Biodiesel Catalyst

NaOH & KOH

Safety Warning

KOH vs NaOH

KOH dissolves a bit easier in methanol than NaOH. Although not everyone notices the difference, most do. Under certain conditions NaOH will make glycerin byproduct that turns to a gel or even solid. Not a problem after the glycerin has been drained, but a big problem if it’s still in your processor or plumbing and goes solid.

KOH is more forgiving on high titration oils than NaOH. High titration oils make a lot of soap. If we use NaOH and there is enough soap you get a tank full of gelatinous goo that contains mostly soap, WVO and some biodiesel. KOH on the other hand being liquid does not seem to interfere with the reaction. The result is that we can process much higher titration oils with KOH than we can with NaOH.

KOH is a heavier molecule than NaOH and since we weigh our catalyst we use more KOH than we use of NaOH. Mathematically we use 1.4 times as much KOH as NaOH. When making biodiesel we use a base of 5 grams per liter for NaOH and 7 grams per liter of KOH. To this we add our titration values. While NaOH is relatively pure, KOH is usually only available with about 90% purity. This requires us divide the 7 grams by .9 to adjust our base up to 7.7 grams per liter.

We titrate our oil using NaOH water to find it titrates to 3, giving us a recipe of 8 grams per liter. The same oil titrates to 4.6 grams per liter using KOH water giving us a recipe of 12.6 grams per liter. If NaOH is 50 cents per pound and KOH is 80 cents per pound then NaOH would cost 3 cents per gallon of biodiesel and KOH would cost 8 cents per gallon of biodiesel. Of course since the amount of catalyst varies with the titration value of the oil, high titration oils will use more and cost more, while low titration oils will use less and cost less.

Buying Catalyst

NaOH is available in the hardware stores in 2lb containers for about $8 each as drain cleaner. Make sure it says “100% Sodium Hydroxide” on the bottle somewhere. Draino and many other drain cleaners will not work because they contain aluminum flakes that poison the chemistry.

Both NaOH and KOH are available over the Internet from various sources like companies that supply soap makers. Typically the sizes available range from 50lb bags to 2lb jars. Due to the special handling requirements of strong caustics and the extra charges for shipping HAZMAT chemicals, they usually cost about $3 to $4 per pound once shipping is added.

If you look in the Yellow pages for your area under chemical suppliers, you can often find a local source for either NaOH or KOH. Sizes range from 50lb bags to 400lb drums and cost about 50cents per pound for NaOH and 80 cents per pound for KOH.

If you go pick up your catalyst, make sure it does not ride in the passenger compartment. Use the trunk only if it is well sealed and completely separate from the passenger compartment. In the back of a pickup is the best way to transport catalyst. Even in a bag, it will give off “fumes” and “dust” that can cause major breathing problems for those confined in the same compartment with the catalyst. Those that have done it once, never do it again.

Liquid Catalyst

Both NaOH and KOH are most commonly found as an aqueous solution (mixed with water). Both are less expensive when purchased as a liquid. There is even an old technique for mixing methoxide by first dissolving the catalyst in water then mixing it with the methanol. This method came about because of the difficulty people were having dissolving NaOH directly in methanol. On the forums it is often referred to as the concentrated aqueous catalyst method.

The advantages are that it’s safer to deal with liquids than dusty caustics and it’s a lot easier to make your methoxide this way.

The disadvantages are that the water lowers the quality of the biodiesel you make, and it sometimes unexpectedly makes glop. ASTM spec biodiesel is very difficult to make using this technique. If your oil is not perfectly dry or you are working with high titration oils, this method often leads to a processor full of soap in the form of gelatinous glop.

Storing Catalyst

Catalyst is most economically purchased in 50 lb bags from a chemical supply house. Both NaOH and KOH are hygroscopic, meaning they draw moisture out of the air. Both will react with CO2 from the air to become a useless carbonate. A 50 lb bag of catalyst will last you a long time giving you lots of opportunity to contaminate your catalyst with water and CO2. Once your catalyst is contaminated with water it clumps up and becomes difficult to dissolve in methanol. The answer is to keep your catalyst dry and minimize it’s exposure to air!

There are two basic methods used to keep catalyst dry.

• Put the bag and all in a 5 gallon bucket with a good sealing lid. This method is great for areas with low relative humidity.
• Divide up the 50lb bag as soon as you get it into smaller containers like half gallon milk jugs or resealable plastic bags. The containers do not all need to be the same size or hold the same amount of catalyst. The best containers would be large mouth HDPE bottles with good sealing lids.

High Humidity Biodiesel Tip

In Atlanta the humidity is so high that on a summer day NaOH can absorb it’s weight in water while weighing it out to mix with methanol. In this case you can adjust your oil and methanol quantities to match the catalyst you divided up in the winter. “Recipe Calculator II” on B100Supply.com in the biodiesel library section works just this way. You plug in the amount of lye in your container, and your titration results and it will tell you how much oil and methanol are needed to use the exact amount of catalyst in your container. No need to weigh out the catalyst, ruining it before you can get it into the methanol.

Other Catalysts

KOH and NaOH are not the only catalysts that can used in transesterification to make biodiesel. NaOH and KOH are the only catalysts used by homebrewers. There are two types of catalyst, those that dissolve in methanol and biodiesel and those that do not. The ones that do not dissolve are called heterogeneous catalysts. The ones that do not dissolve in biodiesel or its byproducts have the advantage of being filtered out and reused. Soap poisons heterogeneous catalysts, so using them to make biodiesel from WVO is not efficient. You end up only getting a couple of uses out of the catalyst before it must be discarded. Calcium Oxide CaO and Barium Hydroxide Ba(OH)2 are the most often mentioned.

Many people will use the term methoxide to describe the methanol / lye solution we use to make biodiesel. This is actually a chemistry term for another chemical. Methoxide or Sodium Methylate is made in very controlled environments by dissolving the metallic Sodium in methanol. They then boil off the methanol. The remaining powder is Sodium Methylate. It is a very dangerous material that if left exposed to humid air can spontaneously catch fire on a cool day. Very nasty and HIGHLY regulated chemical. You cant buy it, so don’t try.

Commercial producers often use “premix” which is 30% sodium methalyate in methanol. When we dissolve NaOH in methanol we create water. Sodium Methalyate in methanol will react with the water removing it from the WVO/biodiesel and effectively reducing the amount of soap produced. It makes great biodiesel, but it’s dangerous, expensive, and very hard to get. I mention it because it comes up on the forums from time to time, but it’s not appropriate for homebrewing environments.