A silicon-containing spherical lignin porous carbon and its preparation method and application

Abstract

The invention discloses a silicon-containing spherical lignin porous carbon and a preparation method and application thereof, and relates to the technical field of high-value conversion and application of biomass. The preparation method comprises the following steps: step S1, dissolving alkali lignin, sodium silicate and an isolating agent in an alkali solution, stirring and mixing, and then adjusting the pH of the solution to acidity with acid and / or acidic gas, filtering after the acidolysis reaction, washing with water, and drying to obtain silicon-containing lignin microspheres; step S2, sequentially carbonizing and alkali-activating the silicon-containing lignin microspheres, acid-washing after cooling, washing with water, and drying to obtain silicon-containing spherical lignin porous carbon. The preparation method of the silicon-containing spherical lignin porous carbon of the invention is simple and suitable for industrial production; and the prepared spherical porous carbon has a strong adsorption capacity for antibiotics and the like.

Description

Technical Field:

[0001] The present invention relates to the technical field of high-value conversion and application of biomass, and particularly relates to a silicon-containing spherical lignin porous carbon, a preparation method thereof, and an application thereof. Background Art:

[0002] Lignin is a natural renewable biomass resource with a very rich content. It is second only to cellulose in the plant body. Its molecular structure has three-dimensional network characteristics, is rich in a large number of aromatic groups and oxygen-containing functional groups, and the carbon content is more than 60%. Because of its advantages of being renewable, widely sourced, cheap and easy to obtain, and high carbon content, it is a good choice for preparing porous carbon. The physical and chemical properties of lignin porous carbon are stable, with a high specific surface area and excellent porosity, and have broad application prospects in the fields of adsorption, catalytic carriers, energy storage materials, etc.

[0003] Compared with powdered activated carbon and granular activated carbon, spherical activated carbon has received extensive attention from researchers because of a series of excellent properties such as high packing density, high mechanical strength, easier control of pore size distribution, and good fluidity.

[0004] The process for preparing spherical porous carbon materials from lignin mainly includes: lignin spheroidization, carbonization, and activation processes. Specifically, lignin is dissolved in an appropriate solvent (such as water, alcohols, or other organic solvents), and spherical lignin particles are prepared by techniques such as spray drying, sol-gel method, emulsion polymerization, or template method. The spherical lignin particles are then subjected to high-temperature carbonization and activation processes to prepare spherical lignin porous carbon with a rich pore structure. Among them, the preparation of spherical lignin with uniform size and stable structure is the key.

[0005] The reported methods for preparing spherical lignin mainly include: solution spray drying method, template method, direct spheroidization method, sol-gel method, etc. Among them, the spherical lignin prepared by the solution spray drying method has relatively uniform size, but has strict requirements for the selection and recovery of solvents and high energy consumption; the spherical lignin prepared by the template method has good uniformity and regularity, and the pore size distribution can be controlled, but the removal of the template often affects the integrity of the spherical particles and the preparation process is complex. The direct spheroidization method has a simple process, but it is difficult to control the uniformity and size of spherical particles and has low efficiency; the sol-gel method can be carried out at a lower temperature, but it is difficult to ensure the scale uniformity. The most common in the sol-gel method is the acid precipitation method of alkali lignin. Alkali lignin will gel and precipitate into fine particles when the pH value is acidic, and then spherical lignin is prepared through acidolysis. However, lignin is prone to agglomerate in a solvent (such as water) during the acid precipitation process due to its complex structure, and uniform spherical particles cannot be obtained.

[0006] When pure spherical lignin is directly carbonized, its structure will soften, collapse or shrink / aggregate at a certain temperature, and the lignin spheres will thus deform or be damaged. Therefore, nano-SiO 2 with good substrate strength and mechanical stress can be used as a hard template agent to support the lignin carbon skeleton and prevent its polycondensation and collapse (Patent CN108751160A). However, a large amount of alkali or hydrofluoric acid is finally required to remove the silica template, and the obtained lignin porous carbon has a honeycomb structure. Summary of the Invention:

[0007] In order to overcome the deficiencies of the prior art, the present invention uses alkali lignin and sodium silicate as raw materials, and utilizes their characteristics of being able to precipitate lignin and SiO 2 through acidolysis precipitation. Water-soluble biopolymers such as dextran or xylan are used as isolation agents to block the coalescence of lignin during the acidification reaction precipitation process, and stable and uniform silicon-containing spherical lignin is prepared; then during the carbonization process of this spherical lignin, the in-situ generated silica is used as a template agent to maintain its structural stability; finally, through activation, silicon-containing spherical lignin porous carbon with a high specific surface area and high adsorption capacity is prepared. The preparation method of this silicon-containing spherical lignin porous carbon is simple and suitable for industrial production; and the prepared spherical porous carbon has a strong adsorption capacity for antibiotics and the like.

[0008] The technical problems to be solved by the present invention are realized by adopting the following technical solutions:

[0009] The first object of the present invention is to provide a preparation method of silicon-containing spherical lignin porous carbon, and the preparation method includes the following steps:

[0010] Step S1: Dissolve alkali lignin, sodium silicate (Na 2 SiO 3 ) and an isolation agent in an alkaline solution, stir and mix evenly, then adjust the pH of the solution to acidic with an acid and / or acidic gas. After the acidolysis reaction is completed, filter, wash with water, and dry to obtain silicon-containing lignin microspheres;

[0011] Step S2: Carbonize and alkali activate the silicon-containing lignin microspheres prepared in step S1 in sequence, cool, wash with acid, wash with water, and dry to obtain silicon-containing spherical lignin porous carbon.

[0012] In the present invention, the alkali lignin is selected from at least one of bamboo pulp alkali lignin, wood pulp alkali lignin, straw pulp alkali lignin or alkali lignin black liquor generated during the pulping process.

[0013] In the present invention, the isolation agent is a water-soluble biopolymer, and is selected from at least one of water-soluble biopolymers such as soluble cellulose, soluble starch, isomaltooligosaccharide, fructan, xylan, mannan oligosaccharide, soybean oligosaccharide, chitosan, dextran, etc.

[0014] In the present invention, the dosage of sodium silicate is 0.5-50% of the mass of alkali lignin; the dosage of the release agent is 0-20% of the mass of alkali lignin.

[0015] In the present invention, adjusting the pH of the solution to acidic is divided into three stages. In the first stage, the pH is adjusted to 7-9, in the second stage, the pH is slowly adjusted to 4-5.5, and in the third stage, the pH is adjusted to 1-4.

[0016] In the present invention, the acid is an inorganic acid and / or an organic acid commonly used in the art.

[0017] In the present invention, the acidic gas is hydrogen chloride, sulfur dioxide, sulfur trioxide.

[0018] Preferably, in the second stage, slow acidification is carried out using an acidic gas or an organic small molecule acid that can be heated and vaporized (such as formic acid, acetic acid, propionic acid, etc.).

[0019] In the present invention, the temperature of the acidolysis reaction is from room temperature to 145 °C, preferably 30-121 °C; the time of the acidolysis reaction is 0.5-4 h.

[0020] In the present invention, the temperature of the carbonization is 400-1100 °C, preferably 500-700 °C; the heating rate does not exceed 15 °C / min, preferably does not exceed 10 °C / min.

[0021] In the present invention, the alkali activation uses alkaline substances such as potassium hydroxide (KOH), sodium hydroxide (NaOH), potassium carbonate (K 2 CO 3 ) as the activator, the carbon-alkali ratio is 1:(1-4), the temperature is 700-1000 °C, and the heating rate is 1-10 °C / min. Pores are formed in the carbonized lignin microspheres through alkali activation to enrich the pore structure.

[0022] In the present invention, the acid washing is carried out with hydrochloric acid, sulfuric acid or acetic acid. The purpose is to remove impurities in the activated carbon and improve the porosity of the activated carbon.

[0023] The second object of the present invention is to provide a silicon-containing spherical lignin porous carbon prepared by the above preparation method.

[0024] The third object of the present invention is to provide the application of the above silicon-containing spherical lignin porous carbon as an adsorbent in wastewater treatment.

[0025] Preferably, the wastewater includes industrial wastewaters such as antibiotic wastewater, medical wastewater, printing and dyeing wastewater, heavy metal ion wastewater, etc.

[0026] The prepared silicon-containing spherical lignin porous carbon of the present invention has regular shape, with a large specific surface area (1715.8 - 2432.5 m 2 / g), contains 0.5 - 27.5% of SiO 2 , and has excellent adsorption performance in the field of wastewater treatment (adsorption capacity: ciprofloxacin 719.6 mg / g, sulfadiazine 702.4 mg / g, tetracycline 508.1 mg / g, creatinine 313.6 mg / g), with good universality and regenerability.

[0027] Advantages of the present invention:

[0028] (1) The present invention uses an in-situ one-step method to prepare silicon-containing lignin microspheres, and then through carbonization / activation, prepares silicon-containing spherical lignin porous carbon. The process is simple, the process flow is short, no special equipment is required, the operation is simple, the product quality is stable, and the raw materials used are inexpensive, so the industrial production prospect is optimistic.

[0029] (2) Aiming at the problems that the structurally complex alkali lignin is prone to aggregation and condensation during the acidification reaction precipitation process and the lignin microspheres are prone to collapse and adhesion during the carbonization process, the present invention first uses water-soluble biopolymers such as dextran or xylan as isolation agents to block the aggregation of lignin during the acid precipitation process, and then adopts a three-stage pH-adjusting control method for the acidification reaction. In the second stage, the solution pH is preferably adjusted by introducing an acidic gas or an organic small molecule acid that can be heated and vaporized to obtain lignin microspheres with uniform particle size distribution and regular morphology; and the content of SiO 2 in the lignin microspheres is controlled by the addition amount of sodium silicate, which greatly improves the ability of the silicon-containing spherical lignin porous carbon to adsorb antibiotics while stabilizing the spherical structure of lignin.

[0030] (3) The water-soluble biopolymers such as lignin, dextran or xylan used in the present invention are all renewable biomass materials, with rich sources and being green and environmentally friendly.

[0031] (4) The prepared silicon-containing spherical lignin porous carbon of the present invention provides a large surface area and two different phases that can undergo adsorption: a non-polar carbonaceous phase and a polar siliceous phase. The surface of SiO 2 is highly polar, which can significantly improve the hydrophilicity of the activated carbon; an appropriate amount of amorphous silicon loaded on the lignin-based spherical porous carbon will not block the pores of the porous carbon, and at the same time, the polar siliceous phase can also improve the adsorption ability of the porous carbon to polar substances. Description of the drawings:

[0032] Figure 1 It is an electron micrograph of the lignin microspheres obtained by acid precipitation of alkali lignin without an isolation agent in Comparative Example 2;

[0033] Figure 2Electron micrograph of lignin microspheres obtained by acid precipitation with alkali lignin and xylooligosaccharide as a spacer in Example 1;

[0034] Figure 3 Electron micrograph of spherical lignin porous carbon obtained without sodium silicate in Comparative Example 1;

[0035] Figure 4 Electron micrograph of silicon-containing spherical lignin porous carbon obtained with sodium silicate in Example 1;

[0036] Figure 5 Electron micrograph of silicon-containing spherical lignin porous carbon obtained by directly adding 70% sulfuric acid to adjust the solution pH without using a three-stage method to adjust the solution pH in Comparative Example 3;

[0037] Figure 6 Regeneration performance of silicon-containing spherical lignin porous carbon for ciprofloxacin adsorption. Detailed implementation method:

[0038] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments and illustrations.

[0039] Example 1

[0040] Dissolve 20 g of wheat straw alkali lignin, 4 g of xylooligosaccharide, and 5 g of Na 2 SiO 3 in 1000 mL of 2% NaOH solution, and stir and mix evenly at 60 °C. Adjust the solution pH using a three-stage method. Add 70% sulfuric acid solution in the first and third stages, and introduce SO 3 gas in the second stage. Adjust the solution pH to 3 by controlling the sulfuric acid flow rate and SO 3 ventilation rate. Acid hydrolyze at 121 °C for 0.5 h. After cooling, filter and wash the precipitate with water until neutral, and dry at 60 °C for 12 h to obtain silicon-containing lignin microspheres.

[0041] Using the silicon-containing lignin microspheres as the carbon precursor, carry out carbonization at 500 °C and KOH activation (carbon-to-alkali ratio is 1:2, 800 °C, hold for 2 h) in sequence. After cooling to room temperature, wash with 2 M hydrochloric acid, filter and wash with water until neutral, and dry at 105 °C for 12 h to obtain silicon-containing spherical lignin porous carbon.

[0042] Example 2

[0043] Dissolve 20 g of pulp alkali lignin, 2 g of dextran, and 8 g of Na 2 SiO 3Dissolve it in 1000 mL of 2% NaOH solution, stir and mix evenly at 60 °C. Pass in hydrogen chloride gas, adjust the pH of the solution to 1 by controlling the gas flow rate in a three-stage manner, carry out acid hydrolysis at 100 °C for 1 h. After cooling, filter by suction and wash the precipitate with water until neutral, then dry at 60 °C for 12 h to obtain silicon-containing lignin microspheres.

[0044] Using the silicon-containing lignin microspheres as the carbon precursor, carry out carbonization at 500 °C and NaOH activation (carbon-to-alkali ratio is 1:3, 700 °C, keep warm for 2 h) in sequence. After cooling to room temperature, wash with 2 M citric acid, filter and wash with water until neutral, then dry at 105 °C for 12 h to obtain silicon-containing spherical lignin porous carbon.

[0045] Example 3

[0046] Dissolve 20 g of bamboo pulp alkali lignin, 3 g of dextran, and 10 g of Na 2 SiO 3 in 1000 mL of 2% NaOH solution, stir and mix evenly at 60 °C. Pass in sulfur dioxide gas, adjust the pH of the solution to 2 by controlling the gas flow rate in a three-stage manner, carry out acid hydrolysis at 90 °C for 2.5 h. After cooling, filter by suction and wash the precipitate with water until neutral, then dry at 60 °C for 12 h to obtain silicon-containing lignin microspheres.

[0047] Using the silicon-containing lignin microspheres as the carbon precursor, carry out carbonization at 700 °C and KOH activation (carbon-to-alkali ratio is 1:2, 800 °C, keep warm for 2 h) in sequence. After cooling to room temperature, wash with 2 M hydrochloric acid, filter and wash with water until neutral, then dry at 105 °C for 12 h to obtain silicon-containing spherical lignin porous carbon.

[0048] Example 4

[0049] Dissolve 10 g of wheat straw alkali lignin, 2 g of chitosan, and 5 g of Na 2 SiO 3 in 1000 mL of 2% NaOH solution, stir and mix evenly at 60 °C. Pass in sulfur dioxide gas, adjust the pH of the solution to 3 by controlling the gas flow rate in a three-stage manner, carry out acid hydrolysis at 90 °C for 2.5 h. After cooling, filter by suction and wash the precipitate with water until neutral, then dry at 60 °C for 12 h to obtain silicon-containing lignin microspheres.

[0050] Using the silicon-containing lignin microspheres as the carbon precursor, carry out carbonization at 600 °C and K 2 CO 3 activation (carbon-to-alkali ratio is 1:4, 700 °C, keep warm for 2 h) in sequence. After cooling to room temperature, wash with 2 M acetic acid, filter and wash with water until neutral, then dry at 105 °C for 12 h to obtain silicon-containing spherical lignin porous carbon.

[0051] Example 5

[0052] Add 5 g of Na to 1000 mL of wheat straw black liquor. 2 SiO 3 Stir and mix well at 60 °C. Pass sulfur trioxide gas, and adjust the pH of the solution to 2 by using a three-stage control of the gas flow rate. Acidify at 105 °C for 1 h. After cooling, filter by suction and wash the precipitate with water until neutral, and dry at 60 °C for 12 h to obtain silicon-containing lignin microspheres.

[0053] Use the silicon-containing lignin microspheres as the carbon precursor, and carry out carbonization at 700 °C and KOH activation (carbon-to-alkali ratio is 1:2, 800 °C, heat preservation for 2 h) in sequence. After cooling to room temperature, wash with 2 M hydrochloric acid, filter and wash with water until neutral, and dry at 105 °C for 12 h to obtain silicon-containing spherical lignin porous carbon.

[0054] Since the wheat straw black liquor itself contains polysaccharides degraded from cellulose and hemicellulose, when using alkaline lignin black liquor as the raw material, an isolating agent can be not added.

[0055] Comparative Example 1

[0056] The method for preparing spherical lignin porous carbon in Comparative Example 1 is the same as that in Example 1, except that Na 2 SiO 3 is not added, and spherical lignin porous carbon is obtained.

[0057] Comparative Example 2

[0058] The method for preparing silicon-containing spherical lignin porous carbon in Comparative Example 2 is the same as that in Example 1, except that xylooligosaccharide is not added as the isolating agent.

[0059] Comparative Example 3

[0060] The method for preparing silicon-containing spherical lignin porous carbon in Comparative Example 3 is the same as that in Example 1, except that in adjusting the pH, the three-stage method is not adopted, but 70% sulfuric acid is added dropwise to directly adjust the pH to 3.

[0061] Figure 1 It is the electron micrograph of the lignin microspheres obtained by acid precipitation of alkaline lignin without adding an isolating agent in Comparative Example 2. It can be seen that the lignin microspheres are severely aggregated.

[0062] Figure 2 It is the electron micrograph of the lignin microspheres obtained by acid precipitation of alkaline lignin with xylooligosaccharide added as the isolating agent in Example 1. It can be seen that there is no stacking phenomenon of the lignin microspheres.

[0063] Figure 3 It is the electron micrograph of the spherical lignin porous carbon obtained without adding sodium silicate in Comparative Example 1. It can be seen that the lignin carbon spheres show melting and aggregation phenomena.

[0064] Figure 4It is the electron micrograph of the silicon-containing spherical lignin porous carbon obtained by adding sodium silicate in Example 1. It can be seen that the lignin carbon spheres are stable, with a smooth surface and no stacking phenomenon.

[0065] Figure 5 It is the electron micrograph of the silicon-containing spherical lignin porous carbon obtained by directly adding 70% sulfuric acid to adjust the solution pH to 3 without using the three-stage method to adjust the solution pH in Comparative Example 3. It can be seen that the lignin carbon spheres are severely aggregated and the morphology is irregular.

[0066] The silicon-containing spherical lignin porous carbon is recovered by pyrolysis:

[0067] Under a nitrogen atmosphere, the silicon-containing spherical lignin porous carbon after adsorbing ciprofloxacin is heated to 700 °C at a heating rate of 10 °C / min and pyrolyzed for 30 min.

[0068] Figure 6 It is the regeneration performance of the silicon-containing spherical lignin porous carbon for the adsorption of ciprofloxacin. From Figure 6 It can be seen that although the adsorption amount of the silicon-containing spherical lignin porous carbon for ciprofloxacin decreases with the increase in the number of recycling times, after 5 cycles, the adsorption efficiency for ciprofloxacin is still very high. Therefore, the silicon-containing spherical lignin porous carbon has good regeneration and economic benefits for the adsorption of ciprofloxacin and has broad application prospects in the field of antibiotic wastewater adsorption.

[0069] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for preparing silicon-containing spherical lignin porous carbon, characterized in that: The preparation method comprises the following steps: Step S1, dissolving alkali lignin, sodium silicate and a release agent in an alkali solution, stirring and mixing, and then adjusting the pH of the solution to acidity with acid and / or acid gas, and filtering after the acid hydrolysis reaction, washing with water, and drying to obtain silicon-containing lignin microspheres; Step S2, sequentially carbonizing and alkali activating the silicon-containing lignin microspheres prepared in step S1, acid washing, water washing, and drying after cooling to obtain silicon-containing spherical lignin porous carbon; The isolation agent is a water-soluble biopolysaccharide; The method of adjusting the solution pH to acidity is divided into three stages: the first stage is to adjust the pH to 7-9, the second stage is to slowly adjust the pH to 4-5.5, and the third stage is to adjust the pH to 1-4; the second stage is to slowly acidify using acidic gas or a heatable and gasifiable organic small molecule acid.

2. The preparation method according to claim 1, characterized in that: The alkali lignin is selected from at least one of bamboo pulp alkali lignin, wood pulp alkali lignin, straw pulp alkali lignin, or alkali lignin-containing black liquor produced in the pulping process.

3. The preparation method according to claim 1, characterized in that: The water-soluble biopolysaccharide is selected from at least one of soluble cellulose, soluble starch, isomaltooligosaccharide, fructan, xylan, oligomannose, soybean oligosaccharide, chitosan and dextran.

4. The preparation method according to claim 1, characterized in that: The amount of sodium silicate used is 0.5-50% of the mass of alkali lignin.

5. The preparation method according to claim 1, characterized in that: The amount of the release agent is 0-20% of the mass of the alkali lignin.

6. The preparation method according to claim 1, characterized in that: The acid is an inorganic acid and / or an organic acid.

7. The preparation method according to claim 1, characterized in that: The acidic gases are hydrogen chloride, sulfur dioxide and sulfur trioxide.

8. The preparation method according to claim 1, characterized in that: The temperature of the acid hydrolysis reaction is room temperature to 145° C.; the time of the acid hydrolysis reaction is 0.5 to 4 h.

9. The preparation method according to claim 8, characterized in that: The temperature of the acid hydrolysis reaction is 30-121°C.

10. The preparation method according to claim 1, characterized in that: The carbonization temperature is 400-1100°C, and the heating rate does not exceed 15°C / min.

11. The preparation method according to claim 10, characterized in that: The carbonization temperature is 500-700°C, and the heating rate does not exceed 10°C / min.

12. The preparation method according to claim 1, characterized in that: The alkali activation uses KOH, NaOH, and K2CO3 as activators, the carbon-alkali ratio is 1: (1-4), the temperature is 700-1000°C, and the heating rate is 1-10°C / min.

13. The preparation method according to claim 1, characterized in that: The pickling is washing with hydrochloric acid, sulfuric acid or acetic acid.

14. Silicon-containing spherical lignin porous carbon prepared by the preparation method according to any one of claims 1 to 13.

15. Use of the silicon-containing spherical lignin porous carbon according to claim 14 as an adsorbent in wastewater treatment.

16. The use according to claim 15, characterized in that: The wastewater includes antibiotic wastewater, medical wastewater, printing and dyeing wastewater, and heavy metal ion wastewater.

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