New Way of Removing Hydrogen Sulfide at a High Temperature

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New way of removing H2S at high temperature: microwave desulfurization using Fe-based sorbent supported on active coke Mengmeng Wu, Zibing Su, Huiling Fan, and Jie Mi Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b00086 • Publication Date (Web): 28 Feb 2017 Downloaded from http://pubs.acs.org on March 13, 2017

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New way of removing H2S at high temperature: microwave desulfurization using Fe-based sorbent supported on active coke Mengmeng Wu*, Zibing Su, 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 Microwave was applied to the high-temperature removal of H2S by Fe-based sorbent supported on active coke (Fe2O3/AC). The influence of loading content, adsorption temperature, and desulfurization way on the sulfidation properties of sorbents was investigated. N2 adsorption, XRD, XPS, and SEM techniques were used to characterize the structure of sorbents before and after desulfurization. The results reveal that the microwave sulfidation performs best at 600 oC, while further increase of temperature leads to lower sulfur capacity and utilization rate of Fe2O3 due to pore structure deteriorating of sorbents. Boltzmann function is suitable for describing the H2S evolution behavior of Fe2O3/AC sorbent bed. Several advantages of microwave sulfidation over conventional way are as follows: much better performance of Fe2O3/AC sorbents, less decline in surface area and pore volume per unit sulfur capacity when removing H2S at 400, 500 and 600 oC, and more S2- and oxygen vacancies species on the surface of used desulfurizers. Compared to conventional desulfurization, there is no notable decrease in apparent activation energy of overall sulfidation reaction by microwave way. The enhancement of desulfurization rate may be due to quicker ion diffusions and/or better mass transfer under microwave conditions.

Keywords: H2S; microwave; kinetics; desulfurization; sorbents; Fe2O3.

*

Corresponding authors. Tel.: +86 351 6018598.

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

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1. Introduction Many industrial processes, such as reforming of natural gas, coal gasification and coking of coal, generate hydrogen sulfide with high concentration 1. However, H2S could do harm to environment, cause corrosion of equipment, and poison catalyst 2. Thus, the removal of H2S to required concentration is necessary. Two major desulfurization technologies have been developed. They are wet desulphurization and dry cleaning, respectively 3, 4. Solvent adsorption is the main mechanism with respect to the former process 4. Dry sulfidation includes processes operated at low, mid- and high temperatures, respectively

4

. Activated carbon, selectively catalyzing the

oxidation of H2S to elemental sulfur, is the most studied low-temperature desulfurizer 5

, while metal oxide is the most widely used when used for H2S sorption at mid- and

high- temperatures 6. In comparison of other technologies, mid- and high- temperature desulfurization process can use the sensible heat more efficiently, and reduce the concentration of H2S to lower levels

4, 7

. Consequently, mid- and high- temperature

desulfurization is seen as ideal process for hydrogen sulfide removal in the case of hot coal gas. Based on the free-energy minimization principle, 11 solids based on the metals (Zn, Cu, Fe, Mn, Ca, Mo, V, Ba, W, Co and Sr) are thermodynamically feasible for high-temperature process for H2S removal of gases with low-Btu, according to the study

8

of Westmoreland and Harrison. ZnO has much higher desulfurization

efficiency among these metal oxides

9, 10

, while it can easily be reduced to element

under reductive atmosphere and completely regeneration should be carried out over 650 oC

4, 6, 11

. As to copper oxide, the equilibrium concentration of H2S can be sub

ppmv levels when copper is kept in oxidation (Cu1+, Cu2+) states

12, 13

. However, the

formation of copper is irresistible when used under reductive conditions. MnO and Mo2O3 could neither reduce the concentration of H2S to low levels nor be regenerated easily

13

. Iron oxide has greater capacity and good desulfurization efficiency

14,15

.

More importantly, it is low-cost, and requires lower regenerating temperature


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compared to most of metal oxides including Zn-based sorbents

13-15

. Therefore,

Fe-based sorbents are promising based on sulfidation and economic considerations. Microwave irradiation shows significant advantages over conventional heating such as volumetric heating, energy-saving and rapid heating 16. Although microwave cannot induce breaking of chemical bonds due to the fact that the energy of microwave photons is significantly lower than that of bonds (hydrogen bond, covalent bond, ionic bond) 17, microwave effects were observed in some chemical reactions

16

and adsorption process 18. Under the conditions of crucial temperature control, Shibata 19

confirmed that microwave radiation can result in the decrease of the activation

energy of the decomposition reaction of NaHCO3. However, Cross 20 believed that the acceleration of the reaction rate during the microwave synthesis of TiC is ascribed to the change in Arrhenius pre-exponential factor (A) other than activation energy. Different absorption selectivity for some gas sorption processes was also found when microwave heating was applied 18. In addition, ion diffusions in solid reaction can be enhanced by microwave irradiation 6, 21, 22. Adsorption of H2S and desorption of H2O will occur during desulfurization reaction of metal oxide 8-15. Also, the reaction is controlled by ion diffusion resistance in the later stage of sulfidation

13, 23, 24

. Therefore, if microwave desulfurization was

adopted, advantages of microwave heating and microwave effects may have positive influence on the reaction activity of sorbents for H2S removal. The composition of coal gas from coal gasification is very complex, and atmosphere effects resulting from CO, H2, CO2, and H2O, can greatly influence the desulfurization behavior of metal oxide

8, 13

. Consequently, it is impossible to clarify the microwave effects caused by

microwave sulfidation. Thus, simple atomosphere (N2+H2S) was chosen in our study in order to understand the effect of microwave on sulfur removal. Also, active coke (AC) with good ability of absorbing microwave is chosen as supporter for Fe2O3. The influence of loading content, reaction temperature, and desulfurization way of Fe2O3/AC sorbents was investigated. The relevant reason for the difference in


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sulfidation by two ways was also discussed.

2. Experimental section 2.1. Preparation of Fe2O3/AC sorbent The raw active coke (Shanxi Xinhua Chemical Co., Ltd) prepared from bituminous coal was used as support. Its ash content in dry basis is 4.1 wt %. The active coke was treated with HNO3 solution described elsewhere

25

. The Fe-based

sorbent with different content of Fe2O3 was prepared by pore volume impregnation 25 of AC with an aqueous solution of Fe(NO3)3·9H2O with different concentration, respectively. The treated sample was dried at ambient temperature for 2 h. Then, it was heated at 50 and 110 oC for 6 h, respectively. Subsequently, the resulting sample was calcinated at 500℃ for 1 h. A serious of sorbents with different Fe2O3 content (0 %, 5 %, 10 %, 15 %, 20 %) was obtained. 2.2. Characteristic of sorbent The crystal structure of the samples was investigated by an X-ray diffraction device (JSM-6360 LV) using Cu Kα radiation. The Fe1-xS crystallite size corresponding to (200) peak at 2θ=29.9o is estimated by Scherrer formula 26:

d 200 =

0.9λ β 200 cosθ 200

(1)

where d200 and λ represent the crystallite size and the wavelength of the X-ray radiation, respectively. β200 and θ200 are the full-width at half-maximum intensity and scattering angles of the (200) peak, respectively. Scanning electron microscopy (SEM, JSM-26360LV) was used to character the morphology of samples. XPS data of samples were collected on a PHI5000C spectrometer using an Al Kα source operating at 250W and 93.9 eV passed energy. The analysis of pore structure was conducted on a Porosity Analyzer (Micromeritics TriStar-3000). The surface area was calculated based on Brunauer-Emmett-Teller (BET) theory. 2.3. Desulfurization tests The microwave sulfidation activity of the sorbents (1.5 g, 40-60 mesh) was


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evaluated in a fixed-bed microwave reactor (manufactured by Tangshan nano source microwave thermal instrument manufacturing co., rated power of furnace is 1.0 kW) at atmospheric pressure using a mixed gas with a composition of 0.25% H2S and N2 (balance gas). A quartz tube (14 mm in inner diameter, 650 mm in length) was inserted in the middle of the reactor. The temperature of the sorbent bed was measured using a special thermocouple (2 mm in diameter) placed inside the reactor and controlled based on PID (Proportional-Integral-Differential) arithmetic. The quartz tube was wrapped by silica wool for thermal insulation. The pipeline before reactor was heated by heat tape (about 300 oC) to preheat the reaction gas. Each sorbent was heated to the reaction temperature (400, 500, 600, 700 oC) in N2 before switching to the reactant stream with a flow rate of 150 mL min-1. The fluctuation margin of reaction temperature was below 5 ℃ during the experiment. Gas chromatograph equipped with a FPD (flame photometric detector) was used to analyze exit gas. For conventional sulfidation, same temperature control method and quartz tube were used in order to study the effect of desulfurization way on the performance of sorbents. The breakthrough time (BT in short) corresponds to the time when the concentration of outlet H2S reaches 500 ppm

27

. Sulfur capacity (SC in short, %)

calculated based on the equation described elsewhere 28, was the ratio of the mass of adsorbed sulfur to that of desulfurizer. The utiliztion rate of Fe2O3 (UR, %) can be calculated from the following equation:

UR =

SC of sorbent - SC of active coke × 100% theoretic SC of Fe2O 3 in sorbent

(2)

where theoretic SC (%) of Fe2O3 is the ratio of the mass of adsorbed sulfur (contributed by Fe2O3 only) to that of sorbent if it was supposed that Fe2O3 in Fe2O3/AC sorbent reacted completely and was firstly converted to Fe2S3 during desulfurization process. The theoretic SC (%) values of Fe2O3 in Fe2O3/AC with 5, 10, 15 and 20% loading content are 3.2, 6.4, 9.6, and 12.8 %, respectively. 2.4. Modeling of curves corresponding to H2S adsorption over Fe2O3/AC


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sorbents Sigmoidal-type curves can be fitted by using a Boltzmann function, the analytical expression is expressed as follows 29, 30: y=

A1 − A2 + A2 1 + e ( x − x0 ) / dx

(3)

where A1 (A2) denotes the asymptotic value for small (large) values of y, which from now on represents C/C0, x0 corresponds to the central point of the transition (when y = (A1+A2)/2,x =x0), and dx denotes the width of the transition 29, 30.

3. Results and Discussion 3.1. Effect of loading content on microwave desulfurization performance The XRD spectra of fresh Fe2O3/AC sorbents with loading content ranging from 5-20 % are presented in Figure 1. Relatively weak diffraction peaks assigned to Fe2O3 are observed, which may be due to uniform dispersion of iron oxide on the active coke (AC) and/or less loading content. The breakthrough curves of H2S adsorption over these fresh sorbents at 500 oC are shown in Figure 2, where C/C0 denotes the H2S concentration ratio of the outlet to inlet. The desulfurizers removing H2S by microwave way are named as M-X%, in which M and X% represent sulfidation way and Fe2O3 content before desulfurization, respectively. As mentioned in Section 2.3, the breakthrough time (BT, min) and sulfur capacity (SC, %) are usually used for evaluating the properties of sorbents. For carbon-based adsorbent removing H2S at high sulfidation temperatures, active carbon-oxygen sites contribute most to H2S adsorption and C-S compounds are the only sulfur-containing products. (> 400℃)

31,

32

. The BT (43 min) and sulfur capacity (2.67%) of AC were both lower than that

reported in literature

31

, although AC was pre-oxidized with HNO3. It is caused by

different structure of two types of carbon-based material. As expected, no new diffraction peaks appear after desulfurization of AC. More importantly, yellow sulfur was not observed during the sulfidation process. Desulfurization also results in little change in the pore structure of AC with just a 1.5 % decrease in the surface area and a


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4.4 % decline in pore volume (see Table 1). As can be calculated from Figures 2 and 4, compared to the M-0%, BT values of sorbents increase by 2.6, 5.0, 6.4, and 6.3 times with the increase of Fe2O3 content (5, 10, 15, and 20 %), respectively. Furthermore, for M-5%, M-10%, M-15%, and M-20%, the values of SC are 3.9, 5.1, 5.8, and 6.4 times of that for M-0%, respectively. The phenomenon is attributed to the fact that iron oxide can chemically adsorb appreciable amounts of hydrogen sulfide

13-15

. Figure 5 depicts the XRD

patterns of used sorbents with different loading content. The diffraction peaks assigned to Fe2O3 disappear, while the diffraction peaks of Fe1-xS (0 < x < 1, 2θ = 29.9°, 33.8°, 43.7°and 53.1°) [Fe1-xS: PDF# 29-0726] are observed. It demonstrates that most of iron oxide reacted with H2S. Furthermore, the intensity of diffraction peaks assigned to Fe1-xS become stronger with loading content. It agrees with greater values of BT and SC for sorbents with higher loading content. Desulfurization usually leads to significant decline in surface area (S) and pore volume (V) of supported sorbents

7, 13

. However, except for M-20%, in comparison with fresh sorbent, slight

decrease in S (by 4.2, 0.7, and 1.0%, respectively) and V (by 4.7, 2.7, and 2.7%, respectively) of M-5%, M-10%, and M-15%, is observed. It indicates that most of iron oxide may disperse on the outer surface of AC other than interior surface of pore structure. Additionally, there are no rules of change in the average pore size of sorbents before and after sulfidation. It is interesting that all sorbents own high (> 100 %) utilization rates of Fe2O3 (UR), which are higher than that (88.4 % 33, 77.5 % 34

) reported in literature. A possible explanation for high UR is the synergistic effect

between AC and Fe2O3 when both of them participate in the desulfurization reaction. As shown in Fig. 5, no diffraction peak attributed to Fe2S3 appears in the XRD patterns of used Fe2O3/AC sorbents. It is due to the decomposition of unstable Fe2S3 to sulfur and other sulfur-containing products under the experimental conditions

35

.

Actually, the elemental sulfur and liquid water were observed on the inside surface of downstream reactor tube which was cooled by air. Combined the analysis above, the


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global sulfidation reaction of Fe2O3 supported on the AC can be expressed as follows: Fe2O3 + 3H 2 S →

2 1 − 3x S Fe1− x S + 3 H 2O + 1− x 1− x

(4)

3.2. Effect of sulfidation temperature on microwave desulfurization performance As mentioned in Section 3.1, both sulfur capacity (13.7%) and UR (173%) are relatively high for M-10% at 500 oC. Thus, Fe2O3/AC with 10% loading content was chosen to investigate the effect of reaction temperature on the performance. The nomenclature of sorbents is as follows: (i) the letter ‘M’, to designate the microwave sulfidation, (ii) the number 400, 500, 600, or 700, to represent the reaction temperature. The desulfurization properties of these sorbents are presented in Figures 6 and 7. The increase of temperature is unfavorable for exothermic desulfurization reaction in terms of thermodynamics

8

. Theoretically, the equilibrium H2S

concentration in the outlet gas from a fixed-bed reactor increases with the increase of temperature. However, the H2S concentration in the outlet gas increases in the order of M-500 < M-600 < M-400 < M-700 at the initial stage (< 150 min) of desulfurization (see Figure S1). Also, compared to M-400, the SC of M-500, M-600, and M-700 increase by 17, 34, and 9%, respectively. These phenomena are mainly attributed to the fact that more H2S can react with iron oxide or active carbon-oxygen sites within the residence time in the adsorbent bed due to faster reaction rate resulting from elevated temperature. It is notable that M-600 has longest BT (310 min) and largest SC (15.7 %), while further increase of temperature leads to shorter BT (290 min), lower SC (12.8 %), and much smaller utilization rate of Fe2O3 (158 %). It suggests that the structure deteriorating of sorbents being subjected to microwave sulfidation at 700 oC may occur. The surface area (S) and pore volume (V) and average pore diameter of fresh and used sorbents are listed in Table 2. The replacement of O atom by S atom caused by sulfidation reaction could lead to plugging of pore structure. As expected, desulfurization results in the decrement of S ranging from 1 to 77 m2 g-1. It is interesting that both S and V of used sorbents increase with sulfidation temperature


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(400 - 600 oC) although higher temperature (500, 600 oC) results in greater sulfur capacity. A possible reason is that the release of gaseous products including H2O and sulfur from the surface of Fe2O3/AC plays a role in the development of pore structure. M-700 have lowest S (533 m2 g-1) and V.(0.34 cm3 g-1). Significant decrease in surface area for the sorbent after desulfurization at 700 oC is also observed. The results indicate that the pore structure of M-700 indeed deteriorate compared to fresh sorbent. In addition, different desulfurization temperature leads to no significant change in the average pore size of sorbents. The XRD patterns of sorbents after microwave desulfurization at different temperatures are depicted in Figure 8. Increasing sulfidation temperature from 400 to 600 oC results in stronger intensity of diffraction peaks ascribed to Fe1-xS. It is attributed to faster growth rate of Fe1-xS grain and more Fe1-xS produced (inferred from greater adsorption quantity of H2S) at 500 and 600 oC. However, for M-700, both the peak area and intensity value of diffraction peaks assigned to Fe1-xS is largest among four used sorbents although its sulfur capacity is lower than that of M-500 and M-600. It may be caused by the sintering of crystalline grain of Fe1-xS due to local overheating resulting from excellent microwave absorbing properties of Fe1-xS. The results are consistent with the performance and the pore structure of M-700. 3.3. Comparison of microwave and conventional desulfurization 3.3.1 Desulfurization performance Figures 6 and 7 compare the performance of sorbents with two desulfurization ways. The desulfurizers removing H2S at different temperature by conventional way are named as C-Y, in which C, and Y corresponds to conventional sulfidation and reaction temperature, respectively. In comparison with conventional sulfidation, as the sulfidation temperature (400, 500, 600, and 700 oC) raises, the BT values of sorbent removing H2S by microwave way increase by 32, 41, 24, and 8%, respectively, while the SC increases by 60, 70, 45, and 9%, respectively. Moreover, compared to conventional desulfurization, the utilization rate of Fe2O3 for M-400, M-500, M-600,


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and M-700, are 1.6, 1.7, 1.4, and 1.0 times of that for sorbents with the same sulfidation temperature, respectively. The results demonstrate that microwave irradiation results in much better desulfurization properties of Fe2O3/AC sorbents. Actually, microwave desulfurization also leads to better sorption ability of sorbents with other loading contents (0, 5, 15, and 20%; results not shown). 3.3.2 Desulfurization kinetics For Fe2O3/AC sorbents, there are two types of desulfurization reactions: reaction of active coke with H2S, sulfidation reaction of iron oxide. Furthermore, two reactions occur simultaneously during the desulphurization process. Therefore, it is impossible to clarify reaction kinetics for each reaction. The overall desulfurization behavior was modeled by Boltzmann function, which was successfully used for fitting the curves of chlorine removal 36. The experimental data and fitting results are presented in Figure 9. The fitting parameters and correlation coefficient (R2) are listed in Table 3. High R2 suggests that the Boltzmann function is suitable for describing the H2S evolution behavior of Fe2O3/AC sorbent bed. The deviation observed when the C/C0 approaches 1.0 can be explained by the measurement error. If 1/dx in Eq. 3 is set as ke, then ke represents the H2S evolution rate constant of desulfurization process

29, 37

. As shown

in Table 3, the Ke of sorbents being subjected to conventional sulfidation range from 0.000634 to 0.00191 s-1, while the Ke values vary from 0.000239 to 0.00662 s-1 in the case of microwave desulfurization. Moreover, regardless of conventional and microwave sulfidation, the order of Ke is contrary to that of sulfur capacity of sorbents removing H2S by same desulfurization way. M-700 undergoes pore structure deterioration, which greatly influence the desulfurization behavior. Therefore, only the results with respect to desulfurization at 400 - 600 oC were used for investigate reaction dynamics. Before the kinetic analysis, the following assumptions are made: 1) The order of overall desulfurization reaction is 1. 2) Based on the fact that the removing rate of H2S increases with the decrease of H2S evolution rate, the value of apparent H2S sorption rate constant (ks, s-1) is supposed to


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follow this equation: (5)

k s = a / ke where a (unit: s-2) represents proportionality coefficient. 3) Arrhenius-type dependence was assumed for ks.

Figure 10 compares results of ln(a/ks) vs. 1/RT for two sulfidation ways. Based on the assumptions above, the apparent activation energy (Ea) of overall desulfurization reaction is equal to the slope of curves shown in Figure 10. Consequently, Ea of sulfidation reaction by conventional and microwave ways, are 24.6 and 24.1 kJ mol-1, respectively. It demonstrates that microwave irradiation results in no significant decrease in the energy barrier of overall desulfurization reaction. However, microwave can enhance the ion diffusion and mass transfer

6, 21, 22

. And the H2S

removal by Fe2O3/AC sorbents is mainly attributed to sulfidation reaction of iron oxide, which is controlled by ion diffusion in the later stage

23, 24

. Therefore, the

increase of desulfurization rate for Fe2O3/AC may be caused by enhancement of ion diffusions and/or mass transfer under microwave conditions. 3.3.3 Pore structure analysis As shown in Table 2, the surface area (S) and total pore volume (V) of M-500 and M-600 is larger than (or same as) that of C-500 and C-600, although the former have greater sulfur capacity. Two parameters named as DS (decrease in S per unit sulfur capacity, m2 g-1) and DV (Decrease in V per unit sulfur capacity, cm3 g-1) are used to describe the influence of sulfidation on the pore structure more accurately. The related data for used sorbents are listed in Table 4. Compared to microwave desulfurization, the increment of DS for conventional desulfurization at 400, 500 and 600 oC, is 67, 169, and 104 m2 g-1, respectively, while DV increase by 0.02, 0.05, and 0.09 cm3 g-1, respectively. The results imply that the pore structure of sorbents faces lesser impacts for microwave way (400 - 600 oC). However, the values of S, V, DS and DV of M-700 with greater sulfur capacity are significantly larger than that of C-700. It is attributed to the pore structure deteriorating of M-700.


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3.3.4 XRD analysis Weak diffraction peaks ascribed to Fe1-xS appear in the spectra (Figure S2) of C-500, C-600, and C-700, while no peaks assigned to Fe1-xS is observed for C-400. More importantly, compared to microwave desulfurization (Figure 8), conventional way results in much weaker intensity of diffraction peaks belong to Fe1-xS for the sorbent removing H2S at same temperature. Furthermore, the Fe1-xS crystallite size (corresponding to (200) peak at 2θ=28.8 ± 0.1o) of M500, M600, and M700 is 2.8, 4.9, 1.9 times of that for sorbents with the same sulfidation temperature under conventional conditions (see Table 5), respectively. It is mainly due to the fact that the grain of inorganic material can grow faster by microwave heating due to lower apparent activation energy of grain growth overheating

effect

because

the

38

. Another possible explanation is local

temperature

of

Fe1-xS

with

excellent

microwave-absorbing properties may be higher than the bulk temperature of sorbent undergoing microwave sulfidation, which facilitates the growth of Fe1-xS grain. 3.3.5 XPS analysis Figures 11-13 show the XPS spectra of Fe 2p3/2, O 1s and S 2p. The BE (binding energy) values and contents of different species obtained from XPS spectra of O 1S and S 2p are summarized in Table 6. The shift of peaks (at 711.2 ev) assigned to Fe 2p3/2 of surface Fe atom in the fresh sorbent toward higher BE (711.3 or 711.4 ev) after desulfurization, is observed. It ascribes the conversion of Fe2O3 to metal sulfide. XPS spectrum of S 2p of used sorbents can be deconvoluted into four peaks

39-42

located at 161.7 ± 0.1 ev, 163.6 ev (or 163.7 ev), 164.8 ± 0.2 ev, and 168.1 ± 0.2 ev, respectively. They are assigned to S2- (Sa), Fe1-xS + C-S (Sb), S8 (Sc), and SO42- (Sd) species, respectively. As listed in Table 6, the main (44 - 46%) sulfur-containing species are Fe1-xS and C-S compounds in the surface of used sorbents except for C-400. During the sulfidation process (400 - 600 oC), sulfur produced via chemical reaction (Eq.4) can diffusion from the inner part to the surface of sorbent, and then to the gas bulk, due to lower melting point (112.8 oC) and boiling point (444.6 oC) of


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sulfur 4. However, the release of all product sulfur to gas phase is impossible due to impact of diffusion. As expected, a considerable content of elemental sulfur with the percentages ranging from 22.5-37.8% is observed. The appearance of SO42- species is attributed to the oxidation of sulfur-containing products (especially elemental sulfur) caused by grinding of samples. Compared to conventional desulfurization, the ratios of S2- species for M-600, and M-700, are 2.4, and 2.7 times of sorbent with the same sulfidation temperature, respectively. Also, about 4.4 % S2- species among sulfur-containing compounds is observed on the surface of sorbent of M-400 and M-500, while no peaks belong to S2- species appear in XPS spectra of C-400 and C-500. Compared to sulfur ion in Fe1-xS (0 < x < 1), S2- owns stronger reducibility. Therefore, more S2- species on the surface of sorbents is beneficial for the succeeding regeneration. It is notable that the maximum difference of peak (S 2p assigned to species of Fe1-xS and C-S, or Fe 2p3/2) positions was 0.1 ev for sorbents with the same sulfidation temperature but different sulfidation ways. It suggests microwave irradiation lead to no notable change in chemical environment around the nucleus of Fe or S atom in Fe1-xS. O 1s XPS spectra (Figure 13) show an asymmetric feature. The peaks in O 1s XPS spectrum of fresh and used sorbents can be deconvoluted into three peaks 43-45 at 529.7- 530.2 eV (Oa, lattice oxygen), 531.6 ev (Ob, the oxygen ions in the oxygen vacancy regions), and 533.4 -533.6 eV (Oc, oxygen in –OH group or adsorbed water and/or SO42-), respectively. The concentrations of Oa on the surface of used sorbents decrease by 61 - 80% in comparison with fresh sorbent. It ascribes to the sulfidation of iron oxide. High percentage of Ob species on the surface of the catalyst can result in better activity for oxidation reaction

44, 45

. Compared to

conventional desulfurization, microwave sulfidation leads to higher proportion of Ob on the surface of sorbents being subjected to the same desulphurization temperature. Therefore, it is favorable for the regeneration of used sorbents if the mixture of O2, H2O, and N2 is used as regeneration atmosphere. 3.3.6 Morphology analysis


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

The morphology of the fresh and used sorbents is presented in Figure 14. The Fe2O3 on the surface of fresh sorbents appear in the form of aggregated nanoparticles with size about 25 nm (Figure 14a). Compared to the fresh sorbent, the surface of used sorbents (Figure 14 b-i) becomes more compact caused by the replacement of O atom by S during the desulfurization process. It is notable that stacking-like structure is observed in most of sorbents after desulfurization by conventional way, which is different from that of sorbents removing H2S by microwave way. It may be due to different sulfidation behavior for two ways. In addition, particles with 10 - 20 nnm wide (Figure S3) appear in the surface of sulfur collected from the experiment. Actually, nanparticles with similar shape is also observed in some regions of used sorbents (Figure S3), which implies the presence of elemental sulfur on the surface of sorbents obtained by two desulfurization ways. It agrees with the results of XPS analysis.

4. Conclusions The microwave desulfurization properties of Fe2O3/AC sorbents with different loading content and reaction temperature, was investigated. The results suggest that the removal of H2S by sorbents is mainly attributed to sulfidation reaction of iron oxide. The optimal desulfurization temperature under microwave conditions is 600 oC, while further increase of temperature leads to lower sulfur capacity and utilization rate of iron oxide due to pore structure deteriorating of sorbents. In comparison of conventional way, microwave sulfidation results in much better performance of Fe2O3/AC sorbents. The analysis of desulfurization kinetic reveal that there is no significant difference in the apparent activation energy of overall sulfidation reaction by conventional (24.6 kJ mol-1) and microwave (24.1 kJ mol-1) ways. The enhancement of desulfurization rate for desulfurizers may be caused by quicker ion diffusions and/or better mass transfer under microwave conditions. The XRD, N2-absorption, XPS, and SEM characterization of sorbents before and after desulfurization indicate that microwave way results in less decrease in S and V per


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Energy & Fuels

unit sulfur capacity of sorbents except for M-700, and more S2- and oxygen vacancies species on the surface of used sorbents. It is favorable for the following regeneration of used sorbents.

Associated content Supporting information Breakthrough curves (0 - 170 min) of sorbents used for microwave sulfidation, XRD patterns of sorbents after conventional desulfurization, and SEM images of sulfur and used sorbents.

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

Notes The authors declare no competing financial interest.

Acknowledgements This work was supported by National Natural Science Foundation of China (21506143).

Refrerences (1) Wang, X.; Liu, Y.; Sun, Z.; Che, D. Energy Fuels 2011, 25, 4865. (2) Zeng B, Yue H, Liu C, Huang, T.; Li, J.; Zhao, B.; Zhang, M.; Liang, B. Energy Fuels 2015, 29, 1860-1867. (3) Dou, B.; Wang, C.; Chen, H.; Song, Y.; Xie, B.; Xu, Y.; Tan, C. Chem. Eng. Res. Des. 2012, 90, 1901-1917 (4) Speight, J.G. The Chemistry and Technology of Coal, Third edition; CRC Press: New York, 2012. (5) Sitthikhankaew, R.; Chadwick, D.; Assabumrungrat, S.; Laosiripojana, N. Fuel Process. Technol. 2014, 124, 249-257. (6) Wu, M.; Hu, C.; Feng, Y.; Fan, H.; Mi, J. Fuel 2015, 146, 56-59.


Energy & Fuels

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(7) Chang, L.; Zhang, Z.; Ren, X.; Li, F.; Xie, K. Energy Fuels, 2009, 23, 762-765. (8) Westmoreland, P.R.; Harrison, D.P. Environ. Sci. Technol. 1976, 10, 659-661. (9) Sadegh-Vaziri, R.; Babler, M.U. Chem. Eng. Sci. 2017, 158, 328-339. (10) Garces, H.F.; Espinal, A.E.; Suib, S.L. J. Phys. Chem. C 2012, 116, 8465-8474. (11) Mureddu, M.; Ferino, I.; Rombi, E.; Cutrufello, M.G.; Deiana, P.; Ardu, A.; Musinu, A.; Piccaluga, G.; Cannas, C. Fuel 2012, 102, 691-700. (12) Dhage, P.; Samokhvalov, A.; McKee, M.L.; Duin, E.C.; Tatarchuk, B.J. Surf. Interface Anal. 2013, 45, 865-872. (13) Cheah, S.; Carpenter, D.L.; Magrini-Bair, K.A. Energy Fuels 2009, 23, 5291-5307. (14) Yu, J.; Yin, F.; Wang, S.; Chang, L.; Gupta, S. Fuel 2013, 108, 91-98. (15) Yin, F.; Yu, J.; Gupta, S.; Wang, S.; Wang, D.; Dou, J. Fuel Process. Technol.

2014, 117, 17-22. (16) Appukkuttan, P.; Mehta, V.P.; Van der Eycken, E.V. Chem. Soc. Rev. 2010, 39, 1467-1477. (17) Stuerga, D.A.C.; Gaillard, P. J. Microwave Power Electromagn. Energy 1996, 31, 87. (18) Turner, M.D.; Laurence, R.L.; Conner, W.C.; Yngvesson, K.S. AIChE J. 2000, 46, 758-768. (19) Shibata, C.; Kashima, T.; Ohuchi, K. Jpn. J. Appl. Phys. 1996, 35, 316. (20) Binner, J.G.P.; Hassine, N.A.; Cross, T.E. J. Mater. Sci. 1995, 30, 5389-5393. (21) Kishimoto, A.; Kamakura, Y.; Teranishi, Hayashi, T.H. Mater. Chem. Phys. 2013, 139, 825-829. (22) Janney, M.A.; Kimrey, H.D.; Allen, W.R.; Kiggans, J.O. J. Mater. Sci. 1997, 32, 1347-1355. (23) Hartmann, V.L. Chem. Eng. J. 2007, 134, 190-194. (24) Agnihotri, R.; Chauk, S.S.; Mahuli, S.K.; Fan, L. Chem. Eng. Sci. 1999, 54, 3443-3453


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(25) Zhu, Z.; Liu, Z.; Liu, S.; Niu, H.; Hu, T.; Liu, T.; Xie, Y. Appl. Catal. B 2000, 26, 25-35. (26) Cugini, A.V.; Krastman, D.; Martello, D.V.; Frommell, E.F.; Wells, A.W.; Holder, G.D. Energy Fuels 1994, 8, 83-87. (27) Xie, W.; Chang, L.; Wang, D.; Xie, K.; Yu, J. Fuel 2010, 89, 868-873. (28) Chen, J.; Wu, M.; Wu, Z.; Fan, H.; Mi, J. J. Mater. Sci. 2016, 51, 2850-2858. (29) Nielsen, L.; Khurana, R.; Coats, A.; Frokjaer, S.; Brange, Vyas, J.S.; Uversky, V.N.; Fink, A.L. 2001, 40, 6036-6046. (30) Brown, A.M. Comput. Methods Prog. Biomed. 2001, 65, 191-200. (31) Cal, M.P.; Strickler, B.W.; Lizzio, A.A. Carbon 2000, 38, 1757-1765. (32) Cal, M.P.; Strickler, B.W.; Lizzio, A.A.; Gangwal, S.K. Carbon 2000, 38, 1767-1774. (33) Feng, Y.; Dou, J.; Tahmasebi, A.; Xu, J.; Li, X.; Yu, J.; Yin, F. Energy Fuels 2015, 29, 7124-7134. (34) Feng, Y.; Hu, T.; Wu, M.; Shangguan, J.; Fan, H.; Mi, J. Fuel Process. Technol.

2016, 148, 35-42. (35) Onufrienok, V.V. Inorg. Mater. 2005, 41, 650-653. (36) Wang, J.; Zhang, D.; Gao, J.; Song, Y. J. Fuel Chem. Technol. 2003, 31, 27-30. (37) Chen, Z. Wang, X. Chang, Y. Chin. J. Inorg. Chem. 2008, 24, 351-356. (38) Yang, D.; Raj, R.; Conrad, H. J. Am. Ceram. Soc. 2010, 93, 2935-2937. (39) Xia, H.; Liu, B.; Li, Q.; Huang, Z.; Cheung, A. Appl. Catal. B 2017, 200, 552-565. (40) Li, Y.; Van Santen, R.A.; Weber, T. J. Solid State Chem. 2008, 181, 3151-3162. (41) Ma, H.; Han, J.; Fu, Y.; Yu, C.; Dong, X. Appl. Catal. B 2011, 102, 417-423. (42) Huang, G.; He, E.; Wang, Z.; Fan, H.; Shangguan, J.; Croiser, E.; Chen, Z. Ind. Eng. Chem. Res. 2015, 54, 8469-8478. (43) Jiang, H.; Dai, H.; Meng, X.; Ji, K.; Zhang, L.; Deng, J. Appl. Catal. B 2011, 105, 326-334.


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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

(44) Shinde, S.S.; Korade, A.P.; Bhosale, C.H.; Rajpure, K.Y. J. Alloys Compd. 2013, 551, 688-693. (45) Guo, L.; Chen, F.; Fan, X.; Cai, W.; Zhang, J. Appl. Catal. B 2010, 96 162-168.


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Energy & Fuels

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

Table 2. Surface area (S) and Pore volume (V) and average pore diameter of fresh sorbents and used sorbents removing H2S by different way or at different temperature

Table 3. The fitting results for different sorbents. Table 4. Change of pore structure for used sorbents. Table 5. The data obtained from XRD data fitting and Scherrer formula. Table 6. Binding energies (BE) and contents of different species obtained from XPS spectra of S 2p and O 1S.

Figure 1. XRD spectra of Fe2O3/AC sorbents with different loading content. Figure 2. Breakthrough curves of H2S adsorption over Fe2O3/AC sorbents (Reaction conditions: 0.25% H2S, N2 as balance gas; 500 oC).

Figure 3. XRD spectra of AC before and after microwave desulfurization. Figure 4. Sulfur capacity and untiliztion rate of Fe2O3 for sorbents with different loading content.

Figure 5. XRD spectra of M-5%, M-10%, M-15%, and M-20%. Figure 6. Breakthrough curves of H2S adsorption at different temperatures (reaction gas: 0.25% H2S, N2 as balance gas; loading content: 10%).

Figure 7. Sulfur capacity and untiliztion rate of Fe2O3 for sorbents with different desulfurization temperature or sulfidation way.

Figure 8. XRD patterns of M-400, M-500, M-600, and M-700. Figure 9. Experimental and modeling results of breakthrough curves for different sorbents.

Figure 10. ln(a/ks) versus 1/RT of different sorbents undergoing desulfurization. Figure 11. Fe 2p2/3 XPS spectra of sorbents before and after desulfurization. Figure 12. S 2p XPS spectra of used sorbents.


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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

Figure 13. O 1s XPS spectra of two used sorbents. Figure 14. SEM images of fresh and used sorbents. (a) fresh sorbent containing 10% Fe2O3, (b) C-400, (c) C-500, (d) C-600, (e) C-700, (f) M-400, (g) M-500, (h) M-600, and (i) M-700.


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Energy & Fuels

Tables 1-6 Table 1. Surface area (S) and Pore volume (V) and average pore diameter of AC and sorbents with different loading content before and after desulfurization Samples

S (m2 g-1)

V (cm3 g-1)

Average pore size (nm)

AC

712

0.45

2.5

M-0%

701

0.43

2.4

M-5%

636 (664)a

0.40 (0.42) a

2.5 (2.5) a

M-10%

606 (610) a

0.36 (0.37) a

2.4 (2.4) a

M-15%

618 (624) a

0.36 (0.37) a

2.5 (2.3) a

M-20%

510 (587) a

0.33 (0.33) a

2.5 (2.3) a

a

Fresh 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

Page 22 of 40

Table 2. Surface area (S) and Pore volume (V) and average pore diameter of fresh sorbents and used sorbents removing H2S by different way or at different temperature Samples

S (m2 g-1)

V (cm3 g-1)

Average pore size (nm)

Fresh sorbent a

610

0.37

2.4

M-400

565

0.34

2.3

M-500

606

0.36

2.4

M-600

609

0.37

2.5

M-700

533

0.34

2.5

C-400

577

0.35

2.5

C-500

594

0.36

2.4

C-600

598

0.36

2.5

C-700

605

0.37

2.5

a

Fe2O3/AC with 10 % loading content.


Page 23 of 40

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Energy & Fuels

Table 3. The fitting results for different sorbents Samples A1

A2

x0 (min)

dx (min) ke (×104 s-1)

R2

C-400

0

1.0

222

8.7

19.1

0.999

C-500

0

0.90

213

14.6

11.4

0.990

C-600

0

0.92

284

23.5

7.10

0.995

C-700

0

0.88

302

26.3

6.34

0.985

M-400

0

0.90

290

25.1

6.62

0.988

M -500

0

0.87

323

38.9

4.28

0.985

M -600

0

0.91

379

69.9

2.39

0.976

M -700

0

0.93

3332

44.1

3.78

0.984


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 4.

Change of pore structure for used sorbents

Samples

Decrease in surface area per unit Decrease in pore volume per unit sulfur capacity (DS, m2 g-1) sulfur capacity (DV, cm3 g-1)

M-400

384

0.25

C-400

451

0.27

M-500

29

0.07

C-500

198

0.12

M-600

6.4

0

C-600

110

0.09

M-700

602

0.23

C-700

42.5

0


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Energy & Fuels

Table 5. The data obtained from XRD data fitting and Scherrer formula Samples

2θ (o)

M-400

29.9

5.2

C-400

-a

-a

M-500

29.9

7.9

C-500

29.7

2.8

M-600

29.8

14.2

C-600

29.9

2.9

M-700

29.9

15.1

C-700

29.9

8.1

a

FeS1-x crystallite size corresponding to (200) peak (nm)

Not available.


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

1

Page 26 of 40

Table 6. Binding energies (BE) and contents of different species obtained from XPS spectra of S 2p and O 1S samples

Fresh sorbent

C-400

C-500

C-600

C-700

M-400

M-500

M-600

M-700

BE (ev)

-a

161.7

161.7

161.7

161.7

161.6

161.6

161.7

161.7

Content (%)

-a

0

0

2.9

4.2

4.3

4.4

7.0

11.4

BE (ev)

-a

163.6

163..7

163.7

163.6

163.6

163.6

163.7

163.6

Content (%)

-a

31.0

44.0

44.9

44.4

44.2

44.1

46.6

44.4

BE (ev)

-a

164.9

164.9

165.0

164.9

165.0

164.9

165.0

164.9

Content (%)

-a

22.5

37.5

26.0

28.8

24.2

26.6

26.3

27.6

BE (ev)

-a

168.3

167.9

168.2

168.0

168.3

168.1

168.1

167.9

Content (%)

-a

46.5

18.5

26.2

22.6

27.3

24.9

20.1

16.6

BE (ev)

530.3

529.9

529.7

529.9

529.7

529.7

529.7

529.9

529.7

Content (%)

6.4

2.2

1.6

2.5

1.8

2.0

2.1

1.3

1.8

BE (ev)

531.6

531.6

531.6

531.6

531.6

531.6

531.6

531.6

531.6

Content (%)

27.0

24.3

23.2

34.5

22.3

24.6

26.6

37.6

22.6

BE (ev)

533.6

533.4

533.7

533.4

533.4

533.4

533.4

533.4

533.4

Content (%)

66.6

73.5

75.2

63.0

75.9

73.4

71.3

61.1

75.6

Sa

Sb S2p Sc

Sd

Oa

O1s

Ob

Oc 2

a

Undetectable.


Page 27 of 40

before desulfurization

♦♦

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

♦ Fe2O3

20% 15% 10% 5%

10

20

30

40

50

60

70

80

o

2θ ( )

1 2

Figure 1. XRD spectra of Fe2O3/AC sorbents with different loading content.

3


Energy & Fuels

1.0

M-0% M-5% M-10% M-15% M-20%

0.8

0.6 C/C0

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 28 of 40

0.4 C/C0=0.2

0.2

Breakthrough concentration: 500 ppm 0.0 0

100

200

300

400 500 600 Time (min)

700

800

900 1000

1 2

Figure 2. Breakthrough curves of H2S adsorption over Fe2O3/AC sorbents (Reaction

3

conditions: 0.25% H2S, N2 as balance gas; 500 oC).

4 5


Page 29 of 40

♠ ♠ SiO 2

♠

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

after desulfurization

W-0%

AC

before desulfurization 10

20

30

40 2θ (deg)

50

60

70

1 2

Figure 3. XRD spectra of AC before and after microwave desulfurization.

3


Energy & Fuels

20 Experimental sulfur capacity (%) Utiliztion rate of Fe2O3(%) 16

250

200

12

150

8

100

4

50

0

Utiliztion rate of Fe2O3(%)

Experimental sulfur capacity (%)

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 40

0

M-0%

M-5%

M-10%

M-15%

M-20%

1 2

Figure 4. Sulfur capacity and untiliztion rate of Fe2O3 for sorbents with different

3

loading content.

4


Page 31 of 40

• •

•

•Fe

S

1-x

• M-20%

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

M-15% M-10%

M-5% 10

20

30

40 o 2θ ( )

50

60

70

1 2

Figure 5. XRD spectra of M-5%, M-10%, M-15%, and M-20%.

3 4


Energy & Fuels

1.0

0.8 C-400 C-500 C-600 C-700 M-400 M-500 M-600 M-700

0.6 C/C0

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 40

0.4 C/C0=0.2

0.2

Breakthrough concentration: 500 ppm 0.0 0

100

200

300

400 500 Time (min)

600

700

800

1 2

Figure 6. Breakthrough curves of H2S adsorption at different temperatures (reaction

3

gas: 0.25% H2S, N2 as balance gas; loading content: 10%).

4


18

Experimental sulfur capacity (%) Utiliztion rate of Fe2O3(%)

16 Experimental sulfur capacity (%)

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

250

200

14 12

150

10 8

100

6 4

Utiliztion rate of Fe2O3(%)

Page 33 of 40

50

2 0

C-400

M-400

C-500

M-500

C-600

M-600

C-700

M-700

0

1 2

Figure 7. Sulfur capacity and untiliztion rate of Fe2O3 for sorbents with different

3

desulfurization temperature or sulfidation way.

4


Energy & Fuels

•

• Fe

•

•

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 34 of 40

S

1-x

• M-700

M-600 M-500 M-400

10

20

30

40

50

60

70

o

2θ ( )

1 2

Figure 8. XRD patterns of M-400, M-500, M-600, and M-700.

3


Page 35 of 40

1.2

(a)

Conventional desulfurization

1.0

C/C0

0.8 C-400 Fiting curve C-400 C-500 Fiting curve C-500 C-600 Fiting curve C-600 C-700 Fiting curve C-700

0.6 0.4 0.2 0.0 0

100

200

300

400

500

600

700

800

Time (min)

1

1.2

(b)

Microwave desulfurization

1.0 0.8 C/C0

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

0.6

M-400 Fiting curve W-400 M-500 Fiting curve W-500 M-600 Fiting curve W-600 M-700 Fiting curve W-700

0.4 0.2 0.0 0

100

200

300

400

500

600

700

800

Time (min)

2 3

Figure 9. Experimental and modeling results of breakthrough curves for different

4

sorbents.

5


Energy & Fuels

-2 -3

Conventioal desulfurization Microwave desulfurization

-4 -5

Ea=24.6 kJ mol

-1

ln(a/ks) (s )

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 40

-6

-1

2

R =0.996

y=24646x-10.55

-7 -8

y=24060x-11.68

-9 -10 0.00013

2

R =0.950

Ea=24.1 kJ mol 0.00014

0.00015

0.00016

-1

0.00017

0.00018

-1

1/RT (mol J )

1 2

Figure 10. ln(a/ks) versus 1/RT of different sorbents undergoing desulfurization.

3


Page 37 of 40

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

Fresh sorbent

711.2

711.3

C-400

711.4

C-500

Raw Backgroud Fitted peak


711.4

C-600

711.3

C-700

M-400

711.4


M-500

711.4

711.3

M-600

M-700

711.3


1

700

705

710

715

705

710

715

Binding energy (ev)

705

710

715

2 3

Figure 11. Fe 2p2/3 XPS spectra of sorbents before and after desulfurization.

4


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

C-500

C-600

C-700

M-400

M-500

M-600

M-700

C-400

160

Sb Sc Sa

1 2

Page 38 of 40

160

165

170

175

160

165

Raw Sum Backgroud

165

170

175

Binding energy (ev) Sd

170

175

Figure 12. S 2p XPS spectra of used sorbents.

3


Page 39 of 40

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

C-500

C-400

fresh sorbent Raw Sum Backgroud

C-600

C-700

M-500

M-600

M-400

Oc

M-700

Ob Oa 524

1 2

528

532

536

540

524

528

532

536

540

524

528

532

Binding energy (ev)

Figure 13. O 1s XPS spectra of two used sorbents.

3


536

540

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 40 of 40

1 (a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

2

3

4 5

Figure 14. SEM images of fresh and used sorbents. (a) fresh sorbent containing 10%

6

Fe2O3, (b) C-400, (c) C-500, (d) C-600, (e) C-700, (f) M-400, (g) M-500, (h) M-600,

7

and (i) M-700.


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