(485f) Bio-Mimetic Hollow Fiber Membrane Contactor Process for Low-Cost High-Purity Oxygen Production

Oxygen production from air has wide applications in oxygen-intensive industries, such as energy production (e.g., IGCC and oxy-combustion systems), fuels, chemicals, and other industries. Cryogenic distillation, pressure swing adsorption, polymeric and ionic transport membrane technologies have been used for air separation. Among these technologies, cryogenic distillation is the most mature technology for large scale and high purity (>99%) O₂ production. However, cryogenic distillation-based air separation is costly and energy-intensive to operate, accounting for up to 15% of the total gasification plant capital cost, and consuming over 35% of in-plant power use.

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 â??blood vesselsâ? and â??bloodâ?.

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.