Tetraethylenepentamine-Modified Activated ... - ACS Publications

Subscriber access provided by University of Newcastle, Australia

Article

Tetraethylenepentamine-modified activated semicoke for CO2 capture from the flue gas Xia Wang, Dongying Wang, Mingjun Song, Chunling Xin, and Wulan Zeng Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b03177 • Publication Date (Web): 07 Feb 2017 Downloaded from http://pubs.acs.org on February 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 35

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

Tetraethylenepentamine-modified activated semicoke for CO2 capture from the flue gas Xia Wanga,∗, Dongying Wangb, Mingjun Songa, Chunling Xina, Wulan Zenga a

Department of Chemistry and Chemical Engineering, Weifang University, Weifang 261061, Shandong, China b College of Chemical Engineering, Qingdao University of Science & Technology, Qingdao 266042, Shandong, China

ABSTRACT: To separate CO2 from coal-fired power plants, the semicoke which is cheap and easy to obtain was further activated to use as the carrier, and tetraethylenepentamine (TEPA) was impregnated in the activated semicoke to prepare solid amine sorbents. The effects of activating agents, adsorption temperature and the presence of water on CO2 sorption were investigated in a fixed-bed reactor, and the regenerability and adsorption kinetics for prepared sorbents were also studied. The equilibrium adsorption capacity for N2-activated semicoke (SE-N2) was 2.70 mmol/g and 2.14 mmol/g at 20 °C when water was absent and present, respectively, and the equilibrium adsorption capacity for 10 wt.% TEPA-modified N2-activated semicoke (SE-N2-TEPA10%) was 3.24 mmol/g and 3.58 mmol/g at 60 °C when water was absent and present, respectively. After ten cyclic regenerations, the adsorption capacity for SE-N2-TEPA10% reduced by 7.7% under dry condition, and SE-N2-TEPA10% showed good regenerability.

Keywords: semicoke; activation; CO2 adsorption; regenerability; kinetics

∗

Corresponding author, Email: [email protected] (X. Wang), Tel/Fax: +86 536 8785283.

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 35

2

1. INTRODUCTION The increasingly intensified environment deterioration problem induced by the greenhouse gas (GHG) effect has received great concerns. The GHG mainly consists of methane (CH4), H2O, nitrous oxide (N2O) and CO2, et al., among which CO2 accounts for approximately 55% and plays great contribution to the GHG effect.1 According to the fifth assessment report from the Intergovernmental Panel Climate Change (IPCC), the effect of CO2 to the atmosphere has been ensured, and the CO2 concentration caused by anthropogenic activities will continuously increase for a long time.2 In China, over 70% of the energy is provided by coal combustion, and coal-fired power plants are the primary point source of CO2 emissions. Reducing CO2 emissions from coal-fired power plants are particularly important. To the industrial application, the required adsorption capacity for the solid sorbents is 2‒3 mmol/g. In addition, good regenerability and low corrosion to the adsorption device are also important requirements. Yan et al. impregnated polyethylenimine (PEI) into the synthesized silica mesocellular foam with a template remaining, and studied the adsorption performance of prepared sorbents in a thermogravimetric analyzer NETZSCH STA 499 F3.3 The results suggested that the CO2 adsorption capacity of the prepared sorbent reached 4.5 mmol/g at 70 °C, and almost remained unchanged after ten adsorption-desorption cycles. Cai et al. synthesized a bi-functional mesoporous structure alumina via amino-functionalization, which showed good adsorption capacity for Cr (IV) and CO2. After further modification with TEPA, the CO2 adsorption capacity was obviously improved.4 Song


Page 3 of 35

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 et al. impregnated the synthesized Titania nanotubes (TINT) with monoethanolamine (MEA), ethylenediamine (EDA), triethylenetetramine (TETA) and TEPA, respectively, and investigated the adsorption performance for CO2 from flue gases in a dynamic packed column.5 Due to the higher amino density of TEPA, 69% of TEPA-modified TINT showed the highest CO2 adsorption capacity of 4.37 mmol/g and 5.24 mmol/g in the absence and presence of moisture, respectively; and the TEPA-functionalized TINT showed stable adsorption-desorption performance without moisture after five adsorption-desorption cycles. In addition, TEPA-modified SBA-15,6 PEI-impregnated SBA-15 molecular basket sorbents,7 PEI-functionalized mesoporous silica capsules,8 PEI-impregnated hexagonal mesoporous silica (HMS) with different textural mesoporosities,9 EDA-grafted a zeolite-like metal organic framework (ZMOF),10 aminosilane-grafted double-walled silica nanotubes (DWSNTs)11 and mesoporous TiO2/graphene oxide nanocomposites,12 et al., all showed high adsorption capacity and good regenerability. Many reviews have detailed the research progress of solid sorbents for CO2 capture,13-17 and our research group prepared a hybrid 3-aminopropyltrimethoxysilane (APTS) and TEPA-modified MCM-41 sorbent using a two-step method,18 a mixture of 2-amino-2-methyl-l-propanol (AMP) and TEPAmodified MCM-4119 and a TEPA-modified composite supporting materials with hierarchical mesoporous structures20 to increase the CO2 adsorption performance and improve the CO2 adsorption efficiency. However, the supporting materials used for synthesizing above sorbents were expensive and the preparation processes were high energy-consumption, which may limit their long-term application.


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 35

4 Coal is rich in China, and injection CO2 in coal seams is considered to improve the production of CH4 from coal seams due to the preferential adsorption of CO2 relative to CH4.21-24 S. Ramasamy et al. investigated the adsorption behavior of CO2 on coal and coal char, and found that the adsorption capacity of coal char was much higher than that of the virgin coal due to the larger surface area and more developed pore structures.25 We also investigated the adsorption behavior of the TEPA-modified water vapor-activated coal char, and found that the TEPA-modified Ordos coal char showed good CO2 adsorption behavior.26 The preparation process of semicoke is simple and relatively low energy-consumption, during which crack systems and abundant surface functional groups are formed, and semicoke has been widely used in desulphurization and adsorption fields.27-30 In this study, we further activated the Ordos semicoke and studied its CO2 adsorption behavior from flue gases. The semicoke from pyrolysis of Ordos coal was further activated by impregnation with HNO3, NaOH and purging with N2 to improve the textural properties and form abundant surface functional groups, and then TEPA was loaded to increase the active sites for CO2 capture. The surface functional groups of semicoke before and after activation were characterized, and the effects of adsorption temperature and moisture on CO2 adsorption were investigated in a fixed-bed reactor. In addition, the adsorption kinetics and regenerability for semicoke-based sorbents were studied.

2. EXPERIMENTAL SECTION


Page 5 of 35

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

5 2.1 Materials. Ordos coal was provided by Ordos Coal Authority, Nei Monggol, China. HNO3 (AR, 65 wt.%) was produced by Yantai Sanhe Chemical Regent, Yantai, China. NaOH (AR) was made by the Sinopharm Chemical Reagent Co., Ltd, Shanghai, China. TEPA (CP, a purity of 90%) was obtained from Tianjin BASF Chemical Co., Ltd, Tianjin, China. Anhydrous ethanol (AR) was provided by Far Eastern Group: Laiyang Fine Chemical Factory, Yantai, China. Highly pure N2 (a purity of 99.999%) and the simulated flue gas which was distributed by mixing highly pure N2 and CO2 (a purity of 99.999%) at a volume ratio of 85% to 15% were obtained from Qingdao Heli Gas Co., Ltd, Qingdao, China. 2.2 Preparation of TEPA-modified activated semicoke. Ordos coal was ground to powder and placed in a fixed-bed reactor, which was purged with N2 for 30 min. The reactor was heated to 500 °C with a heating rate of 20 K/min and held at this temperature for 60 min, and the semicoke was formed, which is labeled as SE. The prepared semicoke was further activated using the methods adopted in the previous literature.26,

30

A certain amount of semicoke was added to HNO3 (a

concentration of 55%) and NaOH (10 wt.%, 60 °C) solutions, respectively, and the systems were slowly stirred for 120 min. The solutions were repeatedly washed with distilled water till that the pH approximately reached 7. Then the solid powder was dried in an oven at 100 °C for 12 h so as to obtain the activated semicoke, which were marked as SE-H55% and SE-OH10% respectively. In addition, the N2-activated semicoke was prepared by pyrolysis semicoke at 700 °C for 2 h under N2 purging atmosphere, and was named as SE-N2. Here, SE-H55%, SE-OH10% and SE-N2


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 35

6 represent that the activated semicoke were obtained from activating semicoke using HNO3 with a concentration of 55%, NaOH with a weight percentage of 10% and N2, respectively. The preparation of TEPA-modified activated semicoke adopted the impregnated method.19 A measured amount of TEPA was dissolved in 30 mL of anhydrous ethanol filled in a beaker, and sonicated at room temperature for 30 min to promote a full dissolution of TEPA. Then, 1 g of the activated semicoke was quickly added to the beaker and the mixture was continuously sonicated for another 180 min. The beaker was transferred to a vacuum drying oven at 85 °C and dried for 12 h. The dried powders were marked as SE-H55%-TEPA10%, SE-OH10%-TEPA10% and SE-N2-TEPA10%, where TEPA10% represents the weight loading percentage of TEPA used for modifying the activated semicoke was 10%. 2.3 Characterization. The changes of the surface functional groups in the semicoke before and after activation were characterized using a Fourier transform infrared spectroscopy (FT-IR) with a TENSOR-27 model (Bruker, Germany), and the spectra were recorded in the frequency range of 4000‒500 cm-1. The textural properties of the activated semicoke were characterized by the physical adsorption of N2 at 77 K using a Quadrasorb SI analyzer (Quantachrome Instruments, USA).

The

specific surface area was calculated using the

Brunauer-Emmett-Teller (BET) equation. The pore volume was obtained according to the adsorption amount of N2 at a relative pressure of 0.974, and the pores size


Page 7 of 35

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

7 distribution curves were determined using the Barrett-Joyner-Halenda (BJH) model from the desorption branch. 2.4 CO2 adsorption-desorption experiments. The CO2 adsorption-desorption experiments were carried out in a self-assembled fixed-bed reactor, as shown in Figure 1. 0.9 g of the dried sample was packed in the reactor and N2 was passed through to exhaust air in the reactor. The reactor was heated to 100 °C in N2 atmosphere and held at this temperature for 60 min to eliminate adsorbed moisture and gases. Then, the temperature was cooled down to an adsorption temperature and the feed gas was switched to the simulated flue gas at a flow rate of 30 mL/min, and the adsorption process began. The CO2 concentrations in the inlet and outlet gases were checked by the gas chromatography (Clarus 500, PerkinElmer, America). When the CO2 concentration in the outlet (C) was equal to that in the inlet (C0), the adsorption process finished. Afterwards, the feed gas was switched to N2 and the temperature was heated to 100 °C to desorb the adsorbed CO2. When CO2 was not detected in the outlet gas, a desorption process finished. Ten adsorption-desorption cycles were carried out to study the regenerability of the semicoke-based sorbent. The breakthrough adsorption experiments for each sorbent were repeated for three times and the mean was selected.

3. RESULTS AND DISCUSSIONS 3.1 Characterization. The N2 adsorption-desorption isotherms, pore size distribution curves and textural properties of the semicoke activated using NaOH, HNO3 and N2 are depicted in Figure 2 (a), (b) and Table 1. After activation using N2,


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 35

8 the semicoke showed a typical type-IV adsorption isotherm and a hysteresis loop at relative pressure over 0.6, suggesting that crack-type mesoporous structure existed in N2-activated semicoke. Moreover, adsorption equilibrium was not reached when the relative pressure was approximate 1.0, indicating that macropores also existed. In SE-OH10% and SE-H55%, similar adsorption isotherms and hysteresis loops were observed, suggesting that crack-type mesopores and macropores also existed in SE-OH10% and SE-H55%. However, the N2 adsorption amount and hysteresis loop for SE-OH10% and SE-H55% were significantly smaller than those for SE-N2, and SE-N2 possessed more developed pore structure. For SE-OH10%, SE-H55% and SE-N2, pore size distributed in both mesoporous and macroporous range, as shown in Figure 2 (b), and SE-N2 showed more mesopores and macropores, with mesopores mainly centering at 20‒30 nm. Comparing with SE-H55%, SE-OH10% possessed more mesopores. The specific surface area and pore volume demonstrated similar variation trend. The FT-IR spectra of the semicoke before and after activation are shown in Figure 3. When SE was activated using HNO3, the characteristic peaks for characterizing ester groups in 1087 cm-1 and 1052 cm-1 are enhanced, suggesting that esters were formed during the activation of SE using HNO3. Compared with SE, new peaks for SE-OH10% centering at 1710 cm-1 and 1521 cm-1 are assigned to the stretching vibration of C=O in ester groups and C=C in aromatic rings of ester groups, which is an indication of the formation of aromatic ester for NaOH-activated semicoke. For N2-actviated semicoke, the new peaks appeared at 1020 cm-1 and 1383


Page 9 of 35

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

9 cm-1 are respectively caused by the asymmetric stretching vibration of C-O-C in the aliphatic ether and aromatic ether, and the new peak centered at 1624 cm-1 are attributed to the stretching vibration of C=C in aromatic rings of quinone or keto-enol groups, showing that ether groups, quinone or keto-enol groups are constructed for N2-activated semicoke. 3.2 The adsorption performance of the activated semicoke. 3.2.1 The effect of the activation methods. The activation to the semicoke induced different surface functional groups and pore structures. To find the most effective activation methods, the CO2 breakthrough adsorption curves for the semicoke before and after activation at 20 °C are shown in Figure 4, and corresponding adsorption capacity data are listed in Table 2. Before and after HNO3 activation, the equilibrium adsorption capacity for the semicoke was 0.62 mmol/g and 0.73 mmol/g, respectively, and the semicoke showed weak breakthrough adsorption behavior. For SE-OH10%, the breakthrough time, breakthrough adsorption capacity and equilibrium adsorption capacity were 2 min, 0.45 mmol/g and 1.08 mmol/g, which were slightly improved than those of the semicoke before and after HNO3 activation. After activation using NaOH, the pore structure for SE was more developed, and new aromatic ester groups appeared, as has been shown in Figure 2 and Figure 3. For N2-activated semicoke, the breakthrough time, breakthrough adsorption capacity and equilibrium adsorption capacity were 8 min, 1.79 mmol/g and 2.70 mmol/g, significantly improved than those of the SE, SE-H55% and SE-OH10%, which may be caused by the much developed pore structure and the formation of ether


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 35

10 groups. As a proton acceptor, ether groups interacted with CO2 by the dipole interactions, and promoted CO2 adsorption in the N2-activated semicoke. In a word, N2-activated semicoke showed good CO2 adsorption performance at room temperature. 3.2.2 The effect of the adsorption temperature. To understand the adsorption characteristics of the N2-activated semicoke, the breakthrough adsorption curves and adsorption capacity for SE-N2 at different temperatures are shown in Figure 5 and Table 2, respectively. As the temperature increased, the breakthrough time, breakthrough and equilibrium adsorption capacity all decreased. Especially when the temperature was above 40 °C, the CO2 adsorption capacity of the N2-activated semicoke significantly decreased, which is an indication of the characteristic of physisorption. As the temperature increased, the kinetic energy of the CO2 molecules increased, and the dipolar interactions and hydrogen interactions between CO2 molecules and the ether groups/hydroxyl groups (~3400 cm-1, Figure 3) were weakened, resulting in the degradation of the CO2 adsorption performance. Therefore, the N2-activated semicoke is suitable for CO2 adsorption at low temperature. 3.3 The adsorption performance of TEPA-modified N2-activated semicoke. 3.3.1 The effect of the adsorption temperature. Given the textural properties of the N2-activated semicoke, the weight loading percentage for TEPA was set as 10%. The breakthrough adsorption curves and adsorption capacity for SE-N2-TEPA10% at different temperatures are shown in Figure 6 (a) and Table 2. With the increase of the adsorption temperature, the breakthrough time, breakthrough adsorption capacity and


Page 11 of 35

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

11 equilibrium adsorption capacity first increased and then decreased, and all reached their maximum values of 10 min, 2.23 mmol/g and 3.24 mmol/g at 60 °C, with the variation trend being similar with that of the PEI-impregnated SBA-157 and PEI-impregnated hexagonal mesoporous silica.9 When the temperature increased, TEPA was well-dispersed in the pores and the kinetic energy for CO2 increased, which promoted CO2 adsorption; However, too high temperature prevented CO2 adsorption due to the exothermic characteristic of adsorption.7, 18, 20 Compared with the N2-activated semicoke, the adsorption capacity for SE-N2-TEPA10% improved a lot, which may be attributed to following two factors. On one hand, the amino groups with high density from TEPA react with CO2 at a molar ratio of 2:1, on the other hand, as a proton acceptor, the ether groups in N2-activated semicoke promote amino to react with CO2 at a molar ratio of 1:1.3 The adsorption mechanisms are separately expressed in following reactions. 2 R2NH + CO2 → R2NH2+ + R2NCOORR′O + R2NH + CO2 → RR′OH+ + R2NCOO-

(1) (2)

3.3.2 The adsorption kinetics of SE-N2-TEPA10%. The Pseudo-first-order, Pseudo-second order and Avrami models were used to fit the adsorption capacity data of SE-N2-TEPA at 60 °C. The model equations are as follows, where , and represent the rate constants, 1/min, g/(mmol·min) and 1/min, respectively; is the adsorption time, min; and are the adsorption capacity at time of and equilibrium time, mmol/g; is the order of the Avrami equation. According to Cestari et al., the fractional order of the Avrami model stems from the complexity of


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 35

12 the reaction mechanisms or the occurrence of more than one reaction pathway,31 and the excellent fit of the Avrami model could account for the CO2 adsorption by physisorption and chemisorption.32 = [(1 − (− ]

=

(2)

(1)

Pseudo-first-order

Pseudo-second-order

= [1 − (−( ]

(3) Avrami

The fitting curves, corresponding parameters were shown in Figure 6 (b) and Table 3, respectively. The CO2 adsorption over SE-N2-TEPA10% appeared to be a two-stage process, the rapid breakthrough adsorption stage and gradual equilibrium adsorption stage. At the breakthrough stage, the adsorption rate was 0.23 mmol/min and the adsorption capacity was 2.23 mmol/g, with which can meet the requirement of adsorption capacity in industrial application. The Pseudo-first-order and Pseudo-second-order models all deviate from the experimental adsorption data during the CO2 adsorption process of SE-N2-TEPA10%, and the correlation coefficient of R2 are 0.9879 and 0.9833, respectively, as shown in Figure 6 (b) and Table 3, suggesting that both the Pseudo-first-order and Pseudo-second-order model don’t fit well with the experimental data. The Avrami model fit well with the experimental data at 60 °C and R2 is 0.9983, indicating that Avrami model reasonably represents the adsorption process of SE-N2-TEPA10%; both physisorption and chemisorption occurred and multiple adsorption paths emerged,31 with reaction (1) and reaction (2) are the main reaction routes. 3.4 The effect of moisture on the adsorption of SE-N2 and SE-N2-TEPA10%.


Page 13 of 35

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

13 In the flue gases from coal-fired power plants, about 9‒12 vol.% of water exists, the existence of which may influence the CO2 adsorption performance of the prepared sorbents. In this study, the CO2 adsorption behavior of SE-N2 at 20 °C and SE-N2-TEPA10% at 60 °C in the presence of 10 vol.% of water were investigated in a fixed-bed reactor, and the breakthrough adsorption curves and adsorption capacity are shown in Figure 7 and Figure 8, respectively. In the presence of water, the breakthrough time, breakthrough and equilibrium adsorption capacity for SE-N2 were 6 min, 1.34 mmol/g and 2.14 mmol/g, respectively, significantly decreasing compared with those of SE-N2 in the absence of water (Figure 7). As discussed in section 3.2.1, the adsorption of SE-N2 was promoted by the appearance of ester groups, and weak dipole interactions occurred between CO2 molecules and ester groups. In the presence of water, competitive adsorption between CO2 and H2O occurred, which resulted in the decrease of CO2 adsorption on the N2-activated semicoke. Under moisture condition, the breakthrough time, breakthrough and equilibrium adsorption capacity for SE-N2-TEPA were 12 min, 2.68 mmol/g and 3.58 mmol/g, respectively, significantly increasing compared with those of SE-N2-TEPA in the absence of water (Figure 8), and similar phenomenon was also observed on PEI-modified porosity-enhanced clay.33 On one hand, the amino groups from R2NH reacted with CO2 at a molar ratio of 1:1 (reaction 3), on the other hand, with the synergetic effect of the ether groups, the amino groups reacted with CO2 at a molar ratio of 1:2 (reaction 4). Therefore, the CO2 adsorption performance of


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 35

14 SE-N2-TEPA10% was significantly improved under moisture condition, and the TEPA-modified N2-activated semicoke is suitable for capturing CO2 from coal-fired power plants. R2NH + CO2 + H2O → R2NH2+ +HCO3-

(3)

RR′O + R2NH + 2CO2 + 2H2O → RR′OH+ + R2NH2+ + 2HCO33.5

The

cyclic

regenerability

of

the

(4)

SE-N2-TEPA10%.

Ten

adsorption-desorption cycles were performed on SE-N2-TEPA10% with good adsorption performance at the adsorption and desorption temperature being 60 °C and 100 °C, respectively. The adsorption capacity of SE-N2-TEPA10% after regeneration under dry condition was shown in Figure 9. During the regeneration process, the equilibrium adsorption capacity of SE-N2-TEPA10% slowly decreased, and after ten cycles, the adsorption capacity decreased from 3.24 mmol/g to 2.99 mmol/g, which declined 7.7% compared with that of the fresh SE-N2-TEPA10%. The regenerability of SE-N2-TEPA10% was comparable with that of TEPA-modified MCM-41.34

4. CONCLUSIONS After activation using N2, the semicoke from Ordos coal characterized mesoporous and macroporous structure, with mesopores mainly centering at the range of 20‒30 nm and the ether groups being formed. The N2-activated semicoke showed good adsorption performance under dry condition, and the breakthrough and equilibrium adsorption capacity at 20 °C were 1.79 mmol/g and 2.70 mmol/g, respectively. The TEPA-modified N2-activated semicoke showed good adsorption behavior both under dry and moisture conditions, with the breakthrough and


Page 15 of 35

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

15 equilibrium adsorption capacity being 2.23 mmol/g and 3.24 mmol/g under dry condition, and 2.68 mmol/g and 3.58 mmol/g under moisture condition. In addition, the SE-N2-TEPA10% showed good regenerability under dry condition after ten adsorption-desorption cycles.

ACKNOWLEDGMENTS The financial support from the Natural Science Foundation of Shandong Province (ZR2013GL005 and ZR2014JL029) is gratefully acknowledged.

SUPPORTING INFORMATION The kinetic fitting curves for SE-N2 and SE-N2-TEPA10% at different temperatures and corresponding reaction rate parameters of k were listed in Figure 1S, Figure 2S and Table 1S. The proximate analysis and elemental analysis for the semicoke (SE) were listed in Table 2S.


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 35

16

REFERENCES (1) Cox, P. M.; Betts, R. A.; Jones, C. D.; Spall, S. A.; Totterdell, I. J. Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature 2000, 408, 184–187. (2) Bala, G.; Bopp, L.; Brovkin, V.; Canadell, J.; Chhabra, A. Working group I contribution to the IPCC fifth assessment report (AR5), climate change 2013: the physical basis, Working group I-twelfth session, Intergovernmental panel on climate change, Stockholm, 2013. (3) Yan, W.; Tang, J.; Bian, Z.; Hu, J.; Liu, H. Carbon dioxide capture by amine-impregnated mesocellular foam-containing template. Ind. Eng. Chem. Res. 2012, 51, 3653‒3662. (4) Cai, W.; Tan, L.; Jaroniec, J. M.; Liu, X.; Cheng, B.; Verpoort, F. Synthesis of amino-functionalized mesoporous alumina with enhanced affinity towards Cr (VI) and CO2. Chem. Eng. J. 2014, 239, 207–215. (5) Song, F.; Zhao, Y.; Cao, Y.; Ding, J.; Bu, Y.; Zhong, Q. Capture of carbon dioxide from flue gases by amine-functionalized TiO2 nanotubes. Appl. Surf. Sci. 2013, 268, 124–128. (6) Sanz-Pérez, E. S.; Olivares-Marín, M.; Arencibia, A.; Sanz, R.; Calleja, G.; Maroto-Valer, M. M. CO2 adsorption performance of amino-functionalized SBA-15 under post-combustion conditions. Int. J. Greenhouse Gas Control 2013, 17, 366–375. (7) Wang, X.; Ma, X.; Song, C.; Locke, D. R.; Siefert, S.; Winans, R. E.; Möllmer, J.;


Page 17 of 35

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

17 Lange,

M.;

Möller,

A.;

Gläser,

R.

Molecular

basket

sorbents

polyethylenimine-SBA-15 for CO2 capture from flue gas: Characterization and sorption properties. Microporous Mesoporous Mater. 2013, 169, 103–111. (8) Qi, G.; Wang, Y.; Estevez, L.; Duan, X.; Anako, N.; Park, Ah-Hyung A.; Li, W.; Jonesc, C. W.; Giannelis, E. P. High efficiency nanocomposite sorbents for CO2 capture based on amine-functionalized mesoporous capsules. Energy Environ. Sci. 2011, 4, 444–452. (9) Chen, C.; Son, Won-Jin; You, Kwang-Seok; Ahn, Ji-Whan; Ahn, Wha-Seung. Carbon dioxide capture using amine-impregnated HMS having textural mesoporosity. Chem. Eng. J. 2010, 161, 46–52. (10) Chen, C.; Kim, J.; Park, Dong-Wha; Ahn, Wha-Seung. Ethylenediamine grafting on a zeolite-like metal organic framework (ZMOF) for CO2 capture. Mater. Lett. 2013, 106, 344–347. (11) Ko, Y. G.; Lee, H. J.; Oh, H. C.; Choi, U. S. Amines immobilized double-walled silica nanotubes for CO2 capture. J. Hazard. Mate. 2013, 250–251, 53–60. (12) Chowdhury, S.; Parshetti, G. K.; Balasubramanian, R. Post-combustion CO2 capture using mesoporous TiO2/graphene oxide nanocomposites. Chem. Eng. J. 2015, 263, 374–384. (13) Kaithwas, A.; Prasad, M.; Kulshreshtha, A.; Verma, S. Industrial wastes derived solid adsorbents for CO2 capture: A mini review. Chem. Eng. Res. Des. 2012, 90, 1632–1641. (14) Ashley, M.; Magiera, C.; Ramidi, P.; Blackburn, G.; Scott, T. G.; Gupta, R.;


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 35

18 Wilson, K.; Ghosh, A.; Biswas, A. Nanomaterials and processes for carbon capture and conversion into useful by-products for a sustainable energy future. Greenhouse Gas Sci. Technol. 2012, 2, 419–444. (15) Wang, Q.; Luo, J.; Zhong, Z.; Borgna, A. CO2 capture by solid adsorbents and their applications: current status and new trends. Energy Environ. Sci. 2011, 4, 42–55. (16) Samanta, A.; Zhao, A.; Shimizu, G. K. H.; Sarkar, P.; Gupta, R. Post-combustion CO2 capture using solid sorbents: A review. Ind. Eng. Chem. Res. 2012, 51, 1438–1463. (17) Wang, S.; Yan, S.; Ma, X.; Gong, J. Recent advances in capture of carbon dioxide using alkali-metal-based oxides. Energy Environ. Sci. 2011, 4, 3805–3819. (18) Wang, X.; Chen, L.; Guo, Q. Development of hybrid amine-functionalized MCM-41 sorbents for CO2 capture. Chem. Eng. J. 2015, 260, 573–581. (19) Wang, X.; Guo, Q.; Zhao, J.; Chen, L. Mixed amine-modified MCM-41 sorbents for CO2 capture. Int. J. Greenhouse Gas Control 2015, 37, 90–98. (20) Wang, X.; Guo, Q.; Kong, T. Tetraethylenepentamine-modified MCM-41/Silica gel with hierarchical mesoporous structure for CO2 capture. Chem. Eng. J. 2015, 273, 472–480. (21)

Brochard,

L.;

Vandamme,

M.;

Pellenq,

J.-M.

R.;

Fen-Chong,

T.

Adsorption-induced deformation of microporous materials: Coal swelling induced by CO2-CH4 competitive adsorption. Langmuir 2012, 28, 2659‒2670. (22) Ottiger, S.; Pini, R.; Storti, G.; Mazzotti, M. Competitive adsorption equilibria of CO2 and CH4 on a dry coal. Adsorption 2008, 14, 539‒556.


Page 19 of 35

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

19 (23) George, J. D. St.; Barakat, M. A. The change in effective stress associated with shrinkage from gas desorption in coal. Int. J. Coal Geol. 2001, 45, 105‒113. (24) Ottiger, S.; Pini, R.; Storti, G.; Mazzotti, M. Measuring and modeling the competitive adsorption of CO2, CH4, and N2 on a dry coal. Langmuir 2008, 24, 9531‒9540. (25) Ramasamy, S., Sripada, P. P.; Khan, M. M.; Tian, S.; Trivedi, J.; Gupta, R. Adsorption behavior of CO2 in coal and coal char. Energy Fuel 2014, 28, 5241–5251. (26) Wang, X.; Guo, Q. CO2 adsorption behavior of activated coal char modified with tetraethylenepentamine. Energy Fuel 2016, 30, 3281–3288. (27) Wang, L.; Li, C.; Yin, H.; Feng, L.; Yu, Y.; Hou, Y.; Li, C. Sulfur removal of FCC gasoline by selective adsorption over activated semi-coke. Chem. Technol. Fuels Oils 2009, 45, 85‒91. (28) Rubio, B.; Izquierdo, M. T.; Mastral, A. M. Influence of low-rank coal char properties on their SO2 removal capacity from flue gases: II. Activated chares. Carbon 1997, 36, 263‒268. (29) Rubio, B.; Izquierdo, M. T. Influence of low-rank coal char properties on their SO2 removal capacity from flue gases: I. Non-activated chares. Carbon 1997, 35, 1005‒1011. (30) Halina, M.; Jadwiga, W. The effect of coal rank and carbonization temperature on SO2 adsorption properties of coal chars. Fuel 1997, 76, 563‒565. (31) Cestari, A. R.; Vieira, E. F. S.; Vieira, G. S.; Almeida, L. E. The removal of anionic dyes from aqueous solutions in the presence of anionic surfactant using


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 35

20 aminopropyl silica-a kinetic study. J. Hazard. Mater. 2006, B138, 133–141. (32) Serna-Guerrero, R.; Dána, E.; Sayari, A. New insights into the interactions of CO2 with amine-functionalized silica. Ind. Eng. Chem. Res. 2008, 47, 9406–9412. (33) Wang, W.; Xiao, J.; Wei, X.; Ding, J.; Wang, X.; Song, C. Development of a new clay supported polyethylenimine composite for CO2 capture. Appl. Energy 2014, 113, 334–341. (34) Liu, Z.; Teng, Y.; Zhang, K.; Cao, Y.; Pan, W. CO2 adsorption properties and thermal stability of different amine-impregnated MCM-41 materials. J. Fuel Chem. Technol. 2013, 41, 469‒476.


Page 21 of 35

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

21 Figure and Table Captions Figure 1. The self-assembled fixed-bed reactor for CO2 adsorption. Figure 2. The (a) N2 adsorption-desorption isotherms and (b) pore size distribution curves for semicoke activated using NaOH, HNO3 and N2, respectively. Figure 3. The FT-IR spectra for the semicoke before and after activation using HNO3, NaOH and N2. Figure 4. The breakthrough adsorption curves for the semicoke at 20 °C before and after activation. Figure 5. The breakthrough adsorption curves for SE-N2 at different adsorption temperatures. Figure 6. The (a) breakthrough adsorption curves for SE-N2-TEPA10% at different adsorption temperatures and (b) corresponding kinetic fitting at 60 °C. Figure 7. The (a) breakthrough adsorption curves and (b) adsorption capacity for the SE-N2 in the absence and presence of water, respectively. Figure 8. The (a) breakthrough adsorption curves and (b) adsorption capacity for the SE-N2-TEPA10% in the absence and presence of water, respectively. Figure

9.

The

adsorption

capacity

of

SE-N2-TEPA10%

during

ten

adsorption-desorption regenerations.

Table 1 The textural properties of semicoke activated using NaOH, HNO3 and N2, respectively. Table 2 The adsorption performance of the semicoke before and after activation and


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 35

22 TEPA modification. Table 3 The parameters of the kinetic models for CO2 adsorption over SE-N2-TEPA10%.


Page 23 of 35

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

23 List of Figures:

Figure 1. The self-assembled fixed-bed reactor for CO2 adsorption.


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 35

24

Figure 2. The (a) N2 adsorption-desorption isotherms and (b) pore size distribution curves for semicoke activated using NaOH, HNO3 and N2, respectively.


Page 25 of 35

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

25

Figure 3. The FT-IR spectra for the semicoke before and after activation using HNO3, NaOH and N2.


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 35

26

Figure 4. The breakthrough adsorption curves for the semicoke at 20 °C before and after activation.


Page 27 of 35

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

27

Figure 5. The breakthrough adsorption curves for SE-N2 at different adsorption temperatures.


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 35

28

Figure 6. The (a) breakthrough adsorption curves for SE-N2-TEPA10% at different adsorption temperatures and (b) corresponding kinetic fitting at 60 °C.


Page 29 of 35

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

29

Figure 7. The (a) breakthrough adsorption curves and (b) adsorption capacity for the SE-N2 in the absence and presence of water, respectively.


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 35

30

Figure 8. The (a) breakthrough adsorption curves and (b) adsorption capacity for the SE-N2-TEPA10% in the absence and presence of water, respectively.


Page 31 of 35

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

31

Figure 9. The adsorption capacity of SE-N2-TEPA10% during ten adsorption-desorption regenerations.


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 35

32 List of Tables: Table 1 The textural properties of semicoke activated using NaOH, HNO3 and N2, respectively. Sorbent

BET surface area (m2/g)

Total Pore volume (cm3/g)

Average pore size (nm)

SE-OH10%

4.7

0.01

49.9

SE-H55%

2.8

0.007

53.8

SE-N2

20.5

0.04

49.9


Page 33 of 35

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

33

Table 2 The adsorption performance of the semicoke before and after activation and TEPA modification. Sample

Adsorption

Breakthrough

Breakthrough adsorption

Equilibrium adsorption

temperature (°C)

time (min)

capacity (mmol/g)

capacity (mmol/g)

SE

20

0

0

0.62

SE-H55%

20

0

0

0.73

SE-OH10%

20

2

0.45

1.08

SE-N2

20

8

1.79

2.70

SE-N2

20

8

1.79

2.70

SE-N2

30

8

1.79

2.69

SE-N2

40

6

1.34

1.91

SE-N2

50

4

0.89

1.62

SE-N2

60

4

0.89

1.50

SE-N2-TEPA10%

40

6

1.34

2.08

SE-N2-TEPA10%

50

8

1.79

2.80

SE-N2-TEPA10%

60

10

2.23

3.24

SE-N2-TEPA10%

70

8

1.79

2.69

SE-N2-TEPA10%

80

4

0.89

1.76


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 34 of 35

34

Table 3 The parameters of the kinetic models for CO2 adsorption over SE-N2-TEPA10%. Kinetic models

Pseudo-first-order

Pseudo-second-order

Parameters

SE-N2-TEPA10%

(mmol/g)

3.97

(1/min)

0.08

R2

0.9879

(mmol/g

5.98

(g/mmol·min

0.009

R2

0.9833

(mmol/g)

3.31

(1/min)

0.11

1.41

R2

0.9983

Avrami


Page 35 of 35

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

35 Table of Contents:


Tetraethylenepentamine-Modified Activated ... - ACS Publications

Recommend Documents