaline solution, and 5% by volume of 2% H2O2 solution and 2.5% EDTA-2Na are added at the same time. Nitrogen gas is introduced and the temperature is raised to 95℃ at 3℃ / min and kept at this temperature for 1.5 h.

[0059] b. Post-processing purification: After the incubation period, cool to room temperature, centrifuge, and filter the supernatant through 0.45μm and 0.22μm nylon membranes in stages, retaining the filtrate; subsequent steps are the same as step c in Example 1.

[0060] Comparative Example 5: EDTA chelation followed by H2O2 oxidation (order reversed).

[0061] The comparative verification of the negative effects of time sequence reversal includes the following steps.

[0062] a. EDTA chelation pretreatment: Dissolve industrial alkali lignin in 10% NaOH alkaline solution, add 2.5% EDTA-2Na, purge with nitrogen gas, heat to 95℃ at 3℃ / min, and keep warm for 1.5 h.

[0063] b. H2O2 oxidation: After the heat preservation is completed, add 5% (v / v) of 2% H2O2 solution while maintaining the temperature, and continue to keep warm for 30 min;

[0064] c. Post-processing purification: Same as step cd in Example 1.

[0065] Comparative Example 6: The ascorbic acid step is missing.

[0066] This comparative study verifies the necessity of removing residual oxidant, and the specific method includes the following steps.

[0067] ab. Same as step ab in Example 1.

[0068] c. Direct acid precipitation: Skip the ascorbic acid treatment and add 0.5 mol / L HCl directly to the filtrate at 20 mL / min until the pH reaches 2.5.

[0069] d. Centrifugation, washing, and drying are the same as in Example 1.

[0070] Comparative Example 7: Parameters outside the range (insufficient H2O2 concentration).

[0071] This comparative example supports the boundary of the claim parameters, and the specific method includes the following steps:

[0072] a. Controlled oxidation of lignin: Industrial alkali lignin is dissolved in 10% NaOH alkaline solution, 0.8% H2O2 solution (lower than 1-3% of claim 1) is added, nitrogen gas is introduced, and the temperature is raised to 95℃ at 3℃ / min and held for 30 min;

[0073] bd. Same as step bd in Example 1.

[0074] Experimental example: Index determination.

[0075] To further illustrate the effects of the present invention, the applicant determined the metal ion content of the lignin samples in each group according to the Chinese National Environmental Protection Standard HJ 766-2015.

[0076] The metal ion content of lignin raw materials and lignin samples after impurity removal was determined by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). Before the determination, the samples were first processed, as follows.

[0077] ① 100 mg sample + 8 mL concentrated nitric acid, digest at room temperature for 30 min.

[0078] ② Transfer to a digestion vessel and digest at 150℃ for 30 min.

[0079] ③ Transfer the resulting liquid to a 25 mL volumetric flask and dilute to volume with deionized water.

[0080] ④ Take 10 mL of liquid and filter it through a 0.22 μm nylon filter membrane. The liquid sample preparation is complete.

[0081] ⑤ Take 10 mL of the digested liquid sample and send it into the equipment for testing.

[0082] The metal ion content (mg / kg) in a solid sample is calculated based on the metal ion concentration (mg / L) in the liquid sample obtained from the test, using the following formula.

[0083] (I).

[0084] Where c1 is the concentration of metal ions in the liquid sample, in mg / L; c2 is the content of metal ions in the solid sample, in mg / kg; m is the mass of the test sample, in kg; and V is the volume of the liquid sample, in L.

[0085] In addition, the metal ion removal rates before and after treatment were compared.

[0086] Removal rate (%) = (Initial content − Final content) / Initial content × 100%.

[0087] The results are summarized in Table 1.

[0088]

[0089] Based on the comparison results in Table 1, this application achieves a significant improvement in metal removal rate through a three-step synergistic mechanism of "controlled oxidation → targeted chelation → gentle purification." Specifically, the efficiency for removing the most difficult metals (such as Ca) exceeds 60%, and the process is universally applicable to three types of lignin. The method described in this application significantly improves demetallization efficiency and ensures product stability, providing a new pathway for the high-value utilization of biomass.

[0090] Application example.

[0091] The lignin carbon of this application is used in the preparation of supercapacitor electrodes.

[0092] 1. Electrode preparation process, as shown in Table 2.

[0093]

[0094] 2. Electrochemical testing conditions.

[0095] Specific capacitance test: three-electrode system, scan rate 5 mV / s (voltage window -0.2~0.8 V).

[0096] Internal resistance test: AC impedance method (frequency 0.01 Hz ~ 100 kHz, amplitude 5 mV).

[0097] Cyclic testing: constant current charge and discharge (1 A / g, 5000 cycles).

[0098] 3. The performance comparison results are shown in Table 3.

[0099]

[0100] Note: The specific capacitance and cycle retention data are the average of three tests, with an error of <±3%.

[0101] Based on performance testing comparisons, the electrode prepared from lignin carbon in this application exhibits higher specific capacitance. This is attributed to the improved conductivity due to low metal residue and the increased effective specific surface area. Furthermore, its internal resistance is low. In contrast, the electrode in Comparative Example 1 exhibits low internal resistance due to the catalytic side reaction of metal impurities (Fe / Mn), which generates an insulating layer that hinders charge transfer. Regarding cycle retention, residual metals (such as Mn) contribute significantly to this. 2+ Oxidation and dissolution lead to the stripping of active materials, resulting in superior structural stability in Example 1 and improved rate performance. This is attributed to the synergistic effect of low internal resistance and high porosity in enhancing high-current response. Furthermore, testing of the Fe and Mn ion content revealed that the carbon material in Example 1 meets the national standard requirements for the metal ion content of activated carbon in supercapacitors.

[0102] This application's method efficiently removes metal impurities (Fe / Mn removal rate >92%), enabling the electrochemical performance of lignin-derived carbon materials to reach industrialization thresholds (specific capacitance >140 F / g, cycle retention >80%), thus solving the problems of low capacity and short lifespan caused by metal residues in traditional lignin electrodes. This application example strongly demonstrates the downstream application value and high level of technological innovation of this invention.

[0103] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for the removal of lignin metal ions in stages with hydrogen peroxide in conjunction with sodium salt of ethylenediaminetetraacetic acid, characterized in that, The method comprises the following steps: (a) controllable oxidative activation: adding hydrogen peroxide solution to the lignin lye, the amount of the hydrogen peroxide solution added being 5-10% of the volume of the lignin lye; then, under the protection of an inert atmosphere, increasing the temperature to 85-105°C at a rate of 2-4°C / min, and maintaining the temperature for 20-40 min; (b) EDTA-Na synergistic chelation: after step (a) is completed, the temperature is maintained, 2-4 wt% of ethylenediaminetetraacetic acid sodium salt solution is added to the reaction system, the reaction is stirred at 500-1200 rpm for 0.5-2 h, after the reaction is completed, the solution is cooled, centrifuged, and fractionally filtered, and the filtrate is taken for standby use; (c) residual oxidant removal: adding ascorbic acid solution to the filtrate, the amount of the ascorbic acid solution added being 1-3% of the volume of the filtrate; stirring under the protection of an inert atmosphere for 15-25 min; (d) gradient acid precipitation purification: after the stirring is completed, the liquid component is taken, acid is added thereto at a rate of 10-30 mL / min to adjust the pH to a value at which lignin no longer precipitates, the solid lignin is separated by centrifugation and washed to neutral, and vacuum drying is performed; The concentration of the hydrogen peroxide solution in step (a) is 1-3 wt%.

2. The method of claim 1, wherein, The lignin lye in step (a) is derived from industrial alkali lignin, sulfite lignin, or biorefinery residual lignin, and the extraction reagent comprises sodium hydroxide, potassium hydroxide, or ammonia water, and the concentration is 5-15 wt%; the inert atmosphere is a nitrogen or argon atmosphere.

3. The method of claim 1, wherein, The ethylenediaminetetraacetic acid sodium salt in step (b) is selected from disodium ethylenediaminetetraacetate or tetrasodium ethylenediaminetetraacetate.

4. The method of claim 1, wherein, The fractionally filtering in step (b) is specifically filtering with 0.45 μm and 0.22 μm nylon filter membranes in sequence.

5. The method of claim 1, wherein, The concentration of the ascorbic acid solution in step (c) is 5-10 wt%.

6. The method of claim 1, wherein, The inert gas in step (c) is nitrogen or argon, and the stirring speed is 500-700 rpm.

7. The method of claim 1, wherein, The acid used for adjusting the pH in step (d) is 0.1-1 mol / L hydrochloric acid, sulfuric acid, or phosphoric acid.

8. The method of claim 1, wherein, The vacuum drying in step (d) is placing the washed lignin in a vacuum drying oven to dry at 40°C for 12-24 h.

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