Isotherm model for moisture-controlled CO₂ sorption

Abstract

Moisture-controlled sorption of CO2, the basis for moisture-swing CO2 capture from air, is a novel phenomenon observed in strong-base anion exchange materials. Prior research has shown that Langmuir isotherms provide...

Kinetic model for moisture-controlled CO2 sorption

“…In this paper and the previous paper focused on equilibrium conditions, 13 the condition a i ∼ C i is satisfied, as long as the equilibrium constants do not change. In contrast to earlier efforts which varied equilibrium constants to capture moisture sensitivity of the sorbent, 26,27 in this model, we treat the hydrated state of the various ions as a simple bound state and keep the equilibrium coefficients constant.…”

“…In a previous paper, we identified the following three governing equations for moisture-controlled CO 2 sorption in anionic exchange resins: 11–13 where, n 1 ≡ z − x n 2 ≡ y − 1 − x − z …”

“…Previously, we noted that the equilibrium concentration of OH − is very small in the regime relevant to CO 2 capture from air. 13 After eliminating OH − terms from these chemical reactions, the overall chemical reaction can be described as 4,13 where, n ≡ n 1 + n 2 = y − 2 x − 1…”

“…When the concentration of OH − and H + are negligible, the condition of charge neutrality simplifies to[A] = [HCO 3 − (H 2 O) x ] + 2[CO 3 2− (H 2 O) y ]where, [A] denotes alkalinity. 13,15 Generally, [X] represents the concentration of the chemical species X. The concentration of the Dissolved Inorganic Carbon (DIC) in a sorbent is defined as[DIC] ≡ [CO 2 ] + [HCO 3 − (H 2 O) x ] + [CO 3 2− (H 2 O) y ]…”

“…This expression for the equilibrium loading (eqn (25)) is identical to the isotherm equation that has been derived and validated in the previous paper. 13,16 In the following section, we rewrite eqn (21) in terms of θ − θ eq , which is more useful from an experimental point of view. A common experiment for measuring sorption kinetics changes the environmental condition ( e.g.…”