Methanol Recovery From Glycerin
Written by troy
This still was posted on the infopop forum in 2005 by troy. It is one of the cleanest simplest stills for recovering methanol from glycerin that I've seen so far. The thread referenced above goes on to discuss several DIY methanol stills.
I've hesitated on posting anything on methanol recovery because of the long history of ethanol stills blowing up. However, recovering the methanol from the glycerin is an important step in disposing of the glycerin. This is true for reasons of both economics and the environment. Remember that your safety and the safety of those around you is solely your responsibility. This material is presented for educational purposes only. Seek professional help in the setting up and the safe operation of a methanol still before trying this yourself. This article only briefly mentions these topics. It's up to you to be safe.
The pot is a converted 30 gallon gas water heater. It has had two ports welded low in the sides to accept two 240V 4500W elements. All the heat is supplied by these elements and the gas portion of the water heater is no longer functional. An electric water heater would serve just as well if you added a second port down low. A third port was welded on top to allow for a short 2” pipe to add glycerin. You close it with a pipe cap and Teflon tape. The elements are wired to 120V giving them an actual power draw of 1,100 watts each. The picture does not show it, but when in use it is heavily insulated with a water heater “blanket” to prevent heat loss through the sides of the tank.
The condenser is a ten foot length of soft 1/2" copper tubing coiled up in a plastic bucket. Running water is used to cool the coil. Water is added in at a slow rate from a garden hose to the top of the bucket. An Aquarium air bubbler was added to this setup to keep the temperature of the water in the bucket from stratifying. Without the airstone, the water on top will get very hot, while the water on bottom will be cool. The copper tubing needs to run down hill to the collection container.
Troy reports that he ran 23-25 gallons of glycerin in a batch. His biodiesel recipe uses 23% methanol by volume and he recovers about 6-7 gallons of methanol from the byproduct. While he does not measure the purity of every batch, he normally gets about 98% purity. That's plenty good enough to reuse. He blends his recovered methanol 50/50 with new methanol with good results. He reports that the whole process takes 6-8 hours. There was no methanol produced for the first hour while things warmed up. He was using 2400W to heat. That brought his cost for electricity to produce 7 gallons to about 15-25 cents per gallon.
When operating a still, it is the temperature at the top (input) of the condenser that is important for distillation. The temperature in the pot can get as high as 250-300F. Troy continues his distillation until the temperature at the top of the condenser reads 180F – 200F. As the temperature at the top of the condenser rises above 165F the water content will also rise dramatically if there is much water in the glycerin to start.
Some final notes, the 5% prewash can reduce the purity of your recovered methanol a little. Troy does not use it. His methanol also comes off his still perfectly clear. If it is tainted brown, then it's likely that you’re using too much heat or too high a watt density heating element.
Do not do this in or around a building and take all necessary safety precautions.