Process        Inputs & Outputs

Key Inputs
Feedstocks
Feedstocks are organically derived fats, oils and greases with free fatty acids whose defining property is its level of free fatty acids (FFA), which range from roughly 1% to over 20%. The typical FFA level used in the production process is less than 2%; untreated high FFA feedstocks have higher glycerol levels and produce soap. In 2006, over 90% of feedstocks were soybean oil, which has a FFA of 1%. Other feedstocks that can be used include palm, rapeseed, cottonseed, sunflower, corn (from corn or distillers dried grains), olive, and fish oils, among other oils, and higher FFA used feedstocks such as animal fats and recycled greases.
Since low FFA feedstocks are most commonly used, and have competing uses such as animal feed, these feedstocks are pricier. Higher FFA feedstocks can be used, but must be pre-treated with acid to remove excess glycerin. As a result, there is an inverse relationship between FFA and price. Being capable of processing high FFA feedstocks make up 70-80% of biodiesel production costs, as it takes 8 pounds of feedstock to make 1 gallon of biodiesel.

Alcohol
Alcohol is used to replace the glycerine in the transesterification process to create biodiesel. Ethanol, methanol or a mix of the two can be used, however methanol is more commonly used because of it is in greater supply and is a lower cost alcohol.

Catalyst
The catalyst is needed to crack the bond of the feedstock in the transesterification process. The two most common caustic catalysts used are sodium hydroxide (NaOH) and potassium hydroxide (KOH). Sodium hydroxide is the most typically used catalyst as it is lower cost and has been found to be more effective.


Outputs
Biodiesel
If done correctly, ASTM grade biodiesel (B100) will be produced. This biodiesel can be used to fuel diesel engines independently or mixed with diesel fuel with the most common mixes B5 and B20 (5% and 20% biodiesel, respectively).

Glycerine
Crude grade glycerine is produced in the process which can easily be turned into soap. With additional refining, technical grade glycerine (97% pure) is produced, which can be used in other commercial applications.