Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Investigation of CO2 Capture in Nonaqueous Ethylethanolamine Solution Mixed with Porous Solids Mengxing Cui, Siming Chen, Tianqinji Qi, and Yongchun Zhang* State Key Laboratory of Fine Chemistry, Department of Chemical Engineering, Dalian University of Technology, Dalian 116024, China S Supporting Information *
ABSTRACT: In this work, the postcombustion CO2 capture performance was explored in 100.000 g of a nonaqueous solution, 30 wt % monoethylethanolamine (EMEA) and 70 wt % diethylethanolamine (DEEA). Porous solids (multiwalled carbon nanotubes (MWCNTs), silica gel (SG), and MCM-41) with mass fractions (0.025, 0.050, 0.100 and 0.200%) were added into the pure nonaqueous solution forming the new absorbents to improve the CO2 capture performance. The CO2 absorption (313 K) and desorption (383 K) of the new absorbents were operated in the absorption−desorption apparatus under atmospheric pressure. The results show that the addition of the porous solids in the nonaqueous solution led to a 2% decrease in the absorption loading, while contributing to a 10 min decrease in the desorption time under the same desorption extent. The maximum desorption rates of the new absorbents peaked about 5 min earlier than that of the nonaqueous solution, with an enhancement order of MWCNTs > MCM-41 > SG. Meanwhile, the new absorbent, nonaqueous solution mixed with 0.050% MWCNTs, had the best enhancement in the desorption process and exhibited a good stability in the absorption−desorption experiment. Analytic methods (XRD, BET, FT-IR, and SEM) were used to characterize MWCNTs before and after the five absorption−desorption cycles, which showed a good stability of MWCNTs with no significant change in the structure and activity.
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INTRODUCTION CO2 from fossil fuels is the main contributor to the greenhouse effect, which has triggered a variety of environmental problems in recent years, such as heat weaves, ocean acidity, and the melting of glaciers.1 Nowadays, the technology of carbon capture and storage (CCS) is an effective and direct option to mitigate CO2 emissions in the atmosphere.2 In CO2 capture, postcombustion CO2 capture using chemical absorption methods, particularly aqueous alkanolamine solutions, is considered as a rather mature and feasible technology due to its fast reaction kinetics and high CO2 loading.3−5 Many available amine-based solvents have been investigated, such as the primary amine, monoethanolamine (MEA); the secondary amine, diethanolamine (DEA); the tertiary amine, N-methyl-ethanolamine (MDEA); and the sterically hindered amine, 2-amino-2-methyl-1-propanol (AMP).6,7 Among them, the primary amine and secondary amine are generally the main absorbents due to their fast absorption rate; however, they have a limited CO2 loading. The tertiary amine has a high CO2 absorption loading, while the low absorption rate is a big limitation.8 Polyamines, such as piperazine (PZ) and tetraethylenepentamine (TEPA), are used as absorption activators.9 Therefore, blended amine solutions consisting of two or more amines are used to obtain the desirable property of each amine.10 It has been reported that aqueous solutions of MEA + diethylenetriamine (DETA) and MEA + MDEA/ © XXXX American Chemical Society
AMP/DMEA/DEEA have a higher CO2 absorption loading, faster CO2 absorption rate, higher cyclic capacity, and less oxidative degradation when compared with the pure MEA solution for CO2 capture.11−13 Despite the obvious advantages of the amine scrubbing method, the high energy consumption for solvent regeneration is an inherent drawback.14,15 Therefore, many researchers focused on solving this problem, and they found that the nonaqueous alkanolamine solution was a good alternative for CO2 capture, in which water was replaced with other organic solvents like alcohols. The main advantage of the nonaqueous amine solution for CO2 capture is the reduction of the CO2 regeneration temperature followed by the reduction of the energy cost, solvent evaporation, amine degradation, and equipment corrosion.16−19 In Guo’s work, a series of nonaqueous alkanolamine solutions have been reported, such as 2-(2-aminoethylamine) ethanol (AEEA) + benzyl alcohol (BP), AEEA + triethylene glycol (TEG), and AEEA + diethylene glycol (DEG), among which, the AEEA + BP displayed a much faster desorption rate.20 However, these nonaqueous solvents used were still limited to alcohols and had a CO2 desorption loading (98 wt % >99 wt % >99.8 wt % >99 wt % >99 wt % >99.99 wt % >99.99 vol % >99.99 vol %
liquid liquid liquid powder powder powder gas gas
110-73-6 100-37-8 64-17-5 112926-00-8 1318-02-1 308068-56-6 7727-37-9 124-38-9
Figure 1. Absorption−desorption apparatus. (1) Mass flow meter, (2) condenser, (3) drying bottle, (4) wet gas flow meter, (5) oil bath, (6) thermometer, (7) three-neck flask, (8) gas chromatograph, (9) computer, and (10) rotor.
solution due to the high viscosity of the nonaqueous solvents.21 Therefore, a kind of tertiary alkanolamine, N,N-diethylethanolamine (DEEA), was proposed as the nonaqueous solvent instead of the alcohols in Chen’s work, which mixed with a kind of secondary alkanolamine, N-ethylmonoethanolamine (EMEA), to form an efficient nonaqueous solution for CO2 capture. The solvent of DEEA could participate in chemical absorption indirectly during CO2 absorption and thus improved the CO2 absorption loading. The nonaqueous solution of EMEA + DEEA exhibited a higher CO2 absorption loading, desorption efficiency, and cyclic absorption capacity compared with those of the other nonaqueous solutions.17,22 In short, EMEA was a typical secondary alkanolamines with an alkyl group, which had the advantages of high CO2 absorption loading and rate, and DEEA was a kind of tertiary alkanolamine, which was first used as the cosolvent. The nonaqueous EMEA + DEEA solution exhibited a better performance in the absorption−desorption process than using alcohols and glycols as cosolvents.17,22−24 Therefore, the nonaqueous solution of EMEA + DEEA will be used as the base liquid in this work. In an effort to improve the performance of CO2 capture using the absorption method, porous solids were added into the absorbents to enhance the mass transfer or thermal conductivity.25 Choi et al.26 proposed nanofluids first by dispersing metallic nanoparticles into the solvent to improve the thermal conductivity of the solvent. Subsequently, some other nanoparticles were added into the water to improve gas absorption, such as activated carbon (AC), TiO2, silica gel (SG), and Al2O3.25,27,28 However, the above-mentioned CO2 absorption methods are limited to physical absorption. Recently, the combination of nanoparticles and chemical absorbents, especially organic amine solutions, has attracted considerable attention. Jiang et al.29,30 concluded that the addition of nanoparticles into aqueous MEA and MDEA solution could increase the mass transfer rate. Rahmatmand et
al.31 further studied the CO2 absorption enhancement by adding SiO2, Fe2O3, carbon nanotubes (CNT), and Al2O3 into water, DEA, and MDEA solutions, respectively. Wang et al.32 found that the nanoparticles of SiO2, TiO2, and Al2O3 enhanced the CO2 absorption and desorption rates in aqueous MEA solution with the enhancement order of TiO2> SiO2> Al2O3. Nevertheless, no work has reported the effects of porous solids on nonaqueous alknolamine solutions for the CO2 removal process. Herein, the effects of porous solids on the CO2 absorption− desorption process in a nonaqueous alkanolamine solution (EMEA + DEEA) were investigated. Three types of porous solids, multiwalled carbon nanotubes (MWCNTs), silica gel (SG), and MCM-41, with different mass fractions (the ratio of the mass of porous solids to the mass of the nonaqueous solution) of 0.025, 0.050, 0.100, and 0.200% were applied to form new absorbents in this work. Among them, MCM-41 was one of the ordered mesoporous molecular sieves and was usually used as a catalyst or absorbent.33 Furthermore, the physical properties, including viscosity, density, and pH, of the nonaqueous solution and the new absorbent (nonaqueous solution mixed with 0.050% MWCNTs) were tested, and the characterizations of MWCNTs before and after five absorption−desorption cycles were analyzed by XRD, BET, FT-IR, and SEM.
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EXPERIMENTAL SECTION Materials. All of the chemicals that were used are listed in Table 1. They all have a high purity and were used without further purification in this work. Preparation of Absorbents. First, porous solids of multiwalled carbon nanotubes (MWCNTs), silica gel (SG), or MCM-41 were mixed with 100.000 g of 30.0 wt % EMEA + 70.0 wt % DEEA solution. Second, the mixtures were mechanically agitated for 40 min to form new absorbents
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DOI: 10.1021/acs.jced.7b00761 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Fourier transform infrared spectroscopy (FT-IR, Brukervector-22) was applied to confirm the functional groups of MWCNTs. Field emission scanning electron microcopy (FESEM, NOVA NanoSEM 450) was used to characterize the morphology of MWCNTs. Data Analysis. The CO2 absorption loading, β1 (mol CO2/ mol EMEA), was calculated by the following equation:
with the desired particles uniformly dispersed into the nonaqueous solution.30 The standard uncertaintiy of mass is u (m) = 0.006 g, and the relative standard uncertainty of mass fraction is ur (w) = 0.1. Absorption−Desorption Process. Figure 1 shows the CO2 absorption−desorption apparatus, which has been reported in Chen’s work.23 The experimental conditions are shown in Table 2. First, N2 was applied to purge the air in the
β1 =
Table 2. Experimental Conditions of CO2 Absorption− Desorptiona pressure absorption temperature desorption temperature gas volume flow rate EMEA mass fraction
V (dot)t1 − V1 1000VmnEMEA
(1)
where V(dot) (mL/min) is the inlet flow rate of CO2, V1 (mL) is the outlet CO2 volume recorded by the wet gas flow meter, Vm (22.4 mol/L) represents the standard molar volume of CO2, nEMEA is the molarity of EMEA, and t1 is the absorption time. The CO2 desorption loading (β2, mol CO2/mol EMEA) can be given as the following:
0.1 MPa 313 K 383 K 266.000 mL/min 30.0 wt %
The standard uncertainties, u, are u (T) = 1 K, u (P) = 2 × 10−7 MPa, and u (Vdot) = 9 mL/min for the gas volume flow rate. The relative uncertainty of the EMEA mass fraction is ur (w) = 0.1. a
β2 =
V2 VmnEMEA
(2)
where V2 is the outlet CO2 volume. The absorption enhancement factor, E1, was defined as the ratio of the average absorption rate (N̅ ′1, mol/min) of the new absorbents (pure nonaqueous solution mixed with porous solids) to that of the pure nonaqueous solution (N̅ 1, mol/min), which is shown in eq 3.32 The desorption enhancement factor, E2, was calculated as mentioned in the absorption process, which is shown in eq 4. Actually, the enhancement factors were used to evaluate the absorption/desorption process of these new absorbents:
apparatus. Second, the prepared absorbent was poured into a 250 mL flask and heated to 313.0 K with a heating rate of 10 K/min. Third, CO2 with a desired volume flow rate was bubbled into the absorbent until achieving saturation (about 90 min). Finally, the temperature was heated to 383.0 K with a heating rate of 10 K/min for CO2 regeneration (about 45 min). The absorption and desorption process were repeated for five cycles to test the stability of the absorbents in CO2 capture. The absorbent, after five cycle tests, was centrifuged to separate the liquid phase and solid phase. Then the separated solid material was washed by ethanol and dried at 373.0 K in vacuum for 24 h. During the absorption−desorption process, the volatility of the amines was neglected due to the reflux of the amines by the reflux condenser, and the rotor was at constant speed. The CO2 loading in the solution was ascertained by the titration method with a difference of 0.001 mol.40 Measurement of Physical Properties. Densities (ρ, g· cm−3) of the nonaqueous solution and the new absorbent (nonaqueous solution mixed with 0.050% MWCNTs) were measured at 313 K with a Petroleum Hydrometers SY-10 instrument (Shanxi Lecktor Measurement and Control CO., Ltd). Kinematic viscosities (v, mm2·s−1) of the nonaqueous solution and the new absorbent were measured at 313 K with a 1834 Capillary Viscometer (Taizhou Jiaojiang Glass Instrument Factory, China), which was calibrated with distilled water. The pH of the nonaqueous solution and the new absorbent were measured at a series of temperatures by the Seven Compact pH meter from Mettler Toledo. Characterization of Multiwalled Carbon Nanotubes. XRD, BET, FT-IR, and SEM were used to characterize MWCNTs before and after five CO2 absorption−desorption cycles. X-ray powder diffraction (XRD, SmartLab 9, Rigaku Corporation, Japan) analysis was carried out to test the identification of MWCNTs on the D/max-2400 diffractometer scanning from 10 to 80° (2θ) and using Cu Kα radiations under 45 kV and 200 mA. Specific surface area was measured by BET methods on the Quantachrome AUTOSORB-1-MP. The average pore volume and size of MWCNTs were calculated by the Barrett−Joyner−Halenda (BJH) model.
E1 =
N1̅ ′ N1̅
(3)
E2 =
N2̅ ′ N2
(4)
The average rate, (N̅ , mol CO2/(mol EMEA min)) is expressed as the following: t
N̅ =
∫0 Ni t
(5)
where N̅ is the absorption average rate (N̅ 1, mol CO2/(mol EMEA min)) within the first 60 min in the absorption process or the desorption average rate (N̅ 2, mol CO2/(mol EMEA min)) within the first 20 min in the desorption process, because the absorption process mainly occurred in the first 60 min and the desorption enhancement of porous solids mainly occurred in the first 20 min; Ni is the instantaneous absorption rate (N1, mol CO2/(mol EMEA min)) or desorption rate (N2, mol CO2/ (mol EMEA min)), which are defined as
Ni =
dβi dt
(6)
The standard uncertainties, u, are u (β1) = 0.0068 mol CO2/ mol EMEA, u (β2) = 0.0069 mol CO2/mol EMEA, u (V2) = 0.093 mL, u (N) = 0.0069 mol CO2/(mol EMEA min) for the CO2 absorption and desorption rate, and u (E) = 0.0097 for enhancement factor. Dynamic viscosity (μ, mPa·s) is defined as the following: μ = ρ · v = ρ · (γ · t ) C
(7) DOI: 10.1021/acs.jced.7b00761 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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where γ (mm2·s−2) is the viscometer constant (0.03068 mm2/ s2), ρ (g·cm−3) is the density of absorbents, v (mm2·s−1) is the kinematic viscosity of absorbents, and t (s) is the flow time of absorbents.
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RESULTS AND DISCUSSION CO2 Absorption Performance. Figure 2 shows the effects of 0.050% porous solids (MWCNTs, SG, and MCM-41) on
Figure 5. Effects of porous solids on the CO2 desorption loading with time.
Figure 2. Effects of different porous solids on CO2 absorption loading with time.
Figure 6. Effects of different porous solids on the CO2 desorption rate with time.
Figure 3. Effects of different porous solids on CO2 absorption rate with time.
Figure 7. Comparison of the CO2 desorption enhancement factors (E2) of porous solids with different mass fractions.
CO2 absorption loading. It is observed that the CO2 absorption loadings of the new absorbents (pure nonaqueous solution with 0.050% porous solids) were slightly reduced compared with that of the pure nonaqueous solution at equilibrium, which indicates the addition of porous solids into the pure nonaqueous solution reduced the CO2 absorption loading. Figure 3 shows the variations of the CO2 absorption rate with time in the pure nonaqueous solution and the new absorbents. It can be seen that the curves of the CO2 absorption rate were almost overlapping in all of the absorbents. The CO 2 absorption rate dropped sharply before 60 min, and then it
Figure 4. Comparison of the CO2 absorption enhancement factors (E1) of porous solids with different mass fractions.
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DOI: 10.1021/acs.jced.7b00761 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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pure nonaqueous solution, and the enhancement order was MCM-41 > MWCNTs > SG. Meanwhile, the desorption time decreased by about 10 min under the same desorption extent from Figure 5, which cut the overall energy added. It can be seen from Figure 6 that the maximum value of the CO2 desorption rate was larger in the new absorbents (nonaqueous solution mixed with porous solids) than that in the pure nonaqueous solution, and the time achieving the maximum value decreased by about 5 min. It demonstrates that the addition of porous solids into the pure nonaqueous solution enhanced the CO2 desorption process, in which a higher desorption rate will result in a smaller stripper. Two kinds of models have been proposed by other researchers for this phenomenon: (1) the thermal conductivity could be boosted due to the Brownian motion, nature of heat transport, and the influence of nanoparticles clustering, ect. by adding porous solids into absorbents;34−36 and (2) the kinetics of bubble formation were strengthened due to the increase of the nucleation sites, which made more bubbles grow and break in a certain time and further strengthened the mass transfer.37 According to these two models, the reasons for the enhancement of the CO2 desorption loading and rate might be an increase in thermal conductivity of the new absorbents and the rough surfaces of the porous solids, which provided more nucleation sites for advancing the mass transfer. The effects of porous solids at different mass fractions on the CO2 desorption process were assessed by the desorption enhancement factor (E2). Figure 7 shows the comparison of the CO2 desorption enhancement factors of the porous solids (MWCNTs, SG, and MCM-41) at different mass fractions (0.025, 0.050, 0.100, and 0.200%). It is observed that all of the values of the desorption enhancement factors were larger than 1, which implies the positive effects of the porous solids on the CO2 desorption process. With the increase of mass fractions, all of the values of the desorption enhancement factors reached the maximum at the mass fraction of 0.050% and then decreased significantly. After that, it was followed by a moderate rise for MCM-41 and SG, which indicates an optimum mass fraction (0.050%) of the porous solids for enhancing the CO2 desorption process. It also can be seen from Figure 7 that the influence of MWCNTs on the CO2 desorption process at the mass fractions of 0.050 and 0.100% was much stronger than that of SG and MCM-4. It might be due to the particular properties of MWCNTs, such as the filiform morphology, which provides more nucleation sites and the low density which facilitates the dispersion of MWCNTs in the pure nonaqueous solution.38 Therefore, the porous solid of MWCNTs at the mass fraction of 0.050% was the best choice for improving the CO2 desorption process in the pure nonaqueous solution. Therefore,
Figure 8. CO2 absorption loading of the pure amine solution and the new absorbent with 0.050% MWCNTs in five absorption−desorption cycles.
leveled off in the next 30 min. This was because the EMEA concentration as a major controlling factor for the CO2 absorption decreased dramatically in this stage.32 The effects of the porous solids with different mass fractions on the CO2 absorption process were assessed by the absorption enhancement factor (E1). Figure 4 shows the CO2 absorption enhancement factors of the porous solids (MWCNTs, SG, and MCM-41) at different mass fractions (0.025, 0.050, 0.100, and 0.200%). It can be seen that all enhancement factors were less than 1, which demonstrates the negative effects of porous solids on the CO2 absorption process. The reason for this phenomenon may be due to the increase of the solvent viscosity and the reduction of the solvent pH after adding porous solids into the pure nonaqueous solution, which would inhibit the partial CO2 diffusion in the liquid-phase zone and reduce the CO2 absorption loading. The enhancement factors at the mass fractions of 0.025 and 0.050% were similar; however, the enhancement factors at the mass fraction of 0.200% were significantly different, and the enhancement order was SG > MWCNTs > MCM-41. These phenomena imply that the CO2 absorption had a significant affinity with the types and mass fractions of the porous solids in the pure nonaqueous solution for CO2 capture. CO2 Desorption Performance. Figures 5 and 6 show the influences of various porous solids (MWCNTs, SG, and MCM41) on the CO2 desorption loading and rate, respectively. It is found from Figure 5 that the CO2 desorption loading and rate were both enhanced by adding 0.050% porous solids into the
Table 3. CO2 Absorption Loading (β1) in Each Cycle at 0.1 MPa, 313 Ka β1/(mol CO2/mol EMEA) cycle-index
30 wt % EMEA + 70 wt % DEEA
30 wt % EMEA + 70 wt % DEEA + 0.050% MWCNTs
enhancement capacity (mol CO2/mol EMEA)
1 2 3 4 5
0.7330 0.6440 0.6450 0.6420 0.6400
0.7110 0.6430 0.6470 0.6560 0.6580
−0.0220 −0.0010 0.0020 0.0140 0.0180
β1 (mol CO2/mol EMEA) is the CO2 absorption loading. The standard uncertainties are u (β1) = 0.0068 mol CO2/mol EMEA, u (T) = 1 K, u (P) = 2 × 10−7 MPa, and ur (w) = 0.1.
a
E
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Table 4. Physical Properties Including Density (ρ), Viscosity (μ), and pH of 30 wt % EMEA + 70 wt % DEEA and 30 wt % EMEA + 70 wt % DEEA + 0.050% MWCNTs at 0.1 MPa, 313 Ka
a
sample
ρ (g·cm−3)
μ (mPa·s)
pH
30 wt % EMEA + 70 wt % DEEA 30 wt % EMEA + 70 wt % DEEA + 0.050% MWCNTs
0.879 0.881
3.830 4.244
10.94 10.85
The standard uncertainties, u, are u (T) = 1 K, u (P) = 2 × 10−7 MPa, ur (w) = 0.1, ur (ρ) = 0.001, ur (μ) = 0.01, and u (pH) = 0.01.
CO2 Absorption−Desorption Cycles. Figure 8 describes the stability of the pure nonaqueous solution and the new absorbent (nonaqueous solution mixed with 0.050% MWCNTs) during the five cycles of the CO2 absorption− desorption process. Table 3 lists the absorption loading values of two absorbents in each cycle. It can be seen from Figure 8 that the first absorption loading was higher than that of the following four cycles for these two absorbents, and the CO2 absorption loading in the following four cycles were relatively stable, which implies a good stability of the absorbents for CO2 absorption. Table 3 shows that the enhancement capacity of the new absorbent increased with the CO2 absorption−desorption cycles. The enhancement capacity was the difference of the CO2 absorption loading between the new absorbent and pure nonaqueous solution. Physical Properties of Amine Solvents and the New Absorbent. Table 4 shows the density, viscosity, and pH of the pure nonaqueous solution and the new absorbent (nonaqueous solution mixed with 0.050% MWCNTs) under 313 K and atmospheric pressure. It is noticed that after adding 0.050% MWCNTs into pure nonaqueous solution, its viscosity increased by 0.414 mPa·s, which inhibited the mass transfer and further reduced the CO2 absorption rate, and its pH slightly decreased by 0.09 at 313 K. Moreover, it is found from Table S1 that the pH of these two absorbents decreased with the temperature increasing; meanwhile, the pH of the new absorbent was lower than that of the pure nonaqueous solution at each measured temperature, which led to the reduction of the CO2 absorption loading and rate. These physical properties also accounted for the phenomena observed in the CO2 absorption experiment. The densities of the pure nonaqueous solution and new absorbent were almost the same, which indicates that the addition of 0.050% MWCNTs had no influence on density of the pure nonaqueous solution. Characterization of Multiwalled Carbon Nanotubes. Figure 9 shows the powder XRD patterns of MWCNTs before and after the five absorption−desorption cycles for comparison. The MWCNTs before and after the five absorption− desorption cycles all had a sharp diffraction peak at around 26° and a broad weak peak at around 43°, which agreed well with the report in literature.39 It indicates that the crystal structure of MWCNTs was not destroyed or disturbed after the five CO2 absorption−desorption cycles. Table 5 shows the surface area, pore volume, and pore size of the porous solids calculated using the N2 absorption− desorption isotherms. It can be seen that the surface area, pore volume, and pore size had no significant change before and after the five CO2 absorption−desorption cycles, which implies the framework pores of MWCNTs were not filled with the amine solvents after the CO2 absorption. This result further verifies the stability of MWCNTs. Figure 10 is used to characterize the function groups existing in MWCNTs before and after the five absorption−desorption cycles. Both of them show the peaks of O−H stretching vibration at 3435 cm−1 and O−H blending vibration at 1626
Figure 9. XRD spectra of MWCNTs before and after the five absorption−desorption cycles.
Table 5. Textural Property of MWCNTs before and after Five Absorption−Desorption Cyclesa surface area (m2/g)
pore volume (cm3/g)
pore size (nm)
a
sample
MWCNTs
before five absorption−desorption cycles after five absorption−desorption cycles before five absorption−desorption cycles after five absorption−desorption cycles before five absorption−desorption cycles after five absorption−desorption cycles
233.0 234.0 1.04 1.09 18.04 18.12
2
The standard uncertainties u are 0.1 m /g for surface area, 0.01 cm3/g for pore volume, and 0.01 nm for pore size.
Figure 10. FT-IR spectra of MWCNTs before and after the five absorption−desorption cycles.
the CO2 absorption−desorption cyclic experiment of the new absorbent (nonaqueous solution mixed with 0.050% MWCNTs) will be further investigated. F
DOI: 10.1021/acs.jced.7b00761 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Figure 11. SEM images of MWCNTs before (A) and after (B) the five absorption−desorption cycles.
cm−1 due to the ambient water on MWCNTs. The new peaks that appeared at 2875−2980 cm−1 were attributed to the stretching vibration of −CH3 and −CH2−. Besides, other new peaks are observed at 1048−1091 cm−1, representing the stretching vibration of C−N and C−C, which indicates the absorption solvent on the surface of MWCNTs due to the dipping in the amine solvent during CO2 capture. Figure 11 shows the SEM micrographs of MWCNTs before and after the five absorption−desorption cycles. It shows that there was no obvious change of the degree of aggregation between the MWCNTs before and after the five absorption− desorption cycles, which further confirms the stability of MWCNTs after the five absorption−desorption cycles.
ORCID
Yongchun Zhang: 0000-0001-7507-7297 Notes
The authors declare no competing financial interest.
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(1) Intergovernmental Panel on Climate Change (IPCC). The physical science basis of climate change; Cambridge University Press: New York, 2007, http://ipcc-wg1.ucar.edu/wg1/. (2) Haszeldine, R. S. Carbon capture and storage: How green can black be? Science 2009, 325, 1647−52. (3) Kim, Y. E.; Moon, S. J.; Yoon, Y. I.; Jeong, S. K.; Park, K. T.; Bae, S. T.; Nam, S. C. Heat of absorption and absorption capacity of CO2 in aqueous solutions of amine containing multiple amino groups. Sep. Purif. Technol. 2014, 122, 112−118. (4) Roth, E. A.; Agarwal, S.; Gupta, R. K. Nanoclay-Based Solid Sorbents for CO2 Capture. Energy Fuels 2013, 27, 4129−4136. (5) Zhang, X.; He, X.; Gundersen, T. Post-combustion Carbon Capture with a Gas Separation Membrane: Parametric Study, Capture Cost, and Exergy Analysis. Energy Fuels 2013, 27, 4137−4149. (6) Kim, Y. E.; Lim, J. A.; Jeong, S. K.; Yoon, Y. I.; Bae, S. T.; Nam, S. C. Comparison of Carbon Dioxide Absorption in Aqueous MEA, DEA, TEA, and AMP Solutions. Bull. Korean Chem. Soc. 2013, 34, 783−787. (7) Mores, P.; Scenna, N.; Mussati, S. Post-combustion CO2 capture process: Equilibrium stage mathematical model of the chemical absorption of CO2 into monoethanolamine (MEA) aqueous solution. Chem. Eng. Res. Des. 2011, 89, 1587−1599. (8) Yu, Y. S.; Lu, H. F.; Wang, G. X.; Zhang, Z. X.; Rudolph, V. Characterizing the Transport Properties of Multiamine Solutions for CO2 Capture by Molecular Dynamics Simulation. J. Chem. Eng. Data 2013, 58, 1429−1439. (9) Ramazani, R.; Mazinani, S.; Jahanmiri, A.; Darvishmanesh, S.; Van der Bruggen, B. Investigation of different additives to monoethanolamine (MEA) as a solvent for CO2 capture. J. Taiwan Inst. Chem. Eng. 2016, 65, 341−349. (10) Osman, K.; Coquelet, C.; Ramjugernath, D. Absorption Data and Modeling of Carbon Dioxide in Aqueous Blends of Bis(2hydroxyethyl)methylamine (MDEA) and 2,2-Iminodiethanol (DEA): 25% MDEA + 25% DEA and 30% MDEA + 20% DEA. J. Chem. Eng. Data 2012, 57, 1607−1620. (11) Conway, W.; Bruggink, S.; Beyad, Y.; Luo, W.; Melián-Cabrera, I.; Puxty, G.; Feron, P. CO2 absorption into aqueous amine blended solutions containing monoethanolamine (MEA), N,N-dimethylethanolamine (DMEA),N,N-diethylethanol- amine (DEEA) and 2-amino2-methyl-1-propanol (AMP) for post-combustion capture processes. Chem. Eng. Sci. 2015, 126, 446−454. (12) Lawal, O.; Bello, A.; Idem, R. The Role of Methyl Diethanolamine (MDEA) in Preventing the Oxidative Degradation of CO2 Loaded and Concentrated Aqueous Monoethanolamine
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CONCLUSION In this research, three different kinds of porous solids (MWCNTs, MCM-41, and SG) at various mass fractions were mixed with a pure nonaqueous solution (30 wt % EMEA + 70 wt % DEEA) to form the new absorbents for improving the CO2 absorption and desorption process. From the experimental results, these three kinds of porous solids had a slightly negative impact on the CO2 absorption process. However, they could strengthen the CO2 desorption process in the order of MWCNTs > MCM-41 > SG. Meanwhile, there was an optimum MWCNTs mass fraction (0.050%) for enhancing the CO2 desorption process. The performance of the CO2 absorption−desorption cycles observed in the new absorbent (nonaqueous solution mixed with 0.050% MWCNTs) was better than that in the pure nonaqueous solution. Furthermore, the various characterization analyses show that the structure of MWCNTs was stable after the five CO2 absorption−desorption cycles.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00761. pH variations at different temperatures, values of absorption/desorption loading in the first absorption−desorption cycle, reproducibility studies, and temperature variation of absorbents with time (PDF)
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REFERENCES
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DOI: 10.1021/acs.jced.7b00761 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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(MEA)−MDEA Blends during CO2 Absorption from Flue Gases. Ind. Eng. Chem. Res. 2005, 44, 1874−1896. (13) Zhu, B.; Liu, Q.; Zhou, Q.; Yang, J.; Ding, J.; Wen, J. Absorption of Carbon Dioxide from Flue Gas using Blended Amine Solutions. Chem. Eng. Technol. 2014, 37, 635−642. (14) Davison, J. Performance and costs of power plants with capture and storage of CO2. Energy 2007, 32, 1163−1176. (15) Wang, M.; Lawal, A.; Stephenson, P.; Sidders, J.; Ramshaw, C. Post-combustion CO2 capture with chemical absorption: A state-ofthe-art review. Chem. Eng. Res. Des. 2011, 89, 1609−1624. (16) Barzagli, F.; Lai, S.; Mani, F.; Stoppioni, P. Novel Non-aqueous Amine Solvents for Biogas Upgrading. Energy Fuels 2014, 28, 5252− 5258. (17) Chen, S.; Chen, S.; Fei, X.; Zhang, Y.; Qin, L. Solubility and Characterization of CO2 in 40 mass % N-Ethylmonoethanolamine Solutions: Explorations for an Efficient Nonaqueous Solution. Ind. Eng. Chem. Res. 2015, 54, 7212−7218. (18) Barbarossa, V.; Barzagli, F.; Mani, F.; Lai, S.; Stoppioni, P.; Vanga, G. Efficient CO2 capture by non-aqueous 2-amino-2-methyl-1propanol (AMP) and low temperature solvent regeneration. RSC Adv. 2013, 3, 12349. (19) Barzagli, F.; Lai, S.; Mani, F. Novel non-aqueous amine solvents for reversible CO2 capture. Energy Procedia 2014, 63, 1795−1804. (20) Guo, C.; Chen, S.; Zhang, Y.; Wang, G. Solubility of CO2 in Nonaqueous Absorption System of 2-(2-Aminoethylamine)ethanol + Benzyl Alcohol. J. Chem. Eng. Data 2014, 59, 1796−1801. (21) Guo, C.; Chen, S.; Chen, S.; Wang, G.; Zhang, Y. Mixture absorption system of non-aqueous MEA solution for CO2 capture. Mod. Chem. Ind. 2014, 34, 107−109 China. (22) Chen, S.; Chen, S.; Zhang, Y.; Chai, H.; Qin, L.; Gong, Y. An investigation of the role f N-methyl-diethanolamine in non-aqueous solution for CO2 capture process using 13C NMR spectroscopy. Int. J. Greenhouse Gas Control 2015, 39, 166−173. (23) Chen, S.; Chen, S.; Zhang, Y.; Qin, L.; Guo, C.; Chen, J. Species distribution of CO2 absorption/desorption in aqueous and nonaqueous N-ethylmonoethanolamine solutions. Int. J. Greenhouse Gas Control 2016, 47, 151−158. (24) Heldebrant, D. J.; Koech, P. K.; Glezakou, V. A.; Rousseau, R.; Malhotra, D.; Cantu, D. C. Water-Lean Solvents for Post-Combustion CO2 Capture: Fundamentals, Uncertainties, Opportunities, and Outlook. Chem. Rev. 2017, 117, 9594−9624. (25) Krishnamurthy, S.; Bhattacharya, P.; Phelan, P. E.; Prasher, R. S. Enhanced mass transport in nanofluids. Nano Lett. 2006, 6, 419−423. (26) Choi, S. U. S.; Eastman, J. A. Enhancing thermal conductivity of fluids with nanoparticles. Asme Fed 1995, 231, 99−105. (27) Ablasser, C.; Hofmann, S.; Hinrichsen, O. The Influence of Interfacial Areas for Gas Absorption in the Presence of Solid Particles. Chem. Eng. Technol. 2014, 37, 1468−1474. (28) Golkhar, A.; Keshavarz, P.; Mowla, D. Investigation of CO2 removal by silica and CNT nanofluids in microporous hollow fiber membrane contactors. J. Membr. Sci. 2013, 433, 17−24. (29) Jiang, J.; Zhao, B.; Cao, M.; Wang, S.; Zhuo, Y. Chemical Absorption Kinetics in MEA Solution with Nano-particles. Energy Procedia 2013, 37, 518−524. (30) Jiang, J.; Zhao, B.; Zhuo, Y.; Wang, S. Experimental study of CO2 absorption in aqueous MEA and MDEA solutions enhanced by nanoparticles. Int. J. Greenhouse Gas Control 2014, 29, 135−141. (31) Rahmatmand, B.; Keshavarz, P.; Ayatollahi, S. Study of Absorption Enhancement of CO2 by SiO2, Al2O3, CNT, and Fe3O4 Nanoparticles in Water and Amine Solutions. J. Chem. Eng. Data 2016, 61, 1378−1387. (32) Wang, T.; Yu, W.; Liu, F.; Fang, M.; Farooq, M.; Luo, Z. Enhanced CO2 absorption and desorption by MEA based nanoparticle suspensions. Ind. Eng. Chem. Res. 2016, 55, 7830−7838. (33) Zhao, X. S.; Lu, G. Q.; Millar, G. J. Advances in mesoporous molecular sieve mcm-41. Ind. Eng. Chem. Res. 1996, 35, 2075−2090. (34) Fan, J.; Wang, L. Review of Heat Conduction in Nanofluids. J. Heat Transfer 2011, 133, 040801.
(35) Pang, C.; Jung, J.-Y.; Lee, J. W.; Kang, Y. T. Thermal conductivity measurement of methanol-based nanofluids with Al2O3 and SiO2 nanoparticles. Int. J. Heat Mass Transfer 2012, 55, 5597− 5602. (36) Vatani, A.; Woodfield, P. L.; Dao, D. V. A survey of practical equations for prediction of effective thermal conductivity of sphericalparticle nanofluids. J. Mol. Liq. 2015, 211, 712−733. (37) Lee, J. S.; Lee, J. W.; Kang, Y. T. CO2 absorption/regeneration enhancement in DI water with suspended nanoparticles for energy conversion application. Appl. Energy 2015, 143, 119−129. (38) Thostenson, E. T.; Ren, Z.; Chou, T. W. Advances in the science and technology of carbon nanotubes and their composites: a review. Compos. Sci. Technol. 2001, 61, 1899−1912. (39) Chen, B.; Wang, Y.; Chang, Z.; Wang, X.; Li, M.; Liu, X.; Zhang, L.; Wu, Y. Enhanced capacitive desalination of MnO2 by forming composite with multi-walled carbon nanotubes. RSC Adv. 2016, 6, 6730−6736. (40) Shen, K. P.; Li, M. H. Solubility of carbon dioxide in aqueous mixtures of monoethanolamine with methyldiethanolamine. J. Chem. Eng. Data 1992, 37, 96−100.
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DOI: 10.1021/acs.jced.7b00761 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
