Recycling Acetic Acid from Polarizing Film of Waste Liquid Crystal

Article pubs.acs.org/est

Recycling Acetic Acid from Polarizing Film of Waste Liquid Crystal Display Panels by Sub/Supercritical Water Treatments Ruixue Wang, Ya Chen, and Zhenming Xu* School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China S Supporting Information *

ABSTRACT: Waste liquid crystal display (LCD) panels mainly contain inorganic materials (glass substrate) and organic materials (polarizing film and liquid crystal). The organic materials should be removed first since containing polarizing film and liquid crystal is to the disadvantage of the indium recycling process. In the present study, an efficient and environmentally friendly process to obtain acetic acid from waste LCD panels by sub/supercritical water treatments is investigated. Furthermore, a well-founded reaction mechanism is proposed. Several highlights of this study are summarized as follows: (i) 99.77% of organic matters are removed, which means the present technology is quite efficient to recycle the organic matters; (ii) a yield of 78.23% acetic acid, a quite important fossil energy based chemical product is obtained, which can reduce the consumption of fossil energy for producing acetic acid; (iii) supercritical water acts as an ideal solvent, a requisite reactant as well as an efficient acid−base catalyst, and this is quite significant in accordance with the “Principles of Green Chemistry”. In a word, the organic matters of waste LCD panels are recycled without environmental pollution. Meanwhile, this study provides new opportunities for alternating fossil-based chemical products for sustainable development, converting “waste” into “fossil-based chemicals”. with ITO film were obtained, and the precious metal indium could be recycled from the glass substrates in the next steps. Nonetheless, recycling of organic parts was somewhat ignored in the past. The waste LCD panels usually are incinerated directly to get the ITO glass for metal recycling. However, incineration could be dangerous to the environment because of the emission of toxic components including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and polychlorinated dioxins (PCDs). These toxic components can be found in the fly ash and the residues.7 Thus far, some research efforts have been done to remove and recover the organic parts from LCD panels. Lu et al. pyrolyzed LCD panels in nitrogen atmosphere and obtained the pyrolysis oil; the oil mainly contained acetic acid and triphenyl phosphate.8 Li et al. separated the polarizing film by a thermal shock method at 230−240 °C and then removed the liquid crystal by an ultrasonic cleaning method.5 Nie et al. removed the polarizing film and liquid crystal by an acetone soaking method.9 However, incineration and pyrolysis might bring polycyclic aromatic hydrocarbons (PAHs) problems.1,10

1. INTRODUCTION With the advantages of light quality, small volume, and low power consumption, Liquid Crystal Display (LCD) is widely used in televisions, computer monitors, etc. and basically replaces the cathode ray tube (CRT).1,2 The total worldwide TV shipments were 233 million in 2012, among which LCD TV sheared 87.3%, while plasma display panel (PDP) TV and CRT TV shared 5.7% and 6.9%, respectively.3 However, most LCD panels have a life span of 3−8 years, which brings large amounts of end-of-life LCD panels waiting for treatment. Figure 1(a) shows the structure of LCD panels. LCD panels mainly contain polarizing film, glass substrate, and liquid crystal, and they are difficult to be separated by physical method. Indium, a kind of precious metal, is sputtered on the glass substrate in the form of indium−tin oxide (ITO) conductive film. In recent years, recycling of indium has drawn much attention from research institutions.2,4−6 In our previous work, we have studied indium recycling by vacuum carbon-reduction and vacuum-chlorinated.2,4 However, polarizing film, glass substrate, and liquid crystal cling together. It is difficult to separate them and is to the disadvantage of indium recycling. Therefore, organic parts (mainly include polarizing film and liquid crystal) should be removed and recovered. In the indium recycling process, recycling organic materials is one of the most important steps. In this study, clean glass substrates © XXXX American Chemical Society

Received: January 7, 2015 Revised: April 13, 2015 Accepted: April 27, 2015

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DOI: 10.1021/acs.est.5b00104 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

Article

Environmental Science & Technology

Figure 1. (a) Structures of LCD panels and (b) major components of polarizing film.

anhydride synthesis and as a solvent for purified terephthalic acid (PTA) production. In the medium and long terms there is potentially a great demand for acetic acid.18,19 Most of the acetic acid in the world is synthesized by a methanol carbonylation process,18,19 and methanol is one of the most important products of the petrochemical industry, the coal chemical industry, and the natural gas chemical industry.20,21 However, the whole world is facing the situation of fossil energy shortage, which brings an urgent need of alterative fossil-based chemical products for sustainable development.22−24 On the basis of our study, taking LCD TV for example, the global shipments of LCD TV were about 200 million in 2012, and these TV sets would be discarded in 3−8 years. 168,000 tons of acetic acid could be obtained by the process in this study when the 200 million LCD TV sets were disposed. Actually, we have measured that the weight of polarizing film is 200 times more than that of liquid crystal. Therefore, in this study, we mainly focus on polarizing film recovery. As shown in Figure 1(b), polarizing film mainly consists of cellulose triacetate (CTA), poly(vinyl alcohol) (PVA), and triphenyl phosphate (TPP). CTA is the ethyl esterification product of cellulose and takes up a much higher ratio than PVA and TPP. Various research has been developed in conversion of cellulose into value-added products in sub/supercritical water.14,25−28 However, reports on the conversion of polarizing film or CTA were rare. In this work, LCD panels were used to produce acetic acid by sub/supercritical water treatments in a semibatch reactor under external-catalyst-free conditions. Gas chromatography - mass spectrometry (GC-MS) analysis and high performance liquid

Meanwhile, severe environmental problems might be triggered by solvent soaking since most organic solvents are often toxic, flammable, or corrosive.11 In our previous research, nitrogen pyrolysis process was used to recycle the organic matter of waste LCD panels.8,12 Acetic acid was the main oil product. However, the process needs a relative high temperature, and the gas products are discommodious to reuse. More importantly, some fly ash and smog are generated during the pyrolysis process, which could bring severe environmental issues. In recent years, supercritical water (SCW, T ≥ 374 °C, P ≥ 22.1 MPa) has been known as an environmentally friendly method to recycle organics due to its low viscosities, high mass transport coefficient, and high solubility for organics.13 Utilization of green solvents in chemical reactions is quite significant, which is one of the “Principles of Green Chemistry”.11,14,15 As one of the nontoxic and nonflammable solvents, water has been considered to be an ideal solvent in chemical reactions compared with traditional organic solvents. As it approaches the critical point, the dissociation constant (Kw) for water is about 3 orders of magnitude higher than that for ambient liquid water; sub/supercritical water can provide abundant H+ and OH−16 and could be an efficient acid or base catalyst for organic reactions.14 Acetic acid is extensively employed as an utmost important raw material of organic synthesis and industrial solvent. According to the statistics, the global sales of acetic acid were 19.13 million tons per year in 2013. The global acetic acid market was valued at $5.93 billion in 2011 and was expected to reach $10.31 billion by 2018.17 Acetic acid is used primarily as a raw material for vinyl acetate monomer (VAM) and acetic B


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Figure 2. Schematic diagram of the semibatch reactor.

approximately 2 g of polarizing film and 11 g of glass with liquid crystal was taken into the reactor tube. The reactor tube length and the diameter were 140 mm and 26 mm, respectively. Then, the constant-flux pump was turned on at a flow rate of 10 mL· min−1, and the heating unit was turned on at a heating rate of 20 °C·min−1 after the pressure reached the set value. The reaction was maintained for a certain time after the temperature reached the set value. The liquid products were gathered by the condensing system, and the gases were collected by the air bag. 2.4. Products Analysis. The liquid products were qualitative and quantitative analyzed by chromatograph−mass spectroscopy (GC-MS, TurboMass, perkin Elmer Corporation, U.S.) and high performance liquid chromatography spectroscopy (HPLC, Waters, 1525/2489). In this process, very little gas was collected during the reaction process due to the laboratory scale. The gas products were analyzed by chromatograph−mass spectroscopy (GC-MS, TurboMass, Perkin Elmer Corporation, U.S.). The main components of the gas products were carbon dioxide, water vapor, and some hydrocarbon compounds. The detailed results were provided in the Supporting Information. Actually, since the air tightness of the whole equipment was under good control, no gases leaked out, and the process did not cause any environmental pollution. The main components of the residue were glass as well as very little carbon black. A Fourier transform infrared (FTIR) spectrogram comparison chart of polarizing film and carbon black from the residue was provided in the Supporting Information. 2.5. Characterization Methods. The recycling effect of LCD panels in this study was characterized by yield of acetic acid, which was defined as eq 1, and the organic conversion rate, which was defined as eq 2. In eq 1, the theoretical mass of acetic acid was calculated on the condition that each glucose triacetate monomer can generate four acetic acids. To be specific, three of the acetic acids came from the three acetyls, while the other one came from the glucose ring. The mass ratio

chromatography (HPLC) analysis were used in the qualitative and quantitative analysis of the products. The effects of reaction temperature, pressure, and time on the organic conversion rate and acetic acid yield were studied. Furthermore, a series of reaction mechanism were proposed. In short, the objectives of this study are (i) to propose an environmentally friendly technology recycling the organic matters before indium recovery and (ii) to obtain acetic acid in the recycling process without environmental pollution and reduce the consumption of fossil energy by producing acetic acid.

2. MATERIALS AND METHODS 2.1. Materials and Chemicals. The LCD panels used in the experiments came from 14 in. Lenovo laptops. Besides, standard substances of acetic acid, phenol, 5-hydroxymethylfurfural, and lactic acid were used in the qualitative and quantitative analysis of the products. 2.2. Hydrogen Nuclear Magnetic Resonance (HNMR) Analysis. HNMR analysis was used to ascertain the proportion of each component by nuclear magnetic resonance spectroscopy (NMR, BRUCK, AVANCE III) at 60 °C. Polarizing film, CTA, TPP, and PVA were analyzed. Deuterated dimethyl sulfoxide (DMSO) was used as solvent. 2.3. Apparatus. Figure 2 presents a schematic diagram of the semibatch reactor. Compared with a batch reactor and a continuous reactor, a semibatch reactor has three merits: First, raw material has no need to be crushed into powder or dissolved in other solvents compared with a continuous reactor. Besides, compared with a batch reactor, products could be easily separated from the reaction system in the reaction process. Furthermore, using the semibatch reactor could avoid long periods of stopping of the products in the system. Therefore, it could reduce side reactions and secondary reactions. Before the reaction process, LCD panels were cut into narrow strips (10 mm × 50 mm) for suiting the reaction tube. In a typical run, about 13 g of samples which contained C


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Figure 3. HNMR spectrum of polarizing film, CTA, TPP, and PVA.

of CTA in polarizing film was calculated by the HNMR result and the molecular structure. yield (%) =

mass of acetic acid × 100 theoretical mass of acetic acid

organic conversion rate (%) mass of raw material − mass of residue = × 100 mass of raw organic material

(1)

(2)

3. RESULTS AND DISCUSSION 3.1. Hydrogen Nuclear Magnetic Resonance (HNMR) Analysis. The HNMR spectrum of polarizing film, CTA, TPP, and PVA, was shown in Figure 3. The peaks at about 2.5 and 3.3 ppm were attributed to the hydrogen of solvent DMSO; however, the specific peak of polarizing film shifted to the lower chemical shift. The peak around 2.0 ppm in polarizing film and CTA was associated with the hydrogen of acetyl in the glucose triacetate monomer of CTA. The peak around 7.3 ppm in polarizing film and TPP was assigned to the hydrogen of the benzene ring in TPP. The peak at about 1.5 ppm was attributed to the hydrogen of methylene in PVA. The peak area was calculated, and the molecular structure was compared. The mass proportion of each component in polarizing film was calculated as follows: CTA, 83.38%; TPP, 12.18%; PVA, 4.44%. 3.2. The Reaction Characteristic under Supercritical Condition. A yield comparison between subcritical and supercritical conditions was discussed for a better understanding of the reaction. Figure 4 presented the cumulative yield of acetic acid in different temperature phases at 16 and 23 MPa. It was obvious that the characteristics were quite different. The increasing of the yield of acetic acid was continuous at 16 MPa with 300−400 °C. However, the vast majority of acetic acid was generated within 360−380 °C at 23 MPa, which

Figure 4. Cumulative yield of acetic acid in different temperature phases at 16 and 23 MPa.

meant the reaction takes place almost instantaneously. Besides, it had been found that water flow velocity of the outlet abruptly increased at about 375 °C during the process. The supercritical point of water is 374 °C, 22.1 MPa, which indicates that the LCD panel reacts violently at the supercritical point of water. Meanwhile, for a visualized understanding of the reaction, distribution of products in different temperature phases at 16 and 23 MPa (the holding time of 400 °C was 5 min) analyzed by GC-MS is shown in Figure 5. The main products of the reaction were acetic acid, phenol, and 5-hydroxymethylfurfural (5-HMF). The results confirmed the reaction characteristics aforementioned: The reaction was continuous and stable within 300−400 °C at 16 MPa. Besides, GC-MS results of the residual liquid meant holding for 5 min might not be enough for 16 MPa. However, acetic acid was generated mainly within 350− 400 °C at 23 MPa, and no acetic acid or other products were D


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obtained in the residual liquid, which meant the reaction was complete under such conditions. 3.3. Effects of Temperature, Pressure, and Holding Time on Organic Conversion Rate. The relations between organic conversion rate and temperature and pressure as well as holding time were demonstrated in Figure 6. Effect of Temperature. The effect of temperature on the organic conversion rate was investigated in the range from 300 to 500 °C at 23 MPa for 5 min. It could be seen from Figure 6(a) that the organic conversion rate exceeded 95% at all temperatures. The organic conversion rate was increased with the temperature increasing. When the temperature reached 400 °C, the organic conversion rate reached 99.77%. The organic conversion rate nearly remained unchanged when the temperature was over 400 °C. Effect of Pressure. The effect of pressure on the organic conversion rate was investigated in the range from 10 to 30 MPa at 400 °C for 5 min. As shown in Figure 6(b), the organic conversion rate slightly decreased when the pressure increased from 10 to 16 MPa and increased notably when the pressure increased to 23 MPa. However, the organic conversion rate changed a little when the pressure increased to 30 MPa. As a matter of fact, spacing of molecules became smaller when the pressure rose, and this would hinder the intermolecular diffusion. This was the reason for a slight decrease of the organic conversion rate. However, it had been reported that cellulose could be dissolved in near and supercritical water,29 which meant CTA was soluble when the pressure rose to 23 MPa. Thus, a homogeneous atmosphere formed in supercritical water, and this resulted in an increase of the organic conversion rate. Effect of Holding Time. The effect of holding time on the organic conversion rate was investigated in the range from 0 to

Figure 5. Distribution of products in different temperature phases at (a) 16 MPa and (b) 23 MPa (In part (a) the holding time of 400 °C is 5 min.).

Figure 6. Relations between organic conversion rate and (a) temperature, (b) pressure, and (c) holding time. E


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Figure 7. Relations between yield of acetic acid and (a) temperature, (b) pressure, and (c) holding time.

30 min at 400 °C, 23 MPa. As shown in Figure 6(c), the effect of holding time on the organic conversion rate was quite small. 3.4. Effects of Temperature, Pressure, and Holding Time on Yield of Acetic Acid. The relations between yield of acetic acid and temperature and pressure as well as holding time are demonstrated in Figure 7. Effect of Temperature. The effect of temperature on the yield of acetic acid was investigated in the range from 300 to 500 °C at 23 MPa for 5 min. It could be seen from Figure 7(a) that the yield of acetic acid increased sharply from 44.86% at 300 °C to 77.70% at 400 °C and actually peaked at 400 °C. When the temperature was over 400 °C, the yield slowly decreased, which meant a higher temperature might result in the decomposition of the product. Effect of Pressure. The effect of pressure on the yield of acetic acid was investigated in the range from 10 to 30 MPa at 400 °C for 5 min. As shown in Figure 7(b), the variation tendency was similar to the organic conversion rate. The yield slightly decreased when the pressure increased from 10 to 16 MPa and increased when the pressure increased to 23 MPa and actually peaked at 23 MPa. When the pressure reached 30 MPa, the yield of acetic acid changed a little. The variation could be explained by the similar reason aforementioned. Spacing of molecules became smaller as the pressure rose, and this would hinder the intermolecular diffusion. This was the reason for a slight decrease of the yield. However, it had been reported that cellulose could be dissolved in supercritical water,29 and CTA was soluble when the pressure rose to 23 MPa. Thus, a homogeneous atmosphere formed in supercritical water, and this resulted in an increase of the yield of acetic acid. Effect of Holding Time. The effect of holding time on the yield of acetic acid was investigated in the range from 0 to 30 min at 400 °C, 23 MPa. As shown in Figure 7(c), the effect of

holding time on the yield was quite small; when the holding time was 5 min, the yield of acetic acid reached 78.23%. 3.5. Liquid Products Analysis. GC-MS was used to analyze the liquid products. The detailed data of the GC-MS results was shown in Table 1. Several conclusions could be drawn from the GC-MS results. First, acetic acid accounted for a large proportion of liquid product, and the peak area% was 66.254. Besides, phenol was the hydrolysis product of TPP and took up a peak area% of 20.072. Meanwhile, some compounds with furan rings were generated in the reaction. 5(Hydroxymethyl)furan-2-carbaldehyde (5-HMF) was a crucial intermediate of acetic acid forming and was discussed in the mechanism part. Furthermore, a few cyclic compounds as well as chain compounds with hydroxyl or carbonyl were detected in the liquid products. 3.6. Mechanism Analysis of Forming Acetic Acid. CTA is the ethyl esterification product of cellulose, and the ethyl ester bond could hydrolyze to acetic acid catalyzed by H+ or OH−. Therefore, acetic acid is mainly generated from CTA in this study. Thus far, recycling acetic acid from CTA has been rarely reported. However, conversion of cellulose into acetic acid and other value-added products under hydrothermal or supercritical conditions has been paid attention worldwide.14,25,27,28,30 Meanwhile, several research groups have proposed a reasonable mechanism.14,26 A reasonable and well-founded reaction mechanism is proposed based on the results of the experiments, sufficient theory foundations, and verified experiments in this study. 3.6.1. Mechanism of Forming Acetic Acid by Hydrolysis of Acetic Ester. The structure of CTA is quite complicated compared with cellulose, which results in multiple reactive sites for CTA. It has been reported that the cellulose could be hydrolyzed to glucose under sub/supercritical conditions, and the hydrolysis reaction is catalyzed by H+ which is provided by F


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Environmental Science & Technology Table 1. Main Components and Molecular Structure of Liquid Products Analyzed by GC-MS

supercritical water due to its high H+ and OH− ion concentration.31,32 Meanwhile, the ester linkages of CTA also could be hydrolyzed with H+ or OH− as catalysts. However, ester linkages are much easier to cleave compared to glycosidic bonds, which means hydrolysis of CTA to acetic acid and cellulose could happen directly without the transformation of CTA to glucose triacetate. Acetic acid and cellulose are generated by hydrolysis of CTA under sub/supercritical conditions. As is known to all, hydrolysis of ester can be catalyzed by acid or base, and supercritical water can boast abundant H+ and OH−. In other words, CTA can be hydrolyzed without an extra catalyst. Actually, the mechanisms of base- or acid-promoted hydrolysis of esters are confirmed by the isotope labeling method.33 The proposed mechanism through base-catalyzed hydrolyses is

demonstrated in Figure 8(a). The hydrolysis reaction follows the nucleophilic addition−elimination mechanism.33 An addition reaction proceeds by OH−, the nucleophile, attacking the carbon of the carbonyl group, and a tetrahedral intermediate is generated. Then, acetic acid and cellulose are generated through electron transformation, elimination, and proton transformation. Figure 8(b) describes the mechanism through acid-catalyzed hydrolyses. First of all, the carbonyl is protonated by H+ for enhancing the eletrophilicity of the carbonyl and followed by proton transformation and forming carbocation. After that, the oxygen from water attacks the carbocation as the nucleophile, and a tetrahedral intermediate is also generated. Then, acetic acid and cellulose are obtained through proton transformation and elimination. G


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Figure 8. Proposed mechanism for forming acetic acid and cellulose by hydrolysis of CTA through (a) base-catalyzed hydrolyses and (b) acidcatalyzed hydrolyses.

decarbonylation and oxidation.14,25−28 In pathway I (b), 5HMF is formed via isomerization and dehydration, followed by oxidation to generate acetic acid.25−28 In this study, trace amounts of glucose are detected by HPLC. Meanwhile, in pathway II, acetic acid could be obtained without LBAE transformation to fructose and also contains two secondary pathways. In pathway II (a), a coproduct, that is, glucose 1,2enediol, is formed via LBAE transformation.14,25,27 Then, glyceraldehyde is formed by cleavage of glucose 1,2-enediol, followed by forming lactic acid, which can generate acetic acid as path I (a).25,26 In pathway II (b), 5-HMF can be directly formed by dehydration of glucose and produce acetic acid by oxidation as in path I (b).14,25,27 Glyceraldehyde, lactic acid, and 5-HMF are the three crucial intermediates in the proposed mechanism. In this study, a small amount of lactic acid and 5-HMF was detected by HPLC and GC-MS, which could support the proposed mechanism. However, glyceraldehyde was not detected, which could probably be attributed to its instability. In addition, a certain amount of phenol, which is the hydrolysis product of TPP, was obtained in the liquid products.

3.6.2. Mechanism of Forming Acetic Acid from Cellulose. Most acetic acid is obtained by hydrolysis of acetic ester from CTA, and a mass of cellulose is generated, which could be hydrolyzed to glucose.21,22 In this study, trace amounts of glucose are detected by HPLC with a differential refractive index detector. It has been reported that acetic acid can be generated through a glucose pathway.14,25−27,30 Meanwhile, a verified experiment with glucose was performed under the same conditions as CTA, and the results confirm that glucose can produce a certain amount of acetic acid. The proposed mechanism for forming acetic acid from glucose is shown in Figure 9. Glucose could be obtained by the hydrolysis of cellulose. Open-chain glucose can produce acetic acid through two pathways in sub/supercritical water. In pathway I, an isomerization from glucose into fructose via Lobry de BruynAlberda van Ekenstein (LBAE) transformation happened, followed by two secondary pathways.28 In pathway I (a), fructose is converted into glyceraldehyde via a reverse aldol reaction, followed by isomerization and dehydrogenation to form lactic acid; lactic acid can generate acetic acid via H


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Figure 9. Proposed mechanism for forming acetic acid from cellulose.

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The mechanism for forming phenol was also proposed and was shown in the Supporting Information. Furthermore, simple assessment was taken to explore the costs and the revenues. Assume that 5 ton of waste LCD panels were treated by the present method, the equipment power was 50 kW. Depreciation cost of equipment and electric energy consumption as well as water consumption were considered. 410 kg of acetic acid could be obtained, and the profit was evaluated as about $183.45. The detailed calculation is shown in the Supporting Information. However, our study remained at the laboratory stage; more detailed estimation and assessment should be done before industrial application. The revenues have not factored in the cost of the transporting-waste, raw materials, or labor. Nonetheless, the Chinese government would offer some subsidies for recycling waste electrical and electronic equipment (WEEE). Meanwhile, in the indium recycling process, removing organic materials is one of the most important steps. In this study, clean glass substrates with ITO film were obtained, and the precious metal indium could be recycled from the glass substrates in the next steps. The revenues will be much higher when government subsidies and indium benefit were taken into account. Furthermore, recycling organic matter from waste LCD panels not only has economic benefits but also has more significant environmental benefits. In the present study, 99.77% of organic matters were removed from the waste LCD panels. Meanwhile, a yield of 78.23% for acetic acid was obtained at 400 °C, 23 MPa for 5 min. To sum up, this study proposed an environmentally friendly technology to recycle the organic matters before indium recovery and could obtain acetic acid in the recycling process without environmental pollution which could reduce the consumption of fossil energy by producing acetic acid. In a way, this study provides new opportunities for alternating fossilbased chemical products for sustainable development, converting “waste” into “fossil-based chemicals”.

ASSOCIATED CONTENT

* Supporting Information S

Figure showing FTIR spectrogram of (A) polarizing film and (B) carbon black of the residue; figure showing proposed mechanism for forming phenol from TPP; table showing the main composition of gaseous products analyzed by GC-MS; and calculations showing the Economic Evaluation. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.5b00104.

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AUTHOR INFORMATION

Corresponding Author

*Phone: 86 21 54747495. Fax: 86 21 54747495. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National High Technology Research and Development Program of China (863 program 2012AA063206) and the National Natural Science Foundation of China (51278293).

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REFERENCES

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Recycling Acetic Acid from Polarizing Film of Waste Liquid Crystal

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