Just wondering what you guys thinks of this. Our oil titrates rather high (7-8 grams per liter or more) so we have been adding glycerol from the previous batch to new oil in the reactor in order to reduce the acidity. This reduces the amount of KOH needed by almost half, therefore reducing cost. I'm wondering if the same thing can be done adding glycerine to the oil in the settling tank before it goes into the processor (so less possibilty of some being left in the reactor). As you can see from the picture, the outlet into the processor is about 15 gallons up from the bottom of the tank. My thought is that the glycerine would settle at the bottom of the tank and be drained out after neutralizing some of the acid in the oil. Would use second round glycerine for this. What do you think?

 

It' worth a try Trent. My WVO titrates about 3-4, so I've never had that problem.

 

I believe in it 100% for a bunch of reasons. You don't ever have enough to do all incoming oil so we just pre-treat oil that is over a titration of 5 or suspected of being a little too wet. Oil that is under five just gets processed as normal. We even built a special "reactor" outside (a 1000 gallon vertical tank on legs) to do nothing but pre-treatment. We put in about 350 gallons of fresh glycerine at room temperature and about 600 gallons of oil that has been heated to 175 degrees. The hotter than normal oil heats the glycerin so we don't have to. We mix for two hours with a 2 inch pump, shut the pump off, and let stand overnight.

 

worked real well with the last batch, cut the titration almost in half to 4.8 g per liter. (I'm envious of those who start with oil better than that...)

 

Did you gain any oil?
We bought 900 gallons of oil from a renderer onetime that smelled like ammonia and titrated at 18 NaOH. Ran it through the glycerin stripper three times and lowered titration to four and gained 200 gallons of oil total. The oil is pulling trapped bio and MeOH from the glyc. That is why all of our glyc will be used onetime to treat oil to pull all of the good stuff out that normaly is burned or thrown away besides the fact that it reduces titration by roughly half.

 

Think you're right, didn't measure but seem to gain a couple gallons on a 35 gallon batch. 2nd round Glycerol is sure thicker and darker than 1st run. need to figure a way to recover methanol off of it, we are afaid that it we put it in the processor, it will plug up as methanol is driven off... Might have to make a seperate processor for that.

 

I don't believe you actually gain oil, but do believe (as brady racing mentioned) that the gain is related to biodiesel and methanol contained in the glycerin. My oil starts out titrating 4-6 and I am getting titrations of 0.5-0.75 consistently. I round it up to 1.0 and use 18% methanol for the reaction. Always passess the 27/3 test.

Interesting side note. I have been using KOH and a few months ago I started having batches that did not pass the 27/3 test. I had to up the KOH base from 7.0 to 9.0 g/L to end the problem.

 

Really? Could this be a case of the KOH being somewhat less than 90% pure? I've never really had much success with a glycerol caustic strip. I have such a crapload of glcyerin though I may as well give it another shot. How are you guys adding it to the processor? My "good oil" could defintely benefit and my "bad oil" might even be made good enough that I can avoid the acid base method or 2 stage base with it. What say you?

 

We add the Glycerol from the prior batch + the new oil, heat to 50c while circulating for 2 hrs, then let sit overnight and drain off the 2nd rd Glycerol. Process as usual after that with 5 gals methoxide (17%) instead of the usual 7+ gals. 2nd rd Glycerol is much darker than 1st rd. Adds a day, but reduces the titration by 40-50%.

 

I'll try that next time and see what it does. I had not done it that way before I had sort of used it like I would a caustic strip in the holding container. I've heard other good things about this and its certainly worthwhile looking into it.