MCM41

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Hot coal gas desulfurization using regenerable ZnO/ MCM41 prepared via one-step hydrothermal synthesis Mengmeng Wu, Lei Jia, Hui-Ling Fan, and Jie Mi Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01615 • Publication Date (Web): 25 Aug 2017 Downloaded from http://pubs.acs.org on August 29, 2017

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Hot coal gas desulfurization using regenerable ZnO/MCM41 prepared via one-step hydrothermal synthesis Mengmeng Wu*, Lei Jia, Huiling Fan, Jie Mi* Key Laboratory of Coal Science and Technology of Shanxi Province and Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China

ABSTRACT

ZnO/MCM41 sorbents with bimodal pore structure were prepared via one-step hydrothermal synthesis. The structure of fresh, sulfided and regenerated sorbents was characterized using XRD, TEM, SEM, nitrogen adsorption isotherms, and XPS techniques. The results indicate that the desulfurizer with 35% ZnO shows the highest sulfur capacity (11.0 g S/100 g sorbents). The optimum regeneration conditions were: 650 oC, 3000 h-1 and 6% O2 concentration. Both ZnO and ZnSiO4 were observed in the regenerated sorbents. The increase of regeneration cycles leads to higher content of the Zn2SiO4. However, it results in no significant effect on the performance of sorbents during five sulfidation/regeneration cycles. It may be due to the transformation of Zn2SiO4 into ZnO under conditions of desulfurization. After 5 successive sulfidation/regeneration cycles, the sorbents still maintain high sulfur capacity (9.8 g S/100 g sorbents) and mechanical strength (80 N/cm).

Keywords: H2S; mesoporous; ZnO; MCM41; desulfurization; sorbents.

*

Corresponding authors. Tel.: +86 351 6018598.

E-mail address: [email protected] (Wu, M.), [email protected] (Mi, J.).

ACS Paragon Plus Environment

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1. INTRODUCTION The gasification of coal, petroleum coke, biomass, and their mixture, is one key technique for clean utilization of these resources [1,2]. However, the release of gasous sulfur species such as hydrogen sulfide and carbonyl sulfide is inevitable during the gasification process

[2]

. H2S does damage to the pipeline and gas turbine

[1-3]

causes poisoning of catalyst used in the subsequent chemical synthesis

. It also [1-3]

. In

addition, it leads to pollution when released into air. Therefore, the removal of H2S is necessary prior to utilization of gasification products either as fuel gas or as synthesis gas

[2-4]

. The techniques of removing H2S involve wet and dry desulfurization. The

former is mainly used for rough desulfurization. It owns large handling capacity, while it cannot realize the high-efficient usage of the sensible heat from the raw gas [3]. Meanwhile, deep desulfurization is often impossible

[2-5]

. Single and mixed metal

oxide is often used in mid- and high-temperature dry desulfurization. Iron oxide is competitive among the sorbents reported due to high sulfur capacity and low cost. Nevertheless, it cannot realize desulfurization with high efficiency [2,5]. In the view of desulfurization depth, ZnO is most attractive sorbent due to favorable sulfidation thermodynamics

[6]

. It can reduce the concentration of H2S from several thousand

ppm to sub ppm levels (350–400 oC)

[6]

. Zinc oxide is most widely used at the mid-temperatures

[7,8]

. Higher desulfurization temperature can result in unfavorable

thermodynamics but larger reaction rate

[6-8]

. However, ZnO can easily be reduced to

elemental Zn under the strong reducing atmosphere at high temperatures (> 600 oC) [9]. The ZnO could be stabilized by addition of TiO2 resulting from the formation of Zn2TiO4 with a spinel structure, while the activity reduction of the sorbents is irresistible [7,10]. According to Novem’s study [11], the optimum sulfidation temperature during the IGCC (integrated gasification combined cycle) process ranges from 350 to 550 oC due to lower overall process cost. Based on the analysis above, the reduction of ZnO may be avoidable and higher desulfurization depth is achievable when using ZnO as sorbent for coal gas desulfurization at 500 oC.


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In comparison with unsupported sorbents, supported desulfurizers are more preferred because of higher reaction activity, mechanical strength, and thermal stability

[7]

. Mesoporous carriers can supply more mesopores (> 2 nm), which is

conducive to the mass transfer. Furthermore, ordered mesoporous support

[12]

(MCM41, MCM48, KIT6) is more attractive due to high surface, large volume, and uniform mesopores

[12,13]

. MCM41 can be used as a good support for sorbents

removing H2S for dry (or low H2O content) hot coal gas although the hydrothermal stability of MCM48 and KIT6 is better than MCM-41

[14]

. In order to obtain the

sorbents with high loading content, two steps are required. The first step including calcinations treatment to remove structure-directing agent (P123, cetyltrimethyl ammonium bromide) is the synthesis of ordered mesoporous carrier

[12,13]

subsequent step involves impregnation, precipitation, or sol-gel method

. Then the

[12,13]

. It is

notable that the calcination operation is also inevitable in the second step. Consequently, the complexity of synthesis procedure becomes the drawback of current preparation process. In addition, supported Zn-based sorbents could remove H2S at higher temperatures compared to supported Cu-based

[7]

sorbents. They also

have high efficiency in comparison with supported Fe-based or Mn-based [5] sorbents. As reported in literature

[12,13]

, Zn-based sorbents supported on mesoporous

carrier own lower sulfur capacity. Furthermore, the related studies mainly focus on the desulfurization evaluation. The regeneration ability is vital for the application of sorbents. However, regeneration (especially multi-cycle regeneration) of these sorbents is less reported. The main objective of this paper is to investigate the feasibility of one-step hydrothermal synthesis of MCM41 supported ZnO sorbents. The regeneration properties under different conditions were investigated. Furthermore, the performance and the structure of sorbents during multiple sulfidation/regeneration process are also analyzed. 2. EXPERIMENTAL 2.1. Preparation of ZnO/MCM41 Sorbent


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Firstly, 10.0 g Na2SiO3·9H2O (analytical pure) was dissolved into 60 mL deionized water. Then, based on mole ratio (1:5) of cetyltrimethyl ammonium bromide (CTAB) to SiO2, an appropriate amount of CTAB was dissolved with 100 mL of deionized water at 50 oC under constant stirring. The resulting solution was added dropwise to the aforementioned solution. The pH of the mixture was adjusted to 10 with 1mol·L-1 H2SO4 solution. The resulting white sol was stirred for a certain time (ct). Then, certain amount zinc source (zs) was added to the white sol with continual stirring at specified temperature (st). 1 mol/L H2SO4 solution was used for adjusting pH of the obtained mixture. The resultant mixture had a molar composition of 1 CTAB: 0.2 SiO2: 120 H2O. After stirring for another 2 h, the treated mixture was heated in a Teflon-lined autoclave at 100 oC for 48 h. The products was filtrated and washed to neutral. Subsequently, the solid product was dried at 80 oC and calcined at 550 oC for 6 h. A series of samples with 10 wt. % ZnO were obtained. They are named as S-A (ct: 4 h; zs: zinc nitrate solution; st: 50 oC), S-B (ct: 2 h; zs: zinc nitrate solution; st: 25 oC), S-C (ct: 4 h; zs: zinc nitrate solution; st: 25 oC), S-D (ct: 4 h; zs: fresh Zn(OH)2 precipitate; st: 50 oC), S-E (ct: 2 h; zs: fresh Zn(OH)2 precipitate; st: 25 C) and S-F (ct: 4 h; zs: fresh Zn(OH)2 precipitate; st: 25 oC), respectively. The pure

o

MCM 41 was prepared via optimum synthesis conditions without addition of zinc source. 2.2. Characteristic of Sorbent X-ray diffraction (XRD) analysis was performed by D/MAX2500 (Pigaku, Japan) using Cu Kα radiation. The crystallite size of ZnO was estimated from (101) XRD peak using Scherrer formula [15]:

d101 =

0.9λ β101 cosθ101

(1)

where d101 and λ are the grain size and the wavelength (0.154056 nm) of the X-ray radiation, respectively; β101 and θ101 represents the full-width at half-maximum intensity and scattering angles of the (101) peak, respectively. The morphology of


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samples was investigated by transmission electron microscope (TEM, JEM-2100) and scanning electron microscopy (SEM, TESCAN MAIA3). The elemental compositions of

samples

were

analyzed

by

energy

dispersive

spectroscopy

(EDS).

ESCALAB250Xi spectrometer (Thermo Fisher Scientific, USA) using an Mg Kα source was used for XPS analysis. C1s was used for the calibration of binding energy. The properties of pore structure were investigated by on JW-BK122W Porosity Analyzer (Beijing JWGB Sci & Tech Co., Ltd.). Brunauer-Emmett-Teller (BET) equation was used for calculating the surface area of samples. 2.3. Desulfurization Evaluation A fixed-bed quartz reactor (17 mm in inner diameter, 650 mm in length) was used to investigate the sulfidation properties of sorbents. 10 mL sorbents located in the central part of the quartz tube were heated to 500 oC under N2 atmosphere at atmospheric pressure. Then the stream was switched to the reaction gas containing 0.25% H2S, 39% H2, 27% CO, 12% CO2, and N2 (balance gas), was passed through the sorbents with cylindrical shape (3 × 3 mm). The volume hourly space velocity is 2000 h-1. The H2S concentration of outlet was determined by gas chromatograph equipped with a flame photometric detector. When the H2S concentration of outlet reaches 500 ppm, the corresponding time is defined as breakthrough time (BT). Sulfur capacity (SC, %), was the ratio of the mass (unit: g) of adsorbed sulfur per 100 g sorbent. The formula for calculating SC is described elsewhere

[8,16]

. The utilization rate of ZnO (UR, %) is the ratio of

experimental SC to the theoretic SC [16]. 2.4. Regeneration The regeneration properties were also evaluated in the same reactor. The reactant gas with a composition of 2–8 vol. % O2 and balance gas N2 was introduced into reaction tube after the used sorbents were heated to the regeneration temperature (550–700 °C) in N2. The regeneration space velocity varied over the range of 2000 to 4000 h-1. The iodometry [17] was used to analyze the concentrations of outlet SO2. The


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regeneration rate (Rr, %) is caculated by the following equation:

Rr =

Sb - Sa Sb

(2)

where Sa and Sb represent the mass of sulfur containing in the sorbent after and before regeneration, respectively. The measurement for sulfur content and mechanical strength of sorbents was described in the previous study [17]. 3. RESULTS AND DISCUSSION 3.1. Effect of Preparation Method Six preparation methods were used, and the small-angel XRD patterns of the resulting ZnO/MCM41 are presented in Figure 1. Initially, the CTAB surfactant as structure-directing agent first forms hexagonal micelles [18]. Then, before the addition of zinc sources, the products from the hydrolysis of silicate and polymerization reactions among hydrolysis products could adsorb on the surface of micelles due to van der waals forces and other weak interaction [19,20]. However, the Zn2+ or Zn(OH)2 could also interact with the micelles, which effects the stability of skeleton structure of MCM41. As shown in Figure 1, compared to zinc nitrate (corresponding to S-A, S-B and S-C), using Zn(OH)2 as zinc source (corresponding to S-D, S-E and S-F) results in much stronger diffraction peaks assigned to MCM41

[18-20]

under the same

synthesis conditions. It is attributed to the fact that Zn2+ with stronger interaction with hexagonal micelles leads to more adverse effect on the ordered character of MCM41. Additionally, in comparison with S-D and S-E, the structure of S-F is more ordered deduced from stronger peaks observed in small-angle XRD patterns. It suggests longer ct and lower st are favorable for the formation of ordered mesoporous structure. It is notable that both the strong peak (belonging to (100) reflection) and two weak signals (corresponding to (110), and (200) reflections) indexed to its typical hexagonal regularity of the channel

[18,21]

appear in the XRD patterns of S-F.

Furthermore, the peaks assigned to ZnO are also observed in the large-angle XRD patterns (Figure 2, discuss later) of supported sorbents. It indicates that one-step


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synthesis of ZnO/MCM41 sorbents but maintaining the ordered mesoporous structure at the same time is feasible. 3.2. Effect of Loading Content The optimal preparation method was used to obtain pure MCM41 and a series of sorbents with different loading content. The sorbents with 15, 20, 25, 30, 35, 40, and 45% zinc oxide are denoted as S-15, S-20, S-25, S-30, S-35, S-40 and S-45. Three typical diffraction peaks assigned to hexagonal regularity of the channel are observed in both MCM41 and ZnO/MCM41. It suggests that the supported sorbents still maintain the ordered pore structure. Strong diffraction peaks (2θ =31.8°, 34.4°, 36.3°, 47.5°, 56.6°, 62.9°, and 68.0°) [PDF# 36-1451] belonging to ZnO phase

[22]

was

observed in the large-angle XRD patterns of ZnO/MCM41 with higher (> 20%) loading content. However, for sorbents with lower (< 25%) content of zinc oxide, diffraction peaks assigned to ZnO are significantly weak or not observed due to lower loading content or better dispersion of zinc oxide. Additionally, the elevation of ZnO content results in the increase in the grain size of ZnO estimated from (101) XRD peak (Figure 2d). However, greater crystalline size could supply less contact area between ZnO and H2S, which is unbeneficial to the desulfurization of sorbents. As shown in Figure 3, the MCM41 appear bent rod-like structure, the width of which is about 500 nm. Furthermore, the hexagonal regularity is also observed by TEM images (Figures 3a and 3b). The morphology of S-35 presented in Figures 3j and 3k indicates that some ZnO in the surface of MCM41 appears hierarchical porous structure formed by the self-assembly of ZnO nanoplates [23]. It is notable that hollow ZnO particles (width: about 200 nm) are also observed in the morphology (Figures 3l and 3m) of sorbents. Furthermore, some hollow particles are ringent, and the opening width is about (or smaller than) 50 nm. Two different morphology of ZnO is also confirmed by EDS spectra (Figures 3q and 3t). The structure character above is favorable for the desulfurization of sorbents. After desulfurization, flake structure becomes less porous (Figure 3u), while no obvious change is observed for hollow


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particles (Figure 3v). Actually, the sorbents with other loading content (the SEM images not given) also show the similar feature. The TEM images of ZnO/MCM41 (Figures 3c-3g) suggest that the penetration depth of zinc species within the MCM41 nanorods is about 30 to 50 nm for sorbents with 30 to 45% ZnO. Furthermore, larger loading content results in the distribution of ZnO in narrower region near the surface of MCM41 microparticles. The nitrogen adsorption–desorption (Figure 4) of MCM-41 and supported sorbents show type IV isotherm

[12,19,21]

and mesoporous feature. A

sharp step up in a narrow range of relative pressure (P/P0 = 0.25–0.4) due to the capillary condensation of N2

[21]

, was also observed, indicating the presence of

uniform mesopores. A sharp peak located at about 3.70–3.83 nm appears in the pore width distribution curves of S-15, S-20, S-30, and S-35. Larger predominant diameter (4.29 nm) for S-25 may be attributed to the non-uniformity of MCM41 with 25% ZnO. It is interesting to see that S-40 and S-45 owns smaller predominant diameter (2.73 and 2.74 nm). It may be due to the plugging of pore structure by ZnO. It is notable that N2 adsorption–desorption of ZnO/MCM-41 also exhibits a well-defined hysteresis loop at higher partial pressures (P/P0 > 0.45). It reveals that there are larger pores in the supported desulfurizer. As expected, pores with size ranging from 10 to 50 nm are observed in the pore size distribution curves. The hierarchical structure via the self-assembly of ZnO nanoplate and ringent ZnO particles are responsible for the formation of these larger pores. The surface area (S) and pore volume (V) and average pore diameter of MCM41 and ZnO/MCM-41 sorbents are summarized in Table 1. The loading of ZnO leads to greater decrease in both S (by 34-65%) and V (by 39–58%). However, it results in larger the average size of sorbents (except for S-40 and S-45). After desulfurization, the decrease of S (by 6-39%) and V (by 5-24%) is also observed due to the replacement of O2- by S2-. As shown in Figure 5, increasing loading content from 15 to 35% results in an increase of the breakthrough time (from 147 to 395 min) and sulfur capacity (from 5.2


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to 11.0%). However, compared to S-15, a decrease of the utilization rate (UR) of ZnO in S-20, S-30 and S-35 is observed. The decrease is attributed to less active site per unit surface or pore volume of sorbents with more ZnO but lower surface area (or pore volume). Further increase of the content of zinc oxide leads to the decline in the breakthrough time, sulfur capacity, and UR. It may be due to worse dispersion of active component for S-40 and S-45. In addition, the sulfur capacity of all sorbents is higher than that reported in literature (0.38–2.45%) [12]. 3.3. Effect of Regeneration Conditions on Desulfurization Performance Used S-35 was for investigating the effect of regeneration condition. Only ZnS is observed (shown later) for used sorbents. The regeneration curves of ZnO/MCM-41 (S-35) are presented in Figure 6. Figure 7 shows the XRD patterns of sorbents after regeneration. The regeneration reaction is mainly dominated by chemical reaction (Eq. 3) at the initial stage, while diffusion through dense ZnO layer is the major resistance of regeneration process in the later stage [7,24,25]. As expected, a large part of the SO2 is released and the reaction rate is larger at the initial stage of regeneration process (see Figure 6), after which the regeneration reaction becomes slow. It takes significantly longer time before the SO2 concentration of outlet reaches zero when used sorbents is regenerated at 550 and 600 oC. It is attributed to the fact that the rate of regeneration reaction at low temperature (< 650 oC) is much lower and more ZnS species are still in the regenerated sorbents deduced from XRD patterns (Figure 7). However, much shorter regeneration time and an increase of the regeneration rate are observed when the regeneration temperature is 650 oC. Although low temperature promotes the formation of ZnSO4, no sulfate was produced even at 550 °C. It may be due to low oxygen concentration (6%). In addition, for sorbents regenerated at 600 and 650 oC, no XRD diffraction peaks belonging to ZnS is observed, while peaks attributed to Zn2SiO4 [26] (PDF#37-1485) appear in the XRD patterns due to the reaction (Eq. 4) of ZnO with SiO2. High temperature is favorable for the formation of Zn2SiO4 from the view of reaction kinetics

[26]

. The reaction of ZnO with SiO2 is conducive to the


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regeneration of ZnS via oxidation reaction based on the theory of chemical equilibrium shift

[27]

. As expected, a slight increase in the regeneration rate was

observed. However, in comparison with the sorbents regenerated at 650 oC, stronger intensity of diffraction peaks assigned to Zn2SiO4 and weaker peaks belonging to ZnO are observed when sorbents is regenerated at 700 oC. It indicates that the there is higher content of Zn2SiO4 with lower desulfurization activity in the regeneration (at 700 oC) products. ZnS + O2 → ZnO + SO2

(3)

2 ZnO + SiO2 → Zn2 SiO4

(4)

Increasing space velocity from 2000 to 3000 h-1 results in greater regeneration rate (95.6 %), which is due to lower mass transfer resistance at higher space velocity [17]

. It is notable that the intensity of XRD peaks assigned to Zn2SiO4 appears much

weaker at the space velocity of 3000 h-1, while further increase of space velocity leads to lower regeneration rate (91.9%), longer regeneration time, and stronger intensity of XRD peaks of Zn2SiO4. The regeneration reaction is typical gas-solid reaction

[7,17]

and the first step is adsorption of O2 and subsequent reaction of adsorbed O2 with ZnS [7]

. Consequently, shorter retention time of O2 on the surface of used sorbents when

regenerated at the space velocity of 4000 h-1 is unfavorable for the oxidization regeneration. It is accountable for low regeneration rate and longer regeneration time. However, the residence time of gas feed has little effect on the solid-solid reaction of ZnO with SiO2 and the larger gas velocity facilitates the removal of the heat from the above reaction (exothermic). It is responsible for more Zn2SiO4 species at high space velocity. As shown in Figure 6c, it requires longer time before the released SO2 concentration reaches zero when used sorbents is regenerated under the atmosphere with 2% O2. Furthermore, low regeneration rate is observed (90.5%). It is attributed to the fact that low oxygen concentration corresponds to lower rate of the oxidization of ZnS with first-order dependence in O2 based on the study

[7,28,29]


of intrinsic reaction

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kinetics. The highest regeneration rate (95.6%) and shorter regeneration time are observed when the concentration of O2 is 6%. However, further increase of oxygen content in the regeneration atmosphere results in longer regeneration time but smaller regeneration rate (93.4%). It is attributed to larger possibility of sintering of ZnS grain under higher O2 concentration resulting from more heat released from the strongly exothermic reaction between ZnS and O2 [28,29]. In addition, 8% O2 in the regeneration gas results in stronger XRD diffraction peaks assigned to Zn2SiO4 with low desulfurization activity. In general, the optimum regeneration conditions are: 650 oC, 3000 h-1 and 6% O2 concentration.

3.4. Multiple Sulfidation/regeneration Properties of Sorbents Multiple sulfidation/regeneration properties are vital for the industrial application of sorbents. Figure 8 presents the desulfurization performance of ZnO/MCM41 (S-35) during the successive sulfidation/regeneration process. Compared to the first sulfidation process, the sorbents show longer breakthrough time and greater sulfur capacity during the process of second sulfidation. It may be due to the thermal stability of sorbents after the first regeneration because the regeneration temperature (650 oC) is higher than caclcination or desulfurization temperature (500 oC) of sorbents. However, the breakthrough time, sulfur capacity, and the utilization of ZnO decrease with the increase of the sulfidation/regeneration cycles (2-5). The changes of structure property are responsible for the decrease. Compared to the fresh desulfurizer, the sulfur capacity of the first, second, third, fourth, and fifth regenerated sorbents decrease by -0.8, 2.4, 5.2, 7.5, and 11.3%, respectively. However, the utilization of ZnO is still larger than 70 % when the sorbents removing H2S for the sixth time. In addition, the mechanical strength of sorbents maintains above 80 N/cm (see Figure 9) during six sulfidation/regeneration cycles. As shown in Figure 10, in addition to ZnO, Zn2SiO4 with poor desulfurization performance is also formed during the regeneration of used sorbents. However, it leads to no significant effects on the sulfidation properties of sorbents. It is interesting


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to see that no peaks belonging to Zn2SiO4 appear in the XRD patterns of sorbents after sulifidation (Figure 11). The results suggest that the decomposition reaction of Zn2SiO4 to ZnO and SiO2 occurs under the desulfurization conditions. As regeneration times increases from 2 to 5, stronger intensity of XRD peaks belonging to Zn2SiO4 for the regenerated sorbents is observed. It agrees with the performance of sorbents. As shown in Figure 11, there are two kinds of ZnS phase for sorbents after desulfurization: wurtzite hexagonal phase and cubic zinc blende phase. Furthermore, the latter contributes most. Table 2 lists the pore structure properties of sorbents during multicycle sulfidation/regeneration process. In general, sulfidation reaction leads to the plugging of pores. However, regeneration may restore (at least partially) the pore structural properties to their original values

[30]

. It is notable that the regeneration of used

ZnO/MCM41 sorbents (except for the third sulfidation/regeneration cycle) leads to the decrease in the surface area (S) and pore volumne (V). It may be attributed to the formation of Zn2SiO4 during the regeneration process. Additionally, the surface area (S) of regenerated sorbents decrease by -1.0, -2.4, 16.9, 3.5, and 1.9% after the second, third, fourth, fifth and sixth sulfidation. The decomposition of Zn2SiO4 may be the reason for little change in pore structure except the fourth sulfidation. No rules in the average pore size resulting from desulfurization or regeneration are observed. XPS is a powerful tool to analyze the surrounding chemical atmosphere of atom (Zn, O, S) [31,32]. Figures 12, 13 and 14 present Zn 2p3/2 , O 1s and S 2p XPS spectra of sorbents during sulfidation/regeneration process, respectively. Compared to the fresh sorbents, the binding energies of sorbents undergoing sulfidation shift to higher values (1022.0 ± 0.1) due to the sulfidation reaction (Eq. 5). The Zn 2p3/2 peaks of four regenerated sorbents were deconvoluted into two peaks (Zna and Znb) by GaussianLorentz fitting, located at 1021.2 ± 0.2 and 1022.7 ± 0.1 eV, respectively. Zna and Znb are ascribed to represents ZnO

[31]

and Zn2SiO4

[32]

phase, respectively. The binding

energies (BE) and contents of different species obtained from XPS spectra of Zn


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2p3/2 and O 1s are listed in Table 3. The ratios of ZnO to all Zn species on the surface of regenerated sorbents decrease with the increase of regeneration times. In composition with the 1st regenerated sorbent, the fraction of ZnSiO4 in all Zn phases increase by 62.2% after 5th regeneration. The results are consistent with XRD analysis. The O 1s XPS spectrum of sorbents exhibits an asymmetric character. They are fitted into three types of peaks (corresponding to Oa, Ob, and Oc), centered at 530.1 ± 0.1, 531.8, 533.4 ± 0.2 eV, respectively. The low binding energy component located at 530.1 ± 0.1 eV is ascribed to the lattice oxygen [33-35]. After desulfurization, the concentration of lattice oxygen on the surface of 1st, 2nd, 3rd, 4th, and 5th regenerated sorbents reduce by 82.2, 67.2, 61.6, 99.9 and 72.5%, respectively. It is attributed to the replacement of O2- by S2-. Oc represents the adsorbed oxygen

[33-36]

,

and it cannot be removed completely, even by annealing in vacuum at high temperature (400 oC)

[36]

. As listed in Table 3, the fractions of Oc on the surface of

regenerated sorbents increase by 36.2, 22.5, 16.6, 31.2, and 48.9%, respectively, when they are subjected to 2nd, 3rd, 4th, 5th and 6th sulfidation. The desulfurization reaction produces H2O, which can interact with mesoporous SiO2. It may be an explanation for more Oc species after sulfidation. Ob can be attributed to the oxygen ions in the oxygen-deficient regions

[34-36]

. The concentration of Ob on the surface of

sulfide desulfurizer increases after each regeneration, which is favorable for the sulfidation of sorbents. The S2p XPS peaks located at 162.5 ± 0.2 eV are observed for all sulfided sorbents. These peaks belong to S2- species

[37]

. The results agree with

XRD results of sorbents after desulfurization.

ZnO + H 2 S → ZnS + H 2 O

(5)

The morphology of regenetated sorbents is presented in Figure 15 a, d, e, g, i, l, m. Both flake structure and irregular particles (hollow or compacted) appear in the SEM images of regenerated sorbents. It suggests that typical morphology of sorbents can restore by regeneration. It is notable that the sulfided sorbents become more compacted, while there are also two typical morphology in the SEM images (Figure


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 37

15 b, c, f, h, j, k, n, o) of used sorbents. It agrees with the better properties of multiple sulfidation/regeneration.

4. CONCLUSION ZnO/MCM41 sorbents were prepared via one-step hydrothermal synthesis. And the sorbents show bimodal pore structure. The ringent ZnO particles (hollow) and hierarchical structure formed by the self-assembly of ZnO nanoplates are responsible for the formation of larger pores (10–50 nm). The effect of loading content and regeneration conditions were investigated. The results suggest that the sorbent with 35% ZnO owns highest sulfur capacity (11.0 g S/100 g sorbents) and durable regeneration ability. The optimum regeneration conditions were: 650 oC, 3000 h-1 and 6% O2 concentration. In addition to ZnO, Zn2SiO4 was also formed during the regeneration process. However, there is less decrease in the desulfurization performance of regeneration sorbents. It may be attributed to the decomposition of Zn2SiO4 to ZnO and SiO2. Additionally, the sorbents also show high sulfur capacity (> 9.8 g S/100 g sorbents) and mechanical strength

(> 80 N/cm) during five

successive

sulfidation/regeneration cycles.

Author information Corresponding Author *Telephone: +86-351-6018598. E-mail: [email protected] (Wu, M.), [email protected] (Mi, J.).

ACKNOWLEDGEMENTS This work was supported by National Natural Science Foundation of China (21506143, 51272170) and Natural Science Foundation of Shanxi Province (201701D221041).

REFERENCES (1) Wang, X.; Liu, Y.; Sun, Z.; Che, D. Energy Fuels 2011, 25, 4865. (2) Ravikumar, A.; Raj, A.; Ibrahim, S.; Rahman, R. K.; Shoaibi, A. Energy Fuels

2016, 30, 10823–10834.


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Energy & Fuels

(3) Zeng, B.; Yue, H.; Liu, C.; Huang, T.; Li, J.; Zhao, B.; Zhang, M.; Liang, B.

Energy Fuels 2015, 29, 1860–1867. (4) Husmann, M.; Müller, M.; Zuber, C.; Kienberger, T.; Maitz, V.; Hochenauer, C.

Energy Fuels 2016, 30, 6458–6466. (5) Li, F. G.; Pan, K. L.; Lee, H. M.; Fellah, M. F. Ind. Eng. Chem. Res. 2015, 55, 11040–11047. (6) Ling, L.; Zhang, R.; Han, P.; Wang, B. Fuel Process. Technol. 2015, 106, 222–230. (7) Cheah, S.; Carpenter, D. L.; Magrini-Bair, K. A. Energy Fuels 2009, 23, 5291–5307. (8) Wu, M.; Hu, C.; Feng, Y.; Fan, H.; Mi, J. Fuel 2015, 146, 56–59. (9) Gibson, J. B.; III; Harrison, D. P. Ind. Eng. Chem. Proc. Des. Dev. 1980, 19, 231–237. (10) Sasaoka, E.; Hirano, S.; Kasaoka, S.; Sakata, Y. Energy Fuels 1994, 8, 763–769. (11) Wang, J.; Liu, L.; Han, L.; Hu, Y.; Chang, L.; Bao, W. Fuel Process. Technol.

2013, 110, 235–241. (12) Hussain, M.; Abbas, N.; Fino, D.; Russo, N. Chem. Eng. J. 2012, 188, 222–232. (13) Mureddu, M.; Ferino, I.; Rombi, E.; Cutrufello, M. G.; Deiana, P.; Ardu, A.; Musinu, A.; Piccaluga, G.; Cannas, C. Fuel 2012, 102, 691–700. (14) Hussain, M.; Fino, D.; Russo, N. J. Hazard. Mater. 2012, 211-212, 255. (15) Cugini, A.V.; Krastman, D.; Martello, D. V.; Frommell, E. F.; Wells, A. W.; Holder, G. D. Energy Fuels 1994, 8, 83–87. (16) Wu, M.; Su, Z.; Fan, H.; Jie, M. Energy Fuels 2017, 31, 4263–4272. (17) Feng, Y.; Mi, J.; Chang, B.; Wu, M.; Shangguan, J.; Fan, H. Fuel 2016, 186, 838–845. (18) Chen, H.; Wang, Y. Ceram. Int. 2002, 28, 541–547. (19) Koyano, K. A.; Tatsumi, T.; Tanaka, Y.; Nakata, S. J. Phys. Chem. B 1997, 101, 9436–9440.


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(20) Tatsumi, T.; Koyano, K. A.; Tanaka, Y.; Nakata, S.; J. Porous Mater. 1999, 6, 13–17. (21) Liu, B. S.; Wan, Z. Y.; Zhan, Y. P.; Au, C. T. Fuel 2012, 98, 95–102. (22) Anderson, N. A.; Ai. X.; Lian, T. J. Phys. Chem. B 2017, 109, 7088–7094. (23) Niu, H.; Yang, Q.; Tang, K.; Xie, Y.; Yu, F. J. Mater. Sci. 2006, 41, 5784–5787. (24) Huang, Z. B.; Liu, B. S.; Wang, F.; Au, C. T. Appl. Surf. Sci. 2015, 353, 1–10. (25) Zhang, J.; Wang, Y.; Ma, R.; Wu, D. Fuel Process. Technol. 2003, 84, 217–227. (26) Yoshizawa, K.; Kato, H.; Kakihana, M. J. Mater. Chem. 2012, 22, 17272–17277. (27) Liu, Y.; Liu ,Y.; Drew, M. J. Math. Chem. 2012, 52, 597–610 (28) Hong, E.; Kim, J. H. Int. J. Hydrogen Energy 2014, 39, 9985–9993. (29) Siriwardane, R V.; Woodruff, S. Ind. Eng. Chem. Res. 1995, 34, 699–702. (30) Bakker, W. J. W.; Kapteijn, F.; Moulijn, J. A. Chem. Eng. J. 2003, 96, 223–235. (31) Zhao, C. X.; Huang, K.; Deng, S. Z.; Xu, N. S.; Chen, J. Appl. Surf. Sci. 2013,

270, 82–89. (32) Dake, L.S.; Baer, D. R.; Zachara, J. M. Surf. Interface Anal. 1989, 14, 71. (33) Jiang, H.; Dai, H.; Meng, X.; Ji, K.; Zhang, L.; Deng, J. Appl. Catal., B 2011,

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2013, 551, 688−693. (35) Guo, L.; Chen, F.; Fan, X.; Cai, W.; Zhang, J. Appl. Catal., B 2010, 96, 162−16 (36) Wang, H.; Xie, C. Physica E 2008, 40, 2724–2729. (37) Li, L.; Hong, C.; Zhang, W.; Chen, W.; Li, P. J. Alloys Compd. 2015, 636, 216–222.


Page 16 of 37

Page 17 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 1. Surface area (S) and Pore volume (V) and average pore diameter of MCM41 and sorbents with different loading content before and after desulfurization

Table

2.

Pore

structure

properties

of

sorbents

during

multicycle

sulfidation/regeneration process

Table 3. Binding energies (BE) and contents of different species obtained from XPS spectra of Zn 2p3/2 and O 1s

Figure 1. XRD spectra of ZnO/MCM41 with different preparation methods. Figure 2. XRD results of MCM41 and ZnO/MCM41. Figure 3. Morpology of MCM41 and ZnO/MCM41. TEM images of samples: (a), (b) MCM41, (c) S-30, (d), (e) S-35, (f) S-40, (g) S-45; SEM images of samples: (h), (i) MCM41, (j)-(n), (p), (s) fresh S-35, (u), (v) used S-35; EDS spectra of a certain point as denoted in (n), (p), (s): (o), (q),(t).

Figure 4. N2 adsorption/desorption isotherms and pore size distribution of MCM41 and ZnO/MCM41.

Figure 5. Desulfurization performance of ZnO/MCM41. Figure 6. Regeneration curves of ZnO/MCM41. Figure 7. XRD patterns of sorbents after regeneration under different conditions. Figure 8. Desulfurization performance of ZnO/MCM41 during the successive sulfidation/regeneration process.

Figure 9. Mechanical strength of fresh and regenerated ZnO/MCM41. Figure 10. XRD patterns of sorbents after regeneration. Figure 11. XRD patterns of sorbents after sulifidation. Figure 12. Zn 2p3/2 XPS spectra of sorbents during sulfidation/regeneration process. Figure 13. O 1s XPS spectra of sorbents during sulfidation/regeneration process Figure 14. S 2p XPS spectra of used sorbents during sulfidation/regeneration process Figure 15. SEM images of regenerated and sulfided sorbents. (a) 1st regeneration, (b), (c) 2nd sulfidation, (d), (e) 2nd regeneration, (f) 3rd sulfidation, (g) 3rd regeneration, (h) 4th sulfidation, (i) 4th regeneration, (j), (k) 5th sulfidation, (l), (m) 5th


Energy & Fuels

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regeneration, (n), (o) 6th sulfidation


Page 18 of 37

Page 19 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 1. Surface area (S) and pore volume (V) and average pore diameter of MCM41 and sorbents with different loading content before and after desulfurization Samples

S (m2 g-1)

MCM-41

1100

1.118

3.07

S-15

732 (468)a

0.620 (0.526)a

3.84 (3.65)a

S-20

679 (568)a

0.613 (0.561)a

3.83 (3.37)a

S-25

673 (445)a

0.607 (0.548)a

3.82 (3.58)a

S-30

592 (424)a

0.603 (0.524)a

3.82 (3.80)a

S-35

565 (342)a

0.561 (0.426)a

3.83 (3.66)a

S-40

421 (340)a

0.484 (0.412)a

3.34 (3.32)a

S-45

379 (358)a

0.470 (0.446)a

3.52 (3.50)a

a

V (cm3 g-1)

Average pore size (nm)

Used sorbents.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table

2.

Pore

structure

properties

of

Page 20 of 37

sorbents

during

multicycle

sulfidation/regeneration process Surface area (S, m2 g-1)

Pore volume (V, cm3 g-1)

Average pore size (nm)

Sulfidation

Sulfidation

Sulfidation

Cycles Regeneration

Regeneration

Regeneration

1

342

208

0.426

0.331

3.66

4.58

2

210

166

0.281

0.273

4.15

4.76

3

170

183

0.274

0.259

4.89

5.03

4

152

141

0.249

0.225

5.88

4.84

5

136

103

0.226

0.215

5.47

5.43

6

101

-

0.206

-

5.55

-

a

Not available.


Page 21 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

Table 3. Binding energies (BE) and contents of different species obtained from XPS spectra of Zn 2p3/2 and O 1s Zn 2p3/2 Samples

Zna

O 1s Znb

Oa

Ob

Oc

BE (eV) Content (%) BE (eV) Content (%) BE (eV) Content (%) BE (eV) Content (%) BE (eV) Content (%) Fresh sorbent

1021.4

100

-

-

530.1

0.1

531.8

31.3

533.5

68.6

1st sulfidation

-

-

-

-

530.1

0

531.8

31.1

533.3

68.9

1st regeneration

1021.2

65.3

1022.7

34.7

530.2

14.5

531.8

49.2

533.6

36.3

2nd sulfidation

-

-

-

-

530.1

2.6

531.8

48.0

533.2

49.4

2nd regeneration 1021.2

50.1

1022.8

49.9

530.2

6.8

531.8

46.4

533.3

46.8

3rd sulfidation

-

-

-

-

530.1

2.2

531.8

40.5

533.3

57.2

3rd regeneration

1021.1

48.5

1022.7

51.5

530.2

4.5

531.8

46.6

533.4

48.9

4th sulfidation

-

-

-

-

530.1

1.7

531.8

41.3

533.4

57.0

4th regeneration

1021.3

46.5

1022.8

53.5

530.2

8.0

531.8

46.0

533.4

46.0

5th sulfidation

-

-

-

-

530.1

0

531.8

39.7

533.2

60.3

5th regeneration

1021.4

43.7

1022.7

56.3

530.2

14.1

531.8

51.9

533.3

34.0

6th sulfidation

-

-

-

-

530.1

3.9

531.8

45.5

533.3

50.6


Energy & Fuels

(100)

(110)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 37

(200)

S-F S-E S-D S-C S-B S-A

2

3

4

5

6

7

2θ (°)

Figure 1. XRD spectra of ZnO/MCM41 with different preparation methods.


Page 23 of 37

(a)

(b)

(100)

(100) (110) (200)

S-45

Intensity (a.u.)

Intensity (a.u.)

MCM41

S-40 S-35 S-30 S-25

(110) 2

3

4

(c)

S-20 S-15

(200) 5 2θ (°)

6

7

8

2

15

(101) ♦ ZnO

♦

14

♦ ♦ ♦

♦

10

20

30

40

2θ ( ° )

50

60

♦

S-45 S-40 S-35 S-30 S-25 S-20 S-15

70

Grain size (nm)

♦

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

3

4

5 2θ ( ° )

6

7

8

(d)

Grain size of ZnO estimated from 13 (1 0 1) peak using Scherrer formula 12 11 10 9 8

80

15%

20%

25% 30% 35% 40% Loading content of ZnO

Figure 2. XRD results of MCM41 and ZnO/MCM41.


45%

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 37

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

(l)

(m)

(n)

(o)


Page 25 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(p)

(t)

(s)

(q)

(u)

(v)

Figure 3. Morpology of MCM41 and ZnO/MCM41. TEM images of samples: (a), (b) MCM41, (c) S-30, (d), (e) S-35, (f) S-40, (g) S-45; SEM images of samples: (h), (i) MCM41, (j)-(n), (p), (s) fresh S-35, (u), (v) used S-35; EDS spectra of a certain point as denoted in (n), (p), (s): (o), (q),(t).


Energy & Fuels

700

(a) MCM-41

400

)

300 200 0.0

0.2

0.1 0.0

10

100

-1

150

0.4

0.6

0.8

100 0.0

1.0

Relative pressure ( p/p0)

0.2

-1

)

(c) S-20

100

0.6

0.8

1.0

(d)S-25

400

3.83nm

0.3

100

0.2

0.2 0.1 10

0.6

-1

250 200 150

100

Pore diameter (nm)

0.4

300

0.8

100 0.0

1.0

350

0.2

3.82 nm

3

150 100 50 0.0

0.2

0.4

0.2

0.4

10

100

0.8

100

250 200 150 100

Pore diameter (nm) 0.6

10

(f) S-35

-1

-1

0.6

-1

200

0.0

0.6

3.83 nm

-1

250

0.4

300

3

300

4.29nm

0.8

Pore diameter (nm) 0.4 0.6 0.8 1.0 Relative pressure ( p/p0)

dV/dD ( cm g nm )

3

Volume adsorbed ( cm g

-1

)

(e) S-30

350

1.2

-1

0.4

3

-1

150

350

3

-1

dV/dD ( cm g nm )

200

dV/dD ( cm g nm )

)

0.4

dV/dD ( cm g nm )

3

250

400 -1

10

Pore diameter (nm)

3

300


3

3.83 nm

450

50 0.0


0.6 0.5 0.4 0.3 0.2 0.1


Volume adsorbed( cm g

)

200

Pore diameter (nm)

350

-1

250

-1

0.2

300

3

0.3

350

dV/dD ( cm g nm )

0.4

3

400

3.79 nm

0.5

-1

500


(b) S-15

-1 3


-1

dV/dD ( cm g nm )

3


-1

)

600

50 0.0

1.0


0.2

0.4 0.2 10 100 Pore diameter (nm)

0.4

0.6

0.8

1.0


300 -1

)

(g) S-40

(h) S-45

-1

)

250

250

3


100

0.0

0.2

0.4

0.4

0.2 0.0 10

150

100

100

0.8


1.0 0.8

2.74 nm

0.6 0.4 0.2 0.0 10

100

Pore diameter (nm)

Pore diameter (nm) 0.6

-1

2.73 nm

-1

0.6

200

3

0.8

-1

150

1.0

3

-1

dV/dD ( cm g nm )

200

dV/dD ( cm g nm )

3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 37

1.0

50 0.0

0.2

0.4

0.6

0.8

1.0


Figure 4. N2 adsorption/desorption isotherms and pore size distribution of MCM41 and ZnO/MCM41.


Page 27 of 37

100

(a)

500 400 300

S-15 S-20 S-25 S-30 S-35 S-40 S-45

(a) 500 ppm

Breakthrough concentration

200

Sulfur capacity (%)

H2S concentration of oultet (ppm)

600

10 80

8 6

60

4

100 0 0

100

200

300

Adsorption time (min)

400

2

15%

20% 25% 30% 35% 40% Loading content of ZnO

Figure 5. Desulfurization performance of ZnO/MCM41.


45%

40

Utilization rate of ZnO (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Energy & Fuels

30

(a)

20 3-

SO2 concentration of outlet gas (g m )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Regeneration rate o

80.3%

o

85.8% 20 90.3% 91.1% 15

550 C

15

25

600 C o 650 C o 700 C

10

o

550 C o 600 C o 650 C o 700 C

5

30

Regeneration rate

2000 h 90.3% -1 3000 h 95.6% 20 -1 4000 h 91.9%

2% O2

90.5%

4% O2 6% O2

93.1%

15

8% O2 o

650 C, 6% O2 -1

2000 h -1 3000 h -1 4000 h

5

10

0

-1

2% O2 4% O2

5

6% O2 8% O2

0

0

0

95.6% 93.4%

650 C, 3000 h

o

10

(c) Regeneration rate

25

-1

-1

2000 h , 6% O2

(b)

Page 28 of 37

200 400 600 800 0

200

400

600 0

200

Regeneration time (min)

Figure 6. Regeneration curves of ZnO/MCM41.


400

600

Page 29 of 37

o

700 C







♦ ZnO ♥ ZnS  Zn2SiO4 2000 h-1, 6% O 2 ♦♦   ♦  ♦  ♦ 

♦ 

o

650 C

♦ ♦♦

o

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

600 C o 550 C 4000 h



-1

♦

♦

♦ o

♦ 

♦♦ 





3000 h

♦

♥♥ ♥

♦



650 C, 6% O2 ♦  ♦  ♦ 

-1

2000 h

-1

8% O2 6% O2 4% O2





o

♦ ♦♦ 

♦

-1

650 C, 3000 h

♦

♦

♦

2% O2

10

20

30

40

50

60

70

80

2θ ( ° )

Figure 7. XRD patterns of sorbents after regeneration under different conditions.


Energy & Fuels

700 Sulfur capacity (%)

Utilization rate of ZnO (%)

H2S concentration of outlet (ppm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 37

600 500 400

12

80

9

60

6

40

3

20

0

300

1

2

3 4

5

Cycle times

6

100

0

100

Breakthrough concentration

0

200

0

500 ppm

200 300 Adsorption time (min)

1st sulfidation 2nd sulfidation 3rd sulfidation 4th sulfidation 5th sulfidation 6th sulfidation

400

500

Figure 8. Desulfurization performance of ZnO/MCM41 during the successive sulfidation/regeneration process.


Page 31 of 37

100

1st regeneration Mechanical strength (N/cm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

3rd regeneration

80

60

40

20

0

Fresh sorbent

2nd regeneration

4th regeneration 5th regeneration

Figure 9. Mechanical strength of fresh and regenerated ZnO/MCM41.


Energy & Fuels

♦ ZnO



Zn2SiO4 

o











♦ 

♦ 

♦

♦ 



♦ 

♦ 

♦

4th regeneration



♦

♦ ♦





♦ 

♦

♦







♦ ♦





5th regeneration



♦



-1

650 C, 3000 h , 6% O2

♦♦



Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 37

♦

3rd regeneration 

♦  

♦

♦

♦

♦

♦

2nd regeneration 

♦

♦ ♦ 

10

20



1st regeneration

♦ 

30

♦



40

50

60

♦♦

70

2θ ( ° )

Figure 10. XRD patterns of sorbents after regeneration.


80

Page 33 of 37

ZnS

♥ ♣ ♣ ♥ ♣

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

♥ ♣

♣

♥ ♣ ♥

♥

♥

♣ ♣ ♥

20

4th sulfidation

♣

♥ ♣ ♣

♣

5th sulfidation

♣

♥

10

♥ Cubic zinc blende phase ♣ wurtzite hexagonal phase ♥ ♥ 6th sulfidation ♣

♣

3rd sulfidation

♣

2nd sulfidation

♥ ♣

30

♣

40

50

♥

1st sulfidation

60

70

2θ ( ° )

Figure 11. XRD patterns of sorbents after sulfidation.


80

Energy & Fuels

Raw Fitted peak Backgroud

Raw Fitted peak Backgroud Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Raw Backgroud Zna


Fresh sorbent

1021.4

2nd sulfidation

1022.1

3rd regeneration

Raw Backgroud Zna

5th sulfidation

1022.0

1st sulfidation

1022.1


Raw Backgroud Zna

Raw Backgroud Zna

2nd regeneration

4th sulfidation

1021.9


Raw Backgroud Zna

1020

1025

1030 1015

1020

5th regeneration

1025

3rd sulfidation

1022.1

4th regeneration

Znb


Znb

1015

1st regeneration

Znb

Znb

Znb


Page 34 of 37

1030 1015

1020

6th sulfidation

1021.9

1025

1030

Binding energy (eV)

Figure 12. Zn 2p3/2 XPS spectra of sorbents during sulfidation/regeneration process.


Page 35 of 37



Fresh sorbent



530

Oa Ob

Oc

2nd sulfidation


Oa Ob

Oc

2nd regeneration


3rd sulfidation

Oa Ob

Oa Ob

Oc

3rd regeneration


Oc Raw Fitted peak Backgroud

4th sulfidation

4th regeneration

Oa Ob

Oa Ob

Oa Ob

Oc

Oc

Oc


5th sulfidation

535

1st regeneration

Oa Ob

Oa Ob

Oc



1st sulfidation

Oc

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

5th regeneration


6th sulfidation

Oa Ob

Oa Ob

Oa Ob

Oc

Oc

Oc

540

530

535

540

530

535

Binding energy (eV)

Figure 13. O 1s XPS spectra of sorbents during sulfidation/regeneration process.


540

Energy & Fuels

6th sulfidation

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 37

5th sulfidation 4th sulfidation 3rd sulfidation

2nd sulfidation 1st sulfidation

160

165

170

175

Binding energy (eV)

Figure 14. S 2p XPS spectra of used sorbents during sulfidation/regeneration process.


Page 37 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

(l)

(m)

(n)

(o)

Figure 15. SEM images of regenerated and sulfided sorbents. (a) 1st regeneration, (b), (c) 2nd sulfidation, (d), (e) 2nd regeneration, (f) 3rd sulfidation, (g) 3rd regeneration, (h) 4th sulfidation, (i) 4th regeneration, (j), (k) 5th sulfidation, (l), (m) 5th regeneration, (n), (o) 6th sulfidation.


MCM41

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