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Phosphine Adsorption Removal from Yellow Phosphorus Tail Gas over CuO-ZnO-La2O3/Activated Carbon Honghong Yi, Qiongfen Yu, Xiaolong Tang,* Ping Ning,* Liping Yang, Zhiqing Ye, and Jinghao Song Faculty of Environmental Science and Engineering, Kunming University of Science & Technology, Kunming 650093, China ABSTRACT: CuO-ZnO-La2O3/activated carbon (AC) adsorbent was used for phosphine (PH3) adsorption removal. The effects of O2 content, PH3 concentration, and adsorption temperature on the PH3 adsorption were investigated. The adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry/thermogravimetric (DSC/ TGA), and X-ray photoelectron spectroscopy (XPS). The results show that PH3 adsorption capacity is enhanced significantly by increasing oxygen content or adsorption temperature. Two bands that appear at 1161.1 and 1008.5 cm-1 in the FTIR spectrum of the exhausted adsorbent are ascribed to H3PO4. An exothermic peak in the DSC curve of exhausted adsorbent is ascribed to desorption of H3PO4 and condensation reactions of H3PO4 adsorbed species. It is observed that both P4O10 (65.09%) and H3PO4 (34.91%) exist over the exhausted adsorbent. The CuO-ZnO-La2O3/AC adsorbs PH3 and PH3 adsorbed is oxidized to form H3PO4 and P4O10. It naturally follows that the CuO-ZnO-La2O3/AC will be a potential adsorbent for PH3 removal from yellow phosphorus tail gas.
1. INTRODUCTION The emission of phosphine (PH3) has been an environmental problem in many important industrial processes. Two examples are (1) the emission of PH3 from the semiconductor and optoelectronic industries and (2) the environmental problems associated with the disposal of the yellow phosphorus tail gas in the phosphorus chemical industry. The latter problem is becoming increasingly severe because the main contents of yellow phosphorus tail gas is about 85%-95% CO,1 which can be used as raw material gas to synthesize chemical products such as methyl formiate, dimethyl ether, methyl carbonate, methanol, and so on. However, the reuse of yellow phosphorus tail gas is restricted strictly because the tail gas contains PH3, which is a potent catalyst poison in CO synthesizing chemistry, even at very low concentration.2,3 Since high-purity carbon monoxide is required as a chemical raw material, pretreatment of yellow phosphorus tail gas is a valuable method. Several methods for recycling the tail gas in an environmentally acceptable manner have been proposed.4 An attractive alternative to those proposed would be gas-solid adsorption. On the basis of the literature,5 it is known that copper is commonly used as the active species for removing hydride gases. Activated carbon (AC) is the most commonly used and most effective modified adsorbent support, because of its high specific surface area and big pore volume,6,7 so adsorbents using activated carbon as the support and the parameters influencing the adsorption capacity are also worth investigating. On the other hand, El-Shobaky et al.8 indicated that treatment of CuO with ZnO increased the degree of dispersion of CuO and much of the stability of CuO/ ZnO. Recently, Radwan9 reported that doping of CuO/MgO with La2O3 led to an effective increase in the degree of dispersion of CuO crystallites for the solids calcined at 350 °C. Yan et al.10 showed that the mixed ZnO-La2O3 catalysts had higher activities than zinc oxide, which correlated well with the effects of lanthanum on enhancing the dispersion of ZnO. r 2011 American Chemical Society
The objective of this research was to prepare CuO-ZnOLa2O3/AC adsorbent for phosphine removal by adsorption from yellow phosphorus tail gas. The effects of inlet O2 concentration, inlet PH3 concentration, and adsorption temperature on the PH3 adsorption removal were experimentally investigated using the phosphine adsorption removal efficiency curve. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry/thermogravimetric analysis (DSC/TGA), and X-ray photoelectron spectrometry (XPS) were employed to characterize the physicochemical properties of the CuO-ZnO-La2O3/ AC adsorbent before and after adsorption in order to analyze the PH3 adsorption mechanism.
2. EXPERIMENTAL SECTION 2.1. Preparation of the CuO-ZnO-La2O3/AC Adsorbents. The AC prepared from a commercial coal-derived carbon (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) was used as adsorbent support in this study. Cu(NO3)2 3 3H2O (99%), Zn(NO3)2 3 6H2O (99%), and La(NO3)3 3 nH2O (La2O3, 44þ%) (Sinopharm Chemical Reagent Co., Ltd.) were used as active components in order to strengthen AC adsorption performance. Before use, the AC support was crushed and sieved to 2.5-3 mm, followed by washing with distilled water, filtration, and drying at 110 °C for 12 h. The CuO-ZnO-La2 O3 /AC adsorbents were prepared by impregnation of the pretreated AC with an aqueous solution of the precursors [Cu(NO 3)2 3 3H 2O, Zn(NO3)2 3 6H 2O, and La(NO3 )3 3 nH2 O] in the appropriate concentrations to obtain proper metal mass loadings. The mass loadings for Cu, Zn, and La were 2.5%, 0.167%, and 0.0833%, respectively. Received: July 29, 2010 Accepted: February 2, 2011 Revised: December 29, 2010 Published: February 23, 2011 3960
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Industrial & Engineering Chemistry Research During the impregnation, a beaker that contained both pretreated AC and an aqueous solution of active components was put in an ultrasonic laboratory cleaner operating at a frequency of 40 kHz with an instrument power of 300 W, and this ultrasonic-assisted impregnation process continued for 40 min at 30 °C. These wet samples were dried in a drying cabinet at 110 °C for 12 h, followed by calcining in a furnace at 350 °C for 6 h. The CuO-ZnO-La 2 O3 /AC adsorbents are referred to as MAC. 2.2. Characterization of the MAC Adsorbents. 2.2.1. FourierTransform Infrared Spectra (FTIR). FTIR measurements were performed on a Thermo Nicolet AVATAR FT-IR 360 instrument. Potassium bromide pellets containing 0.5% of the catalyst were used in FT-IR experiments, and 34 scans were accumulated for each spectrum in transmission, at a spectral resolution of 4 cm-1 . The spectrum of dry KBr was taken for background subtraction. 2.2.2. Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TGA). DSC/TGA analysis was carried out with a TA SDT2960 instrument. A known weight of the adsorbent sample was heated in an aluminum pan at a constant heating rate of 10 °C/min operating in a stream of N2 atmosphere with a flow rate of 100 mL/min from room temperature to about 900 °C. 2.2.3. X-ray Photoelectron Spectroscopy (XPS). XPS (PHI 5500) analysis used Al KR radiation with an energy of Al rake and power of 200 W. Kinetic energies of the photoelectrons were measured by a two-stage spectrometer. The analyzer resolution was 1 eV. An Arþ ion gun was used to sputter clean specimen surfaces. The ion energy was set to 1 keV and the sputtering time was 10 min. The photoelectron spectra were calibrated using the C 1s signal detected at a binding energy of 284.8 eV from adventitious carbon. The reason for using the value of 284.8 eV to calibrate the C 1s is that the samples characterized by XPS analysis are air-exposed materials and the C 1s spectra of the adventitious carbon (284.8 eV) seems to exhibit an instantaneous presence on all air-exposed materials. The detailed discussion of this reason was illustrated by Barr and Seal.11 The pass energy used was 58.7 eV and the pressure in the UHV chamber was 5 10-9 Torr. 2.3. Adsorption of PH3. The PH 3 adsorption process was conducted in a stainless steel adsorption column with an inner diameter of 15 mm. The adsorption column was positioned vertically in the middle of a tubular furnace with a temperature controller (Xiamen Yundian Automation Technology Co., Ltd). Before the adsorption experiment, each sample was first treated at 120 °C for 60 min in N2 and then cooled to the appropriate temperature. Subsequently, the N2 flow was switched to a flowing mixed gas for PH3 adsorption. The total gas flow was 250 mL/min and the GHSV (gas hourly space velocity based on the actual adsorbent volume) was 5000 h-1. The premixed PH3 (1% PH3 in N2) was supplied by Dalian Special Gases Co., Ltd. The influent PH3 concentration (C0) and the effluent PH3 concentration (C) were measured by a C16 potable gas detector (electrochemical detector, supplied by Analytical Technology, Inc.). The PH3 concentration was measured every 30 min until the removal efficiency was below 90%. The breakthrough point of the adsorbent was set at PH3 removal efficiency of 90%. The breakthrough capacity of carbon (q90 ) was then calculated using the integrated area below the adsorption removal efficiency curve, the influent PH3 concentration, mass of carbon, and flow rate.
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Figure 1. Effects of PH3 concentration on PH3 adsorption removal. Experimental conditions: Adsorbent amount = 1.3893 g, T = 70 °C, [O2] = 1%, N2 = the balance, and GHSV = 5000 h-1.
3. RESULTS AND DISCUSSION 3.1. Effect of Inlet PH3 Concentration. Experiments were carried out to investigate the effect of inlet PH3 concentration on the performance of PH3 dynamic adsorption on the MAC adsorbents. The PH3 removal efficiency curves are presented in Figure 1. The PH3 removal efficiency slightly decreases when the inlet concentration of PH3 increases from 613 to 874 ppm, but the PH3 breakthrough adsorption capacity slightly increases from 132.59 to 147.11 mg/g. That is to say, increasing the phosphine inlet concentration will shorten the breakthrough time of phosphine and increase its breakthrough adsorption capacity. The maximum breakthrough adsorption capacity is 147.11 mg/g at a feed concentration of 874 ppm. This may be explained by considering that the driving force for PH3 diffusion through the macropores to the active sites increases with increasing PH3 concentration, resulting in a positive effect on the initial adsorption rate. However, when the concentration of PH3 increases to 1329 ppm, the removal efficiency of PH3 decreases markedly and the PH3 breakthrough adsorption capacity decreases significantly from 147.11 to 118.07 mg/g. This may be because when the initial adsorption rate is increased significantly with the excessive increasing of PH3 feed concentration, many more reaction products are produced quickly, and these products may fill the macropores and increase the PH3 diffusion resistance through the pore structure. Actually, at the same adsorption time, PH3 adsorbed amount increases with increasing feed concentration (partial pressure) of the adsorbed species. When the adsorption time increases to 330 min, the adsorbed amounts with feed concentration of 613, 874, and 1329 ppm are 55.24, 78.56, and 118.07 mg/g, respectively. 3.2. Effect of Oxygen Content. Figure 2 shows the effect of inlet O2 concentration on the performance of PH3 dynamic adsorption on the MAC adsorbents. Oxygen content is one of the most important factors that influenced the PH3 adsorption capacity, and the removal efficiency of PH3 is enhanced significantly by increasing the oxygen content. As observed, in the absence of O2, breakthrough of PH3 occurs in approximately 28 min and the PH3 efficiency decreases markedly to 89.59% at 30 min. As oxygen (0.5 vol %) is introduced into the raw gaseous mixture, the breakthrough time is found to improve significantly 3961
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Figure 2. Effects of oxygen content on PH3 adsorption removal. Experimental conditions: Adsorbent amount = 1.3893 g, T = 70 °C, [PH3] = 1316 ppm, N2 = the balance, and GHSV = 5000 h-1.
Figure 3. Effects of adsorption temperature on PH3 adsorption removal. Experimental conditions: Adsorbent amount = 1.3893 g, [PH3] = 1319 ppm, [O2] = 1%, N2 = the balance, and GHSV = 5000 h-1.
to 270 min. The increases in phosphine removal efficiency are not obvious when the oxygen content is higher than 1%. According to Figure 2, the breakthrough adsorption capacities of different raw gaseous oxygen contents of 0%, 0.5%, 1.0%, 2%, and 3% are 7.44, 97.52, 117.86, 127.52, and 137.55 mg/g, respectively. The above discussion shows that oxygen contained in the raw mixture may take part in the PH3 adsorption removal. Taking account of the strong reductive characterization about PH3, phosphine adsorbed in the MAC adsorbent may be oxidized by oxygen. The results indicate that the mechanism of PH3 adsorption over the MAC adsorbents may be a physical and chemical adsorption process, and this adsorption process can be improved significantly in the presence of O2 molecular. 3.3. Effect of Adsorption Temperature. Figure 3 shows the effect of adsorption temperature on the performance of PH3 removal efficiency on the MAC adsorbents. As shown in Figure 3, adsorption temperature is also one of the most important factors that influence the MAC to adsorb PH3, and the removal efficiency of PH3 will be enhanced significantly by increasing the adsorption temperature. As observed, at an adsorption temperature of 25 °C,
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breakthrough of PH3 occurs in approximately 90 min, and the PH3 efficiency decreases markedly to 88.55% at 120 min. The breakthrough time is found to improve significantly to 150 min when the adsorption temperature is 40 °C. The increases in phosphine removal efficiency are not obvious when the adsorption temperature is higher than 70 °C. According to Figure 3, the PH3 breakthrough adsorption capacities at adsorption temperatures of 25, 40, 50, 60, 70, and 80 °C are 32.33, 54.12, 75.14, 76.83, 95.74, and 98.49 mg/g, respectively. The results indicate that the mechanism of PH3 adsorption over the MAC adsorbents may be a physical and chemical adsorption process. Moreover, both PH3 physisorption and chemisorptions are exothermic processes and become thermodynamically less favorable with the increasing of adsorption temperature. The increasing of breakthrough adsorption capacity is due to an increasing rate of chemisorption reaction with increasing adsorption temperature. Comparing the performance of this MAC adsorbent with the results published by Wang et al.,2 first, the adsorbent published by Wang et al. was modified by HCl and the MAC adsorbent contained Cu (2.5 wt %), Zn (0.167 wt %), and La (0.0833 wt %). Second, the PH3 equilibrium adsorption capacity of the HClmodified adsorbent at 20 °C was only about 40 mg/g in this publication, but the breakthrough adsorption capacity of the MAC adsorbent at 25 °C had increased to 32.33 mg/g. It may readily be supposed that the equilibrium adsorption capacity of the MAC adsorbent will increase to a higher adsorbed amount than that of this publication. Likewise, compared with our previous work,12 first, the main purpose of the previous work was study the influences of mass ratio of Cu, Zn, and Ce. However, the main purpose of this paper was study the effects of O2 content, PH3 concentration, and adsorption temperature on the PH3 adsorption and PH3 adsorption mechanism analysis. Second, the breakthrough capacity of carbon (q90) of the optimal adsorbent (Cu45Zn3Ce1/AC) in our previous work was 94.49 mg/g when the adsorption temperature was 70 °C. This value was slightly lower than the adsorption capacity (95.74 mg/g) of the MAC adsorbent at the same adsorption temperature. The result shows that both the addition of Ce and La can increase the phosphine adsorption capacity of the modified adsorbent, and these adsorbents are more favorable for phosphine adsorption removal from yellow phosphorus tail gas than the adsorbent published by Wang et al.2 3.4. Characterizations of the Adsorbents and Adsorption Mechanism Analysis. The above results show that physical adsorption and chemical adsorption may take place simultaneously over the MAC adsorbent surface. In order to investigate the mechanism of PH3 adsorption over the MAC adsorbents, the MAC adsorbents before and after adsorption were characterized by FTIR, DSC/TGA, and XPS analysis. 3.4.1. FTIR Analysis Results. Infrared spectroscopy provides information on the chemical structure of the adsorbent material. Figure 4 shows FTIR spectra of the MAC adsorbents before and after adsorption. A weak absorption band at about 3740 cm-1 present in the spectra of the MAC adsorbents may be ascribed to isolated O-H groups.13 The band at about 1550 cm-1 for fresh MAC and exhausted MAC adsorbents is ascribed to the CdC vibration in aromatic group. When the MAC adsorbent adsorbs PH3, the two bands that appear at 1161.1 and 1008.5 cm-1 in the spectrum of the exhausted MAC adsorbents are characteristic of the antisymmetric stretching vibration (ν3) of PO43-.14 Chapman et al.15 pointed out that the infrared spectrum of H3PO4 molecule in aqueous solution showed a weak band at 885 cm-1 [P(OH)3 3962
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Figure 4. FTIR analysis results of the MAC adsorbents: (A) fresh MAC adsorbents and (B) MAC adsorbents with adsorbed PH3.
symmetrical and PO stretch, Al stretching mode of PO43-], two very strong bands at 1007 and 1165 cm-1 [P(OH)3 “degenerate” and PO stretch, F2 stretching mode of PO43-], a weak band at about 1070 cm-1 (PdO stretching, F2 stretching mode of PO43-), and a strong shoulder at 1250 cm-1 (P-O-H in-plane deformation). Stefov et al.16 stated that in the region of ν3(PO4) modes in the FTIR spectra of the studied compounds, one very strong band appeared above 1000 cm-1, which, as mentioned above, was somewhat temperature-sensitive and whose frequency was 1008 cm-1 at room temperature. Salah et al.17 also stated that, for PO43-, these were a singlet (A1) at a frequency ν1 = 938 cm-1, a doublet (E) at ν1 = 465 cm-1, and two triply degenerate (F2) modes, ν3 at 1027 cm-1 and ν4 at 567 cm-1. According to these above analyses, it can be concluded that the FTIR absorption band difference between the fresh MAC and the exhausted MAC maybe shows that PH3 adsorbed on the activated carbon would be oxidized to form H3PO4 in the presence of oxygen gas, and the oxidization product could be adsorbed onto activated carbon more easily than PH3. 3.4.2. DSC/TGA Analysis Results. Figure 5 shows the differences between the fresh MAC adsorbents and the exhausted MAC adsorbents in DSC/TGA curves. According to the TGA curves, the total weight loss of the fresh samples and the exhausted samples are 21.73% and 27.70%, respectively. This weight loss difference between the two activated carbon samples resulted from both desorption and condensation reactions of adsorption species and water loss over the exhausted samples during the process of DSC/TGA. An endothermic peak for both two adsorbents that indicates water loss of activated carbon surface is observed in the temperature range 40-100 °C in DSC curves.18 The water contained the fresh MAC adsorbent, and the exhausted adsorbent is ascribed to water adsorption before the DSC/TGA process. It is interesting to note that an exothermic peak is observed at around 264 °C in the DSC curve of exhausted MAC. The exothermic peak may result from both desorption of adsorbed species by evaporation and condensation reactions of adsorbed species. On the one hand, the boiling point temperatures19 of PH3, P2O3, P2O5, and H3PO4 are -87.7, 175.4, 347, and 261 °C, respectively. The sublimation temperature of P2O5 is 300 °C. It may be concluded that PH3 adsorbed on the activated carbon will be oxidized to form H3PO4 in the presence of oxygen
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Figure 5. DSC/TGA analysis results of the MAC adsorbents: Dotted line, fresh MAC adsorbents; solid line, MAC adsorbents with adsorbed PH3.
gas. However, both desorption and evaporation are endothermic processes. On the other hand, in the range of temperature between 200 and 300 °C, phosphoric acid undergoes condensation reactions with loss of water molecules, leading to the formation of pyrophosphoric acid, metaphosphoric acid, and other polyphosphates, and these reactions are exothermic process. Therefore, the exothermic peak at around 264 °C is due to the combined effects of desorption of H3PO4 by evaporation and condensation reactions of H3PO4. Moreover, the heat effect of condensation reactions is more pronounced than that of desorption. The TGA curve for both MAC adsorbents shows continuous mass loss at temperatures above 300 °C. As for the fresh MAC adsorbent, the oxygen that existed in fresh MAC adsorbent will react with carbon when the temperature increases, and the copper species over the activated carbon will accelerate the carbon decomposition, resulting in the weight loss of activated carbon. As for the exhausted MAC, part of the phosphine adsorbed may be oxidized to form P2O5 and then P2O5 adsorbed onto the MAC adsorbent will be desorbed when the temperature increases. Therefore, the mass loss at temperatures above 300 °C is due to the combined effects of the weight loss of activated carbon and desorption of P2O5. On the basis of the TGA curves, the weight loss of exhausted samples is more pronounced than that of fresh samples. The above discussion shows that PH3 adsorbed on the activated carbon may be oxidized to form H3PO4 and P2O5 in the presence of oxygen gas. 3.4.3. XPS Analysis Results. The chemical states of the elements on the MAC adsorbent (before and after adsorption) were examined by XPS analysis. Figures 6 and 7 show the XPS spectra of the two MAC adsorbents and the phosphorus 2p peaks for the exhausted MAC adsorbent. Changes in composition of MAC adsorbents are given in Table 1-3. According to Figure 6, the C 1s is the most intense peak in spectrum A and almost disappears in spectrum B. The change of peak intensity about the MAC adsorbents before and after adsorption is due to the phosphorus adsorbed deposition that results from the adsorption and subsequent oxidation of phosphine on the MAC adsorbent. The peaks of the fresh MAC samples at about 935.61 and 955.12 eV are attributed to Cu 2p3/2 and 2p1/2 (Table 2), respectively, which are consistent with those observed in CuO.20,21 Although Li et al.5 stated that a Cu 2p2/3 peak at around 935.4 eV and a 3963
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Table 1. Change in Composition for MAC Adsorbents As Determined by XPS Analysis % composition of MAC adsorbent atomic
fresh
exhausted
oxygen
98.34
81.61
copper
1.66
phosphorus
0
0.78 17.54
Table 2. Change in Composition of the Cu 2p Peak for MAC Adsorbents change in composition for MAC adsorbent (%)
Figure 6. XPS spectra of two MAC adsorbents: (A) the fresh MAC adsorbent and (B) the exhausted MAC adsorbent.
binding energy (eV)
fresh
exhausted
935.61
27.78
—
955.12
72.22
—
932.59
—
28.84
933.82
—
31.00
952.36 954.32
— —
18.84 21.32
Table 3. Change in Composition of the P 2p Peak for MAC Adsorbents change in composition for MAC adsorbent (%)
Figure 7. The phosphorus 2p peaks for the exhausted MAC adsorbent.
Cu 2p1/2 peak indicate the possible presence of Cu(OH)2, the decomposition temperature of Cu(OH)2 ranged from 134.5 to 150.2 °C.22 Therefore, Cu(OH)2 does not exist in the MAC adsorbent that was calcined at 350 °C for 6 h. As for the exhausted MAC samples, the peaks corresponding to the core level 2p3/2 and 2p1/2 transitions of copper at 933.5 and 954.32 eV, respectively, are shown in Table 2. These values compare well with the reported values for Cu 2p levels in CuO.23-27 Moreover, the peaks of the exhausted MAC samples at about 932.59 and 952.36 eV are ascribed to Cu 2p3/2 and 2p1/2 (Table 2), respectively, which are also consistent with those observed in Cu2O.23,28 This indicates that part of CuO over the fresh MAC samples may be reduced to Cu2O during the phosphine adsorption and oxidation process. As shown in Figure 7 and Table 3, the P2p peak centered at 133.93 eV indicates the possible presence of H3PO4 and the P2p peak centered at 135.16 eV indicates the possible presence of P4O10(P2O5).2,23,29 The H3PO4 and P4O10 species appeared in the exhausted MAC sample are generated by an oxidation process. Fresh MAC adsorbent has no phosphorus species. After adsorption, it is observed that the relative percentage of P4O10 (65.09%) is more than that of H3PO4 (34.91%). It naturally follows that CuO plays a very important role in phospine adsorption and oxidation.
binding energy (eV)
fresh
exhausted
133.93
—
34.91
135.16
—
65.09
3.4.4. PH3 Adsorption Mechanism Analysis. According to the above experimental results and characterizations for MAC adsorbents before and after adsorption, it proves that the phosphine adsorption onto the MAC adsorbent is chiefly chemical adsorption. Two bands that appear at 1161.1 and 1008.5 cm-1 in the FTIR spectrum of the exhausted MAC adsorbents are characteristic to the antisymmetric stretching vibration (ν3) of PO43-. During the DSC/ TGA process, an exothermic peak is observed around 264 °C in the DSC curve of exhausted MAC, and this weight loss is due to the combined effects of desorption of H3PO4 by evaporation and condensation reactions of H3PO4. According to the XPS analysis, fresh MAC adsorbent has no phosphorus species. As for the exhausted MAC adsorbent, the P 2p peak centered at 133.93 eV indicates the possible presence of H3PO4, and the P 2p peak centered at 135.16 eV indicates the possible presence of P4O10(P2O5). It is observed that the relative percentage of P4O10 (65.09%) is more than that of H3PO4 (34.91%). Moreover, the peaks of the exhausted MAC samples at about 932.59 and 952.36 eV are ascribed to Cu 2p3/2 and 2p1/2 peaks in Cu2O, which indicates that part of the CuO over the fresh MAC samples can be reduced to Cu2O during the phosphine adsorption and oxidation process. It can be concluded that O2 contained in the feed gas and CuO existing on the surface of MAC adsorbent play a very important role in the adsorption process. During the PH3 adsorption and oxidation process, the modified activated carbon adsorbs PH3, and then PH3 adsorbed on the activated carbon will be oxidized to form H3PO4 and P2O5 in the presence of copper oxide and oxygen gas. 3964
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4. CONCLUSIONS The above results showed that the CuO-ZnO-La2O3/AC adsorbent was an efficient adsorbent for PH3 removal in the presence of oxygen. They showed high PH3 removal efficiency and adsorption capacity. The PH3 removal efficiency and its adsorption capacity would be enhanced significantly by increasing the oxygen content or adsorption temperature. It showed that the PH3 adsorption over the CuO-ZnO-La2O3/AC adsorbent was mainly chemical adsorption in the presence of oxygen gas. Two bands that appeared at 1161.1 and 1008.5 cm-1 in the FTIR spectrum of the exhausted MAC were ascribed to H3PO4 adsorbed species. An exothermic peak observed around 264 °C in the DSC curve of exhausted MAC was ascribed to desorption of H3PO4 by evaporation and condensation reactions of H3PO4. It was observed that both P4O10 (65.09%) and H3PO4 (34.91%) existed over the exhausted MAC. The MAC adsorbent adsorbed PH3, and then PH3 adsorbed on the MAC was oxidized to form H3PO4 and P4O10. The present study confirmed that the CuOZnO-La2O3/AC adsorbents would be one of the candidates for PH3 removal from yellow phosphorus tail gas by adsorption. ’ AUTHOR INFORMATION Corresponding Author
*X.T.: e-mail,
[email protected]; tel, þ86 871 5170905. P.N.: e-mail,
[email protected]; tel, þ86 871 5170905.
’ ACKNOWLEDGMENT The authors would like to acknowledge financial support from the Key Program of National High Technology Research and Development Program of China (863 Program) (2008AA062602), the Young and Middle-Aged Academic and Technical Back-up Personnel Program of Yunnan Province (2007PY01-10), and the Analysis and Measurement Foundation of Kunming University of Science & Technology. ’ REFERENCES (1) Ma, L. P.; Ning, P.; Zhang, Y. Y.; Wang, X. Q. Experimental and Modeling of Fixed-Bed Reactor for Yellow Phosphorous Tail Tas Purification over Impregnated Activated Carbon. Chem. Eng. J. 2008, 137, 471. (2) Wang, X. Q.; Ning, P.; Shi, Y.; Jiang, M. Adsorption of Low Concentration Phosphine in Yellow Phosphorus Off-Gas by Impregnated Activated Carbon. J. Hazard. Mater. 2009, 171, 588. (3) Quinn, R.; Dahl, T. A.; Diamond, B. W.; Toseland, B. A. Removal of Arsine from Synthesis Gas Using a Copper on Carbon Adsorbent. Ind. Eng. Chem. Res. 2006, 45, 6272. (4) Yu, Q. F.; Yi, H. H.; Tang, X. L.; Ning, P.; Wang, C. Progress on Phosphine Control Technology. Environ. Sci. Technol. (Wuhan, China) 2009, 32, 87. (5) Li, W. C.; Bai, H. L.; Hsu, J. N.; Li, S. N.; Chen, C. C. Metal Loaded Molecular Sieve Adsorbents for Phosphine Removal. Ind. Eng. Chem. Res. 2008, 47, 1501. lvarez, P. M.; McLurgh, D.; Plucinski, P. Copper Oxide (6) A Mounted on Activated Carbon as Catalyst for Wet Air Oxidation of Aqueous Phenol. 2. Catalyst Stability. Ind. Eng. Chem. Res. 2002, 41, 2153. (7) Lu, C. Y.; Bai, H,L.; Wu, B. L.; Su, F. S.; Hwang, J. F. Comparative Study of CO2 Capture by Carbon Nanotubes, Activated Carbons, and Zeolites. Energy Fuels 2008, 22, 3050. (8) EI-Shobaky, G. A.; Fagal, G. A.; Mokhtar, M. Effect of ZnO on Surface and Catalytic Properties of CuO/Al2O3 System. Appl. Catal. A: Gen. 1997, 155, 167.
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dx.doi.org/10.1021/ie101622x |Ind. Eng. Chem. Res. 2011, 50, 3960–3965
