VOC Removal Research Articles

Catalytic Oxidation of Volatile Organic Compounds in Industrial Off-Gases

<p>Processes and apparatuses for catalytic oxidation of VOCs in industrial off-gases are described, including steady state and unsteady state processes, a combined adsorption-catalytic process and an advanced method of ozone induced oxidation for low concentrated exhausts. On the basis of research and development works a series of catalytic incinerators, operating in steady state and unsteady state mode, of various capacity were designed, constructed and tested in the purification of ventilation air and off-gases from VOCs. The principles of operation of different types of catalytic incinerators and possible areas of application are discussed. For VOC concentrations 150-1000 mg/m<sup>3</sup> unsteady state catalytic incinerators of KART type should be used, for concentrations 1000-3000 mg/m<sup>3</sup> steady state KROT apparatuses are recommended, and for concentrations over 3000 mg/m<sup>3</sup> up to 7000 mg/m3 installations TKM-250. It is shown that for the purification of low concentrated gases with the content of organic vapors below 150 mg/m<sup>3</sup> adsorptioncatalytic method or catalytic oxidation with ozone in the installation OKA-3000 are most effective. Main kinetic dependencies of the ozone induced oxidation of toluene and acetone over copper oxide catalyst are given and discussed. It is shown that the efficiency of this method of VOCs removal is based on low operation temperature 313-343 K, by contrast to conventional catalytic incineration by air requiring preliminary heating of the gases to 523-573 K. A special consideration is given to adsorptive damping as an efficient method for leveling the VOCs concentrations in the real industrial exhausts directed to the catalytic treatment. The use of adsorptive dampers filled with carbon allows elimination of large deviations of pollutant concentrations in the gas entering the catalyst bed, thus increasing the VOCs removal efficiency from average values. For calculations of adsorptive dampers, an equation describing the profiles of VOC concentrations in gas phase along the length of the adsorbate bed in the damper was derived.</p>

UV/H2O2: An efficient aqueous advanced oxidation process for VOCs removal

Catalyst deactivation and secondary pollution are the critical issues challenging the traditional heterogeneous catalysis (gas-solid) methods for VOCs removal at room temperature. This process strongly depends on the available OH radicals. Because of the facile formation of OH radicals, H2O2-based advanced oxidation processes (AOPs) may facilitate VOCs removal. In this paper, UV/H2O2, for the first time, was employed to degrade continuous-flow gaseous toluene in batch system with comparison to UV/Fenton and Fenton process. UV/H2O2 process was identified to moderately generate OH radicals and yielded removal efficiency higher than 80% without any loss while it gradually declined to 32% and 45% within 120min in the Fenton and UV/Fenton process, respectively. No emission of gaseous intermediates was identified at the outlet in all the AOPs. Most of the removed toluene was oxidized into CO2 in the UV/H2O2 process, however, many organic intermediates were generated in the solution of Fenton and UV/Fenton process. The superior performance of UV/H2O2 process was mainly ascribed to the continuous formation of OH. This study demonstrates that UV/H2O2 process can be applied as an efficient and environment-benign technology for VOCs treatment.

Hybrid Plasma-Catalytic Oxidation of VOCs with NiMn/Montmorillonite: Plasma and Catalyst Considerations

Bifunctional nanocatalyst of NiMn over alkali activated montmorillonite was prepared with different Mn contents. The prepared catalysts were examined in hybrid plasma-catalytic system for oxidation of volatile organic compounds. The prepared catalysts were characterized by XRD, FESEM, BET, FTIR and EDX analyses. FESEM pictures showed complete and uniform coverage of montmorillonite with metal oxide particles in nano scale. Increasing Mn content from 0 to 9 wt% decreased the BET surface area from 31 to 18 m2 g−1. FTIR spectra illustrated just peaks of montmorillonite and Ni or Mn related peaks were not observed even at high concentrations of Mn. The highest VOC abatement was related to NiMn/montmorillonite with 6 wt% of Mn. This catalyst in hybrid plasma-catalytic oxidation could remove 92% of benzene from polluted air with initial benzene concentration of 1000 ppm in plasma voltage of 20 kV and 9.8 kHz of frequency. While using plasma without catalyst could just remove 74% of benzene in similar conditions. NiMn/montmorillonite nanocatalyst with 6 wt% of Mn was tested at different plasma voltages (10–30 kV) and the highest VOC removal was observed at a voltage of 20 kV. Among 1–9 min residence time, the longest residence time of 9 min had supreme abatement of benzene. Study on mixture of benzene, toluene and xylene in plasma-catalytic system illustrated the highest removal for xylene and the lowest removal for benzene in plasma environment of 20 kV and 9.8 kHz.

Effects of different operating conditions on the VOCs removal performance of UV irradiation reactors

Effects of different operating conditions on the VOCs removal performance of UV irradiation reactors

Synergetic effect between adsorption and photodegradation on nanostructured TiO2/activated carbon fiber felt porous composites for toluene removal

The low quantum efficiency and limited adsorption efficiency of TiO2 makes it only fit for the removal of VOCs with low concentrations. Herein, we for the first time fabricated nanostructured TiO2/activated carbon fiber felt (TiO2/ACFF) porous composites by the in situ deposition of TiO2 microspheres on the carbon fibers in ACFF. Interestingly, the TiO2 microspheres exhibit hierarchical nanostructures constructed by nanocrystals as building blocks. The TiO2/ACFF porous composites possess excellent adsorption and photodegradation properties for toluene because of the synergetic effects between the nanostructured TiO2 and ACFF. The adsorption efficiencies of the TiO2/ACFF porous composites reach approximately 98% at the toluene concentration (<1150ppm) and approximately 77% even at the high concentration of 6900ppm. Moreover, the ACFF in the TiO2/ACFF porous composites significantly enhances photocatalytic property for toluene by hindering the recombination of electron-hole pairs, reducing the TiO2 band gap energy (Eg) to 2.95eV and accelerating toluene adsorption. At the toluene concentrations of 230ppm and 460ppm, the photocatalytic oxidation efficiency of toluene into CO2 arrives at 100% and 81.5%, respectively. Therefore, the TiO2/ACFF porous composites with synergetic adsorption and photocatalytic activities have great potentials for toluene removal.

Metal organic frameworks for gas-phase VOCs removal in a NTP-catalytic reactor

In this study, three different metal organic frameworks, MIL-101, MIL-53, and CPM-5, are used as dual functional adsorbent/catalysts in a non-thermal plasma (NTP)-catalytic reactor. The adsorption and oxidation evaluations of these MOFs for the removal of one (1) ppm toluene and isobutanol are performed at both dry (RH=0%) and humid (RH=30%) conditions. Results show that at dry air condition, MIL-101 possesses the highest adsorption capacity; however, at 30% RH, MIL-53 capacity surpasses MIL-101 and CPM-5. The results of NTP-catalytic oxidation reactions demonstrate a high removal efficiency of isobutanol (100%) and toluene (∼90%) for all three MOFs at dry air condition. At 30% humidity, on the other hand, the catalysts removal performance decreases. During the NTP-oxidation reaction different organic compounds and ozone are detected as by-products. Finally, FTIR spectroscopy of fresh and regenerated catalysts (MIL-101, MIL-53 and CPM-5) does not show a significant structural change.

Multifunctional hybrid porous filters with hierarchical structures for simultaneous removal of indoor VOCs, dusts and microorganisms.

Air purification often requires multiple layers of filters with different functions to remove various air pollutants, which lead to high pressure drop, high air flow path and frequent filter replacement. In this work, a novel multifunctional Ag@MWCNTs/Al2O3 hybrid filter with a depth-type hierarchical structure for simultaneous removal of fine particles, microorganisms and VOCs was designed and fabricated. The novel hybrid air filter showed leading air purification performances to date, achieving 82.24% degradation of formaldehyde at room temperature, 99.99% formaldehyde degradation at 55 °C and complete retention of indoor airborne microorganisms. The complete particle retention rate (100% retention) based on the most penetrating particle size (MPPS, aerodynamic diameter ≦300 nm) of Ag@MWCNTs/Al2O3 was achieved at an only 35.60% pressure drop compared with the pristine Al2O3 filter, leading to the highest quality factor (Qf) ever reported. Furthermore, the Ag@MWCNTs/Al2O3 hybrid filter showed excellent water repellency (water contact angle of 139.6 ± 2.9°), prolonging the service life of the filters and improving the air purification efficiency. The novel Ag@MWCNTs/Al2O3 hybrid filter exhibits remarkable air purification performance in both laboratory synthetic conditions as well as in the "real world" and shows great promise as an effective single replacement for multiple layers of air purifying filters.

Development of arc plasma for removal of high concentration VOCs

Development of arc plasma for removal of high concentration VOCs

Combination of adsorption followed by ozone oxidation with pressure swing adsorption technology for the removal of VOCs from contaminated air streams

This paper reports the application of adsorption followed by ozone oxidation in the pressure swing adsorption (PSA) process for the removal of VOCs from contaminated air streams. For that 13X molecular sieves and o-xylene selected as adsorbent and contaminant (one of the VOCs), respectively. The adsorption capacity of 13X molecular sieves for o-xylene is significantly increased from 0.6 to 2.8mmol/g with pressure from 0.5 to 5.0kg/cm2 and these values are relatively good compatible with the Freundlich isotherm model. The 13X molecular sieves are efficiently regenerated in 70min by ozone oxidation process at 25°C and the adsorbed o-xylene is significantly oxidized to the CO2. In four successive cycles of adsorption followed by ozone oxidation process, the adsorption efficiency of 13X molecular sieves is not affected (±5%). Further, the adsorption-ozone oxidation process embedded PSA system is operated continuously for 50h and there is no breakthrough observed in the fresh air. So that, the combination of adsorption followed by ozone oxidation with PSA process seems to be the better technology for the removal of VOCs from the contaminated air streams.

VOCs Removal by Oxidation/Reduction Reaction of Cu-Doped Photocatalyst

VOCs Removal by Oxidation/Reduction Reaction of Cu-Doped Photocatalyst

Removal of VOCs by catalytic process. A study of MnZnO composites synthesized from waste alkaline and Zn/C batteries

Spent alkaline and zinc-carbon batteries were subjected to a biohydrometallurgy process, in order to recover manganese and mixed manganese zinc oxides. Two solids were synthesized, one of them prepared by reaction of MnSO4 and KMnO4 (MnOx) and the other obtained by chemical precipitation with NaOH (ZnMnO).The characterization by XRD, TPR, FTIR and XPS revealed the presence of Mn3+ and Mn4+ cations in both samples, and the presence of ZnO and Mn-Zn spinels in ZnMnO. The samples were evaluated in the oxidation reaction of ethanol and toluene. The results in the flow reactor showed that ethanol conversion on both catalysts, MnOx and ZnMnO, is rather similar, but toluene conversion is markedly higher on MnOx, due to a greater Mn/Zn ratio and to the absence of a crystallized ZnO phase. The FTIR study demonstrated that ethanol is oxidized to acetaldehyde at low temperature, and to CO2 and CO at 400°C. Traces of CH4 in the gas phase are also detected at high temperature. The formation of ethoxy and acetate groups is observed at the catalyst surface. With respect to toluene oxidation, CO2 is detected at 300°C and when the temperature is increased, CO is also observed in the gas phase. The results showed that: (i) the alkaline and Zn-carbon batteries can be recycled as catalysts and (ii) the solids can be used in the catalytic process for VOCs control.

An efficient photo-catalytic VOC removal process by one-pot synthesized N-F/TiO2 nanoparticles in fluidized-spouted bed reactor

ABSTRACTPhotocatalytic degradation under visible light irradiation is an important task of using solar energy for the removal of environmental pollutants. N-F/TiO2 nanoparticles were synthesized in one-pot sol–gel condition using tetra-isopropyl-orthotitanate as the TiO2 precursor and NH4F as the N-F doping source. Diffuse reflectance spectroscopy (DRS) analysis of the material has shown a reduction of band gap energy and shifting absorption edge to the visible wavelengths. A fluidized-spouted bed reactor equipped with the light source was designed and constructed for the oxidation process of VOC from the high airflow rate under Hg lamp irradiation using synthesized N-F/TiO2 nanoparticles. Acetaldehyde was used as the air pollutant model molecule of VOC in this process. The effluent acetaldehyde concentration was analyzed continuously along the time by an online Gas Chromatography (GC) from the start up to reaching steady conditions. The results have revealed significant enhancement of acetaldehyde removal by the N-F/TiO2 sample fabricated with an equal weight ratio of NH4F/Ti. After steady conditions, almost 100% removal of acetaldehyde was observed in the spouted bed reactor from a high airflow stream of 5 L/min polluted with 1000 ppm acetaldehyde at room-temperature conditions, under 80 W Hg with 500 Lux intensity.

Spouted bed reactor for VOC removal by modified nano-TiO2 photocatalytic particles

Samples of N-doped, F-doped and N–F codoped TiO2 nanoparticles were synthesized by physical and chemical treatments. X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR), Brunauer–Emmett–Teller technique (BET) and UV–vis diffuse reflectance spectroscopy (DRS) were used to characterize the prepared powders. FTIR analysis confirmed that nitrogen and fluorine were replaced in the oxygen sites of TiO2 structure. DRS analysis has revealed that absorption spectra of the N-doped and F–N–TiO2 samples were significantly extended to the visible light region. The photocatalytic activity of the prepared samples was evaluated through the process of acetaldehyde degradation under Hg lamp in a high flow rate spouted bed reactor. F–N–TiO2 sample degraded 98.2% of 1000ppm acetaldehyde in the spouted bed reactor with a flow rate of 1000ml/min. The high photocatalytic activity of TiO2 in the spouted bed reactor can be due to the enhanced properties of modified TiO2 as well as efficient hydrodynamics, effective light scattering to the particles and low mass transfer resistance in spouting conditions. The Langmuir kinetic model was adapted for photocatalytic degradation of acetaldehyde and its kinetic parameters were specified experimentally.

Bioscrubbing of low concentrations of isopropanol from air stream

A biotrickling filter packed with 2.0″ polypropylene Tri-packs was used for testing the removal of isopropyl alcohol (IPA) in an air stream with relatively shorter empty bed residence time (EBRT) for the gas flowing through the packed section. Most of the influent IPA concentrations were controlled in the range of 6–333mg/m3 and EBRTs in 12.8–2.4s. Results indicate that with the operation conditions and a nearly fixed volumetric loading (L) of around 65gIPA/m3h, a 98–100% IPA removal could be obtained, and with an EBRT of 2.4s, L should be less than 30g/m3h to get a nearly total IPA removal. The results show an opportunity for retrofitting a present chemical scrubber to a biotrickling one by just seeding and supplementing microbial nutrients to the circulation liquid to cultivate microbial films on the original packing material. By the retrofit, efficiencies of VOC removal from the influent waste gas stream could certainly be enhanced.

Impact of VOC removal by activated carbon on biodegradation rates of diesel, Syntroleum and biodiesel in contaminated sand

The degradation of conventional diesel (D), synthetic diesel (Syntroleum), and pure fish biodiesel (B100) by indigenous microbes was investigated in laboratory microcosms containing contaminated sand. The fate of volatiles and the influence of volatilization on degradation rates were examined by placing activated carbon (AC) in microcosm headspaces to sorb volatiles. Three AC regimes were compared: no activated carbon (NAC), regular weekly AC change (RAC), and frequent AC change (FAC), where the frequency of activated carbon exchange declined from daily to weekly. Generally, the alternative fuels were biodegraded faster than diesel fuel. Hydrocarbon mineralization percentages for the different fuel types over 28days were between 23% (D) and 48% (B100) in the absence of activated carbon, decreased to 12% (D) – 37% (B100) with weekly AC exchange, and were further reduced to 9–22% for more frequent AC change. Sorption of volatiles to AC lowered their availability as a substrate for microbes, reducing respiration. Volatilization was negligible for the biodiesel. A mass balance for the carbon initially present as hydrocarbons in microcosms with activated carbon in the head space was on average 92% closed, with 45–70% remaining in the soil after 4weeks, 9–37% mineralized and up to 12% volatilized. Based on nutrient consumption, up to 29% of the contaminants were likely converted into biomass.

The 40 m3 Innovative experimental Room for INdoor Air studies (IRINA): Development and validations

Over the last 30years, several experimental chambers were developed and implemented for indoor air studies. Yet, they were not all representative of real indoor air conditions. Either they did not have sufficient volumes or they were hindered by difficulties to control experimental conditions and air exchange rates. In this context, a 40m3 Innovative experimental Room for Indoor Air studies (IRINA) has been developed and validated at Mines Douai (Atmospheric Sciences et Environmental Engineering department (SAGE)) to overcome these drawbacks and above all to perform reproducible indoor air studies avoiding any possible experimental biases. IRINA inner walls are covered with aluminum foils. The room is operated in a closed mode and is equipped with a VOC injection system that relies on the heated and pressurized injection of vaporized VOC. IRINA is also equipped with analytical instruments that allow the analysis of both gas (online and offline measurements) and particle phases. IRINA validation evidenced that: (i) the air exchange rate of the room is well controlled over an one year timespan; (ii) both gaseous and particulate background levels in IRINA remain lower than typical indoor air conditions; (iii) fast homogenization of injected VOC concentrations is reached in the room; (iv) adsorption phenomena on IRINA walls are limited; and (v) there is no VOC matrix impact regarding individual VOC decays. The modelling of VOC natural decay in IRINA based on the new INCA-Indoor model showed that the VOC removal in IRINA is mainly due to the air exchange rate.

The effect of injected ozone on the microbial metabolic characteristics in biofilters treating gaseous toluene

O3 injection technique was developed recently and successfully shown the ability of controlling biomass, allowing enhanced VOCs removal efficiency in biofilters. However, the effect of injected O3 on microbial metabolic patterns is still unknown. In this study, six biofilters treating gaseous toluene were set up and operated continuously for 97days with different inlet O3 concentrations ranging from 0 to 300mgm−3. The metabolic functions and characteristics of the microbial communities in the biofilters were monitored by Biolog microplates cultivation method periodically. According to the profile of average well color development (AWCD), the metabolic activity of microorganisms in the biofilter with 300mgm−3 O3 was increased by 100%. Principle components analysis (PCA) result demonstrated significant changes in biofilters exposed to O3, but eventually had little difference with those without O3 after long-term operation. Among 31 carbon sources in Biolog microplate, the utilization of some non-biodegradable carbon sources including γ-hydroxybutyric acid, d-galactonic acid γ-lactone, d-mannitol, d-cellobiose and β-methyl-d-glucoside were obviously enhanced by injected O3. The analysis on DQ-fd plot showed that the variation trends of metabolic diversity and dominance in biofilters with and without O3 were in some extent different.

Operando DRIFT Spectroscopy Characterization of Intermediate Species on Catalysts Surface in VOC Removal from Air by Non-thermal Plasma Assisted Catalysis

An innovative plasma discharge reactor was developed to fit an infrared cell and to allow the in situ characterization of isopropanol (IPA) and toluene decomposition at the surface of three metal oxides (γ-Al2O3, TiO2 and CeO2). The impact of the plasma discharge on the conversion of these pollutants, with the material placed in the discharge area, was studied under real time conditions at atmospheric pressure via infrared analysis. The plasma treatment of IPA molecules led to the formation of acetone, propene, acetic acid and/or formic acid. By contrast, the toluene oxidation led to the rapid opening of the aromatic ring, followed by the total oxidation through carboxylic formation of the species arising from the toluene molecules fragmentation.

High‐performance PDMS membranes for pervaporative removal of VOCs from water: The role of alkyl grafting

ABSTRACTTo improve the pervaporation performance of PDMS membrane, alkyl groups with different chain length were grafted into PDMS matrix. The prepared membranes were characterized by ATR‐IR, DSC, TGA, PALS, and tensile testing. The effects of alkyl grafting on pervaporation performance of PDMS membrane were investigated in separation of ethyl acetate/water mixture. Experimental results show that the separation factor of PDMS membrane is largely improved by alkyl grafting because of the enhanced preferential sorption of ethyl acetate, and this improvement depends on alkyl grafting ratio and alkyl chain length. The total flux of PDMS membrane reduces after alkyl grafting owing to the decreased free volume. When grafting ratio is above 6.9%, membrane grafted with shorter alkyl groups is preferred for pervaporation. The best pervaporation performance is achieved by 9% octyl grafted PDMS membranes with a separation factor of 592 and a total flux of 188 gm−2 h−1 in separation of 1% ethyl acetate/water mixture at 40 °C. Moreover, this octyl grafted PDMS membrane also exhibits excellent separation performance in removal of butyl acetate, methyl‐tert‐butyl ether, and n‐butanol from water. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43700.

Study of sulfuric acid treatment of activated carbon used to enhance mixed VOC removal

The objective of this work was to study the effect of sulfuric acid treatments of activated carbons on single and binary VOCs adsorptions. Commercial activated carbon (AC) and 5, 10 vol% sulfuric acid treated activated carbon (5S-AC, 10S-AC) were prepared. The physical-chemical properties of activated carbons were characterized by N2 adsorption-desorption isotherms, temperature-programmed desorption (TPD). Measurements of the adsorption behavior of pure concentrations and mixture of benzene and toluene on activated carbon were a flow-typed fixed bed system at room temperature under atmospheric pressure. Of all samples examined, the 10S-AC exhibited the highest adsorption capacity for both benzene and toluene, having both longer breakthrough and separation times. The adsorption amount of toluene and benzene on 10-S-AC was increased by 18% and 47%, compared with that on the AC. This is attributed to the surface oxygen group species of activated carbon and changes the porosity of adsorbents due to sulfuric acid treatment.