Here I assume that the gas has to dissolve as part of the reaction so use CO2(g) instead of CO2(aq) on the left hand side. I get an enthalpy delta of -111.33 kJ/mol. This differs from some homework answers I find online like [4] because I use NaOH(aq) while they use NaOH(s), etc; I hope I'm right for this application.
The easy thing would be to run at least (2b) (causticization) concurrently with (1) so you're always precipitating out CaCO3 and don't accumulate any Na2CO3 solution. It would also be easiest to combine (2a) with (2b) in a single causticization chamber. And it'd be simplest to skip (3) entirely, just treat CaO as a consumable, and be happy that you've sequestered carbon as CaCO3.
However, in a temperate climate, you can imagine doing the following to shift energy around the year (how realistic this is I don't know):
- Only run (2a) during the winter, to heat your home; you'd accumulate Ca(OH)2 solution to be used during the summer in (2b).
- Only run (2b) during the summer, to cool your home. During the winter you'd accumulate Na2CO3 solution from (1), which you'd need to store.
- If you're doing (3), do it during the summer, when a solar furnace can be operated. This gives you a reagent that you'll use in (2a) during the winter.
- You'd want to run (1) all year round, to scrub the CO2.
The main inefficiency this is trying to make useful is that you need to go down in energy with (2a) and back up in (3). And down in energy with (1) and back up in (2b).
I'll next need to understand the soda lime method to compare.
First, some enthalpies of formation (at 298 K and 1 atm, in kJ/mol) (from [1] unless otherwise indicated):
The reactions:1. 2NaOH(aq) + CO2(g) -> Na2CO3(aq) + H2O(l) ... -111.33 kJ/mol (exothermic)
Here I assume that the gas has to dissolve as part of the reaction so use CO2(g) instead of CO2(aq) on the left hand side. I get an enthalpy delta of -111.33 kJ/mol. This differs from some homework answers I find online like [4] because I use NaOH(aq) while they use NaOH(s), etc; I hope I'm right for this application.
2a. CaO(s) + H2O(l) -> Ca(OH)2(aq) .... -81.93 kJ/mol (exothermic)
2b. Na2CO3(aq) + Ca(OH)2(aq) -> 2 NaOH(aq) + CaCO3(s) .... 14.96 kJ/mol (endothermic)
3. CaCO3(s) -> CaO(s) + CO2(g) ... 178.30 kJ/mol (endothermic)
Energy issues:
The easy thing would be to run at least (2b) (causticization) concurrently with (1) so you're always precipitating out CaCO3 and don't accumulate any Na2CO3 solution. It would also be easiest to combine (2a) with (2b) in a single causticization chamber. And it'd be simplest to skip (3) entirely, just treat CaO as a consumable, and be happy that you've sequestered carbon as CaCO3.
However, in a temperate climate, you can imagine doing the following to shift energy around the year (how realistic this is I don't know):
- Only run (2a) during the winter, to heat your home; you'd accumulate Ca(OH)2 solution to be used during the summer in (2b).
- Only run (2b) during the summer, to cool your home. During the winter you'd accumulate Na2CO3 solution from (1), which you'd need to store.
- If you're doing (3), do it during the summer, when a solar furnace can be operated. This gives you a reagent that you'll use in (2a) during the winter.
- You'd want to run (1) all year round, to scrub the CO2.
The main inefficiency this is trying to make useful is that you need to go down in energy with (2a) and back up in (3). And down in energy with (1) and back up in (2b).
I'll next need to understand the soda lime method to compare.
[1] https://en.wikipedia.org/wiki/Standard_enthalpy_of_formation [2] https://webbook.nist.gov/cgi/cbook.cgi?ID=C497198&Mask=2 [3] http://chemistry-reference.com/reaction.asp?rxnnum=454 [4] https://answers.yahoo.com/question/index?qid=20131119075117A...