Interlayer Cation-Controlled Adsorption of Carbon Dioxide in Anhydrous Montmorillonite Clay

Abstract

Widely available natural layered expandable clay minerals (smectites) can sorb carbon dioxide in their interlayer space under specific conditions and hence may show potential for gas separation or carbon sequestration processes. This work presents experimental adsorption and desorption measurements of gaseous, sub-critical carbon dioxide (p = 0.1 bar up to 20 bar, T = −20 °C up to 300 °C) on wellcharacterized anhydrous smectite (Wyoming montmorillonite) and focuses on the effect of the interlayer cation (size). Using seven alkali and alkaline-earth metal cations and three quaternary ammonium cations, a wide range of ionic radii are studied. Physisorption of CO 2 in the interlayer space is confirmed via infrared spectroscopy measurements. The results show that optimally sized interlayer cationscomparable to the thickness of a carbon dioxide monolayeropen the interlayer space to make it easily accessible for CO 2 up to 1.7 mmol g −1 . In particular, Cs-exchanged and tetramethylammonium-exchanged montmorillonite facilitate the rapid sorption of carbon dioxide even at ambient pressure and temperature. These results provide valuable insights into the applicability of widely available natural adsorbent clays for carbon capture and sequestration for the mitigation of climate change.

Influence of CO2 on Nanoconfined Water in a Clay Mineral

“…32,38,39 The equilibrium d-spacing value is close to the one observed experimentally for 1WL (12.2 Å), which reveals the important role of water in the clay swelling when exposed to CO 2 . In agreement with previous 11,18,24,32,33 and current experimental results, compared to the dried state (dspacing equal to 9.1 Å), the water layer decreases the cohesion energy for the layer expansion and creates the physical space for the CO 2 intercalation.…”

“…11,23,24,32,33 Under such conditions, only a limited amount of CO 2 adsorption occurs on the external surfaces. From experimental 11,19,20,[22][23][24]34 and molecular simulation 24,32−36 studies, it is now assumed that smaller cations (such as Na + ) require a sub-monolayer of water to "prop open" the interlayer before CO 2 adsorption occurs, while for larger cations (such as Cs + and NH 4 + ), CO 2 is readily adsorbed even in the absence of water. Similar observations have been made for Ni-Hec, which has a corrensite structure, where under anhydrous conditions, the more open chlorite-like layers adsorb CO 2 , and the more closed smectite layers do not.…”

“…This is due to their low cost, natural abundance, and ability to sorb CO 2 . Indeed, clay minerals have been proposed as being useful in cyclic gas separation processes since the regeneration from their weaker adsorption sites requires less energy input than that from stronger adsorption sites in materials such as the benchmark material zeolite 13X . As large quantities of clay minerals are present in the caprock formation of reservoirs intended for anthropogenic CO 2 capture, understanding molecular interactions between water and CO 2 at clay mineral interfaces is paramount to ensure the long-term stability of such reservoirs.…”

“…Smectites are 2:1 layered clay minerals with layers consisting of an octahedral sheet sandwiched between two tetrahedral sheets, where isomorphic substitutions of metal cations in either the octahedral or tetrahedral sheets produce a net negative charge in the clay layer which is balanced by interlayer cations. Smectites are known to swell in response to, and adsorb, both water − and CO 2 . ,− ,− As a result of its natural abundance and also the possibility of melt-synthesizing high-purity samples, Na + -intercalated smectites have been by far the most studied. − For an expandable clay mineral such as smectite, water enters the 2D nanoporous interlayer and expands the clay in discrete steps. It is now widely accepted that for the case of one water layer (1 WL), the interlayer cation resides close to the tetrahedral sheet, with a ninefold coordination with six basal oxygens and three water molecules, while in the two-water layer (2WL) state, the cation resides at the center of the interlayer coordinating with six water molecules .…”

The Prospects of Clay Minerals from the Baltic States for Industrial-Scale Carbon Capture: A Review

“…One of the main factors affecting the physical sorption of CO 2 onto clay minerals is the type of exchangeable ion within; for example, Cs-exchanged and tetramethylammoniumexchanged montmorillonite have sorption capacity for CO 2 up to 1.70 mmol g −1 even at ambient pressure and temperature [189]. At the same time, in case of fibrous clay minerals, such as sepiolite, the sorption takes place due to the presence of nanocavities, which are acting as a molecular sieve and therefore the CO 2 uptake can reach up to 1.48 mmol g −1 [119].…”