Mesoporous MgO promoted with NaNO3/NaNO2 for rapid and high-capacity CO2 capture at moderate temperatures

Abstract

A series of mesoporous MgO samples with different morphologies were synthesized through a simple hydrothermal treatment and NaNO 3 /NaNO 2 were used as promoters to enhance CO 2 capture capacity at an intermediate temperature range (200-400 °C). The effects of hydrothermal solution pH and content of promoters were examined to determine the optimal synthesis conditions. The influence of operational temperatures, CO 2 partial pressure, and performance over repeated cycles was investigated and the reaction mechanism was discussed. The mesoporous MgO promoted by NaNO 3 /NaNO 2 exhibited a CO 2 capture capacity as high as 19.8 mmol•g-1 at 350 °C in the presence of 0.85 bar of CO 2 within only 50 min. A "three-stage" reaction process was proposed based on a detailed sorption kinetics study, namely Stage I: initiating interactions between CO 2 and exposed MgO; Stage II: generation and accumulation of Mg 2+ and CO 3 2-; and Stage III: fast carbonation. Gradual deterioration of sorbents was found over the first 5 cycles followed by stable regenerability in the 5-15 th cycles. A kinetic study of the 15 th cycle suggests that the deactivation of sorbents inhibited the accumulation of Mg 2+ and CO 3 2in Stage II and suppressed the carbonation in Stage III. A range of characterizations were undertaken revealing the morphology and structure of both fresh and regenerated sorbents. The results confirmed that, other than the sintering effect due to phase transition, the transformation of MgO skeleton is also an important contributor to the gradual deactivation of the sorbents over the first 5 cycles. More severe sintering effect under harsh decarbonation conditions suppressed the stability of the sorbents over cycles.

NaNO3‐Promoted Mesoporous MgO for High‐Capacity CO2 Capture from Simulated Flue Gas with Isothermal Regeneration

“…At 280 °C, the sorption demonstrated a prolonged induction period throughout the entire 12 h of CO 2 exposure, showing only 0.18 mmol g −1 uptake, and never quite showing a significant increase in uptake rate that was observed at the other temperatures tested. These results differed from previous studies that were performed at high concentrations of CO 2 (above molar concentration of 85 % CO 2 ) in that similar materials studied by others typically showed the highest CO 2 capacity in the temperature range between 300 °C and 350 °C …”

“…Mesoporous MgO was synthesized through a modification of a reported method . First, urea (28.83 g) and magnesium acetate tetrahydrate (34.31 g) were added to distilled water (100 mL) and stirred for 1 h to ensure all the salts were completely dissolved.…”

“…Its potential as a promising candidate for CO 2 sorption grew even further following a report that porous MgO promoted by molten alkali metals enabled higher CO 2 sorption capacity and faster uptake kinetics in an intermediate temperature range (250–400 °C) than a bare MgO sorbent . As a result, there has been a growing interest in using such molten‐alkali‐metal‐promoted MgO for CO 2 capture in an intermediate temperature range . Zhang et al.…”

“…showed that a CO 2 sorption capacity of 15 mmol g −1 could be obtained by NaNO 3 ‐promoted MgO, whereas Zhao et al. reported that MgO promoted by an NaNO 3 and NaNO 2 binary mixture showed a sorption capacity of 18.9 mmol g −1 . Harada and Hatton also synthesized (Li–Na–K)NO 3 ‐coated MgO particles that showed a sorption capacity as high as 15.7 mmol g −1 …”

Sensitivity Analysis of Carbonate Looping Process Using Twin Fluidized Bed Model

“…There have been many methods in the literature about post-combustion CO2 captures, such as absorption (Porter et al, 2015), adsorption (Shah and Imae, 2016), cryogenic (Yuan et al, 2014), chemical looping (Leion et al, 2008) and membrane (Zhao et al, 2018;Yang et al, 2019). However, these processes have some bottlenecks including enormous energy losses of 8-14% which increase fuel consumption and environmental concern regarding solvent regeneration (Lasheras et al, 2011;Oh et al, 2016;Liu et al, 2019a, b).…”