Nondimensional Analysis of a Hollow Fiber Membrane Contactor for Direct Air Capture

Negative emissions technologies, including the direct capture of carbon dioxide from the atmosphere, are increasingly seen as important components in solving the coming climate crisis. While contacting units for solid sorbents have been studied extensively, little work has been directed at the design of large-scale air-liquid contacting units for CO2 capture. Herein, we examine a conceptual large-scale gas-liquid contacting unit using hollow fiber membranes filled with a flowing, reactive sorbent liquid. In the proposed concept, the sorbent liquid is fed to a bank of hollow fibers exposed to a blown stream of air, and a sorbent inside the liquid reacts with CO2 in the air. We employ commonly used modeling techniques to describe the reactive absorption of CO2 in the liquid, though in a generalized nondimensional form. Extending this solution to a bank of fibers, we demonstrate a means of extending the solution for few fibers to many fibers and discuss the trade-offs involved in achieving high sorbent utilization. The methodology described here produces a highly general solution to the design of a fiber tube bank for air contacting, and we demonstrate the use of this solution to size an example fiber contacting unit. The proposed design is envisioned to enable new conceptual liquid sorbent chemistries in direct air capture, particularly those envisioned for use with electrochemically mediated regeneration.