Development of MgO-based sorbents promoted by alkali metal salts for CO2 capture

Ana Patricia Bento Correia

Key information

Authors:

Ana Patricia Bento Correia (Ana Patricia Bento Correia)

Supervisors:

Carla Isabel Costa Pinheiro (Carla Isabel Costa Pinheiro); Paula Alexandra Lourenço Teixeira (Paula Alexandra Lourenço Teixeira)

Published in

11/22/2021

Abstract

Carbon capture and storage (CCS) technologies are one of the most viable solutions to achieve carbon neutrality by 2050. MgO sorbents are promising materials, due to the high theoretical CO2 sorption capacity (1.09 g of CO2/ g of MgO) at intermediate temperatures (300 – 500°C), small regeneration energy, wide availability and low cost. Their major drawbacks are exhibiting poor CO2 sorption capacity, low kinetics and thermal stability. In this work, nanosized MgO was produced using the sol-gel method. The sorbents’ performance was further improved by the addition of supports, Ca and Ce-based, and by the doping with alkali metal salts (AMS), using molar percentages of 15%, 25% and 35% of single salt NaNO3 and of a mixture consisting of NaNO3, LiNO3 and KNO3. Cyclic stability was investigated by multiple sorption/ desorption tests using a thermogravimetric analyzer (TGA) and a continuous fixed-bed reactor. After 10 cycles in a fixed-bed under a sorption atmosphere of 100% of CO2, Ca and Ce-based supported MgO sorbents impregnated with 15% of ternary mixture registered carrying capacities of 100 mg CO2/ g sorbent and 152 mg CO2/ g sorbent, respectively, considerably higher than the 44 mg CO2/ g sorbent achieved by the unsupported sorbent. Such improvement was attributed to both the reduction of nitrates’ sintering and segregation and the enhancement of sorbents’ properties along cycles. Textural, mineralogical and morphological characterization of the fresh and spent sorbents was made using X-ray diffraction (XRD), N2 sorption and scanning electron microscope (SEM) techniques, respectively.