Dry Ice from Sea Shells

2023-12-05

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In this video I'm going to turn seashells into dry ice. Sea shells are

mostly made up of limestone - or Calcium Carbonate (CaCO3), which can be

decomposed into Calcium Oxide (CaO) and Carbon Dioxide (CO2) when heated

to around 900C. I used a 500W induction heater i built to heat a sealed

pipe full of sea shells to a hot enough temperature and collected the

CO2 gas into a beach ball by using a vacuum pump to extract it from the

pipe.

For limestone decomposition to occur at a reasonably fast rate, the

temperature really needs to be over ~1000C, so this process took several

hours (even for only ~50 grams of limestone) and required a vacuum pump

to pull off the CO2. I broke down the remainder of my sea shells by

dissolving them in vinnegar, and saved the Calcium Acetate biproduct for

later use as a solid fuel for camping/hiking.

Once I collected a decent volume of CO2, I used a refrigeration

compressor to pump it into a plate-stack heat exchanger and used a

propane-based vapor compression refrigeration system to chill the high

pressure CO2 down to about -30C, so it required only modest pressure to

liquify. The refrigeration system is actually the pre-cooler stage for

my joule-thomson cryocooler, which i borrowed for this video.

Once a decent mass of CO2 has been pumped into the heat exchanger and

liquified, it's discharged through a ~1mm diameter capillary tube into a

thermos with a glass wool baffle to stop high speed gases from carrying

away tiny particles of the ice.

With a little bit of improvement to the limestone furnace temperature,

and some minor tweaks to my refrigeration system, this could be an

extremely cheap way to make dry ice, assuming a limestone source is

available. With the right setup, costs could be as low as a few cents

per pound of ice.

Induction Heater Schematic:

https://drive.google.com/file/d/1WWGMMiXeocOpjPDXXiNxOdZxMykq30Rp/view?usp=sharing

Music Used:

Kevin MacLeod - George Street Shuffle

Kevin MacLeod - Groove Groove

Kevin MacLeod - Lobby Time