Selective Removal of H2S from Biogas Using Solid Amine-Based

Subscriber access provided by Columbia University Libraries

Article

Selective Removal of H2S from Bio-gas Using Solid Amine-based “Molecular Basket” Sorbent Wenying Quan, Xiaoxing Wang, and Chunshan Song Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01473 • Publication Date (Web): 08 Aug 2017 Downloaded from http://pubs.acs.org on August 11, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 48

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_H2S Ads_WQ_MS_v10.8wq_6Aug17

Selective Removal of H2S from Bio-gas Using Solid Amine-based “Molecular Basket” Sorbent

Wenying Quan,a,b,c Xiaoxing Wang,a and Chunshan Song,a,b,c* a

Clean Fuels & Catalysis Program, EMS Energy Institute, PSU-DUT Joint Center for Energy

Research,

b

John and Willie Leone Family Department of Energy and Mineral Engineering, The

Pennsylvania State University, 209 Academic Projects Building, University Park, PA 16802, USA c

PSU-DUT Joint Center for Energy Research, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China * Corresponding author. E-mail: [email protected]

1 ACS Paragon Plus Environment

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 2 of 48

ABSTRACT Bio-gas is an important renewable energy source but its ppm-level hydrogen sulfide (H2S) component must be removed from the gas mixture dominated by CO2 and CH4. In this work, a tertiary-amine-based “molecular basket” sorbent with a mesoporous silica as support was found to be effective for the selective hydrogen sulfide (H2S) removal from gas mixtures simulating bio-gas with a high CO2 concentration up to 40 vol%. Polyallylamine (PA), polyethylenimine (PEI), and tetramethyl hexanediamine (TMHDA) were used as primary, secondary, and tertiary amines to prepare the SBA-15 supported sorbents, respectively, and their H2S sorption performances were evaluated in a flow system in the absence and presence of CO2. The tertiaryamine-based sorbent, TMHDA/SBA-15, can selectively remove H2S in the presence of CO2, and the highest sorption capacity was achieved at 15 wt% TMHDA loading which is close to its monolayer coverage on surface. More importantly, about 90 % of the capacity could be maintained on TMHDA/SBA-15 even with the CO2 concentration as high as 40 vol%. The H2S sorption on TMHDA/SBA-15 fitted with the Langmuir adsorption isotherm well although the estimated adsorption heat with van’t Hoff equation is relatively low. Characterization using N2 physisorption, FT-IR, and XPS demonstrated that the TMHDA is dispersed within the pore channels through the interaction between amine and silanol groups on the surface of SBA-15. The TMHDA/SBA-15 sorbents showed a good regenerability

under a mild regeneration

condition (e.g., 110 ℃), the capacity of which was not impeded by other components in bio-gas such as CH4 and H2O.

Keywords: Mesoporous molecular sieve, Sorption, H2S removal, Molecular basket sorbent, Tertiary amine 2 ACS Paragon Plus Environment

Page 3 of 48

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

1. INTRODUCTION Hydrogen sulfide (H2S) is a colorless, acidic, flammable, and poisonous gas with a bad smell. It is contained in biogas and natural gas and originates from bacterial decomposition processes of organic materials such as anaerobic digestion. Combined with water, H2S can cause corrosion of tanks and pipelines. Furthermore, H2S in fuel gas will convert to sulfur oxides upon combustion, leading to environmental pollution. Additionally, H2S is poisonous to most of the catalysts containing transition metals. Therefore, H2S removal from fuel gas is a critical issue, ensuring safety for technological systems and reducing the impact on the environment. Chemical absorption in aqueous solutions is a conventional sorption process for H2S removal from gas mixtures. Currently, H2S absorption processes use alkaline solutions, monoethanolamine (MEA) or diethanolamine (DEA), which can interact with H2S through acidbase reaction.1 But the presence of CO2 in biogas and in natural gas is inevitable. Since the acidity of CO2 is much stronger than that of H2S, it is easier for CO2 to interact with amine groups with a higher reaction rate. Therefore, CO2 can inhibit H2S absorption into the alkaline solutions by limiting the sorption rate in the process of simultaneous CO2 and H2S removal. Selective H2S removal in industrial field uses tertiary amine solution, such as methyldiethanolamine (MDEA), which can absorb H2S from sour gas directly.2 This kind of sterically hindered amine can decrease the CO2 reaction rate since it cannot interact with CO2 to form carbamate because of the absence of hydrogen on the tertiary amine. Lots of work has been done on the selective removal of H2S from CO2-containing gas mixtures into MDEA based solutions.3-5 However, chemical absorption processes involve gas-liquid processes, which is energy intensive and are limited by the gas-liquid mass transfer rate. Moreover, the solvent 3 ACS Paragon Plus Environment

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 4 of 48

degradation and the corrosion of the amine solution are also major problems. The metal-oxidebased sorbent is another option for selective H2S removal. In 1940s, hydrated iron oxide was developed for low-temperature H2S removal, but the regeneration is an exothermic process which may cause combustion.6 Therefore, zinc oxide has taken the place of iron oxide. As reported by Davidson et al., H2S adsorption over ZnO can convert 40 % ZnO.7 However, the presence of CO and H2O inhibits H2S removal over ZnO.8 To further improve the adsorption ability of H2S removal, other metal oxides have been reported, such as ferric oxyhydroxides (FeOOH),9 iron, copper, and cobalt doped zinc oxide,10 cobalt-zinc-aluminum oxides,11, 12 ironzinc and iron-cobalt mixed oxides,13, 14 and Zn-Ti-based oxides.15-18 However, the regeneration process of the metal-oxide-based sorbents is usually at high temperature (> 400 ºC)

19-21

under

oxygen atmosphere, which consumes extra energy. Therefore, a sorbent that can be operated and regenerated under ambient conditions is more beneficial for the H2S removal process. Recently, a new type of solid sorbents called “molecular basket” sorbent (MBS) has been developed in our laboratory for CO2 or H2S sorption at near-ambient conditions. Combining the advantages of mesoporous silica materials and amine functional groups, MBS is able to remove H2S or CO2 efficiently.22-28 However, in the work of CO2 and H2S separation on MBS, it was found that the presence of CO2 can strongly inhibit the H2S sorption on MBS.29 Based on the computational work, the coexisting CO2 can block H2S sorption on MBS due to the stronger acid-base interaction with amine groups,. Furthermore, the kinetic barrier for CO2 diffusing from the surface into the bulk is also higher than that of H2S. Thus, a higher sorption temperature is favorable for CO2 molecules’ diffusion. At the meantime, the study on the temperature dependence of H2S and CO2 sorption on MBS demonstrated that H2S sorption capacity at 22 ℃ was much higher than that at 75 ℃, while CO2 obtained a higher sorption at 75 ℃.29 Based on the


Page 5 of 48

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

results and the fundamental understanding, a two-stage process for CO2 and H2S removal on MBS was proposed in that work. The first stage was at 75 ℃ for CO2 removal and then the second stage was for H2S removal at 22 ℃. However, the two-stage sorption process consumes extra energy and cost as not all the fuel gas applications need to remove CO2. Besides, CO2 is not a poisonous gas compared to H2S. Therefore, a one-stage H2S sorption process on MBS is necessary to be developed for a more efficient H2S removal process. As is known, primary, secondary, and tertiary amines have different chemical interactions with CO2 or H2S. The involving chemical reactions are shown below.30 Reactions of amine and CO2: + 2 ↔ + ⋯ ⋯ . 1 + 2 ↔ + ⋯ ⋯ . 2 + 2 ↮ ⋯ ⋯ . 3 Reactions of amine and H2S: + 2 ↔ − − ⋯ ⋯ . 4 + 2 ↔ − − ⋯ ⋯ . 5 + 2 ↔ − − ⋯ ⋯ . 6 In 2011, Ko et al. compared primary, secondary, and tertiary amines for CO2 capture.31 (3-Aminopropyl) tri-methoxysilane (APTMS), [3-(methylamino) propyl] trimethoxysilane (MAPTMS), and [3-(diethylamino) propyl] trimethoxysilane (DEAPTMS) representing primary, secondary, and tertiary amine, respectively, were grafted on SBA-15. The CO2 sorption capacity of SBA-15-NH2, SBA-15-NH-CH3, and SBA-15-N(CH2CH3)2 were 0.95, 0.75, and 0.17 mmolCO2/g-sorb, respectively. The comparison proves the weakness of tertiary amine on CO2 capture. In 2014, another work comparing primary, secondary, and tertiary amines for H2S sorption was


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 6 of 48

published by Abdouss et al..32 In this work, the same sorbents were used as those reported by Ko et al..31 The breakthrough time of H2S sorption was about 150 min on NNN/SBA (SBA-15N(CH2CH3)2 in Ko’s work) while this value was about 130 and 180 min on N/SBA (SBA-15NH2 in Ko’s work) and NN/SBA (SBA-15-NH-CH3 in Ko’s work), respectively. Although H2S sorption on NNN/SBA reached to breakthrough point earlier than NN/SBA, it still indicates that H2S can be adsorbed by tertiary amine groups on silica. The interpration of Ko et al. and Abdouss et al. works were published ealier in Huang et al..33 However, no work on the selective H2S removal from CO2-containing gas mixtures has been reported on such sorbents. Tertiary amine can only bond with H2S through the interaction between H from H2S and N from tetiary amine, from which it is hypothesized that loading tertiary amine on SBA-15 may improve the sorption selectivity of H2S from CO2-containing gas mixtures, and thus a one-stage H2S sorption process on MBS could be achieved. The present work aims at selective H2S removal from the gas mixture containing a high concentration

of CO2

using solid

tertiray-amine-based

MBS.

Polyallylamine (PA),

polyethylenimine (PEI), and tetramthyl hexanediamine (TMHDA) representing primary, secondary, and tertiary amines, respectively, were loaded on SBA-15 to compare the H2S sorption performance in the presence of CO2. To investigate the H2S sorption performance on TMHDA loaded MBS, several series of experiments were conducted in a fixed-bed flow system to examine the effects of TMHDA loading level, temperature, inlet gas component concentrations (H2S and CO2), and other components (CH4 and H2O) as well as regenerability and stability of TMHDA loaded MBS.


Page 7 of 48

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

2. EXPERIMENTAL SECTION 2.1 Preparation of sorbents. The detailed preparation method of SBA-15 is described elsewhere,34, 35 so the procedure is described briefly herein. Triblock copolymer Pluronic P123 (EO20PO70EO20, MW=5800, Aldrich) and tetraethyl orthosilicate (TEOS, Aldrich) were mixed homogeneously in hydrochloric acid (2 M) under vigorous stirring at 40 ℃ for 20 hours, followed by aging at 100 ℃ for 24 hours. The solid resultant was filtered, washed, and dried at 100 ℃ overnight prior to calcination at 550 ℃ for 6 hours. A wet impregnation method was used to prepare the SBA-15 supported sorbents.26, 27 Amines with different structures were loaded on the support, which are polyallylamine (10 wt% in water with Mw of 15,000, Polyscience Inc.), polyethylenimine (linear PEI with Mw of 1,800, Polyscience Inc.), and N, N, N′, N′-Tetramethyl-1, 6-hexanediamine (99%, Aldrich) and hereafter denoted as PA, PEI, and TMHDA, respectively, and detailed structures are illustrated in Figure 1. For comparison, the loading amount was fixed at 30 wt%. Other evaluation experiments used a series of TMHDA(X)/SBA-15 sorbents, where the X represents the loading level. Typically, a desired amount of TMHDA was dissolved in methanol (ca. 20 g) under vigorous stirring for 30 min, followed by adding SBA-15 (ca. 2 g) into the mixture and then stirring for 8 h. After the solvent evaporated, the solid resultant was collected after drying in vacuum over at 40 ℃ overnight. 2.2 H2S sorption measurements. The H2S sorption from a CO2-containing gas mixture was carried out using a fixed-bed flow system under atmospheric pressure. Typically, 0.3 g of sorbent was packed into the fixed-bed reactor, and the residual space was filled with glass wool. Prior to the sorption measurement, the sorbent was pretreated with nitrogen (UHP, ca. 25 ml/min) 7 ACS Paragon Plus Environment

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 8 of 48

at 110 ℃ for ~ 12 h to remove the moisture. A model gas, containing 500 ppmv H2S and 10 vol% CO2 balanced with N2, was introduced into the reactor (ca. 15 ml/min) for sorption/desorption process. A schematic illustration of the reaction system is shown in Figure 2. The sorption performance was evaluated by breakthrough capacity (BT cap.) and saturation capacity (S cap.) according to Eqs. 1 and 2, respectively. . = . =

× "#$ % × & $ % × 10 ( × )$% ⋯ ⋯ ./. 1 *+,- × # 1

× "#$ % × 0& $& − 1 %2) × 10 ( *+,- × #

⋯ ⋯ ./. 2

In the equations, FR is the flow rate (ml/min), Vmol is the molar volume of gas (24.4 ml/mmol at standard conditions), W is the weight of the sorbent (g), c0 and ct stand for the inlet and outlet concentrations of H2S, and t(BT) represents the breakthrough time (min) when the outlet H2S concentration reaches 2 ppm. 2.3 Characterization. The N2 adsorption-desorption isotherms for both bare support and sorbents were measured using a Micromeritics TriStar II analyzer to examine the porous properties of sorbents. The samples were degassed at 383 K for 8 h prior to analyses. Specific surface areas were estimated by using the BET method. Pore size distributions were obtained by applying the B.J.H. formalism to the desorption branch of the isotherms. The IR spectra of bare support and TMHDA-loaded sorbent were collected using a Nicolet NEXUS 470 FT-IR spectrometer equipped with a Smart Collector environment chamber (Thermo Electron Corp.). About 20 mg of sample was used for each measurement, and the pretreatment was carried out under the same conditions as the sorption measurement. KBr (IR grade, Aldrich) was used as background. A resolution of 4 cm-1 was used, and every spectrum was acquired by 64 scans. The interferograms were collected and analyzed by OMNIC ver. 7. 8 ACS Paragon Plus Environment

Page 9 of 48

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

XPS experiments were performed using a Physical Electronics VersaProbe II instrument equipped with a monochromatic Al Kα X-ray source (℃υ=1,486.7 eV) and a concentric hemispherical analyzer. Charge neutralization was performed using both low energy electrons (< 5 eV) and argon ions. The binding energy axis was calibrated using sputter cleaned Cu foil (Cu 2p3/2 = 932.7 eV, Cu 2p3/2 = 75.1 eV). Peaks were charge referenced to CHx band in the carbon 1s spectra at 284.8 eV. Measurements were made at a takeoff angle of 45° with respect to the sample surface plane. This resulted in a typical sampling depth of 3-6 nm (95% of the signal originated from this depth or shallower). Quantification was done using relative sensitivity factors (RSFs) derived from triplicate measurements on air fractured Wale silica bars. The thermostability of the sorbents was evaluated using a thermogravimetric analyzer (TA Q600-SDT TGA-DSC). A typical TGA program starts from room temperature to 700 ℃ with a ramp rate of 5 ℃/min under the environment of N2 (ca. 100 ml/min). 3. RESULTS AND DISCUSSION 3.1 H2S sorption performance of supported amines. In order to investigate the effect of different amine groups on the H2S sorption performance in the absence and presence of CO2, sorbents loaded with different amines were prepared and tested under atmospheric condition. Specifically, polyallylamine (PA), polyethylenimine (PEI), and tetramethyl hexanediamine (TMHDA) were introduced representing primary amine, secondary amine, and tertiary amine, respectively, and their structures are shown in Figure 1. Figure 3 illustrates the H2S sorption breakthrough curves in the absence and presence of 10 vol% CO2 over PA/SBA-15, PEI/SBA-15, and TMHDA/SBA-15 for which the loading level was fixed at 30 wt% for comparison. Apparently, the breakthrough time for both PA/SBA-15 and PEI/SBA-15 (Figure 3-a and 3-b, respectively) reduced dramatically after introducing CO2 into the gas mixture. In sharp contrast, 9 ACS Paragon Plus Environment

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 10 of 48

the breakthrough time of TMHDA/SBA-15 remained nearly unchanged after CO2 introduction (Figure 3-c). The corresponding H2S breakthrough sorption capacity (BT cap.) was also quantified and summarized in Table 1. In the presence of 10 vol% CO2, the PA or PEI loaded sorbents lost ca. 97 % of the BT cap. compared to the condition without CO2; however, the TMHDA loaded sorbent only exhibited 4 % of the capacity loss in the meantime. Moreover, the TMHDA/SBA-15 adsorbed 2.2 and 1.6 times more H2S than PA- and PEI/SBA-15, respectively. Additionally, Figure 3-d illustrates the H2S sorption selectivity on different amines-loaded SBA15, wherein the sorption selectivity was defined as the ratio of the H2S sorption capacity with CO2 to that without CO2. The change of CO2 concentration after sorption from the outlet is not measurable due to its high concentration in the inlet and the small amount of the loaded sorbents. As depicted in Figure 3-d, the tertiary amine-loaded MBS exhibits stable sorption selectivity in 40 min sorption, and the value is as high as 0.96. In contrast, the sorption selectivity of both primary and secondary amine-loaded MBSs starts to decline at 18 min and eventually drop to 0.41 at 40 min sorption. These results strongly support our hypothesis and clearly confirm that the tertiary amine-loaded SBA-15 sorbent is capable of selectively removing H2S from a CO2containing gas mixture. These observations demonstrate that tertiary-amine-loaded MBS, TMHDA/SBA-15 sorbents, is promising for selective H2S removal from the gas mixture containing a high concentration of CO2. As shown in Rxn. 1-6, it is speculated that the CO2 molecules are able to occupy the active sites of the primary and secondary amine groups first due to the strong acidbase interaction, thereof leading to the formation of RHNCOO- and R2NCOO-, respectively, and further inhibiting H2S sorption on other available sites. On the contrary, since the N in the tertiary amine has no bonded hydrogen, CO2 cannot interact with the tertiary amine directly to


Page 11 of 48

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

form carbamate. Instead, one molecule H2S can interact with two molecules NR3 through two HN bonds (H from H2S and N from NR3), through which the selective H2S removal on TMHDA/SBA-15 is achieved even in the presence of CO2. 3.2 Characterization of the TMHDA/SBA-15 sorbents. Figure 4-a illustrates the isotherms of the SBA-15 support and a representative TMHDA(15)/SBA-15 sorbent. Clearly, they both exhibit a typical character of mesoporous molecular sieve, namely a reversible adsorption isotherm (type IV), indicating that the pore structure of the SBA-15 is maintained well after the impregnation. Figure 4-b compares the pore size distribution of corresponding samples. The average pore diameter is narrowed after loading TMHDA as the peak shifts toward lower values. The N2 physisorption was also conducted on other TMHDA-loaded sorbents with different loading levels, and corresponding properties are summarized in Table 2. Significant reductions of BET surface area, pore volume, and pore diameter are observed with the increase of TMHDA loading level, which could be ascribed to the formation of the organic layer within the pore structure of SBA-15. The FTIR spectra of calcined SBA-15 and TMHDA/SBA-15 sorbents are shown in Figure 5. The spectrum of calcined SBA-15 exhibits two sharp peaks at 3747 and 1629 cm-1, as well as a broad band around 3500 cm-1, corresponding to single Si-OH and hydrogen-bonded SiOH, respectively.36 The peak intensity of the single Si-OH gradually decreases with increasing TMHDA loading level and disappears when the TMHDA loading is 30 wt% (see Figure 5). This indicates that there exists an interaction between the TMHDA molecules and hydroxyl group (OH) during the loading, through which the isolated Si-OH groups are consumed. Two other bands, centered at 2936 and 2855 cm-1, are observed for the interferograms of TMHDA-loaded sorbents, the peak intensities of which become stronger with the increase of TMHDA loading


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 12 of 48

level. Clearly, these bands could be assigned to the symmetric and asymmetric CH2/CH3 stretching vibrations of TMHDA chain, respectively. Similarly, the bands, centered at 1458 and 1376 cm-1, were due to the bending vibration of CH2 and CH3, respectively, as the intensities also enhance monotonically with the increase of TMHDA loading level. In addition, a weak band, centered at 1299 cm-1, is observed as well, corresponding to the bending vibration of C-N. However, the relevant stretching vibration of C-N, centered at 1000-1200 cm-1,37 is unresolved because of the interference of the Si-O-Si stretching vibration within the same range.38 The TMHDA loading-dependent behavior of these identified bands demonstrate that there is an interaction of the TMHDA molecules with the surface of the SBA-15 (Si-OH), which is also reflected by their slight shifts compared to normal positions.27 3.3 Effect of TMHDA loading level. Since the TMHDA-loaded sorbent with tertiary amine can selectively remove H2S from a CO2-containing gas mixture, it would be of interest to examine the effect of the amine loading level on the H2S sorption. Thus, a series of TMHDA(X)/SBA-15 based sorbents were prepared with 0-60 wt%, TMHDA loading and the results are shown in Table S1. Figure 6 depicts the changes of sorption capacity as a function of TMHDA loading level. In general, the H2S sorption capacity achieves the maximum at 15 wt% of TMHDA loading (1.28 mg-H2S/g-sorb). According to our previous work, the interaction between the primary/secondary amine of the PA and PEI molecules and silanol groups on the surface of SBA-15 shall follow the reactions below:39 3 − + → 3 − ⋯ ⋯ . 7 3 − + → 3 − ⋯ ⋯ . 8 Similarly, the interaction between TMHDA molecules and silanol groups is proposed as below:


Page 13 of 48

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 − + → 3 − ⋯ ⋯ . 9 where one silanol group interacts with one TMHDA molecule. The density of silanol groups on the surface of SBA-15 is about 1.07 groups/nm2,40 from which the highest monolayer loading of TMDHA is estimated to be 21 wt% if each TMHDA molecule interacts with one surface –OH group. However, this is an ideal model for the loading of TMDHA because not all of the TMHDA molecules could be loaded on the surface of SBA-15 due to the steric hindrance. In this work, the highest H2S sorption capacity is obtained at 15 wt% of TMHDA, which is a practical limit of a maximum monolayer loading. As a benchmark, the H2S sorption was also conducted on the bare support and unsupported TMHDA. The results are shown in Table S1 and the H2S breakthrough curves on unsupported TMHDA in the absence and presence of CO2 is shown in Figure S1. Both the support and unsupported TMHDA exhibited very limited capacities towards H2S sorption. In contrast, the supported TMHDA displayed a substantial improvement on the sorption capacity, demonstrating the crucial role of support in the dispersion of sorption sites. However, since TMHDA is an absorbent of liquid phase, the H2S sorption capacity cannot be simply normalized and compared based on the unit of mg-H2S/g-sorb. For comparison, the sorption ability of non-supported and supported amines was compared in the unit of amine-based capacity (N-based Cap.), which is normalized the H2S sorption capacity on the basis of total amine amount (i.e., mmol-H2S/mol-N), and the results are depicted Figure S2. The amine-based capacity of non-supported TMHDA was much lower than that of supported TMHDA. This is due to the much higher transport limit encountered in the gas-liquid absorption which resulted in a low absorption rate of gas into liquid. Therefore, the enhancement of the sorption capacity with the increase of loading level up to 15 wt% results from the increasing amount of active sites. Noticeably, the H2S sorption capacity of 7 wt% loading is even lower than that of the bare


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 48

support. This interesting change could be attributed to the reduction of active sites as the silanol groups, which is responsible for H2S sorption over SBA-15 alone, are covered by TMHDA at this loading level. On the other hand, when TMHDA loading level is higher than 15 wt%, H2S sorption capacity decreases with further increase of TMHDA loading. Another possible factor is that at the TMHDA loading levels close to 15 wt%, some remaining surface hydroxyl groups could act in concert with the tertiary amine groups in TMHDA, but beyond this loading level more of the surface hydroxyl groups are covered or inaccessible. At 40 and 60 wt%, the saturation capacity reaches the lowest, 0.53 and 0.51 mg-H2S/g-sorb, respectively, which is even less than the SBA-15 alone. The significant reduction of the surface area and the pore volume of the sorbents (see Table 1), could lead to a lower capacity. Another factor is the coverage of accessible active sites resulting from the stack of multilayers of TMHDA due to the excessive loading amount. As mentioned above, the function of TMDHA is also subject to the steric hindrance in addition to the loading level. To further address this effect, the sorption mode of H2S is proposed as described in Figure 7. It is assumed that two types of loaded-TMHDA molecules exist on the surface of SBA-15, including a standing and a lying type. The former one means the silanol group on the surface only interacts with one tertiary amine of TMHDA, while the other one is still available for H2S adsorption. In other words, two TMHDA molecules are responsible for adsorbing one molecule of H2S for this type. The other one, the lying type, implies both tertiary amine groups are occupied from the interaction with the silanol groups so that the TMHDA molecule lies down on the surface of SBA-15. Apparently, this lying type should be inactive for H2S adsorption. Thus, at low loading level, the large unoccupied surface area would facilitate the dispersion of TMHDA molecules in the lying type at the expense of consuming silanol groups


Page 15 of 48

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

which could otherwise contribute to sorption of H2S. This explains the observed lower capacity on TMHDA(7)/SBA-15 than the bare support. To verify the assumption, X-ray photoelectron spectrum (XPS) was performed to analyze the surface information of TMHDA-loaded SBA-15, the full scan, C 1s and N 1s XP spectra of which are shown in Figures S3, S4, and Figure 8, respectively. If this assumption (of two types of TMHDA interactions with surface OH) is true, the TMHDA-loaded sorbent should exhibit a linear superimposition of distinct XP spectra in the N 1s region with two components, one is the protonated N (hereafter denoted as C-N+) bonding with silanol groups, the other is the nonprotonated N in the free side (hereafter denoted as C-N). Indeed, an intense peak with a shoulder is observed in the XP spectra in the N 1s region for all TMHDA(X)/SBA-15, as depicted in Figure 8. The deconvolution analysis shows two components centering at 401.5 eV and 399.4 eV, corresponding to the BEs of C-N+ and C-N species, respectively.41 The areas of these two peaks are dependent upon the TMHDA loading. Such loading-dependent behavior can be used in determining the dominant type of bonding. Thus, the composition of each spectrum was quantified and summarized in Table 3. The chemisorbed TMHDA with a single amine group bonding to the hydroxyl groups on silica would have a (C-N)/(C-N+) ratio of 1, while a doublybonded TMHDA monomer would be entirely protonated and thus have a ratio of 0. On the other hand, a physisorbed TMHDA would show no evidence of protonated nitrogen and thus have a ratio of infinity. In order to further understand the loading types of TMHDA/SBA-15, four samples with the loading levels below and above a theoretical monolayer coverage were comparatively examined. As shown in Table 3, with the loading increase from 7 to 30 wt%, the N composition increases and then decreases after reaching a maximum at 15 wt%, and so as C composition. The slight loss of TMHDA at 30 wt% might be due to the physisorbed molecules


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 16 of 48

which were flushed away under the vacuum condition. This also indicates that the sample with less than 15 wt% loading would be similar to a monolayer coverage, and the sample with 15 wt% loading contained the highest amount of a monolayer TMHDA, which is in line with our hypothesis. The deconvolution analysis reveals that the compositions of C-N and C-N+ exhibit a similar trend as N, and they both maximize at 15 wt%. Under the circumstance of a coverage of monolayer, a higher ratio of C-N/C-N+ indicates more standing-type chemisorbed TMHDA molecules. In other words, more free C-Ns on the opposite side of the monomer will be available for the adsorption and thus result in the observed superior H2S sorption capacity. With a further increase of TMHDA loading level to 30 wt%, the ratio of (C-N)/(C-N+) increases, indicating that more of TMHDA molecules are physisorbed (or stacked up) on SBA-15, thus leading to a reduction of H2S sorption capacity on TMHDA(30)/SBA-15. 3.4 H2S adsorption isotherm. The adsorption isotherms at different temperatures (e.g., 25 and 50 ℃) for H2S on TMHDA(15)/SBA-15 are plotted in Figure 9-a. Clearly, the sorption capacity is enhanced with the increase of equilibrium concentration of H2S and exhibits a nonlinear relationship. As proposed in the adsorption mode above, one of the tertiary amine groups in TMHDA molecules at this loading level, namely 15 wt%, shall interact with the silanol groups in the standing type, while the other is responsible for the H2S sorption. Thus, such monolayer-like sorption could be considered as the chemical adsorption and, thereof, assumed to obey the Langmuir isotherm (see Eq. 3): /=

8/+ 9 ⋯ ⋯ ./. 3 1 + 89

where Ce is the concentration of H2S in the mixed gas, q is the saturation capacity at equilibrium, K stands for the adsorption equilibrium constant, and qm is the maximum adsorption saturation


Page 17 of 48

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

capacity. If the H2S sorption on TMHDA/SBA-15 obeys Langmuir isotherms, 1/q and 1/Ce shall display a straight line, as shown in Eq. 4. 1 1 1 = + ⋯ ⋯ ./. 4 / 8/+ 9 /+ The data has been replotted as 1/q vs. 1/Ce in Figure 9-b. Both fitting lines for different temperatures exhibit a good linear relationship with acceptable values of R2 (e.g., 0.9957 and 0.9944 for 25 and 50 ℃, respectively). Moreover, according to the fitted linear equation, the qm and K values could be estimated and were 0.21 mmol-H2S/g-sorb and 9.7 × 10-4 at 25 ℃ and 0.15 mmol-H2S/g-sorb and 6.0 × 10-4 at 50 ℃, respectively. Clearly, both equilibrium adsorption capacity and adsorption constant at 25 ℃ are higher than those at 50 ℃, implying that the sorption strength is stronger at lower temperatures. Thus, lower temperatures would be favorable for H2S sorption over TMHDA/SBA-15 sorbents. Based on the Van’t Hoff equation (Eq. 5), the adsorption heat of H2S on TMHDA(15)/SBA-15 could be estimated: :

8 −Δ= 1 1 = > − ? ⋯ ⋯ ./. 5 8; ;

where, ∆Hs is the adsorption heat, and R is the gas constant. The adsorption heat of H2S sorption on TMHDA(15)/SBA-15 is 15.4 kJ/mol, indicating that H2S sorption on TMHDA(15)/SBA-15 belonged to a weak acid-base chemisorption. 3.5 Effect of sorption temperature. According to the last section, the estimated adsorption heat is as low as 15.4 kJ/mol, indicating that the H2S molecules might be easily desorbed from TMHDA/SBA-15 with the increase of the sorption temperature, thereof, decreasing the H2S sorption capacity. Therefore, the effect of sorption temperature was examined at 25, 50, and 75 ℃. The breakthrough capacity, the saturation capacity, as well as the amine


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 18 of 48

efficiency are summarized in Table S2. Note that the amine efficiency was obtained as the Nbased efficiency by assuming the ratio of N/H2S as 2/1. Figure 10 depicts the changes of H2S sorption capacities and corresponding N-based capacity as a function of the sorption temperature. Apparently, both breakthrough and saturation capacities decreased with increasing temperature, and so does the N-based capacity (defined in section 3.3). Quantitatively, from 25 to 75 ℃, the breakthrough capacity decreased from 0.43 to 0.15 mg-H2S/g-sorb with a loss of 70 %, while the saturation capacity declined from 1.28 to 0.60 mg-H2S/g-sorb with a similar percentage loss. Meanwhile, the amine efficiency decreased by half (Table S2). The sorption capacity is impacted by the temperature significantly as expected. Due to the low adsorption heat (ca. 15.4 kJ/mol), the interaction between H2S and tertiary amine is weak so that the H2S desorbs easily form the sorbent at higher temperatures. This observation is in line with our previous work, where the PEI/SBA-15 showed a similar temperaturedependent behavior for H2S sorption 27. Based on the computational work, the kinetic barrier of transferring the adsorbed H2S into the bulk of PEI is lower than that of the adsorbed CO2, which makes it easier for the H2S molecules to diffuse into the PEI bulk and at lower temperatures.26, 27, 29

Moreover, the low temperature is thermodynamically favorable in enhancing the equilibrium

sorption capacity. Thus, a better sorption performance at lower temperatures would be anticipated. On the other side, since the acidity of H2S is weaker in comparison to that of CO2, the acid-base interaction between H2S molecules is not strong enough to stabilize the H2S molecules on the surface of the sorbent at higher temperatures. As a result, the H2S sorption capacity decreases. 3.6 Effect of inlet CO2 concentration. Since the CO2 composition in real biogas lies within the range of 10-50 vol%, such great amount of CO2 may block the H2S adsorption due to


Page 19 of 48

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

its stronger acidic property. Thus, it would be necessary to investigate the impact of CO2 concentration on the sorption performance over TMHDA-loaded sorbents. A series of sorption experiments were carried out on TMHDA(15)/SBA-15 by introducing a wide range of inlet CO2 concentration (e.g., 0-40 vol%), and resultant sorption curves are presented in Figure 11-a, along with the saturation capacity in Figure 11-b. As depicted in Figure 11-a, it is evident that the sorption reaches the breakthrough point earlier upon the addition of CO2. On the other hand, the H2S sorption capacity drops slightly from 1.33 mg-H2S/mg-sorb without CO2 to 1.28 mg-H2S/g-sorb with 10 vol% of CO2 in the inlet and further down to 1.21 mg-H2S/g-sorb with 20 vol% of CO2. With further increase of CO2 concentration to even 40 vol%, no significant reduction is observed, and the H2S sorption capacity is maintained around 1.20 mg-H2S/g-sorb. This observation is promising because at least 90 % of the sorption capacity could be maintained at 40 vol% of CO2 in the inlet, which is a representative concentration for real bio-gas. Thus, the tertiary-amine-loaded MBS sorbents are promising for selective H2S removal in the presence of CO2. Two reasons may cause the reduction of the sorption capacity in a CO2-containing gas mixture. One is the competitive sorption of H2S and CO2 on the sorbent. As discussed in section 3.4, physisorption, apart from chemisorption, may also contribute to the H2S sorption on TMHDA/SBA-15 as evidence of the low adsorption heat (e.g., 15.4 kJ/mol). Generally, the strength of this part of adsorption is not as strong as that of chemisorption. Thus, in order to further quantify the contribution of physisorption in the total, the sorbent was treated with N2 (e.g., 25 ml/min) at room temperature overnight to remove the physisorbed adsorbate, and results are shown in Figure 12. Evidently, the H2S physisorption capacity declines as well when introducing 10 vol% of CO2, the reduction of which (e.g., 18 %) is even more than that of total


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 20 of 48

sorption capacity (e.g., 4 %). This implies that the physisorption of CO2 on TMHDA/SBA-15 is more competitive than that of H2S, indicating that the reduction of this part of H2S should be primarily responsible for the observed total loss of capacity. The other reason derives from the SBA-15 itself which possesses a weak sorption ability towards CO2 (5.0 mg-CO2/g-sorb) and H2S (0.034 mg-H2S/g-sorb) due to the presence of silanol groups on the surface.24 Therefore, the adsorption of CO2 may consume the hydroxyl groups in the first place due to its stronger acidity, which can block the H2S adsorption. Nevertheless, such reduction is limited as a result of the weak sorption ability of SBA-15 alone in comparison to the TMHDA loaded sorbent. 3.7 Regenerability and thermostability. For practical application, not only should the sorption capacity be considered but also the regenerability. Thus, the sorption/desorption cycles in the presence of CO2 were carried out. Figure 13 illustrates the H2S sorption capacity on TMHDA(15)/SBA-15 within 5 cycles, where the desorption was conducted using N2 (ca. 25 ml/min) at 110 ℃ overnight. During these cycles, the regenerated sorption capacity practically maintained constant, and the averaged value is ca. 1.18 mg-H2S/g-sorb. This indicates that TMHDA/SBA-15 sorbents are easily regenerated at mild conditions for selective H2S removal in the presence of CO2. By contrast, even though the metal-oxide-based sorbents are able to remove H2S selectively from the gas mixture, they require more severe conditions for regeneration, such as high temperatures (e.g. > 400 ℃) under oxygen atmosphere. 19-21 The analysis of the stability of the sorbents TMHDA(X)/SBA-15 with various loading levels was carried out using a thermogravimetric analyzer (TGA) from room temperature to 700 ℃ under N2 flow. The resulting weight loss was plotted as a function of temperature in Figure 14. With the increase of TMHDA loading level, the sorbent becomes easier to lose weight at lower


Page 21 of 48

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

temperatures. At 10 wt% of loading, the weight loss begins at ca. 200 ℃; however, this temperature gradually shifts to the lower temperatures and finally drops to as low as 76 ℃ for the sorbent with 60 wt% of loading. Moreover, the curve becomes sharper with the increase of TMHDA loading level, indicating that the decomposing of TMHDA happens fast. The sorbents with 40 and 60 wt% of loading show a two-step weight loss with the increase of temperature including a turning point around 150 ℃. In the first period, TMHDA(40)/SBA-15 and TMHDA(60)/SBA-15 lose their weights rapidly by 22 and 47 %, respectively, which could be attributed to the loss of those unbonded TMHDA molecules. In the following step, both of them started to decompose at 150 ℃ and completed at ca. 320 ℃, corresponding to evaporation of TMHDA molecules as the boiling point of TMHDA is 209 ℃. The analysis of thermal stability is also promising in determining the temperature range for H2S desorption. As discussed before, the TMHDA(15)/SBA-15 exhibits a superior sorption performance, and a suitable desorption temperature is ca. 110 ℃ as it starts to decompose at ca. 160 ℃. 3.8 Effect of CH4 and H2O. Since a high concentration of CH4 exists in bio-gas, it is of interest to see if there is any effect of CH4 on the H2S sorption performance over TMHDA loaded-MBS. The sorption experiments were carried out on TMHDA(15)/SBA-15 by introducing the gas mixtures of 500 ppm H2S and 10 vol.% CO2 balancing with N2 and CH4, respectively, for comparison, and, the resulting H2S sorption breakthrough curves were shown in Figure 15. The H2S sorption capacities with both N2 and CH4 were the same at 1.24 mg-H2S/gsorb. Clearly, the coexisting CH4 hardly affects the H2S sorption performance on TMHDAloaded SBA-15. This result is expected because the CH4 is a nonpolar hydrocarbon molecule,


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 48

whose adsorption is uncompetitive with that of acidic molecules, such as H2S and CO2, on the basic sorbents. H2O is another component in bio-gas producing during the digestion and its presence may affect the H2S removal from a CO2-containing gas mixture because tertiary amine is active for CO2 adsorption under wet conditions, as described in Rxns. 10 and 11. + + ↔ − − ⋯ ⋯ . 10 + + ↔ + ⋯ ⋯ . 11 Therefore, the effect of H2O on the selective removal of H2S was examined by flowing 500 ppm H2S with/without 10 vol% CO2 balanced with dry and wet N2 on TMHDA(15)/SBA-15. The H2S sorption breakthrough curves are shown in Figure 16. Clearly, the sorption performance was improved by 21 % with H2O in the absence of CO2 (from 1.35 to 1.63 mgH2S/g-sorb). The improvement is due to the interaction between H2S and H2O on the tertiary amine as shown in Rxn. 10, in which one tertiary amine molecule can fix one H2S molcule under wet conditions, while two molecules of tertiary amine are necessary for adsorbing one molecule H2S under dry conditions. Thus, the presence of H2O can promote the H2S sorption on TMHDAloaded MBS. On the other side, it is interesting to note that the H2S sorption performance was essentially not impacted by H2O in the presence of CO2 as can be seen from Figure 16, where the H2S sorption capacities under dry and wet conditions were 1.24 and 1.17 mg-H2S/g-sorb, respectively. Such similarity in the H2S sorption capacity, regardless of H2O, might be attributed to the dissociation of H2S in H2O and the interaction between CO2 and tertiary amine with H2O (Rxn. 11). One possibility is that H+ and HS- dissociated from H2S in H2O can react with HCO3and R3NH+ (Rxn. 11), respectively, through acid-base interactions.


Page 23 of 48

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

4. CONCLUSION Towards developing effective sorbent for bio-gas desulfurization, a series of SBA-15supported MBS sorbents with various amine groups were prepared and examined for H2S removal from CO2-rich gas mixtures. Detailed characterization results demonstrated that the amine-based molecules dispersed inside the pores of the SBA-15 through the interaction between the amine groups and the silanol groups on the surface of SBA-15. Compared to the primary and secondary-amine-loaded sorbents, the tertiary-amine-based sorbent, namely TMHDA(X)/SBA-15, can selectively remove H2S from a gas mixture containing a high-level concentration of CO2 (e.g., 10-40 vol%). The highest H2S sorption capacities were achieved when the TMHDA loading level was 15 wt%, where the surface of the support was covered by a monolayer of TMHDA molecules in standing type. The Langmuir adsorption isotherm was found to fit for the H2S sorption over TMHDA/SBA-15. However, the low adsorption heat (e.g., 15.4 kJ/mol) indicated that the physisorption, apart from the chemisorption, contributed to the overall capacity to some extent. Introducing CO2 into the feed gas had a negative impact on the H2S sorption capacity over the sorbent using primary and secondary amines, however, 90 % of the capacity could be maintained with tertiary amine-based sorbent, even at 40 vol% CO2. These results demonstrate the great potential of the TMHDA/SBA-15 sorbent for selective H2S removal from biogas. In addition, the TMHDA/SBA-15 sorbent could be regenerated at mild conditions (e.g., 110 ℃), and results of the sorption/desorption cycles indicated its stable sorption performance. Other components (i.e., CH4 and H2O) in bio-gas had little impact on the H2S sorption over TMHDA/SBA-15. More investigations are necessary to further improve the H2S sorption performance and understand the mechanism of H2S sorption on the tertiary-amine-based “molecular basket” sorbent. 23 ACS Paragon Plus Environment

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 48

ASSOCIATED CONTENT Supporting Information H2S sorption breakthrough curves of H2S sorption on TMHDA in the absence and presence of CO2; Comparison of amine-based capacity on non-supported and supported tertiary in the absence and presence of CO2; XP spectra of TMHDA(X)/SBA-15 in full scans; C 1s XP spectra of TMHDA(X)/SBA-15; Effect of TMHDA loading level on H2S sorption over TMHDA/SBA15; Effect of sorption temperature of H2S sorption on TMHDA(15)/SBA-15. (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was supported in part by The Pennsylvania State University through the Joint Center for Energy Research established between Penn State and Dalian University of Technology. The XPS analysis was performed at the Materials Characterization Laboratory of the Penn State Materials Research Institute, for which the assistance of Jeff Shallenberger is gratefully acknowledged. One of the authors (Wenying Quan) thankfully acknowledges the financial support from Chinese Scholarship Council (CSC), China.


Page 25 of 48

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

REFERENCE 1.

Huertas, J. I.; Giraldo, N.; Izquierdo, S., Removal of H2S and CO2 from biogas by amine

absorption. InTech: 2011. 2.

Jou, F.-Y.; Mather, A. E.; Otto, F. D., Ind. Eng. Chem. Process Des. Dev. 1982, 21, 539-

544. 3.

Mandal, B. P.; Biswas, A. K.; Bandyopadhyay, S. S., Sep. Purif. Technol. 2004, 35, 191-

202. 4.

Kennedy, N.; Zhao, Q.-B.; Ma, J.; Chen, S.; Frear, C., Sep. Purif. Technol. 2015, 144,

240-247. 5.

Lu, J.-G.; Zheng, Y.-F.; He, D.-L., Sep. Purif. Technol. 2006, 52, 209-217.

6.

Hopton, G. U.; Griffith, R. H., Gas J. 1946, 274, 4311.

7.

Davidson, J. M.; Lawrie, C. H.; Sohail, K., Ind. Eng. Chem. Res. 1995, 34, 2981-2989.

8.

Sasaoka, E.; Hirano, S.; Kasaoka, S.; Sakata, Y., Energy Fuels 1994, 8, 1100-1105.

9.

Baird, T.; Campbell, K. C.; Holliman, P. J.; Hoyle, R.; Stirling, D.; Williams, B. P., J.

Chem. Soc., Faraday Trans. 1996, 92, 445-450. 10.

Baird, T.; Denny, P. J.; Hoyle, R.; McMonagle, F.; Stirling, D.; Tweedy, J., J. Chem. Soc.,

Faraday Trans. 1992, 88, 3375-3382. 11.

Baird, T.; Campbell, K. C.; Holliman, P. J.; Hoyle, R.; Stirling, D.; Willams, B. P., J.

Chem. Soc., Faraday Trans. 1995, 91, 3219-3230. 12.

Kang, S.-H.; Bae, J. W.; Kim, S.-M.; Jun, K.-W., Energy Fuels 2008, 22, 2580-2584.

13.

Baird, T.; Campbell, K. C.; Holliman, P. J.; Hoyle, R. W.; Huxam, M.; Stirling, D.;

Williams, B. P.; Morris, M., J. Mater. Chem. 1999, 9, 599-605. 14.

Baird, T.; Campbell, K. C.; Holliman, P. J.; Hoyle, R.; Noble, G.; Stirling, D.; Williams,

B. P., J. Mater. Chem. 2003, 13, 2341-2347. 15.

Polychronopoulou, K.; Fierro, J. L. G.; Efstathiou, A. M., Appl. Catal., B-Environ 2005,

57, 125-137. 16.

Polychronopoulou, K.; Cabellogalisteo, F.; Lopezgranados, M.; Fierro, J.; Bakas, T.;

Efstathiou, A., J. Catal. 2005, 236, 205-220. 17.

Jun, H. K.; Koo, J. H.; Lee, T. J.; Ryu, S. O.; Yi, C. K.; Ryu, C. K.; Kim, J. C., Energy

Fuels 2004, 18, 41-48. 25 ACS Paragon Plus Environment

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 26 of 48

18.

Mojtahedi, W.; Abbasian, J., Energy Fuels 1995, 9, 429-434.

19.

Ham, V. d. Regenerative high temperature desulfurization of coal gas in a circulating

fluidized bed. University of Twente, Enschede, Netherlands, 1994. 20.

Khare, G. P.; Delzer, G. A.; Kubicek, D. H.; Greenwood, G. J., Environ. Prog. 1995, 14,

146-150. 21.

Li, Z.; Flytzani-Stephanopoulos, M., Ind. Eng. Chem. Res. 1997, 36, 187-196.

22.

Xu, X.; Song, C.; Andresen, J. M.; Miller, B. G.; Scaroni, A. W., Energy Fuels 2002, 16,

1463-1469. 23.

Xu, X.; Song, C.; Andrésen, J. M.; Miller, B. G.; Scaroni, A. W., Microporous

Mesoporous Mater. 2003, 62, 29-45. 24.

Xu, X.; Song, C.; Miller, B. G.; Scaroni, A. W., Ind. Eng. Chem. Res. 2005, 44, 8113-

8119. 25.

Xu, X.; Song, C.; Miller, B. G.; Scaroni, A. W., Fuel Process. Technol. 2005, 86, 1457-

1472. 26.

Wang, X.; Ma, X.; Xu, X.; Sun, L.; Song, C., Top. Catal. 2008, 49, 108-117.

27.

Wang, X.; Ma, X.; Sun, L.; Song, C., Green Chemistry 2007, 9, 695-702.

28.

Xu, X.; Novochinskii, I.; Song, C., Energy Fuels 2005, 19, 2214-2215.

29.

Ma, X.; Wang, X.; Song, C., J. Am. Chem. Soc. 2009, 131, 5777-5783.

30.

Kohl, A.; Nielsen, R., Gas Purification. 5th ed.; Gulf Publishing Company: Houston,

Texas, 1997. 31.

Ko, Y. G.; Shin, S. S.; Choi, U. S., J. Colloid Interface Sci. 2011, 361, 594-602.

32.

Abdouss, M.; Hazrati, N.; Miran Beigi, A. A.; Vahid, A.; Mohammadalizadeh, A., RSC

Advances 2014, 4, 6337-6345. 33.

Huang, H. Y.; Yang, R. T.; Chinn, D.; Munson, C. L., Ind. Eng. Chem. Res. 2003, 42,

2427-2433. 34.

Zhao, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G.

D., Sci. 1998, 279, 548-552. 35.

Wang, X.; Zhang, Q.; Yang, S.; Wang, Y., J. Phys. Chem. B 2005, 109, 23500-23508.

36.

Jaroniec, C. P.; Kruk, M.; Jaroniec, M.; Sayari, A., J. Phys. Chem. B 1998, 102, 5503-

5510.


Page 27 of 48

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

37.

Wang, X.; Lin, K. S. K.; Chan, J. C. C.; Cheng, S., J. Phys. Chem. B 2005, 109, 1763-

1769. 38.

White, L. D.; Tripp, C. P., J. Colloid Interface Sci. 2000, 232, 400-407.

39.

Wang, X.; Schwartz, V.; Clark, J. C.; Ma, X.; Overbury, S. H.; Xu, X.; Song, C., J. Phys.

Chem. C 2009, 113, 7260-7268. 40.

Nozaki, C.; Lugmair, C. G.; Bell, A. T.; Tilley, T. D., J. Am. Chem. Soc. 2002, 124,

13194-13203. 41.

Shallenberger, J. R.; Metwalli, E.; Pantano, C. G.; Tuller, F. N.; Fry, D. F., Surf. Interface

Anal. 2003, 35, 667-672.


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 28 of 48

CAPTION TO FIGURES Figure 1 The chemical structure of poly allylamine (PA), poly ethylenimine (PEI), and tetramethyl hexanediamine (TMHDA). Figure 2 Schematic of the fixed-bed flow system for H2S adsorption from a CO2-containing gas mixture. (MFC = mass flow controller.) Figure 3 H2S sorption breakthrough curve on (a) PA(30)/SBA-15, (b) PEI(30)/SBA-15 and (c) TMHDA(30)/SBA-15 in the presence/absence of CO2, (d) H2S sorption selectivity. Conditions: 0.33 g of sorbent, 25 °C, 500ppmvH2S/(10 vol%CO2)/N2 with a flow rate at 15 ml/min. Figure 4 (a) N2 adsorption-desorption isotherms and (b) pore size distribution for SBA-15 and TMHDA(15)/SBA-15 at 77 K. Figure 5 FT-IR spectra of (a) SBA-15, (b) TMHDA(7)/SBA-15, (c) TMHDA(15)/SBA-15, (d) TMHDA(30)/SBA-14, (e) TMHDA(40)/SBA-15, and (f) TMHDA(60)/SBA-15. Figure 6 Effect of TMHDA loading levels in TMHDA(X)/SBA-15 on the H2S sorption capacity. Conditions: 0.33 g of sorbent, 25 °C, 500ppmvH2S/(10 vol%CO2)/N2 with a flow rate at 15 ml/min. Figure 7 The proposed sorption process on TMHDA/SBA-15. Figure 8 N 1s XP spectra of fresh TMHDA(X)/SBA-15 sorbent. Figure 9 (a) Adsorption isotherms of and (b) plots of 1/q versus 1/Ce for TMHDA(15)/SBA-15 at 25 and 50 ºC. Conditions: 0.33 g of sorbent, 25 or 50 °C, H2S/10 vol%CO2/N2 with a flow rate at 15 ml/min. Figure 10 H2S sorption capacity and N-based capacity on TMHDA(15)/SBA-15 at 25 °C, 50 °C and 75 °C. Conditions: 0.33 g of sorbent, 500ppmv H2S/10 vol%CO2/N2 with a flow rate at 15 ml/min. Figure 11 (a) H2S sorption breakthrough curves and (b) H2S sorption capacity on TMHDA(15)/SBA-15 with different CO2 inlet concentrations. Conditions: 0.33 g of sorbent, 500ppmv H2S/CO2/N2 with a flow rate at 15 ml/min. Figure 12 The contribution of physisorption in the overall H2S sorption capacity on TMHDA(15)/SBA-15. Figure 13 Regenerability of TMHDA(15)/SBA-15. Conditions: 0.33 g of sorbent, 500ppmv H2S/10 vol%CO2/N2 with a flow rate at 15 ml/min. Figure 14 The change of weight loss as a function of temperature on TMHDA(X)/SBA-15. 28 ACS Paragon Plus Environment

Page 29 of 48

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

Figure 15 Breakthrough curves of the H2S sorption from N2 and CH4, respectively. Conditions: 0.33 g of sorbent, 25 °C, 500 ppmv H2S/10 vol% CO2/balanced with N2 or CH4 with a flow rate at 15 ml/min. Figure 16 Breakthrough curves of H2S sorption on TMHDA(15)/SBA-15 in the absence and presence of H2O. Conditions: 0.33 g of sorbents, 25 °C, 500 ppmv H2S/(10 vol% CO2)/N2 with a flow rate at 15 ml/min.


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 30 of 48

Table 1 The comparison of H2S breakthrough sorption capacity with and without CO2 on PA(30)/SBA15, PEI(30)/SBA-15, and TMHDA(30)/SBA-15 BT cap. (mg-H2S/g-sorb) Cap. drop (%) Sample w/o CO2 w/ CO2 PA(30)/SBA-15 PEI(30)/SBA-15 TMHDA(30)/SBA-15

3.16 4.94 0.25

0.11 0.15 0.24

97 97 4


Page 31 of 48

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 2 Porous properties of TMHDA loaded SBA-15 with different TMHDA loading weight percentage BET surface area Pore volume a) Pore diameter b) Sorbent (m2/g) (cm3/g) (nm) SBA-15

879

1.21

6.4

TMHDA(10)/SBA-15

651

1.07

6.0

TMHDA(15)/SBA-15

423

0.74

5.7

TMHDA(20)/SBA-15

413

0.73

5.5

TMHDA(30)/SBA-15

242

0.55

5.2

TMHDA(40)/SBA-15

165

0.41

5.0

TMHDA(60)/SBA-15

22

0.05

4.7

a) b)

BJH desorption cumulative pore volume. BJH desorption average pore diameter.


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 32 of 48

Table 3 Surface chemical composition of TMHDA(X)/SBA-15 determined by XPS Composition a) / at% Composition of N1s b) / at% Sample C N C-N c) C-N+ d)

C-N/C-N+ ratio

TMHDA(7)/SBA-15

7.9

1.5

0.9

0.6

1.5

TMHDA(10)/SBA-15

11.9

2.6

1.9

0.7

2.6

TMHDA(15)/SBA-15

21.0

4.6

3.8

0.8

4.7

TMHDA(30)/SBA-15 18.5 4.3 3.6 0.7 5.2 a) Determined by the XP spectra in the whole range (see Figure S1 in supporting information). b) Determined by the deconvolution analysis of XP spectra in the region of N 1s (survey scan). c) BE at 399.4 eV. d) BE at 401.5 eV.


Page 33 of 48

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

Figure 1 The chemical structure of polyallylamine (PA), polyethylenimine (PEI), and tetramethyl hexanediamine (TMHDA).


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

Page 34 of 48

Figure 2 Schematic of the fixed-bed flow system for H2S adsorption from a CO2-containing gas mixture. (MFC = mass flow controller.)


Page 35 of 48

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

Figure 3 H2S sorption breakthrough curve on (a) PA(30)/SBA-15, (b) PEI(30)/SBA-15 and (c) TMHDA(30)/SBA-15 in the presence/absence of CO2, (d) H2S sorption selectivity. Conditions: 0.33 g of sorbent, 25 °C, 500ppmvH2S/(10 vol%CO2)/N2 with a flow rate at 15 ml/min. 35 ACS Paragon Plus Environment

Energy & Fuels

900 (a)

0.6

SBA-15 TMHDA(15)/SBA-15

750

SBA-15 TMHDA(15)/SBA-15

(b)

0.5

D(V)/cm3/nm-1g-1

Volume adsorbed (cm3/g)

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

Page 36 of 48

600 450 300

0.4 0.3 0.2 0.1

150

0.0 0 0.0

0.2

0.4

0.6

0.8

1.0

5

P/P0

10

15

20

Pore diameter (nm)

Figure 4 (a) N2 adsorption-desorption isotherms and (b) pore size distribution for SBA-15 and TMHDA(15)/SBA-15 at 77 K.


Page 37 of 48

2936 2855

0.5

1458 1376 1299

Absorbance (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

Energy & Fuels

(f) (e) (d) (c) (b) (a)

1629 3747

4000

3500

3000

2500

2000

1500

1000

Frequency (cm-1) Figure 5 FT-IR spectra of (a) SBA-15, (b) TMHDA(7)/SBA-15, (c) TMHDA(15)/SBA-15, (d) TMHDA(30)/SBA-15, (e) TMHDA(40)/SBA-15, and (f) TMHDA(60)/SBA-15.


Energy & Fuels

1.4

Sorp. cap. (mg-H2S/g-sorb)

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

Page 38 of 48

1.2 1.0 0.8 0.6 0.4

0

10

20

30

40

50

60

TMHDA loading level (wt%) Figure 6 Effect of TMHDA loading levels in TMHDA(X)/SBA-15 on the H2S sorption capacity. Conditions: 0.33 g of sorbent, 25 °C, 500ppmvH2S/(10 vol%CO2)/N2 with a flow rate at 15 ml/min.


Page 39 of 48

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

Figure 7 The proposed sorption mode of H2S on TMHDA/SBA-15.


Energy & Fuels

CPS (*10-1)

1000

TMHDA(7)/SBA-15

C-N: 399.4 eV

1400

C-N+: 401.5 eV

950 900

1100 1000

800

900 404

400

396

408

392

404

TMHDA(15)/SBA-15

400

396

392

B.E. (eV)

B.E. (eV) 1400

C-N: 399.4 eV

C-N+: 401.5 eV

1200

850

408

TMHDA(10)/SBA-15

1300

CPS (*10-1)

1050

1600 C-N: 399.4 eV

1200

TMHDA(30)/SBA-15

C-N: 399.4 eV

1400

1000

CPS (*10-1)

CPS (*10-1)

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

Page 40 of 48

C-N+: 401.5 eV

800

1200 C-N+: 401.5 eV

1000

600 408

404

400

396

392

800

B.E. (eV)

408

404

400

396

392

B.E. (eV)

Figure 8 N 1s XP spectra of fresh TMHDA(X)/SBA-15 sorbent.


Page 41 of 48

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

Figure 9 (a) Adsorption isotherms of and (b) plots of 1/q versus 1/Ce for TMHDA(15)/SBA-15 at 25 and 50 ºC. Conditions: 0.33 g of sorbent, 25 or 50 °C, H2S/10 vol%CO2/N2 with a flow rate at 15 ml/min.


Energy & Fuels

24

BT Cap. S Cap. N-based Cap.

1.2

21

0.9

18

0.6

15

0.3

12

0.0

25

50

75

N-based Cap. (mmol-H2S/mol-N)

1.5

Sorp. Cap. (mg-H2S/g-sorb)

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

Page 42 of 48

9

Temp. (oC) Figure 10 H2S sorption capacity and N-based capacity on TMHDA(15)/SBA-15 at 25 °C, 50 °C and 75 °C. Conditions: 0.33 g of sorbent, 500ppmv H2S/10 vol%CO2/N2 with a flow rate at 15 ml/min.


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

1.6 (b)

Sorp. cap. (mg-H2S/g-sorb)

Page 43 of 48

1.2 1.33

1.28

1.21

0

10

20

1.20

0.8

0.4

0.0

30

40

Inlet CO2 Conc. (vol%) Figure 11 (a) H2S sorption breakthrough curves and (b) H2S sorption capacity on TMHDA(15)/SBA-15 with different CO2 inlet concentrations. Conditions: 0.33 g of sorbent, 500ppmv H2S/CO2/N2 with a flow rate at 15 ml/min.


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

Page 44 of 48

Figure 12 The contribution of physisorption in the overall H2S sorption capacity on TMHDA(15)/SBA-15.


Page 45 of 48

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

Figure 13 Regenerability of TMHDA(15)/SBA-15. Conditions: 0.33 g of sorbent, 500ppmv H2S/10 vol%CO2/N2 with a flow rate at 15 ml/min.


Energy & Fuels

100

Weight percentage (%)

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

Page 46 of 48

90

10% loading

80

15% 20%

70

30%

60

40%

50 60%

40 0

100

200

300

400

500

600

700

Temp (oC) Figure 14 The change of weight loss as a function of temperature on TMHDA(X)/SBA-15.


Page 47 of 48

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

Figure 15 Breakthrough curves of the H2S sorption from N2 and CH4, respectively. Conditions: 0.33 g of sorbent, 25 °C, 500 ppmv H2S/10 vol% CO2/balanced with N2 or CH4 with a flow rate at 15 ml/min.


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

Page 48 of 48

Figure 16 Breakthrough curves of H2S sorption on TMHDA(15)/SBA-15 in the absence and presence of H2O. Conditions: 0.33 g of sorbents, 25 °C, 500 ppmv H2S/(10 vol% CO2)/N2 with a flow rate at 15 ml/min.


Selective Removal of H2S from Biogas Using Solid Amine-Based

Recommend Documents