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Recycling waste tire powder for the recovery of oil spills
Resources, Conservation and Recycling 52 (2008) 1162–1166
Contents lists available at ScienceDirect
Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec
Recycling waste tire powder for the recovery of oil spills Chitsan Lin a,∗ , Chun-Lan Huang b , Chien-Chuan Shern a a b
Department of Marine Environmental Engineering, National Kaohsiung Marine University, 142 Haijhuan Road, Nanzih District, Kaohsiung 81157, Taiwan Department of Aquaculture, National Kaohsiung Marine University, 142 Haijhuan Road, Nanzih District, Kaohsiung 81157, Taiwan
a r t i c l e
i n f o
Article history: Received 13 February 2008 Received in revised form 24 May 2008 Accepted 17 June 2008 Available online 24 July 2008 Keywords: Spilled oil recovery Oil adsorbent Resources recycling Oil spill Scrap tire
a b s t r a c t Waste tire related environmental problems and its recycling techniques have been a major challenge to society. Current waste tire recycling market is too small to accommodate the tire generated annually. Therefore, it is of crucial importance to develop new markets for waste tires. Tire rubber is flexible and has hydrophobic (oil-philic) characteristics, making it a good candidate as an oil adsorbent. In this paper, the possibility of applying waste tire powder as a sorbent for the recovery of spilled oil was explored. The results indicate that 2.2 g of motor oil can be adsorbed to each gram of 20 mesh tire powder. Due to its elastic property, waste tire powder is re-usable for over 100 times without decreasing its oil absorption efficiency. Therefore, at least 220 g of motor oil can be recovered per gram of waste tire powder, which is very competitive to commercial sorbent. The results of this study indicated that sorption efficiency increased as the tire powder particle size decreased, and decreased as the environmental temperature increases. When applying the waste tire powder to oil slicks on seawater, the oil sorption efficiency is shown to be better than if it was on fresh water. Efforts have been made to enhance the waste tire powder’s oil sorption efficiency. Results indicated that the highest efficiency was obtained when the waste tire powder was pre-cleaned by n-hexane, followed by water cleaning > un-cleaned > dishwashing liquid cleaned > seawater cleaned. Compared to a commercial oil sorbent, the result indicated that waste tire powder was economically more feasible, if it was re-used for 100 times. More efforts are encouraged to enhance the waste tire powder’s oil sorption capacity without decreasing its re-usable characteristics. © 2008 Elsevier B.V. All rights reserved.
1. Introduction According to Rubber Manufactures Association (RMA, 2006), about 299 million tires were generated in the United States in 2005; where 52% of the scrap tires were converted into tire-derived fuel (TDF), 16% were used by the civil engineering applications, 12% were recycled by the ground rubber applications, 14% were land disposed, 2% were exported, and 4% of other applications. Waste tires are virtually non-degradable and take up landfill spaces (Weng and Chang, 2001). If not properly disposed, waste tires may accumulate water, and subsequently can cause the spread of mosquito-borne diseases (Chang, 2008; Yang, 1993). Often tire fires occur and cause serious air, water, and soil pollutions (Fan et al., 2005). Nevertheless, tire rubber has a high heat value (12,000–16,000 Btu/lb). In the United States, Canada, Germany, the United Kingdom, and Japan, waste tires have been used as a supplemental fuel for the cement kilns (Prisciandaro et al., 2003) and in the paper mills (Barlaz et al., 1993). Waste tires can also be recycled as a roadway pavement material (Huang et al., 2007; Siddique and Naik, 2004), refuse
∗ Corresponding author. Tel.: +886 7 3651472; fax: +886 7 3651472. E-mail address: [email protected] (C. Lin). 0921-3449/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2008.06.003
derived fuel (Wan et al., 2008; Murugan et al., 2008; Mastral et al., 2000), or reproduced as tires (Douglah and Everett, 1998; Everett and Douglah, 1998). Sometimes, waste tire is used to produce rubber mats, roadway guard rails, as engineered protective cushions or bumpers, and for building and construction materials (Topc¸u and Sarıdemir, 2008; Turatsinze et al., 2005). In marine applications, waste tire can also be used as a wave breaking material, ship/dock protective bumpers, or even to construct artificial reefs (Chapman and Clynick, 2006) in the ocean farming industry. It seems that discarded tires are of useful in many recycling alternatives. However, the markets appear to be small compared to the number of tires generated each year. Therefore, it is of interest to explore any new application/market for the scrap tire reclaiming industry. According to Gunasekara et al. (2000), tires are primarily composed of rubber (40–45%) vulcanized with sulfur (1.5–2.5%), steel, and carbon black (27–33%). The carbon black, used to strengthen the rubber, is similar to activated carbon (Snoeyink et al., 1967), a good sorbent to remove dissolved organic substances from wastewater. In a permeation of organic compounds through rubber gaskets study, Park and Bontoux (1991) reported that rubber is a good sorbent for organic compounds. Kim et al. (1997) reported that organic compounds were sorbed primarily onto tire rubber polymeric materials and partially carbon black in the tire
C. Lin et al. / Resources, Conservation and Recycling 52 (2008) 1162–1166
rubber, and the partition coefficients had a logarithmic linear relationship with the octanol–water partition coefficients. Gunasekara et al. (2000) further investigated the use of ground discarded tires to remove naphthalene and toluene from water. Moreover, tire rubber is a flexible and hydrophobic (oil-philic), making it a good candidate as an oil sorbent. In this research, the possibility of utilizing waste tire powder as oil sorbent for the recovery of spilled oil has been explored. Oil spills in a marine environment will not only cause property loss, but it could also have a strong negative impact on the entire ecosystem. According to the UNEP report (United Nations Environment Programme, 1991), compared to 1976, the amount of oil spilled in 1991 indicated a decreasing trend. Nevertheless, crude oil and petroleum products that have found their ways into the marine environment were in an amount to about 10,000–100,000 tons annually in the past decade. Therefore, the marine oil spill prevention has always been a global awaking subject that requires further attention. If the proposed ideal of this research is applicable to utilize tire particle as an oil sorbent in oil spill recovery, not only will it benefit to the oil pollution prevention, but will also bring profit to the scrap tire recycling industry. 2. Experimental methods 2.1. Materials Ground tire powders of 5, 10, 20, and 40 mesh were obtained from a local scrap tire recycling facility in Kaohsiung, southern Taiwan. The 20 mesh waste tire powder was used as the sample to study the oil sorption behavior. 5W-40 motor oil produced by the Shell Company was used to simulate spilled oil. The motor oil was air stripped at 90 ◦ C for 2 h to remove the volatile organic compounds (VOCs), so as to minimize the quantification error due to the loss of VOCs during the sorption experiment. After stripping, only 0.163% weight loss was recorded, and a control test at room temperature had shown that no discernible loss of VOCs during the time period of sorption experiment. A thin meshy non-woven PET (polyethylene terephthalate) sheet which allowed the passing of oil was utilized as a packing material to contain the tire powder for sorption experiments. PET fiber is strong, durable, and impact resistant making it a feasible packing material. American Society of Testing and Materials F726-99 method (ASTM, 2006) was referenced for oil sorption capability tests that are detailed as follows. 2.2. Oil sorption capability tests of waste tire powder Packing material (PET sheet) was used to produce round-shaped sorbent bags of the same size (5.5 cm in diameter), and each bag contained 1 g of 20 mesh tire powder. The sorbent bag was submerged into a 50-mL motor oil bath contained by a 250-mL glass beaker, and the sorbent bag was allowed to saturate. If more sorbent bags were tested at the same time, bigger containers were used. The sorption speed and the time required to saturate the sorbent bag were monitored. All sorption experiments were performed in an air conditioned room at about 20 ◦ C. A tweezer was used to remove the saturated sorbent bag, and it was hung in the air for 30 s (ASTM, 2006) to allow the excess motor oil to drip from the bag. The remaining sorbed oil was estimated to represent the unit “practical sorption amount” by subtracting the amount sorbed by a parallel control experiment of a blank sorbent bag without tire powder. The practical sorption amount will include the oil adhered on the surface of the sorbent bag, and could actually be recovered during a practical oil recovering processes assuming a 30-s free drop time before the oil was captured.
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2.3. Waste tire powder adsorbent re-usability experiment A key point of our proposal is that the waste tire sorbent bag can be re-used many times without losing its oil sorption capability, due to the elastic nature of tire materials. To study the re-usability, one sorbent bag was chosen, and its “practical sorption amount” was monitored each time after re-use for up to 100 times, to see if its adsorption capability decreased because of re-utilization. Each time the sorbent bag was used, and the recovered oil on the bag was mechanically pressed out to simulate each oil recovery cycle. The pressing equipment equipped with two adjustable rollers at 2 mm spacing. Three pressings were performed for each repetitive sorption experiment. 2.4. Application of the sorbent bag in seawater and fresh water We are all aware of major oil spills that occur in the world’s oceans. However, spills also occur in inland fresh water systems during the transportation process. During an emergency response, the sorbent bag may become wetted by seawater or fresh water before reaching the oil slick, and subsequently, the sorption efficiency may decrease. To study the effects of wetting and compare how the water wetted surface affected the oil adsorption efficiency, the sorbent bags were immersed into and completely soaked by each of seawater and fresh water, then hung in the air, allowed the water to drip from the sorbent bag for 30 s before carrying out the oil adsorption experiments. 2.5. Effects of different pre-treatment methods on the oil sorption efficiency Untreated waste tire powder may contain cokes and some aqueous soluble impurities. As part of enhancing sorption efficiency efforts, different pre-cleaning treatments were studied, including (1) water cleaned, (2) n-hexane cleaned, (3) surfactant (dish cleaner) cleaned, and (4) seawater cleaned. After each 10 min cleaning by ultrasonic cleaner (Branson 3510, 40 kHz), the filtered tire powder was directly dried in a 100 ◦ C oven before use. All results were compared to the un-cleaned waste tire powder. 2.6. Effects of tire powder particle size and temperature on the oil sorption efficiency The smaller tire powder particle size and the larger specific surface area are obtained. A series of experiments were performed to evaluate the effects of tire powder particle size on the oil sorption efficiency with 5, 10, 20, and 40 mesh tire powder tested. Moreover, in order to assess the temperature of the oil spill environment on the sorption efficiency, 20 and 40 mesh tire powders were used to study the effects of temperature on the oil sorption efficiency ranging from 0 to 40 ◦ C. Tested oil and tire powder were equilibrated with a constant temperature refrigerating circulator (TKS RCB411) before the sorption experiments were conducted. 3. Results and discussion 3.1. Oil sorption capability tests of waste tire powder Results of the oil sorption experiments indicated that it took about 5 min to saturate the waste tire sorbent bag with oil in an undisturbed environment. The practical sorption amount was averaged at 2.17 ± 0.01 g (n = 10), which means that each gram of 20 mesh tire powder can pick up about 2.2 g of motor oil.
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Fig. 1. Results of the re-usability test indicate that waste tire powder sorbent can be re-used for more than 100 times without losing its sorption capacity.
3.2. Waste tire powder adsorbent re-usability Fig. 1 presents the results of the re-usability test of a tire powder sorbent bag. Results indicated that the sorption capacity was not affected after 100 times of re-use. This is not surprising because the tire powder is made of rubber material with an elastic characteristic. Therefore, it can sustain repeated mechanical pressing without wearing out, while the sorbed oil is being recovered. After re-used for 100 times (mechanically pressing 300 times), except the containment bag slightly deformed, the out looking and performance of the tire powder appeared not changed. Note that the re-usability experiments did not proceed beyond 100 times, even though it is reasonable to assume that it could be re-used continuously until the packing material was worn out. Assuming that the waste tire sorbent bag was only re-used 100 times, then the practical total adsorption amount would be 220 g of motor oil per gram of waste tire powder. 3.3. Sorption efficiency of the wetted and un-wetted tire powder Fig. 2 compares the sorption efficiency of the wetted and unwetted tire powder during the oil recovery operation. Results indicated that un-wetted tire powder performed better followed by powders wetted with seawater and fresh water respectively. The surface of the wetted tire powder may partially turn into
Fig. 3. Effects of various types of pre-cleaning methods on the sorption capacity.
hydrophilic from water soaked on the surface that accounts for the decrease of the sorption efficiency. Therefore, it is important that during the oil spill recovery processes, the waste tire sorbent pad is thrown right onto the oil slick surface, because if the sorbent pad is thrown onto the water surface, and becomes wetted, the sorption efficiency of the pad will decrease. 3.4. Effects of different pre-treatment methods on the oil sorption efficiency Unless otherwise specified in this text, all results are monitored as the practical sorption amount per gram of waste tire powder (g/g), without accounting its re-usability value. Fig. 3 compares the effects of different ways of waste tire powder pre-treatment on the sorption capacity. The results indicated that n-hexane cleaned waste tire powder has the best sorption capacity, followed by water cleaned > un-cleaned > dish detergent cleaned > seawater cleaned. n-Hexane can wash out a layer of brownish constituents to expose the hydrophobic surface of the rubber tire powder. Water cannot wash out the brownish constituents, but it does wash out some hydrophilic impurities to allow the oil to pass more easily through the tire powder. A local purchased dish detergent was applied to simulate the surfactant treatment effect. Results indicated that the sorption capacity decreased if dish detergent cleaned and if the cleaning was not followed by a water rinse to rinse off the surfactant. A possible explanation for that is that because the hydrophilic end of dried-out surfactant on the surface of the tire powder will stand out to hamper the oil sorption efficiency. When treated by seawater, and without rinsing off the salt, the hydrophilic salty materials would become dried out on the surface of the tire powder, and subsequently would hamper the oil sorption efficiency. Although, for the sake of efficiency of the tire powder sorbent, solvent cleaning (n-hexane or alcohol) is helpful, it may possibly not be preferred due to cost and the environmental unfriendly nature of the solvents. Therefore, water cleaning or surfactant cleaning followed by a complete water rinsing is recommended. When applying in salty water, a complete fresh water rinsing is a critical step before drying and storing for later use. 3.5. Effects of particle size and temperature on the oil sorption efficiency
Fig. 2. Comparison of wetted and un-wetted tire powder sorption efficiency.
Fig. 4 compares oil sorption efficiency of 5, 10, 20, and 40 mesh waste tire powders. As expected, adsorption efficiency was increased as particle size decreases. However, not much adsorption efficiency was gained with particle size decreased from 5, 10
C. Lin et al. / Resources, Conservation and Recycling 52 (2008) 1162–1166
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Table 1 Comparison of 20 mesh waste tire powder and the Ecosol for motor oil recovery Items
20 mesh waste tire powder
Ecosol
Specific gravity Bulk density (kg/m3 ) Oil sorption speed Practical sorption amount (g motor oil/g sorbent) Re-usability (times) Sorption amount, if re-used for more than 100 times (g motor oil/g adsorbent) Operation
>Water 388.1 Slow 2.2
>100 >220
1 103.3
Easy
Adsorbent cost The cost to recover 1 ton of oil After treatment
USD$0.065/kg USD$0.295 Incineration (note that tire particle is non-biodegradable)
May drift with the wind USD$65/kg USD$630 Incineration or Ecosol foam is biodegradable
Fig. 4. Sorption capability increases as tire powder particle size decreases.
to the 20 mesh with a significant improvement with the 40 mesh powder. Although, fine powder has advantage to the oil sorption efficiency, its handling and production costs need to be evaluated before commercial application. Oil spills do not only occur in the warm waters, but can also take place in cold areas where temperature is low. Fig. 5 compares oil sorption efficiency versus temperature. It is clear that sorption efficiency increased as temperature decreased in the cold region. On the opposite, sorption efficiency can decrease significantly as temperature increases in tropical areas where ambient temperature can reach as high as 40 ◦ C. 3.6. Comparison of waste tire powder versus commercial oil sorbent A very competitive commercial oil sorbent, Ecosol foam, distributed by the Spill Response New Zealand Limited, was compared with the 20 mesh waste tire powder sorbent. As indicated in Table 1, Ecosol is a very light (9.6 kg/m3 at loose form) oil sorbent with porosity higher than 90%. It adsorbs oil quickly at the practical sorption amount of 103.3 g of motor oil per gram of sorbent. It seems that Ecosol has a much higher unit sorption capacity than that of the waste tire powder (2.2 g/g). However, Ecosol can only be used
once when pressed to recover oils. If the re-usability is taken into consideration, 1 g of tire powder can be re-used for more than 100 times, thus recovering far more than 220 g of motor oil. Ecosol costs about USD$65/kg, and the whole sale recycled waste tire powder costs only USD$0.065/kg locally. Assuming waste tire powder sorbent bags are re-used 100 times, the material cost to recover 1 ton of spilled oil is USD$0.295, compared to USD$630 for Ecosol which can only be used once. 4. Conclusions Waste tire powder is flexible and has oil-philic characteristics, making it a suitable candidate as an oil sorbent for the recovery of oil spills. In this paper, the possibility of using tire powders to adsorb oil was explored. The preliminary results indicated that 1 g of 20 mesh tire powder could recover 2.2 g of motor oil. Due to its elastic property, the waste tire powder can be used for more than 100 times without decreasing its oil sorption efficiency. Therefore, the unit sorption capacity can be increased to at least 220 g of motor oil. Taking re-usability into account, the raw material cost to recover 1 ton of spilled oil is only about USD$0.3, which is very competitive. Finer particle was observed with increased sorption capability. However, the ease of handling and production costs of tire powders need to be optimized when designing the commercial product. An effort was made to enhance the oil sorption efficiency of the waste tire powder. Results indicated that the best efficiency was obtained if the waste tire powder was pre-cleaned with n-hexane and dried before use, followed by water cleaning > un-cleaned > dishwashing detergent cleaned > seawater cleaning. Moreover, un-wetted tire powder performs better than that of the wetted; therefore, it is important to apply the sorbent pad directly onto the oil slick. After use, it is important to rinse off the contacted seawater and to maintain the sorbent under dry conditions for later use. More efforts are encouraged to enhance the waste tire powder’s oil sorption capacity without decreasing its re-usability advantages. Acknowledgments This project was sponsored by the National Science Council of Taiwan under the project number NSC-90-2626-E-022-001. The authors are thankful for its financial support. References
Fig. 5. Sorption capacity decreases as temperature increases.
American Society of Testing and Materials, ASTM F726-99. Standard method of testing sorbent performance of adsorbents [accessed 01.10.06].
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Barlaz MA, Eleazer WE, Whittle DJ. Potential to use waste tires as supplemental fuel in pulp and paper mill boilers, cement kilns and in road pavement. Waste Manage Res 1993;11:463–80. Chang NB. Economic and policy instrument analyses in support of the scrap tire recycling program in Taiwan. J Environ Manage 2008;86:435–50. Chapman MG, Clynick BG. Experiments testing the use of waste material in estuaries as habitat for subtidal organisms. J Exp Mar Biol Ecol 2006;338:164–78. Douglah S, Everett JW. Scrap tire disposal. I. Survey of state programs. J Solid Waste Technol Manage 1998;25:40–50. Everett JW, Douglah S. Scrap tire disposal. II. Case study and recommendations. J Solid Waste Technol Manage 1998;25:51–60. Fan KS, Lin CH, Chang TC. Management and performance of Taiwan’s waste recycling fund. J Air Waste Manage Assoc 2005;55:574–82. Gunasekara AS, Donovan JA, Xing B. Ground discarded tires remove naphthalene, toluene, and mercury from water. Chemosphere 2000;41:1155–60. Huang Y, Bird RN, Heidrich O. A review of the use of recycled solid waste materials in asphalt pavements. Resour Conserv Recycl 2007;52:58–73. Kim JY, Park JK, Edil TB. Sorption of organic compounds in the aqueous phase onto tire rubber. J Environ Eng 1997;123:827–35. Mastral AM, Murillo R, Callen MS, Garcia T. Optimisation of scrap automotive tyres recycling into valuable liquid fuels. Resour Conserv Recycl 2000;29:263–72. Murugan S, Ramaswamy MC, Nagarajan G. Performance, emission and combustion studies of a DI diesel engine using Distilled Tyre pyrolysis oil–diesel blends. Fuel Process Technol 2008;89:152–9.
Park JK, Bontoux L. Effects of temperature, repeated exposure, and aging on polybutylene permeation by organic chemicals. J Appl Polym Sci 1991;42:2989–95. Prisciandaro M, Mazziotti G, Veglió F. Effect of burning supplementary waste fuels on the pollutant emissions by cement plants: a statistical analysis of process data. Resour Conserv Recycl 2003;39:161–84. Rubber Manufactures Association (RMA). Scrap tire markets in the United States. 2005 ed. Washington, DC: RMA; 2006. Siddique R, Naik TR. Properties of concrete containing scrap-tire rubber—an overview. Waste Manage 2004;24:563–9. Snoeyink VL, Walter J, Weber WJ. The surface chemistry of active carbon. Environ Sci Technol 1967;1:228–34. Topc¸u I˙ B, Sarıdemir M. Prediction of rubberized concrete properties using artificial neural network and fuzzy logic. Constr Build Mater 2008;22:532–40. Turatsinze A, Bonnet S, Granju JL. Mechanical characterisation of cement-based mortar incorporating rubber aggregates from recycled worn tyres. Build Environ 2005;40:221–6. United Nations Environment Programme. Marine environment. Nairobi: The State of the World Environment; 1991. p. 35–48 [Chapter 5]. Wan HP, Chang YH, Chien WC, Lee HT, Huang CC. Emissions during co-firing of RDF-5 with bituminous coal, paper sludge and waste tires in a commercial circulating fluidized bed co-generation boiler. Fuel 2008;87:761–7. Weng YC, Chang NB. The development of sanitary landfill in Taiwan and its cost structure analysis. Resour Conserv Recycl 2001;33:181–201. Yang CC. Recycling of discarded tires in Taiwan. Resour Conserv Recycl 1993;9:191–9.
Contents lists available at ScienceDirect
Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec
Recycling waste tire powder for the recovery of oil spills Chitsan Lin a,∗ , Chun-Lan Huang b , Chien-Chuan Shern a a b
Department of Marine Environmental Engineering, National Kaohsiung Marine University, 142 Haijhuan Road, Nanzih District, Kaohsiung 81157, Taiwan Department of Aquaculture, National Kaohsiung Marine University, 142 Haijhuan Road, Nanzih District, Kaohsiung 81157, Taiwan
a r t i c l e
i n f o
Article history: Received 13 February 2008 Received in revised form 24 May 2008 Accepted 17 June 2008 Available online 24 July 2008 Keywords: Spilled oil recovery Oil adsorbent Resources recycling Oil spill Scrap tire
a b s t r a c t Waste tire related environmental problems and its recycling techniques have been a major challenge to society. Current waste tire recycling market is too small to accommodate the tire generated annually. Therefore, it is of crucial importance to develop new markets for waste tires. Tire rubber is flexible and has hydrophobic (oil-philic) characteristics, making it a good candidate as an oil adsorbent. In this paper, the possibility of applying waste tire powder as a sorbent for the recovery of spilled oil was explored. The results indicate that 2.2 g of motor oil can be adsorbed to each gram of 20 mesh tire powder. Due to its elastic property, waste tire powder is re-usable for over 100 times without decreasing its oil absorption efficiency. Therefore, at least 220 g of motor oil can be recovered per gram of waste tire powder, which is very competitive to commercial sorbent. The results of this study indicated that sorption efficiency increased as the tire powder particle size decreased, and decreased as the environmental temperature increases. When applying the waste tire powder to oil slicks on seawater, the oil sorption efficiency is shown to be better than if it was on fresh water. Efforts have been made to enhance the waste tire powder’s oil sorption efficiency. Results indicated that the highest efficiency was obtained when the waste tire powder was pre-cleaned by n-hexane, followed by water cleaning > un-cleaned > dishwashing liquid cleaned > seawater cleaned. Compared to a commercial oil sorbent, the result indicated that waste tire powder was economically more feasible, if it was re-used for 100 times. More efforts are encouraged to enhance the waste tire powder’s oil sorption capacity without decreasing its re-usable characteristics. © 2008 Elsevier B.V. All rights reserved.
1. Introduction According to Rubber Manufactures Association (RMA, 2006), about 299 million tires were generated in the United States in 2005; where 52% of the scrap tires were converted into tire-derived fuel (TDF), 16% were used by the civil engineering applications, 12% were recycled by the ground rubber applications, 14% were land disposed, 2% were exported, and 4% of other applications. Waste tires are virtually non-degradable and take up landfill spaces (Weng and Chang, 2001). If not properly disposed, waste tires may accumulate water, and subsequently can cause the spread of mosquito-borne diseases (Chang, 2008; Yang, 1993). Often tire fires occur and cause serious air, water, and soil pollutions (Fan et al., 2005). Nevertheless, tire rubber has a high heat value (12,000–16,000 Btu/lb). In the United States, Canada, Germany, the United Kingdom, and Japan, waste tires have been used as a supplemental fuel for the cement kilns (Prisciandaro et al., 2003) and in the paper mills (Barlaz et al., 1993). Waste tires can also be recycled as a roadway pavement material (Huang et al., 2007; Siddique and Naik, 2004), refuse
∗ Corresponding author. Tel.: +886 7 3651472; fax: +886 7 3651472. E-mail address: [email protected] (C. Lin). 0921-3449/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2008.06.003
derived fuel (Wan et al., 2008; Murugan et al., 2008; Mastral et al., 2000), or reproduced as tires (Douglah and Everett, 1998; Everett and Douglah, 1998). Sometimes, waste tire is used to produce rubber mats, roadway guard rails, as engineered protective cushions or bumpers, and for building and construction materials (Topc¸u and Sarıdemir, 2008; Turatsinze et al., 2005). In marine applications, waste tire can also be used as a wave breaking material, ship/dock protective bumpers, or even to construct artificial reefs (Chapman and Clynick, 2006) in the ocean farming industry. It seems that discarded tires are of useful in many recycling alternatives. However, the markets appear to be small compared to the number of tires generated each year. Therefore, it is of interest to explore any new application/market for the scrap tire reclaiming industry. According to Gunasekara et al. (2000), tires are primarily composed of rubber (40–45%) vulcanized with sulfur (1.5–2.5%), steel, and carbon black (27–33%). The carbon black, used to strengthen the rubber, is similar to activated carbon (Snoeyink et al., 1967), a good sorbent to remove dissolved organic substances from wastewater. In a permeation of organic compounds through rubber gaskets study, Park and Bontoux (1991) reported that rubber is a good sorbent for organic compounds. Kim et al. (1997) reported that organic compounds were sorbed primarily onto tire rubber polymeric materials and partially carbon black in the tire
C. Lin et al. / Resources, Conservation and Recycling 52 (2008) 1162–1166
rubber, and the partition coefficients had a logarithmic linear relationship with the octanol–water partition coefficients. Gunasekara et al. (2000) further investigated the use of ground discarded tires to remove naphthalene and toluene from water. Moreover, tire rubber is a flexible and hydrophobic (oil-philic), making it a good candidate as an oil sorbent. In this research, the possibility of utilizing waste tire powder as oil sorbent for the recovery of spilled oil has been explored. Oil spills in a marine environment will not only cause property loss, but it could also have a strong negative impact on the entire ecosystem. According to the UNEP report (United Nations Environment Programme, 1991), compared to 1976, the amount of oil spilled in 1991 indicated a decreasing trend. Nevertheless, crude oil and petroleum products that have found their ways into the marine environment were in an amount to about 10,000–100,000 tons annually in the past decade. Therefore, the marine oil spill prevention has always been a global awaking subject that requires further attention. If the proposed ideal of this research is applicable to utilize tire particle as an oil sorbent in oil spill recovery, not only will it benefit to the oil pollution prevention, but will also bring profit to the scrap tire recycling industry. 2. Experimental methods 2.1. Materials Ground tire powders of 5, 10, 20, and 40 mesh were obtained from a local scrap tire recycling facility in Kaohsiung, southern Taiwan. The 20 mesh waste tire powder was used as the sample to study the oil sorption behavior. 5W-40 motor oil produced by the Shell Company was used to simulate spilled oil. The motor oil was air stripped at 90 ◦ C for 2 h to remove the volatile organic compounds (VOCs), so as to minimize the quantification error due to the loss of VOCs during the sorption experiment. After stripping, only 0.163% weight loss was recorded, and a control test at room temperature had shown that no discernible loss of VOCs during the time period of sorption experiment. A thin meshy non-woven PET (polyethylene terephthalate) sheet which allowed the passing of oil was utilized as a packing material to contain the tire powder for sorption experiments. PET fiber is strong, durable, and impact resistant making it a feasible packing material. American Society of Testing and Materials F726-99 method (ASTM, 2006) was referenced for oil sorption capability tests that are detailed as follows. 2.2. Oil sorption capability tests of waste tire powder Packing material (PET sheet) was used to produce round-shaped sorbent bags of the same size (5.5 cm in diameter), and each bag contained 1 g of 20 mesh tire powder. The sorbent bag was submerged into a 50-mL motor oil bath contained by a 250-mL glass beaker, and the sorbent bag was allowed to saturate. If more sorbent bags were tested at the same time, bigger containers were used. The sorption speed and the time required to saturate the sorbent bag were monitored. All sorption experiments were performed in an air conditioned room at about 20 ◦ C. A tweezer was used to remove the saturated sorbent bag, and it was hung in the air for 30 s (ASTM, 2006) to allow the excess motor oil to drip from the bag. The remaining sorbed oil was estimated to represent the unit “practical sorption amount” by subtracting the amount sorbed by a parallel control experiment of a blank sorbent bag without tire powder. The practical sorption amount will include the oil adhered on the surface of the sorbent bag, and could actually be recovered during a practical oil recovering processes assuming a 30-s free drop time before the oil was captured.
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2.3. Waste tire powder adsorbent re-usability experiment A key point of our proposal is that the waste tire sorbent bag can be re-used many times without losing its oil sorption capability, due to the elastic nature of tire materials. To study the re-usability, one sorbent bag was chosen, and its “practical sorption amount” was monitored each time after re-use for up to 100 times, to see if its adsorption capability decreased because of re-utilization. Each time the sorbent bag was used, and the recovered oil on the bag was mechanically pressed out to simulate each oil recovery cycle. The pressing equipment equipped with two adjustable rollers at 2 mm spacing. Three pressings were performed for each repetitive sorption experiment. 2.4. Application of the sorbent bag in seawater and fresh water We are all aware of major oil spills that occur in the world’s oceans. However, spills also occur in inland fresh water systems during the transportation process. During an emergency response, the sorbent bag may become wetted by seawater or fresh water before reaching the oil slick, and subsequently, the sorption efficiency may decrease. To study the effects of wetting and compare how the water wetted surface affected the oil adsorption efficiency, the sorbent bags were immersed into and completely soaked by each of seawater and fresh water, then hung in the air, allowed the water to drip from the sorbent bag for 30 s before carrying out the oil adsorption experiments. 2.5. Effects of different pre-treatment methods on the oil sorption efficiency Untreated waste tire powder may contain cokes and some aqueous soluble impurities. As part of enhancing sorption efficiency efforts, different pre-cleaning treatments were studied, including (1) water cleaned, (2) n-hexane cleaned, (3) surfactant (dish cleaner) cleaned, and (4) seawater cleaned. After each 10 min cleaning by ultrasonic cleaner (Branson 3510, 40 kHz), the filtered tire powder was directly dried in a 100 ◦ C oven before use. All results were compared to the un-cleaned waste tire powder. 2.6. Effects of tire powder particle size and temperature on the oil sorption efficiency The smaller tire powder particle size and the larger specific surface area are obtained. A series of experiments were performed to evaluate the effects of tire powder particle size on the oil sorption efficiency with 5, 10, 20, and 40 mesh tire powder tested. Moreover, in order to assess the temperature of the oil spill environment on the sorption efficiency, 20 and 40 mesh tire powders were used to study the effects of temperature on the oil sorption efficiency ranging from 0 to 40 ◦ C. Tested oil and tire powder were equilibrated with a constant temperature refrigerating circulator (TKS RCB411) before the sorption experiments were conducted. 3. Results and discussion 3.1. Oil sorption capability tests of waste tire powder Results of the oil sorption experiments indicated that it took about 5 min to saturate the waste tire sorbent bag with oil in an undisturbed environment. The practical sorption amount was averaged at 2.17 ± 0.01 g (n = 10), which means that each gram of 20 mesh tire powder can pick up about 2.2 g of motor oil.
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Fig. 1. Results of the re-usability test indicate that waste tire powder sorbent can be re-used for more than 100 times without losing its sorption capacity.
3.2. Waste tire powder adsorbent re-usability Fig. 1 presents the results of the re-usability test of a tire powder sorbent bag. Results indicated that the sorption capacity was not affected after 100 times of re-use. This is not surprising because the tire powder is made of rubber material with an elastic characteristic. Therefore, it can sustain repeated mechanical pressing without wearing out, while the sorbed oil is being recovered. After re-used for 100 times (mechanically pressing 300 times), except the containment bag slightly deformed, the out looking and performance of the tire powder appeared not changed. Note that the re-usability experiments did not proceed beyond 100 times, even though it is reasonable to assume that it could be re-used continuously until the packing material was worn out. Assuming that the waste tire sorbent bag was only re-used 100 times, then the practical total adsorption amount would be 220 g of motor oil per gram of waste tire powder. 3.3. Sorption efficiency of the wetted and un-wetted tire powder Fig. 2 compares the sorption efficiency of the wetted and unwetted tire powder during the oil recovery operation. Results indicated that un-wetted tire powder performed better followed by powders wetted with seawater and fresh water respectively. The surface of the wetted tire powder may partially turn into
Fig. 3. Effects of various types of pre-cleaning methods on the sorption capacity.
hydrophilic from water soaked on the surface that accounts for the decrease of the sorption efficiency. Therefore, it is important that during the oil spill recovery processes, the waste tire sorbent pad is thrown right onto the oil slick surface, because if the sorbent pad is thrown onto the water surface, and becomes wetted, the sorption efficiency of the pad will decrease. 3.4. Effects of different pre-treatment methods on the oil sorption efficiency Unless otherwise specified in this text, all results are monitored as the practical sorption amount per gram of waste tire powder (g/g), without accounting its re-usability value. Fig. 3 compares the effects of different ways of waste tire powder pre-treatment on the sorption capacity. The results indicated that n-hexane cleaned waste tire powder has the best sorption capacity, followed by water cleaned > un-cleaned > dish detergent cleaned > seawater cleaned. n-Hexane can wash out a layer of brownish constituents to expose the hydrophobic surface of the rubber tire powder. Water cannot wash out the brownish constituents, but it does wash out some hydrophilic impurities to allow the oil to pass more easily through the tire powder. A local purchased dish detergent was applied to simulate the surfactant treatment effect. Results indicated that the sorption capacity decreased if dish detergent cleaned and if the cleaning was not followed by a water rinse to rinse off the surfactant. A possible explanation for that is that because the hydrophilic end of dried-out surfactant on the surface of the tire powder will stand out to hamper the oil sorption efficiency. When treated by seawater, and without rinsing off the salt, the hydrophilic salty materials would become dried out on the surface of the tire powder, and subsequently would hamper the oil sorption efficiency. Although, for the sake of efficiency of the tire powder sorbent, solvent cleaning (n-hexane or alcohol) is helpful, it may possibly not be preferred due to cost and the environmental unfriendly nature of the solvents. Therefore, water cleaning or surfactant cleaning followed by a complete water rinsing is recommended. When applying in salty water, a complete fresh water rinsing is a critical step before drying and storing for later use. 3.5. Effects of particle size and temperature on the oil sorption efficiency
Fig. 2. Comparison of wetted and un-wetted tire powder sorption efficiency.
Fig. 4 compares oil sorption efficiency of 5, 10, 20, and 40 mesh waste tire powders. As expected, adsorption efficiency was increased as particle size decreases. However, not much adsorption efficiency was gained with particle size decreased from 5, 10
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Table 1 Comparison of 20 mesh waste tire powder and the Ecosol for motor oil recovery Items
20 mesh waste tire powder
Ecosol
Specific gravity Bulk density (kg/m3 ) Oil sorption speed Practical sorption amount (g motor oil/g sorbent) Re-usability (times) Sorption amount, if re-used for more than 100 times (g motor oil/g adsorbent) Operation
>Water 388.1 Slow 2.2
>100 >220
1 103.3
Easy
Adsorbent cost The cost to recover 1 ton of oil After treatment
USD$0.065/kg USD$0.295 Incineration (note that tire particle is non-biodegradable)
May drift with the wind USD$65/kg USD$630 Incineration or Ecosol foam is biodegradable
Fig. 4. Sorption capability increases as tire powder particle size decreases.
to the 20 mesh with a significant improvement with the 40 mesh powder. Although, fine powder has advantage to the oil sorption efficiency, its handling and production costs need to be evaluated before commercial application. Oil spills do not only occur in the warm waters, but can also take place in cold areas where temperature is low. Fig. 5 compares oil sorption efficiency versus temperature. It is clear that sorption efficiency increased as temperature decreased in the cold region. On the opposite, sorption efficiency can decrease significantly as temperature increases in tropical areas where ambient temperature can reach as high as 40 ◦ C. 3.6. Comparison of waste tire powder versus commercial oil sorbent A very competitive commercial oil sorbent, Ecosol foam, distributed by the Spill Response New Zealand Limited, was compared with the 20 mesh waste tire powder sorbent. As indicated in Table 1, Ecosol is a very light (9.6 kg/m3 at loose form) oil sorbent with porosity higher than 90%. It adsorbs oil quickly at the practical sorption amount of 103.3 g of motor oil per gram of sorbent. It seems that Ecosol has a much higher unit sorption capacity than that of the waste tire powder (2.2 g/g). However, Ecosol can only be used
once when pressed to recover oils. If the re-usability is taken into consideration, 1 g of tire powder can be re-used for more than 100 times, thus recovering far more than 220 g of motor oil. Ecosol costs about USD$65/kg, and the whole sale recycled waste tire powder costs only USD$0.065/kg locally. Assuming waste tire powder sorbent bags are re-used 100 times, the material cost to recover 1 ton of spilled oil is USD$0.295, compared to USD$630 for Ecosol which can only be used once. 4. Conclusions Waste tire powder is flexible and has oil-philic characteristics, making it a suitable candidate as an oil sorbent for the recovery of oil spills. In this paper, the possibility of using tire powders to adsorb oil was explored. The preliminary results indicated that 1 g of 20 mesh tire powder could recover 2.2 g of motor oil. Due to its elastic property, the waste tire powder can be used for more than 100 times without decreasing its oil sorption efficiency. Therefore, the unit sorption capacity can be increased to at least 220 g of motor oil. Taking re-usability into account, the raw material cost to recover 1 ton of spilled oil is only about USD$0.3, which is very competitive. Finer particle was observed with increased sorption capability. However, the ease of handling and production costs of tire powders need to be optimized when designing the commercial product. An effort was made to enhance the oil sorption efficiency of the waste tire powder. Results indicated that the best efficiency was obtained if the waste tire powder was pre-cleaned with n-hexane and dried before use, followed by water cleaning > un-cleaned > dishwashing detergent cleaned > seawater cleaning. Moreover, un-wetted tire powder performs better than that of the wetted; therefore, it is important to apply the sorbent pad directly onto the oil slick. After use, it is important to rinse off the contacted seawater and to maintain the sorbent under dry conditions for later use. More efforts are encouraged to enhance the waste tire powder’s oil sorption capacity without decreasing its re-usability advantages. Acknowledgments This project was sponsored by the National Science Council of Taiwan under the project number NSC-90-2626-E-022-001. The authors are thankful for its financial support. References
Fig. 5. Sorption capacity decreases as temperature increases.
American Society of Testing and Materials, ASTM F726-99. Standard method of testing sorbent performance of adsorbents [accessed 01.10.06].
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