463411 Bio-Mimetic Hollow Fiber Membrane Contactor Process for Low-Cost High-Purity Oxygen Production
Supported by the US Department of Energy (No. DE-FE0024080), we are developing a novel technology to produce greater than 95% oxygen from air via a single-stage gas-liquid membrane contactor with oxygen carrier solutions as solvent. In this process, air is sent to a membrane absorber and passes through small-diameter membrane tubes, roughly 15 mil inside diameter, while a lean O2 carrier solution flows counter currently on the shell side of the membrane. Unlike the other production alternatives, the air stream needs to be compressed to only a few psi and does not require heating for the ion transport through membranes or cooling for cryogenic separations. The O2 permeates through the membrane pores and is absorbed in the O2 carrier solution. The O2-rich carrier solution can be regenerated in a second membrane module (desorber) operated in a reverse process. In that case, the O2-rich carrier solution is fed to the shell side of the hollow fibers and vacuum is used to draw O2 into the pore side of hollow fibers. In this bio-mimetic process, a membrane module with hollow fibers and O2 carrier solution mimics “blood vessels” and “blood”.
In our study, low-cost poly(ethyleneimine)-cobalt (PEI-Co) complex solutions with high O2 absorption capacity (as high as 750 mL O2 (STP)/L solution), low viscosity (< 3 times of water), and fast O2 absorption rate have been developed. The O2 equilibrium absorption capacity increases with the PEI/Co ratio and reaches a plateau at ratio of 10. Two different approaches were employed in the desorption process: 1) vacuum, and 2) using argon as sweep gas. By using the second approach, O2 concentration as high as 99% was observed in desorbed gas stream on an argon free basis. The production of concentrated O2 has been validated experimentally in the bio-mimetic process. The estimated cost including capital, operating, maintenance, and energy use for the bio-mimetic O2 separation technology is $19.96/ton O2, which is only about 56% of the benchmark cryogenic distillation ($35.80/ton O2). This technology has potential to produce oxygen with purity as high as 99.9% for applications in IGCC, oxy-combustion, and other advanced power generation technologies.