7 replies to this topic

[Adamsdr3]

Hi guys,

 

I have a tank that is 95% water and 5% a mixture of acids and bases (mostly KOH, HF, NH4F and HCl). I need to do a heat gain calculation on the tank in the scenario that 9 gallons of HF is added to the tank containing 500 gallons of the composition listed above.

 

1. Is it safe to assume that the vast majority of the heat generated is by the dilution of HF and not the neutralization?

 

2. Does anyone know of a good software program to run this sort of calculation in addition to chemical compatibility between chemicals?

 

Thanks in advance.

[breizh]

Hi ,

As an option , why don't you perform the work in a lab ?

I don't think you will find any software to support your work . I may be wrong .

Good luck . Safety is key with these materials .

Breizh

[Adamsdr3]

The work cannot be preformed in a lab because the system doesn't exist yet. It is still in design phase.

 

As for the program, there's got to be some sort of program that says "if you mix this with this, the properties of the fluid will be this."...

[MrShorty]

I'm not sure there is enough information to really answer the question. A few thoughts:

 

1) When you say you are adding 9 gallons of HF, is this 9 gallons of anhydrous HF, or 9 gallons of an aqueous HF solution? From what I understand, there is a substantial difference between the heat of mixing of H2O and anhydrous HF and the heat of dilution of H2O with an aqueous HF solution.

 

2) I don't think it is a fair assumption to assume that the heat of neutralization (OH + H -> H2O, I assume you mean) is minor. From my experience, the heat of reaction of acids and bases is substantial. Of course, a lot of this is going to depend on exactly what your starting solution contains. Is there excess KOH to participate in the neutralization reaction, or are the acids in excess so that the KOH really exists as KF and KCl?

 

3) I don't think fancy software should be needed for this (at least for a seat of the pants first guess calculation). Stoichiometry will be important as you try to determine which reaction (dilution or neutralization) is going to dominate.

Edited by MrShorty, 27 April 2015 - 10:50 AM.

[PingPong]

mixture of acids and bases (mostly KOH, HF, NH4F and HCl)

You can't have a mixture that contains both bases, like KOH, and acids, like HF and HCl. They will react and what you get is a mixture of salts, and the acid or base that was in excess (not both).

So I suggest you first find out what is the actual composition of that mixture.

 

Also you need to know the HF concentration in the 9 gallons of liquid that you add.

 

It seems to me that, if you know all the concentrations, and you know what you are doing, it is fairly simple to calculate by hand.

[Adamsdr3]

I'm not sure there is enough information to really answer the question. A few thoughts:

 

1) When you say you are adding 9 gallons of HF, is this 9 gallons of anhydrous HF, or 9 gallons of an aqueous HF solution? From what I understand, there is a substantial difference between the heat of mixing of H2O and anhydrous HF and the heat of dilution of H2O with an aqueous HF solution.

 

2) I don't think it is a fair assumption to assume that the heat of neutralization (OH + H -> H2O, I assume you mean) is minor. From my experience, the heat of reaction of acids and bases is substantial. Of course, a lot of this is going to depend on exactly what your starting solution contains. Is there excess KOH to participate in the neutralization reaction, or are the acids in excess so that the KOH really exists as KF and KCl?

 

3) I don't think fancy software should be needed for this (at least for a seat of the pants first guess calculation). Stoichiometry will be important as you try to determine which reaction (dilution or neutralization) is going to dominate.

 

 

 

mixture of acids and bases (mostly KOH, HF, NH4F and HCl)

You can't have a mixture that contains both bases, like KOH, and acids, like HF and HCl. They will react and what you get is a mixture of salts, and the acid or base that was in excess (not both).

So I suggest you first find out what is the actual composition of that mixture.

 

Also you need to know the HF concentration in the 9 gallons of liquid that you add.

 

It seems to me that, if you know all the concentrations, and you know what you are doing, it is fairly simple to calculate by hand.

 

 

I am adding 9 gallons of aqueous 90% HF. HF is being diluted in 500 gallons of 95% water and 5% salt solution. What I am asking is that if the 5% makes the solution slightly basic (only slightly because it's really less than 5% base), When I do the heat gain calc, is it safe to neglect the heat generated by the acid/base neutralization reaction between HF and KOH and focus mainly on the heat generated by diluting the 90% HF.

[MrShorty]

When I do the heat gain calc, is it safe to neglect the heat generated by the acid/base neutralization reaction between HF and KOH and focus mainly on the heat generated by diluting the 90% HF.

It might be, but I don't think I would make the assumption without some calculation to demonstrate that it can be neglected. It will probably depend on how much excess KOH is present in the original salt solution.

 

I expect that the heart of determining if the heat of neutralization be ignored is going to be calculating how much (moles) free KOH is in the original salt solution and how much (moles) of HF you are adding to the solution. From that, you should be able to figure out how much water will be made during the reaction, then estimate the amount of heat from the heat of reaction for H(+) + OH(-) -> H2O.

 

If you do not know how much free KOH you have, I would come up with a worst case scenario (maybe all 5% is KOH and there are none of the other acids), and estimate the heat of neutralization from that.

 

From that, you should be able to determine if the heat of neutralization will be insignificant compared to the heat of dilution or not.

 

I think the ultimate decision on this is going to depend strongly on how much free KOH is present in your salt solution.

[PingPong]

The heat of neutralization, per mol HF, is much higher than the heat of dilution, per mol HF.

 

So it depends on the available amount of KOH in the 500 gallons, how much heat is generated by the neutralization.

 

As it seems you have no idea how much KOH is present, you prefer to ignore any heat of neutralization and hope that we can confirm that the heat of dilution is all you need to look at.

 

Well, bad luck for you, you really need to figure out how much KOH is present, as heat of neutralization is likely determining.