Porous chain popcorn-like calcium oxide calcium-based sorbent and method of making same

Abstract

The present application relates to a porous chain popcorn-like calcium oxide calcium-based absorbent and its preparation method, including introducing nitrogen element in CaO by relying on urea polymer structure crystallization to form porous popcorn-like clusters between the crystal grains and link to form chain structure, each popcorn-like cluster is assembled by 3-7 CaO crystal grains, the distance between the farthest two CaO in the popcorn-like cluster is 200-400 nm, each popcorn-like cluster contains micropores and mesopores; the chain structure linked by popcorn-like clusters is composed of 3-8 popcorn-like clusters, and the macropores are formed by the dispersed accumulation between the chains. The present application introduces nitrogen element in CaO lattice and enriches it on the pore edge, which strengthens the CO2 absorption capacity and carbonization conversion efficiency of the absorbent, and has good cycle stability; the preparation method is simple, low in cost and easy to synthesize.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon dioxide control and emission reduction absorbent materials, and particularly relates to a porous chain popcorn-shaped calcium oxide calcium-based absorbent and a preparation method. BACKGROUND

[0002] To solve the problem of high CO2 emission, the calcium-based absorbent for capturing carbon dioxide (CO2) has the advantages of high theoretical capacity, low cost and large-scale application, and has attracted widespread attention from the academic and industrial circles in the past decade. The absorbent composed of inorganic nano calcium oxide particles can greatly improve the CO2 capture efficiency. The calcium cycle process is a very promising CO2 capture technology, which utilizes the reversible reaction between CO2 and CaO, CaO+CO2=CaCO3, ΔH=179.2KJ / mol, CaCO3=CaO+CO2, ΔH=-179.2KJ / mol. It is generally called carbonation and calcination, and has high absorption rate. It is suitable for CO2 capture under high temperature conditions. However, due to the influence of CO2 partial pressure, carbonation temperature, carbonation time and pollutants on CO2 capture, the CO2 capture capacity will be sharply reduced during the cycle operation. The sintering of absorbent particles leads to poor reversibility in the regeneration process of the absorbent, which is the main challenge of using CaO-based absorbent to capture CO2 under high temperature.

[0003] In recent years, many people have tried to use various improved means to improve the absorption efficiency of CaO-based absorbent for CO2, such as doping, chemical pretreatment, introduction of inert carriers with high Tamman temperature, etc. Among them, the doping of metal elements such as Ce, Mn, Ti, etc. can effectively improve the absorption efficiency of CaO-based absorbent and inhibit the sintering of CaO particles. However, there is no report on the doping of non-metallic nitrogen element. In the present application, urea is added in batches under nitrogen atmosphere during different stages of CaO stirring, and after 4-6h of hydrothermal environment at 160-180℃, the nitrogen element is doped into CaO to replace part of the Ca ions in the CaO lattice to form a covalent bond that changes the electronegativity of adjacent Ca ions. The strong interaction between the nitrogen-doped structure formed by the N atoms entering the CaO lattice and the Ca ions is more conducive to the doping of nitrogen atoms. In addition, after the nitrogen atoms are doped into the CaO lattice, they form an active region that is conducive to accommodating active substances, and the nitrogen atoms can accelerate the adsorption and activation of reactants, and even directly participate in the reaction. The strong interaction between nitrogen atoms and CO2 molecules in the active region promotes the adsorption and activation of CO2 in the nitrogen atoms doped into the CaO lattice. By promoting the adsorption and activation of CO2, the CO2 absorption efficiency of CaO is improved. Suitable nitrogen content is conducive to promoting the adsorption of CO2 and the separation and transfer of photo-generated electron-hole pairs, thereby improving the performance of CaO in absorbing CO2, and the nitrogen atoms can act as binding points to form close contact with Ca ions to achieve high-quality bonding. In the existing literature, ion doping modification of CaO absorbent is focused on metal ions, and the prepared CaO mostly has poor dispersion and grain fusion aggregation structure, which is difficult to maintain high conversion rate and cycle stability, and the cost is very high. Therefore, it is of great significance to develop a non-metallic element doped, low-cost, sintering-resistant, and new morphology CaO absorbent. SUMMARY

[0004] OBJECTIVE

[0005] To solve the problems of CaO particle sintering, poor crystal fusion aggregation stability, and decreased cycle absorption rate of calcium-based absorbent in the prior art, the present application provides a porous chain popcorn-like calcium oxide calcium-based absorbent and a preparation method thereof. The porous chain popcorn-like calcium oxide calcium-based absorbent of the present application has the characteristics of approaching the theoretical maximum conversion rate of 95%, good crystal grain size stability, and excellent CO2 absorption cycle performance.

[0006] TECHNICAL SCHEME

[0007] A porous chain popcorn-like calcium oxide calcium-based absorbent, comprising: introducing nitrogen element in CaO by crystallizing etourea polymer structure to form porous popcorn-like clusters between the crystal grains and link to form a chain structure, each of the popcorn-like clusters is assembled by 3-7 CaO crystal grains, the distance between the farthest two CaO in the popcorn-like cluster is 200-400 nm, and each popcorn-like cluster contains micropores of 1.3-2 nm and mesopores of 2-20 nm, and the size of each CaO crystal grain in the popcorn-like cluster is 60-100 nm; the chain structure linked by the popcorn-like clusters is composed of 3-8 popcorn-like clusters, and the chains are dispersed and stacked between the chains to form macropores of 70-190 nm.

[0008] A preparation method of a porous chain popcorn-like calcium oxide calcium-based absorbent, comprising the following steps: taking CaO and urea as raw materials, relying on the network structure characteristics of biuret and trimer hexacyclic compound trimer cyanic acid polymers which are hydrolysis products of urea in an ethanol aqueous solution hydrothermal reaction system, through hydrogen bonding and electrostatic complexation, Ca(OH)2 dissolution ion groups formed by CaO non-uniformly nucleate along the carbon-nitrogen nodes in the polymer network to generate CaCO3 polycrystalline products containing associated nitrogen; after calcination, the original backbone hexacyclic ring structure is destroyed to obtain a chain-like morphology feature with popcorn-like cluster structure as a structural unit, and C and N elements can be oxidized into gas to form mesopores and micropores, and the outer layer is connected by CaO obtained by calcining CaCO3 to form the porous chain popcorn-like calcium oxide calcium-based absorbent.

[0009] The preparation method of the above-mentioned porous chain popcorn-like calcium oxide calcium-based absorbent, comprising the following steps:

[0010] Step one, respectively weigh deionized water and ethanol, the volume ratio of deionized water to ethanol is 1:2-4, pour into a beaker and mix and stir thoroughly;

[0011] Step two, weigh CaO powder, pour into an alcohol water solution that can fully dissolve CaO;

[0012] Weigh the urea powder, the urea content is ≥99%, the mass ratio of urea to CaO is 1.6-5:1, pour the urea powder into the alcohol water solution containing CaO in the step two and stir;

[0013] Step four, after the stirring of the mixed solution in the step three is completed, put it into a hydrothermal reaction kettle, and put the hydrothermal reaction kettle into an oven to perform hydrothermal reaction, take it out after the hydrothermal reaction is completed, wait for it to cool to room temperature naturally, wash the product with excess ethanol, first centrifuge to separate the solid and liquid, then dry, grind in a grinding tank, and then calcine to obtain the porous chain popcorn-like calcium oxide calcium-based absorbent.

[0014] As a further description of the above scheme, the solution obtained from the step one, step two and step three is stirred by a sealed atmosphere stirrer, the stirring speed is 800-1300 rpm, the stirring temperature is 60-70℃, and the stirring environment is under nitrogen atmosphere.

[0015] As a further description of the above scheme, the temperature for the hydrothermal reaction in the hydrothermal reactor in the step four is 160-180℃, the reaction time is 4-6h, after the product is taken out, it is washed twice or more than twice by excess anhydrous ethanol, and dried at 70-80℃ for 4-8h, then the calcination in the step four is calcined in a muffle furnace for 20-30min, the calcination temperature is 900-950℃, thus the porous chain popcorn-like calcium oxide calcium-based absorbent is obtained.

[0016] As a further description of the above scheme, the step four is centrifuged by a centrifuge tube, the centrifugal speed is 3800-4200 rad / min, and the centrifugal time is 8-12min.

[0017] As a further description of the above scheme, the grinding in the step four is by using a force of 4-6N, and the grinding speed is 100-120 rounds / min.

[0018] As a further description of the above scheme, in the step three, the urea powder is poured into the alcohol solution containing CaO in the step two for three times, the first time is to pour 20% of the total mass of the urea powder, after 20-25min, the second time is to pour 20% of the total mass of the urea powder into the solution in the step two, after 20-25min, the remaining urea powder is poured into the solution in the step two, and the stirring is continued for 5-10min.

[0019] Advantages and effects

[0020] (1) The porous chain popcorn-like calcium oxide calcium-based absorbent has the advantages that after the CaO is poured into the urea in batches during the stirring in the water bath at 60-70℃ for 45-60min, and the stirring is continued for 5-10min for morphology control, the obtained CaO crystal grains are small, the dispersibility and the sintering resistance are good, the porosity structure is more loose and dispersed, the specific surface area is larger, and the mesopores and micropores are more.

[0021] (2) Using urea as a morphology modifier, and CaO and urea as raw materials, based on the structural characteristics of biuret (C2H5N3O2) and cyanuric acid (C3H3N3O3), which are hydrolysis products of urea in different stages of the hydrothermal reaction system of ethanol-water solution, the Ca(OH)2 dissolved ion clusters formed by CaO will undergo heterogeneous nucleation along the carbon and nitrogen nodes in the above polymer network through hydrogen bonding and electrostatic complexation, generating CaCO3 polycrystalline products containing associated nitrogen. After calcination, the original six-membered ring skeleton structure of CaCO3 polycrystalline products is destroyed, and a chain-like morphology with popcorn-like cluster structure as the structural unit is obtained. The C and N elements are oxidized into gas and escape to form mesopores and micropores. The outer layer is connected by CaO obtained from calcined CaCO3, so that the formed hydrothermal products are loose and porous and contain nitrogen elements that are conducive to structural anchoring, thus forming a high-performance and stable calcium oxide calcium-based absorbent.

[0022] (3) The preparation method is simple, the cost is low and it is easy to synthesize. The calcium-based absorbent of porous chain popcorn-shaped calcium oxide of the present invention can achieve an initial CO2 adsorption rate of 90-95% during the carbonation cycle (carbonation temperature is 650℃ and carbonation time is 40 minutes). After 10 cycles, it still has high CO2 absorption capacity and cycle stability, and has good industrial application prospects. Attached Figure Description

[0023] Figure 1 The image is a 20,000x scanning electron microscope (SEM) image of the porous chain popcorn-shaped calcium oxide calcium-based absorbent prepared in Example 2.

[0024] Figure 2 X-ray diffraction (XRD) pattern of the porous chain popcorn-shaped calcium oxide calcium-based absorbent prepared in Example 2;

[0025] Figure 3 The image is a 10,000x scanning electron microscope (SEM) image of the fifth cycle of the porous chain popcorn-shaped calcium oxide calcium-based absorbent prepared in Example 2.

[0026] Figure 4 The adsorption pore size distribution curve of the calcium-based absorbent BJH for porous chain popcorn-shaped calcium oxide prepared in Example 2;

[0027] Figure 5 The graph shows the cyclic CO2 absorption rate of the porous chain popcorn-shaped calcium oxide calcium-based absorbent prepared in Examples 2 and 4, compared with that of CaO.

[0028] Figure 6 The sealed atmosphere stirrer used when preparing the porous chain popcorn-shaped calcium oxide calcium-based absorbent in Example 2. Detailed Implementation

[0029] The technical solutions of the present application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, but not all the embodiments.

[0030] In order to more clearly explain the technical solutions in the specific embodiments or prior art, the drawings needed to be used in the specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0031] The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application.

[0032] The chemical reagents used in the embodiments of the present application are all commercially available chemical reagents; the micro-morphology detection in the embodiments of the present application uses SU-8010 field emission scanning electron microscope; the pore structure detection in the embodiments of the present application uses Vsorb2800P specific surface area and pore size analyzer; and the centrifuge in the embodiments of the present application is LDZ4-1.8 centrifuge.

[0033] A porous chain popcorn-like calcium oxide calcium-based absorbent, relying on urea polymer structure crystallization to introduce nitrogen element in CaO to form porous popcorn-like clusters between the crystal grains and link to form chain structure, each popcorn-like cluster is assembled by 3-7 CaO crystal grains, the distance between the farthest two CaO in the popcorn-like cluster is 200-400 nm, and each popcorn-like cluster contains 1.3-2 nm micropores and 2-20 nm mesopores, and the size of each CaO crystal grain in the popcorn-like cluster is 60-100 nm; the chain structure linked by popcorn-like clusters is composed of 3-8 popcorn clusters, and the chains are dispersed and stacked between the chains to form 70-190 nm macropores.

[0034] The preparation method of the porous chain popcorn calcium oxide calcium-based absorbent of the embodiment of the present application comprises the following steps: taking CaO and urea as raw materials, relying on the network structure characteristics of biuret and trimer hexa-ring compound trimer cyanic acid polymer products of urea at different stages in the hydrothermal reaction system of ethanol aqueous solution, through hydrogen bond and electrostatic complexation, Ca(OH)2dissolved ion groups formed by CaO non-uniformly nucleate along the carbon-nitrogen nodes in the polymer network to generate CaCO3polycrystalline products containing associated nitrogen; after calcination, the original backbone hexa-ring structure is destroyed to obtain a chain morphology feature with popcorn cluster structure as a structural unit, and C and N elements are oxidized into gas to form mesopores and micropores; the outer layer is connected by CaO obtained by calcining CaCO3to form the porous chain popcorn calcium oxide calcium-based absorbent. The present application uses urea as a morphology control agent, takes CaO and urea as raw materials, relies on the network structure characteristics of biuret (C2H5N3O2) and trimer hexa-ring compound trimer cyanic acid (C3H3N3O3) products of urea at different stages in the hydrothermal reaction system of ethanol aqueous solution, through hydrogen bond and electrostatic complexation, Ca(OH)2dissolved ion groups formed by CaO non-uniformly nucleate along the carbon-nitrogen nodes in the polymer network to generate CaCO3polycrystalline products containing associated nitrogen. After calcination of the CaCO3polycrystalline product, the original backbone hexa-ring structure is destroyed to obtain a chain morphology feature with popcorn cluster structure as a structural unit, wherein part of C and N elements are oxidized into gas to form mesopores and micropores, and the outer layer is connected by CaO obtained by calcining CaCO3, so that the hydrothermal product formed is loose and porous and contains nitrogen elements beneficial to structural anchoring, thereby forming a high-performance and stable calcium oxide calcium-based absorbent.

[0035] The preparation method of the porous chain popcorn calcium oxide calcium-based absorbent described above comprises the following steps:

[0036] Step one, respectively weigh deionized water and ethanol, the volume ratio of deionized water to ethanol is 1:2-4, pour into a beaker and mix and stir thoroughly;

[0037] Step two, weigh CaO powder, pour into an alcohol-water solution that can dissolve CaO thoroughly;

[0038] Step three, weigh urea powder, the urea content is ≥99%, the mass ratio of urea to CaO is 1.6-5:1, pour the urea powder into the alcohol-water solution containing CaO in step two and stir;

[0039] Step four, after the mixing solution in step three is stirred, it is put into a hydrothermal reactor, the hydrothermal reactor is put into an oven to perform hydrothermal reaction, after the hydrothermal reaction is finished, the product is taken out, and after the product is naturally cooled to room temperature, the product is washed with excess ethanol, and is centrifuged to separate solid and liquid, and then is dried, ground in a grinding tank, calcined, and the porous chain popcorn-like calcium oxide calcium-based absorbent is obtained. The preparation method is simple, low in cost and easy to synthesize, the porous chain popcorn-like calcium oxide calcium-based absorbent has a first CO2 adsorption rate of 90-95% in a carbonation cycle (carbonation temperature is 650 DEG C, and carbonation time is 40 minutes), still has high CO2 absorption capacity (85%) and cycle stability after 10 cycles, and has good industrial application prospect.

[0040] The solution obtained in steps one, two and three is stirred by using a sealed atmosphere stirrer, the stirring speed is 800-1300 rpm, the stirring temperature is 60-70 DEG C, and the stirring is performed in a nitrogen atmosphere, so that CO2 in air does not affect the PH value of the solution in step two, and urea is not hydrolyzed in advance. After the CaO is stirred in a water bath at 60-70 DEG C for 45-60 minutes, the CaO is poured into urea, and the stirring is continued for 5-10 minutes to obtain CaO grains with small size, good dispersibility and sintering resistance, more porous structure, more loose and dispersed, larger specific surface area, more mesopores and micropores.

[0041] In step three, the urea is added into the solution in step two in three times, and the first two times are to keep the solution alkaline, so that the urea added in the last time is not hydrolyzed.

[0042] In step four, the hydrothermal reaction in the hydrothermal reactor is performed at a temperature of 160-180 DEG C for 4-6 hours, the product is washed with excess anhydrous ethanol twice or more than twice, and is dried at 70-80 DEG C for 4-8 hours; the calcination in step four is performed in a muffle furnace for 20-30 minutes at a calcination temperature of 900-950 DEG C, and the porous chain popcorn-like calcium oxide calcium-based absorbent is obtained.

[0043] In step four, the centrifugation is performed by using a centrifugal tube, the centrifugal speed is 3800-4200 rad / min, and the centrifugal time is 8-12 minutes.

[0044] In step four, the grinding is performed by using a force of 4-6 N, and the grinding speed is 100-120 rounds / min.

[0045] The urea powder in step three of the embodiment of the present application is poured into the alcohol and water solution containing CaO in step two for three times, 20% of the total mass of the urea powder is poured into the solution in step two for the first time, after 20-25 minutes, 20% of the total mass of the urea powder is poured into the solution in step two again, after 20-25 minutes, the remaining urea powder is poured into the solution in step two, and the stirring is continued for 5-10 minutes.

[0046] Example 1

[0047] In step one, a graduated cylinder is used to measure deionized water and ethanol, the volume ratio of the deionized water and the ethanol is 1:2, the mixture is poured into a 250ml beaker and stirred, the stirring speed is 1000rpm, and the stirring temperature is 70°C;

[0048] In step two, an electronic balance is used to weigh CaO powder calcined at 950°C for 20 minutes in a muffle furnace, and the CaO powder is poured into the alcohol and water stirring solution which has been heated and mixed; an electronic balance is used to weigh urea powder, the urea content is ≥99%, and the mass ratio of the urea to CaO is 1.648:1, when the CaO powder is stirred in the alcohol and water stirring solution which has been heated and mixed for 40 minutes, the urea is poured in, and the stirring is continued for 5 minutes;

[0049] In step three, after the stirring of the solution is completed, the solution is put into a hydrothermal reaction kettle and transferred into an oven for hydrothermal reaction, the hydrothermal reaction conditions are a temperature of 160°C and a time of 6 hours, after the hydrothermal reaction is completed, the solution is taken out and naturally cooled to room temperature, the product is washed twice or more than twice with excess ethanol, a 60ml centrifuge tube is used for centrifugation, the centrifugation speed is 4200rad / min, the centrifugation time is 8 minutes, after centrifugal drying, the product is transferred into a grinding tank for grinding, the grinding uses a force of 4N and 120 circles per minute, and then calcination is performed, the calcination is performed at 950°C in a muffle furnace for 20 minutes.

[0050] Example 2

[0051] In step one, a graduated cylinder is used to measure deionized water and ethanol, the volume ratio of the deionized water and the ethanol is 1:3, the mixture is poured into a 250ml beaker and stirred, the stirring speed is 1000rpm, and the stirring temperature is 70°C;

[0052] In step two, an electronic balance is used to weigh CaO powder calcined at 950°C for 20 minutes in a muffle furnace, and the CaO powder is poured into the alcohol and water stirring solution which has been heated and mixed; an electronic balance is used to weigh urea powder, the urea content is ≥99%, and the mass ratio of the urea to CaO is 2.47:1, when the CaO powder is stirred in the alcohol and water stirring solution which has been heated and mixed for 50 minutes, the urea is poured in, and the stirring is continued for 7 minutes;

[0053] Step three, after the end of the solution stirring, put into the hydrothermal reactor into the oven for hydrothermal reaction, the conditions of hydrothermal reaction are temperature 170℃, time 5h, after the hydrothermal reaction, take out, wait for its natural cooling to room temperature, the product is washed twice or more than twice with excess ethanol, using 60ml centrifuge tube centrifugation, centrifugal speed is 4000rad / min, centrifugal time is 9min, after centrifugal drying, transfer to the grinding tank, grinding, grinding using 5N force, 110 turns / min, then calcination, in the muffle furnace 930℃ calcination 25min.

[0054] Example 3

[0055] Step one, use the measuring cylinder to measure deionized water and ethanol respectively, the volume ratio of deionized water to ethanol is 1:3, pour into a 250ml beaker, mix well and stir, stirring speed is 1000rpm, stirring temperature is 70℃;

[0056] Step two, use electronic balance to weigh CaO powder calcined at 950℃ for 20min by muffle furnace, pour into the mixed alcohol water stirring solution which has been heated; use electronic balance to weigh urea powder, urea content≥99%, the mass ratio of urea to CaO is 3.3:1, when the CaO powder is stirred in the mixed alcohol water stirring solution which has been heated for 55min, pour into the weighed urea, continue to stir for 9min;

[0057] Step three, after the end of the solution stirring, put into the hydrothermal reactor into the oven for hydrothermal reaction, the conditions of hydrothermal reaction are temperature 180℃, time 4h, after the hydrothermal reaction, take out, wait for its natural cooling to room temperature, the product is washed twice or more than twice with excess ethanol, using 60ml centrifuge tube centrifugation, centrifugal speed is 3900rad / min, centrifugal time is 11min, after centrifugal drying, transfer to the grinding tank, grinding, grinding using 5N force, 120 turns / min, then calcination, in the muffle furnace 920℃ calcination 27min.

[0058] Example 4

[0059] Step one, use the measuring cylinder to measure deionized water and ethanol respectively, the volume ratio of deionized water to ethanol is 1:4, pour into a 250ml beaker, mix well and stir, stirring speed is 1000rpm, stirring temperature is 70℃;

[0060] Step two, use electronic balance to weigh CaO powder calcined at 950℃ for 20min by muffle furnace, pour into the mixed alcohol water stirring solution which has been heated; use electronic balance to weigh urea powder, urea content≥99%, the mass ratio of urea to CaO is 4.1:1, when the CaO powder is stirred in the mixed alcohol water stirring solution which has been heated for 55min, pour into the weighed urea, continue to stir for 10min;

[0061] Step three, after the end of the solution stirring, put into the hydrothermal reactor into the oven for hydrothermal reaction, the conditions of hydrothermal reaction are temperature 180℃, time 5h, after the hydrothermal reaction, take out, wait for its natural cooling to room temperature, the product is washed twice or more than twice with excess ethanol, using 60ml centrifuge tube centrifugation, centrifugal speed is 3800rad / min, centrifugal time is 12min, after centrifugal drying, transfer to the grinding tank, grinding, grinding using 6N force, 100 turns / min, then calcination, in the muffle furnace 900℃ calcination 30min.

[0062] Example 5

[0063] Step one, use the measuring cylinder to measure deionized water and ethanol respectively, the volume ratio of deionized water and ethanol is 1:4, pour into a 250ml beaker, mix and stir, stirring speed is 1000rpm, stirring temperature is 70℃;

[0064] Step two, use electronic balance to weigh CaO powder calcined at 950℃ for 20min by muffle furnace, pour into the mixed alcohol water stirring solution which has been heated, use electronic balance to weigh urea powder, urea content≥99%, the mass ratio of urea and CaO is 5:1, after the CaO powder is stirred in the mixed alcohol water stirring solution which has been heated for 55min, pour the weighed urea, continue to stir for 10min;

[0065] Step three, after the end of the solution stirring, put into the hydrothermal reactor into the oven for hydrothermal reaction, the conditions of hydrothermal reaction are temperature 180℃, time 5h, after the hydrothermal reaction, take out, wait for its natural cooling to room temperature, the product is washed twice or more than twice with excess ethanol, using 60ml centrifuge tube centrifugation, centrifugal speed is 3800rad / min, centrifugal time is 12min, after centrifugal drying, transfer to the grinding tank, grinding, grinding using 6N force, 100 turns / min, then calcination, in the muffle furnace 900℃ calcination 30min.

[0066] Performance test:

[0067] In order to detect the performance of the porous chain popcorn-like calcium oxide calcium-based absorbent prepared by the application, first, the porous chain popcorn-like calcium oxide calcium-based absorbent of example 3 and CaO are respectively put into different porcelain boats, then the two porcelain boats are put into a vacuum box-type high-temperature electric furnace, CO2 is introduced into the vacuum box-type high-temperature electric furnace to carry out carbonation reaction, the carbonation conditions are temperature 650℃, time 40min, after the carbonation is completed, the two porcelain boats are taken out and transferred into a muffle furnace with a high temperature of 900℃ for calcination, the calcination time is 20min. Repeat the carbonation and calcination, the mass of the absorbent sample after each carbonation and calcination is measured by an electronic balance, and the carbonation conversion rate is calculated according to the mass change, as shown in formula (1).

[0068]

[0069] wherein X N is carbonation conversion rate; N is cycle number; m0is initial mass of absorbent sample, unit is g; m N is mass of carbonated sample after N cycles, unit is g; b is content of CaO in initial sample.

[0070] The test results are shown in Figure 5 FIG. 1, wherein the abscissa is cycle number and the ordinate is carbonation conversion rate. Under the same reaction conditions, the carbonation conversion rate of CaO is only 73% for the first time, and the carbonation conversion rate is reduced to 39.7% after the 10th cycle, and the conversion rate is greatly attenuated; while the carbonation conversion rate of the porous chain popcorn-like calcium oxide calcium-based absorbent of the present application is 95% for the first time, and the conversion rate can be maintained at 88% after 10 cycles, which is 2.22 times of CaO. The results show that the porous chain popcorn-like calcium oxide calcium-based absorbent of the present application can not only improve the carbonation conversion rate of the cyclic absorption of CO2, but also improve the cyclic stability of calcium oxide, which is mainly due to the morphology control of CaO by the hydrothermal reaction of urea in the hydrothermal environment at 160-180℃ and the doping of nitrogen atoms into the crystal lattice of CaO to form active regions with them as the center which are beneficial to accommodate active substances, and the nitrogen atoms can accelerate the adsorption and activation of reactants, and even directly participate in the reaction, thereby obtaining higher performance.

[0071] The 20000 times scanning electron microscope (SEM) image of the porous chain popcorn-like calcium oxide calcium-based absorbent is shown in Figure 1 FIG. 2, Figure 1 wherein a cluster of popcorns is 200-400 nm in size and is assembled by 3-7 CaO grains, contains 1.3-2 nm micropores and 2-20 nm mesopores, and each CaO grain is 60-100 nm in size; a porous chain is composed of 3-8 clusters of popcorns, and the chains are dispersed and stacked to form 70-190 nm macropores (as shown in the circles in the figure), Figure 2is the X-ray diffraction (XRD) pattern of the porous chain popcorn-like calcium oxide calcium-based absorbent. By analyzing the XRD pattern of the product and comparing it with the PDF card of CaO, it is found that the peaks of the XRD of the product are shifted to the right, which can prove that the nitrogen element is doped into the CaO crystal lattice, and then forms an active area with them as the center which is conducive to accommodating active substances, and the nitrogen atom can accelerate the adsorption and activation of the reactants, and even directly participate in the reaction. The strong interaction between nitrogen atoms and CO2 molecules in the active area can promote the adsorption and activation of CO2 in the nitrogen atom doped into the CaO crystal lattice. By promoting the adsorption and activation of CO2, the CO2 absorption efficiency of CaO is improved. The appropriate nitrogen content is conducive to promoting the adsorption of CO2 and the separation and transfer of photo-generated electron-hole pairs, thereby improving the performance of CaO in absorbing CO2. Moreover, nitrogen atoms can act as binding points and form close contact with Ca ions to ensure high CO2 conversion rate of the absorbent. Figure 3 is the 10000 times scanning electron microscope (SEM) image of the calcium-based absorbent of the porous chain popcorn-like calcium oxide after 5 cycles. It can be found that after 5 cycles, the synthesized calcium-based absorbent still has a chain popcorn morphology, thereby ensuring the stability of the absorbent.

[0072] The pore size distribution comparison curve of the calcium-based absorbent of the porous chain popcorn-like calcium oxide and CaO is shown in Figure 4 The abscissa is the pore diameter in nm, and the ordinate is the pore volume in cm 3 / g. The figure shows that the absorbent contains pore structures of different sizes, including micropores of 1.3-2 nm, mesopores of 2-20 nm, and macropores of 70-190 nm between the crystal grains. Compared with CaO, the mesopores and micropores increase significantly, thereby providing a channel for the internal CaO to react with CO2 when CaCO3 layer is formed on the surface of CaO during the absorption of CO2, effectively reducing the diffusion resistance of CO2 into the interior of CaO. In addition, the calcium-based absorbent of the porous chain popcorn-like calcium oxide has a high specific surface area, so that the synthesized calcium-based absorbent has high CO2 absorption performance and cycle stability. Figure 6 is a sealed atmosphere stirrer used in the experiment. The sealed atmosphere stirrer is a product of the prior art. The gas cylinder has a volume of 1-2 L, the inlet pipe is 20-25 cm long, and the outlet pipe is 10-15 cm long. When preparing the product, the inlet pipe gas valve is opened to introduce N2 into the stirrer to maintain N2 atmosphere, so that the pH value of the solution remains unchanged to inhibit the hydrolysis of urea.

[0073] Obviously, the above embodiments of the present application are merely example for clearly explaining the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made, and here all the embodiments cannot be exhausted, and any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

Claims

1. A porous chain popcorn calcium oxide calcium-based sorbent characterized in that, The calcium-based absorbent takes CaO and urea as raw materials, and relies on the network structure characteristics of biuret and trimer hexacyclic compound cyanuric acid polymer, which are hydrolysis products of urea in the hydrothermal reaction system of ethanol aqueous solution. Through hydrogen bond and electrostatic interaction, Ca(OH)2dissolved ion group formed by CaO non-uniformly nucleates along the carbon-nitrogen nodes in the polymer network to generate CaCO3polycrystalline product containing associated nitrogen; after calcination of the CaCO3polycrystalline product, the original backbone hexacyclic ring structure is destroyed to obtain chain-like morphology characteristics with popcorn-like cluster structure as the structural unit, and C and N elements are oxidized into gas to form mesopores and micropores, and nitrogen elements are doped into the crystal lattice of CaO; The calcium-based absorbent includes nitrogen elements introduced into CaO by relying on urea polymer structure crystallization to form porous popcorn-like clusters between crystal grains and link to form chain structures, each of the popcorn-like clusters is assembled by 3-7 CaO crystal grains, the distance between the two farthest CaO in the popcorn-like cluster is 200-400 nm, and each popcorn-like cluster contains 1.3-2 nm micropores and 2-20 nm mesopores, and the size of each CaO crystal grain in the popcorn-like cluster is 60-100 nm; the chain structure linked by the popcorn-like clusters is composed of 3-8 popcorn-like clusters, and the chains are dispersed and stacked between the chains to form 70-190 nm macropores.

2. The method for producing a porous chain popcorn-like calcium oxide calcium-based sorbent according to claim 1, characterized by, The calcium-based absorbent takes CaO and urea as raw materials, and relies on the network structure characteristics of biuret and trimer hexacyclic compound cyanuric acid polymer, which are hydrolysis products of urea in the hydrothermal reaction system of ethanol aqueous solution. Through hydrogen bond and electrostatic interaction, Ca(OH)2dissolved ion group formed by CaO non-uniformly nucleates along the carbon-nitrogen nodes in the polymer network to generate CaCO3polycrystalline product containing associated nitrogen; after calcination of the CaCO3polycrystalline product, the original backbone hexacyclic ring structure is destroyed to obtain chain-like morphology characteristics with popcorn-like cluster structure as the structural unit, and C and N elements are oxidized into gas to form mesopores and micropores; the outer layer is connected by CaO obtained by calcining CaCO3to form a calcium-based absorbent of porous chain popcorn-like calcium oxide.

3. The method for preparing the porous chain popcorn-shaped calcium oxide calcium-based absorbent according to claim 2, characterized in that: The calcium-based absorbent takes CaO and urea as raw materials, and relies on the network structure characteristics of biuret and trimer hexacyclic compound cyanuric acid polymer, which are hydrolysis products of urea in the hydrothermal reaction system of ethanol aqueous solution. Through hydrogen bond and electrostatic interaction, Ca(OH)2dissolved ion group formed by CaO non-uniformly nucleates along the carbon-nitrogen nodes in the polymer network to generate CaCO3polycrystalline product containing associated nitrogen; after calcination of the CaCO3polycrystalline product, the original backbone hexacyclic ring structure is destroyed to obtain chain-like morphology characteristics with popcorn-like cluster structure as the structural unit, and C and N elements are oxidized into gas to form mesopores and micropores; the outer layer is connected by CaO obtained by calcining CaCO3to form a calcium-based absorbent of porous chain popcorn-like calcium oxide. The calcium-based absorbent takes CaO and urea as raw materials, and relies on the network structure characteristics of biuret and trimer hexacyclic compound cyanuric acid polymer, which are hydrolysis products of urea in the hydrothermal reaction system of ethanol aqueous solution. Through hydrogen bond and electrostatic interaction, Ca(OH)2dissolved ion group formed by CaO non-uniformly nucleates along the carbon-nitrogen nodes in the polymer network to generate CaCO3polycrystalline product containing associated nitrogen; after calcination of the CaCO3polycrystalline product, the original backbone hexacyclic ring structure is destroyed to obtain chain-like morphology characteristics with popcorn-like cluster structure as the structural unit, and C and N elements are oxidized into gas to form mesopores and micropores; the outer layer is connected by CaO obtained by calcining CaCO3to form a calcium-based absorbent of porous chain popcorn-like calcium oxide. The calcium-based absorbent takes CaO and urea as raw materials, and relies on the network structure characteristics of biuret and trimer hexacyclic compound cyanuric acid polymer, which are hydrolysis products of urea in the hydrothermal reaction system of ethanol aqueous solution. Through hydrogen bond and electrostatic interaction, Ca(OH)2dissolved ion group formed by CaO non-uniformly nucleates along the carbon-nitrogen nodes in the polymer network to generate CaCO3polycrystalline product containing associated nitrogen; after calcination of the CaCO3polycrystalline product, the original backbone hexacyclic ring structure is destroyed to obtain chain-like morphology characteristics with popcorn-like cluster structure as the structural unit, and C and N elements are oxidized into gas to form mesopores and micropores; the outer layer is connected by CaO obtained by calcining CaCO3to form a calcium-based absorbent of porous chain popcorn-like calcium oxide. ​ Step four, after the end of the stirring of the mixed solution in step three, the solution is put into a hydrothermal reactor, and the hydrothermal reactor is put into an oven for hydrothermal reaction. After the hydrothermal reaction, the product is washed with excess ethanol, and then centrifuged to separate the solid and liquid. After drying, the product is ground in a grinding tank, and then calcined to obtain the calcium-based absorbent with porous chain popcorn-like calcium oxide.

4. The method of claim 3, wherein the porous chain popcorn calcium oxide calcium-based sorbent is prepared by: The solutions obtained in steps one, two and three are stirred using a sealed atmosphere stirrer, the stirring speed is 800-1300 rpm, the stirring temperature is 60-70℃, and the stirring environment is in a closed nitrogen atmosphere.

5. The method of claim 3, wherein the porous chain popcorn calcium oxide calcium-based sorbent is prepared by: In step four, the temperature for hydrothermal reaction in the hydrothermal reactor is 160-180℃, the reaction time is 4-6h, and the product is washed with excess anhydrous ethanol twice or more times, and then dried at 70-80℃ for 4-8h. In step four, the calcination is carried out in a muffle furnace for 20-30min at a calcination temperature of 900-950℃, and the calcium-based absorbent with porous chain popcorn-like calcium oxide is obtained.

6. The method of claim 3, wherein the porous chain popcorn calcium oxide calcium-based sorbent is prepared by: In step four, centrifugation is carried out using a centrifuge tube, the centrifugation speed is 3800-4200 rad / min, and the centrifugation time is 8-12min.

7. The method for preparing the porous chain popcorn-shaped calcium oxide calcium-based absorbent according to claim 3, characterized in that: In step four, the grinding is carried out using a force of 4-6N, and the grinding speed is 100-120 rounds / min.

8. The method of claim 3, wherein the porous chain popcorn calcium oxide calcium-based sorbent is prepared by: In step three, the urea powder is divided into three portions and added into the alcohol and water solution containing CaO in step two. The first portion of urea powder is 20% of the total mass, and after 20-25 minutes, the second portion of urea powder is added into the solution in step two, which is also 20% of the total mass. After 20-25 minutes, the remaining urea powder is added into the solution in step two, and the stirring is continued for 5-10 minutes.

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