Derk Willem Frederik Brilman

CO2 sorbents play a central role in many carbon capture technologies. Visual monitoring of the sorbent behavior during CO2 capture could provide direct feedback and enable the optimization of both the sorbent and the reactor, which remains largely unexplored. In this work, we develop a self-reporting CO2 sorbent, prove its quantitative indication of CO2 absorption and desorption, and apply this method to evaluate different methods of sorbent regeneration. A pH indicator, thymol blue (TB), was embedded into polyethyleneimine (PEI) hydrogel particles, revealing a clear color transition from blue to green, yellow, and orange during CO2 absorption. This optical response was quantified by extracting Hue, a color coordinate in the Hue, Saturation, Value (HSV) space, from the particle images. Time-resolved analysis of the CO2 absorption revealed that Hue closely follows the measured CO2 uptake. A previously developed diffusion-reaction model was employed to investigate the relationship between the optical response and the internal chemistry of the particles. The measured Hue evolution more closely follows the modeled protonation response averaged over a substantial fraction of the particle volume than that of the shallow near-surface regions, supporting its potential use as an optical indicator for CO2 uptake. The robustness of the optical response was further confirmed by evaluating particles with different water contents, and excellent reversibility of the optical response was demonstrated during steam regeneration. As a final step, microwave regeneration was optically evaluated via this method, and shown to be much faster but less complete than steam regeneration. These results demonstrate that PEI/TB hydrogel particles can provide a timely, direct, and convenient optical signal during CO2 absorption and regeneration, enabling pathways for optimization at particle and potentially reactor scales.

Biogas upgrading by vacuum-pressure swing adsorption involves the selective adsorption of CO₂ over CH₄ on a sorbent material to separate both components. This work assesses numerically the performance of the previously characterized Cs-exchanged bentonite clay for this separation. This benchmarking study includes the effect of the process cycle configuration (seven different configurations using one stage and up to three columns), the ambient temperature (15 or 25 °C), the feed biogas composition (CO₂ mole fraction of 0.35 or 0.45, balance CH₄), and the process operating parameters. Specific constraints on CH₄ purity and CH₄ recovery provide Pareto fronts for maximum productivity and minimum specific energy consumption. A two-column unit operated at ambient feed pressure can upgrade 0.097 Nm³ feed biogas (CO₂ mole fraction of 0.45, balance CH₄) per kg sorbent per h to a bio-CH₄ product with a purity of 0.906 and with a CH₄ recovery of 0.967 at a comparatively low specific energy consumption of only 0.072 kWh per produced Nm³ of CH₄. Using more columns and pressure equalization steps further enhances the CH₄ recovery. The low bentonite cost, the comparatively low specific energy consumption due to the favorable linear CO₂ adsorption isotherms, and the high recovery due to the high CO₂/CH₄ selectivity make Cs-bentonite an excellent alternative for conventional sorbent materials.

Layered swelling clay minerals like montmorillonite (MMT) can competitively and synergistically adsorb CO₂ and H₂O in their interlayer galleries. This work examines how different interlayer cations, relative humidity levels (and amount of cosorbed H₂O), and (de)hydration history affect CO₂ adsorption on MMT and MMT-rich bentonite at near-ambient pressure and temperature. For CO₂ to be adsorbed, the MMT requires either large (e.g., Cs⁺) or hydrated interlayer cations to provide a sufficiently wide interlayer gallery, and must not have too much H₂O adsorbed competitively with CO₂. Na-MMT and initially anhydrous Mg- and Ca-MMT studied under increasing relative humidity conditions adsorb little CO₂. However, Mg- and Ca-MMT can effectively adsorb CO₂ if first hydrated and then mildly dried such that the cations remain hydrated while the competitively adsorbed excess H₂O is removed. Because of their high stability and the favorable shape of their CO₂ adsorption isotherms, low-cost (near-)natural Mg- and Ca-bentonite can be used for (cyclic) CO₂ adsorption and separation purposes, similar to the more expensive Cs-bentonite.

An optimisation strategy to optimize adsorption-based direct air capture processes for year-round production at various locations around the world.

CO₂ from air is one of the few sustainable carbon sources. Technologies to capture and concentrate this CO₂ are being demonstrated on an increasingly large scale. Adsorption using supported-amine sorbent via a temperature-vacuum swing adsorption process is such technology. This work provides a detailed description of this technology and identifies options for process optimization based on experimental results. For this, a novel kg-scale pilot unit was designed and constructed with four parallel fixed bed reactors. Reproducible results were obtained during the complete experimental campaign of several weeks. The base case scenario led to a productivity of 1.3 kg CO₂ per day or 0.27 kg CO₂ kg_s ⁻¹ per day with an energy consumption of 14.5 MJ kg CO₂ ⁻¹. The sensible heat of sorbent and inert material was the major contributor to the energy duty, while gas–solid contacting only accounted for a minor part. Various optimization options were identified based on the experimental results. Including these options, this potentially reduces the energy consumption of this direct air capture process to 5.1 MJ kg CO₂ ⁻¹.