Is acid washed biodiesel darker?

[dgs]

I have a process running at the moment where I am splitting the de methed bio 50/50. One half will be water washed with a small amount of acetic acid (it really does help the wash) and the other half will be washed just with water.

My obsession with light coloured bio continues and since I have been adding a small amount of acetic acid to the wash I suspect it has increased the colour of the bio. This test using the same batch of bio will hopefully tell if I am correct.

I never add the acid until the soap level is <200ppm so as not to return a significant amount of ffa's to the final product.

One thing that does puzzle me about acid washing is that the emulsified layer between the water and bio that we all suspect is due to monoglycerides is either very small or non existant.

The monoglyceride molecule is a glycerine molecule with one fatty acid chain attatched, so how does a very dilute solution of acetic acid stop this emulsifying with water.

[Head Womble]

From my days of acid washing I found it did make the bio darker.

Have you tried Acetone in the wash water ?
I found just 40mm in a 180L batch worked really well.

[neisel]

One half will be water washed with a small amount of acetic acid (it really does help the wash)

How?

In what way?

[dgs]

From my days of acid washing I found it did make the bio darker.

Have you tried Acetone in the wash water ?
I found just 40mm in a 180L batch worked really well.

Hi mark,

I remember you telling me about your method at last years bbb. I never tried it as I had no acetone. I got some from Nige this year so will give it a go.

When you say 40 mls, is that per wash or say 10mls per wash for 4 washes.

Presumably you have never found the addition of acetone darkens the bio.

[dgs]

One half will be water washed with a small amount of acetic acid (it really does help the wash)

How?

In what way?

Hi neisel,

Bio and water splits sooner, Number of washes are less. Mono layer is not there or very tiny. Soap is non detectable in the dried bio. TAN test on the bio indicates 0.1 to 0.2 Spec is 0.5.

To do a TAN test (total acid number) titrate your bio as if you were titrating oil with 0.1% KOH, a 1.0 ml sample will do but 1.1mls (1gm) is better. max allowed titration is 0.5 ie 0.5 mgs KOH/gram of bio.

I simply did this to confirm that I hadn't 'overwashed' it with acid.

[Head Womble]

From my days of acid washing I found it did make the bio darker.

Have you tried Acetone in the wash water ?
I found just 40mm in a 180L batch worked really well.

Hi mark,

I remember you telling me about your method at last years bbb. I never tried it as I had no acetone. I got some from Nige this year so will give it a go.

When you say 40 mls, is that per wash or say 10mls per wash for 4 washes.

Presumably you have never found the addition of acetone darkens the bio.

I used 40ml in each wash (I think it was 40ml, was a long time ago now), that was when I was doing the testing, I later just added a glug/splash as exact amounts I didn't find critical.

The tests were done in the same controlled way as you, as in, split a batch in 1/2 so the raw product was the same and then wash one 1/2 with acetone and the other 1/2 without.

I did this with a couple of batches and had the same result.

The use of acetone reduced the amount of washes needed, sometimes I could get away with just two.

I did soap tests at each stage, but lost all the info when my PC died.

I never noticed any colour change with the addition of acetone.

The way I see it is adding acid  may / may not have a detrimental effect on the finished product (I know I had a slurry type layer dropout when I was doing acid washing, others reported the same), however as acetone is used by many veg and bio runners to increase MPG, so if any is still present after washing it can't be a bad thing.

Just for clarification, I was doing 180L batches, two stage non-titration, 10L prewash using only the gly present in the second stage, 25L of water in each wash with 40ml of acetone (pump washing).

[dgs]

Thanks Mark, I will give it a try.

Will post up the results of the acid/no acid comparative tests when they are done. Hopefully with some pics.

[dgs]

Yes, it is darker.

Photo's to follow later.

[dgs]

left hand cubie is normal water washed. Centre cubie is washed with a small amount of acetic acid in the water (15 mls in one wash and 10mls in another)

Right hand cubie is same (acid washed) as middle one but has been in the sun for 4 days.

next up is to try Marks acetone addition in the wash water.

BTW Apologies to Julian regarding the length of my grass.

[Head Womble]

I look forward to reading your results.

[DavidShinn]

Hello!

I will try the 40ml addition of acetone with my next batch.

David

[dgs]

I have just cleaned the centrifuge, probably the 1st time for months, certainly 1000 litres of bio.

There are some brown deposits inside. It could be the dark slurry deposits that Mark mentioned, because of the acid washing.

The last time I took it apart it had certainly as much bio through it as now (when I was water washing with no acid addition) and it was totally clean.

Will try to post a pic.

[dgs]

     


     

[neisel]

If that's all that's there after 1000L I'd retire the 'fuge.

[dgs]

Better out than in, neisel.