Using an Appropriate Amount of Methanol: Methanol Calculator and Molecular Weight Calculator Can Help
by Dev Shrestha, Associate Professor, Biodiesel Education Program, University of Idaho
During the biodiesel reaction, each molecule of methanol reacts with one of the three fatty acids of the triglyceride to produce biodiesel and glycerol. In addition, excess methanol is needed to push the reaction to completion. Biodiesel producers need to make sure they are using enough (but not too much) methanol so that they achieve as complete a reaction as possible without wasting methanol.
The appropriate amount of methanol depends on how many molecules a feedstock contains per unit of mass (the feedstock's molecular weight). Some feedstocks, such as palm kernel oil, contain more molecules per unit of mass than other feedstocks, such as rapeseed oil. In order to calculate the molecular weight of a particular feedstock, you must first find its fatty acid profile (which is not always easy), and then perform complex calculations based on the percent of each fatty acid in that feedstock.
Fortunately, there is an easier answer. We have created a molecular weight calculator, as well as a methanol calculator.
If you are using a standard feedstock, simply choose your feedstock from the drop-down "triglyceride feedstock" menu of the methanol calculator, and the calculator will let you know how much methanol you need.
If you are using a feedstock that is not listed, you can use the molecular weight calculator to plug in the percentage of fatty acids, and the calculator will give you the molecular weight. For the most accurate fatty acid profile for a non-standard feedstock, send a sample of the feedstock to a lab for analysis. However, you can also find average fatty acid profiles of triglycerides by doing a literature search.
During the biodiesel reaction, each molecule of methanol reacts with one of the three fatty acids of the triglyceride to produce biodiesel and glycerol. In addition, excess methanol is needed to push the reaction to completion. Biodiesel producers need to make sure they are using enough (but not too much) methanol so that they achieve as complete a reaction as possible without wasting methanol.
The appropriate amount of methanol depends on how many molecules a feedstock contains per unit of mass (the feedstock's molecular weight). Some feedstocks, such as palm kernel oil, contain more molecules per unit of mass than other feedstocks, such as rapeseed oil. In order to calculate the molecular weight of a particular feedstock, you must first find its fatty acid profile (which is not always easy), and then perform complex calculations based on the percent of each fatty acid in that feedstock.
Fortunately, there is an easier answer. We have created a molecular weight calculator, as well as a methanol calculator.
If you are using a standard feedstock, simply choose your feedstock from the drop-down "triglyceride feedstock" menu of the methanol calculator, and the calculator will let you know how much methanol you need.
If you are using a feedstock that is not listed, you can use the molecular weight calculator to plug in the percentage of fatty acids, and the calculator will give you the molecular weight. For the most accurate fatty acid profile for a non-standard feedstock, send a sample of the feedstock to a lab for analysis. However, you can also find average fatty acid profiles of triglycerides by doing a literature search.