A waste paper-based biochar, its preparation method and application

Abstract

The present invention discloses a waste paper-based biochar, its preparation method and application, belonging to the technical field of solid waste treatment. The preparation method of the waste paper-based biochar of the present invention is to first pretreat waste paper with an aqueous solution of L-cysteine nitrate ionic liquid as a treatment agent; then carbonize the pretreated waste paper-based fibers to form waste paper-based biochar; wherein the aqueous solution of L-cysteine nitrate ionic liquid as a treatment agent can not only remove residual substances such as lignin in waste paper, but also effectively improve the porosity and specific surface area of the biochar, so that the finally prepared waste paper-based biochar has strong adsorption performance, and the removal rate of organic pollutants can reach more than 99%, avoiding the use of strong acids and bases as well as strong oxidants and reducing environmental pollution.

Description

Technical Field

[0001] The present invention relates to a waste paper-based biochar, a preparation method thereof and an application thereof, and belongs to the technical field of solid waste treatment. Background Art

[0002] As an environment-friendly and economical new carbon material, biochar has unique structural and physicochemical properties such as rich microporous structure, large specific surface area, and strong adsorption capacity, and is widely used in multiple fields such as adsorption, soil remediation, and catalysis.

[0003] The organic raw materials for preparing biochar include agricultural wastes such as solid wastes like straws, rice husks, coconut husks, and municipal sludge. Different raw materials have different elemental compositions and ratios, so the prepared biochars will also exhibit different properties. There are many deficiencies in the raw biochar. In order to better meet the application requirements in the environment, the biochar often needs to be post-treated. The most commonly used post-treatment method at present is to impregnate the biomass carbonized with a high-concentration acid-base or oxidant solution to increase the porosity and specific surface area of the biochar; since acid-base and oxidants generally have a greater impact on the environment and the health of operators, it is necessary to study a more environmentally friendly treatment method.

[0004] Waste paper is one of the most common domestic wastes in life. At present, the recycling methods of waste paper are mainly as raw materials for building materials, fillers or secondary newsprint. Since using waste paper as a biochar raw material requires deinking treatment of the waste paper, the process is complex, and the waste paper-based biochar after deinking treatment has a lower porosity and specific surface area and a smooth surface, which is not conducive to the adsorption of pollutants.

[0005] Therefore, there are few relevant reports on using waste paper as a biochar raw material at present. Summary of the Invention

[0006] [Technical Problem]

[0007] In the prior art, the activation treatment of raw biochar usually requires the use of a high-concentration acid-base or oxidant solution, which is likely to cause a greater impact on the environment and the health of operators; especially for waste paper raw biochar, it usually requires pre-treatment of the waste paper for deinking, the process is complex, and the waste paper-based biochar after treatment has a lower porosity and specific surface area and a smooth surface, which is not conducive to the adsorption of pollutants.

[0008] [Technical Solution]

[0009] In view of the above existing technical problems, the present invention provides a waste paper-based biochar, a preparation method thereof and an application. The method has a simple process and uses an environmentally friendly ionic liquid as a pretreatment agent to treat waste paper, which can effectively remove residual substances such as lignin in waste paper and improve the porosity and specific surface area of the primary biochar of waste paper. Then, the pretreated waste paper-based fibers are prepared into biochar, which has a high adsorption capacity for various organic substances, and the removal rate can reach 99.99%. It effectively avoids the use of strong acids, strong bases and oxidants and reduces environmental pollution.

[0010] The first object of the present invention is to provide a preparation method of waste paper-based biochar, and the preparation method includes the following steps:

[0011] (1) Waste paper pretreatment

[0012] Pretreat waste paper with an aqueous solution of L-cysteine nitrate ionic liquid as a treatment agent to obtain waste paper-based fibers;

[0013] (2) Preparation of waste paper-based biochar

[0014] Place the waste paper-based fibers obtained in step (1) in a tubular furnace and carry out carbonization treatment in a nitrogen environment. Control the temperature rising rate at 5 °C / min and carbonize at 650-850 °C for 60-70 min; after taking out, wash until neutral and dry to obtain waste paper-based biochar (K-C-BC).

[0015] In one embodiment, the pretreatment in step (1) is to mix L-cysteine nitrate ionic liquid with waste paper in an autoclave at 105-110 °C and 0.01-0.02 Mpa for 3-5 h; after cooling to room temperature, take out, filter to separate the solid and liquid, and then wash repeatedly with deionized water. Leave the solid sample until there are no bubbles in the waste liquid after washing; then wash with absolute ethanol 2-3 times, and dry the washed sample to form waste paper-based fibers.

[0016] In one embodiment, the liquid-solid ratio of the aqueous solution of L-cysteine nitrate ionic liquid to waste paper in step (1) is 20-30:1, ml:g; the mass concentration of L-cysteine nitrate ionic liquid in the aqueous solution of L-cysteine nitrate ionic liquid is 70-75%.

[0017] In one embodiment, the preparation of the aqueous solution of L-cysteine nitrate ionic liquid in step (1) includes the following steps:

[0018] 1) Pour nitric acid and water into a beaker, slowly stir and add L-cysteine to mix evenly to form a mixed solution;

[0019] 2) Place the mixed solution prepared in step (1) in a water bath, stir and react at a constant temperature until there is no precipitate in the beaker and the solution is colorless and transparent, thus obtaining an aqueous solution of L-cysteine nitrate ionic liquid;

[0020] The molar ratio of the nitric acid to L-cysteine is: 1:1 to 1:3;

[0021] The conditions for the constant-temperature stirring reaction are: the temperature is 60°C to 70°C, and the time is 0.5 to 1 h.

[0022] In one embodiment, the drying in step (2) is carried out at 105 - 110°C for 12 - 16 h.

[0023] The second object of the present invention is to provide a waste paper-based biochar (K-C-BC) prepared by the above-mentioned preparation method.

[0024] The third object of the present invention is the application of the waste paper-based biochar described above in the field of solid waste treatment.

[0025] The fourth object of the present invention is to provide a method for removing organic pollutants from waste liquid, and the method is to use the waste paper-based biochar prepared above as an adsorbent to treat the waste liquid.

[0026] In one embodiment, the treatment of the waste liquid specifically is to mix the biochar and the wastewater solution according to a solid-liquid ratio of 1:1 to 2, g:ml, stir in the dark, and then separate the solid from the liquid.

[0027] In one embodiment, the organic pollutants include one or more of enrofloxacin, bisphenol A, ciprofloxacin, and tetracycline.

[0028] In one embodiment, the stirring time in the dark is 4 - 6 h.

[0029] In one embodiment, the solid-liquid separation is to pass the mixed liquid through a 0.22-μm filter membrane to separate the solid from the liquid.

[0030] [Beneficial effects]

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] (1) The method for pre-treating waste paper in the present invention does not require additional removal of the ink on the waste paper, simplifying the preparation process of the waste paper-based biochar

[0033] (2) Pretreatment before carbonization can remove more than 70% of substances such as lignin in the waste paper, thereby increasing the porosity and specific surface area of the biochar;

[0034] (3) The biochar prepared from the waste paper-based fibers obtained after pretreatment in the present invention can achieve a removal rate of 99% for organic pollutants enrofloxacin (ENR), bisphenol A (BPA), ciprofloxacin (CIP), and tetracycline (TC) when used to remove organic pollutants in waste liquid. Description of the Drawings

[0035] Figure 1 It is a data graph of the removal rates of different organic pollutants by the biochar fibers prepared in Example 2 and Comparative Example 5 of the present invention;

[0036] Figure 2 It is a data graph of the removal rates of different organic pollutants by the biochar fibers prepared in Example 2 and Comparative Examples 2-4 of the present invention. Detailed Embodiments

[0037] The present invention will be further described below in conjunction with specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0038] 1. Determination method of lignin

[0039] It is determined with reference to the Van Soest method;

[0040] 2. Calculation method of antibiotic removal rate:

[0041] E(%) = (C0 - C t ) / C0 * 100%;

[0042] In the formula: C0 - original concentration of the organic pollutant aqueous solution (mg·L -1 );

[0043] C t —Concentration of the organic pollutant aqueous solution after adsorption (mg·L -1 ).

[0044] 3. Preparation of enrofloxacin aqueous solution

[0045] Accurately weigh 0.0251 g of enrofloxacin powder into a beaker, add 10 mL of 0.1 mol / L sodium hydroxide solution, stir to dissolve it, and make up the volume to 500 mL with deionized water in a brown volumetric flask to prepare a concentration of 50 mg / L;

[0046] The concentrations of the organic pollutant aqueous solutions involved in the examples and comparative examples in the present invention are all 50 mg·L -1 ; The waste paper is ordinary laser printing waste paper.

[0047] Example 1

[0048] A method for pretreating waste paper, the method comprising the following steps:

[0049] (1) Take 66.19 mL of 68% nitric acid and 31.74 mL of deionized water and pour them into a beaker. Slowly stir and add 121.16 g of L-cysteine and mix evenly.

[0050] (2) Place the mixed solution prepared in step (1) in a water bath. Stir evenly and react at a constant temperature of 70 °C for 0.5 h until there is no precipitate in the beaker and the solution is colorless and transparent, which is the L-cysteine nitrate ionic liquid aqueous solution.

[0051] (3) Weigh 1.00 g of waste paper and add 20.00 g of L-cysteine nitrate ionic liquid aqueous solution according to a solid-liquid ratio of 1:20. Place it in an autoclave and react at 105 °C and 0.01 - 0.02 Mpa for 3 h. After cooling to room temperature, take it out, filter it to separate the solid and liquid, and then repeatedly wash the remaining solid sample with deionized water until there are no bubbles in the waste liquid after washing. Wash it two or three times with absolute ethanol, and put the washed sample into an oven at 65 °C and dry it for 24 h to form waste paper-based fibers.

[0052] The lignin removal rate during the waste paper treatment process was calculated to be 71.58%.

[0053] Example 2

[0054] A preparation method of waste paper-based biochar, the method comprising the following steps:

[0055] (1) React the waste paper-based fibers prepared in Example 1 in a TL1200 tubular furnace under a nitrogen environment, control the temperature rising rate at 5 °C / min, and carbonize at 650 °C for 70 min.

[0056] (2) Wash the product obtained in step (1) with deionized water until neutral, and dry it at 105 °C for 12 h; the dried product is biochar (K-C-BC).

[0057] Weigh 20.00 mg of K-C-BC, add 20 mL of 50 mg / L enrofloxacin aqueous solution according to a solid-liquid ratio of 1:1, stir in the dark for 4 h, take out the sample and filter it through a 0.22-μm filter membrane to separate the solid and liquid. Preserve the separated solution and measure the enrofloxacin content in the solution. The calculated enrofloxacin removal rate is 99.64%.

[0058] Referring to the above method for enrofloxacin removal, replace enrofloxacin with aqueous solutions of bisphenol A, ciprofloxacin, and tetracycline. The removal rates of different organic pollutants are shown in Table 1.

[0059] Table 1 Comparison table of removal rates of aqueous solutions prepared from different organic pollutants

[0060] aqueous solution of organic pollutants aqueous solution of bisphenol A aqueous solution of ciprofloxacin aqueous solution of tetracycline removal rate / % 99.99 99.76 99.30

[0061] Comparative Example 1

[0062] Ionic liquids were prepared with reference to Example 1. Cysteine was replaced with glycine, lysine, and proline respectively, and other conditions remained unchanged. Aqueous solutions of glycine nitrate ionic liquid, cysteine nitrate ionic liquid, and proline nitrate ionic liquid were prepared respectively.

[0063] Weigh 1.00 g of waste paper respectively, add 20.00 g of the above three aqueous ionic liquid solutions according to a solid-liquid ratio of 1:20, place them in an autoclave, and react at 105 °C and 0.01 - 0.02 Mpa for 3 h. After cooling to room temperature, take them out, filter to separate the solid and liquid, then wash the remaining solid sample repeatedly with deionized water until there are no bubbles in the washing waste liquid; then wash with absolute ethanol two or three times, put the washed sample into an oven at 65 °C and dry for 24 h to make waste paper-based fibers. Finally, the lignin removal rates are calculated as shown in Table 2.

[0064] Table 2. Comparison table of lignin removal rates of aqueous ionic liquid solutions prepared with different amino acids

[0065] amino acid ionic liquid glycine nitrate ionic liquid lysine nitrate ionic liquid proline nitrate ionic liquid lignin removal rate / % 42.89 47.20 45.22

[0066] Comparative Example 2

[0067] Waste paper-based biochar was prepared with reference to Example 2. The waste paper-based fibers prepared with L-cysteine nitrate ionic liquid were replaced with waste paper-based fibers prepared with glycine nitrate ionic liquid to obtain waste paper-based biochar (K-G-BC). Referring to the method of Example 2 to remove organic pollutants in the aqueous solution, the removal rates of K-G-BC for different organic pollutants are shown in Table 3.

[0068] Table 3. Removal rates of K-G-BC for different organic pollutants.

[0069]

[0070] Comparative Example 3

[0071] Waste paper-based biochar was prepared with reference to Example 2. The waste paper-based fibers prepared with L-cysteine nitrate ionic liquid were replaced with waste paper-based fibers prepared after pretreatment with 1 mol / L NaOH (the difference from Example 1 is only that the aqueous solution of L-cysteine nitrate ionic liquid was replaced with 1 mol / L NaOH solution) to obtain waste paper-based biochar (K-L-BC). Referring to the method of Example 2 to remove organic pollutants in the aqueous solution, the removal rates of K-L-BC for different organic pollutants are shown in Table 4.

[0072] Table 4. Removal rates of K-L-BC for different organic pollutants

[0073]

[0074] Comparative Example 4

[0075] The waste paper-based biochar was prepared with reference to Example 2. The waste paper-based fibers prepared with L-cysteine nitrate ionic liquid were replaced with waste paper-based fibers prepared after pretreatment with 1 mol / L hydrochloric acid (the only difference from Example 1 was that the L-cysteine nitrate ionic liquid aqueous solution was replaced with a 1 mol / L hydrochloric acid solution), and the waste paper-based biochar (K-P-BC) was obtained. The method of Example 2 was referred to remove organic pollutants in the aqueous solution, and the removal rates of K-P-BC for different organic pollutants are shown in Table 5.

[0076] Table 5. Removal rates of K-P-BC for different organic pollutants

[0077]

[0078] Comparative Example 5

[0079] The waste paper-based biochar was prepared with reference to Example 2. The waste paper-based fibers prepared with L-cysteine nitrate ionic liquid were replaced with waste paper, and the biochar (K-BC) was obtained. The method of Example 2 was referred to remove organic pollutants in the aqueous solution, and the removal rates of different organic pollutants are shown in Table 6:

[0080] Table 6 Comparative table of removal rates of aqueous solutions prepared with different organic pollutants

[0081]

Claims

1. A method for removing organic pollutants from waste liquid, characterized in that, The method uses waste paper-based biochar as an adsorbent to treat waste liquid; The organic pollutants include one or more of enrofloxacin, bisphenol A, ciprofloxacin, and tetracycline; The preparation method of the waste paper-based biochar includes the following steps: (1) Waste paper pretreatment The waste paper is pretreated with an aqueous solution of L-cysteine nitrate ionic liquid as a treatment agent to obtain waste paper-based fibers; (2) Preparation of waste paper-based biochar The waste paper-based fibers obtained in step (1) are placed in a tubular furnace and carbonized in a nitrogen environment, controlling the temperature rising rate at 5 °C / min and carbonizing at 650-850 °C for 60-70 min; after taking out, it is washed to neutral and dried to obtain waste paper-based biochar.

2. The method according to claim 1, wherein The pretreatment is to mix L-cysteine nitrate ionic liquid with waste paper, place it in an autoclave, react at 105-110 °C and 0.01-0.02 Mpa for 3-5 h; after cooling to room temperature, take it out, filter it to separate the solid and liquid, and then repeatedly wash the remaining solid sample with deionized water until there are no bubbles in the waste liquid after washing; then wash it with absolute ethanol 2-3 times, and dry the washed sample to form waste paper-based fibers.

3. The method according to claim 2, characterized in that, The liquid-solid ratio of the aqueous solution of L-cysteine nitrate ionic liquid to waste paper is 20-30:1 ml:g; Among them, the mass concentration of L-cysteine nitrate ionic liquid is 70-75%.

4. The method according to any one of claims 1 to 3, characterized in that The preparation of the L-cysteine nitrate ionic liquid includes the following steps: 1) Pour nitric acid and water into a beaker, slowly stir and add L-cysteine to mix evenly to form a mixed solution; 2) Place the mixed solution prepared in step 1) in a water bath, stir and react at a constant temperature until there is no precipitate in the beaker and the solution is colorless and transparent, then the aqueous solution of L-cysteine nitrate ionic liquid is obtained.

5. The method according to claim 4, wherein The molar ratio of nitric acid to L-cysteine in step 1) is 1:1-1:

3.

6. The method according to claim 1, wherein The specific treatment of the waste liquid is to mix the biochar and the wastewater solution according to a solid-liquid ratio of 1:1-2 g:ml, stir in the dark, and separate the solid and liquid.

Images