Performance Evaluation of Deep-Eutectic-Solvent Anchored on Mesoporous Silica for CO2 Capture Applications

Abstract

Carbon dioxide (CO2) levels in the atmosphere have been steadily rising since the industrial revolution, and this phenomenon contributes to global warming. One effective solution is carbon capture and storage (CCS), specifically CO2 adsorption utilizing mesoporous materials. The current study focuses on the synthesis of mesoporous silica from sand dunes, which is abundantly available in the UAE. Sand dunes were collected from the desert in Ras Al Khaimah and Abu Dhabi. The Energy Dispersive Spectroscopy (EDS) analysis showed that the average silica content is ~12% and ~34% from Ras Al Khaimah and Abu Dhabi, respectively. Multiple purification techniques were employed; with one technique has successfully purified (100%) of SiO2 from sand. Herein, sodium silicate and cetyltrimethylammonium bromide (CTAB) were used as a silica precursor and surfactant, respectively, to synthesize mesoporous silica of the Mobil Composition of Matter No. 41 (MCM-41). Different synthesis conditions (temperature, precursor concentration, and time) were carried out to synthesize MCM-41, and their CO2 adsorption was investigated. The synthesis of MCM-41 from sand dune (SMCM-41) was characterized using SAXS, XRPD, FTIR, TGA, TEM, SEM and N2-sorption analysis, and compared with commercial MCM-41 (CMCM-41). The results showed that MCM-41 made from RAK sand dune (SRMCM-41) had a higher pore volume of 1.002 cm3 /g and BET surface area of 1120 m2 /g than CMCM41. In addition, deep eutectic solvents (DES), which is ChCl:MEA in a molar ratio of 1:6, were synthesized using a thermal technique. By using a wet-impregnation technique, the DES was anchored onto the MCM-41 pores. Herein, all up-mentioned physiochemical characterizations were successfully confirmed impregenation of ChCl:MEA onto SMCM-41 and CMCM-41. This study further explored various impregnation percentages to optimize the CO2 adsorption capacity. The CO2 adsorption at 25°C as a function of pressure was evaluated and experimental data was fitted to adsorption kinetic models (BET model, Langmuir model, Freundlich model, and Temkin model). The highest CO2 adsorption achieved at 25 °C and 1 bar using SRMCM-41 is 1.17 mmol/g, while that of CMCM-41 is 0.96 mmol/g, showing higher selectivity toward CO2 than N2. The maximum CO2 adsorption after impregnation with ChCl:MEA was 2.32 mmol/g from a commercial source (15%ChCl:MEA/CMCM-41), followed by 2.11 mmol/g from (20%ChCl:MEA/CMCM-41). While the maximum CO2 adsorption achieved from a source of sand dunes at 10%ChCl:MEA/SAMCM-41 is 0.95 mmol/g. For CMCM-41, and SMCM-41, 15-20%ChCl:MEA/CMCM-41, CO2 adsorption was also tested at various temperatures (40 °C, 60 °C, and 80 °C), decreasing as the temperature increases. Regeneration study is measured across three cycles showing enhancement performance with the impregnation of ChCl:MEA, showing stability enhancement upon impregnation.

Date of Award	22 Dec 2023
Original language	American English
Supervisor	Cheng Kui (Supervisor)