(285d) Effect of Viscosity of Deep Eutectic Solvent on CO2 Capture Performance in an Energy Efficient Membrane Contactor Based Process

Greenhouse gas contributions to climate change have driven intense interest in separation of CO₂ from wet flue gas streams. Absorption of CO₂ in green solvents is one useful approach to address this challenge. Deep eutectic solvents (DES) are an emerging class of highly selective CO₂ absorbents. A prototypical DES, reline, is a mixture of choline chloride and urea. Reline is a thermally stable, non-toxic, and biodegradable solvent with negligible volatility and inexpensive. We demonstrate a scalable, and energy-efficient hollow fiber membrane contactor (HFMC)-based process using a green solvent for CO₂ capture. This process uses a deep eutectic solvent (DES) in a HFMC to provide close interfacial interactions and contact between the DES and CO₂. This approach overcomes disadvantages associated with direct absorption in DES and could potentially be applied to a variety of solvent-based CO₂ capture methods. Commercial low-cost polymer hollow fiber membranes (e. g., microporous polypropylene) were evaluated for CO₂ capture with reline, a prototypical DES. Single gas measurements showed the DES-based polypropylene HFMC can capture and separate CO₂ while rejecting N₂. From a mixed gas containing N₂ and CO₂, the DES-based HFMC separated CO₂ with a purity of 96.9 mol%. The effect of several process parameters including reline flow rate, pressure, temperature on the CO₂ separation performance was studied. The effect of viscosity of reline on the CO₂ capture performance was investigated by adding water to reline. By adding 30% water to reline, its viscosity reduced from 1600 centipoise to about 20 centipoise. The reduction in reline viscosity led to CO₂ flux increased by a factor 5 in the membrane contactor system due to enhanced absorption and desorption kinetics. In-situ Fourier transform infrared (FTIR) measurements combined with density functional theory (DFT) based molecular dynamics simulations revealed that reline absorbs CO₂ by physical absorption without forming a new chemical compound, and CO₂ separation by reline occurs via pressure swing mechanism. This research provides fundamental insights about physical solvent-based separation processes and a pathway towards practical deployment.

Reference

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