(675c) Molecular Simulation of CO2 Absorption in Sorbent-Solvent  Suspension and Interface Regions

CO₂ absorption by using solvents and adsorption by using sorbents have their respective advantages and disadvantages in carbon capture applications. Recently, Smit and coworkers ^[1] have investigated the slurry concept for CO₂ capture. By suspending a ZIF8 nano-prorous sorbent in the 2-methylimidazole glycol mixture solvent, the slurry system combines the low cost and efficiency of a nano-porous sorbent and the processing ease of a solvent-based separation process. Additionally, Azizi et al. have found that propane and propylene gas solubilities and absorption rates in the N-methyl pyrolidone solvent are increased when dispersing only 0.3 vol% TiO₂ nanoparticles in the solvent ^[2], which is partly due to the solvent structure perturbation in the presence of the nano-particle ^[3]. Even though all these experimental results indicate that sorbent-solvent suspension/slurry could be useful in CO₂ capture, there are still many important questions to be addressed, such as the suspension thermo-physical properties, CO₂ solubility and diffusivity in the bulk solution and in the interface region, CO₂ selectivity over other gases, and the effect of water and other gas impurities on the suspension performance. In this work, we address some of these important questions, which will be very useful to develop more efficient suspension systems for CO₂ capture. Our emphasis in particular is on the properties of the interface region, which will significantly affect CO₂ absorption in the suspension but cannot be determined using common experimental characterization procedures.

In this work, we have modeled a suspension system by dispensing nano-sized ZIF8 porous material into a polyethylene glycol siloxane (PEGS) solvent. It was found that the PEGS density in the ZIF8-PEGS interface region is about 10% larger compared with the bulk PEGS solvent density. Due to this increased PEGS density in the interface region, the CO₂ loading, diffusivity, in the PEGS interface region are significantly smaller compared with the corresponding values in the bulk PEGS solvent. Additionally, we present the viscosity, surface tension, and CO₂ absorption for the suspension system.

1. Liu, H.; et al. Nature Communications 2014, 5, 1-7.

1. Azizi, S.; et al. Heat Mass Transfer 2014, 50, 1699-1706 .

1. Shi, w.; et al. J. Phys. Chem. B 2010, 114, 15029-15041.