Direct Air Capture (DAC) and high-throughput
testing using small adsorption columns
Applying and developing adsorbents for Direct Air Capture involves studying the influence of the parameters like adsorption/desorption kinetics, temperature, relative humidity and hydrodynamics. Studying these effects in real-time is much easier using high-throughput equipment.
Fig. 1 : Adsorption was carried out isothermally, desorption was carried out using temperature swing at a controlled ramp rate
Figure 1 shows the effluent concentration of three adsorption columns tested in parallel, together with an empty column across three adsorption and three desorption cycles. Momentarily, Avantium studies these types of applications using 8 columns, however scaling to 16 or even 32 is possible. The great advantage of this new equipment is that breakthrough curves are measured on-line and no need to wait for the analysis. Because all equipment is completely automated, it is easy to change process parameters automatically. In this way a unit may operate 24/7 to measure adsorption/desorption cycles during different process conditions.
Scaling-down is performed by keeping the ratio of column diameter to particle diameter constant. This is only valid as long as the internal mass transfer is not influenced by the decreasing particle diameter. However, after crushing the particle, the pressure drop over the small particles increases considerably depending of the fluid viscosity and/or bed height. Besides external mass-transfer rates depend greatly on the hydrodynamic flow near the pellets. Several CFD models have shown the large influence of packing and particle shape on the hydrodynamics. To decouple hydrodynamics from the adsorption kinetics, high-throughput testing in single column single particle tube is the answer. Using high-throughput means that a lot of different process conditions can be tested, resulting in a very accurate kinetic adsorption model. The pellet used in our high-throughput equipment is comparable with the industrial scaled column, this also means that the porosity, the average linear velocity and the throughput can be kept constant. Besides it is possible to test different hydrodynamic conditions by changing the residence time, the variance and other parameters of the flow distribution. Especially the variance is important as this is influenced by dead-zones and recirculation flows.
To compensate for this effect the adsorption column can be filled with both the adsorbent and smaller – inert – beads. As Avantium uses 4 to 8 columns per unit the influence of a changing variance on the mass-transfer and thus the adsorption kinetics can be investigated. Scaling single-pellet single-tube columns to industrial size is possible. Using 8 columns gives the possibility to measure the needed parameters for the geometrical, kinetic, thermal and mass-transfer region. High-throughput testing using small adsorption columns can deliver the needed parameters to model your full scale adsorption unit for the separation or purification of today’s challenges like CO2 capture, VOC removal, isomer separation etc. This powerful technology, combining multiple-parallel, small-scale columns, with fast & online analytics and automated operation will enable a significant acceleration in the development of new adsorbents and processes, in comparison current industry practice.