Abstract
Greenhouse gas contributions to climate change have driven intense interest in the separation of CO(2) from wet flue gas streams. Deep eutectic solvents (DESs) are an emerging class of highly selective CO(2) absorbents. A prototypical DES, reline, is a mixture of choline chloride and urea. Reline is a thermally stable, nontoxic, and biodegradable solvent with negligible volatility and is inexpensive. We demonstrate a scalable and energy-efficient hollow fiber membrane contactor (HFMC)-based process using a green solvent for CO(2) capture. This process uses reline in HFMC to provide close interfacial interactions and contact between DES and CO(2). This approach overcomes the disadvantages associated with direct absorption in DES and could potentially be applied to a variety of solvent-based CO(2) capture methods. Commercial, low-cost polymer hollow fiber membranes were evaluated for the capture of CO(2) with reline. From a mixed gas containing N(2) and CO(2), the DES-based HFMC separated CO(2) with a purity of 97 mol %. The effect of the viscosity of reline on the CO(2) capture performance was investigated by adding water to the reline. The addition of water to reline significantly reduced its viscosity, which led to a permeate flux of 170 mmol/(m(2)·h) at 35 °C, 4 bar, and 60 wt % water in solvent, which was approximately 8 times higher than that of the pure reline in the membrane contactor system. In situ Fourier transform infrared spectroscopy and nuclear magnetic resonance (NMR) revealed that reline absorbs CO(2) by physical absorption without forming new chemical compounds and that CO(2) separation by reline occurs via the pressure swing mechanism. This research provides fundamental insights about green physical solvent-based separation processes and a pathway toward industrial deployment.