S by Triethanolamine-Modified Mesoporous Molecular Sieve SBA-15

Article pubs.acs.org/IECR

Study on Sorption Behaviors of H2S by Triethanolamine-Modified Mesoporous Molecular Sieve SBA-15 Xiaozhong Chu,*,† Zhipeng Cheng,† Yijiang Zhao,† Jiming Xu,† Hui Zhong,† Weiguang Zhang,† Jinshun Lü,† Shouyong Zhou,† Fengxia Zhu,† Yaping Zhou,‡ and Li Zhou‡ †

Jiangsu Key Laboratory for Chemistry of Low-Dimensional Materials, School of Chemistry and Chemical Engineering, Huaiyin Normal University, Huai’an 223300, People's Republic of China ‡ High Pressure Adsorption Laboratory, State Key Laboratory of Chemical Engineering, Tianjin University, Tianjin 300072, People's Republic of China ABSTRACT: A key technology for natural gas vehicles is the removal of H2S trace content from fuel. In previous studies, purification based on the adsorption principle has been proved to have low separation cost, and the selection of an adsorbent is a crucial factor in this method. To enhance H2S sorption capacity, an ordered SBA-15 silica mesoporous material with a high specific surface area is synthesized as a carrier of triethanolamine (TEA). The mesoporous molecular sieve SBA-15 coated with a TEA film considerably enhances H2S sorption capacity. The effects of operational variables on H2S removal efficiency, including the amount of TEA-loading, adsorption pressure, flow rate, and fixed bed length, are investigated with a single-column adsorption apparatus. A model demonstrating H2S dynamic sorption processes through as TEA-modified adsorbent bed is proposed. The model fits well the experimental data and can be applied to the H2S sorption process simulation and optimal process design.

1. INTRODUCTION With the rapid decrease in petroleum availability, the number of natural gas vehicles is expected to continuously increase. However, hydrogen sulfide (H2S) is a major contaminant of natural gas even after preliminary sweetening treatment. To protect the environment, the H2S content in natural gas must be reduced to less than 6 mg/m3 before feeding it to compressed natural gas (CNG) vehicles. The practical content is often higher than 100 mg/m3 in some places. The removal of H2S contamination residue has become an important and compulsive task required in developing CNG vehicles. However, the methods currently used to remove H2S do not meet the required H2S low content.1−8 Generally, purification based on the adsorption principle has low separation cost, and the selection of an adsorbent is a crucial factor in this process.9 The authors have previously reported that triethanolamine (TEA)-modified silica gel could enhance H2S sorption capacity and possibly allow regeneration at ambient temperature.10,11 However, the H2S sorption capacity is still at a low level because the specific surface area of silica gel used is relatively low. To understand further the H2S transport process from the gas stream to the surface of TEA-modified adsorbent and to improve H2S sorption capacity, a mesoporous molecular sieve SBA-15 with a high specific surface area is synthesized as a TEA carrier. The effects of operational variables on H2S removal efficiency, including the amount of TEA-loading, adsorption pressure, flow rate, and fixed bed length, are also investigated using the single-column adsorption apparatus shown in Figure 1. The different ways to set up a simulation model for dynamic adsorption processes include the equilibrium,12,13 linear driving force,14−16 and pore diffusion17,18 models. However, none of these methods can be directly applied to the H2S sorption process of the adsorbent covered by a liquid film. A simulation model for the H2S sorption behaviors on TEA-modified adsorbents © 2012 American Chemical Society

is proposed to understand better the dynamic sorption process of H2S and provide a theoretical basis for scaling up an adsorption bed.

2. EXPERIMENTAL SECTION 2.1. Materials and Instrument. An SBA-15 silica mesoporous material with two-dimensional and ordered channels has been synthesized under acidic condition. A nonionic oligomeric alkyl-ethylene oxide surfactant (Pluronic P123) is used as the structure-directing agent, and tetraethyl orthosilicate of analytical grade is used as the silica source. Details of the synthesis are previously reported by the authors.19,20 Physically adsorbed water on the SBA-15 is removed before the experiments are heated in vacuum at 120 °C. The solvent selected to coat adsorbents is ensured to satisfy several requirements. The solvent should possess a selective solubility of H2S. The H2S solubility must also be sensitive to bulk gas pressure. The solvent should also be chemically stable and must possess a high boiling point. On the basis of previous studies, TEA has a stable higher normal boiling point (360 °C) and stronger basic property.10,11 This organic compound is used in the current study because of its higher stability and has a larger H2S sorption capacity. To ensure an even film of TEA on the SBA-15 material surface, TEA is first dissolved in acetone. Second, a definite weight of SBA-15 material is immersed in the TEA− acetone solution before slowly evaporating the acetone solvent at ∼60 °C. The H2S sorption capacity of the prepared adsorbents depends on the TEA loading ratio (LR) that is defined as the weight percentage of TEA over SBA-15. Larger LR results Received: Revised: Accepted: Published: 4407

October 15, 2011 January 30, 2012 February 22, 2012 February 22, 2012 dx.doi.org/10.1021/ie202360h | Ind. Eng. Chem. Res. 2012, 51, 4407−4413

Industrial & Engineering Chemistry Research

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Figure 1. Apparatus for testing H2S breakthrough curves.

adsorption apparatus (Figure 1). The prepared adsorbent is initially filled in a fixed bed that is soaked in a water bath at constant temperature. Then, the overall apparatus is adjusted to a desired flow rate and pressure with carrier gas CH4 after its evacuation. The feed gas mixture enters the adsorption bed and then passes through the column at the given flow rate and pressure. The concentration of H 2S is simultaneously measured using H2S detectors at the column outlets. CH4 is collected and compressed in a gas tank for subsequent use. The effects of LR, operational pressure, flow rate, and bed length are investigated in breakthrough experiments. Breakthrough curves are also used to evaluate the H2S sorption capacity of adsorbents. Details of the calculation method are described previously.10

in relatively high H2S sorption capacity, but the regeneration cost of saturated adsorbent is also high.11 Specific surface area and pore volume of adsorbents at different LRs are listed in Table 1, whereas the major parameters Table 1. Specific Surface Area and Pore Volume of Adsorbents at Different LRs volumetric loading ratio (LR, %) specific surface area (m2/g) pore volume (mL/g)

0 653.3 0.91

9.8 507.0 0.55

14.3 448.8 0.51

18.8 401.2 0.46

23.0 326.7 0.35

of breakthrough experiments are provided by Table 2. CH4 (purity 99.9%) used as the carrier gas is provided by Liu-Fang

3. MODEL 3.1. Formulation of the Model. The H2S sorption process on TEA-modified SBA-15 adsorbents includes bulk phase diffusion, internal pore diffusion, surface diffusion, absorption by a TEA liquid film, and diffusion through the boundary layer of the liquid film to the adsorbent surface. Other assumptions include the following: (1) Ideal gas is postulated for the gas phase. (2) Plug flow is postulated for gas passing through the adsorbent bed. (3) The pressure over the adsorbent bed is constant. (4) The temperature of the adsorbent bed is constant. These assumptions are reasonable considering the low H2S concentration in the feed gas, low flow rate, and large ratio of length to diameter (L/d = 40) of the adsorption bed.9 Compared with the adsorption capacity of H2S on a TEA-modified adsorbent, the adsorption capacity of CH4 on this type of adsorbent is negligible. CH4 is therefore regarded as an inert carrier gas. The mass balance equation for the H2S component i in the adsorption bed is described as

Table 2. Parameters for Adsorbent, Adsorbent Bed, and Experimental Condition specific surface area ag (m2/kg) particle radius, Rp (m) bulk density, ρb (kg/m3) bed diameter, d (m) bed length, L (m) void fraction in packed bed, εb porosity of adsorbent particle, εp σ (m2/m3)

6.53 × 105 temperature, T (K)

298.15

1.5 × 10−4 pressure, p (MPa) 667.5 flow rate, u (m/s)

0.1−0.8 0−0.026 3.13 × 10−5

0.20 0.61

H2S content in feed gas, Cf (kmol/m3) gas density, ρ (kg/m3) gas viscosity, μ (Pa·s)

0.47

(∑υ)A (cm3/mol) for CH4 24.42

0.005

2.86 1.02 × 10−5

1.71 × 108 (∑υ)B (cm3/mol) for H2S 20.96

High-Tech Co., Tianjin, China. The standard mixture of CH4 and H2S is supplied by Longkou City Gas Plant, Shandong, China. The mass flow controller (precision, 1.5%) is provided by Shengye Technical and Development Co., Beijing. The ND1005, ND-1010, and ND-1020 H2S detectors are supplied by Nanjing Jiangda Technology Co. Ltd., Nanjing, China. The SA-3100 Plus specific surface area and pore size analyzer is provided by Beckman Coulter, Brea, CA, USA. The KK8 gas compressor is supplied by Dürr Technik, Bietigheim-Bissingen, Germany. The rotary pump is provided by Vacuum Pump Co., Wuxi, China. The adsorption bed is made of stainless steel with a 5 mm inner diameter and 20 cm length. The H2S concentration in the gas mixture is 195 ppm. 2.2. Experimental Apparatus and Operational Procedures. H2S sorption behaviors are examined by a single-column

∂Ci ∂ 2C ∂(uCi) 1 − ε b ∂qi = Dei 2i − − ∂t ∂z ε b ∂t ∂z

(1)

The mass balance eq 1 that describes the concentration distribution along the column accounts for the rate of uptake in the column, the axial dispersion, the convection term, and the rate of mass transfer into the particles. The flow rate at the entrance and exit points can be considered equal if the concentration of the adsorbed component is less than 20% in the gas mixture.21,22 This assumption is 4408

dx.doi.org/10.1021/ie202360h | Ind. Eng. Chem. Res. 2012, 51, 4407−4413


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absolutely valid for the present situation where the total H2S content in the gas mixture is only 195 ppm. Therefore, the flow rate of the gas stream is considered constant, and the variation of u along the adsorbent bed is omitted. Equation 1 is thus simplified to ∂Ci ∂ 2C ∂C 1 − ε b ∂qi = Dei 2i − u i − ∂t ∂z ε b ∂t ∂z

(2)

where ∂qi/∂t is the sorption rate of H2S and is determined as follows. The H2S flux per unit interface area is expressed as

N = K i(pg − pi* )

(3)

The overall transfer coefficient Ki is described as 1 1 1 1 1 = + + + Ki σ kg σ k lσ ksσ kf σ

Figure 3. Relationship between saturation capacity and the LR of TEA at 25 °C and p* = 0.087 kPa.

from eq 6. The isotherm equation qi is obtained via the variable separation

(4)

where kg is the mass-transfer coefficient in the bulk gas phase and kl is the mass-transfer coefficient in the TEA liquid film. The very high value of kl is due to the large solubility and fast diffusion of H2S in the basic liquid TEA film. Thus, the liquid film mass-transfer resistance 1/kl is neglected. ks denotes the pore mass-transfer and surface mass-transfer coefficient of the TEA-modified adsorbent, whereas kf is the mass-transfer coefficient that represents the transfer through the boundary layer of the TEA liquid film to the adsorbent surface. Given that ∂qi/∂t is based on unit volume adsorbent and is the product of N and σi, then

⎡ ⎤ 0.18 ⎥k−1p* + qi = q(p*, LR) = ⎢ 2.62 i ⎢⎣ (0.32 − LR)2 + 0.012 ⎥⎦ (7)

Equation 5 is then rewritten as ∂qi ∂t

⎡ ⎤−1 0.18 ⎢ a= + 2.62⎥ k ⎢⎣ (0.32 − LR)2 + 0.012 ⎥⎦

(5)

where σi is the total interface area per unit volume of the adsorbent at different TEA LRs. Both LR and partial pressure of H2S affect the saturation sorption capacity. Assuming that the effects of these two parameters are mutually independent to simplify the experimental process, then q(p*, LR) = kf (p*) g (LR)

(8)

where

∂qi

= σiK i(pg − pi* ) ∂t

= σiaK i[(bCi − qi)]

⎡ ⎤ 0.18 ⎥k−1RT + b=⎢ 2.62 ⎢⎣ (0.32 − LR)2 + 0.012 ⎥⎦

(9)

(10)

The initial condition is

(6)

t = 0,

For error compensation of this approximate method, a correct parameter k is introduced. H2S adsorption isotherms on selected adsorbents are shown in Figures 2 and 3 at different conditions,

Ci = 0,

qi = 0

(11)

The boundary condition is ∂Ci = −u(C f − Ci) ∂z

z = 0,

Dei

z = L,

∂Ci =0 ∂z

(12)

(13)

Equations 2, 7, and 8, together with the initial and boundary conditions, constitute the proposed model. These equations are numerically solved by the finite difference method.23 The space differential in the model is discretized by the central difference form, and a set of ordinary differential equations is obtained from the solution using the Gear method.24 The values of the involved model parameters are listed in Tables 1 and 2. 3.2. Evaluation of Model Parameters. kg and the diffusion coefficient Dei are evaluated from the following empirical equations:25−27

Figure 2. Relationship between saturation capacity and the partial pressure of H2S at 25 °C and LR = 0.23.

Sh = 2.0 + 1.1Sc1/3Re 0.6 = k gd p/Dm

from which adsorption isotherm equations q(p*,0.23) and q(0.087,LR) are obtained with linear fit and Lorentz fit, respectively. The functions of f(p*) and g(LR) are derived

Re = 4409

2R puρ μ

,

Sc =

μ ρDm

(14)

(15)


Industrial & Engineering Chemistry Research Dm =

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10−5T1.75(1/MA + 1/MB)1/2 p[(∑ vA )1/3 + ∑ v B)1/3 ]2

(16)

ε bDzi = 20 + 0.5ScRe Dm

(17)

Dei = Dzi ε b/κ = Dzi ε b2

(18)

Assuming that the pore and surface diffusions on the TEAmodified adsorbent occurred simultaneously, then ks and kf are evaluated by the following empirical equations:28,29 −1 ⎡ ⎤ 60(1 − ε b) ⎢ 1 ⎛ 1 dq ⎥ 1 ⎞ 1 Ds ksσ = ε ⎜ + ⎟ + 2 ρs ⎢ k2 p⎝ Dm Dk ⎠ dP ⎥⎦ d p2 κ ⎣

Figure 5. TEM image of SBA-15.

(19)

−2

Ds = 1.6 × 10

exp( −0.45ΔH /(2RT ))

(20)

1/2

Dk =

2 ⎛⎜ 8RT ⎞⎟ 3 ⎝ πM ⎠

Rp

2/3 ⎛ d puρ ⎞−1/2 kf ⎛ μ ⎞ ⎟ = 1.15⎜ ⎟ ⎜ μ /ε b ⎝ ρDm ⎠ ⎝ με b ⎠

(21)

(22)

Compared with Dm and Dk, the value of Ds is very small on the basis of eqs 16, 20, and 21 because the total adsorption heat ΔH in the system includes physical adsorption heat and chemical absorption heat. The term 1/κ2ρs(dq/dP)Ds in eq 19 is therefore neglected.28

Figure 6. N2 adsorption−desorption isotherms of different SBA-15 samples before and after loading TEA.

4. RESULTS AND DISCUSSION 4.1. Structural Property of SBA-15. The ordered and two-dimensional pore structures of the SBA-15 adsorbent are demonstrated with the transmission electron microscopy (TEM) photographs in Figures 4 and 5. The specific surface

Figure 7. XRD patterns of SBA-15 samples before and after loading TEA.

4.2. Breakthrough Curves of H2S. The H2S breakthrough curves on different mesoporous adsorbents are measured under several operational conditions, including LR variation, adsorption pressure, flow rate, and fixed bed length. 4.2.1. Effect of LR. The H2S breakthrough curves are tested on adsorbents with different LRs at 25 °C, 0.4 MPa, and a flow rate of 280 cm3(STP) min−1. The experimental data in Table 1 and Figure 3 show that the specific surface area and pore volume decrease significantly at LR = 23%, whereas H2S saturation sorption capacity increases slowly at LR > 23%. This phenomenon is caused by the numerous adsorbent pores filled by TEA. On the basis of the previous study, large LR results in relatively high H2S capacity, but the regeneration cost of saturated adsorbent is also high.11 Therefore, breakthrough curves for LR = 0, 9.8, 14.3, 18.8, and 23.0% are selected for the

Figure 4. TEM image of SBA-15.

area of prepared SBA-15 adsorbents is measured using the Brunauer−Emmett−Teller (BET) method.30 All nitrogen adsorption−desorption curves for the different SBA-15 materials have a hysteresis loop that is associated with mesoporosity and capillary condensation (Figure 6).30 The detailed changes in the specific surface area and pore volume are listed in Table 1. The X-ray diffraction (XRD) patterns of SBA-15 adsorbents are shown in Figure 7. Although θ shifts slightly to the right and the peak intensity decreases with increased LR, the basic peak pattern does not change. Modified SBA-15 adsorbents are found to retain a mesoporous structure. 4410



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measurements (dotted lines in Figure 8). The breakthrough time is prolonged with increasing LR, and this change is more remarkable at LR = 23.0%.

Table 3. Sorption Amount under Different Experimental Condition operation conditions LR = 0% (p = 0.4 MPa; L = 0.2 m; flow rate, 280 cm3(STP) min−1) LR = 9.8% (p = 0.4 MPa; L = 0.2 m; flow rate, 280 cm3(STP) min−1) LR = 14.3% (p = 0.4 MPa; L = 0.2 m; flow rate, 280 cm3(STP) min−1) LR = 18.8% (p = 0.4 MPa; L = 0.2 m; flow rate, 280 cm3(STP) min−1) LR = 23.0% (p = 0.4 MPa; L = 0.2 m; flow rate, 280 cm3(STP) min−1) p = 0.1 MPa (LR = 23.0%; L = 0.2 m; flow rate, 280 cm3(STP) min−1) p = 0.2 MPa (LR = 23.0%; L = 0.2 m; flow rate, 280 cm3(STP) min−1) p = 0.4 MPa (LR = 23.0%; L = 0.2 m; flow rate, 280 cm3(STP) min−1) p = 0.6 MPa (LR = 23.0%; L = 0.2 m, flow rate 280 cm3(STP) min−1) p = 0.8 MPa (LR = 23.0%, L = 0.2 m; flow rate, 280 cm3(STP) min−1) flow rate, 180 cm3(STP) min−1 (LR = 23.0%; L = 0.2 m; p = 0.4 MPa) flow rate, 280 cm3(STP) min−1 (LR = 23.0%; L = 0.2 m; p = 0.4 MPa) flow rate, 380 cm3(STP) min−1 (LR = 23.0%; L = 0.2 m; p = 0.4 MPa) flow rate, 480 cm3(STP) min−1 (LR = 23.0%; L = 0.2 m; p = 0.4 MPa) L = 0.1 m (LR = 23.0%; p = 0.4 MPa; flow rate, 480 cm3(STP) min−1) L = 0.15 m (LR = 23.0%; p = 0.4 MPa; flow rate, 480 cm3(STP) min−1) L = 0.2 m (LR = 23.0%; p = 0.4 MPa; flow rate, 480 cm3(STP) min−1)

Figure 8. Experimental and simulated breakthrough curves at different LR values: (1) k = 0.98; (2) k = 0.92; (3) k = 0.90; (4) k = 0.89; (5) k = 0.85.

4.2.2. Effect of Operational Pressure. The breakthrough curves of different pressure levels are measured at 25 °C and a flow rate of 280 cm3(STP) min−1 with LR = 23.0%. The breakthrough curves obtained at 0.1, 0.2, 0.4, 0.6, and 0.8 MPa are plotted in dotted lines in Figure 9. The breakthrough time is

sorption amount (mg/g) 0.07426 0.08408 0.1021 0.1186 0.1441 0.04714 0.07973 0.1441 0.2078 0.2616 0.1447 0.1441 0.1169 0.08842 0.1418 0.1412 0.1441

Figure 9. Experimental and simulated breakthrough curves at different pressure levels: (1) k = 0. 97; (2) k = 0.93; (3) k = 0.85; (4) k = 0. 86; (5) k = 0.80.

prolonged with increasing operational pressure, and this change is relatively obvious at 0.4 MPa on the basis of data in Table 3. Lower operation pressure is preferable in practice, but the adsorption capacity of the adsorbent at this level is also small. Considering the balance of energy cost and adsorption capacity, 0.4 MPa is selected as the suitable operating pressure. 4.2.3. Effect of Flow Rate. The breakthrough curves of different flow rates are calculated at 25 °C and 0.4 MPa with LR = 23.0%. The breakthrough curves obtained at flow rates of 180, 280, 380, and 480 cm3(STP) min−1 are shown in dotted lines in Figure 10. The breakthrough time is shortened as the flow rate increases. However, H2S sorption capacity also slightly decreases when the flow rate is larger than 280 cm3(STP) min−1 according to the sorption amount in Table 3. This phenomenon is caused by the partial purging of physically adsorbed H2S out of the adsorption bed with CH4. Hence,

Figure 10. Experimental and simulated breakthrough curves at different flow rates: (1) k = 0.87; (2) k = 0.85; (3) k = 0.85; (4) k = 0.82

280 cm3(STP) min−1 is considered as the suitable flow rate in the present system. 4.2.4. Effect of Fixed Bed Length. All tests mentioned above are for 0.20 m bed length. To investigate the effect of bed length on purification, additional 0.15 and 0.10 m bed lengths are tested for the adsorbent bed. The breakthrough curves that are measured for these bed lengths at 25 °C, 0.4 MPa, and a flow rate of 280 cm3(STP) min−1 with LR = 23.0% are shown in dotted lines in Figure 11. Prolonged breakthrough time is obtained as the bed length is increased, that is, as the throughput of the adsorption bed becomes larger. However, 4411



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other conditions. The amount of H2S adsorbed on the TEAmodified SBA-15 is 1.85 times more than that on the TEAmodified silica gel. A model for H2S breakthrough processes on SBA-15 adsorbents covered with a film of TEA is proposed on the basis of mass-transfer theory, dissolution equilibrium of H2S in TEA, and the effect of LR on the adsorbent capacity. The model is used to simulate breakthrough curves of H2S under different conditions, and the predicted breakthrough curves agree well with the experimental ones. Therefore, the model is beneficial not only for discussing the effects of major operational variables but is also applicable in process simulation.

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Figure 11. Experimental and simulated breakthrough curves at different bed lengths: k = 0.85.

AUTHOR INFORMATION

Corresponding Author

*Tel.:86-0517-83525041. Fax:86-0517-83525795. E-mail: [email protected].

the H2S sorption amount on per gram sorbent has almost no change on the basis of data in Table 3. 4.3. Sorption Isotherm of H2S. On the basis of breakthrough curves, the sorption isotherm of H2S on the TEA-modified SBA-15 is obtained in Figure 12 at 25 °C with

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work is financially supported by the National Natural Science Foundation of China (Grants 21106051, 51106061), the Natural Science Foundation of Jiangsu Universities (Grants 11KJA150004, 09KJA530001), the Foundation of Jiangsu Key Laboratory for Chemistry of Low-Dimensional Materials (Grant JSKC11103), and the Program for Science and Technology Development of Huai’an (Grant HAG2011030).

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ag C Ci C0 Dm

Figure 12. Sorption isotherms of H2S.

Dzi Dei Dk kg kl dp MA MB p pg p*

LR = 23.0%. The results show that the sorption isotherm of H2S nearly conforms to the linear correlation at low pressure; moreover, the amount of H2S adsorbed on the TEA-modified SBA-15 is 1.85 times more than that on the TEA-modified silica gel because the sorption capacity increases with the increase of LR. The details of this sorption mechanism were discussed in our previous paper.11 4.4. Simulated Breakthrough Curves. The breakthrough curves of H2S in Figures 8−11 are simulated by numerically solving the mathematical model in section 3 on the basis of parameters given in Tables 1 and 2. The smooth curves with solid lines in Figures 8 and 10−12 indicate that the simulation results are consistent with the experimental data. The agreement between the simulated and the experimental results facilitates the use of the proposed model in the H2S process design and optimization of operational variables.

q R Re Sc Sh t T u z

5. CONCLUSION Ordered SBA-15 silica mesoporous molecular sieve and its TEA-modified adsorbents have been synthesized. The breakthrough curves of H2S on different adsorbents are measured at different LRs, operational pressures, flow rates, and fixed bed lengths. Removal efficiency is better at 0.4 MPa, LR = 23.0%, a flow rate of 280 cm3(STP) min−1, and 0.2 m bed length than at

NOMENCLATURE specific surface area of adsorbent, m2/kg total concentration of the feed stream, mol/m3 concentration of H2S in gas phase, mol/m3 concentration of H2S in feed stream, mol/m3 molecular diffusion coefficient of H2S in gas phase, m2/s axial diffusion coefficient, m2/s effective axial diffusion coefficient, m2/s Knudsen diffusion coefficient, m2/s mass-transfer coefficient in the gas film, m/s liquid film absorption coefficient, m/s adsorbent particle diameter, m molecular weight of species A (H2S) molecular weight of species B (CH4) total pressure, MPa partial pressure of H2S, kPa partial pressure of H2S in equilibrium with the sorbed amount q, MPa average amount adsorbed of adsorbent, mol/kg gas constant, J/(mol·K) Reynolds number in gas phase Schmidt number in gas phase Sherwood number in gas phase contacting time, s temperature, K flow gas velocity in adsorbent bed, m/s axial distance of adsorption bed, m

Greek Letters

εb σ κ 4412

void fraction in packed bed, kg/m3 surface area in unit volume of adsorbent, m2/m3 tortuosity factor dx.doi.org/10.1021/ie202360h | Ind. Eng. Chem. Res. 2012, 51, 4407−4413


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(19) Liu, X. W.; Li, J. W.; Zhou, L.; Su, W.; Sun, Y.; Zhou, Y. P. Mesoporous Silica Adsorbents Synthesis, Characterization, and Their Adsorption Equilibrium Properties for CO2, N2 and CH4. Chem. Phys. Lett. 2005, 415, 198. (20) Chu, X. Z.; Zhou, Y. P.; Zhang, Y. Z.; Su, W.; Zhou, L. Adsorption of Hydrogen Isotopes on Micro- and Mesoporous Adsorbents with Orderly Structure. J. Phys. Chem. B 2006, 110, 22596. (21) Malek, A.; Farooq, S. Effect of Velocity Variation Due to Adsorption-Desorption on Equilibrium Data from Breakthrough Experiments. Chem. Eng. Sci. 1995, 50, 727. (22) Chu, X. Z. Studies on the Adsorption of Hydrogen Isotopes. Ph.D. Dissertation, Tianjin University, China, 2007. (23) Chu, X. Z.; Zhao, Y. J.; Kan, Y. H.; Zhang, W. G.; Zhou, S. Y.; Zhou, Y. P.; Zhou, L. Dynamic Experiments and Model of Hydrogen and Deuterium Separation with Micropore Molecular Sieve Y at 77 K. Chem. Eng. J. 2009, 152, 428. (24) Chu, X. Z. Studies on the Mechanism and Model of Chemical Oscillations. M.S. Dissertation, Tianjin University, China, 2004. (25) Jothimurugesan, K.; Harrison, D. P. Reaction between H2S and Zinc Oxide-Titanium Oxide Sorbents. 2. Single-Pellet Sulfidation Modeling. Ind. Eng. Chem. Res. 1990, 29, 1167. (26) Abolfazl, K.; Leila, V.; Ali Akbar, S. Experimental and Theoretical Studies of Pressure Swing Adsorption Process to Remove H2S from Methane in a Packed Bed. Sci. Res. Essays 2010, 5, 2391. (27) Ruthven, D. M. Principles of Adsorption and Adsorption Process; Wiley: New York, 1984. (28) Nishikawa, M.; Tanaka, K. I.; Uetake, M. Mass Transfer Coefficients in Cryosorption of Hydrogen Isotopes on Molecular Sieves or Activated Carbon at 77.4 K. Fusion Technol. 1995, 28, 1738. (29) Siadek, K. J.; Gilliland, E. R.; Baddour, R. F. Diffusion on Surfaces. II. Correlation of Diffusivities of Physically and Chemically Adsorbed Species. Ind. Eng. Chem. Fundam. 1974, 13, 100. (30) Rouquerol, F.; Rouquerol, J.; Sing, K. Adsorption by Powders and Porous Solids: Principles, Methodology and Applications; Academic Press: London, 1999.

(∑v)A, (∑v)B molecular diffusion volume of species CH4 and H2S, respectively, cm3/mol μ viscosity of gas phase, Pa·s ρ density of gas phase, kg/m3 ρb density of packed bed, kg/m3 ρs density of particles, kg/m3

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REFERENCES

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S by Triethanolamine-Modified Mesoporous Molecular Sieve SBA-15

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