A method for preparing a microalgae-based CO2 solid adsorbent by using a deep eutectic solvent hydrothermal treatment

Abstract

The application discloses a method for preparing a microalgae-based CO2 solid adsorbent by using a deep eutectic solvent hydrothermal treatment, which comprises five steps, (1) preparing an algal liquid and a deep eutectic solvent; (2) mixing and stirring choline chloride and an organic acid; (3) separating after hydrothermal reaction; (4) heating under a nitrogen environment and then cooling to room temperature; (5) mixing KOH, heating under a nitrogen environment, cooling to room temperature and washing with hydrochloric acid. The porous carbon prepared by the method has a large specific surface area and an ultramicroporous structure, and the surface is rich in nitrogen and oxygen functional groups. The porous carbon obtained has a CO2 adsorption capacity of 4.50 mmol / g under the conditions of 25 DEG C and 1 bar, and a CO2 adsorption capacity of 6.14 mmol / g under the conditions of 1 bar and 0 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to biomass energy utilization technology, in particular to a method for preparing a CO2 solid adsorbent by pyrolysis activation after hydrothermal pretreatment of wet algal biomass using a deep eutectic solvent. BACKGROUND

[0002] The work of CO2 capture and storage technology mainly focuses on the CO2 capture of flue gas after combustion in fossil fuel power plants. Among the numerous capture materials, solid adsorbents are the most potential post-combustion CO2 capture materials. Among them, biomass-derived porous carbon materials have the advantages of wide source, renewable, low cost, environmental friendliness and simple preparation process, and have become the focus of current porous carbon material research.

[0003] Among various biomass porous carbon precursors, microalgae provide an extremely attractive option for the production of biochar due to their high photosynthetic efficiency, fast growth rate, and low demand for arable land. However, the microalgae biochar prepared by traditional pyrolysis and chemical activation methods has an undesirable pore structure and a loss of nitrogen and oxygen elements, resulting in poor CO2 adsorption capacity. The CO2 adsorption capacity at 25℃ is only 3.44mmol / g. Although the use of an external nitrogen source during chemical activation can increase the content of N elements, which is helpful for CO2 adsorption, it will convert the microporous structure into mesoporous structure, hindering CO2 capture.

[0004] Therefore, efficient utilization of nitrogen and oxygen elements in microalgae and synergistic activation methods to prepare porous carbon with ultramicroporous and large specific surface area are the key to preparing high-efficiency CO2 solid adsorbents. SUMMARY

[0005] The present application provides a method for preparing a microalgae-based CO2 solid adsorbent using a deep eutectic solvent hydrothermal treatment, which specifically comprises the following steps:

[0006] 1) Grinding an algal species with a carbon element content of 48% to 50%, a nitrogen element content of 9% to 11%, and an oxygen element content of 26% to 28% into algal powder (the remaining mass is H element, ash, and a small amount of S element); mixing the microalgae algal powder with deionized water at a ratio of 1:10 (g:ml) and stirring on a magnetic stirrer to obtain a uniform algal slurry suspension;

[0007] 2) The method for preparing a deep eutectic solvent is: mixing choline chloride and an organic acid at a molar ratio of 1:2, and stirring the mixture;

[0008] 3) The deep eutectic solvent obtained in (2) is added to the algal slurry suspension obtained in (1) at a volume ratio of 1:4, the mixture is transferred into the inner container of a reaction kettle, and heated in an oil bath at 160 DEG C for 10-60 minutes, after the hydrothermal reaction is completed, the mixture is naturally cooled to room temperature, then the hydrothermal product is poured into a centrifuge tube, separated in a centrifuge, and the solution in the centrifuge tube is discarded, and the obtained solid product is dried at 105 DEG C for 8-12 hours;

[0009] 4) The solid obtained in (3) is placed in a corundum boat of a tube furnace, heated to 500-800 DEG C in a N2 atmosphere, and kept at a constant temperature for 2 hours, then cooled to room temperature in a N2 atmosphere, and naturally cooled to room temperature after the reaction is completed, to obtain the original carbon material;

[0010] 5) The original carbon material obtained in (4) is mixed with KOH at a mass ratio of 1:2, the mixture is placed in a corundum boat of a tube furnace, then heated to 500-800 DEG C in a N2 atmosphere, kept at a constant temperature for 2 hours, then cooled to room temperature in a N2 atmosphere, washed with a hydrochloric acid solution to completely remove the residual KOH, and then washed repeatedly with deionized water until the pH is 7. Finally, the solid black particles are dried, and the dried solid is the CO2 solid adsorbent.

[0011] The algae used in step (1) include but are not limited to green algae (including chlorella, nannochloropsis and botryococcus), diatoms (including navicula, chaetoceros and phaeodactylum), and cyanobacteria (including spirulina, microcystis and fishy algae), and the stirring time is 20-30 min.

[0012] The stirring temperature in step (2) is 40-60 DEG C, and the stirring time is 20-30 min.

[0013] The organic acid in step (2) is any one of formic acid, acrylic acid and maleic acid.

[0014] The centrifugal speed in step (3) is 7000 rpm-8000 rpm, and the centrifugal time is 3-5 min. The drying temperature is 105 DEG C, and the time is 12 h.

[0015] The drying temperature in step (5) is 105 DEG C, and the drying time is 8-12 h.

[0016] The concentration of hydrochloric acid in step (5) is 1 mol / L.

[0017] In step (5), the particle size of the mixture is less than 50 mesh.

[0018] In step (5), the N2 concentration during the constant temperature cooling process is 50 / 80 ml / L.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] 1. Microalgae are characterized by high photosynthetic efficiency, strong carbon fixation ability, and extremely short growth cycle. They also contain a large amount of protein, carbohydrates, and lipids, and are rich in elements such as N and O. Therefore, chemical modification of carbon material surfaces can be achieved without the need for external heteroatom doping.

[0021] 2. Microalgae are pre-carbonized by hydrothermal treatment using a deep eutectic solvent. The deep eutectic solvent can act as a catalyst and co-solvent to depolymerize and dissolve microalgae proteins and carbohydrates into water, thereby promoting the interaction polymerization of proteins and carbohydrates under hydrothermal conditions through reactions such as Maillard, embedding their own nitrogen and oxygen atoms into the carbon skeleton to inhibit the loss of nitrogen and oxygen elements.

[0022] 3. The porous carbon prepared by this method has a large specific surface area and an ultramicroporous structure, with its surface rich in nitrogen and oxygen functional groups.

[0023] 4. The obtained porous carbon has a CO2 adsorption capacity of 4.50 mmol / g at 25℃ and 1 bar, and an adsorption capacity of up to 6.14 mmol / g at 1 bar and 0℃. Attached Figure Description

[0024] Figure 1 This is a flowchart of a method for preparing microalgae-based CO2 solid adsorbents using deep eutectic solvent hydrothermal treatment.

[0025] Figure 2 Aperture distribution map

[0026] Figure 3 This is the carbon dioxide adsorption isotherm (0℃).

[0027] Figure 4 This is the carbon dioxide adsorption isotherm (25℃). Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0029] like Figure 1 The method for preparing CO2 solid adsorbent by hydrothermal pretreatment of wet algal biomass followed by pyrolysis activation using a deep eutectic solvent specifically includes the following steps:

[0030] (1) Take microalgae powder with C content of 48% to 50%, N content of 9% to 11% and O content of 26% to 28% and mix it with deionized water at a ratio of 1:10 (g: ml). Stir on a magnetic stirrer for 20 to 30 minutes to obtain a uniform algae slurry suspension.

[0031] (2) Mix choline chloride and organic acid in a molar ratio of 1:2, and stir the mixture at 40-60°C to form a homogeneous solution. The organic acid here includes formic acid, acrylic acid and maleic acid.

[0032] (3) The deep eutectic solvent obtained from (2) is added to the algae solution obtained from (1) at a ratio of 25%, and the mixture is heated at 160°C in a reaction kettle for 10-60 min. After the hydrothermal reaction, the product is naturally cooled to room temperature, then poured into a centrifuge tube, centrifuged at 7000-8000 rpm for 4 min, the solution in the centrifuge tube is discarded, and the obtained solid product is dried in an oven at 105°C for 8-12 h.

[0033] (4) The solid obtained from (3) is placed in a corundum boat in a tube furnace and heated to 500-800°C in a N2 atmosphere for 2 h. Then cooled to room temperature in a N2 atmosphere to obtain the original carbon material. The nitrogen flow rate is 80-120 ml / min.

[0034] (5) The original carbon material obtained is mixed with KOH at a mass ratio of 1:2, and the mixture is placed in a tube furnace and heated to 500-800°C in a N2 atmosphere for 2 h. Then cooled to room temperature in a N2 atmosphere. The nitrogen flow rate is 80-120 ml / min. Washed with 1 mol / L hydrochloric acid solution to completely remove the residual KOH, then washed repeatedly with deionized water until the pH is 7. Finally dried in an oven at 105°C for 8-12 h, and the dried solid is the CO2 solid adsorbent.

[0035] The CO2 adsorption performance of the prepared CO2 solid adsorbent is determined by a gas adsorption instrument.

[0036] The following examples can enable a person skilled in the art to more fully understand the present application, but do not limit the present application in any way.

[0037] Example 1

[0038] Chlorella powder with C element content of 49.97%, N element content of 10.65%, and O element content of 27.76% was mixed with deionized water at a ratio of 1:10 (g:ml) and stirred on a magnetic stirrer for 20-30 min to obtain a uniform algal slurry suspension. The deep eutectic solvent was prepared by mixing choline chloride and formic acid at a molar ratio of 1:2 and stirring at 60°C for 10 min. 11.45 ml of algal liquid and 3.45 ml of deep eutectic solvent were added to a 25 ml reaction kettle, heated at 160°C for 10 min, and then naturally cooled to room temperature. The hydrothermal product was poured into a centrifuge tube and centrifuged at 8000 rpm for 4 min, and the solution in the centrifuge tube was discarded. The obtained solid product was dried in an oven at 105°C for 12 h. After drying, the solid was placed in a tube furnace corundum boat and heated to 800°C at a heating rate of 8°C / min in a N2 atmosphere, and then held at 800°C for 2 h. Subsequently, it was cooled to room temperature in a N2 atmosphere at a flow rate of 80 ml / min to obtain the original carbon material. The obtained original carbon material was mixed with KOH at a mass ratio of 1:2 and ground to 50 mesh or less. The powder was placed in a tube furnace corundum boat,

[0039] heated to 800°C at a heating rate of 8°C / min in a N2 atmosphere, and then held at 800°C for 2 h. Subsequently, it was cooled to room temperature in a N2 atmosphere at a flow rate of 80 ml / min. Washing with 1 mol / L hydrochloric acid solution completely removed the residual KOH, and then repeated washing with deionized water until the pH was 7. Finally, drying in an oven at 105°C for 8-12 h, the dried solid was the CO2 solid adsorbent. The CO2 adsorption performance was determined by a gas adsorption instrument.

[0040] Example 2

[0041] Chlorella powder with C element content of 49.97%, N element content of 10.65%, and O element content of 27.76% was mixed with deionized water at a ratio of 1:10 (g:ml) and stirred on a magnetic stirrer for 20-30 min to obtain a uniform algal slurry suspension. Deep eutectic solvent was prepared by mixing choline chloride and acrylic acid at a molar ratio of 1:2 at 60°C for 10 min. 11.45 ml of algal liquid and 3.45 ml of deep eutectic solvent were added to a 25 ml reaction kettle, which was heated at 160°C for 10 min, and then naturally cooled to room temperature. The hydrothermal product was poured into a centrifuge tube and centrifuged at 8000 rpm for 4 min, and the solution in the centrifuge tube was discarded. The obtained solid product was dried in an oven at 105°C for 12 h. After drying, the solid was placed in a tube furnace corundum boat and heated to 600°C at a heating rate of 8°C / min in a N2 atmosphere, and then held at 600°C for 2 h. Subsequently, it was cooled to room temperature in a N2 atmosphere at a flow rate of 80 ml / min to obtain the original carbon material. The obtained original carbon material was mixed with KOH at a mass ratio of 1:2 and ground to 50 mesh or less. The powder was placed in a tube furnace corundum boat and heated to 600°C at a heating rate of 8°C / min in a N2 atmosphere, and then held at 600°C for 2 h. Subsequently, it was cooled to room temperature in a N2 atmosphere at a flow rate of 80 ml / min. Washing with 1 mol / L hydrochloric acid solution completely removed the residual KOH, and then repeated washing with deionized water until the pH was 7. Finally, it was dried in an oven at 105°C for 8-12 h, and the dried solid was the CO2 solid adsorbent. The CO2 adsorption performance was determined by a gas adsorption instrument.

[0042] Example 3

[0043] Chlorella powder with C element content of 49.97%, N element content of 10.65%, and O element content of 27.76% was mixed with deionized water at a ratio of 1:10 (g:ml) and stirred on a magnetic stirrer for 20-30 min to obtain a uniform algal slurry suspension. The deep eutectic solvent was prepared by mixing choline chloride and maleic acid at a molar ratio of 1:2 at 60°C for 30 min. 11.45 ml of algal liquid and 3.45 ml of deep eutectic solvent were heated in a 25 ml reaction kettle at 160°C for 10 min, and then naturally cooled to room temperature. The hydrothermal product was poured into a centrifuge tube and centrifuged at 8000 rpm for 4 min, and the solution in the centrifuge tube was discarded. The obtained solid product was dried in an oven at 105°C for 12 h. After drying, the solid was placed in a tube furnace corundum boat and heated to 600°C at a heating rate of 8°C / min in a N2 atmosphere, and then held at 600°C for 2 h. Subsequently, it was cooled to room temperature in a N2 atmosphere at a flow rate of 80 ml / min to obtain the original carbon material. The obtained original carbon material was mixed with KOH at a mass ratio of 1:2 and ground to less than 50 mesh. The powder was placed in a tube furnace corundum boat and heated to 600°C at a heating rate of 8°C / min in a N2 atmosphere, and then held at 600°C for 2 h. Subsequently, it was cooled to room temperature in a N2 atmosphere at a flow rate of 80 ml / min. Washing with 1 mol / L hydrochloric acid solution completely removed the KOH residue, and then repeated washing with deionized water until the pH was 7. Finally, drying in an oven at 105°C for 8-12 h, the dried solid was the CO2 solid adsorbent. The CO2 adsorption performance was determined by a gas adsorption instrument.

[0044] Finally, it should be noted that the above enumeration is only a specific embodiment of the present application. Obviously, the present application is not limited to the above embodiment, but can have many variations. All variations that can be directly derived or inferred from the disclosure of the present application by those of ordinary skill in the art should be considered as falling within the scope of the present application.

Claims

1. A method for preparing microalgae-based CO2 solid adsorbents using deep eutectic solvent hydrothermal treatment, characterized in that, Specifically, the following steps are included: 1) Grind algae with a carbon content of 48%–50%, a nitrogen content of 9%–11%, and an oxygen content of 26%–28% into algae powder; mix the microalgae powder with deionized water at a ratio of 1g:10:ml and stir on a magnetic stirrer to obtain a uniform algae slurry suspension. 2) The method for preparing the deep eutectic solvent is as follows: choline chloride and organic acid are mixed at a molar ratio of 1:2, and the mixture is stirred at a temperature of 40-60℃ for 20-30 minutes; 3) Add the deep eutectic solvent obtained in (2) to the algal slurry suspension obtained in (1) at a volume ratio of 1:

4. Transfer the mixture to the inner liner of the reactor and place it in an oil bath to heat at 160°C for 10-60 minutes. After the hydrothermal process is completed, allow it to cool naturally to room temperature. Then pour the hydrothermal product into a centrifuge tube and separate it in a centrifuge at a speed of 7000 rpm to 8000 rpm for 3-5 minutes. Then discard the solution in the centrifuge tube and dry the obtained solid product at 105°C for 8-12 hours. 4) The solid obtained in (3) is placed in a corundum boat in a tube furnace and heated to 500-800℃ in a N2 atmosphere. After holding at the temperature for 2 hours, it is cooled to room temperature in a N2 atmosphere. After the reaction is complete, it is naturally cooled to room temperature to obtain the original carbon material. 5) The original carbon material obtained in (4) is mixed and ground with KOH at a mass ratio of 1:

2. The mixture is placed in a corundum boat in a tube furnace and heated to 500-800℃ in N2 atmosphere. After being kept at the temperature for 2 hours, it is cooled to room temperature in N2 atmosphere. It is washed with hydrochloric acid solution to completely remove KOH residue. Then it is repeatedly washed with deionized water until the pH is 7. Finally, the solid black particles are dried. The dried solid is the CO2 solid adsorbent.

2. The method for preparing microalgae-based CO2 solid adsorbents using hydrothermal treatment with a deep eutectic solvent according to claim 1, characterized in that, The algae used in step (1) include, but are not limited to, green algae, diatoms, and blue algae, and the stirring time is 20 to 30 minutes.

3. The method for preparing microalgae-based CO2 solid adsorbents using hydrothermal treatment with a deep eutectic solvent according to claim 1, characterized in that, In step (2), the organic acid is any one of formic acid, acrylic acid, and maleic acid.

4. The method for preparing microalgae-based CO2 solid adsorbents using hydrothermal treatment with a deep eutectic solvent according to claim 1, characterized in that, In step (5), the drying temperature is 105℃ and the drying time is 8-12h.

5. The method for preparing microalgae-based CO2 solid adsorbents using hydrothermal treatment with a deep eutectic solvent according to claim 1, characterized in that, In step (5), the particle size of the dried mixture is less than 50 mesh.

6. The method for preparing microalgae-based CO2 solid adsorbents using deep eutectic solvent hydrothermal treatment according to claim 1, characterized in that, The N2 concentration during the constant temperature and cooling process is 50~80 ml / L.

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