I am performing enzymatic protein hydrolisis in a 300 l reactor to obtain free amino acids from a crude slurry of blue-green microalgae. Hydrolysis proceeds properly, but when at a last step I try to lower pH by adding nitric acid the volume of the hydrolysate suddenly increases.
Data:
- Hydrolysis takes place at 50 ºC
- Unless it was necessary to avoid its use, I prefer to use nitric acid instead of other strong acids
- At the end of the hydrolysis step, pH must be lowered from 7 to 3 to prevent growth of fungi
- The issue (formation of microbubbles leading to a huge volume increase) takes place mainly between neutrality and pH 4. Below pH 4, apparently nitric acid can be poured without gas formation.
Thanks in advance for any suggestion or for a explanation that could help me solve this issue
Hi Federico
Change to Sulfuric or Phosphoric acid could help you, if it is just the pH that is influencing.
How concentrazed is your Nitric acid? In lower molarities you can have better chances to have everything already dissolved, try 10 or 20% of concentration.
Do you just want to stop the growth of the fungus? You can possibly try to reach a biostatic situation with additives if you use 1000ppm of Sodiumazide or >2000ppm formic aldehyd if this is not too evaporative for your following application or work-up process
Thanks Frank,
I am using 60% NO3H in order to avoid dilution of the product (amino acid hydrolysate - fertilizer). However, I can try the dilutions you recommend.
Yes, I try to stop proliferation of fungi. I cannot use azide or formaldehyde because of the Eco label. I am using authorised fungicides (copper-based ones) but we also lower the pH to increase the shell life of the product.
Maybe you get a formation of nitroso gases if stronger ions like chloride or sulfates are present. In that case, maybe the change of concentration is not helping and you need to change to this acids or phosphoric acid, a slightly increased sulfate or phosphate level should not give you ecological problems, anyway less than the Nitrate-Level does...
are you using Copper octanoate or something similar?
I think you could think about usage of Formalin too, You have a permission of usage formic aldehyd up to 2000ppm, absolute in liquid, in cosmetics and textile formulations that are designed for the direct and ready usage and handling for human purpose, it is not accumulating in the environment and is easily degraded and is exhausting extremly easy because of its boiling point.
I am using copper sulfate. I will check all those compounds you recommend. Thanks. Your help has been very valuable.
Hi,
for what purpose is your enzymatic hydrolysis?
In fact I am interested in enzymatic hydrolysis in order to desintegrate the cell wall of the microalgae to recover the intracellular protein and the bounded protein to the membrane. My final product will have potentilly some food applications. So I am not queen to use nitric acid. Do you have any protocol for that? That wold be very helpful.
Thanks
We develop a fertilizer, Ines. We low pH with nitric acid because of its dual purpose role (acid and nutrient). I´m sorry I don't have a protocol for food applications with aa, but I suppose there are lots of factors involved and maybe they are included in manufacturation regulations. In principle you don't need to use strong acids for conservation of the product. Instead, you can use sorbate or any other authorized microbicide agent.
Good luck
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