(647b) Temperature-Vacuum Swing Adsorption Process for Direct Air Capture of CO2

The removal of carbon dioxide (CO₂) from gas streams has traditionally been utilized to purify other components of the source gas stream, e.g., hydrogen (H₂) in steam methane reforming, methane in natural gas purification, etc. The removal of metabolic CO₂ from air has also been of interest for many years, particularly with the advent of human space flight and underwater exploration. For instance, considerable effort has been put forth by NASA to remove metabolic CO₂ from spacecraft cabin air.

Removal of CO₂ from gas streams combined with the capture of the isolated CO₂ has become of increasing interest in recent years as CO₂ released from transportation, industrial processes and the electric power industry has been implicated and widely accepted as being a cause of climate change. Moreover, as improved methods for utilization of high purity CO₂ have been developed, for instance in green technologies as a fuel source, as an extraction solvent, and in algae and plant cultivation, the gas separations industry has shown great interest in improving methodologies for separating and capturing CO₂ from CO₂-containing gases, including direct capture from the air.

Adsorption technology, especially temperature-vacuum swing adsorption (TVSA), has been proposed and studied extensively for CO₂ capture. Gas separation by TVSA is achieved by coordinated pressure and temperature cycling and flow reversals over an adsorbent bed that preferentially adsorbs a component of the mixture, e.g., CO₂. Traditionally, TVSA has been utilized to supply high oxygen content streams, e.g., medical oxygen. TVSA has also been utilized in the removal of CO₂ as the final step in hydrogen synthesis for use in oil refineries, in the production of ammonia (NH₃), in the removal of hydrogen sulfide (H₂S) from hydrogen feed and recycle streams of hydrotreating and hydrocracking units, as well as in the separation of CO₂ from biogas so as to increase the methane (CH₄) ratio. Unfortunately, conventional TVSA processes make inefficient use of applied energy, and as such have remained economically unfeasible, particularly when considering separation of CO₂ from a hydrated gas stream, such as air.

What are needed are systems that can provide for improved separation of CO₂ from a gas stream, and, in particular, from a gas stream that also includes water vapor. Methods that can provide high purity CO₂ from a hydrated feed stream, for instance directly from air, could be particularly beneficial in green technologies such as algae production. This presentation will discuss a TVSA system for capturing CO₂ from a hydrated gaseous stream and, in particular, for direct air capture (DAC) of CO₂. The system utilizes a low energy TVSA process and includes two desiccant beds for the removal of water vapor coupled together with two CO₂ capture beds for the capture and concentration of CO₂. This system can produce a very pure CO₂ stream or a stream containing only a few vol% of CO₂, depending on the application. Specific details about this 4-bed TVSA system will be provided during this presentation, along with performance results obtained via process simulation using the UofSC dynamic adsorption process simulator (DAPS). One application of interest is to produce a stream containing a few vol% CO₂ for use in algae production.