Mixing Methoxide for Making Biodiesel

Crossposted from: The Collaborative Biodiesel Tutorial
by Maria "Mark Alovert

 

mixing methoxide 1

Rocking Carboy
to agitate

In the past homebrewers used an electric mixer of some kind to mix together methanol and lye. The drawbacks were complexity, and the obvious safety issues around static, sparks, and fumes. But if you just add lye to methanol at the same time that you start heating your oil, and rock the container occasionally instead of mixing it with a motorized mixer, you will dissolve the lye in 30 minutes to two hours. This is called 'methoxide the easy way' on JTF.

I updated it by adding some plumbing that directs the methoxide into your reaction tank, eliminating any further handling.

If you use KOH instead of NaOH for your catalyst, this method is perfect- KOH dissolves very easily in methanol. There is absolutely no need for any vigorous motorized mixing with KOH.

I use a closed HDPE plastic jug ('carboy'), and some occasional swirling- every 10 minutes if I'm not in a hurry, more if I am. You don't have to pick up the jug and shake it (heavy)- just swirl. Or you can leave it on the ground and rock it back and forth occasionally.

It is very important to do the first swirl or shake as soon as you add lye- if it initially sets up into a solid clump the passive method doesn't work as well. If the lye doesn't dissolve by the time your oil is to temperature, step up the agitation a little (ie rock the carboy back and forth for a few minutes). You can also try dissolving the lye the night before, though it's unnecessary.

lid with hose barb

Lid with hose barb

The see-through HDPE 'carboy', a heavy duty jug used for water or kerosene in some applications, is an ideal container to use. You can see through the bottom and know when the lye clumps dissolve.

Carboys have a second set of plugged, optional threads molded into the lid. You cut the plug out with a knife, and the internal threads then fit ¾ standard pipe fittings such as hose barbs. One type of carboy with these lids is the US Plastics 'Fortpak'- item number 75023 at www.usplastic.com . In the SF Bay Area, carboys are available through Biofuel Oasis in Berkeley (they don't do mail order) , and also through TAP Plastics (check the phone book, several stores in the area) Buy two or more lids- one for storing the carboy, and one for the hose barb attachment. If you can't get two lids, then add a ball valve to your lid before the barb so that it seals securely. Also, make sure you get a carboy with a vent cap, and don't lose the vent cap.

carboy lid with ball valve

Carboy lid with ball valve

My methanol vendor is willing to pump methanol directly into carboys, and this eliminates one methanol handling step- I take the carboy home, add lye to it when I'm ready to make fuel, and then use it as the methoxide dispenser as part of my reactor- so I never have to pump methanol around. The only time I open the carboy is when I add lye.

How to use it:

1. fill with methanol to the proper level (carboys are graduated in gallons)

adding lye to carboy

Adding lye to carboy

2. perform a titration on your oil to test for ffa, measure the lye or KOH, and add this catalyst to the methanol in the carboy. Work outside, and hold your breath when opening the methanol carboy. Wear safety glasses and PVC gloves.

3. immediately after adding lye to each carboy, pick up the carboy and give it a gentle swirl (you don't have to shake it hard or pick it up high, you can just rock it if it's heavy)

4. repeat the swirling over the next couple of hours. In hot weather NaOH will dissolve in 15-30 minutes, in cold weather it might take longer. You can place it into a tub of hot water to speed things up.

5. check that the lye is dissolved: first, check that the carboy lid lid isn't going to leak on you. Then pick up the carboy, set it on a table, and look into the bottom of it to see if there are clumps of lye. If you see clumps or particles, then it's time for more swirling or more time.

6. when it is dissolved it will keep for a long period of time, so label it well with the quantity of lye used, and store until ready to make fuel

 

7. when you're ready to make fuel, attach the lid with the barb, attach the hose of your reactor to the barb. Lift the carboy onto a shelf above the level of the mixing pump, and meter in the methoxide into the reactor.

by the way the other end of the hose is attached to a valve that is plumbed into the pump-agitated water heater reactor. See 'tankenstein' and 'Appleseed Processor- open source plans' threads for more details.



Q & A:
:
Question: I have seen that you use a check valve near where the methoxide flows into the oil stream. I got a check valve at the plumbing store but it required too much pressure to make it open--meaning my gravity-fed carboy wouldn't open it--do you use a lighter duty check valve? This one was a brass one designed for home water pipes/water plumbing system
any suggestions?

Answer: check valves. I assume you're using the same sort of water heater-based reactor as found on this forum.

carboy dispensing last dregs tipped

Carboy dispensing last dregs tipped

I also use a swing check valve on the Appleseed reactor, and it has problems opening because the pump ... er.. doesn't suck. Not very well anyway. If we used a more expensive, more powerful pump you wouldn't have that problem, but with the Harbor Freight Tools #1479, there's just not all that good of a 'pull' from the inlet of the pump (about to experiment with the next size up of pump). SO I unfortunately have to close off the oil valve at the reactor just a bit, until I just begin to see a color change in the pump output tubing. Another solution with this kind of sealed system, if you were doing something other than the carboys for a methoxide tank, would be to install a pressure equalizing tube from the top of the reactor to the top of the methoxide tank, which would even out the pressures of the two liquids as they enter the plumbing and the pump. My friend Lu calls this 'Eustacian tube (sp?) after those found in your ear.

 

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