Process for the preparation of porous carbons with mesopore size and applications thereof

Abstract

The present application relates to the preparation method and application of porous carbon with mesoporous aperture, and belongs to the technical field of activated carbon.The present application provides a preparation method of porous carbon with mesoporous aperture, which is summarized as follows: after ball milling, the rice husk is acid washed to remove impurities, mixed with a phosphoric acid solution after drying, dried, pre-carbonized at a lower temperature, activated at a medium temperature, treated at a higher temperature, washed with alkali to remove silicon, and treated by microwave-vapor to obtain porous carbon with mesoporous aperture, which can be applied to organic dye wastewater treatment and pharmaceutical wastewater treatment.The present application uses rice husk as a natural template to generate mesopores, does not need to add a template agent additionally, uses CO2 to assist pore expansion at a lower temperature, a medium temperature and a higher temperature simultaneously, finally uses microwave irradiation combined with water vapor treatment to repair the pore defects generated in the high-temperature carbonization process and enhance the stability of the surface oxygen-containing functional groups, so as to obtain porous carbon with mesoporous aperture, which can effectively adsorb pollutants with a pore size greater than 2nm.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of activated carbon, and relates to a preparation method of porous carbon with a mesopore size and application thereof. BACKGROUND

[0002] Activated carbon is a kind of porous carbon material processed by a special process. Due to its developed pore structure and large specific surface area, it is used as an efficient adsorbent in the environmental protection field. However, the traditional activated carbon is mainly characterized by microporous (<2nm) pore structure, which has obvious limitations in actual application. For example, there may be various compounds or macromolecules with a molecular size greater than 2nm in organic dye wastewater or pharmaceutical wastewater, and the microporous structure will produce a steric hindrance effect, thereby reducing the adsorption capacity. Secondly, the narrow pore structure causes the pollutant molecules to need to undergo a long diffusion process to reach the internal adsorption sites. Furthermore, the micropores are prone to structural collapse during the regeneration process, which seriously affects the service life of the material. SUMMARY

[0003] The purpose of the application is to provide a preparation method of porous carbon with a mesopore size and application thereof. The application generates mesopores by using rice husks as a natural template without adding additional template agents. The rice husks are pre-carbonized at a low temperature, activated at a medium temperature, treated at a high temperature, and assisted by CO2 to expand the pores. Finally, microwave irradiation is combined with steam treatment to repair the pore defects generated in the high-temperature carbonization process and enhance the stability of the surface oxygen-containing functional groups, so that a kind of porous carbon with a mesopore size is obtained, which can effectively adsorb pollutants with a pore size greater than 2nm.

[0004] The purpose of the application can be achieved by the following technical solutions.

[0005] The preparation method of porous carbon with a mesopore size comprises the following steps:

[0006] Step one, the rice husks are ball milled, acid washed to remove impurities, and dried to obtain raw materials;

[0007] Step two, the raw materials are mixed with a phosphoric acid solution and dried to obtain activated raw materials;

[0008] Step three, the activated raw materials are pre-carbonized at a low temperature, activated at a medium temperature, and treated at a high temperature to obtain carbonized products;

[0009] Step four, the carbonized products are alkali washed to remove silicon and subjected to microwave-steam treatment to obtain porous carbon with a mesopore size.

[0010] Further, the ball milling in step one refers to ball milling at a rotating speed of 400-500 rpm for 2.5-3.5 h; the acid pickling refers to soaking in a 0.8-1.2 mol / L hydrochloric acid solution for 2-3 h, and washing with deionized water until neutral; the drying temperature is 80℃.

[0011] Further, the mass ratio of the raw material to the phosphoric acid solution in step two is 1:1.4-1.6; the content of phosphoric acid in the phosphoric acid solution is 31-35 wt%; the mixing refers to setting the ultrasonic frequency to 30-50 kHz, the ultrasonic power to 300-400 W, and ultrasonic irradiation for 0.8-1.2 h; the drying refers to drying at 120℃ until the weight is constant.

[0012] Further, the lower temperature pre-carbonization in step three refers to heating to 298-302℃ at a rate of 1.5-2.5℃ / min in a nitrogen atmosphere, and maintaining the temperature for 1-2 h.

[0013] Further, the medium temperature activation in step three refers to heating to 590-610℃ at a rate of 4.5-5.5℃ / min, and maintaining the temperature for 2-3 h.

[0014] Further, the higher temperature treatment in step three refers to heating to 780-820℃ at a rate of 2.5-3.5℃, and maintaining the temperature for 0.5-0.7 h while passing in CO2 at a flow rate of 45-55 mL / min.

[0015] Further, the alkali washing to remove silicon in step four refers to soaking in a 1.5-2.5 mol / L sodium hydroxide solution for 5-7 h, and washing with deionized water until neutral.

[0016] Further, the microwave-steam treatment in step four refers to microwave irradiation at 550-650 W for 2.5-3.5 min, and microwave irradiation while passing in water vapor at a flow rate of 8-12 mL / min.

[0017] Further, the porous carbon is applied to organic dye wastewater treatment and pharmaceutical wastewater treatment.

[0018] The beneficial effects of the present application are:

[0019] (1) The present application generates mesopores using rice husks as a natural template without the need for additional template agents. Through lower temperature pre-carbonization, medium temperature activation, and higher temperature treatment while using CO2 to assist in pore expansion, and finally using microwave irradiation combined with water vapor treatment, the defects in the pores generated during high temperature carbonization are repaired, and the stability of the surface oxygen-containing functional groups is enhanced, obtaining a porous carbon with mesopore size, which can effectively adsorb pollutants with a pore size greater than 2 nm.

[0020] (2) The hemicellulose and cellulose in the rice husk pyrolyze and release CO2, H2O and small molecule organic matters to form an initial carbon skeleton during temperature treatment, at this time, the phosphoric acid penetrates into the biomass, and dehydration promotes the condensation between the biomass molecules to form microporous and mesoporous rudiments; then, the phosphoric acid is decomposed into polyphosphoric acid during medium temperature activation to further promote the carbonization reaction and form mesopores through pore forming and pore expanding; finally, CO2 assists pore expanding during high temperature treatment to dredge the pore channels and improve the connectivity and structural stability of the pore channels. DETAILED DESCRIPTION

[0021] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined object, the specific embodiments, structures, features and effects according to the present application are described in detail below in combination with examples.

[0022] All the examples and comparative examples in the present application are directly purchased from the market, and are purchased from

[0023] Example 1

[0024] The preparation method of the porous carbon with mesopore size comprises the following steps:

[0025] Step one, the rice husk is ball milled, acid washed, and dried to obtain a raw material;

[0026] Step two, the raw material is mixed with a phosphoric acid solution, and dried to obtain an activated raw material;

[0027] Step three, the activated raw material is subjected to low-temperature pre-carbonization, medium-temperature activation, and high-temperature treatment to obtain a carbonized product;

[0028] Step four, the carbonized product is subjected to alkali washing to remove silicon, and microwave-vapor treatment to obtain the porous carbon with mesopore size.

[0029] The ball milling in step one refers to ball milling at a speed of 400 rpm for 2.5 h; the acid washing refers to soaking in a 0.8 mol / L hydrochloric acid solution for 2 h and washing with deionized water until neutral; and the drying temperature is 80℃.

[0030] The mass ratio of the raw material to the phosphoric acid solution in step two is 1:1.4; the content of phosphoric acid in the phosphoric acid solution is 31 wt%; the mixing refers to setting the ultrasonic frequency to 30 kHz and the ultrasonic power to 300 W, and ultrasonic treatment for 0.8 h; and the drying refers to drying at 120℃ until constant weight.

[0031] The low-temperature pre-carbonization in step three refers to heating to 298℃ at a rate of 1.5℃ / min under a nitrogen atmosphere, and holding for 1 h.

[0032] The medium temperature activation in step three refers to temperature rising to 590℃ at a rate of 4.5℃ / min, and holding for 2h.

[0033] The higher temperature treatment in step three refers to temperature rising to 780℃ at a rate of 2.5℃, and holding for 0.5h while CO2 is passed in at a flow rate of 45mL / min.

[0034] The alkali washing to remove silicon in step four refers to soaking in 1.5mol / L sodium hydroxide solution for 5h, and washing with deionized water until neutral.

[0035] The microwave-steam treatment in step four refers to microwave irradiation at 550W for 2.5min, and microwave irradiation while passing in water vapor at a flow rate of 8mL / min.

[0036] The porous carbon is applied to organic dye wastewater treatment and pharmaceutical wastewater treatment.

[0037] Example 2

[0038] The method for preparing the porous carbon with mesopore diameter comprises the following steps:

[0039] Step one, milling rice husks, acid washing to remove impurities, and drying to obtain raw materials;

[0040] Step two, mixing the raw materials with a phosphoric acid solution, and drying to obtain activated raw materials;

[0041] Step three, pre-carbonizing the activated raw materials at a lower temperature, activating at a medium temperature, and treating at a higher temperature to obtain carbonized products;

[0042] Step four, washing the carbonized products with alkali to remove silicon, and microwave-steam treating to obtain the porous carbon with mesopore diameter.

[0043] The milling in step one refers to milling at a speed of 430rpm for 2.8h; the acid washing refers to soaking in 0.9mol / L hydrochloric acid solution for 2.3h, and washing with deionized water until neutral; and the drying temperature is 80℃.

[0044] The mass ratio of the raw materials to the phosphoric acid solution in step two is 1:1.46; the content of phosphoric acid in the phosphoric acid solution is 32wt%; the mixing refers to setting the ultrasonic frequency to 35kHz, the ultrasonic power to 320W, and ultrasonic for 0.9h; and the drying refers to drying at 120℃ until constant weight.

[0045] The lower temperature pre-carbonization in step three refers to temperature rising to 299℃ at a rate of 1.8℃ / min under nitrogen atmosphere, and holding for 1.3h.

[0046] The medium temperature activation in step three refers to temperature rising to 595℃ at a rate of 4.8℃ / min, and holding for 2.2h.

[0047] The higher temperature treatment in step three refers to temperature rising to 790℃ at a rate of 2.6℃, and holding for 0.55h while CO2 is passed in at a flow rate of 48mL / min.

[0048] The alkali washing to remove silicon in step four refers to soaking in 1.8mol / L sodium hydroxide solution for 5.7h, and washing with deionized water until neutral.

[0049] The microwave-steam treatment in step four refers to 570W microwave irradiation for 2.8min, and microwave irradiation while passing in water vapor at a flow rate of 9mL / min.

[0050] The porous carbon is applied to organic dye wastewater treatment and pharmaceutical wastewater treatment.

[0051] Example 3

[0052] The method for preparing the porous carbon with mesopore diameter comprises the following steps:

[0053] Step one, acid washing and drying of the milled rice husk to obtain raw material;

[0054] Step two, mixing the raw material with phosphoric acid solution and drying to obtain activated raw material;

[0055] Step three, lower temperature pre-carbonization, medium temperature activation, and higher temperature treatment of the activated raw material to obtain carbonized product;

[0056] Step four, alkali washing to remove silicon and microwave-steam treatment of the carbonized product to obtain porous carbon with mesopore diameter.

[0057] The ball milling in step one refers to ball milling at a speed of 450rpm for 3h; the acid washing refers to soaking in 1mol / L hydrochloric acid solution for 2.5h, and washing with deionized water until neutral; and the drying temperature is 80℃.

[0058] The mass ratio of the raw material to the phosphoric acid solution in step two is 1:1.5; the content of phosphoric acid in the phosphoric acid solution is 33wt%; the mixing refers to setting the ultrasonic frequency to 40kHz, the ultrasonic power to 350W, and ultrasonic for 1h; and the drying refers to drying at 120℃ until constant weight.

[0059] The lower temperature pre-carbonization in step three refers to temperature rising to 300℃ at a rate of 2℃ / min under nitrogen atmosphere, and holding for 1.5h.

[0060] The medium temperature activation in step three refers to temperature rising to 600℃ at a rate of 5℃ / min, and holding for 2.5h.

[0061] The higher temperature treatment in step three refers to temperature rising to 800℃ at a rate of 3℃, and holding for 0.6h while CO2 is passed in at a flow rate of 50mL / min.

[0062] The alkali washing to remove silicon in step four refers to soaking in 2mol / L sodium hydroxide solution for 6h, and washing with deionized water until neutral.

[0063] The microwave-steam treatment in step four refers to 600W microwave irradiation for 3min, and microwave irradiation while passing in water vapor at a flow rate of 10mL / min.

[0064] The porous carbon is applied to organic dye wastewater treatment and pharmaceutical wastewater treatment.

[0065] Example 4

[0066] The method for preparing the porous carbon with mesopore size comprises the following steps:

[0067] Step one, milling rice husks, acid washing to remove impurities, and drying to obtain raw materials;

[0068] Step two, mixing the raw materials with a phosphoric acid solution, and drying to obtain activated raw materials;

[0069] Step three, pre-carbonizing the activated raw materials at a lower temperature, activating at a medium temperature, and treating at a higher temperature to obtain carbonized products;

[0070] Step four, washing the carbonized products with alkali to remove silicon, and microwave-steam treating to obtain the porous carbon with mesopore size.

[0071] The milling in step one refers to milling at a speed of 470rpm for 3.3h; the acid washing refers to soaking in 1.1mol / L hydrochloric acid solution for 2.6h, and washing with deionized water until neutral; and the drying temperature is 80℃.

[0072] The mass ratio of the raw materials to the phosphoric acid solution in step two is 1:1.58; the content of phosphoric acid in the phosphoric acid solution is 34wt%; the mixing refers to setting the ultrasonic frequency to 45kHz, the ultrasonic power to 360W, and ultrasonic for 1.1h; and the drying refers to drying at 120℃ until constant weight.

[0073] The lower temperature pre-carbonization in step three refers to temperature rising to 301℃ at a rate of 2.4℃ / min under nitrogen atmosphere, and holding for 1.6h.

[0074] The medium temperature activation in step three refers to temperature rising to 605℃ at a rate of 5.2℃ / min, and holding for 2.7h.

[0075] The higher temperature treatment in step three refers to temperature rising to 810℃ at a rate of 3.4℃, and holding for 0.64h while CO2 is passed in at a flow rate of 52mL / min.

[0076] The alkali washing to remove silicon in step four refers to soaking in 2.2mol / L sodium hydroxide solution for 6.5h, and washing with deionized water until neutral.

[0077] The microwave-steam treatment in step four refers to 630W microwave irradiation for 3.2min, and microwave irradiation while passing in water vapor at a flow rate of 11mL / min.

[0078] The porous carbon is applied to organic dye wastewater treatment and pharmaceutical wastewater treatment.

[0079] Example 5

[0080] The method for preparing the porous carbon with mesopore diameter comprises the following steps:

[0081] Step one, acid washing and drying of the milled rice hull to obtain raw material;

[0082] Step two, mixing the raw material with phosphoric acid solution, and drying to obtain activated raw material;

[0083] Step three, lower temperature pre-carbonization, medium temperature activation, and higher temperature treatment of the activated raw material to obtain carbonized product;

[0084] Step four, alkali washing to remove silicon and microwave-steam treatment of the carbonized product to obtain porous carbon with mesopore diameter.

[0085] The ball milling in step one refers to ball milling at a speed of 500rpm for 3.5h; the acid washing refers to soaking in 1.2mol / L hydrochloric acid solution for 3h, and washing with deionized water until neutral; and the drying temperature is 80℃.

[0086] The mass ratio of the raw material to the phosphoric acid solution in step two is 1:1.6; the content of phosphoric acid in the phosphoric acid solution is 35wt%; the mixing refers to setting the ultrasonic frequency to 50kHz, the ultrasonic power to 400W, and ultrasonic for 1.2h; and the drying refers to drying at 120℃ until constant weight.

[0087] The lower temperature pre-carbonization in step three refers to temperature rising to 302℃ at a rate of 2.5℃ / min under nitrogen atmosphere, and holding for 2h.

[0088] The medium temperature activation in step three refers to temperature rising to 610℃ at a rate of 5.5℃ / min, and holding for 3h.

[0089] The higher temperature treatment in step three refers to temperature rising to 820℃ at a rate of 3.5℃, and holding for 0.7h while CO2 is passed in at a flow rate of 55mL / min.

[0090] The alkali washing to remove silicon in step four refers to soaking in 2.5mol / L sodium hydroxide solution for 7h, and washing with deionized water until neutral.

[0091] The microwave-steam treatment in step four refers to 650W microwave irradiation for 3.5min, and microwave irradiation while passing in water vapor at a flow rate of 12mL / min.

[0092] The porous carbon is applied to organic dye wastewater treatment and pharmaceutical wastewater treatment.

[0093] Example 6

[0094] On the basis of example 3, the content of phosphoric acid in the phosphoric acid solution is changed to 20wt%, and other conditions remain the same as in example 3.

[0095] Example 7

[0096] On the basis of example 3, the content of phosphoric acid in the phosphoric acid solution is changed to 50wt%, and other conditions remain the same as in example 3.

[0097] Comparative example 1

[0098] On the basis of example 3, other conditions remain the same, and the preparation method of the porous carbon with mesoporous pore size is changed to the following steps:

[0099] Step one, the rice husk is ball milled, acid washed to remove impurities, dried, and the raw material is obtained;

[0100] Step two, the raw material is mixed with a phosphoric acid solution, dried, and the activated raw material is obtained;

[0101] Step three, the activated raw material is subjected to medium temperature activation and higher temperature treatment to obtain a carbonization product; at this time, the medium temperature activation refers to temperature rising to 600℃ at a rate of 5℃ / min, and holding for 4h;

[0102] Step four, the carbonization product is subjected to alkali washing to remove silicon and microwave-steam treatment to obtain the porous carbon with mesoporous pore size.

[0103] Comparative example 2

[0104] On the basis of example 3, other conditions remain the same, and the preparation method of the porous carbon with mesoporous pore size is changed to the following steps:

[0105] Step one, the rice husk was ball milled, and then acid washed to remove impurities, and dried to obtain the raw material;

[0106] Step two, the raw material was mixed with phosphoric acid solution, and dried to obtain the activated raw material;

[0107] Step three, the activated raw material was pre-carbonized at a lower temperature, and then treated at a higher temperature to obtain the carbonized product; at this time, the higher temperature treatment refers to heating to 800℃ at a rate of 3℃, and at the same time, CO2 was passed in at a flow rate of 50mL / min for 3.1h;

[0108] Step four, the carbonized product was alkali washed to remove silicon, and then treated by microwave-vapor to obtain the porous carbon with mesoporous pore size.

[0109] Comparative Example 3

[0110] On the basis of Example 3, the other conditions were kept unchanged, and the preparation method of the porous carbon with mesoporous pore size was changed to the following steps:

[0111] Step one, the rice husk was ball milled, and then acid washed to remove impurities, and dried to obtain the raw material;

[0112] Step two, the raw material was mixed with phosphoric acid solution, and dried to obtain the activated raw material;

[0113] Step three, the activated raw material was pre-carbonized at a lower temperature, and then treated at a higher temperature to obtain the carbonized product; at this time, the higher temperature treatment refers to heating to 800℃ at a rate of 3℃, and at the same time, CO2 was passed in at a flow rate of 50mL / min for 3.1h;

[0114] Step four, the carbonized product was alkali washed to remove silicon, and then treated by microwave-vapor to obtain the porous carbon with mesoporous pore size.

[0115] Comparative Example 4

[0116] On the basis of Example 3, the other conditions were kept unchanged, and the operation of pre-carbonization at a lower temperature was changed to heating to 300℃ at a rate of 4.5℃ / min under nitrogen atmosphere, and keeping for 1.5h.

[0117] Comparative Example 5

[0118] On the basis of Example 3, the other conditions were kept unchanged, and the keeping time of the activation at a medium temperature was changed to 1h.

[0119] Comparative Example 6

[0120] On the basis of Example 3, the other conditions were kept unchanged, and the keeping time of the activation at a medium temperature was changed to 4h.

[0121] Comparative Example 7

[0122] On the basis of Example 3, the other conditions were kept unchanged, and the flow rate of CO2 during the higher temperature treatment was changed to 20mL / min.

[0123] Comparative Example 8

[0124] On the basis of Example 3, keeping other conditions unchanged, the power during microwave-steam treatment was changed to 400 W.

[0125] Comparative Example 9

[0126] On the basis of Example 3, keeping other conditions unchanged, the power during microwave-steam treatment was changed to 800 W.

[0127] The porous carbon prepared in Examples 1-7 and Comparative Examples 1-9 was used as a sample, and the mesopore size (average) and mesopore ratio thereof were tested, and the test results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] As can be seen from Table 1, the mesopore size of the porous carbon prepared by the present application is stably in the range of 4.3±0.2 nm, and the mesopore ratio is in the range of 76-78%. Although the mesopore size and mesopore ratio of some of the comparative examples are higher than those of the examples, a larger mesopore size and a higher mesopore ratio are prone to collapse in actual application. In addition, the increase in some values is based on the change in preparation parameters, such as the increase in phosphoric acid concentration and the increase in power during microwave-steam treatment, which is prone to cause burden to the equipment in actual operation, thereby increasing the operating cost, etc. Therefore, compared with the comparative examples, the present application provides a porous carbon with mesopores and a relatively stable mesopore ratio, which has a good application prospect.

[0132] The above description is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with reference to the preferred embodiments, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any indirect modification, equivalent change and modification of the above embodiments based on the technical essence of the present application are still within the scope of the technical solution of the present application.

Claims

1. A method for the preparation of porous carbon having a mesopore size, characterized in that: The preparation method of the porous carbon with mesoporous pore size comprises the following steps: Step one, the rice husk is ball milled, acid washed, and dried to obtain a raw material; Step two, the raw material is mixed with a phosphoric acid solution, and dried to obtain an activated raw material; Step three, the activated raw material is subjected to low-temperature pre-carbonization, medium-temperature activation, and high-temperature treatment to obtain a carbonized product; Step four, the carbonized product is subjected to alkali washing to remove silicon and microwave-steam treatment to obtain the porous carbon with mesoporous pore size; The low-temperature pre-carbonization in step three refers to heating to 298-302 DEG C at a rate of 1.5-2.5 DEG C / min under a nitrogen atmosphere, and maintaining for 1-2 h; The medium-temperature activation in step three refers to heating to 590-610 DEG C at a rate of 4.5-5.5 DEG C / min, and maintaining for 2-3 h; The high-temperature treatment in step three refers to heating to 780-820 DEG C at a rate of 2.5-3.5 DEG C / min, and maintaining for 0.5-0.7 h while passing in CO2 at a flow rate of 45-55 mL / min; The alkali washing to remove silicon in step four refers to soaking in a 1.5-2.5 mol / L sodium hydroxide solution for 5-7 h, and washing with deionized water until neutral; The microwave-steam treatment in step four refers to microwave irradiation at 550-650 W for 2.5-3.5 min, while passing in water vapor at a flow rate of 8-12 mL / min.

2. The method of claim 1, wherein the porous carbon having a mesopore diameter is prepared by: The ball milling in step one refers to ball milling at a speed of 400-500 rpm for 2.5-3.5 h; the acid washing refers to soaking in a 0.8-1.2 mol / L hydrochloric acid solution for 2-3 h, and washing with deionized water until neutral; and the drying temperature is 80 DEG C.

3. The method of claim 1, wherein: The mass ratio of the raw material to the phosphoric acid solution in step two is 1:1.4-1.6; the content of phosphoric acid in the phosphoric acid solution is 31-35 wt%; the mixing refers to setting an ultrasonic frequency of 30-50 kHz, an ultrasonic power of 300-400 W, and ultrasonic treatment for 0.8-1.2 h; and the drying refers to drying at 120 DEG C until constant weight.

4. Use of the porous carbon having a mesopore diameter prepared by the method of any one of claims 1 to 3. The porous carbon is applied to organic dye wastewater treatment and pharmaceutical wastewater treatment.

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