Calcium Carbonate & Dicalcium Phosphate - CO2 Problem

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Discussion Overview

The discussion revolves around the issue of CO2 production in a mixture of calcium carbonate (CaCO3) and dicalcium phosphate (CaHPO4) under varying temperature and moisture conditions. Participants explore the underlying chemical reactions, potential solutions to mitigate CO2 production, and the effects of environmental factors on the reactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant describes observing CO2 production at room temperature and increased production at higher temperatures, questioning the underlying reactions responsible.
  • Another participant suggests a reaction equation involving CaCO3 and CaHPO4 leading to the formation of Ca3(PO4)2, H2O, and CO2, but expresses uncertainty about the legitimacy of the equation.
  • There is a proposal to use a desiccant to reduce moisture content and potentially limit CO2 production, with questions about its effectiveness in shifting the reaction equilibrium.
  • Some participants discuss the thermodynamic favorability of Ca3(PO4)2 and the complexity of calcium phosphate systems, suggesting that keeping the mixture dry might slow the process but not completely stop it.
  • Questions arise about whether the presence of the two ingredients alone could lead to CO2 production without thermal breakdown, with some suggesting that a solid phase reaction could still occur at lower temperatures.
  • Suggestions are made regarding cooling the mixture and using humectants to slow the reaction, with participants agreeing that both strategies might help reduce CO2 production.

Areas of Agreement / Disagreement

Participants express a range of views on the reactions involved and potential solutions, with no clear consensus on the effectiveness of proposed methods or the exact nature of the reactions occurring. The discussion remains unresolved regarding the best approach to mitigate CO2 production.

Contextual Notes

Participants note the complexity of calcium phosphate systems and the potential influence of environmental factors such as temperature and moisture on the reactions, but do not reach a definitive conclusion on the implications of these factors.

yaboynov
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Hello everyone,
I would really appreciate your help on figuring out the issue of undesirable CO2 production in this situation.

Homework Statement


In a mixture of CaCO3 + CaHPO4; I am observing undesirable CO2 production under conditions of 20-25°C (room temp) and an undesirable excess of CO2 production under conditions of 50+°C. The time of exposure to these temperatures is a repetitive 6 hour oscillation (to 50°C) and an 18 hour de-oscillation (to 25°C).
High moisture content in the environment is a factor, but is outside the immediate physical contact with the material. Without moisture in the environment though, CO2 production still does occur.

1. I am trying to understand why the CO2 production is occurring and the equation responsible.
2. I am trying to understand possible solutions for stopping the CO2 producing reaction.
3. Does the high moisture content move the equation towards accelerating CO2 producing?
4.


Homework Equations



1. H3PO4 + CaCO3 → CaHPO4 + CO2 + H20 (not the exact equation, but the most informative)
2. CaCO3 + CaHPO4 + Heat → (CO2 producing equation)?
3. CaCO3 + CaHPO4 + Heat + H20 → (CO2 producing equation)?
4. CaCO3 releases CO2 in interactions with acids - and CaHPO4 is an acid.

5. 2(CaHPO4) + CaCO3 →300-900°C C2P2O7 + CaCO3 + H20 → further → 2(C2P2O7) + CaCO3 →>900°C Ca3(PO4)2 + CO2 (how does this compare to a repetitive exposure to 50°C)


The Attempt at a Solution


Well...these are my thoughts
1. CaCO3 (thermal decomposition) → CaO + CO2
CaCO3 degrades towards CO2 production as a byproduct under high heat conditions (around 800°C), though in my problem I am experiencing CO2 production at a much lower temp. (≈50°C)
2. Would simply cooling down the mixture below room temp stop the CO2 producing reaction? Would a desiccant be effective in reducing the CO2 production by reducing the moisture content in an enclosed heated situation?
3. Is there a material that can be included within the solution to prevent this reaction from occurring?


Any and all help will be appreciated. Thanks for your time.
 
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Why not just

CaCO3 + 2CaHPO4 -> Ca3(PO4)2 + H2O + CO2
 
Borek said:
Why not just

CaCO3 + 2CaHPO4 -> Ca3(PO4)2 + H2O + CO2


I figured that both might interact and form CO2 regardless of heat - but wasn't exactly sure of the equation or the legitimacy. Thank you for that.

My goal is to try to keep the reaction to the left as to limit the production of CO2 - if I added a desiccant to limit H20 presence, would this push the equation more-so to the left therefore limiting CO2 production? Would that have any bearing on preventing H20 production, or would it just be an after-the-fact solution of removing H20?

Would you personally have any suggestions on how to keep the reaction from occurring if it is at all possible? Any kind of help I'd be thankful for.
 
If the Ca3(PO4)2 is thermodynamically favored there is not much you can do. Keeping the mixture dry will probably slow the process, but I doubt it will stop it completely. Besides, removing water will shift the equilibrium to the right, which is not what you want.

I am afraid I can't help you much - as far as I am aware calcium phosphate systems are quite complicated, with many possible variants of composition, including basic phosphates (hydroxyapatite). That means it not easy to predict how will the system evolve.
 
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Would the equation that you posted remove the need for thermal breakdown for production into CO2? Just the presence of the two ingredients together would incur CO2 production? Thanks
 
Thanks for your response Borek. Off the top of your head, would decreasing the temperature be the simplest thing to do to limit this reaction?

Or would a humectant help slow the reaction?
 
Last edited:
yaboynov said:
Would the equation that you posted remove the need for thermal breakdown for production into CO2? Just the presence of the two ingredients together would incur CO2 production? Thanks

I don't think you need thermal breakdown for the reaction to occur. It will be slow, as its a solid phase reaction, but IMHO it will still happen just because the substances are mixed.

yaboynov said:
Off the top of your head, would decreasing the temperature be the simplest thing to do to limit this reaction?

Or would a humectant help slow the reaction?

Both keeping it cold and keeping it dry should slow down the reaction.
 

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