两段循环流化床吸附有机气体实验

以Ambersorb 600为吸附剂,甲苯为吸附质,在两级循环流化床吸附装置内进行了吸附特性的实验. 采用PGM-7600型VOCs分析仪测量甲苯的浓度,得到两段循环流化床的压力和空隙率分布及浓度随床高的分布;研究了气体进口浓度和表观气速对吸附效率的影响. 在实验条件下吸附装置效率为95%~98%.     

Environmental plasma-catalysis for the energy-efficient treatment of volatile organic compounds

Nonthermal plasma (NTP) coupled with catalysis is a promising technique for the abatement of dilute volatile organic compounds (VOCs), because it is operable under mild reaction conditions, i.e., low temperature and atmospheric pressure. This review addresses the mechanistic aspects of catalyst activation by NTP, such as the generation and fixation of reactive species, facilitation of redox cycles, photocatalysis, and local heating, to clarify the combined effects of plasma and catalysis. The plasma-catalytic removal of VOCs preferentially requires the catalyst to have a large specific surface area, high surface oxygen storage capacity, and to be highly reducible. The energy consumption and deactivation of catalysts are considered by comparing continuous and cyclic operations in terms of specific input energy, VOC removal and energy efficiencies, and byproduct formation. Based on the information in the literature, a plasma-catalytic system operating in cyclic adsorption-oxidation mode is recommended for the treatment of air contaminated by dilute VOCs. Finally, the effects of NTP on the regeneration of deactivated catalysts are also discussed.     

活性炭纤维布吸附与电热脱附挥发性有机化合物研究进展(英文)

A general research program,focusing on activated carbon fiber cloths(ACFC) and felt for environmental protection was performed.The objectives were multiple:(i) a better understanding of the adsorption mechanisms of these kinds of materials;(ii) the specification and optimization of new processes using these adsorbents;(iii) the modeling of the adsorption of organic pollutants using both the usual and original approaches;(iv) applications of ACFC in industrial processes.The general question was:how can activated carbon fiber cloths and felts be used in air treatment processes for the protection of environment.In order to provide an answer,different approaches were adopted.The materials(ACFC) were characterized in terms of macro structure and internal porosity.Specific studies were performed to get the air flow pattern through the fabrics.Head loss data were generated and modeled as a function of air velocity.The performances of ACF to remove volatile organic compounds(VOCs) were approached with the adsorption isotherms and breakthrough curves in various operating conditions.Regeneration by Joule effect shows a homogenous heating of adsorber modules with rolled or pleated layers.Examples of industrial developments were presented showing an interesting technology for the removal of VOCs,such as dichloromethane,benzene,isopropyl alcohol and toluene,alone or in a complex mixture.     

Breakthrough data analysis of adsorption of volatile organic compounds on granular activated carbon

Volatile Organic Compounds (VOCs) such as methanol, ethanol, methyl ethyl keton, benzene, n-propanol, toluene, and o-xylene were adsorbed in a laboratory-scale packed-bed adsorber using granular activated carbon (GAC) at 101.3 kPa. The adsorber was operated batchwise to obtain the breakthrough curves of VOCs under the adsorption conditions such as adsorption temperatures (298–323 K), flow rates of nitrogen (60×10⁻⁶-150×10⁻⁶m³/min), GAC amount of 0.002 kg, and concentration of VOCs (3,000–6,000 ppmv). The adsorption kinetics was obtained by fitting the experimental breakthrough data to the deactivation model, combining the adsorption of VOCs and the deactivation of GAC. The adsorption isotherm, and adsorbed amount and adsorption heat of VOCs were obtained using the breakthrough curve: the former for comparison with the conventional isotherm models, the latter for correlation with the physical properties of VOCs.     

Adsorption/desorption of toluene on a hypercrosslinked polymeric resin in a highly humid gas stream

In many sources of volatile organic compounds(VOCs), large amounts of water vapor come from the air and the reactors. The relative humidity(RH) of exhaust gas is normally N60% and is supersaturated. Maintaining the property of adsorbent on VOCs in a highly humid gas stream is a serious industrial problem. In this study, the adsorption/desorption behavior of toluene in a micro-mesoporous polymeric resin was investigated in a highly humid environment to explore the influence of abound water vapor on resin adsorption and regeneration.This resin could selectively adsorb toluene at an RH of 80%, and its adsorption property was unaffected by the presence of water vapor. In the case of humidity saturation, the resin displayed a high adsorption capacity at a moisture content of b30%. Therefore, the polymer resin is an excellent water-resistant adsorbent of VOCs.In the regenerative experiment, the resin maintained its original adsorption capability after four adsorption/desorption cycles of toluene purging with nitrogen gas at 120 °C. The resin exhibited excellent regeneration performance at high humidity.     

Effect of temperature on the release of volatile and odorous compounds in flax fibers

The behavior of flax fibers was investigated at temperatures of 80 °C, 200 °C, 215 °C, and 230 °C for a period of 60 min. First, thermogravimetric and colorimetric analyzes were carried out to characterize the impact of the temperature on the weight loss and the color of the fibers. Then, the release of volatile and odorous compounds from flax fibers was studied using both chemical and sensory approaches. Solid phase micro extraction was done to isolate the volatile organic compounds (VOCs) from the headspace of the sample while gas chromatography‐mass spectrometry (GC‐MS) and olfactometry (O) were used to determine the volatile and odorous compounds released at each temperature. About 24 VOCs were identified in the volatile fraction of flax fibers with a high occurrence of aliphatic aldehydes, phenols, and furans. Quantification by GC‐MS and by the aroma extract dilution analysis method was implemented. The results point to a critical temperature between 215 °C and 230 °C from which the odor of flax fibers becomes more intense, more complex, and with unpleasant features. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43497.     

Development of adsorption buffer and pressure swing adsorption (PSA) unit for gasoline vapor recovery

The effect of a double layered adsorber on the recovery of gasoline from gas emitted from a gasoline storage tank was investigated. The adsorber consists of two different adsorbents: silica gel and activated carbon. A pilot system consisting of an adsorptive buffer for the collection of contaminated air sporadically emitted and a PSA system was installed and operated. Gas from a gasoline tank was fed to the adsorption buffer for a period of time, and subsequently the enriched hydrocarbon stream obtained during the regeneration of the adsorptive buffer was treated by the PSA system. Regeneration of the adsorbent was done by flowing clean air under vacuum. Approximately 21–48 liters of gasoline per hour was recovered with the pilot-scale PSA unit filled with 435 kg of adsorbent in total. The gas emitted from the system contains light hydrocarbon less than 100 ppmv.     

Novel design and performance of a medical oxygen concentrator using a rapid pressure swing adsorption concept

A novel design of a compact rapid pressure swing adsorption system consisting of a single adsorber enclosed inside a product storage tank is proposed for application as a medical oxygen concentrator (MOC). A self‐contained test unit for the process is constructed which is capable of directly and continuously producing 1–3 sl/m of 90% O₂ from compressed air. Pelletized LiLSX zeolite is used as the air separation adsorbent. Steady state process performance data [bed size factor (BSF) and O₂ recovery (R) as functions of total cycle time (t_c)], as well as transient, cyclic, adsorber pressure, and temperature profiles are presented. A four‐step Skarstrom‐like pressure swing adsorption cycle was used. Two options for column pressurization, (a) using compressed feed air cocurrently or (b) using a part of the oxygen‐enriched product gas counter‐currently were evaluated. Option (b) exhibited superior performance. The optimum total cycle time for option (b) was 5–6 s where the BSF was lowest (～45 kgs/TPD O₂) and the corresponding R was ～29.3%. These numbers indicate that the adsorbent inventory of a MOC can be potentially reduced by a factor of three while offering a ～10–20% higher O₂ recovery compared to a typical commercial unit. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3330–3335, 2014     

Advanced oxidant regeneration of granular activated carbon for controlling air‐phase VOCs

The Pennsylvania State University is researching an advanced oxidation (AO) system for controlling volatile organic compounds (VOCs) (Cannon et al. 1994). The system includes an air‐phase photolytic chamber, an air/water stripping tower, and granular activated carbon (GAC) beds, and the work herein describes he evaluation of the GAC beds. Field GACs have been evaluated, which had previously been loaded with VOCs and regenerated with AO for several years at several full scale installations. Full scale response then was simulated in laboratory‐scale experiments.

Results revealed that following 500 to 1000 daily loading and regeneration cycles, one field GAC lost 35% of its micropore volume, and 17–35% of its capacity to adsorb several VOCs. Under another condition, for a furniture coating GAC, 80% of the micropore volume was lost after several years of loading and reactivation cycles, and 23 to 63% of the VOC adsorption capacity was lost.

Laboratory results revealed that prolonged AO regeneration destroyed or desorbed most of the MIBK within the first inch of a GAC bed. AO regeneration also removed a fourth of the MIBK in the next five inches of the packed GAC bed. Several byproducts were created by the MIBK destruction, which generally contained one‐to‐three fewer carbon atoms than does MIBK, and also contained more oxygen functional groups.

Concurrent with these experiments, thermogravimetric analysis (TGA) tests were performed to evaluate the rate and extent of MIBK adsorption onto virgin GAC, and revealed that the MIBK adsorption capacity was fairly insensitive to the ranges of concentration and temperature that were employed. A modeling analysis of the diffusion characteristics onto virgin GAC revealed that during the time frame of three to five hours, the mass transfer rate appeared to be governed by restricted diffusion.     

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.     

Separation of VOCs from N2 using poly(ether block amide) membranes

This work deals with the separation of volatile organic compounds (VOCs) from nitrogen streams for organic vapour emission control by poly(ether block amide) membranes. As representative air pollutant VOCs, n‐pentane, n‐hexane, cyclohexane, n‐heptane, methanol, ethanol, n‐propanol, n‐butanol, acetone, dimethyl carbonate, and methyl tert‐butyl ether were used in this study. The separation of both binary VOC/N₂ and multicomponent VOCs/N₂ gas mixtures was carried out, and the membranes exhibited good separation performance. A VOC concentration of more than 90 mol% was achieved at a feed VOC concentration of 5 mol%. It was found that the permeances of the VOCs were mainly dominated by their solubilities in the membrane, whereas the permeance of N₂ was affected by the presence of the VOCs. The permeance of N₂ in the VOC/N₂ mixtures was shown to be higher than pure N₂ permeance due to membrane swelling induced by the VOCs dissolved in the membrane. Nevertheless, theVOC/N₂ selectivity increased with an increase in the feed VOC concentration. Among the VOCs studied, the membrane showed a higher permeance to alcohol VOCs than paraffin VOCs. The effects of feed VOC concentration, temperature, stage cut, and permeate pressure on the separation performance were investigated.     

Volatile Foraging Kairomones in the Littoral Zone: Attraction of an Herbivorous Freshwater Gastropod to Algal Odors

Volatile organic compounds (VOCs) produced by algae and cyanobacteria are primarily responsible for odors in fresh waters. Among other functions, VOCs may serve as important infochemicals in biofilms of benthic primary producers. VOCs liberated by benthic, mat-forming cyanobacteria can be used as habitat-finding cues by insects, nematodes, and possibly other organisms. We developed a new gastropod behavioral assay that allows detection of food preference without offering food, thus allowing the distinction between taste, which requires direct contact with the food source, and the detection of odorous infochemicals, which work over distance. We demonstrated that VOCs released from disintegrated cells of a benthic, mat-forming, green alga (Ulothrix fimbriata) are food-finding cues (“foraging kairomones”) that attract the herbivorous freshwater snail Radix ovata. A mixture of three C₅ lipoxygenase compounds and 2(E),4(E)-heptadienal that mimic the major VOCs released by U. fimbriata attracted the snails, whereas neither the mixture of C₅ compounds nor 2(E),4(E)-heptadienal were effective when given alone. This study suggests that VOCs can play a steering role as infochemicals in freshwater benthic habitats, as has been established for many organismic interactions in terrestrial ecosystems.     

UV photocatalytic oxidation of paint solvent compounds in air using an annular TiO2‐supported reactor

BACKGROUND: One of the most important industrial sources of volatile organic compounds (VOCs) is related to coating and painting applications. In this sense, photocatalytic oxidation can become an innovative and promising alternative for the remediation of air polluted by VOCs. In this study the UV photodegradation of m‐xylene, toluene and n‐butyl acetate, as representative compounds of paint solvents, was carried out in an annular reactor using a TiO₂–glass wool supported catalyst. RESULTS The removal of each component and their mixture, simulating an industrial emission, was evaluated under different operational conditions. A maximum elimination capacity of 12, 18 and 80 mg C m^?3 s^?1 was reached for m‐xylene, toluene and n‐butyl acetate, respectively. A simple Langmuir–Hinshelwood kinetic model was used to match the experimental data. Photocatalytic oxidation was found to be more effective for all compounds when humidified air was used. CONCLUSIONS: No mass transfer limitation was found under the experimental conditions. n‐butyl acetate was the easiest to degrade and m‐xylene the most recalcitrant. In the abatement of the mixture, competitive adsorption between the pollutants was observed, with the degradation of toluene especially hindered. A nearly linear correlation was found between the UV light intensity and kinetic constants. Copyright © 2010 Society of Chemical Industry     

Oxygen partial pressure-dependent behavior of various catalysts for the total oxidation of VOCs using cycled system of adsorption and oxygen plasma

In this work, comprehensive investigation was done on the oxygen partial pressure-dependent behavior of the various catalysts using a flow-type plasma-driven catalyst (PDC) reactor. These data provide a useful guideline for the optimization of the cycled system using adsorption and the O₂ plasma-driven catalysis of adsorbed volatile organic compounds (VOCs). The potentials of the tested catalysts for the cycled system were evaluated based on the enhancement factor and the adsorption capability. All the tested materials (TiO₂, γ-Al₂O₃, zeolites) exhibited positive enhancement factor, while negative values with the dielectric-barrier discharge (DBD) plasma alone. TiO₂ catalysts showed the highest enhancement factor of about 100 regardless of the type of metal catalysts and their supporting amount. Based on the experimental findings in this study and the literature information, a plausible mechanism of plasma-driven catalysis of VOCs was suggested.     

Modelling of adsorption in cyclic operation of a PSA plant for H2 recovery

A pressure swing adsorption process for hydrogen recovery from coke oven gases comprises the steps of adsorption at pressures above 6 bar, cocurrent and countercurrent depressurization, purging with hydrogen at ambient pressure and repressurization. The process was investigated in the cyclic mode, on a laboratory scale, using an adsorber filled with 1.3 litres of carbon molecular sieve. Based on the test results of concentrations and pressures within the adsorber during complete cycles, a pseudo-homogeneous model was developed for the adsorption step. Adsorption equilibrium parameters were determined by separate measurements, while the transport parameters were evaluated by fitting the experiments of the fixed bed adsorber. It was possible to consider the residual load, resulting from an incomplete regeneration, by the assumption of a load distribution in the inlet region of the adsorber.     

Content of trans,trans‐2,4‐decadienal in deep‐fried and pan‐fried potatoes

Trans,trans‐2,4‐decadienal is a by‐product of frying oil that is also transferred to fried food. This aldehyde has been found and quantified both in frying oils and fumes generated during frying. Furthermore, it has been reported that 2,4‐decadienal has cytotoxic and genotoxic effects and promotes LDL oxidation. In the present work trans,trans‐2,4‐decadienal was detected directly in fried potatoes (french‐fries). Moreover, the influence of frying conditions (deep‐frying, pan‐frying), the oil type (olive oil, sunflower oil, cottonseed oil, palm oil and a vegetable shortening) and the degree of thermal deterioration (eight successive frying sessions without replenishment) on the production of 2,4‐decadienal in oil and potatoes was studied. The isolation of the aldehyde was performed by methanol extraction, while the identification and quantification was performed by RP‐HPLC. The quantity of trans,trans‐2,4‐decadienal produced during successive pan‐frying demonstrated a peak at the third and fourth frying session. The highest concentration of trans,trans‐2,4‐decadienal was detected in potatoes fried in sunflower oil, and the lowest in olive oil. The quantity of trans,trans‐2,4‐decadienal in fried potatoes decreased during successive deep‐frying at the seventh frying session or remained stable, except for cottonseed oil. The quantity of trans,trans‐2,4‐decadienal in fried potatoes was considered to be dependent on the oil used, on the frying process and, to a lesser extent, on the oil deterioration. In all cases tested, the highest concentration of trans,trans‐2,4‐decadienal was detected during deep‐frying. The unsaturation degree of the frying oil was considered to promote the formation of trans,trans‐2,4‐decadienal. Considering the quantity of 2,4‐decadienal found in french‐fries and in the respective frying medium, direct quantification of 2,4‐decadienal is required in order to make an estimation of intake from french‐fries.     

Surface modification of polyethersulfone membrane to improve its hydrophobic characteristics for waste frying oil filtration: Radio frequency plasma treatment

In this study, polyethersulfone (PES) membrane was subjected to surface modification using hexamethyldisiloxane (HMDSO) and 1,1,1,3,3,3‐hexafluoro‐2‐propanol ( HFIP) in radio frequency (RF) plasma system to improve its hydrophobic property for recovery of waste frying oil. Structural and morphological changes on the membrane surfaces were characterized by contact angle measurements, Fourier transform infrared spectroscopy‐attenuated total reflection (FTIR‐ATR) and atomic force microscopy (AFM). Permeate fluxes, physical and chemical properties of waste frying oil and waste frying oil–methanol micella (oil/methanol 1/3, 1/1, 1/3, v/v) after filtration through unmodified and modified PES membranes were investigated. The results showed that PES membranes modified with HMDSO at 75 W for 5 min (discharge power–exposure time) selectively rejected total polar compounds (TPC) and free fatty acids (FFAs) of waste frying oil to the extent of 46.9–48% and 35.3–40%, respectively. Furthermore, the viscosity of waste frying oil was reduced to the extent of 9.4–12.8%. RF‐plasma‐treated PES membranes appeared to improve the regeneration of waste frying oils and allow these oils to be used for either repeated frying operations or biodiesel production. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123:3402–3411, 2012     

低浓度挥发性有机物吸附浓缩材料的研究进展

由于挥发性有机物（VOCs）会对环境造成严重的危害，因此VOCs的处理一直备受人们的关注，但发展高效的VOCs处理技术仍然存在严峻的挑战。本文针对大风量、低浓度VOCs的处理展开了综述，重点围绕吸附、催化燃烧处理展开讨论。对于大风量的低浓度VOCs，虽然浓度较低但VOCs排放量非常巨大。通过VOCs浓缩技术，提高浓度减少风量成为降低VOCs处理成本的有效途径。其中，发展高性能VOCs吸附材料是VOCs浓缩技术的关键。阐明了活性炭、分子筛等重要吸附材料的性质及其吸附VOCs的原理，并对吸附材料性质和VOCs种类对吸附效果的影响进行了探讨。展望了活性炭浓缩-催化燃烧技术和分子筛转轮浓缩-催化燃烧技术在大风量的低浓度VOCs处理中的应用前景。     

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.     

Surfactant‐Enhanced Carbon Regeneration in a Vapor‐Phase Application

Abstract

Coal‐based granular activated carbon (GAC) is saturated with trichloroethylene (TCE) by passing air through a fix bed adsorber. In surfactant‐enhanced carbon regeneration, an aqueous solution of anionic surfactant, sodium dodecyl sulfate (SDS), is passed through the bed to induce desorption of TCE. More than 95% of the sorbed TCE was removed in the desorption operation with a 0.1 M SDS solution at a superficial flow rate of 1 cm/min. The desorption rate of TCE from pores of GAC is limited by pore diffusion and not significantly affected by either the concentration of SDS in the regenerant (when well above the critical micelle concentration) or its flow rate. From the breakthrough curve of a subsequent adsorption cycle without a flushing step following the desorption, only 7% of the virgin carbon effective adsorption capacity is observed for the regenerated carbon. With a water flushing step following the regeneration step, the effective adsorption capacity is significantly improved to about 15% of that of virgin carbon. Increased temperature of the flushing water also enhances the effective adsorption capacity of the regenerated GAC. Separate batch adsorption‐desorption isotherms of SDS on GAC support the enhanced desorption of SDS at elevated temperatures. The drastic reduction in the effective adsorption capacity of regenerated GAC results from the residual SDS remaining in the pores of GAC as confirmed by thermal gravimetric analysis. Both the regeneration and water flush steps are rate limited under conditionsused here.