Degumming: How To Remove Gums And Improve The Fatty Acid Content Of Oil
Cooking oil, and all forms of oil obtained from plants and animals, contain gums which must be removed from those intended to make fuel by a process called, "De-gumming". But the practice of De-gumming preceeds the use of oil to make Bio-fuel. Lecithin, which is a very popular food-grade emulsifier, widely used in food processing industry and Pharmaceuticals, is made chiefly by the process of De-gumming vegetable oil.
How is Degumming important to Bio-diesel? Like high FFA content in oil, high gum content is bad for Biodiesel production. It increases refining loss because gums can initiate emulsification with some of the neutral oil which can be trapped in soap, if we decide to use base (Alkaline) to remove free fatty acids from the oil.
what are gums in oil?
Gums are simply phosphatides. They are similar to oil molecules (Triglycerides) except that they are phospholipids products where one of the three fatty acid chains are substituted by a phosphatide. Phosphatides exists in different forms but four types are more apparent as evident in the percentage content in Lecithin. They are:
• Phosphotidylethanolamine and
• Phosphatidic acid
Except Phosphotidylethanolamine which is weakly soluble, the other three are very soluble in water giving rise to two types of gums:
• Non-hydratable gums and
• Hydratable gums
About 10% of newly extracted vegetable oil exists as non-hydratable Phospholipids. But the percentage content is dictated by three factors:
• The type of the seed, ie. Rubber seed oil will be different from Jatropha seed.
• The quality of the seed and
• The oil extraction condition.
Non-hydratable gums can be removed from oil by using either,
• Acid Degumming or
• Enzymatic De-gumming
Acid De-gumming involves mixing the oil with either Phosphoric acid or Citric acid which can cause the gums to swell up and come out of the solution.
Enzymatic degumming on the other hand, involves using microbial enzymes Phospholipase to cleave phospholipids via hydrolysis to release the phosphotide.
Most phosphatide in oil (hydratable gums) can absorb water and become insoluble in the oil. The hydrophilic phosphatide with other hydrophilic substances such as sugar, can come out of the oil with glycerine in the Glycerine-Phase during Bio-diesel production , or can be removed by,
• Normal Settling
• Water wash followed by settling
The process of using water to remove hydratable gums from oil is referred to as "Water De-gumming" Phosphatidic acid, Phosphotidylcholine, and Phosphotidylinositol are all soluble in water and can be removed from oil by this process.
Water degumming is the most popular and oldest method of degumming. It is the method used in making commercial Lecithin from soybean oil. Although it is intended to remove hydratable gums, it can also remove other hydrophilic substances such as carbohydrates.
The process of water degumming involves adding hot water (2% volume of the total oil) to to the oil at a temperature of 160°F to 176°F, and the water and oil are mixed for 10 to 15 minutes. During this period, the Phospholipids absorbs water and their Lipophilic characteristics, thus becoming insoluble in the oil. The insoluble Phospholipids later combines to form the gum. Once formed, the gums can be separated by centrifugation.
All the possible way of degumming are incorporated into an array of specialized motorised systems called degumming machines. Such Machines can cater for large scale degumming processes required to purify large quantities of oil for Bio-diesel, normal purification of cooking vegetable oil, fuel oil, or as a process of extraction of lecithin for food processing. Some of the Machines are in combined forms so that they can remove both gums and free fatty acids. Such machines are called "oil degumming and neutralization machines".
Some combined machines can take advantage of the volatile nature of the FFA to neutralise the oil by heating out the FFA. While the removal of the Gums involves mixing systems that can input acid and water, or support enzymatic activities, before terminating at centrifugation and separation.
Oil degumming is an active business with rich internet business directories on degumming machine suppliers from Europe, Asia, and the US.