Freeze Granulated Zeolites X and A for Biogas Upgrading

Abstract

Biogas is a potential renewable energy resource that can reduce the current energy dependency on fossil fuels. The major limitation of utilizing biogas fully in the various applications is the presence of a significant volume fraction of carbon dioxide in biogas. Here, we used adsorption-driven CO2 separation using the most prominent adsorbents, NaX (faujasite) and CaA (Linde Type A) zeolites. The NaX and CaA zeolites were structured into hierarchically porous granules using a low-cost freeze granulation technique to achieve better mass transfer kinetics. The freeze granulation processing parameters and the rheological properties of suspensions were optimized to obtain homogenous granules of NaX and CaA zeolites 2–3 mm in diameter with macroporosity of 77.9% and 68.6%, respectively. The NaX and CaA granules kept their individual morphologies, crystallinities with a CO2 uptake of 5.8 mmol/g and 4 mmol/g, respectively. The CO2 separation performance and the kinetic behavior were estimated by breakthrough experiments, where the NaX zeolite showed a 16% higher CO2 uptake rate than CaA granules with a high mass transfer coefficient, 1.3 m/s, compared to commercial granules, suggesting that freeze-granulated zeolites could be used to improve adsorption kinetics and reduce cycle time for biogas upgrading in the adsorption swing technology.

Optimization of CO2 Adsorption and Physical Properties for Pelletization of Zeolite 5A

“…Therefore, the density of pellets increased (less pore volume) with increasing compression force, amount of binder, and compression time, making it more difficult for CO 2 molecules to reach active sorbents. As a result, the internal mass transfer of CO 2 in zeolite pellet is lower [30,31]. A schematic illustration of the CO 2 sensing mechanism for the interior of the zeolite pellet ash is shown in Figure 6.…”

Biogas Upgrading Using Cation-Exchanged Bentonite Clay

“…For the measurements that require particles instead of a powder, the clays were pelletized by mixing the exchanged bentonite powders with an aqueous suspension (100 g L −1 ) of the nonexchanged (i.e., Na + -activated) bentonite in a 1:1.1 mass ratio, where the nonexchanged bentonite serves as a binder material. 17 Particles (with particle diameters d p = 2−4 mm or 2 cm; Figure S1) were hand-rolled from the resulting paste and dried in an oven at 60 °C. After evaporation of the solvent, the particles thus contain ∼91% exchanged bentonite and ∼9% binder material.…”

“…Ideally, sorbents should have a high (equilibrium or kinetic) CO 2 /CH 4 selectivity for high CH 4 and CO 2 output purity and recovery, they should adsorb CO 2 quickly and be easy to regenerate, and they should have a high working capacity to limit the required amount of sorbent and equipment size. − In addition, they should be readily available, stable, and safe. Typical adsorbents include zeolites − ,,− and activated carbon − (both equilibrium-based separation) and carbon molecular sieves (CMS; kinetics-based separation). ,,,, Adversely, these materials often suffer from a trade-off between high CO 2 /CH 4 selectivity and easy regeneration. , For example, Zeolite 13X, which has a high CO 2 /CH 4 selectivity, also has a high isosteric heat of CO 2 adsorption (43–55 kJ mol –1 ) and steep CO 2 adsorption isotherms. ,,− It thus requires a high energy input, a relatively high temperature, , and/or low vacuum pressure ,, for complete regeneration. On the other hand, materials that weakly bind CO 2 , e.g., activated carbon, typically have low CO 2 /CH 4 selectivity. − Furthermore, kinetics-based sorbents (may) demonstrate relatively slow CO 2 adsorption and desorption kinetics as compared to equilibrium-based sorbents. ,, It is thus imperative to find low-cost sorbents with high CO 2 /CH 4 selectivity that can rapidly adsorb and desorb CO 2 .…”

Zeolitic Microporous Materials and Their Applications

“…In the contribution from Narang et al [ 13 ], the use of commercial low silica zeolites NaX (FAU) and CaA (LTA) as CO 2 adsorbents for biogas upgrading is reported. The zeolite powders were structured by optimizing a freeze granulation process to form hierarchically porous granules able to perform the separation of CO 2 from CH 4 .…”

“…The characterization of hierarchical zeolites Y prepared by surfactant templating procedures is also revised, either for the materials prepared incorporating the surfactant during the synthesis of zeolite Y or in post-synthesis treatments. The review ends with another methodology for obtaining hierarchical zeolites based on the assembly of small zeolitic grains, which was also the topic of one of the contributions mentioned above [ 13 ]. In this case, the porosity is generated by modification of granules that contain a mixture of the zeolite with a binder, avoiding the use of expensive surfactants.…”