Competition for Sodium and Toxic Metals Capture on Sorbents

The removal of toxic heavy metals by sorbents has been the focus of much recent research. In single metal/single sorbent systems, laboratory experiments have demonstrated capture of lead and cadmium by kaolinite and lime at high temperatures. However, practical systems (i.e., pulverized coal fired boilers) generally involve sodium as well as toxic metals and the amount of sodium usually exceeds that of the toxic metals. The purpose of this paper is to explore the effect of sodium on the capture of lead and cadmium by sorbents. Experiments were conducted in a 16 kW, 0.15 m ID, 6 m tall laboratory downflow furnace. Aqueous solutions of toxic metals and metal/sodium pairs were introduced into the furnace through a natural gas flame via atomization and subse quent vaporization. For all experiments, the total metal/sorbent equivalence ratio was maintained at 0.7. Approximately 0.5g/min of lime or kaolinite powder (mean particle diameter congruent 1.4 mu m) was injected along the furnace centerline in the post flame at a temperature of 1500 K. Further downstream, at 1200 K, particulate samples were isokinetically extracted and size segregated in a Berner low pressure impactor. Experimental results showed that cadmium and sodium were captured by lime. Furthermore, cadmium was captured by lime preferentially over sodium. Lead capture by lime occurred at a much slower rate than that for cadmium or sodium. Kaolinite, on the other hand, showed a preference for lead and sodium capture over cadmium. Consequently, for capture of multiple metals, a sorbent mixture of lime and kaolinite might be more effective than a single sorbent.     

二氧化碳捕集技术研究进展

随着全球工业的快速发展,二氧化碳的大量排放被认为是造成气候变暖最主要原因,二氧化碳的捕集和封存已经成为研究的热点,本文综述了近年来CO2捕集技术的研究进展,主要有燃烧后捕集、燃烧前捕集和富氧燃烧三条技术路线,最后提出了可以提高二氧化碳捕集能力的策略与展望。     

对苯醌电化学捕获CO2机理研究及捕获产物的结构分析

利用循环伏安法(CV)、现场红外光谱法、恒电位电解法开展了BQ在乙腈溶液中的电化学捕获CO2的研究.结果显示,CO2在BQ还原过程中被一价阴离子自由基BQ·-所捕获,表明BQ·-是可以当作亲核试剂来捕获CO2.采用恒电位电解的方法,得到了BQ电化学捕获CO2后的终产物.1H-NMR、IR、13C-NMR以及元素分析的结果表明,捕获CO2后的终产物为BQ与CO2进行化学反应的加合物,其化学计量比为1:2,且亲核进攻CO2的是BQ羰基上的氧,形成较为稳定的羧酸式结构.产物酸化处理生成对苯酚,进一步证明BQ电化学捕获CO2产物结构.     

Structure sensitivity of CO oxidation over model Au/TiO2 2 catalysts

Model catalysts of Au clusters supported on TiO₂ thin films were prepared under ultra-high vacuum (UHV) conditions with average metal cluster sizes that varied from ~2.5 to ~6.0 nm. The reactivities of these Au/TiO₂ catalysts were measured for CO oxidation at a total pressure of 40 Torr in a reactor contiguous to the surface analysis chamber. Catalyst structure and composition were monitored with Auger electron spectroscopy (AES) and scanning tunneling microscopy and spectroscopy (STM/STS). The apparent activation energy for the reaction between 350 and 450 K varied from 1.7 to 5 kcal/mol as the Au coverage was increased from 0.25 to 5 monolayers, corresponding to average cluster diameters of 2.5–6.0 nm. The specific rates of reaction ((product molecules) × (surface site)^-1 × s^-1 were dependent on the Au cluster size with a maximum occurring at 3.2 nm suggesting that CO oxidation over Au/TiO₂(001)/Mo(100) is structure sensitive. This revised version was published online in July 2006 with corrections to the Cover Date.     

TiO2对铝硼硅酸盐玻璃结构和性能的影响

采用熔融法制备不同TiO2含量的RO(包括CaO、MgO)-Al2O3-SiO2-B2O3系玻璃。利用红外光谱技术研究TiO2对玻璃结构的影响,分别探讨了玻璃密度、化学稳定性和介电性能的变化规律。结果表明:少量TiO2的加入能够增大玻璃结构聚合度,过多的TiO2将使玻璃结构变得相对疏松;随着TiO2含量的增加,介电常数和介电损耗在1MHz频率下先减小后增大,玻璃析晶倾向和密度呈现增大的趋势,耐酸和耐碱失重比呈现先减小后增大的变化。     

The Effects of Water on CO Oxidation over TiO2 Supported Au Catalysts

Polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) was used to investigate the effects of water on CO oxidation catalyzed by TiO₂ supported Au. The introduction of water into the reactant mixture caused two effects: (1) a decrease in the CO coverage; and (2) the appearance of a carbonate species. Since both effects inhibit CO oxidation, the promotional effects of water found by previous researchers can only be rationalized by its effects on molecular oxygen adsorption and activation. Although this argument is not confirmed by the PM-IRAS data alone, this conclusion is consistent with previous studies. It is further inferred from this study that carbonate species first form on TiO₂ sites and then migrate to Au sites. Surface hydroxyl species may play the same promotional role as adsorbed water.     

聚苯胺基多孔炭制备及 CO 捕集性能研究

以聚苯胺为原料,采用NaOH活化法,在原料与活化剂质量比为1砄4的情况下,研究了不同的活化时间（0.5 h、1 h、2 h）对多孔炭孔隙结构和CO2吸附性能的影响。通过N2吸附脱附、扫描电子显微镜（SEM）、透射电子显微镜（TEM）,对样品的孔隙结构和形貌进行了表征。采用变压吸附法在常温常压下测试了样品对CO2的吸附性能。结果表明：当活化时间为1 h时,比表面积达到最大值2024 m2／g,微孔孔容达到最大值0.926 cm3／g。然而,当活化时间为0.5 h时, CO2吸附量达到了最大值159 mg／g,表明了CO2吸附量与窄微孔孔径分布有直接关系。     

火电厂CO2捕获方式

随着社会经济的迅速发展,人类对于化石燃料的需求量越来越大,燃料燃烧后排放的有害物质也越来越多,全球环境污染问题严峻,温室效应尤为严重。CO2是主要温室气体,CO2总排放量的75%是由石化燃料燃烧产生的,我国CO2排放总量的一半来自电力工业[1]。中国作为负责任的国家,到2020年,中国要实现单位国内生产总值CO2排放量比2005年下降40%～45%这一目标。因此,火电厂CO2减排任务重大,采用CO2捕集与封存技术能减少电厂80%~95%排放量,理论上具有巨大的减排潜力,是当今世界公认的CO2减排的重要途径。目前电厂捕集技术大体上分作三种:燃烧前捕集、燃烧后捕集和富氧燃烧捕集。     

在TiO2上CO的光催化氧化

最近在“氧化的”ＴｉＯ２（即表面无氧空位和Ｔｉ＾３＋）上进行的ＣＯ光催化氧化研究发现：室温下,以黑光灯（峰值λ＝３６５ｎｍ）光照时,“氧化的”ＴｉＯ２无ＣＯ催化氧化的活性,但以杀菌灯（峰值λ＝２５３．７ｎｍ）光照时,则对ＣＯ产生显著的催化活性。参照ＣＯ在过渡金属表面的催化氧化机理,对本现象进行了解释：黑光灯照时,Ｏ２在ＴｉＯ２表面只生成Ｏ＾－２（ａ）,而Ｏ＾－２（ａ）不能使ＣＯ氧化,只有以杀菌灯照     

The influence of Si-modified TiO2 on the activity of Ag/TiO2 in CO oxidation

Nanocrystalline TiO₂ and Si-modified TiO₂ with Si/Ti ratios 0.01, 0.05, 0.1, and 0.3 were prepared by the solvothermal method and employed as the supports for Ag/TiO₂ catalysts for CO oxidation reaction. The incorporation of Si into the TiO₂ lattice in the form of Ti–O–Si as revealed by FT-IR results could inhibit the agglomeration of TiO₂ crystallites, resulting in an increase of both surface area and metal dispersion. However, there existed an optimum content of Si/Ti at ca. 0.05–0.1 which resulted in an improved catalytic activity of Ag/TiO₂ in CO oxidation. Based on the O₂-temperature program desorption (O₂-TPD) results, the catalysts with appropriate amounts of Si/Ti exhibited higher amount of O₂ adsorption and much lower desorption temperature. It is suggested that the presence of Ti–O–Si promoted the formation of active oxygen species and increased the mobility of lattice oxygen so that the catalytic activity was enhanced. There was no improvement in CO oxidation activity of the Ag/TiO₂ catalyst when the Si/Ti was further increased to 0.3 due probably to the formation of amorphous SiO₂ instead of the Ti–O–Si bond.     

Na2CO3-Based Sorbents Coated on Metal Foil: Post Testing Analysis

Worldwide increase in energy demand coupled with a continued reliance on fossil fuel resources have contributed to a significant increase in atmospheric levels of carbon dioxide. According to the International Energy Agency’s (IEA’s) World Energy Outlook 2010 main scenario, the projected growth in energy demand will translate into a 21 % rise in energy related CO₂ emissions between 2008 and 2035, mostly due to robust economic growth in developing countries. This quantity of greenhouse gas emissions would make it next to impossible to meet a 2 ºC goal thought to avoid the worst consequences of global climate change without additional actions. Scenarios for stabilizing climate-forcing emissions suggest atmospheric CO₂ stabilization can only be accomplished through the development and deployment of a robust portfolio of solutions, of which carbon capture and sequestration represent one component. In previous work [1], Na₂CO₃/Al₂O₃ distributed on metal foil was shown to be effective for CO₂ capture. In the current work, Na₂CO₃/Al₂O₃ prepared in the powder-form and foil-form were tested in a fixed-bed reactor and characterized by X-ray diffraction, BET surface area, Raman spectroscopy and scanning electron microscopy, before and after testing, to better understand the performance of the sorbents. The powder sorbents exhibited higher performance, in general, but one of the foil samples showed the highest performance out of all the power and foil sorbents. The same sorbent was also tested for 500 cycles to understand the long-term stability.     

Characterization of Porous Carbonaceous Sorbents Using High Pressure CO2 Adsorption Data

In this paper we present adsorption isotherms of carbon dioxide on five different activated carbons from CHEMVIRON CARBON Belgium (Centaur HSV, BPL 410, F30-470, WS 42, Reactivated) and on a carbon molecular sieve from BERGBAU FORSCHUNG Gmbh (CMS II). The temperature is 303 K and the pressure ranges from 100 kPa up to 4000 kPa. Such conditions correspond to relative pressures ranging from 0.01 to 0.5. We also provide, for the same six sorbents, the nitrogen isotherms at 77 K (pressure: 0.001 to 100 kPa, relative pressure: 10^-5 to 1). A theoretical treatment based on the Dubinin-Radushkevich and Stoeckli concept is presented and applied to the experimental results in order to obtain the micropore size distribution function (considered as Gaussian) of each sorbent. Using the CO₂ data, it is possible to point out important structural differences between the six carbons. The theoretical treatment provides micropore size distribution functions in agreement with what is physically expected. Using N₂ data, the structural differences are not so well marked. As a consequence, the structural parameters provided by the theoretical treatment are not reliable: except for the total micropore volume, they fluctuate strongly when changing the relative pressure domain of the used data.     

CO Spillover and Oxidation on Pt/TiO2

The adsorption of CO has been measured on a 2.5 wt% Pt/TiO₂ catalyst using TPD. A somewhat surprising observation is that (i) CO₂ is produced, even though oxygen is not dosed into the system, (ii) repeated experiments result in the same amount of CO₂ desorption. The results appear to be due to a combination of factors–(i) is due to spillover of CO from the Pt to the TiO₂ support, while (ii) is due to the diffusion of Ti³⁺ into the bulk of the TiO₂ crystallite, which effectively removes the surface non-stoichiometry which might otherwise be expected.     

CO adsorption and oxidation on Au/TiO2

Preoxidized Au/TiO₂ showed no initial activity during a first heating stage up to 70°C, while prereduction yielded a high initial CO conversion at room temperature. With FTIRS, two different CO absorption bands were detected. One band is usually attributed to CO on an oxidic gold species (2151 cm^-1), the other one is characteristic of CO on metallic gold (2112 cm^-1). The presence of the first species appears to have a detrimental effect on the CO oxidation by O₂. The present results do not support a model in which the activity of supported gold catalysts in CO oxidation is ascribed to ionic Au particles. This revised version was published online in July 2006 with corrections to the Cover Date.     

二氧化碳捕集技术的现状与最新进展

CO_2的捕集是缓解温室效应的有效手段,可分为燃烧前分离、发电技术的改进、燃烧后分离。IGCC、化学链燃烧技术、富氧燃烧等技术的主要目的是富集CO_2,降低分离成本。燃烧后分离技术较成熟,主要介绍了其中的吸收分离法、吸附分离法、膜法的原理、优缺点及最新进展。     

氨法捕集CO2工艺研究进展

介绍了CO2捕集回收的工艺方法,简要分析了氨法捕集回收工艺存在的问题,以期利用化工模拟软件优化研究工艺参数,从而降低吸收成本。     

FTIR studies on the CO,CO2 and H2 co-adsorption over Ru-RuO x /TiO2 catalyst

FTIR spectra of a Ru-RuO_x/TiO₂ catalyst obtained on co-adsorption of CO, CO₂ and H₂ in the temperature range of 300–500 K were found to be the sum total of corresponding spectra observed during methanation of individual oxides. The two oxides compete for metal sites and at each temperature they reacted simultaneously to form distinct transient Ru(CO)_n type species even though the nature, the stability and the reactivity of these species were different in the two cases. The monocarbonyl species formed during adsorption/reaction of CO alone or of CO + H₂ were bonded more strongly than those formed during CO₂ + H₂ reaction.     

Parallel Reactor Activity Studies of the Preferential Oxidation of CO on Transition Metals Supported on TiO2 and TiO2 Nanotubes

The preferential oxidation of carbon monoxide in the presence of hydrogen (PROX reaction) was studied on Cu catalysts promoted with Fe, Nb, Ce, and Ni supported on TiO₂ and on TiO₂ nanotubes. The surface area of the untreated TiO₂ anatase (150 m²/g) support was increase to 350 m²/g when transformed into TiO₂ nanotubes (NT). XRD and SEM results confirm the formation of nanotubular structures responsible of the increase in BET surface area. The activity results indicate that a 10% Cu/5% Nb/TiO₂-NT catalyst is highly active for this reaction compared to other transition metals and with a catalyst with the same composition supported on untreated TiO₂. We found close to 80% CO conversion and 40% selectivity to CO₂ formation at 170 °C. The higher activity is ascribed to a higher dispersion of Cu on the TiO₂ NT structures.     

血晶素负载TiO2光催化还原CO2的研究

光催化还原CO2是时下研究的热点课题.建立了一个相对高效、稳定的非均相光催化还原CO2体系.将血晶素作为助催化剂负载于TiO2的表面,对比了负载前后TiO2的晶形变化和血晶素负载量对还原效果的影响,选择合适的溶剂,优化了该体系最佳反应条件.[Ru(bpy)3]2+作为光敏剂,BIH、TEOA作为牺牲剂,在乙腈溶液中光催化还原CO2,体系最高TONCO可达832.     

中空纤维膜结构对脱除烟气中CO_2影响的数值研究

相对于传统的脱碳方法,中空纤维膜脱除烟气中CO2是一种清洁、高效的技术方法。运用有限单元法建立了一个疏水性中空纤维膜脱除烟气中CO2的二维模型,考察了膜丝直径、壁厚、孔隙率、曲折因子、纤维膜根数、膜柱内径和长度等方面对CO2脱除率的影响,模型结果与实验值相符。结果表明四种吸收剂的脱除率从大到小依次为EDAMEADEAAMP。当液速为0.1 m·s–1、气速0.211 m·s–1、操作压力为0.1 MPa时,减小曲折因子、膜丝壁厚和膜柱内径,增大孔隙率、膜丝内径与膜柱长度都有利于膜吸收CO2。