Controllable Microwave-Assisted Polycarbonate Waste Chemical Recycling

Transcription

1 Controllable Microwave-Assisted Polycarbonate Waste Chemical Recycling Controllable Microwave-Assisted Polycarbonate Waste Chemical Recycling Mir Mohammad Alavi Nikje * and Mohammad Askarzadeh Chemistry Department, Faculty of Science, IKIU, Qazvin, Iran, PO Box: 288 Received: 11 June 2012, Accepted: 29 October 2012 Summary A simple, convenient and novel method was developed for the recovery of bisphenol-a from polycarbonate wastes under microwave irradiation. In this study bisphenol-a was recovered at a % yield by using a mixture of glycerol/water as the green solvent and sodium hydroxide as the catalyst, respectively. This methodology can overcome the disadvantages existing in traditional methods such as long reaction times, high energy consumptions, use of harmful reagents and environmental problems, and is applicable to all types of polycarbonates. Keywords: Polycarbonate wastes, Bisphenol-A, Microwave-assisted reactions, Green solvents Introduction Bisphenol-A (BPA) is one of the widely used raw materials in the production of polycarbonate block materials, fibres, optical materials, polycarbonate (PC) sheets and epoxy resins. In 2005, the world capacity of BPA production was reported as 50,000 tons/year, but in 2007 and 2008, only China s BPA production capacity soared to 176,000 and 296,000 tons/year, respectively. It is estimated that by the end of 2012, China s BPA production capacity will reach 760,000 tons/year [1, 2]. Due to increasing PC production and in order to recycle used PCs, demands for PC waste recycling have increased dramatically and as a result, scientists have been trying to find an economical, green and convenient method for the chemical recycling of polycarbonate wastes and the recovery of BPA. Drmm.alavi@gmail.com Smithers Rapra Technology, 2013 Progress in Rubber, Plastics and Recycling Technology, Vol. 29, No. 3,

2 Mir Mohammad Alavi Nikje and Mohammad Askarzadeh For example, some recycling processes have been reported in which PC decomposes into BPA. Thermal degradation of PC wastes via pyrolysis is a possible alternative for polymer recycling, however, its low selectivity and the condensation reactions among the aromatic rings makes it a particularly unsuitable process because it reduces the yield of the monomer and raises that of the by-products [3]. For example, Shwu-jer Chiu and co-workers studied the efficiency of metal chloride catalysts on the thermal degradation of polycarbonate wastes and recovered BPA in moderate yields [4]. Trends in the use of methanol and methanol-water mixtures as destroying reagents in a semi-continuous lab-plant were performed by Pinero and co-workers [5]. Another recovery process based on the hydrolysis of PC wastes with subcritical liquid water was investigated by Bolzano s research group [6]. In addition, the depolymerization of poly (bisphenol-a carbonate) in subcritical and supercritical toluene has been reported by Pan and co-workers [7]. Other studies have reported on the sole recycling of PC or when blended with other polymers [8-14]. Among all the processes recently reported, an environmentally friendly strategy for the methanolysis of PC in the recovery of BPA and dimethyl carbonate (DMC) was developed in an ionic liquid using a conventional heating method [15]. The same research group, studied thermal and alkali-catalysed methanolysis and hydrolysis of PC in N-methyl-2-pyrrolidone, 1, 4-dioxane, tetrahydrofuran solvent with a BPA recovery yield of 94% [16]. All reported methods on PC waste recycling have their own merits and drawbacks. The main drawbacks in the reported procedures are the application of critical reaction conditions, use of hazardous reagents and solvents, and prolonged reaction times [17]. In a continuation of our previous work on PC chemical recycling using MW methodology [18], we decided to examine the role of this technique in combination with glycerin as a green solvent in the BPA recovery from the waste of CDs and DVDs. The main aim of our report is based on minimizing recovery times, green solvent use and performing the reaction under controllable conditions. Experimental Materials and Methods PC pellets were obtained from used CDs and DVDs and washed with hot water, and dried before being charged into the reactor. BPA, glycerin and 170 Progress in Rubber, Plastics and Recycling Technology, Vol. 29, No. 3, 2013

3 Controllable Microwave-Assisted Polycarbonate Waste Chemical Recycling sodium hydroxide were purchased from Merck and used without further purification; the water for performing the reactions was doubly distilled. FT-IR spectra were performed using a BRUKER Tensor 27 spectrometer. 1 HNMR and ¹³CNMR spectra were determined using a BRUKER CRX 300 instrument using deuterated CDCl 3 as a solvent and tetramethylsilane (TMS) as an internal standard. The recycling processes were performed in a Milestone Mico SYNTH NP Ethos 1600 programmable microwave. General Procedure A two-necked flask was charged with PC wastes (2.5 g), glycerin, water (solvent total weight 2.5 g) and NaOH (1 % based on total waste and solvent weights) as the catalyst. In order to study the effect of reaction temperature on BPA recovery yields, two sets of reactions were performed at 150 and 180 C respectively, and the data collected is shown in Tables 1 and 2. Separation and purification of BPA was achieved by crystallization in water. Further filtration and drying of the product led to BPA crystals which were characterized structurally and the data compared with an authentic data sample. Table 1. conditions and solvent ratios in MW assisted depolymerization of PC wastes at 150 C Entry Glycerin/Water (w/w) time (min) time at Ramp (min) time at Hold (min) BPA recovery yield (%) 1 80: : : : : conditions: Catalyst- NaOH (1 % pbw of total solvent weight), reaction temperature C, MW irradiation followed in Ramp and Hold temperatures at 150 C, in all reactions maximum MW power settled down as 800 and 700 watt, respectively Progress in Rubber, Plastics and Recycling Technology, Vol. 29, No. 3,

4 Mir Mohammad Alavi Nikje and Mohammad Askarzadeh Table 2. conditions and solvent ratios in MW assisted depolymerization of PC wastes at 180 C Entry Glycerin/ Water (w/w) 80:20 60:40 50:50 40:60 time (min) time at Ramp (min) 0.5 time at Hold (min) BPA recovery yield (%) 5 20: conditions: Catalyst- NaOH (1 % pbw of total solvent weight), reaction temperature- 180 C, MW irradiation followed in Ramp and Hold temperatures at 180 C, in all reactions maximum MW power settled down as 800 and 700 watt, respectively Results and Discussion Scheme Scheme 1 shows the alkaline-catalysed depolymerization reaction of PC. As indicated in the scheme, the first step is related to a Bronsted and Lowry acidbase reaction with the conversion of glycerin and/or water to the corresponded ions, which are responsible for acting as a nucleophile by attaching to the carbonate functional group of PC and forming the intermediate. Further Scheme 1. pathway for BPA recovering 172 Progress in Rubber, Plastics and Recycling Technology, Vol. 29, No. 3, 2013

5 Controllable Microwave-Assisted Polycarbonate Waste Chemical Recycling hydrolysis of the intermediate led to libration of BPA. By increasing the water ratio, the concentration of the hydroxide ion is increased and competes with the alkoxide ion by attaching to a carbonyl group resulting in a prolonged reaction time (Tables 1 and 2). This phenomenon is due to the weaker hydroxide ion nucleophilicity in comparison with the alkoxide ion. Solvent Composition Studies The main aim of this study was performing the reaction under green condition as well as finding green solvent compositions containing high water content. For this purpose, the effects of various water/glycerin ratios were studied and the BPA recovery yields determined; the data collected in shown in Tables 1 and 2, respectively. As indicated in the tables, the overall BPA recovery yields reached % under all conditions, but prolonged reaction times were observed when the water ratio in the solvent composition was increased. The use of water alone allows the procedure to be labelled as totally green, however, due the economic drawback of an extended reaction time, the reaction needs the application of glycerin as a co-solvent. Recovered BPA Structural Elucidation Recovered BPA was characterized using spectroscopic methods in order to elucidate the chemical structure and the data was compared with an authentic sample. The 1 HNMR spectrum of recovered BPA is presented in Figure 1. The peaks at 1.53, 4.50 and ppm are related to methyl Figure 1. 1 HNMR spectrum of recovered BPA Progress in Rubber, Plastics and Recycling Technology, Vol. 29, No. 3,

6 Mir Mohammad Alavi Nikje and Mohammad Askarzadeh groups, hydroxyl and aromatic functional groups, and protons, respectively. All 1 HNMR data was similar to data from an authentic sample which reveals successful recovery under the designed experimental conditions. The result obtained from the ¹³CNMR spectrum is shown in Figure 2. In this spectrum, the peaks at 115 (C 3 ), 127 (C 4 ), 141 (C 5 ) and 155 (C 6 ) ppm are related to the aromatic ring carbons. In addition, the signals at 31 and 41 ppm are attributed to the methyl groups (C 1 ) and C 2 carbons, respectively. In addition, the FT-IR spectrum of the recovered BPA fully confirmed the NMR data (Figure 3). Figure CNMR spectrum of recovered BPA Figure 3. FTIR spectrum of recovered BPA 174 Progress in Rubber, Plastics and Recycling Technology, Vol. 29, No. 3, 2013

7 Controllable Microwave-Assisted Polycarbonate Waste Chemical Recycling Conclusion A water/glycerin mixture acts as a hydroglycolysis solvent in BPA recovery in green, convenient and microwave-assisted conditions under atmospheric pressure. The results confirm that a microwave can be used as an energy source in PC chemical recycling as an adequate, simple and convenient method with considerable performance i.e., short reaction times. This methodology can be added to eco-friendly and green methods for BPA recovery from CD and DVD wastes. In the meantime, the studied strategy overcomes the existing disadvantages when using traditional methods such as unfeasible reuse of solvents, tedious work-up procedures and environmental problems. References 1. Industry news-bisphenol-a, (2011). 2. Research and Markets: Polycarbonate World Market Outlook, (2011). 3. Jang B.N., and Wilkie C.A., Polymer Degradation and Stability, 86, (2004) Chiu S.J., Chen S.H., and Tsai C.T., Waste Management, 26, (2006) Pinero R., Garcia J., and Cocero M.J., Green Chemistry, 7, (2005) Bozzano G., Dente M., and Rosso R.D., 20th European Symposium ESCAPE20, (2010). 7. Pan Z.Y., Bao Z., and Chen Y.X., Chinese Chemical Letters, 17, (2006) Lin C.H., Lin H.Y., Liao W.Z., and Dai S.A., Green Chemistry, 9, (2007) Jang B.N., and Wilkie C.A., Thermochimica Acta, 426, (2005) Kim J., Gracz H.S., Roberts G.W., and Kiserow D.J., Polymer, 49, (2008) Bozi J., Czegeny Z.S., Meszaros E., and Blazso M., Journal of Analytical and Applied Pyrolysis, 79, (2007) Uyar T., Aslan E., Tonelliand A.E., and Hacaloglu J., Polymer Degradation and Stability, 91, (2006) Fraisse F., Verney V., Commereuc S., and Obadal M., Polymer Degradation and Stability, 90, (2005) Jung J.H., Ree M., and Kim H., Catalysis Today, 115, (2006) Liu F., Li L., Yu S., Lv Z., and Ge X., Journal of Hazardous Materials, 189, (2011) 249. Progress in Rubber, Plastics and Recycling Technology, Vol. 29, No. 3,

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