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Treatment of cooking oil fume by low temperature catalysis
Applied Catalysis B: Environmental 58 (2005) 123–131 www.elsevier.com/locate/apcatb
Treatment of cooking oil fume by low temperature catalysis Ji Yang*, Jinping Jia, Yaling Wang, Weisong You School of Environmental Science and Engineering, Shanghai Jiao Tong University, Minhang Dongchuan Road 800, Shanghai 200240, PR China Received 5 September 2004; received in revised form 13 November 2004; accepted 30 November 2004 Available online 8 January 2005
Abstract Similar to cigarette smoke, fumes from cooking oil contain lots of carcinogens such as aromatic amines, polycyclic aromatic hydrocarbons (PAHs), nitro-polycyclic aromatic hydrocarbons, etc. and are notoriously difficult to remove by traditional static method. In this paper, low temperature catalytic oxidation was employed to treat cooking oil fume. A novel catalyst, based on MnO2/CuO, was developed successfully and its characteristics were studied. Catalytic activity was studied under different oil temperatures, catalyst temperatures and contact times results show that the method employed in this work can give impressive treatment effect on cooking oil fume. Lifetime experiments, poisoning experiments by water steam, and thermal stability study of catalyst were also performed to check the catalyst robustness. # 2004 Elsevier B.V. All rights reserved. Keywords: Cooking oil fumes; Catalysis; Polycyclic aromatic hydrocarbons (PAHs); Organic gas; Volatile organic carbon (VOC); Oxidization
1. Introduction Several carcinogens, including polycyclic aromatic hydrocarbons (PAHs), aromatic amines and nitro-polycyclic aromatic hydrocarbons, which are also found in cigarette smoke, can be found in the fumes from cooking oil and appear in the kitchens of Asian homes where women prepare food daily [1]. Animal studies have found that PAH can cause cancer in the epithelium of rat cervices [2]. Cooking oil fumes have been suggested to increase the risk of lung cancer in oriental women by exposing them to mutagenic substances [3]. In addition, fumes from cooking oils have been found to be genotoxic by several such short-term tests as the Ames test, sister chromatid exchange, and the SOS chromotest [4,5]. Because of the complexity of components, cooking oil fumes are notoriously difficult to treat using static method. Adsorption and washing are effective, while frequent maintenance is required. Thermal oxidation is also an option, but expensive equipment, high operating and maintenance cost and production of NOx will offset the benefits of organics removal [6]. Heterogeneous catalysis is important in the
* Corresponding author. Tel.: +86 21 54742817; fax: +86 21 54742817. E-mail address: [email protected] (J. Yang). 0926-3373/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2004.11.021
removal of organic wastes from gaseous effluents, as oxidation to carbon oxides and water can be achieved at suitably low temperatures (200–600 8C) [7]. In this paper, a novel catalyst, based on MnO2/CuO, has been developed for the oxidative destruction of cooking oil fumes under low temperature. Although the fumes composition is complex and some components are difficult to remove, the research has shown that catalyst is very effective at mineralization of organics and could be tailored for specific applications such as industrial organic gases. The catalysts show high oxidation activity, high temperature tolerance, immunization from water steam and long-term stable activity and therefore, have potential use in environmental pollution control. 2. Experiment and materials 2.1. Experimental setup Fig. 1 shows the schematic setup of the equipment. Fresh air (with oxygen partial pressure around 159.6 mmHg) was dried to remove moisture using silica gel and pumped (Fluid Metering Inc., Oyster Bay, NY) into a three-neck flask which was filled with commercial sunflower cooking oil (Molinos, Cholesterol Free, Argentina). The flask was sealed with only
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Fig. 1. Schematic setup of catalysis process.
inlet for pumped air and outlet for fumes brought out by air. A thermal meter was inserted under oil surface to monitor the temperature. The desired flow-rate was maintained by a flow-meter. The cooking oil fume feed exiting the three-neck flask was heated to 140 8C in a fume heater controlled by a CN76030 heat controller (Omega). The effluent from this process was introduced to a small column reactor whose temperature was controlled by a CN76030 heat controller (Omega) and monitored using platinum RTD probes (Omega) and the probes demonstrated that the reactor was isothermal. To prevent oil fumes condensation, all the connecting pipes are stainless steel and were wrapped with heating belt to keep temperature around 140 8C. The small column reactor was packed with catalyst. Table 1 shows the packing details. 2.2. Preparation of catalyst Six hundred grams of an aluminum sulfate solution (Al2O3 8 wt.%) and 320 g of a sodium aluminate solution (Al2O3 27% and Na/Al atomic ratio 1.20) were simultaTable 1 Small column reactor operating conditions Column length (cm) Column diameter (cm) Catalyst weight (g) Catalyst bed density (g/cm3) Catalyst bed porosity
6 1 2.64 0.56 0.22
neously poured into 1000 ml of deionized water with stirring from each different pouring ports slowly. The temperature was controlled at 65 8C throughout. This amorphous alumina hydrate slurry (pH 9.5 and Al2O3 around 8.3 wt.%) was supplied immediately to a vacuum filter for obtaining a filter cake; thereafter, said cake was washed by sprinkling 0.1% aqueous ammonia thereon, and then this cake was repulped in 0.7% nitric acid solution. MnO2 and CuO powder (particle size smaller than 125 mesh size) were completely mixed into the cake thereon (MnO2 0.6 dry wt.% and CuO 0.4%). Next, the above-mentioned cake was subjected to a filter press for dehydrating. Small round ball shaped catalyst was made out of this cake and was dried at 105 8C for 12 h, thereafter, at 360 8C for 1.5 h and further at 650 8C for 2.5 h. The specific area of the catalyst was estimated by N2 adsorption–desorption porosimetry at 77 K via BET method. The instrument employed was a Fisons 1900 Sorptomatic system. The catalyst was also observed by scanning electron microscopy (SEM) using a Hitachi S-2150 instrument. Plain Al2O3 support was prepared without the addition of MnO2 and CuO powder following the same above procedures. Truly supported catalyst was also prepared by wetting plain Al2O3 support with water and then sprayed MnO2 and CuO powder (particle size smaller than 125 mesh size, MnO2 0.6 dry wt.% and CuO 0.4%) to its surface. The prepared catalyst was thereafter dried at 105 8C for 12 h, thereafter, at 360 8C for 1.5 h and further at 650 8C for 2.5 h.
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Fig. 3. Oil concentrations in the feed under different oil temperatures (expressed as carbon). Fig. 2. A typical SEM of prepared catalyst surface (mixed). Table 2 Physical characteristics of prepared catalyst
2.3. Chemical analysis The cooking oil fumes effluent from the small column rector were collected in the impinger filled with 30 ml CCl4 (Regent Grade) for 5 min (three replicates) continuously, and the oil concentrations were measured using a OIL Infrared Oil Meter (Huaxia Inc., Beijing, China). GC–MS (QP2010NC, Shimadzu, Japan) was also used to characterize cooking oil fume samples (collected in CH2Cl2). The concentration of CO and CO2 was determined using standard methods [8,9].
Description
Catalyst mixture
Truly supported catalyst
Average particle radius (mm) Catalyst particle density (g/cm3) Catalyst solid density (g/cm3) Catalyst particle porosity Specific area (m2/g)
0.3 0.72 0.92 0.25 79.5
0.3 0.76 0.92 0.23 32.7
catalyst was heated to 750 8C in oven for 2 h and cooled to room temperature to compare the catalyst performance before and after heat treatment.
2.4. Poisoning experiment and thermal stability 3. Results and discussions Experiments were performed to study the robustness of the catalyst under different conditions. Water was put into the three-neck flask instead of oil, the flask was heated and maintained at 90 8C and the rest of the conditions were kept the same as described in Section 2.1. Also, the prepared
3.1. Characteristics of catalyst Table 2 shows some basic information of prepared catalyst and Fig. 2 is a typical SEM picture of the catalyst
Fig. 4. Catalyst performance under different oil and catalyst temperatures.
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Fig. 5. Catalyst performance under different reactor temperatures.
surface (mixed). It can be seen that MnO2/CuO powder was completely mixed into Al2O3 cake.
Since 1 mole of carbon requires 1 mole of oxygen for total oxidation,
3.2. Catalytic activity
C þ O2 ! CO2
Cooking oil is mainly composed by saturated and unsaturated fats and is sensitive to light and oxygen. When cooked, it will be oxidized and decomposed. Under the best scenario, complete catalysis will assist the process for cooking oil fumes in following way: oil þ O2 ! CO2 þ H2 O
(1)
Fig. 3 gives the average initial oil concentrations in the fumes (expressed as carbon, three replicates) exiting the three-neck flask at different oil temperatures, when the flowrate is 0.23 L/min.
(2)
when the oil temperature is 220 8C (the oil concentration is the highest in this work), theoretically, the oxygen consumption is at least: oxygen requirement ¼ carbon amount
molecular weight of oxygen molecular weight of carbon
32 ¼ 1:6 104 mg=L (3) 12 Yet in the fresh air, oxygen accounts for about 21% of the total volume and thus the concentration is around 300 mg/L, which is more than enough and guarantees the total oxidation. ¼ 5:82
Fig. 6. Catalyst performance under different contact times.
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Fig. 7. Non-catalytic decomposition of organics and decomposition over plain Al2O3 (oil temperature 220 8C).
Fig. 4 shows the oil fume removal with prepared mixed catalyst. The contact time in the catalyst column was controlled around 1.06 s. The organic removal goes up with the increased catalyst. It can be learned that although the contact time is short, the catalyst is able to remove over 80% of the organics from 170 8C oil fumes. Fig. 4 also shows that fumes from higher temperature oil are more difficult remove than that from lower temperature oil. This could be explained that under high temperature, the oil will decompose in the three-neck flask with oxygen existence and increase the complexity of fumes, thus levels the treatment difficulty. Standard methods were used to determine COx concentration before and after catalytic treatment. Table 3 shows the results. It can be learned that CO was not detected throughout the process, which could be explained that oxygen is always more than enough in the column and the oxidation is complete. CO2 concentration increased after the treatment, and its concentration matches the organics
Table 3 Concentration of COx after the treatment (contact time 1.06 s, catalyst temperature 300 8C) 170 8C
180 8C
220 8C
CO (mg/L, carbon) Initial After
/ /
/ /
/ /
CO2 (mg/L, carbon) Initial After Carbon removed (mg/L)
/ 0.82 0.90
/ 1.65 1.96
/ 4.31 5.02
The symbol (/) means below detection limit.
removal (expressed in carbon) very well, verifying that those organics removed in the reactor were mineralized to CO2 and H2O. Fig. 5 shows the reactor performance under different contact times. The contact times were manipulated by varying air flow-rate that was pumped into the three-neck
Fig. 8. Organics decomposition over truly supported catalyst (oil temperature 220 8C).
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Fig. 9. GC–MS results of catalytically treated cooking oil fumes.
flask. The oil temperature was kept around 180 8C throughout the experiments. Fig. 5 displays that as the catalyst temperature increases the organic removal also goes up, which is consistent with Fig. 4. Prolonged contact time also gives more favorable results. When the contact time is
1.59 s and the catalyst temperature is 300 8C, the oil fume removal is close to 90%. To further study the relationship between contact time and fume removal, experiments were performed under 180 8C, and the catalyst temperature was kept at 200 8C.
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Table 4 Chemicals in fume samples taken during experiments Chemicals Non-treated
200 8C
250 8C
300 8C
2-Heptanone ketone, 4-pentenal, 2,2-dimethyl, ethanol, 2-butoxy-, ethanedioic acid, bis(1-methylpropyl) ester,2-heptenal, (Z)-,1-heptanol,1-octen-3-ol, 3-octanone, furan, 2-pentyl-,3,7-decadiene, 2,9-dimethyl-,cyclohexanol, 2,4-dimethyl-, octanal, 4-ethylcyclohexanol,2,4-heptadienal, (E,E)-,formic acid, heptyl ester,1,3-hexadiene, 3-ethyl-2-methyl-,cyclohexanol, 2,4-dimethyl-2-nonen-1-ol, (Z)-,1,2-epoxynonane, 2(3H)-furanone, 5-ethyldihydro-, benzene, butyl-, 2-octenal, (E)-, 2-octen-1-ol, (E)-, 1-octanol,heptanoic acid, 1-nonen-3-ol, 2,4-octanedione, 5-nonen-2-one, 8-hydroxy-2-octanone, butyric acid, 4-pentadecyl ester,4-nonenal, (E)-, undecane, nonanal, 2,4-octadienal, 4,6-decadiene, trans-3-Nonen-2-one, cycloheptanol, 2-methylene, 2(3H)-furanone, dihydro-5-pentyl-, 2-nonenal, (E)-, octanoic acid, 9-oxa-bicyclo[3.3.1]nona-3,6-dien-2-one, trans-2-undecenoic acid, 2-undecanone, 6,10-dimethyl-, 2,4-nonadienal, (E,E)-, trans-undec-4-enal, dodecane, decanal, hexyl octyl ether, 2,4-nonadienal, (E,E)-, 3-hexadiene, 3-ethyl-2-methyl-, 1,4-cyclooctanedione, 13-tetradece-11-yn-1-ol, 3-isopropyl-5-methylhexan-2-one, 2(3H)-furanone, 5-butyldihydro-, 2-decenal, nonanoic acid, 6-undecanone, hexanoic acid, tridecyl ester, 2,4-decadienal, tridecanal, bicyclo[3.3.1]nonane-2,7-dione, 2,4-decadienal, 1-undecene, 8-methyl-, 2-undecenal, 9-hexadecenoic acid, 6-dodecanone, 2,4-dodecadiene, (E,Z)-, 2-methyl-7-oxabicyclo[2.2.1]heptane, 3-nonen-5-yne, 4-ethyl-, (Z)-, 14-bromo-2-methyltetradec-1-en-3-ol, tridecanal, 7-pentadecyne 9-octadecene, (E)-, tetradecane, S-butyl methyl ethylphosphonate, hexatriacontane 2-Heptanone,2-tridecene, (E)-,heptanal,2-hexene, 2,3-dimethyl-,2-heptenal, (Z)-,benzaldehyde,pentanoic acid, 1-octen-3-ol,1-nonen-3-ol,furan, 2-pentyl-1-octanol, 2-butyl-, n-octaldehyde,1,3-hexadiene, 3-ethyl-2-methyl-, 4-ethylcyclohexanol, 2-octenal, (E)-, nonanal, 2-nonenal, (E)-,2-decenal, (E)-, 2,4-decadienal, (E,E)-,1(2H)-naphthalenone, octahydro-, cis-,2,4-decadienal, 1-undecene, 8-methyl-, 2-undecenal, hex-3-ene-1,6-diol, 14-bromo-2-methyltetradec-1-en-3-ol, 1-tridecanol,9-nonadecene 2-Heptanone, n-heptaldehyde, cyclopentane, 1-ethyl-1-methyl-, 2-heptenal, (Z)-benzaldehyde, 1-octen-3-ol,furan, 2-pentyl-, n-octanal, 1,3-hexadiene, 3-ethyl-2-methyl-, 4-ethylcyclohexanol, 2-octenal, (E)-, nonanal, 1(2H)-naphthalenone, octahydro-, cis-, cholesteryl benzoate 2-Heptanone, n-heptaldehyde, cyclopentane, 1-ethyl-1-methyl-, 2-heptenal, (Z)-, benzaldehyde, 1-octen-3-ol, furan, 2-pentyl-, n-octanal, 2-octenal, (E)-, nonanal, 1(2H)-naphthalenone, octahydro-, cis-allyl n-octyl ether $$ allyl octyl ether
Fig. 6 gives the result. It can be seen that the removal effect is strengthened as the contact time is prolonged. When the contact time is 3.18 s, the oil fume removal is over 96%, while the catalyst temperature is just 200 8C. It is obvious that the removal is not linear with contact time, and the equation that might be used to describe the relationship is shown in Fig. 6. Experiments were also done with empty column and using just prepared plain Al2O3. The results are shown in Fig. 7. It is shown in Fig. 7 that no meaningful decomposition occurs in empty column and over plain Al2O3. The small removal may be deterred by tubing connection or adsorbed by Al2O3 support.
Experiments were also performed using truly supported catalyst prepared as described in previous section. Fig. 8 shows the results. It could be learned that the fume removal is not as satisfying as that by mixed catalyst. As shown in Table 2, the specific area of truly supported catalyst is significantly smaller than that of mixed catalyst, which may explain the difference.
Fig. 10. SEM of catalyst surface treated by steam.
Fig. 11. SEM catalyst surface treated by heat.
3.3. GC–MS analysis Samples were taken during catalytic experiment when the oil temperature was controlled 180 8C and the contact time was 1.06 s. It can be learned from Fig. 9 that the composition
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Fig. 12. Catalyst performance vs. time.
of non-treated fumes is complex and contains lots of saturated and non-saturated fats. After passing catalyst at different temperatures, the number of components was decreased significantly from 75 to just 11 (catalyst temperature from 200 8C to 300 8C) and the concentration also goes down dramatically, which indicates that mineralization and not other process dominates the cooking oil fumes removal process (Fig. 9). Table 4 gives the detailed information of components that were found in cooking oil fumes during experiment.
Table 5 Experimental results with treated catalyst (oil temperature 180 8C, contact time 1.06 s, three replicates)
3.4. Durability experiments Thermal stability is a very important index for this kind of catalyst since the temperature of catalytic reactor may be periodically increased to burn out some residual. Also, since a lot of steam is produced when cooking, the catalyst must be immune from water vapor poisoning. Table 5 proves that the catalyst performance was not negatively affected by steam existence and thermal treatment. Figs. 10 and 11 show that typical SEM pictures of catalyst treated by steam and heat. Compared with Fig. 2, these two pictures almost give the same image. Experiments (200 8C catalyst temperature, 180 8C oil temperature, 1.06 s contact time) were carried out continuously to check the lifetime of the mixed catalyst. Fig. 12 shows the catalyst performance versus time. It is shown that the catalytic activity of the mixed catalyst did not decrease after being used continuously for 300 h.
impressing results. It has been pointed out that within experimental temperature range (200–300 8C), the catalyst can mineralize most organics while the contact time is less than 1 s (as shown in Figs. 4 and 5). If the contact is prolonged to 3.18 s, 96% removal could be achieved at 200 8C (as shown in Fig. 6). Results also show that fume from high temperature oil is relatively more difficult to remove than that from low temperature oil (as shown in Figs. 4 and 5). Poisoning experiments and thermal stability study on the prepared catalyst were also performed. It is displayed that the catalyst is stable with high moisture existence and is not negatively affected by thermal treatment up to 750 8C. For the experiment done, the catalytic activity of the mixed catalyst is stable even being used continuously for 300 h. Overall, the catalyst is very effective at organics mineralization and might be employed in other applications such as industrial organic gas treatment.
4. Conclusion
References
Because of its complexity, cooking oil fumes are notoriously difficult to remove using traditional methods. This work successfully developed a MnO2/CuO mixed catalyst and employed it to treat cooking oil fumes with
[1] T.A. Chiang, P.F. Wu, L.F. Wang, H. Lee, C.H. Lee, Y.C. Ko, Mutat. Res.-Fundam. Mol. Mech. Mutagen. 381 (2) (1997) 157–161. [2] V.N. Anisimov, I.G. Popovich, A.V. Shtylik, M.A. Zabezhinski, H. BenHuh, P. Gurevich, V. Berman, Y. Tendler, I. Zusman, Exp. Toxicol. Pathol. 52 (1) (2000) 71–76.
Temperature (8C)
200 250 300
Removal (%) Non-treated catalyst
Steamed treated
Thermal treated
51.26 58.16 66.83
50.37 57.39 66.16
50.25 59.50 67.35
J. Yang et al. / Applied Catalysis B: Environmental 58 (2005) 123–131 [3] Y.C. Ko, C.H. Lee, M.J. Chen, C.C. Huang, W.Y. Chang, H.J. Lin, H.Z. Wang, P.Y. Chang, Int. J. Epidemiol. 26 (1) (1997) 24–31. [4] T.A. Chiang, P.F. Wu, Y.C. Koi, Environ. Res. 81 (1) (1999) 18–22. [5] T.A. Chiang, P.F. Wu, L.S. Ying, L.F. Wang, Y.C. Ko, Food Chem. Toxicol. 37 (23) (1999) 125–134. [6] C.M. Martinson, Chem. Process. 66 (7) (2003) 41. [7] F. Garin, Catal. Today 89 (3) (2004) 255–268.
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[8] ASTM, D3162-94(2000)e1 standard test method for carbon monoxide in the atmosphere (continuous measurement by nondispersive infrared spectrometry), in: ASTM Standards, 11.03, American Society for Testing and Materials, PA, USA, 2003. [9] ASTM, D513-02 standard test methods for total and dissolved carbon dioxide in water, in: ASTM standards, 11.01, American Society for Testing and Materials, PA, USA, 2003.
Treatment of cooking oil fume by low temperature catalysis Ji Yang*, Jinping Jia, Yaling Wang, Weisong You School of Environmental Science and Engineering, Shanghai Jiao Tong University, Minhang Dongchuan Road 800, Shanghai 200240, PR China Received 5 September 2004; received in revised form 13 November 2004; accepted 30 November 2004 Available online 8 January 2005
Abstract Similar to cigarette smoke, fumes from cooking oil contain lots of carcinogens such as aromatic amines, polycyclic aromatic hydrocarbons (PAHs), nitro-polycyclic aromatic hydrocarbons, etc. and are notoriously difficult to remove by traditional static method. In this paper, low temperature catalytic oxidation was employed to treat cooking oil fume. A novel catalyst, based on MnO2/CuO, was developed successfully and its characteristics were studied. Catalytic activity was studied under different oil temperatures, catalyst temperatures and contact times results show that the method employed in this work can give impressive treatment effect on cooking oil fume. Lifetime experiments, poisoning experiments by water steam, and thermal stability study of catalyst were also performed to check the catalyst robustness. # 2004 Elsevier B.V. All rights reserved. Keywords: Cooking oil fumes; Catalysis; Polycyclic aromatic hydrocarbons (PAHs); Organic gas; Volatile organic carbon (VOC); Oxidization
1. Introduction Several carcinogens, including polycyclic aromatic hydrocarbons (PAHs), aromatic amines and nitro-polycyclic aromatic hydrocarbons, which are also found in cigarette smoke, can be found in the fumes from cooking oil and appear in the kitchens of Asian homes where women prepare food daily [1]. Animal studies have found that PAH can cause cancer in the epithelium of rat cervices [2]. Cooking oil fumes have been suggested to increase the risk of lung cancer in oriental women by exposing them to mutagenic substances [3]. In addition, fumes from cooking oils have been found to be genotoxic by several such short-term tests as the Ames test, sister chromatid exchange, and the SOS chromotest [4,5]. Because of the complexity of components, cooking oil fumes are notoriously difficult to treat using static method. Adsorption and washing are effective, while frequent maintenance is required. Thermal oxidation is also an option, but expensive equipment, high operating and maintenance cost and production of NOx will offset the benefits of organics removal [6]. Heterogeneous catalysis is important in the
* Corresponding author. Tel.: +86 21 54742817; fax: +86 21 54742817. E-mail address: [email protected] (J. Yang). 0926-3373/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2004.11.021
removal of organic wastes from gaseous effluents, as oxidation to carbon oxides and water can be achieved at suitably low temperatures (200–600 8C) [7]. In this paper, a novel catalyst, based on MnO2/CuO, has been developed for the oxidative destruction of cooking oil fumes under low temperature. Although the fumes composition is complex and some components are difficult to remove, the research has shown that catalyst is very effective at mineralization of organics and could be tailored for specific applications such as industrial organic gases. The catalysts show high oxidation activity, high temperature tolerance, immunization from water steam and long-term stable activity and therefore, have potential use in environmental pollution control. 2. Experiment and materials 2.1. Experimental setup Fig. 1 shows the schematic setup of the equipment. Fresh air (with oxygen partial pressure around 159.6 mmHg) was dried to remove moisture using silica gel and pumped (Fluid Metering Inc., Oyster Bay, NY) into a three-neck flask which was filled with commercial sunflower cooking oil (Molinos, Cholesterol Free, Argentina). The flask was sealed with only
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Fig. 1. Schematic setup of catalysis process.
inlet for pumped air and outlet for fumes brought out by air. A thermal meter was inserted under oil surface to monitor the temperature. The desired flow-rate was maintained by a flow-meter. The cooking oil fume feed exiting the three-neck flask was heated to 140 8C in a fume heater controlled by a CN76030 heat controller (Omega). The effluent from this process was introduced to a small column reactor whose temperature was controlled by a CN76030 heat controller (Omega) and monitored using platinum RTD probes (Omega) and the probes demonstrated that the reactor was isothermal. To prevent oil fumes condensation, all the connecting pipes are stainless steel and were wrapped with heating belt to keep temperature around 140 8C. The small column reactor was packed with catalyst. Table 1 shows the packing details. 2.2. Preparation of catalyst Six hundred grams of an aluminum sulfate solution (Al2O3 8 wt.%) and 320 g of a sodium aluminate solution (Al2O3 27% and Na/Al atomic ratio 1.20) were simultaTable 1 Small column reactor operating conditions Column length (cm) Column diameter (cm) Catalyst weight (g) Catalyst bed density (g/cm3) Catalyst bed porosity
6 1 2.64 0.56 0.22
neously poured into 1000 ml of deionized water with stirring from each different pouring ports slowly. The temperature was controlled at 65 8C throughout. This amorphous alumina hydrate slurry (pH 9.5 and Al2O3 around 8.3 wt.%) was supplied immediately to a vacuum filter for obtaining a filter cake; thereafter, said cake was washed by sprinkling 0.1% aqueous ammonia thereon, and then this cake was repulped in 0.7% nitric acid solution. MnO2 and CuO powder (particle size smaller than 125 mesh size) were completely mixed into the cake thereon (MnO2 0.6 dry wt.% and CuO 0.4%). Next, the above-mentioned cake was subjected to a filter press for dehydrating. Small round ball shaped catalyst was made out of this cake and was dried at 105 8C for 12 h, thereafter, at 360 8C for 1.5 h and further at 650 8C for 2.5 h. The specific area of the catalyst was estimated by N2 adsorption–desorption porosimetry at 77 K via BET method. The instrument employed was a Fisons 1900 Sorptomatic system. The catalyst was also observed by scanning electron microscopy (SEM) using a Hitachi S-2150 instrument. Plain Al2O3 support was prepared without the addition of MnO2 and CuO powder following the same above procedures. Truly supported catalyst was also prepared by wetting plain Al2O3 support with water and then sprayed MnO2 and CuO powder (particle size smaller than 125 mesh size, MnO2 0.6 dry wt.% and CuO 0.4%) to its surface. The prepared catalyst was thereafter dried at 105 8C for 12 h, thereafter, at 360 8C for 1.5 h and further at 650 8C for 2.5 h.
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Fig. 3. Oil concentrations in the feed under different oil temperatures (expressed as carbon). Fig. 2. A typical SEM of prepared catalyst surface (mixed). Table 2 Physical characteristics of prepared catalyst
2.3. Chemical analysis The cooking oil fumes effluent from the small column rector were collected in the impinger filled with 30 ml CCl4 (Regent Grade) for 5 min (three replicates) continuously, and the oil concentrations were measured using a OIL Infrared Oil Meter (Huaxia Inc., Beijing, China). GC–MS (QP2010NC, Shimadzu, Japan) was also used to characterize cooking oil fume samples (collected in CH2Cl2). The concentration of CO and CO2 was determined using standard methods [8,9].
Description
Catalyst mixture
Truly supported catalyst
Average particle radius (mm) Catalyst particle density (g/cm3) Catalyst solid density (g/cm3) Catalyst particle porosity Specific area (m2/g)
0.3 0.72 0.92 0.25 79.5
0.3 0.76 0.92 0.23 32.7
catalyst was heated to 750 8C in oven for 2 h and cooled to room temperature to compare the catalyst performance before and after heat treatment.
2.4. Poisoning experiment and thermal stability 3. Results and discussions Experiments were performed to study the robustness of the catalyst under different conditions. Water was put into the three-neck flask instead of oil, the flask was heated and maintained at 90 8C and the rest of the conditions were kept the same as described in Section 2.1. Also, the prepared
3.1. Characteristics of catalyst Table 2 shows some basic information of prepared catalyst and Fig. 2 is a typical SEM picture of the catalyst
Fig. 4. Catalyst performance under different oil and catalyst temperatures.
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Fig. 5. Catalyst performance under different reactor temperatures.
surface (mixed). It can be seen that MnO2/CuO powder was completely mixed into Al2O3 cake.
Since 1 mole of carbon requires 1 mole of oxygen for total oxidation,
3.2. Catalytic activity
C þ O2 ! CO2
Cooking oil is mainly composed by saturated and unsaturated fats and is sensitive to light and oxygen. When cooked, it will be oxidized and decomposed. Under the best scenario, complete catalysis will assist the process for cooking oil fumes in following way: oil þ O2 ! CO2 þ H2 O
(1)
Fig. 3 gives the average initial oil concentrations in the fumes (expressed as carbon, three replicates) exiting the three-neck flask at different oil temperatures, when the flowrate is 0.23 L/min.
(2)
when the oil temperature is 220 8C (the oil concentration is the highest in this work), theoretically, the oxygen consumption is at least: oxygen requirement ¼ carbon amount
molecular weight of oxygen molecular weight of carbon
32 ¼ 1:6 104 mg=L (3) 12 Yet in the fresh air, oxygen accounts for about 21% of the total volume and thus the concentration is around 300 mg/L, which is more than enough and guarantees the total oxidation. ¼ 5:82
Fig. 6. Catalyst performance under different contact times.
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Fig. 7. Non-catalytic decomposition of organics and decomposition over plain Al2O3 (oil temperature 220 8C).
Fig. 4 shows the oil fume removal with prepared mixed catalyst. The contact time in the catalyst column was controlled around 1.06 s. The organic removal goes up with the increased catalyst. It can be learned that although the contact time is short, the catalyst is able to remove over 80% of the organics from 170 8C oil fumes. Fig. 4 also shows that fumes from higher temperature oil are more difficult remove than that from lower temperature oil. This could be explained that under high temperature, the oil will decompose in the three-neck flask with oxygen existence and increase the complexity of fumes, thus levels the treatment difficulty. Standard methods were used to determine COx concentration before and after catalytic treatment. Table 3 shows the results. It can be learned that CO was not detected throughout the process, which could be explained that oxygen is always more than enough in the column and the oxidation is complete. CO2 concentration increased after the treatment, and its concentration matches the organics
Table 3 Concentration of COx after the treatment (contact time 1.06 s, catalyst temperature 300 8C) 170 8C
180 8C
220 8C
CO (mg/L, carbon) Initial After
/ /
/ /
/ /
CO2 (mg/L, carbon) Initial After Carbon removed (mg/L)
/ 0.82 0.90
/ 1.65 1.96
/ 4.31 5.02
The symbol (/) means below detection limit.
removal (expressed in carbon) very well, verifying that those organics removed in the reactor were mineralized to CO2 and H2O. Fig. 5 shows the reactor performance under different contact times. The contact times were manipulated by varying air flow-rate that was pumped into the three-neck
Fig. 8. Organics decomposition over truly supported catalyst (oil temperature 220 8C).
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Fig. 9. GC–MS results of catalytically treated cooking oil fumes.
flask. The oil temperature was kept around 180 8C throughout the experiments. Fig. 5 displays that as the catalyst temperature increases the organic removal also goes up, which is consistent with Fig. 4. Prolonged contact time also gives more favorable results. When the contact time is
1.59 s and the catalyst temperature is 300 8C, the oil fume removal is close to 90%. To further study the relationship between contact time and fume removal, experiments were performed under 180 8C, and the catalyst temperature was kept at 200 8C.
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Table 4 Chemicals in fume samples taken during experiments Chemicals Non-treated
200 8C
250 8C
300 8C
2-Heptanone ketone, 4-pentenal, 2,2-dimethyl, ethanol, 2-butoxy-, ethanedioic acid, bis(1-methylpropyl) ester,2-heptenal, (Z)-,1-heptanol,1-octen-3-ol, 3-octanone, furan, 2-pentyl-,3,7-decadiene, 2,9-dimethyl-,cyclohexanol, 2,4-dimethyl-, octanal, 4-ethylcyclohexanol,2,4-heptadienal, (E,E)-,formic acid, heptyl ester,1,3-hexadiene, 3-ethyl-2-methyl-,cyclohexanol, 2,4-dimethyl-2-nonen-1-ol, (Z)-,1,2-epoxynonane, 2(3H)-furanone, 5-ethyldihydro-, benzene, butyl-, 2-octenal, (E)-, 2-octen-1-ol, (E)-, 1-octanol,heptanoic acid, 1-nonen-3-ol, 2,4-octanedione, 5-nonen-2-one, 8-hydroxy-2-octanone, butyric acid, 4-pentadecyl ester,4-nonenal, (E)-, undecane, nonanal, 2,4-octadienal, 4,6-decadiene, trans-3-Nonen-2-one, cycloheptanol, 2-methylene, 2(3H)-furanone, dihydro-5-pentyl-, 2-nonenal, (E)-, octanoic acid, 9-oxa-bicyclo[3.3.1]nona-3,6-dien-2-one, trans-2-undecenoic acid, 2-undecanone, 6,10-dimethyl-, 2,4-nonadienal, (E,E)-, trans-undec-4-enal, dodecane, decanal, hexyl octyl ether, 2,4-nonadienal, (E,E)-, 3-hexadiene, 3-ethyl-2-methyl-, 1,4-cyclooctanedione, 13-tetradece-11-yn-1-ol, 3-isopropyl-5-methylhexan-2-one, 2(3H)-furanone, 5-butyldihydro-, 2-decenal, nonanoic acid, 6-undecanone, hexanoic acid, tridecyl ester, 2,4-decadienal, tridecanal, bicyclo[3.3.1]nonane-2,7-dione, 2,4-decadienal, 1-undecene, 8-methyl-, 2-undecenal, 9-hexadecenoic acid, 6-dodecanone, 2,4-dodecadiene, (E,Z)-, 2-methyl-7-oxabicyclo[2.2.1]heptane, 3-nonen-5-yne, 4-ethyl-, (Z)-, 14-bromo-2-methyltetradec-1-en-3-ol, tridecanal, 7-pentadecyne 9-octadecene, (E)-, tetradecane, S-butyl methyl ethylphosphonate, hexatriacontane 2-Heptanone,2-tridecene, (E)-,heptanal,2-hexene, 2,3-dimethyl-,2-heptenal, (Z)-,benzaldehyde,pentanoic acid, 1-octen-3-ol,1-nonen-3-ol,furan, 2-pentyl-1-octanol, 2-butyl-, n-octaldehyde,1,3-hexadiene, 3-ethyl-2-methyl-, 4-ethylcyclohexanol, 2-octenal, (E)-, nonanal, 2-nonenal, (E)-,2-decenal, (E)-, 2,4-decadienal, (E,E)-,1(2H)-naphthalenone, octahydro-, cis-,2,4-decadienal, 1-undecene, 8-methyl-, 2-undecenal, hex-3-ene-1,6-diol, 14-bromo-2-methyltetradec-1-en-3-ol, 1-tridecanol,9-nonadecene 2-Heptanone, n-heptaldehyde, cyclopentane, 1-ethyl-1-methyl-, 2-heptenal, (Z)-benzaldehyde, 1-octen-3-ol,furan, 2-pentyl-, n-octanal, 1,3-hexadiene, 3-ethyl-2-methyl-, 4-ethylcyclohexanol, 2-octenal, (E)-, nonanal, 1(2H)-naphthalenone, octahydro-, cis-, cholesteryl benzoate 2-Heptanone, n-heptaldehyde, cyclopentane, 1-ethyl-1-methyl-, 2-heptenal, (Z)-, benzaldehyde, 1-octen-3-ol, furan, 2-pentyl-, n-octanal, 2-octenal, (E)-, nonanal, 1(2H)-naphthalenone, octahydro-, cis-allyl n-octyl ether $$ allyl octyl ether
Fig. 6 gives the result. It can be seen that the removal effect is strengthened as the contact time is prolonged. When the contact time is 3.18 s, the oil fume removal is over 96%, while the catalyst temperature is just 200 8C. It is obvious that the removal is not linear with contact time, and the equation that might be used to describe the relationship is shown in Fig. 6. Experiments were also done with empty column and using just prepared plain Al2O3. The results are shown in Fig. 7. It is shown in Fig. 7 that no meaningful decomposition occurs in empty column and over plain Al2O3. The small removal may be deterred by tubing connection or adsorbed by Al2O3 support.
Experiments were also performed using truly supported catalyst prepared as described in previous section. Fig. 8 shows the results. It could be learned that the fume removal is not as satisfying as that by mixed catalyst. As shown in Table 2, the specific area of truly supported catalyst is significantly smaller than that of mixed catalyst, which may explain the difference.
Fig. 10. SEM of catalyst surface treated by steam.
Fig. 11. SEM catalyst surface treated by heat.
3.3. GC–MS analysis Samples were taken during catalytic experiment when the oil temperature was controlled 180 8C and the contact time was 1.06 s. It can be learned from Fig. 9 that the composition
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Fig. 12. Catalyst performance vs. time.
of non-treated fumes is complex and contains lots of saturated and non-saturated fats. After passing catalyst at different temperatures, the number of components was decreased significantly from 75 to just 11 (catalyst temperature from 200 8C to 300 8C) and the concentration also goes down dramatically, which indicates that mineralization and not other process dominates the cooking oil fumes removal process (Fig. 9). Table 4 gives the detailed information of components that were found in cooking oil fumes during experiment.
Table 5 Experimental results with treated catalyst (oil temperature 180 8C, contact time 1.06 s, three replicates)
3.4. Durability experiments Thermal stability is a very important index for this kind of catalyst since the temperature of catalytic reactor may be periodically increased to burn out some residual. Also, since a lot of steam is produced when cooking, the catalyst must be immune from water vapor poisoning. Table 5 proves that the catalyst performance was not negatively affected by steam existence and thermal treatment. Figs. 10 and 11 show that typical SEM pictures of catalyst treated by steam and heat. Compared with Fig. 2, these two pictures almost give the same image. Experiments (200 8C catalyst temperature, 180 8C oil temperature, 1.06 s contact time) were carried out continuously to check the lifetime of the mixed catalyst. Fig. 12 shows the catalyst performance versus time. It is shown that the catalytic activity of the mixed catalyst did not decrease after being used continuously for 300 h.
impressing results. It has been pointed out that within experimental temperature range (200–300 8C), the catalyst can mineralize most organics while the contact time is less than 1 s (as shown in Figs. 4 and 5). If the contact is prolonged to 3.18 s, 96% removal could be achieved at 200 8C (as shown in Fig. 6). Results also show that fume from high temperature oil is relatively more difficult to remove than that from low temperature oil (as shown in Figs. 4 and 5). Poisoning experiments and thermal stability study on the prepared catalyst were also performed. It is displayed that the catalyst is stable with high moisture existence and is not negatively affected by thermal treatment up to 750 8C. For the experiment done, the catalytic activity of the mixed catalyst is stable even being used continuously for 300 h. Overall, the catalyst is very effective at organics mineralization and might be employed in other applications such as industrial organic gas treatment.
4. Conclusion
References
Because of its complexity, cooking oil fumes are notoriously difficult to remove using traditional methods. This work successfully developed a MnO2/CuO mixed catalyst and employed it to treat cooking oil fumes with
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Temperature (8C)
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Removal (%) Non-treated catalyst
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51.26 58.16 66.83
50.37 57.39 66.16
50.25 59.50 67.35
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