545498 PEI Impregnated Mesoporous Carbon Spheres As Ideal Sorbent for Post-Combustion CO2 Capture from Natural Gas Power Plant

Wednesday, June 5, 2019: 10:54 AM
Republic ABC (Grand Hyatt San Antonio)
Qingjun Chen Sr.1, De Chen2, Kumar Rout3 and Siyu Wang2, (1)Chemimcal Engineering, Norwegian University of Science and Technology, Trondheim, Norway, (2)Chemical Engineering, Norwegian University of Science and Technology, Trondheim, Norway, (3)SINTEF, Trondheim, Norway

PEI Impregnated Mesoporous Carbon Spheres as Ideal Sorbent for Post-Combustion CO2 Capture from Natural Gas Power Plant

Qingjun Chen,1 Siyu Wang,1 Kumar R. Kent,2 De Chen1,*

1 Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway.

2 SINTEF Industry, 7465 Trondheim, Norway

* Corresponding author: Email: de.chen@ntnu.no 

1. Introduction:

      The development of novel materials and new technologies for CO2 capture and storage has received great attentions due to the global warming issues. Among the different carbon capture and storage (CCS) technologies, post-combustion CO2 capture has attracted increasing attentions because this technology can be easily retrofitted into the existing power plants. There are two conventional options that the CO2 can be captured in existing power plants by amines absorption or solid sorbents. Low temperature CO2 absorption process with amines absorption has been used in industry, which is a technology adapted from natural gas sweetening. This conventional technology has faced several challenges, such as low energy efficiency and high cost. In addition to this, the amine solvent loss due to regeneration as well as its degradation has resulted in challenges and environmental concerns. The CO2 capture by solid sorbent may diminish the environmental impact of the CO2 capture and at the same time result in a lower energy penalty, thus solid adsorption process may be an alternative to achieve CO2 capture.

     The objective of this work is to develop promising innovative solutions for CO2 capture towards natural gas combined cycle (NGCC) power plant, with a potential to provide significant cost reductions. This work emphasised on the synthesis of PEI impregnated mesoporous carbon spheres with high CO2 capture capacity, fast kinetics for CO2 capture. The results showed that mesoporous carbon spheres (MCS) with perfect spherical morphology and control pore structure were prepared by a hard-template assisted reverse emulsion method. After impregnation with PEI, the CO2 capture capacity was up to 3.22 mmol/g at CO2 partial pressure of 0.05 bar (5 v%, a typical concentration of the tail gas from nature gas power plant) and temperature of 75 oC, outperforming the best solid amine sorbents reported at similar condition.

2. Experimental

      MCS was prepared by a hard-template assisted reverse emulsion method using formaldehyde and resorcinol as the carbon precursors and silica nanoparticles (LUDOX® SM-30) as the template. Paraffin oil and sorbitan monooleate (Span 80) were used as the disperse phase (oil phase) and surfactant. Formaldehyde, resorcinol and silica nanoparticles were first mixed in deionized water under stirring. After pre-polymerization at 45 °C for 20 min, the solution was transferred to a glass reactor containing a mixture of paraffin oil and Span 80. The hybrid polymer spheres were formed after the stirring with a speed of 200 rpm at 85 °C for 60 min. After further washing, drying, pyrolysis, and removal of silica template, the MCS were obtained. In order to control the pore structure of the MCS, different C/Si ratio (0.75, 1, 1.5) was used in this work. PEI impregnated MCS were prepared by a wet impregnation method. In a typical preparation, the desired amounts of PEI (Mw of 600) were dissolved in 2 g of methanol at 35 oC under stirring for 30 min, and then 0.3 g of MCS was added to the above solution and further stirred for one night to remove methanol.

       CO2 adsorption at 0.05 bar and dry condition was performed on a TA Instruments Q600 TGA thermogravimetric analyzer.  In a typical process, about 10 mg of the adsorbent was placed in a platinum sample pan. Before the adsorption test, the adsorbents were pretreated at 100 oC under a N2 flow at 200 mL for 100 min to remove the moisture and adsorbed CO2 as much as possible; then the temperature was decreased to the design temperature. The gas was then switched from N2 to CO2 (5% CO2, 200ml/min), and the adsorbent was held at that temperature for 100 min for the adsorption study. The CO2 capture capacity of the adsorbent in mmol/g sorbent was calculated from the weight gain of the adsorbent in the adsorption process. The MCS and PEI impregnated MCS were characterized by SEM, digital camera, N2-physisorption, TEM, TGA, FTIR, etc.

3. Results and discussion

Fig. 1 SEM (a) and digital (b, 5× magnification) images of the MCS-1, pore structure (c) and CO2 capture capacity (0.05 bar, 75 oC) (d) of PEI/MCS for CO2 removal

       The SEM images of MCS prepared at the C/Si ratio of 1 are shown in Fig.1 (a). Perfect spherical morphology of the MCS is observed with very smooth and clean surface. The diameters of the MCS-1 are very homogeneous and in the region of 0.3-0.4 mm. The digital image in Fig. 1(b) also shows the excellent and homogeneous spherical structures, which make the spheres wonderful mobility and dust-free property. The pore structures of the MCS were measured by N2 physisorption. The N2 adsorption-desorption isotherms of MCS with different C/Si ratio are presented in Fig. 1(c). The combination of Type I and IV isotherms indicates the co-existence of micropores and the mesopores/macropores. The micropore volumes (0.16-0.18 cm3/g) of MCS are similar and mesopore/macroporous volume increased with the C/Si ratio. The total volumes of MCS with C/Si of 0.75, 1, 1.5 are 1.25, 1.61, and 2.68 cm3/g, respectively. The specific surface areas of the MCS are in the region of 817-1097 m2/g. The developed pore structure of MCS allows a high amount of PEI loading with good dispersion.

       The effect of PEI loading on the CO2 capture was studied. The results showed that there is an optimal loading for the MCS, where larger or smaller PEI loading can result in a smaller CO2 capacity.  The optimal PEI loadings depending on the pore structure of MCS were 55, 63, and 70wt. % for MCS-0.75, MCS-1, and MCS-1.5, respectively.  The adsorption temperature also significantly affects the CO2 capacity. There is a balance between the CO2 adsorption/desorption and diffusion in the PEI film in the sorbent. High temperature improves the CO2 diffusion, but decreases the CO2 adsorption. Low temperature is benefit for the adsorption, but it causes a low PEI utilization due to the diffusion limitation.  75 oC is the best temperature for the CO2 adsorption over PEI/MCS. The CO2 adsorption capacity measured at CO2 partial pressure of 0.05 bar and 75 oC are shown in Fig. 1(d). The PEI impregnated MCS with medium pore volume (65PEI/MCS-1) exhibited the highest CO2 capacity of 3.22 mmol/g, which outperforms the best solid sorbents reported at similar condition.1,2 The PEI impregnated MCS also exhibited excellent sorption kinetics and regeneration performance (97-99%). 

4. Conclusions

       Mesoporous carbon spheres (MCS) with perfect spherical morphology and control pore structure were prepared by a hard-template assisted reverse emulsion method. After impregnation with PEI, the obtained sorbent showed excellent CO2 capacity at low CO2 partial pressure, which can be used as excellent sorbent for post-combustion CO2 capture from natural gas power plant.

Reference:

1. J. Wang, M. Wang, W. Li, W. Qiao, D. Long, L. Ling, AIChE J. 2015, 61, 972-980.

2. K.  Min, W. Choi, C. Kim,  M. Choi, Nat. Commun. 2018, 9, 726.


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