Impregnation of PEI in Novel Porous MgCO3 for Carbon Dioxide

Mar 4, 2019 - Department of Chemical Engineering, University of New Brunswick , Fredericton , New Brunswick E3B 5A3 , Canada. Ind. Eng. Chem...
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Impregnation of PEI in Novel Porous MgCO3 for Carbon Dioxide Capture from Flue Gas Xia Wan,† Xiaojuan Lu,† Jie Liu,† Yuanfeng Pan,‡ and Huining Xiao*,§ †

Department of Environmental Science and Engineering, North China Electric Power University, Baoding 071003, P. R. China Guangxi Key Lab of Petrochemical Resource Processing and Process Intensification Technology, School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, P. R. China § Department of Chemical Engineering, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada Ind. Eng. Chem. Res. Downloaded from pubs.acs.org by UNIV OF EDINBURGH on 03/19/19. For personal use only.

‡

ABSTRACT: CO2 emission has caused serious environmental problems, and the reduction of CO2 has become a global issue. The use of amine-impregnated solid adsorbents for CO2 capture from flue gas has been an effective approach. Herein, a novel porous MgCO3 was synthesized by a facile and template-free method and further impregnated with polyethylenimine (PEI) to prepare porous adsorbent for highly efficient CO2 capture. Moreover, during the synthesis of MgCO3, CO2 was used as one of the reactants in an attempt to improve the potential utilization of CO2. The effects of PEI loading, temperature, and coexisting gases (H2O, NO, and SO2) on CO2 adsorption performance were identified in a fixed bed. The results indicated that the adsorption capacity of the adsorbent toward CO2 was increased significantly after PEI impregnation. With the increase of temperature, the capture capacity of CO2 decreased because of the dominated thermodynamic control on the low PEI-loaded adsorbents, however, increased due to the governed kinetic control on the high PEI-loaded adsorbents. In addition, the adsorbent loaded with 20 wt % PEI showed the highest CO2 capture capacity, up to 1.07 mmol/g at 75 °C, and exhibited a 19.6% increase by introducing 10 vol % of water vapor. Meanwhile, the CO2 capture capacity was almost unaffected by NO; however, SO2 in flue gas could have some negative effects on CO2 adsorption due to the stronger acidity. Finally, the cyclic adsorption/desorption tests demonstrated excellent regenerability and stability of adsorbent. The results indicated that the PEI-modified porous MgCO3 is a very promising adsorbent for CO2 capture.

1. INTRODUCTION Global warming and other consequential environmental problems resulting from the greenhouse effect have received a great deal of attention in recent years. Since CO2 is the major contributor to greenhouse gases, it is particularly important and urgent to reduce the amount of CO2 emitted into the atmosphere due to the utilization of fossil fuels.1 Considered to be a critical solution to global CO2 emission reduction, CO2 capture and storage (CCS) technology has been given an urgent requirement for its own development.2 Among the various CCS technologies, the chemical absorption using aqueous solutions of amines, such as monoethanolamine (MEA), methyldiethanolamine (MDEA), and diethanolamine (DEA), is the most mature and well-established one for CO2 capture.3,4 However, this process presents major drawbacks, such as high operating costs, evaporation of amine solution, and equipment corrosion,5 which lowered the production efficiency of coal-fired power plants by 10−12%.6 Thus, there is a growing demand on new energy-efficient CO2 capture techniques for CCS applications. The adsorption process with the use of solid adsorbents has been developed to overcome these drawbacks in chemical absorption and showed the © XXXX American Chemical Society

advantages of high product purity, low energy consumption, low toxicity, and ease of adsorption and regeneration,7−9 which displayed a broad application prospect in adsorptive separation of CO2 from flue gas.10,11 During recent years, numerous studies have reported that the CO2 capture capacity of porous solid adsorbents could be greatly enhanced by amine modification.12,13 These amine-modified solid adsorbents can be simply obtained by physically impregnating the porous supports with amine,14 which showed a higher CO2 capture capacity and lower cost compared to the grafting methods.15 An excellent amine-modified adsorbent should have unobstructed pore structure for CO2 transfer16 and a high capture capacity of CO2. To develop efficient amine-modified adsorbents, the supports with high-amine-loading capability and amine with high-nitrogen content are highly demanded. Besides, the methods for introducing amine to the support should also be effective, and enable a superior adsorbent Received: Revised: Accepted: Published: A

December 12, 2018 February 9, 2019 March 4, 2019 March 4, 2019 DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research performance.17,18 Among various amine-modified adsorbent supports, e.g. zeolites,19 metal organic frameworks (MOFs),20 and porous carbon,21 the ordered mesoporous silica materials, such as SBA-15,22 MCM-41,23 and KIT-6,24 were considered as excellent supports due to their high specific surface area and porosity. Combined with a proper dispersion of amine into the pores of these supports, the adsorption properties of silicabased mesoporous adsorbents have been efficiently improved.25,26 Previous studies indicated that the mesoporous silica materials after polyethylenimine (PEI) impregnation exhibited superior stability and CO2 capture capacity, compared to either support alone or pure PEI.27−29 Moreover, these adsorbents could possess a high thermal stability30 and be regenerated at a relatively low temperature.31 Although amine-modified mesoporous silica-based materials exhibit excellent CO2 adsorption properties, the preparation of mesoporous silica is not cost-effective due to the use of expensive silica sources and surfactants in the synthesis, leading to difficulties with large scale manufacturing.32 Besides, it is an essential step to remove the organic surfactants after the synthesis of silica materials, which indeed involves the use of high temperature and chemicals that could increase the cost and the environmental burden.33 Therefore, the easily synthesized and environmentally friendly porous materials with superior performance and desired economics urgently need to be developed as the support of amine-modified adsorbents. Moreover, in addition to N2 and CO2, the flue gas also contains water vapor, SO2, and NOX, which may affect the performance of amine-modified adsorbents during CO 2 capture. Thus, it is necessary to take full account of the influence of flue gas composition on the adsorbents for the industrial application of CO2 capture. However, most reports only focused on CO2 adsorption without considering the effects of other coexisted gases. In this work, a relatively novel porous MgCO3 was prepared as support using a template-free and simple-synthesis approach. The raw materials are cost-effective and readily obtained, and the reaction for synthesis is straightforward, thus facilitating the potential scale-up of preparation. The porous MgCO3 was further treated by the impregnation of highamino-content PEI to generate a range of amine-modified adsorbents for CO2 capture. The physicochemical properties of the adsorbents were systematically characterized by N2 adsorption/desorption, Fourier transform infrared (FTIR) spectrometry, and scanning electron microscope (SEM). And the potential influencing factors for CO2 adsorption behaviors, such as the PEI loading, temperature, and coexisting gases (H2O, NO, and SO2) in simulated flue gas were discussed. Besides, the cyclic adsorption stability was investigated as well. Moreover, as the support of CO2 adsorbent, the MgCO3 itself is a kind of CO2-storage material, using CO2 as one of the reactants during the synthesis process, which benefits the entire utilization of CO2.

by North Special Gas Co., Ltd. (Baoding, China). All reagents were used without future purification. 2.2. Synthesis of Adsorbents. The porous MgCO3 was prepared as the procedure reported previously.34 Briefly, MgO was mixed with methanol, after stirring under 3 bar CO2 pressure at 50 °C for 3 h, the mixture reacted under 1 bar CO2 pressure at 25 °C, followed by drying at 70 °C for 3 days, the dried product was calcined at 250 °C for 3 h with a 3 h ramp time. On the basis of this method, in order to select the best support, the following 5 samples (M1 to M5) were synthesized under different experimental conditions, which are shown in Table 1, respectively. Table 1. Synthesis Conditions of Porous MgCO3 reagents samples MgO (g) methanol (mL) toluene (mL) M1 M2 M3 M4 M5

2 2 2 2 2

30 30 12 20 25

0 0 18 10 5

reaction time at 25 °C (d) 2 4 4 4 4

PEI-modified MgCO3 adsorbents were prepared via a wet impregnation method.35 The desired amount of PEI dissolved uniformly in ethanol was added to the sufficiently dried MgCO3. The resulting slurry was stirred and refluxed at 80 °C for 2 h. After completely evaporating the ethanol at 80 °C, the sample was dried at 100 °C for 2 h in an oven. The obtained adsorbent was denoted as xP-M, where x (x = 10, 20, 30) indicated the mass percentage of PEI. The synthetic process of porous MgCO3 and PEI-modified MgCO3 adsorbents is illustrated schematically in Figure 1. 2.3. Characterization. N2 adsorption/desorption analysis was performed at −196 °C with a surface area and pore size analyzer (Beckman Coulter SA 3100, U.S.A.). Each sample was outgassed prior to each measurement under vacuum at 95 °C for 10 h. The Brunauer−Emmett−Teller (BET) method was used to calculate the specific surface area at a relative pressure (PS/P0) range of 0.05−0.2. The Barrett−Joyner−Halenda (BJH) model was used to determine the pore size distribution from the desorption branch of isotherm. The total pore volume was determined according to the volume of liquid nitrogen adsorbed at PS/P0 = 0.98. The surface functionalities of the adsorbents were analyzed using the Fourier transform infrared (FTIR) spectrometer (Bruker Optics Tensor II, German) over the range 400−4000 cm−1, with a resolution of 4 cm−1.The surface morphologies of the samples were revealed using a scanning electron microscope (SEM, JEOL-LV6500, Japan), and the samples were coated with a thin layer of gold prior to analysis. 2.4. Adsorption Measurements. The CO2 adsorption experiments were performed at atmospheric pressure in a fixed bed reactor shown in Figure 2. In a typical adsorption process, 1 g of dried adsorbent was packed into the reactor which was a quartz glass tube (5 mm in diameter, 250 mm in length) with a temperature control device outside. The temperature could be controlled within ±0.5 °C. Both ends of the reactor were plug by quartz wool to reduce the loss of adsorbent during the adsorption process. The adsorbent was first degassed at 100 °C in a highly pure N2 stream at a flow rate of 100 mL/min for 1 h. When the adsorbent was cooled to the desired adsorption

2. EXPERIMENTAL SECTION 2.1. Materials. Magnesium oxide (MgO, 99.99%) and polyethylenimine (PEI, 99%) were purchased from Aladdin. Methanol (99.9%) was purchased from Concord Technology Co., Ltd. (Tianjin, China). Toluene (AR) and ethanol (AR) were purchased from Kermel Chemical Reagent, Ltd. (Tianjin, China). N2 (99.99%), NO (500 ppm in N2), SO2 (500 ppm in N2), CO2 (99.99%), and CO2 (15 v/v% in N2) were supplied B

DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 1. A schematic diagram of the synthesis of porous MgCO3 and the impregnation process of PEI.

Figure 2. Diagram of experimental apparatus for CO2 adsorption.

Figure 3. N2 adsorption/desorption isotherms (a) and pore size distribution curves (b) of the prepared groups of MgCO3.

the adsorption was considered to have finished until the outlet CO2 concentration was the same as that in the inlet. After adsorption, the gas was switched to pure N2 at the same flow rate to perform desorption at 100 °C, the cyclic adsorption

temperature and kept steady, the gas steam was switched to 100 mL/min of simulated flue gas for a CO2 adsorption test. The CO2 concentration at the outlet of the fixed bed was measured by an online CO2 analyzer (Xibi, GXH-510, China), C

DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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with the large specific surface area (190.5 m2/g) and pore volume, which made M4 an excellent support. It could be inferred that a proper amount of toluene could promote the pore formation and increase the specific surface area and the pore volume of MgCO3. It is worth noting that the mesopores are mainly located in the primary particles of MgCO3, which aggregate and form the porous MgCO3. 3.2. PEI-Modified Adsorbents. N2 adsorption/desorption isotherms and pore size distribution curves of adsorbents with different PEI loadings are shown in Figure 4a,b. The type-IV isotherm with a capillary condensation step between PS/P0 = 0.6−0.8 and uniform pore size distribution demonstrated the existence of mesopore in the PEI-modified adsorbents. With increasing PEI loading from 0 to 30 wt %, as expected, an obviously decrease in specific surface area, pore volume and pore size (Table 2) was observed as a result of the partial filling of pores by PEI, which indicated the successful modification with PEI. However, no significant change to the shape of curves was found, implying the pore structure was not destroyed after modification. Figure 5 shows the surface functionalities of the adsorbents before and after PEI modification. For all four samples, the

stability was tested by several cycles of CO2 adsorption/ desorption in the same manner. The CO2 capture capacity on an adsorbent was calculated by integrating the adsorption breakthrough curve. The integral equation of adsorption breakthrough curve is presented in eq 1: ÄÅ t ÉÑ ÅÅ Ñ 1 P Å v × (C0 − C) dt ÑÑÑÑ × Q= × ÅÅ Å Ñ (1) m ÅÇ 0 ÑÖ R × T where Q is the capture capacity of CO2 (mmol/g), m is the weight of adsorbent (g), v is the inlet gas flow rate (mL/min), C0 and C are the CO2 concentrations at the inlet and outlet of the fixed bed, respectively (vol %), t is the adsorption time (s), P is the operation pressure (kPa), T is the operation temperature (K), and R is the gas constant (8.314J·mol−1·K−1).

∫

3. RESULTS AND DISCUSSION 3.1. Characteristics of MgCO3 Supports. N2 adsorption/ desorption isotherms and pore size distribution curves of all MgCO3 prepared are shown in Figure 3a,b; and the specific surface area (SBET), pore volume (Vp), and average pore diameter (dp) are summarized in Table 2. As seen, M1 had the Table 2. Structural Properties of Unmodified and PEIModified MgCO3 Samples Revealed by BET Testing samples

SBET (m2/g)

Vp (mL/g)

dp (nm)

M1 M2 M3 M4 M5 10P-M 20P-M 30P-M

280 101 184.1 190.5 178.5 90.1 47.79 22.52

0.178 0.512 0.578 0.407 0.190 0.254 0.176 0.080

3.932 12.99 15.80 9.960 4.638 8.358 7.726 6.482

largest specific surface area among the 5 samples, but the microporous structure did not show the possibility to be the support. Despite the large pore volume and relatively narrow pore size distribution, the specific surface area of M2 was only 101 m2/g. The specific surface area and pore volume of M3 was appropriate, but the pore size distribution was too broad. The pore volume of M5 was small. As for M4, the isotherm was of IUPAC-defined type IV36 with an obvious hysteresis at high relative pressures, which strongly indicated a mesoporous structure and a concentrated pore size distribution, coupled

Figure 5. FTIR spectra of M4 and adsorbents with different PEI loadings.

bands observed at 860 cm−1, 1103 cm−1, and 1460 cm−1 correspond to the carbonate group37 and the broad absorbance

Figure 4. N2 adsorption/desorption isotherms (a) and pore size distribution curves (b) of M4 and adsorbents with different PEI loadings. D

DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research band at 3420 cm−1 corresponds to adsorbed water.38 Compared to the FTIR spectra of M4, some additional bands could be observed in that of PEI-modified samples. The band presented in 1580 cm−1 was associated with N−H bending vibration,39 while the band in 3270 cm−1 was due to N−H stretching vibration.40 Two bands for C−H stretching vibrations appeared at 2850 and 2940 cm−1.41 These bands were all characteristic bands of amine functional groups in PEI. It was also found that the intensity of the characteristic bands increased as the increase of PEI loading. Therefore, FTIR results further confirmed that PEI was incorporated into M4 effectively during impregnation. Figure 6 shows the SEM images of MgCO3 before and after PEI modification. Figure 6a clearly displays the porous textural

from the surface into the pore of the adsorbent and contact with the amino-active sites of PEI. The process of surface adsorption is mainly controlled by thermodynamics factors, whereas the process of the diffusion into the PEI from the surface is controlled by the kinetic resistance. The above two steps together determine the adsorption performance of CO2 on PEI loaded MgCO3. 3.3.1. Effect of PEI Loading on CO2 Adsorption. Figure 7a,b shows the breakthrough time decreased with increasing PEI loading at 25 and 40 °C. With the increasing of PEI loading, the porosity of adsorbents decreased and the PEI layers were thickened, so that the diffusion of CO2 into the depth of the PEI was hindered. At a low temperature, the CO2 adsorption remained diffusion-limited due to the high viscosity of PEI at low temperature.42 As a result, the CO2 capture capacity of highly PEI-loaded adsorbent was lower than that of the low PEI-loaded one. With the increase of PEI loading, the CO2 capture capacity increased first and then decreased both at 60 and 75 °C shown in Figure 7c,d; and the longest breakthrough time appeared in 20P-M. With increasing PEI loading, the active sites to CO2 adsorption increased, resulting in the increase of CO2 capture capacity correspondingly. However, when the loading was up to 30%, most of the pores were occupied, leading to a significant reduction of pore volume, which in turn increased the mass transfer resistance of CO2 entering the pores. As a result, the reaction between CO2 and the active site was difficult to proceed completely. Moreover, as shown in SEM image, excessive PEI adhered on the surface of porous MgCO3 support, leading to the agglomeration of primary particles of the adsorbent and the disappearing of active sites, which was not conducive to the adsorption process. In contrast, after loaded with sufficient amount of PEI, the 20P-M still retained certain porosity for CO2 entering the pores and reaching amino functional groups. 3.3.2. Effect of Temperature on CO2 Adsorption. Temperature has a direct influence on CO2 capture capacity in an adsorption process. As seen in Figure 8, for the adsorbents with low PEI loading (10P-M), the CO2 capture capacity decreased with increasing temperature, which indicated the adsorption process was thermodynamically controlled.43 It can be interpreted as that the interaction between CO2 and adsorbent was weakened due to the increasing of movement of CO2 molecules at higher temperature in the case of insufficient active sites to CO2. For the highly loaded adsorbents (20P-M, 30P-M), the CO2 capture capacity increased with increasing temperature, indicating a kinetic control over the adsorption process. There was a significant sterically hindered effect at high PEI loading, but the increase of temperature was beneficial to overcome the kinetic barriers and reduced the diffusion resistance, which was conducive to the diffusion of adsorbed CO2 from the surface into the bulk of PEI. 3.3.3. Effect of H2O on CO2 Adsorption. Water vapor is an important constituent in the flue gases from the power plant, accounting for about 10 vol %, which may affect CO2 capture. 20P-M was selected for further adsorption test due to its highest CO2 capture capacity. Figure 9a shows the CO2 breakthrough curves of 20P-M under various concentrations of water vapor at 75 °C. The results showed the breakthrough time was prolonged in the presence of 5 vol %, 10 vol %, and 15 vol % of water vapor and the corresponding CO2 capture capacities (Figure 9b) increased by 5.6%, 19.6%, and 11.2%, respectively, compared with dry flue gas. It indicated that the

Figure 6. SEM images of M4 (a), and adsorbents with different PEI loadings:10P-M (b), 20P-M (c), and 30P-M (d).

properties of M4. After PEI loading, the morphology changed significantly. 10P-M almost retained the original morphology of M4 (Figure 6b). For 20P-M, the uniform morphology suggested that the loaded PEI completely filled the pore channels of M4, which should benefit the CO2 adsorption (Figure 6c). With continuously increasing PEI loading up to 30 wt %, the adsorbent particles agglomerated clearly and larger clusters were discerned (Figure 6d), which strongly indicated that the loading amount of PEI was in excess of the accommodation capacity of M4, resulting in that the PEI not only occupied the majority of the pores but also coated or adhered on the external surface of the porous MgCO3, leading to the obvious agglomeration. The finding from SEM images is consistent with N2 adsorption/desorption results shown in Figure 3. However, the porous structures revealed by SEM imaging do not represent the mesopore in porous MgCO3, and the mesopores mainly exist in the primary particles of MgCO3. 3.3. CO2 Adsorption Properties. The CO2 adsorption experiments were performed in the fixed bed operated at 25 °C, 40 °C, 60 °C, and 75 °C, respectively. The breakthrough curves are shown in Figure 7. The capacity of CO2 capture was calculated based on eq 1, and the results are presented in Table 3. The results showed that capacity of CO2 capture was improved remarkably after PEI modification. 20P-M showed a CO2 capture capacity as high as 1.07 mmol/g. Briefly, the adsorption process of CO2 is divided into two steps. First, CO2 molecules were adsorbed on the surface of the adsorbent, after that, these adsorbed CO2 molecules diffuse E

DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 7. Breakthrough curves of CO2 of M4 and adsorbents with different PEI loadings at 25 °C (a), 40 °C (b), 60 °C (c), and 75 °C (d).

of CO2 adsorption on the amine-modified adsorbents is a result of the acid−base reaction.44 In the absence of water, the primary and secondary amines (RNH2, R2NH) included in PEI can react with CO2 to form ammonium carbamates at a molar ratio of 2:1, as shown in eqs 2 and 3. However, in the presence of water vapor, CO2 reacts with the amino functional groups to form bicarbonate ions, where only 1 mol of amino groups are consumed for the adsorption of 1 mol of CO2, as shown in eqs 4 and 5. Moreover, when the water vapor content increased further to 20 vol %, the capture capacity of CO2 decreased. It can be attributed to the water film formed by the excessive water vapor on the adsorbent, or the pore was blocking by the previously generated bicarbonate, thus hindering the contact between CO2 and amino active sites.

Table 3. CO2 Capture Capacities of M4 and Adsorbents with Different PEI Loadings CO2 capture capacities (mmol/g) samples

25 °C

40 °C

60 °C

75 °C

M4 10P-M 20P-M 30P-M

0.45 0.84 0.77 0.62

0.39 0.81 0.79 0.72

0.31 0.70 0.94 0.82

0.27 0.67 1.07 0.94

CO2 + 2RNH 2 → RNHCOO− + RNH+3

(2)

CO2 + 2R 2NH → R 2NCOO− + R 2NH+2

(3)

CO2 + RNH 2 + H 2O → RNH+3 + HCO−3

(4)

CO2 + R 2NH + H 2O → R 2NH+2 + HCO−3

(5)

3.3.4. Effect of NO on CO2 Adsorption. The breakthrough curves and CO2 capture capacities of 20P-M obtained at different NO concentrations in flue gas from 0 to 250 ppm are shown in Figure 9c,d. The data indicated that no obvious variation of CO2 capture capacity was observed with the increase of NO concentration, thus, NO had little influence on CO2 adsorption in the range of test concentrations. 3.3.5. Effect of SO2 on CO2 Adsorption. Figure 9e presents the breakthrough curves of 20P-M with SO2 concentrations of 0, 50, 100, 150, 200, and 250 mg/m3, respectively, and the

Figure 8. Effect of adsorption temperature on the CO2 capture capacities of M4 and adsorbents with different PEI loadings.

water vapor can greatly promote the CO2 adsorption performance of amine modified adsorbent. The mechanism F

DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 9. Effects of H2O, NO, and SO2 on the breakthrough curves (a), (c), (e), and CO2 capture capacity (b), (d), and (f) of 20P-M at 75 °C.

With the increase of adsorption/desorption recycle number, a slight reduction of the CO2 capture capacity was observed during the cyclic tests in both dry and humid flue gas. This drop could be most likely associated with the evaporation of the impregnated PEI in the process of CO2 desorption under flowing N2. About 92.5% and 93.7% of the CO2 capture capacity can be retained after 10 cycles for dry and humid flue gas, which indicated that the adsorbent had better stability under humid conditions compared with dry flue gas. The result showed the adsorbent 20P-M possessed excellent stability and regenerability during the cyclic operation.

calculated the CO2 capture capacities are shown in Figure 9f. With increasing SO2 concentration, an obvious drop can be seen on the CO2 capture capacities. When the concentration of SO2 was reached 250 mg/m3, the capture capacity of CO2 decreased by 14% compared with that without SO2. This phenomenon could be explained by that the acidity of SO2 is stronger than that of CO2, so that SO2 could effectively compete with CO2 to bind to the amine groups, leading to form thermally stable sulfite/sulfate compounds, which may block the pores of adsorbent.45 3.4. Cyclic Adsorption Stability Tests. Stability and regenerability are important parameters to evaluate the possibility of the adsorbent for potential industrial applications. The cyclic CO2 adsorption/desorption measurement of 20P-M was conducted over 10 cycles of adsorption at 75 °C and desorption at 100 °C under flowing N2 in dry flue gas and flue gas with 10 vol % H2O, respectively. The CO2 capture capacities at above-mentioned cycles are shown in Figure10.

4. CONCLUSIONS A variety of MgCO3 with different porous structures were successfully synthesized and characterized. The synthesis of MgCO3 was based on a facile and template-free method and utilized CO2 as reactant, allowing the porous MgCO3 to be new and promising CO2-storage materials. Meanwhile, the G

DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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ing (KLIEEE-15-02); Nature Science Foundation of Hebei Province (B2016502063) China; and NSERC Canada.

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(1) Vargas, D. P.; Balsamo, M.; Giraldo, L.; Erto, A.; Lancia, A.; Moreno-Piraján, J. C. Equilibrium and dynamic CO2 adsorption on activated carbon honeycomb monoliths. Ind. Eng. Chem. Res. 2016, 55, 7898−7905. (2) Sandhu, N. K.; Pudasainee, D.; Sarkar, P.; Gupta, R. Steam regeneration of polyethylenimine-impregnated silica sorbent for postcombustion CO2 capture: a multicyclic study. Ind. Eng. Chem. Res. 2016, 55, 2210−2220. (3) Fu, D.; Zhang, P.; Wang, L. M. Absorption performance of CO2 in high concentrated [Bmim][Lys]-MDEA aqueous solution. Energy 2016, 113, 1−8. (4) Zhang, P.; Tian, X. F.; Fu, D. CO2 removal in tray tower by using AAILs activated MDEA aqueous solution. Energy 2018, 161, 1122−1132. (5) Castellazzi, P.; Notaro, M.; Busca, G.; Finocchio, E. CO2 capture by functionalized alumina sorbents: DiEthanolAmine on γ-alumina. Microporous Mesoporous Mater. 2016, 226, 444−453. (6) Hahn, M. W.; Jelic, J.; Berger, E.; Reuter, K.; Jentys, A.; Lercher, J. A. Role of amine functionality for CO2 chemisorption on silica. J. Phys. Chem. B 2016, 120, 1988−1995. (7) Jing, Y.; Wei, L.; Wang, Y.; Yu, Y. Synthesis, characterization and CO2 capture of mesoporous SBA-15 adsorbents functionalized with melamine-based and acrylate-based amine dendrimers. Microporous Mesoporous Mater. 2014, 183, 124−133. (8) Wang, J.; Chen, H.; Zhou, H.; Liu, X.; Qiao, W.; Long, D.; Ling, L. Carbon dioxide capture using polyethylenimine-loaded mesoporous carbons. J. Environ. Sci. 2013, 25, 124−132. (9) Balsamo, M.; Budinova, T.; Erto, A.; Lancia, A.; Petrova, B.; Petrov, N.; Tsyntsarski, B. CO2 adsorption onto synthetic activated carbon: Kinetic, thermodynamic and regeneration studies. Sep. Purif. Technol. 2013, 116, 214−221. (10) Xian, S.; Wu, Y.; Wu, J.; Wang, X.; Xiao, J. Enhanced dynamic CO2 adsorption capacity and CO2/CH4 selectivity on polyethylenimine-impregnated UiO-66. Ind. Eng. Chem. Res. 2015, 54, 11151− 11158. (11) Quang, D. V.; Soukri, M.; Tanthana, J.; Sharma, P.; Nelson, T. O.; Lail, M.; Coleman, L. J. I.; Abu-Zahra, M. R. M. Investigation of CO2 adsorption performance and fluidization behavior of mesoporous silica supported polyethyleneimine. Powder Technol. 2016, 301, 449− 462. (12) 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. (13) Yao, M.; Dong, Y.; Hu, X.; Feng, X.; Jia, A.; Xie, G.; Hu, G.; Lu, J.; Luo, M.; Fan, M. Tetraethylenepentamine-modified silica nanotubes for low-temperature CO2 capture. Energy Fuels 2013, 27, 7673− 7680. (14) Kuwahara, Y.; Kang, D. Y.; Copeland, J. R.; Brunelli, N. A.; Didas, S. A.; Bollini, P.; Sievers, C.; Kamegawa, T.; Yamashita, H.; Jones, C. W. Dramatic enhancement of CO2 uptake by poly (ethyleneimine) using zirconosilicate supports. J. Am. Chem. Soc. 2012, 134, 10757−10760. (15) Liu, Y.; Lin, X.; Wu, X.; Liu, M.; Shi, R.; Yu, X. Pentaethylenehexamine loaded SBA-16 for CO2 capture from simulated flue gas. Powder Technol. 2017, 318, 186−192. (16) Dao, D. S.; Yamada, H.; Yogo, K. Large-pore mesostructured silica impregnated with blended amines for CO2 capture. Ind. Eng. Chem. Res. 2013, 52, 13810−13817. (17) Wang, J.; Huang, L.; Yang, R.; Zhang, Z.; Wu, J.; Gao, Y.; Wang, Q.; O’Hare, D.; Zhong, Z. Recent advances in solid sorbents for CO2 capture and new development trends. Energy Environ. Sci. 2014, 7, 3478−3518. (18) Yu, C. H.; Huang, C. H.; Tan, C. S. A review of CO2 capture by absorption and adsorption. Aerosol Air Qual. Res. 2012, 12, 745−769.

Figure 10. CO2 capture capacity of 20P-M during 10 cycles of CO2 adsorption/desorption in dry and 10 vol % H2O contained flue gas.

synthesis strategy developed is also beneficial to the potential utilization of CO 2 . Among those as-prepared MgCO 3 materials, M4 with the optimal morphology was selected as support for CO2 adsorbent. A series of adsorbents with different PEI loadings were prepared by effective impregnation while the microstructure of the adsorbents was well maintained afterward. The capacity of CO2 capture in PEI-modified adsorbents was significantly increased, particularly for the adsorbent with 20% PEI loading (4 times higher than the one without PEI at 75 °C, up to 1.07 mmol/g). At low temperature (25 and 40 °C), because of the sterically hindered effect, adsorbents with relatively low PEI loading performed better than the highly loaded ones. On the contrary, the high PEIloaded adsorbents were advantageous at higher temperature (60 and 75 °C) where the diffusion resistance was reduced. Moreover, CO2 adsorption could be promoted by a proper amount of water vapor coexisted, i.e., 19.8% enhancement in the presence of 10 vol % H2O. NO had little effect on CO2 adsorption, whereas SO2 had a negative effect on the adsorption due to the strong acidic impact, thus it is important to remove SO2 prior to CO2 adsorption. Overall, the PEIimpregnated MgCO3 is a promising adsorbent toward CO2 capture, attributed to various advantages including the high capture capacity at relatively high temperature, low regeneration temperature, and the utilization of CO2 during the preparation.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Tel: 1-506-453-3532. E-mail: [email protected]. ORCID

Jie Liu: 0000-0002-9685-5825 Huining Xiao: 0000-0003-3500-2308 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Fundamental Research Funds for the Central Universities (2016XS111, 2017MS138, and 2016MS109); NSF China (Grant #: 51379077, 21507029, 21501138, and 21466005); Open Foundation of Key Laboratory of Industrial Ecology and Environmental EngineerH

DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research

cellular foam (MCF) in humidified gas. Microporous Mesoporous Mater. 2014, 186, 84−93. (41) Drage, T. C.; Arenillas, A.; Smith, K. M.; Snape, C. E. Thermal stability of polyethylenimine based carbon dioxide adsorbents and its influence on selection of regeneration strategies. Microporous Mesoporous Mater. 2008, 116, 504−512. (42) Sanz, R.; Calleja, G.; Arencibia, A.; Sanz-Pérez, E. S. CO2 adsorption on branched polyethyleneimine-impregnated mesoporous silica SBA-15. Appl. Surf. Sci. 2010, 256, 5323−5328. (43) Heydari-Gorji, A.; Belmabkhout, Y.; Sayari, A. Polyethylenimine-impregnated mesoporous silica: effect of amine loading and surface alkyl chains on CO2 adsorption. Langmuir 2011, 27, 12411− 12416. (44) Didas, S. A.; Kulkarni, A. R.; Sholl, D. S.; Jones, C. W. Role of amine structure on carbon dioxide adsorption from ultradilute gas streams such as ambient air. ChemSusChem 2012, 5, 2058−2064. (45) Rezaei, F.; Jones, C. W. Stability of supported amine adsorbents to SO2 and NOx in postcombustion CO2 capture. 1. singlecomponent adsorption. Ind. Eng. Chem. Res. 2013, 52, 12192−12201.

(19) Lee, C. H.; Hyeon, D. H.; Jung, H.; Chung, W.; Jo, D. H.; Shin, D. K.; Kim, S. H. Effects of pore structure and PEI impregnation on carbon dioxide adsorption by ZSM-5 zeolites. J. Ind. Eng. Chem. 2015, 23, 251−256. (20) Martínez, F.; Sanz, R.; Orcajo, G.; Briones, D.; Yángüez, V. Amino-impregnated MOF materials for CO2 capture at postcombustion conditions. Chem. Eng. Sci. 2016, 142, 55−61. (21) Guo, L.; Yang, J.; Hu, G.; Hu, X.; DaCosta, H.; Fan, M. CO2 removal from flue gas with amine-impregnated titanate nanotubes. Nano Energy 2016, 25, 1−8. (22) Kishor, R.; Ghoshal, A. K. Amine-modified mesoporous silica for CO2 adsorption: The role of structural parameters. Ind. Eng. Chem. Res. 2017, 56, 6078−6087. (23) Rao, N.; Wang, M.; Shang, Z.; Hou, Y.; Fan, G.; Li, J. CO2 adsorption by amine-functionalized MCM-41: a comparison between impregnation and grafting modification methods. Energy Fuels 2018, 32, 670−677. (24) Kishor, R.; Ghoshal, A. K. Polyethylenimine functionalized assynthesized KIT-6 adsorbent for highly CO2/N2 selective separation. Energy Fuels 2016, 30, 9635−9644. (25) Chen, C.; Zhang, S.; Row, K. H.; Ahn, W. S. Amine-silica composites for CO2 capture: A short review. J. Energy Chem. 2017, 26, 868−880. (26) Guo, X.; Ding, L.; Kanamori, K.; Nakanishi, K.; Yang, H. Functionalization of hierarchically porous silica monoliths with polyethyleneimine (PEI) for CO2 adsorption. Microporous Mesoporous Mater. 2017, 245, 51−57. (27) Son, W. J.; Choi, J. S.; Ahn, W. S. Adsorptive removal of carbon dioxide using polyethyleneimine-loaded mesoporous silica materials. Microporous Mesoporous Mater. 2008, 113, 31−40. (28) Yan, X.; Zhang, L.; Zhang, Y.; Yang, G.; Yan, Z. Aminemodified SBA-15: effect of pore structure on the performance for CO2 capture. Ind. Eng. Chem. Res. 2011, 50, 3220−3226. (29) Ahmed, S.; Ramli, A.; Yusup, S. Development of polyethylenimine-functionalized mesoporous Si-MCM-41 for CO 2 adsorption. Fuel Process. Technol. 2017, 167, 622−630. (30) 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. (31) Zhang, Z.; Ma, X.; Wang, D.; Song, C.; Wang, Y. Development of silica-gel-supported polyethylenimine sorbents for CO2 capture from flue gas. AIChE J. 2012, 58, 2495−2502. (32) Gérardin, C.; Reboul, J.; Bonne, M.; Lebeau, B. Ecodesign of ordered mesoporous silica materials. Chem. Soc. Rev. 2013, 42, 4217− 4255. (33) Garcia-Bennett, A. E. Synthesis, toxicology and potential of ordered mesoporous materials in nanomedicine. Nanomedicine 2011, 6, 867−877. (34) Forsgren, J.; Frykstrand, S.; Grandfield, K.; Mihranyan, A.; Strømme, M. A template-free, ultra-adsorbing, high surface area carbonate nanostructure. PLoS One 2013, 8, No. e68486. (35) Yue, M. B.; Chun, Y.; Cao, Y.; Dong, X.; Zhu, J. H. CO2 capture by as-prepared SBA-15 with an occluded organic template. Adv. Funct. Mater. 2006, 16, 1717−1722. (36) Gregg, S. J.; Sing, K. S. W.; Salzberg, H. W. Adsorption surface area and porosity. J. Electrochem. Soc. 1967, 114, 279C−279C. (37) Zhang, P.; Forsgren, J.; Strømme, M. Stabilisation of amorphous ibuprofen in Upsalite, a mesoporous magnesium carbonate, as an approach to increasing the aqueous solubility of poorly soluble drugs. Int. J. Pharm. 2014, 472, 185−191. (38) Ma, X.; Wang, X.; Song, C. “Molecular basket” sorbents for separation of CO2 and H2S from various gas streams. J. Am. Chem. Soc. 2009, 131, 5777−5783. (39) Ghoul, M.; Bacquet, M.; Crini, G.; Morcellet, M. Novel sorbents based on silica coated with polyethylenimine and crosslinked with poly (carboxylic acid): preparation and characterization. J. Appl. Polym. Sci. 2003, 90, 799−805. (40) Subagyono, D. J. N.; Marshall, M.; Knowles, G. P.; Chaffee, A. L. CO2 adsorption by amine modified siliceous mesostructured I

DOI: 10.1021/acs.iecr.8b06153 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX