多孔碳结构调控及其在二氧化碳吸附领域的应用

CO_2大量排放引发的温室效应已成为当今世界面临的重要环境问题。燃煤发电厂是CO_2的集中排放源,其排放量约占总排放量的42%,因此,燃煤发电厂烟道气中CO_2的高效捕集迫在眉睫。吸附技术操作简便、能耗低,易于实际应用,被认为是最具前景的烟道气CO_2捕集技术。近年来,多孔碳吸附剂因原料来源广、理化特性可控性强以及目标吸附质适应性高等优点,成为当前CO_2捕集技术的研究热点。综述了近年来多孔碳的制备方法,物理活化法、化学活化法、炭气凝胶法和模板法等,以及制备方法对孔径结构、杂元素掺杂缺陷和多孔碳表面性能的调控;并阐述了孔径结构、元素掺杂和表面官能团改性对CO_2吸附量、循环稳定性、烟道气中CO_2吸附选择性的影响,归纳了多孔碳吸附在实际应用中亟需解决的问题和关键技术。可进一步深入研究机理,协同制备出更高效且适用于CO_2吸附的多孔碳。     

Water absorption by coals: effects of pore structure and surface oxygen

The water-holding capacity of various coals from lignite to anthracite was measured and its relation to their oxygen content and pore structure was investigated. Both factors were found to play important roles in determining the water-holding capacity. Pyrolysis of a lignite at 400 °C decreased its water-holding capacity by more than two-thirds, because of the decrease in the number of hydrophilic sites. This was caused by the decomposition of oxygen-containing groups and the decrease in surface area which resulted from the plugging of small pores by volatile matter condensation, making their surfaces inaccessible to water.     

物理吸附仪测定活性炭载体比表面积及孔结构的方法

介绍了利用物理吸附仪测定活性炭的基本原理、模型及测定方法。通过改变相对压力点（P／Po）使活性炭孔结构的测定更加准确。     

活性炭表面含氧官能团对水中卤乙酸吸附去除的影响

为了改善极性、亲水性卤乙酸(HAAs)分子在非极性、疏水性活性炭上的吸附性能,利用N₂等温吸附实验、X射线光电子能谱实验（XPS）、HAAs等温吸附实验等方法,对几种不同产地的活性炭孔隙结构、表面元素形态结构组成,以及HAAs吸附性能进行了研究,考察了活性炭孔结构及含氧官能团对HAAs吸附性能的影响.活性炭表面含氧官能团对HAAs的吸附性能影响显著,当活性炭表面含氧官能团组成较小时,其HAAs吸附能力较强.     

Surface area and pore structure of thorium dioxide

Water vapour isotherms at 35° were measured on two samples of thorium dioxide, one crystalline and the other an amorphous gel. Specific surface areas and pore size distributions were estimated and compared with those obtained from nitrogen adsorption at ?196°. The effect of thermal treatment on both samples was also investigated at 35–500°. It was shown that the adsorption of water vapour on thoria gel is purely physical in nature, and that the gel surface is characterised by the existence of pores of very particular sizes, namely of hydraulic radii 4–6 ǎ. On the other hand, water seems to interact chemically with the surface of the crystalline sample. In this case the specific surface area could not be evaluated from the adsorption branch of the isotherm, but was successfully evaluated through the application of the ‘corrected modelless’ method to the desorption branch of the water isotherms. This gave the surface area of the total pore system which was found to be in good agreement with the B.E.T.-nitrogen area.     

Hierarchical pore structure of activated carbon fabricated by CO2/microwave for volatile organic compounds adsorption

An activated carbon pore-expanding technique was achieved through innovative reactivation by CO_2/microwave.The original and modified activated carbons were characterized by nitrogen adsorption–desorption,scanning electron microscopy,transmission electron microcopy,and Fourier transform infrared spectroscopy.The mesopore volume increased from 0.122 cm~3·g~(-1) to 0.270 cm~3·g~(-1),and a hierarchical pore structure was formed.A gradual decrease in the phenolic hydroxyl and carboxyl groups on the surface of activated carbon enhanced the surface inertia of granular activated carbon(GAC).The toluene desorption rate of the modified sample increased by 8.81% compared with that of the original GAC.Adsorption isotherm fittings revealed that the Langmuir model was applicable for the original and modified activated carbons.The isosteric adsorption heat of toluene on the activated carbon decreased by approximately 50%,which endowed the modified sample with excellent stability in application.The modified samples showed an enhanced desorption performance of toluene,thereby opening a way to extend the cycle life and improve the economic performance of carbon adsorbent in practical engineering applications.     

ZL50活性炭吸附脱除二氧化硫的吸附动力学模型(英文)

A semi-empirical adsorption kinetic model was proposed with the time compensation method to describe the chemisorption of SO2 in flue gas by carbon adsorbents for flue gas purification. The change in adsorption capacity and adsorption rate with time at different water vapor concentrations and different SO2 concentrations was studied. The model was in good agreement with experimental data. The surface reaction was probably the rate controlling step in the early stage for SO2 adsorption by ZL50 activated carbon. The parameters m and n in the nth order adsorption kinetic model were related to the magnitude of the time compensation and adsorption driving force, respectively. The change of parameter n with water vapor concentrations and sulfur dioxide concentrations was studied and some physical implications were given. The sum of square errors was less than 1.0 and the average absolute percentage deviations ranged from 0.5 to 3.2. The kinetic model was compared with other models in the literature.     

Deformations of fossil coals on swelling in an atmosphere of carbon dioxide

The results of the simultaneous control of the sorption of gaseous CO₂ and the swelling of fossil coals from the Donets Basin under quasi-equilibrium conditions were analyzed. It was established that the isotherms of sorption and deformation obey the Langmuir formula in the region of sorbate pressures to 4.5MPa. A linear correlation between the Langmuir sorption and deformation coefficients was found for a group of coals with the high yield of volatile substances, and a swelling criterion was established. A nonlinear relationship between the swelling of coal and the amount of the sorbed substance was obtained.     

煤体理化性质对其孔隙结构和甲烷吸附性能影响的研究进展

煤层气主要成分为甲烷（CH₄）,其主要以吸附态形式存在于煤层中。明确煤体理化性质和煤体孔隙结构及CH₄吸附性能间构效关系,对于高效开采CH₄资源至为关键。为此,本文阐明了煤体理化性质对其孔隙结构和CH₄吸附性能的作用规律,并指出了后续研究趋势。分析表明：煤体微孔结构和其CH₄吸附容量之间呈正线性相关性;煤体介/大孔主要影响CH₄在煤层内部的吸附/扩散速率。具有墨水瓶形孔或富含镜质体的煤体通常具有较强CH₄吸附性能。煤中矿物质和水分对煤体吸附性能产生不利影响。煤中小分子有机物的抽提能够提高煤体孔隙表面积和孔容积,进而提升煤体吸附性能。为了深入研究煤体理化性质及其吸附性能的作用规律,后续需开展以下工作：研究煤体孔隙结构参数和煤体吸附/解吸性能之间的耦合作用关系;利用多重分形理论精确揭示煤体内复杂的孔隙结构信息;优化并建立考虑煤体非均质性的BET和BJH等孔隙结构参数计算模型;以煤基质表面含氧官能团在煤体孔隙内部的赋存空间为切入点,阐明煤体官能团和孔隙结构对其CH₄吸附性能的协同作用规律;从理论模拟和实验科学入手,阐明煤层中水分对煤体孔隙结构的影响;建立更为科学的含水煤体吸附性能评价方法。     

The effect of carbon pore structure on the adsorption of cigarette smoke vapour phase compounds

The pore size, distribution and volume of activated carbon are extremely important for maximizing adsorption of vapours formed during cigarette smoking. Increasing micropore volume leads to an increase in the removal efficiency. Because of the relatively high flow rates encountered during the smoking process, mesopores appear to be beneficial as transport pores especially in cases where the micropore volume is relatively low and thus the most accessible micropore sites may be rapidly saturated. Film diffusion limitations seem to be present at the very high space velocities encountered in a filter under the conditions of cigarette smoking. The removal efficiency from smoke is approximately inversely proportional to the vapour pressure of the constituents.     

Low temperature oxidation of coals: Effects of pore structure and coal composition

The low-temperature oxidation of five coals, ranging in rank from subbituminous to anthracite, was studied in the temperature range 30–250 °C, and the reaction kinetics were elucidated. The reaction rates were independent of particle diameter <1 mm. The orders of reaction for CO₂ and CO formation were 0.50 and 0.54, respectively, with respect to oxygen. Activation energies of 51.5–59.4 kJ mol^?1 were obtained for the CO₂ and CO formation reactions. The rates of formation of CO₂ and CO were correlated to the internal surface area and the oxygen contents of the coals. It was found that pores having radii >100 Å, and the oxygen-containing groups which decompose to CO₂ and/or CO, were playing important roles in low-temperature oxidation of coals.     

变压吸附分离工业废气二氧化碳的研究进展

概述了未来人类对过量二氧化碳排放的处理办法,即碳的捕获和存储(CCS).简介了4种二氧化碳的分离工艺及特点和工业中二氧化碳的捕获系统.阐述了变压吸附工艺的基本原理和其在捕获工业废气中二氧化碳上的应用,以及变压吸附分离二氧化碳的工艺在循环结构设计、吸附剂材料和数值模拟等方面的研究进展和国内外的工业化应用.分析了目前该工艺仍存在的问题,指出该技术具有广阔的应用前景.     

Microporosity of carbon deposits collected in the Tore Supra tokamak probed by nitrogen and carbon dioxide adsorption

Nitrogen and carbon dioxide adsorption experiments have been used to investigate the porosity of carbon deposits formed in the Tore Supra tokamak as a consequence of the erosion of the plasma-facing components. We compare BET, α_s-, and Dubinin-Raduskevich methods to distinguish between micropore volume (∼0.04 cm³ g⁻¹) and external surface (∼90 m² g⁻¹). Consistent results have been obtained for nitrogen and carbon dioxide, and the smallest pores are shown to be reversibly closed and opened under air exposure and outgassing at 600 °C, respectively, probably due to blocking of pore entrances by surface oxides. Pore size distribution is calculated using the non-local density functional theory: a novel and straightforward method is used to fit the experimental isotherms by Lorentzian distributions of pores centered in some relevant pore size regions. We thus show that the tokamak sample micropores are mainly ultra-micropores (∼75%) whose widths are centered at 0.6 nm. This latter result is in good qualitative agreement with the outgassing effect and in good quantitative agreement with what is deduced from α_s-plot.     

Thermogravimetry and differential scanning calorimetry of Kentucky bituminous coals

A detailed investigation has been made of the thermal characteristics of six Kentucky bituminous coals undergoing pyrolysis in an inert atmosphere at three different heating rates. The specific heats of the coals and the enthalpy changes characterizing their thermal degradation were measured by differential scanning calorimetry. Thermogravimetry was employed to measure the attendant weight changes, which were used to normalize the heat flow data to unit sample weight, enabling a quantitative comparison of the thermal behaviour of the several coals. The specific heats of the dry coals lie in the range 1.21–1.47 J gK^?1, 100–300 °C. The exothermic heat flow from 300 to 550 °C, where the major weight loss occurs, has been associated with the primary carbonization process, the development of the plastic state, and the onset of secondary gasification, which is responsible for coke formation. In the high pyritic sulphur coals, the endothermic pyrite/pyrrhotite transformation at ≈580 °C is clearly defined. A preliminary global kinetic analysis of the thermogravimetric data has been made, using a modified Kissinger equation at the maximum rate of weight loss. Activation energy and pre-exponential factor values of the order 198–220 kJ mol ^?1 and 2–85×10¹²s^?1 have been obtained. These compare well with the limited published values for similar coals.     

A fundamental study on the removal of air pollutants (sulfur dioxide,nitrogen dioxide and carbon dioxide) by adsorption on activated carbon

Gravimetrically measured adsorption and desorption dynamics of sulfur dioxide, nitrogen dioxide and carbon dioxide on a commercial activated carbon are interpreted by a single-particle model based on three transport processes: macropore, micropore and sorbed-phase diffusion. Additional phenomena, concentration-dependent sorbed-phase diffusivity and sorbent non-isothermality, are incorporated to expand the applicability of the model. The dynamic sorption behaviour of all three gases is adequately described, without resorting to a different particle tortuosity factor for each sorbate. The value of the tortuosity factor (8) and the extracted diffusion coefficients are consistent with literature values. The affinity of the activated carbon for the adsorbates is, in increasing order, CO₂ < SO₂ < NO₂, while the extracted diffusion coefficients show the reverse trend, NO₂ < SO₂ < CO₂.     

Structure of coals studied by iodine and water adsorption

Vitrinite in coal is considered as a macromolecular system exhibiting intermolecular microporosity. The surface of this microporosity reflects the structures of the macromolecular system. Adsorption of nitrogen and carbon dioxide provide micropore volumes; adsorption of water and ammonia respond to surface polarity; adsorption of iodine responds to electron availability to form charge transfer complexes. Iodine was adsorbed, both from the vapour phase and aqueous KI solution, by a rank range of coals, fresh, oxidized and pyrolysed. Extents of iodine adsorption were greater from aqueous solution and increased with increasing coal rank to about 87wt% C and then decreased. Extents decreased with increasing severity of oxidation from both vapour and aqueous phases; extents of iodine adsorption increased with increasing heat treatment temperature of coal pyrolysis to decrease subsequently on charring and coking. Results are interpreted in terms of aromaticity of coals, the extent of cross-linkage, and mechanisms of oxidation and pyrolysis.     

Selective adsorption of carbon dioxide, methane and ethane by porous clays heterostructures

The separation of binary mixture representatives of natural and landfill gases by selective adsorption using adsorbent porous clay heterostructures has been investigated. Using Wyoming clay as a starting material, the solids are prepared by the gallery-templated approach from the polymerization of two silica sources, tetraethoxysilane (TEOS) and phenyltriethoxysilane (PhOS), at several molar ratios. In this way, the surface chemistry and the porosity characteristics of the samples are modified. The adsorbents presented specific surface areas up to 634 m² g⁻¹, micropore-size distributions with maxima near to 0.6 nm, thermal stability up to 400 °C and also hydrophobic characteristics. The selectivity for the separation of various binary mixtures such as CO₂/CH₄, CO₂/C₂H₆ and C₂H₆/CH₄, estimated by a methodology based on the determination of the Gibbs free energy, is discussed.     

Hydrocarbon synthesis and carbon dioxide adsorption on iron catalysts

Adsorption isotherms have been measured for carbon dioxide on iron synthetic-NH₃ catalyst and on low-grade iron ore at six temperatures in the range 100–350°C and at pressures up to one atmosphere. The results indicate that at least two dissimilar types of adsorbed CO₂ exist on the surface of the iron synthetic-NH₃ catalyst, one of which is generated only at temperatures >250°C. By contrast, only one form of adsorbed CO₂ was detected on the iron ore catalyst at all temperatures up to 350°C. The kinetics of carbon monoxide hydrogenation are comparable over the two catalysts, and both exhibit virtually identical selectivities for methane formation at equivalent total CO conversions.