A desulfurization absorbent and a preparation method thereof

Abstract

The application discloses a desulfurization absorbent and a preparation method thereof, and relates to the technical field of flue gas desulfurization, wherein the absorbent takes biomass waste as a carbon source precursor and is prepared through steps of hydrothermal carbonization, in-situ gas-phase calcium loading and controllable activation. The prepared absorbent has a unique calcium-carbon coupling structure, a high specific surface area and a multistage pore structure.

Description

Technical Field

[0001] This invention relates to the field of flue gas desulfurization technology, and more specifically to a desulfurization absorbent and its preparation method. Background Technology

[0002] Calcium-based desulfurization absorbents, such as lime or limestone, are widely used in flue gas desulfurization due to their abundant raw material sources and low cost. However, existing traditional calcium-based desulfurization absorbents face a series of inherent technical challenges. First, their calcium utilization rate is generally low, typically below 40%, meaning that a large amount of active calcium fails to effectively participate in the desulfurization reaction, resulting in resource waste. Second, the products generated during the reaction are often dense, easily clogging the internal pore structure of the material, thus hindering the further diffusion and reaction of sulfur dioxide, leading to a decrease in desulfurization efficiency. Furthermore, traditional desulfurization processes generate a large amount of waste desulfurization slag. The accumulation and treatment of this slag not only increases operating costs but may also cause secondary pollution problems, placing an additional burden on the environment.

[0003] To overcome the aforementioned shortcomings, existing technologies have attempted to improve calcium-based materials through various approaches. Common strategies include introducing sodium-based, magnesium-based promoters, or other types of catalysts into the calcium-based materials, or loading them onto porous supports such as activated carbon or diatomaceous earth. These methods improve desulfurization performance to some extent, but they are essentially physical mixing or simple impregnation loading of different functional components. This improvement approach suffers from the following fundamental drawbacks:

[0004] 1. The active components and the carrier are mostly bonded by physical adhesion or weak chemical interaction. This fragile interfacial bonding means that during the use of the material, especially under high temperature or high gas velocity erosion conditions, the active components are easily separated from the carrier due to wear, sintering, etc., and thus quickly lose their activity.

[0005] 2. The pore structure of existing carrier materials is mostly randomly distributed, lacking a targeted design for the effective diffusion of sulfur dioxide molecules and the discharge of reaction products. This suboptimal pore structure easily leads to premature blockage of the pores inside the material during the desulfurization reaction, thereby limiting the utilization rate of active sites and the overall desulfurization capacity.

[0006] 3. While using high-purity chemical reagents or expensive commercial carriers (such as carbon nanotubes) can improve desulfurization performance to some extent, this significantly increases the preparation cost of the desulfurization absorbent, making it uneconomical for large-scale industrial applications. Furthermore, these methods do not fundamentally address the environmental burden; for example, the production process of high-purity reagents may introduce new environmental impacts.

[0007] 4. Although some studies have attempted to use biomass (such as rice husks) as adsorbent carriers after carbonization, it is usually only regarded as an "inert framework" that provides specific surface area. This approach fails to fully explore and utilize the alkali metals (such as potassium K) contained in biomass itself and its unique natural hierarchical pore structure, and fails to achieve the "gene-level" targeted transformation from waste to high-performance functional materials, thus missing the potential to significantly improve material performance and reduce costs.

[0008] Therefore, it is necessary to propose a desulfurization absorbent and its preparation method to solve the above problems. Summary of the Invention

[0009] The purpose of this invention is to solve the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0011] A desulfurization absorbent, wherein the desulfurization absorbent is a composite particle obtained by directional conversion of waste biomass, and the composite particle has the following characteristics:

[0012] a) Its carbon skeleton is derived from waste biomass with a total cellulose and hemicellulose content of more than 60 wt% and an inherent potassium content between 0.5 wt% and 5.0 wt%.

[0013] b) It has an inherited and enhanced natural hierarchical porous structure of biomass, which includes a network of macropores, mesopores and micropores.

[0014] c) Potassium is uniformly distributed in the carbon skeleton in the form of potassium carbonate, potassium oxalate, or atomically dispersed KOC, and the potassium content is 1% to 4% of the total mass of the composite absorbent;

[0015] d) Calcium species are firmly bonded to carbon skeleton and potassium species in the form of chemical bonds such as CO-Ca and Ca-OK, and the content of calcium species is 15% to 35% of the total mass of the composite absorbent.

[0016] Furthermore, in the hierarchical porous structure, the pore size of macropores is greater than 50 nm, the pore size of mesopores is between 2 nm and 50 nm, and the pore size of micropores is less than 2 nm.

[0017] Furthermore, the carbon skeleton has partially graphitized regions, and its Raman spectral ID / IG ratio is approximately 1.2 to 1.5.

[0018] Furthermore, the waste biomass is selected from one or more of rice husks, wheat straw, waste culture medium after mushroom cultivation, sugarcane bagasse, or oat husks.

[0019] Furthermore, it includes the following steps performed in sequence:

[0020] Step S1: Hydrothermal carbonization pretreatment, waste biomass crushed to 20-100 mesh is mixed with deionized water at a mass ratio of 1:5 to 1:15, and hydrothermal reaction is carried out at a temperature range of 180℃ to 250℃ for 6 to 12 hours. Then it is washed and dried to obtain pretreated carbon material.

[0021] Step S2: In-situ gas-phase calcium loading. The pretreated carbon material obtained in step S1 is placed in the constant temperature zone of a tube furnace, and the organic acid calcium precursor is placed in the upstream independent heating zone. Under an inert gas atmosphere, the area where the pretreated carbon material is located is first heated to 450°C to 550°C at a rate of 2-10°C / min and held for 30 to 60 minutes. Then, the precursor heating zone is heated to its sublimation / decomposition temperature at a rate of 2-5°C / min and held for 1 to 3 hours. The precursor vapor flows through the pretreated carbon material area under the transport of the carrier gas to achieve the chemical adsorption, decomposition reaction and chemical bonding of calcium species with the carbon skeleton.

[0022] Step S3: Controlled activation. After step S2 is completed, maintain the temperature of the constant temperature zone of the tubular furnace or further adjust it to the range of 500°C to 700°C, and continue heat treatment at this temperature for 1 to 3 hours. At the same time, introduce a small amount of activator to selectively etch the carbon skeleton. After activation is completed, cool to room temperature under an inert atmosphere to obtain the desulfurization absorbent.

[0023] Furthermore, in step S2, the organic acid calcium precursor is calcium acetate.

[0024] Furthermore, in step S2, the sublimation / decomposition temperature of the calcium acetate is 300°C.

[0025] Furthermore, the activator is CO2 or water vapor, and the flow rate is 10-50 mL / min.

[0026] Further, in step S2, the inert gas is argon or nitrogen, and the flow rate is 100-300 mL / min.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. This invention uses waste biomass as the sole starting material, achieving high-value utilization of solid waste and transforming it into high-performance functional materials. The entire preparation process generates very little wastewater and waste gas, aligning with the principles of circular economy and sustainable development, and demonstrating significant environmental benefits.

[0029] 2. The desulfurization absorbent of this invention inherits and develops the natural hierarchical porous structure of biomass. It provides a high-speed network from macropores to active mesopores for sulfur dioxide molecules, greatly reducing the mass transfer resistance of sulfur dioxide inside the material, thereby improving the reaction rate and efficiency.

[0030] 3. The CO-Ca chemical bond strength formed on the carbon skeleton by the chemical vapor deposition (CVD) process is much higher than that of the traditional physical impregnation method. This ensures that the calcium active centers are not easily detached or lost under harsh conditions such as long-term use or high-velocity scouring, thus significantly improving the stability and service life of the desulfurization absorbent.

[0031] 4. Potassium (K) species retained in situ in biomass and calcium (Ca) species loaded in the gas phase are spatially adjacent, forming a unique "K-Ca" dual active center. Potassium can effectively reduce the chemisorption activation energy of sulfur dioxide and promote the activation of sulfur dioxide molecules. The activated intermediate products can be rapidly captured and fixed by the adjacent calcium centers, realizing a synergistic effect of "adsorption-activation-fixation", exhibiting significant kinetic advantages and higher calcium utilization.

[0032] 5. This invention uses inexpensive and readily available waste biomass as raw material, resulting in extremely low raw material costs. Simultaneously, the entire preparation process is highly integrated, avoiding the costs of separately purchasing active components, accelerators, and expensive carrier materials, thereby significantly reducing the production cost of desulfurization absorbents and enhancing their market competitiveness.

[0033] 6. The preparation process of this invention has high flexibility and controllability. By selecting different types of biomass, adjusting hydrothermal carbonization conditions, controlling gas phase loading parameters, and optimizing activation conditions, the performance of the final desulfurization absorbent can be directionally controlled to adapt to the desulfurization requirements of different industrial flue gas conditions. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1: Preparation of calcium-carbon coupled desulfurization absorbent CC-Sorbent-1 using mushroom waste culture medium (cottonseed hull base) as raw material

[0036] 1. Raw material preparation: The fully dried waste mushroom culture medium is pulverized, with cottonseed hulls as the main component, and passed through a 60-mesh sieve. Testing revealed that the raw material contains 68% cellulose and hemicellulose and 1.8% inherent potassium.

[0037] 2. Hydrothermal carbonization pretreatment: Weigh 20g of the prepared mushroom waste culture medium powder, add 200g of deionized water, mix thoroughly, and place in a 1L high-pressure reactor. Heat the reactor to 220℃ and maintain the reaction at this temperature for 8 hours. After the reaction, remove the product, filter it, wash it thoroughly with deionized water until neutral, and then dry it in an oven at 80℃ for 12 hours to obtain the pretreated carbon material PCM-1.

[0038] 3. In-situ vapor-phase calcium loading: Weigh 10 g of PCM-1 and spread it evenly in a quartz boat, placing it in the isothermal heating zone of a tube furnace. Separately weigh 5 g of calcium acetate as an organic calcium precursor and place it in the upstream independent heating zone of the tube furnace. Introduce argon (Ar) as the carrier gas at a flow rate of 200 mL / min. First, raise the temperature of the isothermal heating zone to 500 °C at a rate of 5 °C / min and hold at this temperature for 30 minutes. Then, raise the temperature of the upstream independent heating zone to 320 °C at a rate of 3 °C / min and hold at this temperature for 1 hour, allowing the calcium acetate to fully sublimate and be transported to the PCM region with the argon flow, achieving chemical vapor deposition and bonding of calcium species.

[0039] 4. Controlled Activation: After calcium loading deposition, the temperature of the tube furnace isothermal zone was further increased to 600℃ and maintained at this temperature. At this time, the argon gas flow was switched to an argon mixture containing 5% water vapor, with the total flow rate controlled at 50 mL / min, for activation treatment for 1.5 hours. After activation, the atmosphere was switched back to pure argon, and the tube furnace was naturally cooled to room temperature, finally yielding the calcium-carbon coupled desulfurization absorbent sample CC-Sorbent-1.

[0040] 5. Characterization and performance testing:

[0041] Structural characterization: BET (Brunauer-Emmett-Teller) tests were performed on CC-Sorbent-1, and the results showed that its specific surface area reached 580 m². 2 / g, total pore volume is 0.85cm³ 3 / g. The pore size distribution exhibits a distinct bimodal characteristic, mainly concentrated in the 3-5 nm and 30-80 nm regions, confirming its hierarchical porous structure. Scanning electron microscopy (SEM) images reveal a clear honeycomb-like macroporous framework with abundant mesoporous structures attached to its surface. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of CO-Ca chemical bonds in the material. Raman spectroscopy analysis shows an ID / IG ratio of 1.32, indicating that the carbon framework exhibits partial graphitization characteristics.

[0042] Desulfurization performance testing: Desulfurization performance was evaluated in a fixed-bed reactor. The simulated flue gas composition was: SO2 concentration 2000 ppm, O2 content 5%, CO2 content 10%, with the remainder being N2 balance gas. The reaction temperature was set at 120℃ and the space velocity was 3000 h⁻¹. -1 Using the SO2 concentration at the reactor outlet exceeding 100 ppm as the breakthrough point, the calcium utilization rate of the desulfurization absorbent (based on the sulfur capacity calculated from the active calcium) was calculated. The results show that the calcium utilization rate of CC-Sorbent-1 is as high as 85%, while the calcium utilization rate of traditional slaked lime is usually about 35%, which is significantly higher than that of traditional slaked lime desulfurization absorbents.

[0043] Comparative Example 1: Preparation of desulfurization absorbent PM-1 by physical mixing method

[0044] To compare the advantages of the coupling bonding of this invention, a physically mixed desulfurization absorbent sample, PM-1, was prepared. Commercial calcium hydroxide powder and potassium carbonate powder with calcium and potassium content equivalent to CC-Sorbent-1 in Example 1 were weighed. These powders were mechanically ball-milled with a carbon material (i.e., PCM-1) that had undergone the same hydrothermal carbonization treatment on a mushroom culture medium but without gas-phase calcium loading, for 2 hours. The desulfurization performance of PM-1 was tested under the same conditions as in Example 1. The results showed that its calcium utilization rate was only 52%, significantly lower than that of CC-Sorbent-1. Furthermore, potassium escape was observed in the early stages of the reaction, indicating poor stability of the physical mixture.

[0045] Comparative Example 2: Preparation of Desulfurization Absorbent IM-1 by Traditional Impregnation Method

[0046] To compare the advantages of gas-phase loading in this invention, a conventional impregnation method desulfurization absorbent sample, IM-1, was prepared. PCM-1 was impregnated in a mixed solution of calcium nitrate and potassium nitrate. The calcium-potassium molar ratio in the solution was the same as in Example 1, and impregnation lasted for 12 hours to ensure sufficient loading of the active component. After impregnation, the material was dried at 80°C and then calcined at 500°C under a nitrogen atmosphere for 2 hours to obtain the impregnated sample IM-1. The desulfurization performance of IM-1 was tested under the same conditions as in Example 1. Its calcium utilization rate was 68%, higher than that of the physical mixing method, but still lower than that of CC-Sorbent-1. More importantly, after 10 SO2 adsorption-regeneration cycles, the desulfurization activity of IM-1 decreased by approximately 40%, while the activity of CC-Sorbent-1 decreased by only approximately 15% after the same number of cycles, fully demonstrating the excellent cycle stability of the coupling structure of this invention.

[0047] Example 2: Preparation of calcium-carbon coupled desulfurization absorbent CC-Sorbent-2 using rice husk as raw material

[0048] 1. Raw material preparation: Dried rice husks were selected as the raw material. Testing revealed that the total cellulose and hemicellulose content of the rice husks was 62%, and the inherent potassium content was 2.5%.

[0049] 2. Hydrothermal carbonization pretreatment: Rice husks were crushed and passed through an 80-mesh sieve. 20 grams of the crushed rice husks were mixed with 150 grams of deionized water and placed in a high-pressure reactor. The reaction temperature was set to 240℃, and the reaction time was 10 hours. After the reaction, the mixture was filtered, washed, and dried at 100℃ for 8 hours to obtain the pretreated carbon material PCM-2.

[0050] 3. In-situ gas-phase calcium loading: 10 g of PCM-2 was placed in a quartz boat and placed in the isothermal zone of a tube furnace. 6 g of calcium acetate was weighed and placed in the upstream independent temperature zone. Nitrogen gas was introduced at a rate of 250 mL / min. The isothermal zone was heated to 480 °C at a rate of 6 °C / min and held for 40 minutes. The upstream zone was heated to 310 °C at a rate of 4 °C / min and held for 1.5 hours for calcium loading.

[0051] 4. Controlled activation: After deposition, the temperature of the tubular furnace isothermal zone was raised to 650℃, and an argon gas mixture containing 10% CO2 was introduced at a total flow rate of 40 mL / min for activation treatment for 2 hours. Subsequently, pure nitrogen gas was switched back, and the mixture was cooled to room temperature to obtain the calcium-carbon coupled desulfurization absorbent sample CC-Sorbent-2.

[0052] 5. Characterization and performance testing: The BET specific surface area of ​​the obtained sample CC-Sorbent-2 is 510 m². 2 / g. SEM characterization showed that it has a regular macroporous structure formed by a typical rice husk siliceous framework, which is conducive to gas transport. At 150℃ and higher space velocities (5000 h⁻¹), it was found to be effective. -1 Under the desulfurization performance test conditions, CC-Sorbent-2 still achieved a calcium utilization rate of 78%, demonstrating excellent mass transfer ability and anti-sintering performance.

[0053] Example 3: Preparation of calcium-carbon coupled desulfurization absorbent CC-Sorbent-3 using wheat straw as raw material

[0054] 1. Raw material preparation: Dried wheat straw was selected as the raw material. Testing showed that the total cellulose and hemicellulose content of the wheat straw was 70%, and the inherent potassium content was 1.0%.

[0055] 2. Hydrothermal carbonization pretreatment: Wheat straw was crushed and passed through a 40-mesh sieve. 30 grams of crushed wheat straw was mixed with 300 grams of deionized water and placed in a high-pressure reactor. The reaction temperature was set to 200℃, and the reaction time was 9 hours. After the reaction, the mixture was filtered, washed, and dried at 90℃ for 10 hours to obtain the pretreated carbon material PCM-3.

[0056] 3. In-situ gaseous calcium loading: 15 g of PCM-3 was placed in a quartz boat and placed in the isothermal zone of a tube furnace. 7 g of calcium acetate was weighed and placed in the upstream independent temperature zone. Argon gas was introduced at a rate of 220 mL / min. The isothermal zone was heated to 480 °C at a rate of 4 °C / min and held for 30 minutes. The upstream zone was heated to 310 °C at a rate of 3 °C / min and held for 1.2 hours for calcium loading.

[0057] 4. Controlled Activation: After deposition, the temperature of the tubular furnace isothermal zone was maintained at 550℃, and a trace amount of CO2 was introduced at a flow rate of 20 mL / min as an activator for 2 hours. Then, pure argon gas was switched back and cooled to room temperature to obtain the calcium-carbon coupled desulfurization absorbent sample CC-Sorbent-3.

[0058] 5. Characterization and performance testing: The BET specific surface area of ​​the obtained sample CC-Sorbent-3 is 550 m². 2 / g, with a pore size distribution similar to that of Example 1, exhibiting a good hierarchical pore structure. At 130°C and a space velocity of 3500 h⁻¹, -1 Under the desulfurization performance test conditions, CC-Sorbent-3 achieved a calcium utilization rate of 80%, demonstrating desulfurization efficiency and activity comparable to or even slightly superior to CC-Sorbent-1 and CC-Sorbent-2.

[0059] Sample Name Raw material type <![CDATA[BET specific surface area (m 2 / g)]]> Desulfurization test temperature (°C) <![CDATA[Desulfurization test space velocity (h -1 )]]> Calcium utilization rate (%) Notes / Performance Characteristics CC-Sorbent-1 Waste culture medium for mushroom cultivation (cottonseed hull base) 580 120 3000 85 Highly efficient desulfurization; activity decreases by approximately 15% after 10 cycles. PM-1 (Comparative Example 1) Physical mixing of waste mushroom culture medium and carbon materials Not mentioned 120 3000 52 Low calcium utilization, potassium escape observed, and poor stability. IM-1 (Comparative Example 2) Carbon material impregnation method for mushroom waste culture medium Not mentioned 120 3000 68 After 10 cycles, the activity decreased by approximately 40%, and its stability was inferior to CC-Sorbent-1. CC-Sorbent-2 rice husk 510 150 5000 78 Excellent mass transfer capability and anti-sintering properties CC-Sorbent-3 wheat straw 550 130 3500 80 Excellent hierarchical pore structure, high desulfurization efficiency

[0060] The active components of absorbents prepared by traditional impregnation methods exhibit inferior dispersibility and stability compared to the gas-phase loading and coupling technology employed in this invention, making them prone to deactivation during cycling. The CC-Sorbent series of absorbents, through their unique preparation method, demonstrate significant advantages in calcium utilization, cycling stability, pore structure, and mass transfer capacity, far surpassing absorbents prepared by traditional physical mixing and impregnation methods, thus providing a highly efficient, stable, and environmentally friendly desulfurization solution.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the content of the present invention's specification shall also be included within the scope of protection of the present invention.

Claims

1. A method for producing a desulfurization absorbent, characterized by, The method comprises the following steps in sequence: Step S1: hydrothermal carbonization pretreatment, waste biomass crushed to 20-100 mesh is mixed with deionized water at a mass ratio of 1:5 to 1:15, and a hydrothermal reaction is carried out at a temperature of 180-250 DEG C for 6-12 hours, followed by washing and drying to obtain a pretreated carbon material; Step S2: in-situ gas phase calcium loading, the pretreated carbon material obtained in step S1 is placed in the constant temperature zone of a tube furnace, and the calcium organic acid precursor is placed in the upstream independent heating zone; under an inert gas atmosphere, first, the region where the pretreated carbon material is located is heated at a rate of 2-10 DEG C / min to 450-550 DEG C and kept for 30-60 minutes, then the precursor heating zone is heated at a rate of 2-5 DEG C / min to its sublimation / decomposition temperature and kept for 1-3 hours, and the precursor vapor is flowed through the pretreated carbon material region under the transport of the carrier gas, realizing the chemical adsorption, decomposition reaction and chemical bonding of calcium species with the carbon skeleton; Step S3: controllable activation, after step S2 is completed, the temperature of the constant temperature zone of the tube furnace is maintained or further adjusted to 500-700 DEG C, and heat treatment is continued at this temperature for 1-3 hours, while a small amount of activation agent is introduced to selectively etch the carbon skeleton, and after activation, it is cooled to room temperature under an inert atmosphere to obtain the desulfurization absorbent.

2. The method for producing a desulfurization absorbent according to claim 1, characterized by, In step S2, the calcium organic acid precursor is calcium acetate.

3. The method for producing a desulfurization absorbent according to claim 2, characterized by, In step S2, the sublimation / decomposition temperature of the calcium acetate is 300 DEG C.

4. The method for producing a desulfurization absorbent according to claim 1, characterized by, The activation agent is CO2 or water vapor, and the flow rate is 10-50 mL / min.

5. The method of claim 1, wherein the desulfurization absorbent is prepared by adding the absorbent to the absorbent solution. In step S2, the inert gas is argon or nitrogen, and the flow rate is 100-300 mL / min.

6. The method of claim 1, wherein the desulfurization absorbent is prepared by adding the absorbent to the absorbent solution. In step S2, the carbon skeleton has a partially graphitized region, and the Raman spectrum ID / IG ratio is 1.2-1.

5.

7. The method for preparing the desulfurization absorbent according to claim 1, characterized in that, In step S1, the waste biomass is selected from one or more of rice husk, wheat straw, waste culture medium after mushroom cultivation, sugarcane bagasse or oat hulls.