Msg. to kenvlach: Contd. 1

[bbqnw12]

Thanks for your reply. The heat derived is to be used in lowering the viscosity of the main process subject. CaO has been elected in the hope that it would form product Ca(OH)2 which hopefully should neutralise, in situ, any acid impurities likely to be produced as the reaction progresses.

An engineer I am working close with has proposed the possible use of naphtha instead of an alkane as the 'carrier liquid'. Is this a good idea?

The initial naphtha + CaO temperature is 52deg.C. The idea behind preheating is that heat loss is 'minimised' to allow for efficiency with tackling the viscosity. ie. Keeps the heat around a certain wanted level, taking into account possible/probable heat loss.

Calculated temperature rise from the CaO + H2O rxn is <300deg.C, on the basis of 1kg CaO : 1kg H2O. The vessel will not be purged, or shouldn't need to be, I don't think. It is an O2 free atmosphere anyway so there shouldn't be a huge risk of the alkane being ignited. Not sure about that one though.

Hope to hear from you soon. Thanx again.

kenvlach (Materials) Jul 30, 2003
OK, let me see if I understand the setup.
The alkane liquid will preheat and transport the CaO through a pipe to a reactor where it mixes with water and creates heat. I presume the heated alkane will be floated off the water and recycled back.

I still don’t understand how you will use the heat, and have some concerns about temperature and flammability.
What is your initial alkane + CaO temperature?
Why do you want to use preheat? Or is this something that will naturally happen once the alkane gets heated in the reactor?
What is the calculated temperature rise from the CaO + H2O reaction (depends upon quantity of water and your inert liquid)?
Will you purge your vessel with N2 to prevent igniting the alkane?

The vapor pressure of C6H14 may be too high for your temperatures; maybe use C10H22.

 

[kenvlach]

More questions.

What acid impurities are you talking about? An unspecified main process?

Preheating the organic liquid will not help in moving the CaO slurry. The liquid may flow easier, but a denser liquid would be better for moving the solid.

“Calculated temperature rise from the CaO + H2O rxn is <300deg.C, on the basis of 1kg CaO : 1kg H2O”

Your calculated temperature rise may be high. The heat absorbed by vaporization of your organic carrier and the excess water will prevent the temperature from rising much above 100^oC (depends upon how strongly the 'water of hydration' is held). For equal weights, the overall rxn. is

CaO(s) + 3.11 H₂O(l) + organic --> Ca(OH) ₂(hydrated) + 2.11 H₂O(l) + organic

Available enthalpy is &[ignore]Delta[/ignore];H_Rxn + &[ignore]Delta[/ignore];H_hydration = -15.56 kcal/mol + ? [do you have a value?]

But, for the temperature rise, we have to subtract 2.11 x &[ignore]Delta[/ignore];H_{vap, H2O} and &[ignore]Delta[/ignore];H_{vap, organic} before dividing by C_p(RHS).

Since &[ignore]Delta[/ignore];H_{vap, H2O} ~ 10 kcal/mol, not much useful heat left over.

If you have some other process that contains acid and requires heating, why not just feed the CaO directly into that reactor? Or, feed the CaO into a feedstock stream. Avoids setting up a 2nd reactor for CaO hydration, pumping slurry in, separating off a hot organic (condenser?) and pumping a hot Ca(OH)₂ slurry.

P.S. For neutralizing acidity, it only makes sense to bother with CaO or Ca(OH)₂ if the material cost is significant. I use NaOH solution since pumpable, faster reacting and small quantities.