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Environmental and Carbon Dioxide Issues
Energy and Economic Analysis for the Post-Combustion CO2 Capture using Amine-Functionalized Adsorbents in a Temperature Vacuum Swing Process Changan Zhou, Kaiwu He, Wenyao Lv, Yaxin Chen, Siyang Tang, Changjun Liu, Hairong Yue, and Bin Liang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02837 • Publication Date (Web): 19 Oct 2018 Downloaded from http://pubs.acs.org on October 28, 2018
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Energy & Fuels
Energy and Economic Analysis for the Post-Combustion CO2 Capture using Amine-Functionalized Adsorbents in a Temperature Vacuum Swing Process Changan Zhou1, Kaiwu He1, Wenyao Lv1, Yaxin Chen1, Siyang Tang1, Changjun Liu1,2, Hairong Yue1,2*, and Bin Liang1,2 1
Multi-phases Mass Transfer and Reaction Engineering Laboratory, School of Chemical
Engineering, Sichuan University, Chengdu 610065, China; 2
Institute of New Energy and Low-Carbon Technology, Sichuan University, Chengdu
610207, China *Corresponding author:
[email protected], TEL/FAX: (+86) 22-85997677
Graphic Abstract
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Abstract Post-combustion CO2 capture using amine-functionalized solid adsorbents has been extensively investigated during the past two decades; however, the preparation of industrial adsorbents still underlies some key issues, and the energy consumption and economy of this process are not clear. Herein, we investigated the preparation of industrial M-MCM-T adsorbents via the conventional extrusion method, emphasizing the mechanical properties and CO2 capture performance of the adsorbents. The 40M-MCM55T adsorbent, with 40% montmorillonite as a binder and 55% tetraethylenepentamine, exhibited the maximum CO2 adsorption capacity of 101.6 mg·g-1 at 75 ℃ and a high mechanical strength of 112.2 N·cm-1. Based on the experimental results, the temperature vacuum swing (TVS) process with a capacity of 300 t/a CO2 was designed to estimate the cost and energy requirements of this process; it revealed a cost of $29.68/tCO2 and an energy consumption of about 4.20GJ/tCO2. The results suggest the superiority and potential of using amine-functionalized solid adsorbents in the TVS process for CO2 capture from flue gas in industry. Key words: CO2 capture, amine-functionalized adsorbents, mechanical strength, economic analysis, temperature vacuum swing process 1.
Introduction The increase in anthropogenic CO2 emissions, mainly caused by the combustion of
fossil fuels, has caused a global greenhouse effect,1 and the CO2 concentration in the atmosphere has reached 406 ppm.2 Carbon capture and storage technologies are promising methods to reduce the concentration of CO2 in the atmosphere.3 Common techniques for post-combustion CO2 capture are solvent absorption,4 membrane 2 ACS Paragon Plus Environment
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Energy & Fuels
separation,5 and adsorption methods.6 The aqueous amine solution absorption and solid adsorbent absorption methods are appropriate for post-combustion CO2 capture. However, the amine solvent adsorption process has several drawbacks, such as strong corrosion, high energy consumption, and solvent evaporation.7 Solid adsorbents, especially mesoporous silicates, may overcome these drawbacks because of their low energy consumption, good thermal stability, and easy regeneration.8 Furthermore, the aminefunctionalized adsorbent exhibited excellent CO2 adsorption capacities through physical adsorption based on its large pore volumes and high specific surface areas and chemical adsorption of the surface functional groups of organic amines. Reports to date on amine-functionalized adsorbents have primarily focused on the surface chemistry, recyclability, and CO2 adsorption capacity. Zhu et al.9, 10 synthesized MCM-41- and SBA-15-supported adsorbents functionalized with tetraethylenepentamine (TEPA) with a maximum CO2 adsorption capacity (237 and 173 mg·g-1, respectively). Our previous work reported mine-grafted mesoporous copper silicates for CO2 capture with excellent cyclic regenerability (maximum deviation of 3.51% after 20 tests).11 However, there are scarce systematic investigations into the shaping process and mechanical properties of the shaped adsorbents for industrial applications based on the large pressure drop of the powder adsorbents in gas-solid systems.12 Thakkar et al. fabricated aminosilica monoliths using a three-dimensional printing method; the maximum CO2 adsorption capacities reached 2.23 mmol·g-1 under dry conditions and 3.12 mmol·g-1 under humid conditions.13 Klinthong et al. reported a simple, one-pot synthetic method to produce pelletized adsorbents, and the optimal sample exhibited a CO2 adsorption capacity of 147 mg·g-1 under 15% CO2 in N2.14 These molding methods
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could fabricate adsorbents with excellent CO2 adsorption performances. The methods to produce vast industrial adsorbents are also needed for industrial applications. To obtain desirable physicochemical and mechanical properties for industrial applications, extrusion is a very common method for the fabrication of industrial catalysts and adsorbents. Zhao et al. explored the effect of Cu loading on the mechanical properties and catalytic activities of an extruded Cu/SiO2 cylinder as an ideal catalyst for dimethyl oxalate hydrogenation in industrial applications.15 Qin et al. found that CaObased adsorbents fabricated using a screw extrusion method showed a good attrition resistance and mechanical strength.16 In addition, the binders played an important role in enhancing the mechanical strength of the adsorbents. Montmorillonite is a natural mineral of silicate and can form colloidal materials that function as a bridge to absorb onto the porous structure of the support via van der Waals forces.17 Roth et al. reported CO2 uptakes
of
7.5
wt.%
for
montmorillonite
nanoclay
treated
with
3-
aminopropyltrimethoxysilane and polyethylenimine (PEI).18 Wang et al. reported that an acid-treated montmorillonite adsorbent loaded with 50 wt.% PEI could reach a CO2 adsorption capacity of 112 mg CO2/g-sorbent.19 Therefore, systematically investigating the preparation of industrial amine-functionalized adsorbents via the extrusion method, and clarifying the mechanical properties and CO2 capture performance are crucial for the CO2 adsorption process. In addition, the cost and energy assessments of the CO2 capture process are vital for industrial applications. Investigations into the economics of CO2 capture using aminefunctionalized sorbents are scarce. Li et al. reported CO2 capture from flue gas using aqueous monoethanolamine (MEA) using the Aspen Plus software (AspenTech) with a 4 ACS Paragon Plus Environment
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Energy & Fuels
total energy consumption of 4.44 MJ/kgCO2.20 Kulkarni et al. analyzed temperature swing adsorption (TSA) processes for directing air capture using a TRI-PE-MCM-41 adsorbent in a daily throughput of ~1.1 tCO2 (88.5%), and the net operating cost of the total process was about $100/tCO2, and the total energy was 6745 MJ/tCO2.21 Jones and co-workers developed amine-functionalized monolithic CO2 sorbents for CO2 capture from air with a process cost of about $100/tCO2.22 The current technologies for regenerating solid adsorbents include pressure swing adsorption, vacuum swing adsorption (VSA), and TSA processes. The temperature vacuum swing (TVS) process is an energy-efficient process to deal with flue gas in large quantities,23-25 which could use low-grade steam stripping for regeneration of solid adsorbents, and obtain high concentration CO2 by removing liquid water after condensation.26 In addition, the presence of appropriate water (humidity ≈ 5%-10%) on the adsorbents can greatly enhance the CO2 capacity.27 However, excess H2O also causes adverse effects: the binding strength of adsorbed CO2 increases and more energy is required for adsorbent regeneration,28-30 and CO2 adsorption processes may be inhibited.31,
32
Therefore, the TVS process combined with VSA and TSA
processes might be a highly efficient method for CO2 capture. The above studies provided useful insights into the development of CO2 capture technologies. However, no study has yet reported detailed cost and energy analyses for CO2 capture from flue gas on the shaped industrial adsorbents by modeling a TVS process. In this study, the preparation of industrial M-MCM-T adsorbents using the extrusion method was systematically investigated with emphasis on the mechanical properties and CO2 capture performance of the adsorbents. Based on the experimental results, a 300t/a CO2 TVS process was designed, and the cost and energy requirements of
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the flue gas CO2 capture process were estimated. This work confirms the superiority of using solid adsorbents for the capture of CO2 from flue gas for industrial applications. 2.
Experimental section
2.1. Materials The MCM-41 support was purchased from the Nankai University Catalyst Co. Ltd. (Tianjin, China). The montmorillonite binder was obtained from Shanghai Titan Scientific Co. Ltd. Soluble starch, anhydrous ethanol, and TEPA were purchased from Kelong Chemical Reagent Co. Ltd. 2.2. Preparation of amine-functionalized M-MCM-T adsorbents The
preparation
of
amine-functionalized
M-MCM-T
adsorbents
involved
granulation of the MCM-41 powder and the subsequent impregnation of TEPA. The detail steps are shown in Figure 1. The MCM-41 powder was first calcined at 900°C for 12 h to remove the template in nitrogen atmosphere. The calcined MCM-41 powder (1000 g) was ground to particle sizes
