Capturing CO2 from air: Technical performance and process control improvement

Direct air capture (DAC) is a technology for collecting and concentrating carbon dioxide from ambient air. If driven with renewable power, DAC is potentially a negative CO2 emissions technology that can compensate emissions from non-point sources such as aviation, shipping and land-use change. This study presents the results of 10 days capture campaign done between May and July 2018 plus a process control improvement test. The bench scale DAC device is composed of eight beds containing amine-functionalized adsorbent and follows a temperature and vacuum swing adsorption (TVSA) operation cycle. The outlet CO2 concentration reached less than 100 ppm at the start of the adsorption. Dynamic atmospheric conditions (varying T, relative humidity) affect the capture profile of the beds. Desorption is accomplished by heating the bed up to around 80 degrees C coupled with vacuum. The product gas has purity range of 95-vol% to 100-vol% CO2. Major impurities are O-2, N-2, and H2O. The DAC system also produced water at molar ratio of 3.9 moles H2O per mole of CO2. Water production is affected by air humidity. Measurement-based process control increased the production to 3.4 kg CO2 per cycle with specific energy requirement of 10 kW h kg(-1). The thermal energy requirement accounted for 76% of the total energy input during the improvement test.