Rebreather World - View Single Post - Chemistry of CO2 Neutralisation - Can weight be used as an indicator of scruber life?

diveoceanos · 12th April 2008, 15:31

Quote: (Originally Posted by diveoceanos)

I had a second look at the scrubber quantitative situation. This can be used as a guidance and might also be proved to be wrong. Here we go:

Sofnolime contains more than 70% of its weight in Ca(OH)2.

Therefore for a 2,5 Kg sorb (axial scrubber of Meg) there is more than 1750g of Ca(OH)2.

The mole of Ca(OH)2 is 74g. So we have in the scrubber 23 moles of Ca(OH)2.

Each mole of Ca(OH)2 can neutralise 1 mole of CO2. Since the mole of CO2 is 44g, theoretically we would expect that 23 X 44g of CO2 would be added to to weight of the scrubber if the efficiency of the scrubber is 100% (taking into account only the Ca(OH)2 which is the predominating base).

That is approximately 1 Kg of CO2.

Let's suppose that on average a diver produces 0,9 litres (1,77g) of CO2 per minute.

Theoretically again the scrubber would be good for 570 minutes under these CO2 production rates.

However since the scrubber is in the form of pellets one would expect that its efficiency is not 100%. ISC clearly states that the scrubber is good for 3,5 hours. We then assumpt that the scrubber efficiency is 210 minutes divided by 570 minutes (approximately 35%).

With 35% efficiency i would expect that 35% of 1Kg of CO2 could be neutralised in the Meg's axial scrubber. The is approximately 365g.

I would therefore assumpt that at the end of the scrubber life it will weight 365g more compare to its initial weight.

Assumption #1: All the water that is being produced inside the scrubber remains inside the scrubber

Assumption #2: No water from other sources is entering the scrubber.

Please note that the above are just assumptions and need to be modified according to actual findings from real experiments.

proposal: Check the scrubber weight after 3,5 hours of use at more or the less oxygen consumption of 1 LPM and compare it with the calculated expected weight increase of 14,5%. (365g over 2500 g).

Further to the above hypothesis today I did my first weighing. Not all parameters were measured as this was a preliminary experiment to check if the hypothesis is anywhere close to correct. Apparently the results are encouranging and I am planning to continue this experiement in a proper and standardised protocol.

Todays Measurements:

TOTAL DIVE TIME: 182 minutes (3 dives).

INITIAL WEIGHT: 2500 g

FINAL WEIGHT 25 minutes after opening the canister: 2835 g

FINAL WEIGHT 3 hours after opening the canister: 2830 g.

WEIGHT CHANGE EXPECTED: 316 g MEASURED: 330 - 335 g

The initial hypotheis was that a Meg scrubber would have an increase of 365 g after 3,5 hours of use (or 14,5% weight increase given the 2,5 Kg initial weigh). Given the analogies one would expect a weight increase of 316 g after 182 minutes of use. Of course there will always be a deviation as not all dives are of the same activity level. My dives where relaxed and the activity level minimal. These findings are anyhow, in line with the above hypothesis and therefore the whole issue requires further investigation. Gathering and analysing more data would be ideal, so anyone who has the extra time may please contribute to this? IMHO it worths a try.

P.S. For those who want to contribute please see the attached excel file for data recording.

12th April 2008, 15:31	#33 (permalink)
diveoceanos New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Apr 2007 Location: Cyprus Posts: 43	Re: Chemistry of CO2 Neutralisation - Can weight be used as an indicator of scruber l Quote: (Originally Posted by diveoceanos) I had a second look at the scrubber quantitative situation. This can be used as a guidance and might also be proved to be wrong. Here we go: Sofnolime contains more than 70% of its weight in Ca(OH)2. Therefore for a 2,5 Kg sorb (axial scrubber of Meg) there is more than 1750g of Ca(OH)2. The mole of Ca(OH)2 is 74g. So we have in the scrubber 23 moles of Ca(OH)2. Each mole of Ca(OH)2 can neutralise 1 mole of CO2. Since the mole of CO2 is 44g, theoretically we would expect that 23 X 44g of CO2 would be added to to weight of the scrubber if the efficiency of the scrubber is 100% (taking into account only the Ca(OH)2 which is the predominating base). That is approximately 1 Kg of CO2. Let's suppose that on average a diver produces 0,9 litres (1,77g) of CO2 per minute. Theoretically again the scrubber would be good for 570 minutes under these CO2 production rates. However since the scrubber is in the form of pellets one would expect that its efficiency is not 100%. ISC clearly states that the scrubber is good for 3,5 hours. We then assumpt that the scrubber efficiency is 210 minutes divided by 570 minutes (approximately 35%). With 35% efficiency i would expect that 35% of 1Kg of CO2 could be neutralised in the Meg's axial scrubber. The is approximately 365g. I would therefore assumpt that at the end of the scrubber life it will weight 365g more compare to its initial weight. Assumption #1: All the water that is being produced inside the scrubber remains inside the scrubber Assumption #2: No water from other sources is entering the scrubber. Please note that the above are just assumptions and need to be modified according to actual findings from real experiments. proposal: Check the scrubber weight after 3,5 hours of use at more or the less oxygen consumption of 1 LPM and compare it with the calculated expected weight increase of 14,5%. (365g over 2500 g). Further to the above hypothesis today I did my first weighing. Not all parameters were measured as this was a preliminary experiment to check if the hypothesis is anywhere close to correct. Apparently the results are encouranging and I am planning to continue this experiement in a proper and standardised protocol. Todays Measurements: TOTAL DIVE TIME: 182 minutes (3 dives). INITIAL WEIGHT: 2500 g FINAL WEIGHT 25 minutes after opening the canister: 2835 g FINAL WEIGHT 3 hours after opening the canister: 2830 g. WEIGHT CHANGE EXPECTED: 316 g MEASURED: 330 - 335 g The initial hypotheis was that a Meg scrubber would have an increase of 365 g after 3,5 hours of use (or 14,5% weight increase given the 2,5 Kg initial weigh). Given the analogies one would expect a weight increase of 316 g after 182 minutes of use. Of course there will always be a deviation as not all dives are of the same activity level. My dives where relaxed and the activity level minimal. These findings are anyhow, in line with the above hypothesis and therefore the whole issue requires further investigation. Gathering and analysing more data would be ideal, so anyone who has the extra time may please contribute to this? IMHO it worths a try. P.S. For those who want to contribute please see the attached excel file for data recording. Last edited by diveoceanos : 12th April 2008 at 15:34.
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