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Cylinder-less CO2 incubator

Nicey Nichey
  [vote for,

Biologists often use a CO2 incubator - it's a chamber that not only maintains a constant chamber, but also maintains a constant CO2 concentration, typically around 5%. This is necessary because many cultured cells grow best at these higher CO2 concentrations.

A CO2 incubator is normally fed from a CO2 cylinder. A solenoid valve opens to let CO2 in, when necessary, and the chamber itself is more-or-less airtight to limit the loss of CO2. However, this is a huge faff. You have to have a big (eg 34kg) CO2 cylinder, which is typically rented from a supplier; it has to have a leak-free connection to the incubator; and you have to replace the cylinder when it gets low. If it runs out over a weekend, it can be bad news for your cells. So an ideal setup has _two_ cylinders connected to a gadget that automatically switches from the empty cylinder to the full one, ensuring continuity of supply.

Now, all this is a bit silly. CO2 is very easy to make by combustion. So, I suggest a better way.

Inside the incubator, we place a little battery-powered or mains-fed gizmo consisting of a alcohol burner, an electronic ignition, and a snuffer. It also has a CO2 sensor (like current CO2 incubators). When the CO2 level falls, the electronic igniter lights the wick, burning alcohol to produce CO2. After a couple of seconds, the snuffer drops down over the wick to extinguish the flame. If the CO2 level is still too low, the process repeats every few minutes.

One problem is that the burning will raise the temperature in the incubator, which would be very bad. However, if the small flame is active for only a couple of seconds every few minutes, the heater control of the incubator will compensate, and the temperature deviation will be negligible.

A level sensor can warn the user when the alcohol needs topping up. No CO2 cylinders or automated changeover gadget are needed. It also means that you can run a CO2 incubator in locations too remote for regular cylinder deliveries.

MaxwellBuchanan, Aug 26 2019

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[bs0u0155, Aug 26 2019]


       Potential bun, but I want to see some math about how much the flame will affect the carbon dioxide concentration and the temperature.
notexactly, Aug 26 2019

       Well, I don't have the math but I do have an experiment. Burning an alcohol-soaked tissue in my CO2 incubator for about 5 seconds sent the CO2 concentration up into the 10s of percent, and caused a brief blip of about 5°C. +5°C is completely unacceptable, but I also produced far too much CO2. I think a much smaller flame for a couple of seconds would give me 5% CO2 for a temperature rise of maybe 0.5°C. An even smaller flame in short bursts would reach 5% CO2 without a significant temperature change.   

       If you were really worried about temperature fluctuations, you could have the burner thermally isolated from the chamber, and just chimnify the resulting CO2-rich gas into the chamber. But I don't think that would be necessary.
MaxwellBuchanan, Aug 26 2019

       A look at the numbers, Aigas charge us about $1.80/kg for CO2, Decon charge about $15/kg for EtOH, now a kg of EtOH = 2 kg of CO2 when combusted, but it still turns out dramatically expensive. Then there's doing the combustion in a clean way, you'll have water to deal with, and worse there's non-CO2 combustion products, just a little CO for example could mess things up.   

       Now, HCl is cheap, and baking soda can be bought for ~$1/kg. Dosing is a microcontroller and a cheap peristaltic pump. No flames, purity guaranteed.
bs0u0155, Aug 26 2019

       One problem I have with incubators, they can only INCREASE CO2. A total pain, I blame the cancer people who have cells that can't be bothered actually doing any real respiration. Consequently, if you have a full incubator of cells that actually use their mitochondria, the CO2 can go above 5% over the weekend.   

       Another tactic, used by labs with relaxed attitudes, is to have a nice healthy bacterial colony living in the water at the bottom. Always an interesting smell come monday.
bs0u0155, Aug 26 2019

       //$15/kg for EtOH// Jeezus that's cheap! Where exactly did you find that? I pay a fortune for 96% ethanol, even without duty. But, we can use methanol instead, which I believe is much cheaper.   

       Agreed, CO would be bad - but how much CO is produced when burning alcohol in what is essentially air? As for water - many incubators are humidified anyway.   

       The baking soda/HCl option is sort of nice, but not as simple as an alcohol burner. And the main consideration was not cost (which won't be great in any case) but faff.
MaxwellBuchanan, Aug 26 2019

       See link, we get it even cheaper via the hospital pharmacy, but the lady who orders is on hols, so I have no idea exactly how much. It still involves a fax machine for some reason.   

       I know many incubators are humidified, but you have to be able to deal with an excess. Actually, there needs to be an auto-top up on incubators. I have one on my fish tank, they're not pricey.   

       HCl/Limestone? Could use an XYZ controlled dropper to slowly acid etch your own face into a block of stone.   

       Or, how about using Pd/Pt catalysis for oxidation of the natural gas? no flame, entirely gaseous. The only problem I can think of is the sulfur compounds they put in the gas. Buggers a lot of catalysts right up and probably cells too.
bs0u0155, Aug 26 2019

       Ah, America. Land of the home and the brave of the free. I guess high ethanol prices are a UK thing. I forget the last price I paid but it was over £200 for 2.5l of 96%.   

       Natural gas - does bottled gas have sulphur? I guess it must have a sulphur-containing odorant (since it still smells bad). Otherwise it would be a good solution; you could use the same camping-gas cylinders that you use for lab bunsens.
MaxwellBuchanan, Aug 26 2019

       They put the stinky stuff in everything that might get near a consumer. Still, a great commercial opportunity to sell activated charcoal filters. No CO2, just recurring filters...
bs0u0155, Aug 26 2019


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