Coffee grounds-based activated carbon, its preparation method and uses

Abstract

This invention relates to a coffee grounds-based activated carbon, its preparation method, and its uses. The preparation method includes: (1) sequentially soaking, drying, acid-leaching, and activating coffee grounds to obtain an activated carbon precursor; (2) immersing the activated carbon precursor obtained in step (1) in a modifier solution, and then sequentially subjecting it to solid-liquid separation, drying, and microwave activation to obtain coffee grounds-based activated carbon. The preparation method of this invention uses a modifier solution to modify the activated carbon precursor, which can enrich the types of functional groups in the activated carbon. Subsequently, microwave radiation activation can improve the activity of adsorbed species on the surface of the coffee grounds-based activated carbon, thereby improving its mercury removal performance. The raw materials are inexpensive and readily available, the preparation process is simple, and it is easy to operate and scale up.

Description

Technical Field

[0001] This invention belongs to the field of waste gas treatment and resource utilization technology in the fields of environmental protection and governance, energy conservation and comprehensive resource utilization, and particularly relates to a coffee grounds-based activated carbon, its preparation method and uses. Background Technology

[0002] Currently, activated carbon in my country is mainly divided into coal-based activated carbon and wood-based activated carbon, with coal-based activated carbon being the dominant type. However, due to the non-renewable nature of raw coal resources and the significant increase in carbon dioxide emissions during its production, the long-term competitive advantage of coal-based activated carbon is far lower than that of wood-based activated carbon made from sawdust, fruit shells, and other raw materials. The main raw materials for producing wood-based activated carbon in my country are hard fruit shells, such as walnut shells and coconut shells. However, these raw material resources are limited, restricting its development. Therefore, there is an urgent need to develop new raw materials for activated carbon preparation.

[0003] According to statistics, the world consumes at least 400 billion cups of coffee annually, generating 8 million tons of coffee grounds. Because coffee beans contain woody fibers, recycling coffee grounds has significant economic value. The British company Bio-Bean processes thousands of tons of coffee grounds into biofuel, but its utilization rate is extremely low. Recycling them and using them as biomass to produce activated carbon could not only expand new avenues for the resource utilization of coffee grounds but also effectively reduce environmental pollution.

[0004] Coal combustion is one of the largest anthropogenic sources of mercury emissions, including elemental mercury (Hg). 0 Hg is volatile and insoluble, accounting for over 80% of emissions in coal-fired flue gas. Therefore, reducing Hg in coal-fired flue gas is crucial. 0 The emission of mercury is of paramount importance. Activated carbon has yielded numerous research findings on mercury removal from flue gas. Because activated carbon adsorbs mercury from flue gas with rapid adsorption speed and high efficiency, and because activated carbon adsorption technology is mature, most institutions choose activated carbon for mercury removal from flue gas.

[0005] However, due to the low mercury removal efficiency of pure activated carbon, there is an urgent need to develop a modified activated carbon to improve its efficiency. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides coffee grounds-based activated carbon, its preparation method, and its applications. The raw materials for the coffee grounds-based activated carbon are inexpensive and readily available, and the preparation method is simple. The activated carbon, after modification with a modifier and microwave activation, has a higher specific surface area, richer functional groups, and excellent mechanical properties. It can achieve efficient one-time removal of mercury from coal-fired flue gas, reducing the risk of secondary mercury release.

[0007] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing coffee grounds-based activated carbon, the method comprising the following steps:

[0009] (1) Coffee grounds were soaked, dried, acid-soaked and activated in sequence to obtain activated carbon precursor;

[0010] (2) The activated carbon precursor described in step (1) is immersed in a modifier solution, and then subjected to solid-liquid separation, drying and microwave activation in sequence to obtain coffee grounds-based activated carbon.

[0011] The preparation method of the present invention obtains activated carbon precursor by soaking, drying, acid leaching and high temperature activation of coffee grounds, and then modifies it with a modifier and activates it by microwave radiation to obtain coffee grounds-based activated carbon for mercury removal from flue gas. The raw materials are cheap and readily available, the preparation process is simple, and it is easy to operate and scale up.

[0012] It is worth noting that the present invention uses a modifier solution to modify the activated carbon precursor, which can enrich the types of functional groups of activated carbon. Then, microwave radiation activation is used to improve the activity of adsorbed species on the surface of coffee grounds-based activated carbon, thereby improving the mercury removal performance of activated carbon.

[0013] As a preferred technical solution of the present invention, the number of soaking times in step (1) is ≥3 times, for example, it can be 4 times, 5 times, 6 times, 7 times or 8 times, preferably 3-8 times.

[0014] Preferably, the soaking in step (1) is carried out in water.

[0015] Preferably, the drying temperature in step (1) is 105-120°C, for example, it can be 107°C, 110°C, 112°C, 114°C, 116°C or 118°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] As a preferred technical solution of the present invention, the acid leaching solution in step (1) includes a phosphoric acid solution.

[0017] Preferably, the concentration of the phosphoric acid solution is 6%-20%, for example, it can be 8%, 10%, 12%, 14%, 16% or 18%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0018] Preferably, the mass-to-volume ratio of coffee grounds to phosphoric acid solution is 1:(4-10)g / mL, for example, it can be 1:5g / mL, 1:6g / mL, 1:7g / mL, 1:8g / mL or 1:9g / mL, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] It is worth noting that the present invention uses a specific concentration and proportion of phosphoric acid solution to activate the coffee grounds matrix, thereby promoting the decomposition of the oils contained in the coffee grounds and creating conditions for subsequent high-temperature activation.

[0020] Preferably, the acid leaching in step (1) is performed under ultrasound.

[0021] Preferably, the acid leaching time in step (1) is 2-4 hours, for example, it can be 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours or 3.8 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] In this invention, step (1) further includes solid-liquid separation and drying between acid leaching and activation.

[0023] As a preferred technical solution of the present invention, the heating rate for activation in step (1) is 8-12℃ / min, for example, it can be 8.5℃ / min, 9℃ / min, 9.5℃ / min, 10℃ / min, 10.5℃ / min, 11℃ / min or 11.5℃ / min, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the activation temperature in step (1) is 300-500℃, for example, it can be 320℃, 340℃, 360℃, 380℃, 400℃, 420℃, 440℃, 460℃ or 480℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] In this invention, the activation in step (1) is carried out in a muffle furnace, and after activation, it is naturally cooled to room temperature, and then washed with water until neutral and dried.

[0026] Preferably, the activation holding time in step (1) is 1-3h, for example, it can be 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h or 2.8h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] As a preferred technical solution of the present invention, the mass fraction of the modifier solution in step (2) is 0.1-10wt%, for example, it can be 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, or 9wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the mass ratio of the activated carbon precursor to the modifier in the modifier solution described in step (2) is 1:(0.02-0.1), for example, it can be 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08 or 1:0.09, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] It is worth noting that modifying the activated carbon precursor with a modifier enriches the types of functional groups in the activated carbon precursor, and the modifying element has a greater effect on Hg. 0 Stronger binding force, thus increasing the adhesion of activated carbon to Hg. 0 The excellent adsorption performance of activated carbon results in superior mercury removal, and the modifier plays a crucial role in this. Therefore, the amount of modifier added must be carefully controlled. If too much modifier is added, the specific surface area and pore volume of the material will decrease significantly due to clogging of the activated carbon pores; if too little modifier is added, the adsorption performance of the material will not improve significantly due to insufficient activation sites.

[0030] As a preferred technical solution of the present invention, the modifier in the modifier solution in step (2) includes any one or at least two of halides, sulfur-containing materials or selenium-containing materials. Typical but not limited combinations include: a combination of halides and sulfides, a combination of halides and selenides, or a combination of halides, sulfides and selenides, etc.

[0031] In this invention, the halide includes ammonium halide or sodium halide, etc., and the halogen in the halide includes any one or a combination of at least two of Cl, Br or I.

[0032] In this invention, the sulfur-containing material includes sulfur-containing oxides, sulfur-containing hydroxides, or hydrogen sulfates, etc.

[0033] In this invention, the selenium-containing material includes selenium powder.

[0034] Preferably, the solvent in the modifier solution in step (2) includes the following:

[0035] a) When the modifier is a halide or sulfide, the solvent includes any one of water, hydrochloric acid, nitric acid, or aqua regia; or

[0036] b) When the modifier is a selenide, the solvent includes an aqueous solution of sodium hydroxide or an aqueous solution of sodium borohydride.

[0037] In this invention, when the modifier is a halide or sulfide, water or an acidic solution is used to dissolve the modifier; when the modifier is a selenide, an alkaline solution is used to dissolve the modifier.

[0038] Preferably, the soaking time in step (2) is 2-14 hours, for example, it can be 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours or 13 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] As a preferred technical solution of the present invention, the drying temperature in step (2) is 40-100℃, for example, it can be 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃ or 90℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the irradiation frequency for microwave activation in step (2) is 2450MHz.

[0041] Preferably, the irradiation time for microwave activation in step (2) is 5-30 min, for example, it can be 7 min, 10 min, 12 min, 15 min, 17 min, 20 min, 25 min or 28 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] It is worth noting that the microwave irradiation activation method used in this invention, compared to high-temperature activation, can effectively avoid high-temperature ashing of activated carbon. Furthermore, the activated carbon absorbs microwaves, generating a very effective instantaneous deep heating effect (internal heating), which can simultaneously heat at different depths. This not only results in faster but also more uniform heating, without temperature gradients or hysteresis effects, significantly shortening sample processing time and making the activation effect of the sample more uniform.

[0043] As a preferred technical solution of the present invention, the microwave activation in step (2) is carried out in a protective atmosphere.

[0044] Preferably, the protective atmosphere includes any one of nitrogen, argon, or helium.

[0045] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0046] (1) Soak coffee grounds in water ≥3 times, dry them at 105-120℃, then acid-soak them in a 6%-20% phosphoric acid solution for 2-4 hours, then activate them by heating at a rate of 8-12℃ / min to 300-500℃ and holding for 1-3 hours to obtain activated carbon precursor.

[0047] The mass-to-volume ratio of coffee grounds to phosphoric acid solution is 1:(4-10)g / mL; the acid leaching is performed under ultrasonication.

[0048] (2) The activated carbon precursor described in step (1) is immersed in a modifier solution with a mass fraction of 0.1-10 wt%, then subjected to solid-liquid separation, dried at 40-100℃, and then microwave activated at 2450MHz for 5-30 min to obtain coffee residue-based activated carbon.

[0049] The mass ratio of the activated carbon precursor to the modifier in the modifier solution in step (2) is 1:(0.02-0.1); the impregnation time is 2-14h; the modifier in the modifier solution includes any one or a combination of at least two of halides, sulfur-containing materials or selenium-containing materials.

[0050] Secondly, the present invention provides a coffee grounds-based activated carbon, which is prepared by the preparation method described in the first aspect.

[0051] Preferably, the particle size of the coffee grounds-based activated carbon is 20-80 mesh, for example, it can be 30 mesh, 40 mesh, 50 mesh, 60 mesh, 70 mesh or 75 mesh, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] Preferably, the specific surface area of ​​the coffee grounds-based activated carbon is 150-500 m². 2 / g, for example, could be 170m 2 / g、200m 2 / g、250m 2 / g、300m 2 / g, 350m 2 / g、400m 2 / g or 450m 2 / g mesh, etc., but not limited to the listed values; other unlisted values ​​within this range also apply, preferably 200-260m. 2 / g.

[0053] The coffee grounds-based activated carbon prepared by this invention has a high specific surface area and an appropriate amount of surface-modified functional groups.

[0054] Thirdly, the present invention provides a use of coffee grounds-based activated carbon as described in the second aspect, wherein the coffee grounds-based activated carbon is used for mercury removal from flue gas.

[0055] In this invention, the coffee grounds-based activated carbon can not only remove mercury efficiently in one go, but also has excellent resistance to SO2 and H2O.

[0056] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The preparation method of the present invention obtains activated carbon precursor by soaking, drying, acid leaching and high temperature activation of coffee grounds. The activated carbon precursor is modified by a modifier solution, which can enrich the functional group types of the activated carbon precursor. Then, microwave radiation activation is used to improve the activity of adsorbed species on the surface of coffee grounds-based activated carbon, thereby improving the mercury removal performance of activated carbon. It can recycle worthless coffee grounds, reduce the accumulation and discharge of waste, and has the advantages of low raw material cost, simple process, easy operation and scale-up.

[0059] (2) The coffee grounds-based activated carbon of the present invention has a particle size of 20-80 mesh and a specific surface area of ​​150-500 m². 2 / g, which can achieve efficient one-time removal of mercury from coal flue gas, reduce the risk of secondary mercury release, and also has good resistance to SO2 and H2O, making it suitable for mercury removal from smelting flue gas. Attached Figure Description

[0060] Figure 1 The image shows the adsorption effect of coffee grounds-based activated carbon prepared in Example 1 and Comparative Example 3 on mercury removal from flue gas. Detailed Implementation

[0061] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0062] Example 1

[0063] This embodiment provides a method for preparing coffee grounds-based activated carbon, the preparation method comprising the following steps:

[0064] (1) Soak coffee grounds in water for 10 minutes and then filter them. Repeat the process 4 times until the filtrate is colorless. Then dry it at 105°C for 12 hours and pass it through a 40-60 mesh sieve. After that, soak it in a 15% phosphoric acid solution for 3.5 hours. After filtration and drying at 105°C for 12 hours, heat it to 400°C at a heating rate of 10°C / min for activation and keep it at that temperature for 2.5 hours. After naturally cooling to room temperature, wash it until it is neutral and then dry it to obtain the activated carbon precursor.

[0065] The mass-to-volume ratio of coffee grounds to phosphoric acid solution is 1:5 g / mL; the acid leaching is performed under ultrasonication.

[0066] (2) The activated carbon precursor described in step (1) is immersed in an aqueous solution of NH4Cl with a mass fraction of 1 wt%, then filtered and dried at 80°C, and then activated by microwave irradiation at a nitrogen atmosphere and a frequency of 2450 MHz for 10 min to obtain coffee grounds-based activated carbon.

[0067] The mass ratio of the activated carbon precursor to NH4Cl is 1:0.1; the impregnation is carried out under stirring for 12 hours.

[0068] Example 2

[0069] This embodiment provides a method for preparing coffee grounds-based activated carbon, the preparation method comprising the following steps:

[0070] (1) Soak coffee grounds in water for 5 minutes and then filter them. Repeat the process 6 times until the filtrate is colorless. Then dry it at 110°C for 12 hours and pass it through a 60-80 mesh sieve. After that, soak it in a 12% phosphoric acid solution for 2 hours. After filtration and drying at 110°C for 12 hours, heat it to 300°C at a heating rate of 10°C / min for activation and keep it at that temperature for 1.5 hours. After naturally cooling to room temperature, wash it until it is neutral and then dry it to obtain the activated carbon precursor.

[0071] The mass-to-volume ratio of coffee grounds to phosphoric acid solution is 1:8 g / mL; the acid leaching is performed under ultrasonication.

[0072] (2) The activated carbon precursor described in step (1) is immersed in a mixture of modifiers, then filtered, vacuum dried at 50°C, and then activated by microwave irradiation at 2450MHz under nitrogen atmosphere for 5 minutes to obtain coffee residue-based activated carbon.

[0073] The modifier mixture solution is a CuCl2 aqueous solution with a mass fraction of 0.3 wt% and a selenium powder solution with a mass fraction of 0.14 wt%. The preparation method of the selenium powder solution includes: dissolving 0.132 g of sodium borohydride in 100 mL of water and stirring at 90 °C, and then adding 0.138 g of selenium powder; the mass ratio of the activated carbon precursor to CuCl2 and selenium powder is 1:0.0596:0.0276.

[0074] The impregnation was carried out with stirring for 2 hours.

[0075] Example 3

[0076] This embodiment provides a method for preparing coffee grounds-based activated carbon, the preparation method comprising the following steps:

[0077] (1) Soak coffee grounds in water for 8 minutes and then filter them. Repeat the process 6 times until the filtrate is colorless. Then dry it at 110°C for 12 hours and pass it through a 60-80 mesh sieve. After that, soak it in a 10% phosphoric acid solution for 4 hours. After filtration and drying at 110°C for 12 hours, heat it to 500°C at a heating rate of 10°C / min for activation and keep it at that temperature for 2 hours. After naturally cooling to room temperature, wash it until it is neutral and then dry it to obtain the activated carbon precursor.

[0078] The mass-to-volume ratio of coffee grounds to phosphoric acid solution is 1:6 g / mL; the acid leaching is performed under ultrasonication.

[0079] (2) The activated carbon precursor described in step (1) is immersed in a selenium powder solution with a mass fraction of 0.1828 wt%, then filtered, vacuum dried at 80°C, and then activated by microwave irradiation at a nitrogen atmosphere and a frequency of 2450 MHz for 15 min to obtain coffee grounds-based activated carbon.

[0080] The mass ratio of the activated carbon precursor to selenium powder is 1:0.0356; the preparation method of the selenium powder solution includes: dissolving 0.0792g of sodium borohydride in 100mL of water and stirring at 90℃, and then adding 0.1828g of selenium powder to it.

[0081] The impregnation was carried out with stirring for 2 hours.

[0082] Example 4

[0083] This embodiment provides a method for preparing coffee grounds-based activated carbon. The mass ratio of the activated carbon precursor to the total amount of modifier is 1:0.1. Except that the modifier mixture solution consists of a 10 wt% NH4Br aqueous solution, a 0.214 wt% CuSO4 aqueous solution, and a 0.276 wt% selenium powder solution; the preparation method of the selenium powder solution includes: dissolving 2 g of sodium hydroxide in 100 mL of water and stirring at 90 °C, and then adding 0.276 g of selenium powder; all other conditions are the same as in Example 1.

[0084] Example 5

[0085] This embodiment provides a method for preparing coffee grounds-based activated carbon. Except for the activation temperature of 200°C in step (1), all other conditions are the same as in Example 1.

[0086] Example 6

[0087] This embodiment provides a method for preparing coffee grounds-based activated carbon. Except for the activation temperature of 600°C in step (1), all other conditions are the same as in Example 1.

[0088] Example 7

[0089] This embodiment provides a method for preparing coffee grounds-based activated carbon. Except for the mass ratio of activated carbon precursor to NH4Cl in step (2) being 1:0.01, all other conditions are the same as in Example 1.

[0090] Example 8

[0091] This embodiment provides a method for preparing coffee grounds-based activated carbon. Except for the mass ratio of activated carbon precursor to NH4Cl in step (2) being 1:0.2, all other conditions are the same as in Example 1.

[0092] Example 9

[0093] This embodiment provides a method for preparing coffee grounds-based activated carbon. Except for the NH4Cl aqueous solution in step (2) having a mass fraction of 15 wt%, all other conditions are the same as in Example 1.

[0094] Example 10

[0095] This embodiment provides a method for preparing coffee grounds-based activated carbon. Except for the microwave irradiation activation time of 3 minutes in step (2), all other conditions are the same as in Example 1.

[0096] Example 11

[0097] This embodiment provides a method for preparing coffee grounds-based activated carbon. Except for the microwave irradiation activation time of 40 min in step (2), all other conditions are the same as in Example 1.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing coffee grounds-based activated carbon. Except for step (2), which does not involve modification with NH4Cl aqueous solution, all other conditions are the same as in Example 1.

[0100] Comparative Example 2

[0101] This comparative example provides a method for preparing coffee grounds-based activated carbon. Except for step (2), which does not involve microwave irradiation activation, all other conditions are the same as in Example 1.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing coffee grounds-based activated carbon. Except for step (2), all other conditions are the same as in Example 1.

[0104] Comparative Example 4

[0105] This comparative example provides a method for preparing coffee grounds-based activated carbon. Except for replacing “microwave activation” in step (2) with “activation in a muffle furnace at a heating rate of 10℃ / min to 300℃ and holding for 1.5h”, all other conditions are the same as in Example 1.

[0106] Comparative Example 5

[0107] This comparative example provides a method for preparing coffee grounds-based activated carbon, the method comprising the following steps:

[0108] Coffee grounds were soaked in water for 10 minutes and then filtered. The process was repeated 4 times until the filtrate was colorless. The filtrate was then dried at 105°C for 12 hours and passed through a 40-60 mesh sieve. After that, the filtrate was acid-soaked in a 15% phosphoric acid solution for 3.5 hours. After filtration and drying at 105°C for 12 hours, the coffee grounds were soaked in a 1 wt% NH4Cl aqueous solution. After filtration and drying at 80°C, the filtrate was activated by heating to 400°C at a rate of 10°C / min and held at that temperature for 2.5 hours. After naturally cooling to room temperature, the filtrate was washed until neutral and then dried to obtain coffee grounds-based activated carbon.

[0109] The mass ratio of coffee grounds to NH4Cl is 1:0.1; the soaking is carried out under stirring for 12 hours.

[0110] The coffee grounds-based activated carbon prepared in the above examples and comparative examples was characterized for performance testing and its mercury removal performance in flue gas was tested. The test results are shown in Table 1 and Table 2. Figure 1 As shown.

[0111] Mercury removal performance test of coal flue gas

[0112] Mercury adsorption performance was evaluated in a fixed-bed reaction system with an adsorbent mass of 100 mg, a total gas flow rate of 250 mL / min, and a mercury concentration of 190 ± 10 μg / m³. 3 Mass airspeed 150,000 cm⁻¹ 3 / (g·h -1 The reactions were all carried out at 120℃ under simulated flue gas conditions of 5% O2 + N2, and the breakthrough curve of Hg adsorption was tested. The outlet mercury concentration could be measured online in real time using a mercury analyzer, and the inlet mercury concentration was measured by a bypass. The amount of mercury adsorbed was calculated using formula (1):

[0113]

[0114] Among them, C ad denoted as Mercury adsorption capacity (μg / g), Q as simulated flue gas flow rate (mL / min), m as adsorbent mass (g), and t1 and t2 as reaction start and end times (min), respectively. Mercury concentrations at the inlet and outlet (μg / m³)3 ).

[0115] Mercury removal efficiency is calculated using equation (2):

[0116]

[0117] Where η is the mercury removal efficiency (%).

[0118] Table 1

[0119]

[0120]

[0121] Among them, Q e =85% means that the penetration concentration reaches 85% of the initial concentration;

[0122] The following points can be drawn from Table 1:

[0123] (1) The preparation method provided in Examples 1-4 of this invention produces coffee grounds-based activated carbon with a microporous structure, high specific surface area, and excellent flue gas mercury removal performance, with a mercury removal rate ≥99%.

[0124] (2) As can be seen from the comparison between Example 1 and Example 4, compared with the modification of only halides, the mercury removal performance of the material is better when modified by combination of halides, sulfur-containing materials and selenium-containing materials, because the active sites on activated carbon are more diverse.

[0125] (3) As can be seen from the comparison between Example 1 and Example 5-6, when the activation temperature of step (1) is low, the material’s mercury removal performance is poor because the carbon and oxygen functional groups are not fully activated. When the activation temperature of step (1) is high, the material’s mercury removal performance is slightly improved because the carbon and oxygen functional groups are fully activated and their number increases, but the cost increases.

[0126] (4) As can be seen from the comparison of Examples 1, 7-9 and Comparative Example 1, when the amount of modifier added in step (2) is small, the mercury removal performance of the material is poor due to the small number of mercury binding sites; when the amount of modifier added in step (2) is excessive, the mercury removal performance of the material decreases due to the blockage of activated carbon micropores by the modifier; when the concentration of the modifier solution in step (2) is high, the mercury removal performance of the material no longer improves due to the saturation of active sites on the surface of activated carbon; when no modifier is used, the mercury removal performance of the material is poor due to the small number of functional groups and small specific surface area of ​​the coffee grounds-based precursor.

[0127] (5) As can be seen from the comparison of Examples 1 and 11-12 and Comparative Example 2, when the microwave irradiation activation time is too short, the material is not fully activated due to the low temperature, resulting in poor mercury removal performance; when the microwave irradiation activation time is too long, the activated carbon is ashed due to the high temperature, resulting in reduced mercury removal performance; when no microwave irradiation activation is performed, the material is poor in mercury removal performance due to the low activity of adsorbed species on the surface of activated carbon.

[0128] (6) As can be seen from the comparison between Example 1 and Comparative Example 5, when NH4Cl modification is carried out directly after acid modification, the active sites are occupied, resulting in poor mercury removal performance of the material.

[0129] The coffee grounds-based activated carbon prepared in Example 1 was used for mercury removal from smelting flue gas. The evaluation conditions were: adsorbent mass 100 mg, total gas flow rate 250 mL / min, and mercury concentration 190 ± 10 μg / m³. 3 Mass airspeed 150,000 cm⁻¹ 3 / (g·h -1 The reactions were all carried out at 120℃ under simulated flue gas conditions of 5% O2 + 200ppm SO2 + 5% H2O + N2, and the mercury removal rate was 99%.

[0130] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing coffee grounds-based activated carbon for mercury removal from flue gas, characterized in that, The preparation method includes the following steps: (1) Coffee grounds are soaked, dried, acid-leached and activated in sequence to obtain activated carbon precursor; the activation temperature is 300-500℃; the acid-leaching solution includes phosphoric acid solution; (2) The activated carbon precursor described in step (1) is immersed in a modifier solution, and then subjected to solid-liquid separation, drying and microwave activation in sequence to obtain coffee grounds-based activated carbon; the modifier in the modifier solution includes any one or a combination of at least two of halides, sulfides or selenium-containing materials. The mass ratio of the activated carbon precursor to the modifier in the modifier solution is 1:(0.02-0.1); the irradiation time for microwave activation is 5-30 min.

2. The preparation method according to claim 1, characterized in that, The soaking process in step (1) is repeated ≥ 3 times.

3. The preparation method according to claim 2, characterized in that, The soaking process in step (1) is repeated 3-8 times.

4. The preparation method according to claim 1, characterized in that, Step (1) involves soaking in water.

5. The preparation method according to claim 1, characterized in that, The drying temperature in step (1) is 105-120℃.

6. The preparation method according to claim 1, characterized in that, The concentration of the phosphoric acid solution is 6%-20%.

7. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of coffee grounds to phosphoric acid solution is 1:(4-10)g / mL.

8. The preparation method according to claim 1, characterized in that, The acid leaching in step (1) is performed under ultrasound.

9. The preparation method according to claim 1, characterized in that, The acid immersion time in step (1) is 2-4 hours.

10. The preparation method according to claim 1, characterized in that, The heating rate for activation in step (1) is 8-12℃ / min.

11. The preparation method according to claim 1, characterized in that, The activation holding time in step (1) is 1-3 hours.

12. The preparation method according to claim 1, characterized in that, The mass fraction of the modifier solution in step (2) is 0.1-10 wt%.

13. The preparation method according to claim 1, characterized in that, The solvent in the modifier solution in step (2) includes the following: a) When the modifier is a halide or sulfide, the solvent includes any one of water, hydrochloric acid, nitric acid, or aqua regia; or b) When the modifier is a selenium-containing material, the solvent includes an aqueous solution of sodium hydroxide or an aqueous solution of sodium borohydride.

14. The preparation method according to claim 1, characterized in that, The soaking time in step (2) is 2-14 hours.

15. The preparation method according to claim 1, characterized in that, The drying temperature in step (2) is 40-100℃.

16. The preparation method according to claim 1, characterized in that, The irradiation frequency for microwave activation in step (2) is 2450 MHz.

17. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Soak coffee grounds in water ≥3 times, dry them at 105-120℃, then acid-soak them in a 6%-20% phosphoric acid solution for 2-4 hours, then activate them by heating them to 300-500℃ at a heating rate of 8-12℃ / min and keeping them at that temperature for 1-3 hours to obtain activated carbon precursor. The mass-to-volume ratio of coffee grounds to phosphoric acid solution is 1:(4-10)g / mL; the acid leaching is performed under ultrasonication. (2) The activated carbon precursor described in step (1) is immersed in a modifier solution with a mass fraction of 0.1-10wt%, then subjected to solid-liquid separation, dried at 40-100℃, and then microwave activated at 2450MHz for 5-30min to obtain coffee residue-based activated carbon. The mass ratio of the activated carbon precursor to the modifier in the modifier solution in step (2) is 1:(0.02-0.1); the impregnation time is 2-14h; the modifier in the modifier solution includes any one or a combination of at least two of halides, sulfides or selenium-containing materials.

18. A coffee grounds-based activated carbon for mercury removal from flue gas, characterized in that, The coffee grounds-based activated carbon is prepared using the preparation method described in any one of claims 1-17.

19. The coffee grounds-based activated carbon according to claim 18, characterized in that, The coffee grounds-based activated carbon has a particle size of 20-80 mesh.

20. The coffee grounds-based activated carbon according to claim 18, characterized in that, The specific surface area of ​​the coffee grounds-based activated carbon is 150-500 m². 2 / g.

21. The use of coffee grounds-based activated carbon as described in any one of claims 18-20, characterized in that, The coffee grounds-based activated carbon is used for mercury removal from flue gas.

Images