Graphene Oxide-PEEK Hybrid Membrane Process for CO2 Capture

The Department of Energy (DOE), through its Carbon Capture Program, is investigating transformational, low-cost CO₂ separation and capture technologies that can be installed in new or retrofitted into existing pulverized coal power plants to separate and capture ≥ 90% of the CO₂ with 95% CO₂ purity at a cost of electricity (COE) 30% less than the baseline CO₂ capture approaches. The COEs for DOE Case 11 (no CO₂ capture) and Case 12 (benchmark technology amine absorption) are about 6.83 c/kWh and 12.36 c/kWh respectively, all in 2012$. To meet DOE’s cost target, the COE should be less than 8.65 c/kWh.

Supported by DOE (Office of Fossil Energy’s National Energy Technology Laboratory), we are developing an energy efficient graphite oxide (GO)-PEEK hybrid membrane process for post-combustion CO₂ capture. This new process uses a conventional gas separation membrane unit (Unit 1) to capture the bulk of the CO₂ from coal-fired flue gas followed by a polyether ether ketone (PEEK) hollow fiber membrane contactor (HFMC) unit (Unit 2) to further capture CO₂ to achieve DOE’s target of 90% CO₂ capture rate with 95% CO₂ purity. The Unit 1, conventional gas membrane process, has been proven to be very efficient at partial CO₂ capture (40-60%). In the current study, the Unit 1 is based on advanced ultrathin graphene oxide (GO) membranes that we recently published in Science.The singular Unit 2, PEEK HFMC process, currently at pilot-scale development stage (DE-FE-0012829), is effective in capturing CO₂ from low CO₂-concentration feeds. The integration of the advanced GO conventional gas separation process with the PEEK HFMC process takes advantages of the “Pros” of these two processes while overcoming their “Cons”, which offers a new opportunity to explore further reductions in the cost of CO₂ capture.

A facile and scalable coating process was developed to prepare ultrathin graphene oxide (GO)-based membranes on polyethersulfone hollow fibers for highly efficient CO₂/N₂ separation. The GO-based membranes developed to date exhibited extraordinary separation performance under simulated flue gas conditions with CO₂ permeance of 1,020 GPU and a CO₂/N₂ selectivity as high as 680, demonstrating its great potential or capturing a bulk of the CO₂ from flue gases. At the same time, we have fabricated new PEEK fibers (the third generation PEEK fibers) through optimization of the hydrophobic coating layer. Two-inch-diameter modules containing these fibers showed intrinsic CO₂ permeances as high as 3,000-3,300 GPU in a temperature range of 24-60 °C. The PEEK membrane was effective in capturing CO₂ from low CO₂-concentration feeds (range tested: 1-9 vol.%) in membrane contactor with OASE Purple solvent. For a CO₂ feed concentration of 1 vol.%, the treated simulated flue gas CO₂ concentration as low as 0.12 vol.%. It is anticipated that the integrated GO-PEEK process will be tested early 2018.