Biofuel from waste oils and fats
Waste oils and fats contain free fatty acids, which can be converted to biodiesel using methanol. This process is an esterification, and occurs under acidic circumstances. That is why sulphuric acid is added to the reaction as a catalyst. Phase separation allows the water that is formed to be separated from the oil phase (the remainder of the raw material with biodiesel) and deployed for processing by-products. The product of the esterification is then a mixture of non-reacted raw material and biodiesel. This mixture then proceeds to the next reaction step.
The second important component of the raw material is glycerides. This can actually react to become biodiesel under basic conditions. Again, methanol is used for this. Potassium hydroxide (KOH) is added to create the basic conditions. Because a glyceride is already an ester, and a different ester (biodiesel) is created, this process is called a trans-esterification. The by-product of this reaction step is glycerine. Glycerine and biodiesel are separated in the reactor by phase separation. This is possible because biodiesel and glycerine do not mix well.
In this step the biodiesel phase from the trans-esterification is purified to a quality which meets the highest standards for biodiesel. This occurs through distillation (separation based on a difference in boiling point). This distillation occurs in a vacuum. The object here is to remove the heavy organic particles from the biodiesel. These particles form a stream which is called Bio Heating Oil (BHO). This stream can be used as a sustainable fuel for the generation of energy in the form of steam.
The by-products of the esterification (acid water) and the trans-esterification (glycerine phase) are mixed in this part of the process, yielding a mixture of solid matter and two fluids. These three are separated from each other with a type of centrifuge (tricanter). The oil part of the fluid phase is again deployed in the process. The watery fluid part (a mixture of glycerine, water and methanol) is separated further through two distillations. This produces three streams: raw glycerine, water and methanol, which can again be deployed in the process.