Since I started doing the acid step, I have not been able to get the same great-looking, clear BD as with base-only.
My last post (can't find it) talked about something similar, and it was suggested that I should not do methanol recovery after the acid step b/c I might be causing a reverse reaction. So here's what I tried this time:

Acid
Dry wvo: 85L, titrated at 14 (titration solution made from 90% purity KOH)
Methanol: 12%
H2SO2: 14-3 = 11 * 0.2 = 2.2mls / L
Mix: 12 hr
End titration: 4
Settle: 12 hr
Drained: ~2L "black" water
Mixed, waited, re-tested; titration at 4

Base #1
Methanol: 10% (in addition to acid stage)
KOH: 8 + 4 = 12 g / L (90% purity)
Mix: ~2hr
Settle: 12hr
Drained: ~19L glycerine layer
3/27: failed

Base #2
Methanol: 4L
KOH: 1.6g/L
Mix: ~2hr
Settle: 12hr
Drained: ~2L glycerine
3/27: passed

> vacuum-recovered methanol from BD <

3/27: passed again

Wash
- slowly introduce bio up through 70L water
- settle, drain water (very white)
- add 70L water, mix by hand
- settle, drain water (still white)
- add 70L water, bubble mix
- settle, drain water (somewhat cloudy)
- add 70L water, bubble mix
- settle, drain water (looks clear)

Dry
- heat to 55C
- circulate w/ spray-dry method

Final 3/27: passed

I got clear, dry BD. However, the next day it turned cloudy again when I pumped it out. This is the same thing that has been happening before: The BD drops a layer of light-brown "mud" in the bottom of the tank. When I pump BD out, this mud stirs up into the BD and makes it look cloudy -- just like BD that isn't dry.

??

The only thing I can think of is maybe the wash is incomplete. I switched from using micro-bubblers (fish-tank blocks) to a pipe with small holes drilled. I figured the larger bubbles would agitate the BD/water better and give a better wash without risking oxygenating the fuel as much.

??

-Adam

what does the BD look like during the later washes? mines usually turning or has turned clear by the end of the last wash.

-dkenny

It does clear up with washing, but not as dramatic as the batches processed with the base stages only.

I do know that acid/base process seems to create more soap than base only..so washing is more important. also making sure the prewashed fuel passed the 27/3 test..

-dkenny

I did several 27/3 tests after reacting, de-meth, and after washing. All the tests passed.

I let the batch settle for 3 days, per Graham's instructions in another thread. I harvested the BD from the top, leaving the mud layer undisturbed. This BD looks clear and stays clear. It passes the "shake em' up" test quite nicely.

So the conclusion is I have BD that is VERY difficult to wash (with my washing technique) when I include the acid stage. Next time, I will try a 5% water prewash, and I will plan to let the product settle for a week to purify.

Graham says water washing and subsequent drying is eliminated by this method. I hope so. My wash tank will become my settling tank.

by all means use the 5% prewash...it'll remove 75% or more the soaps..mine is close to 10%. but its not done quite the same way..

most add 5% water and mix for 15-20 minutes..
mines much more passive but works well.
I just add 5-10% water to the wash tank then pump the BD/GLY in to the tank. settle and drain the gly/soap out. generally 3 washes are all thats needed.

if you prewash forgot misting its too slow...

-dkenny