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气候问题已成为全球性问题,根据CAIT(世界资源研究所)相关数据分析,在过去十年中,世界CO2排放量以每年2.4%的增长率增加[1]。中国碳排放量位居全球首位,实施低碳发展战略,对缓减全球变暖具有重要现实意义[2]。
碱金属基固体吸附剂低温脱除烟气中CO2技术反应温度低、吸附剂与CO2反应速率快、转化率高、无二次污染[3]。以胺基为活性组分加多孔材料的新型二氧化碳吸附剂研究相对成熟。其中胺基改性介孔二氧化硅气凝胶吸附剂(AMSA)的吸附容量在25℃时可达6.97 mmol·g-1 [4]。钠基吸附剂资源丰富、价格低廉,但吸附剂反应活性低[5]。钙基吸附剂在碳酸化之后因内部结构烧结而导致吸附率急剧下降,且废气中的SO2与CaO反应生成CaSO4无法再生,使CaO有效含量下降,吸附性能降低[6]。关于以钾基为活性组分的CO2吸附剂是近年研究热点,根据载体材料不同,国内外学者进行了一系列脱碳特性研究,见表1。研究表明,钾基碳酸盐与微观结构发达、机械强度高的载体材料结合,碳酸钾利用率得以提升,碳酸化性能得到极大改善[7]。
由于载体本身微观特性影响,K2CO3负载能力有限,使吸附剂微观结构和吸附容量因饱和负载而被限制。因此,需要制备一种具有良好微观特性的载体材料,负载活性组分K2CO3制成高CO2吸附量、低成本的改性钾基吸附剂。气凝胶是一种高比表面积、高孔隙率、低密度的非晶纳米多孔材料,在吸附、催化、催化剂载体领域有广泛应用。余煜玺等以仲丁醇铝为前驱体制备氧化铝气凝胶热稳定性高,比表面积达744.50 m2·g-1 [16]。Guo等用TEOS为硅源制备硅凝胶负载K2CO3做吸附剂, CO2吸附量可达1.32 mmol·g−1,碳酸化性能优良[14]。以TEOS和有机醇盐作为溶胶的硅源铝源不仅成本高而且毒性较大[16]且上述研究仅限于超低CO2浓度,无法满足燃煤电厂烟气气氛。
燃煤电厂除尘器排放的飞灰是目前世界上排放量最大的工业废料之一,主要化学成分为SiO2和Al2O3。刘博等[18]利用煤矸石制备二元复合气凝胶比表面积达483.23 m2·g−1,比孔容积1.87 cm3·g−1;陈娜等[19]分别以六甲基二硅胺烷和正丁醇为表面改性剂制备SiO2-Al2O3复合气凝胶比表面积分别为114 m2·g−1、183 m2·g−1;蒲鲲等[20]利用飞灰制备SiO2-Al2O3复合气凝胶比表面积较小,仅为44.47 m2·g−1。
钾基吸附剂对CO2的脱除与活性组分相关,上述研究侧重载体制备、凝胶结构差距较大、以分解率为指标误差较大,且由SiO2-Al2O3复合气凝胶负载K2CO3的碳酸化反应研究相对较少,机理解释不充分。基于此,本文旨在利用飞灰制备SiO2-Al2O3复合气凝胶、K2CO3负载改性,集制备和负载于一体,用作 CO2吸附剂。研究不同负载率下CO2吸附性能,探究吸附剂脱碳特性及循环机理,为今后脱碳提供理论依据。
碳酸钾改性SiO2-Al2O3复合气凝胶制备及脱碳特性
Preparation and decarburization characteristics of SiO2-Al2O3 composite aerogel modified by potassium carbonate
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摘要: 本文对碳酸钾改性SiO2-Al2O3复合气凝胶的制备、K2CO3碳酸化特性及再生循环脱碳特性进行了研究,采用固定床反应器研究负载率对CO2吸附的影响,结合SEM、BET对样品微观结构进行分析。结果表明,Na2CO3碱熔烧结过程中,Si—O—Si、Si—O—Al键断裂,晶相结构被破坏,莫来石的共价键转化为霞石的离子键;经正交试验以气凝胶比表面积为衡量指标确定最佳煅烧条件为:900℃、反应60 min、Na2CO3添加比例0.5;K2CO3负载量越多,载体表面相应活性位点越少,且负载量为30%时,CO2吸附量最大为2.86 mmol·g−1;过量K2CO3会堵塞孔结构,破坏CO2扩散,降低扩散和利用效率;介孔孔体积百分比由94.21%下降至89.32%,说明活性组分K2CO3主要填充在介孔;经过10次循环-再生试验,吸附剂的CO2吸附量下降幅度为10.49%,吸附剂孔隙结构稳定,脱碳性能优良。
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关键词:
- SiO2-Al2O3复合气凝胶 /
- 吸附CO2 /
- 碳酸化特性 /
- 微观特性
Abstract: The preparation of potassium carbonate modified SiO2-Al2O3 composite aerogel, the carbonation characteristics of K2CO3 and the decarbonization characteristics of the regeneration cycle were studied. Using a fixed bed reactor to study the effect of loading rate on CO2 adsorption. Analyze the microstructure of samples combined with SEM and BET. The results show that during the Na2CO3 alkali fusion and sintering process, the Si—O—Si and Si—O—Al bonds are broken, the crystal structure is destroyed, and the covalent bond of mullite is transformed into ionic bond of nepheline. The orthogonal test uses the specific surface area of the aerogel to determine the best calcination system as follows: 900℃, 60 min reaction, and 0.5 Na2CO3 addition ratio. The more K2CO3 loading, the fewer K2CO3 active sites can be attached to the surface of the carrier. When the load is 30%, the maximum CO2 adsorption capacity is 2.86 mmol·g-1. Excessive K2CO3 will block the pore structure, destroy CO2 diffusion, and reduce diffusion and utilization efficiency. The volume percentage of mesopores decreased from 94.21% to 89.32%, indicating that the active component K2CO3 was mainly filled in the mesopores. After 10 cycles-regeneration tests, the CO2 adsorption capacity of the adsorbent decreased by 10.49%, the pore structure of the adsorbent was stable, and the decarburization performance was excellent. -
表 1 K2CO3基吸附剂CO2吸附量对比
Table 1. Comparison of CO2 adsorption capacity of K2CO3-based adsorbent
吸附剂
AdsorbentK2CO3负载量/%wt
K2CO3 load吸附条件
Adsorption conditions转化率/%
Conversion ratesCO2吸附量/(mmol·g−1)
CO2 adsorption capacity参考文献
ReferencesK2CO3/AC 30 60℃,1% CO2+9%H2O — 1.95 [8-9] 30 20℃,0.5% CO2+1.8%H2O — 0.87 [10] K2CO3/AC1 30 60℃,15% CO2+15%H2O 89.20 — [11] K2CO3/AC2 30 60℃,15% CO2+15%H2O 87.90 — [11] K2CO3/Al2O3 30 60℃,1% CO2+9%H2O — 1.93 [8-9] 24.5 60℃,18% CO2+18%H2O 95.20 -- [12] 30 20℃,0.5% CO2+1.8%H2O — 1.18 [10] K2CO3/MgO 30 60℃,1% CO2+9%H2O — 2.70 [8-9] K2CO3/5A 33 70℃,5%CO2+10%H2O 78.20 — [13] 30 20℃,0.5% CO2+1.8%H2O — 0.34 [10] K2CO3/SG 20 20℃,1% CO2+2%H2O 88.62 1.32 [14] 30 60℃,15% CO2+15%H2O 18.80 — [11] K2CO3/SiO2 30 60℃,1% CO2+9%H2O — 0.23 [8-9] K2CO3/ZrO2 30 60℃,1%CO2+9-11%H2O — 1.73-1.87 [6,15] K2CO3/DT 19.1 60℃,18% CO2+18%H2O 33.90 — [12] K2CO3/TiO2 30 60℃,1% CO2+9%H2O — 1.89-2.05 [8-9] 表 2 煤粉炉飞灰化学组成(来自太原古交电厂)
Table 2. Chemical composition of fly ash from pulverized coal furnace
主要成分
Main ingredients质量分数/%
Quality scoreSiO2 50.26 Al2O3 35.88 Fe2O3 6.00 CaO 2.43 TiO2 1.54 K2O 1.35 SO3 1.11 other 1.43 表 3 因素水平表
Table 3. Factor Level Table
水平
Level因素
Factor反应温度/℃
Temperature reflex反应时间/min
Reaction time碱添加比例/(m灰:m碳酸钠)
Alkali addition ratio1 800 60 0.5 2 850 90 0.6 3 900 120 0.7 表 4 正交试验L9(33)和极差分析
Table 4. Orthogonal test L9 (33) and range analysis
试验号
Test number因素
factor比表面积/(m2 ·g−1)
Specific surface area反应温度 /℃
Temperature reflex反应时间
Reaction time碱添加比例/(m灰:m碳酸钠)
Alkali addition ratio1 800 60 0.5 274 2 800 90 0.6 143 3 800 120 0.7 202 4 850 60 0.6 219 5 850 90 0.7 215 6 850 120 0.5 231 7 900 60 0.7 239 8 900 90 0.5 209 9 900 120 0.6 276 K1 206 244 238 — K2 222 189 213 — K3 241 236 219 — R 35 55 25 — 表 5 不同负载量吸附剂孔结构参数
Table 5. Structure parameters of adsorbent pores with different loadings
K2CO3负载量/%
K2CO3 loadBET比表面积/
(m2·g-1)
BET specific
surface area累积孔体积/
(cm3·g-1)
Cumulative pore
volume平均孔径/nm
Average pore
diameter孔隙丰富度
Pore
richness Z相对比孔容积/%
Relative pore volume微孔
Microporous介孔
Mesoporous大孔
Big hole10 153.9782 0.3639 8.4944 423.1600 0.2130 93.0500 6.7370 20 110.7819 0.2749 8.9543 402.9385 0.3338 94.2127 5.4536 25 96.6573 0.2695 9.9113 358.6302 0.0988 92.7080 7.1932 30 90.4104 0.2626 11.2873 344.2894 0.0282 90.8132 9.1586 40 85.2602 0.2254 9.5784 378.2618 0.1780 89.3174 10.5027 表 6 钾基吸附剂循环结构参数变化
Table 6. Changes of potassium-based adsorbent circulation structure parameters
BET比表面/(m2 ·g−1)
BET specific surface累积孔体积/(cm3 ·g−1)
Cumulative pore volume最可几孔径/nm
Most probable aperture孔隙丰富度
Pore richness Z30%负载量吸附剂 90.4104 0.2626 11.2873 321.3945 10次循环再生后 85.3012 0.2263 9.7932 368.5217 -
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