Session: ASME Undergraduate Student Design Expo

Paper Number: 175876

Porous Activated Carbon Coatings Using Yeast-Engineering 

This work details the development of yeast-engineered coatings using powdered activated carbon (AC) for carbon dioxide separation (CO₂). The coating process involves making a slurry using AC, yeast, xanthan gum, and sugar in water, applying it to a suitable substrate, letting it proof at a controlled temperature, and then calcining it. The void spaces that form during this process create a porous structure similar to that of edible cakes, yet firm and rigid. The AC powder does not readily mix with water compared to yeast and sugar. Hence, it ends up creating a thin film on the slurry ingredients when calcinated. Such behavior yields excellent performance in the coated form because all the AC is out of the matrix, adhering to it using binders like xanthan gum contrary to a hydrophilic adsorbent like zeolite 13X, where some of the zeolite particles are in the yeast and xanthan gum matrix, preventing them from being available for gas separation. The transport phenomena responsible for this behavior, which include the hydrophobicity of AC and its concomitant slurry viscosity behavior, are not well characterized.

This work characterizes the viscosity of the adsorbent slurry for zeolite 13X and AC as a function of variable solid fractions using a Texas Instrument HR-30 Rheometer. This viscosity is mapped and quantified over the void fraction range created during the sample fabrication. For instance, the Zeolite 13X slurry, with a 41% solid fraction, yields a zero-shear viscosity of 180 Pa · s. For 13X, this solid fraction yielded excellent coating results. However, the same solid fraction using PAC yields a viscosity of 89 Pa · s, indicating significant dilution with AC before the yeast begins proofing. This significant variation in viscosity is clearly attributed to AC being hydrophobic. Both slurries exhibit shear thinning; however, the low-strain-rate viscosity is crucial for the substrate coating and subsequent proofing process. This dilution using AC for the same solid fractions also results in samples without any voids because the slurry’s viscosity to too low to retain the bubbles formed by the yeast for a long enough period to allow for calcination to solidify the structure. This issue is resolved by gradually thickening the AC slurry using less water, yielding respectable void fraction results for a 53% solid fraction.

The final output of this work will be a comprehensive understanding of how the hydrophobicity of AC alters the viscosity of the coating recipe, which in turn affects the void fractions in the coating and the CO₂ capture performance.

Presenting Author: Kaleem Bocus Florida Institute of Technology

Presenting Author Biography: Kaleem Marc Anthony Bocus is a senior Mechanical Engineering undergraduate. He is a CAPE scholarship awardee from Trinidad and Tobago. Kaleem has co authored on two papers and currently is working on another paper. He has worked with PhD students to design and manufacture adsorption beds and solutions to a number of issues that appear in the lab. His main areas of interest are currently design and manufacturing.

Authors:

Kaleem Bocus Florida Institute of Technology
Darshan Pahinkar Florida Institute of Technology