Biodiesel: Process Summary
Pre-Treatment of Crude Oils
Crude vegetable oils and animal fats have Phosphorus, Free Fatty Acids (FFA), and Moisture along with other impurities (such as waxes, color pigments, and sulfur) depending upon the type of oil. In order to meet ASTM 6751 or EN 14214 specifications, biodiesel must be produced with feedstocks that are free of these impurities.
Degumming, Deacidification, and Dehydration via Chemical Refining
Treatment with phosphoric acid, water, and caustic soda removes gums and fatty acids. Gums and soaps formed in the process are separated by using a centrifuge. The oil is washed to remove traces of gums and soaps. Water is separated by using another centrifuge. The washed oil is dehydrated in a dehydrator vessel. The waste water may need to be treated prior to disposal. If water is a scare resource, the same operation can be performed without water but with use of solid adsorbents.
Degumming, Deacidification, and Dehydration via Physical Refining
Oils (such as Palm) and inedible animal fats containing higher Free Fatty Acids (FFA) should not be refined via Chemical Refining Process because of higher levels of processing losses. Such oils are refined with an alternate process known as Physical Refining. This process uses phosphoric acid to precipitate gums. Gums are separated by use of a centrifuge and/or filters. The oil is dried and deacidified under high temperature and low pressure. This process is a much cleaner process because it uses relatively very little water and does not produce soap. This process can also be used for lower FFA oils.
Trans-Esterification
Degummed, Deacidified, and Dehydrated oil is reacted with methanol in a series of reactors in the presence of a catalyst. The oil reacts with methanol to form methyl ester (biodiesel) and glycerin.
Biodiesel & Glycerin Separation
The mixture of biodiesel and glycerin is allowed to settle in settling tanks, coalescers, or centrifuges located after each reactor. The two phases--biodiesel and glycerin--are separated.
Methanol Recovery from Biodiesel
The biodiesel phase is contaminated with unused methanol. The biodiesel is heated to remove methanol. Methanol is evaporated and collected in a condenser. The methanol concentration in biodiesel after methanol recovery is expected to be negligible.
Biodiesel Washing & Drying
The biodiesel is washed with water to remove soaps and salts. The biodiesel is then treated with silica earth to remove traces of soaps and methanol. The filtered biodiesel is dehydrated to remove moisture before being sold. If desired, biodiesel wash can be accomplished without use of water.
Methanol Recovery from Glycerin
The glycerin phase also contains unused methanol. The glycerin phase is heated to remove methanol. Methanol is evaporated and collected in a condenser. The resulting glycerin has a concentration of 80 to 85% with the rest being mainly water. Higher grades of Glycerin (including pharmaceutical grade) can be produced with additional equipment.
Methanol Rectification
Methanol collected from biodiesel and glycerin phases contains moisture. The moisture is removed in a distillation column so that the resulting methanol is dry enough to be reused.
|
