不同孔径活性炭吸附挥发性有机物的分子模拟

借助Materials Studio软件建立了0.902nm、1.997nm、3.000nm、4.000nm孔径的活性炭狭缝孔模型,采用巨正则蒙特卡洛模拟（Grand Canonical Monte Carlo）的模拟方法计算了其对挥发性有机物（VOCs,如异己烷、苯、甲苯、丙酮和甲醇）的吸附数据,考察了活性炭孔径的变化对VOCs吸附性能的影响,并对实际应用进行指导。模拟结果显示：活性炭对VOCs的吸附受孔径和吸附能的共同影响,在293.15K、各物质饱和蒸气压p₀下,随着孔径的增大,吸附质吸附剂之间的亲和力呈下降趋势。活性炭孔径由0.902nm增加到4.000nm对异己烷、苯、甲苯的饱和吸附量逐渐增大,而4.000nm孔径活性炭对丙酮饱和吸附量小于3.000nm孔径活性炭,3.000nm、4.000nm孔径活性炭对甲醇饱和吸附量小于1.997nm孔径活性炭。在工业废气VOCs吸附回收中选择0.902～1.997nm孔径活性炭能够达到最佳效果。     

Removal of volatile organic compounds by cryogenic condensation followed by adsorption

Removal of volatile organic compounds (VOCs) from gaseous effluents by cryogenic condensation and adsorption has been studied. Mathematical models have been developed to predict the extent of removal of a binary mixture of VOCs in air by these two methods under a wide range of operating conditions. The model results are verified with the published work. A model parametric study carried out in this work suggests that if the concentrations of VOCs in the effluent stream vary over a wide range, condensation followed by adsorption is an effective technique to control the emissions. Condensation is found to be suitable if the VOCs emission levels are high (>1%). On the other hand, if the emission levels are low i.e. parts per millions (ppm) or sub ppm, adsorption is a preferred technique for removing the VOCs from the effluent stream. The model results in this work have significance from the perspective of understanding the mechanism of removal of VOCs by these two methods, determining the key operating parameters that control the removal process and also, defining an effective VOC control strategy.     

Adsorption of volatile organic compounds by means of activated carbon fibre-based monoliths

Activated carbon fibre monoliths (ACFMs) were prepared from the rejects of polymeric fibres (Nomex™). These were carbonised, agglomerated with a phenolic resin and steam activated at burnoff degrees between 0 and 40%. Adsorption experiments with n-butane at 30 °C show that, at high adsorbate concentrations, the amount adsorbed is a function of pore volume, but at low concentrations this mainly depends on pore size distribution. The porosity of Nomex-based ACFMs is formed by narrow micropores, which permit higher amounts of vapour to be adsorbed in low concentrations compared to monoliths prepared from different commercial activated fibres and a commercial granular activated carbon, which exhibits wider pores. The agglomeration of Nomex-fibres to form ACFMs does not cause any loss in adsorption properties with respect to non-agglomerated activated fibres. From the adsorption experiments of different vapours on a Nomex-based ACFM (40% burnoff) it was found that at high concentrations (p/p_o=1) the adsorbed volume was independent of the nature of the adsorbate and depended only on pore volume. However, at low vapor concentrations (p/p_o=0.004), the amount adsorbed depended on the adsorbate being well correlated to the molecular parachor and the polarizability of the adsorbates     

Liquid and vapor phase adsorption of chlorinated volatile organic compounds on hydrophobic molecular sieves

This work focused on the potential application of various hydrophobic molecular sieves for the sorption of four model chlorinated volatile organic compounds (CVOCs, i.e., chloroform, trichloroethylene, tetrachloroethylene, and carbon tetrachloride) from dilute liquid water streams.

Results obtained thus far have shown that silicalite-1 has a high affinity for these CVOCs, higher in fact than Centaur^® activated carbon, used as a benchmark in this study. Loading results for trichloroethylene from both liquid and vapor phase indicated that the liquid phase did not penetrate the pores of silicalite-1, while the solution did penetrate the pores of Centaur^® and a dealuminated NaY used for comparison.

Finally, three definitions from the literature for the “hydrophobicity” of molecular sieves were considered. An alternative definition for hydrophobicity is introduced here, which is easy to determine and is based on water retention.     

挥发性有机化合物催化氧化技术

基于环境友好,对使用催化氧化法去除挥发性有机化合物(VOCs)的原理、特点以及催化剂、工艺流程等研究进行综述。挥发性有机化合物完全催化氧化机理分为:Mars-van Krevelen(MVK)模型、Langmuir-Hinshelwood(L-H)模型和Eley-Rideal(E-R)模型。复合金属氧化物催化剂是研究的热点,去除VOCs的核心是使反应温度降低,即具有低温和高活性的催化剂。延长催化剂寿命、提高去除效率也可以带来良好的节能效果和降低投资成本。对于低浓度和大体积VOCs排放,可通过吸附+催化混合法先进技术实现去除,且成功应用于实践。     

活性炭吸附法在挥发性有机物治理中的应用研究进展

挥发性有机化合物(VOCs)是一类重要的大气污染物,其所带来的环境污染问题已经引起全世界的关注.活性炭吸附法是治理VOCs污染的有效手段.本文从介绍VOCs治理技术出发,简述了活性炭吸附法在VOCs治理中的使用现状,概括了活性炭吸附法治理VOCs的工艺技术和存在问题,指出变温-变压吸附、变电吸附以其高效节能环保的优点,在VOCs治理中具有较好的发展前景.分析了活性炭表面化学性质、吸附质的物性、操作条件对活性炭吸附法治理VOCs的影响,为VOCs治理专用活性炭的改进和新产品的开发,提供了理论依据.在总结现有研究进展的基础上,预测了活性炭吸附法治理VOCs技术的发展趋势,提出对工艺的改进以及与其他VOCs废气处理技术的耦合使用,针对不同VOCs排放场所开发不同活性炭品种和VOCs回收装置将是以后研究的重要方向.     

活性炭纤维吸附挥发性有机化合物的研究进展

简述了挥发性有机化合物、活性炭纤维以及活性炭纤维吸附挥发性有机化合物的机理及其优点,重点介绍国内外关于活性炭纤维吸附挥发性有机化合物的研究进展。活性炭纤维凭着自身显著的优点,在吸附挥发性有机化合物方面具有很大的潜力。     

Utilization of Crofton weed for preparation of activated carbon by microwave induced CO2 activation

Crofton weed was converted into a high-quality activated carbon (CWAC) via microwave-induced CO₂ physical activation. The operational variables including activation temperature, activation duration and CO₂ flow rate on the adsorption capability and activated carbon yield were identified. Additionally the surface characteristics of CWAC were characterized by nitrogen adsorption isotherms, FTIR and SEM. The operating variables were optimized utilizing the response surface methodology and were identified to be an activation temperature of 980 °C, an activation duration of 90 min and a CO₂ flow rate of 300 ml/min with a iodine adsorption capacity of 972 mg/g and yield of 18.03%. The key parameters that characterize quality of the porous carbon such as the BET surface area, total pore volume and average pore diameter were estimated to be 1036 m²/g, 0.71 ml/g and 2.75 nm, respectively. The findings strongly support the feasibility of microwave heating for preparation of high surface area porous carbon from Crofton weed via CO₂ activation.     

A mini-review on the modeling of volatile organic compound adsorption in activated carbons: Equilibrium,dynamics, and heat effects

The research on the adsorption equilibria, kinetics, and increase in process temperature of the volatile organic compound (VOC) adsorption in porous materials ensures safe production, thereby reducing production costs and improving separation efficiency. Therefore, it is critical in predicting the entire adsorption process based on minimal or no experimental input of the adsorbate and adsorbent. We discuss, in this review, the factors that affect the adsorption performance of VOCs in activated carbons, including the adsorption equilibrium, adsorption kinetics, and exotherm during adsorption. Subsequently, the existing prediction models are summarized and compared concerning the adsorption equilibrium, adsorption kinetics, and exothermic process of adsorption. We then propose a new prediction model based on intermolecular interaction and provide an outlook toward the design and manipulation of efficient adsorbents for the VOC system.     

顶空气相色谱法测定烟用胶粘剂中的有机挥发物

采用顶空气相色谱法对烟用胶粘剂中的有机挥发物（甲醇、丙酮、乙酸甲酯、叔丁醇、乙酸乙烯酯、乙酸乙酯）进行分析,讨论了气相色谱柱的升温方式、顶空平衡温度、平衡时间、胶粘剂加入量对分析结果的影响,从而获得优化的检测工艺参数。该检测方法对上述六种有机挥发物的线性范围分别为甲醇0～400礸,丙酮0～40礸,乙酸甲酯0～92礸,叔丁醇0～32,乙酸乙烯酯,0～75礸,乙酸乙酯0～45礸;测定结果的相对标准偏差为0.6%～2.7%;样品的回收率为90.8%～104.2%;可用于烟用胶粘剂中有机挥发物的分析,方法简便、快速、重现性好。     

微波加热核桃壳制取活性炭及孔结构表征

以核桃壳为原料,采用微波加热-水蒸汽活化法制备了活性炭。研究了微波功率、活化时间和水蒸汽流量等因素对吸附性能的影响。最佳工艺条件为：微波功率600 W、活化时间7 min、水蒸汽流量5 mL/min,活性炭产品的碘吸附值1076．57 mg/g,亚甲基蓝吸附值195 mg/g,得率25．11%。该工艺将常规加热方法的炭化和活化简化为一个过程,所需加热时间仅为传统方法的1/21,产品活性炭的亚甲基蓝吸附值为国家一级品标准的1．44倍。同时测定了该活性炭的氮吸附等温线,通过BET计算了活性炭的比表面积,并通过H—K方程和密度函数理论表征了活性炭的孔结构。结果表明,该活性炭为微孔型,BET 比表面积1 154．91 m~2/g,总孔体积0．564 9 mL/g,微孔占总孔体积(体积分数,下同) 79．86%,中孔体积分数19．97%,大孔占0．17%。     

Removal of volatile organic compound by activated carbon fiber

Experiments were carried out to study adsorption/desorption of volatile organic compound (VOC) on the activated carbon fiber (ACF) under dynamic conditions. The primary objective was to experimentally demonstrate the suitability of ACF in effectively adsorbing VOCs from inert gaseous stream under varying operating conditions, and compare its performance vis-à-vis that of the other commercially available adsorbents, such as granular activated carbon (GAC), silica gel, and zeolites. The adsorption experiments were carried out in a fixed tubular packed bed reactor under various operating conditions including temperature (35-100 °C), gas concentration (2000-10,000 ppm), gas flow rate (0.2-1.0 slpm) and weight of the adsorbent (2-10 g). A mathematical model was developed to predict the VOC breakthrough characteristics on ACF. The model incorporated the effects of the gas-particle film mass transfer resistance, adsorbent pore diffusion and the adsorption/desorption rates within the pore. The experimental data and the corresponding model simulated results were compared and found to be in good agreement. The ACF repeatedly showed a good regeneration capability following desorption by DC electrical heating.     

沸石分子筛用于VOCs吸附脱除的应用研究进展

挥发性有机化合物（volatile organic compounds,VOCs）作为空气中有机污染物的主要成分,对环境与人类健康造成了严重的危害。吸附法可有效富集低浓度VOCs气体,成本低、易操作,是末端治理去除VOCs的主要技术。沸石分子筛具有高度有序、孔径可调的微孔孔道,可实现VOCs分子的选择性吸附,且热稳定性极佳,易于脱附再生,是一种优良的VOCs气体吸附剂。本文分别从沸石分子筛的结构性质、复合型分子筛吸附剂以及整体式分子筛吸附剂三方面详细介绍了沸石分子筛用于VOCs吸附脱除的研究进展。结果表明,变换骨架拓扑结构以及补偿阳离子类型,可实现对VOCs分子进行选择性吸附;提高结构疏水性可有效降低高湿度条件下水分子对VOCs的竞争吸附,增强分子筛吸附剂的环境适应性;通过孔道多级化或与其他介/大孔构建复合型吸附剂,可提高分子筛吸附剂的比表面积和孔容,增大对VOCs的吸附容量;沸石分子筛可构建为整体式吸附剂,相较于颗粒型吸附剂,其机械强度更高,应用性更强。文章还指出,作为整体式分子筛吸附剂的典型代表,分子筛转轮吸附技术在高通量、高压降等吸附工况条件下均表现出极佳的VOCs吸附脱除效率,已广泛应用于工业排放VOCs的有效治理。     

Effects of activated carbon surface chemistry and pore structure on the adsorption of organic contaminants from aqueous solution

The objective of this research was to develop activated carbon selection criteria that assure the effective removal of trace organic contaminants from aqueous solution and to base the selection criteria on physical and chemical adsorbent characteristics. To systematically evaluate pore structure and surface chemistry effects, a matrix of activated carbon fibers (ACFs) with three activation levels and four surface chemistry levels was prepared and characterized. In addition, three granular activated carbons (GACs) were studied. Two common drinking water contaminants, relatively polar methyl tertiary-butyl ether (MTBE) and relatively nonpolar trichloroethene (TCE), served as adsorbate probes. TCE adsorbed primarily in micropores in the 7-10 Å width range while MTBE adsorbed primarily in micropores in the 8-11 Å width range. These results suggest that effective adsorbents should exhibit a large volume of micropores with widths that are about 1.3 to 1.8 times larger than the kinetic diameter of the target adsorbate. Hydrophobic adsorbents more effectively removed both TCE and MTBE from aqueous solution than hydrophilic adsorbents, a result that was explained by enhanced water adsorption on hydrophilic surfaces. To assure sufficient adsorbent hydrophobicity, the oxygen and nitrogen contents of an activated carbon should therefore sum to no more than about 2 to 3 mmol/g.     

Removal of thiophenic compounds from liquid fuel by different modified activated carbon cloths

The adsorption behavior of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from n-heptane was investigated onto activated carbon cloth (ACC) and its modified forms at 30 °C in batch condition. ACC was modified by HNO₃, (NH₄)₂S₂O₈, H₂SO₄, HCl and NaOH at ambient temperature. The adsorbents were characterized using nitrogen adsorption/desorption. It was found that the adsorbents are mainly microporous but differ in their surface chemistry, which is related to the effect of oxidizing agent. The adsorption process was studied from both equilibrium and kinetics point of view. The equilibrium experimental data were fitted to the Langmuir, Freundlich and Langmuir-Freundlich by non-linear method. Among the tested adsorbents, the modified ACC with HNO₃ (ACC-HNO₃) had the highest capacity for adsorption of DBT. Kinetic characterization of the adsorption process indicated that the mixed-order and modified pseudo-n-order models can describe the kinetics of adsorption of thiophenic compounds onto ACCs. The ACC and ACC-HNO₃ were used to test the removal efficiency of total sulfur contents (BT, DBT and DMDBT, 150 ppmw for each of them), too. The effect of shaking and ultrasound methods and also temperature and time on the regeneration of saturated ACC-HNO₃ with DBT was studied.     

挥发性有机化合物催化消除前沿技术及研究进展

挥发性有机化合物(VOCs)是可吸入有害物质形成的重要前体,是大气污染物的重要组成部分。催化氧化法作为末端技术是目前处理VOCs最有效的途径之一。本文讨论了VOCs的热催化氧化、光催化氧化和光热协同催化氧化的研究进展,重点研究常用VOCs的催化氧化机理以及相关催化剂的构筑。其中,热催化燃烧主要以贵金属(Pt、Pd、Au、Ag等)、过渡金属(Mn、Co、Cr等氧化物)及复合型催化剂研究展开;光催化氧化以TiO₂和C₃N₄为典型催化剂进行讨论;光热协同催化研究主要包括碳基催化剂、贵金属负载型以及过渡金属负载型催化剂的开发与应用。此外,本文对基于催化剂的热催化、光催化和光热催化去除VOCs的开发和研究提出了进一步的展望。     

Sorption and diffusion of volatile organic compounds in polydimethylsiloxane membranes

Sorption and diffusion of ethanol, 1,1,1-trichloroethane (TCA), and trichloroethylene (TCE) were investigated in polydimethylsiloxane (PDMS) membranes using a gravimetric technique. The thermodynamic equilibrium and kinetic properties were evaluated at temperatures of 25, 100, and 150°C. The sorption isotherms for TCA and TCE can be correlated well using the Flory-Huggins model. However, a three parameter Koningsveld-Kleinjtens variation to the Flory-Huggins equation is required for correlation of the ethanol isotherm. The solubility coefficients of TCA and TCE increase with activity, but it remains almost constant for ethanol. The calculated sorption energies reveal high positive heat of mixing for ethanol. TCA and TCE sorption in PDMS decreases strongly with temperature as opposed to ethanol. Clustering function analysis is used to explain the anomalous ethanol sorption and diffusion behavior in PDMS. TCA and TCE diffusivities do not exhibit large variations with volatile organic compound activity. However, ethanol demonstrates a maxima in its diffusivity at activities where it has minimum clustering tendencies. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 165–175, 1998     

建筑涂料中挥发性有机物含量的测定

采用气相色谱法测定建筑涂料中挥发性有机物的含量,进行了大量的实验与研究。测定结果表明,水分测定相对偏差为0.03%~0.05%,挥发性有机物相对偏差0.3%~0.5%,加标回收率98%~102%。该方法准确可行,适用于各种建筑涂料样品的生产和监控。