WATER WASHING WITH ADDED ACID

[whatarascal]

Acid washing can leave the bio acidic.

Does anyone test their finnished bio to see if it is acidic and if they do

HOW do they test it

[whatarascal]

Furthermore if found to be acidic say ph6 what could be done to raise the ph to normal.

[Julian]

This cropped up a little while ago and this is my take on things based on no knowledge of chemistry

Only aqueous solutions can be acidic or alkaline.  Therefore pure biodiesel cannot be acidic.  If there is any residual water in the bio, then it may be possible to detect acidity or alkalinity.

I was very concerned about the same thing when I first started acid washing, but testing wet bio with litmus paper showed a neutral pH after the second wash with water.  So, from my limited experience and zero knowledge of chemistry, I recon if bio has several water washes after the acid and is thoroughly dry, it shouldn't be a problem.

[Head Womble]

From my understanding,
if you do a titrated acid wash you're only adding enough acid to neutralise the bio (raw bio is has a high PH value),
so we're bring the bio to PH7 (neutral).

I have found that acid washed bio will show as having an artificially low soap content when doing titrated soap testing, this is due to it being neutralised during the wash,
if the  bio was acidic it would show a zero soap content in these tests.

[Bill]

Only aqueous solutions can be acidic or alkaline.  Therefore pure biodiesel cannot be acidic. 

How does this fit with organic acids, free fatty acids, titrating for free fatty acids etc. Depends on how you define acidic. pH can only be measured in aqueous solutions but organic solutions can be titrated to determine an acid (or alkaline) value using the range of colour changing indicators.
Water washing should wash out the acid (or alkaline) but I guess the only way to test would be a titration using the appropriate indicator. As you do when you titrate bio to determine the amount of acid to use to neutralise the remaining catalyst.

[Julian]

Only aqueous solutions can be acidic or alkaline.  Therefore pure biodiesel cannot be acidic. 

How does this fit with organic acids, free fatty acids, titrating for free fatty acids etc. Depends on how you define acidic. pH can only be measured in aqueous solutions but organic solutions can be titrated to determine an acid (or alkaline) value using the range of colour changing indicators.
Water washing should wash out the acid (or alkaline) but I guess the only way to test would be a titration using the appropriate indicator. As you do when you titrate bio to determine the amount of acid to use to neutralise the remaining catalyst.

I wish when you quoted, you hadn't excluded the bits that say "based on no knowledge of chemistry" and "from my limited experience and zero knowledge of chemistry" ... does put things more into perspective.

So you are saying that biodiesel can be either acidic or alkaline, we just need a means of quantifying it.

[Bill]

it could be acidic or alkaline or anywhere in between.
Why titrate a sample after conversion to see how much acid to add if its not alkaline at that point?
Doesn't oxidised biodiesel become 'acidic'?

ps nothing like quoting someone out of context, perhaps I should have been a journalist

[whatarascal]

I washed my last couple of batches with water with a small amount of acid added.
The first batch had been demethed and settled for two weeks and soaps were still present in 50/50 shake up tests.
In this batch I only used 10 litres of water with 25ml of 30% Hydrochloric acid.
Dried and 50/50 shake up test showed clear,the clear water in test was ph6.

The last batch I added 10 litres of water with 25ml of 30% hydrochloric acid at 2nd stage before dropping glycerol. Then another 10 litres of water pumped and bubbled untill no methanol .50/50 water test showed clear and water was ph6.
My water is naturally ph 7.

was there any point in me doing these tests and having done them what do they mean.

I was initially worried about acidic fuel "thats why I tested the wash water"but surely if bio was left soapy it would be alkali and as such just as corrosive.

180 litre batches

[RichardP]

I'll check the pH of the wash water with litmus paper, when it's the same as the clean water going in at pH7  then I'm happy.

[uberveg]

Organic acids can migrate into the bio if you over do it with adding acid to the wash. Litmus paper won't be any good if you dip into bio, need to titration the bio to find the ph. Get your burettes out lol