CN113244881A

CN113244881A - Method for preparing lithium orthosilicate material by taking KIT-6 as silicon source, modification and application thereof

Info

Publication number: CN113244881A
Application number: CN202110713140.3A
Authority: CN
Inventors: 魏建文; 贾燕飞; 李誉; 袁苑; 耿琳琳; 周小斌; 廖雷
Original assignee: Guilin University of Technology
Current assignee: Guilin University of Technology
Priority date: 2021-06-25
Filing date: 2021-06-25
Publication date: 2021-08-13

Abstract

The invention discloses a method for preparing a lithium orthosilicate material by taking KIT-6 as a silicon source, and modification and application thereof, wherein in the step a, a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is taken as a template agent, and tetraethyl silicate is taken as a silicon source to synthesize a KIT-6 mesoporous silicon oxide precursor; step b reaction of Li₂CO₃Mixing the precursor and the silicon precursor in the step a in absolute ethyl alcohol according to a molar ratio and heating; c, stirring the solution obtained in the step b for a period of time to uniformly mix the solution; step d, calcining the product in the step c at a certain temperature to obtain Li₄SiO₄An adsorbent material. Then to Li₄SiO₄The adsorbent material is modified by metal cation eutectic, alkali carbonate machinery and mechanical doping of the metal cation eutectic and the alkali carbonate. Adsorbent materialThe material can obtain high-purity Li in lower calcining temperature and shorter calcining time₄SiO₄And can broaden CO₂Effective adsorption temperature interval.

Description

Method for preparing lithium orthosilicate material by taking KIT-6 as silicon source, modification and application thereof

Technical Field

The invention belongs to the technical field of air pollution control, and particularly relates to a method for preparing a lithium orthosilicate material by taking KIT-6 as a silicon source, and modification and application thereof.

Background

In the eighties of the last century till now, carbon dioxide (CO)₂) Methane (CH)₄) Nitrous oxide (N)₂O), sulfur hexafluoride (SF)₆) Global climate problems caused by the annual increase in the emission of greenhouse gases (GHGs) have attracted worldwide researchers' attention, and 99% of greenhouse gases are derived from CO₂And (5) discharging.

At present, can be applied to CO in coal-fired power plants₂The recovery method mainly comprises the technologies of pre-combustion capture, post-combustion capture and oxygen-enriched combustion, and the post-combustion carbon capture technology is the most mature CO used at present₂The recovery process, common capture separation methods include liquid amine solvent absorption technology, cryogenic distillation technology, membrane separation technology, solid adsorbent adsorption technology and the like. In 2002, Kato et al first proposed Li₄SiO₄For CO at high temperatures₂And (4) adsorbing. Li₄SiO₄Has the problems of compact structure, large particle size, easy sintering and the like, and seriously influences the CO₂Adsorption and cyclic regeneration properties, so researchers have utilized different synthesis methods and precursors to prepare Li₄SiO₄To improve the adsorption effect. The synthesis method mainly comprises a high-temperature solid phase method, a dipping precipitation method, a sol-gel method, a combustion method and the like; the lithium source precursor mainly comprises LiOH and LiNO₃、Li₂CO₃Lithium acetate, lithium lactate and the like, and the precursor of the silicon source mainly comprises SiO₂Tetraethyl silicate, silica sol, zeolite molecular sieve, cheap silicon source and the like. At present, makeSynthesis of Li by using industrial by-product, solid waste or cheap silicon source instead of traditional silicon-lithium precursor₄SiO₄Materials have attracted extensive attention, allowing waste resources to be reused while saving costs.

The high-temperature solid phase method is simple and convenient to operate and low in cost, but has the problems of high calcination temperature, long calcination time, poor adsorption performance of a synthetic material and the like due to nonuniform mixing of precursors. The dipping precipitation method and the sol-gel method can fully and uniformly mix reactants and are suitable for flow treatment, and the synthesized material has stronger adsorption performance, but the latter is easy to generate sintering phenomenon and impurity phase compared with the former. Emerging Li₄SiO₄The synthesis method can improve the performance of the adsorbent, but has complex operation and higher cost, and is difficult to be applied in large scale in practice. For Li₄SiO₄The modification method of the material mainly comprises the steps of optimizing microstructure, metal ion doping substitution, alkali metal carbonate doping and the like.

Lithium orthosilicate (Li)₄SiO₄) The high-temperature CO is regarded as a high-temperature CO with great development prospect due to the advantages of high theoretical adsorption quantity, lower regeneration temperature and the like₂A solid adsorbent. But CO in the flue gas of the plant₂Lower concentration (< 20 vol%) of Li under these conditions₄SiO₄The adsorption rate is low and the adsorption performance is poor. Therefore, increase Li₄SiO₄At low CO₂The adsorption performance under a concentration atmosphere is a major research point.

Disclosure of Invention

The embodiment of the invention aims to provide a method for preparing Li by taking KIT-6 as a silicon source₄SiO₄The method for preparing the material, the modification and the application thereof, and the problems that the precursor has larger grain diameter and is not uniformly mixed, so that the calcination temperature is high, the calcination time is long, the adsorption performance of the synthetic material is poor, and the sintering phenomenon and the impurity phase occur in the prior art, and the prior Li₄SiO₄CO in plant flue gas₂Low adsorption rate and poor adsorption performance when the concentration is low, complex operation, high cost and difficult large-scale application in practice.

The technical scheme adopted by the invention is thatPreparation of Li by using KIT-6 as silicon source₄SiO₄The preparation method of the material comprises the following steps:

step a: synthesizing a KIT-6 mesoporous silica precursor by using a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer as a template agent and tetraethoxysilane as a silicon source;

step b: mixing Li₂CO₃B, mixing the silicon precursor prepared in the step a and the silicon precursor in absolute ethyl alcohol according to a certain molar ratio, and heating;

step c: b, stirring the solution obtained in the step b for a period of time to uniformly mix the solution;

step d: calcining the product in the step c at a certain temperature for a period of time to obtain Li₄SiO₄An adsorbent material.

Further, the step a specifically comprises: dissolving 4g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) in 144mL of ultrapure water, adding 6.7mL of HCl (35% by mass), stirring in a water bath at 35 ℃ at 350r/min for 4h until the P123 is completely dissolved, slowly dropwise adding 4.94mL of n-butanol at a constant speed, and continuously stirring for 1 h; increasing the temperature to 40 ℃, adding 9.24mL tetraethyl silicate at a constant speed under the stirring of 450r/min, and stirring for 24 hours; transferring the liquid and the precipitate in the three-neck flask into a high-pressure reaction kettle together, and performing hydrothermal crystallization at 100 ℃ for 24 hours; after the reaction kettle is naturally cooled to room temperature, taking the liquid and the solid matter in the kettle, and centrifuging for 10min at 12000 r/min; carrying out vacuum filtration on the precipitate until no foam exists, and drying the white viscous solid obtained by filtration at 100 ℃ for 24 hours; and calcining the dried white solid product in a resistance furnace at 550 ℃ for 6 hours to obtain the ordered mesoporous silica KIT-6 with the three-dimensional cage-shaped intercommunicated pore structure.

Li in step b₂CO₃The molar ratio of the precursor to the silicon precursor is Li to Si (4.1-4.3): 1, and the heating condition is 100 ℃ for heating in an oil bath.

Li in step b₂CO₃The molar ratio of Li to Si precursor was 4.2: 1.

And c, condensing and refluxing for 2h under magnetic stirring to fully and uniformly mix the two precursor powders.

And d, removing the condensing device in the step d, continuously stirring the mixed solution until the ethanol is completely volatilized to obtain a white powder mixture, and calcining the white powder mixture at the temperature of 750-900 ℃ for 2-6 h.

Furthermore, in the step d, the calcining temperature is 800 ℃, and the calcining time is 2 hours.

Step d, with the increase of the calcination time, synthesized KIT-6-Li₄SiO₄The surface of the adsorbent is rougher, and the bulges are denser.

The other technical scheme adopted by the invention is that metal cation eutectic crystal doping modified Li₄SiO₄The preparation method of the adsorbent comprises the following steps:

the method comprises the following steps: synthesizing a KIT-6 mesoporous silica precursor by using a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer as a template agent and tetraethoxysilane as a silicon source;

step two: mixing Li₂CO₃、CaCO₃/Na₂CO₃And the silicon precursor prepared in the step a according to the mol ratio of Li₂CO₃:KIT-6:CaCO₃＝(2.1～2)x:1:2x、Li₂CO₃:KIT-6:Na₂CO₃Mixing (2.1-2) x:1:2x in absolute ethyl alcohol, and heating in an oil pan at 100 ℃;

step three: condensing and refluxing the solution obtained in the step two for 2 hours under magnetic stirring to fully and uniformly mix the solution;

step four: calcining the product obtained in the third step at 750-900 ℃ for 2-6 h to obtain the eutectic doping modified adsorbent material.

Further, in the first step, the value range of x is 0.01-0.10;

in the first step, when CaCO₃For KIT-6-Li₄SiO₄When the metal cation eutectic is doped, new Li appears in the material when x is more than or equal to 0.03₂CaSiO₄The phase being present in Li₄SiO₄A surface; when Na is present₂CO₃For KIT-6-Li₄SiO₄When the metal cation eutectic doping is carried out, when x is more than or equal to 0.06, Li begins to appear in the material₃NaSiO₄The phase being present in Li₄SiO₄A surface;

in the first step, the pore size distribution of the material is gradually reduced along with the gradual increase of the metal doping amount;

doped with Ca²⁺Occurrence of Li₂CaSiO₄Concentration point of phase and doping with Na⁺Occurrence of Li₃NaSiO₄Concentration point of phase comparison, x_(Na)Is x_(Ca)Is 2 times higher than that of Na, indicating that the valence state of the metal is doped with Li₄SiO₄The limiting solubility in (1) has an influence.

The effective adsorption temperature is increased from 500 ℃ to 600 ℃, and the metal cation eutectic is doped with modified Li₄SiO₄The adsorption rates of the adsorbents in the initial 10min are similar, the adsorption rate is gradually increased along with the temperature rise in the initial stage and the final adsorption amount is also gradually increased along with the extension of the adsorption time, which shows that in the temperature range, the higher the temperature is, the more obvious the improvement effect on the surface adsorption and ion diffusion of the modified material is.

The other technical scheme adopted by the invention is that alkali carbonate is mechanically doped and modified Li₄SiO₄The preparation method of the adsorbent comprises the following steps:

the method comprises the following steps: the raw materials are mixed according to the mol ratio of KIT-6-Li₄SiO₄:Na₂CO₃＝1:x、KIT-6-Li₄SiO₄:K₂CO₃Mixing the powder 1: x in absolute ethyl alcohol, and heating in an oil pot at 100 ℃;

step two: condensing and refluxing for 2 hours under magnetic stirring to ensure that the raw materials are fully and uniformly mixed;

step three: the condensing device is removed, and the mixed solution is continuously stirred until the ethanol is completely volatilized.

Furthermore, in the step I, the value range of x is 5-20 wt%;

further, in step (i), Na₂CO₃The doping amount is x-5 wt%;

the other technical scheme adopted by the invention is that a metal cation eutectic crystal and alkali metal carbonate mechanical doping method are used for modifying Li₄SiO₄AdsorptionThe preparation method of the preparation comprises the following specific steps:

step 1), carrying out first-step modification by a metal cation eutectic doping modification preparation method, wherein the metal cation is Na⁺The eutectic doping amount x is 0.06;

step 2) the product obtained in step 1) is further modified by mechanical doping modification with an alkali metal carbonate, wherein the alkali metal carbonate is Na₂CO₃And the mechanical doping amount x is 5 wt%.

The invention also provides the Li₄SiO₄Adsorbent material and modified Li₄SiO₄Use of an adsorbent material, said Li₄SiO₄Adsorbent material and modified Li₄SiO₄The adsorbent material is used as an adsorbent for coal-fired power plants and carbon dioxide.

Li of the present application₄SiO₄Adsorbent material and modified Li₄SiO₄The adsorbent material improves the adsorption rate and the adsorption capacity, widens the effective adsorption temperature range, reduces the calcination temperature, shortens the calcination time and reduces the production energy consumption of the adsorbent.

The invention has the beneficial effects that: the preparation method comprises the steps of synthesizing KIT-6 mesoporous silica by taking polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) as a template agent and tetraethoxysilane as a silicon source, and synthesizing KIT-6-Li by adopting an immersion precipitation method₄SiO₄A high temperature adsorbent. Compared with gas phase SiO₂By using KIT-6 as a precursor, high-purity Li can be obtained in a lower calcining temperature and a shorter calcining time₄SiO₄And can broaden CO₂Effective adsorption temperature interval. The suitable calcining temperature range is 800-900 ℃, the suitable calcining time is 2-6 h, and the effective adsorption temperature range is 350-650 ℃. Wherein KIT-6-Li with the temperature of 800 ℃ for 2h, 4h and 6h is calcined₄SiO₄And gas phase SiO calcined for 6h at 900 DEG C₂-Li₄SiO₄The adsorbents all obtain the optimal adsorption quantity at 600 ℃.

Preparation of Ca by dipping precipitation method²⁺、Na⁺Eutectic doping modified KIT-6-Li₄SiO₄An adsorbent. Ca²⁺By addition of Li₄SiO₄The crystal morphology reduces the grain size; doped Na⁺Participating in Li₄SiO₄Formation process, replacement of Li⁺Occupied in the crystal lattice. Li₄SiO₄The specific surface area and pore volume of the material is not its CO₂The main influencing factor of the adsorption performance. Ca²⁺When the doping amount was 0.03, the maximum adsorption amount (29.17 wt%), Na was obtained⁺The maximum adsorption amount (35.35 wt%) was obtained when the doping amount was 0.06, and the optimum adsorption temperature was 600 ℃. After 10 times of adsorption/desorption cycles, the KL-Ca0.03 adsorption quantity is reduced by 38.8 percent, and the KL-Na0.06 adsorption quantity is shown to be firstly increased and then reduced.

Preparation of Na by impregnation method₂CO₃、K₂CO₃Mechanically doped modified KIT-6-Li₄SiO₄An adsorbent. The modified material is at Na at 600 DEG C₂CO₃Maximum adsorption capacity (32.59 wt%), K, was obtained when the doping amount x was 5 wt%₂CO₃The maximum adsorption amount (31.78 wt%) was obtained when the doping amount was 10 wt%. The surface porosity of the modified material can be increased in the cyclic absorption/desorption process by doping the alkali metal carbonate, and the cyclic regeneration performance is improved.

Na⁺、Na₂CO₃Co-doped modified KIT-6-Li₄SiO₄-Na0.06-Na₂CO₃(5 wt%) the adsorption capacity at 600 ℃ was 36.50 wt%, reaching 99.4% of the theoretical adsorption capacity. The co-doping improves the ion diffusion rate of the single doping modified adsorbent at higher temperature and greatly improves the adsorption capacity. The two doping methods generate synergistic effect, and the adsorption rate, adsorption capacity, effective adsorption temperature range and cycling stability of the material are improved. Double exponential model for Li₄SiO₄Adsorption of CO₂Has higher fitting degree, and higher temperature is beneficial to CO of the material₂Surface adsorption behavior, and Li⁺、O^2-The ion diffusion process is Li₄SiO₄Adsorption of CO₂And limiting the performance.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is KIT-6 and KIT-6-Li₄SiO₄Small angle XRD pattern spectrum of;

FIG. 2 is KIT-6-Li₄SiO₄(A) And gas phase SiO₂-Li₄SiO₄(B) Wide angle XRD pattern spectrum of (1);

FIG. 3 is an SEM image of KL-800-2(A), KL-800-4(B), KL-800-6(C) and SL-900-6 (D);

FIG. 4 is Li₄SiO₄N of adsorbent₂Adsorption/desorption isotherm (a) and BJH pore size distribution (B);

FIG. 5 is CO of an adsorbent during continuous temperature ramp₂Adsorption/desorption curves;

FIG. 6 is CO at different temperatures for KL-800-2(A), KL-800-4(B), KL-800-6(C) and SL-900-6(D)₂Adsorption curve diagram;

FIG. 7 is CO of KL-800-2(A), KL-800-4(B), KL-800-6(C) and SL-900-6(D) during 5 cycles₂Adsorption/desorption curve diagram;

FIG. 8 shows that KL-800-2(A), KL-800-4(B), KL-800-6(C) and SL-900-6(D) adsorb CO at different temperatures₂Fitting a curve graph by using a double-index model;

FIG. 9 is a wide angle XRD pattern of KL-Ca (A) and KL-Na (B);

FIG. 10 is an SEM image of KL-Ca0.01(A) (C), KL-Ca0.10(B) (D), KL-Na0.01(E) and KL-Na0.10 (F);

FIG. 11 is N of KL-Cax and KL-Nax adsorbents₂Adsorption/desorption isotherms (a) (C) and BJH pore size distributions (B) (D);

FIG. 12 is KIT-6-Li₄SiO₄-Cax (A) and KIT-6-Li₄SiO₄-Nax (B) CO at 600 ℃₂Adsorption curve diagram;

FIG. 13 is CO of KL-Ca0.03(A) and KL-Na0.06(B) at different temperatures₂Adsorption curve diagram;

FIG. 14 is CO of KL-Ca0.03(A) and KL-Na0.06(B) during 10 cycles₂Adsorption/desorption curve diagram;

FIG. 15 shows that KL-Cax (A), KL-Nax (B) adsorbs CO at 600 deg.C₂And KL-Ca0.03(C), KL-Na0.06(D) adsorbing CO at different temperatures₂Fitting a curve graph by using a double-index model;

FIG. 16 is KL-Na₂CO₃(x) (A) and KL-K₂CO₃(x) (B) CO at 600 ℃₂Adsorption curve diagram;

FIG. 17 is KL-Na₂CO₃(5) (A) and KL-K₂CO₃(10) (B) CO at different temperatures₂Adsorption curve diagram;

FIG. 18 is KL-Na₂CO₃(5) (A) and KL-K₂CO₃(10) (B) CO during 10 cycles₂Adsorption/desorption curve diagram;

FIG. 19 is KL-Na₂CO₃(x)(A)，KL-K₂CO₃(x) (B) adsorption of CO at 600 ℃₂And KL-Na₂CO₃(5)(C)，KL-K₂CO₃(10) (D) adsorption of CO at different temperatures₂Fitting a curve graph by using a double-index model;

FIG. 20 is KIT-6-Li₄SiO₄-Na0.06-Na₂CO₃(5 wt%) CO at different temperatures₂Adsorption curve diagram;

FIG. 21 is KIT-6-Li₄SiO₄-Na0.06-Na₂CO₃(5 wt%) (A) CO during 10 cycles₂Comparing the absorption/desorption curve with the 10-cycle adsorption capacity of the three modified materials (B);

FIG. 22 is KL-Na0.06-Na₂CO₃(5) Adsorption of CO at different temperatures₂Fitting the graph in a two-exponential model.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Preparation of Li by using KIT-6 as silicon source₄SiO₄The method for preparing the material, modification and application thereof specifically comprise the following steps:

EXAMPLE 1 preparation of KIT-6 mesoporous molecular sieves

Dissolving 4g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) in 144mL of ultrapure water, adding 6.7mL of HCl (35 mass percent), stirring in a water bath at 35 ℃ at 350r/min for 4h until the P123 is completely dissolved, slowly dropwise adding 4.94mL of n-butanol at a constant speed, and continuously stirring for 1 h. The temperature is increased to 40 ℃, 9.24mL tetraethyl silicate is added at a constant speed and stirred for 24 hours under the stirring of 450 r/min. And transferring the liquid and the precipitate in the three-neck flask into a high-pressure reaction kettle together, and performing hydrothermal crystallization at 100 ℃ for 24 hours. And after the reaction kettle is naturally cooled to room temperature, taking the liquid and the solid matter in the kettle, and centrifuging for 10min at 12000 r/min. The precipitate was filtered off under vacuum until no foam was present and the white viscous solid obtained by filtration was dried at 100 ℃ for 24 h. And calcining the dried white solid product in a resistance furnace at 550 ℃ for 6 hours to obtain the ordered mesoporous silica KIT-6 with the three-dimensional cage-shaped intercommunicated pore structure.

Example 2Li₄SiO₄Preparation of the adsorbent

First Li₂CO₃With KIT-6 and gas phase SiO respectively₂The precursor of silicon is mixed in anhydrous ethanol according to the mol ratio of Li to Si (4.1-4.3) to 1, and a small amount of sublimation occurs under the high-temperature calcination condition, so that a slight excess of Li is used to counteract sublimation of Li during high-temperature calcination. If the selection of the right Li, Si 4:1, may result in insufficient Li during calcination, excess Si, and excess Li when the amount of added Li is too large, both of which may affect the adsorbent purity. Li and Si can react completely when Li: Si ═ 4.2: 1. Then heating in an oil bath kettle at 100 ℃, wherein the ethanol can be well volatilized completely at the temperature; and condensing and refluxing under magnetic stirringAnd 2h, ensuring that the two precursor powders are fully and uniformly mixed. And then the condensing device is removed, and the mixed solution is continuously stirred until the ethanol is completely volatilized, so that the influence of the mixed solution on the subsequent heating temperature is avoided. Calcining the obtained white powder mixture in a resistance furnace according to the required conditions to obtain Li₄SiO₄Adsorbent material (temperature 750 ℃, 800 ℃, 900 ℃, time length: 2h, 4h, 6 h). The specific sample numbers of the obtained products and the preparation conditions thereof are shown in table 1.

TABLE 1 sample information for adsorbents

Sample numbering	Raw materials	Calcination temperature	Calcination time
				KL-750-6	KIT-6、Li₂CO₃	750℃	6h
KL-800-2	KIT-6、Li₂CO₃	800℃	2h
				KL-800-4	KIT-6、Li₂CO₃	800℃	4h
KL-800-6	KIT-6、Li₂CO₃	800℃	6h
				SL-800-6	Gas phase SiO₂、Li₂CO₃	800℃	6h
SL-900-4	Gas phase SiO₂、Li₂CO₃	900℃	4h
				SL-900-6	Gas phase SiO₂、Li₂CO₃	900℃	6h

Example 3 eutectic doping of Metal cations with modified Li₄SiO₄Preparation of the adsorbent

The dopant was selected to be a metal cation carbonate to prevent other anions from affecting the results of the experiment. In molar ratio of Li₂CO₃:KIT-6:CaCO₃＝(2.1～2)x:1:2x、Li₂CO₃:KIT-6:Na₂CO₃The precursor and the dopant are mixed in absolute ethyl alcohol according to the proportion of (2.1-2) x:1:2x, if the proportion is less than the proportion, the modification effect is not obvious or is lower than the detection limit of an instrument, and if the proportion is more than the proportion, the impurity phase is too much, so that the Li is influenced₄SiO₄Amount of adsorbent synthesized. Heating in oil pan at 100 deg.C. Condensing reflux under magnetic stirringAnd 2h, ensuring that the raw materials are fully and uniformly mixed. And (3) removing the condensing device, continuously stirring the mixed solution until the ethanol is completely volatilized, and calcining the obtained white powder mixture in a resistance furnace at 800 ℃ for 4 hours to obtain the eutectic doping modified adsorbent material. The specific sample numbers and the doping amounts of the obtained products are shown in table 2.

TABLE 2 sample information for eutectic doping modified sorbents

Sample numbering	Raw materials	Calcination conditions	Amount of doping
				KL-Ca0.01	KIT-6、Li₂CO₃、CaCO ₃	800℃、4h	x＝0.01
KL-Ca0.03	KIT-6、Li₂CO₃、CaCO ₃	800℃、4h	x＝0.03
				KL-Ca0.06	KIT-6、Li₂CO₃、CaCO ₃	800℃、4h	x＝0.06
KL-Ca0.10	KIT-6、Li₂CO₃、CaCO ₃	800℃、4h	x＝0.10
				KL-Na0.01	KIT-6、Li₂CO₃、Na₂CO₃	800℃、4h	x＝0.01
KL-Na0.03	KIT-6、Li₂CO₃、Na₂CO₃	800℃、4h	x＝0.03
				KL-Na0.06	KIT-6、Li₂CO₃、Na₂CO₃	800℃、4h	x＝0.06
KL-Na0.10	KIT-6、Li₂CO₃、Na₂CO₃	800℃、4h	x＝0.10

Example 4 mechanical doping of alkali metal carbonates with modified Li₄SiO₄Preparation of the adsorbent

According to the mass ratio of KIT-6-Li₄SiO₄:Na₂CO₃＝1:x、KIT-6-Li₄SiO₄:K₂CO₃X the raw materials were mixed in absolute ethanol and heated in an oil kettle at 100 ℃. Condensing and refluxing for 2h under magnetic stirring to ensure that the raw materials are fully and uniformly mixed. And (4) removing the condensing device, and continuously stirring the mixed solution until the ethanol is completely volatilized to obtain the mechanically doped and modified adsorbent material. The specific sample numbers and the amounts of the impurities of the obtained products are shown in Table 3.

TABLE 3 sample information for mechanically doped modified sorbents

Sample numbering	Raw materials	Calcination conditions	Amount of doping
				KL-Na₂CO₃(5)	KIT-6-Li₄SiO₄、Na₂CO₃	800℃、4h	x＝5wt％
KL-Na₂CO₃(10)	KIT-6-Li₄SiO₄、Na₂CO₃	800℃、4h	x＝10wt％
				KL-Na₂CO₃(15)	KIT-6-Li₄SiO₄、Na₂CO₃	800℃、4h	x＝15wt％
KL-Na₂CO₃(20)	KIT-6-Li₄SiO₄、Na₂CO₃	800℃、4h	x＝20wt％
				KL-K₂CO₃(5)	KIT-6-Li₄SiO₄、K₂CO₃	800℃、4h	x＝5wt％
KL-K₂CO₃(10)	KIT-6-Li₄SiO₄、K₂CO₃	800℃、4h	x＝10wt％
				KL-K₂CO₃(15)	KIT-6-Li₄SiO₄、K₂CO₃	800℃、4h	x＝15wt％
KL-K₂CO₃(20)	KIT-6-Li₄SiO₄、K₂CO₃	800℃、4h	x＝20wt％

Example 5 phase composition analysis of adsorbents

Taking the products prepared in example 1 and example 2, conducting phase composition analysis of the adsorbent using an X' PertPRO powder diffraction analyzer (PANalytica, Holland) under the measurement conditions of a Cu-ka radiation source, a 40kV tube voltage, a 40mA tube current, a scanning step of 0.03 °, small and wide ranges of 2 θ of 0.6 to 5 °, 10 to 80 °, respectively, and calculating the grain size using the Scherrer formula, which specifically is:

wherein D is the crystal grain size, nm; k is the Xiele constant; λ is the X-ray wavelength, nm; beta is the full width at half maximum, rad, of the diffraction peak in the XRD map; θ is the bragg angle (degrees).

Shown in FIG. 1 as KIT-6 and KIT-6-Li₄SiO₄The small-angle XRD pattern of (1) shows that KIT-6 has a sharper diffraction peak at the 2 theta-0.9 degrees, and a shoulder peak at the 2 theta-1.05 degrees, which respectively correspond to the crystal faces of the three-dimensional cubic system (211) and (220) of space group Ia3 d; a series of weak diffraction peaks corresponding to crystal faces (321), (400), (420) and (332) appear in 2 theta-1.3-1.8 degrees, and prove that the KIT-6 mesoporous silica molecular sieve with a three-dimensional cubic structure is successfully prepared. KIT-6-Li in FIG. 1₄SiO₄The diffraction peak corresponding to KIT-6 does not exist any more, which shows that the ordered mesoporous structure of KIT-6 is destroyed after the sample is synthesized, which is consistent with the result that the collapse and the destruction of KIT-6 pore channels are caused by high-temperature calcination.

Synthesis of Li by high-temperature calcination₄SiO₄The principle of (1) is as follows: under the condition of high temperature, the Li source precursor wraps the surface of the Si source precursor, and the Li source precursor and the Si source precursor are contacted and gradually react to generate Li₄SiO₄(ii) a KIT-6 has the microscopic characteristics of rich internal pore channels, thin pore wall, high specific surface area and the like, can greatly increase the contact area with a Li source, and accelerates the complete reaction.

FIG. 2 shows KIT-6-Li₄SiO₄And gas phase SiO₂-Li₄SiO₄The wide-angle XRD pattern of the compound is determined according to a PDF2 database card of the International diffraction data center. As shown in FIG. 2(A), KIT-6-Li₄SiO₄Calcination of the adsorbent at 750 ℃ for 6h will have Li present₂SiO₃(PDF:70-0330) impurity phase, but when the calcination temperature is increased to 800 ℃, the high-purity Li can be obtained within 2 hours of shorter calcination time₄SiO₄(PDF:37-1472), its unit cell parameters

And β ═ 90.25 ° corresponds to a dense monoclinic crystal structure. As can be seen from FIG. 2(B), SiO is present in the gas phase₂Calcining the adsorbent synthesized by the silicon source at 900 ℃ for 6 hours to obtain high-purity Li₄SiO₄. Thus, compared to gas phase SiO₂The KIT-6 is taken as a silicon source, and high-purity Li can be obtained in a lower calcining temperature and a shorter calcining time₄SiO₄。

Li in XRD pattern₄SiO₄At the 22.4 DEG characteristic diffraction peak, the result of calculating the grain size by using the Scherrer formula is D_(KL-750-6)＝58.5nm、D_(KL-800-2)＝59.8nm、D_(KL-800-4)＝51.4nm、D_(KL-800-6)＝51.0nm；D_(SL-800-6)＝47.7nm、D_(SL-900-4)＝47.4nm、D_(SL-900-6)45.8 nm. It can be seen that as the calcination temperature is increased and the calcination time is prolonged, the crystal grain size is reduced to some extent; gas phase SiO₂-Li₄SiO₄The grain size is generally lower than KIT-6-Li₄SiO₄Due to the silicon source precursor gas phase SiO₂The particle size is smaller than KIT-6 particles.

Example 6 preparation of Li Using KIT-6 as silicon Source₄SiO₄Adsorbent pair CO₂Adsorption Property

KIT-6-Li prepared in example 2 was taken₄SiO₄-800-2、KIT-6-Li₄SiO₄-800-4、KIT-6-Li₄SiO₄800-6 and gas phase SiO₂-Li₄SiO₄900-6, surface microtopography of the adsorbent using a field emission scanning electron microscope (SU5000, HITACHI), the adsorbent being dried in an oven at 80 ℃ for 12h before testing. During testing, the conductive adhesive is firmly adhered to the sample base, and a small amount of adsorbent is uniformly dispersed on the surface of the conductive adhesive. And spraying gold for 30s after blowing off the non-adhered adsorbent powder, and observing the surface micro-morphology of the adsorbent under the accelerating voltage of 5 kV. KIT-6-Li₄SiO₄-800-2、KIT-6-Li₄SiO₄-800-4、KIT-6-Li₄SiO₄800-6 and gas phase SiO₂-Li₄SiO₄The scanning electron micrograph of-900-6 magnified 8000 times is shown in FIG. 3, and all adsorbents have no holes, indicating Li₄SiO₄The adsorbent is in a non-porous particulate state. Li prepared from two silicon source precursors₄SiO₄The adsorbent surface exhibits different morphologies, as shown in FIGS. 3(A), (B) and (C), the KIT-6-precursor material surface has many hilly protrusions accompanied by tearing-type pores, which are beneficial to increase CO₂The contact area with the surface of the adsorbent provides more reactive sites, and the surface morphology is favorable for enhancing Li₄SiO₄CO of the material₂Adsorption performance; in contrast, SiO in the gas phase₂The material synthesized for the precursor is shown in fig. 3(D)) has a relatively flat surface and relatively few protrusions and pores. Furthermore, KIT-6-Li was synthesized as the calcination time was extended from 2h to 6h₄SiO₄The surface of the adsorbent is rougher, and the bulges are denser.

Low temperature N of adsorbent₂The adsorption/desorption curve was determined at-196 ℃ using an ASAP2460 specific surface and porosity analyzer (Micromeritics). All adsorbents were degassed under vacuum at 300 ℃ for 6h before the experiment. The specific surface area value of the material is calculated by a BET method (Brunauer-Emmett-Teller), the pore size distribution is calculated by a BJH method (Barrett-Joyner-Halenda), and the pore volume is calculated at a relative pressure P/P₀Calculated at 0.99, the results are shown in fig. 4, and it can be seen from fig. 4(a) that KIT-6-Li₄SiO₄And gas phase SiO₂-Li₄SiO₄Low temperature N of adsorbent₂Adsorption/desorption isothermsThe line is a type II isotherm corresponding to a non-porous material; at a relative pressure P/P₀In the range of more than 0.4, the isotherm presents an H3-type hysteresis loop obtained by a crack hole; these four adsorbents KIT-6-Li₄SiO₄-800-2、KIT-6-Li₄SiO₄-800-4、KIT-6-Li₄SiO₄800-6 and gas phase SiO₂-Li₄SiO₄The BET specific surface area and pore volume of-900-6 are shown in Table 4, which also indicates that no channels are present in the material. In conclusion, it can be shown that KIT-6-Li is prepared₄SiO₄And gas phase SiO₂-Li₄SiO₄The adsorbent is a non-porous granular material with partial tearing type pores on the surface, and KIT-6-Li along with the extension of the calcination time₄SiO₄The increasing values of the specific surface area of the adsorbent indicate a gradual increase of the wrinkles and pores of the material surface, which is consistent with the results observed by SEM tests. Gas phase SiO₂-Li₄SiO₄The adsorbent exhibits the largest specific surface area, which is associated with the smallest grain size obtained at high calcination temperatures of the material. Fig. 4(B) shows BJH pore size distribution of the adsorbent, which is a channel formed by stacking of non-porous particles. The pore diameters of the four materials are mostly distributed at 15nm, the average pore diameter is between 6.5 and 8.5nm, and the materials belong to the mesoporous range. The pore size distribution of the material shows a decreasing trend with the increasing calcining temperature and time, and the particle size of the four adsorbents is gradually reduced according to the calculation result of the Scherrer formula, so that the diameter of the channel formed by the particle stacking is also gradually reduced.

TABLE 4 physical Properties of the adsorbents

Adsorbent and process for producing the same	Specific surface area (m)²/g)	Pore volume (cm)³/g)	Average pore diameter (nm)
				KIT-6-Li₄SiO₄-800-2	1.1551	0.008570	8.3934
KIT-6-Li₄SiO₄-800-4	1.2085	0.006830	7.2682
				KIT-6-Li₄SiO₄-800-6	1.5234	0.007644	6.5135
Gas phase SiO₂-Li₄SiO₄-900-6	1.5956	0.009168	7.5909

Study of Li Using TGA method₄SiO₄To CO₂Adsorption performance of (1), import CO₂The concentration was 15 vol%, and the gas flow rate was 100 mL/min.

The effective adsorption and desorption temperature interval of the adsorbent is determined as follows: the dynamic adsorption curve is obtained by testing a Beijing Hengjiu HCT-1 type microcomputer differential thermal balance under normal pressure. The adsorbent was pre-dried at 80 ℃ for 12h, the instrument was started and preheated for 40min before testing, and the parameters of the dynamic adsorption experiment were set as shown in table 5. Placing about 6mg of adsorbent in a quartz crucible, adsorbingBefore the process is started, the adsorbent is firstly N₂Heating to 110 deg.C at programmed temperature (10 deg.C/min) in atmosphere (100mL/min) for 50min, introducing CO₂(N₂) Mixed gas (CO)₂ Volume fraction 15 vol%), heated from 110 ℃ temperature program (10 ℃/min) to 850 ℃. The adsorbent is subjected to the change of adsorption weight gain and desorption weight loss in the process, and the inflection point of the curve change is the temperature boundary point of adsorption-desorption reaction, so that the effective adsorption and desorption temperature interval of the material is determined.

TABLE 5 TGA dynamic adsorption Performance procedure parameters

Fig. 5 shows the mass change of four adsorbents during continuous temperature rise. In the range of 320-650 ℃, the mass of the adsorbent is gradually increased along with the temperature rise; the mass of the adsorbent gradually decreases after the temperature exceeds 650 ℃, and a desorption process occurs. This is because of the temperature vs. Li₄SiO₄The influence of the adsorption performance of the material is double-sided, from the viewpoint of chemical reaction kinetics, high temperature can promote molecular thermal motion, improve the molecular collision probability and accelerate the reaction rate, and from the viewpoint of chemical balance, Li₄SiO₄Adsorption of CO₂The process belongs to exothermic reaction, and the high temperature is favorable for desorption reaction. Thus, with increasing temperature, FIG. 5 shows increasing and decreasing CO₂Adsorption profile. The inflection points of the curves of the four adsorbents appear at about 650 ℃, and the desorption temperature in the circulation process is determined to be 700 ℃. Compared with the high desorption temperature (900 ℃) of CaO adsorption, Li₄SiO₄The material can reduce the desorption temperature of about 200 ℃ and greatly reduce energy consumption.

As can be seen from FIG. 5, SiO is in the gas phase₂The adsorbent prepared for the precursor starts to undergo CO after 400 deg.C₂Adsorption of KIT-6-Li₄SiO₄Begin to adsorb CO at 320-350 ℃₂It can be seen that the adsorbent prepared by using KIT-6 as a precursor can broaden CO₂Effective temperature zone of adsorptionIn the middle, CO can be carried out at a lower temperature₂Adsorption process, which is associated with different surface morphologies of the two adsorbents. KIT-6-Li₄SiO₄The maximum adsorption capacity of-800-2 at the inflection point is significantly lower than the other three materials because of KIT-6-Li₄SiO₄Calcination time of-800-2 is short, Li₄SiO₄The incomplete formation of the crystal lattice, and the large particle size and relatively low specific surface area influence its CO₂And (4) adsorption performance. The adsorption rates of the four adsorbents showed a steep increase after about 500 deg.C, which indicates that higher than 500 deg.C favors Li₄SiO₄The adsorption process is carried out, so four temperature points of 500 ℃, 550 ℃, 600 ℃ and 650 ℃ are determined as the temperature conditions for constant-temperature adsorption of the material.

The adsorbent was pre-dried at 80 ℃ for 12h and the instrument was started to preheat for 40min before testing. The parameters set for the adsorption experiments are shown in table 6, taking an adsorption temperature of 600 ℃ as an example. Weighing about 6mg of adsorbent in a quartz crucible, wherein the adsorbent is in N state before the adsorption process formally begins₂Heating to 110 deg.C at programmed temperature (10 deg.C/min) in atmosphere (100mL/min), maintaining for 50min to remove surface adsorbed water and impurity gas, and continuing to add N₂Heating to 600 deg.C at programmed temperature (10 deg.C/min) in atmosphere (100mL/min), introducing CO₂/N₂Mixed gas (wherein CO)₂15 vol%), the material was adsorbed at 600 ℃ for 180 min. Calculating CO according to the mass change values of the material before and after adsorption₂The amount of adsorption. The calculation formula is as follows:

wherein q is_eIs adsorbent mass m_eCO of (1)₂Adsorption capacity, wt%; m is_eMg is the mass of the adsorbent at a certain moment in the adsorption process; m is_dTo adsorbThe mass of the pre-adsorbent (after removing surface adsorbed water and impurity gases at a constant temperature of 110 ℃), mg; 44.01 is CO₂Molar mass of (a), g/mol.

TABLE 6 TGA constant temperature sorption Performance Programming parameters

FIG. 6 is CO at different temperatures for four adsorbents₂Adsorption profile. It can be seen that the adsorption curves of KL-800-2 and SL-900-6 are increased and then decreased at 650 ℃, which indicates that the two materials are desorbed after adsorption and can not perform long-time stable adsorption behavior at higher temperature, while the other two materials can achieve stable adsorption balance due to the short calcination time of KL-800-2 and the gas phase SiO of SL-900-6₂The high temperature adsorption stability caused for the precursor is poor. Below 600 c, the adsorption capacity of all four materials increased with increasing temperature, indicating that the reaction kinetics dominate at ≦ 600 c. In the initial stage of adsorption, the four adsorbents show the fastest adsorption rate at 550 ℃, and the maximum adsorption capacity appears at 600 ℃, which indicates that 550 ℃ is more suitable for Li₄SiO₄Surface CO of adsorbent₂Adsorption behavior, Li as the reaction proceeds₂CO₃And Li₂SiO₃The double-shell structure gradually appears, and the higher temperature is 600 ℃ to Li⁺、O^2-The ion diffusion process has a positive effect and thus exhibits the maximum adsorption capacity for CO of the four materials₂The order of the adsorption capacity: KL-800-6(15.18 wt%)>KL-800-4(14.73wt％)>SL-900-6(14.28wt％)>KL-800-2(10.03 wt%). In addition, the furnace body of the TGA analyzer used in the experiment is in a vertical state, gas enters from bottom to top, and 100 vol% N is in a high-temperature state₂Atmosphere was switched to 15 vol% CO₂A slight lag in the mixing of the gases occurs. From the viewpoints of rising of hot air and falling of cold air, the higher the temperature in the furnace, the longer the time for the normal temperature gas to reach the temperature required for the experiment, and the initial CO to the material₂The adsorption efficiency being produced in small partInfluence. As can be seen from FIGS. 6(A), (B), (C), KIT-6-Li is observed as the calcination time of the material is prolonged₄SiO₄The adsorption capacity at four different temperatures is gradually increased, and the time for approaching the adsorption equilibrium is shortened, which shows that the longer the calcination time is, the more complete the crystal lattice growth is, and the higher the specific surface area is, the more beneficial the KIT-6-Li is₄SiO₄The adsorption performance of (3).

The material is subjected to CO at the optimal adsorption temperature of 600 DEG C₂CO is turned off after 60min of adsorption₂Gas path, switched to N₂Gas path, rising to desorption temperature of 700 deg.C at a rate of 10 deg.C/min, maintaining for 30min, cooling to adsorption temperature of 600 deg.C, and switching to CO₂And (5) adsorbing by the gas circuit. After the second adsorption for 60min, switching to N₂Gas path, circulating for many times according to the above steps, CO₂Gas path and N₂The flow rate of the gas path is 100 mL/min.

FIG. 7 shows the results of 5 cycles of adsorption at 600 deg.C for 60min and desorption at 700 deg.C for 30 min. As the number of adsorption-desorption cycles increases, the adsorption capacity of all adsorbents tends to decrease because the material sinters and agglomerates at high temperatures, reducing the adsorbent surface and CO₂The contact area of (a). After 5 cycles, the percentage reduction sequence of the adsorption capacity of the four materials compared with that of the first adsorption is as follows: KL-800-2 (27.4%)>KL-800-6(24.4％)>KL-800-4(23.4％)>SL-900-6 (13.3%). Among these four adsorbents, KIT-6-Li₄SiO₄Worst cycle stability of-800-2, gas phase SiO₂-Li₄SiO₄900-6 shows excellent regeneration performance, that is, the high calcination temperature and time enable the adsorbent to maintain a complete crystal lattice structure after repeated high-temperature desorption at 700 ℃ but the gas phase SiO₂-Li₄SiO₄The overall adsorption capacity of-900-6 is low.

The cyclic regeneration performance of the four adsorbents is poor, and the cyclic regeneration performance needs to be further improved by a doping modification method. The KIT-6 is taken as a precursor, and the two adsorbents calcined for 4h and 6h are similar in the aspects of adsorption capacity, adsorption rate, regeneration performance and the like, so that the high adsorption performance and the low energy consumption are considered, and the two adsorbents are selectedSelect KIT-6-Li₄SiO₄Analysis of two doping modification methods on KIT-6-Li based on-800-4 material₄SiO₄Improvement of adsorption Performance 800-4.

Use of a double exponential model for modifying Li before and after modification₄SiO₄CO of the material₂Fitting the high temperature adsorption data to analyze the material versus CO₂Kinetics of reversible adsorption. The model equation is as follows:

y＝Aexp(-k₁t)+Bexp(-k₂t)+C (4)

wherein y is the adsorption capacity, wt%; t is adsorption time, min; k is a radical of₁And k₂Are each CO₂Rate constants of direct adsorption process and adsorption process affected by ion diffusion on material surface, min^-1(ii) a A. B is an index pre-factor, wt%; c is y-axis intercept, wt%.

Fig. 8 shows the adsorption reaction kinetic model fitting results of the four adsorbents, and the kinetic parameters of the model fitting results are shown in table 7. As can be seen from FIG. 8, the adsorption curves of all adsorbents at different temperatures can be well fitted by a double-index model except the adsorption curves of KL-800-2 and SL-900-6 at 650 ℃, and the obtained correlation coefficient R²Is more than 0.98; the obtained fitting coefficient k₁＞k₂Description of Li⁺、O^2-The ion diffusion is KIT-6-Li₄SiO₄And gas phase SiO₂-Li₄SiO₄Adsorption of CO by materials₂The limiting step of the process. The adsorption curve of the SL-900-6 modified material at 550 ℃ obtains the maximum k₁Value of initial CO of the most suitable material at this temperature₂The surface adsorption behavior, as can also be seen from fig. 8(D), is within 60min of adsorption, with the maximum adsorption capacity of the adsorption curve at 550 ℃; the curve after 60min is flat and gradually reaches saturation, so that the k of the ion diffusion process is₂The value is small. Maximum k₂The values and the maximum adsorption were obtained at the adsorption curve at 600 ℃ and the curve at this time showed the greatest upward trend after 180 min.

KIT-6-Li₄SiO₄K of adsorbent₁The value is gradually increased within the range of 500-600 ℃ and within the range of 600-650 DEG CDecrease, optimum k₁Value adsorption temperature of gas phase SiO₂-Li₄SiO₄50 ℃ higher, indicating higher temperature for KIT-6-Li₄SiO₄CO of the material₂The surface adsorption behavior has a positive influence. K of KL-800-2 material at 500 DEG C₂The maximum value, the material will reach saturation state the fastest; k at 550 ℃ and 600 DEG C₂The smaller value indicates that the material has not approached the adsorption equilibrium, which is the same as the result of the two curves 180min in fig. 8(a) showing a certain upward trend. Maximum k of KL-800-4₂The value and maximum adsorption occur at the 600 ℃ adsorption curve, which indicates that the ion diffusion rate of the adsorbent is the fastest at this time, and the adsorbent reaches adsorption equilibrium in a shorter time and has the highest saturated adsorption value. KL-800-6 k at 500 deg.C₂The maximum value is that the material reaches the saturation state most quickly, and as can be seen from fig. 8(C), the adsorption curve at this temperature is substantially balanced after 60min, but the saturated adsorption value is lower. KIT-6-Li with three different calcination temperatures₄SiO₄Maximum k of adsorbent₂The values occur at different adsorption temperatures because the lattice growth of KL-800-4 is better than that of the material calcined for 2h, but the adsorbent lattice calcined for 4h has a small number of defects compared to KL-800-6, which has a more complete lattice growth, and this helps to increase CO₂Area of contact with material and subsequent Li⁺、O^2-Diffusion of ions. Therefore, compared with other adsorption temperatures, KL-800-4 obtains the highest CO at 600 DEG C₂Surface adsorption rate, ion diffusion rate, and adsorption capacity.

TABLE 7 adsorption of CO by KL-800-2, KL-800-4, KL-800-6 and SL-900-6₂Kinetic parameters of

Sample name	Adsorption temperature	k₁(min^-1)	k₂(min^-1)	k₁/k₂	R²
						KL-800-2	500℃	2.7720×10^-2	2.6265×10^-2	1.06	0.9801
	550℃	3.5816×10^-2	6.2584×10^-3	5.72	0.9992
							600℃	3.7685×10^-2	6.8244×10^-3	5.52	0.9983
	650℃	3.7618×10^-2	2.6608×10^-2	1.41	0.8541
						KL-800-4	500℃	2.8836×10^-2	2.2382×10^-2	1.29	0.9951
	550℃	4.7556×10^-2	1.8247×10^-2	2.61	0.9992
							600℃	5.5696×10^-2	2.6187×10^-2	2.13	0.9987
	650℃	2.2705×10^-2	1.9513×10^-2	1.16	0.9992
						KL-800-6	500℃	2.6503×10^-2	1.8964×10^-2	1.40	0.9877
	550℃	3.3247×10^-2	1.6645×10^-2	2.00	0.9975
							600℃	3.2579×10^-2	1.7954×10^-2	1.81	0.9955
	650℃	2.5356×10^-2	1.6824×10^-2	1.51	0.9982
						SL-900-6	500℃	2.3873×10^-2	1.9272×10^-2	1.24	0.9987
	550℃	3.3640×10^-2	1.6715×10^-2	2.01	0.9950
							600℃	2.8507×10^-2	2.2331×10^-2	1.28	0.9942
	650℃	2.5805×10^-2	5.5317×10^-3	4.66	0.9117

Example 7 Metal cation Ca²⁺/Na⁺Eutectic doping modified KIT-6-Li₄SiO₄Adsorbent pair CO₂Adsorption Property

The Ca in example 3 is taken to dope KIT-6-Li₄SiO₄And Na-doped KIT-6-Li₄SiO₄The same adsorbent as in example 5 was analyzed by phase XRD analysis, and FIG. 9 shows that KIT-6-Li was doped with Ca₄SiO₄And Na is dopedHetero KIT-6-Li₄SiO₄The wide angle XRD pattern of (A) and the comparison result is determined by a card of a PDF2 database of the International centre for diffraction data. As can be seen from FIG. 9(A), under the conditions of the experimental method and the selected doping ratio, the Ca is adsorbed by the adsorbent²⁺Limiting solubility x ═ 0.01, i.e. Li_3.98Ca_0.02SiO₄When only Li is in the material₄SiO₄Phase exists, but XRD pattern shows unit cell parameters of

β＝90.33°，Ca²⁺To Li₄SiO₄The crystal morphology of (a) has a certain influence; when x is 0.03, new Li appears in the material₂CaSiO₄Phase (PDF: 72-1729); further increase of doping amount, Li₂SiO₃Phase also follows. In Li₄SiO₄At 22.4 ℃ diffraction peak, Li was calculated using the Scherrer formula₄SiO₄Grain size of D_(KL-Ca0.01)＝50.1nm、D_(KL-Ca0.03)＝49.8nm、D_(KL-Ca0.06)＝45.5nm、D_(KL-Ca0.10)33.9 nm. Compared with Li not doped with metal elements₄SiO₄The size of the adsorbent (51.4nm) is obviously reduced with the gradual increase of the adding amount of the dopant, and the produced Li₂CaSiO₄Well inhibit Li₄SiO₄Particle agglomeration, small amount of Li₂CaSiO₄Only in Li₄SiO₄A surface.

FIG. 9(B) is Na⁺Doping KIT-6-Li₄SiO₄When x is 0.01, only Li is detected in the material as well₄SiO₄Phases are present, but when x is increased to 0.03, Li is present in the material₂SiO₃Phase, indicating that there is a very small amount of Na⁺Disperse into the adsorbent and influence Li₄SiO₄Forming crystal grains; when x is more than or equal to 0.06, Li begins to appear in the material₃NaSiO₄Phase and unreacted Li₂CO₃Phase (PDF: 22-1141), is Na⁺Participating in Li₄SiO₄Formation Process, Na⁺Substitution of Li⁺Present in the crystal lattice, resulting in a small fraction of Li₂CO₃Does not participate in the reaction. In Li₄SiO₄At the 22.4-degree characteristic diffraction peak, the grain size calculated by using the Scherrer formula is D_(KL-Na0.01)＝51.6nm、D_(KL-Na0.03)＝51.0nm、D_(KL-Na0.06)＝53.8nm、D_(KL-Na0.10)52.4 nm. Compared with Li not doped with metal elements₄SiO₄The size of the adsorbent (51.4nm), the dosage of the dopant and the grain size have no obvious increase and decrease rule, but when x is more than or equal to 0.06, the grain size is slightly enlarged, which may be Na⁺Ionic radius greater than Li⁺Ionic radius, Na⁺Substitution of Li⁺Present in the crystal lattice, resulting in slightly larger grain sizes.

In addition, Ca is doped under the doping amount condition selected in the experiment²⁺Occurrence of Li₂CaSiO₄Concentration point of phase and doping with Na⁺Occurrence of Li₃NaSiO₄Concentration point of phase comparison, x_(Na)Is x_(Ca)Is 2 times higher than that of Na, indicating that the valence state of the metal is doped with Li₄SiO₄The limiting solubility in (1) has an influence.

Emission scanning electron microscope analysis was carried out in the same manner as in example 6, and FIG. 10 is a scanning electron microscope photograph at 200 times and 15000 times magnification of KL-Ca0.01, KL-Ca0.10, and KL-Na0.01 and KL-Na0.10, respectively, and 15000 times magnification. As can be seen from FIGS. 10(A) (B), Ca is accompanied²⁺Increased doping amount, Li₄SiO₄The particles become finely divided, a phenomenon which is related to Li calculated by Scherrer's formula₄SiO₄Grain size is from D_(KL-Ca0.01)50.1nm down to D_(KL-Ca0.10)Results were consistent at 33.9 nm. As shown in FIGS. 10(C) and (D), Ca²⁺Doped Li₄SiO₄The adsorbent becomes smooth and takes on a stacked state of flaky particles, and the addition of Ca changes Li₄SiO₄The crystal morphology is consistent with the results of the changes of unit cell parameters in XRD patterns. When the doping amount x is 0.01, a large number of pore channels formed by stacking particles appear, indicating that Ca prevents the agglomeration of crystal grainsThe phenomenon of sintering; when the doping amount is increased to x 0.10, the adsorbent surface is coated and stacked with a large number of small spherical particles which may not participate in the generation of Li₂CaSiO₄Is attached to the surface of the adsorbent.

FIG. 10(E) and (F) are each Na⁺The microstructure of the adsorbent with the doping amount x of 0.01 and x of 0.10 was magnified 15000 times. The surface of the material has a large number of bulges and folds and unmodified Li₄SiO₄Similarly, the XRD cell parameters are consistent, indicating Na⁺The addition of (2) has no influence on the crystal morphology of the material. When the doping amount is increased from x to 0.01 to x to 0.10, a small part of channels appear between crystal grains, which may be Na⁺Substituted Li⁺Certain influence is generated on crystal agglomeration; from Li₂CO₃Small particles of different sizes, composed of Na not participating in the reaction, are attached to the surface of the adsorbent.

The same procedure as in example 6 was used to lower the temperature N₂Adsorption/desorption analysis, FIG. 11 is (A) (C) N of KL-Cax and KL-Nax adsorbents₂Adsorption/desorption isotherms and (B) (D) BJH pore size distribution. As can be seen from FIGS. 11(A) and (C), the low temperature N of the adsorbent after doping with a metal element₂The adsorption/desorption isotherm is a type II isotherm corresponding to a non-porous material with unmodified Li₄SiO₄The same; at a relative pressure P/P₀In the range > 0.4, the isotherm exhibits a hysteresis loop of type H3, obtained by fissuring pores or by strip pores. The BET specific surface area, pore volume and average pore diameter of the eight modified materials are shown in Table 8.

TABLE 8 physical Properties of Metal modified sorbents

Adsorbent and process for producing the same	Specific surface area (m)²/g)	Pore volume (cm)³/g)	Average pore diameter (nm)
				KIT-6-Li₄SiO₄	1.2085	0.006830	7.2682
KIT-6-Li₄SiO₄-Ca0.01	0.7208	0.003582	8.4422
				KIT-6-Li₄SiO₄-Ca0.03	0.7299	0.004388	7.8009
KIT-6-Li₄SiO₄-Ca0.06	1.0567	0.006204	8.1731
				KIT-6-Li₄SiO₄-Ca0.10	1.1116	0.006977	9.7317
KIT-6-Li₄SiO₄-Na0.01	0.7098	0.003768	7.7764
				KIT-6-Li₄SiO₄-Na0.03	0.6810	0.003258	9.5771
KIT-6-Li₄SiO₄-Na0.06	0.6232	0.003970	12.8755
				KIT-6-Li₄SiO₄-Na0.10	0.3782	0.001386	15.2059

The specific surface area and pore volume of the modified material are lower than those of the unmodified sample, but in terms of CO₂The adsorption result shows that the adsorption capacity of the modified material is obviously improved, and the specific surface area and the pore volume are not Li₄SiO₄Adsorption of CO₂The main influencing factor of the performance. As can be seen from fig. 112(B) (D), as the doping amount of the metal is gradually increased, the pore size distribution of the material is gradually decreased, which may be caused by filling fine particles generated by doping into the pores of the raw adsorbent.

It was subjected to CO by the same test method as in example 6₂Adsorption Performance test, FIG. 12 is Ca-doped²⁺And Na⁺CO at optimum adsorption temperature of 600 ℃ for materials with different concentrations₂Adsorption profile. As can be seen from FIG. 12(A), Ca²⁺The addition of (A) significantly increases the CO of the material₂The adsorption performance shows that the adsorption capacity of the modified material tends to increase and then decrease with the increase of the doping amount of the doping agent, the maximum adsorption capacity is obtained when the doping amount x is 0.03, and the adsorption capacities of the four materials under the conditions are sequentially as follows: KL-Ca0.03(29.17 wt%)>KL-Ca0.06(26.51wt％)>KL-Ca0.10(23.67wt％)>KL-Ca0.01(21.63 wt%), the adsorption capacity of KL-Ca0.03 reaches unmodified Li₄SiO₄2 times of the total weight of the powder. Ca²⁺Doping modified material to CO²The reaction equation for adsorption is shown in formula (5). Doping with an appropriate amount of Ca²⁺The shape of crystal grains of the adsorbent is influenced, and the pore channel formed by stacking the flaky particles is wide and low in agglomeration property, so that CO is generated₂Contact with more material surface to increase CO₂Surface adsorption performance, therefore, in the initial reaction stage, KL-Ca0.03 shows the fastest adsorption rate; ca²⁺By addition of Li₄SiO₄Structural formation defects, favoring Li⁺、O^2-Diffusion in the double shell structure and thus exhibits the maximum adsorption capacity. But excessive Ca²⁺Added, will form more CaCO in the reaction process₃Possibly resulting in sintering of the material. Furthermore, the four curves of the modified material in fig. 12(a) show similar rising trends after 180min of adsorption, failing to reach adsorption equilibrium, indicating Ca, compared to fig. 12(B)²⁺Doped with p-Li⁺、O^2-Ion diffusion has a positive effect.

Li₄SiO₄(s)+Li₂CaSiO₃(s)+CO₂(g)→Li₂CO₃(s)+Li₂SiO₃(s)+CaCO₃(s) (5)

Li₄SiO₄(s)+Li₃NaSiO₃(s)+CO₂(g)→Li₂CO₃(s)+Li₂SiO₃(s)+Na₂CO₃(s) (6)

With doping of Ca²⁺Same as Na⁺The adsorption capacity of the doping material also shows a tendency of increasing and then decreasing with the increase of the addition amount. As shown in FIG. 12(B), Na²⁺In the presence of CO of the material₂The adsorption capacity is obviously improved, the maximum adsorption value is obtained when the doping amount x is 0.06, and the adsorption capacity sequences of four modified materials under the conditions are as follows: KL-Na0.06(35.35 wt%) > KL-Na0.03(30.00 wt%) > KL-Na0.01(28.57 wt%) > KL-Na0.10(28.48 wt%), the adsorption capacity of KL-Na0.06 reaches that of unmodified Li₄SiO₄2.4 times of the total amount of the adsorbent to reach the theoretical adsorption capacity96.3% of. Na (Na)²⁺Doping modified material to CO₂The reaction equation of adsorption is shown in formula (6). Na (Na)⁺When the doping amount x is 0.10, the modified adsorbent shows the highest adsorption rate at the initial stage, the adsorption equilibrium is reached in 90min, and the other three modified materials with smaller doping amounts show stably rising adsorption performance. This is because part of Na⁺In place of Li⁺Into the crystal lattice to form structural defects, Na⁺The more CO is supplied₂The more surface adsorption active sites, the greater the initial adsorption rate; but excessive Na⁺Addition of Li resulting in efficient adsorption⁺Less, subsequent Li⁺The adsorption amount in the diffusion stage becomes small. In addition, the adsorbent with the added amount x being 0.01 and 0.03 obtains similar adsorption capacity, when the amount x is increased to 0.06, the adsorption capacity is obviously improved, and simultaneously, the first occurrence of Li in XRD test is realized₃NaSiO₄Doping amount of phase, Na gradually formed during adsorption₂CO₃Will react with Li₂CO₃The shell forms a low-temperature eutectic body, and reduces Li⁺、O^2-Diffusion resistance.

According to FIG. 12, Ca²⁺Doping amount x is 0.03 and Na⁺The modified material with the doping amount x being 0.06 shows the best adsorption performance at 600 ℃. Therefore, the adsorption performance of the two materials at different temperatures was selectively studied, and the results are shown in fig. 13. As can be seen from FIG. 13(A), the fastest CO for the KL-Ca0.03 material₂The surface adsorption rate and maximum adsorption capacity occur at 600 ℃. The adsorption curve at 500 ℃ is relatively flat, with CO increasing with temperature₂The adsorption curve gradually shows an upward trend, which indicates that the low temperature is not suitable for Ca²⁺Surface adsorption of modified materials and Li⁺、O^2-Diffusion of (2). The material showed the lowest adsorption rate and adsorption capacity at 650 ℃, and even desorption occurred later, which may be Ca²⁺The crystal lattice structure of the adsorbent is destroyed, so that the long-term adsorption stability of the modified material under the high-temperature condition is deteriorated. In contrast, the adsorption performance of KL-Na0.06 at different temperatures is generally better than that of KL-Ca0.03, as shown in FIG. 13 (B). During the process of rising the temperature of 500 ℃ to 600 ℃, the adsorption rate of the adsorbent in the initial 10min is similarThe initial adsorption rate is gradually increased along with the temperature rise along with the extension of the adsorption time, and the final adsorption amount is also gradually increased, which shows that in the temperature range, the higher the temperature is, the more obvious the improvement effect on the surface adsorption and ion diffusion of the modified material is; after the temperature is raised to 650 ℃, KL-Na0.06 shows a higher adsorption rate at the initial stage, and the adsorption equilibrium is reached within about 60min, but the adsorption capacity is relatively lower. Therefore, CO of KL-Na0.06 modified material is treated at high temperature₂The surface chemisorption process has a positive influence and Li is not yet reached⁺、O^2-The diffusion phase of (a) tends to equilibrium adsorption. In combination, the metal cation Ca²⁺、Na⁺The optimum adsorption temperature of the eutectic doped modified adsorbent was still 600 ℃.

FIG. 14 shows the results of 10 cycles of adsorption at 600 deg.C for 60min and desorption at 700 deg.C for 30min of KL-Ca0.03 and KL-Na0.06. It can be seen from FIG. 14(A) that the cyclic adsorption capacity of the KL-Ca0.03 modified material gradually decreased due to the formation of CaCO during the adsorption process₃Produces a sintering phenomenon of CaCO₃It needs to be at 900 ℃ to generate CO₂The desorption behavior is far higher than the desorption temperature of 700 ℃ selected in the experiment. The adsorption amount of the KL-Ca0.03 after 10 times of adsorption/desorption cycles is reduced by 38.8 percent compared with that of the first adsorption. FIG. 14(B) shows that the adsorption capacity of KL-Na0.06 shows a tendency to increase and then decrease with the increase of the number of cycles because Na is present during the adsorption/desorption cycles₂CO₃The presence of (b) causes the adsorption surface to become increasingly porous. KL-Na0.06 obtains the maximum adsorption capacity in the 5 th cycle of adsorption, and the adsorption amount is 121.0 percent of that in the first adsorption; the adsorption capacity in the 10 th cycle was 104.5% of the first adsorption. The later half of the adsorption curve is flatter with the cycle number, the material reaches adsorption equilibrium more quickly, which shows that Na₂CO₃The adsorption rate of the adsorbent can be increased during the cycle.

FIG. 15 shows that KL-Cax and KL-Nax adsorb CO at 600 deg.C₂And KL-Ca0.03 and KL-Na0.06 adsorb CO at different temperatures₂The corresponding kinetic parameters are shown in table 9. Removing KL-Ca0.03 and 650 ℃ kojiOutside the line, all the adsorption curves can be well fitted by a double-index model, and the obtained correlation coefficient R²Is more than 0.98; the obtained fitting coefficient k₁＞k₂Description of Li⁺、O^2-The ion diffusion is that the metal cation doping modified material adsorbs CO₂The limiting step of the process. Ca²⁺K of doped modified adsorbent₁、k₂Become larger, indicate Ca²⁺For Li₄SiO₄Adsorption of CO₂Both processes of (a) have a positive effect. K of KL-Ca0.03 adsorption Curve₁Maximum value, i.e. initial CO₂The surface adsorption rate is highest; k of KL-Ca0.06 adsorption Curve₂The value is maximum; i.e. the ion diffusion process is faster and the adsorption equilibrium is easier to achieve in the shortest time. CO is carried out when KL-Ca0.03 is at different temperatures₂Adsorption curve k corresponding to 600 ℃ during adsorption₁Maximum value, indicating initial CO at this time₂The surface adsorption rate is high, and as can be seen from fig. 15(C), the adsorption capacity at 600 ℃ is 2-3 times higher than that at other temperatures in the first 30min of the adsorption process; adsorption curve k corresponding to 650 DEG C₂At the maximum, the adsorbent under these conditions reaches adsorption equilibrium more quickly.

TABLE 9 KL-Cax and KL-Nax adsorption of CO₂Kinetic parameters of

Sample name	Adsorption temperature	k₁(min^-1)	k₂(min^-1)	k₁/k₂	R²
						KIT-6-Li₄SiO₄	600℃	5.5696×10^-2	2.6187×10^-2	2.13	0.9987
KL-Ca0.01	600℃	4.5575×10^-1	6.2278×10^-2	7.32	0.9992
						KL-Ca0.03	500℃	3.3114×10^-2	5.3518×10^-3	6.19	0.9996
	550℃	4.3045×10^-2	5.3219×10^-3	8.09	0.9998
							600℃	4.6496×10^-1	4.6778×10^-2	9.94	0.9990
	650℃	1.0076×10^-1	5.6401×10^-2	1.79	0.9271
						KL-Ca0.06	600℃	3.8454×10^-1	8.5338×10^-2	4.51	0.9994
KL-Ca0.10	600℃	3.6405×10^-1	6.2118×10^-2	5.86	0.9993
						KL-Na0.01	600℃	6.2423×10^-2	5.9988×10^-3	10.41	0.9991
KL-Na0.03	600℃	8.5456×10^-2	6.8403×10^-3	12.49	0.9991
						KL-Na0.06	500℃	7.4897×10^-2	1.1207×10^-2	6.68	0.9989
	550℃	1.2426×10^-1	1.3818×10^-2	8.99	0.9985
							600℃	1.1828×10^-1	1.0418×10^-2	11.35	0.9985
	650℃	5.8631×10^-2	2.2299×10^-5	2629.33	0.9898
						KL-Na0.10	600℃	1.5914×10^-1	2.3920×10^-2	6.65	0.9966

Na²⁺K of doped adsorbent₁The value becomes large and k of the adsorbent is modified₁、k₂The value increases with increasing doping amount, indicating that Na²⁺Doping pairs initial CO₂The surface adsorption process and the ion diffusion process both have positive effects, and the higher the doping amount is, the faster the adsorption equilibrium is reached. It can also be seen from fig. 15(B) that the adsorption amount of KL-na0.10 is the greatest in 60min, the adsorption late stage is nearly saturated, the adsorption amounts of the other three materials with smaller doping amounts still show an increasing trend in the adsorption late stage, and the KL-na0.06 obtains the greatest adsorption amount after 180 min. KL-Na0.06 CO at different temperatures₂Adsorption experiment, k of adsorption curve at 550 ℃ and 600 DEG C₁Values of similar, and k at 500 ℃ and 650 DEG C₁Of lesser value, i.e. initial CO₂The surface adsorption rate is low. K of 650 ℃ adsorption Curve₁Is k ₂10 of³Description of the materials in CO₂The surface adsorption stage basically tends to be saturated; k of the 600 ℃ adsorption curve compared to other temperatures₂The values are smaller, reaching adsorption equilibrium the slowest, so the 600 ℃ adsorption curve in fig. 15(D) shows the greatest upward trend at 180 min.

EXAMPLE 8 alkali metal carbonate Na₂CO₃/K₂CO₃Mechanically doped and modified KIT-6-Li₄SiO₄Adsorbent pair CO₂Adsorption Property

Taking the alkali metal of example 4Carbonate Na₂CO₃/K₂CO₃Mechanically doped modified KIT-6-Li₄SiO₄800-4, CO carrying out the same test conditions as in example 6₂And (5) testing the adsorption performance. FIG. 16 shows KL-Na₂CO₃(x) (A) and KL-K₂CO₃(x) (B) CO at 600 ℃₂The adsorption curve, as can be seen from FIG. 16, is Na compared to the unmodified adsorbent₂CO₃And K₂CO₃The adsorption rate of the doping modified material in the initial stage is gradually increased with the increase of the doping amount, because Na₂CO₃And K₂CO₃Doping into Li₄SiO₄The different particle size between molecules disturbs Li₄SiO₄In an ordered arrangement of CO₂The beneficial condition is provided by entering molecular gaps, and the CO is improved₂Adsorption rate of the surface adsorption process. However, the adsorption capacity of the modifier is not necessarily as high as possible when the amount of the dopant is large, and Na is used as shown in FIG. 16(A)₂CO₃The adsorbent obtains the maximum adsorption capacity when the doping amount is x-5 wt%, and the maximum adsorption capacity reaches 2.2 times of the adsorption capacity of the unmodified material, and the adsorption capacity of the modified material is as follows: KL-Na₂CO₃(5)(32.59wt％)>KL-Na₂CO₃(10)(30.03wt％)>KL-Na₂CO₃(15)(27.42wt％)>KL-Na₂CO₃(20) (25.50 wt%). The adsorption capacity tends to decrease as the doping amount is gradually increased, since the proper amount of doping is advantageous for the formation of Li₂CO₃-Na₂CO₃Low temperature eutectic of (2), promoting Li⁺、O^2-Migrating; but excessive Na₂CO₃May coat Li₄SiO₄Ambient, affecting the adsorbent and CO₂And (4) contacting. K shown in FIG. 16(B)₂CO₃The doping amount is 10 wt% to obtain the maximum adsorption capacity which is 2.1 times of the adsorption capacity of the unmodified material, and the adsorption capacities are as follows: KL-K₂CO₃(10)(31.78wt％)>KL-K₂CO₃(15)(28.51wt％)>KL-K₂CO₃(20)(25.83wt％)>KL-K₂CO₃(5)(21.74wt％)。

As can be seen from FIG. 16, KIT-6-Li₄SiO₄-Na₂CO₃-5 wt% and KIT-6-Li₄SiO₄-K₂CO₃-10 wt% of the two modified sorbents to obtain optimum CO at 600 ℃₂The two materials are selected to further examine the CO at different temperatures₂The adsorption performance and the results are shown in FIG. 17. As can be seen from FIG. 17(A), KL-Na₂CO₃(5) Initial stage of CO (2)₂Surface adsorption process and late stage Li⁺、O^2-The diffusion process of the ions shows the most excellent performance at 600 ℃. Within the temperature range of 500-600 ℃, the surface adsorption and ion diffusion quantity are gradually increased along with the temperature rise, and are reduced after the temperature is higher than 600 ℃, which indicates that Na₂CO₃The doping has high requirements on temperature. KL-K₂CO₃(10) The adsorption behavior at different temperatures exhibited different trends, as shown in FIG. 17(B), the modified material exhibited the highest initial CO at 550 ℃₂Surface adsorption rate, but maximum adsorption capacity was obtained at 600 ℃ indicating temperature vs KL-K₂CO₃(10) The influence of the two adsorption processes is different, while Li promoted at higher temperatures⁺、O^2-Diffusion is the controlling step of the overall adsorption process. Furthermore, KL-K₂CO₃(10) The modified material shows relatively excellent adsorption performance at 650 ℃, compared with Na₂CO₃Modification by doping, K₂CO₃CO of modified material₂The adsorption capacity is less affected by the temperature.

FIG. 18 is KIT-6-Li₄SiO₄-Na₂CO₃-5 wt% and KIT-6-Li₄SiO₄-K₂CO₃The test results of 10 times of circulation of 10 times of adsorption of 10 wt% of two modified adsorbents at 600 ℃ for 60min and desorption at 700 ℃ for 30 min. With the increase of the adsorption/desorption cycle times, the adsorption capacities of the two modified materials show a trend of increasing firstly and then decreasing, because the alkali metal carbonate doped modified material can react with Li in the adsorption process₂CO₃Low-temperature eutectic is formed on the surface of the material, and pores on the surface of the material are expanded after desorption, so that the purpose of activating the adsorbent is achievedAnd the adsorption capacity in the subsequent circulation process is improved.

As seen in FIG. 18(A), KL-Na₂CO₃(5) The modified material obtained the maximum adsorption capacity (32.19 wt%) on the 7 th cycle adsorption, which is 143.4% of the initial cycle adsorption, in comparison with KL-Na₂CO₃(5) The adsorption capacities after 180min of adsorption at 600 ℃ are basically the same; the 10 th cycle adsorption capacity was 127.1% of the initial adsorption capacity. As shown in FIG. 18(B), KL-K₂CO₃(10) The modified material obtained the maximum adsorption capacity (31.91 wt%) in the 3 rd cycle adsorption, which is 122.1% of the initial cycle adsorption capacity, compared with KL-K₂CO₃(10) The adsorption capacity after 180min of adsorption at 600 ℃ is 0.13 wt% higher; the 10 th cycle adsorption capacity was 94.3% of the initial adsorption capacity. This indicates that Na₂CO₃And K₂CO₃Not only is the doping beneficial to increasing Li₄SiO₄The adsorption capacity of the material can also greatly improve the cyclic regeneration performance. Na (Na)₂CO₃Modified KIT-6-Li₄SiO₄Is superior to K in adsorption capacity and cyclic regeneration performance₂CO₃Modified KIT-6-Li₄SiO₄And Na₂CO₃The optimum doping amount of the catalyst is lower, and the catalyst is more suitable for being used in an actual factory.

FIG. 19 shows KL-Na₂CO₃(x)、KL-K₂CO₃(x) Adsorption of CO at 600 ℃₂And KL-Na₂CO₃(5)、KL-K₂CO₃(10) Adsorption of CO at different temperatures₂The corresponding kinetic parameters are shown in table 10. All adsorption curves can be well fitted by a double-index model, and the obtained correlation coefficient R²Is more than 0.98; fitting coefficient k₁＞k₂，Li⁺、O^2-The ion diffusion is still the CO adsorption of the alkali metal carbonate doped modified material₂The limiting step of the process.

TABLE 10 KL-Na₂CO₃(x) And KL-K₂CO₃(x) Adsorption of CO₂Kinetic parameters of

Sample name	Adsorption temperature	k₁(min^-1)	k₂(min^-1)	k₁/k₂	R²
						KIT-6-Li₄SiO₄	600℃	5.5696×10^-2	2.6187×10^-2	2.13	0.9987
KL-Na₂CO₃(5)	500℃	7.6175×10^-2	5.9320×10^-3	12.84	0.9995
							550℃	1.0984×10^-1	9.9064×10^-3	11.09	0.9997
	600℃	1.1361×10^-1	1.0789×10^-2	10.53	0.9974
							650℃	4.9411×10^-2	1.4381×10^-6	34357.12	0.9884
KL-Na₂CO₃(10)	600℃	1.4684×10^-1	7.1971×10^-3	20.40	0.9993
						KL-Na₂CO₃(15)	600℃	1.6583×10^-1	9.1293×10^-3	18.16	0.9997
KL-Na₂CO₃(20)	600℃	1.3207×10^-1	8.3215×10^-3	15.87	0.9993
						KL-K₂CO₃(5)	600℃	7.7804×10^-2	1.1217×10^-2	6.94	0.9965
KL-K₂CO₃(10)	500℃	1.2386×10^-1	1.3078×10^-2	9.47	0.9994
							550℃	1.3593×10^-1	1.0633×10^-2	12.78	0.9995
	600℃	1.0541×10^-1	1.0780×10^-2	9.78	0.9976
							650℃	6.9683×10^-2	1.6789×10^-2	4.15	0.9997
KL-K₂CO₃(15)	600℃	1.0586×10^-1	7.8934×10^-3	13.41	0.9991
						KL-K₂CO₃(20)	600℃	1.4003×10^-1	1.8595×10^-2	7.53	0.9986

Na₂CO₃、K₂CO₃Doping to k of the adsorbent₁Increase, indicating that doping increases initial CO₂Surface adsorption rate, which is related to the destruction of Li₄SiO₄Ordered arrangement of molecules to increase CO₂The contact area is relevant. With Na₂CO₃The doping amount is increased, KL-Na₂CO₃(15) K of (a)₁Maximum value, and KL-Na₂CO₃(5) K of (a)₂Maximum value and k₁/k₂Minimum value, indicating Na₂CO₃When the doping amount is higher, the surface adsorption rate is favorably improved, and the ion diffusion process is more favorably realized by small amount of doping; when KL-Na₂CO₃(5) CO at different temperatures₂At the time of adsorption, k₁And k₂The maximum values are all shown in the adsorption curve at 600 ℃ when KL-Na is present₂CO₃(5) Also exhibits the maximum adsorption capacity. Furthermore, KL-Na₂CO₃(5) K at 650 ℃ adsorption₁Ratio k₂Large 10⁴Description of the materials in the CO₂The surface adsorption process tends to saturate resulting in a very low rate of ion diffusion. When K is₂CO₃K of adsorption curve of modified material when doping amount is x-20 wt%₁、k₂Maximum value, but KL-K₂CO₃(10) Maximum adsorption of (2) indicates a high K₂CO₃The doping amount is beneficial to CO₂The surface adsorption process and the ion diffusion process are carried out, but the saturated adsorption value of the material is influenced, which may be excessive K₂CO₃Coated with Li₄SiO₄Surface, of part of Li₄SiO₄Not involved in the reaction.

Example 9 two doping methods synergistically modifying KIT-6-Li₄SiO₄Adsorbent pair CO₂Adsorption performance of

Metallic cation Na⁺Eutectic doping amount x is 0.06, alkali metal carbonate Na₂CO₃Mechanical doping amount x is 5 wt%, for KIT-6-Li₄SiO₄Co-doping modification was carried out and the CO of the bifunctional material was investigated using the same experimental conditions as in example 6₂And (4) adsorption performance. FIG. 20 shows the modified adsorbent KIT-6-Li co-doped with metal cation and alkali metal carbonate₄SiO₄-Na0.06-Na₂CO₃(5 wt%) CO at different temperatures₂The adsorption curves, as can be seen by comparing FIG. 13(B) and FIG. 17(A), for CO-doped modified materials at various temperatures, are the initial CO₂The surface adsorption rate and the adsorption capacity are both obviously improved. 500E ^ eCO of two adsorption processes within 600 deg.C₂The adsorption capacity increases with increasing temperature; at 600 ℃, the adsorbent exhibited rapid CO for the first 15min₂Surface adsorption behavior followed by an inflection point in adsorption rate due to Li₂CO₃And Li₂SiO₃Formation of a double-shell structure with material incorporated into Li⁺、O^2-In the ion diffusion adsorption process, the adsorbent entering the process still shows a high adsorption rate, and the adsorption capacity (36.50 wt%) after reaction for 180min reaches 99.4% of the theoretical adsorption capacity (36.72 wt%). The adsorption capacity of the codoped modified adsorbent reaches 32.18 wt% at 650 ℃, and is respectively Na⁺Eutectic doping, Na₂CO₃The mechanical doping adsorption capacity is 1.79 and 2.27 times that of the material, so that the high-temperature CO of the material is improved₂And (4) adsorption performance. KIT-6-Li synergistically modified by two doping methods₄SiO₄The adsorption rate, the adsorption capacity and the effective adsorption temperature range are improved.

FIG. 21 is KIT-6-Li₄SiO₄-Na0.06-Na₂CO₃(5 wt%) 60min at 600 deg.C, 30min at 700 deg.C, 10 times of cycle test results, and 10 times of cycle adsorption quantity comparison of single doping modification and co-doping modification three materials. In cycle 1, co-doping of modified KL-Na0.06-Na₂CO₃(5 wt%) the material showed the highest adsorption capacity; the maximum adsorption capacity obtained in cycle 2 was slightly higher than that of KL-Na0.06, cycle 5, KL-Na₂CO₃(5 wt%) maximum adsorption capacity obtained in 7 th cycle, and the co-doped material shows the most stable adsorption performance with the increase of cycle number, the adsorption capacity of 5 times of recycling after KL-Na0.06 obtains the maximum adsorption capacity is reduced by 13.7% compared with the maximum value, and KL-Na₂CO₃(5 wt%) the adsorption capacity, which was recycled 3 times after obtaining the maximum adsorption capacity, was reduced by 11.4% from the maximum, KIT-6-Li₄SiO₄-Na0.06-Na₂CO₃(5 wt%) the adsorption capacity, which was recycled 8 times after the maximum adsorption capacity was obtained, was reduced by 11.3% from the maximum. In conclusion, the two methods synergistically modify KIT-6-Li₄SiO₄At adsorption rate, adsorptionThe capacity, the effective adsorption temperature interval, the cycle stability and other aspects are obviously improved.

FIG. 22 shows KL-Na0.06-Na₂CO₃(5) CO capture at different adsorption temperatures₂The corresponding kinetic parameters are shown in table 11. It can be seen that the adsorption curves can be well fitted by a double-index model, and the obtained correlation coefficient R²Is more than 0.99; fitting coefficient k₁＞k₂，Li⁺、O^2-The ion diffusion is that the modified material CO-doped with metal cation and alkali carbonate adsorbs CO₂The step of limiting. At 650 deg.C, KL-Na0.06, KL-Na₂CO₃(5) And KL-Na0.06-Na₂CO₃(5) Fitting coefficient k of adsorption curve₁Close in value, k₁/k₂Values of 2629.33, 34357.12 and 1415.30, respectively, bifunctional material k₁/k₂The value of (A) is obviously reduced, which shows that co-doping generates a synergistic effect, improves the ion diffusion rate of the single doping modified material at a higher temperature, and greatly improves the adsorption capacity. At 600 ℃ the fitting coefficient k₁Medium, and k₂This is low because the material does not reach adsorption equilibrium under the current conditions, as can also be seen in FIG. 23, the CO of the material at 500 deg.C, 550 deg.C, 650 deg.C is gradually increased with the adsorption time₂The adsorption curve gradually becomes gentle and even reaches a saturated state, and the adsorption curve at 600 ℃ still shows an ascending trend after 180min, which shows that KL-Na0.06-Na₂CO₃(5) The adsorption behavior of the catalyst is easily influenced by temperature, and the catalyst is suitable for CO at 600 ℃ for a long time₂And (4) adsorbing.

TABLE 11 KL-Na0.06-Na₂CO₃(5) Adsorption of CO at different temperatures₂Kinetic parameters of

All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims

1. The method for preparing the lithium orthosilicate material by taking KIT-6 as a silicon source is characterized by comprising the following preparation steps:

2. The method for preparing lithium orthosilicate material by taking KIT-6 as silicon source according to claim 1, wherein Li in the step b₂CO₃The molar ratio of the precursor to the silicon precursor is Li to Si (4.1-4.3): 1, and the heating condition is 100 ℃ for heating in an oil bath pot;

the step c is specifically that the mixture is condensed and refluxed for 2 hours under magnetic stirring, so that the two precursor powders are fully and uniformly mixed;

3. The method for preparing lithium orthosilicate material by using KIT-6 as silicon source according to claim 2, wherein the calcination temperature in step d is 800 ℃ and the calcination time is 2 h.

4. A preparation method of a metal cation eutectic doping modified lithium orthosilicate adsorbent is characterized by comprising the following preparation steps:

5. The preparation method of the metal cation eutectic doping modified lithium orthosilicate adsorbent according to claim 4, wherein in the second step, the value range of x is 0.01-0.10;

when CaCO is present₃For KIT-6-Li₄SiO₄When the metal cation eutectic is doped, new Li appears in the material when x is more than or equal to 0.03₂CaSiO₄The phase being present in Li₄SiO₄A surface; when Na is present₂CO₃For KIT-6-Li₄SiO₄When the metal cation eutectic doping is carried out, when x is more than or equal to 0.06, Li begins to appear in the material₃NaSiO₄The phase being present in Li₄SiO₄A surface.

6. A preparation method of an alkali metal carbonate mechanical doping modified lithium orthosilicate adsorbent is characterized by comprising the following preparation steps:

7. The preparation method of the alkali metal carbonate mechanical doping modified lithium orthosilicate adsorbent according to claim 6, wherein the value of x is in the range of 5 wt% to 20 wt%.

8. The preparation method of the alkali metal carbonate mechanical doping modified lithium orthosilicate adsorbent according to claim 7, characterized in that Na₂CO₃The doping amount is x-5 wt%.

9. A preparation method of a lithium orthosilicate adsorbent modified by a metal cation eutectic and alkali metal carbonate mechanical doping method is characterized by comprising the following specific steps:

10. The use of the adsorbents according to claims 1 to 9, wherein the lithium orthosilicate adsorbent material and the modified lithium orthosilicate adsorbent material are used as adsorbents for carbon dioxide in coal-fired power plants.