- Email: [email protected]
Removal of dimethylsulfide by adsorption on ion-exchanged zeolites
Applied Catalysis B: Environmental 93 (2010) 363–367
Contents lists available at ScienceDirect
Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb
Removal of dimethylsulfide by adsorption on ion-exchanged zeolites Chien-Liang Hwang a,b,*, Nyan-Hwa Tai a a b
Department of Materials Science and Engineering, National Tsing Hua University, Taiwan Material and Chemical Research Laboratories, ITRI, No. 321, Kuang Fu Rd., Sec. 2, Hsinchu City 300, Taiwan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 18 December 2008 Received in revised form 1 October 2009 Accepted 2 October 2009 Available online 17 October 2009
Removal of low-concentration sulfide in clean rooms is important in the semiconductor industry. In dry conditions, silver–manganese exchanged Y zeolite (Ag–Mn/Na-Y) has high removal efficiency and high saturation adsorption capacity towards dimethylsulfide (DMS). However, the removal efficiency of DMS on Ag–Mn/Na-Y decreases with increasing water concentration in inlet gas at room temperature and normal pressure. In high humidity conditions, the removal efficiency and saturation adsorption capacity of DMS is high for silver–manganese exchanged ZSM zeolite (Ag–Mn/ZSM-5). In this paper, the influence of water concentration on the removal efficiency of DMS on Ag–Mn/zeolites was examined. The variations of functional group detected in FT-IR spectroscopy and temperature programmed desorption (TPD) confirm that water molecules influence the ability of DMS adsorption by Ag–Mn/zeolites. Crown Copyright ß 2009 Published by Elsevier B.V. All rights reserved.
Keywords: Dimethylsulfide Desulfurization Relative humidity Adsorption Ion-exchanged zeolite
1. Introduction Dimethylsulfide (DMS), an odor chemical with very low threshold concentration (0.0004 ppmv), can be produced by the reduction of dimethy sulfoxide (DMSO) in nature, where DMSO is a byproduct of algal growth [1,2]. DMSO has almost no odor, no significant harm to health, and high solubility in water. DMSO is the main solvent in the stripper agent used by the semiconductor and the display industrials. Most of the used stripper agents were recovered by cooling absorption and the residual stripper after the stripping process was channeled to the wastewater system. Under anoxic conditions in the wastewater treatment process, DMSO is reduced to DMS and dimethyl disulfide (DMDS). In semiconductor industrials, the exhausted gas containing DMS is often purified through filters before being channeled into clean rooms. However, it is difficult to remove DMS by the filters that are commercially available. When DMS is present in the clean room, the H2S sensor can be easily set off, leading to a serious and undesirable shutdown. The approaches to remove sulfide include adsorption [3,4], absorption [5], catalytic oxidation [6–8], plasma destruction [9], and advanced oxidation [10]; the aforementioned methods, except adsorption and absorption, are unsuitable for eliminating sulfide compounds due to complex operating processes or requirement of
* Corresponding author at: Material and Chemical Research Laboratories, ITRI, No. 321, Kuang Fu Rd., Sec. 2, Hsinchu City 300, Taiwan. Tel.: +886 3 5732977; fax: +886 3 5732346. E-mail address: [email protected] (C.-L. Hwang).
large space. However, the removal efficiency of absorption is low under low sulfide concentration conditions; thus, adsorption is a proper approach for removing sulfide. Zeolites are often used as catalytic supports and adsorbents to eliminate pollutants in the gas stream, due to the unique structure and hydrophilicity character. Wakita et al. [11] used Na-Y, Na-X, Ca-X, H-b, and H-ZSM-5 as adsorbents to remove DMS and tbutylmercaptan (TBM). They studied the phenomena when zeolites with different structures adsorbed DMS and TBM. However, the initial removal efficiency and the saturation adsorption capacities of DMS on the adsorbents addressed above are too low to be used in the filtration system of a clean room. Satokawa et al. [12] used Ag/Na-Y to adsorb DMS and they found that the capacities of the adsorbents increased with the silver contents in the adsorbents. By adding a trace of water, Satokawa et al. examined the effect of water molecules on the removal efficiency of DMS on Ag/Na-Y. However, the amount of added water (1000 ppm, 6.4 101 g/kg dry air) is much lower than that exists in clean rooms, which is about 10 g/kg dry air. Therefore, the influences of water concentration on the removal efficiency and the saturation adsorption capacity of DMS on the ion-exchanged zeolite in high humidity remain unclear. In the presented work, we studied the capacity of DMS on Ag– Mn/zeolites in low relative humidity (<2%) and the removal efficiency of DMS on Ag–Mn/zeolites in various relative humidity conditions at room temperature. Ag–Mn/ZSM-5 showed excellent removal efficiency of DMS in high relative humidity (60%) at room temperature. The effect of water molecules on the adsorption of DMS on Ag–Mn/zeolites was also examined.
0926-3373/$ – see front matter . Crown Copyright ß 2009 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2009.10.009
C.-L. Hwang, N.-H. Tai / Applied Catalysis B: Environmental 93 (2010) 363–367
364
Table 1 The weight percent and the degree of exchange of the metal ions in the zeolites. Zeolites
Ag–Mn/Na-Y Ag–Mn/HY Ag–Mn/ZSM-5
The weight percent of metal ions in zeolites
The degree of exchange of the metal ions (wt %)
Ag
Mn
Ag
Mn
4.30 0.64 1.24
2.32 0.95 0.21
20.5 11.9 36.9 Under-exchanged
19.5 33.8 12.1 Under-exchanged
2. Experiment
3. Results and discussion
2.1. Preparation of adsorbents
3.1. Adsorption of DMS on adsorbents in dry condition
Na-Y (CBV-100, SiO2/Al2O3 = 5.1), H-Y (CBV-720, SiO2/ Al2O3 = 30), and NH4+-ZSM-5 (CBV-5524G, SiO2/Al2O3 = 50) purchased from Zeolyst Corp. were used as received. Ag–Mn/Na-Y, Ag– Mn/H-Y, and Ag–Mn/ZSM-5 were prepared as follows: the asreceived zeolite (20 g) was mixed with water (120 ml at 50 8C) under vigorous stirring, and 15 ml of 0.55 M AgNO3 aqueous solution was added dropwised into the suspension and stirred for 2 h at 50 8C. After filtration and washing with deionized water, the cake-like mixture was re-dispersed in deionized water at 50 8C, and 20 ml of 0.47 M Mn(CH3COO)2 aqueous solution was poured dropwised following by stirring for 2 h. The color of solution changed from white to pale gray after stirring. After filtration and rinsing with deionized water, the mixture was dried at 80 8C followed by calcinations at 420 8C for 3 h. After pelletizing, crushing, and sieving (16–30 mesh), the as-prepared adsorbents were ready for use. The weight percent of Ag in Ag–Mn/Na-Y, Ag– Mn/H-Y, and Ag–Mn/ZSM-5 were 4.30, 0.64, and 1.24%, respectively, and the weight percent of Mn were 2.32, 0.95, and 0.21%, respectively. The weight percent and the degree of exchange of the metal ions in the zeolites are presented in Table 1.
Fig. 1 shows the adsorption curves for 10 ppm DMS/air on Na-Y, H-Y, and NH4+-ZSM-5 in dry conditions (RH < 2%) at room temperature and atmosphere pressure. The ratio of C/C0 represents the concentration ratio of DMS in the outlet and the inlet. The initial removal efficiency of DMS on Na-Y was over 99% and the saturation adsorption capacity of DMS was 4.7 wt% (0.8 mmol/g). The initial removal efficiencies of DMS on H-Y and NH4+-ZSM-5 were 93 and 97%, respectively; and the saturation adsorption capacities of DMS on H-Y and NH4+-ZSM-5 were 3.3 and 3.0 wt%, respectively. Na-Y performs better than H-Y and NH4+-ZSM-5 in the initial removal efficiency and in the saturation adsorption capacity of DMS. Garcia and Johannes [13] explored the adsorption mechanism of ZSM-5 and found that light thiols were adsorbed on cations (Na+ or Al3+). Therefore, for the same type of zeolite, the saturation adsorption capacity of DMS on the zeolite with low ratio of SiO2/Al2O3 is higher than that with higher ratio of SiO2/Al2O3. The adsorption curves of 10 ppm DMS/air on Ag–Mn/zeolites in dry conditions are illustrated in Fig. 2. The initial removal efficiency of DMS on Ag–Mn/H-Y and Ag–Mn/ZSM-5 reached to 99%. The result revealed that the exchanged ions (Ag+ and Mn2+) were more efficient than Na+ and Al3+ in adsorbing DMS [12]. The saturation adsorption capacities of DMS on Ag–Mn/Na-Y, Ag–Mn/ H-Y, and Ag–Mn/ZSM-5 were 10.9, 2.8, and 4.2 wt%, respectively. The saturation adsorption capacities of DMS on Ag–Mn/Na-Y and Ag–Mn/ZSM-5 were higher than the original zeolites, whereas the saturation adsorption capacity of DMS on Ag–Mn/H-Y was lower than the original zeolite.
2.2. Adsorption and purge methods The adsorption and purge tests were proceeded in a fixed-bed glass reactor (11.5 mm I.D.), and the volume of the absorbent was 1 cm3 (0.36–0.47 g) and the temperature and the pressure were controlled at 25 8C and 1 atm, respectively. The DMS/air was generated by diluting 2071 ppm DMS/N2 gas with air to 10 ppm. The flow rate and the superficial velocity were kept at 3 L/min and 0.48 m/s, respectively. The water concentration of the tested gas was adjusted by bubbling part of the gas through water. The concentration of DMS in the inlet and the outlet gases was analyzed by photo-ionization detector (PID, RAE System PGM7240). The lower detection limit for DMS is 1 ppb. 2.3. Characterization of adsorbent The samples before and after DMS adsorption were analyzed by diffuse reflection spectroscopy (HORIBA FT-730). The range of scanned frequency was 400–4000 cm1 and the resolution of the infrared spectra was 4 cm1. The samples were heated to 150 8C for 15 h in air and cooled to room temperature in a desiccator. Temperature programmed desorption (TPD) was carried out by an automatic temperature programmed desorption apparatus (Altamira AMI-1) equipped with a quadrupole mass detector (Thermo VG ProLab). Samples (0.3 g) were placed in a U type quartz tube. The program of TPD began with a He (30 ml/min) flush at 36 8C for 60 min and then the temperature was increased to 500 8C by the rate of 10 8C/min and held at 500 8C for 10 min. The ionic intensities of mass-to-charge ratio (m/e) equal to 15, 18, 34, and 62 in the desorbed gas were analyzed by the mass spectrometer.
3.2. Adsorption of DMS under various relative humidity condition Fig. 3 shows the removal efficiencies of 1.5 ppm DMS/air (C0) on Ag–Mn/Na-Y under various relative humidities and Ag–Mn/ZSM-5 at RH = 60% at room temperature. Curve (a) depicts that the removal efficiency of Ag–Mn/Na-Y is over 99% at RH = 20% but decreases rapidly when the RH of the gas in the inlet is adjusted to 60%. The DMS concentration of the gas in the outlet increased abruptly to 3.2 times of C0, as shown in curve (b), which was higher than that of the inlet gas. The DMS concentration in the outlet gradually decreased to 0.4 times of C0 at RH = 60%. The removal efficiency of Ag–Mn/Na-Y gradually increased with the decrease of RH, as shown in curves (c) and (d), and reached 99% at RH = 20%, as depicted in curve (a). The curve (f) in Fig. 3 represents the removal efficiency of DMS on Ag–Mn/ZSM-5 at RH = 60%. The removal efficiency of the adsorbent was preserved at 99% during the test. The results for Ag– Mn/zeolites adsorbed DMS at various relative humidities revealed that Ag–Mn/Na-Y is sensitive to water molecules and Ag–Mn/ZSM5 has excellent resistance to water molecules. The competitive adsorption between water and hydrocarbon is familiar and is depending on the nature of hydrocarbon and catalyst [14]. Abdullah et al. investigated the competitive
C.-L. Hwang, N.-H. Tai / Applied Catalysis B: Environmental 93 (2010) 363–367
Fig. 1. Adsorption curves of 10 ppm DMS on (a) Na-Y, (b) H-Y, and (c) NH4+-ZSM-5 in dry conditions with RH < 2% at room temperature.
365
Fig. 4. IR spectra of (a) NH4+-ZSM-5 after adsorption of DMS, (b) Ag–Mn/ZSM-5 after adsorption of DMS, and (c) Ag–Mn/ZSM-5 after adsorption of DMS and then was purged by RH = 60% air for 2 h at room temperature.
The competitive adsorption between water and DMS was obvious in Ag–Mn/Na-Y when the RH was over 20% at room temperature (4.0 g water/kg dry air). It was assumed that the water clusters located in the channel and framework block the diffusion of DMS to metal ions located on site II in Ag–Mn/Na-Y, as a result, lower the removal efficiency of the adsorbent. Moreover, the water molecules probably replaced the adsorbed DMS molecules, which leaded to the concentration of DMS in the outlet is higher than that in the inlet under high concentration of water molecule. 3.3. IR spectra of adsorbents
Fig. 2. Adsorption curves of 10 ppm DMS on Ag–Mn/zeolites in dry conditions with RH < 2% at room temperature.
adsorption between water and hydrocarbon in the study of catalytic combustion of ethyl acetate and benzene in an air stream over Cr-ZSM-5 catalyst [15]. Their study showed that water molecules aggregate to water clusters and block the internal diffusion path of hydrocarbon molecules when the water concentration of the inlet gas reaches 9000 ppm (5.6 g water/kg dry air). Besides, Coatenoble and Maes studied the distribution of silver in Ag/Na-Y by the crystallography, and they found that the silver ions in Ag/Na-Y are located at sites I, I0 , II and delocalized sites. Site II located in channels and cavities is the favored locations of Ag+ in Na-Y for the adsorption of sulfur compounds [16].
Fig. 4 shows the IR spectra of three zeolites over the region of C– H stretching vibrations (2800–3010 cm1). After DMS adsorption, NH4+-ZSM-5 showed absorption bands at 2869 and 2931 cm1, as shown in curve (a) in Fig. 4. These absorption bands were assigned to the C–H stretching vibrations of DMS which adsorbed by NH4+ZSM-5. The IR spectrum of Ag–Mn/ZSM-5 after DMS adsorption was different from that of NH4+-ZSM-5. The IR spectrum of Ag–Mn/ ZSM-5 after DMS adsorption depicted absorption band located at 2935 cm1, as shown in curve (b) of Fig. 4. The absorption band was assigned to the C–H stretching vibrations of DMS adsorbed by exchanged metal ions in Ag–Mn/ZSM-5. The curve (c) in Fig. 4 was the IR spectrum of Ag–Mn/ZSM-5 after adsorption of DMS and then was purged by RH = 60% air for 2 h at room temperature. The absorption band located at 2935 cm1 still appeared after purge of which illustrated that the adsorbed DMS on exchanged metal ions (Ag+ or Mn2+) in Ag–Mn/ZSM-5 was not removed. 3.4. Characterization of DMS adsorbed on Ag–Mn/Na-Y
Fig. 3. DMS removal efficiency of Ag–Mn/Na-Y at RH (a) 20%, (b) 60%, (c) 46%, (d) 30% and (e) <2% and Ag–Mn/ZSM-5 at (f) RH = 60% at room temperature.
Fig. 5 shows the TPD profiles for DMS on Ag–Mn/Na-Y after DMS adsorption. The fragments of m/e = 15, 34, and 62 were assigned to CH3, H2S, and (CH3)2S, respectively. The TPD profiles of m/e = 15, 34, and 62 were observed at temperatures ranging from 80 to 450 8C. The TPD profile of m/e = 62 showed two peaks, and the temperature ranges of the first and the second peaks were 80–200 and 250–450 8C, respectively. The second peak was accompanied by a shoulder on the high temperature side. The temperature range of the first peak agreed with that of Na-Y after adsorption in DMS/ N2 reported by Wakita et al. [11]. Compared with the results obtained by Satokawa et al. [12], the temperature range of the second peak shifted to high temperature side. The first and the second peaks were regarded as cations (Na+ or Al3+) and exchanged metal ions on the active sites of adsorbing DMS, respectively.
366
C.-L. Hwang, N.-H. Tai / Applied Catalysis B: Environmental 93 (2010) 363–367
Fig. 5. TPD profiles of the Ag–Mn/Na-Y after adsorption of DMS.
Fig. 7. TPD profiles and the ratio curve of m/e = 15 and m/e = 62 of the Ag–Mn/ZSM-5 after adsorption of DMS.
Fig. 6. TPD profiles of m/e = 62 on the Ag–Mn/Na-Y after adsorption of DMS (a) before purging, (b) subjected to purge for 6 min, and (c) subjected to purge for 2 h by RH = 60% air at room temperature.
Fig. 8. TPD profiles of m/e = 62 on the Ag–Mn/ZSM-5 after adsorption of DMS (a) before purging, (b) subjected to purge for 6 min, and (c) subjected to purge for 2 h by RH = 60% air at room temperature.
After DMS adsorption, Ag–Mn/Na-Y was purged by air with RH = 60% at room temperature for 6 min and 2 h. Curve (a) in Fig. 6 represents the TPD curve of the Ag–Mn/Na-Y sample before purge. Curves (b) and (c) in Fig. 6 are the TPD curves of the purged samples. Curve (b) in Fig. 6 shows that only one peak is presented at 380 8C and the intensity of the peak is lower than that of the peak in curve (a). The result indicated that most of the DMS on cation (Na+ or Al3+) sites and a part of the DMS on exchanged metal ions active sites were removed from Ag–Mn/Na-Y after purging for 6 min. After purge for 2 h, the TPD curve, as depicted in curve (c), was almost linear, indicating most of the DMS on Ag–Mn/Na-Y were removed no matter where the active sites were located. The cation exchanged Y zeolite presented a strong adsorption capability to water. The water molecules adsorb on the hydrophilic sites and gradually form a monolayer on the walls of supercages in cation exchanged Y zeolite by hydrogen bonds [17]. The adsorbed DMS molecules on Ag–Mn/Na-Y are replaced by water molecules and are carried away by air. The fact that water molecules replace the DMS molecules on Ag–Mn/Na-Y can be applied in the in situ regeneration of the adsorbent.
The desorption temperature of the third peak of m/e = 62 on Ag– Mn/ZSM-5 is ranging from 310 to 480 8C, which is higher than that of Ag–Mn/Na-Y. The result illustrates that the adsorption strength of DMS on Ag–Mn/ZSM-5 is much stronger than that on Ag–Mn/Na-Y. The TPD peaks of m/e = 62 were attributed to desorption of the whole DMS molecules and the TPD peaks of m/e = 15 were attributed to desorption of the DMS fragment. Based on the mass spectrum of DMS, the ratio of ionic intensity of m/e = 15 and m/ e = 62 (15/62) is 0.22. As shown in Fig. 7, the ratio is between 0.1 and 0.5 in the temperature ranging from 100 to 420 8C, and then increases abruptly and reaches a maximum of 6.4 at 480 8C. Because the ionic intensity of m/e = 62 is low but the ionic intensity of m/e = 15 is still high at 480 8C. Besides, the ionic intensity of m/e = 62 was below 1 1010 Torr at 500 8C, while the ionic intensities of m/e = 15 and m/e = 34 were preserved at 1–4 1010 Torr. Satokawa et al. observed significant increase in the fragment (m/e = 34) of TBM in TPD when TBM was adsorbed on Ag/Na-Y in TBM/N2 [12]. They concluded that it is attributed to the decomposition of silver sulfide clusters formed on Ag/Na-Y after adsorption in TBM/N2. However, it is still unclear whether the species of m/e = 34 is formed during the adsorption process or TPD test. The fragments of m/e = 15 and m/e = 34 of DMS were unexpectedly increased in the TPD after the adsorption of DMS on Ag–Mn/ZSM-5 between 440 and 500 8C. This is due to the decomposition of DMS adsorbed on Ag–Mn/ZSM-5. The result indicates that the desorbing behavior of DMS on Ag–Mn/ZSM-5 is different from that on Ag–Mn/Na-Y at high temperature [12,18].
3.5. Characterization of DMS adsorbed on Ag–Mn/ZSM-5 After DMS adsorption, the TPD profiles of DMS on Ag–Mn/ ZSM-5 are very dissimilar to that of Ag–Mn/Na-Y, as shown in Fig. 7. The TPD profile of m/e = 62 shows three desorbed peaks at 120, 250 and 440 8C, indicating Ag–Mn/ZSM-5 has three or more active sites in adsorbing DMS. Most of the DMS molecules were desorbed above 300 8C, which imply the exchanged metal ions were the main active sites on Ag–Mn/ZSM-5 for adsorbing DMS.
C.-L. Hwang, N.-H. Tai / Applied Catalysis B: Environmental 93 (2010) 363–367
After DMS adsorption, Ag–Mn/ZSM-5 was purged by the air with RH = 60% at room temperature for 6 min (curve (b)) and 2 h (curve (c)). Fig. 8 shows the TPD profiles of Ag–Mn/ZSM-5 after DMS adsorption before and after purges. The ionic intensity of all desorption peaks decrease after purge for 6 min. The peak at 120 8C almost disappears but the peaks at 250 and 440 8C show slightly decreases. Compared with curves (b) and (c), the peak at 250 8C is kept unchanged but the peak at 440 8C shows slightly decrease. A detailed study of the adsorption of aromatic hydrocarbons in Ag+-exchanged zeolites was carried out using FT-IR spectroscope [19]. The study shows that cation hydration is a critical factor to determine the adsorption of hydrocarbon molecules and the peculiarity of Ag+ in ZSM-5 for trapping hydrocarbon is due to the resistance of Ag+ to water molecules. As depicted in the TPD result, most of the DMS molecules that coordinated with Na+ or Al3+ in Ag–Mn/ZSM-5 were removed during the purge process. Thus, the cation hydration affected the adsorption of DMS on Ag–Mn/ZSM-5 is obvious. However, a few DMS molecules that coordinated with the exchanged metal ions in Ag–Mn/ZSM-5 were removed during the purge process, therefore, it is concluded that the exchanged metal ions in Ag–Mn/ZSM-5 has an unique resistance to water molecules in adsorbing DMS molecules. 4. Conclusion The water concentration of the gas at the inlet influences significantly the initial adsorption efficiency of DMS on Ag–Mn/NaY. The removal efficiency of Ag–Mn/Na-Y drops abruptly when the relative humidity is over 20% at room temperature and decreases with an increase in water concentration of the gas at inlet. The adsorption capacity of DMS on Ag–Mn/ZSM-5 is lower than that on Ag–Mn/Na-Y but the former shows unique resistance to water molecules for adsorbing DMS molecules. The removal efficiency of DMS on Ag–Mn/ZSM-5 is still over 99% when the relative humidity of the gas at inlet reached 60% at room temperature. Based on TPD profiles, it shows most of DMS molecules that were coordinated with metal cations in Ag–Mn/Na-Y were replaced by the water molecules after the purge process in RH = 60% at room temperature. The DMS molecules coordinated with Na+ or Al3+ in Ag–Mn/ZSM-5 were replaced by the water molecules but a part of the DMS molecules were still adsorbed on the exchanged metal ions in Ag–Mn/ZSM-5 after the purge process
367
in RH = 60% at room temperature. The difference that Ag–Mn/ZSM5 and Ag–Mn/Na-Y adsorbed DMS in the presence of water might be due to that the adsorption of DMS with the exchanged metal ions in Ag–Mn/ZSM-5 is stronger than that in Ag–Mn/Na-Y or due to that the Ag–Mn/ZSM-5 is less hydrophilic than Ag–Mn/Na-Y. The property that Ag–Mn/ZSM-5 has a unique resistance to water molecules in adsorbing DMS molecules is important when the adsorbent is applied in the filtration system in the semiconductor industry. Acknowledgement Special thanks are due to Dr. Wu and Dr. Hwung of ITRI for reading the manuscript and making several helpful suggestions. References [1] D. Glindemann, J. Novak, J. Witherspoon, Environmental Science & Technology 40 (2006) 202. [2] S.H. Lin, C.S. Chang, Journal of the Chinese Institute of Chemical Engineers 37 (2006) 527. [3] L.M. Le Leuch, A. Subrenat, P. Le Cloirec, Langmuir 19 (2003) 10869. [4] L.M. Le Leuch, A. Subrenat, P. Le Cloirec, Environmental Technology 26 (2005) 1243. [5] A. Couvert, I. Charron, A. Laplanchea, C. Rennerb, L. Patriab, B. Requiemec, Chemical Engineering Science 61 (2006) 7240. [6] G. Ok, Y. Hanai, T. Katou, Chemosphere 26 (1993) 2167. [7] D. Pope, D.S. Walker, R.L. Moss, Journal of Catalysis 47 (1977) 33. [8] J.A. Rossin, Industrial & Engineering Chemistry Research 28 (1989) 1562. [9] M. Okubo, H. Kametaka, K. Yoshida, T. Yamamoto, Japanese Journal of Applied Physics Part 1-Regular Papers Brief Communications & Review Papers 46 (2007) 5288. [10] N. Lesauze, A. Laplanche, G. Martin, H. Paillard, Ozone-Science & Engineering 13 (1991) 331. [11] H. Wakita, Y. Tachibana, M. Hosaka, Microporous and Mesoporous Materials 46 (2001) 237. [12] S. Satokawa, Y. Kobayashi, H. Fujiki, Applied Catalysis B: Environmental 56 (2005) 51. [13] C.L. Garcia, A.L. Johannes, Journal of Physical Chemistry 95 (1991) 10729. [14] K.S. Song, D. Klvana, J. Kirchnerova, Applied Catalysis A 213 (2001) 113. [15] A.Z. Abdullah, M.Z. Bakar, S. Bhatia, Industrial & Engineering Chemistry Research 42 (2003) 6059. [16] M. Coatenoble, A. Maes, Journal of the Chemical Society-Faraday Transactions 74 (1978) 131. [17] J.C. Moı¨se, J.P. Bellat, A. Me´thivier, Microporous and Mesoporous Materials 46 (2001) 91. [18] M. Ziolek, M. Sugioka, Research on Chemical Intermediates 26 (2000) 385. [19] X.S. Liu, K.L. Jordan, A.A. Dmitrii, J.F. Robert, Applied Catalysis B: Environmental 35 (2001) 125.
Contents lists available at ScienceDirect
Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb
Removal of dimethylsulfide by adsorption on ion-exchanged zeolites Chien-Liang Hwang a,b,*, Nyan-Hwa Tai a a b
Department of Materials Science and Engineering, National Tsing Hua University, Taiwan Material and Chemical Research Laboratories, ITRI, No. 321, Kuang Fu Rd., Sec. 2, Hsinchu City 300, Taiwan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 18 December 2008 Received in revised form 1 October 2009 Accepted 2 October 2009 Available online 17 October 2009
Removal of low-concentration sulfide in clean rooms is important in the semiconductor industry. In dry conditions, silver–manganese exchanged Y zeolite (Ag–Mn/Na-Y) has high removal efficiency and high saturation adsorption capacity towards dimethylsulfide (DMS). However, the removal efficiency of DMS on Ag–Mn/Na-Y decreases with increasing water concentration in inlet gas at room temperature and normal pressure. In high humidity conditions, the removal efficiency and saturation adsorption capacity of DMS is high for silver–manganese exchanged ZSM zeolite (Ag–Mn/ZSM-5). In this paper, the influence of water concentration on the removal efficiency of DMS on Ag–Mn/zeolites was examined. The variations of functional group detected in FT-IR spectroscopy and temperature programmed desorption (TPD) confirm that water molecules influence the ability of DMS adsorption by Ag–Mn/zeolites. Crown Copyright ß 2009 Published by Elsevier B.V. All rights reserved.
Keywords: Dimethylsulfide Desulfurization Relative humidity Adsorption Ion-exchanged zeolite
1. Introduction Dimethylsulfide (DMS), an odor chemical with very low threshold concentration (0.0004 ppmv), can be produced by the reduction of dimethy sulfoxide (DMSO) in nature, where DMSO is a byproduct of algal growth [1,2]. DMSO has almost no odor, no significant harm to health, and high solubility in water. DMSO is the main solvent in the stripper agent used by the semiconductor and the display industrials. Most of the used stripper agents were recovered by cooling absorption and the residual stripper after the stripping process was channeled to the wastewater system. Under anoxic conditions in the wastewater treatment process, DMSO is reduced to DMS and dimethyl disulfide (DMDS). In semiconductor industrials, the exhausted gas containing DMS is often purified through filters before being channeled into clean rooms. However, it is difficult to remove DMS by the filters that are commercially available. When DMS is present in the clean room, the H2S sensor can be easily set off, leading to a serious and undesirable shutdown. The approaches to remove sulfide include adsorption [3,4], absorption [5], catalytic oxidation [6–8], plasma destruction [9], and advanced oxidation [10]; the aforementioned methods, except adsorption and absorption, are unsuitable for eliminating sulfide compounds due to complex operating processes or requirement of
* Corresponding author at: Material and Chemical Research Laboratories, ITRI, No. 321, Kuang Fu Rd., Sec. 2, Hsinchu City 300, Taiwan. Tel.: +886 3 5732977; fax: +886 3 5732346. E-mail address: [email protected] (C.-L. Hwang).
large space. However, the removal efficiency of absorption is low under low sulfide concentration conditions; thus, adsorption is a proper approach for removing sulfide. Zeolites are often used as catalytic supports and adsorbents to eliminate pollutants in the gas stream, due to the unique structure and hydrophilicity character. Wakita et al. [11] used Na-Y, Na-X, Ca-X, H-b, and H-ZSM-5 as adsorbents to remove DMS and tbutylmercaptan (TBM). They studied the phenomena when zeolites with different structures adsorbed DMS and TBM. However, the initial removal efficiency and the saturation adsorption capacities of DMS on the adsorbents addressed above are too low to be used in the filtration system of a clean room. Satokawa et al. [12] used Ag/Na-Y to adsorb DMS and they found that the capacities of the adsorbents increased with the silver contents in the adsorbents. By adding a trace of water, Satokawa et al. examined the effect of water molecules on the removal efficiency of DMS on Ag/Na-Y. However, the amount of added water (1000 ppm, 6.4 101 g/kg dry air) is much lower than that exists in clean rooms, which is about 10 g/kg dry air. Therefore, the influences of water concentration on the removal efficiency and the saturation adsorption capacity of DMS on the ion-exchanged zeolite in high humidity remain unclear. In the presented work, we studied the capacity of DMS on Ag– Mn/zeolites in low relative humidity (<2%) and the removal efficiency of DMS on Ag–Mn/zeolites in various relative humidity conditions at room temperature. Ag–Mn/ZSM-5 showed excellent removal efficiency of DMS in high relative humidity (60%) at room temperature. The effect of water molecules on the adsorption of DMS on Ag–Mn/zeolites was also examined.
0926-3373/$ – see front matter . Crown Copyright ß 2009 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2009.10.009
C.-L. Hwang, N.-H. Tai / Applied Catalysis B: Environmental 93 (2010) 363–367
364
Table 1 The weight percent and the degree of exchange of the metal ions in the zeolites. Zeolites
Ag–Mn/Na-Y Ag–Mn/HY Ag–Mn/ZSM-5
The weight percent of metal ions in zeolites
The degree of exchange of the metal ions (wt %)
Ag
Mn
Ag
Mn
4.30 0.64 1.24
2.32 0.95 0.21
20.5 11.9 36.9 Under-exchanged
19.5 33.8 12.1 Under-exchanged
2. Experiment
3. Results and discussion
2.1. Preparation of adsorbents
3.1. Adsorption of DMS on adsorbents in dry condition
Na-Y (CBV-100, SiO2/Al2O3 = 5.1), H-Y (CBV-720, SiO2/ Al2O3 = 30), and NH4+-ZSM-5 (CBV-5524G, SiO2/Al2O3 = 50) purchased from Zeolyst Corp. were used as received. Ag–Mn/Na-Y, Ag– Mn/H-Y, and Ag–Mn/ZSM-5 were prepared as follows: the asreceived zeolite (20 g) was mixed with water (120 ml at 50 8C) under vigorous stirring, and 15 ml of 0.55 M AgNO3 aqueous solution was added dropwised into the suspension and stirred for 2 h at 50 8C. After filtration and washing with deionized water, the cake-like mixture was re-dispersed in deionized water at 50 8C, and 20 ml of 0.47 M Mn(CH3COO)2 aqueous solution was poured dropwised following by stirring for 2 h. The color of solution changed from white to pale gray after stirring. After filtration and rinsing with deionized water, the mixture was dried at 80 8C followed by calcinations at 420 8C for 3 h. After pelletizing, crushing, and sieving (16–30 mesh), the as-prepared adsorbents were ready for use. The weight percent of Ag in Ag–Mn/Na-Y, Ag– Mn/H-Y, and Ag–Mn/ZSM-5 were 4.30, 0.64, and 1.24%, respectively, and the weight percent of Mn were 2.32, 0.95, and 0.21%, respectively. The weight percent and the degree of exchange of the metal ions in the zeolites are presented in Table 1.
Fig. 1 shows the adsorption curves for 10 ppm DMS/air on Na-Y, H-Y, and NH4+-ZSM-5 in dry conditions (RH < 2%) at room temperature and atmosphere pressure. The ratio of C/C0 represents the concentration ratio of DMS in the outlet and the inlet. The initial removal efficiency of DMS on Na-Y was over 99% and the saturation adsorption capacity of DMS was 4.7 wt% (0.8 mmol/g). The initial removal efficiencies of DMS on H-Y and NH4+-ZSM-5 were 93 and 97%, respectively; and the saturation adsorption capacities of DMS on H-Y and NH4+-ZSM-5 were 3.3 and 3.0 wt%, respectively. Na-Y performs better than H-Y and NH4+-ZSM-5 in the initial removal efficiency and in the saturation adsorption capacity of DMS. Garcia and Johannes [13] explored the adsorption mechanism of ZSM-5 and found that light thiols were adsorbed on cations (Na+ or Al3+). Therefore, for the same type of zeolite, the saturation adsorption capacity of DMS on the zeolite with low ratio of SiO2/Al2O3 is higher than that with higher ratio of SiO2/Al2O3. The adsorption curves of 10 ppm DMS/air on Ag–Mn/zeolites in dry conditions are illustrated in Fig. 2. The initial removal efficiency of DMS on Ag–Mn/H-Y and Ag–Mn/ZSM-5 reached to 99%. The result revealed that the exchanged ions (Ag+ and Mn2+) were more efficient than Na+ and Al3+ in adsorbing DMS [12]. The saturation adsorption capacities of DMS on Ag–Mn/Na-Y, Ag–Mn/ H-Y, and Ag–Mn/ZSM-5 were 10.9, 2.8, and 4.2 wt%, respectively. The saturation adsorption capacities of DMS on Ag–Mn/Na-Y and Ag–Mn/ZSM-5 were higher than the original zeolites, whereas the saturation adsorption capacity of DMS on Ag–Mn/H-Y was lower than the original zeolite.
2.2. Adsorption and purge methods The adsorption and purge tests were proceeded in a fixed-bed glass reactor (11.5 mm I.D.), and the volume of the absorbent was 1 cm3 (0.36–0.47 g) and the temperature and the pressure were controlled at 25 8C and 1 atm, respectively. The DMS/air was generated by diluting 2071 ppm DMS/N2 gas with air to 10 ppm. The flow rate and the superficial velocity were kept at 3 L/min and 0.48 m/s, respectively. The water concentration of the tested gas was adjusted by bubbling part of the gas through water. The concentration of DMS in the inlet and the outlet gases was analyzed by photo-ionization detector (PID, RAE System PGM7240). The lower detection limit for DMS is 1 ppb. 2.3. Characterization of adsorbent The samples before and after DMS adsorption were analyzed by diffuse reflection spectroscopy (HORIBA FT-730). The range of scanned frequency was 400–4000 cm1 and the resolution of the infrared spectra was 4 cm1. The samples were heated to 150 8C for 15 h in air and cooled to room temperature in a desiccator. Temperature programmed desorption (TPD) was carried out by an automatic temperature programmed desorption apparatus (Altamira AMI-1) equipped with a quadrupole mass detector (Thermo VG ProLab). Samples (0.3 g) were placed in a U type quartz tube. The program of TPD began with a He (30 ml/min) flush at 36 8C for 60 min and then the temperature was increased to 500 8C by the rate of 10 8C/min and held at 500 8C for 10 min. The ionic intensities of mass-to-charge ratio (m/e) equal to 15, 18, 34, and 62 in the desorbed gas were analyzed by the mass spectrometer.
3.2. Adsorption of DMS under various relative humidity condition Fig. 3 shows the removal efficiencies of 1.5 ppm DMS/air (C0) on Ag–Mn/Na-Y under various relative humidities and Ag–Mn/ZSM-5 at RH = 60% at room temperature. Curve (a) depicts that the removal efficiency of Ag–Mn/Na-Y is over 99% at RH = 20% but decreases rapidly when the RH of the gas in the inlet is adjusted to 60%. The DMS concentration of the gas in the outlet increased abruptly to 3.2 times of C0, as shown in curve (b), which was higher than that of the inlet gas. The DMS concentration in the outlet gradually decreased to 0.4 times of C0 at RH = 60%. The removal efficiency of Ag–Mn/Na-Y gradually increased with the decrease of RH, as shown in curves (c) and (d), and reached 99% at RH = 20%, as depicted in curve (a). The curve (f) in Fig. 3 represents the removal efficiency of DMS on Ag–Mn/ZSM-5 at RH = 60%. The removal efficiency of the adsorbent was preserved at 99% during the test. The results for Ag– Mn/zeolites adsorbed DMS at various relative humidities revealed that Ag–Mn/Na-Y is sensitive to water molecules and Ag–Mn/ZSM5 has excellent resistance to water molecules. The competitive adsorption between water and hydrocarbon is familiar and is depending on the nature of hydrocarbon and catalyst [14]. Abdullah et al. investigated the competitive
C.-L. Hwang, N.-H. Tai / Applied Catalysis B: Environmental 93 (2010) 363–367
Fig. 1. Adsorption curves of 10 ppm DMS on (a) Na-Y, (b) H-Y, and (c) NH4+-ZSM-5 in dry conditions with RH < 2% at room temperature.
365
Fig. 4. IR spectra of (a) NH4+-ZSM-5 after adsorption of DMS, (b) Ag–Mn/ZSM-5 after adsorption of DMS, and (c) Ag–Mn/ZSM-5 after adsorption of DMS and then was purged by RH = 60% air for 2 h at room temperature.
The competitive adsorption between water and DMS was obvious in Ag–Mn/Na-Y when the RH was over 20% at room temperature (4.0 g water/kg dry air). It was assumed that the water clusters located in the channel and framework block the diffusion of DMS to metal ions located on site II in Ag–Mn/Na-Y, as a result, lower the removal efficiency of the adsorbent. Moreover, the water molecules probably replaced the adsorbed DMS molecules, which leaded to the concentration of DMS in the outlet is higher than that in the inlet under high concentration of water molecule. 3.3. IR spectra of adsorbents
Fig. 2. Adsorption curves of 10 ppm DMS on Ag–Mn/zeolites in dry conditions with RH < 2% at room temperature.
adsorption between water and hydrocarbon in the study of catalytic combustion of ethyl acetate and benzene in an air stream over Cr-ZSM-5 catalyst [15]. Their study showed that water molecules aggregate to water clusters and block the internal diffusion path of hydrocarbon molecules when the water concentration of the inlet gas reaches 9000 ppm (5.6 g water/kg dry air). Besides, Coatenoble and Maes studied the distribution of silver in Ag/Na-Y by the crystallography, and they found that the silver ions in Ag/Na-Y are located at sites I, I0 , II and delocalized sites. Site II located in channels and cavities is the favored locations of Ag+ in Na-Y for the adsorption of sulfur compounds [16].
Fig. 4 shows the IR spectra of three zeolites over the region of C– H stretching vibrations (2800–3010 cm1). After DMS adsorption, NH4+-ZSM-5 showed absorption bands at 2869 and 2931 cm1, as shown in curve (a) in Fig. 4. These absorption bands were assigned to the C–H stretching vibrations of DMS which adsorbed by NH4+ZSM-5. The IR spectrum of Ag–Mn/ZSM-5 after DMS adsorption was different from that of NH4+-ZSM-5. The IR spectrum of Ag–Mn/ ZSM-5 after DMS adsorption depicted absorption band located at 2935 cm1, as shown in curve (b) of Fig. 4. The absorption band was assigned to the C–H stretching vibrations of DMS adsorbed by exchanged metal ions in Ag–Mn/ZSM-5. The curve (c) in Fig. 4 was the IR spectrum of Ag–Mn/ZSM-5 after adsorption of DMS and then was purged by RH = 60% air for 2 h at room temperature. The absorption band located at 2935 cm1 still appeared after purge of which illustrated that the adsorbed DMS on exchanged metal ions (Ag+ or Mn2+) in Ag–Mn/ZSM-5 was not removed. 3.4. Characterization of DMS adsorbed on Ag–Mn/Na-Y
Fig. 3. DMS removal efficiency of Ag–Mn/Na-Y at RH (a) 20%, (b) 60%, (c) 46%, (d) 30% and (e) <2% and Ag–Mn/ZSM-5 at (f) RH = 60% at room temperature.
Fig. 5 shows the TPD profiles for DMS on Ag–Mn/Na-Y after DMS adsorption. The fragments of m/e = 15, 34, and 62 were assigned to CH3, H2S, and (CH3)2S, respectively. The TPD profiles of m/e = 15, 34, and 62 were observed at temperatures ranging from 80 to 450 8C. The TPD profile of m/e = 62 showed two peaks, and the temperature ranges of the first and the second peaks were 80–200 and 250–450 8C, respectively. The second peak was accompanied by a shoulder on the high temperature side. The temperature range of the first peak agreed with that of Na-Y after adsorption in DMS/ N2 reported by Wakita et al. [11]. Compared with the results obtained by Satokawa et al. [12], the temperature range of the second peak shifted to high temperature side. The first and the second peaks were regarded as cations (Na+ or Al3+) and exchanged metal ions on the active sites of adsorbing DMS, respectively.
366
C.-L. Hwang, N.-H. Tai / Applied Catalysis B: Environmental 93 (2010) 363–367
Fig. 5. TPD profiles of the Ag–Mn/Na-Y after adsorption of DMS.
Fig. 7. TPD profiles and the ratio curve of m/e = 15 and m/e = 62 of the Ag–Mn/ZSM-5 after adsorption of DMS.
Fig. 6. TPD profiles of m/e = 62 on the Ag–Mn/Na-Y after adsorption of DMS (a) before purging, (b) subjected to purge for 6 min, and (c) subjected to purge for 2 h by RH = 60% air at room temperature.
Fig. 8. TPD profiles of m/e = 62 on the Ag–Mn/ZSM-5 after adsorption of DMS (a) before purging, (b) subjected to purge for 6 min, and (c) subjected to purge for 2 h by RH = 60% air at room temperature.
After DMS adsorption, Ag–Mn/Na-Y was purged by air with RH = 60% at room temperature for 6 min and 2 h. Curve (a) in Fig. 6 represents the TPD curve of the Ag–Mn/Na-Y sample before purge. Curves (b) and (c) in Fig. 6 are the TPD curves of the purged samples. Curve (b) in Fig. 6 shows that only one peak is presented at 380 8C and the intensity of the peak is lower than that of the peak in curve (a). The result indicated that most of the DMS on cation (Na+ or Al3+) sites and a part of the DMS on exchanged metal ions active sites were removed from Ag–Mn/Na-Y after purging for 6 min. After purge for 2 h, the TPD curve, as depicted in curve (c), was almost linear, indicating most of the DMS on Ag–Mn/Na-Y were removed no matter where the active sites were located. The cation exchanged Y zeolite presented a strong adsorption capability to water. The water molecules adsorb on the hydrophilic sites and gradually form a monolayer on the walls of supercages in cation exchanged Y zeolite by hydrogen bonds [17]. The adsorbed DMS molecules on Ag–Mn/Na-Y are replaced by water molecules and are carried away by air. The fact that water molecules replace the DMS molecules on Ag–Mn/Na-Y can be applied in the in situ regeneration of the adsorbent.
The desorption temperature of the third peak of m/e = 62 on Ag– Mn/ZSM-5 is ranging from 310 to 480 8C, which is higher than that of Ag–Mn/Na-Y. The result illustrates that the adsorption strength of DMS on Ag–Mn/ZSM-5 is much stronger than that on Ag–Mn/Na-Y. The TPD peaks of m/e = 62 were attributed to desorption of the whole DMS molecules and the TPD peaks of m/e = 15 were attributed to desorption of the DMS fragment. Based on the mass spectrum of DMS, the ratio of ionic intensity of m/e = 15 and m/ e = 62 (15/62) is 0.22. As shown in Fig. 7, the ratio is between 0.1 and 0.5 in the temperature ranging from 100 to 420 8C, and then increases abruptly and reaches a maximum of 6.4 at 480 8C. Because the ionic intensity of m/e = 62 is low but the ionic intensity of m/e = 15 is still high at 480 8C. Besides, the ionic intensity of m/e = 62 was below 1 1010 Torr at 500 8C, while the ionic intensities of m/e = 15 and m/e = 34 were preserved at 1–4 1010 Torr. Satokawa et al. observed significant increase in the fragment (m/e = 34) of TBM in TPD when TBM was adsorbed on Ag/Na-Y in TBM/N2 [12]. They concluded that it is attributed to the decomposition of silver sulfide clusters formed on Ag/Na-Y after adsorption in TBM/N2. However, it is still unclear whether the species of m/e = 34 is formed during the adsorption process or TPD test. The fragments of m/e = 15 and m/e = 34 of DMS were unexpectedly increased in the TPD after the adsorption of DMS on Ag–Mn/ZSM-5 between 440 and 500 8C. This is due to the decomposition of DMS adsorbed on Ag–Mn/ZSM-5. The result indicates that the desorbing behavior of DMS on Ag–Mn/ZSM-5 is different from that on Ag–Mn/Na-Y at high temperature [12,18].
3.5. Characterization of DMS adsorbed on Ag–Mn/ZSM-5 After DMS adsorption, the TPD profiles of DMS on Ag–Mn/ ZSM-5 are very dissimilar to that of Ag–Mn/Na-Y, as shown in Fig. 7. The TPD profile of m/e = 62 shows three desorbed peaks at 120, 250 and 440 8C, indicating Ag–Mn/ZSM-5 has three or more active sites in adsorbing DMS. Most of the DMS molecules were desorbed above 300 8C, which imply the exchanged metal ions were the main active sites on Ag–Mn/ZSM-5 for adsorbing DMS.
C.-L. Hwang, N.-H. Tai / Applied Catalysis B: Environmental 93 (2010) 363–367
After DMS adsorption, Ag–Mn/ZSM-5 was purged by the air with RH = 60% at room temperature for 6 min (curve (b)) and 2 h (curve (c)). Fig. 8 shows the TPD profiles of Ag–Mn/ZSM-5 after DMS adsorption before and after purges. The ionic intensity of all desorption peaks decrease after purge for 6 min. The peak at 120 8C almost disappears but the peaks at 250 and 440 8C show slightly decreases. Compared with curves (b) and (c), the peak at 250 8C is kept unchanged but the peak at 440 8C shows slightly decrease. A detailed study of the adsorption of aromatic hydrocarbons in Ag+-exchanged zeolites was carried out using FT-IR spectroscope [19]. The study shows that cation hydration is a critical factor to determine the adsorption of hydrocarbon molecules and the peculiarity of Ag+ in ZSM-5 for trapping hydrocarbon is due to the resistance of Ag+ to water molecules. As depicted in the TPD result, most of the DMS molecules that coordinated with Na+ or Al3+ in Ag–Mn/ZSM-5 were removed during the purge process. Thus, the cation hydration affected the adsorption of DMS on Ag–Mn/ZSM-5 is obvious. However, a few DMS molecules that coordinated with the exchanged metal ions in Ag–Mn/ZSM-5 were removed during the purge process, therefore, it is concluded that the exchanged metal ions in Ag–Mn/ZSM-5 has an unique resistance to water molecules in adsorbing DMS molecules. 4. Conclusion The water concentration of the gas at the inlet influences significantly the initial adsorption efficiency of DMS on Ag–Mn/NaY. The removal efficiency of Ag–Mn/Na-Y drops abruptly when the relative humidity is over 20% at room temperature and decreases with an increase in water concentration of the gas at inlet. The adsorption capacity of DMS on Ag–Mn/ZSM-5 is lower than that on Ag–Mn/Na-Y but the former shows unique resistance to water molecules for adsorbing DMS molecules. The removal efficiency of DMS on Ag–Mn/ZSM-5 is still over 99% when the relative humidity of the gas at inlet reached 60% at room temperature. Based on TPD profiles, it shows most of DMS molecules that were coordinated with metal cations in Ag–Mn/Na-Y were replaced by the water molecules after the purge process in RH = 60% at room temperature. The DMS molecules coordinated with Na+ or Al3+ in Ag–Mn/ZSM-5 were replaced by the water molecules but a part of the DMS molecules were still adsorbed on the exchanged metal ions in Ag–Mn/ZSM-5 after the purge process
367
in RH = 60% at room temperature. The difference that Ag–Mn/ZSM5 and Ag–Mn/Na-Y adsorbed DMS in the presence of water might be due to that the adsorption of DMS with the exchanged metal ions in Ag–Mn/ZSM-5 is stronger than that in Ag–Mn/Na-Y or due to that the Ag–Mn/ZSM-5 is less hydrophilic than Ag–Mn/Na-Y. The property that Ag–Mn/ZSM-5 has a unique resistance to water molecules in adsorbing DMS molecules is important when the adsorbent is applied in the filtration system in the semiconductor industry. Acknowledgement Special thanks are due to Dr. Wu and Dr. Hwung of ITRI for reading the manuscript and making several helpful suggestions. References [1] D. Glindemann, J. Novak, J. Witherspoon, Environmental Science & Technology 40 (2006) 202. [2] S.H. Lin, C.S. Chang, Journal of the Chinese Institute of Chemical Engineers 37 (2006) 527. [3] L.M. Le Leuch, A. Subrenat, P. Le Cloirec, Langmuir 19 (2003) 10869. [4] L.M. Le Leuch, A. Subrenat, P. Le Cloirec, Environmental Technology 26 (2005) 1243. [5] A. Couvert, I. Charron, A. Laplanchea, C. Rennerb, L. Patriab, B. Requiemec, Chemical Engineering Science 61 (2006) 7240. [6] G. Ok, Y. Hanai, T. Katou, Chemosphere 26 (1993) 2167. [7] D. Pope, D.S. Walker, R.L. Moss, Journal of Catalysis 47 (1977) 33. [8] J.A. Rossin, Industrial & Engineering Chemistry Research 28 (1989) 1562. [9] M. Okubo, H. Kametaka, K. Yoshida, T. Yamamoto, Japanese Journal of Applied Physics Part 1-Regular Papers Brief Communications & Review Papers 46 (2007) 5288. [10] N. Lesauze, A. Laplanche, G. Martin, H. Paillard, Ozone-Science & Engineering 13 (1991) 331. [11] H. Wakita, Y. Tachibana, M. Hosaka, Microporous and Mesoporous Materials 46 (2001) 237. [12] S. Satokawa, Y. Kobayashi, H. Fujiki, Applied Catalysis B: Environmental 56 (2005) 51. [13] C.L. Garcia, A.L. Johannes, Journal of Physical Chemistry 95 (1991) 10729. [14] K.S. Song, D. Klvana, J. Kirchnerova, Applied Catalysis A 213 (2001) 113. [15] A.Z. Abdullah, M.Z. Bakar, S. Bhatia, Industrial & Engineering Chemistry Research 42 (2003) 6059. [16] M. Coatenoble, A. Maes, Journal of the Chemical Society-Faraday Transactions 74 (1978) 131. [17] J.C. Moı¨se, J.P. Bellat, A. Me´thivier, Microporous and Mesoporous Materials 46 (2001) 91. [18] M. Ziolek, M. Sugioka, Research on Chemical Intermediates 26 (2000) 385. [19] X.S. Liu, K.L. Jordan, A.A. Dmitrii, J.F. Robert, Applied Catalysis B: Environmental 35 (2001) 125.