[popay73]

Hi, I have a few question regarding neutralization of active pharmaceutical ingredients (API) waste waters.

First question is that in some article says that for 1 L of waste water is needed 10e-6 mols/L of Reagent (HCl or NaOH)- how did they come o that value, becouse it's used in neutralization calculations ?
 
Second question:

It's batch process and it involves 3 possibilities which confuses me.

First one: for acid solutions I guess.

1. bring pH to 2 (with NaOH addition)
2. heat reactor to 80 °C
3. keep it at that temperature for 30 min
4. cool it to 30 °C
5. adjust pH to 5,5 - 9,5

Questions: why step 1 ?  Why don't we bring pH to 7 in one go ? Why heating ? Is it becouse API decomposes more at higher temperature and lower pH if we have ACID solution. I assume this prosedure is for acid solutions.


Second one: for base solutions I guess.

1. bring pH to 12 (with HCl addition)
2. heat reactor to 80 °C
3. keep it at that temperature for 30 min
4. cool it to 30 °C
5. adjust pH to 5,5 - 9,5

Questions: why step 1 ?  Why don't we bring pH to 7 in one go ? Why heating ? Is it becouse API decomposes more at higher temperature and higher pH if we have BASE solution. I assume this prosedure is for base solutions.

Third one: with H2O2, when API oxidation is needed

1. bring pH to 6,2 (with NaOH or HCl addition)
2. heat reactor to 60 °C and add H2O2
3. when Oxygen level reaches maximum, heat to 90 °C and keep for 30 min
4. cool it to 40 °C

Questions: When H2O2 oxydies API, does H2O2 also decomposes to H2O and O2...and that's why we monitor O2 level ?

I thank U for any answers given,

Regards, Tom !

[eugenedakin]

Hi popay73,

Great questions!

First question is that in some article says that for 1 L of waste water is needed 10e-6 mols/L of Reagent (HCl or NaOH)- how did they come o that value, becouse it's used in neutralization calculations ?

This creates an excess of ions needed for he reaction. 

For acid solutions, step one is needed to increase the pH (this assumes that your pH was already below 2.  This is why NaOH is added to bring the pH up to 2. If you bring the pH to 7, there is no longer an excess of Hydrogen ions. These excess ions assist in neutralizing ingredients in the waste water.  Added heat increases the reaction rate.

Question #2 has the same relative answers as #1 - but in reverse.

Third question answer: Yes.

I hope this helps,

Sincerely,

Eugene

[Arkcon]

There's a lot in each part of your question.  Basically, the 5.5-9.5 is just to comply with local sewage laws, they're pretty uniform; conduits, treatment facility equipment, and bodies of water, worldwide pretty much need to be "about" neutral to handle the effluent stream, and 5.5 - 9.5 are pretty much what I'm used to for lab waste output requirements.

If you neutralize the API before you decompose it, you might encounter solubility problems, as a charged molecule, it remains more soluble, and reacts better with water and heat otherwise, it will precipitate or "oil out", and you might not even get it out of the tank.  Double check my point, see if the first one, you apply to acids, actually applies to basic API, and vice versa.

[popay73]

pH of acid solutions is above 2...so I think they want to make it more acidic which combined with higher temperature makes API more decomposed ? 
And the other way around for bases.

And back to first question, if 10 e-6 is excess concentration, what would be theoretical one, how to calculate it ?

Thx againg in advance !

Hi popay73,

Great questions!

First question is that in some article says that for 1 L of waste water is needed 10e-6 mols/L of Reagent (HCl or NaOH)- how did they come o that value, becouse it's used in neutralization calculations ?

This creates an excess of ions needed for he reaction. 

For acid solutions, step one is needed to increase the pH (this assumes that your pH was already below 2.  This is why NaOH is added to bring the pH up to 2. If you bring the pH to 7, there is no longer an excess of Hydrogen ions. These excess ions assist in neutralizing ingredients in the waste water.  Added heat increases the reaction rate.

Question #2 has the same relative answers as #1 - but in reverse.

Third question answer: Yes.

I hope this helps,

Sincerely,

Eugene

[eugenedakin]

Hi popay73,

What Arkcon mentioned is quite right, alot of this material deals with solubility.

I don't have the work instruction right in front of me, so I would be relying on what Arkcon mentioned.

If 10 e-6 is an excess, then you need to determine the reaction, balance the equation, and calculate stoichometrically.

I hope this helps, and thanks for the added information Arkcon!

Eugene