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Materials Science in Additive Manufacturing Emerging 3D-printed zeolitic gas adsorbents

Table 5. Comparison of commonly used structured gas absorbents
Feature Structure
Pellet Granule Monolith Membrane
Manufacturing method Die-based extrusion; pelletization Granulation Die-based extrusion; coating; 3D printing Coating; 3D printing
Common shape Spherical or cylindrical Irregular Honeycomb, cylinder, and cuboid Flat or tubular
Size 0.5 – 5 mm 0.5 – 5 mm 1 – 10 cm 0.1 – 1 mm
Porosity Low to medium Low to medium High Low to medium
Surface area Low to medium Low to medium High High
Zeolite loading Low to medium Low to medium High Low to medium
Durability Moderate Moderate High Moderate

with a thickness of around 300 μm for the 3D printing of for gas adsorption, which improves the overall adsorption
zeolite monolith with an average channel width of 650 μm. capacity of the material. In addition, hierarchical porosity
The monolith was tested for adsorption and separation gas adsorbents have the potential to be more durable
of CO and N through isotherms and breakthrough and stable under high-pressure conditions compared to
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experiments. The resulting materials showed CO adsorption traditional honeycomb structures. 3D printing has been
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properties similar to the parent powder SAPO-34, with a utilized to create mesoporous zeolite monoliths with
moderate decrease in capacity due to the presence of binder oriented hierarchical mesopores, which exhibit high
in the monolithic structures [101] . For extrusion-based 3D adsorption capacity and selectivity. The incorporation of
printing, the precision of the structure of zeolite monoliths is hierarchical porosity, which consists of both micro- and
mainly dependent on the size of the nozzle, which limits the meso-pores, can improve the adsorption properties of
ability to design the structure with finer details. By utilizing the printed zeolitic adsorbents. For the extrusion-based
the DLP 3D printing technique, Zhang et al. reduced the 3D printing technique, the zeolite monoliths printed
wall thickness of the zeolite monolith to 250 μm, resulting through DIW in the study by Li et al. exhibited hierarchical
in improved dynamic adsorption performance . The porosity with pore sizes ranging from 1.5 nm to 1 μm.
[95]
breakthrough width of the printed monolith reached 5.6 min, The BET surface area of the samples ranged from 17 to
which was shorter than 6.8 min for commercial pellets, 326 m /g, while the micropore area and micropore volume
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indicating that the refinement of the structure improved the were determined using the t-plot method. The total pore
dynamic adsorption rate of the zeolite monolith and showed volume of the samples ranged from 0.27 to 1.02 cm /g,
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fast adsorption kinetics . Lawson et al. discussed the effects with micropore volume ranging from 0.01 to 0.13 cm /g
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[95]
of cell density and intrinsic porosity on structural properties and mesopore volume ranging from 0.17 to 1.01 cm /g [119] .
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and adsorption kinetics in 3D-printed zeolite monoliths [100] . As an alternative to DIW, SLA has high resolution and
The monoliths were printed with three cell densities of 200, superior forming capability, which allows for the creation
400, and 600 cpsi, while their wall porosities were in the of intricate geometries with high accuracy and precision.
range from 0.23 to 0.46 based on the mercury intrusion Merilaita et al. found that SLA can create hierarchically
porosimetry measurements. The study found that monoliths porous zeolite structures with porosity on three scales:
made from a macroporous binder had a faster CO mass printed flow channels for rapid gas transportation, porosity
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transfer rate, while those with increased cell density had a between primary particles allowing gas to flow into the
reduced CO mass transfer rate [100] . structure, and micropores characteristic to the material
2 [98]
Recent research has also focused on the 3D printing of itself, where adsorption finally occurs .
zeolites with hierarchical porosity structures, which have 3.3. Influence of printing process parameters
larger pore sizes and higher surface areas compared to
conventional structures such as honeycombs. Honeycomb Besides material development, recent research has focused
structures typically have a uniform pore size distribution, on optimizing the process parameters to improve the
limiting their ability to selectively adsorb gases based performance of the 3D-printed zeolitic gas adsorbents. By
on size and shape. In contrast, hierarchical porosity gas controlling the process parameters, not only can the quality
and precision of the printed adsorbent can be enhanced,
adsorbents have a range of pore sizes, including both but its utilization efficiency can also be improved.
micro- and meso-pores, which allow them to capture
a broader range of gas molecules more effectively. The Chu et al. conducted a study on the extrusion-
hierarchical structure also provides a larger surface area based 3D printing of zeolite monolith to optimize the

Volume 2 Issue 4 (2023) 13 https://doi.org/10.36922/msam.1880