Dr. Tao Wang's Sorbent Prep

Dr. Tao Wang has been one of OpenAir’s advisors on moisture swing DACC from the beginning. His support and expertise have been crucial in getting the Violet project off the ground.

Unfortunately, we’ve run into several issues with the sorbent sheets/cartridges we purchased from him in Dec 2020 (received Feb 2021).

Check out the unboxing video here)

After having built the initial Violet Decarbonizer prototype around one of these cartridges, we discovered they weren’t releasing CO2 in the wetting process. After several attempts to figure out the issue, we theorized that the sorbent had not been prepped prior to being shipped to us or that the sorbent had become unprepped in travel. As specified in Dr. Wang’s paper here, the ion exchange resin must go through a prepping process that removes the chlorine to allow it to bond with Co2.

We were significant increase in Co2 release when we attempted to prep the sorbent ourselves, but were not able to achieve the same levels Dr. Wang reported in his lab. We recently attempted to reproduce his prep methods more rigorously, despite the difficulties of attempting this outside of a lab/industrial setting.

Unfortunately, we immediately ran into issues (detailed here). When attempting the “hot soak” (soaking in 85-95c water for 48hrs) the sorbent sheets disintegrated to the point of no longer being viable.

Our next steps are to discuss as a team how we should proceed. I recommend a lower temp or room temperature soak prior to washing and additional conversations with Dr. Wang to find alternative recommendations. Hopefully, we will find a way to activate the remaining sheets and cartridges we have, if not I propose we find a safe way of disposing of the them and pruning this branch of research.

Good news, we got a helpful response from Dr. Tao Wang:

we hope our experimental procedure could address your issue related to adsorbents you mentioned.
The temperature we take for heat treatment ranges from 70℃ to 80℃ for 48 hours because the softening temperature of PVC is in 80~85℃ and then the sheets become disintergration. Besides, Our procedure for adsorption sheets preparation is that the sorbents pulverized are poured in the PVC slurry and then the mixer molding about 12h. After that, the sheets with adsorbents dip in carbonate solution for a couple of times. Finally, the sheets are soaked in a carbonate solution or deionized water for 48 hours.As you mentioned, a heat soak of adsorption materials before embedded in PVC may influence formability and swelling property, we are also now making some attempts.Maybe the preheat treatment of adsorbents is a interesting idea. we could also find a time to discuss interest ideas about the enhance the capacity and stability in next couples of weeks.

We’re working on setting up a meeting with Dr. Wang and we’ll discuss internally next steps.

We spoke with Dr. Wang’s current and former grad students (Has and Chenglong respectively). After consulting with them, we have plan for attempting to prep their sorbent.

  1. Hot soak their sorbent in a 1M sodium carbonate for 48 hours, maintaining a temperature under 80℃, probably 70℃ to be safe. We are going to use a manual slow cooker and a “Dorkfood DSV” to maintain the temperature for the duration.

  2. Wash the sorbent in a 1M solution for at least 2 hours, while stirring the solution. We will test the solution after each wash with the chloride sensor and repeat until the chloride level is within a least an order of magnitude of the pre-wash solution.

  3. Test the for prepped sorbent in our simple sorbent tester and compare the results with the previous results.

  4. Test the sorbent in the new MST (Mega Sorbent Tester) and compare the results to the levels Dr Wang is achieving.

I will update this blog as these steps are completed.