Summary of clay-based CO2 capture

https://doi.org/10.1016/j.ijggc.2020.103005

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Clay based materials have attracted attention for CO₂ capture applications due to their potential to overcome issues related to commercial availability, cost, and hydrothermal stability (Wang et al., 2013b, b). Clays are cost effective materials that are available abundantly in nature having a molecular structure that comprises a combinatorial sheet of tetrahedral silicates and octahedral hydroxides. These characteristics together with appreciable chemical and mechanical stability make clays appropriate as support materials for CO₂ capture (Jozefaciuk and Bowanko, 2002; Karahan et al., 2006; Roth et al., 2013), though acid or alkaline treatment is often necessary in order to overcome deficiencies related to textural features, which may compromise their application potential (Jozefaciuk and Matyka-Sarzynska, 2006; Wang et al., 2014b). This section examines works on various clay – supported PEI sorbent systems based on montmorillonite, kaolinite, sepiolite, saponite, palygorskite, halloysite, and bentonite.

Formation of BPEI – impregnated clays for CO₂ adsorption was reported by Wang et al. (Wang et al., 2014b). The clays were pretreated with either acid or alkali in order to increase surface area and pore volume, and thereby to enhance BPEI impregnation efficiency. The authors examined the suitability of two types of clays, i.e., kaolinite and montmorillonite (MMT). In comparison to other studied systems, MMT treated with 6 M HCl exhibited significantly enhanced surface area and porosity. At 75 °C, the observed CO₂ adsorption capacities for MMT with 50 wt% PEI loading were ca. 2.55 mmol g⁻¹ and 3.23 mmol g⁻¹ in dry conditions and at 3% moisture, respectively, coupled also to appreciable cycling and thermal stabilities. Gomez-Pozuelo et al. (Gómez-Pozuelo et al., 2019) developed a series of PEI – impreganated clays, and CO₂ capacities of 1.53, 1.52, 1.38, 1.27, and 1.04 mmol g⁻¹ were recorded at 45 °C and 1 bar into palygorskite, saponite, MMT, sepiolite, and bentonite, respectively, after 37 wt% PEI loading.

Vilarrasa-Garcia et al. (Vilarrasa-García et al., 2017b) designed a solid CO₂ sorbent based on sepiolite by following initial microwave radiation aided by HNO₃ treatment and subsequent PEI impregnation. For such an adsorbent with 30 wt% of BPEI (M_n = 600), a CO₂ uptake of ca. 1.70 mmol g⁻¹ was observed at 1 atm and 65 °C. Additionally, high CO₂/N₂ selectivity value of ca. 440 mol CO₂/mol N₂ was achieved. Ouyang et al. (Ouyang et al., 2018) presented the fabrication of CO₂ adsorbent through the PEI loading into HCl – treated sepiolite clay fibers. Acid treatment of sepiolite clay resulted in the generation of MgO-SiO₂ nanowires. The obtained CO₂ adsorption capacity at 75 °C and 1 atm was 2.48 mmol g⁻¹ for PEI loading of 50 wt%. This system maintained ca. 98 % of its adsorption capacity after 10 successive adsorption-desorption cycles.

Cai et al. (Cai et al., 2015) reported the functionalization of halloysite nanotubes (HNTs) by PEI impregnation for CO₂ capture. Adsorption studies at room temperature (25 °C) revealed a capacity of 1.25 mmol g⁻¹ for 35 wt% PEI loading, with appreciable regenerability for over 50 cycles. In another work, Niu et al. (Niu et al., 2016) reported a nanocomposite adsorbent designed by impregnating PEI into pre-treated HNTs for CO₂ capture. HNTs pre-treatment, which included calcination and subsequent HCl treatment, resulted in generation of silica mesoporous nanotubes with enhanced specific surface area and pore volume. After PEI impregnation, this material displayed an adsorption uptake of ca. 2.75 mmol g⁻¹ at 85 °C for 50 wt% PEI. Also, cyclic analysis underlined the promising regenerability for this adsorbent. An uptake of 7.84 mmol g⁻¹ was reported by Taheri et al. (Taheri et al., 2019) at 9 bar and 20 °C for a nanocomposite adsorbent consisting of 30 wt% PEI (M_n = 800) – modified silica mesoporous nanotubes, Notably, the drop in adsorption performance was limited to only 5 % after 15 adsorption-desorption cycles.

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