Modeling Volatile Organic Compound Sorption in Activated Carbon. I: Dynamics and Single-Component Equilibrium

Design and development of new sorption technologies for control of volatile organic compound (VOC) laden air discharges from industrial sources require characterization of proposed novel processes and systems. Extensive capital, labor, and time are needed to obtain multicomponent adsorption characteristic data through laboratory experiments. As a substitute for laboratory characterization experiments, this paper presents steps for computationally predicting VOC sorption equilibrium and nonequilibrium processes in activated carbon. The method of predicting sorption equilibrium has been described in detail, since it is critical for modeling even nonequilibrium sorption dynamic processes that are constructed as successions of equilibria steps. An accurate single-component “thermal equation of equilibrium adsorption” (TEEA) is presented by modifying the Dubinin–Astakhov (DA) adsorption isotherm. DA-TEEA is capable of accurately predicting thermodynamics of single-component vapor adsorption in ultra- and supernanoporous adsorbents. The adsorption affinity factor, determined from dispersion interaction theory, enables the DA-TEEA to predict adsorption equilibrium characteristics of VOCs from adsorption equilibrium data of only one similar reference adsorbate.     

Mercury Adsorption Properties of Sulfur-Impregnated Adsorbents

Carbonaceous and noncarbonaceous adsorbents were impregnated with elemental sulfur to evaluate the chemical and physical properties of the adsorbents and their equilibrium mercury adsorption capacities. Simulated coal combustion flue gas conditions were used to determine the equilibrium adsorption capacities for Hg0 and HgCl2 gases to better understand how to remove mercury from gas streams generated by coal-fired utility power plants. Sulfur was deposited onto the adsorbents by monolayer surface deposition or volume pore filling. Sulfur impregnation increased the total sulfur content and decreased the total and micropore surface areas and pore volumes for all of the adsorbents tested. Adsorbents with sufficient amounts of active adsorption sites and sufficient microporous structure had mercury adsorption capacities up to 4,509 μg?Hg/g adsorbent. Elemental sulfur, organic sulfur, and sulfate were formed on the adsorbents during sulfur impregnation. Correlations were established with R2>0.92 between the equilibrium Hg0/HgCl2 adsorption capacities and the mass concentrations of elemental and organic sulfur. This result indicates that elemental and organic sulfur are important active adsorption sites for Hg0 and HgCl2.     

Adsorption of 1,1,1,2-Tetrafluoroethane by Various Adsorbents

Experiments have been conducted to investigate gas-phase adsorption characteristics of 1,1,1,2-tetrafluoroethane (HFC-134a) by activated carbon fiber, extruded activated carbon, granular activated carbon, activated alumina, and molecular sieve. HFC-134a is currently regarded as an excellent replacement for chlorofluorocarbon-12, a refrigerating and cooling agent extensively used previously in all automobiles and many cooling systems. Performances of HFC-134a adsorption were characterized by the equilibrium adsorption capacity, time to reach equilibrium, and desorption efficiency of exhausted adsorbent. A simple thermal treatment process with proper operating temperature and treatment duration was found to be effective for the regeneration of exhausted adsorbents. Adsorption isotherms of the empirical Freundlich and Jossens types were observed to adequately represent the equilibrium adsorption data. A mass transfer model based on the pseudo steady state squared driving force was adopted to describe the mass transfer process of HFC-134a adsorption.     

Adsorption of Carbon Disulfide (CS2) in Water by Different Types of Activated Carbon—Equilibrium, Dynamics, and Mathematical Modeling

Adsorption equilibrium and kinetics of carbon disulfide in water by granular activated carbon (GAC), powdered activated carbon (PAC), and activated carbon fiber (ACF) were investigated and compared in an effort to elucidate the fundamentals for optimizing the control process design. It has been shown that the BET expression can satisfactorily describe the adsorption equilibrium of carbon disulfide (CS2) on GAC, PAC, and ACF and the corresponding kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the CS2 adsorption is the rate-limiting step. A two-phase mathematical model was developed to simulate CS2 transfer in fixed-bed operation filled with the GAC, PAC, and ACF, and the equilibrium and kinetics information is subsequently used in the model to characterize the dynamics of adsorption. The model includes mechanisms such as axial dispersion, advection, liquid-to-solid mass transport, and intraparticle mass transport by pore and surface diffusion. It is manifested that the model was able to predict the dynamic breakthrough curve of CS2 in a fixed-bed adsorption column filled with GAC, PAC, and ACF at varied conditions (standard deviations for 1.5?cm/min is 12.13% and for 2.2?cm/min is 16.12%), based on BET-3 equilibrium and second-order kinetics, which indicates that the methodology proposed by this work could be employed for adsorbents selection, adsorption design, and process optimization for CS2 waste-water emission control.     

含氮有机物对活性碳纤维还原吸附银的影响

用H3PO4、ZnCl2等活化剂分别制备了两种化学活化的活性碳纤维（HPSACF和ZCSACF）,并通过水蒸汽活化制备了水蒸气活化活性碳纤维（SACF）。研究了它们对水溶液中Ag(NH3)2^ 的还原吸附性能,并与活性碳（AC）的还原吸附进行了比较。不同方法制备的活性碳纤维（ACF）对Ag(NH3)2^ 的还原吸附能力有显著的差异,以磷酸活化法制备的ACF的还原能力最强,而AC有一定的还原吸附能力。含氮有机物的吸附对活性碳纤维或活性碳的还原吸附能力有很大的影响,一般而言,吸附至碳吸附剂上的对硝基苯酚和苯胺可促进AC、SACF和HPSACF的还原能力,且苯胺的促进作用大于硝基苯酚的促进作用。     

Adsorption on Carbon and Zeolite of Pollutants from Flue Gas during Incineration

The volatile organic compound, polycyclic aromatic hydrocarbon, dioxin, and metallic components released from incineration threaten human health. These pollutants, appearing in a molecular state, cannot be effectively removed by baghouse and electrostatic precipitators through capture and filtration mechanisms. Previous studies indicate that activated carbon is conventionally used to remove organic compounds from gas at low temperatures (less than 30°C). However, the adsorption characteristics of organic compounds from a gas phase at high temperatures (over 120°C) are seldom mentioned. Moreover, the complex compositions of flue gas cause the adsorption characteristics of organic compounds and heavy metals on adsorbent tubes to be more complicated. This research examines the adsorption characteristics of organic compounds and heavy metals at various incineration conditions. The evaluated parameters include: (1) the operating temperatures; (2) the characteristics of adsorbents (activated carbon and zeolite); and (3) waste compositions and the presence of heavy metals. The results indicate that activated carbon has a high adsorption capacity compared with zeolite.     

Equilibrium Adsorption of Phenol-, Tire-, and Coal-Derived Activated Carbons for Organic Vapors

Adsorption isotherms for alkane, aromatic, and ketone vapors were determined for activated carbon fiber cloth, tire-derived activated carbon and coal-derived activated carbon adsorbents. Physical and chemical properties of the vapors and adsorbents were used to interpret these results that were obtained from 20 to 50°C, with a more limited data set at 125 and 175°C and relative pressures between 0 and 0.99. Fitted isotherms using the Freundlich and Dubinin–Radushkevich adsorption models had mean total relative errors <5.6 and 9.2% for the microporous and mesoporous/macroporous adsorbents, respectively, at the temperature range from 20 to 50°C. The predictive direct quantitative structure activity relationship model had mean total relative errors <9.7 and 61% for the microporous and mesoporous/macroporous adsorbents, respectively, at the temperature range from 20 to 50°C without requiring experimental input.     

Adsorption Equilibrium Modeling of Space Station Wastewaters

An adsorption equilibrium model was developed for predicting the total organic carbon (TOC) removal by the International Space Station water processor's multifiltration beds. Ideal adsorbed solution theory is used to describe the competitive interactions between fictive components (FCs) that make up the TOC. The FC physical properties were based on several identified compounds to represent the distribution adsorbing compounds in the wastewaters. The TOC isotherms were performed using the wastewaters on three absorbents (a coconut-based granular activated carbon, a coal-based granular activated carbon, and a polymeric-based resin), which are contained in the multifiltration beds. The isotherms were used to validate the model for all three adsorbents. The FCs were determined in such a way that they can describe the TOC concentration for multiple beds in series.     

Modeling of Adsorption and Regeneration of Volatile Organic Compounds on Activated Carbon Fiber Cloth

A mathematical model is developed to predict continuous adsorption-regeneration cycling of volatile organic compounds (VOCs) on activated carbon fiber cloth (ACFC) at the indoor VOC concentration levels. The adsorption-regeneration model incorporates both the adsorption equilibrium and mass transfer fundamentals. It assumes local equilibrium between the gas-phase and the solid-phase, and axially dispersed-flow, film transfer, and intraparticle transport by surface and pore diffusion. Successful agreement between model simulations and experimental data was obtained and the kinetic properties of the adsorption/regeneration cycling on the ACFC were characterized. For the adsorption process, the film transfer is the dominant factor for mass transfer at low flow rates (45–184 L/min), and the intraparticle mass transfer rate controls over the gas-phase rate as the flow rates increase. The regeneration concentration profiles are most sensitive to the adsorption isotherms at the temperatures of interest, especially as desorption is initiated. The surface diffusivity also contributes to the shape of the regeneration profile: the tailing of desorption profile shifts up with the increase of surface diffusivity.     

Capacity of Activated Carbon Derived from Peach Stones by K2CO3 in the Removal of Acid, Reactive, and Direct Dyes from Aqueous Solution

The present research deals with the production of activated carbon by chemical activation using peach stones and its adsorption behavior. The prepared activated carbon was used for the adsorption of three kinds of textile dyes, acid, reactive, and direct dyes, from aqueous solution. The results indicated that the overall adsorption process followed the pseudo-second-order kinetic model. The equilibrium data were found to be well represented by the Langmuir adsorption isotherm model. The calculated adsorption capacities for Reactive Orange 16, Acid Yellow 11, and Direct Red 23 onto activated carbon were 667, 539, and 427?mg?g?1 at 50°C, respectively. Thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were also calculated and indicated that the adsorption of dyes onto activated carbon was spontaneous and endothermic in nature.     

Modeling Volatile Organic Compound Sorption in Activated Carbon. II: Multicomponent Equilibrium

A new approach is presented for modeling multicomponent volatile organic compound (VOC) sorption equilibrium in ultra- and supernanoporous activated carbons. The model uses “Dubinin–Astakhov thermal equation of equilibrium adsorption” (DA-TEEA) for single-component adsorption thermodynamics and “ideal/real adsorbed solution theories” (IAST/RAST) for the multicomponent mixing rules. Use of the Henry’s Law adsorption isotherm resolves the singularity of DA-TEEA at zero-coverage conditions. The introduced method predicts multicomponent adsorption equilibria of VOCs based on equilibrium data of only one similar component. Single and binary adsorption equilibria of acetone and benzene vapors in Kynol ACFC-5092-20 activated-carbon-fiber-cloth adsorbents are predicted with the presented models and compared with modeled and measured characterization data available in the literature. The Wilson model for nonideal binary solution mixtures is used to predict the activity coefficients needed in DA-TEEA/RAST. Modeled results are compared against measured characterization data. The selected Henry’s Law upper-bound pressure (HUBP) is found to be an important factor controlling the accuracy of the multicomponent equilibrium models. An optimum HUBP can generate highly accurate results from both DA-TEEA/IAST and DA-TEEA/RAST. The accuracy realized by applying this method to acetone–benzene mixtures is sufficient for engineering design and development purposes.     

Thermal Behavior of Activated Carbon Cloths Heated by Joule Effect

Activated carbon cloths (ACC) are promising adsorbents for the treatment of air loaded with volatile organic compounds (VOC). Their characteristics and properties allow them particularly high adsorption capacities and useful handling. Moreover, the Joule effect regeneration of these media may be used as a regeneration process. These peculiarities make it possible to design and size ACC filters for a wide range of industrial applications: low VOC concentration and flow for indoor air quality as well as high concentration and flow in some industrial effluents. Hence, innovating reactors could be equipped with such an adsorption-desorption process which permit us to recover the condensed compounds. The heating of ACC by Joule effect (between 20 and 250°C) is generally highly homogeneous, and the spatial distribution of the temperatures is directly connected to the activation level distribution in the material. A characterization method and a modeling approach are proposed to describe the ACC thermal behavior and to compare and select the best media in term of regeneration process. This allows sizing of future industrial processes.     

Neural Network Modeling of Organics Removal by Activated Carbon Cloths

The adsorption of organic compounds onto an activated carbon cloth is studied in a dynamic reactor. An experimental design is carried out to investigate the influence of operating conditions (initial concentration C0, flow velocity U0, and bed thickness Z) and adsorbate's characteristics. A slow intraparticular diffusion is shown by flattened breakthrough curves, and adsorption capacities are high and range between 50 and 250 mg g?1. The transfer zone Z0, assessed by the Adams and Bohart equation, is low (3 mm). All experimental results are modeled by a neural network to take into account the specific diffusion of cloths. Parameters related to the adsorbate-adsorbent affinity in a batch reactor are consequently introduced in the input layer of the neural network (intraparticular coefficient Kw and Freundlich parameters Kf and l∕n), added to operating conditions whose influence was shown (C0, U0, and Z) and time t. The statistical quality of the neural network modeling is high (r2 = 0.956). Furthermore, the Garson connection weight method allows the relative influence of input neurons to be determined. This analysis confirms the influence of parameters relative to adsorbant-adsorbate affinity.     

Different Approaches for the Development of Low-Cost CO2 Adsorbents

Different carbon materials were tested as precursors for the production of CO2 adsorbents. The chemical modification of the surface of the prepared adsorbents was studied by means of three different approaches: impregnation with amines, electrophilic aromatic substitution, and heat treatment in the presence of ammonia. The samples were chemically characterized and the porous texture was evaluated from the N2 adsorption isotherms at ?196°C. The CO2 adsorption capacities of the adsorbents at 25 and 100°C were evaluated in a thermogravimetric analyzer. In general, the incorporation of basic nitrogen functionalities enhanced the CO2 capture capacities of the modified carbons, but this increase depended on the textural properties of the support and the surface modification methodology. CO2 adsorption capacities of up to 111?mg CO2/g at room temperature were attained. All the tested samples were completely regenerated when subjected to heat treatment at 100°C under inert atmosphere.     

活性炭钎维织物(炭布)在氰化液中吸附金银直接电解金试验研究

以国产活性炭纤维织物(炭布)代替活性炭吸附氰化液中的贵金属,本文主要研究了活性炭布吸附金、银的特性,即吸附速度和吸附容量与活性炭的比较;活性炭布与活性炭耐磨性的比较;活性炭布在氰化液中吸附金、银后做为阳极直接电解金的可能性的研究;电解后的炭布活化再生的研究。试验证明了活性炭布比颗粒活性炭吸附金、银具有许多优点;吸附容量大,吸附速度快,金属回收率高,使用寿命长,吸附了金、银的炭布可做为阳极直接电解金,省去了解吸工序,降低了成本。     

载铝改性活性炭纤维电吸附水中Cr(Ⅵ)

以活性炭纤维、异丙醇铝为原料,通过溶胶—凝胶法制备载铝改性活性炭纤维电极(ACF-Al),通过单因素和正交试验研究其对模拟废水中Cr(Ⅵ)的电吸附性能;采用XRD、FTIR、SEM对电极材料进行表征;达到吸附平衡后对电极进行再生。试验结果表明,电吸附Cr(Ⅵ)适宜工艺条件为:模拟废水初始浓度40mg/L、pH=2.5、电极电位0.3V、极板间距6mm、ACF-Al电极板面积100cm^2,Cr(Ⅵ)吸附率接近100%,比开路条件下提高了26.25个百分点;电吸附过程更符合Langmuir等温线模型和准二级动力学方程;对ACF-Al电极进行4次循环再生处理后,其对Cr(Ⅵ)的吸附率仍保持在87%以上。表征结果显示,活性氧化铝被成功负载到活性炭纤维表面,提高了其导电性,增强了Cr(Ⅵ)向电极板的定向迁移性,并在表面羧基、羟基等官能团的作用下,使Cr(Ⅵ)得到有效去除。     

气相多环芳烃的吸附净化技术研究进展

多环芳烃（PAHs）是近年来在大气污染问题中逐渐受到关注的一类污染物,不仅其自身严重威胁着人体健康,还可作为低挥发性物质促进二次颗粒物的生长.世界多国开始不断通过各种技术手段对废气中PAHs的排放进行控制,PHAs已成为大气环境领域共同关注的热点问题.吸附法是最具潜力且已被工业应用认可的一类PAHs控制净化关键技术,吸附剂对PAHs的吸、脱附性能是其中的关键.目前国内外学者无论是基于传统碳类吸附剂,还是新型的介孔吸附剂,都针对此类特殊低挥发性气体的吸附相平衡、动力学以及脱附特性做了相关研究,探悉了获取PAHs吸脱附最优平衡的关键因素以及最适吸附剂.本文针对这些结果及相关应用进行了综述,对比分析了介孔吸附剂较传统吸附剂在PAHs吸脱附特性上呈现的优势,旨在为PAHs及其他低挥发性气体吸附净化的相关工作提供有效参考.      

Axial Dispersion and Mass Transfer Controlled Simulation Study of Chromium (VI) Adsorption onto Tree Leaves and Activated Carbon

In this paper, the feasibility and efficacy of chromium (Cr(VI)) removal using three different kinds of tree leaves viz. Emblica officinalis, Azadirachta indica, Eucalyptus agglomerata, and the activated carbon is examined through batch and continuous flow experiments. Pretreatments were given to the selected tree leaf powders to remove the natural pigments and lignin present. Batch and continuous flow experiments have been conducted to study the kinetics of adsorption, effects of pH, adsorbent dose, contact time, bed depth, flow rate, and initial Cr(VI) concentration on Cr(VI) adsorption onto the selected adsorbents. The adsorption capacity is observed higher for Emblica officinalis followed by Eucalyptus agglomerata and Azadirachta indica. The adsorption equilibrium is reached in less than 30 min and the maximum Cr(VI) uptake occurred at pH 3.0 under the test conditions. The results are also compared with the commercially available activated carbon. A mathematical model incorporating diffusion, advection, and mass transfer mechanisms available in the literature has been simplified and is then tested to simulate the laboratory and literature data. A simple method for the determination of saturation Cr(VI) concentration along the length of column has been presented. The study reveals that the model incorporating the molecular diffusion and the mass transfer mechanisms simulates better the Cr(VI) adsorption onto tree leaf powders than the literature model and the advection term plays only a negligible role due to low flow rates applied during the experiments. The model parameters, i.e., axial dispersion coefficient, “DL” and the external mass transfer coefficient, “kf” are found in the order of 10?5–10?6?m2/s and 10?9–10?11?m/s, respectively.     

改性兰炭烟气SO2吸附材料的制备及其再生性能

利用活性炭（焦）等吸附剂将烟气中的污染物分离出来是一种有效的烟气治理与资源化方式。兰炭作为一种廉价半焦碳素材料,是一种有潜力代替现有商用活性焦的多孔材料。本文采用陕西兰炭作为研究对象,研究炭化时间、炭化温度、黏结剂添加量等改性工艺对所制备的吸附剂性能的影响,考察了微观形貌变化,利用X射线光电子能谱（XPS）探究在吸附解吸过程中的表面官能团的变化。结果表明,炭化温度对耐磨强度、耐压强度指标影响显著,炭化时间对饱和脱硫值和穿透脱硫值影响显著;在煤焦油添加比例50%,700 ℃炭化20 min,900 ℃活化60 min条件下制得改性兰炭参数为:耐磨强度95.81%,抗压强度536.1 N·cm?1,每克兰炭饱和脱硫值45.71 mg,每克兰炭穿透脱硫值23.45 mg;经历多次吸脱附过程第一次失活时,表面被大面积刻蚀,孔隙与小颗粒增多。兰炭吸附剂失活后可以通过二次活化的方式提高其吸附性能,但衰减速度比新改性兰炭要快。二次失活后,在酸蚀刻、水蒸气扩孔等共同作用下致使骨架结构过度烧蚀而坍塌;改性兰炭表面含氧基团的量和构成比例会影响吸附性能。含氧与含碳基团的比值与吸附性能相对应,含氧基团比例越高,吸附性能越差。二次活化再生改变了各含氧基团所占比例,令C=O显著下降,O?C=O显著增加,C?O变化不大。O?C=O官能团尽管含氧,但可能对吸附抑制作用不显著。本研究将为工业烟气治理提供一种新型吸附剂的制备方法,同时也为兰炭表面改性以及二氧化硫吸附解吸机制的研究提供参考。      

Effect of rare earth addition on Cu-Fe/AC adsorbents for phosphine adsorption from yellow phosphorous tail gas

Phosphine(PH3) is a highly toxic air pollutant,commonly produced in phosphorous chemical industry.But it has received less research attention due to its handling difficultly.CO is the main content of the phosphorous chemical industry tail gas,the concentration of which is always more than 80 vol.%,and it can be the feed gas to produce various valuable products such as formate,oxalate,and methanol and so on.But,PH3 is one of the important barriers,which is harmful to the following chemical process.In order to make use of the tail gas,PH3 should be removed firstly,and CO should be covered in the whole purified procedure at the same time.In this work,the modified activated carbon(MAC) was used as the adsorbent to separate PH3 from the mixture tail gas.Series of MAC adsorbents were prepared for the adsorption of PH3,which loaded Cu-Fe and Ce(La),or separately.The PH3 adsorption capacities,chemical and physical properties of MAC were all investigated.The results showed that over 99% PH3 adsorption efficiency was achieved when used MAC adsorbents.The removal efficiency and PH3 adsorption capacity of the Cu-Fe-Ce/AC(20:1:0.4) were both much higher than those modified activated carbons.The maximum PH3 adsorption capacity was 71 mg of PH3/g of MAC on the Cu-Fe-Ce/AC,which were much higher than literature data using CuO only for adsorbing hydride gases.