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Removal of Hydrogen Sulfide in Simulated Coke Oven Gas with Low-grade Iron Ore Yuuki Mochizuki, and Naoto Tsubouchi Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01353 • Publication Date (Web): 10 Jul 2017 Downloaded from http://pubs.acs.org on July 11, 2017
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Removal of Hydrogen Sulfide in Simulated Coke Oven Gas with Low-grade Iron Ore Yuuki Mochizuki, and Naoto Tsubouchi* Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Kita 13 Nishi 5, Kita-ku, Sapporo 060-8628, Japan *Corresponding author. Tel.: +81-11-706-6850; fax: +81-11-726-0731. E-mail address:
[email protected] (N. Tsubouchi). Keywords; Hydrogen sulfide; Removal; Breakthrough curve; Limonite; Coke oven gas Abstract The hydrogen sulfide (H2S) removal performance of limonite in the presence of coke oven gas (COG) components (H2, CH4, CO, CO2, and H2O) has been studied in a cylindrical flow-type quartz-made fixed-bed reactor at 300-800 °C under a high space velocity of 51,000 h-1 to develop a novel hot gas cleanup method. The H2S removal behavior by reduced limonite in He does not change at the temperatures examined. On the other hand, the breakthrough curves in 50%H2/He depend on the temperature, and high performance is found at lower temperatures. An investigation of the breakthrough curves of H2S in the presence of COG components at 300-600 oC reveals that the addition of 30%CH4 to 50%H2/He does not influence the performance below 500 oC, whereas the coexistence of 5%CO with 50%H2/30%CH4/He drastically decreases the H2S removal ability of reduced
limonite.
In
addition,
the
breakthrough
curves
in
5%CO2
coexisting
with
50%H2/30%CH4/5%CO/He are similar with to those of 50%H2/30%CH4/5%CO/He. However, the addition of 5%H2O to 50%H2/30%CH4/5%CO/He dramatically improves the H2S removal performance of reduced limonite. Similar tendencies are observed in simulated COG (50%H2/30%CH4/5%CO2/5%H2O/He). Furthermore, the H2S breakthrough curve strongly depends on the space velocity. 1. Introduction Coke oven gas (COG) produced from the cokemaking process is generally utilized as a fuel source in the iron steel-making process. However, COG has recently attracted much attention as a low-cost hydrogen source and a value-added product for the chemical industry 1. In conventional processes, hot raw COG (> 800 °C) must be quenched to near room temperature using an aqueous ammonia solution to remove tarry materials contained in the COG 1. However, this wet process results in a loss of heat energy of the hot raw gas and requires high capital cost for large waste water treatment facilities. Purification of COG at higher temperatures by a hot gas clean up method would further improve the power generation efficiency and increase the utilization of COG. However, volatilized-S compounds
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such as H2S, COS, CS2, and tar-S, which are generated from S in coal upon coal carbonization, are also found in COG and are detrimental in some industrial applications 2. It is well known that H2S, organic-S, and tar-S not only serve as sources of SOx but also as toxic catalysts used for COG reforming and/or gas tube corrosion. S in COG mainly exists as H2S, in the amount of several thousand parts per million by (ppmv). Therefore, it is very important to develop a removal method for gaseous-S species in COG. Our research group has been investigating the catalytic decomposition of NH3 or model tar-N compounds (pyridine or pyrrole) using inexpensive iron catalysts
3-13
, and it has been found that fine
particles of metallic iron (α-Fe) formed from low-grade iron ore (limonite) provide high activity in the decomposition of NH3, pyridine, or pyrrole in an inert or simulated gasification fuel gas
5-13
. In
addition, we recently showed that limonite-derived α-Fe can provide stable activity for the decomposition of 100 ppmv C5H5N to N2 in COG components 7,12. On the other hand, it is well known that iron oxide is effective for the H2S removal in fuel gas at 300-700°C
14-18
. Thus, it is possible that
limonite-derived α-Fe will be a good adsorbent for H2S in COG. However, only a few studies have reported H2S removal in COG using iron-based adsorbents 19-24. It is well-known that a typical COG is composed of 54-59%H2, 24-28%CH4, 4-7%CO, 1-3%CO2 and 1-3%H2O with impurities, but the influence of the individual COG components on H2S removal has not been investigated in previous studies 19-22. In this study, therefore, we investigated H2S removal performance using Australian limonite in the presence of COG components to develop a novel gas-cleaning method for removing H2S. 2. Experimental 2.1. Catalyst material and preparation An Australian low-grade iron ore (limonite) with approximately 70 % goethite (α-FeOOH) was used in the present study. The metal composition of the limonite was Fe, 44; Si, 9.4; Al, 7.2; Mg, 0.15; and Ca, 0.07 mass%-dry
12
, and the particle size was 250-500 µm. The Brunauer-Emmett-Teller (BET)
specific surface area was 40 m2/g. 2.2. Removal of hydrogen sulfide Experiments to evaluate the H2S removal performance were carried out in a cylindrical fixed-bed quartz-made reactor (8 mm i.d.) under ambient pressure. The details of the experimental apparatus have been described elsewhere 12. Approximately 0.25 g of limonite was first charged into the reactor with quartz wool. The reactor was then heated electrically to 500 °C in a flow of high-purity He (> 99.99995 %) after taking precautions against leakage. At 500 oC, the high-purity He was replaced with high-purity H2 (> 99.9999 %) and the limonite was reduced by H2 for 2 h. After the reduction pretreatment, the atmosphere was switched to high-purity He, and the reactor was maintained at temperatures of 300-800 °C. The H2S removal experiments started by passing 3000ppmv H2S diluted with
He
and
simulated
COG
compositions
(50%H2/He,
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50%H2/30%CH4/5%CO/He, 50%H2/30%CH4/5%CO/5%CO2/He, 50%H2/30%CH4/5%CO/5%H2O/He or 50%H2/30%CH4/5%CO/5%CO2/5%H2O/He) over the reduced-limonite bed. The space velocity (SV) was maintained at 51,000 h-1 throughout each run unless otherwise noted. 2.3. Gas analysis In the H2S removal experiments, the H2S concentration in the exit gas of the reactor was measured using a standard detector tube (Gastec) at arbitrary times to obtain the breakthrough curves. The breakthrough and saturation points were defined as Ci/C0 = 0.1 and 0.9, respectively. Here, C0 and Ci are the initial concentration and the H2S concentration in the outlet gas of the reactor at an arbitrary time, respectively. The extent of sulfidation (H2S/Fe) was calculated based on the iron content in the limonite and the results of the breakthrough curves. 2.4. Characterization Powder X-ray diffraction (XRD; Shimadzu) measurements of the samples (as-received, after H2 reduction and after H2S removal) were performed with Mn-filtered Fe-Kα radiation. To avoid rapid oxidation of the α-Fe particles upon exposure to laboratory air, the sample after H2 reduction and H2S removal was passivated using 1% O2/He at room temperature and then recovered from the reactor 5. The background-removed X-ray diffraction line was deconvoluted into FeS and Fe1-xS by the curve-fitting method using Gaussian peak shapes. In this method, the XRD peaks at diffraction angle (2θ) of 55.0 and 55.7 degrees are assigned to FeS and Fe1-xS, respectively, according to data book of Joint Committee on Powder Diffraction Standards, and the corresponding full width at halfmaximum are fixed at 0.5 ± 0.3 degree. Temperature-programmed oxidation (TPO) was carried out to quantify the amounts of carbonaceous material formed during H2S removal. In a TPO run, the sample in the reactor after H2S removal was first quenched to room temperature in a stream of high-purity He and then heated at 10 °C/min to 950 °C in 10% O2/He. The concentrations of CO and CO2 evolved in this process were monitored using a micro gas chromatograph (Inficon). Some samples after TPO were also subjected to XRD measurements. 3. Results and discussion 3.1 H2S removal performance in He or 50%H2/He Figure 1 shows the temperature dependencies of the breakthrough curves of H2S in He at different temperatures. Although there is scattering of the plots, the breakthrough and saturation points were observed at 40-50 min and 70-80 min, respectively, at all temperature examined. In addition, these breakthrough curves are similar, and temperature dependencies in He were not observed. Figure 2 presents the results of breakthrough curves of H2S in 50% H2/He at different temperatures. The breakthrough points for the 300-600 oC runs were found at 20-40 min, and these times decreased with increasing temperature. The saturation points were measured at 60-70 min at 300-600 oC runs.
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The breakthrough curves at the 700-800 oC runs achieved breakthrough points up to 1 min after the start of the experiment. The H2S amount in the outlet gas increased with increasing time on stream, and the saturation point was observed at 80-90 min. Although the reason of small breakthrough point at 700-800oC is not clear, difference of H2S adsorption form may influence on H2S removal performance, as after-described. As seen in Fig. 2, the breakthrough curves at 300-600 oC and 700-800 o
C were quite different. In other words, temperature dependencies of H2S removal performance were
found in the reduction atmosphere. Table 1 lists the sulfidation extent (H2S/Fe) at the breakthrough and saturation points calculated based on the results of Figs.1 and 2. Here, H2S/Fe was calculated from the H2S concentration in the reactor outlet gas and Fe amount in limonite, and the calculation based on the assumption of 1 mol H2S reacts with 1 mol Fe in reduced-limonite. Although pyrrohtite (Fe1-xS) was detected in XRD measurement in solid phase recovered after experimental run, identification of “x” in Fe1-xS was difficult in this study because the XRD peaks position of Fe1-xS (x = 0.818-0.9) observed at 300-600 oC runs are very close, as after-described. Therefore, the calculation was carried out assuming that FeS was produced by the reaction of Fe and H2S. The H2S/Fe at the breakthrough and saturation points were 0.87-0.88 and 0.99-1.03, respectively, at all temperatures examined in He. On the other hand, in 50%H2/He, the H2S/Fe at the breakthrough points dramatically decreased from 0.82 to less than 0.01 at all runs, and the H2S/Fe = 1.02 at the saturation points observed at the 300 oC run also decreased to 0.83 at the 800 oC run. These results show the H2S removal performance by reduced limonite is quite different between an inert and a reduction atmosphere. The XRD measurements of the sample recovered after the H2S removal runs were carried out to clarify the difference in performance between He and 50%H2/He, as seen in Figs. 1 and 2. The results are shown in Figures S1 and S2 in the Supporting Information and in Figure 3. When the as-received limonite, which composed α-FeOOH according to the XRD patterns, was reduced in pure H2, a distinct peak attributable to α-Fe appeared, as shown in Fig. S1. Diffraction signals attributed to pyrrhotite (Fe1-xS) were observed in the sample recovered after the experiment at all temperature in He, and the peak intensities increased with increasing temperature (Fig. S2). Peaks of Fe1-xS were also detected in samples recovered after runs at 300-400 oC in 50%H2/He, as shown in Fig. 3. However, above 500 oC, the signal attributable to FeS was found at approximately 56o, along with that of Fe1-xS, and the XRD pattern at 800 oC became the latter signals only. As seen in Fig. 3, the peaks of Fe1-xS and FeS were redundant. Deconvolution was thus carried out against the XRD pattern observed at 53-58o in Fig. 3 to investigate the proportions of Fe1-xS and FeS in the samples. The results are shown in Figure 4 and Table 2. The production of FeS was observed at temperatures above 500 oC, and production increased with increasing temperature, whereas that of Fe1-xS decreased with increasing temperature and completely disappeared at 800 oC. These results suggest that H2S removal with reduced limonite occurs by chemical reaction adsorption accompanied by Fe1-xS and FeS formation. Furthermore, it was estimated that differences in the breakthrough curves between inert and reduction atmospheres were caused by differences in the adsorption forms. The temperature of 300-600 oC was
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therefore used for subsequent investigations because a dramatic decrease in H2S removal performance was observed at 700-800 oC in 50%H2/He. The desulfurization extents (H2S/Fe) measured in Figs. 1 and 2 were over the theoretical value calculated (H2S/Fe = 1.0 at 67 min) from the amount of introduced H2S and the amount of Fe present in the limonite. Although it is not clear at present, desulfurization mechanism blew described and gangue components in limonite, which can adsorb H2S, may influence. As is well known, H2S decomposition by sulfide compounds proceeds according to Eq. (1)-(3) 25: MxSy + zH2S → MxSy+z + zH2
(1)
0
MxSy+z → MxSy + zS
(2)
0
H2S → H2 + S
(3)
It has been also reported that Fe7S8 and H2 were produced by pyrrotite (Fe1-xS) reacts with H2S 26. Therefore, desulfurization extents at 300-600 oC runs may be greater than theoretical values because Fe1-xS as H2S adsorption form can adsorb H2S more than FeS. In addition, the equilibrium hydrogen concentrations for thermal dissociation of H2S according to Eq.(3) at 400-1000 oC is 0.1-13.4 vol%, and the reaction favors above 600 oC (1.3 vol.%-H2) 27. The elemental-S formation according to Eq.(3) may occur at 600-800 oC runs, and the desulfurization extents at high temperature may thus be greater than that of theoretical values. The details will be subject in future work. 3.2 Effects of CH4 and CO coexisting with 50%H2/He on H2S removal Figure 5 and Table 3 show the breakthrough curves of H2S in 30%CH4 coexisting with 50%H2/He at 300-600 oC runs and H2S/Fe at the breakthrough and saturation points. The breakthrough points at the 300-400 and 500 oC runs were measured at approximately 30-35 and 25-30 min, respectively. These curves in 50%H2/30%CH4/He at 300-500 oC were similar to those in 50%H2/He. On the other hand, H2S was detected in the outlet gas up to 5 min at 600 oC run, and the reduced limonite attained breakthrough at 15 min. This result was slightly different from that in 50%H2/He. H2S/Fe at the breakthrough point decreased from 0.73 at 300 oC to 0.31 at 600 oC with increasing temperature (Table 3), and a similar tendency was found for H2S/Fe at the saturation points. As is well known, the decomposition of CH4 is according to Eq. (4). CH4 → C + 2H2 (⊿G300-600oC = 6.1- -1.4 kcal/mol)
(4)
o
This reaction is likely to occur at temperature above 600 C in the present condition from the viewpoint of the thermodynamic results because the standard Gibbs free energy (⊿G) at is -1.4 kcal/mol. Therefore, decrease of H2S removal performance in 30%CH4 coexisting with 50%H2/He at 600 oC (Fig. 5) may be caused by C deposition on the active adsorption sites of the reduced limonite surface via CH4 decomposition. The ⊿G600oC of Fe3C formation from the reactions of deposited-C and Fe or CH4 and Fe are 1.0 and -0.35 kcal/mol, respectively, and these reactions are supported thermodynamically. However, ⊿G600oC of FeS production from the reaction of Fe3C and H2S is -43 kcal/mol, and this reaction is more likely to occur than the above two reactions. The decreased H2S removal performance at 600 oC by Fe3C formation may thus be negligible.
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Figure 6 presents the results of the addition of 5%CO to 50%H2/30%CH4/He. Table 3 also summarizes H2S/Fe at the breakthrough and saturation points in Fig. 6. The reduced limonite attained breakthrough points up to 15 and 5-10 min at 300 and 400-600 oC, respectively, and the H2S adsorption ability dramatically decreased as compared to those in 50%H2/He and 50%H2/30%CH4/He. H2S/Fe at the breakthrough points at the 300-600 oC runs, as seen in Table 3 ranged from 0.28 to 0.11, and H2S/Fe decreased with increasing temperature. H2S/Fe at the breakthrough and saturation points in coexisting 5%CO were one-third to one-half those of the 30%CH4 addition. As is well known, the disproportionation reaction of CO (Eq. (5)) and Eq. (6) easily occurs at lower temperatures. 2CO → C + CO2 (⊿G300-600oC = -17- -4.3 kcal/mol)
(5)
CO + H2 → C + H2O (⊿G300-600oC = -13- -2.6 kcal/mol)
(6)
Although the above reactions were supported thermodynamically in the present conditions, the disproportionation reaction of CO may be dominant because ⊿G at Eq. (5) is smaller than that in Eq. (6) at the same temperature. Therefore, the decrease in H2S removal performance may be caused by C deposition derived from Eq. (5) on the active adsorption sites on the reduced limonite surface. 3.3 Effects of CO2 and H2O coexisting with 50%H2/30%CH4/5%CO/He on H2S removal Figure
7
shows
the
breakthrough
curves
of
H2S
in
5%CO2
coexisted
with
o
50%H2/30%CH4/5%CO/He. The breakthrough points at the 300 and 400-600 C runs were found at 15-20 and 5-10 min, respectively, and the curves observed were similar to those in 50%H2/30%CH4/5%CO/He. The results show that the addition of CO2 to 50%H2/30%CH4/5%CO/He did not affect the H2S removal performance by reduced limonite. Table 3 also lists H2S/Fe at the breakthrough and saturation points against Fig. 7. H2S/Fe in 50%H2/30%CH4/5%CO/5%CO2/He shows values similar to those in 50%H2/30%CH4/5%CO/He. As described above, when it is assumed that the decrease in H2S removal performance at 5%CO coexisted with 50%H2/30%CH4/He is caused by C deposition, Eq. (7) is not supported thermodynamically for 5%CO2 added to 50%H2/30%CH4/5%CO/He under the present conditions. C + CO2 → 2CO (⊿G300-600oC = 17- 4.2 kcal/mol)
(7)
It may thus be possible that the results obtained in 50%H2/30%CH4/5%CO/5%CO2/He were similar to those in 50%H2/30%CH4/5%CO/He. The breakthrough curves of H2S in 5%H2O added to 50%H2/30%CH4/5%CO/He are illustrated in Figure 8. H2S/Fe at the breakthrough and saturation points are summarized in Table 3. At 300-400 oC, the reduced limonite exhibited breakthrough times of 30-40 min after H2S was detected in the outlet gas at approximately 20 min. The breakthrough points at 500 and 600 oC are observed at around 5 and 18 min, respectively, and H2S removal performance tended to decrease at higher temperatures. Furthermore, these breakthrough curves were almost similar to those in 50%H2/30%CH4/He, and the desulfurization ability in 50%H2/30%CH4/5%CO/He improved with the coexistence of H2O. H2S/Fe at breakthrough or saturation points ranged from 0.77 to 0.25 or from 1.07 to 0.88 at 300-600 oC, values
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that are almost the same as those in 50%H2/30%CH4/He. The Eqs. (8)-(10) are estimated H2O affects for H2S removal under this conditions. CO + H2O → CO2 + H2 (⊿G300-600oC = -4.2- -1.7 kcal/mol)
(8)
C + H2O → CO + H2 (⊿G300-600oC = 13- 2.5 kcal/mol)
(9)
C + 2H2O → CO2 + 2H2 (⊿G300-600oC = 8.6- 0.9 kcal/mol)
(10)
It is possible that the H2S removal performance was improved by inhibiting C deposition from the CO disproportionation reaction for H2O coexisting with 50%H2/30%CH4/5%CO/He because Eq. (8) is the most thermodynamically supported among three equations (Eqs. (8)-(10)). On the other hand, the addition of H2O does not affect CH4 decomposition because ⊿G600oC = 1.2 kcal/mol at Eq. (11). Although ⊿G600oC at Eq. (12) is -0.47 kcal/mol, the value is smaller than that in Eq. (4), and Eq. (12) is unlikely to occur under this condition at 600 oC. Therefore, it is thought that the H2S removal performance at 600 oC in 50%H2/30%CH4/5%CO/5%H2O/He is smaller than that at 300-500 oC. Similar tendencies, which the removal ability is improved by addition of H2O to simulated COG, were observed for NH3 and C5H5N decomposition runs by reduced limonite 13,23.
Figure
CH4 + H2O → CO + 3H2 (⊿G300-600oC = 19 - 1.2 kcal/mol)
(11)
CH4 + 2H2O → CO2 + 4H2 (⊿G300-600oC = 15- -0.47 kcal/mol)
(12)
9
shows
the
breakthrough
curves
in
simulated
COG
(50%H2/30%CH4/5%CO/5%CO2/5%H2O/He) at different temperatures. These breakthrough curves are similar to those for 50%H2/30%CH4/He and 50%H2/30%CH4/5%CO/5%H2O/He, and the highest performance is observed at the 300 oC run. Table 3 also shows H2S/Fe at the breakthrough and saturation points against Fig. 9. Although there is scattering, the values are similar to those of 50%H2/30%CH4/He. From these results, it was found that the H2S removal ability dramatically decreased in CO coexisting with 50%H2/30%CH4/He but it was greatly improved by the addition of H2O to 50%H2/30%CH4/5%CO/He regardless of temperature. 3.4 Effect of space velocity on H2S removal performance The breakthrough curves with changing SVs from 51,000 to 5,600 h-1 were investigated to clarify the influence of SV on H2S removal performance in simulated COG atmosphere at different temperatures. Figure 10 shows the breakthrough curves examined at SV = 5,600 h-1. No measurable H2S in the outlet gas was detected up to 180 min at 300 oC, and the breakthrough point was measured at approximately 240 min. At 400 oC, H2S was detected in the exit gas of the reactor beyond 120 min, and the reduced limonite reached breakthrough at 170 min. Although the 100% desulfurization was observed up to 60 and 30 min at 500 and 600 oC, respectively, reduced limonite attained breakthrough points up to 120 and 50 min, at 500 and 600 oC, respectively. At 700 oC, the breakthrough time was measured at approximately 10 min. As shown in Fig. 9, the breakthrough points at SV = 51,000 h-1 was observed up to 35 min at all temperatures examined. On the other hand, at SV = 5,600 h-1 (Fig. 10), the breakthrough times at 300, 400, 500, 600, and 700oC were 240, 160, 120, 50, and 10 min, respectively, and these values increased by approximately 5-6 times as compared to the case at 51,000
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h-1. These results show that SV is an important factor for H2S removal performance. 3.5 Possible Mechanisms of Influence of COG Gas Components on H2S removal
Figure S3 in Supporting Information presents the XRD patterns of the samples recovered after the experiments shown in Figs. 5-9. Moreover, Table 4 shows the proportions of Fe1-xS and FeS in the deconvolution results against the pattern of 53-58o shown in Fig. S3. α-Fe in the reduced limonite changed to Fe1-xS and FeS for all the any gas components examined. Although change of Fe was similar to that in 50%H2/He, the intensity of the main peak observed at approximately 55o was smaller than that of 50%H2/He. Although the reason for this is unclear, it may be a cause of the H2S removal performance. On the other hand, the clear peak attributable to α-Fe was not observed in Fig. S3, despite the fact that H2S/Fe was 0.38-0.56 at 5%CO and 5%CO/5%CO2 coexisting with 50%H2/30%CH4/He. This is the reason why the surface was sulfurized, and thus Fe was not detected because the penetration depth of X-rays in XRD measurements is always 0.01 - 20 µm. This result shows that desulfurization by reduced limonite proceeds according to the unreacted-core model
24,28
.
As shown in Fig. 2, H2S adsorption form changes with temperature in reduction atmosphere (in 50%H2, 30%CH4, 5%CO, 5%CO2, 5%H2O coexisting). In addition, adsorption form of Fe1-XS was determined at low temperature (300-400 oC), whereas FeS was mainly observed at high temperature (≥500 oC) in all atmosphere, except in He, as seen in Figs. 3, S2, S3 and Table 4. From the viewpoint of stoichiometry, Fe1-xS is possible to adsorb H2S more than FeS. Therefore, it is suggested that breakthrough curve decreases above 500 oC in reduction atmosphere (in 50%H2 coexisting). As above mentioned, it is estimated that C deposition on activated site of reduced-limonite surface inhibits H2S removal ability in CO coexisting runs. TPO runs thus were carried out against recovered samples to clarify the reason for the decrease and improvement of the H2S removal performance in 5%CO added to 50%H2/30%CH4/He and in 5%H2O coexisting with 50%H2/30%CH4/5%CO/He. There was almost no measurable CO or CO2 evolution during TPO of the sample recovered after the 50%H2/30%CH4/He run 23. However, during TPO of the sample after the 50%H2/30%CH4/5%CO/He run, CO and CO2 were evolved at 300 oC, and main and shoulder peaks of the CO and CO2 formation rates occurred at approximately 350 and 450 °C, respectively 23. In addition, CO and CO2 formation stopped at around 600oC. Similar behavior of CO and CO2 was observed for the sample recovered after the 50%H2/30%CH4/5%CO/5%CO2/He run 23. On the other hand, the peaks of the CO and CO2 formation profiles from the samples recovered after the 50%H2/30%CH4/5%CO/5%H2O/He and 50%H2/30%CH4/5%CO/5%CO2/5%H2O/He runs were considerably smaller than those for 30%CH4/5%CO and 30%CH4/5%CO/5%CO2 coexisted with 50%H2/He
23
. As is well known,
amorphous-C has high reactivity. It may thus be possible that deposited-C in present study is amorphous-C. Table 5 summarizes the amounts of CO and CO2 evolved from the recovered samples after H2S removal during TPO until 950 oC. The total amounts of CO and CO2 evolved from the recovered samples after the 50%H2/30%CH4/He runs were very small at all temperatures examined. On the other hand, the evolution amounts of CO and CO2 from the samples obtained after the
ACS Paragon Plus Environment
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Energy & Fuels
50%H2/30%CH4/5%CO/He and 50%H2/30%CH4/5%CO/5%CO2/He runs were 170-290 and 1100-1400 µmol/g-sample, respectively, and these values were greater than those from 50%H2/30%CH4/He. These CO and CO2 amounts during TPO decreased for samples recovered after the 50%H2/30%CH4/5%CO/He runs. The order of CO and CO2 evolved amounts during TPO was 50%H2/30%CH4/He
