Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

An experimental investigation of mesoporous MgO as a potential pre-combustion CO2 sorbent

An experimental investigation of mesoporous MgO as a potential pre-combustion CO2 sorbent Mater Renew Sustain Energy (2015) 4:8 DOI 10.1007/s40243-015-0050-0 ORIGINAL PAPER An experimental investigation of mesoporous MgO as a potential pre-combustion CO sorbent 1 1 1 1 • • • Sushant Kumar Surendra K. Saxena Vadym Drozd Andriy Durygin Received: 10 May 2014 / Accepted: 8 May 2015 / Published online: 22 May 2015 The Author(s) 2015. This article is published with open access at Springerlink.com Abstract We examined the CO capture capacity of to be the major CO contributor [2].There are three main 2 2 mesoporous MgO (325 mesh size, surface technological approaches for CO capture- post-, oxy- and area = 95.08 ± 1.5 m /g) as a potential pre-combustion pre-combustion. Post-combustion systems capture CO CO sorbent. Our results show that 96.96 % of MgO was from N -rich flue gas stream, produced by burning fossil 2 2 converted to MgCO at 350 C and 10 bars CO pressure. fuel in air. Oxy-combustion uses pure stream of O , instead 3 2 2 The sorbent could be completely regenerated at 550 C of air, to combust coal and thus produces CO -rich gas under argon flow. The sorption rate parameters such as stream. On the other hand, pre-combustion systems are surface area and pore size were investigated. designed mainly to remove CO from the syngas (CO ? H ) prior to its combustion for power production Keywords Capture capacity  Mesoporous [3]. Under pre-combustion conditions, after the water–gas Pre-combustion  Sorbent  Surface area  Pore size shift reactor ðCO þ H O ! CO þ H Þ, the gas stream 2 2 2 mainly consists of CO ,H O and H . The partial CO 2 2 2 2 pressure for pre-combustion capture conditions is around Introduction 20–30 bar and the temperature is between 250 and 450 C [4]. Fossil fuel accounts for the world’s major energy supply Both the physical and chemical solvents can be used for and its use is anticipated to be continued throughout the pre-combustion CO capture. Unlike chemical solvent, 21st century [1]. The use of fossil fuel is always accom- physical solvent (such as Selexol and Rectisol) selectively panied with a vast emission of CO . The anthropogenic absorbs CO without forming any chemical bonds. Thus, CO emissions upset the natural carbon cycle leading to an the physical solvent requires relatively less regeneration increased atmospheric CO concentration. No one can deny energy as compared to that of chemical solvent [5]. that there is an urgent need to develop methods for CO However, these physical solvent-based processes suffer mitigation. severe disadvantages: (1) lose pressure during regeneration Currently, a large focus is devoted on capturing CO step, and (2) require a low operating temperature. There- from coal-fired power plant flue streams, which continues fore, syngas needs to be cooled prior to CO absorption step to attain a relatively low operating temperature. After CO absorption, the remaining hydrogen gas stream re- Electronic supplementary material The online version of this quires to be reheated to the gas turbine inlet temperature. article (doi:10.1007/s40243-015-0050-0) contains supplementary However, chemical solvents have the advantage of high material, which is available to authorized users. mass transfer driving force into solution and better acid gas & Sushant Kumar selectivity. Also, chemical solvents can be used in pro- skuma002@fiu.edu cesses that utilize thermal swing regeneration and generate the CO at elevated pressure [6]. But chemical solvents 1 2 Center for the Study of Matter at Extreme Conditions, increase the energy and cost penalty and thus are down- College of Engineering and Computing, Florida International graded as a future CO sorbent [7]. University, Miami, FL 33199, USA 123 8 Page 2 of 8 Mater Renew Sustain Energy (2015) 4:8 Currently, the focus is to develop advanced physical and the use in IGCC applications. Therefore, we study the CO chemical solvent systems that have the potential to provide capture capacity of MgO in the relatively high temperature significant improvements in both cost and performance as and pressure condition of 300–375 C and 10–50 bars, compared to the Selexol and Rectisol for pre-combustion respectively. CO capture. The challenges are to modify regeneration conditions to recover the CO at a higher pressure, improve selectivity to reduce H losses, and develop a solvent that Experimental procedure has a high CO loading at a higher temperature, which would increase integrated gasification combined cycle The reaction (IGCC) efficiency. In the same line, another vital task is to MgOðÞþ s CO ðÞ g $ MgCO ðÞ s develop a new sorbent which could be highly efficient for was studied experimentally. The carbonation reaction was pre-combustion capture conditions. Consequently, the US performed in a closed system which permits us to effi- Department of Energy (DOE) performed the thermody- ciently maintain high temperature and pressure for a long namic modeling activities that included screening analyses period of time. The decomposition reaction of carbonate for a number of different metal oxides, zirconates, silicates was examined using Thermo gravimetric Analysis (TGA) and titanates under various operating conditions to identify technique. new solid sorbents for pre-combustion CO capture. About About 0.2 g of 325-mesh-sized magnesium oxide (de- 18 sorbents were modeled and finally seven candidates are livered by Alfa Aesar) was put inside a closed cylindrical chosen—magnesium oxide (MgO), calcium oxide (CaO), 00 00 vessel (1.25 long and 0.35 internal diameter). About lithium zirconate (Li ZrO ), calcium zirconate (CaZrO ), 2 3 3 0.1 ml of water was also introduced on the vessel walls. barium zirconate (BaZrO ), barium titanate (BaTiO ) and 3 3 Chemically pure CO gas (Airgas) was passed into this barium silicate (BaSiO ) for further investigations [8]. 2 system. Before experiments, CO gas was flushed three Among these solid sorbents, MgO and CaO are attractive times to ensure a pure CO atmosphere inside the reactor. because of their easy accessibility and favorable thermo- 2 The reaction was performed for 30 min at a desired tem- dynamic properties [9]. perature and pressure condition. Once the reaction com- The alkaline earth metal oxides (such as CaO and MgO) pleted, the system was air-cooled. The product was then combine with CO to form thermodynamically stable car- ground using mortar and pestle. The powder particle was bonates. Metal carbonates, when heated, liberate pure again put back for another reaction at the same ex- stream of CO gas and regenerate the oxides. Eventually, perimental condition. This cycle was repeated until no in- the generated pure CO gas can either be sequestered un- crement in weight of the product was observed. derground or used for enhanced oil recovery [10]. CaO are Thermo gravimetric analysis (TGA) of the product was abundant and thus relatively easily accessible than MgO. done using TGA 2950 Thermo gravimetric analyzer. The However, CaO as CO sorbent suffers severe major samples (10 mg) were heated under argon purge, at a drawbacks and a detailed discussion can be found else- heating rate of 10 C/min to a final temperature of 800 C. where [11]. It is a fact that regeneration of oxides needs a The TGA provides continuous measurements of the sample lot of energy [12]. MgO and Mg(OH) are known to be weight as a function of time and temperature. The amount better candidates than CaO for CO capture applications of formation of MgCO was analyzed by the percent loss in due to their low regeneration energy requirement and low weight of the sample while heating up to 800 Cinan operating temperature [13]. Thus, MgO (periclase), argon atmosphere. although occurs only rarely as an oxide, we choose it here The product characterization was performed using X-ray for our study. One should note that MgO when recycled powder diffraction method. Bruker GADDS/D8 is equip- between naturally occurring magnesite or dolomite can ped with Apex Smart CCD Detector and direct-drive ro- cause relatively lesser energy or carbon emission penalty tating anode. The MacSci rotating anode (Molybdenum) [14]. operates with a 50 kV generator and 20 mA current. X-ray The CO absorption capacity of MgO was studied as a beam size can vary from 50 to 300 lm. The usual collec- function of particle size, surface area, temperature, pres- tion time is 1200 s. sure, support and concentration of water vapor. The CO An isothermal gas adsorption was employed to measure uptake capacity on different MgO sorbents at different internal surface areas of the powder particles. Mi- conditions is listed in Table 1. Most of the experiments are cromeritics Tristar II 3020 (surface area and porosimetry restricted to low temperature and ambient or low pressure analyzer instrument) was used with N as adsorptive gas at condition. Hence, the reported sorption capacities of CO 77 K (liquid nitrogen bath). The samples were first de- on MgO are not very high. However, the sorbents which gassed under 300 C with a N gas flow for 1 h to remove can operate in the range of 300–350 C would be ideal for 2 123 Mater Renew Sustain Energy (2015) 4:8 Page 3 of 8 8 Table 1 CO uptake capacity of MgO obtained from the literature Sorbent Gas stream Carbonation Pressure (bar) or, Particle Size Regeneration CO capture capacity References temperature flow rate temperature (mmol/g) (C) (C) conversion, % 1 MgO Pure CO 50–1000 100 mL/min (flow rate) – – 0.99 [15] 2 MgO/Al O (10 wt. % MgO) (13 v % H O, 13 v % CO ) 30, 150 1 (20–40) mesh size 350 1.36 [16] 2 3 2 2 3 MgO (11 v % H O, 1 v % CO ) 50–100 0.01 – 150–400 1.05 [17] 2 2 4K CO /MgO (11 v % H O, 1 v % CO ) 50–100 – – 150–400 2.98 [17] 2 3 2 2 5 MgO 330/660 ppm in air 0, 100 0.2 – – 0.64, 0.43 [18, 19] 6 MgO/MCM-41 Pure CO 25 1 – – 1.06 [20] 7 Mesoporous MgO Pure CO 25, 100 1 – – 1.82, 2.27 [21] 8 Nonporous MgO Pure CO 25 1 – – 0.45 [21] 9 MgO–ZrO Pure CO 30, 150 1 – – 1.15,1.01 [22, 23] 2 2 10 MgO (31.7 wt%)/Al O (22.4 wt%) Pure CO 20, 200, 300 1 – – 0.13, 0.24, 0.5 [24] 2 3 2 11 MgO (33.8 wt%)/ Al O (20.8 wt%) Pure CO 20, 200, 300 1 – – 0.08, 0.12, 0.5 [24] 2 3 2 12 K CO /MgO/Al O Flue gas 60 1 – 480 2.49 [25] 2 3 2 3 13 K CO /MgO (9 v % H O, 1 v % CO ) 60 40 mL/min (flow rate) – 400 2.7 [26] 2 3 2 2 14 MgO nanocrystal Flue gas 60 25sccm (flow rate) 5 nm 60–600 6.4 [27] 15 MgO Pure CO 350 1.33, 3.33 – – 0.089, 0.091 [28] 16 MgO Pure CO 300–500 9–36 \44 lm – 70–80 % (*200 min) [29] 17 MgO Pure CO – 20–40 \44 lm – 100 % (*120 min) [30] 2 8 Page 4 of 8 Mater Renew Sustain Energy (2015) 4:8 the moisture and other adsorbed gases before analysis. The Figure 2 depicts the adsorption/absorption model for internal surface area was calculated using the Brunauer– MgO–CO –H O reaction. Based on the previous work, it 2 2 Emmett–Teller (BET) method. The pore volume was also could be reasonable to corroborate that water vapor sur- 2- calculated from the adsorbed nitrogen after complete pore rounds MgO particles where CO reacts to form CO 2 3 ? ?2 condensation (P/P = 0.9925) using the ratio of the den- ions and H ions [34–36]. Free Mg ions could further 2- sities of liquid and gaseous nitrogen. The pore size was react with the CO ions to form MgCO . However, 3 3 calculated using the Barrett–Joyner–Halenda (BJH) MgCO forms an impervious layer around unreacted MgO method. particles and hinders the further diffusion of CO molecules. Here, we used mortar and pestle to grind the product. As Results and discussion mentioned earlier, we conducted each experiment for 30 min and ground the sample after that. Grinding helps in Figure 1 confirms the formation of MgCO at different scrubbing off the outer nonporous layer of MgCO . And we temperatures and CO pressures. MgO, Mg(OH) , 2 2 performed grinding until we noticed no change in product MgO2MgCO and MgCO were identified conventionally 3 3 weight after subsequent experiments. In general, after 3–4 by their corresponding Joint Committee Powder Diffrac- cycles, we observed no change in the weight of product. It tion Standard (JCPDS) card number 79-0612,82-2345,31- is certain that such intermittent grinding step is limited to 0804 and 86-2345, respectively. the laboratory and cannot be seen as an industrial op- One of the vital factors in gas–solid carbonation reaction eration. Therefore, it is recommended to have an ag- is the presence of water and there have been numerous gregative fluidization regime for a fluidized bed reactor observations where water acts as a catalyst [31–34]. while scaling up MgO–CO reaction. Also, increasing the Therefore, we have also used water (0.1 ml) for the MgO– amount of water vapor cannot lead to the complete car- CO reaction. In absence of water, no CO was absorbed at 2 2 bonate conversion of MgO. Thus, in addition to the amount these conditions due to the kinetic limitations. The CO of steam, surface properties of MgO (such as surface area, sorption capacity of MgO increases significantly in the particle size, porosity) are also very crucial parameters for presence of water vapor. Under humid condition, MgO the carbonation process. rapidly locks CO in the form of MgCO . Recently, 2 3 The thermal analysis curve does not show any sig- Fagerlund et al. [29] proposed the reaction mechanism for nificant differences in amounts of carbonate in the high- MgO carbonation in the presence of steam: pressure (50 bars) experiments. We obtained almost similar TGA plots and XRD patterns for different temperatures MgO þ H O $ MgO  H O 2 2 300–375 C and 50 bars CO pressure. However, the ex- MgO  H O þ CO $ MgCO þ H O 2 2 2 periment performed at 300 C and 10 bars did indicate that MgO þ CO $ MgCO the product was not simply MgCO . The X-ray diffraction 2 3 1- MgCO (86-2345) 1- MgCO (86-2345) (a) (b) 2- MgO (79-0612) 2- MgO (79-0612) 3- Mg(OH) (82-2453) 4- MgO.2MgCO (31-0804) 4- MgO.2MgCO (31-0804) 375°C 350°C 350°C 1 1 2 1 1 11 1 1 325°C 300°C 1 1 300°C 1 1 1 1 1 1 1 1 1 4 1 1 1 1 1 4 3 1 2 4 3 10 20 30 10 20 30 2Θ (degrees) 2Θ (degrees) Fig. 1 XRD patterns for MgCO formation after reaction at various temperatures and CO pressure of a 10 bars and b 50 bars 3 2 123 dm/dT dm/dT Mater Renew Sustain Energy (2015) 4:8 Page 5 of 8 8 Fig. 2 The adsorption/absorption model for MgO–CO –H O reaction 2 2 (a) 1.5 (b) 1.5 (350°C,10 bars) (300°C,10 bars) 1.0 1.0 6.5% 0.5 0.5 11.5% 0.0 0.0 ~345°C ~474°C -0.5 -0.5 50.7 % ~539°C 25.01% ~550°C -1.0 -1.0 60 60 -1.5 -1.5 -2.0 -2.0 40 -2.5 40 -2.5 100 200 300 400 500 600 700 100 200 300 400 500 600 700 Temperature (C) Temperature (C) Fig. 3 DTG plots for product at a 300 C and 10 bars and b 350 C and 10 bars pattern in Fig. 1a confirms the presence of Mg (OH) and The steps to calculate % conversion of MgO to relatively high amount of MgO2MgCO at 300 C and 10 MgCO is explained in supplementary section [S1]. A 3 3 bars. DTG curve (Fig. 3a) also evidences the similar si- conversion of 30.54 and 96.96 % for MgO to MgCO was tuation. The two peaks around 350 and 475 C were at- observed at 300 and 350 C, respectively. Here, we ob- tributed to the losses of water of crystallization and served the formation of relatively high amount of oxy- hydroxyl water, respectively. However, another peak at magnesite (MgO2MgCO )at300 C and 10 bars. It can 550 C corresponds to the complete decomposition of be easily calculated that the CO capture capacity of MgCO . But at a temperature and pressure of 350 C and oxymagnesite is about two-third that of MgCO . Hence, 3 3 10 bars, respectively, only MgCO was formed. This is formation of oxymagnesite can markedly reduce the evidenced by both DTG (Fig. 3b) and X-ray diffraction overall uptake of CO by MgO particles. However, it can analysis (Fig. 1a). be observed from X-ray patterns (Fig. 1) that at higher % Weight % Weight 8 Page 6 of 8 Mater Renew Sustain Energy (2015) 4:8 Table 2 Surface properties of MgO particles before and after carbonation reaction 350 C, 10 bars 2 3 6 -1 Sample Surface area (m /g) Pore volume (cm /g) Pore size (nm) SA/PV(10 m ) As-received MgO 95.08 ± 1.5 0.22 9.09 439.59 After reaction at (350 C, 10 bars) 4.15 ± 0.05 0.01 16.25 246.15 temperature or pressure, the formation of oxymagnesite is suppressed. In the same line, recent study reveals that oxymagnesite 120 (a) MgO Powder forms as an intermediate during the thermal decomposition Surface area = 95.08m /g of hydrated magnesium carbonate [37]. Moreover, oxy- magnesite can also be formed as a product of reaction between Mg (OH) and CO in anhydrous synthesis [29] Desorption 2 2 and/or solid-state reaction of MgO and CO using steam [38]. In this regard, Duan et al. [13] calculated the phase Adsorption diagram of MgO–Mg(OH) –MgCO , which suggests that 2 3 the transition temperature for direct conversion of MgCO to Mg(OH) increases with increase in P . Here, when 2 H2O temperature increases from 300 to 350 C, partial pressure 0.2 0.4 0.6 0.8 1.0 of water also increases and consequently transition tem- Relative Pressure, P/P perature also increased. At 300 C, a relatively less amount of MgO transforms to its carbonates. This can be attributed Fig. 4 N adsorption–desorption isotherm of as-received MgO to a possible high conversion of MgCO to Mg(OH) , 3 2 which is in agreement with the phase diagram. Moreover, a received MgO follows Type IV isotherms (as per IUPAC significant formation of oxymagnesite at 300 C and 10 classification); typical for mesoporous substances [39]. bars also leads to a less direct conversion of MgO to Also, the hysteresis pattern is H3 (following IUPAC clas- MgCO . Thus, it can be deduced that a high amount of sification) indicating the presence of slit-like pores. After oxymagnesite forms at a low partial pressure of water. capture of CO at 350 C and 10 bars, surface area dra- Therefore, the reaction mechanism is changed to: matically decreased to (4.15 ± 0.05) m /g. The ratio of MgO þ CO $ MgCO surface area to pore volume is also reduced by almost half and results in high diffusion paths. The significant decrease MgO þ 2MgCO $ MgO  2MgCO 3 3 in surface area attributes to the basicity of mesoporous MgO  2MgCO þ CO $ 3MgCO 3 3 MgO. The mesoporous MgO is highly basic with well- Moreover, at 50 bars of CO pressure and a temperature of ordered pores to hold high CO at both lower and higher 2 2 300 C, MgO has the highest yield of 98.54 %. At high temperatures. It is well known that porous materials allow temperatures (300–375 C) but constant pressure (50 bars), molecules to pass through their pore aperture for storage, we observe a slight but continuous decrease in the ab- separation or conversion [36]. MgO with a fine particle size sorption of CO , which is in congruence with previously (\44 lm) has a high content of mesopores, which leads to reported results [30]. It is well known that at low tem- good mass transfer properties during the absorption pro- perature, the physisorption process dominates but at cess. The mechanism for metal oxide reaction with CO elevated temperature CO chemisorbs on MgO and thus gas has been discussed a lot [40–43]. CO molecules dif- CO uptake capacity gradually starts decreasing. fuse through the pores of mesoporous MgO and the present CO -uptake capacity of a metal oxide is primarily large active sites hold these CO molecules [19]. The dominated by the factors such as surface area, pore volume, trapped CO molecules further react to form MgCO . 2 3 pore functionality and pore size [28]. BET surface area It can be observed from Table 2 that at 350 C and 10 measurement, pore volume and average pore sizes pre- bars, 96.96 % of MgO was converted to MgCO and almost sented in Table 2 indicates the significant role of CO to all the pores have been utilized after reaction with CO 2 2 influence the particle structure. As received, 325 mesh size molecules. Henceforth, almost no CO molecules could mesoporous MgO has a pore size of 9.09 nm and a high have diffused further in the pores. Noticeably, pore size surface area (95.08 ± 1.5 m /g). Figure 4 illustrates that increased to 16.25 nm. Thus, it is apparent that the porosity the N adsorption–desorption isotherm curves for as- of MgO particles plays a very vital role for CO uptake. 2 2 Quantity adsorbed (cm /g) STP Mater Renew Sustain Energy (2015) 4:8 Page 7 of 8 8 Previously, Beruto et al. has reported a very low CO temperature and pressure. Interestingly, the present study absorption capacity of MgO in absence of water vapor [27]. also illustrate that a high amount of oxymagnesite forms at a An uptake capacity of 0.089 and 0.091 mmol CO /g MgO low partial pressure of water. was observed at 350 C in 1.33 and 3.33 bars of CO , re- Open Access This article is distributed under the terms of the spectively. Thus, it was concluded that there is a high acti- Creative Commons Attribution 4.0 International License (http:// vation energy barrier to MgO recarbonation. On the contrary, creativecommons.org/licenses/by/4.0/), which permits unrestricted Feng et al. [14] heated the sorbent (MgO) to 1000 C in pure use, distribution, and reproduction in any medium, provided you give CO and noted a low but almost constant (for 8 cycles) ab- appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were sorption capacity of 0.99 mmol CO /g MgO. Thus, unlike made. CaO-based sorbents, MgO does not show a fast decline in their CO capture capacity over a large number of car- bonation–calcination cycles. Bhagiyalakshmi et al. [20] synthesized basic mesoporous MgO (surface area of 250 m / References g) using mesoporous carbon obtained from SBA-15 and obtained a maximum CO adsorption of 2.27 mmol CO /g at 2 2 1. Kumar, S.: Clean hydrogen production methods, Springer Briefs in energy. Springer, New York (2015) 100 C and nearly 1.81 mmol CO /g at 25 C for a feed flow 2. Merkel, T.C., Lin, H., Wei, X., Baker, R.: Power plant post- rate of 30 ml/min CO gas (99.9 % purity). Therefore, it is combustion carbon dioxide capture: an opportunity for mem- evident that even for a relatively lower surface area (95 m /g branes. J. Membr. Sci. 359, 126–139 (2010) compared to 250 m /g), MgO can have a better CO uptake 2 3. Davison, J.: Performance and costs of power plants with capture at a higher temperature (here, 300–375 C) and higher CO and storage of CO . Energy 32, 1163–1176 (2007) 4. Burton, B.P., Dupin, N., Fries, S.G., Grimvall, G., Fernandez pressure (10–50 bars). Recently, Fagerlund et al. [28] re- Guillermet, A., Miodownik, P., Oats, W. A., Vinograd, V., Z. ported a very high % conversion of MgO to MgCO under Metallkd 92, 514 (2001) high temperature and pressure conditions. However, MgO 5. Miller, B., Tillman, D.: Combustion engineering issues for solid fuel systems. pp. 449–451. Elsevier (2008) showed a slow conversion rate (50 % for *7 h) for the 6. DOE/NETL: Carbon dioxide capture and storage RD&D road- condition [P (*18–19 bar), P (*1–2 bar) and CO2 H2O map, (2010) 300–350 C] which can be suitable for pre-combustion 7. Yu, C.H., Huang, C.H., Tan, C.S.: A review of CO capture by capture process. The reason could be the deposition of im- absorption and adsorption. Aerosol Air Qual. Res. 12, 745–769 (2012) pervious carbonate layer on the surface of MgO which does 8. Evaluation of Dry Sorbent Technology; Presentation at the 2010 not allow CO molecules to further diffuse in the pores. NETL CO Capture Technology Meeting, Pittsburgh, PA, Therefore, continuous removal of these nonporous layers of September 13–17, 2010 carbonates is needed. As mentioned earlier, we recom- 9. Kumar, S., Saxena, S.K.: A comparative study of CO sorption properties for different oxides. Mater. Renew. Sustain. Energy 3, mend to have an aggregative fluidization regime for a flu- 30 (2014) idized bed reactor while scaling up MgO–CO reaction. 10. Benson, S.M., Cole, D.R.: CO sequestration in deep sedimentary In summary, we demonstrate the increase in uptake of formations. Elements 4, 325–331 (2008) CO by mesoporous MgO at high temperature and pressure 2 11. Gruene, P., Belova, A.G., Yegulalp, T.M., Farrauto, R.J., Cas- taldi, M.J.: Dispersed calcium oxide as a Reversible and efficient in the humid environment. We observed the significant role CO -sorbent at intermediate temperatures. Ind. Eng. Chem. Res. of temperature, pressure, water vapor and porosity of the 50, 4042–4049 (2011) sorbent on the improvement of the CO absorption capacity 12. Rackley, S.: Carbon capture and storage. Elsevier, Burlington of mesoporous MgO. (2010) 13. Duan, Y., Sorescu, D.C.: CO capture properties of alkaline earth metal oxides and hydroxides: a combined density functional theory and lattice phonon dynamics study. J. Chem. Phys. 133, Conclusion 074508–074511 (2010) 14. Feng, B., An, H., Tan, E.: Screening of CO adsorbing materials MgO is a promising candidate for pre-combustion CO 2 for zero emission power generation systems. Energy Fuels 21, 426–434 (2007) capture due to their stable absorption capacity of CO , ade- 15. Li, L., Wen, X., Fu, X., Wang, F., Zhao, N., Xiao, F., Wei, W., quate mechanical strength, high attrition resistance and good Sun, Y.: MgO/Al O sorbent for CO capture. Energy Fuels 24, 2 3 2 regenerability. We observed a 96.96 % of MgO conversion 5773–5780 (2010) to MgCO at 350 C and 10 bars CO pressure. Moreover, 3 2 16. Lee, S.C., Chae, H.J., Lee, S.J., Choi, B.Y., Yi, C.K., Lee, J.B., Ryu, C.K., Kim, J.C.: Development of regenerable MgO-based CO uptake capacity of MgO can be increased by performing sorbent promoted with K CO for CO capture at low tem- 2 3 2 the reaction in the presence of slight humid environment and peratures. Environ. Sci. Technol. 42, 2436–2471 (2008) scrubbing off the outer non-porous layer of MgCO . We also 17. Ward, S.M., Braslaw, J., Gealer, R.L.: Carbon dioxide sorption demonstrate that MgO has a low regeneration temperature studies on magnesium oxide. Thermochim. Acta 64, 107–114 (1983) (550 C) and stable CO capture capacity over wide range of 123 8 Page 8 of 8 Mater Renew Sustain Energy (2015) 4:8 18. Choi, S., Drese, J.H., Jones, C.W.: Adsorbent materials for car- development, evaluation, and reaction modeling. Fuel 89, bon dioxide capture from large anthropogenic point sources. 1287–1297 (2010) Chemsuschem 2, 796–854 (2009) 33. Kato, Y., Yamashita, N., Kobayashi, K., Yoshizawa, Y.: Kinetic 19. Fu, X., Zhao, N., Li, J., Xiao, F., Wei, W., Sun, Y.: Carbon study of the hydration of magnesium oxide for a chemical heat dioxide capture by MgO-modified MCM-41 materials. Adsorpt. pump. Appl. Therm. Eng. 16, 853–862 (1996) Sci. Technol. 27, 593–601 (2009) 34. Liu, C., Shih, S.: Kinetics of the reaction of iron blast furnace 20. Bhagiyalakshmi, M., Lee, J.Y., Jang, H.T.: Synthesis of meso- slag/hydrated lime sorbents with SO2 at low temperatures: effects porous magnesium oxide: its application to CO chemisorption. of the presence of CO ,O , and NO . Ind. Eng. Chem. Res. 48, 2 2 2 X Int. J. Greenhouse Gas Control 4, 51–56 (2010) 8335–8340 (2009) 21. Liu, S., Zhang, X., Li, J., Zhao, N., Wei, W., Sun, Y.: Preparation 35. Zevenhoven, R., Teir, S., Eloneva, S.: Heat optimisation of a and application of stabilized mesoporous MgO–ZrO solid base. staged gas-solid mineral carbonation process for long-term CO 2 2 Catal. Commun. 9, 1527–1532 (2008) storage. Energy 33, 362–370 (2008) 22. Li, B., Wen, X., Zhao, N., Wang, X.Z., Wei, W., Sun, Y., Ren, 36. Zevenhoven, R., Eloneva, S., Teir, S.: A study on MgO-based Z.H., Wang, Z.J.: Preparation of high stability MgO–ZrO solid mineral carbonation kinetics using pressurized thermogravimetric base and its high temperature CO capture properties. J. Fuel analysis. GHGT-8, Norway, (2006) Chem. Technol. 38, 473–477 (2010) 37. Frykstrand, S., Stietzel, C., Forsgren, J., Angstrom, J., Potin, V., 23. Yong, Z., Mata, V., Rodrigues, A.E.: Adsorption of carbon Stromme, M.: Synthesis, electron microscopy and X-ray char- dioxide onto hydrotalcite-like compounds (HTlcs) at high tem- acterization of oxymagnesite, MgO2MgCO , formed from peratures. Ind. Eng. Chem. Res. 40, 204–209 (2001) amorphous magnesium carbonate. CrystEngComm 16, 24. Li, L., Li, Y., Wen, X., Wang, F., Zhao, N., Xiao, F., Wei, W., 10837–10844 (2014) Sun, Y.: CO capture over K CO /MgO/Al O dry sorbent in a 38. Fagerlund, J., Nduagu, E., Romao, I., Zevenhoven, R.: CO 2 2 3 2 3 2 fluidized bed. Energy Fuels 25, 3835–3842 (2011) fixation using magnesium silicate minerals part 1: process de- 25. Lee, S.C., Choi, B.Y., Lee, T.J., Ryu, C.K., Soo, Y.S., Kim, J.C.: scription and performance. Energy 41, 184–191 (2012) CO absorption and regeneration of alkali metal-based solid 39. Li, R., Chen, G., Dong, G., Sun, X.: Controllable synthesis of sorbents. Catal. Today 111, 385–390 (2006) nanostructured TiO2 by CTAB-assisted hydrothermal route. New 26. Ruminski, A.M., Jeon, K.J., Urban, J.J.: Size-dependent CO J. Chem. 38, 4684–4689 (2014) capture in chemically synthesized magnesium oxide nanocrystals. 40. Deng, H., Grunder, S., Cordova, K.E., Valente, C., Furukawa, H., J. Mater. Chem. 21, 11486–11491 (2011) Hmadeh, M., Gandara, F., Whalley, A.C., Liu, Z., Asahina, S., 27. Beruto, D., Botter, R., Searcy, A.W.: Thermodynamics of two, Kazumori, H., O’Keeffe, M., Terasaki, O., Stoddart, F.J., Yaghi, two–dimensional phases formed by CO chemisorption on MgO. O.M.: Large-pore apertures in a series of metal-organic frame- J. Phys. Chem. 91, 3578–3581 (1987) works. Science 336, 1018–1023 (2012) 28. Lu, W., Yuan, D., Sculley, J., Zhao, D., Krishna, R., Zhou, H.C.: 41. Bhatia, S.K., Perlmutter, D.D.: Effect of the product layer on the Sulfonate-grafted porous polymer networks for preferential CO kinetics of the CO –Lime Reaction. AIChE J. 29, 79–86 (1983) 2 2 adsorption at low pressure. J. Am. Chem. Soc. 133, 18126–18129 42. Butt, D.P., Lackner, K.S., Wendt, C.H., Conzone, S.D., Kung, H., (2011) Lu, Y.C., Bremser, J.K.: Kinetics of thermal dehydroxylation and 29. Fagerlund, J., Highfield, J., Zevenhoven, R.: Kinetics studies on carbonation of magnesium hydroxide. J. Am. Ceram. Soc. 79, wet and dry gas-solid carbonation of MgO and Mg(OH) for CO 1892–1898 (1996) 2 2 sequestration. RSC Adv. 2, 10380–10393 (2012) 43. Kumar, S.: The effect of elevated pressure, temperature and 30. Highfield, J., Bu, J., Fagerlund, J., Zevenhoven, R.: ICCDU-XI particle morphology on the carbon dioxide capture using zinc (2011) oxide. J. CO Util. 8, 60–66 (2014) 31. Butt, D.P., Pile, S.P., Park, Y., Vaidya, R., Lackner, K.S., Wendt, C.H., Nomura, K.: Report LA-UR-98-7631 (1998) 32. Hassanzadeh, A., Abbasian, J.: Regenerable MgO-based sorbents for high-temperature CO removal from syngas: 1. sorbent http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Materials for Renewable and Sustainable Energy Springer Journals

An experimental investigation of mesoporous MgO as a potential pre-combustion CO2 sorbent

Download PDF
8 pages

Loading next page...
 
/lp/springer-journals/an-experimental-investigation-of-mesoporous-mgo-as-a-potential-pre-QNAqZpO5Ts

References (44)

Publisher
Springer Journals
Copyright
Copyright © 2015 by The Author(s)
Subject
Material Science; Materials Science, general; Renewable and Green Energy; Renewable and Green Energy
ISSN
2194-1459
eISSN
2194-1467
DOI
10.1007/s40243-015-0050-0
Publisher site
See Article on Publisher Site

Abstract

Mater Renew Sustain Energy (2015) 4:8 DOI 10.1007/s40243-015-0050-0 ORIGINAL PAPER An experimental investigation of mesoporous MgO as a potential pre-combustion CO sorbent 1 1 1 1 • • • Sushant Kumar Surendra K. Saxena Vadym Drozd Andriy Durygin Received: 10 May 2014 / Accepted: 8 May 2015 / Published online: 22 May 2015 The Author(s) 2015. This article is published with open access at Springerlink.com Abstract We examined the CO capture capacity of to be the major CO contributor [2].There are three main 2 2 mesoporous MgO (325 mesh size, surface technological approaches for CO capture- post-, oxy- and area = 95.08 ± 1.5 m /g) as a potential pre-combustion pre-combustion. Post-combustion systems capture CO CO sorbent. Our results show that 96.96 % of MgO was from N -rich flue gas stream, produced by burning fossil 2 2 converted to MgCO at 350 C and 10 bars CO pressure. fuel in air. Oxy-combustion uses pure stream of O , instead 3 2 2 The sorbent could be completely regenerated at 550 C of air, to combust coal and thus produces CO -rich gas under argon flow. The sorption rate parameters such as stream. On the other hand, pre-combustion systems are surface area and pore size were investigated. designed mainly to remove CO from the syngas (CO ? H ) prior to its combustion for power production Keywords Capture capacity  Mesoporous [3]. Under pre-combustion conditions, after the water–gas Pre-combustion  Sorbent  Surface area  Pore size shift reactor ðCO þ H O ! CO þ H Þ, the gas stream 2 2 2 mainly consists of CO ,H O and H . The partial CO 2 2 2 2 pressure for pre-combustion capture conditions is around Introduction 20–30 bar and the temperature is between 250 and 450 C [4]. Fossil fuel accounts for the world’s major energy supply Both the physical and chemical solvents can be used for and its use is anticipated to be continued throughout the pre-combustion CO capture. Unlike chemical solvent, 21st century [1]. The use of fossil fuel is always accom- physical solvent (such as Selexol and Rectisol) selectively panied with a vast emission of CO . The anthropogenic absorbs CO without forming any chemical bonds. Thus, CO emissions upset the natural carbon cycle leading to an the physical solvent requires relatively less regeneration increased atmospheric CO concentration. No one can deny energy as compared to that of chemical solvent [5]. that there is an urgent need to develop methods for CO However, these physical solvent-based processes suffer mitigation. severe disadvantages: (1) lose pressure during regeneration Currently, a large focus is devoted on capturing CO step, and (2) require a low operating temperature. There- from coal-fired power plant flue streams, which continues fore, syngas needs to be cooled prior to CO absorption step to attain a relatively low operating temperature. After CO absorption, the remaining hydrogen gas stream re- Electronic supplementary material The online version of this quires to be reheated to the gas turbine inlet temperature. article (doi:10.1007/s40243-015-0050-0) contains supplementary However, chemical solvents have the advantage of high material, which is available to authorized users. mass transfer driving force into solution and better acid gas & Sushant Kumar selectivity. Also, chemical solvents can be used in pro- skuma002@fiu.edu cesses that utilize thermal swing regeneration and generate the CO at elevated pressure [6]. But chemical solvents 1 2 Center for the Study of Matter at Extreme Conditions, increase the energy and cost penalty and thus are down- College of Engineering and Computing, Florida International graded as a future CO sorbent [7]. University, Miami, FL 33199, USA 123 8 Page 2 of 8 Mater Renew Sustain Energy (2015) 4:8 Currently, the focus is to develop advanced physical and the use in IGCC applications. Therefore, we study the CO chemical solvent systems that have the potential to provide capture capacity of MgO in the relatively high temperature significant improvements in both cost and performance as and pressure condition of 300–375 C and 10–50 bars, compared to the Selexol and Rectisol for pre-combustion respectively. CO capture. The challenges are to modify regeneration conditions to recover the CO at a higher pressure, improve selectivity to reduce H losses, and develop a solvent that Experimental procedure has a high CO loading at a higher temperature, which would increase integrated gasification combined cycle The reaction (IGCC) efficiency. In the same line, another vital task is to MgOðÞþ s CO ðÞ g $ MgCO ðÞ s develop a new sorbent which could be highly efficient for was studied experimentally. The carbonation reaction was pre-combustion capture conditions. Consequently, the US performed in a closed system which permits us to effi- Department of Energy (DOE) performed the thermody- ciently maintain high temperature and pressure for a long namic modeling activities that included screening analyses period of time. The decomposition reaction of carbonate for a number of different metal oxides, zirconates, silicates was examined using Thermo gravimetric Analysis (TGA) and titanates under various operating conditions to identify technique. new solid sorbents for pre-combustion CO capture. About About 0.2 g of 325-mesh-sized magnesium oxide (de- 18 sorbents were modeled and finally seven candidates are livered by Alfa Aesar) was put inside a closed cylindrical chosen—magnesium oxide (MgO), calcium oxide (CaO), 00 00 vessel (1.25 long and 0.35 internal diameter). About lithium zirconate (Li ZrO ), calcium zirconate (CaZrO ), 2 3 3 0.1 ml of water was also introduced on the vessel walls. barium zirconate (BaZrO ), barium titanate (BaTiO ) and 3 3 Chemically pure CO gas (Airgas) was passed into this barium silicate (BaSiO ) for further investigations [8]. 2 system. Before experiments, CO gas was flushed three Among these solid sorbents, MgO and CaO are attractive times to ensure a pure CO atmosphere inside the reactor. because of their easy accessibility and favorable thermo- 2 The reaction was performed for 30 min at a desired tem- dynamic properties [9]. perature and pressure condition. Once the reaction com- The alkaline earth metal oxides (such as CaO and MgO) pleted, the system was air-cooled. The product was then combine with CO to form thermodynamically stable car- ground using mortar and pestle. The powder particle was bonates. Metal carbonates, when heated, liberate pure again put back for another reaction at the same ex- stream of CO gas and regenerate the oxides. Eventually, perimental condition. This cycle was repeated until no in- the generated pure CO gas can either be sequestered un- crement in weight of the product was observed. derground or used for enhanced oil recovery [10]. CaO are Thermo gravimetric analysis (TGA) of the product was abundant and thus relatively easily accessible than MgO. done using TGA 2950 Thermo gravimetric analyzer. The However, CaO as CO sorbent suffers severe major samples (10 mg) were heated under argon purge, at a drawbacks and a detailed discussion can be found else- heating rate of 10 C/min to a final temperature of 800 C. where [11]. It is a fact that regeneration of oxides needs a The TGA provides continuous measurements of the sample lot of energy [12]. MgO and Mg(OH) are known to be weight as a function of time and temperature. The amount better candidates than CaO for CO capture applications of formation of MgCO was analyzed by the percent loss in due to their low regeneration energy requirement and low weight of the sample while heating up to 800 Cinan operating temperature [13]. Thus, MgO (periclase), argon atmosphere. although occurs only rarely as an oxide, we choose it here The product characterization was performed using X-ray for our study. One should note that MgO when recycled powder diffraction method. Bruker GADDS/D8 is equip- between naturally occurring magnesite or dolomite can ped with Apex Smart CCD Detector and direct-drive ro- cause relatively lesser energy or carbon emission penalty tating anode. The MacSci rotating anode (Molybdenum) [14]. operates with a 50 kV generator and 20 mA current. X-ray The CO absorption capacity of MgO was studied as a beam size can vary from 50 to 300 lm. The usual collec- function of particle size, surface area, temperature, pres- tion time is 1200 s. sure, support and concentration of water vapor. The CO An isothermal gas adsorption was employed to measure uptake capacity on different MgO sorbents at different internal surface areas of the powder particles. Mi- conditions is listed in Table 1. Most of the experiments are cromeritics Tristar II 3020 (surface area and porosimetry restricted to low temperature and ambient or low pressure analyzer instrument) was used with N as adsorptive gas at condition. Hence, the reported sorption capacities of CO 77 K (liquid nitrogen bath). The samples were first de- on MgO are not very high. However, the sorbents which gassed under 300 C with a N gas flow for 1 h to remove can operate in the range of 300–350 C would be ideal for 2 123 Mater Renew Sustain Energy (2015) 4:8 Page 3 of 8 8 Table 1 CO uptake capacity of MgO obtained from the literature Sorbent Gas stream Carbonation Pressure (bar) or, Particle Size Regeneration CO capture capacity References temperature flow rate temperature (mmol/g) (C) (C) conversion, % 1 MgO Pure CO 50–1000 100 mL/min (flow rate) – – 0.99 [15] 2 MgO/Al O (10 wt. % MgO) (13 v % H O, 13 v % CO ) 30, 150 1 (20–40) mesh size 350 1.36 [16] 2 3 2 2 3 MgO (11 v % H O, 1 v % CO ) 50–100 0.01 – 150–400 1.05 [17] 2 2 4K CO /MgO (11 v % H O, 1 v % CO ) 50–100 – – 150–400 2.98 [17] 2 3 2 2 5 MgO 330/660 ppm in air 0, 100 0.2 – – 0.64, 0.43 [18, 19] 6 MgO/MCM-41 Pure CO 25 1 – – 1.06 [20] 7 Mesoporous MgO Pure CO 25, 100 1 – – 1.82, 2.27 [21] 8 Nonporous MgO Pure CO 25 1 – – 0.45 [21] 9 MgO–ZrO Pure CO 30, 150 1 – – 1.15,1.01 [22, 23] 2 2 10 MgO (31.7 wt%)/Al O (22.4 wt%) Pure CO 20, 200, 300 1 – – 0.13, 0.24, 0.5 [24] 2 3 2 11 MgO (33.8 wt%)/ Al O (20.8 wt%) Pure CO 20, 200, 300 1 – – 0.08, 0.12, 0.5 [24] 2 3 2 12 K CO /MgO/Al O Flue gas 60 1 – 480 2.49 [25] 2 3 2 3 13 K CO /MgO (9 v % H O, 1 v % CO ) 60 40 mL/min (flow rate) – 400 2.7 [26] 2 3 2 2 14 MgO nanocrystal Flue gas 60 25sccm (flow rate) 5 nm 60–600 6.4 [27] 15 MgO Pure CO 350 1.33, 3.33 – – 0.089, 0.091 [28] 16 MgO Pure CO 300–500 9–36 \44 lm – 70–80 % (*200 min) [29] 17 MgO Pure CO – 20–40 \44 lm – 100 % (*120 min) [30] 2 8 Page 4 of 8 Mater Renew Sustain Energy (2015) 4:8 the moisture and other adsorbed gases before analysis. The Figure 2 depicts the adsorption/absorption model for internal surface area was calculated using the Brunauer– MgO–CO –H O reaction. Based on the previous work, it 2 2 Emmett–Teller (BET) method. The pore volume was also could be reasonable to corroborate that water vapor sur- 2- calculated from the adsorbed nitrogen after complete pore rounds MgO particles where CO reacts to form CO 2 3 ? ?2 condensation (P/P = 0.9925) using the ratio of the den- ions and H ions [34–36]. Free Mg ions could further 2- sities of liquid and gaseous nitrogen. The pore size was react with the CO ions to form MgCO . However, 3 3 calculated using the Barrett–Joyner–Halenda (BJH) MgCO forms an impervious layer around unreacted MgO method. particles and hinders the further diffusion of CO molecules. Here, we used mortar and pestle to grind the product. As Results and discussion mentioned earlier, we conducted each experiment for 30 min and ground the sample after that. Grinding helps in Figure 1 confirms the formation of MgCO at different scrubbing off the outer nonporous layer of MgCO . And we temperatures and CO pressures. MgO, Mg(OH) , 2 2 performed grinding until we noticed no change in product MgO2MgCO and MgCO were identified conventionally 3 3 weight after subsequent experiments. In general, after 3–4 by their corresponding Joint Committee Powder Diffrac- cycles, we observed no change in the weight of product. It tion Standard (JCPDS) card number 79-0612,82-2345,31- is certain that such intermittent grinding step is limited to 0804 and 86-2345, respectively. the laboratory and cannot be seen as an industrial op- One of the vital factors in gas–solid carbonation reaction eration. Therefore, it is recommended to have an ag- is the presence of water and there have been numerous gregative fluidization regime for a fluidized bed reactor observations where water acts as a catalyst [31–34]. while scaling up MgO–CO reaction. Also, increasing the Therefore, we have also used water (0.1 ml) for the MgO– amount of water vapor cannot lead to the complete car- CO reaction. In absence of water, no CO was absorbed at 2 2 bonate conversion of MgO. Thus, in addition to the amount these conditions due to the kinetic limitations. The CO of steam, surface properties of MgO (such as surface area, sorption capacity of MgO increases significantly in the particle size, porosity) are also very crucial parameters for presence of water vapor. Under humid condition, MgO the carbonation process. rapidly locks CO in the form of MgCO . Recently, 2 3 The thermal analysis curve does not show any sig- Fagerlund et al. [29] proposed the reaction mechanism for nificant differences in amounts of carbonate in the high- MgO carbonation in the presence of steam: pressure (50 bars) experiments. We obtained almost similar TGA plots and XRD patterns for different temperatures MgO þ H O $ MgO  H O 2 2 300–375 C and 50 bars CO pressure. However, the ex- MgO  H O þ CO $ MgCO þ H O 2 2 2 periment performed at 300 C and 10 bars did indicate that MgO þ CO $ MgCO the product was not simply MgCO . The X-ray diffraction 2 3 1- MgCO (86-2345) 1- MgCO (86-2345) (a) (b) 2- MgO (79-0612) 2- MgO (79-0612) 3- Mg(OH) (82-2453) 4- MgO.2MgCO (31-0804) 4- MgO.2MgCO (31-0804) 375°C 350°C 350°C 1 1 2 1 1 11 1 1 325°C 300°C 1 1 300°C 1 1 1 1 1 1 1 1 1 4 1 1 1 1 1 4 3 1 2 4 3 10 20 30 10 20 30 2Θ (degrees) 2Θ (degrees) Fig. 1 XRD patterns for MgCO formation after reaction at various temperatures and CO pressure of a 10 bars and b 50 bars 3 2 123 dm/dT dm/dT Mater Renew Sustain Energy (2015) 4:8 Page 5 of 8 8 Fig. 2 The adsorption/absorption model for MgO–CO –H O reaction 2 2 (a) 1.5 (b) 1.5 (350°C,10 bars) (300°C,10 bars) 1.0 1.0 6.5% 0.5 0.5 11.5% 0.0 0.0 ~345°C ~474°C -0.5 -0.5 50.7 % ~539°C 25.01% ~550°C -1.0 -1.0 60 60 -1.5 -1.5 -2.0 -2.0 40 -2.5 40 -2.5 100 200 300 400 500 600 700 100 200 300 400 500 600 700 Temperature (C) Temperature (C) Fig. 3 DTG plots for product at a 300 C and 10 bars and b 350 C and 10 bars pattern in Fig. 1a confirms the presence of Mg (OH) and The steps to calculate % conversion of MgO to relatively high amount of MgO2MgCO at 300 C and 10 MgCO is explained in supplementary section [S1]. A 3 3 bars. DTG curve (Fig. 3a) also evidences the similar si- conversion of 30.54 and 96.96 % for MgO to MgCO was tuation. The two peaks around 350 and 475 C were at- observed at 300 and 350 C, respectively. Here, we ob- tributed to the losses of water of crystallization and served the formation of relatively high amount of oxy- hydroxyl water, respectively. However, another peak at magnesite (MgO2MgCO )at300 C and 10 bars. It can 550 C corresponds to the complete decomposition of be easily calculated that the CO capture capacity of MgCO . But at a temperature and pressure of 350 C and oxymagnesite is about two-third that of MgCO . Hence, 3 3 10 bars, respectively, only MgCO was formed. This is formation of oxymagnesite can markedly reduce the evidenced by both DTG (Fig. 3b) and X-ray diffraction overall uptake of CO by MgO particles. However, it can analysis (Fig. 1a). be observed from X-ray patterns (Fig. 1) that at higher % Weight % Weight 8 Page 6 of 8 Mater Renew Sustain Energy (2015) 4:8 Table 2 Surface properties of MgO particles before and after carbonation reaction 350 C, 10 bars 2 3 6 -1 Sample Surface area (m /g) Pore volume (cm /g) Pore size (nm) SA/PV(10 m ) As-received MgO 95.08 ± 1.5 0.22 9.09 439.59 After reaction at (350 C, 10 bars) 4.15 ± 0.05 0.01 16.25 246.15 temperature or pressure, the formation of oxymagnesite is suppressed. In the same line, recent study reveals that oxymagnesite 120 (a) MgO Powder forms as an intermediate during the thermal decomposition Surface area = 95.08m /g of hydrated magnesium carbonate [37]. Moreover, oxy- magnesite can also be formed as a product of reaction between Mg (OH) and CO in anhydrous synthesis [29] Desorption 2 2 and/or solid-state reaction of MgO and CO using steam [38]. In this regard, Duan et al. [13] calculated the phase Adsorption diagram of MgO–Mg(OH) –MgCO , which suggests that 2 3 the transition temperature for direct conversion of MgCO to Mg(OH) increases with increase in P . Here, when 2 H2O temperature increases from 300 to 350 C, partial pressure 0.2 0.4 0.6 0.8 1.0 of water also increases and consequently transition tem- Relative Pressure, P/P perature also increased. At 300 C, a relatively less amount of MgO transforms to its carbonates. This can be attributed Fig. 4 N adsorption–desorption isotherm of as-received MgO to a possible high conversion of MgCO to Mg(OH) , 3 2 which is in agreement with the phase diagram. Moreover, a received MgO follows Type IV isotherms (as per IUPAC significant formation of oxymagnesite at 300 C and 10 classification); typical for mesoporous substances [39]. bars also leads to a less direct conversion of MgO to Also, the hysteresis pattern is H3 (following IUPAC clas- MgCO . Thus, it can be deduced that a high amount of sification) indicating the presence of slit-like pores. After oxymagnesite forms at a low partial pressure of water. capture of CO at 350 C and 10 bars, surface area dra- Therefore, the reaction mechanism is changed to: matically decreased to (4.15 ± 0.05) m /g. The ratio of MgO þ CO $ MgCO surface area to pore volume is also reduced by almost half and results in high diffusion paths. The significant decrease MgO þ 2MgCO $ MgO  2MgCO 3 3 in surface area attributes to the basicity of mesoporous MgO  2MgCO þ CO $ 3MgCO 3 3 MgO. The mesoporous MgO is highly basic with well- Moreover, at 50 bars of CO pressure and a temperature of ordered pores to hold high CO at both lower and higher 2 2 300 C, MgO has the highest yield of 98.54 %. At high temperatures. It is well known that porous materials allow temperatures (300–375 C) but constant pressure (50 bars), molecules to pass through their pore aperture for storage, we observe a slight but continuous decrease in the ab- separation or conversion [36]. MgO with a fine particle size sorption of CO , which is in congruence with previously (\44 lm) has a high content of mesopores, which leads to reported results [30]. It is well known that at low tem- good mass transfer properties during the absorption pro- perature, the physisorption process dominates but at cess. The mechanism for metal oxide reaction with CO elevated temperature CO chemisorbs on MgO and thus gas has been discussed a lot [40–43]. CO molecules dif- CO uptake capacity gradually starts decreasing. fuse through the pores of mesoporous MgO and the present CO -uptake capacity of a metal oxide is primarily large active sites hold these CO molecules [19]. The dominated by the factors such as surface area, pore volume, trapped CO molecules further react to form MgCO . 2 3 pore functionality and pore size [28]. BET surface area It can be observed from Table 2 that at 350 C and 10 measurement, pore volume and average pore sizes pre- bars, 96.96 % of MgO was converted to MgCO and almost sented in Table 2 indicates the significant role of CO to all the pores have been utilized after reaction with CO 2 2 influence the particle structure. As received, 325 mesh size molecules. Henceforth, almost no CO molecules could mesoporous MgO has a pore size of 9.09 nm and a high have diffused further in the pores. Noticeably, pore size surface area (95.08 ± 1.5 m /g). Figure 4 illustrates that increased to 16.25 nm. Thus, it is apparent that the porosity the N adsorption–desorption isotherm curves for as- of MgO particles plays a very vital role for CO uptake. 2 2 Quantity adsorbed (cm /g) STP Mater Renew Sustain Energy (2015) 4:8 Page 7 of 8 8 Previously, Beruto et al. has reported a very low CO temperature and pressure. Interestingly, the present study absorption capacity of MgO in absence of water vapor [27]. also illustrate that a high amount of oxymagnesite forms at a An uptake capacity of 0.089 and 0.091 mmol CO /g MgO low partial pressure of water. was observed at 350 C in 1.33 and 3.33 bars of CO , re- Open Access This article is distributed under the terms of the spectively. Thus, it was concluded that there is a high acti- Creative Commons Attribution 4.0 International License (http:// vation energy barrier to MgO recarbonation. On the contrary, creativecommons.org/licenses/by/4.0/), which permits unrestricted Feng et al. [14] heated the sorbent (MgO) to 1000 C in pure use, distribution, and reproduction in any medium, provided you give CO and noted a low but almost constant (for 8 cycles) ab- appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were sorption capacity of 0.99 mmol CO /g MgO. Thus, unlike made. CaO-based sorbents, MgO does not show a fast decline in their CO capture capacity over a large number of car- bonation–calcination cycles. Bhagiyalakshmi et al. [20] synthesized basic mesoporous MgO (surface area of 250 m / References g) using mesoporous carbon obtained from SBA-15 and obtained a maximum CO adsorption of 2.27 mmol CO /g at 2 2 1. Kumar, S.: Clean hydrogen production methods, Springer Briefs in energy. Springer, New York (2015) 100 C and nearly 1.81 mmol CO /g at 25 C for a feed flow 2. Merkel, T.C., Lin, H., Wei, X., Baker, R.: Power plant post- rate of 30 ml/min CO gas (99.9 % purity). Therefore, it is combustion carbon dioxide capture: an opportunity for mem- evident that even for a relatively lower surface area (95 m /g branes. J. Membr. Sci. 359, 126–139 (2010) compared to 250 m /g), MgO can have a better CO uptake 2 3. Davison, J.: Performance and costs of power plants with capture at a higher temperature (here, 300–375 C) and higher CO and storage of CO . Energy 32, 1163–1176 (2007) 4. Burton, B.P., Dupin, N., Fries, S.G., Grimvall, G., Fernandez pressure (10–50 bars). Recently, Fagerlund et al. [28] re- Guillermet, A., Miodownik, P., Oats, W. A., Vinograd, V., Z. ported a very high % conversion of MgO to MgCO under Metallkd 92, 514 (2001) high temperature and pressure conditions. However, MgO 5. Miller, B., Tillman, D.: Combustion engineering issues for solid fuel systems. pp. 449–451. Elsevier (2008) showed a slow conversion rate (50 % for *7 h) for the 6. DOE/NETL: Carbon dioxide capture and storage RD&D road- condition [P (*18–19 bar), P (*1–2 bar) and CO2 H2O map, (2010) 300–350 C] which can be suitable for pre-combustion 7. Yu, C.H., Huang, C.H., Tan, C.S.: A review of CO capture by capture process. The reason could be the deposition of im- absorption and adsorption. Aerosol Air Qual. Res. 12, 745–769 (2012) pervious carbonate layer on the surface of MgO which does 8. Evaluation of Dry Sorbent Technology; Presentation at the 2010 not allow CO molecules to further diffuse in the pores. NETL CO Capture Technology Meeting, Pittsburgh, PA, Therefore, continuous removal of these nonporous layers of September 13–17, 2010 carbonates is needed. As mentioned earlier, we recom- 9. Kumar, S., Saxena, S.K.: A comparative study of CO sorption properties for different oxides. Mater. Renew. Sustain. Energy 3, mend to have an aggregative fluidization regime for a flu- 30 (2014) idized bed reactor while scaling up MgO–CO reaction. 10. Benson, S.M., Cole, D.R.: CO sequestration in deep sedimentary In summary, we demonstrate the increase in uptake of formations. Elements 4, 325–331 (2008) CO by mesoporous MgO at high temperature and pressure 2 11. Gruene, P., Belova, A.G., Yegulalp, T.M., Farrauto, R.J., Cas- taldi, M.J.: Dispersed calcium oxide as a Reversible and efficient in the humid environment. We observed the significant role CO -sorbent at intermediate temperatures. Ind. Eng. Chem. Res. of temperature, pressure, water vapor and porosity of the 50, 4042–4049 (2011) sorbent on the improvement of the CO absorption capacity 12. Rackley, S.: Carbon capture and storage. Elsevier, Burlington of mesoporous MgO. (2010) 13. Duan, Y., Sorescu, D.C.: CO capture properties of alkaline earth metal oxides and hydroxides: a combined density functional theory and lattice phonon dynamics study. J. Chem. Phys. 133, Conclusion 074508–074511 (2010) 14. Feng, B., An, H., Tan, E.: Screening of CO adsorbing materials MgO is a promising candidate for pre-combustion CO 2 for zero emission power generation systems. Energy Fuels 21, 426–434 (2007) capture due to their stable absorption capacity of CO , ade- 15. Li, L., Wen, X., Fu, X., Wang, F., Zhao, N., Xiao, F., Wei, W., quate mechanical strength, high attrition resistance and good Sun, Y.: MgO/Al O sorbent for CO capture. Energy Fuels 24, 2 3 2 regenerability. We observed a 96.96 % of MgO conversion 5773–5780 (2010) to MgCO at 350 C and 10 bars CO pressure. Moreover, 3 2 16. Lee, S.C., Chae, H.J., Lee, S.J., Choi, B.Y., Yi, C.K., Lee, J.B., Ryu, C.K., Kim, J.C.: Development of regenerable MgO-based CO uptake capacity of MgO can be increased by performing sorbent promoted with K CO for CO capture at low tem- 2 3 2 the reaction in the presence of slight humid environment and peratures. Environ. Sci. Technol. 42, 2436–2471 (2008) scrubbing off the outer non-porous layer of MgCO . We also 17. Ward, S.M., Braslaw, J., Gealer, R.L.: Carbon dioxide sorption demonstrate that MgO has a low regeneration temperature studies on magnesium oxide. Thermochim. Acta 64, 107–114 (1983) (550 C) and stable CO capture capacity over wide range of 123 8 Page 8 of 8 Mater Renew Sustain Energy (2015) 4:8 18. Choi, S., Drese, J.H., Jones, C.W.: Adsorbent materials for car- development, evaluation, and reaction modeling. Fuel 89, bon dioxide capture from large anthropogenic point sources. 1287–1297 (2010) Chemsuschem 2, 796–854 (2009) 33. Kato, Y., Yamashita, N., Kobayashi, K., Yoshizawa, Y.: Kinetic 19. Fu, X., Zhao, N., Li, J., Xiao, F., Wei, W., Sun, Y.: Carbon study of the hydration of magnesium oxide for a chemical heat dioxide capture by MgO-modified MCM-41 materials. Adsorpt. pump. Appl. Therm. Eng. 16, 853–862 (1996) Sci. Technol. 27, 593–601 (2009) 34. Liu, C., Shih, S.: Kinetics of the reaction of iron blast furnace 20. Bhagiyalakshmi, M., Lee, J.Y., Jang, H.T.: Synthesis of meso- slag/hydrated lime sorbents with SO2 at low temperatures: effects porous magnesium oxide: its application to CO chemisorption. of the presence of CO ,O , and NO . Ind. Eng. Chem. Res. 48, 2 2 2 X Int. J. Greenhouse Gas Control 4, 51–56 (2010) 8335–8340 (2009) 21. Liu, S., Zhang, X., Li, J., Zhao, N., Wei, W., Sun, Y.: Preparation 35. Zevenhoven, R., Teir, S., Eloneva, S.: Heat optimisation of a and application of stabilized mesoporous MgO–ZrO solid base. staged gas-solid mineral carbonation process for long-term CO 2 2 Catal. Commun. 9, 1527–1532 (2008) storage. Energy 33, 362–370 (2008) 22. Li, B., Wen, X., Zhao, N., Wang, X.Z., Wei, W., Sun, Y., Ren, 36. Zevenhoven, R., Eloneva, S., Teir, S.: A study on MgO-based Z.H., Wang, Z.J.: Preparation of high stability MgO–ZrO solid mineral carbonation kinetics using pressurized thermogravimetric base and its high temperature CO capture properties. J. Fuel analysis. GHGT-8, Norway, (2006) Chem. Technol. 38, 473–477 (2010) 37. Frykstrand, S., Stietzel, C., Forsgren, J., Angstrom, J., Potin, V., 23. Yong, Z., Mata, V., Rodrigues, A.E.: Adsorption of carbon Stromme, M.: Synthesis, electron microscopy and X-ray char- dioxide onto hydrotalcite-like compounds (HTlcs) at high tem- acterization of oxymagnesite, MgO2MgCO , formed from peratures. Ind. Eng. Chem. Res. 40, 204–209 (2001) amorphous magnesium carbonate. CrystEngComm 16, 24. Li, L., Li, Y., Wen, X., Wang, F., Zhao, N., Xiao, F., Wei, W., 10837–10844 (2014) Sun, Y.: CO capture over K CO /MgO/Al O dry sorbent in a 38. Fagerlund, J., Nduagu, E., Romao, I., Zevenhoven, R.: CO 2 2 3 2 3 2 fluidized bed. Energy Fuels 25, 3835–3842 (2011) fixation using magnesium silicate minerals part 1: process de- 25. Lee, S.C., Choi, B.Y., Lee, T.J., Ryu, C.K., Soo, Y.S., Kim, J.C.: scription and performance. Energy 41, 184–191 (2012) CO absorption and regeneration of alkali metal-based solid 39. Li, R., Chen, G., Dong, G., Sun, X.: Controllable synthesis of sorbents. Catal. Today 111, 385–390 (2006) nanostructured TiO2 by CTAB-assisted hydrothermal route. New 26. Ruminski, A.M., Jeon, K.J., Urban, J.J.: Size-dependent CO J. Chem. 38, 4684–4689 (2014) capture in chemically synthesized magnesium oxide nanocrystals. 40. Deng, H., Grunder, S., Cordova, K.E., Valente, C., Furukawa, H., J. Mater. Chem. 21, 11486–11491 (2011) Hmadeh, M., Gandara, F., Whalley, A.C., Liu, Z., Asahina, S., 27. Beruto, D., Botter, R., Searcy, A.W.: Thermodynamics of two, Kazumori, H., O’Keeffe, M., Terasaki, O., Stoddart, F.J., Yaghi, two–dimensional phases formed by CO chemisorption on MgO. O.M.: Large-pore apertures in a series of metal-organic frame- J. Phys. Chem. 91, 3578–3581 (1987) works. Science 336, 1018–1023 (2012) 28. Lu, W., Yuan, D., Sculley, J., Zhao, D., Krishna, R., Zhou, H.C.: 41. Bhatia, S.K., Perlmutter, D.D.: Effect of the product layer on the Sulfonate-grafted porous polymer networks for preferential CO kinetics of the CO –Lime Reaction. AIChE J. 29, 79–86 (1983) 2 2 adsorption at low pressure. J. Am. Chem. Soc. 133, 18126–18129 42. Butt, D.P., Lackner, K.S., Wendt, C.H., Conzone, S.D., Kung, H., (2011) Lu, Y.C., Bremser, J.K.: Kinetics of thermal dehydroxylation and 29. Fagerlund, J., Highfield, J., Zevenhoven, R.: Kinetics studies on carbonation of magnesium hydroxide. J. Am. Ceram. Soc. 79, wet and dry gas-solid carbonation of MgO and Mg(OH) for CO 1892–1898 (1996) 2 2 sequestration. RSC Adv. 2, 10380–10393 (2012) 43. Kumar, S.: The effect of elevated pressure, temperature and 30. Highfield, J., Bu, J., Fagerlund, J., Zevenhoven, R.: ICCDU-XI particle morphology on the carbon dioxide capture using zinc (2011) oxide. J. CO Util. 8, 60–66 (2014) 31. Butt, D.P., Pile, S.P., Park, Y., Vaidya, R., Lackner, K.S., Wendt, C.H., Nomura, K.: Report LA-UR-98-7631 (1998) 32. Hassanzadeh, A., Abbasian, J.: Regenerable MgO-based sorbents for high-temperature CO removal from syngas: 1. sorbent

Journal

Materials for Renewable and Sustainable Energy – Springer Journals

Published: May 22, 2015

There are no references for this article.