The same time as the prices for petroleum fuels are rising the demand for biodiesel is rising too which is very much obvious. But the consequence is the more biodiesel is produced the more expansive the renewable feedstock is going to be. And if we look for alternative feedstock to produce biodiesel, animal fat as a waste product seems to be our cheapest and available at huge scale.
To process animal fat into biodiesel usually we can use the following method, which is most common. For this an alkaline catalyst Sodium Hydroxide or Potassium Hydroxide is used. It is dissolved in methanol and, then, mixed with the feedstock. Making biodiesel from animal fat requires a lot of considerations.
Animal fat melts between 40 and 50 degree Celsius, but to avoid that the methanol evaporates – methanol starts to boil at 60 degree Celsius – and then, consequently, not enough methanol will be available for the transesterification the process temperature should always be kept under 60. Secondly, when processing animal fat into biodiesel this feedstock reacts very sensitive if we use just too much catalyst. The consequence is that easily so much soap is formed that the whole mixture turns into some kind of thick glob, which would ruin everything. And the more of the so-called Free Fatty Acids (FFA) we find in the animal feedstock the more soap is formed which results in production loss.
With the two-step-process the amount of FFA is first reduced in a pre-step using sulphuric acid as catalyst and methanol. Then, when the amount of FFA reached a level of less than 1% the normal alkaline-based process can take place using methanol and lye as catalyst, which would speed up the reaction. . Hence, it is always advisable to process a feedstock which has less than 1% FFA using the one-step-process. It is faster, cheaper and more biodiesel will be produced and in today’s world time is money.
But because animal fat turns very easily into a thick glob of soap if we use just too much lye the right amount of catalyst will be crucial for the production.
The biodiesel produced from animal fat has some other properties than the one produced from vegetable oil. First, after settling the glycerol from animal fat turns solid when it cools down. The same thing happens to the glycerol produced from palm oil. This circumstance needs some special considerations when settling because cold and solid glycerol can’t be drained from the bottom of the settle tank.
Second, in contrast to biodiesel produced from vegetable oil the freezing point of biodiesel from animal fat is much higher. This means that the cold filter plugging point (CFPP) can be – depending on the fat the biodiesel is produced from – between 15 and 20 degree Celsius. In order to run cars on biodiesel produced from animal fat also in other seasons than summer it is necessary to blend the biodiesel from animal fat with biodiesel produced from, e.g., rapeseeds. A percentage of 10 to 15% biodiesel from animal fat seems to be appropriate. Biodiesel produced from animal fat is, therefore, the perfect fuel to admix and use.
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