Adsorption of Hydrogen Sulfide from Gas Streams Using the

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Adsorption of hydrogen sulfide from gas streams using amorphous composite of #-FeOOH and activated carbon powder Seongwoo Lee, Taejin Lee, and Daekeun Kim Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04747 • Publication Date (Web): 02 Mar 2017 Downloaded from http://pubs.acs.org on March 2, 2017

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Industrial & Engineering Chemistry Research

Submitted for publication in Industrial & Engineering Chemistry Research December 7, 2016 And in revised form February 8, 2017

Adsorption of hydrogen sulfide from gas streams using amorphous composite of α-FeOOH and activated carbon powder

Seongwoo Lee†, Taejin Lee‡, Daekeun Kim*‡

†

Department of Energy and Environmental Engineering, Seoul National Science and Technology, Seoul 139-743, Republic of Korea

‡

Department of Environmental Engineering, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea

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ACS Paragon Plus Environment


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ABSTRACT The aim of this study was to identify the characteristics of α-FeOOH based composite for the removal of hydrogen sulfide in room temperature gas streams. α-FeOOH was supported on commercial-activated carbon powder to avoid the agglomeration problem of composite fabrication. α-FeOOH was prepared by using FeCl3 solution (as an Fe precursor) and NH4HCO3(as a pH control). The formation of α-FeOOH was confirmed by observing α-Fe2O3 under the hydrothermal condition. The results of the experiment indicate that the activated carbon powder functioned effectively as the support material of the composite, providing a large active site on the surface of the composite, preventing the agglomeration of precipitate particles of FeOOH, and then allowing high breakthrough capacity (0.171 g H2S/g composite) compared to that of α-FeOOH alone (0.046 g H2S/g α-FeOOH). The textural analyses showed that the composite of the α-FeOOH and activated carbon powder had a mesoporous structure with a BET surface area of 500 m2/g, while the surface area was 188 m2/g for α-FeOOH alone. This study established that the synthesized material can be used as a heterogeneous adsorbent for the effective removal of hydrogen sulfide from gas streams.

ABSTRACT GRAPHIC

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1. INTRODUCTION Increasing interest has been shown in biogas for renewable energy production using landfill and digestion gas.1 The composition of biogas is 40%-60% CH4, 30%-40% CO2, and other compounds such as sulfur and nitrogen.2 The majority of sulfur compounds exist as hydrogen sulfide, which is typically the most problematic impurity because it is poisonous, odorous, and highly corrosive in many renewable energy applications. In addition, hydrogen sulfide is produced in various industrial facilities such as coke oven process in the iron works, syngas, and coal gas.3-5 Because it is highly corrosive in many equipment, decrease of equipment life time and pipeline corrosion are inevitable.6 Hence, hydrogen sulfide removal is necessary for clean gas and gas utilization process.7-8 The method most typically used for hydrogen sulfide removal from biogas is adsorption on chemically active solid media such as zinc, cobalt, and iron.9-13 Hussain et al.10 reported the application of ZnO adsorbents for hydrogen sulfide removal, demonstrating an adsorption capacity of 3.23 wt% (g S/g adsorbent), while Yuan and Bandosz14 reported the fabrication of metal sludge derived adsorbents with a hydrogen sulfide adsorption of 20 mg/g. Fang et al.11 demonstrated that the adsorption capacities and reactivity of adsorbents with active metal oxides differ to those of hydrogen sulfide. Other studies12,13 have reported that iron hydroxide can remove hydrogen sulfide at high efficiency adsorption even at room temperature and ambient pressure. Iron hydroxides are typically generated by using different types of Fe precursors and base solutions through the precipitation method.13 It has been demonstrated that iron hydroxide (i.e., α, β, γ-FeOOH) composites show high reactivity to and adsorption capacity for hydrogen 3



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sulfide.12,13 The final reaction products of iron hydroxides have been fabricated depending on temperature, agitating speed, pH solution and solution types.15 α-FeOOH has been produced using FeCl3 and NaHCO3 solutions,16 and using FeSO4 and Na2CO3 at pH 8-11.13 γ-FeOOH was acquired using Fe(NO3)3 solution.17 Based on the above studies, it is well known that ferric chloride can be used to prepare iron hydroxide as a cost-effective iron(III) precursor. Iron hydroxide particles tend to be aggregated and it is not difficult to reduce the surface area of particles, resulting in the easily lost reaction and adsorption capacity for iron hydroxide particles.18 Hence, field-scale application has been limited by the lack of feasibility of the materials. The prevention of aggregation problems is deemed essential for the application of iron hydroxide to remove hydrogen sulfide from gas streams. An alternative is to use support materials such as activated carbon, silica, and diatomaceous, which function to enhance the physical properties of the materials because the surface area of iron hydroxides need to be secured.19-21 Activated carbon has been considered to be a stable support material and has exhibited favorable adsorption characteristics especially in the fields of aqueous systems. The objective of this study is to understand the characteristics of α-FeOOH based adsorbent, which was prepared by using FeCl3 solution as the Fe precursor, for the removal of hydrogen sulfide in gas streams. For this purpose, this study focused on the following objectives. First, the formation of α-FeOOH was experimentally verified by observing α-Fe2O3 under the hydrothermal condition because α-FeOOH forms α-Fe2O3 based on thermodynamics. Second, for avoiding agglomeration of α-FeOOH particles, a support material such as activated carbon powder was tested; and this study attempted to examine the possibility that the composite of αFeOOH and activated carbon powder could enhance the overall performance of hydrogen sulfide 4


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adsorption in gas streams.

2. MATERIALS AND METHODS 2.1. Preparation of synthesized materials. A reagent 38% FeCl3 supplied by Hongik-Iseo Chemical (Korea) combined with 95% NH4HCO3 (Samchun Chemical, Korea) was used as the precipitating reagent. FeCl3 solution was titrated slowly with NH4HCO3 solution at the mass ratio of 1 to 5.5. The reagents were agitated continuously by a magnetic stirrer for 2 h. The pH in the reaction was set to be about 7.0. The precipitated materials (namely as α-FeOOH) were filtered by a vacuum pump and dried at 110°C for 12 h after washing with deionized (DI) water. The obtained precipitate was further calcined at 200, 350, and 500°C for 15 min under the hydrothermal condition and then cooled at room temperature in order to identify the hydrothermal production of the hematite. Since the aggregation problem should be avoided during the preparation of α-FeOOH, activated carbon powders (E&Chem Sol., Korea) as the support material were employed to provide an active site on the fabricated materials. Different contents of activated carbon powder (calculated as 10wt%, 20wt%, and 30wt% based on the final α-FeOOH product) were fed during the precipitation reaction, and the adsorbents were referred to as FeOOH/AC10, FeOOH/AC20, and FeOOH/AC30, respectively.

2.2. Characteristics of synthesized materials. The structure of the iron oxides and hydroxides were analyzed with an X-ray diffractometer (Bruker DE/D8 Advance powder, Bruker Co., Germany) using Cu-Kα radiation 5



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(λ=1.5406). The XRD patterns were recorded from 20° to 70° over a 2θ with a 0.02° step size. N2 adsorption-desorption isotherms were given at 77 K by using a surface area analyzer (BELSORP-mini II, BEL japan Inc., Japan). The specific surface area, SBET, and total pore volume, Vt, were calculated using the Brunauer-Emmett-Teller (BET) method. The meso-pore volume, Vmeso, and pore size distributions were obtained using the Barett-Joyner-Halenda (BJH) model. The micro-pore volume, Vmic, was calculated by subtracting Vmeso from Vt. SEM images were taken using a scanning electron microscope (SEM, TESCAN VEGA3, Tescan Korea, Czech) with a voltage of 20 kV. The Fourier transform-infrared (FT-IR) spectra were recorded using a FT-IR microscope (Vertex 80V, Bruker, Germany). The absorption spectra were obtained by the recording of 100 scans between 400 and 4,000 cm-1 with a resolution of 4 cm-1. The thermogravimetric analysis was performed on a DTG-60H (Shimadzu, Japan). For this purpose, about 8.2 mg of the sample was heated in an air stream (100 mL/min) from room temperature to 700°C at a rate of 10 °C /min.

2.3. H2S breakthrough test. A H2S breakthrough test was carried out using a glass bed (internal diameter of 1 cm; length of 15 cm; total volume of 11.7 mL) at room temperature under a dry condition. 4.7 mL of the test material was loaded in the bed. H2S gas with 3,333 ppmv of inlet concentration of balanced N2 gas, was passed through the fixed bed. The flow rate was regulated by using a mass flow controller (KOFLOC-3660, Kojima instrument Inc., Japan) and set to 0.3 L/min, corresponding to the space velocity of 64 min-1. H2S was analyzed using a sensor with a photoionic detector (TG-501, Graywolf sensing 6


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solution, US) at up to 50 ppm and gas chromatography (YL6100GC, Younglin Co., Ltd., Korea) with an equipped pulsed flame ionization detector (model-5380, O·I analytical, US) at over 50 ppm of H2S concentration. The adsorption capacity of the synthesized materials for H2S removal was calculated by measuring the breakthrough point of 5% inlet concentration.

3. RESULTS AND DISCUSSION 3.1. Characterization of synthesized materials. Figure 1 shows the powder X-ray diffraction (XRD) pattern of the α-FeOOH sample compared to the samples obtained by hydrothermal transformation. Figure 1 shows that the product obtained without thermal processing was poorly crystalline solid. However, the degree of crystallinity of the product was improved at high temperature. The XRD pattern of the materials obtained at 500°C indicates the presence of hematite (α-F2O3). All the diffraction peaks were well matched with the standard hexagonal structure of hematite reflection (JCPDS NO. 330664), and impurities peaks were not observed in the patterns, demonstrating that amorphous goethite was completely transformed into hematite. The amorphous state is believed to be metastable, but can be transformed to a more stable crystalline state by hydrothermal reaction,2224

which contributes to the homogeneous nucleation of amorphous materials.25 Figure 2 shows the TGA and DTA curves of the α-FeOOH sample. The first mass loss of

7.1% was observed over the ambient at 100°C, which corresponds to the elimination of adsorbed water (indicated as stage A). The temperature range of 100 to 455 °C corresponds to the dehydration (loss of H2O) and dehydroxylation (loss of OH) stage of the sample (stage B). The third mass loss was observed at the primary exothermic peak around 527°C, indicating that 7



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goethite was transformed into hematite (stage C). Schwertmann et al.26 observed that amorphous goethite can crystallize at 385 °C through dehydrogenation. In another study, goethite samples with a particle size of

Adsorption of Hydrogen Sulfide from Gas Streams Using the

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