Enhanced CO₂ Adsorption Using MgO-Impregnated Activated Carbon: Impact of Preparation Techniques

Abstract

The development of a facile and sustainable approach to produce magnesium oxide (MgO) activated carbons impregnated through a single-step activation of biochar is reported. In a single-step activation process, biochar is impregnated with 3 and 10 wt % of magnesium salt solutions followed by steam activation. In a two-step method, activated carbon, the product of steam activation of biochar, is impregnated with magnesium salt using the incipient wetness and excess solution impregnation process and calcined. The impacts of activation method, impregnation method, and metal content are evaluated, and the product qualities are compared in terms of porosity and surface chemistry. The sorbents are then used for CO2 capture in low partial pressure of CO2 at 25 and 100 °C from a feed containing 15% CO2 in N2 in a fixed-bed reactor. The incipient wetness of activated carbons results in the highest CO2 uptake (49 mg/g) at 25 °C, while single-step impregnation of biochar with rinsing step yields the largest surface area (760 m2/g) and the second highest CO2 uptake (47 mg/g). The increase in Mg content from 3 to 10 wt % results in the smaller surface area and higher CO2 uptake suggesting that the metal content has a greater impact than porosity and surface area. Rinsing the Mg impregnated activated carbon with water results in the larger surface area and higher CO2 uptake in all samples. Moreover, the CO2 adsorption runs at 100 °C shows a 65% increase using MgO impregnated activated carbon as compared to steam activated carbon indicating that MgO impregnation of activated carbon can overcome the limitation of using nontreated activated carbon at moderate operating temperature of 100 °C and low partial pressure of CO2 of 15 mol %