(181i) Tailoring Surface Wettability of 3-D Printed Minimal Surfaces Using iCVD for Implementation As Packing in Gas-Liquid Absorption Columns

Packing
used in gas-liquid absorption columns can be classified as random or
structured. The main disadvantage with structured packing is channeling,
wherein the packing is not fully wetted by the liquid and remains dry or
covered with a thin, stagnant liquid film. While the problem of channeling is
less severe with random packing, they can result in high pressure drop of the
gas across the column, leading to liquid build-up and eventually flooding of
the column.   

A design based on the concept of minimal surfaces is
explored to improve energy efficiency of the operation of gas-liquid absorption
columns. A minimal surface can be described mathematically as a surface that locally minimizes its area, which is
equivalent to having a mean curvature of zero, with the simplest example being
a plane. The minimization of area within the confines of a given boundary
allows for very thin, yet strong structures, which are important in mass
transfer applications due to lower material costs.  Once a minimal
surface is generated, it can be replicated to a larger scale using 3-D printing
technology to generate packing for mass transfer applications. Illustrations of
minimal surfaces are given in the figures – (1) gyroid and (2) gyroid showing
labyrinths and repeating units.   

In addition to geometry, surface wettability
of the packing could be used as a parameter for minimizing pressure drop across
the column.  However, current 3-D printing technology has significant
limitations with respect to tailoring surface wettability of the packing by
incorporating multiple polymer types in one 3-D print.  Hence, initiated chemical
vapor deposition (iCVD) will be explored to control the wetting characteristics
of the packing by coating it with an appropriate polymer. iCVD is especially
suitable for such modification because of three reasons: 1) it can be used to
deposit a variety of polymers 2) it provides conformal coatings on complex
substrate shapes, and 3) it can be calibrated to yield the desired film
thickness on the substrate. Polymer iCVD has not been reported in the
literature for gas-liquid absorption packing or for minimal surfaces. Deposition
on complex 3-D substrates would require additional considerations that would
not be factors with flat 2-D substrates. Therefore, the study described above
to tailor surface wettability of the 3-D printed packing would represent a
novel endeavor in the field of polymer iCVD. In the study, packing will be
produced using 3-D printing and coated with different polymers using iCVD.
Contact angle measurements and electron microscopy will be used to evaluate
film thickness and wettability as a function of substrate height. Pressure drop
across a packed column will then be measured for both uncoated and coated
packing to complete the assessment of the feasibility of surface modification
of the packing using iCVD.  

References:

[1]
R. C. Ryan, Minimal
Surface Area Mass and Heat Transfer Packing, in Patent 9,440,216. 2016: USA

[2] K. K. Gleason (Ed)
(2015) CVD Polymers: Fabrication of Organic Surfaces and Devices, Weinheim,
Germany: Wiley-VCH