CO2 absorption and regeneration of alkali metal-based solid sorbents

Potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property were measured in the presence of H₂O in a fixed-bed reactor, during multiple cycles at various temperature conditions (CO₂ capture at 60 °C and regeneration at 130–400 °C). Sorbents such as K₂CO₃/AC, K₂CO₃/TiO₂, K₂CO₃/MgO, and K₂CO₃/Al₂O₃, which showed excellent CO₂ capture capacity, could be completely regenerated above 130, 130, 350, and 400 °C, respectively. The decrease in the CO₂ capture capacity of K₂CO₃/Al₂O₃ and K₂CO₃/MgO, after regeneration at temperatures of less than 200 °C, could be explained through the formation of KAl(CO₃)₂(OH)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely converted to the original K₂CO₃ phase. In the case of K₂CO₃/AC and K₂CO₃/TiO₂, a KHCO₃ crystal structure was formed during CO₂ absorption, unlike K₂CO₃/Al₂O₃ and K₂CO₃/MgO. This phase could be easily converted into the original phase during regeneration, even at a low temperature (130 °C). Therefore, the formation of the KHCO₃ crystal structure after CO₂ absorption is an important factor for regeneration, even at the low temperature. The nature of support plays an important role for CO₂ absorption and regeneration capacities. In particular, the K₂CO₃/TiO₂ sorbent showed excellent characteristics in CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (mg CO₂/g sorbent) and fast and complete regeneration at a low temperature condition (1 atm, 150 °C).     

Effect of K2CO3 doping on CO2 sorption performance of silicate lithium-based sorbent prepared from citric acid treated sediment

In this paper, a low-cost and environmental-friendly leaching agent citric acid (C₆H₈O₇) was used to treat the sediment of Dianchi Lake (SDL) to synthesize lithium silicate (Li₄SiO₄) based CO₂ sorbent. The results were compared with that treated with strong acid. Moreover, the effects of preparation conditions, sorption conditions and desorption conditions on the CO₂ sorption performance of prepared Li₄SiO₄ were systematically studied. Under optimal conditions, the Li₄SiO₄ sorbent was successfully synthesized and its CO₂ sorption capacity reached 31.37% (mass), which is much higher than that synthesized from SDL treated with strong acid. It is speculated that the presence of some elements after C₆H₈O₇ treatment may promote the sorption of synthetic Li₄SiO₄ to CO₂. In addition, after doping with K₂CO₃, the CO₂ uptake increases from the original 12.02% and 22.12% to 23.96% and 32.41% (mass) under the 20% and 50% CO₂ partial pressure, respectively. More importantly, after doping K₂CO₃, the synthesized Li₄SiO₄ has a high cyclic stability under the low CO₂ partial pressure.     

Na2CO3基吸附剂颗粒制备及其脱碳性能

采用挤压-滚圆法制备Na₂CO₃基CO₂吸附剂微球颗粒,在自行设计的CO₂吸收系统中对制备的样品进行脱碳性能测试。结合相关表征测试,探明不同载体、不同负载量的Na₂CO₃基吸附剂的微观结构、脱碳性能以及机械性能的变化规律和内在原因。研究表明：不同载体的Na₂CO₃基吸附剂颗粒脱碳性能存在明显差异,其中氧化铝负载的吸附剂（Na₂CO₃/Al₂O₃）的脱碳性能最好,可达1.14mmol/g。铝酸钙水泥负载的吸附剂（Na₂CO₃/CA）机械性能较好,但其脱碳性能最差。结合吸附剂脱碳和机械性能的综合考量,Na₂CO₃/Al₂O₃是最为合适的CO₂吸附剂,并进一步研究不同Na₂CO₃负载量的影响。研究发现随着Na₂CO₃负载量的变化,吸附剂的微观结构、脱碳性能以及机械性能都存在明显的差异。虽然60%负载量的Na₂CO₃/Al₂O₃吸附剂颗粒的机械性能和脱碳效果较好,但其成球度较差,影响其实际应用。质量分数40%负载量的Na₂CO₃/Al₂O₃吸附剂颗粒具有良好的脱碳性能、机械性能以及成球度,CO₂脱除量为1.36mmol/g。总体而言,利用挤压-滚圆法制备的Na₂CO₃基吸附剂颗粒具有良好的流动特性、脱碳性能和机械性能,适用于电厂烟气中的CO₂脱除。     

氨基修饰复合型钠基吸收剂的脱碳特性

为弥补常规钠基吸收剂活性差、脱碳量低的不足,制备了多种表面氨基修饰的新型复合型钠基吸收剂并研究其脱碳特性。通过比较氨基流失率和实际脱碳量,选定二氧化硅的前驱物正硅酸乙酯为载体前驱物,以碳酸钠为活性成分,分别以3-氨基丙基三甲氧基硅烷(APS)、3-氨基丙基三乙氧基硅烷(APTES)、二乙烯三胺(DETA)、三乙烯四胺(TETA)为氨基前驱物,制备得到多种表面氨基修饰的复合型钠基吸收剂。探究各种吸收剂的孔隙结构与脱碳特性,结果表明,APS、APTES修饰后吸收剂孔隙特性较差,脱碳量较低,DETA、TETA修饰后吸收剂孔隙结构得到改善,脱碳量较高。     

Parametric study and effect of calcination and carbonation conditions on the CO2 capture performance of lithium orthosilicate sorbent

The world is currently facing the challenges of global warming and climate change. Numerous efforts have been taken to mitigate CO_2 emission, among which is the use of solid sorbents for CO_2 capture. In this work, Li_4SiO_4 was synthesised via a sol–gel method using lithium nitrate(LiNO_3) and tetraethylorthosilicate(Si C8 H20 O4) as precursors. A parametric study of Li:Si molar ratio(1-5), calcination temperature(600–800 °C) and calcination time(1–8 h) were conducted during sorbent synthesis. Calcination temperature(700–800 °C) and carbonation temperature(500–700 °C) during CO_2 sorption activity were also varied to confirm the optimum operating temperature. Sorbent with the highest CO_2 sorption capacity was finally introduced to several cyclic tests to study the durability of the sorbent through 10 cycles of CO_2 sorption–desorption test. The results showed that the calcination temperature of 800 °C and carbonation temperature of 700 °C were the best operating temperatures, with CO_2 sorption capacity of 7.95 mmol CO_2?(g sorbent)-1(93% of the theoretical yield). Throughout the ten cyclic processes, CO_2 sorption capacity of the sorbent had dropped approximately 16.2% from the first to the tenth cycle, which was a reasonable decline. Thus, it was concluded that Li_4SiO_4 is a potential CO_2 solid sorbent for high temperature CO_2 capture activity.     

TiO2掺杂对Na2CO3/Al2O3吸收剂CO2捕捉性能的影响

钠基固体吸收剂脱除燃煤烟气CO₂技术具有反应温度低、能耗低等优点,日益受到学术界的关注。该技术的主要不足是吸收剂的活性成分碳酸钠与CO₂的反应（碳酸化反应）活性较低。针对这一问题,本文旨在研制一种新型改性钠基固体吸收剂,采用活性氧化铝作为载体、TiO₂作为掺杂剂进行改性,利用热重分析装置、XRD、SEM和氮吸附仪研究钠基固体吸收剂的CO₂捕捉性能。结果表明：掺杂TiO₂后,钠基固体吸收剂与CO₂的反应速率加快,CO₂捕捉量增加;反应前后除TiO₂外无其他含Ti化合物生成;碳酸化反应产物为NaHCO₃和Na₅H₃（CO₃）₄;然而TiO₂掺杂过多会堵塞吸收剂的微观孔道,不利于甚至阻碍碳酸化反应的进行,因此,TiO₂的掺杂量应控制在一定的范围内。     

胺基CO2固体吸附剂脱碳特性及SO2的影响

燃煤电厂烟气中存在的微量SO₂对胺基CO₂固体吸附剂的碳酸化反应及循环特性有不利影响。利用固定床反应器,针对采用溶胶凝胶法制备的胺基CO₂固体吸附剂的碳酸化特性及其在含SO₂气氛下的失效规律进行了实验研究,并结合红外光谱、有机元素分析、BET等测试手段,研究其失效机理。结果表明,所制备的胺基CO₂固体吸附剂在反应温度50℃时具有较好的碳酸化反应特性和循环特性。当反应气氛中存在SO₂时,由于生成了不可再生的亚硫酸/硫酸盐类物质而导致胺基活性位损失,孔隙结构发生变化,影响了吸附剂的脱碳性能,但适当提高反应温度可提高吸附剂的碳酸化反应竞争性。     

负载型K2CO3/Al2O3吸收剂吸收CO2反应机理

利用热重分析仪、扫描电镜和氮吸附仪对不同粒径的K₂CO₃颗粒和负载型K₂CO₃/Al₂O₃二氧化碳吸收剂的碳酸化特性进行研究。负载后的吸收剂比表面积和孔隙结构得到较大改善,使得碳酸化反应速率和转化率均提高,吸收剂碳酸化特性得到改善。纯K₂CO₃颗粒吸收剂的反应速率和转化率随着粒径的增加而减小,负载型吸收剂的反应速率和转化率随着粒径的增加略增大。研究了不同粒径和反应时间对K₂CO₃/Al₂O₃颗粒微观结构的影响,结果表明K₂CO₃/Al₂O₃颗粒具有较稳定的微观结构。采用负载型粒子模型对K₂CO₃/Al₂O₃吸收剂吸收CO₂碳酸化过程进行研究,所建立的粒子模型计算结果与试验值吻合较好。利用建立的模型对不同CO₂浓度下K₂CO₃/Al₂O₃吸收剂碳酸化反应特性进行模拟计算,模拟结果具备一定的合理性和准确性,为开展进一步研究提供了基础。     

二元复合溶液脱除烟气中CO2的过程模拟与评价

为探究吸收容量大、再生能力较强的吸收剂复合吸收燃烧烟气中CO₂的性能,采用N-甲基二乙醇胺-哌嗪（MDEA-PZ）、碳酸钾-哌嗪（K₂CO₃-PZ）以及氨水-哌嗪（NH₃-PZ）3种二元复合溶液,基于Rate-based模型对其进行脱碳性能过程模拟。以吸收剂的摩尔流量、温度以及摩尔分数配比（X∶PZ）3个因素进行单因素研究,并在此基础上采用正交试验的方法得出最佳工艺方案。结果表明,随着吸收剂的摩尔流量上升、温度下降以及吸收剂中PZ摩尔分数上升,CO₂吸收效率呈上升趋势。在最佳工艺方案中,K₂CO₃-PZ二元复合溶液最佳吸收温度为40℃,MDEA-PZ和NH₃-PZ两种二元复合溶液最佳吸收温度为30℃;3种二元复合溶液最佳摩尔流量为3.5×10⁵kmol/h,最佳摩尔分数配比为60%∶40%。在各自最佳工艺以及其他条件相同的情况下,吸收CO₂性能的优劣依次为MDEA-PZ、NH₃-PZ以及K₂CO₃-PZ。     

Direct carboxylation of thiophene with CO2 in the solvent-free carboxylate-carbonate molten medium: Experimental and mechanistic insights

A feasible synthesis route is devised for realizing direct carboxylation of thiophene and CO₂ in a relatively mild solvent-free carboxylate-assisted carbonate (semi) molten medium. The effects of reaction factors on product yield are investigated, and the phase behavior analysis of the reaction medium is detected through the thermal characterization techniques. Product yield varies with the alternative carboxylate co-salts, which is attributed to the difference in deprotonation capacity caused by the base effect within the system. Besides, the detailed mechanism of this carbonate-promoted carboxylation reaction is studied, including two consecutive steps of the formation of carbanion through breaking the C—H bond(s) via the carbonate and the nucleophile attacking the weak electrophile CO₂ to form C—C bond(s). The activation energy barrier in C—H activation step is higher than the following CO₂ insertion step whether for the formation of the mono- and/or di-carboxylate, which is in good agreement with that of kinetic isotope effect (KIE) experiments, indicating that the C—H deprotonation is slow and the forming presumed carbanion reacts rapidly with CO₂. Both the activation energy barriers in deprotonation steps are the minimal for the cesium cluster system since there have the weak the cesium Cs-heteroatom S (thiophene) and Cs-the broken proton interactions compared to the K₂CO₃ system, which is likely to enhance the acidity of C—H bond, lowering the C—H activation barrier. Besides, these mechanistic insights are further assessed by investigating base and C—H substrate effects via replacing Cs₂CO₃ with K₂CO₃ and furoate (1a) with thiophene monocarboxylate (1b) or benzoate (1c).     

碱/碱土金属修饰Ni基催化剂的CO2吸附与甲烷化性能

采用分步浸渍法制备了碱/碱土金属修饰Ni基催化剂Ni-M/Al₂O₃ (M=K₂CO₃, Na₂CO₃, MgO, CaO)。探究了碱/碱土金属的添加对改性Ni基催化剂CO₂吸附和甲烷化性能的影响。研究发现,碱/碱土金属的添加提高了Ni/Al₂O₃催化剂表面的碱性活性位点密度,强化了其CO₂吸附性能。碱/碱土金属类型影响Ni-M/Al₂O₃催化剂碱性活性位点的分布、NiO物相的转化及Ni的分散度,进而影响其甲烷化性能。MgO添加使NiO物相转化为与载体呈强相互作用的β型和γ型NiO,降低了催化剂表面的强碱性活性位点比例,有利于CO₂吸附活化。Ni-MgO/Al₂O₃的CO₂吸附容量最高为0.68mmolCO₂/g,其CO₂转化率和CH₄选择性分别高达58.4%和95.4%,其在烟气CO₂捕集与原位甲烷化中极具应用前景。     

K2CO3对兰炭催化气化特性的影响

在固定床中考察了不同K₂CO₃植入浓度和不同温度条件下兰炭催化气化特性。结果表明，5%的催化剂植入浓度主要起到填充孔隙的作用，当植入浓度增加到10%以后，催化剂发生堆积会使颗粒表面及内部形成较多孔隙。提高气化温度可提高兰炭转化率，超过750℃之后碳转化率增幅减缓，催化剂饱和装载浓度为10%。在颗粒表面和开放孔隙中的高浓度C(O)才具有较高的脱附速率，并提高CO生成速率。在非催化条件下，随着气化的进行CO/CO₂下降，而H₂/(2CO₂+CO)先增后减。在催化条件下，H₂/(2CO₂+CO)稳定在1.5～1.7。催化剂兰炭样品中出现了K₂Ca(CO₃)₂双金属碳酸盐、K₂O、KO₂等活性组分，并随催化剂植入浓度的增加而增加。催化剂植入浓度的增加会导致失活现象加重，但兰炭在750℃条件下气化1 h 催化剂没有完全失活。     

吸附强化蒸汽重整制氢中CO2固体吸附剂的研究进展

吸附强化蒸汽重整（SESR）制氢技术是集重整反应（H₂生产）和选择性分离（CO₂吸附）于一体的新型技术。该技术的特点为采用固体吸附剂在高温下对CO₂进行原位脱除,以改变反应的正常平衡极限,提高烃类转化率,提高H₂产量,减少CO₂排放。在整个SESR制氢技术中,吸附剂的选择与反应条件至关重要。本文探讨了CaO、水滑石、Li₂ZrO₃、Li₂SiO₃以及双功能吸附剂在SESR制氢过程中的性能,总结了提高这些吸附剂吸附性能的不同方法。确定了固体吸附剂的反应条件,如温度、压力、水蒸气量等因素的影响及相关的反应机理。分析表明,CaO基吸附剂由于其低廉的价格及较高的吸附能力,被认为是最具潜力的吸附剂,然而在SESR制氢过程中,CaO基吸附剂面临着多次循环再生后吸附能力衰减的挑战。集吸附与催化双重功能的吸附催化材料由于可以克服SESR制氢中不同固体催化剂和吸附剂的匹配问题、降低所用固体材料的成本,从而使其在吸附强化蒸汽重整制氢方面具有巨大优势,并成为该领域未来研究的一个重要方向。     

CO2 capture by double metal modified CaO-based sorbents from pyrolysis gases

High-temperature pyrolysis technology can effectively solve the problem of municipal solid waste pollution. However, the pyrolysis gas contains a large amount of CO₂, which would adversely affect the subsequent utilization. To address this problem, a novel method of co-precipitation modification with Ca, Mg and Zr metals was proposed to improve the CO₂ capture performance. X-ray diffraction (XRD) patterns and energy dispersive X-ray spectroscopy analysis showed that the two inert supports MgO and CaZrO₃ were uniformly distributed in the modified calcium-based sorbents. In addition, the XRD results indicated that CaZrO₃ was produced by the reaction of ZrO₂ and CaO at high temperatures. The effects of doping ratios, adsorption temperature, calcination temperature, CO₂ concentration and calcination atmosphere on the adsorption capacity and cycle stability of the modified calcium-based sorbent were studied. The modified calcium-based sorbent achieved the best CO₂ capture performance when the doping ratio was 10:1:1 with carbonation at 700 ℃ under 20% CO₂/80% N₂ atmosphere and calcination at 900 ℃ under 100% N₂ atmosphere. After ten cycles, the average carbonation conversion rate of Ca-10 sorbent was 72%. Finally, the modified calcium-based sorbents successfully reduced the CO₂ concentration of the pyrolysis gas from 37% to 5%.     

Enhancement of CO2 capture and microstructure evolution of the spent calcium-based sorbent by the self-reactivation process

The effect of self-reactivation on the CO_2 capture capacity of the spent calcium based sorbent was investigated in a dual-fixed bed reactor.The sampled sorbents from the dual-fixed bed reactor were sent for XRD,SEM and N_2 adsorption analysis to explain the self-reactivation mechanism.The results show that the CaO in the spent sorbent discharged from the calciner absorbs the vapor in the air to form Ca(OH)_2 and further Ca(OH)_2·2 H_2 O under environmental conditions,during which process the CO_2 capture capacity of the spent sorbent can be self-reactivated.The microstructure of the spent sorbent is improved by the self-reactivation process,resulting in more porous microstructure,higher BET surface area and pore volume.Compared with the calcined spent sorbent that has experienced 20 cycles,the pore volume and BET surface area are increased by 6.69 times and 56.3% after self-reactivation when φ=170%.The improved microstructure makes it easier for the CO_2 diffusion and carbonation reaction in the sorbent.Therefore,the CO_2 capture capacity of the spent sorbent is enhanced by self-reactivation process.A self-reactivation process coupled with calcium looping process was proposed to reuse the discharged spent calcium based sorbent from the calciner.Higher average carbonation conversion and CO_2 capture efficiency can be achieved when self-reactivated spent sorbent is used as supplementary sorbent in the calciner rather than fresh CaCO_3 under the same conditions.     

水合盐基中低温热化学储热材料性能测试及数值研究

以水合盐K₂CO₃·1.5H₂O和膨胀石墨（EG）分别作为化学蓄热材料和多孔基质,研制了复合储热吸附剂K₂CO₃@EG。对该复合吸附剂和未掺杂膨胀石墨的纯水合盐就脱附储热、吸附性能、循环稳定性等方面进行了对比分析。结果表明,复合吸附剂所需的脱附温度降低,对吸附质的吸附动力学性能也有明显提升且可有效避免潮解现象。经过连续15次的脱附-水合循环实验后,纯盐和复合吸附剂的储热密度分别下降27.6%和10.9%。此外,对储热单元的数值研究结果初步验证了该蓄热体系的可行性。     

Theoretical and experimental study on the fluidity performance of hard-to-fluidize carbon nanotubes-based CO2 capture sorbents

Carbon nanotubes-based materials have been identified as promising sorbents for efficient CO₂ capture in fluidized beds, suffering from insufficient contact with CO₂ for the high-level CO₂ capture capacity. This study focuses on promoting the fluidizability of hard-to-fluidize pure and synthesized silica-coated amine-functionalized carbon nanotubes. The novel synthesized sorbent presents a superior sorption capacity of about 25 times higher than pure carbon nanotubes during 5 consecutive adsorption/regeneration cycles. The low-cost fluidizable-SiO₂ nanoparticles are used as assistant material to improve the fluidity of carbon nanotubes-based sorbents. Results reveal that a minimum amount of 7.5 and 5 wt% SiO₂ nanoparticles are required to achieve an agglomerate particulate fluidization behavior for pure and synthesized carbon nanotubes, respectively. Pure carbon nanotubes + 7.5 wt% SiO₂ and synthesized carbon nanotubes + 5 wt% SiO₂ indicates an agglomerate particulate fluidization characteristic, including the high-level bed expansion ratio, low minimum fluidization velocity (1.5 and 1.6 cm·s^–1), high Richardson−Zakin index (5.2 and 5.3 > 5), and low Π value (83.2 and 84.8 < 100, respectively). Chemical modification of carbon nanotubes causes not only enhanced CO ₂ uptake capacity but also decreases the required amount of silica additive to reach a homogeneous fluidization behavior for synthesized carbon nanotubes sorbent.     

空气中直接捕集CO2技术研究进展

减少碳排放并推动碳中和是应对气候变化、促进经济社会绿色转型的重要途径之一,碳中和技术已成为工业界和学术界的关注焦点。目前碳捕集与封存主要对工业固定源排放的CO₂进行处置捕集,而对占CO₂总排放近50%的分布源CO₂关注度不高。直接空气捕集(direct air capture,DAC)技术不仅可对数以百万计的小型化石燃料燃烧装置以及数以亿计的交通工具等分布源排放的CO₂进行捕集处理,还可有效降低大气中CO₂浓度。介绍了DAC的发展历史、研究现状以及发展趋势,综述了已有DAC技术的工艺流程以及反应装置,对DAC现行工艺中涉及的空气捕捉模块、吸收剂或吸附剂再生模块、CO₂储存模块进行了叙述,对比了几种工艺的优缺点以及吸附剂类型和再生方式,指出DAC技术发展的关键在于研发高效低成本的吸收/吸附材料和设备。分析了DAC吸收/吸附材料的作用原理以及吸附效果,碱性溶液原料成本相对低廉,但再生过程中能耗较高。分子筛及金属有机框架吸附剂虽然再生能耗较低,但对空气中CO₂的吸附容量和吸附选择性表现一般。胺类吸附剂具有较好的吸附能力,由于其再生温度较低,可使用工业废热或少量热能为系统供能;使用胺类吸附剂时吸附和解吸在一个单元中逐步发生,具有更高的效率和操作时间,有望降低DAC系统成本。对比了DAC与其他碳捕集技术的成本并进行了技术经济性分析,DAC成本主要包含运营和维护成本(N_Q&M)、吸附剂材料成本(N_S)和工厂设备的净成本(N_bop);指出目前限制DAC工业化应用的主要因素之一在于吸收/吸附材料和相关工艺成本过高,随着阴离子交换树脂等新型吸附剂的出现和工艺的发展,DAC成本逐年下降。全面探究吸收/吸附材料稳定性、动力学、吸附容量、选择性、再生能量损失等综合性能,研发利于快速装载和卸载吸附剂的相关装置,开发成本低廉的工艺系统是目前DAC领域的发展方向和迫切需求。DAC技术将为减少全球碳排放、实现碳中和提供重要技术支撑。     

K_2CO_3活化制备淀粉基碳分子筛

以可溶性淀粉为碳源、三嵌段共聚物F127为模板剂和K_2CO_3为活化剂,采用一步合成法制备系列淀粉基碳分子筛。通过扫描电子显微镜和N_2吸附-脱附分析淀粉基碳分子筛孔隙形貌和孔结构,采用热重-TG和傅里叶红外光谱表征原料和样品的物质结构官能团。结果表明,K_2CO_3浓度、F127添加比例、反应时间和反应温度影响淀粉基碳分子筛的孔隙结构。在炭化温度800℃、K_2CO_3浓度为0.50 mol·L~(-1)、F127与淀粉质量比=1∶3、反应温度50℃和反应时间12 h条件下制备的淀粉基碳分子筛,孔径集中于0.63 nm,比表面积为1 069.290 4 m~2·g~(-1),单点孔容0.667 901 cm~3·g~(-1)。     

Tuning porosity of coal-derived activated carbons for CO2 adsorption

A simple method was developed to tune the porosity of coal-derived activated carbons, which provided a model adsorbent system to investigate the volumetric CO₂ adsorption performance. Specifically, the method involved the variation of the activation temperature in a K₂CO₃ induced chemical activation process which could yield activated carbons with defined microporous (< 2 nm, including ultra-microporous < 1 nm) and meso-micro-porous structures. CO₂ adsorption isotherms revealed that the microporous activated carbon has the highest measured CO₂ adsorption capacity (6.0 mmol∙g^–1 at 0 °C and 4.1 mmol∙g^–1 at 25 °C), whilst ultra-microporous activated carbon with a high packing density exhibited the highest normalized capacity with respect to packing volume (1.8 mmol∙cm⁻³ at 0 °C and 1.3 mmol∙cm^–3 at 25 °C), which is significant. Both experimental correlation analysis and molecular dynamics simulation demonstrated that (i) volumetric CO₂ adsorption capacity is directly proportional to the ultra-micropore volume, and (ii) an increase in micropore sizes is beneficial to improve the volumetric capacity, but may lead a low CO₂ adsorption density and thus low pore space utilization efficiency. The adsorption experiments on the activated carbons established the criterion for designing CO₂ adsorbents with high volumetric adsorption capacity.