Crude glycerine is a viscous liquid with a naturally sweet taste and light yellow to dark brown in color. It is the impure form of refined glycerine. Crude glycerine is derived from both natural and chemical feedstocks. Glycerine occurs in combined form in vegetable oils and fats as triglycerides. It is also found in animal fats. Crude glycerine is obtained as a byproduct from the biodiesel manufacturing plant and oleochemical industries.
Emphasis has been placed on the usage of renewable energy, resulting in an increase in the production of biodiesel. As crude glycerine is a byproduct in the production of biodiesel, there is a corresponding increase in the production of crude glycerine. Crude glycerine specification commonly includes 80% glycerine and the rest is made up of impurities such as methanol, soap, catalyst, salts, non-glycerine organic matter, and water.
Recovery of fat
First of all, animal fats are collected from slaughterhouses. The fat tissue from animal parts is cooked. The elevated temperature ensures the fat to be released in liquid state and promotes cell rupture. On the other hand, an alternative method requires partial heating and the mechanical rupture of the fat tissue to release fat.
The degumming process of animals is the removal of dissolved phosphatides through centrifugation. Water is added to the oil that allows the precipitation of phosphatides. The newly formed precipitate is heavier as phosphatides readily absorb water. The centrifugation process separates the heavy phosphatides from the oil phase to the water phase.
Bleaching of oil is required to release unwanted pigment and other oxidizing agents that may alter the appearance of the product. Bleaching is performed by adding charcoal or earth clay. The existing pigment from the oil will be adsorbed by the charcoal. On the other hand, an additional method by chemical reaction is required for edible oils (oxidation and reduction reaction).
The adsorbed oils are further treated for scent and foul odour removal. Steam distillation is utilized to remove any volatile impurities that contribute to the unpleasant smell. Steam distillation makes use of the non volatile animal fat to remove any aldehydes, ketones, and other compounds that are classified as an impurity. In a distillation chamber, high pressure is injected under vacuum conditions around 180-250 degrees centigrade. The non-volatile triglyceride remains unchanged while volatile impurities cascade upwards and are removed from the animal fat.
The animal fat is decomposed by hydrolysis reaction under high temperature and pressure. The process utilizes water to break down the chains of triglycerides into glycerol/glycerine and chains of fatty acid. In this step, glycerine becomes available for extraction; however, further refining is required for the newly made glycerine to be called refined glycerine.
Crude glycerine has a high metabolizable – digestible energy ratio that is almost identical to soybean oil. The source of energy from glycerine is used to feed cattle and other herbivorous animal farms.
The remaining crude glycerine is utilized as an intermediary chemical through thermo-chemical conversions. The product propylene glycol is manufactured from crude glycerine through a process called hydrogenolysis. The propylene glycol is utilized as an antifreeze compound and as a fuel additive in methanol fueled vehicles.
Crude glycerine is able to be used in composting through various biological conversions. The product succinic acid is produced from the fermentation process of crude glycerine with the bacterium Anaerobiospirillum succinici. In addition, further research has suggested that algal fermentation may convert crude glycerine into omega-3 polyunsaturated fatty acid.