Biodiesel, Methanol & Glycerin Distillation
ASTM specs are becoming more stringent over time and the industry is expecting purer form of biodiesel. This level of purity can only be achieved with Biodiesel Distillation. Biodiesel Distillation has an added advantage that the Biodiesel appears much more aesthetic because it is a colorless liquid; hence it shows no trace of the feedstock used to produce it. The main purpose of Biodiesel Distillation is to purify Biodiesel by reducing the amount of mono-, di-, and tri-glycerides. Although simple one-stage distillation provides adequate purification of biodiesel, Technochem recommends multi-stage distillation and rectification to produce even purer biodiesel.
The unused Methanol must be recovered and distilled in order to reuse it. The unused methanol is concentrated in two streams—wash water and glycerin. The two streams are mixed and subject to evaporation of water and methanol. Technochem suggests recovery of both water and methanol because both can be reused in the process. This helps to prevent discharge of waste water.
The recovered mixture of water and methanol is subject to methanol stripping and rectification to separate water from methanol; resulting in one stream of pure methanol and another of adequately pure water. The Methanol is reused in Trans-Esterification process and water is reused in water wash of biodiesel.
The glycerin phase is stripped of methanol and most of the water but it contains biodiesel, soap and salts. For most plants, glycerin is a waste product that is sold as is. However, some plants recover the fatty material (biodiesel and soap). This is accomplished by treating the Glycerin phase with Acid to convert soaps into Fatty Acids. Fatty Acids and Biodiesel being lighter than Glycerin float to the top and are decanted. The resulting Glycerin is pH adjusted by adding Caustic Soda, although this process increases the salt content of the Glycerin stream. However, it makes the Glycerin neutral in pH and relatively easier to store and transport.
Glycerin Distillation can purify Glycerin by removing salts and traces of fatty materials and produce Pharma (USP) grade Glycerin.