Simultaneous removal of volatile organic compounds from cooking oil fumes by using gas-phase ozonation over Fe(OH)3 nanoparticles

Journal of Environmental Chemical Engineering 3 (2015) 1530–1538

Contents lists available at ScienceDirect

Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece

Simultaneous removal of volatile organic compounds from cooking oil fumes by using gas-phase ozonation over Fe(OH)3 nanoparticles Bao Lin* , Shu-Liang Liaw Graduate Institute of Environmental Engineering, National Central University, 300 Jhongda Road, Jhongli, Taoyuan, Taiwan

A R T I C L E I N F O

A B S T R A C T

Article history: Received 12 January 2015 Accepted 28 May 2015

The ozonation technology is widely used for treating indoor air pollution. This technology was developed using Fe(OH)3 as a catalyst for the vapor-phase removal of volatile organic compounds (VOCs) from cooking oil fumes (COF). The nanocrystalline Fe(OH)3 was prepared in an acidic environment in the presence of chloride ions. The hydroxylation of salicylic acid through catalytic ozonation indicated that the average molar ratio of hydroxyl radical:ozone was 0.67–0.69. The adsorption and oxidation by ozone showed that the nondissociated species on the catalyst surface reflected the reactivity of COF with respect to the hydroxyl radicals. The catalytic selectivity of Fe(OH)3 was altered with the amount of hydroxyl radicals. Long-term testing for 300 h at 190
C proved the thermal stability of Fe(OH)3, with a mean removal efficiency of VOCs of up to 95%. The retention time was as short as 0.05 s. The residual ozone concentrations were stable at less than 0.01 ppm. ã 2015 Elsevier Ltd. All rights reserved.

Keywords: Cooking oil fumes Indoor air Fe(OH)3 Catalytic ozonation

Introduction Evidence has increasingly shown that exposure to cooking oil fumes (COF) is linked to lung cancer [1]. Among COF pollutants, ultrafine particles (UFPs) and volatile organic compounds (VOCs) are the most considerable [2–4]. Electric precipitation significantly removes 0.1–1.0-mm of oil smoke particles from flowing gas [5]. Conventional technologies for VOC removal include biofilters, wet scrubbers, and catalytic oxidation [6–8]. However, these technologies cannot be used because of their large size, high capital and maintenance costs, and the formation of undesirable byproducts that require additional treatments. Environmentally benign, costeffective treatment technologies are necessary to remove VOCs from COF. Ozone technology is widely studied for treating indoor air pollution. The use of ozone catalytic oxidation for treating VOCs has shown potential because higher conversions can be achieved at low reaction temperatures [9,10]. In this study, a nanosized Fe (OH)3 catalytic ozonation process was developed for the gas-phase removal of VOCs from COF. Fe(OH)3 is frequently used as an adsorbent to remove various heavy metals from contaminated soil and water [11]. The interest

* Corresponding author. Tel: +886 2772 0922; fax: +886 2550 8047. E-mail address: [email protected] (B. Lin). http://dx.doi.org/10.1016/j.jece.2015.05.026 2213-3437/ ã 2015 Elsevier Ltd. All rights reserved.

in proposed metal is triggered by its abundant hydroxide groups [12]. In general, Fe(OH)3 nanocrystals are synthesized using a FeCl3 solution at a high pH (>11) [13–15]. However, a high pH leads to hydroxide ions being less competitive for structural sites than chloride ions. Fe(OH)3 can be formed at a relatively low pH in the presence of chloride ions [16–18]. In addition, because an unpredictable amount of steam is produced during cooking, high thermal energy causes any moisture coated on the surface of the catalyst pellets to evaporate, thus increasing the gas–solid mass transfer coefficients. The morphological performance of a catalyst depends on the calcination temperature because the morphology transformation is involved in the complex multistep solid-phase thermal decomposition of a metal salt precursor to a metal oxide [19–22]. In this study, the conventional Fe(OH)3 synthesis process was altered; the reaction was performed in an acidic environment (pH 5) in the presence of chloride ions, and the product was then calcined at different temperatures. To optimize the ozone consumed, the adsorption and oxidation of COF by ozone at the Fe(OH)3 surface were performed. Gas-phase characterization enabled examining the surface oxidation mechanisms. After optimizing the consumed ozone, a long-term testing of the COF treatment was conducted for 300 h to evaluate the thermal durability of Fe(OH)3 and the retention time for the operation parameters necessary for a scale-up design.

B. Lin, S.-L. Liaw / Journal of Environmental Chemical Engineering 3 (2015) 1530–1538

Experimental and methods Catalyst preparation In this study, Fe(OH)3 nanoparticles were prepared as follows. 100 g of reagent-grade FeCl36H2O and 10 g of Na2SO4 were simultaneously dissolved in 25 g of aqueous ammonia (15 wt%) for hydrolysis. The total volume of the solution was 300 mL. The solution was slowly titrated with an appropriate amount of HCl (0.1 M) until its pH was adjusted to 5. The reaction temperature of 25
C and a stirring speed of 500 rpm were strictly maintained throughout titration. The resulting gel was separated by centrifugation at 18,000 rpm for 30 min, and the gel was then washed repeatedly with deionized water. To confirm the removal of chloride ions in the hydrated iron oxide gel, the chloride ions in the deionized water were tested using an AgNO3 solution (0.05 M). The deionized water was replaced approximately 10 times until no more chloride ions were detected. The resulting cake was freezedried in a bench freeze drier (DF1, Thermovac) until the temperature of the gel reached ambient temperature. The freeze-drying conditions were similar to those reported previously [23]. After freeze-drying, the synthesized catalyst was divided into several groups for 2-h calcination at 25, 100, 200, 250, 300, and 350
C in a conventional muffle furnace in the presence of air. Catalytic activity measurements Catalytic reactor The catalytic ozonation system included a fixed-bed reactor and an ozone generator (Fig. 1). The reaction chamber was a steel cylinder (with a length of 300 mm and an inner diameter of 200 mm) containing a catalyst filter. The filter consisted of 20 g of catalyst powder, which was coated on 200 g of cordierite ceramic honeycomb substance under vacuum. The coating steps followed those described in the U.S. patent 7,521,087 [24]. The coated substrate was packaged in a wire mesh shell with a mesh size of 0.1 mm. Ozone gas was generated using a pure-oxygen-feed ozone generator (OA100C, Japan) with a maximum output of 0.1 L/min at 150 ppm. Salicylic acid testing The formed hydroxyl radicals were determined using the hydroxylation of salicylic acid (SAL) [25]. A filter paper was

1531

impregnated with SAL to adsorb hydroxyl radicals generated from the catalytic decomposition of ozone in the gas phase. The experiment was performed at room temperature and atmospheric pressure. Clean air was pumped as a carrier gas, which conveyed influent ozone into the reactor for 20 min. The influent ozone concentration was fixed at 100 ppm, the gas flow rate was fixed at 50 mL/min, and the residence time was fixed at 0.5 s. The relative humidity of the influent air was altered using a water bubbling system. The hydroxyl radicals emitted from the reactor were collected on a filter paper with an inner diameter of 200 mm. The paper was dripped equably with a 15-mL solution containing 1.0 g of SAL and anhydrous ethanol (99.9%). In addition, the paper was dried and weighed until all the solution was loaded on. Throughout the hydroxylation of SAL by hydroxyl radicals at the gas–solid interface, the film collection efficiency was approximately 100%. The chemicals present on the paper were carefully removed using 500 mL deionized water for characterization. COF testing The experimental setup mainly linked the catalytic reactor to a 2-L impinger, which was filled with 1 L of sunflower cooking oil of South African origin (Fig. 2). The oil was heated to its smoke point (180
C) to produce COF [26,27]. The relative humidity of influent air was altered using a water bubbling system. The adsorption and oxidation procedure consisted of five major steps: (i) activating the catalyst sample at 150
C for 1 h to remove water and other adsorbed hydrocarbon species to guarantee surface repeatability; (ii) adsorbing COF on the catalyst surface (the COF passes through the sorbent sites until they are saturated); (iii) flushing the adsorbent bed with dry airflow to remove reversibly adsorbed species and desorb the molecules with the weakest heat of adsorption (i.e., physisorbed species, leaving only the irreversibly adsorbed molecules on the catalyst surface); (iv) surface exposition by switching on ozone generator with influent ozone concentration of 100, 200 and 300 ppm; (v) closing the ozone supply after 20 min and purging the system under dry synthetic airflow for a few minutes. After the aforementioned experiment was completed, the long-term test was performed by continuously feeding COF into the reactor for catalyzed oxidation. The operational conditions used in the experiment are listed in Table 1. The COF was sampled on-line before and after the treatment for characterization.

Fig. 1. Equipment setup for measuring hydroxyl radicals.

1532

B. Lin, S.-L. Liaw / Journal of Environmental Chemical Engineering 3 (2015) 1530–1538

Fig. 2. Experimental setup for COF decomposition.

Table 1 Experimental conditions in the long-term testing. Condition

Value

Gas flow rate (L/min) Reaction temperature (
C) Relative humidity (%) Retention time (s) Influent ozone concentration (ppm) Initial THC concentration of COF (ppm) Duration of experiment in each run (h)

10–500 190 80 0.5–0.01 300 200–220 48–300

Analyses The morphologies of the catalyst samples were observed using a scanning electron microscope (SEM, Hitachi S-2150, Japan). The surface characteristics of the catalysts were studied using X-ray diffraction (XRD, Bede D1, UK) operating at 40 kV and 40 mA tube current provided by Philips X’Pert Pro with CuK radiation. The XRD patterns of the solids were recorded in the range 10–90
. The characteristic reflection peaks were matched with those in the data files of the Joint Committee on Powder Diffraction Standards (JCPDS), and the crystalline phases were identified. The average chloride ion content of the samples was determined using an energy dispersive spectroscopy (EDS, JSM-840A, Japan). Specific surface area measurements of the fresh catalyst were based on the N2 adsorption–desorption porosimetry at 77 K, and the surface areas were measured using the Brunauer–Emmett–Teller (BET) method (Micromeritics Gemini-2380). The crystallite size was

determined using XRD patterns and the Scherrer equation at 2u = 30
. The mean pore diameter (in nm) was determined using the following equation [28]: d¼

ð2  103 eÞ SBET

(1)

where the pore volume (e) is expressed in cm3/g and the BET surface area (SBET) is expressed in m2/g. Ozone concentrations were monitored using an ozone ultraviolet photometry analyzer (Ld SOZ-302C, Japan). The presence of 2,3-dihydroxybenzoic acid, catechol, and 2,5-dihydroxybenzoic acid in the deionized water was determined using high-performance liquid chromatography (Waters 600, Japan). The obtained chromatographic parameters were similar to those reported previously [29]. The mechanism of SAL hydroxylation by hydroxyl radicals is shown in Fig. 3. The hydroxyl radical concentration was measured by monitoring the concentrations of 2,3-dihydroxybenzoic acid, catechol, and 2,5-dihydroxybenzoic acid resulting from the attack of the hydroxyl radicals. The catalytic activity was determined using the hydroxyl radical concentration, which is obtained using the following equation:
 P radical Ci  V L  N (2) ¼ C OH Fg  t cm3 where Ci is the concentration of the hydroxylated derivatives formed during sampling (mol/L), VL is the volume of the scrubbing solution after sampling (L), N is the Avogadro’s number, Fg is the airflow rate (mL/min), and t is the sampling period (min).

Fig. 3. Reaction scheme of SAL hydroxylation by hydroxyl radicals.

B. Lin, S.-L. Liaw / Journal of Environmental Chemical Engineering 3 (2015) 1530–1538

1533

The kinetics order of the hydroxyl radical formation was determined using the method of initial rates. The method of variation in the initial rates involves measuring the rate of reaction for short durations before any significant change occurs in the concentration, and is obtained using n¼

logðdC OH1 =dtÞ  logðdC OH2 =dtÞ logC 1  logC 2

(3)

where n is the order of the degradation of the reactant, C1 and C2 are the initial known concentrations of the reactant in the experiment (g/cm3), and ðdC OH1 =dtÞ and ðdC OH2 =dtÞ are the yield rates of hydroxyl radicals at various initial concentrations. The compounds of COF were characterized using gas chromatography–mass spectroscopy (QP2010NC, Japan). The amount of CO2 produced was determined using gas chromatography with a thermal conductivity detector (China Chromatography 3000, Taiwan). The catalytic selectivity of Fe(OH)3 from the COF to CO2 is obtained as follows:    (4) Selectivity %Þ ¼ Q CO2 =Q COFðirrÞ  100% where Q CO2 is the total amount of CO2 resulting from the oxidation of COF, and QCOF(irr) is the total quantity of COF pollutants irreversibly adsorbed on the catalyst surface. Total hydrocarbon (THC) concentrations were determined using gas chromatography with a flame ionization detector (China GC-8601, Taiwan). The removal efficiency of VOCs is calculated as follows: Re ¼

ðC in  C out Þ  100% C in

(5)

where Re represents the removal efficiency, and Cin and Cout are the THC concentrations of VOCs before and after the catalytic reaction, respectively. Results and discussion Physical properties of the prepared samples Fig. 4 shows the XRD patterns of the obtained products at 25, 200, and 300
C. The XRD patterns of the products at 100, 250, and

Fig. 5. SEM image of Fe(OH)3 at 5000  magnification. (a) Effect of ozone concentration. (b) Effect of relative humidity.

350
C were similar to those at 25, 200, and 300
C, respectively. The sample at 25
C revealed the tetragonal body-centered crystalline phase of Fe(OH)3, which was confirmed by the JCPDS pattern no. 22-0346. The crystalline phase of Fe(OH)3 remained unchanged at 100
C. However, it transformed to that of akaganeite (JCPDS pattern no. 34-1266) at 200
C and finally to hematite (a-Fe2O3, JCPDS pattern no. 33-0664) at 300
C. The increase in the calcination temperature gradually transformed the Fe(OH)3 structure to the b-FeOOH intermediate before its final transition to a-Fe2O3. Fe(OH)3 is a precursor of a-Fe2O3 particles and features in the mechanism of the formation of a-Fe2O3 particles from b-FeOOH. Fig. 5 shows an SEM image of Fe(OH)3. According to the figure, all Fe(OH)3 grains had a similar morphology and a size range of 20–80 mm. The EDS results indicated that the average chloride content was approximately 0.8%. The existence of chloride contamination of less than 1% indicated that the chloride ions were not thoroughly removed during synthesis. Table 2 shows the experimental data for pore diameter distribution, pore volume, and crystallite size of all the products.

Fig. 4. XRD patterns of the as-prepared iron oxide products.

1534

B. Lin, S.-L. Liaw / Journal of Environmental Chemical Engineering 3 (2015) 1530–1538

Table 2 Physical characterization of all hydrated iron oxides. Sample

SBET (m2/g)

Range of pore diameter (nm)

Mean pore volume, e (m3/g)

Mean crystallite size (nm)

Mean pore diameter, (nm)

Fe(OH)3 (25
C) Fe(OH)3 (100
C) b-FeOOH (200
C) b-FeOOH (250
C) a-Fe2O3 (300
C) a-Fe2O3 (350
C)

430 431 436 432 310 254

2–6 2.1–6 2.2–6.8 2.2–6.8 3.3–8.9 5–15

0.56 0.56 0.52 0.51 0.46 0.42

3.6 3.6 4.6 6.1 6.3 6.6

2.605 2.575 1.944 2.372 2.895 3.308

The uncalcined Fe(OH)3 had a SBET of 430 m2/g, a total pore volume of 0.56 m3/g, a pore size in the range 2–6 nm, and a maximum (predominant) pore diameter of 2.605 nm. This nanocrystalline size is considerably smaller than that reported elsewhere [30], and SBET is higher than reported values, which could be partially attributed to the small crystallite size [31]. The physical characterization of the materials did not change significantly until the calcination temperature was increased to 300
C. One reason for this observation is that digestion under a high temperature reduced the water content in the resulting gel; therefore, the initial particle structure was retained during drying and calcination. Another reason is that the rate of crystallization of the initial particles increased during the digestion and the defects on the surface were reduced; therefore, sintering caused by surface diffusion was limited. Hydroxyl radical formation Effect of hydroxyl groups on the catalyst surface Fig. 6(a) shows that the hydroxyl radical yield increased linearly with an increase in the ozone concentration. For an ozone concentration of 100–300 ppm, Fe(OH)3 produced 1.65  1015 to 5.10  1015 OH radicals/cm3. The average molar ratio of hydroxyl

radical:ozone was 0.67–0.69. The b-FeOOH produced 1.65  1015 to 5.10  1015 OH radicals/cm3, yielding an average hydroxyl radical: ozone molar ratio of 0.29–0.31. In addition, a-Fe2O3 produced no hydroxyl radicals. Thus, Fe(OH)3 exhibited a much higher hydroxyl radical generation efficiency than did b-FeOOH and a-Fe2O3. As expressed in Eq. (6), ozone adsorption on hydrated iron(III) oxide can be mainly described as weakly bonded molecules that form hydrogen bonds with hydroxyl groups and are physically adsorbed on the surface [32]:  FeIII OH þ O3ðgÞ ?  FeIII OH  O3  FeIII OH  O3ðgÞ ! FeII  O2 þ HO2  HO2  þ O3 ! OH þ 2O2

(6)

The decomposition of ozone on a reduced metal surface could lead to the formation of hydroxyl radicals, in accordance with the reaction of ozone with Fe(II). The yield rate of hydroxyl radicals through the catalytic ozonation was calculated using the following equation: rOH ¼ k½O3 ½OH 

(7)

The yield rate of hydroxyl radicals (rOH) was obtained using second-order kinetics with respect to the ozone concentration [O3] and hydroxyl radical concentration [OH]. If the ozone consumption is considered fixed, then the generation of hydroxyl radicals on the catalyst surface is determined with the hydroxyl group concentrations. The catalyst activities of the as-prepared ironbased materials follow the order Fe(OH)3 > b-FeOOH > a-Fe2O3 and are directly proportional to the hydroxyl group concentrations. Effect of relative humidity Fig. 6(b) shows the hydroxyl radical density in the gas stream at various relative humidity. The increase in the relative humidity caused a decrease in the hydroxyl radical density. This result matched those reported by Jin et al. [33] and Sahle-Demessie and Devulapelli [34]. Increasing moisture levels inhibits ozone decomposition because of the competitive adsorption of ozone and water molecules on the catalyst surface. Water covers the surface of the catalyst and reduces the metal surface area of the catalyst pellets, thereby decreasing the overall mass transfer of ozone into the interior of the catalyst and consequently reducing the hydroxyl radical generation. COF adsorption

Fig. 6. Hydroxyl radical yield at different (a) ozone concentrations and (b) relative humidities.

COF containing a mean initial THC concentration of 211 ppm was introduced into the experimental apparatus at a flow rate of 1.0 L/min for 30 min (breakthrough). After 30 min, dry air was flushed into the apparatus. The COF breakthrough and flushing curves for Fe(OH)3 are shown in Fig. 7. The rising part of the curve corresponds to the adsorption of COF on the catalyst. The decaying part of the curve corresponds to the desorption of the weakly bonded COF from the catalyst surface. The difference between the

B. Lin, S.-L. Liaw / Journal of Environmental Chemical Engineering 3 (2015) 1530–1538

1535

Table 4 Various compounds detected in the COF sample during catalytic ozonation. Ozone consumed (ppm) compounds

100

200

300

Ketones 2-Heptanone

2-Heptanone

2-Heptanone

2(3H)-Furanone

2(3H)-Furanone

3-Octanone

5-Nonen-2-one

6-Undecanone

2,4-Octanedione

2Heptanone 6Undecanone 5-Nonen-2one

2-Undecanone

5-Nonen-2-one 2-Undecanone trans-3-Nonen-2one

2(3H)-Furanone 6-Undecanone 5-Nonen-2-one

Fig. 7. COF breakthrough curve and flushing curve monitored on the Fe(OH)3 surface at a flow rate of 1 L/min in dry synthetic air at 150
C.

flushing curve and the breakthrough curve enables determining the reversibly adsorbed fraction of COF on the catalyst; that is, weakly bonded species. The amount of COF initially adsorbed on Fe (OH)3 was determined to be 0.20 mg THC/m2. Flushing led to the desorption of 0.056 mg THC/m2 of reversibly adsorbed COF. The subtraction of the two values yielded the irreversibly adsorbed COF on the catalyst surface, 0.144 mg THC/m2.

2-Undecanone 2(3H)-Furanone 6-Dodecanone 2(3H)-Furanone 3-Isopropyl-5methylhexan-2one Alkenes 2-Tridecene 1,3-Hexadiene 2-Tridecene 4,6-Decadiene

Oxidation of adsorbed COF by ozone Following flushing, the surfaces of the hydrated iron oxide samples were covered only by irreversibly adsorbed COF. Fig. 8 displays the evolution of CO2 production during the exposure of COF—irreversibly adsorbed catalyst surfaces to catalytic ozonation for 20 min. The amount of CO2 produced for each catalyst was obtained through the integration of the respective temporal profiles shown in Fig. 8. Table 3 indicates that CO2 was not produced until 200 ppm ozone was consumed. The performance remained constant until the ozone supply was shut off. The CO2 production and the ozone consumed by the adsorbents confirmed that the hydroxyl radicals could oxidize and mineralize the COF adsorbed on the Fe(OH)3 surface. In addition, the catalyst selectivity of Fe(OH)3 for 300 ppm ozone consumed was 65%, and those for 200 and 100 ppm ozone

Alcohols 1-Octen-3-ol 2-Pentyl-1-octanol 4-Ethylcyclohexanol 1-Tridecanol Aldehydes 2,3-Dimethyl-2heptenal 2-Butyl-noctaldehyde 2-Octenal (E)-Heptanal (E)-2-Decenal 2-Nonenal

Fig. 8. Mineralization performance for various ozone concentrations consumed.

Table 3 The mineralization performance of COF under various ozone concentrations consumed. Ozone concentration (ppm)

100

200

300

CO2 production (mg/m2) Mineralization efficiency (%)

0 0

0.021 16.659

0.094 65.129

Acids trans-2-Undecenoic acid 9-Hexadecenoic acid

2-Tridecene

4,6-Decadiene

(E)-Heptanal-2hexene 9-Nonadecene 1,3-Hexadiene 2-Tridecene 1-Undecene 4,6-Decadiene

2-Methylene

1-Octen-3-ol

2,2Dimethylethanol Cycloheptanol

Hex-3-ene1,6-diol 1Tridecanol

4-Pentenal

2-Octenal

2-Heptenal

(E)-2Decenal

(E,E)-3-Hexadiene 9-Nonadecene

2-Pentyl-1octanol 4Cyclohexanol Ethylcyclohexanol 1-Tridecanol

2,3-Dimethyl-2heptenal 2-Butyl-noctaldehyde 2-Octenal 8-Methyl-2undecenal (E)-Heptanal cis-2,4Decadienal (E)-2-Decenal 2-Nonenal

1,3Hexadiene 4,6Decadiene

2,4-Octadienal 2,4-Nonadienal 2,4Dimethyloctanal Decanal 4-Nonenal Tridecanal 8-Methyl-2undecenal Butyl-2-octenal 2,4-Decadienal 2,4-Heptadienal 2-Undecenal (E)-2,4-Decadienal

trans-2-Undecenoic Formic acid acid Hexanoic acid Acetic acid

Hexanoic acid

trans-2Undecenoic acid 9-Hexadecenoic acid Hexanoic acid

(E)-Octanoic acid Nonanoic acid Acetic acid

(E)-Octanoic acid Nonanoic acid Acetic acid

(E)-Octanoic acid Nonanoic acid Formic acid Acetic acid Butyric acid

Butyric acid

Hexanoic acid

1536

B. Lin, S.-L. Liaw / Journal of Environmental Chemical Engineering 3 (2015) 1530–1538

Fig. 9. Long-term COF decomposition in ozonation treatments.

Fig. 10. Effect of the gas retention time on COF removal efficiency and catalytic selectivity.

consumed were 16.6% and 0%, respectively. This behavior is consistent with that of the oxidation achieved by altering the amount of ozone consumed. This result can be explained through a competitive adsorption between the absorbent and the ozone consumed [35,36]. In heterogeneous catalytic ozonation, an organic substance is adsorbed on an oxidized catalyst and then oxidized by an electron-transfer reaction to regenerate the reduced catalyst [32,35,37]. When VOCs adsorb onto the catalyst surface, only a small fraction of the surface sites are accessible for the adsorption of ozone molecules. An insufficient amount of hydroxyl radicals converted from the residual active sites degrades the untreated VOCs into complex intermediate products. The competitive adsorption between the species on the catalyst sites consequently leads to the release of the reacted compounds in the gas phase [38]. However, a sufficient amount of hydroxyl radicals mineralizes COF simultaneously to CO2 and H2O through a pathway of direct decomposition without the creation of additional intermediate products.

This theory can be confirmed by the qualitative analysis of various chemicals present in the COF samples taken in the experiments. In Table 4, column 1 shows the untreated COF for reference. Columns 2–4 present various components of the treated COF. The sunflower oil was mainly composed of saturated and unsaturated fats. Untreated COF consisted mainly of alkenes, ketones, aldehydes, alcohols, and carboxylic acids. Compared with untreated COF, for 100 ppm ozone consumption, there was no significant difference between the compounds. For 200 ppm ozone consumption, the amount of alkenes and alcohols decreased, and that of aldehydes, ketones, and carboxylic acids increased. For 300 ppm ozone consumption, the number of components was significantly reduced and no additional intermediate products were generated. Thermal durability Fig. 9 shows the evolution of CO2 production and VOCs concentration through introduction of the VOCs concentration of 200–220 ppm COF for ozonation treatments. The test was continuously conducted for 300 h under the following conditions: a fixed retention time of 0.5 s, an influent concentration of ozone of 300 ppm, and a reaction temperature of 190
C. The figure shows that there was no significant difference in the VOCs concentration of treated COF through ozonation alone. However, the ozone concentration varied slightly from 300 to 290 ppm. The ozone consumption could be due to the following mechanisms: cooking fumes contain particulate matter (PM), particularly of ultrafine size. When soluble PM passes through the water in the denuder to adjust the humidity, they absorb water on their outer surfaces, causing the formation of an aqueous phase of PM when they leave the denuder. Ozone molecules can dissolve in this formed liquid

Table 5 Summary of optimal operational parameters for studies on COF treatment. Technology type

Reaction temperature (
C)

Retention time (s)

Removal efficiency of VOCs (%)

Biofilter [4] Chemical scrubber [5] Catalytic combustion [6] Catalytic ozonation

50 Normal temperature 200–300 190

72–9 17 3.5–0.5 0.5–0.05

95 85 95 95

B. Lin, S.-L. Liaw / Journal of Environmental Chemical Engineering 3 (2015) 1530–1538

phase and react as an oxidant with speciated elements available in PM [39,40]. Additionally, the VOCs concentration of the treated COF was less than 5 ppm, and the CO2 production was 75 ppm throughout the catalytic ozonation. The removal efficiency of VOCs was up to 95%, and the mean catalytic selectivity, calculated using the mass ratio of CO2 produced to initial THC concentration, was 75%. Because high thermal energy is necessary to evaporate moisture from the surface of the catalyst pellets, the temperature of 190
C was selected, because it is the highest temperature at which the morphology of Fe(OH)3 can be maintained. Therefore, the observation evaluated the thermal tolerance of Fe(OH)3 at a critical reaction temperature before the morphology transformation from Fe(OH)3 to b-FeOOH. The residual ozone concentration after catalytic ozonation was of less than 0.01 ppm, thus satisfying the Taiwan Environmental Protection Agency maximum limit of 0.06 ppm for outdoor working establishments [41]. Retention time The COF removal tests at various retention times were conducted under the same operating conditions. The experiments were continuously performed for 48 h for each run. As shown in Fig. 10, the removal efficiency of VOCs (95%) and the catalytic selectivity (75%) were constant, within a retention time range 0.5–0.05 s. The values decreased significantly when the retention time were shorter than 0.05 s. As seen in Table 5 [6–8], a comparison of the technologies for COF treatment revealed that the optimal VOCs removal efficiency (95%) with the developed catalyst was higher than that (85%) of a wet scrubber. In addition, based on the similar VOC removal efficiency (95%), the experiment indicated that the optimal retention time (0.05 s) was obviously shorter than the time duration required for catalytic oxidation (0.5 s) and a biofilter (9 s). The retention time is derived according to the ratio of reactor volume:influent flow rate. For a continuous reactor without recycling the gas and a similar influent rate and conversion efficiency, a shorter retention time indicated a less reactor volume. Table 5 indicates that the retention times were shorter than those reported previously. The retentiontime tests indicated that the experimental volume is smaller than those reported previously, which is significant for COF emitted from densely populated areas that lack installation space. Conclusions In summary, ozonation in the presence of Fe(OH)3 nanoparticles as a catalyst resulted in the average molar ratio of hydroxyl radical:ozone of 0.67–0.69. This value is higher than those obtained for b-FeOOH (0.29–0.31) and a-Fe2O3 (zero). This was realized by increasing the hydroxyl radical generation efficiency through higher hydroxyl group concentrations. The Fe (OH)3 lowered ozone consumption per mole of converted organic compounds. The nondissociated COF on the catalyst surface was reactive toward hydroxyl radicals. The presence of sufficient hydroxyl radicals led to direct COF mineralization, which was followed by unselective decomposition steps. Continuous treatment for 300 h demonstrated the thermal durability of this catalyst at 190
C, with removal efficiencies of VOCs of up to 95%. The retention time was as short as 0.05 s. The operational safety of the proposed technology was demonstrated by residual ozone concentrations of less than 0.01 ppm. In conclusion, this technology is a viable alternative for controlling COF. Conflicts of interest All interests from the paper and the study belong only to the National Central University, Taiwan.

1537

Acknowledgments The authors thank the National Central University, Taiwan, for its financial and technical support. References [1] T. Lee, F. Gany, Cooking oil fumes and lung cancer: a review of the literature in the context of the U.S. population, J. Immigr. Minor. Health 15 (3) (2013) 646– 652, doi:http://dx.doi.org/10.1007/s10903-012-9651-1. 22678304. [2] G. Buonanno, G. Johnson, L. Morawska, L. Stabile, Volatility characterization of cooking-generated aerosol particles, Aerosol Sci. Technol. 45 (9) (2011) 1069– 1077, doi:http://dx.doi.org/10.1080/02786826.2011.580797. [3] M.A. Torkmahalleh, I. Goldasteh, Y. Zhao, N.M. Udochu, A. Rossner, P.K. Hopke, A.R. Ferro, PM 2.5 and ultrafine particles emitted during heating of commercial cooking oils, Indoor Air 22 (6) (2012) 483–491, doi:http://dx.doi.org/10.1111/ j.1600-0668.2012.00783. 22486983. [4] M. Amouei Torkmahalleh, Y. Zhao, P.K. Hopke, A. Rossner, A.R. Ferro, Additive impacts on particle emissions from heating low emitting cooking oils, Atmos. Environ. 74 (2013) 194–198, doi:http://dx.doi.org/10.1016/j.atmosenv.2013.03.038. [5] EPA, Control Technology Manual of Air Pollution from Food Manufacturing, Environmental Protection Administration, Taiwan, 2001. [6] J. Miao, L. Zheng, X. Guo, Restaurant emissions removal by a biofilter with immobilized bacteria, J. Zhejing Univ. Sci. B 6 (5) (2005) 433–437, doi:http:// dx.doi.org/10.1631/jzus.2005.B0433. [7] H.H. Cheng, C.C. Hsieh, Integration of chemical scrubber with sodium hypochlorite and surfactant for removal of hydrocarbons in cooking oil fume, J. Hazard. Mater. 182 (1–3) (2010) 39–44, doi:http://dx.doi.org/10.1016/j.jhazmat.2010.05.122. 20633996. [8] J. Yang, J. Jia, Y. Wang, W. You, Treatment of cooking oil fume by low temperature catalysis, Appl. Catal. B. Environ. 58 (1–2) (2005) 123–131, doi:http:// dx.doi.org/10.1016/j.apcatb.2004.11.021. [9] P. Hunter, S.T. Oyama, Control of Volatile Organic Compound Emissions: Conventional and Emerging Technologies, John Wiley & Sons, New York, 2000. [10] S.T. Oyama, Chemical and catalytic properties of ozone, Catal. Rev. 42 (3) (2000) 279–322, doi:http://dx.doi.org/10.1081/CR-100100263. [11] Z.N. Felegari, B.N. Haghi, Gh. Amoabediny, S.M. Mousavi, M.A. Torkmahalleh, An optimized integrated process for the bioleaching of a spent refinery processing catalysts, Int. J. Environ. Res. 8 (2014) 621–634. [12] K. Kanie, A. Muramatsu, S. Suzuki, Y. Waseda, Influence of sulfate ions on conversion of Fe(OH)3 gel to b-FeO(OH) and a-Fe2O3, Mater. Trans. 45 (2004) 968–971, doi:http://dx.doi.org/10.2320/matertrans.45.968. [13] S. Krehula, S. Popovic, S. Musi c, Synthesis of acicular a-FeOOH particles at a very high pH, Mater. Lett. 54 (2002) 108–113, doi:http://dx.doi.org/10.1016/ S0167-577X(01)00546-8. [14] X.P. Gu, T.Y. Chen, P.S. Wu, Applying an organic phosphine complex additive to preparing a-FeOOH by alkaline methods, J. Inorg. Mater. 16 (2001) 961–964. [15] E. Zhang, G. Wang, X. Long, Z. Wang, Synthesis and influence of alkaline concentration on a-FeOOH nanorods shapes, Bull. Mater. Sci. 37 (2014) 761– 765, doi:http://dx.doi.org/10.1007/s12034-014-0003-8. [16] U. Schwertmann, R.M. Cornell, Iron Oxides in the Laboratory, VCH, New York, 1991, pp. 95. [17] A. Šari c, S. Musi c, K. Nomura, S. Popovi c, Microstructural properties of Fe-oxide powders obtained by precipitation from FeCl3 solutions, Mater. Sci. Eng. B 56 (1) (1998) 43–52, doi:http://dx.doi.org/10.1016/S0921-5107(98)00212-8. [18] X. Xin, L. Zhu, Q. Meng, X. Zhang, P. Wu, A. Dai, Studies on alkali metal promoted iron catalyst for ammonia synthesis (V): effect of chloride ion, Chem. J. Chinese U. 3 (1982) 162–168. [19] E. Campagnoli, A. Tavares, L. Fabbrini, Y.I. Rossetti, A. Dubitsky, A. Zaopo, L. Forni, Effect of preparation method on activity and stability of LaMnO3 and LaCoO3 catalysts for the flameless combustion of methane, Appl. Catal. B. 55 (2005) 133–139, doi:http://dx.doi.org/10.1016/j.apcatb.2004.07.010. [20] Y. Lu, Z. Zhao, C. Xu, A. Duan, P. Zhang, Effects of calcination temperature on the acidity and catalytic performances of HZSM-5 zeolite catalysts for the catalytic cracking of n-butane, J. Nat. Gas Chem. 14 (2005) 213–220. [21] A. Jia, X. Liang, Z. Su, T. Zhu, S. Liu, Synthesis and the effect of calcination temperature on the physical–chemical properties and photocatalytic activities of Ni, La codoped SrTiO3, J. Hazard. Mater. 178 (1–3) (2010) 233–242, doi: http://dx.doi.org/10.1016/j.jhazmat.2010.01.068. 20149529. [22] A. Gaber, M.A. Abdel-Rahim, A.Y. Abdel-Latief, Mahmoud. N. Abdel-Salam, Influence of calcination temperature on the structure and porosity of nanocrystalline SnO2 synthesized by a conventional precipitation method, Int. J. Electrochem. Sci. 9 (2014) 81–95. [23] T.M. Eggenhuisen, P. Munnik, H. Talsma, P.E. de Jongh, K.P. de Jong, Freezedrying for controlled nanoparticle distribution in Co/SiO2 Fischer–Tropsch catalysts, J. Catal. 297 (2013) 306–313, doi:http://dx.doi.org/10.1016/j. jcat.2012.10.024. [24] I. Bull, W.M. Xue, P. Burk, R.S. Boorse, W.M. Jaglowski, G.S. Koermer, A. Moini, J. A. Patchett, J.C. Dettling, M.T. Caudle, Copper CHA zeolite catalysts, U.S. Patent 7601662, 2009. [25] J. Jen, M. Leu, T.C. Yang, Determination of hydroxyl radicals in an advanced oxidation process with salicylic acid trapping and liquid chromatography, J.

1538

[26] [27]

[28]

[29]

[30]

[31]

[32]

[33]

B. Lin, S.-L. Liaw / Journal of Environmental Chemical Engineering 3 (2015) 1530–1538 Chromatogr. A 796 (2) (1998) 283–288, doi:http://dx.doi.org/10.1016/S00219673(97)01019-4. R.L. Wolke, Where There’s Smoke, There’s a Fryer, The Washington Post, 2007. M. Grootveld, C.J.L. Silwood, A. Claxson, B. Bonet Serra, M. Viana, Health effects of oxidized heated oils, J. Foodserv. 13 (2001) 41–55, doi:http://dx.doi.org/ 10.1111/j.1745-4506.2001.tb00028. J.D.F. Ramsay, B.O. Booth, Neutron scattering and adsorption isotherm studies of structure in oxide sols and gels, Stud. Surf. Sci. Catal. 10 (1982) 211–225, doi: http://dx.doi.org/10.1016/S0167-2991(09)61337-9. L. Diez, M.H. Livertoux, A.A. Stark, M. Wellman-Rousseau, P. Leroy, Highperformance liquid chromatographic assay of hydroxyl free radical using salicylic acid hydroxylation during in vitro experiments involving thiols, J. Chromatogr. B Biomed. Sci. Appl. 763 (1–2) (2001) 185–193, doi:http://dx.doi. org/10.1016/S0378-4347(01)00396-6. 11710577. R. Parameshwari, P. Priyadarshini, G. Chandrasekaran, Optimization, structural, spectroscopic and magnetic studies on stable akaganeite nanoparticles via co-precipitation method, Am. J. Mater. Sci. 1 (1) (2011) 18–25, doi:http://dx. doi.org/10.5923/j.materials.20110101.04. A.K. Shah, K.J. Prathap, M. Kumar, S.H.R. Abdi, R.I. Kureshy, N.H. Khan, H.C. Bajaj, Fe(OH)3 nano solid material: an efficient catalyst for regioselective ring opening of aryloxy epoxide with amines under solvent free condition, Appl. Catal. A Gen. 469 (2014) 442–450, doi:http://dx.doi.org/10.1016/j. apcata.2013.10.003. B. Legube, N.K.V. Leitner, Catalytic ozonation: a promising advanced oxidation technology for water treatment, Catal. Today 53 (1) (1999) 61–72, doi:http:// dx.doi.org/10.1016/S0920-5861(99)00103-0. S.J. Jin, X.S. Chen, S. Li, X.W. Zhang, X.Y. Shen, Catalytic activity of TiO2 pillared bentonite for degradation of gaseous toluene: relationship between the effect of humidity and the catalyst structure, Huan Jing Ke Xue 29 (12) (2008) 3331– 3336. 19256363.

[34] E. Sahle-Demessie, V.G. Devulapelli, Oxidation of methanol and total reduced sulfur compounds with ozone over V2O5/TiO2 catalyst: effect of humidity, Appl. Catal. A Gen. 361 (1–2) (2009) 72–80, doi:http://dx.doi.org/10.1016/j. apcata.2009.03.035. [35] L. Sivachandiran, F. Thevenet, P. Gravejat, A. Rousseau, Isopropanol saturated TiO2 surface regeneration by non-thermal plasma: influence of air relative humidity, Chem. Eng. J. 214 (2013) 17–26, doi:http://dx.doi.org/10.1016/j. cej.2012.10.022. [36] T. Zhang, J. Ma, Z.L. Chen, H. Qi, J. Guo, Effect of organic acids adsorption on catalytic ozonation with metal oxides, Environ. Sci. 26 (5) (2005) 85–88. [37] B. Kasprzyk-Hordern, M. Ziółek, J. Nawrocki, Catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment, Appl. Catal. B Environ. 46 (4) (2003) 639–669, doi:http://dx.doi.org/10.1016/S0926-3373 (03)00326-6. [38] F. Arsac, D. Bianchi, J.M. Chovelon, C. Ferronato, J.M. Hermann, Experimental microkinetic approach of the photocatalytic oxidation of isopropyl alcohol on TiO2. Part 1. Surface elementary steps involving gaseous and adsorbed C3HxO species, J. Phys. Chem. A. 110 (2006) 4202–4212. 16553371. [39] M. Amouei Torkmahalleh, L. Lin, T.M. Holsen, D.H. Rasmussen, P.K. Hopke, Cr speciation changes in the presence of ozone and reactive oxygen species at low relative humidity, Atmos. Environ. 71 (2013) 92–94, doi:http://dx.doi.org/ 10.1016/j.atmosenv.2013.02.005. [40] M.A. Torkmahalleh, L. Lin, T.M. Holsen, D.H. Rasmussen, P.K. Hopke, The impact of deliquescence and pH on Cr speciation in ambient PM samples, Aerosol Sci. Technol. 46 (6) (2012) 690–696, doi:http://dx.doi.org/10.1080/ 02786826.2011.654285. [41] EPA, The Air Quality Management Act, Environmental Protection Administration, Taiwan, 2012.