Development of Sodium-Based Borate Adsorbents for CO2 Capture at High Temperatures

Abstract

The excessive amounts of CO2 emissions to the atmosphere are a critical issue due to the global warming phenomenon. Development of CO2 adsorbents at high temperatures is of paramount importance because of their widespread application. In this investigation, sodium-based borate adsorbents have been developed for the CO2 capture process. Four different sodium precursors (NaOH, NaCl, Na2CO3, and NaNO3) have been employed as a sodium source, their effects on a boric acid material was investigated, and they were tested for CO2 capture application under different temperatures (500–700 °C). The proposed adsorbent materials showed promising results in terms of CO2 capture efficacy. The maximum CO2 uptake (5.45 mmol/g) and the fastest kinetic (90% of its capture uptake achieved within the first minute) have been obtained from the proposed NB4 (NaNO3@H3BO3) material at 600 °C and 1 bar. However, NB2 (NaCl@H3BO3) and the pristine materials (boric acid) showed no capacity toward CO2. Time on stream has also been tested for NB1, NB3, and NB4 after multiple cyclic adsorption–desorption. The materials showed high stability after eight consecutive adsorption–desorption cycles. For further investigation, XRD, FTIR, SEM, and TGA-DSC techniques have been performed for the proposed materials to study their crystalline composition structures, bonding interactions, material degradation, and melting points. The excellent performance of the newly synthesized materials is attributed to the chemical reaction of sodium borate with CO2 with the aid of the molten phase that facilitates CO2 diffusion over the proposed materials. The newly proposed materials could open a new avenue for CO2 capture technology.