Effects of porous carbon additives on the CO2 absorption performance of lithium orthosilicate
Graphical abstract
Introduction
Increasing atmospheric CO2 concentration, which is mostly due to the burning of fossil fuels, has been identified as a major contributor to global warming [1]. Because the direct capture of CO2 from power plants is economically viable, zeolites [2], amine-based materials [3], magnesium and calcium oxides [4], [5], [6], and lithium-based oxide composites [7], [8], [9], [10], [11] have been tested as high temperature CO2 sorbents. In particular, among lithium-based oxide sorbents, lithium orthosilicate (Li4SiO4) has been recognized as an attractive sorbent, since it has theoretical CO2 absorption capacity of up to 36.7 wt% of its original weight (Li4SiO4 + CO2 ↔ Li2CO3 + Li2SiO3) [12]. It is also known to have reasonable material costs. However, most reported Li4SiO4 sorbents have displayed slow kinetics and the partial reaction with CO2, which lead low absorption capacities [13], [14]. Because the introduction of a high concentration of active sites on Li4SiO4 sorbents can solve this problem, various efforts have been made to synthesize the Li4SiO4 with a large surface area and small particle size. For example, diatomite has been used as a silica precursor to yield Li4SiO4 having a higher surface area. This high surface area arises from the uniform pore structure of diatomite (pore size, ∼500 nm), which can produce macropores in the Li4SiO4 sorbent unlike solids synthesized using analytically pure silica [15], [16]. As a result, this Li4SiO4 with a high surface area had superior CO2 absorption properties in terms of kinetics and capacity. Recently Choi et al. reported that decreasing the synthesis temperature prevented sintering, allowing the formation of a macroporous structure, and enhancing both the CO2 absorption capacity and rate in comparison to nonporous Li4SiO4 [17]. Ball-milling is a facile method to reduce particle size and increase the surface area of the nanomaterials. In the synthesis of Li4SiO4, ball-milling resulted in the formation of sorbent particles that were 30-times smaller and had 12-times the surface area of bulk Li4SiO4 [18]. The sol-gel method was also used to generate nano-sized particles, which result from the better mixing of reactants and the higher reaction rate, which showed the distinguishable properties like CO2 absorption capacity and kinetics with Li4SiO4 synthesized by solid-state methods [19], [20].
In spite of efforts to form advantageous structures for CO2 absorption, these morphologies are often not maintained during high-temperature CO2 absorption/desorption cycles, leading to capacity losses. Because Li2CO3, which is formed from the reaction between Li4SiO4 and CO2, exists as a molten phase in the range of the absorption temperature, the initial textural properties are lost by severe agglomeration [21]. Previously, as a trial to maintain the original morphology of some oxide materials, various additives have been introduced in the synthetic process. The Colon group used carbon-based material as an additive to prepare TiO2 nanoparticles, which play a role in preventing the formation of an irregular morphology; furthermore, this additive leads to the formation of a high surface area [22]. Mahinpey et al. reported that the composite of CaO sorbents with Al2O3 additives showed the improved cyclability by retaining its original capacity. The authors claimed that this result was attributed to the more active CaO sites induced by the co-existing alumina. [23]. On this wise, the introduction of additives to Li4SiO4 sorbents can be a feasible solution to improve the textural properties and physical stability.
Our strategy is the introduction of porous materials to provide the CO2 diffusion pathways and high surface area into Li4SiO4 sorbents. The additives chosen for use in the synthesis of Li4SiO4 must be non-reactive with the lithium precursors to avoid undesirable production of unnecessary species for CO2 absorption. In this sense, we selected highly porous carbon, CMK-3, which has a surface area of 1520 m2 g−1 and a total pore volume of 1.3 cm3 g−1, as an additive due to its low reactivity with lithium [24], [25]. The embedded porous carbon in Li4SiO4 produced through the facile wet-mixing method affords more CO2 diffusion pathways in the resultant Li4SiO4 sorbents; this is expected to affect their CO2 absorption behavior. In this paper, we describe our investigation into the roles of the porous carbon materials on enhancing the CO2 absorption properties of Li4SiO4 by synthesizing Li4SiO4 and carbon composites with different kinds and amounts of porous carbon.
Section snippets
Materials
Analytical grade chemicals lithium hydroxide monohydrate (LiOH·H2O, >98.0%), silica, fumed (SiO2, 0.007 μm powder), and carbon nanotube, multi-walled, carboxylic acid functionalized (MWCNT, >8% carboxylic acid functionalized) were purchased from Aldrich. All of these chemicals have been used without additional purification. CMK-3 was synthesized according to a previous report [25].
Pristine Li4SiO4 (p-Li4SiO4)
p-Li4SiO4 was synthesized according to a previous report [18]. LiOH·H2O (0.29 g, 6.8 mmol) and SiO2 (0.10 g, 1.7 mmol)
Synthesis and characterizations of p-Li4SiO4 and porous carbon-containing Li4SiO4 (Li4SiO4@CMK)
CMK-3 was added and well-dispersed in the water solution of the Li4SiO4 precursors (LiOH·H2O and SiO2) to intermingle it with Li4SiO4 homogeneously, and then water was eliminated by heating. Because, at high absorption temperatures, porous carbon species are not expected to absorb CO2, the excess quantity of CMK-3 can cause a gravimetric disadvantage. Thus, to control the effective amount of CMK-3, additional calcination was conducted in air at 700 °C (Scheme 1). For the second calcination, the
Conclusions
We synthesized Li4SiO4 sorbents that included porous carbon, CMK-3, as an additive. The formed sorbents had higher surface areas and pore volumes than p-Li4SiO4, and showed characteristics of CO2 diffusion. These characteristics may be due to the addition of porous carbon additives into Li4SiO4 that gives CO2 diffusion pathways; in addition, this may be attributed to not only the porosity of the additive itself but also the voids between Li4SiO4 and porous carbon material. The Li4SiO4@CMK
Acknowledgments
This work was supported by the Basic Science Research Program through the National Research Foundation (NRF) of Korea (NRF-2014M1A8A1049255; 2013K1A3A1A04076417). J.H.L. acknowledges the Global PhD Fellowship (NRF-2013H1A2A1033501). We are grateful to Prof. Sang Hoon Joo for helpful discussion.
References (29)
- et al.
Lithium based ceramic materials and membranes for high temperature CO2 separation
Prog. Mater. Sci.
(2009) - et al.
Novel lithium-based sorbents from fly ashes for CO2 capture at high temperatures
Int. J. Greenhouse Gas Control
(2010) - et al.
Facile synthesis of macroporous Li4SiO4 with remarkably enhanced CO2 adsorption kinetics
Chem. Eng. J.
(2015) - et al.
Microstructural and CO2 chemisorption analyses of Li4SiO4: effect of surface modification by the ball milling process
Thermochim. Acta
(2013) - et al.
A novel preparation of high surface area TiO2 nanoparticles from alkoxide precursor and using active carbon as additive
Catal. Today
(2002) - et al.
Life cycle assessment of a pulverized coal power plant with post-combustion capture, transport and storage of CO2
Int. J. Greenhouse Gas Control
(2008) Review of solutions to global warming air pollution, and energy security
Energy Environ. Sci.
(2009)- et al.
Adsorption of CO2, N2, and O2 on natural zeolites
Energy Fuels
(2003) - et al.
CO2 capture by tertiary amine absorbents: a performance comparison study
Ind. Eng. Chem. Res.
(2013) - et al.
A novel porous MgO sorbent fabricated through carbon insertion
J. Mater. Chem. A
(2014)
Change in limestone sorbent morphology during CaO-CaCO3 looping at pilot scale
Chem. Eng. Technol.
Design and synthesis of stable supported-CaO sorbents for CO2 capture
J. Mater. Chem. A
Analysis of the CO2 chemisorption reaction mechanism in lithium oxosilicate (Li8SiO6): a new option for high temperature CO2 capture
J. Mater. Chem. A
Kinetic and reaction mechanism of CO2 sorption on Li4SiO4: study of the particle size effect
Ind. Eng. Chem. Res.
Cited by (20)
Preparation of Li<inf>4</inf>SiO<inf>4</inf> from lithium-ion battery cathode waste and diamond wire saw silicon powder using a two-step process
2024, Journal of Environmental Chemical EngineeringCO<inf>2</inf> capture by Li<inf>4</inf>SiO<inf>4</inf> Sorbents: From fundamentals to applications
2022, Separation and Purification TechnologyLi<inf>4</inf>SiO<inf>4</inf>-based sorbents from expanded perlite for high-temperature CO<inf>2</inf> capture
2021, Chemical Engineering JournalDevelopment of KNaTiO<inf>3</inf> as a novel high-temperature CO<inf>2</inf> capturing material with fast sorption rate and high reversible sorption capacity
2020, Chemical Engineering JournalCitation Excerpt :Alkali silicate-based sorbents have attracted tremendous attention owing to its high CO2 capture capacity and lower regeneration temperature compared with CaO. A series of alkali silicate-based adsorbents including Li4SiO4 [27], Li4-xNaxSiO4 [28], Li2MnSiO4 [29], Li8SiO6, Li6Si2O7, Li2SiO3 [30], Li2Si2O5, Li2Si3O7, and CaSiO3 [31], have been studied for high-temperature CO2 capture. Among these materials, Li4SiO4 is considered to be the most potential material [19].
Sorption of CO<inf>2</inf> on NaBr co-doped Li<inf>4</inf>SiO<inf>4</inf> ceramics: Structural and kinetic analysis
2019, Fuel Processing TechnologyCitation Excerpt :Solid-state Li4SiO4 fabricated by traditional methods has an extremely low porosity and typically very large particle/grain size, making the reaction between Li4SiO4 and CO2 relatively slow [16]. To decrease particle sizes and increase its specific surface area, several synthetic routes, including ball milling [17,18], impregnated suspension [19–21], precipitation [22], sol–gel techniques [23–25], carbon templates or porous carbon [26–28] and hydration [29], have been suggested. Unfortunately, these morphologically-improved particles still exhibited unsatisfactory reaction kinetics (~10−4 s−1) under typical hot flue gases in thermal power applications or under SE-SMR conditions [29,30].
Thermokinetic evaluation of iron addition on lithium metazirconate (Fe-Li <inf>2</inf> ZrO <inf>3</inf> ) for enhancing carbon dioxide capture at high temperatures
2019, Thermochimica ActaCitation Excerpt :Since that time, other lithium and sodium containing ceramics have been proposed as possible high temperature CO2 captors [2–7]. Among all these ceramics, lithium orthosilicate (Li4SiO4) [8–14], lithium cuprate (Li2CuO2) [15–17], lithium ferrite (Li5FeO4) [18] as well as lithium and sodium zirconates (Li2ZrO3 [19–22] and Na2ZrO3 [23–27]) seem to possess some of the best physicochemical properties for CO2 sorption processes. To improve the CO2 capture properties on alkaline ceramics, different structural and microstructural modifications have been performed [25,28–32].