- Email: [email protected]
Exfoliated Graphite as a New Sorbent for Removal of Engine Oils from Wastewater
Spill Science & Technology Bulletin, Vol. 8, Nos. 5–6, pp. 569–571, 2003 2003 Elsevier Ltd. All rights reserved Printed in Great Britain 1353-2561/$ - see front matter
doi:10.1016/S1353-2561(03)00070-7
Exfoliated Graphite as a New Sorbent for Removal of Engine Oils from Wastewater CZUK & MICHIO INAGAKIà BEATA TRYBA *, ANTONI W. MORAWSKI , RYSZARD J. KALEN Department of Water Technology and Environment Protection, Technical University of Szczecin, ul. Pułaskiego 10, 70-322 Szczecin, Poland àDepartment of Applied Chemistry, Aichi Institute of Technology, Yakusa, Toyota 470-0392, Japan
A commercial exfoliated graphite was used for checking its sorption capabilities for removing engine oil and dyes from wastewater. Slight oxidation of exfoliated graphite in the air at 400 C was found to be effective to improve adsorption capacity for dyes, methylene blue and methyl orange. However, its treatment in HNO3 reduced all capacities for engine oil and dyes. A possibility for simultaneous removal of oil and dyes dispersed in wasted water was revealed. 2003 Elsevier Ltd. All rights reserved. Keywords: Exfoliated graphite, sorption, engine oil, methylene blue, methyl orange
Introduction In 1996, Cao et al. (1996) reported on heavy oil sorption by an exfoliated graphite, but their sorption capacity was not markedly high. Later, Toyoda et al. (1998) reported that a commercial exfoliated graphite (EG) can sorb a large amount of heavy oil, more than 80 g of heavy oil with relatively low viscosity per 1 g of exfoliated graphite, floating on the water, and be easily recovered. They found marked dependences of sorption capacity on bulk density of EG and viscosity of heavy oil (Toyoda et al., 1999; Toyoda & Inagaki, 2000). They also pointed out the preferential sorption of heavy oil and only a trace of water in heavy oil recovered from EG was noted. These experimental results suggest the possibility of efficient removal of oil in wastewater in industries. On the other hand, the present authors found out a pronounced enhancement of adsorption of trihalo-
*Corresponding author.
methanes (THMs) into an activated carbons derived from a phenol resin by additional oxidation treatment (Morawski & Inagaki, 1997; Morawski et al., 2000). In the present work, the effect of oxidation of exfoliated graphite on sorption of oil and some organic substances dispersed in water was examined, in order to check the applicability to simultaneous removal of all organic contaminants, including oil, in wastewater.
Experimental An exfoliated graphite produced from residue compounds of natural graphite with sulfuric acid in an industry was used, of which bulk density was 60 kg/m3 and was exactly the same as Toyoda et al. used (Toyoda et al., 1999). Its oxidation treatments were performed at 400 C in air for 4 h and also in 13% nitric acid at room temperature. In Table 1, the oxidation conditions are shown, together with sample codes used in the present work. BET surface area of 569
B. TRYBA et al. Table 1 Oxidation conditions and capacities of exfoliated graphite samples Sample
EG 44-EG NA-EG 44-NA-EG
Oxidation conditions
BET surface area [m2 /g]
Oil sorption capacity [g/g]
Methylene blue adsorption capacity [g/g]
Methyl orange adsorption capacity [g/g]
As-received Oxidized at 400 C for 4 h Treated in 13% HNO3 at r.t. Treated in 13% HNO3 at r.t. and then oxidized at 400 C for 4 h
69 72 26 28
13.2 14.4 4.7 1.5
0.25 0.25 0.10 0.12
0.23 0.30 0.14 0.21
samples was calculated from adsorption–desorption isotherm of nitrogen at 77 K. Sorption isotherms for oil and organic substances: wasted engine oil, methylene blue and methyl orange used in the present work, were measured to determine the sorption capacities of the as-received and oxidized exfoliated graphites. The known amount of wasted engine oil was dispersed in 100 ml water by stirring. The exfoliated graphite sample of 0.05 g was added into this mixture and then stirred again for about 0.5 h. After that exfoliated graphite was separated from the water by filtration and then dried at 100 C for 1 h to remove the water. It was verified by a complementary test that no water was left on exfoliated graphite sample by this drying process. The amount of sorbed oil was calculated from the weight increase of exfoliated graphite after sorption. By changing the amount of engine oil in water, the maximum sorption capacity of exfoliated graphite was determined. Adsorption measurements of dyes, methylene blue and methyl orange, were performed in a conical flask using water with 0.01 g/l concentration of dyes by using various amounts of exfoliated graphite from 20 to 70 mg under the agitation for 4.5 h. Concentration of dyes remained in water after adsorption was determined with a spectrophotometer (Specord M40). Maximum adsorption capacity was calculated from the Freundlich equation describing the dependence on adsorption capacity versus equilibrium concentration.
et al., 1998, 1999). This is probably due to the dispersion of exfoliated graphite particles and even destruction of their characteristic worm-like morphology in water by rigorous stirring and also due to the character of engine oil which contains some unreacted byproducts of combustion. On adsorption capacities for dyes, however, exfoliated graphite has rather high value, 0.25 g/g for methylene blue (7.8 · 10 4 mol/g) and 0.23–0.30 g/g for methyl orange (7.0–9.2 · 10 4 mol/g). However, this capacity becomes less than a half after the treatment by HNO3 (samples NA-EG and 44-NA-EG). This might be explained by the change in pore structure
Results and Discussion BET surface area and capacities of exfoliated graphites oxidized for oil, methylene blue and methyl orange were listed in Table 1, comparing with those of as-received one (EG). Oxidation of exfoliated graphite at 400 C is found to give certain increases in surface area and capacities, particularly capacity for methyl orange (sample 44-EG). However, surface area and all capacities of exfoliated graphite decrease by oxidation in HNO3 (sample NA-EG), which cannot be recovered by oxidation in air at 400 C (sample 44-NA-EG). On sorption capacity for oil, even as-received sample (EG) shows small value, much smaller than the reported on the same exfoliated graphite (Toyoda 570
Fig. 1 Adsorption–desorption isotherms of nitrogen at 77 K for exfoliated graphite samples: (a) as-received (EG) and (b) treated in HNO3 (NA-EG). Spill Science & Technology Bulletin 8(5–6)
EXFOLIATED GRAPHITE AS A NEW SORBENT
before and after HNO3 treatment. In Fig. 1(a) & (b), adsorption–desorption isotherms of N2 at 77 K are shown on EG and NA-EG, respectively. The former is classified into type II, suggesting the existence of macropores and dose not show a hysteresis between adsorption and desorption isotherms. A pronounced hysteresis, however, is observed on the latter, which suggests the existence of mesopores. The sample 44EG showed very similar isotherms to EG, and 44-NAEG to NA-EG. By taking into account the fact that BET surface area also decreases after NHO3 treatment, it may conclude that some of micropores are converted to mesopores by HNO3 treatment, of which main chemical reaction with graphite is oxidation.
Conclusions The present experiment did not give very high sorption capacity for oil, but adsorption capacities for dyes dissolved into water were found to be improved by slight oxidation in air at 400 C. If we consider the fact that macropores existing both in the particles of exfoliated graphite and among the particles are responsible for oil sorption and micropores in the par-
Spill Science & Technology Bulletin 8(5–6)
ticles for the adsorption of dyes, we may have the possibility to remove dispersed oil and dissolved dyes simultaneously from wastewater by optimizing the mixing conditions, not rigorous stirring but give enough contact between wastewater and exfoliated graphite. References Cao, N.Z., Shen, W.C., Wen, S.Z., Gu, J.Z., Wang, Z.D., 1996. The adsorption performance of heavy oil on expanded graphite. In: European Conference ‘‘CarbonÕ96’’, Newcastle upon Tyne, UK. p. 114. Morawski, A.W., Inagaki, M., 1997. Application of modified synthetic carbon for adsorption of trihalomethanes (THMs) from water. Desalination 114, 23–27. Morawski, A.W., Kale nczuk, L., Inagaki, M., 2000. Adsorption of trihalomethanes (THMs) onto carbon spheres. Desalination 130, 107–192. Toyoda, M., Inagaki, M., 2000. Heavy oil sorption by exfoliated graphite – New application of exfoliated graphite to protect heavy oil pollution. Carbon 38, 199–210. Toyoda, M., Aizawa, J., Inagaki, M., 1998. Sorption and recovery of heavy oil using exfoliated graphite. Desalination 115, 199– 201. Toyoda, M., Moriya, K., Inagaki, M., 1999. Sorption of heavy oil into exfoliated graphite. Influence of bulk density and pore for sorption. In: TANSO 187, vol. 187. pp. 96–100 (in Japanese).
571
doi:10.1016/S1353-2561(03)00070-7
Exfoliated Graphite as a New Sorbent for Removal of Engine Oils from Wastewater CZUK & MICHIO INAGAKIà BEATA TRYBA *, ANTONI W. MORAWSKI , RYSZARD J. KALEN Department of Water Technology and Environment Protection, Technical University of Szczecin, ul. Pułaskiego 10, 70-322 Szczecin, Poland àDepartment of Applied Chemistry, Aichi Institute of Technology, Yakusa, Toyota 470-0392, Japan
A commercial exfoliated graphite was used for checking its sorption capabilities for removing engine oil and dyes from wastewater. Slight oxidation of exfoliated graphite in the air at 400 C was found to be effective to improve adsorption capacity for dyes, methylene blue and methyl orange. However, its treatment in HNO3 reduced all capacities for engine oil and dyes. A possibility for simultaneous removal of oil and dyes dispersed in wasted water was revealed. 2003 Elsevier Ltd. All rights reserved. Keywords: Exfoliated graphite, sorption, engine oil, methylene blue, methyl orange
Introduction In 1996, Cao et al. (1996) reported on heavy oil sorption by an exfoliated graphite, but their sorption capacity was not markedly high. Later, Toyoda et al. (1998) reported that a commercial exfoliated graphite (EG) can sorb a large amount of heavy oil, more than 80 g of heavy oil with relatively low viscosity per 1 g of exfoliated graphite, floating on the water, and be easily recovered. They found marked dependences of sorption capacity on bulk density of EG and viscosity of heavy oil (Toyoda et al., 1999; Toyoda & Inagaki, 2000). They also pointed out the preferential sorption of heavy oil and only a trace of water in heavy oil recovered from EG was noted. These experimental results suggest the possibility of efficient removal of oil in wastewater in industries. On the other hand, the present authors found out a pronounced enhancement of adsorption of trihalo-
*Corresponding author.
methanes (THMs) into an activated carbons derived from a phenol resin by additional oxidation treatment (Morawski & Inagaki, 1997; Morawski et al., 2000). In the present work, the effect of oxidation of exfoliated graphite on sorption of oil and some organic substances dispersed in water was examined, in order to check the applicability to simultaneous removal of all organic contaminants, including oil, in wastewater.
Experimental An exfoliated graphite produced from residue compounds of natural graphite with sulfuric acid in an industry was used, of which bulk density was 60 kg/m3 and was exactly the same as Toyoda et al. used (Toyoda et al., 1999). Its oxidation treatments were performed at 400 C in air for 4 h and also in 13% nitric acid at room temperature. In Table 1, the oxidation conditions are shown, together with sample codes used in the present work. BET surface area of 569
B. TRYBA et al. Table 1 Oxidation conditions and capacities of exfoliated graphite samples Sample
EG 44-EG NA-EG 44-NA-EG
Oxidation conditions
BET surface area [m2 /g]
Oil sorption capacity [g/g]
Methylene blue adsorption capacity [g/g]
Methyl orange adsorption capacity [g/g]
As-received Oxidized at 400 C for 4 h Treated in 13% HNO3 at r.t. Treated in 13% HNO3 at r.t. and then oxidized at 400 C for 4 h
69 72 26 28
13.2 14.4 4.7 1.5
0.25 0.25 0.10 0.12
0.23 0.30 0.14 0.21
samples was calculated from adsorption–desorption isotherm of nitrogen at 77 K. Sorption isotherms for oil and organic substances: wasted engine oil, methylene blue and methyl orange used in the present work, were measured to determine the sorption capacities of the as-received and oxidized exfoliated graphites. The known amount of wasted engine oil was dispersed in 100 ml water by stirring. The exfoliated graphite sample of 0.05 g was added into this mixture and then stirred again for about 0.5 h. After that exfoliated graphite was separated from the water by filtration and then dried at 100 C for 1 h to remove the water. It was verified by a complementary test that no water was left on exfoliated graphite sample by this drying process. The amount of sorbed oil was calculated from the weight increase of exfoliated graphite after sorption. By changing the amount of engine oil in water, the maximum sorption capacity of exfoliated graphite was determined. Adsorption measurements of dyes, methylene blue and methyl orange, were performed in a conical flask using water with 0.01 g/l concentration of dyes by using various amounts of exfoliated graphite from 20 to 70 mg under the agitation for 4.5 h. Concentration of dyes remained in water after adsorption was determined with a spectrophotometer (Specord M40). Maximum adsorption capacity was calculated from the Freundlich equation describing the dependence on adsorption capacity versus equilibrium concentration.
et al., 1998, 1999). This is probably due to the dispersion of exfoliated graphite particles and even destruction of their characteristic worm-like morphology in water by rigorous stirring and also due to the character of engine oil which contains some unreacted byproducts of combustion. On adsorption capacities for dyes, however, exfoliated graphite has rather high value, 0.25 g/g for methylene blue (7.8 · 10 4 mol/g) and 0.23–0.30 g/g for methyl orange (7.0–9.2 · 10 4 mol/g). However, this capacity becomes less than a half after the treatment by HNO3 (samples NA-EG and 44-NA-EG). This might be explained by the change in pore structure
Results and Discussion BET surface area and capacities of exfoliated graphites oxidized for oil, methylene blue and methyl orange were listed in Table 1, comparing with those of as-received one (EG). Oxidation of exfoliated graphite at 400 C is found to give certain increases in surface area and capacities, particularly capacity for methyl orange (sample 44-EG). However, surface area and all capacities of exfoliated graphite decrease by oxidation in HNO3 (sample NA-EG), which cannot be recovered by oxidation in air at 400 C (sample 44-NA-EG). On sorption capacity for oil, even as-received sample (EG) shows small value, much smaller than the reported on the same exfoliated graphite (Toyoda 570
Fig. 1 Adsorption–desorption isotherms of nitrogen at 77 K for exfoliated graphite samples: (a) as-received (EG) and (b) treated in HNO3 (NA-EG). Spill Science & Technology Bulletin 8(5–6)
EXFOLIATED GRAPHITE AS A NEW SORBENT
before and after HNO3 treatment. In Fig. 1(a) & (b), adsorption–desorption isotherms of N2 at 77 K are shown on EG and NA-EG, respectively. The former is classified into type II, suggesting the existence of macropores and dose not show a hysteresis between adsorption and desorption isotherms. A pronounced hysteresis, however, is observed on the latter, which suggests the existence of mesopores. The sample 44EG showed very similar isotherms to EG, and 44-NAEG to NA-EG. By taking into account the fact that BET surface area also decreases after NHO3 treatment, it may conclude that some of micropores are converted to mesopores by HNO3 treatment, of which main chemical reaction with graphite is oxidation.
Conclusions The present experiment did not give very high sorption capacity for oil, but adsorption capacities for dyes dissolved into water were found to be improved by slight oxidation in air at 400 C. If we consider the fact that macropores existing both in the particles of exfoliated graphite and among the particles are responsible for oil sorption and micropores in the par-
Spill Science & Technology Bulletin 8(5–6)
ticles for the adsorption of dyes, we may have the possibility to remove dispersed oil and dissolved dyes simultaneously from wastewater by optimizing the mixing conditions, not rigorous stirring but give enough contact between wastewater and exfoliated graphite. References Cao, N.Z., Shen, W.C., Wen, S.Z., Gu, J.Z., Wang, Z.D., 1996. The adsorption performance of heavy oil on expanded graphite. In: European Conference ‘‘CarbonÕ96’’, Newcastle upon Tyne, UK. p. 114. Morawski, A.W., Inagaki, M., 1997. Application of modified synthetic carbon for adsorption of trihalomethanes (THMs) from water. Desalination 114, 23–27. Morawski, A.W., Kale nczuk, L., Inagaki, M., 2000. Adsorption of trihalomethanes (THMs) onto carbon spheres. Desalination 130, 107–192. Toyoda, M., Inagaki, M., 2000. Heavy oil sorption by exfoliated graphite – New application of exfoliated graphite to protect heavy oil pollution. Carbon 38, 199–210. Toyoda, M., Aizawa, J., Inagaki, M., 1998. Sorption and recovery of heavy oil using exfoliated graphite. Desalination 115, 199– 201. Toyoda, M., Moriya, K., Inagaki, M., 1999. Sorption of heavy oil into exfoliated graphite. Influence of bulk density and pore for sorption. In: TANSO 187, vol. 187. pp. 96–100 (in Japanese).
571