Biogas desulfurization by adsorption on thermally treated sewage-sludge

Depósito de Investigación de la Universidad de Sevilla https://idus.us.es/ This is an Accepted Manuscript of an article published by Elsevier in Separation and Purification Technology, Vol. 123, on February 2014, available at: https://doi.org/10.1016/j.seppur.2013.12.025 © 2014 Elsevier En idUS Licencia Creative Commons CC BY-NC-ND Biogas desulfurization by adsorption on thermally treated sewagesludge F. J. Gutiérrez Ortiz, P. G. Aguilera, P. Ollero Departamento de Ingeniería Química y Ambiental, Universidad de Sevilla Camino de los Descubrimientos, s/n. 41092 Sevilla, Spain Phones: + 34 95 448 72 68 / 60 e-mail: “Francisco Javier Gutiérrez Ortiz” frajagut[email protected] Abstract Biogas is a renewable source for power production, but the H2S present must be removed because it is very corrosive and may damage the combustion engines. The adsorption using activated carbon is one of the most used desulfurization methods. The operational life of the activated carbon could be extended if the H2S concentration was reduced prior entering the activated carbon bed by using other cheaper adsorbent. Sewage sludge is a possible inexpensive precursor to obtain adsorbents, and thus it would be valorized. An experimental study was performed using three types of sludge from three Spanish locations, which were activated to increase their adsorption capacity. Two thermal treatments were tested using nitrogen (pyrolysis) and air (calcination), as well as three heating temperatures. The adsorption dynamics of the prepared adsorbents were investigated in a fixed-bed column, determining the breakthrough curves and adsorption capacity of adsorbents. Besides, both their surface properties and their chemical properties were analyzed to get more insight about the adsorbent behavior. In addition, the effect of the oxygen content, relative humidity and the chemical impregnation, using different procedures, were also studied. As a relevant result, the adsorbent obtained by calcination at 700 °C of one of the three kinds of sludge showed a capacity twice of that of a commercial activated carbon without impregnation, although somewhat lower than that of a commercial activated carbon impregnated with a NaOH solution. The results showed that the use of this kind of precursors is very attractive to achieve adsorbents with a relative high adsorption capacity valuable to apply them in an economically feasible pretreatment. Keywords Biogas, H2S, hydrogen sulfide, desulfurization, breakthrough, adsorption, sewage sludge 1. Introduction The organic matter that is present in a landfill collecting municipal solid waste is degraded in an anaerobic process, which generates a gas mixture called biogas or landfill gas. Biogas is obtainable in a relatively economical way from anaerobic digestion [1]. The main constituents of biogas are methane and carbon dioxide, but it also contains nitrogen and oxygen, due to air incursion into the gas collection system; oxygen concentration is continuously monitored and held low for safety reasons. Due to the high calorific value of methane and its high concentration, biogas is currently considered a renewable energy source. When biogas is used as a fuel for electricity generation, several trace compounds may damage the combustion engines, requiring expensive repairs and causing service interruptions. Among all of the specific contaminants to biogas utilization, hydrogen sulfide (H2S) is the most relevant one, because it is highly corrosive during the combustion process. Because hydrogen sulfide concentration is of up to 1000–2000 ppm, H2S removal is necessary to avoid operational problems, such as corrosion in pipes, turbines or other units [2], as well as environmental problems such as global warming or acid rain [3]. Biogas desulfurization is normally performed by wet scrubbing, biological methods, adsorption, or selective catalytic oxidation [4]. The activated carbon adsorption process is normally penalized with high operational costs related to the price of the adsorbent. Among these methods, adsorption by dry treated sludge, such as that coming from the municipal wastewater treatment, may be beneficial as a pretreatment of the biogas, before entering another system, such as an adsorber using activated carbon. In this way, the activated carbon would deal with biogas with a lower H2S concentration, and its useful operational life would be extended. Thereby, sewage sludge, which is an inevitable byproduct of wastewater treatment, could be valorized. Generally, three sludge-stabilization methods are typically used: thermal, chemical and biological [5]. Surplus sludge produced during the biological treatment of wastewater requires costly disposal procedures. The most frequent methods of disposal are landfill, commercial composting and incineration. With increasing environmental and legislative constraints, increasing sludge production and lessening disposal options, new recycling alternatives have to be found [6]. The adsorption dynamics of the prepared adsorbents was investigated in a fixed-bed column, using a simulated biogas and determining the adsorption capacity of the adsorbents. Three carbon-based adsorbents from dry sewage sludge (low-cost precursors) were tested after suffering a thermal treatment to increase the adsorption capacity. The research work was focused on studying the effects of the thermal treatment, heating temperature, and physicochemical properties of the precursors on the removal of H2S, in the absence of oxygen and humidity. Additionally, the influences of the relative humidity and the oxygen present in the biogas entering the adsorber were tested, as well as the effect of chemical impregnation. One of the main novelty aspects of the present study is the use of air as agent to thermally treat the precursors, instead of a pyrolysis (performed under N2 atmosphere), which has been the usual thermal procedure in the previous studies encountered in the literature. This has a great importance, if the process is to be implanted in a commercial scale, where using air instead of nitrogen would reduce the operating costs. Another significant point of this paper is the use of a simulated biogas, and not a mixture of H2S and air normally used in most studies found in the literature, because CO2 may compete against H2S in adsorption depending on the porous structure of the adsorbent and the alkali constituents, since both of them are acid gases. 2. Experimental section 2.1. Materials Two commercial activated carbons, labeled as CAT and CAA, were used as references to compare the results using the precursor-sludge. CAT is a fresh activated carbon, without impregnation, while CAA is activated carbon impregnated with a NaOH solution. Both of them were milled and sieved between 1.41 and 2.83 mm, as the rest of the materials tested. Likewise, three types of air-dried sewage-sludge were crushed to pass between 1.41 and 2.83 mm sieve. They are referred to as LG, LL, and LF, respectively, based on their Spanish provenance. Table 1 shows the elemental and immediate analyses of the two activated carbons and the three types of sewage-sludge, as received, i.e., before undergoing any treatment. Experiments were carried out by a certified mixture of CH4 (60 vol.%), H2S (2000 ppmv) and CO2 (balance). 2.2. Methods Precursors were treated in order to improve their adsorption capacity by thermal and chemical procedures. Then, they were tested by an experimental unit to obtain their H2S breakthrough capacity and characterized by different analytical techniques. 2.2.1. Thermal treatment of sludge Physical activation involves calcination or pyrolysis of a precursor. The thermal treatment was performed in a tubular furnace, illustrated in Figure 1. The pyrolysis (heat treatment carried out in an inert atmosphere) was performed with 100 g of precursor using a nitrogen flow-rate of 1 L/min from room temperature up to 500ºC. Beyond this temperature, no more nitrogen was used and an air flow-rate of 0.125 L/min passed through the tubular furnace until reaching the final temperature (500ºC, 700ºC or 900ºC). During this latter step, calcination takes place and the metals present in the sample are oxidized. The code of this method was ‘PA’. As a second method, the calcination was performed entering air from room temperature up to the final temperature. It was coded using the letter ‘A’. The heating rate was always 5ºC/min and the holding time was always 30 minutes, which was selected by a prior screening test. After that time, samples were withdrawn from the furnace. The samples were coded as follows: first, the acronym of the precursor (LL, LF and LG), then the maximum temperature reached, and finally the treatment (PA or A). 2.2.2. Experimental adsorption unit A lab-scale facility was designed and assembled to carry out the adsorption tests. It consists of three main parts: gas feeding, adsorption system and H2S analyzer. Figure 2 depicts a scheme of the experimental unit. Experiments were carried out at controlled room temperature (20±2 ºC), using a simulated biogas flow-rate of 1.1 L/min. The fixed bed tower was a glass tube (30-mm ID and 430 mm height), with a perforated plate acting as gas distributor and adsorbent support. The adsorbent bed was 100 mm height. H2S was measured by a continuous gas analyzer, based on ultraviolet radiation, with three possible ranges (0-200 ppm, 0-1200 ppm and 0-2500 ppm). A humidification system based on three bubblers serially assembled was used for tests with humidification. To investigate the effect of humidity on H2S removal efficiency, specific H2S removal tests were performed by two ways (at room temperature): (1) by pre-humidifying the adsorbent using a saturated air flow-rate of 1.1 L/min for one hour (in this case, the ‘PH’ symbol is added at the end of the label), or (2) directly, by using a saturated biogas (100% relative humidity at 20 °C), adding ‘H’ at the end of the code. Additionally, the effect of the oxygen on the H2S removal was studied by adding oxygen (5 vol.%) to the dry biogas stream before entering the fixed bed.. Adsorption/removal capacities, x/M (mg H2S/g material), were calculated by integrating the corresponding breakthrough curves and by applying Eq. (1) [7]:            s t 0 s0 M dt)t(ctc Vw MWQ M x [1] where Q is the total inlet flow rate (m3/s), w is the weight of sludge-based material introduced into the column (g), MW is the molecular weight of H2S (34 g/mol), VM is the molar volume (22.4 L/mol), c0 is the inlet gas H2S concentration (ppmv), c(t) is the gas outlet concentration (ppmv), and ts is the bed saturation/exhaustion time (s). The test was stopped at the breakthrough concentration of 200 ppm; thus, ts is the time corresponding to this concentration. Experimental tests were validated by performing, at least, three replicates, verifying thus the reproducibility and the feasibility of the tests. 2.2.3. Preparation of impregnated precursors With the aim of improving the activated carbons performance, these may be impregnated with caustic materials such as NaOH or KOH. Unlike activated carbons, sewage-sludge, (either thermally treated or not treated) cannot be immersed in stirred caustic solutions because they disaggregate and partially dissolve. Then, impregnation procedures were performed by other two ways: (1) milling the NaOH or KOH lentils and mixing with the sludge-based material, and (2) atomizing a concentrated aqueous solution of NaOH or KOH on the precursor. In this latter case, due to the addition of water, the precursors were partially dissolved forming an unwieldy paste that led to a poor result after calcination. The agents were added using an agent-to-precursor mass ratio ranged from 0.10 to 0.40. 2.2.4. Characterization of sludge Surface properties and chemical properties of the precursors were determined to get more insight about the adsorbent behavior. The surface properties of adsorbents that affect the adsorption capacity are mainly surface area, pore volume, and pore size distribution [8]. The BET surface area as well as the micropores and mesopores areas and volumes were obtained by means of the Micromeritics ASAP 2420 System, which based on physisorption determination that uses nitrogen as adsorptive. The IUPAC nomenclature was followed: micropores correspond to pore size lower than 2 nm and mesopores ranges from 2 to 50 nm. The BET surface area and the micropores volume were computed using the Harkins and Jura Thickness equation, and the mesopores and macropores volume were calculated using the tmethod by Barrer-Joyner-Halenda. Before each test, samples were degasified at 150ºC for ten hours. Regarding the chemical analyses, direct analyses of major elements (C, H, N, S, and O) of the dry sludge and thermally treated precursors (both before and after carrying out the H2S adsorption test) were performed using LECO Instruments (CHNS-932). Trace metals were determined by means of inductively coupled plasma atomic (optical) emission spectroscopy (Horiba Jobin Yvon Ultima 2 High resolution ICP-OES spectrometer). In order to obtain structural information on an atomic scale of both crystalline and noncrystalline (amorphous) materials, X-ray Diffraction (XRD) analyses were carried out by a Bruker D8 Advance A25, equipped with an X-ray tube of 40 kV and 30 mA, Δ2θ of 3-70º, step scanning with a step size of 0.015° (2θ) and a scan step time of 0.1s. X-ray Photoelectron Spectroscopy (XPS) was used (Leybold-Hereus LHS-10/20) to discriminate on the different oxidation states. Scanning Electronic Microscopy (SEM) observations were carried out with a Philips XL30 microscope with secondary and backscattered electron imaging, equipped with an integrated Energy Dispersive X-Ray Spectrometer to analyze the elements and their contents. 3. Results and Discussion Hydrogen sulfide can be physically adsorbed, due to the porous structure of the adsorbent, and chemically adsorbed, because of the presence of some metals, acting as reagents or catalysts, and the surface alkalinity. Table 2 shows the content of potential catalytic or reagent metals in the three types of virgin dry sludge as well as for some of them after thermal treatment. The possible catalytic activity of some of the metals and the reactivity of some others towards hydrogen sulfide is discussed below. The results indicate high contents of calcium and iron in the adsorbents, which should have a positive effect on the hydrogen sulfide oxidation. Other alkali metals, such as sodium and potassium, are in a too low concentration to have a significant effect on the H2S removal. Apart from iron, alkali metals and alkaline earth metals, copper and zinc oxides also have a catalytic activity for H2S removal [9, 10]. Table 3 shows the weight loss of precursors in the tubular furnace as well as the adsorption capacity in the fixed-bed experimentally obtained, in the absence of humidity and oxygen. Pyrolysis or calcination result in changes in the sludge chemistry with a significant weight loss between 200 and 500ºC due to volatization of organic matter, but probably also by dehydroxylation of hydroxides and decomposition of inorganic salts as pointed previously by other researchers [11]. More than 50% of the dry weight was lost during the thermal treatment. account the relative high proportion of phosphorous in the tested samples, phosphoric acid may be probably formed during the adsorption process. Additionally, other metals such as copper and zinc can act as catalyst in a second stage, once sulfate is formed, based on the following reactions: Me2+ + H2S + 2SO42-  MeS(s) + 2HSO4- [6] MeS(s) + 2 Fe3+  Me2+ + 2 Fe2+ + S0 [7] 2Fe2+ + 1/2 O2 + 2HSO4-  2 Fe3+ + 2SO42- + H2O [8] One basic point is the low solubility of the intermediate metallic sulfides in acid media, which is a characteristic of Cu and Zn [18]. However, reactions (4-8) are limited by the presence of a liquid phase (water) on the adsorbent surface. In the absence of added water to the biogas or the precursor, water may be adsorbed from the environment, once disposed in the bed, or coming from the reaction (3). In any case, it does not seem very probable that these redox-reactions can take place in a large extent. Therefore, the adsorption capacity of the precursor is quite limited in this way. In the above reactions, the absence of oxygen avoids the re-oxidation of Fe2+ to Fe3+ (reactions 3, 5 and 8) so the enhancement of the adsorption capacity lowers because the catalytic activity of some metals is limited. As the hydrogen sulfide diffuses into the pellet, the active reagents begin to be depleted, so mainly the physical adsorption takes place but at a lower rate [19]. Finally, the presence of alkali metals or alkaline earth metals (Na, K, Ca and Mg) makes it possible to increase the H2S removal, because the metal hydroxide reacts with the hydrogen sulfide to obtain hydrogen-sulfide ions, which could be oxidized to elemental sulfur if oxygen was present, as described below. Taking into account that the adsorbent bed continuously stores hydrogen sulfide from zero to saturation, the basicity of the adsorbent will change from moderately high values, corresponding to a surface pH higher than 7.0, to low values. Therefore, probably, the first chemical adsorption that will probably take place is that involving a process where elemental sulfur can be formed. Then, when pH falls, the H2S removal leads to sulfuric acid, which may plug the pores, but also provide an acid medium to enhance the catalytic effect of other metals like Cu and Zn. Indeed, if sulfuric acid is mainly formed, it may participate in a redox reaction to produce elemental sulfur. 3.5. Influence of the relative humidity Adsorption of hydrogen sulfide in the presence of moisture was also studied by obtaining the corresponding breakthrough curves. Several tests were carried out, but the results did not bring out a clear improvement. Figure 10 shows the breakthrough curves obtained using saturated biogas. Results obtained by pre-humidifying the adsorbent bed were similar, so they are not shown. No clear effect of the experimental conditions was noticed and the adsorption capacities measured using dry and saturated biogas were almost the same. A slightly better performance of the precursor in dry conditions may suggest that water contributes to deactivation of surface-active centers in the H2S retention, counteracting a clearer positive effect. Probably, it is because the inorganic phase of the sewage-sludge contains alkaline earth oxides that are nonreactive with water, as pointed out by other researchers [20]. In addition, water in the gas mixture hinders the adsorption capacity because it plugs the pore structure. In any case, this finding agrees with a result encountered in a previous study [12]; some other researchers found a positive effect (the breakthrough time increases as the humidity increases), although in studies carried out using a mixture of air and H2S instead of a simulated or real biogas [9]. Finally, the water present in the biogas is adsorbed on the adsorbent particles, providing a liquid phase where CO2 may be dissolved, forming carbonates and contributing to the formation of sulfurous acid, which deactivates the basic catalytic sites, resulting in a lower capacity. The use of air may have an important effect due to the oxygen content, as next described. 3.6. Influence of the oxygen presence To test the effect of the oxygen on the H2S removal, oxygen was added to the dry biogas stream before entering the fixed bed. For safety reasons, the oxygen content was limited to 5 vol.%, due to the methane presence. Compared to the results obtained in the absence of oxygen, the adsorption capacity of precursor LG is doubled at 500 ºC and at 700 ºC, using the treatment PA, and tripled at 900 ºC, in the presence of oxygen. The activated carbons CAA and CAT were also tested under these conditions and their adsorption capacities increased from 12.8 to 77.4 mg/g, and from 4.4 to 7.3 mg/g, respectively. This significant increase in the adsorption capacity was also detected for impregnated active carbons [21]. The adsorption capacity of the LG precursor has a moderately adsorption capacity higher than that of CAT activated carbon. However, the CAA adsorption capacity is much higher than the best adsorbent obtained (17.3 mg/g for LG 700 PA), in the presence of oxygen. The oxygen may oxidize the hydrogen sulfide to elemental sulfur that would be physically adsorbed in micropores zone, fixing thus the sulfur to the adsorbent. The primary dehydroxylation of inorganic species is expected to occur at ca. 400ºC [11], resulting in an increase in the basicity of precursors. CAA activated carbon was impregnated with a solution of NaOH, and the results showed the H2S breakthrough capacity increases six times. However, neither CAT activated carbon nor the three kind of sewage sludge were impregnated with a basic solution, and the increase in the adsorption capacity was clearly lower (somewhat less than double). This may indicate that the amount of OH- present on the surface is a factor that favors the adsorption capacity. By increasing the basicity of the precursor, hydroxide ions cause an increase in the HS- ion concentration. These ions can be further oxidized to elemental sulfur, until the basic environment is no longer maintained. Therefore, possible reactions involved when oxygen is present may be the following: H2S + OH-  H2O + HS- [9] HS- +1/2 O2  S0 + OH- [10] 3.7. Influence of a chemical impregnation Chemical activation uses as agents mainly alkali and alkaline earth metals, such as potassium or sodium hydroxide or carbonate as well as zinc, aluminum or magnesium chlorides. It is published that impregnated activated carbons remove gaseous pollutants via an irreversible reaction between the additives and pollutants. A basic media is one of the required conditions for an efficient desulfurization process [22]. As it can be observed in Table 2, thermal treatment increases the alkali and alkaline earth metals content and, hence, the basicity of the precursors, leading to a higher adsorption capacity. Most of the previous studies showed that impregnated activated carbons have a very positive effect on the desulfurization performance, increasing the adsorption capacity of the adsorbent considerably [21, 23]. However, when carrying out different procedures of chemical activation and testing the so-activated pretreated sludge, a significant improvement was not appreciated, i.e., the effect of the impregnation was not clearly detected, probably to an inefficient impregnation procedure. Effectively, two different procedures of impregnation were applied to the virgin precursors with and without performing thermal treatment. The adsorption capacity of adsorbents after atomizing a basic solution was lower than that obtained without impregnation. The best performance was obtained by milling and mixing NaOH with the precursor and after heating to 700 ºC, using the treatment PA and an agent-to-precursor mass ratio of 0.25. Anyway, the improvement was also small compared to the case in which no impregnation was used. 4. Conclusions Carbon-based adsorbents from thermally treated sewage sludge can be used along with activated carbon to boost the removal efficiency of the H2S present in a biogas, providing a longer operational life for the activated carbon and making the purification process more costeffective. Experimentally, different thermal treatments, heating temperature and adsorption conditions were tested, and the adsorption dynamics of the prepared adsorbents were obtained in a fixed-bed column, using three precursors from sewage sludge (coded as LL, LF, LG). The physical and chemical properties were widely studied to acquire a better knowledge of the adsorbent behavior. The BET surface area of interest is that associated to the micropores, and not the total value due to all of the pore structure. Indeed, the development of porosity and formation of new mineral-like catalytic components depend on the thermal treatment for a given precursor. By this means, it was identified the best precursor, which was that obtained from sewage-sludge LG pyrolyzed up to 500 ºC and then calcined up to 700 ºC (PA thermal treatment). The adsorption capacities of the three kinds of sewage-sludge thermally treated were similar and even higher than that of the non-impregnated commercial activated carbon. Precursors LL and LG showed similar capacities and the best one was the precursor LG, probably due to surface characteristics, especially the micropore volume and its corresponding surface area, as well as the content in Fe, Ca and Mg, which may boost the chemical fixation of H2S as elemental sulfur. Additionally, a pyrolysis treatment is not necessary, contrary to that mainly pointed out in the literature, since using air as an agent in the thermal treatment allows high adsorption capacities near those obtained by pyrolysis. Likewise, the presence of oxygen (but limited for safety) in the biogas entering the adsorber will improve the process performance. The relative humidity did not enhance the adsorption efficiency, although more experiments should be carried out, using a biogas with oxygen. The presence of alkali metals and iron seems to be a positive effect. 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Choi, Adsorption dynamics of hydrogen sulfide in impregnated activated carbon bed, Adsorption 14 (2008) 533–538 [22] A. Bagreev, F. Adib, T.J. Bandosz, pH of the activated carbon surface as an indication for its suitability for removal of hydrogen sulphide from wet air streams, Carbon 39 (2001) 1905–87 [23] Y. Xiao, S. Wang, D. Wu, Q. Yuan, Experimental and simulation study of hydrogen sulfide adsorption on impregnated activated carbon under anaerobic conditions, J. Hazard. Mater. 153 (2007) 1193–1200 Tables and Figures Captions Table 1. Immediate and elemental analyses of activated carbons and sewage sludge Table 2. Trace metal composition of precursors and adsorbents obtained Table 3. Weight loss of adsorbents after being thermally treated and adsorption capacity Table 4. BET surface area and pore structure for some samples of the treated precursor LG Table 5. BET surface area and pore structure for some samples of the treated precursors LL and LF Figure 1. Facility scheme for thermally treating the precursors in a controlled atmosphere Figure 2. Scheme of the laboratory plant for performing the adsorption tests Figure 3. Breakthrough curves for the activated carbons used as reference framework Figure 4. Breakthrough curves for the precursors thermally treated at three temperatures in the absence of humidity and oxygen: precursor (a) LF, (b) LL, (c) LG Figure 5. Comparison of adsorption capacities of precursors for the two thermal treatments Figure 6. XRD of adsorbents obtained from the precursor LG Figure 7. SEM micrographs of the adsorbents for LG and LL at 700ºC and treatment PA, once used for H2S adsorption Figure 8. EDS analysis of the adsorbents for LG and LL at 700ºC and treatment PA, once used for H2S adsorption Figure 9. XPS analysis (general spectrum with embedded sulfur spectrum) of the precursor LG heated at 500 and 700ºC, following the treatment PA Figure 10. Breakthrough curves for the precursors thermally treated at three temperatures in the absence of oxygen: precursor (a) LF, (b) LL, (c) LG Parameter (dry basis) wt% Activated carbon CAT Activated carbon CAA Sludge LL Sludge LF Sludge LG Carbon 88.12 73.32 38.49 39.12 36.90 Hydrogen 0.76 0.81 5.42 5.48 5.07 Nitrogen 0.79 0.48 6.54 5.86 4.72 Oxygen 1.37 8.10 19.42 19.77 16.38 Sulfur 0.35 0.30 1.32 1.26 1.54 Ash Balance Balance Balance Balance Balance Ash (wet basis) (8.25) (14.67) (27.11) (26.79) (32.96) Volatiles (wet basis) (2.48) (11.84) (57.42) (58.56) (54.62) Fixed Carbon (wet basis) (85.09) (59.81) (9.57) (8.63) (5.53) Moisture (wet basis) (4.18) (13.69) (5.90) (6.02) (6.89) Table 1 Precursors Si mg/g Al mg/g Fe mg/g Ca mg/g Mg mg/g Na mg/g K mg/g P mg/g S mg/g Cu mg/g Zn mg/g LL 91.77 17.67 30.43 36.32 11.07 1.63 3.21 18.11 9.05 0.36 0.56 0 300 600 900 1200 1500 1800 2100 2400 3000 Counts 10 20 30 40 50 60 2Theta (Coupled TwoTheta/Theta) WL=1,54060 0 300 600 900 1200 1500 1800 2100 2400 3000 Counts 10 20 30 40 50 60 2Theta (Coupled TwoTheta/Theta) WL=1,54060 0 1000 2000 3000 Counts 10 20 30 40 50 60 2Theta (Coupled TwoTheta/Theta) WL=1,54060 0 1000 2000 3000 Counts 10 20 30 40 50 60 2Theta (Coupled TwoTheta/Theta) WL=1,54060 0 300 600 900 1200 1500 1800 2100 2400 2700 Counts 10 20 30 40 50 60 2Theta (Coupled TwoTheta/Theta) WL=1,54060 0 300 600 900 1200 1500 1800 2100 2400 2700 Counts 10 20 30 40 50 60 2Theta (Coupled TwoTheta/Theta) WL=1,54060 Figure 6 (a) (b) (c) Figure 7 (a) (b) (c) (d) Figure 8 Figure 9 10k 200 400 600 800 1000 1200 1400 15k 20k 25k 30k 35k 40k 5k 0k 10k10k 200200 400400 600600 800800 10001000 12001200 14001400 15k15k 20k20k 25k25k 30k30k 35k35k 40k40k 5k5k 0k0k Kinetic Energy eV Intensity CPS Mg(1s)Mg(1s) C(AES)C(AES) Ca(AES)Ca(AES) N(AES)N(AES) O(AES)O(AES) Fe(AES)Fe(AES) Fe(2p) O(1s) Ca(2p) Mg(AES) N(1s) Ca(2s) C(1s) Si(2s) P(2s) S(2p) P(2p) Al(2s) Si(2p) Mg(2s) Al(2p) O(2s) 1150 178 176 174 172 170 168 166 164 162180 1200 1250 1300 1350 169.6 Binding Energy eV (-5.47) Intensity CPS SULFUR SPECTRUM LG 5 00 PA 10k 200 60k 50k 40k 30k 20k 0 400 600 800 1000 1200 1400 Mg(1s) Si(2s) Kinetic Energy eV Intensity CPS C(AES) N(AES) Ca(AES) O(AES) Fe(AES) Fe(2p) O(1s) Ca(2p) Mg(AES) P(2s) N(1s) Ca(2s) S(2p) P(2p) Al(2s) Si(2p) Mg(2s) Al(2p) O(2s) C(1s) 10k 200 60k 50k 40k 30k 20k 0 400 600 800 1000 1200 1400 10k10k 200200 60k 50k 40k 30k 20k 00 400400 600600 800800 10001000 12001200 14001400 Mg(1s)Mg(1s) Si(2s) Kinetic Energy eV Intensity CPS C(AES)C(AES) N(AES)N(AES) Ca(AES)Ca(AES) O(AES)O(AES) Fe(AES)Fe(AES) Fe(2p) O(1s) Ca(2p) Mg(AES) P(2s) N(1s) Ca(2s) S(2p) P(2p) Al(2s) Si(2p) Mg(2s) Al(2p) O(2s) C(1s) 180 178 176 174 172 170 168 166 164 162 1050 1100 1150 1200 1250 1300 169.7 Binding Energy eV (-4.13) Intensity CPS 164.2 LG 700 PA SULFUR SPECTRUM (a) 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 Time (min) H 2 S outlet concentration (ppmv) CAT LF 700 PA LF 900 PA LF 700 PAH LF 900 PAH (b) 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 Time (min) H 2 S outlet concentration (ppmv) CAT LL 700 PA LL 900 PA LL 700 PAH LL 900 PAH (c) 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 60 70 80 90 100 110 120 Time (min) H 2 S outlet concentration (ppmv) CAT LG 700 PA LG 900 PA LG 700 PAH LG 900 PAH Figure 10