glycerine prewash - Diesel Forum

vapawv · 11-13-2005, 12:16 PM

Have been reading about adding 5% water to the processor before the glycerine settles out, they say this would help preventing emulsion with first wash.....tried it out with 36 liters of new soy oil, seems to have worked well, less than 3 cups of emulsion to clean up aftr the first wash, and overall much easier to wash also.....one thing that i didnt expect was that only the glyerine came out after settling. I had expected a water layer but there was none....anybody doin this routinely that can tell me info?

macinco · 11-13-2005, 03:31 PM

I do this routinely. Tried it once and never went back. It REALLY makes washing easier. The water and glycerin combine and settle out togther. To my guesstimation, here is what happens. There is still some NaOH or KOH in the freshly brwed bio that would have to be washed out. When you add the water, it latches onto this excess/extra Na/KOH. And because the water really has a tendency to latch onto glycerin also, it all settles out, and... the subsequent washing is easier.

I don't recover excess methanol from the glycerin, but one would have to think that if you did, you probably would want to skip this 5%prewash and deal with more difficult/delicate washing.

Spencnaz · 11-13-2005, 04:08 PM

So you're saying to add 5% by volume of water to the biodiesel/glycerin in the processor prior to draining the tank or just after the 1 to 2 hour agitation?

I'm curious about this as I'm having difficulties with washing biodiesel.

dssamp · 11-13-2005, 04:33 PM

Check out this "prewash" link....
Pre-Wash

vapawv · 11-13-2005, 05:45 PM

yep...really am liking the ease of washing using this technique...strange though if you all are saying the 1.8liters of water come out with the glycerine then i am still puzzled, think i only drained about 1.2 liters total of glycerine...i know there is still some water probably absorbed in the biodiesel though. maybe thats where it is hiding....thanks for the comments..

macinco · 11-13-2005, 08:38 PM

[ QUOTE ]
yep...really am liking the ease of washing using this technique...strange though if you all are saying the 1.8liters of water come out with the glycerine then i am still puzzled, think i only drained about 1.2 liters total of glycerine...i know there is still some water probably absorbed in the biodiesel though. maybe thats where it is hiding....thanks for the comments..

[/ QUOTE ]

Uh oh..... I think you said you were doing a 36 liter batch. At 20% methanol, that would be 7.2 liters of methanol going in and I would guestimate you would end up with ~7.2 liters of glycerine byproduct (without the prewash) or ~9 liters byproduct with the 5% prewash.

Seriously incomplete reaction? Tell us what process you use. (You should end up with ~ the same amount of glycerine as the methanol, not considering the prewash water amount.)

BobbySnider · 11-13-2005, 09:03 PM

[ QUOTE ]
So you're saying to add 5% by volume of water to the biodiesel/glycerin in the processor prior to draining the tank or just after the 1 to 2 hour agitation?

[/ QUOTE ]

I did this on my second batch and it worked great. After your reaction time, add the water and run your pump another 10-15 minutes. There was a noticable difference in the required washing.