The capture of CO2 from the atmosphere via Direct Air Capture using solid supported-amine sorbents is an important option to reduce the atmospheric concentration of CO2. It addresses CO2 emissions from dispersed sources and delivers a location independent, sustainable carbon source. This study evaluates the possibility for a continuous adsorption process for direct air capture in a radial flow contactor, using both batch and continuous mode of operation. Gas and solid flow were varied to determine hydrodynamic feasible operating conditions. The operation modes are compared by their capture efficiencies in the optimal adsorption time range of 0.5 tstoB and 1.5 tstoB. A 15–25% lower capture efficiency is found for a continuous process compared to a batch process in the relevant range for direct air capture. This decline in gas-solid contact efficiency is more pronounced at longer adsorption time and higher superficial gas velocity. Overall, a batch process is preferred over a continuous process in the majority of operating conditions.

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The extraction of CO 2 directly from the atmosphere (Direct Air Capture) is commonly employed using supportedamine sorbents. This adsorption technology is under rapid development with novel sorbent materials emerging and with processes being demonstrated on increasingly larger scale. Optimization of such processes requires accurate knowledge on sorbent characteristics and knowledge on how operational variables affect process performance. This study primarily focuses on the latter, where we aim to quantify the influence of operational parameters on the energy duty and CO 2 productivity. In addition, we examine the influence of weather conditions on the adsorption rate. For this, we develop a dynamic model of the complete temperature-vacuum swing adsorption cycle (TVSA). This model was validated by experimental results on a kg-scale direct air capture system. The impact of selected operational variables was assessed by two-dimensional sensitivity analyses. We show that desorption temperature is preferably high, limited by the chemical stability of the sorbent material in this particular case. In addition, the sorbent working capacity should be high when opting for an optimization towards energy duty, whereas it reaches a clear optimum in terms of CO 2 productivity. Finally, we conclude that weather conditions and diurnal variations can significantly affect the performance of a direct air capture process and should certainly be considered during design and operation. With these insights and the developed model, this study provides a sound basis for further process development and optimization of direct air capture using fixed bed technology combined with solid amine sorbents.

Disruption of the carbon cycle by human activity has led to a continuous increase in carbon dioxide (CO 2 ) levels in the atmosphere during the past centuries and is still ongoing. As a consequence, the global temperature is rising, which shows by, f example, the shrinking of ice caps, glacier retreat and increased frequency of extreme weather events. To counteract this change in climate, the net CO 2 emission must be reduced and eventually become completely zero. A crucial step is the development of closed carbon cycles on a short time scale. Alternative carbon sources are required, since fossil-based carbon is primarily responsible for the increase in atmospheric CO 2 .Chapter 1 illustrates that alternative carbon sources are limited to atmospheric CO 2 , biomass and recycled carbon from waste streams. This thesis concerns the acquisition of atmospheric CO 2 , commonly referred to as 'Direct Air Capture' or 'DAC'. This concept has been around since the end of the previous century and developments accelerated in the last decade. Two major technologies found their way towards commercial scale: absorption using alkaline solutions and adsorption with supported-amine sorbents. This thesis focuses on the latter, with the main goal to design, develop and optimise a DAC process with temperature-vacuum swing regeneration.The dilute nature of CO 2 concentration in the atmosphere means that a huge amount of air must be processed. Efficient gas-solid contacting is therefore essential, which stands or falls with the design and operation of the gas-solid contactor. A fixed bed contactor with a shallow bed of sorbent particles is envisioned as suitable. Chapter 2 compares and evaluates two operation modes of such a contactor: batch wise operation in a fixed bed or continuous operation in a cross-flow moving bed. This study was performed using a radial flow contactor, which is able to operate in both operation modes. First, we validated whether it is possible to operate a moving bed configuration in the desired operating range regarding gas and solid flowrates. No restrictions in solids flow were found up to 0.4 kg s /m r 2 /s. On the other hand, solids flow was inhibited when the cross-flow superficial gas velocity exceeded 0.25 m/s. The moving bed configuration showed a reduced capture efficiency compared to the fixed bed configuration. This reduction varied between 15 and 25 %, with the highest reduction at long adsorption time and high superficial gas velocity.An accurate, validated model of the DAC process is essential for process optimization. Chapter 3 presents the development and validation of such model that incorporates the complete temperature-vacuum swing adsorption process. The model represents chapter page

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