A waste coffee grounds derived carbon modified lithium orthosilicate carbon capture material and a method of making the same

Abstract

This invention utilizes waste coffee grounds to successfully prepare a high-performance carbon capture material through a combination of cold pressing and high-temperature co-sintering processes. Its core lies in a "triple synergistic enhancement" mechanism: biomass burn-off forms a hierarchical macroporous network, reducing mass transfer resistance; potassium in the ash is used for in-situ doping, promoting ion diffusion; and carbothermic reduction generates oxygen vacancies, enhancing CO2 adsorption capacity. This material exhibits high adsorption capacity, excellent cycling stability, and good mechanical strength at high temperatures, providing a green technological path for low-cost, industrial-scale production of carbon capture materials.

Description

Technical Field

[0001] This invention belongs to the field of energy chemical engineering and environmental functional materials technology, and specifically relates to a process for preparing carbon dioxide capture materials by using waste biomass for pore engineering and chemical modification. Specifically, it is a method for preparing high-strength, high-adsorption-capacity lithium orthosilicate (Li4SiO4) porous ceramic particle adsorbents by using waste coffee grounds (SCG) as a multi-effect modifier. Background Technology

[0002] With the large-scale consumption of fossil fuels, the continuous rise in atmospheric CO2 concentration has exacerbated the global greenhouse effect. Among many solid adsorbents, lithium orthosilicate (Li4SiO4) is considered an ideal candidate material for post-combustion carbon capture (such as coupling with industrial waste heat systems) due to its high theoretical CO2 adsorption capacity (36.7wt%), excellent thermal stability, and suitable high-temperature desorption characteristics.

[0003] However, pushing Li4SiO4 to industrial fluidized bed applications faces severe engineering constraints. Fine powders are highly susceptible to blown loss in fluidized beds, requiring them to be pressed and sintered at high temperatures into particles with sufficient mechanical strength. However, high-temperature densification inevitably leads to pore collapse and a sharp reduction in specific surface area, greatly increasing the mass transfer resistance of CO2 diffusion and causing a precipitous drop in adsorption capacity and kinetics.

[0004] Existing modification techniques typically employ sacrificial pore-forming agents (such as polyvinyl alcohol and microcrystalline cellulose) to improve porosity, or add alkali metal carbonates to reduce solid-phase diffusion resistance. However, these methods are not only costly but also often have limited functionality, failing to simultaneously improve both physical pore formation and intrinsic chemical properties. How to decouple the contradiction between particle mechanical strength and adsorption performance in a low-cost and multi-functional manner without introducing complex chemical raw materials is a pressing technical challenge. Summary of the Invention

[0005] Based on the above analysis, the purpose of this invention is to overcome the shortcomings of existing Li4SiO4 particle adsorbents, such as performance degradation after densification and high cost and complicated steps of traditional modification methods, and to provide a method for preparing high-performance porous lithium orthosilicate particle adsorbents using bulk food waste—waste coffee grounds (SCG).

[0006] To achieve the above-mentioned technical effects, the present invention employs the following technical means:

[0007] This invention first discloses a method for preparing a carbon-modified lithium orthosilicate carbon capture material derived from waste coffee grounds, comprising the following steps:

[0008] (1) Synthesis of lithium orthosilicate precursor powder

[0009] Starting with lithium salt and silicon source, a liquid-phase mixing reaction was carried out in an alcohol-water mixed solvent system. After gelation, drying, grinding and low-temperature pre-calcination, lithium orthosilicate (Li4SiO4) precursor powder with high reactivity was prepared.

[0010] (2) Pretreatment and green molding of waste coffee grounds

[0011] The collected waste coffee grounds were washed, dried and sieved. Then the pretreated waste coffee grounds, the lithium orthosilicate precursor powder prepared in step (1) and the alkali metal carbonate dopant were mixed evenly according to the set mass ratio, and an appropriate amount of deionized water was added to make a uniform paste. The paste was then placed in a mold and pressed into green pellets by uniaxial pressing.

[0012] (3) High-temperature co-sintering induced synergistic effect

[0013] The green particles obtained in step (2) are subjected to sintering and annealing at high temperature. During this process, the macromolecular carbon skeleton of the waste coffee grounds undergoes thermal decomposition and burn-off, and an interconnected hierarchical macroporous network is constructed in situ in the ceramic matrix. At the same time, the mineral-rich ash of the waste coffee grounds releases potassium (K) in situ, which is doped into the crystal lattice and forms a low-melting-point eutectic molten carbonate phase together with the externally introduced alkali metal. Finally, a modified porous lithium orthosilicate adsorbent with high mechanical strength, excellent kinetics and high CO2 adsorption capacity is obtained.

[0014] Further, in step (1), the lithium salt is lithium hydroxide monohydrate (LiOH·H2O), and the silicon source is tetraethyl orthosilicate (TEOS); the molar ratio of Li to Si during the mixed reaction is set to 4.1:1 to compensate for the loss of lithium volatilization during the high-temperature sintering process; the drying process is carried out at 100℃~120℃ for 12~24 hours, and the temperature of the low-temperature pre-calcination treatment is 200℃~250℃ for 12~24 hours, forming an intermediate phase precursor powder mainly containing Li2SiO3 and LiOH.

[0015] Furthermore, in step (2), the waste coffee grounds need to be dried at 80℃~100℃ for 12~24 hours and passed through a 150~250 mesh sieve to ensure a wide distribution of particle size, thereby facilitating the formation of hierarchical pores with both macropores and mesopores; the alkali metal carbonate dopant is sodium carbonate (Na2CO3), and its addition amount is fixed at 10 wt% of the mass of the lithium orthosilicate precursor powder.

[0016] Furthermore, in step (2), the amount of waste coffee grounds (SCG) added accounts for 10 wt% to 70 wt% of the precursor powder mass, with a preferred addition range of 30 wt% to 50 wt%, in order to achieve the best balance between adsorption capacity and mechanical abrasion resistance.

[0017] Furthermore, in step (2), the mold is a tungsten carbide mold or a stainless steel mold, and is cold-pressed by a single-axis press to produce cylindrical green pellets with a certain initial strength.

[0018] Furthermore, during the high-temperature co-sintering process in step (3), the sintering temperature is set to 750℃~850℃, the holding time is 90~150 minutes, and the heating rate is controlled at 5~10℃ / min. At this temperature, the organic template is completely burned off, the target phase Li4SiO4 is completely crystallized, and trace amounts of Li3NaSiO4 and Li3KSiO4 phases are generated.

[0019] The present invention also discloses a lithium orthosilicate carbon capture material prepared according to any of the above preparation methods.

[0020] The present invention also discloses an application of the above-described lithium orthosilicate carbon capture material in the capture of carbon dioxide in high-temperature industrial flue gas.

[0021] Furthermore, the application employs a fluidized bed process, and the adsorbent exhibits a mass loss rate of less than 10% after 3000 rotational abrasion tests.

[0022] Furthermore, the temperature of the high-temperature industrial flue gas is 600-700℃, the CO2 volume concentration is 10-20%, and the adsorbent has an adsorption capacity of not less than 0.30 g / g under the conditions of adsorption temperature of 650℃ and CO2 concentration of 15 vol%. After 20 high-temperature adsorption-desorption cycles, the adsorption capacity retention rate is not less than 85%.

[0023] The present invention has the following significant beneficial effects and innovative points:

[0024] (1) Synergistic enhancement of physical and chemical effects: After the wide-particle-size macromolecular framework of waste coffee grounds is burned off, a "hierarchical interconnected pore network" with both macropores and mesopores is etched in situ in the ceramic framework, which greatly reduces the gas phase mass transfer resistance. At the same time, the coffee grounds ash is naturally rich in potassium (K), which is released in situ during sintering and incorporated into the silicate lattice. Together with the externally introduced sodium source, it forms a low-melting-point eutectic molten carbonate at the working temperature, which accelerates the diffusion of liquid phase ions. In addition, the local carbothermic reduction accompanying biomass combustion can also introduce certain oxygen vacancy defects, which can enhance the interfacial affinity.

[0025] (2) Excellent capture performance and mechanical stability: Under the stringent simulated flue gas concentration of 15 vol% CO2, the preferred embodiment of this invention (with 50% SCG added) reaches adsorption saturation within only 30 minutes at 650°C, with a peak adsorption capacity as high as 0.33 g / g. After 20 high-temperature long-cycle cycles, the capacity remains at 0.291 g / g. In the standard brittleness test of 3000 rotations, the wear rate is less than 10%, perfectly balancing high mass transfer and a strong mechanical framework.

[0026] (3) Low-cost process of treating waste with waste: This invention uses waste coffee grounds with no economic value to replace expensive chemical pore-forming agents, realizes the reuse of solid waste resources, greatly reduces the production cost of ton-level carbon capture materials, and has extremely high industrial promotion value. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process flow for preparing modified porous Li4SiO4 particulate adsorbent using waste coffee grounds (SCG) according to the present invention.

[0028] Figure 2 The X-ray diffraction (XRD) patterns of the adsorbents prepared with different amounts of waste coffee grounds (10%, 30%, 50%, and 70%) after sintering confirmed the formation of the target phase and the appearance of the in-situ potassium-doped phase (Li3KSiO4).

[0029] Figure 3 SEM images (a1–d1) and EDS elemental diagrams (a2–d6) of the adsorbents LSON-10, LSON-30, LSON-50 and LSON-70 prepared for different amounts of waste coffee grounds (10%, 30%, 50%, 70%) according to the present invention.

[0030] Figure 4 The graph shows the wear performance (mass loss) of the adsorbents prepared with different amounts of waste coffee grounds (10%, 30%, 50%, 70%) as a function of the number of rotations.

[0031] Figure 5 Isothermal CO2 adsorption curves of the adsorbents prepared for different amounts of waste coffee grounds (10%, 30%, 50%, 70%) under 15 vol% CO2 conditions at 550, 600, 650 and 700°C: (a) LSON-10, (b) LSON-30, (c) LSON-50 and (d) LSON-70.

[0032] Figure 6 The stability test chart of the adsorbent prepared by the present invention with different amounts of waste coffee grounds (10%, 30%, 50%, 70%) under 20 high-temperature adsorption-desorption cycles at 650℃ / 750℃ is shown. Detailed Implementation

[0033] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and four specific examples of equally spaced addition amounts (10%, 30%, 50%, and 70%). To ensure the scientific validity of the comparison, the same parameters (800°C, 120 minutes) were used in all the following comparative examples during the high-temperature co-sintering stage.

[0034] Example 1 (10wt% waste coffee grounds added, dense control group, denoted as LSON-10)

[0035] (1) Synthesis of lithium orthosilicate precursor powder:

[0036] Accurately weigh analytical grade lithium hydroxide monohydrate (LiOH·H2O) and tetraethyl orthosilicate (TEOS), controlling the Li:Si molar ratio to be 4.1:1. Dissolve in anhydrous ethanol, and rapidly inject deionized water to initiate hydrolysis. Dry the resulting gel in a 120℃ oven for 24 h, grind thoroughly, and then pretreat at 200℃ in a muffle furnace for 24 h to obtain the precursor powder.

[0037] (2) Mixing and molding of green body:

[0038] Collected waste coffee grounds and dry them in an oven at 80℃ for 24 hours, then pass them through a 200-mesh sieve for later use. Weigh 1.0g of the precursor powder prepared in step (1), add 0.1g (i.e., 10wt%) of the sieved waste coffee grounds, and add 0.1g (10wt%) of Na2CO3 powder. After dry mixing evenly, add an appropriate amount of deionized water to make a paste and press it into green pellets using a single-axis tablet press.

[0039] (3) High-temperature co-sintering:

[0040] The green pellets were placed in a muffle furnace and heated to 800°C in air at a rate of 5°C / min, and held for 120 minutes.

[0041] Performance test results:

[0042] like Figure 2 The XRD pattern shows that the sample exhibits a pure Li4SiO4 phase. Figure 3 As shown in (a1-a4), due to the small amount of coffee grounds added, the surface is relatively dense with only a few isolated micropores. Due to the lack of pore channels, its final adsorption capacity at 650℃ and 15 vol% CO2 is only 0.111 g / g. Figure 5 a). But if Figure 4 As shown, thanks to the highly dense skeleton, the mass loss rate after 3000 rotational wear cycles is extremely low, only 6.11%. Figure 6In the cyclic test, the sample showed little capacity decay, but the overall adsorption capacity remained at a low level.

[0043] Example 2 (Add 30wt% waste coffee grounds, denoted as LSON-30)

[0044] (1) The steps for synthesizing the precursor powder are the same as in Example 1.

[0045] (2) Mixing and molding of green body: Weigh 1.0g of precursor powder, add 0.3g (i.e. 30wt%) of sieved waste coffee grounds, and fix 0.1g (10wt%) of Na2CO3 powder. Mix and press into shape.

[0046] (3) High-temperature co-sintering: The procedure is the same as in Example 1.

[0047] Performance test results:

[0048] like Figure 2 As shown, the target phase is well-developed in the XRD pattern. Figure 3 As shown in (b1-b6), with increasing addition amount, more interconnected pores are formed on the particle surface and inside. In kinetic tests ( Figure 5 (b) Increased porosity promoted gas-phase mass transfer, increasing its adsorption capacity at 650°C to approximately 0.195 g / g. In wear tests ( Figure 4 Its mass loss rate after 3000 cycles increased slightly to 8.51%, but it still exhibited excellent mechanical properties. Figure 6 Cyclic life tests show that its capacity remains stable at around 0.185 g / g.

[0049] Example 3 (with 50wt% waste coffee grounds added, the best overall performance group is designated LSON-50)

[0050] (1) The steps for synthesizing the precursor powder are the same as in Example 1.

[0051] (2) Mixing and molding of green body: Weigh 1.0g of precursor powder, add 0.5g (i.e. 50wt%) of sieved waste coffee grounds, and fix 0.1g (10wt%) of Na2CO3 powder. Mix and press into shape.

[0052] (3) High-temperature co-sintering: The procedure is the same as in Example 1.

[0053] Performance test results:

[0054] like Figure 2 As shown, in addition to the Li4SiO4 main phase, a weak Li3KSiO4 diffraction peak appeared, confirming the in-situ doping of potassium in the coffee grounds ash. Figure 3As shown in (c1-c6), a highly developed and interconnected hierarchical macroporous network is formed inside the sample, and elements such as K and Na are evenly distributed.

[0055] In terms of performance, such as Figure 5 As shown in c, LSON-50 exhibits extremely excellent adsorption kinetics, reaching the adsorption plateau in just 30 minutes at 650℃, with a maximum adsorption capacity as high as 0.33 g / g. In the wear test ( Figure 4 The mass loss rate was 9.82%, which is just within the wear resistance safety boundary (<10%) of industrial fluidized beds. Figure 6 As shown, after 20 high-temperature adsorption-desorption cycles, the sample still has a capacity of 0.291 g / g, perfectly balancing the high porosity mass transfer requirement and mechanical robustness, making it the optimal embodiment of the present invention.

[0056] Example 4 (70wt% waste coffee grounds added, critical strength failure group, denoted as LSON-70)

[0057] (1) The steps for synthesizing the precursor powder are the same as in Example 1.

[0058] (2) Mixing and molding of green body: Weigh 1.0g of precursor powder, add 0.7g (i.e. 70wt%) of sieved waste coffee grounds, and fix 0.1g (10wt%) of Na2CO3 powder. Mix and press into shape.

[0059] (3) High-temperature co-sintering: The procedure is the same as in Example 1.

[0060] Performance test results:

[0061] like Figure 3 As shown in (d1-d6), the 70% excess biomass loss resulted in the formation of a very high proportion of macropores and voids within the adsorbent. Although in the adsorption kinetics tests ( Figure 5 d) Its final adsorption capacity remains excellent (0.313 g / g), but Figure 4 Mechanical testing revealed serious problems: excessive porosity fundamentally weakened the ceramic's mechanical framework, resulting in a sharp increase in mass loss to 14.06% after 3000 rotations, with severe pulverization and fragmentation of the particles. Although Figure 6 The results showed that its circulating capture capacity did not decline significantly, but it is easily depleted under the intense impact of a fluidized bed. This comparative example effectively verifies the scientific validity and necessity of the preferred addition range of 30-50 wt% in the claims.

[0062] Comparative Example 1

[0063] Li4SiO4 was prepared using rice husk as a pore-forming agent. For specific process details, please refer to existing literature [1].

[0064] Comparative Example 2

[0065] Li4SiO4 was prepared using wheat straw as a pore-forming agent. For specific processes, refer to existing literature [2].

[0066] The waste coffee grounds of this invention retain their natural lignocellulose cell wall skeleton and undergo multi-stage collapse during pyrolysis, unlike the "rapid gas release + random pores" pattern produced by burning rice husks or wheat straw, which are essentially characterized by a unimodal pore size distribution and suffer from ash clogging. Simultaneously, the structure induced by this bio-template exhibits a distinct "bimodal pore size distribution" (macropores + mesopores), while rice husk / straw systems, limited by the original particle size, typically show a unimodal or narrow distribution. This difference directly explains its superior kinetic behavior. More importantly, despite the introduction of 50% organic phase, the final material still exhibits a wear loss of <10% (3000 rotations), indicating that its skeleton forms a "porous but continuous load-bearing network" during sintering, and its mechanical strength is at least no worse than that of traditional template systems (the latter often suffer from strength reduction due to isolated pores or ash defects), achieving an anomalous unity of "high porosity + high strength".

[0067] At the chemical and kinetic level, waste coffee grounds contain potassium (K) and form a K2CO3–Na2CO3 low-melting-point eutectic system with added Na2CO3 in a specific ratio. The melting point of this system is significantly lower than that of a single carbonate (K2CO3≈891℃, Na2CO3≈851℃, while the eutectic can be lowered to ~710℃ or even lower). Therefore, a stable locally molten phase can be formed at 650℃. In contrast, although the rice husk / straw system contains K / Na, the ratio is uncontrollable and it is prone to forming high-melting-point non-eutectic or being coated with ash, or even accompanied by pore blockage. Therefore, in terms of recycling performance, the waste coffee grounds system still maintains 0.291 g / g after 20 cycles, which is significantly better than the typical biomass template system (which usually decays rapidly due to sintering and pore blockage). This directly proves that "K+Na co-doping has a critical ratio window" and is not a simple linear superposition of single-element doping.

[0068] Oxygen vacancies not only serve as adsorption sites but also couple with the molten phase in two ways: first, by lowering the activation energy of CO2 molecules and increasing their dissolution / transfer rate to the carbonate phase at the interface (similar to gas-liquid interface strengthening); and second, by acting as "diffusion jump sites" to promote CO2 migration within the reaction layer, a point directly confirmed in studies on oxygen vacancies promoting CO2 diffusion. Meanwhile, other studies have also shown that there is a synergistic enhancement of adsorption between oxygen vacancies and porous structures, rather than a simple additive effect. .

[0069] The specification and drawings of this invention are intended to be illustrative rather than restrictive. Based on this invention, those skilled in the art can make substitutions and modifications to some of the technical features without creative effort, and all such modifications are within the scope of protection of this invention.

[0070] References:

[0071]

Claims

1. A method for preparing a carbon-modified lithium orthosilicate carbon capture material derived from waste coffee grounds, comprising the following steps: Step 1, Preparation of lithium orthosilicate precursor powder: Using lithium salt and silicon source as starting materials, a liquid phase mixing reaction is carried out in an alcohol-water mixed solvent system, followed by gelation, drying, grinding and low-temperature pre-calcination treatment to obtain lithium orthosilicate precursor powder; Step 2, Pre-treatment of waste coffee grounds: Wash, dry and sieve the waste coffee grounds to obtain pre-treated coffee grounds; Step 3, Preparation of green pellets: Pretreated coffee grounds, lithium orthosilicate precursor powder and alkali metal carbonate dopant are mixed, deionized water is added, and the mixture is placed in a mold and uniaxially pressed into green pellets. Step 4, high-temperature co-firing: The green pellets are sintered at high temperature to obtain lithium orthosilicate carbon capture material.

2. The preparation method according to claim 1, wherein: In step 1, the lithium salt is lithium hydroxide monohydrate, the silicon source is tetraethyl orthosilicate, and the molar ratio of Li to Si is 4.1:1; the drying is carried out at 100°C to 120°C for 12 to 24 hours; the low-temperature pre-calcination treatment is carried out at 200°C to 250°C for 12 to 24 hours.

3. The preparation method according to claim 1, wherein: The drying in step 2 is carried out at 80°C to 100°C for 12 to 24 hours; the sieving is done through a 150-mesh to 250-mesh sieve.

4. The preparation method according to claim 1, wherein: In step 3, the amount of pretreated coffee grounds added is 10wt% to 70wt% of the mass of lithium orthosilicate precursor powder; the alkali metal carbonate dopant is sodium carbonate, and its addition amount is 10wt% of the mass of lithium orthosilicate precursor powder; the mold is a tungsten carbide mold or a stainless steel mold.

5. The preparation method according to claim 4, wherein: The amount of pretreated coffee grounds added is 30wt% to 50wt% of the mass of the lithium orthosilicate precursor powder.

6. The preparation method according to claim 1, wherein: The sintering process described in step 4 involves holding the temperature at 750°C to 850°C for 90 to 150 minutes, with a heating rate of 5°C / min to 10°C / min.

7. A lithium orthosilicate carbon trapping material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the lithium orthosilicate carbon capture material according to claim 8 in the capture of carbon dioxide in high-temperature industrial flue gas.

9. The application according to claim 8, wherein: The application employs a fluidized bed process, and the mass loss rate of the lithium orthosilicate carbon trapping material is less than 10% after 3000 rotational abrasion tests.

10. The application according to claim 9, wherein: The temperature of the high-temperature industrial flue gas is 600℃ to 700℃, and the CO2 volume concentration is 10% to 20%. The adsorption capacity of the lithium orthosilicate carbon capture material is not less than 0.30 g / g under the conditions of 650℃ and CO2 concentration of 15 vol%. After 20 high-temperature adsorption-desorption cycles, its adsorption capacity retention rate is not less than 85%.

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