Separation of volatile compounds by condensation in a fluidized bed

A depollution process by separation in fluidized bed has been studied. Volatile compounds are condensed and captured by fluidized porous particles before being renewed in an evaporation reactor. This study shows that low superficial gas velocity, cold bed temperature gave a high and stable abatement rate as well as they provided a good use of the internal porosity of the particles to stock the liquid condensates. The bed remained correctly fluidized until the particles are saturated with adsorbate. Simulations by a previously developed model have then be compared to empirical results. Particle internal porosity proved to be well used as a storage capacity for the liquid fractions of pollutants before any liquid fraction concentrated on the external surface provoked defluidization. Experiences of particle regeneration by heating confirmed the mass balance precision and also proved the feasibility of the whole process.     

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.     

挥发性有机化合物的净化处理技术

有机废气中大多含有低浓度的苯、甲苯、苯乙烯、多环芳烃等挥发性有机化合物（VOCs）。治理VOCs污染是大气污染治理的重要组成部分。叙述了吸收法、吸附法、生物法和低温等离子体4种废气净化技术的原理和国内外研究进展情况,并对其发展前景和研究方向进行了探讨。最后认为有机废气的联合协同处理方法是今后的一个重要研究方向。     

植物释放VOOs的研究

植物源释放的挥发性有机物（BVOCs）占到了全球挥发性有机物（VOCs）排放总量约70％,在生态系统中起着重要的作用,且与人们健康息息相关,对环境安全和人类生存健康具有重要的影响。主要综述了BVOCs中异戊二烯及单萜烯等几种重要的植物释放物,概括了它们的分类、作用、释放影响因素以及对它们的研究情况。     

Combustion of volatile organic compounds in two-component mixtures over monolithic perovskite catalysts

Activity of monolithic perovskite catalysts in oxidation of selected hydrocarbons and oxy-derivatives, oxidized individually and in two-component mixtures, as well as the reaction selectivity were investigated. One bulk perovskite (LaMn₂O₃) catalyst and two catalysts based on LaMn₂O₃ with addition of silver (25 at.%) coated on cordierite support were prepared for the study. The efficiency of oxy-derivatives oxidation was higher than that of hydrocarbon oxidation, but some by-products (first of all aldehydes) were detected in the flue gases. Addition of silver to the active phase improved catalyst activity and selectivity to CO₂ and water. The “mixture effect” on catalyst activity and selectivity depended on composition of the reaction mixture and the catalyst used. The presence of oxy-derivative in the reaction mixture inhibited oxidation of hydrocarbons. Toluene inhibited the process of oxy-derivatives conversion and increased the concentration of incomplete oxidation products.     

Coordination polymers: Opportunities and challenges for monitoring volatile organic compounds

Coordination polymers (CPs) are emerging as the next generation of macromolecules for many industrial and technological applications. The highly porous nature of these CPs offers the opportunity to exploit them as very effective adsorbents for gaseous molecules, including volatile organic compounds (VOCs). Release of VOCs into the environment is highly undesirable as they can be extremely harmful to general public health and environmental quality. Lately, a large volume of the scientific literature has pointed toward the potentially important role of CPs in the monitoring and analysis of VOCs, offering unprecedented detection limits. This review discusses the opportunities and challenges for the use of CP materials in such applications, describing their general working principles, analytical performance, advantages, and limitations. Recent progress in the application of CPs in the detection, monitoring, and analysis of VOCs is critically reviewed. The discussion is further extended to cover future applications and current research activities in this emerging analytical field.     

Support effect on complete oxidation of volatile organic compounds over Ru catalysts

Catalytic combustion of ethyl acetate, acetaldehyde, and toluene was investigated on various supported Ru catalysts prepared by the impregnation method, and the effect of reduction treatment on the activity was examined. Among the as-calcined catalysts tested, Ru/CeO₂ showed the highest activity for all tests regardless of the pre-treatment in hydrogen atmosphere. The catalytic activity of Ru/SnO₂ was significantly degraded by the reduction treatment, whereas the activity of Ru/ZrO₂ and Ru/γ-Al₂O₃ was enhanced. To reveal these phenomena, the as-calcined and reduced catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and BET surface area. The dispersion of ruthenium on the supports was evaluated by chemisorption methods of carbon monoxide. The catalytic activity was strongly related to ruthenium species easily oxidizable and reducible at low temperatures. Such ruthenium species were loaded on CeO₂ in a highly dispersed state, resulting in the highest activity.     

Catalytic oxidation of trichloroethylene in two-component mixtures with selected volatile organic compounds

The activity of two noble metal catalysts (Pt and Pd) on metallic monolithic support and one perovskite (La_0.5Ag_0.5MnO₃) on cordierite monolith was tested in the oxidation of selected volatile organic compounds (VOCs) and trichloroethylene (TCE), oxidized alone and in two-component mixtures of TCE with a non-halogenated compound. Only over the Pt catalyst each compound in the reaction mixtures strongly enhanced TCE oxidation. Over Pd, promoting effect on TCE oxidation was observed for toluene and ethanol only. Over perovskite, each non-chlorinated compound was found to inhibit TCE oxidation. The presence of TCE was found to inhibit the oxidation of each compound added over both noble metal catalysts, but it had no influence on the oxy-derivatives oxidation over the perovskite catalyst.     

Gas-solid adsorption of selected volatile organic compounds on titanium dioxide Degussa P25

This paper focuses on the adsorption of gaseous trichloroethylene, toluene and chlorobenzene on the photocatalyst TiO₂ Degussa P25. An optimized EPICS (Equilibrium Partitioning In Closed Systems) methodology was used to study equilibrium partitioning. For the three compounds investigated, equilibrium adsorption was reached within of incubation. Adsorption isotherms, determined at a temperature (T) of and relative humidities (RH) of 0.0% and 57.8% were found to be linear (R²>0.993,n=5), indicating that no monolayer surface coverage was reached in the concentration interval studied ). Within the linear part of the isotherm, the influence of both relative humidity and temperature was investigated in a systematic way and discussed from a thermodynamic point of view. Data analysis resulted in a double linear regression for 22% ?RH?90% and . The equilibrium adsorption coefficient represents the equilibrium concentration ratio and ΔU_ads is the internal energy of adsorption . At RH=0.0%, experimental K values were a factor 5-10 higher than those expected from the regression equation, indicating that another adsorption mechanism becomes important below monolayer surface coverage of TiO₂ by water vapour molecules. Since surface interactions are of primary importance in photocatalytic reactions, this paper contributes to a better understanding of the basic mechanisms of TiO₂ mediated heterogeneous photocatalysis and is an interesting tool for developing optimized mathematical models.     

Concentration control of volatile organic compounds by ionic liquid absorption and desorption

Volatile organic compounds (VOCs) are difficult to be eliminated safely and effectively because of their large concentration fluctuations. Thus, maintaining a stable concentration of VOCs is a significant study. In this research, H₂O, Tween-80,[Emim]BF₄,[Emim]PF₆, and[Hnmp]HSO₄ were applied to absorb and desorb simulated VOCs. The ionic liquid[Emim]BF₄ demonstrated the best performance and was thus selected for further experiments. As the ionic liquid acted as a buffer, the toluene concentration with a fluctuation of 2000-20000 mg·m^-3 was stabilized at 6000-12000 mg·m^-3. Heating distillation (90℃) was highly efficient to recover[Emim]BF₄ from toluene. The regenerated[Emim]BF₄ could retain its initial absorption capacity even after multiple cycles. Moreover,[Emim]BF₄ had the same buffer function on various aromatic hydrocarbons.     

Modeling of fuel mixing in fluidized bed combustors

This paper presents a three-dimensional model for fuel mixing in fluidized bed combustors. The model accounts for mixing patterns which were experimentally shown to govern mixing in risers with geometry and operational conditions representative for furnaces in fluidized bed combustors. The mixing process is modeled for three different solid phases in the furnace and the model, which includes the return leg, can be applied both under bubbling and circulating regimes. The semi-empirical basis of the model was previously validated in different large-scale fluidized bed combustors and is combined with a model for fuel particle conversion to obtain the fuel concentration field. Model results are compared with experimental data from the Chalmers 12 MW_th CFB combustor, yielding a reasonable agreement.     

Catalytic combustion of volatile organic compounds on gold/iron oxide catalysts

Catalytic oxidation of 2-propanol, methanol, ethanol, acetone and toluene was investigated on coprecipitated Au/Fe₂O₃ catalysts in the presence of excess of oxygen. Gold catalysts have been found to be very active in the oxidation of tested volatile organic compounds (VOCs). The high activity of these systems has been related to the capacity of highly dispersed gold to weaken the Fe–O bond thus increasing the mobility of the lattice oxygen which is involved in the VOCs oxidation probably through a Mars–van Krevelen reaction mechanism.     

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。     

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。     

Kinetic study for photocatalytic degradation of volatile organic compounds in air using thin film TiO2 photocatalyst

The present paper examined the kinetics of photocatalytic degradation of volatile organic compounds (VOCs) including gaseous trichloroethylene (TCE), acetone, methanol and toluene. Variable parameters were initial concentration of VOCs, water vapor content and photon flux of ultra-violet (UV) light. A batch photo-reactor was specifically designed for this work. The photocatalytic degradation rate increased with increasing the initial concentration of VOCs, but maintained almost constant beyond a certain concentration. It matched well with the Langmuir–Hinshelwood (L–H) kinetic model. For the influence of water vapor in a gas phase photocatalytic degradation rate, there was an optimum concentration of water vapor in the degradation of TCE and methanol. And, water vapor enhanced the photocatalytic degradation rate of toluene, whereas it inhibited that of acetone. As for the effect of photon flux, it was found that photocatalytic degradation occurs in two regimes with respect to photon flux.     

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。     

Influence of catalyst pretreatments on volatile organic compounds oxidation over gold/iron oxide

This paper reports a study on the influence of calcination pretreatments on the catalytic behaviour of the Au/iron oxide system towards the combustion of some representative volatile organic compounds (2-propanol, ethanol, methanol, acetone and toluene). The catalytic activity of Au/Fe₂O₃ samples towards the total oxidation to CO₂ has been found to be strongly dependent on the catalyst pretreatment, decreasing on increasing the calcination temperature. On the basis of characterisation data (XPS, FT-IR, XRD, BET surface area) it has been proposed that the catalytic behaviour is related to the gold state and/or the iron oxide phase. It appears plausible to suggest that the gold oxidation state and/or the particle size play a key role in the catalytic combustion of volatile organic compounds.     

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     

Biodegradation of organic compounds in fluidized bed reactors

Biodegradation of organics in fluidized bed reactors was studied experimentally. Both single-substrate and mixed-substrate systems were considered. With the use of a previously developed biofilm model, parameters pertinent to the degradation of mixed-substrate systems and their single substrate system counterparts were evaluated and compared. Two approaches attempted to predict the degradation of a mixed-substrate system. One assumed independent biodegradaion and diffusion of individual substrates while the other used a lumped concentration approach. The latter approach was found to give better agreement with experiments than the former.     

挥发性有机物处理技术的特点与发展

挥发性有机物(VOCs)产生于有机化工生产过程及有机产品被使用的自身挥发过程,对环境和人类健康有害。本文综述了VOCs的定义、来源、危害、相关法律法规和排放情况。介绍了现有VOCs处理技术,包括化学氧化法、物理分离法、生物分解法、光解法、电化学法以及新兴复合型处理技术等的特点。阐述了这些技术的原理、工艺流程、优势、使用限制和市场的占有率,其中吸附法应用最为广泛,催化燃烧法和低温等离子法发展最快,复合型处理技术处理效果最好且无二次污染是VOCs处理技术发展的一个重要方向。选择合适VOCs处理工艺应依据其主要成分的浓度、气体流量、物化性质等因素并考虑到整个处理工艺的经济效益。并对新兴复合型处理技术的发展趋势作了展望,指出降低成本、简化操作是该技术进一步推广的关键。