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.     

Fe2Mo3O8 nanoparticles self-assembling 3D mesoporous hollow spheres toward superior lithium storage properties

Unique self-assembled iron(II)molybdenum(IV)oxide(Fe₂Mo₃O₈)mesoporous hollow spheres have been facilely constructed via the bubble-template-assisted hydrothermal synthesis method combined with simple calcination.The compact assembly of small nanoparticles on the surface of the hollow spheres not only provides more active sites for the Fe₂Mo₃O₈,but also benefits the stability of the hollow structure,and thus improved the lithium storage properties of Fe2Mo3O8.The Fe₂Mo₃O₈ mesoporous hollow spheres exhibit high initial discharge and charge capacities of 1189 and 997 mA?h?g^?1 respectively,as well as good long-term cycling stability(866 mA?h?g^?1 over 70 cycles)when used as a lithium-ion battery anode.This feasible material synthesis strategy will inspire the variation of structural design in other ternary metal molybdates.     

Efficient CO2 adsorption and mechanism on nitrogen-doped porous carbons

In this work, nitrogen-doped porous carbons (NACs) were fabricated as an adsorbent by urea modification and KOH activation. The CO₂ adsorption mechanism for the NACs was then explored. The NACs are found to present a large specific surface area (1920.72– 3078.99 m²·g⁻¹) and high micropore percentage (61.60%–76.23%). Under a pressure of 1 bar, sample NAC-650-650 shows the highest CO₂ adsorption capacity up to 5.96 and 3.92 mmol·g⁻¹ at 0 and 25 °C, respectively. In addition, the CO₂/N₂ selectivity of NAC-650-650 is 79.93, much higher than the value of 49.77 obtained for the nonnitrogen-doped carbon AC-650-650. The CO₂ adsorption capacity of the NAC-650-650 sample maintains over 97% after ten cycles. Analysis of the results show that the CO₂ capacity of the NACs has a linear correlation (R² = 0.9633) with the cumulative pore volume for a pore size less than 1.02 nm. The presence of nitrogen and oxygen enhances the CO₂/N₂ selectivity, and pyrrole-N and hydroxy groups contribute more to the CO₂ adsorption. In situ Fourier transform infrared spectra analysis indicates that CO₂ is adsorbed onto the NACs as a gas. Furthermore, the physical adsorption mechanism is confirmed by adsorption kinetic models and the isosteric heat, and it is found to be controlled by CO₂ diffusion. The CO₂ adsorption kinetics for NACs at room temperature and in pure CO₂ is in accordance with the pseudo-first-order model and Avramís fractional-order kinetic model.     

Preparation and characterization of novel carbon molecular sieve membrane/PSSF composite by pyrolysis method for toluene adsorption

Carbon molecular sieve membrane (CMSM)/paper-like stainless steel fibers (PSSF) has been manufactured by pyrolyzing poly (furfuryl alcohol) (PFA) coated on the metal fibers. PFA was synthesized using oxalic acid dihydrate as a catalyst and coated on microfibers by dip coating method. For the purpose of investigating the effects of final carbonization temperature, the composites were carbonized between 400°C and 800°C under flowing nitrogen. The morphology and microstructure were examined by X-ray diffraction, Fourier transforms infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption and desorption, Raman spectra and X-ray photoelectron spectra. The consequences of characterization showed that the CMSM containing mesopores of 3.9 nm were manufactured. The specific surface area of the CMSM/PSSF fabricated in different pyrolysis temperature varies from 26.5 to 169.1 m²∙g⁻¹ and pore volume varies from 0.06 to 0.23 cm³∙g⁻¹. When pyrolysis temperature exceeds 600°C, the specific surface, pore diameter and pore volume decreased as carbonization temperature increased. Besides, the degree of graphitization in carbon matrix increased with rising pyrolysis temperature. Toluene adsorption experiments on different structured fixed bed that was padded by CMSM/PSSF and granular activated carbon (GAC) were conducted. For the sake of comparison, adsorption test was also performed on fixed bed packed with GAC. The experimental results indicated that the rate constant k′ was dramatically increased as the proportion of CMCM/PSSF composites increased on the basis of Yoon-Nelson model, which suggested that structured fixed bed padded with CMSM/PSSF composite offered higher adsorption rate and mass transfer efficiency.     

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%.     

镁负载CaO基吸附剂捕集CO2性能及抗烧结机理

复合钙基吸附剂制备成本过高是限制其工业化应用的主要瓶颈问题。本文以不可溶的CaCO₃和Ca(OH)₂作为钙源,通过燃烧合成法制备钙镁复合吸附剂,在双固定床反应器上研究了其循环捕集CO₂性能。结果显示：制备得到的钙镁复合吸附剂具有更发达的孔隙结构,吸附剂表面Ca和Mg分散均匀,MgO均匀分布于CaO晶粒之间,有效提高了钙镁复合吸附剂的抗烧结特性,因此钙镁复合吸附剂循环反应过程中具有高捕集CO₂活性。以Ca(OH)₂作为钙源时,燃烧合成过程中Ca和Mg均匀同时析出,分散更加均匀,有效避免了CaCO₃作为钙源时Mg的团聚问题,因此得到的钙镁复合吸附剂循环捕集CO₂性能最优。最佳的Ca/Mg摩尔比为(8∶2)~(7.5∶2.5)。本研究以不可溶钙源制备得到高活性钙镁复合吸附剂,有效控制了吸附剂成本,具有更好的工程应用前景。     

Effect of sodium bicarbonate solution on methyltrimethoxysilane-derived silica aerogels dried at ambient pressure

Here we present an economical ambient pressure drying method of preparing monolithic silica aerogels from methyltrimethoxysilane precursor while using sodium bicarbonate solution as the exchanging solvent. We prepared silica aerogels with a density and a specific surface area of 0.053 g∙cm⁻³ and 423 m²∙g⁻¹, respectively. The average pore diameter of silica aerogels is 23 nm as the pore specific volume is 1.11 cm³∙g⁻¹. Further, the contact angle between water droplet and the surface of silica aerogels in specific condition can be as high as 166°, which indicates a super-hydrophobic surface of aerogels.     

High-temperature CO2 sorbents with citrate and stearate intercalated Ca—Al hydrotalcite-like as precursor

CO₂, one of the main components of greenhouse gases, increased rapidly because of the growing use of fossil fuels. And CaO sorbents possess the capability to be used in capture of CO₂ at high temperature. In the work, Ca—Al complex oxides derived from citrate and stearate intercalated layered double hydroxides were fabricated and their CO₂ adsorption capacity was compared with that from CO₃^2- intercalated layered double hydroxides. The results presented that the sorbents (Ca/Al = 5) with Ca—Al—citrate layered double hydroxides as precursors performed best and displayed remarkable CO₂ capture capacity of 52.0% (mass) at the carbonization temperature of 600 ℃ without distinct recession during cycling adsorption/desorption tests. The excellent CO₂ adsorption capacity of the sorbent was ascribed to its smaller crystallite size of calcinated particles, optimized pore size distribution as well as homogeneous distributed Ca and Al in the sorbent.     

Using ultrasound to improve the sequential post-synthesis modification method for making mesoporous Y zeolites

Mesoporous Y zeolites were prepared by the sequential chemical dealumination (using chelating agents such as ethylenediaminetetraacetic acid, H₄EDTA, and citric acid aqueous solutions) and alkaline desilication (using sodium hydroxide, NaOH, aqueous solutions) treatments. Specifically, the ultrasound-assisted alkaline treatment (i.e., ultrasonic treatment) was proposed as the alternative to conventional alkaline treatments which are performed under hydrothermal conditions. In comparison with the hydrothermal alkaline treatment, the ultrasonic treatment showed the comparatively enhanced efficiency (with the reduced treatment time, i.e., 5 min vs. 30 min, all with 0.2 mol·L⁻¹ NaOH at 65°C) in treating the dealuminated Y zeolites for creating mesoporosity. For example, after the treatment of a dealuminated zeolite Y (using 0.1 mol·L⁻¹ H₄EDTA at 100°C for 6 h), the ultrasonic treatment produced the mesoporous zeolite Y with the specific external surface area (S_external) of 160 m²·g⁻¹ and mesopore volume (V_meso) of 0.22 cm³·g⁻¹, being slightly higher than that by the conventional method (i.e., S_external = 128 m²·g⁻¹ and V_meso = 0.19 cm³·g⁻¹). The acidic property and catalytic activity (in catalytic cracking of n-octane) of mesoporous Y zeolites obtained by the two methods were comparable. The ultrasonic desilication treatment was found to be generic, also being effective to treat the dealuminated Y zeolites by citric acid. Additionally, the first step of chemical dealumination treatment was crucial to enable the effective creation of mesopores in the parent Y zeolite (with a silicon-to-aluminium ratio, Si/Al= 2.6) regardless of the subsequent alkaline desilication treatment (i.e., ultrasonic or hydrothermal). Therefore, appropriate selection of the condition of the chemical dealumination treatment based on the property of parent zeolites, such as Si/Al ratio and crystallinity, is important for making mesoporous zeolites effectively.     

不同钙基吸附剂捕集CO2后的硫酸化反应特性研究

钙基吸附剂进行多次CO₂捕集后,碳酸化效率会大幅衰减,此时的吸附剂能否高效脱硫利用是值得重点关注的问题。鉴于此,筛选了高性能合成钙基吸附剂和天然石灰石吸附剂,通过热重分析仪分析对比其在多循环CO₂捕集后的碳酸化和硫酸化反应性能,采用微粒模型研究其硫酸化反应动力学特征。结果发现,高性能合成钙基吸附剂的碳酸化反应速率和CO₂吸附能力明显高于石灰石吸附剂。在长达500循环的CO₂捕集试验后,高性能合成钙基吸附剂的CO₂吸附能力比石灰石高10倍以上,其SO₂吸附能力相较于石灰石提升约40%。经历多次CO₂捕集反应循环后,2种吸附剂的硫酸化能力均有提升:其中,石灰石吸附剂的提升幅度更大,硫酸化转化率从26%提升到35%,而高性能合成钙基吸附剂的硫酸化转化率则从38%提升到43%。通过微粒模型计算发现,2种吸附剂的硫酸化反应均是与SO₂浓度相关的一级反应,多循环捕集CO₂反应后,石灰石吸附剂的硫酸化反应活化能下降接近30%,而高性能合成钙基吸附剂的硫酸化反应活化能只下降了5%。研究结果说明2种不同钙基吸附剂在进行循环CO₂捕集后,脱硫能力得到了不同程度的提高,且均可以较好地应用于SO₂的脱除。     

Carbon-doped surface unsaturated sulfur enriched CoS2@rGO aerogel pseudocapacitive anode and biomass-derived porous carbon cathode for advanced lithium-ion capacitors

As a hybrid energy storage device of lithium-ion batteries and supercapacitors, lithium-ion capacitors have the potential to meet the demanding needs of energy storage equipment with both high power and energy density. In this work, to solve the obstacle to the application of lithium-ion capacitors, that is, the balancing problem of the electrodes kinetic and capacity, two electrodes are designed and adequately matched. For the anode, we introduced in situ carbon-doped and surface-enriched unsaturated sulfur into the graphene conductive network to prepare transition metal sulfides, which enhances the performance with a faster lithium-ion diffusion and dominant pseudocapacitive energy storage. Therefore, the lithium-ion capacitors anode material delivers a remarkable capacity of 810 mAh∙g^–1 after 500 cycles at 1 A∙g^–1. On the other hand, the biomass-derived porous carbon as the cathode also displays a superior capacity of 114.2 mAh∙g^–1 at 0.1 A∙g^–1. Benefitting from the appropriate balance of kinetic and capacity between two electrodes, the lithium-ion capacitors exhibits superior electrochemical performance. The assembled lithium-ion capacitors demonstrate a high energy density of 132.9 Wh∙kg^–1 at the power density of 265 W∙kg^–1, and 50.0 Wh∙kg^–1 even at 26.5 kW∙kg^–1. After 10000 cycles at 1 A∙g^–1, lithium-ion capacitors still demonstrate the high energy density retention of 81.5%.     

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.     

Preparation and Application of the Sol-Gel Combustion Synthesis-Made CaO/CaZrO3 Sorbent for Cyclic CO2 Capture Through the Severe Calcination Condition

abstract Calcium looping method has been considered as one of the efficient options to capture CO2 in the combustion flue gas. CaO-based sorbent is the basis for application of calcium looping and shou...     

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.     

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.     

Cl含量对钙基吸收剂微观结构以及动力学性能的影响

通过浸渍法向分析纯CaCO₃中添加Cl,在双固定床反应器系统和热重分析仪上研究了其对钙基吸收剂循环捕集CO₂性能的影响,利用离子反应模型对添加Cl后吸收剂化学反应控制阶段进行动力学分析。结果显示：Cl对钙基吸收剂循环捕集CO₂性能具有不利影响。当Cl/Ca摩尔比大于0.25%后,随Cl/Ca摩尔比增加,化学反应控制阶段反应速率和持续时间均减小,导致在该阶段最终碳酸化转化率降低。对添加Cl前后吸收剂孔隙分布特性进行分析发现,添加Cl导致煅烧后吸收剂烧结加剧,比表面积降低,10~120nm范围内孔分布减少,导致CO₂在吸收剂内部扩散阻力增加,同时能与CO₂反应的CaO量减少,这是导致吸收剂化学反应控制阶段碳酸化反应速度较慢、最终碳酸化转化率较低的主要原因。鉴于Cl的不利影响,在选择钙基材料作为CO₂吸收剂或合成高活性复合吸收剂时,应避免吸收剂中Cl含量过高。     

磷石膏制备纳米氧化钙基 二氧化碳吸附剂工艺的优化

以磷石膏作为钙源,优化了磷石膏制备氧化钙基二氧化碳吸附剂的工艺参数（反应时间、反应温度、二氧化碳通量、搅拌速度和杂质含量）,并考察了纳米氧化钙基二氧化碳吸附剂粒径对吸附性能的影响。得到的最佳工艺条件为：反应时间为50 min,温度为30 ℃,二氧化碳通量为251 mL/min,搅拌速率越慢越好,杂质含量越少越好。纳米氧化钙基二氧化碳吸附剂的粒径越小,其吸附量就越大,吸附速率也越快,其稳定性也就越高。     

容量法测量5 A分子筛静态吸附CH4、CO和CO2的研究

采用容量法分别测量CH₄、CO和CO₂在5A分子筛上的等温吸附曲线,探究吸附温度和吸附压力对CH₄、CO和CO₂吸附量的影响。实验结果表明,吸附量随着吸附压力的上升逐渐增大。设定吸附温度在30 ℃、50 ℃和70 ℃时,5A分子筛在30 ℃时对CH₄吸附量最大,为13.60 cm³·g^-1;对CO和CO₂吸附量均在50 ℃时呈现最大值,分别为17.68 cm³·g^-1 和94.38 cm³·g^-1。而吸附温度70 ℃时,对3种气体的吸附量均减小。     

Supported ionic liquid sorbents for CO2 capture from simulated flue-gas

Supported ionic liquid (IL) sorbents for CO₂ capture were prepared by impregnating tetramethylammonium glycinate ([N₁₁₁₁] [Gly]) into four types of porous materials in this study. The CO₂ adsorption behavior was investigated in a thermogravimetric analyzer (TGA). Among them, poly(methyl methacrylate) (PMMA)-[N₁₁₁₁] [Gly] exhibits the best CO₂ adsorption properties in terms of adsorption capacity and rate. The CO₂ adsorption capacity reaches up to 2.14 mmol·g^-1 sorbent at 35℃. The fast CO₂ adsorption rate of PMMA-[N₁₁₁₁] [Gly] allows 60 min of adsorption equilibrium time at 35℃ and much shorter time of 4 min is achieved at 75℃. Further, Avrami's fractional-order kinetic model was used and fitted well with the experiment data, which shows good consistency between experimental results and theoretical model. In addition, PMMA-[N₁₁₁₁] [Gly] remained excellent durability in the continuous adsorption-desorption cycling test. Therefore, this stable PMMA-[N₁₁₁₁] [Gly] sorbent has great potential to be used for fast CO₂ adsorption from flue-gas.     

One-step synthesis of recoverable CuCo2S4 anode material for high-performance Li-ion batteries

A facile one-step hydrothermal method has been adopted to directly synthesize the CuCo₂S₄ material on the surface of Ni foam. Due to the relatively large specific surface area and wide pore size distribution, the CuCo₂S₄ material not only effectively increases the reactive area, but also accommodates more side reaction products to avoid the difficulty of mass transfer. When evaluated as anode for Li-ion batteries, the CuCo₂S₄ material exhibits excellent electrochemical performance including high discharge capacity, outstanding cyclic stability and good rate performance. At the current density of 200 mA·g⁻¹, the CuCo₂S₄ material shows an extremely high initial discharge capacity of 2510 mAh·g⁻¹, and the cycle numbers of the material even reach 83 times when the discharge capacity is reduced to 500 mAh·g⁻¹. Furthermore, the discharge capacity can reach 269 mAh·g⁻¹ at a current of 2000 mA·g⁻¹. More importantly, when the current density comes back to 200 mA·g⁻¹, the discharge capacity could be recovered to 1436 mAh·g⁻¹, suggesting an excellent capacity recovery characteristics.