Modeling of Drying of Gaseous Mixtures in TSA System with Fixed Bed of Solid Desiccants

A nonisothermal, nonequilibrium mathematical model was developed to theoretically analyze adsorptive drying of gaseous mixtures containing water and volatile organic compounds (VOCs). The analysis concerns a four-bed cyclic temperature swing adsorption (TSA) system. The two fixed beds are formed of silica gel primarily as the water vapor adsorbent. The other two consist of activated carbon as the adsorbent of the organic component (e.g., benzene, isopropanol). In the model, possible insignificant interactions among the VOCs and water during adsorption and desorption were neglected. The following parameters were considered to study their effect on the process efficiency: relative humidity of the inlet gas, temperature of the purge gas, and height of the adsorbent beds. Simulation results showed that both the shape of the adsorption isotherm and heat effects played an important role in the breakthrough behavior of water vapor adsorption on silica gel. The model accurately simulated experimental data taken from literature.     

变压吸附处理二组分有机废气

变压吸附(PSA)处理挥发性有机气体是一个新的领域。以活性炭CAN-230为吸附剂,采用两塔三步骤变压吸附过程对甲苯、二甲苯混合气体进行处理,考察了脱附压力、湿度等因素对处理效果的影响以及甲苯、二甲苯之间的相互影响。结果表明:采用常压吸附、真空脱附的变压吸附过程处理甲苯、二甲苯二组分废气时,脱附压力不宜高于0.03 MPa;相对湿度在50%以下时,对处理效果的影响不大,当相对湿度大于60%时,水蒸汽对有机气体的吸附有很强的抑制作用,净化气的浓度随湿度增大而增大;甲苯、二甲苯之间存在竞争吸附,进气中一种物质浓度的增大会使得另一种物质在净化气中的浓度升高。     

复合吸附剂MWCNT/MgCl2的水蒸气吸附性能

通过研磨将多壁碳纳米管分别与质量分数为30%、40%和50%的无水氯化镁复合,制备了3种不同配比的复合吸附剂MWCNT/MgCl₂。采用数字化扫描电子显微镜（SEM）观察复合吸附剂表面材质的结构样貌,通过Hot Disk热常数分析仪测得复合吸附剂的热导率,使用恒温恒湿箱选取具有代表性的温湿度,测试复合吸附剂在不同工况下的水蒸气吸附性能,并采用准二级动力学模型对25℃、50% RH工况下的实验数据进行拟合,应用Autosorb-IQ全自动气体分析仪测试了三种样品在25℃下的等温吸湿曲线。实验结果表明,相同温湿度工况下,随着氯化镁含量增加,复合吸附剂的吸附量提高,25℃、50% RH下氯化镁含量为30%、40%和50%的复合吸附剂M1、M2和M3的吸附量分别为0.62、0.79和0.94 g/g;恒定湿度为50% RH,温度变化为15~35℃时,复合吸附剂吸附量受温度和饱和水蒸气分压力的双重影响,表现为先增加后减小;温度固定为25℃,相对湿度从50% RH增加到80% RH时,复合吸附剂吸附量均大大提升;复合吸附剂在35℃、25% RH中高温、低湿条件下仍表现出较好的吸附能力;在相对压力P/P₀为0.3时,M1、M2和M3的吸附量分别为0.24、0.25和0.30 g/g,随着吸附压力的增加,复合吸附剂的吸附量也不断提升,最大吸附量分别达到3.54、3.75和4.42 g/g。复合吸附剂MWCNT/MgCl₂的制备研究,为吸附剂的性能研究提供了基础,对太阳能吸附式空气取水的研究具有潜在意义。     

石墨烯-13X/LiCl复合吸附剂开式吸附-解吸性能

利用不同质量分数的石墨烯（MLG）与13X/LiCl合成新型复合吸附剂。通过扫描电镜（SEM）和N₂吸附表征复合吸附剂的微观形貌和孔隙特性,测试了复合吸附剂开式环境下的水蒸气吸附及解吸性能,并探究复合吸附剂中石墨烯质量分数对吸附解吸性能的影响。通过80%相对湿度（RH）的高湿工况进一步筛选出盐的质量分数为18.4%的13X/LiCl为最佳盐含量的吸附剂（MZ）作为合成复合吸附剂的基质。实验结果表明：石墨烯增加了复合吸附剂的结构性参数（比表面积,孔体积及孔径）,其中比表面积由未添加石墨烯的MZ [(262±3)g/m²],最大可提升至12G-MZ [(304±4)g/m²];复合吸附剂表现出优异的水蒸气吸附性能,所有复合吸附剂的相对吸附量均高于MZ（0.554g/g）,3G-MZ吸附性能最佳,水蒸气吸附量高达0.587g/g,是13X的2.7倍;除12G-MZ外,随着吸附剂中石墨烯质量分数的增加,水蒸气解吸率随之增加,其中9G-MZ的解吸率接近90%,较MZ（81.8%）提升了9.7%。该研究可为复合吸附剂应用于吸附空气取水提供基础研究数据。     

一步快速活化法制备生物质活性炭及其对乙酸乙酯的吸附再生

活性炭吸附法因技术成熟、简单易行、吸附效率高等优点而被广泛应用于挥发性有机化合物（VOCs）的处理中。本文以山林废弃物的野山桃核为原料,烟道废气及硝酸铁为活化剂,制备了一系列生物质活性炭,并利用固定床吸附装置对其吸附、再生性能进行了研究。利用二氧化碳和水蒸气模拟烟气,在固定流量的烟气活化氛围中进行活化,并探讨了不同硝酸铁的量对活性炭的孔隙结构及其吸附再生性能的影响。利用N₂ 吸附-脱附实验、扫描电镜、拉曼光谱和红外光谱等技术研究了活性炭详细特征。结果表明：当硝酸铁的质量分数为0.2% 时,所制备的活性炭AC-3具有最大的比表面积和平均孔径,分别为923m2/g及2.57nm。其对乙酸乙酯的饱和吸附量也最大,为973.04mg/g。利用烟气对AC-3活性炭进行活化再生处理,经过3次重复吸附-解吸再生实验,其饱和吸附能力仍可达91.5％以上,实现了废弃烟气资源化利用及活性炭的循环回收,从而达到废气治理的目标。     

Superb VOCs capture engineering carbon adsorbent derived from shaddock peel owning uncompromising thermal-stability and adsorption property

High applied thermal-stability and superior structural property for activated carbon adsorbent are extremely promising, which also is the determining short slab in volatile organic compounds (VOCs) adsorption applications. Herein, we develop the outstanding engineering carbon adsorbents from waste shaddock peel which affords greatly-enhanced thermal-stability and super structural property (S_Lang?=?4962.6?m²·g^-1, V_micro?=?1.67?cm³·g^-1). Such character endows the obtained adsorbent with ultrahigh adsorption capture performance of VOCs specific to benzene (16.58?mmol·g^-1) and toluene (15.50?mmol·g^-1), far beyond traditional zeolite and activated carbon even MOFs materials. The structural expression characters were accurately correlated with excellent adsorption efficiency of VOCs by studying synthetic factor-controlling comparative samples. Ulteriorly, adsorption selectivity prediction at different relative humidity was demonstrated through DIH (difference of the isosteric heats), exceedingly highlighting great superiority (nearly sixfold) in selective adsorption of toluene compared to volatile benzene. Our findings provide the possibility for practical industrial application and fabrication of waste biomass-derived outstanding biochar adsorbent in the environmental treatment of threatening VOCs pollutants.     

典型液体危化品吸附材料性能

目前用于典型液体危化品吸附的材料类型主要有树脂型和有机高聚物超细纤维型,两种类型中分别选取甲基丙烯酸酯吸油树脂和聚丙烯纤维吸附材料,对此两种吸附材料的吸附相关特性进行了对比实验研究,包括吸附倍率与时间的关系、吸附选择性以及循环吸附/解吸特性等。结果表明,两种吸附材料吸附甲苯的吸附平衡时间均为4 s左右,其中聚丙烯纤维吸附材料的平衡吸附倍率为17.82 g/g,为甲基丙烯酸酯吸油树脂的2.2倍;两种吸附材料都具有较好的吸附选择性;聚丙烯纤维吸附材料在吸附甲苯后能够通过挤压方式解吸附实现循环使用,平均解吸率在80%以上;甲基丙烯酸酯吸油树脂在吸附甲苯后无法通过挤压方式进行解吸附。实验结果将为基于吸附材料的水面液体危化品回收设备的研发奠定基础。     

Superhigh selective capture of volatile organic compounds exploiting cigarette butts-derived engineering carbonaceous adsorbent

Herein, we develop cost-efficient superhigh-performance of engineering carbonaceous adsorbent from cigarette butts using combined wet-impregnated and re-dispersed method of KOH, which optimizes the implant approach of activator, breaking the restriction of selective capture of toluene using traditional activated carbon. The Brunauer-Emmett-Teller (BET) surface area and pore volume of targeted adsorbent can attain 3088 m²·g^-1 and 1.61 cm³·g^-1, respectively, by optimizing the temperature-dependent synthetic factor effect of the adsorbent. The adsorption capacity of resultant adsorbent for presenting volatile benzene and toluene shows a positive correlation with increasing carbonization temperature of carbon precursor. Besides, we demonstrated the unsmoked and smoked butts derived adsorbents afford feeble difference in saturated adsorbed capacity of volatile organic compounds (VOCs). The highest adsorption capacity of sample CF-800 for benzene and toluene in CF group is as high as 1268.1 and 1181.6 mg·g^-1 respectively, slightly higher than that of sample UF-800, but far outperforming reported other adsorbents. The predicted adsorption selectivity of CF-800 and UF-800 for C₇H₈/H₂O (g) using the DIH (difference of isosteric heats) equation reach up to ca. 3800 and 7500 respectively, indicating the weak adsorbability of water vapor on the developed adsorbent and greater superiority of the smoked butts derived adsorbents in selective capture of VOCs at low relative humidity in the competitive adsorption process for practical mixed VOCs.     

多级孔硅铝酸盐的结构特性及其除湿性能

采用水热法制备出具有深度除湿功能（RH<20%）、高饱和吸附量和中低温快速脱附性能（<100℃）的除湿轮用多级孔硅铝酸盐吸附剂。采用N₂-吸附脱附、XRD、透射电镜、FT-IR和NMR等技术表征吸附剂的微观结构;采用动态水汽吸附分析仪（DVS）测试其吸附-脱附性能。结果发现,通过控制制备前体的微晶温度,可调控吸附剂在中低湿度工况下的除湿性能：微晶温度是通过影响吸附剂微观结构中有序介孔和类微孔结构的比例,来影响吸附剂的深度除湿功能;升高微晶温度会提高吸附剂中类微孔和骨架Al比例从而强化其深度除湿能力,但会显著降低介孔有序度及总孔容,削弱其饱和吸附量及脱附性能;过高的类微孔和骨架Al比例会提高吸附剂的脱附再生温度,增大除湿能耗。     

The water vapor sorption behavior of flax fibers—Analysis using the parallel exponential kinetics model and determination of the activation energies of sorption

Sorption kinetic data for the interaction of water vapor with flax (Linum usitatissimum L.) were analyzed used the parallel exponential kinetics (PEK) model, with excellent fits to the data being obtained. The PEK model is the sum of two exponential kinetics processes (fast and slow), which have characteristic times and moisture contents associated with them. The slow adsorption and desorption processes exhibited important differences in their characteristic times, although hysteresis in the moisture contents was found to be predominantly associated with the fast process. The kinetics was examined over a range of relative humidity (RH) values and at different temperatures, enabling the determination of activation energies for the adsorption and desorption kinetic processes throughout the hygroscopic range (from 5–95% RH). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dynamic Analysis of Diffusion and Adsorption of Water‐Miscible and Water‐Immiscible Organic Vapors in Soil

A dynamic analysis of the diffusion and adsorption of water‐miscible volatile organic compounds (methanol and acetone) and water‐immiscible volatile organic compounds (benzene and toluene) in a soil pellet has been performed experimentally by using the single pellet moment technique. The experiments were conducted in a one‐sided single pellet adsorption cell at a temperature of 30 °C and varying relative humidities (0, 20, and 40 %). The results obtained with dry and wet systems showed that volatile organic tracers were adsorbed reversibly onto the soil. The overall adsorption equilibrium constants of both water‐miscible and water immiscible volatile organic compounds decreased with relative humidity. The sorption of water‐immiscible VOCs (benzene) onto soil was found to be much less than that of water‐miscible VOCs (methanol). The effective diffusivity of water‐immiscible volatile organic vapor (benzene) in the soil did not show a considerable change with relative humidity. In contrast, there was an appreciable change in the effective diffusivity for water‐miscible VOCs (methanol) with moisture.     

The influence of porosity and surface oxygen groups of peat-based activated carbons on benzene adsorption from dry and humid air

Activated carbons (ACs) prepared from peat were used for benzene adsorption (5 ppmv) from dry and humid (relative humidity (RH) 70%) air streams. Benzene uptake by the ACs was lower in the presence of water vapor due to competition between benzene and water molecules for the adsorption sites. Adsorption of benzene from dry and humid air on the ACs with low content of surface oxygen groups was attributed to the presence of narrow micropores (size <0.7 nm). A linear correlation between the amount of adsorbed benzene and micropore volume calculated from CO₂ adsorption isotherms was found. The coefficients of determination R² were 0.87 for benzene adsorption in the absence of water vapor and 0.83 for adsorption at relative humidity 70%. It was shown that the presence of surface groups in the ACs reduces benzene uptake more profoundly in the presence of moisture than in the dry conditions.     

Electrical Properties of Porous Titania Ceramic Humidity Sensors

Ceramic humidity sensors made with pure TiO₂ powder as the starting material are investigated. The sensor can be reversibly operated without repeated high-temperature thermal desorption, and the conductance versus relative humidity (rh) sensitivity of the sensor is more than 4 orders of magnitude in the range ∼15% to 95% rh at 400 Hz and 25°C. The sensor can be polarized similar to electrolytes in the charging process, and the degree of polarization is enhanced with increasing rh. The conduction carriers of the sensor in the humid atmosphere are ions and electrons, and ions are the dominant conduction carrier. The relative dielectric dispersion k'(ω) is almost proportional to ω^−1.84 for rh ∼50% to 95% at low frequencies, where ω is the angular frequency. An inductive effect is also observed in a low-humidity atmosphere, which implies desorption of water vapor with the regeneration of the adsorption sites.     

中高温环境下VOCs在活性炭上的吸附性能研究

选用3种商用活性炭及其分别经HCl溶液和KOH溶液浸渍改性的商用活性炭,研究中高温烟气环境下,反应空速、吸附温度对挥发性有机物（VOCs）吸附性能的影响,以及VOCs种类、吸附剂特性等与VOCs吸脱附效果的关系。研究发现：空速对吸附穿透时间影响较大,但对饱和吸附量影响不显著。吸附温度与VOCs浓度对饱和吸附量存在较大影响,150℃时甲苯的饱和吸附量仅能达到90℃时的40％。高沸点吸附质更易被吸附,更难被脱附。     

Activated carbon cloth adsorption-cryogenic system to recover toxic volatile organic compounds

There is an emergent need to reduce the emissions of toxic volatile organic compounds (VOCs) to the atmosphere. One strategy to reduce the emissions of VOCs from point sources is to use air pollution control devices on the sources' discharge streams. This paper describes the development of a new activated carbon cloth (ACC) adsorption system that is integrated with cryogenic vapor recovery to reduce the amount of VOCs emitted to the atmosphere from point sources and provide for reuse of the VOCs that are recovered. Electrical current is used to regenerate the ACC. ACC adsorption followed by electrothermal regeneration results in formation of a concentrated organic vapor which is cryogenically condensed from the gas phase. Electrothermal desorption allows for careful control of the desorption time and the concentration profile of the desorbed VOC to allow minimal use of cryogen. Adsorption, followed by cryogenic treatment enables VOC sources to meet air quality control regulations while providing a high quality liquid VOC product for reuse.     

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.     

气相低浓度甲苯在超稳Y分子筛的吸附-脱附性能

为提高Y分子筛对可挥发性有机废气的选择性吸附能力,采用高温水热处理技术对NaY分子筛进行骨架脱铝制备超稳Y分子筛(USY),并在固定床反应器中考察了USY在水汽存在下动态吸附低浓度甲苯的性能。结果表明,随着USY分子筛骨架Si/Al比的增加,虽然其微孔孔体积和比表面积发生了下降,但形成了较多的中孔结构。并且骨架硅含量增加后,USY对非极性的甲苯分子选择性吸附能力明显增加,当Si/Al为22左右,在相对湿度50%下,单位面积甲苯吸附量要比水吸附量大5.6倍。热重脱附研究表明,经过改性后,甲苯脱附温度可从NaY的300℃下降到超稳Y分子筛的160℃,具有优良的热再生性能。     

Adsorption of tetrachloroethylene (PCE) in gas phase on zeolites of faujasite type: Influence of water vapour and of Si/Al ratio

This study is focused on the adsorption of a chlorinated volatile organic compound, the tetrachloroethylene (PCE), on dealuminated faujasite type zeolites with framework Si/Al ratio between 5 and 100. PCE dynamic adsorption experiments with and without water vapour (relative humidity of, respectively, 50% and 0%) were carried out in a fixed bed reactor at 50 °C. Breakthrough curves were fitted by a model using the integral of a Gauss distribution. PCE adsorption capacities depend on the adsorbent microporous volume. However, in presence of water vapour, PCE adsorption is favoured on hydrophobic zeolites but also depends on the diffusional limitations inside the porous system. In order to have a better understanding of water molecules adsorption, isotherms were measured using thermogravimetric method at 25 °C. The presence of water vapour generally decreases PCE uptake but its influence decreases as the Si/Al ratio of the adsorbent increases. Experiments with various gases hourly space velocity (GHSV) and inlet PCE concentrations were also performed. PCE complete desorption was obtained on HFAU(Si/Al = 17) at 180 °C. This easy regeneration of the sample permitted adsorption/regeneration cycles maintaining good adsorption properties.     

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。