Elsevier

Renewable Energy

Volume 144, December 2019, Pages 180-187
Renewable Energy

Regenerable sodium-based lithium silicate sorbents with a new mechanism for CO2 capture at high temperature

https://doi.org/10.1016/j.renene.2018.08.039Get rights and content

Highlights

  • A sorbent containing Li3NaSiO4 and Li4SiO4 was developed for CO2 capture.

  • The sorbent was prepared by mixing LiOH with Na2SiO4 solution in a 2:1 M ratio.

  • Li3NaSiO4 was contributed to CO2 capture at high temperature.

  • Li3NaSiO4 is the primary active material in the sorbent.

Abstract

Recently, lithium-ion batteries have become widespread as a source of power or energy for everything from portable electronics to electric vehicles. As a result, the consumption of lithium is rapidly increasing, accompanied by an increase in its price. This study reports the synthesis of a regenerable sodium-based lithium silicate solid sorbent that uses less lithium than Li4SiO4 solid sorbents. The regenerable sodium-based lithium silicate solid sorbent was prepared by mixing LiOH with a sodium silicate solution in a 2:1 M ratio, which steadily maintained its CO2 capture capacity during multiple cycles. In addition to Li4SiO4 present in the developed solid sorbent, we attribute CO2 sorption and regeneration to a new structure, namely Li3NaSiO4. Notably, the LONS2 solid sorbent exhibits a faster CO2 sorption rate than that of the Li4SiO4 sorbent. Moreover, the LONS2 solid sorbent containing both Li3NaSiO4 and Li4SiO4 phases has potential for CO2 capture at high temperature.

Introduction

The increase in greenhouse gases, especially carbon dioxide (CO2) generated by the combustion of fossil fuels (oil, natural gas, and coal), is widely known as the main cause of global warming and climate change. Coal-fired power plants emit significant amounts of CO2 in all industrial processes [1,2]. With growing global awareness of the negative effects of CO2 emission, regulations and technologies are currently being developed for its reduction.

For large-scale CO2 emissions sites such as coal-fired power plants, a major concern for capturing CO2 is reducing the of regeneration energy required for CO2 desorption. Park et al. proposed a multi-stage solid sorbent CO2 capture process in order to reduce this regeneration energy requirement for CO2 desorption. This multi-stage CO2 capture process consisted of three-stages of different sorption and desorption temperatures: low temperature (40–150 °C, amine-based sorbent), medium temperature (300–450 °C, alkali-promoted MgO), and high-temperature (600–750 °C, Li4SiO4) [3,4]. This previous report focused on the development of a novel CO2 capture process that can reduce 30% of the operating costs of CO2 capture for application in coal-fired power plants [3]. For the success of energy exchange-type three-stage CO2 capture processes, it is essential to develop a solid sorbent with optimal performance (i.e., CO2 capture capacity, sorption rate, and long-term stability) at each stage.

In this study, we focused on developing solid sorbents with excellent performance for CO2 capture at high temperature. CaO [[5], [6], [7]] and lithium orthosilicate (Li4SiO4) solid sorbents [[8], [9], [10]] are able to capture CO2 at high temperature and both are able to sorb CO2 continuously during reversible sorption and desorption processes. In the case of the CaO solid sorbent, the reverse calcination reaction is performed in the high temperature range of 850–950 °C. The CaO solid sorbent is very cheap and has a high CO2 capture capacity for CO2 sorption at high temperatures. However, it has the disadvantage of requiring a large amount of energy for complete regeneration (>900 °C) following long-term operation over several cycles [10]. By comparison, the Li4SiO4 solid sorbent is considered one of the most promising CO2 acceptor materials at high temperatures, because it can be used at temperatures (450–800 °C) lower than those required with the CaO solid sorbent [10,11]. The Li4SiO4 solid sorbent can theoretically sorb CO2 in amounts up to 0.36 g CO2/g sorbent. It has been widely reported that the Li4SiO4 solid sorbent reacts reversibly with CO2 leading to the formation of Li2CO3 and Li2SiO3 as follows: Li4SiO4 + CO2 ↔ Li2SiO3 + Li2CO3 [[12], [13], [14], [15], [16]]. However, deactivation caused by sintering during cycling must be overcome to facilitate the regeneration of Li4SiO4-based solid sorbents [17,18]. These problems have been significantly improved by many techniques including the use of additives [15,19,20], nanoparticles [17,21,22], the preparation of various precursors [[23], [24], [25], [26], [27], [28]], and alkali metal doping [[29], [30], [31], [32]].

Recently, however, the lithium ion battery [33,34] industry has been attracting attention as the most important technology of the ‘Smartization era’ due to the fourth industrial revolution. Lithium ion batteries are widely deployed as a source of power or energy 76 for everything from portable electronics to electric vehicles. As a result, the consumption of lithium is increasing rapidly, which is directly related to an increase of its price [35]. With this trend, worldwide lithium-ion battery demand is expected to nearly double in 2018 compared with 2017, and is expected to increase 6–7 fold by 2026 [36]. This is clearly not economical as such consumption would increase the cost of synthesizing Li4SiO4–based solid sorbents.

In this study, a sodium-based lithium silicate sorbent is developed that uses less lithium than that consumed in the synthesis of Li4SiO4-based solid sorbents. Despite this difference, the developed sorbent exhibited almost similar performance to Li4SiO4 solid sorbents. The CO2 capture capacities of these solid sorbents were investigated during multiple cycles in the presence of 10 vol% CO2 and 10 vol% H2O in a fixed-bed reactor. Additionally, the performances of the developed sodium-based lithium silicate solid sorbents were characterized by studying their CO2 capture capacity, sorption rate, cyclic stability, and CO2 sorption/desorption through powder X-ray diffraction (XRD) and temperature-programmed desorption (TPD) analyses.

Section snippets

Preparation of sorbents

First, lithium silicate-based solid sorbents (Li4SiO4 and/or Li2SiO3) were synthesized using the solid-state method. Lithium carbonate (Li2CO3, Aldrich, 99.9%) and silica oxide (SiO2, Aldrich, 99.9%) were mixed in 1:1 and 2:1 M ratios. The obtained mixture was then placed in an alumina crucible and calcined in an electric muffle furnace under air for 5 h at 700 °C. The temperature ramping rate was maintained at 5 °C/min. These samples are denoted as LSx, where L and S represent Li2CO3 and SiO2,

Characterization of novel sodium-based lithium silicate solid sorbents

Fig. 2 shows the XRD patterns of the LS1, LS2, LONS1, LONS2, and LONS3 solid sorbents before CO2 capture. The lithium silicate-based LS1 and LS2 solid sorbents were prepared by mixing 1 and 2 mol of Li2CO3 with SiO2 powder, respectively. Likewise, the LONS1, LONS2, and LONS3 solid sorbents were prepared by mixing 1, 2, and 3 mol of LiOH as the Li precursor with a sodium silicate solution (instead of SiO2 powder), respectively. In the case of the LS1 solid sorbent, its corresponding XRD pattern

Conclusion

The CO2 capture capacity of the regenerable sodium-based lithium silicate solid sorbents (LONS2) developed in this study was maintained at approximately 253–223 mg CO2/g sorbent during multiple sorption/regeneration tests in the high temperature range between 550 and 700 °C. The CO2 sorption rate of the LONS2 solid sorbent was much faster than the Li4SiO4 (LS2) solid sorbent. Notably, we found that the LONS2 solid sorbent contained Li4SiO4 as well as Li3NaSiO4 phases. The new Li3NaSiO4 phase

Acknowledgment

This work was supported by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology [grant number 2009-0093819]. Support from the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea [grant number 20173010050110] is also acknowledged.

References (36)

  • Ke Wang et al.

    Development of metallic element-stabilized Li4SiO4 sorbents for cyclic CO2 capture

    Int. J. Hydrogen Energy

    (2017)
  • Ke Wang et al.

    Synthesis of a highly efficient Li4SiO4 ceramic modified with a gluconic acid-based carbon coating for high-temperature CO2 capture

    Appl. Energy

    (2016)
  • T. Yamaguchi et al.

    Lithium silicate based membranes for high temperature CO2 separation

    J. Membr. Sci.

    (2007)
  • IPCC

    IPCC Special Report on Carbon Dioxide Capture and Storage

    (2005)
  • Y. Duan et al.

    CO2 capture properties of lithium silicates with different ratios of Li2O/SiO2: an ab initio thermodynamic and experimental approach

    Phys. Chem. Chem. Phys.

    (2013)
  • H.K. Rusten et al.

    Numerical investigation of sorption enhanced steam methane reforming using Li2ZrO3 as CO2-acceptor

    Ind. Eng. Chem. Res.

    (2007)
  • K. Nakagawa et al.

    A novel method of CO2 capture from high temperature gases

    J. Electrochem. Soc.

    (1998)
  • R. Rodriguez-Mosqueda et al.

    Thermokinetic analysis of the CO2 chemisorption on Li4SiO4 by using different gas flow rates and particle sizes. 356

    J. Phys.Chem. A.

    (2010)
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    Yong Mok Kwon and Soo Chool Lee have contributed equally to this work.

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