Electrodialysis Process for the Recycling and Concentrating of

Article pubs.acs.org/IECR

Electrodialysis Process for the Recycling and Concentrating of Tetramethylammonium Hydroxide (TMAH) from Photoresist Developer Wastewater Yaoming Wang, Zenghui Zhang, Chenxiao Jiang, and Tongwen Xu* CAS Key Laboratory of Soft Matter Chemistry, Laboratory of Functional Membranes, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China ABSTRACT: A large amount of developer wastewater containing tetramethylammonium hydroxide (TMAH) is discharged from semiconductors and photoelectric industries. The electrodialysis technique was employed for the recovering and concentrating of TMAH from developer wastewater. The effect of current density on the recovery process was investigated by considering the stability of membranes and process cost. Results indicated that the optimal current density was chosen at 30 mA•cm−2. TMAH can be concentrated in the range of 7.45%−8.33%. The used membranes in the experiments were stable and suitable for this wastewater treatment. The total process cost was estimated to be 36.4 $/t without considering the profit of the recovered TMAH. Naturally, electrodialysis is a cost-effective and environmentally friendly technology for treating developer wastewater. high as ∼$200/t. Therefore, more economical and efficient techniques for treating developer wastewater should be explored in an environmentally friendly and economical manner to satisfy the increasing need of environment protection. It is more desirable to recover the valuable TMAH from developer wastewater plus a profit. According to the characteristics of developer wastewater, this wastewater is composed of TMAH (2.38% w/w), chelating organic agents ( 11). The high alkalinity of this developer wastewater will deeply decrease the lifespan of the membranes. After the ceramic membrane filtration process, the suspended solids were almost completely removed. Traditionally, activated carbon was one of the most commonly used decolorization materials,19 but in this case, the decolorization of this developer wastewater by using active carbon is not successful. For commercial secrets protection, the developer manufacturer does not give detailed information about the concentration and the composition of this developer.

Table 1. Main Characteristics of Membranes Used in the Experimentsa AEM CEM a

membranes

thickness (μm)

ion exchange capacity (mmol/g)

water ratio (%)

area resistance (Ω•cm2)

transport no. (%)

JAM-II-07 JCM-II-07

160−230 160−230

1.8−2.2 2.0−2.9

24−30 35−43

4−8 4−8

90−95 90−95

The data were collected from the product brochure provided by manufactures. 18357

dx.doi.org/10.1021/ie4023995 | Ind. Eng. Chem. Res. 2013, 52, 18356−18361

Industrial & Engineering Chemistry Research

Article

Figure 2. The effect of current density on the voltage and current drop of the electrodialysis stack.

Therefore, it is difficult to identify the chemical components of the colored matter in the wastewater. According to the rough description by the developer manufacturer and literature reports, it is estimated that these colored matters were composed of some kind of chelating metal. These matters cannot be removed by the activated carbon absorption process. 3.2. ED Process. Figure 2a shows the effect of initial current density on the treatment of developer wastewater. It is indicated that the voltage drops of the ED stack were increased with elapse of time and reached a plateau. This highest voltage value is the limit of the power supply. Meantime, the higher the current density is, the faster the voltage drop reaches a maximum value. This is common sense since the higher current density means higher driven force, but due to the limitation of the power supply (the maximum voltage supply is 60 V), the constant current mode was not maintained during the entire ED experiments. The operation mode of the ED stack was switched from constant current mode to constant voltage mode. Nevertheless, this does not restrict the evaluation the performance of the ED process. Figure 2b shows the variations of currents in the ED stack when the initial current densities are in the range of 20−50 mA·cm−2. It can be seen that the currents keep stable for a period of time and then decrease to a low value. This is consistent with the variation of voltage drop curves. TMAH will be easily dissociated into OH− ions and (CH3)4N− ions in an aqueous solution. The other impurities in the developer contribute the minority of the conduction of current in the ED process. The conductivity of the feed chamber increases sharply with the migration of OH− ions and (CH3)4N− ions into the concentrate chamber during the ED process. As a consequence, the currents drop from their initial set values. The required times for the voltage reaching the maximum 60 V are 105, 78, 35, and 21 min, at the initial current density of 20, 30, 40, and 50 mA·cm−2, respectively. It seems that it is more effective to treat developer wastewater by using ED at higher current density. Figure 3 shows the concentrations of recovered TMAH in the concentrate compartment for four kinds of current densities. The product TMAH concentration increases with the elapse of time. TMAH concentrations increase rapidly with increasing time in the initial period of experiment, and then the

Figure 3. The recovered TMAH concentration during the entire experiment period.

TMAH concentrations increase asymptotically and gradually approach to a constant value. This is ascribing to the decrease of current density when the ED stack voltage drop reaches the maximum value of the power supply. In the initial period of experiment, TMAH concentration nearly proportionally increases with time. In this time interval, the higher the current density is, the higher the concentration of TMAH will be. It is logically true that a higher current density results in an accelerated driving force, but the highest TMAH concentration appears at the current density of 30 mA•cm−2. It is indicated that a higher current density does not facilitate the recovery of the TMAH in this developer wastewater. There are two possible reasons to account for this phenomenon. On one hand, there is a water electro-osmosis phenomenon in the ED process. Electro-osmosis causes ions moving through an ion exchange membrane to drag water molecules from the feed chamber to the concentrate chamber. This electro-osmosis phenomenon becomes more pronounced with an increase in the current field. On the other hand, the osmotic pressure 18358



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difference between the feed and concentrate chamber becomes higher with the continuous migration of ions. Water molecules can be transported from the feed chamber into the concentrate chamber for this reason. These electro-osmosis and osmoticpressure-difference osmosis will increase the volume of the concentrate chamber, leading to a decrease in TMAH concentration. Nevertheless, the final TMAH concentration is in the range of 7.45%−8.33%, suggesting the high efficiency of the ED process for developer wastewater treatment. Figure 4 shows the demineralization rate and concentrate ratio of the ED process for developer wastewater treatment. It

chamber during the electrodialysis process. The reclaimed developer was reused by Hefei Maofeng Electronics Technology Co., Ltd. (developer supplier for BOE Technology Group Co., Ltd.) for the photoresist process and found to feature the same effect as a fresh commercial developer. This recovered TMAH solution can be directly reused for the photoresist process. 3.3. The Stability of Membranes. Due to the high alkalinity of the TMAH, the long-term stability of the membranes in this spent developer wastewater should be investigated. Figure 5 shows the variations of membranes dry

Figure 4. The demineralization rate and concentrate ratio of ED process for developer wastewater treatment.

Figure 5. The variation of membrane dry weights after immersion in a 25% TMAH solution.

weights after immersion in a 25% TMAH solution within 16 days. The weights of both the anion and cation exchange membranes fluctuate within a narrow range. This variation of membranes weight is caused by measurement error in the experiment. There is no visible morphology change after immersion in a 25% TMAH solution for 16 days. The transport numbers of the membranes were tested before and after the electrodialysis process. There is no difference between these two values. Moreover, there is no obviously decrement in the performance of electrodialysis process between the pristine membranes and the membranes used for dozens of times. For example, the demineralization rate and concentrate ratio of TMAH under current density of 30 mA cm−2 in the pristine membranes were about 93.7% and 3.50, respectively, compared with that of about 92.8% and 3.46 in the same membranes used for dozens of times under the same conditions. Considering the much higher alkalinity condition in the membrane stability experiment compared with the practical wastewater, it is concluded that these kinds of membranes are suitable for this developer wastewater treatment. 3.4. Process Economy. Estimation of the operating cost of ED for developer wastewater treatment is important to determine the economical feasibility of this process. The process cost is calculated according to the literature,20 and the result is listed in Table 3. This process cost is estimated under the optimal current density of 30 mA cm−2 as afore discussed. When the voltage drop of the ED stack reaches the limitation of power supply, the performance of the ED will decrease dramatically. Therefore, in a batch ED mode for developer wastewater treatment, the experiment can be terminated at this time. In fact, a high demineralization rate has been obtained at

is indicated that a maximum value is obtained at the current density of 30 mA cm−2. The explanation is the same as discussed above. The highest demineralization value is 93.7%, suggesting the most account of TMAH has been recovered from the developer wastewater. A higher demineralization value can be expected by alternating a more powerful direct current supply. TMAH concentration can be concentrated at 3.5 times of the initial concentration in the spent developer wastewater. It is necessary to mention that the recovered TMAH is a transparent solution and the colored matters in the feed chamber are not transported across the membranes. Table 2 indicates that most potassium ions and about half part of the sulfate ions are removed by the ED process. The other compositions of the developer wastewater are not changed significantly considering the volume change in the feed Table 2. Main Components of Developer Wastewater before and after the Electrodialysis Experiment item

before ED

after ED

K (g-K/L) Na (g-Na/L) Ca (mg-Ca/L) Mg (mg-Mg/L) Fe (mg-Fe/L) Cu (mg-Cu/L) Mn (mg-Mn/L) Ag (g-Ag/L) P (g-P/L) S (g-S/L)

2.50 0.31 22.20 23.5 44.8 5.40 0.60 0.07 0.16 2.43

0.15 0.36 18.50 22.7 12.9 7.90 0.70 0.13 0.19 1.28 18359



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Table 3. Estimation of the Cost of the ED Process parameters repeating units current density (mA/cm2) experiment time (min) effective membrane area (cm2) electrolyte (Na2SO4) concentration (mol/L) fluid flow speed (L/h) developer waster volume (L) energy consumption (KW•h/L) process capacity (L/year) electricity charge ($/kW·h−1) energy cost ($/L) membrane lifetime and amortization of the peripheral equipment (year) anion membrane price ($/m2) cation membrane price ($/m2) membrane cost ($) stack cost ($) peripheral equipment cost ($) total investment cost ($) amortization ($/year) interest ($/year) maintenance ($/year) total fixed cost ($/year) total fixed cost ($/L) total process cost ($/L)

Article

AUTHOR INFORMATION

Corresponding Author

ED process

*Phone: 86-551-63601587. Fax: 86-551-63601592. E-mail: [email protected].

4 30 78 70 0.3 22 1 0.0743 3840 0.2 0.0156 3

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research is supported in part by the National Natural Science Foundation of China (Nos. 21206154, 21206155, 21025626), the 6th China Postdoctoral Science Special Foundation (2013T60624), the Fundamental Research Funds for the Central Universities (2013M501058), and the National High Technology Research and Development Program 863 (No. 2012AA03A608).

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200 170 41.44 62.16 93.24 155.40 51.80 12.43 15.54 79.77 0.0208 0.0364

REFERENCES

(1) Templeton, M. K.; Szmanda, C. R.; Zampini, A. On the dissolution kinetics of positive photoresist: the secondary structure model. Proc. SPIE 1987, 771, 136. (2) Tabata, O.; Asahi, R.; Funabashi, K.; Sugiyama, S. Anisotropic etching of silicon in TMAH solution. Sens. Actuators, A 1992, 34, 51. (3) Lin, C. C.; Yang, C. C.; Ger, J.; Deng, J. F. Tetramethylammonium hydroxide poisoning: An emerging and potentially lifethreatening hazard in semi-conductor and photoelectric industries. Clin. Toxicol. 2008, 46, 595. (4) Wu, C. L.; Su, S. B.; Chen, J. L.; Lin, H. J.; Guo, H. R. Mortality from dermal exposure to tetramethylammonium hydroxide. J. Occup. Health 2008, 50, 99. (5) Lee, C. H.; Wang, C. L.; Lin, H. F.; Chai, C. Y.; Hong, M. Y.; Ho, C. K. Toxicity of tetramethylammonium hydroxide: Review of two fatal cases of dermal exposure and development of an animal model. Toxicol. Ind. Health 2011, 27, 497. (6) Lin, C. C.; Yang, C. C.; Ger, J.; Deng, J. F.; Hung, D. Z. Tetramethylammonium hydroxide poisoning. Clin. Toxicol. 2010, 48, 213. (7) Hirano, K.; Okamura, J.; Taira, T.; Sano, K.; Toyoda, A.; Ikeda, M. An efficient treatment technique for TMAH wastewater by catalytic oxidation. Trans. Semicond. Manuf. 2001, 14, 202. (8) Prahas, D.; Liu, J. C.; Ismadji, S.; Wang, M. J. Adsorption of tetramethylammonium hydroxide on activated carbon. J. Environ. Eng.ASCE 2012, 138, 232. (9) Kelleher, B. P.; Doyle, A. M.; O’Dwyer, T. F.; Hodnett, B. K. Preparation and use of a mesoporous silicate material for the removal of tetramethyl ammonium hydroxide (TMAH) from aqueous solution. J. Chem. Technol. Biotechnol. 2001, 76, 1216. (10) Lei, C. N.; Whang, L. M.; Chen, P. C. Biological treatment of thin-film transistor liquid crystal display (TFT-LCD) wastewater using aerobic and anoxic/oxic sequencing batch reactors. Chemosphere 2010, 81, 57. (11) Hu, T. H.; Whang, L. M.; Liu, P. W. G.; Hung, Y. C.; Chen, H. W.; Lin, L. B.; Chen, C. F.; Chen, S. K.; Hsu, S. F.; Shen, W.; Fu, R.; Hsu, R. Biological treatment of TMAH (tetra-methyl ammonium hydroxide) in a full-scale TFT-LCD wastewater treatment plant. Biores. Technol. 2012, 113, 303. (12) Lin, H. L.; Chen, B. K.; Hsia, H. P. et al. Use of two-stages biological processing in treating thin film transistor liquid crystal display wastewater of tetramethylammonium hydroxide. Sustainable Environ. Res. 2011, 21, 155. (13) Hu, T. H.; Whang, L. M.; Lei, C. N.; Chen, C. F.; Chiang, T. Y.; Lin, L. B.; Chen, H. W.; Liu, P. W. G.; Cheng, S. S. Evaluation of methanogenic treatment of TMAH (tetra-methyl ammonium hydroxide) in a full-scale TFT-LCD wastewater treatment process. Water Sci. Technol. 2010, 62, 403. (14) Hampton, D.; Zatman, L. J. The metabolism of tetramethylammonium chloride by bacterium 5H2. Biochem. Soc. Trans. 1973, 1, 667.

this moment. For example, the demineralization rate is about 88.7% at the appearance of maximum voltage drop of 78 min. The process cost was estimated at this time interval. The total process cost is estimated to be 0.0364 $•L−1. The energy consumption accounts for 43% of the total process cost. Considering the high price of the TMAH solution and the high cost for treating the developer wastewater, it is very costeffective and environmentally friendly to recycle developer wastewater treatment by using electrodialysis.

4. CONCLUSION An electrodialysis process was used for the recycling of developer wastewater. The ceramic filtration and activated carbon were performed for pretreatment of this developer wastewater. Results indicated that the suspended solids were almost completely removed after a pretreatment process. The influence of current density on the performance of the recovery process was investigated. The optimal current density was found at a current density of 30 mA cm−2 by considering electro-osmosis and osmotic-pressure-difference osmosis in the electrodialysis process. Meantime, it was indicated that the most amount of TMAH could be recovered from the spent developer wastewater with the recovery TMAH concentration in the range of 7.45%−8.33%. The membrane stability experiment indicated that the used membranes in the experiment were stable and suitable for this developer wastewater treatment. The total process cost was estimated to be 0.0364 $ L−1 with the energy consumption cost accounting for about 43% of the total process cost. In general, the ED showed that it can be used as a promising, economical, and environmental method to treat the spent developer wastewater. 18360



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(15) Chen, T. K.; Ni, C. H.; Chen, J. N. Nitrification-denitrification of opto-electronic industrial wastewater by anoxic/aerobic process. J. Environ. Sci. Health, Part A: Toxic/Hazard. Subst. Environ. Eng. 2003, 38, 2157. (16) Urakami, T.; Araki, H.; Kobayashi, H. Isolation and identification of tetramethylammonium-biodegrading bacteria. J. Ferment. Bioeng. 1990, 70, 41. (17) Feng, H. Z.; Huang, C. H.; Xu, T. W. Production of tetramethyl ammonium hydroxide using bipolar membrane electrodialysis. Ind. Eng. Chem. Res. 2008, 47, 7552. (18) Aggarwal, V.; Sunshine, I. Determination of sulfonylureas and metabolites by pyrolysis gas chromatography. Clin. Chem. 1974, 20/2, 200. (19) Hertzog, E. S.; Broderick, S. J. Activated carbon for sugar decolorization. Ind. Eng. Chem. Res. 1941, 33, 1192. (20) Wang, Y. M.; Wang, A. L.; Zang, X.; Xu, T. W. Simulation of electrodialysis with bipolar membranes: estimation of process performance and energy consumption. Ind. Eng. Chem. Res. 2011, 50, 13911.

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Electrodialysis Process for the Recycling and Concentrating of

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