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WITHDRAWN: Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent
Waste Management xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent Sushant B. Wath ⇑, Mayuri N. Katariya, Sanjeev K. Singh, Atul N. Vaidya CSIR-National Environmental Engineering Research Institute (NEERI), Nehru Marg, Nagpur 440 020, India
a r t i c l e
i n f o
Article history: Received 5 March 2015 Accepted 15 May 2015 Available online xxxx Keywords: E-waste Recovery Processes Printed circuit boards N-methyl-2-pyrrolidone NMP
a b s t r a c t Printed circuit boards (PCBs) in electrical and electronic equipment (EEE) abide of valuable and hazardous materials and due to its complex and discrete make-up across manufacturers, processing waste PCBs (WPCBs) is a massive challenge. And therefore either completely novel or improved processes are needed for the recycling of WPCBs and recovery of valuable materials from it. In the present study, the processing of WPCBs was performed using N-methyl-2-pyrrolidone (NMP) as a solvent. Various parameters, which include WPCB sizes, solid to liquid (S/L) ratio, temperature and time were investigated to understand the processing of WPCBs by dissolving bromine epoxy resin using NMP. Experimental results showed that the dissolution rate of the bromine epoxy resin increased with respect to various parameters studied. The optimum condition of thorough separation of WPCBs was S/L ratio of 1:5 and WPCB size/area of 4 mm/16 mm2 and 100 °C for 90 min. The used NMP were vaporised and condensed under the decompression for retrieving regenerated NMP. This novel process using NMP as solvent can be an environmental friendly and effective option for the separation and recovery of various valuable materials such as metals, and glass fibres from WPCBs. Ó 2015 Published by Elsevier Ltd.
1. Introduction Printed circuit boards (PCBs) are the essential, integral and predominant part of almost all electrical and electronic equipment (EEE). PCB provides the platform to mount various electronic items, such as resistors, relays capacitors, diodes, integrated circuits in a rigid manner. The rapid growth of technology (Wath et al., 2011) along with the high rate of obsolescence has increase E-waste generation and consequently waste PCBs (WPCBs) (Ping and Guobang, 2002; Huang et al., 2009), both in developed and developing countries. Typically, PCB contains 50% polymer (epoxy resin or phenolic resin, along with brominated flame retardants (BFR), etc.), 20% glass fibre and 30% metals [20% Cu, 8% Fe, 4% Tn, 2% Ni, 2% Pb, 1% Zn, 0.2% Ag, 0.1% Au and 0.005% Pd] (Huang et al., 2009). However there is a considerable variance in composition of WPCBs coming from different appliances, manufacturers and year of production. Though precious and valuable metals in PCBs are only 1% by weight, it accounts for 80% of the total intrinsic value (Park and Fray, 2009) and are thus gaining recycling attention from both formal and in-formal recycler. Recovered material can be used as a worthy secondary source for various scarce materials. ⇑ Corresponding author. Tel./fax: +91 712 2249758. E-mail address: [email protected] (S.B. Wath).
Furthermore, PCBs consists of multi-layers of etched metal conductive tracks laminated with fibre glass sheet, bonded with mixtures of polymer materials (thermoplastic and thermosetting resins). Thermoset resin such as brominated epoxy resin is utilized as a flame retardant because PCBs are often exposed to high temperature both during manufacturing and operations (Hutapea and Grenestedt, 2003). The epoxy resins are intermingled with metals (Jie et al., 2008) and glass fibre many times, and thus is not present only along the surface. Due to this, individual components separation from WPCBs and size reduction of WPCBs for recycling is an arduous task (Ping et al., 2009; Gu et al., 2008). PCB recycling involves two steps. Preliminary step involves mechanical–physical or metallurgical processing for the dismantling and/or separation of different components and materials (Veit et al., 2005; Duan et al., 2009; Yoo et al., 2009; Jiang et al., 2009) while the second step involves further separation and processing of metal streams; which probably is the most imperative step from economic and environmental viewpoints. Meanwhile, many studies, such as bio-metallurgy (Xiang et al., 2010), combustion (Ni et al., 2012), hydrometallurgy (Ping et al., 2009), pyro-metallurgy (Vanbellen et al., 2003), pyrolysis (Chien et al., 2000), supercritical fluid (Xiu and Zhang, 2010), ionic liquid (Zhu et al., 2012) were carried out for recycling of WPCB. However these processes have its own limitations, the mechanical–physical
http://dx.doi.org/10.1016/j.wasman.2015.05.020 0956-053X/Ó 2015 Published by Elsevier Ltd.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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S.B. Wath et al. / Waste Management xxx (2015) xxx–xxx
processes are predominantly time and labour intensive. Whereas the secondary metallurgical processes are energy and capital intensive as well as hazardous to environment as may lead to formation of dioxins and furans due to the presence of BFRs in PCBs (Huang et al., 2009; Zhou et al., 2010; Duan et al., 2011). While some processes may generate massive amount of waste acid, alkaline liquid and sludge, which may cause secondary pollution. This provides the necessity for the continued research on the recycling of WPCBs. Kamo et al. (2009) used tar derived from Japanese cedar and benzyl alcohol to liquefy the epoxy board at 250–300 °C under atmospheric pressure. Xing and Zhang (2013) employed a batch type reactor sub- and supercritical water to simultaneously degrade brominated epoxy resin and recover metals from WPCBs. Lin-zhuan and Tao (2010) and Guan et al. (2011), attempted to dissolve brominated epoxy resin in PCBs using nitric acid; however the leaching rates were too low. However, only Zhu et al. (2013a,b) use organic solvent dimethyl sulfoxide (DMSO) as a non-aqueous solvent to separate WPCBs. The present study targets the use of non-aqueous organic solvent N-methyl-2-pyrrolidone (NMP) (C5H9NO) for the dissolution of BFR from the substrate and separation of WPCBs. NMP is a dipolar aprotic, colourless with mild amine odour, and is miscible with water and with most common organic solvents. Other properties include high boiling point (202 °C) and high viscosity (1.67 cP@25 °C); molecular weight of 99.1 g/mol. NMP effectively dissolves numerous organic and inorganic chemicals but does not corrode metal. More importantly NMP is a basic and polar compound with high stability, slowly oxidized by air, hygroscopic and non-corrosive. Due to its excellent safety characteristics NMP has important applications; in paint stripping and cleaning (in microelectronic, petro-chemical, and plastic industries); as intermediate (in pharmaceutical, agro-chemical industries) and as a solvent for cellulose dissolution exploiting its non-volatility and ability to dissolve diverse materials. NMP has lower volatility (i.e., vapour pressure = 0.190 Torr at 25 °C) and evaporation rate – 0.03 (BuOAc = 1), thus its use releases fewer organic emissions to the atmosphere. Therefore it can be summarized and infer that NMP has high thermal stability and can be recycled many times. Furthermore, NMP biodegrades readily and has low toxicity to aquatic life (Harreus et al., 2011). The acute toxicity of NMP (3.6 g/kg for rat) is lesser than other dipolar aprotic solvents like sulfolane (1.9 g/kg) and DMF (dimethyl formamide) (2.8 g/kg). In this paper, the effect of heating, particle size and solvent ratio (S/L) are evaluated on the dissolution of epoxy resin of the WPCB using NMP. The problem of copper extraction from waste PCBs due to the encapsulation of thin metallic sheet by plastic/epoxy resin material has been solved by the liberation of thin layers of metallic sheet by organic swelling. The aim of this research is to develop a novel technique for separating valuable materials from WPCBs and to prevent environmental pollution from WPCBs. To the best of our knowledge there has been no previous reported study investigating the separation of WPCBs using NMP.
systematically and carefully detached manually using appropriate tools, to minimize occupational and environmental impact arising out of the various hazardous materials present in it. The bare WPCBs (after removal of mounted components from its surface) were cut into 3 cm 3 cm size manually using plier/cutter and were further reduced to size using laboratory mixer grinder (Make Sujata-Dynamix DX). The size reduced samples were separated according to particle size using an electromagnetic sieve shaker (Make – Electro Lab; Model – EMS8; Dimension-L339 W312 H270 mm). Mesh size of sieves used were 10, 8, 6, 4, 2, 1 and 0.71 mm. Sample was placed in the top sieve with the largest mesh and shaken in continuous and intermittent mode for 5 and 2 min respectively. The residue remaining on the sieves of mesh sizes 8, 6 and 4 mm of approximate size/area – 4 mm/16 mm2; 6 mm/36 mm2 and 8 mm/64 mm2 were used for conducting the experiments. All reagents used in these experiments were analytical grade products from Fisher Scientific Pvt. Ltd., Mumbai, India. 2.2. Methods The experiments were conducted using a 0.5 L, three-neck flask equipped with a continuous water circulating condenser unit. Fig. 1 shows the experimental set-up for separating the WPBCs. Reactor was charged with 5 g of WPCB samples each time along with appropriate solvent quantity. And once the desired
Port for sampling & stirring Water out
Water in Refluxing
Thermometer
3-Way flask NMP WPCB
Sand bath Heater
Fig. 1. Experimental set-up for treating WPCBs in NMP solvent.
2. Materials and methods 2.1. Materials WPCBs for this study were collected from the discarded PCs (manufactured in 2003) from the stores’ of NEERI (National Environmental Engineering Research Institute) Nagpur, India. WPCB of motherboard extracted from desktop personal computer was used for this study. Components such as ICs, transformers, fan, resistors, capacitors, pins, heat sink, motors, and batteries, mounted on the PCBs were
Fig. 2. Flowchart for dissolution of epoxy resin and regeneration of NMP.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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Fig. 5. Photographs of NMP (A) unused, (B) used and (C) regenerated.
Fig. 3. Effects of (A) WPCB sizes/area, (B) solid to liquid ratio (S/L) and (C) temperature on concentration of the bromine epoxy resin dissolution from WPCBs.
temperature was reached, the set up was held constant at that temperature for 180 min. After every 30 min interval, a fixed quantity of solvent was withdrawn and the concentration was analysed in triplicate and only its mean values have been reported in the paper. The experiments on WPCBs were carried out using NMP with a varying parameters and experimental conditions such as WPCBs size/area (4 mm/16 mm2, 6 mm/36 mm2, 8 mm/64 mm2); temperature (70 °C, 80 °C, 90 °C, 100 °C; time period (30, 60, 90, 120, 150, 180 min); solid to liquid ratios (w/v) (1:2; 1:3; 1:4; 1:5) with random manual stirring. The amount of bisphenol A, which is a component of bromine epoxy resin was measured to determine the bromine epoxy resin concentration in NMP (Ye, 1991). The 0.10 g pure bisphenol A was transferred to a 100 ml volumetric flask, dissolved and make up to volume with anhydrous ethanol to get stock solution of 1000 lg/ml. The concentration of 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 lg/mL were prepared for making a standard curve. The amount of bisphenol A was determined using UV–Vis spectrophotometer (AU-2701U, Systronics) with 1.0 cm matched quartz cells at a wavelength of 282 nm. To ascertain the accuracy of measurement the instrument was calibrated periodically using the standard procedure. Rotary evaporation process was exercised to treat the used NMP under reduced pressure of 6.6 mbar at temperature 60 °C and the
A
B
Solder
C
D
E
Fig. 4. Photographs of (A) WPCB (B) WPCBs treated with NMP (C) copper foil and solder (D) liquid photo resist (E) glass fibre.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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Fig. 6. GC–MS chromatogram of (A) unused NMP and (B) used NMP.
condenser was used to cool the vaporised gases at room temperature for NMP regeneration and residues were separated out. Fig. 2 shows a flowchart for dissolution of bromine epoxy resin and regeneration of NMP. The residues i.e. WPCBs were washed with distilled water and dried at 85 °C for 6 h. Photographic images were taken of treated WPCBs using a digital camera. Transition in the chemical composition of the used and unused NMP was analysed using gas chromatography mass spectrometry, Perkin Elmer-Clarus 680 (GC) & Clarus 600-C (MS). The GC system was operated in split less
injection mode. A 30 m DB-5 column (ID-320 lm) was used for component separation with the following temperature program: 150 °C for 10 min. Helium was used as the carrier gas at a constant flow rate of 1 mL/min. The GC injector temperature and MS ion source temperature were maintained at 150 °C. Sample extract (1 lL)/standard solution was auto-sampled. The mass spectrometer was operated with electron ionization (EI) mode with electron energy of 70 eV. Turbo mass software was used for the instrument parameters optimization as well as for the data acquisition and analysis.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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3. Results and discussion The absorbency curves were plotted for the bisphenol A using the wavelength ranging from 200 nm to 300 nm. Bisphenol A shows maximum absorbance for UV light for the wavelength of 282 nm. Therefore, the concentration of bromine epoxy resin dissolved into NMP can be characterized by UV–Vis spectrophotometer by determining the amount of bisphenol A. Fig. 3A–C shows the effects of (A) WPCB size/area (B) solid to liquid (S/L) ratio and (C) temperature respectively, on concentration of the bromine epoxy resin dissolution in NMP from WPCBs. The maximum bisphenol A concentration for the 4 mm/16 mm2 size fraction can be seen in Fig. 3A, because the decrease in the size of WPCB sample increases the surface-contact area with the solvent NMP, which facilitate the mass transfer to cause the increase in dissolution of bromine epoxy resin, in comparison to the bigger size particles with smaller surface-contact area. It can be observed that the concentrations of bromine epoxy resin in NMP increased with an increased in solid to liquid ratios (Fig. 3B). This phenomenon can be explained by the fact that NMP increases with the increase of S/L ratio, leading to increase in concentration. The concentration of bisphenol A is maximum for the ratio 1:5 in comparison with ratio 1:2, and shows almost linear increase in concentration with respect to time. It can be observed from the Fig. 3C that with the increase in temperature the concentration of bromine epoxy resin dissolution increases, may be due to fact that increase in temperature enhances the mass transfer. Graph shows almost linear hike in epoxy resin dissolution from 70 °C to 100 °C with a maximum at 100 °C after 90 min. And maximum dissolution is noted in between 90 and 120 min. While solvent properties are significant in determining the separation performances (Ismail and Lai, 2003), data are still lacking to fully understand the role of solvents in separation. Due to the complexity of solvent–polymer interactions in the reactions which differ in each type of polymer and solvent for a specific membrane type, it is difficult to accurately predict solubility behaviour (Adams et al., 2013). And therefore, further studies and analysis are required for better understanding of the WPCB separation behaviour in NMP under varying process parameters. Finally, the metals (copper foils), glass fibres and liquid photo solder resists (A thin layer of polymer applied to Cu traces of a PCB for protection against oxidation and to prevent solder bridge (unintended electrical connection) formation between closely spaced solder pads) are distinctly detached from one another and
(A) H-O hydrogen bond
can be easily separated using NMP as solvent. Further, various techniques can be applied for its separation, based on the density difference principle. Fig. 4 depicts the photographs of WPCBs treated under the condition of solid to liquid ratio of 1:5, WPCBs area of 6 mm/36 mm2, 180 min. It can be observed from Fig. 4 that the copper foils and the glass fibres were separated from the WPCBs and the solders were still bonded to the surfaces of the copper foils. Furthermore, the liquid photo solder resists were detached from the copper foils (Fig. 4B and C). The copper foil does not show any mark of corrosion which also substantiate the non-corroding property of NMP towards metal. Rotary evaporation process was exercised to treat the used NMP and the condenser was used to cool the vaporised gases for NMP regeneration and thus the bromine epoxy resin dissolved in NMP was separated. The Fig. 5 shows the photograph of the used, unused and regenerated NMP. It is noteworthy for this process that NMP can be regenerated from the perspective of protection of environment and processing cost. Moreover this new process does not produce bromine volatilize which can cause secondary environmental pollution. From Fig. 5, it can be precisely ascertained that the unused NMP (Fig. 5A) and the regenerated NMP (Fig. 5C) were colourless, whereas the used NMP was greenish (Fig. 5B). This is because NMP dissolves bromine epoxy resin in WPCBs to cause its colour change. The Fig. 6 shows the GC–MS chromatogram and fragmentation patterns of the used and unused NMP which clearly reflects the identical characteristic peaks and patterns of the NMP, which indicates that the chemical properties of the used and unused NMP has not change. Polar solvent NMP is a good hydrogen bond acceptor that results in the formation of various possible hydrogen bonds between the hydroxyl and N–O group of NMP and brominated epoxy resin, which may be responsible for the separation of bromine epoxy resin. Fig. 7A shows the hydrogen bond between H–O. The hydrogen from the hydroxyl group in the brominated epoxy resin pulls electrons towards the oxygen in the NMP. Fig. 7B shows that the hydrogen in the methyl group of the NMP which may form hydrogen bonds with bromine and oxygen in brominated epoxy resins. Fig. 7C shows the hydrogen bonds of H–N. The strongly electronegative nitrogen in the NMP pulls the hydrogen in the hydroxyl group of the brominated epoxy resin.
(B) H-O and H-Br hydrogen bond
(C) H-N hydrogen bond
Fig. 7. Potential role of hydrogen bonding between NMP and bromine epoxy resin.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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4. Conclusion Organic solvents such as NMP can be used for processing the WPCBs of a typical electronic waste. NMP can be used to comprehensively separate the various layers of the WPCBs, which enables easy recovery of valuable materials including metals, glass fibres and polymers. The optimal condition was temperature of 100 °C at 90 min, solid to liquid ratio of 1:5, whereas WPCBs size/area of 4 mm/16 mm2. Rotary evaporation process was exercised to treat the used NMP and the condenser was used to cool the vaporised gases for NMP regeneration. NMP not only dissolved the bromine epoxy resin of WPCBs but also did not react with metals, liquid photo solder resists, and glass fibres. This new process does not produce bromine volatilize to cause secondary environmental pollution, which complies with the principle of sustainable development by decreasing the manufacturing cost of treating WPCBs to achieve thorough separation and recovery of reusable resources.
Acknowledgments Authors are thankful to Director, CSIR-NEERI and Head, BDTT division for their necessary support and guidance. The authors are also grateful to CSIR, New Delhi for the necessary approval and funding to undertake this research activity under the XII five year plan project.
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Hutapea, P., Grenestedt, J.L., 2003. Effect of temperature on elastic properties of woven-glass epoxy composites for printed circuit board applications. J. Electron. Mater. 32, 221–227. Ismail, A.F., Lai, P.Y., 2003. Effects of phase inversion and rheological factors on formation of defect-free and ultrathin-skinned asymmetric polysulfone membranes for gas separation. Sep. Purif. Technol. 33, 127–143. Jiang, W., Jia, L., Zhen-Ming, X., 2009. A new two-roll electrostatic separator for recycling of metals and non-metals from waste printed circuit board. J. Hazard. Mater. 161, 257–262. Jie, G., Ying-Shun, L., Mai-Xi, L., 2008. Product characterization of waste printed circuit board by pyrolysis. J. Anal. Appl. Pyrol. 83, 185–189. Kamo, T., Yufeng, L., Akaishi, N., Adachi, M., Yasuda, H., Nakagome, H., 2009. Liquefaction of printed circuit board by using waste biomass derived tar. In: The 5th Symposium on Feedstock and Mechanical Recycling of Polymeric Materials (ISFR2009). Chengdu (China), pp. 186–192. Lin-zhuan, M.A., Tao, L.I., 2010. Recovery of epoxy resin in waste printed circuit boards by solvent method. J. Kunming Univ. Sci. Technol. (Sci. Technol.) 35, 85– 88. Ni, M., Xiao, H., Chi, Y., Yan, J., Buekens, A., Jin, Y., Lu, S., 2012. Combustion and inorganic bromine emission of waste printed circuit boards in a high temperature furnace. Waste Manage. 32, 568–574. Park, Y.J., Fray, D.J., 2009. Recovery of high purity precious metals from printed circuit boards. J. Hazard. Mater. 164, 1152–1158. Ping, Z., Guobang, G., 2002. Recovery of gold and copper from waste printed circuits. Chin. J. Rare Met. 26, 214–216. Ping, Z., ZeYun, F., Jie, L., Qiang, L., GuangRen, Q., Ming, Z., 2009. Enhancement of leaching copper by electro-oxidation from metal powders of waste printed circuit board. J. Hazard. Mater. 166, 746–750. Vanbellen, F., Wesseldij, Q., Umicore, Belgium, 2003. Precious metals recycling of precious metals. In: Conference Metal and Energy Recovery in Skelleftea in Sweden, pp. 25–26. Veit, H.M., Diehl, T.R., Salami, A.P., Rodrigues, J.S., Bernardes, A.M., Tenório, J.A.S., 2005. Utilization of magnetic and electrostatic separation in the recycling of printed circuit boards scrap. Waste Manage. 25, 67–74. Wath, S.B., Dutt, P.S., Chakrabarti, T., 2011. E-waste scenario in India, its management and implications. Environ. Monit. Assess. 172, 249–262. Xiang, Y., Wu, P., Zhu, N., Zhang, T., Liu, W., Wu, J., Li, P., 2010. Bioleaching of copper from waste printed circuit boards by bacterial consortium enriched from acid mine drainage. J. Hazard. Mater. 184, 812–818. Xing, M., Zhang, F.S., 2013. Degradation of brominated epoxy resin and metal recovery from waste printed circuit boards through batch sub/supercritical water treatments. Chem. Eng. J. 219, 131–136. Xiu, F.R., Zhang, F.S., 2010. Materials recovery from waste printed circuit boards by supercritical methanol. J. Hazard. Mater. 178, 628–634. Ye, M.J., 1991. Determination of trace amounts of bisphenol A in epoxy resins using UV spectrophotometry. Chem., World, 553–556. Yoo, J.M., Jeong, J., Yoo, K., Lee, J.C., Kim, W., 2009. Enrichment of the metallic components from waste printed circuit boards by a mechanical separation process using a stamp mill. Waste Manage. 29, 1132–1137. Zhou, Y., Wu, W., Qiu, K., 2010. Recovery of materials from waste printed circuit boards by vacuum pyrolysis and vacuum centrifugal separation. Waste Manage. 30, 2299–2304. Zhu, P., Chen, Y., Wang, L.Y., Zhou, M., 2012. Treatment of waste printed circuit board by green solvent using ionic liquid. Waste Manage. 32, 1914–1918. Zhu, P., Chen, Y., Wang, L., Qian, G., Zhang, W.J., Zhou, M., Zhou, J., 2013a. Dissolution of brominated epoxy resins by dimethyl sulfoxide to separate waste printed circuit boards. Environ. Sci. Technol. 47, 2654–2660. Zhu, P., Chen, Y., Wang, L.Y., Zhou, M., Zhou, J., 2013b. The separation of waste printed circuit board by dissolving bromine epoxy resin using organic solvent. Waste Manage. 33, 484–488.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent Sushant B. Wath ⇑, Mayuri N. Katariya, Sanjeev K. Singh, Atul N. Vaidya CSIR-National Environmental Engineering Research Institute (NEERI), Nehru Marg, Nagpur 440 020, India
a r t i c l e
i n f o
Article history: Received 5 March 2015 Accepted 15 May 2015 Available online xxxx Keywords: E-waste Recovery Processes Printed circuit boards N-methyl-2-pyrrolidone NMP
a b s t r a c t Printed circuit boards (PCBs) in electrical and electronic equipment (EEE) abide of valuable and hazardous materials and due to its complex and discrete make-up across manufacturers, processing waste PCBs (WPCBs) is a massive challenge. And therefore either completely novel or improved processes are needed for the recycling of WPCBs and recovery of valuable materials from it. In the present study, the processing of WPCBs was performed using N-methyl-2-pyrrolidone (NMP) as a solvent. Various parameters, which include WPCB sizes, solid to liquid (S/L) ratio, temperature and time were investigated to understand the processing of WPCBs by dissolving bromine epoxy resin using NMP. Experimental results showed that the dissolution rate of the bromine epoxy resin increased with respect to various parameters studied. The optimum condition of thorough separation of WPCBs was S/L ratio of 1:5 and WPCB size/area of 4 mm/16 mm2 and 100 °C for 90 min. The used NMP were vaporised and condensed under the decompression for retrieving regenerated NMP. This novel process using NMP as solvent can be an environmental friendly and effective option for the separation and recovery of various valuable materials such as metals, and glass fibres from WPCBs. Ó 2015 Published by Elsevier Ltd.
1. Introduction Printed circuit boards (PCBs) are the essential, integral and predominant part of almost all electrical and electronic equipment (EEE). PCB provides the platform to mount various electronic items, such as resistors, relays capacitors, diodes, integrated circuits in a rigid manner. The rapid growth of technology (Wath et al., 2011) along with the high rate of obsolescence has increase E-waste generation and consequently waste PCBs (WPCBs) (Ping and Guobang, 2002; Huang et al., 2009), both in developed and developing countries. Typically, PCB contains 50% polymer (epoxy resin or phenolic resin, along with brominated flame retardants (BFR), etc.), 20% glass fibre and 30% metals [20% Cu, 8% Fe, 4% Tn, 2% Ni, 2% Pb, 1% Zn, 0.2% Ag, 0.1% Au and 0.005% Pd] (Huang et al., 2009). However there is a considerable variance in composition of WPCBs coming from different appliances, manufacturers and year of production. Though precious and valuable metals in PCBs are only 1% by weight, it accounts for 80% of the total intrinsic value (Park and Fray, 2009) and are thus gaining recycling attention from both formal and in-formal recycler. Recovered material can be used as a worthy secondary source for various scarce materials. ⇑ Corresponding author. Tel./fax: +91 712 2249758. E-mail address: [email protected] (S.B. Wath).
Furthermore, PCBs consists of multi-layers of etched metal conductive tracks laminated with fibre glass sheet, bonded with mixtures of polymer materials (thermoplastic and thermosetting resins). Thermoset resin such as brominated epoxy resin is utilized as a flame retardant because PCBs are often exposed to high temperature both during manufacturing and operations (Hutapea and Grenestedt, 2003). The epoxy resins are intermingled with metals (Jie et al., 2008) and glass fibre many times, and thus is not present only along the surface. Due to this, individual components separation from WPCBs and size reduction of WPCBs for recycling is an arduous task (Ping et al., 2009; Gu et al., 2008). PCB recycling involves two steps. Preliminary step involves mechanical–physical or metallurgical processing for the dismantling and/or separation of different components and materials (Veit et al., 2005; Duan et al., 2009; Yoo et al., 2009; Jiang et al., 2009) while the second step involves further separation and processing of metal streams; which probably is the most imperative step from economic and environmental viewpoints. Meanwhile, many studies, such as bio-metallurgy (Xiang et al., 2010), combustion (Ni et al., 2012), hydrometallurgy (Ping et al., 2009), pyro-metallurgy (Vanbellen et al., 2003), pyrolysis (Chien et al., 2000), supercritical fluid (Xiu and Zhang, 2010), ionic liquid (Zhu et al., 2012) were carried out for recycling of WPCB. However these processes have its own limitations, the mechanical–physical
http://dx.doi.org/10.1016/j.wasman.2015.05.020 0956-053X/Ó 2015 Published by Elsevier Ltd.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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processes are predominantly time and labour intensive. Whereas the secondary metallurgical processes are energy and capital intensive as well as hazardous to environment as may lead to formation of dioxins and furans due to the presence of BFRs in PCBs (Huang et al., 2009; Zhou et al., 2010; Duan et al., 2011). While some processes may generate massive amount of waste acid, alkaline liquid and sludge, which may cause secondary pollution. This provides the necessity for the continued research on the recycling of WPCBs. Kamo et al. (2009) used tar derived from Japanese cedar and benzyl alcohol to liquefy the epoxy board at 250–300 °C under atmospheric pressure. Xing and Zhang (2013) employed a batch type reactor sub- and supercritical water to simultaneously degrade brominated epoxy resin and recover metals from WPCBs. Lin-zhuan and Tao (2010) and Guan et al. (2011), attempted to dissolve brominated epoxy resin in PCBs using nitric acid; however the leaching rates were too low. However, only Zhu et al. (2013a,b) use organic solvent dimethyl sulfoxide (DMSO) as a non-aqueous solvent to separate WPCBs. The present study targets the use of non-aqueous organic solvent N-methyl-2-pyrrolidone (NMP) (C5H9NO) for the dissolution of BFR from the substrate and separation of WPCBs. NMP is a dipolar aprotic, colourless with mild amine odour, and is miscible with water and with most common organic solvents. Other properties include high boiling point (202 °C) and high viscosity (1.67 cP@25 °C); molecular weight of 99.1 g/mol. NMP effectively dissolves numerous organic and inorganic chemicals but does not corrode metal. More importantly NMP is a basic and polar compound with high stability, slowly oxidized by air, hygroscopic and non-corrosive. Due to its excellent safety characteristics NMP has important applications; in paint stripping and cleaning (in microelectronic, petro-chemical, and plastic industries); as intermediate (in pharmaceutical, agro-chemical industries) and as a solvent for cellulose dissolution exploiting its non-volatility and ability to dissolve diverse materials. NMP has lower volatility (i.e., vapour pressure = 0.190 Torr at 25 °C) and evaporation rate – 0.03 (BuOAc = 1), thus its use releases fewer organic emissions to the atmosphere. Therefore it can be summarized and infer that NMP has high thermal stability and can be recycled many times. Furthermore, NMP biodegrades readily and has low toxicity to aquatic life (Harreus et al., 2011). The acute toxicity of NMP (3.6 g/kg for rat) is lesser than other dipolar aprotic solvents like sulfolane (1.9 g/kg) and DMF (dimethyl formamide) (2.8 g/kg). In this paper, the effect of heating, particle size and solvent ratio (S/L) are evaluated on the dissolution of epoxy resin of the WPCB using NMP. The problem of copper extraction from waste PCBs due to the encapsulation of thin metallic sheet by plastic/epoxy resin material has been solved by the liberation of thin layers of metallic sheet by organic swelling. The aim of this research is to develop a novel technique for separating valuable materials from WPCBs and to prevent environmental pollution from WPCBs. To the best of our knowledge there has been no previous reported study investigating the separation of WPCBs using NMP.
systematically and carefully detached manually using appropriate tools, to minimize occupational and environmental impact arising out of the various hazardous materials present in it. The bare WPCBs (after removal of mounted components from its surface) were cut into 3 cm 3 cm size manually using plier/cutter and were further reduced to size using laboratory mixer grinder (Make Sujata-Dynamix DX). The size reduced samples were separated according to particle size using an electromagnetic sieve shaker (Make – Electro Lab; Model – EMS8; Dimension-L339 W312 H270 mm). Mesh size of sieves used were 10, 8, 6, 4, 2, 1 and 0.71 mm. Sample was placed in the top sieve with the largest mesh and shaken in continuous and intermittent mode for 5 and 2 min respectively. The residue remaining on the sieves of mesh sizes 8, 6 and 4 mm of approximate size/area – 4 mm/16 mm2; 6 mm/36 mm2 and 8 mm/64 mm2 were used for conducting the experiments. All reagents used in these experiments were analytical grade products from Fisher Scientific Pvt. Ltd., Mumbai, India. 2.2. Methods The experiments were conducted using a 0.5 L, three-neck flask equipped with a continuous water circulating condenser unit. Fig. 1 shows the experimental set-up for separating the WPBCs. Reactor was charged with 5 g of WPCB samples each time along with appropriate solvent quantity. And once the desired
Port for sampling & stirring Water out
Water in Refluxing
Thermometer
3-Way flask NMP WPCB
Sand bath Heater
Fig. 1. Experimental set-up for treating WPCBs in NMP solvent.
2. Materials and methods 2.1. Materials WPCBs for this study were collected from the discarded PCs (manufactured in 2003) from the stores’ of NEERI (National Environmental Engineering Research Institute) Nagpur, India. WPCB of motherboard extracted from desktop personal computer was used for this study. Components such as ICs, transformers, fan, resistors, capacitors, pins, heat sink, motors, and batteries, mounted on the PCBs were
Fig. 2. Flowchart for dissolution of epoxy resin and regeneration of NMP.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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Fig. 5. Photographs of NMP (A) unused, (B) used and (C) regenerated.
Fig. 3. Effects of (A) WPCB sizes/area, (B) solid to liquid ratio (S/L) and (C) temperature on concentration of the bromine epoxy resin dissolution from WPCBs.
temperature was reached, the set up was held constant at that temperature for 180 min. After every 30 min interval, a fixed quantity of solvent was withdrawn and the concentration was analysed in triplicate and only its mean values have been reported in the paper. The experiments on WPCBs were carried out using NMP with a varying parameters and experimental conditions such as WPCBs size/area (4 mm/16 mm2, 6 mm/36 mm2, 8 mm/64 mm2); temperature (70 °C, 80 °C, 90 °C, 100 °C; time period (30, 60, 90, 120, 150, 180 min); solid to liquid ratios (w/v) (1:2; 1:3; 1:4; 1:5) with random manual stirring. The amount of bisphenol A, which is a component of bromine epoxy resin was measured to determine the bromine epoxy resin concentration in NMP (Ye, 1991). The 0.10 g pure bisphenol A was transferred to a 100 ml volumetric flask, dissolved and make up to volume with anhydrous ethanol to get stock solution of 1000 lg/ml. The concentration of 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 lg/mL were prepared for making a standard curve. The amount of bisphenol A was determined using UV–Vis spectrophotometer (AU-2701U, Systronics) with 1.0 cm matched quartz cells at a wavelength of 282 nm. To ascertain the accuracy of measurement the instrument was calibrated periodically using the standard procedure. Rotary evaporation process was exercised to treat the used NMP under reduced pressure of 6.6 mbar at temperature 60 °C and the
A
B
Solder
C
D
E
Fig. 4. Photographs of (A) WPCB (B) WPCBs treated with NMP (C) copper foil and solder (D) liquid photo resist (E) glass fibre.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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Fig. 6. GC–MS chromatogram of (A) unused NMP and (B) used NMP.
condenser was used to cool the vaporised gases at room temperature for NMP regeneration and residues were separated out. Fig. 2 shows a flowchart for dissolution of bromine epoxy resin and regeneration of NMP. The residues i.e. WPCBs were washed with distilled water and dried at 85 °C for 6 h. Photographic images were taken of treated WPCBs using a digital camera. Transition in the chemical composition of the used and unused NMP was analysed using gas chromatography mass spectrometry, Perkin Elmer-Clarus 680 (GC) & Clarus 600-C (MS). The GC system was operated in split less
injection mode. A 30 m DB-5 column (ID-320 lm) was used for component separation with the following temperature program: 150 °C for 10 min. Helium was used as the carrier gas at a constant flow rate of 1 mL/min. The GC injector temperature and MS ion source temperature were maintained at 150 °C. Sample extract (1 lL)/standard solution was auto-sampled. The mass spectrometer was operated with electron ionization (EI) mode with electron energy of 70 eV. Turbo mass software was used for the instrument parameters optimization as well as for the data acquisition and analysis.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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3. Results and discussion The absorbency curves were plotted for the bisphenol A using the wavelength ranging from 200 nm to 300 nm. Bisphenol A shows maximum absorbance for UV light for the wavelength of 282 nm. Therefore, the concentration of bromine epoxy resin dissolved into NMP can be characterized by UV–Vis spectrophotometer by determining the amount of bisphenol A. Fig. 3A–C shows the effects of (A) WPCB size/area (B) solid to liquid (S/L) ratio and (C) temperature respectively, on concentration of the bromine epoxy resin dissolution in NMP from WPCBs. The maximum bisphenol A concentration for the 4 mm/16 mm2 size fraction can be seen in Fig. 3A, because the decrease in the size of WPCB sample increases the surface-contact area with the solvent NMP, which facilitate the mass transfer to cause the increase in dissolution of bromine epoxy resin, in comparison to the bigger size particles with smaller surface-contact area. It can be observed that the concentrations of bromine epoxy resin in NMP increased with an increased in solid to liquid ratios (Fig. 3B). This phenomenon can be explained by the fact that NMP increases with the increase of S/L ratio, leading to increase in concentration. The concentration of bisphenol A is maximum for the ratio 1:5 in comparison with ratio 1:2, and shows almost linear increase in concentration with respect to time. It can be observed from the Fig. 3C that with the increase in temperature the concentration of bromine epoxy resin dissolution increases, may be due to fact that increase in temperature enhances the mass transfer. Graph shows almost linear hike in epoxy resin dissolution from 70 °C to 100 °C with a maximum at 100 °C after 90 min. And maximum dissolution is noted in between 90 and 120 min. While solvent properties are significant in determining the separation performances (Ismail and Lai, 2003), data are still lacking to fully understand the role of solvents in separation. Due to the complexity of solvent–polymer interactions in the reactions which differ in each type of polymer and solvent for a specific membrane type, it is difficult to accurately predict solubility behaviour (Adams et al., 2013). And therefore, further studies and analysis are required for better understanding of the WPCB separation behaviour in NMP under varying process parameters. Finally, the metals (copper foils), glass fibres and liquid photo solder resists (A thin layer of polymer applied to Cu traces of a PCB for protection against oxidation and to prevent solder bridge (unintended electrical connection) formation between closely spaced solder pads) are distinctly detached from one another and
(A) H-O hydrogen bond
can be easily separated using NMP as solvent. Further, various techniques can be applied for its separation, based on the density difference principle. Fig. 4 depicts the photographs of WPCBs treated under the condition of solid to liquid ratio of 1:5, WPCBs area of 6 mm/36 mm2, 180 min. It can be observed from Fig. 4 that the copper foils and the glass fibres were separated from the WPCBs and the solders were still bonded to the surfaces of the copper foils. Furthermore, the liquid photo solder resists were detached from the copper foils (Fig. 4B and C). The copper foil does not show any mark of corrosion which also substantiate the non-corroding property of NMP towards metal. Rotary evaporation process was exercised to treat the used NMP and the condenser was used to cool the vaporised gases for NMP regeneration and thus the bromine epoxy resin dissolved in NMP was separated. The Fig. 5 shows the photograph of the used, unused and regenerated NMP. It is noteworthy for this process that NMP can be regenerated from the perspective of protection of environment and processing cost. Moreover this new process does not produce bromine volatilize which can cause secondary environmental pollution. From Fig. 5, it can be precisely ascertained that the unused NMP (Fig. 5A) and the regenerated NMP (Fig. 5C) were colourless, whereas the used NMP was greenish (Fig. 5B). This is because NMP dissolves bromine epoxy resin in WPCBs to cause its colour change. The Fig. 6 shows the GC–MS chromatogram and fragmentation patterns of the used and unused NMP which clearly reflects the identical characteristic peaks and patterns of the NMP, which indicates that the chemical properties of the used and unused NMP has not change. Polar solvent NMP is a good hydrogen bond acceptor that results in the formation of various possible hydrogen bonds between the hydroxyl and N–O group of NMP and brominated epoxy resin, which may be responsible for the separation of bromine epoxy resin. Fig. 7A shows the hydrogen bond between H–O. The hydrogen from the hydroxyl group in the brominated epoxy resin pulls electrons towards the oxygen in the NMP. Fig. 7B shows that the hydrogen in the methyl group of the NMP which may form hydrogen bonds with bromine and oxygen in brominated epoxy resins. Fig. 7C shows the hydrogen bonds of H–N. The strongly electronegative nitrogen in the NMP pulls the hydrogen in the hydroxyl group of the brominated epoxy resin.
(B) H-O and H-Br hydrogen bond
(C) H-N hydrogen bond
Fig. 7. Potential role of hydrogen bonding between NMP and bromine epoxy resin.
Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020
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4. Conclusion Organic solvents such as NMP can be used for processing the WPCBs of a typical electronic waste. NMP can be used to comprehensively separate the various layers of the WPCBs, which enables easy recovery of valuable materials including metals, glass fibres and polymers. The optimal condition was temperature of 100 °C at 90 min, solid to liquid ratio of 1:5, whereas WPCBs size/area of 4 mm/16 mm2. Rotary evaporation process was exercised to treat the used NMP and the condenser was used to cool the vaporised gases for NMP regeneration. NMP not only dissolved the bromine epoxy resin of WPCBs but also did not react with metals, liquid photo solder resists, and glass fibres. This new process does not produce bromine volatilize to cause secondary environmental pollution, which complies with the principle of sustainable development by decreasing the manufacturing cost of treating WPCBs to achieve thorough separation and recovery of reusable resources.
Acknowledgments Authors are thankful to Director, CSIR-NEERI and Head, BDTT division for their necessary support and guidance. The authors are also grateful to CSIR, New Delhi for the necessary approval and funding to undertake this research activity under the XII five year plan project.
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Please cite this article in press as: Wath, S.B., et al. Removal and separation of bromine epoxy resin for recovering valuable materials from waste printed circuit board using organic solvent. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.05.020