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Biodiesel
From theEthanolSource.com
Please see The Biodiesel Process with Calculators
Contents |
Overview
Biodiesel is an alternative to diesel fuel. It is produced by the transesterification of vegetable oil. There are four steps to the biodiesel process: titration, catalyst mixing, transesterification and washing. Tranesterification requires a strong base and an alcohol. The base in this process is lye. Potassium hydroxide and sodium hydroxide are two suitable bases. Methanol and ethanol are two suitable alcohols. The oil is titrated to measure the amount of free fatty acids (FFAs) present in the oil. The base is first mixed with an alcohol. This forms our catalyst. We then add an additional amount of lye to our catalyst to balance the pH of the oil. The catalyst is added to the oil, brought to 120F and agitated mechanically. After separation, the bottom layer is siphoned or bled off. This layer contains glycerin, unused catalyst, and a portion of ethanol/methanol that can be recovered. The top later that remains is our biodiesel. Washing uses water to further remove particulates, unused catalyst and glycerin that may be caught in the biodiesel layer. After washing, biodiesel can be directly used in a diesel vehicle, or blended further.
Oils
The transesterification process relies on a catalyst to convert vegetable oils to methyl/or ethyl esters. Clean vegetable oils low in free fatty acids will work best, and can be converted cheaply because they require less pH adjustment. Oil should be free of water. Filter your oil first. Oil should be free of particulates.
Methanol
The methanol process for biodiesel yields methyl esters. Methanol is mixed with either potassium hydroxide (KOH) to form potassium methodoxide, or mixed with sodium hydroxide (NaOH) to form sodium methodoxide. Industrially, potassium hydroxide is preferred. Even though it requires approximately 1.6 times as much KOH as NaOH to carry out the same reaction, potassium hydroxide solubility in methanol far exceeds sodium hydroxide's solubility.
Ethanol
The ethanol process for biodiesel yields ethyl esters. Ethanol is mixed with potassium hydroxide (KOH) to form potassium ethodoxide. Sodium hydroxide is not a suitable base because of its solubility issues. The process for ethyl esters is more difficult. The vegetable oil, potassium hydroxide and ethanol all have to be free of water. As much as 2% volume of water will destroy the transesterification process as water competes with potassium hydroxide in the process.
Sodium Hydroxide
The lye used must be of 96% purity or greater. Water present in the process can cause separation issues. While sodium hydroxide is technically a "stronger" base than potassium hydroxide, its solubility issues with alcohols are a major concern. If using methanol and a good source of oil, sodium hydroxide offers a method of reducing cost. Less sodium hydroxide is needed to produce the same amount of catalyst.
Potassium Hydroxide
Potassium hydroxide is the standard and industrially chosen lye for producing biodiesel. Potassium hydroxide is normally available in pellets or flake. When using methanol, 85% purity is common for potassium hydroxide, but 96% or 99% should be used if at all possible. If producing biodiesel with ethanol, potassium hydroxide used should be 96% purity or higher. Potassium hydroxide is hygroscopic, and absorbs water from the air. It should be stored in vacuum, or at least in a sealed container.
Titration
Titration uses phenolpthalein, pH test strips or a digital pH meter to measure the amount of free fatty acids present in our vegetable oil.
