Rapid thermal swing adsorption gas separation for low-cost carbon capture

Abstract

The majority of carbon dioxide is emitted at point sources co-located with rejection of waste heat contributing to the fact that two thirds of primary energy is wasted. The rapid thermal swing adsorption (RTSA) process can make use of lowest grades of waste heat (<80°C) that processes like thermal swing adsorption cannot use. The RTSA maturity was demonstrated in heat driven heat pumps that offer a clean technology for cooling or heating utilizing waste or renewable heat as driving energy. The RTSA process constitutes a similar step improvement as rapid pressure swing adsorption for air separation. A controlled fast temperature jump setup (TJS) accurately measures temperatures and sorption processes based on chamber pressure as function of time following fast temperature steps. The sorption material is mounted as a layers with varying thickness onto aluminum carries that are temperature controlled with microchannel heat exchangers. Acquisition of cycled mass in 2-8 minute cycles, thermal resistance and mass transport resistance enabled screening and optimization of materials and directed pore formation. TJS measurements were carried out as function of diverse sorbent materials, gas type (CO2, N2, H2O) including mixtures, gas pressure, cycling time, temperature gradient, layer thickness, and layer structuring. To accelerate the material and structuring optimization effort a selection parameter was defined that contains exchanged mass per cycle, adsorption and desorption speed as well as layer thickness - parameters that maximize the performance of an RTSA gas separation process. The objective was to demonstrate similar performance increases for zeolites, carbonaceous materials, and coated mesoporous carrier materials in efficient separation of CO2 from nitrogen compared to unstructured counterparts. Improvement factors up to 10 for this selection parameter are demonstrated as part of the effort to develop the RTSA process for low cost selective capture of CO2 from flue gasses and to establish RTSA as a viable alternative to other carbon capture processes. Selected materials are currently being tested in gas separation column prototypes. A key is an inexpensive and scalable route for the fabrication of adsorptive coatings with vertically open channels and thermal bridges that improves mass transport. Combined with methods to improve thermal transport, accelerates the RTSA process strongly reducing carbon capture cost to levels below 20$ per ton.