Typical vegetable and animal oils are chemically identified as triglycerides,
meaning that their molecules consist of three esters attached to a glycerol
"backbone." Glycerol, a relatively complex alcohol, can cause
problems in diesel engines, since it can create deposits which interfere
with normal engine operation. During transesterification, the esters are
transferred from glycerol to a different alcohol molecule (typically methanol).
After the transesterification process, the "oily" biodiesel methyl
esters (esters attached to methanol) float to the top of the solution, and
the "watery" glycerol settles to the bottom. Soon, distinct layers
appear, following the principle that "oil and water don't mix."
The glycerin layer is drained away, and the biodiesel layer is further processed
to improve its purity. |
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Canola Oil (triglycerides) before transesterification
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Biodiesel (methyl esters) and glycerol layers after
transesterification |
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