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

printing resolution and mechanical stability of the in the presence of air or another oxidizing agent. However,
printed structures [120] . The study investigated the effects the specific conditions and duration of calcination may
of several parameters, including nozzle diameter, nozzle need to be optimized to ensure that the desired properties
height, printing speed, and ink viscosity, on the printing and performance of the 3D-printed zeolite monoliths are
process. A variety of zeolite catalysts with different heights achieved. It is recommended to consult the literature for more
were prepared and analyzed for their morphology and specific guidance on the calcination process for a given zeolite
mechanical strength. It was found that lower solid content system. Thakkar et al. made the printed zeolite calcinated at
in the ink resulted in easier extrusion from the nozzle. The 700°C for 2 – 4 h to remove the organic content, leading to an
size and morphology of ink deposition were controlled by increase in both the mesoporosity and mechanical strength
adjusting the ratio of extrusion speed to printing speed and of the final product . Couck et al. adopted a calcination
[91]
the height of the nozzle. It was found that the ink deflection condition of 823 K for 3 h to ensure that the printed ZSM-5
was proportional to the span, which was defined as the monolith retained its crystalline nature .
[96]
distance between two supporting points of the printed
structure. Specifically, the influence of span on deflection 4. Applications of 3D-printed zeolitic gas
was studied by printing structures whose spans were absorbents
1800, 1300, and 950 μm, respectively. The measurement Recent advancements in 3D printing technology have
revealed that fine ink deposition without deflection could enabled the fabrication of complex zeolite structures with
be ensured when the span was < 920 μm. The printed precise control over their pore size and geometry. This has
zeolite monolith experienced roughly a 53% volume opened new possibilities for designing and optimizing
shrinkage and displayed a surface fluctuation of about zeolitic adsorbents for specific gas separation, purification,
100 μm, while the sidewalls fluctuated around 200 μm, and storage applications.
indicating a high level of precision in its formation. The
mechanical strength of the structure reached up to 11 MPa 4.1. Gas separation
but decreased as the layer height increased [120] . As for the
other printing techniques, most of the existing research 3D-printed zeolite monoliths have shown significant
has been performed on the material development for the potential for use in gas separation. One typical application
zeolitic gas adsorbents, whereas few studies have focused of 3D-printed zeolite structures for gas separation is the
on the optimization of printing process parameters. selective removal of CO from CH in natural gas streams.
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It is because that the existence of CO would lower the
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3.4. Post-processing of 3D-printed zeolites heating value of gas, leading to corrosion when water is
also present in pipelines [122,123] . Lawson et al. measured
Calcination is another crucial post-processing step in the adsorption isotherms for CO and CH at 25°C from
fabricating 3D-printed zeolitic gas adsorbents, as it can 0 to 1 bar for four different 3D-printed zeolite structures
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affect their morphology, crystallinity, and surface chemistry. [94]
Calcination helps remove the organic additives used in that made of 13X, 5A, ZSM-5, and South Asia (SA) . It
was found that the South Asia zeolite monolith exhibited
the 3D printing process, leaving behind only the inorganic a CO /CH selectivity of approximately 50 with a
zeolite framework. This is important because the presence of corresponding uptake capacity of approximately 3 mmol/g
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organic materials in the zeolite can significantly compromise [94]
its porosity and adsorption performance [121] . Calcination at a pressure of 0.15 bar . In the study by Wang et al.,
helps to activate the zeolite framework and remove any 3D-printed NaX zeolite monoliths were shown to be
residual water molecules or impurities trapped within it. highly effective in separating CO and CH gases in fuel
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gas purification. Dynamic adsorption breakthrough tests
This process results in an increase in the surface area and
pore volume of the zeolite, which is vital for achieving high demonstrated the superiority of 3D-printed zeolites over
adsorption capacity and selectivity toward the target gas commercial benchmark ones for flue gas purification and
molecules [99-101] . Calcination also improves the mechanical natural gas upgrading. The equilibrium CO uptake of the
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strength and stability of the 3D-printed zeolite structure, 3D-printed zeolite monoliths reached up to 5.58 mmol/g
at a temperature of 298 K and pressure of 1 bar. The
making it more robust and resistant to deformation or
cracking during subsequent handling [27,105] . Calcination 3D-printed gas adsorbents displayed an ultra-strong CO
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time and duration for 3D-printed zeolite monoliths depend affinity compared to the parental NaX zeolite powders,
[27]
on several factors, such as the type of zeolite, the type of particularly at low partial pressure .
binder, and the desired properties and performance of One promising approach for the removal of CO from
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the final product. Typically, calcination is performed at natural gas streams is the use of electric swing adsorption
temperatures between 400°C and 800°C for several hours (ESA) technology. In the traditional temperature swing
Volume 2 Issue 4 (2023) 14 https://doi.org/10.36922/msam.1880