Method for preparing activated carbon by potassium salt catalyzed self-activation of biomass in confined space

Abstract

The application relates to a method for preparing activated carbon by limited self-activation of biomass with trace potassium salt, and belongs to the field of biomass resource utilization. The specific scheme comprises the following steps: adding potassium salt into water-containing biomass, placing the reactor in a tubular furnace, heat-treating the reactor at a certain temperature for a certain time, and obtaining activated carbon. The mass fraction of the potassium salt in the dried biomass is 5-10%, the reactor is in a semi-closed state, the semi-closed state refers to a space which is relatively isolated from the outside world, the import and export are limited, and the natural ventilation is poor, that is, when the container is in a positive pressure state, the internal gas is allowed to be discharged, and the external gas cannot enter. The environment of the reactor is a circulating air environment. Based on the characteristics of high water content of the biomass, trace potassium salt is added to realize the synergistic activation effect of the water content of the biomass, and the performance of the carbon material is maximally improved under the premise of low economic cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biomass resource utilization, and particularly relates to a method for preparing activated carbon by limited self-activation of high-moisture biomass catalyzed by trace potassium salt. BACKGROUND

[0002] High-moisture biomass such as distiller's grains, bagasse and cassava residues is a byproduct with huge output in the process of wine making, sugar making and starch processing. It is prone to spoilage, difficult to store and transport, and difficult to fully develop and utilize by the existing technology. At present, domestic enterprises mainly sell such high-moisture biomass as animal feed, obtaining low economic benefits, and the potential of biomass application is not fully utilized. Therefore, it is urgent to find a suitable technical route to realize its high-value conversion. At present, biomass carbon materials as a new type of biological carbon-based functional materials can be applied in the fields of environmental protection and energy storage, becoming a new hotspot for high-value utilization of such biomass.

[0003] At present, one of the main research directions for preparing activated carbon materials based on biomass is to treat biomass on a laboratory scale, and to achieve heteroatom doping and physical and chemical activation of biochar by using complex chemical reagents to obtain biomass porous carbon with high adsorption or energy storage properties. However, in this process, reagents such as melamine with certain pollution and KOH with strong corrosion are often involved. If this method is used to treat fresh high-moisture biomass, not only high treatment cost is needed, but also greater burden in waste gas and wastewater treatment will be brought.

[0004] The patent application with Chinese patent publication number CN 117550935 A discloses a preparation method of a distiller's grains-based potassium-loaded biochar. The method uses distiller's grains as raw material and potassium acetate as catalyst to prepare biochar material by pyrolysis reaction under oxygen-limited conditions, and is applied to soil improvement. The cumulative release rate of biochar under 25-day leaching environment is 82.35%, which can be used as controlled-release potassium fertilizer to effectively reduce the loss of potassium nutrients. However, the preparation method needs to first dry the distiller's grains completely, which consumes high energy consumption, and uses nitrogen to create an oxygen-limited environment during pyrolysis, which has high cost of pure nitrogen flow and is difficult to apply to large industrial scenes.

[0005] The patent application with the publication number CN 109499532A discloses a preparation method of a composite activated carbon adsorbent for adsorbing heavy metal Cr(Ⅵ). The method mixes plant bark, municipal sludge and oil sludge, and prepares biochar through steps such as crushing, oxidation, carbonization, activation, acid washing and drying, and is applied to water body heavy metal ion adsorption. Hexavalent chromium is selected as the adsorption object, the maximum adsorption capacity is 80.58 mg / g, and the adsorption capacity can reach 65% to 75% of the original adsorption capacity after secondary regeneration. However, the KOH used in the method embodiment has strong corrosiveness, which can cause damage to the equipment, and the content of the activator is high, the activation time is long (12 to 24 hours), and the cost and energy consumption are large.

[0006] Therefore, there is still a need in the art to explore a simple, environmentally friendly, efficient and low-cost technical route for the preparation of high-moisture biomass-based carbon materials suitable for actual industrial production. SUMMARY

[0007] In order to solve the problems of difficult treatment and low utilization rate of high-moisture biomass, and the problems of complicated preparation process, long time consumption and high production cost of high-moisture biomass-based activated carbon, and the problems of complex technical route and environmental pollution in the industrial production of high-moisture biomass-based activated carbon, the present application provides a method for preparing activated carbon by catalyzing the self-activation of high-moisture biomass in a limited area with a small amount of potassium salt.

[0008] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] A method for preparing activated carbon by catalyzing the self-activation of biomass in a limited area with a small amount of potassium salt, comprising the following steps: adding potassium salt to the water-containing biomass, placing it in a reactor, placing the reactor in a tubular furnace for heat treatment at a certain temperature for a certain time to obtain activated carbon, which is named T-H-S-P (T represents pyrolysis temperature, H represents moisture content, S represents salt content, and P represents pyrolysis time), the mass fraction of the potassium salt in the dried biomass is 5-10%, and the reactor is in a semi-closed state.

[0010] Further, the semi-closed state refers to a space that is relatively isolated from the outside world, with limited import and export and poor natural ventilation, that is, when the container is in a positive pressure state, the internal gas is allowed to be discharged while the external gas cannot enter.

[0011] Further, the environment of the reactor is a flowing air environment.

[0012] Further, the moisture content of the water-containing biomass material is 10% to 70%, and preferably, the moisture content of the water-containing biomass material is 30% or 50%.

[0013] Further, the temperature of the heat treatment is 500-800℃, preferably 600℃ or 700℃, and the time of the heat treatment is 2-30min, preferably 5min or 10min.

[0014] Further, the potassium salt includes a combination of one or more of potassium carbonate, potassium hydroxide, potassium bicarbonate, potassium dihydrogen phosphate.

[0015] Further, the water-containing biomass includes a combination of one or more of vinasse, bagasse, cassava residue.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] (1) The present application is based on the characteristics of high water content of biomass, and adds a small amount of potassium salt to realize synergistic activation with the water content of biomass, thereby realizing the maximum improvement of the performance of carbon materials under the premise of low economic cost.

[0018] (2) The pyrolysis process of the prior art often uses inert atmosphere (such as nitrogen), but the cost of pure nitrogen flow is high, which is difficult to apply to large industrial scenes. The pyrolysis method proposed by the present application is realized based on semi-closed oxygen-limited conditions, and the test results show that the adsorption performance of the biochar is better than that of the sample prepared in a nitrogen atmosphere.

[0019] (3) The present application does not need to completely dry the biomass with high water content, and the entire carbon preparation process can be completed in a pyrolysis furnace with constant temperature in a few minutes, which is suitable for simple and rapid processing of large quantities of biomass. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a comparison chart of the adsorption capacity of the biochar prepared by the method described in Example 9, Example 4, Example 10, and Example 11 at 30min;

[0021] Figure 2 is a comparison chart of the adsorption capacity of the biochar prepared by the method described in Example 2, Example 3, Example 4, and Example 5 at 30min;

[0022] Figure 3 is a comparison chart of the adsorption capacity of the biochar prepared by the method described in Example 6, Example 1, Example 3, and Example 7 at 30min;

[0023] Figure 4 is a dynamic adsorption capacity curve chart of Example 1, Comparative Example 2 within 24h; DETAILED DESCRIPTION

[0024] The technical solutions in the present application will be described clearly and completely in the embodiments combined with the drawings and the embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present application.

[0025] Example 1

[0026] Preparation of distiller's grain biochar

[0027] (1) Material mixing: fresh distiller's grain with water content of 30% (water mass is 30% of dry grain mass) was taken, and potassium carbonate with mass of 5% of dry grain mass was added, and mixed uniformly.

[0028] (2) Biomass charring: the mixture was placed in a semi-closed nickel-based alloy reactor and pyrolyzed in a tube furnace; the pyrolysis temperature was 600 DEG C, and the pyrolysis time was 5 min. The reactor was in a semi-closed state. The semi-closed state refers to a space that is relatively isolated from the outside world, with limited inlet and outlet and poor natural ventilation, that is, when the container is in a positive pressure state, the internal gas is allowed to be discharged, but the external gas cannot enter. The environment of the reactor is a flowing air environment.

[0029] (3) The pyrolysis product was naturally cooled to room temperature, taken out and ground to obtain distiller's grain biochar, which was named as 600-30%-5%-5-K2CO3.

[0030] Example 2

[0031] The difference from example 1 is that the reactor containing the biomass and potassium carbonate mixture is pyrolyzed at 500 DEG C for 10 min in step (2) of the preparation of the distiller's grain biochar material, and the remaining steps are the same as example 1. The obtained biochar is named as 500-30%-5%-10-K2CO3.

[0032] Example 3

[0033] The difference from example 1 is that the reactor containing the biomass and potassium carbonate mixture is pyrolyzed at 600 DEG C for 10 min in step (2) of the preparation of the distiller's grain biochar material, and the remaining steps are the same as example 1. The obtained biochar is named as 600-30%-5%-10-K2CO3.

[0034] Example 4

[0035] The difference from example 1 is that the reactor containing the biomass and potassium carbonate mixture is pyrolyzed at 700 DEG C for 10 min in step (2) of the preparation of the distiller's grain biochar material, and the remaining steps are the same as example 1. The obtained biochar is named as 700-30%-5%-10-K2CO3.

[0036] Example 5

[0037] The difference from Example 1 is in the step (2) of the production of the distiller's grains biochar material, the reactor with the mixture of biomass and potassium carbonate is pyrolyzed at 800°C for 10 min, the rest of the steps are the same as in Example 1, the obtained biochar is named 800-30%-5%-10-K2CO3.

[0038] Example 6

[0039] The difference from Example 1 is in the step (2) of the production of the distiller's grains biochar material, the reactor with the mixture of biomass and potassium carbonate is pyrolyzed at 600°C for 2 min, the rest of the steps are the same as in Example 1, the obtained biochar is named 600-30%-5%-2-K2CO3.

[0040] Example 7

[0041] The difference from Example 1 is in the step (2) of the production of the distiller's grains biochar material, the reactor with the mixture of biomass and potassium carbonate is pyrolyzed at 600°C for 30 min, the rest of the steps are the same as in Example 1, the obtained biochar is named 600-30%-5%-30-K2CO3.

[0042] Example 8

[0043] The difference from Example 1 is in the step (1) of the production of the distiller's grains biochar material, 10% of the mass of dry grains of potassium carbonate is added to the fresh distiller's grains with the water content of 30% (the mass of water is 30% of the mass of dry grains), the mixture is uniform, the rest of the steps are the same as in Example 1, the obtained biochar is named 600-30%-10%-5-K2CO3.

[0044] Example 9

[0045] The difference from Example 4 is in the step (1) of the production of the distiller's grains biochar material, 5% of the mass of dry grains of potassium carbonate is added to the fresh distiller's grains with the water content of 10% (the mass of water is 10% of the mass of dry grains), the mixture is uniform, the rest of the steps are the same as in Example 4, the obtained biochar is named 700-10%-5%-10-K2CO3.

[0046] Example 10

[0047] The difference from Example 4 is in the step (1) of the production of the distiller's grains biochar material, 5% of the mass of dry grains of potassium carbonate is added to the fresh distiller's grains with the water content of 50% (the mass of water is 50% of the mass of dry grains), the mixture is uniform, the rest of the steps are the same as in Example 4, the obtained biochar is named 700-50%-5%-10-K2CO3.

[0048] Example 11

[0049] The difference from Example 4 is that in the step (1) of the preparation of the biochar material from distiller's grains, 5% of potassium bicarbonate by mass of dry grains is added to the fresh distiller's grains with a moisture content of 30% (30% of the mass of water in dry grains), and mixed uniformly, and the remaining steps are the same as Example 4. The obtained biochar is named as 600-30%-5%-5-KHC03.

[0050] Example 12

[0051] The difference from Example 1 is that in the step (1) of the preparation of the biochar material from distiller's grains, 5% of potassium bicarbonate by mass of dry grains is added to the fresh distiller's grains with a moisture content of 30% (30% of the mass of water in dry grains), and mixed uniformly, and the remaining steps are the same as Example 1. The obtained biochar is named as 600-30%-5%-5-KHC03.

[0052] Example 13

[0053] The difference from Example 1 is that in the step (1) of the preparation of the biochar material from distiller's grains, 5% of potassium bicarbonate by mass of dry grains is added to the fresh distiller's grains with a moisture content of 30% (30% of the mass of water in dry grains), and mixed uniformly, and the remaining steps are the same as Example 1. The obtained biochar is named as 600-30%-5%-5-KHC03.

[0054] Example 14

[0055] The difference from Example 1 is that in the step (1) of the preparation of the biochar material from distiller's grains, 5% of potassium bicarbonate by mass of dry grains is added to the fresh distiller's grains with a moisture content of 30% (30% of the mass of water in dry grains), and mixed uniformly, and the remaining steps are the same as Example 1. The obtained biochar is named as 600-30%-5%-5-KHC03.

[0056] Example 15

[0057] Preparation of bagasse biochar:

[0058] (1) Material mixing: Take fresh bagasse with a moisture content of 30% (30% of the mass of water in dry grains), and add 5% of potassium carbonate by mass of dry grains, and mix uniformly.

[0059] (2) Biomass carbonization: Place the mixture in a semi-closed nickel-based alloy reactor and pyrolyze in a tube furnace; the pyrolysis temperature is 600°C, and the pyrolysis time is 5 min. The reactor is in a semi-closed state. The semi-closed state refers to a space that is relatively isolated from the outside world, with limited inlet and outlet and poor natural ventilation, i.e., when the container is in a positive pressure state, the internal gas is allowed to be discharged while the external gas cannot enter. The environment of the reactor is a flowing air environment.

[0060] (3) The pyrolysis product was naturally cooled to room temperature, taken out and ground to obtain the bagasse biochar.

[0061] Example 16

[0062] Preparation of cassava residue biochar:

[0063] (1) Material mixing: fresh cassava residue with water content of 30% (water mass is 30% of dry cassava residue) was taken, and potassium carbonate with mass of 5% of dry residue mass was added, and mixed uniformly.

[0064] (2) Biomass carbonization: the mixture was placed in a semi-closed nickel-based alloy reactor and pyrolyzed in a tube furnace; the pyrolysis temperature was 600°C, and the pyrolysis time was 5 min. The reactor was in a semi-closed state. The semi-closed state refers to a space that is relatively isolated from the outside world, with limited import and export and poor natural ventilation, that is, when the container is in a positive pressure state, the internal gas is allowed to be discharged, but the external gas cannot enter. The environment of the reactor is a flowing air environment.

[0065] (3) The pyrolysis product was naturally cooled to room temperature, taken out and ground to obtain the bagasse biochar.

[0066] Comparative Example 1

[0067] Fresh distiller's grains were completely dried to obtain dry distiller's grains.

[0068] Comparative Example 2

[0069] The difference from Example 1 is that the mixture was placed in a non-closed reactor and pyrolyzed in a tube furnace with nitrogen as the atmosphere in the material preparation step (2) of the distiller's grains biochar, and the remaining steps were the same as Example 1. The obtained biochar is named N2-600-30%-5%-5-K2CO3.

[0070] Comparative Example 3

[0071] The difference from Example 1 is that fresh distiller's grains with water content of 30% (water mass is 30% of dry distiller's grains) were taken in the material preparation step (1) of the distiller's grains biochar, but no potassium salt was added, and the remaining steps were the same as Example 1. The obtained biochar is named 600-30%-0%-5-K2CO3.

[0072] Test Example

[0073] Different biochars and dry distiller's grains adsorb methylene blue test:

[0074] The adsorption capacity of different biochar samples and dry distiller's grains for methylene blue (MB) was tested by liquid phase adsorption experiment to characterize the adsorption capacity of the biochar and dry distiller's grains prepared in the application for typical liquid phase organic pollutants.

[0075] (1) Prepare a methylene blue solution of a certain concentration, measure its absorption spectrum using a UV-Vis spectrophotometer, and select the wavelength of 665.9 nm as its characteristic peak to determine the concentration of the methylene blue solution to be tested.

[0076] (2) Use methylene blue solutions of known concentrations of 0.001 / 0.0025 / 0.005 / 0.01 / 0.02 / 0.03 / 0.04 / 0.05 / 0.1 g / L to calibrate the concentration curves, and fit the results in segments based on the calibration results.

[0077] (3) Take 50 ml of methylene blue solution with a concentration of 50 mg / L and add 30 mg of biochar or dried distiller's grains. Stir magnetically for 24 h at room temperature and determine the saturated adsorption capacity of methylene blue.

[0078] (4) For the methylene blue solution in step (3) above, take a small amount of solution at the set time (5 / 10 / 15 / 30 / 45 / 60 / 90 / 120 / 180min), and use a UV-ultraviolet spectrophotometer to test the concentration of the methylene blue solution and determine its kinetic adsorption process.

[0079] The adsorption characteristics of methylene blue in Examples 9, 4, 10, and 11 were tested after 30 min, and the adsorption capacities were found to be 14.41 mg / g, 35.82 mg / g, 29.12 mg / g, and 14.44 mg / g, respectively. It can be seen that under the same conditions (pyrolysis temperature of 700℃, K2CO3 dosage of 5%, and pyrolysis time of 10 min), activated carbon exhibits the best adsorption performance when the biomass moisture content is 30%.

[0080] The adsorption characteristics of methylene blue for Examples 2, 3, 4, and 5 were tested after 30 min, and the adsorption capacities were 43.90 mg / g, 51.58 mg / g, 35.82 mg / g, and 15.48 mg / g, respectively. It can be seen that under the same conditions (biomass moisture content 30%, K2CO3 dosage 5%, pyrolysis time 10 min), the activated carbon exhibits the best adsorption performance at a pyrolysis temperature of 600℃. This means that excessively high or low temperatures will reduce the adsorption performance of biochar.

[0081] The adsorption characteristics of methylene blue for Examples 6, 1, 3, and 7 were tested after 30 minutes, and the adsorption capacities were found to be 62.18 mg / g, 71.86 mg / g, 51.58 mg / g, and 25.50 mg / g, respectively. It can be seen that under the same conditions (biomass moisture content of 30%, K2CO3 dosage of 5%, pyrolysis temperature of 600℃), the activated carbon exhibits the best adsorption performance at a pyrolysis time of 5 minutes.

[0082] That is, among the above series of experimental conditions, the carbon material prepared at 600℃, 30% moisture content, 5% salt content, and 5min pyrolysis time has the relatively highest water body pollutant adsorption performance.

[0083] The pyrolysis-activation process proposed in the present application is realized in a semi-closed oxygen-limited environment, and a trace amount of potassium salt is added to form a chemical-physical synergistic activation effect with the high-moisture content of the biomass itself. To verify the effect of these two points on the improvement of the adsorption properties of biochar, the adsorption performance of the samples prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 for MB was tested using the above method.

[0084] During the experiment, it was found that the addition of the activated carbon prepared in Example 1 to the MB solution showed a relatively obvious and rapid color fading. The saturated adsorption amount of the 600-30-5%-5-K2CO3 activated carbon prepared in Example 1 was the highest, which could reach 71.65mg / g, and it showed a higher adsorption speed than the other three groups. The test results showed that the trace potassium salt catalyzed high-moisture content biomass confined self-activation strategy proposed in the present application has certain advantages compared with the currently commonly used methods of completely drying and then pyrolyzing in an inert atmosphere, and activating using a large amount of salt. The adsorption amount of some similar biochar adsorbents reported in recent literature is about 8.5-165.3mg / g. By comparison, it can be seen that the adsorption capacity of the biochar prepared in the present application is at a medium to high level.

[0085] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity. The skilled person should consider the specification as a whole, and the technical solutions in each example can be appropriately combined to form other embodiments that can be understood by the skilled person.

Claims

1. A method for preparing activated carbon by confined self-activation of biomass catalyzed by trace potassium salt, characterized in that, The method comprises the following steps: adding potassium salt into the water-containing biomass, placing the reactor in a tubular furnace for heat treatment at a certain temperature for a certain time to obtain activated carbon, the mass fraction of the potassium salt in the dried biomass being 5-10%, the reactor being in a semi-closed state; the semi-closed state refers to a state of relative isolation from the outside world, limited import and export, poor natural ventilation, i.e. when the container is in a positive pressure state, the internal gas is allowed to be discharged while the external gas cannot enter; the water content of the water-containing biomass material is 10-70% by mass; the temperature of the heat treatment is 500-800 DEG C, and the time of the heat treatment is 2-30 min; the potassium salt comprises one or a combination of potassium carbonate, potassium hydroxide, potassium bicarbonate and potassium dihydrogen phosphate; the water-containing biomass comprises one or a combination of vinasse, bagasse and cassava residue.

2. The method of claim 1, wherein: The water content of the water-containing biomass material is 30% by mass.

3. The method of claim 1, wherein: The temperature of the heat treatment is 600 DEG C, and the time is 5 min.

4. The method of claim 1, wherein: The environment where the reactor is located is a flowing air environment.

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