The development of porosity in heat-treated polymer carbons upon activation by carbon dioxide

A series of microporous carbons was prepared from cellulose triacetate by heat-treatment in the range 1230–2275°K and a parallel series of carbons was prepared by activation of members of the heat-treated series to 30% burn-off by reaction with carbon dioxide. The changes in porosity with heat-treatment temperature (HTT) were investigated by adsorption of carbon dioxide in the range 195–248°K and by measurement of mercury densities. By comparing porosity in unactivated and activated carbons the extents to which closed porosity can be recovered and open porosity developed by activation were investigated as a function of HTT. The predominant effect of heat-treatment was found to be conversion of open micropores to closed micropores with little change in total pore volume. Activation of 1230 and 1475°K carbons is confined almost entirely to development of micropores. With increasing HTT (meso- + macro-) pore development increases on activation while development of open micropores and opening of closed micropores become less significant.     

Adsorption equilibria of two halogenated carbons on a carbon fiber

Chlorofluorocarbons (CFCs) are presently considered to be the prime contribution to stratospheric ozone depletion. In this study, a microporous activated carbon felt (KF-1500) was used as a useful adsorbent for adsorption of trichlorofluoromethane and methylene chloride. The isotherms of these organic vapors on a microporous carbon felt were measured and the equilibrium parameters based on Dubinin-Radushkevich correlation were evaluated. Besides, the isosteric heats of adsorption were evaluated from the equilibrium data. It was found that equilibrium data for this carbon felt were well described by Dubinin-Radushkevich correlation.     

活性炭预处理对模型油吸附脱硫性能的影响

选取了两种商业活性炭(分别标记为AC_1和AC_2),以二苯并噻吩的正辛烷溶液为模型油,测定了温度、时间、硝酸预处理浓度、吸附剂用量对脱硫性能的影响。结果表明,AC_2的脱硫性能明显优于AC_1;在45℃,140 min,吸附剂用量为1.4 g(模型油10 mL),AC_2的脱硫率达96%。     

Adsorption dynamics of carbon dioxide in molecular sieving carbon

The sorption equilibrium isotherm of carbon dioxide at 20 °C on a commercially manufactured carbon molecular sieve has been measured with a variable volume (vacuum to high pressure) volumetric adsorption apparatus. Measurement was taken over the pressure range <10-2000 Torr and the isotherm is characterized by Dubinin-Radushkevich analysis which provides the micropore size distribution. The equilibrium information is subsequently employed to characterize the dynamics of adsorption and it is shown that the uptake of carbon dioxide is Fickian with some deviation from Fickian behavior noted at lower pressures. The derived mobility parameter agrees reasonably well with that predicted by the Darken relation over more than a 200-fold change in pressure.     

Adsorption of carbon dioxide onto BDA-CP-MS41

Carbon dioxide was adsorbed onto mesoporous adsorbent of butylene diamine immobilized CP-MS41 (BDA-CP-MS41), which was synthesized by chloropropyl functionalized MCM-41 (CP-MS41) with butylene diamine in a laboratory-scale packed-bed. The adsorber was operated batchwise with the charge of adsorbent in the range of 1–3 g to obtain the breakthrough curves of CO₂. Experiments were carried out at different adsorption temperatures (20–40 °C) and flow rates of nitrogen (10–20 cm³/min) to investigate the effects of these experimental variables on the breakthrough curves. The deactivation model was tested for these curves by combining the adsorption of CO₂ and the deactivation of adsorbent particles. The observed values of the adsorption rate constant and the deactivation rate constant were evaluated through analysis of the experimental breakthrough data using a nonlinear least squares technique. The experimental breakthrough data fitted very well to the deactivation model than the adsorption isotherm models in the literature.     

Adsorption of cyanogen chloride on impregnated active carbon

The adsorption of cyanogen chloride on impregnated carbon containing copper and chromium compounds and other additives is accompanied by the formation of carbon dioxide. Presorbed water enhances the formation of carbon dioxide and decreases the desorption of cyanogen chloride. Cyanogen chloride is adsorbed irreversibly because hydrolysis takes place at a rate higher than that of desorption.     

Adsorption of bromine by carbons from solution in carbon tetrachloride

Adsorption of bromine from solution in carbon tetrachloride by a number of carbon blacks as well as sugar charcoal is shown to be partly reversible and partly irreversible. While reversible adsorption appears to be due to surface effects, irreversible adsorption is found to be only partly due to chemisorption in substitution for hydrogen and addition at unsaturated sites. A fairly large amount of it seems to be entrapped within some of the pores of the adsorbents or imbibed by the particles and requires energy of activation to diffuse out of the system.     

Adsorption of carbon dioxide on hydrotalcite-like compounds of different compositions

The adsorption of carbon dioxide on hydrotalcite-like compounds was investigated. Two different powdered hydrotalcites were used containing the cations nickel and iron. The powdered materials were screened for carbon dioxide adsorption using a thermogravimetric method and it was found that NiMgAl (Sample 1) hydrotalcite has the largest capacity for CO₂, adsorbing 1.58 mmol g⁻¹ at 20 °C, and highest rate of adsorption of up to 0.17 mmol g⁻¹ min⁻¹. This represented an increase of 53% in adsorption capacity, compared with NiMgAlFe (Sample 2). In order to improve the rheological behaviour of hydrotalcite paste for extrusion, hydrotalcite powders were combined with boehmite alumina (70:30 and 50:50 ratios of hydrotalcite:boehmite) before extrusion into pellets suitable for use in a fixed bed adsorber. These pellets were then re-crushed and further tested by thermogravimetric methods. The effects of temperature, composition and pre-treatment of the hydrotalcites on the adsorption of carbon dioxide and nitrogen are reported. At 20 °C, the amount of carbon dioxide adsorbed was between 2.0 and 2.5 mmol g⁻¹ for all the hydrotalcite/alumina samples in this study, although this decayed rapidly with increasing temperature. The results are compared with silica gel as a common sorbent reference, and with literature values. Hydrotalcite/alumina samples have thermal stability and a high adsorption capacity for carbon dioxide over a wide range of temperatures. The composition of the hydrotalcite/alumina pellets investigated in this study has less effect upon the adsorption behaviour compared with the non-calcined hydrotalcite powder, thus allowing a wide choice of pellet compositions to be used.     

Adsorption of carbon dioxide in plasma polymers prepared from silicon compounds and carbon dioxide separation membrane

Summary Three silicon compounds, dimethyldimethoxysilane (DMDMOS), decamethylcyclopentasiloxane (DMCPS), and 1,1,3,3-tetramethyldisiloxane (TMDSO), were plasma-polymerized, and the solubility coefficient and the permeation coefficient of carbon dioxide and nitrogen gas were determined. The permeation properties of the deposited films were discussed. The plasma polymers formed from DMDMOS, DMCPS, and TMDSO showed preferential solubility for carbon dioxide. The solubility coefficient of carbon dioxide was closely related to the concentration of Si-(O-)₄ moieties in the plasma polymers. However, these plasma polymers showed no selective permeation of carbon dioxide. The diffusion process rather than the solution process controlled the permeation of carbon dioxide across the plasma polymers. Plasma polymers formed from silicon compounds, if the polymers are less cross-linked, are expected to be a good material for CO₂-selective membrane.     

Adsorption of carbon dioxide onto PDA-CP-MS41 adsorbent

Carbon dioxide was adsorbed onto mesoporous adsorbent of PDA-CP-MS41, which was synthesized by CP-MS41 with propylene diamine, in a laboratory-scale packed-bed. Experiments were carried out at different adsorption temperatures (30–60 °C), amounts of adsorbent (1–3 g), and flow rates of nitrogen (15–60 cm³/min) to obtain the breakthrough curves of CO₂. These curves were tested by the deactivation model, which combined the adsorption of CO₂ and the deactivation of adsorbent particles. The adsorption rate constant and the deactivation rate constant were evaluated through analysis of the experimental breakthrough data using a nonlinear least squares technique. The experimental breakthrough data were fitted very well to the deactivation model than the adsorption isotherm models in the literature.     

Adsorption of gases on microporous carbons

A study has been made of the adsorption of nitrogen at ?195 °C, carbon dioxide at 78 °C and 22 °C and sulphur dioxide at 25 °C on a series of microporous active carbons. The amounts adsorbed were measured using conventional gas adsorption apparatus and the heats of adsorption were determined using the flow microcalorimeter.The nitrogen adsorption data were analysed using the three-parameter B.E.T. equation and the porosity interpreted using the V—t plot.It was found that the carbon dioxide isotherms at 22°C obeyed the Dubinin—Polanyi equation and the sulphur dioxide isotherms conformed to the Langmuir equation.The adsorption potentials calculated from the gradient of the Dubinin—Polanyi plots were shown to be in accord with the measured heats of adsorption. Applying the Clausius—Clapeyron equation to the Dubinin—Polanyi plots gave heats of adsorption very similar to the measured values.     

Adsorption properties of active carbon from lignin

Regularities of changing the adsorption characteristics of lignin-based active carbon (AC) with the temperature and time of activation with steam are studied. The extreme changes in the plots of the specific surface and adsorption activity with respect to methylene blue (MB) and iodine with maxima at 800°C are observed with an increase in the activation temperature from 400 to 900°C. The dependence of the AC yield on the activation time at 800°C indicates the presence of two regions of interaction of lignin with steam. The gasification rate in region I (τ_a up to 30 min) is by 33 times higher than that in region II (τ_a = 30–120 min), which is determined by different reactivities of structural fragments of two types. The gasification of the highly reactive structural fragments of the type I results in the formation of a porous system of AC, and their complete burning-out corresponds to limiting values of the specific surface and adsorption activity with respect to iodine. Subsequent activation is determined by the gasification of the structural fragments of the type II and leads to the formation of AC characterized by the maximum adsorption activity with respect to MB.     

离子液体作为CO2吸附剂的研究进展

离子液体(ILs)是完全由特定阳、阴离子构成的在室温或近于室温下呈液态的物质,是一类新型软功能材料或介质,CO2能与ILs发生强相互作用,在其中具有很高的溶解度。本文综述了CO2在传统离子液体、功能化离子液体、聚合离子液体及其他形式离子液体中的溶解度,讨论了CO2在离子液体中溶解度的影响因素以及计算机模拟在离子液体溶解CO2研究中的应用,指出了离子液体作为吸收剂的优缺点,展望了其代替传统CO2吸收剂的研究前景。     

Preparation of sulfur-doped microporous carbons for the storage of hydrogen and carbon dioxide

Structurally well ordered, sulfur-doped microporous carbon materials have been successfully prepared by a nanocasting method using zeolite EMC-2 as a hard template. The carbon materials exhibited well-resolved diffraction peaks in powder XRD patterns and ordered micropore channels in TEM images. Adjusting the synthesis conditions, carbons possess a tunable sulfur content in the range of 1.3–6.6 wt.%, a surface area of 729–1627 m² g^?1 and a pore volume of 0.60–0.90 cm³ g^?1. A significant proportion of the porosity in the carbons (up to 82% and 63% for surface area and pore volume, respectively) is contributed by micropores. The sulfur-doped microporous carbons exhibit isosteric heat of hydrogen adsorption up to 9.2 kJ mol^?1 and a high hydrogen uptake density of 14.3 × 10^?3 mmol m^?2 at ?196 °C and 20 bar, one of the highest ever observed for nanoporous carbons. They also show a high CO₂ adsorption energy up to 59 kJ mol^?1 at lower coverages (with 22 kJ mol^?1 at higher CO₂ coverages), the highest ever reported for any porous carbon materials and one of the highest amongst all the porous materials. These findings suggest that S-doped microporous carbons are potential promising adsorbents for hydrogen and CO₂.