The expected stratification did not appear? (Biodiesel)
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I have been working on a biodiesel project recently. Potassium hydroxide and ethanol are added to animal fat (which has a color similar to that of edible oil), and the mixture is heated to initiate a reaction. The solution changed from light yellow to brown, and it became clear. The instructions state that a stratification phenomenon will occur. However, no stratification was observed after the solution was left overnight. Could that person analyze the reasons? But when washed with water, all the brown color was washed into the water, leaving only a light yellow oil on the surface. That’s the basic process of the experiment. During the experiment, a lactide formation reaction occurred. Thank you. :)
It is presumed that there were too many impurities in the food oil; the transesterification reaction did not proceed as desired, which is why neither glycerin nor biodiesel was produced. This is likely because no pretreatment was carried out, resulting in high levels of impurities； Therefore, the reactants also consist of multiple components, so they cannot separate into layers.
My first impression is that your oil is likely acidic; you can test it to see. If it is acidic, that would explain a lot. Raw oils generally contain a high amount of free acids. The catalyst you are using is potassium hydroxide – does potassium hydroxide still have catalytic properties in acidic conditions? So the transesterification reaction did not occur. The brown substance is potassium salts. Try first to see if the crude oil is acidic; let’s discuss further after we’ve done that test
This is exactly what I do; let me share my thoughts with you: 1. The acid value of the crude oil you use must be low – refined oil is preferable – otherwise, the potassium hydroxide added will be neutralized by the free fatty acids in the crude oil, **reducing the efficiency of the catalyst**； 2. The so-called change in color of the solution from light yellow to brown is due to the formation of glycerol as a result of base-catalyzed transesterification; after separation, the glycerol in the lower layer is removed, and the fatty acid methyl ester in the upper layer is then washed with water ； 3. During the washing process, the brown color was washed into the water; it is glycerin water, along with potassium salts and other substances. Although your experiment yields what is known as yellow oil at the upper stage, namely fatty acid methyl esters, I believe the yield is very low, with a large amount of crude oil remaining unconverted.
Thanks for the answer from above. In my experiment, \"potassium hydroxide and ethanol were added, and the mixture was heated to initiate the reaction.\" The solution changed from light yellow to brown; it remained clear with no separation occurring. “ Upon reviewing the literature, it was found that the most likely reason is the low amount of water and glycerin produced. So, when washed with water, a stratification phenomenon occurred. What should be separated out is glycerin water, which has a somewhat sticky texture. There should be some free acid present; we need to wait for the test results.
The acid value was measured: for ordinary oil: 1. Around 12, refined oil: 0. Around 15. Does this have any impact on anyone? :)
My sample is animal oil. Thank you. . .
The acid value is quite appropriate. The reasons for no stratification are as follows: 1. The reaction did not proceed thoroughly, possibly due to moisture in the raw materials or in your ethanol. It is recommended that you heat the oil to around 120 degrees to remove water, and at the same time check whether your ethanol is anhydrous and whether it is stored properly in a sealed container. Ethanol easily absorbs water to become 95% ethanol. 2. Animal fats have high viscosity and freezing points, which can affect phase separation; it is recommended to heat the material first and then separate it using a centrifuge.
Some acid can be added during layering to speed things up by disrupting the emulsification conditions.