(634a) Supported Amine Adsorbents for CO2 Capture Via Particle Molecular Layer Deposition

CO₂ capture from power generation sources provides a concentrated CO₂ stream and the possibility of incorporating the captured CO₂ into useful industrial processes. However, in order to implement these technologies on the scales we require, we must develop economically feasible methods and materials. Traditional CO₂ capture technology relied on liquid amines that requires substantial energy to strip the CO­₂ that leads to substantial costs for the process.¹ Addressing the limitations of the liquid process, solid adsorbent materials have become a research focus over the past few decades. Popular materials have included zeolites, activated carbons, metal organic frameworks and supported amines. Supported amines are an attractive material as they take advantage of the traditional basic chemistry, are tolerant of humidity, and require moderate regeneration conditions. As such, they have received much attention in literature as researchers vary the functionalization method, support materials, and amine-containing groups to increase the adsorption capacity. Current processes of loading the amines through impregnation face poor regeneration stability and transport limitations, while grafted sorbents tend to have low adsorption capacities.² Mesoporous silicas such as MCM-41 and SBA-15 are very popular support materials due to high surface areas above 800 m²/g. However, these materials are not produced on commercial scales and are expensive to make which would inhibit the implementation of this technology.

This research focuses on development of a regenerable, high capacity, and inexpensive supported amine adsorbent materials. Here, we introduce particle molecular layer deposition (MLD) as a novel functionalization method to improve upon the limitations of current methods. MLD is closely related to atomic layer deposition (ALD). Both processes involve stepwise reactions between gaseous reactants on a solid surface to create thin films.³ Here we use MLD to deposit a covalently bonded aminopropylsiloxane network on fumed silica nanoparticles (380 m²/g). Two MLD chemistries have been confirmed: (3-aminopropyl)triethoxysilane (mono-amine) and N1-(3-trimethoxysilylpropyl)diethylene triamine (tri-amine). Both precursors were deposited at 150°C. Adsorption capacity and regeneration stability were investigated using a thermogravimetric analyzer (TGA). Adsorption capacity of the amine functional groups increased to ~2mmol/g or 0.005 mmol/m² as the number of MLD cycles increased. On the basis of surface area, this capacity is competitive with other surface functionalization methods and well performing adsorbents in literature. Low regeneration temperatures were demonstrated by both the mono-amine and tri-amine. The MLD sorbents with 10 cycles of MLD underwent 25 regeneration cycles with adsorption at 30°C and desorption at 80°C. Both materials appear stable and robust over these cycling conditions. These materials will be stable for adsorption/desorption cycling temperatures below the deposition temperature of 150°C. Preliminary cost approximations estimate the cost of this sorbent is less than $10/kg. This work demonstrates a new functionalization method and capture material to the field of solid CO₂ capture research that could aid in widespread CO₂ capture implementation.

(1) Wang, J.; Huang, L.; Yang, R.; Zhang, Z.; Wu, J.; Gao, Y.; Wang, Q.; O'Hare, D.; Zhong, Z. Recent advances in solid sorbents for CO2capture and new development trends. Energy Environ. Sci. 2014, 7 (11), 3478.

(2) Ünveren, E. E.; Monkul, B. Ö.; Sarıoğlan, Ş.; Karademir, N.; Alper, E. Solid amine sorbents for CO 2 capture by chemical adsorption: A review. Petroleum 2017, 3 (1), 37.

(3) George, S. M. Atomic Layer Deposition: An Overview. Chemical Reviews 2010, 110 (1), 111.