View Full Version : Dewatering WVO with petrol.

23rd July 2018, 11:48 PM
Hi Everyone, someone on one of the UK forums asked me to do a little test some weeks ago and I thought the info would be interesting for you guys 'down under'

I think we all realise that adding petrol to WVO encourages water and residue to fall. The test was to see the difference in water content before and after.

I tested the water in some (not good quality) but well settled oil with my Sandy Brae water tester.
It came out at 1425ppm.

I added 10% petrol and shook well. After a few hours I noticed a residue layer forming at the bottom of the separating funnel. I left the sample 30 hours and tested again for water. The result was 345ppm.

Tony From West Oz
24th July 2018, 12:13 AM
Does your Sandy Brae water tester measure water in the presence of vegetable oil as accurately as it measures water in the presence of petrol and/or other fluids?

Your test results show a significant reduction in water content after the petrol / oil mix was settled for 30 hours. Did you decant the oil from above the residue layer before testing? Would it have made any difference ?

Now you need to determine the optimal amount of petrol to add to wet oil, for the most cost effective dewatering.
What impact does the reduction of water from 1425ppm to 345ppm on a typical batch of biodiesel? Would it be cost effective to reduce the water content further, if using the oil for biodiesel production?

What other "contaminants" were present in the residue layer?

Keep up the good work

24th July 2018, 02:04 AM
I can't answer all of your questions Tony as I've never ran on WVO. I assume the SB is as accurate with oil as it is for bio. The sample size of 30mls (variable) is added to 10mls of anhydrous petroleum distillate which I assume releases most of the dissolved water so the calcium hydride reacts faster.

I used a pipette to draw the 30ml sample from the top of the treated oil.

The amount of dissolved water that biodiesel will hold is around 1000ppm depending on temperature, so at 1400ppm bio would be cloudy with suspended water.

Although I've been concious over the years re water in my finished bio and dry it to <300ppm most others don't.A lot of the samples (hundreds over the years) that I've tested for other brewers are over the limit of 500ppm. Unless the bio is cloudy with suspended water I have never known anyone to have trouble with water a content of around 800ppm.

It seems as though the old yardstick of 'clear and bright' is accurate enough.

I don't think this proceedure would be of use to dry oil for bio production. It wouldn't be cost effective and I don't know what effect the petrol would have on the process.

The residue formed after the petrol addition was quite light in colour. After a few days a small brown layer appeared at the bottom of the residue.

I'll do some more tests when I have time.

Dr Mark
13th March 2019, 10:42 PM
Sorry you're right - didn't notice. It's deleted