Article pubs.acs.org/IECR
Cite This: Ind. Eng. Chem. Res. 2018, 57, 11625−11635
Investigation of Y2O3/MxOy‑Incorporated Ca-Based Sorbents for Efficient and Stable CO2 Capture at High Temperature Donglin He, Changlei Qin,* Zonghao Zhang, Shuai Pi, Jingyu Ran, and Ge Pu
Ind. Eng. Chem. Res. 2018.57:11625-11635. Downloaded from pubs.acs.org by KAOHSIUNG MEDICAL UNIV on 09/04/18. For personal use only.
Key Laboratory of Low-grade Energy Utilization Technologies and Systems of Ministry of Education, College of Power Engineering, Chongqing University, Chongqing 400044, China ABSTRACT: The control of anthropogenic CO2 emissions has attracted worldwide attention because of global warming. Among diverse carbon capture technologies, calcium looping (CaL) is proposed as a favorable approach for postcombustion CO2 mitigation. However, the sorbents’ capacitive loss with increased CaL cycling has severely limited the efficient application of the method. Therefore, obtaining sintering-resistant Ca-based sorbents with high capture capacity, fast capture kinetics, and superior stability is considered a research priority. Here, we reported our latest work on the development of a novel Y2O3/MxOy-modified Ca-based sorbent with superior CO2 sorption performance. Y20/Mg20, i.e., synthetic Cabased sorbents with Y and Mg incorporated at the mass ratio of 1:1, achieved a significantly high conversion (above 90%) in 20 CaL cycles at a typical calcination temperature (∼900 °C) and was stabilized at the CO2 uptake of 0.311 g of CO2/g of sorbent even after 122 CaL cycles. A comprehensive investigation revealed that the outstanding performance arose from the characteristics of (1) superior surface area and pore volume, provided by pores with radii of 900 °C and ≥70% CO2 in volume), the capacity loss is intensified. Until now, the capacity loss of Ca-based sorbents has attracted significant research attention; various strategies have been developed to enhance and stabilize the CO2-capturing capacity of sorbents.14−18 Naturally occurring materials such as limestone and dolomite, often used as CO2-capturing sorbents, possess superior economic efficiency. However, their distinct decreases in CO2 sorption performance are inevitable and unsolvable.19,20 Depending on the situation, several potentially viable options have been proposed to counteract this deactivation. Anthony and Manovic21 studied the effects of thermal pretreatment on the CO2-capturing capacity of various limestone-based sorbents. Extensive research22−24 has also demonstrated that the hydration of spent sorbents is a promising reactivation strategy. In addition, Li et al.25 observed that dolomite modified by chemical pretreatment yielded sorbents with superior activity compared to the original materials. The slight improvements in CO2 sorption achieved by these measures indicate that they are not ultimate solutions. In contrast, the synthesis of Ca-based sorbents via the incorporation of CaO in inert and refractory supports could
1. INTRODUCTION CO2 is a major anthropogenic greenhouse gas, and its emission via the combustion of fossil fuels contributes considerably to global climate change. Increases in average air temperature and sea level are evident warming signs in the global climate. According to the Intergovernmental Panel on Climate Changes (IPCC), the global mean sea level is estimated to increase by 0.18 to 0.59 m; the expected global temperature increase is 1.1−6.4 K this century.1 Meanwhile, global CO2 emission continues to increase; it is estimated to reach 40.2 Gt by 2030.2 Therefore, the implementation of CO2 emission control is of great significance to mitigate global climate change. The developing technology of CO2 capture and storage (CCS) recently emerged as a potential method for meeting greenhouse gas emission reduction targets. With significant research efforts underway to develop more efficient and less costly CO2 capture technologies,3−7 calcium looping (CaL), characterized by the looping of a Ca-based sorbent in carbonation/calcination cycles, has been rapidly developed as one of the most promising CO2 capture technologies.8−13 While offering significant advantages, CaL suffers the wellknown problem of capacity loss, which severely deteriorates the efficiency and stability of CaL and hinders its large-scale industrial application. Under realistic CaL conditions with low CO2 concentrations (≤15% in volume) in carbonating and high temperatures and high CO2 concentrations in the © 2018 American Chemical Society
Received: Revised: Accepted: Published: 11625
May 11, 2018 July 14, 2018 July 31, 2018 July 31, 2018 DOI: 10.1021/acs.iecr.8b02064 Ind. Eng. Chem. Res. 2018, 57, 11625−11635
Article
Industrial & Engineering Chemistry Research
Figure 1. Pore structure parameters of various fresh sorbents after initial calcination.
2. MATERIALS AND METHODS 2.1. Sample Preparation. Calcium nitrate tetrahydrate (Ca(NO3)2·4H2O, 99.9% purity), magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, 99.9% purity), and yttrium nitrate hexahydrate (Y(NO3)3·6H2O, 99.9% purity) from Aladdin Industrial Co. Ltd. were used as CaO and support precursors, respectively. Sorbents were synthesized via a sol−gel combustion method. For each sorbent, a calculated amount of raw materials were dissolved into deionized water and then added into a citric acid (C6H8O7·H2O, 99.9% purity, Aladdin Industrial Co. Ltd.) solution dropwise. The molar ratios of metal ions to citric acid were set as 1:3. Subsequently, the solution was stirred at 100 °C in a thermostatic water bath for at least 5 h to produce well-dispersed sol. To form a wet gel, the sol was placed under room temperature for 24 h. Afterward, the wet gel was dried at 110 °C until it was completely dehydrated and then it was milled to get a uniform particle size of
