Preparation method of activated carbon for improving COD (Chemical Oxygen Demand) removal efficiency

Abstract

The invention provides an activated carbon preparation method capable of improving COD (Chemical Oxygen Demand) removal efficiency, and relates to the technical field of activated carbon preparation. The preparation method of the activated carbon mainly comprises the following steps: crushing coconut shells, soaking in a saturated sodium chloride solution, steaming, freeze-drying, heating for carbonization, continuously heating, spraying and activating by using the saturated sodium chloride solution, soaking in a ferric nitrate solution, filtering, drying and the like. The defects in the prior art are overcome, the prepared activated carbon can have high COD removal efficiency under the condition of low dosage, the wastewater treatment cost is comprehensively reduced, and the activated carbon has a wide application range.

Description

Technical Field

[0001] The present invention relates to the technical field of activated carbon preparation, and specifically relates to a method for preparing activated carbon for improving the COD removal efficiency. Background Art

[0002] Chemical oxygen demand, abbreviated as COD, is an important indicator of the content of organic matter and reducing inorganic matter in water bodies, reflecting the degree of organic matter pollution in water bodies. COD is an indicator reflecting the amount of reducing substances in water, and the reducing substances in water include various organic matters, nitrites, sulfides, ferrous salts, etc., but mainly organic matters. This kind of wastewater rich in organic matter is usually organic wastewater, which is prone to cause eutrophication of water quality and has relatively great harm. These wastewaters contain a large amount of organic matters such as carbohydrates, fats, proteins, and cellulose. If directly discharged, it will cause serious pollution. Some organic wastewaters contain aromatic compounds and heterocyclic compounds, and also contain sulfides, nitrides, heavy metals, and toxic organic matters. The wastewater has poor biodegradability and is toxic to microorganisms, and it is difficult to be treated by general biochemical methods.

[0003] Activated carbon is a substance that can effectively adsorb pollutants in water bodies, especially the adsorption of organic or inorganic pollutants in sewage. Therefore, activated carbon is usually used for adsorption in sewage treatment at present stage. However, the adsorption effect of conventional activated carbon is poor, and the adsorption dosage of activated carbon is large, and the relative cost for water body purification treatment is high. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a method for preparing activated carbon for improving the COD removal efficiency, which can achieve a high COD removal efficiency with a lower activated carbon dosage, comprehensively reduce the cost of wastewater treatment, and enable the activated carbon to have a wider range of use.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0006] A method for preparing activated carbon for improving the COD removal efficiency, the activated carbon preparation method includes the following steps:

[0007] S1. Raw material pretreatment: Select coconut shells as raw materials, wash them cleanly and then crush them, and then add sodium chloride solution for soaking, steaming, and freeze-drying to obtain the pretreated raw materials for standby;

[0008] S2. Preliminary carbonization: Place the above-mentioned pretreated raw materials in a rotary kiln, heat up to 400 - 500 °C, and perform carbonization treatment for 1 - 3 h to obtain the original carbon materials for standby;

[0009] S3. Preliminary modification treatment: Place the above-mentioned raw carbon materials in a rotary kiln and heat them up to 600 - 650 °C. Then spray a saturated sodium chloride solution on the surface of the raw carbon materials. After heat preservation for 2 - 3 minutes, cool down to 300 - 350 °C and spray a saturated sodium chloride solution again. Then keep it at a constant temperature for 10 - 20 minutes to obtain preliminarily modified carbon.

[0010] S4. Secondary modification: Take out the above-mentioned preliminarily modified carbon directly and place it in a ferric nitrate solution at 80 - 100 °C for stirring treatment. After natural cooling and standing to room temperature, filter and dry it to obtain the finished activated carbon for standby.

[0011] Preferably, in step S1, the size of the crushed coconut shells is 0.1 - 1 cm.

[0012] Preferably, in step S1, the sodium chloride solution is a saturated sodium chloride solution, and the soaking time is 4 - 6 h.

[0013] Preferably, in step S1, the steaming method is to steam with hot steam at 102 - 120 °C for 20 - 30 minutes.

[0014] Preferably, in step S2, the heating method is to heat at a rate of 3 - 5 °C / min, and nitrogen is used to replace air in the whole rotary kiln for carbonization treatment.

[0015] Preferably, in step S3, the amount of the saturated sodium chloride solution sprayed each time is 2 - 3 times the total volume of the raw carbon materials.

[0016] Preferably, in step S3, the heating and cooling rates are both 5 - 10 °C / min, and the whole preliminary modification process is carried out under nitrogen protection.

[0017] Preferably, in step S4, the concentration of the ferric nitrate solution is 2 - 4 mol / L.

[0018] Preferably, in step S4, the drying method is to dry at 100 - 120 °C until constant weight.

[0019] The present invention provides a method for preparing activated carbon to improve the COD removal efficiency. Compared with the prior art, the advantages are as follows:

[0020] The present invention uses coconut shells as raw materials for producing activated carbon. By soaking coconut shells in brine and then steaming and freeze-drying them in the early stage, certain pores can be formed in the coconut shell materials. Subsequent carbonization treatment can obtain biochar with uniform pores. Then, by activating the biochar with a saturated sodium chloride solution at high temperature, the pores can be enriched to a certain extent while the adsorption effect of the activated carbon is improved. Subsequently, mixing with a ferric nitrate solution, standing, and drying can effectively improve the static adsorption efficiency of the activated carbon, and further improve the efficiency of the activated carbon in removing COD from wastewater. Description of the Drawings

[0021] Figure 1 These are the electron micrographs of the activated carbons prepared in the examples and comparative examples of the present invention, where a is the activated carbon prepared in Example 1; b is the activated carbon prepared in Comparative Example 1; c is the activated carbon prepared in Comparative Example 2; d is the activated carbon prepared in Comparative Example 3. Detailed implementation manners

[0022] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Example 1:

[0024] Preparation of activated carbon - 1:

[0025] (1) Select coconut shell as the raw material. After cleaning and crushing it to a particle size of 0.1 - 1 cm, add a saturated sodium chloride solution and soak it at room temperature for 5 h. Then take it out and steam it under 110 °C hot steam for 25 min, and then freeze - dry it to obtain the pretreated raw material for standby;

[0026] (2) Place the above - mentioned pretreated raw material in a rotary kiln, displace the air in the kiln with nitrogen, and heat it to 450 °C at a rate of 3 - 5 °C / min for carbonization treatment for 2 h to obtain the raw carbon material for standby;

[0027] (3) Continue to heat the above - mentioned raw carbon material in the rotary kiln (nitrogen atmosphere) to 600 °C at a rate of 5 - 10 °C / min. Then spray a saturated sodium chloride solution 3 times the total volume of the raw carbon material on the surface of the raw carbon material, keep it warm for 3 min, and then cool it to 350 °C at a rate of 5 - 10 °C / min and spray a saturated sodium chloride solution 2 times the total volume of the raw carbon material on the surface of the raw carbon material, and then keep it warm for 15 min to obtain the preliminarily modified carbon;

[0028] (4) Take out the above - mentioned preliminarily modified carbon while it is hot and directly place it in a 3 mol / L ferric nitrate solution at 100 °C, stir it, naturally cool it and let it stand to room temperature, then filter it and dry it to constant weight at 120 °C to obtain activated carbon - 1.

[0029] Comparative Example 1:

[0030] Preparation of activated carbon - 2:

[0031] (1) Select coconut shell as the raw material. After cleaning it, crush it to a particle size of 0.1 - 1 cm, then add it to clean water and soak it at room temperature for 5 h. Then take it out and steam it under 110 °C hot steam for 25 min, and then freeze-dry it to obtain the pretreated raw material for standby;

[0032] (2) Place the above pretreated raw material in a rotary kiln, displace the air in the kiln with nitrogen, heat it up to 450 °C at a rate of 3 - 5 °C / min, and carry out carbonization treatment for 2 h to obtain the original carbon material for standby;

[0033] (3) Continue to heat the above original carbon material in the rotary kiln (nitrogen atmosphere) to 600 °C at a rate of 5 - 10 °C / min. Then spray a sodium chloride saturated solution 3 times the total volume of the original carbon material on the surface of the original carbon material, keep it warm for 3 min, and then cool it down to 350 °C at a rate of 5 - 10 °C / min and spray a sodium chloride saturated solution 2 times the total volume of the original carbon material on the surface of the original carbon material, and then keep it warm for 15 min to obtain the preliminarily modified carbon;

[0034] (4) Take out the above preliminarily modified carbon while it is hot and directly place it in a 3 mol / L iron nitrate solution at 100 °C, stir it, and let it cool naturally and stand still until room temperature, then filter it and dry it to constant weight at 120 °C to obtain activated carbon - 2.

[0035] Comparative Example 2:

[0036] Preparation of activated carbon - 3:

[0037] (1) Select coconut shell as the raw material. After cleaning it, crush it to a particle size of 0.1 - 1 cm to obtain the pretreated raw material for standby;

[0038] (2) Place the above pretreated raw material in a rotary kiln, displace the air in the kiln with nitrogen, heat it up to 450 °C at a rate of 3 - 5 °C / min, and carry out carbonization treatment for 2 h to obtain the original carbon material for standby;

[0039] (3) Continue to heat the above original carbon material in the rotary kiln (nitrogen atmosphere) to 600 °C at a rate of 5 - 10 °C / min. Then spray a sodium chloride saturated solution 3 times the total volume of the original carbon material on the surface of the original carbon material, keep it warm for 3 min, and then cool it down to 350 °C at a rate of 5 - 10 °C / min and spray a sodium chloride saturated solution 2 times the total volume of the original carbon material on the surface of the original carbon material, and then keep it warm for 15 min to obtain the preliminarily modified carbon;

[0040] (4) Take out the above preliminarily modified carbon while it is hot and directly place it in a 3 mol / L iron nitrate solution at 100 °C, stir it, and let it cool naturally and stand still until room temperature, then filter it and dry it to constant weight at 120 °C to obtain activated carbon - 3.

[0041] Comparative Example 3:

[0042] Preparation of activated carbon - 4:

[0043] (1) Select coconut shell as the raw material. After cleaning it, crush it to a particle size of 0.1 - 1 cm. Then add it to a saturated sodium chloride solution and soak it at room temperature for 5 h. Then take it out and steam it under 110 °C hot steam for 25 min. After that, freeze-dry it to obtain the pretreated raw material for standby.

[0044] (2) Place the above pretreated raw material in a rotary kiln. Replace the air in the kiln with nitrogen, and heat it to 450 °C at a rate of 3 - 5 °C / min for carbonization treatment for 2 h to obtain the original carbon material for standby.

[0045] (3) Continue to heat the above original carbon material in the rotary kiln (in a nitrogen atmosphere) to 600 °C at a rate of 5 - 10 °C / min. Then spray 3 times the total volume of the original carbon material of clear water on the surface of the original carbon material, keep it warm for 3 min. Then cool it to 350 °C at a rate of 5 - 10 °C / min and spray 2 times the total volume of the original carbon material of clear water on the surface of the original carbon material, and then keep it warm for 15 min to obtain the preliminarily modified carbon.

[0046] (4) Take out the above preliminarily modified carbon while it is hot and directly place it in a 3 mol / L ferric nitrate solution at 100 °C, stir it, and let it cool naturally and stand still until room temperature. Then filter it and dry it to constant weight at 120 °C to obtain activated carbon - 4.

[0047] Detection:

[0048] 1. Conduct an apparent morphology detection on the activated carbon - 1, activated carbon - 2, activated carbon - 3, and activated carbon - 4 prepared above. The specific results are as Figure 1 shown. Among them, activated carbon - 1 and activated carbon - 4 ( Figure 1 a and Figure 1 d) have more pores and a larger surface area. However, there are flaky structures on the surface of activated carbon - 4, which is somewhat different from that of activated carbon - 1.

[0049] 2. Detection of the removal efficiency of COD in sewage by each group of activated carbon:

[0050] Use the same batch of wastewater as the experimental material. Detect that the COD content in the wastewater is 1132 mg / L. Add the above different activated carbon to the wastewater at an addition amount of 0.5 g / L respectively. After stirring evenly, let it stand still at room temperature. Then take samples at different times to detect the COD content in the wastewater and calculate the removal rate. The specific results are shown in Table 1 below:

[0051] Table 1

[0052]

[0053] As can be seen from the above table, the activated carbon prepared in Example 1 reached the adsorption saturation state in about 30 minutes, and the overall COD removal rate was above 92%. The final COD removal rate of Comparative Example 1 was about 90%, which was not much different from that of Example 1. However, Comparative Example 1 could reach a certain saturation state only at 60 minutes. The overall adsorption capacity and adsorption rate of Comparative Example 2 were also significantly lower than those of Example 1. In addition, the adsorption rate of Comparative Example 3 was slightly higher than that of Example 1 in the early stage, but the total adsorption capacity was lower than that of Example 1. That is, overall, the activated carbon in Example 1 had a better COD adsorption effect.

[0054] The above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of activated carbon for improving the COD removal efficiency, characterized in that, The method for preparing the activated carbon comprises the following steps: S1. Pretreatment of raw materials: Select coconut shells as raw materials, wash them cleanly, crush them, then soak them in a sodium chloride solution, steam them, and then freeze-dry them to obtain pretreated raw materials for standby; S2. Primary carbonization: Place the above-mentioned pretreated raw materials in a rotary kiln, heat up to 400 - 500 °C, and carry out carbonization treatment for 1 - 3 h to obtain primary carbon materials for standby; S3. Primary modification treatment: Place the above-mentioned primary carbon materials in a rotary kiln, heat up to 600 - 650 °C, then spray a saturated sodium chloride solution on the surface of the primary carbon materials, keep them warm for 2 - 3 min, then cool down to 300 - 350 °C and spray a saturated sodium chloride solution again, and then keep them warm for 10 - 20 min to obtain primarily modified carbon; S4. Secondary modification: Directly take out the above-mentioned primarily modified carbon and place it in a ferric nitrate solution at 80 - 100 °C, stir it, let it cool naturally and stand still until room temperature, then filter and dry it to obtain finished activated carbon for standby.

2. The preparation method according to claim 1, wherein: In the step S1, the size of the crushed coconut shells is 0.1 - 1 cm.

3. The preparation method according to claim 1, wherein: In the step S1, the sodium chloride solution is a saturated sodium chloride solution, and the soaking time is 4 - 6 h.

4. The preparation method according to claim 1, wherein: In the step S1, the steaming method is to carry out steaming treatment with hot steam at 102 - 120 °C for 20 - 30 min.

5. The preparation method according to claim 1, characterized in that: In the step S2, the heating method is to heat up at a rate of 3 - 5 °C / min, and nitrogen is used to displace air in the whole rotary kiln for carbonization treatment.

6. The preparation method according to claim 1, characterized in that: In the step S3, the amount of the saturated sodium chloride solution sprayed each time is 2 - 3 times the total volume of the primary carbon materials.

7. The preparation method according to claim 1, characterized in that: In the step S3, the heating and cooling rates are both 5 - 10 °C / min, and the whole primary modification process is carried out under nitrogen protection.

8. The preparation method according to claim 1, characterized in that: In the step S4, the concentration of the ferric nitrate solution is 2 - 4 mol / L.

9. The preparation method according to claim 1, characterized in that: In the step S4, the drying method is to dry it to constant weight at a temperature of 100 - 120 °C.

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