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Chicken Fat
Chicken fat is an animal lipid that is obtained (usually as a by-product) from chicken rendering and processing and can be converted to biodiesel. It is often used as flavoring of chicken soup and components of pet food, and now it is also a feedstock for renewable energy resources. Since the beginning of 21st century, many big companies around the world, like Tyson Foods, have started to use chicken fat for biodiesel production.[1] As a raw-material for biodiesel, chicken fat has great potential because of its low price and nice properties. However, there are still some challenges and issues about using chicken fat for biodiesel， such as the contaminants in the fuel. [2]
Potential as Biodiesel
Chicken fat is high-quality energy source for its large quantity and high energy content. Chicken is popular food for humans, but chicken fat is considered inedible. Therefore, billions of tons of chicken fat are wasted after chicken processing every year. However, chicken fat is rich in energy, and 1 kg of chicken fat can generate about 38000 J of energy which is equal to the energy in 2.2 kg of lead-acid battery.[3][4] Thus, we are able to get a great deal of energy from chicken fat.
Now most biodiesel stock is soybean oil, but the price of soybean oil is growing. The price of soybean oil was $0.12 per pound in 2001, while this price is $0.34 per pound in 2017.[5] The increasing cost of ingredient is pushing industries to use animal fats for biodiesel. Animal fats are cheaper than vegetable oil because animal fats have more limited market. Some large meat and oil companies have been working on producing renewable resources with chicken fat. Tyson Foods, the American biggest meat company, produces about 2.3 billion pounds of chicken fat each year, so taking advantages of the vast quantity of waste fat can bring it lots of profits. In 2006, Tyson Foods built a renewable energy department , and it annually converts the chicken fat from poultry plants into about 300 million gallons fuel, which is worth 1.2 billion dollars.[1][2][6] Another example is Neste Oil Corporation, an oil refining and marketing company in Finland. Neste Oil's renewable diesel refinery in Rotterdam (one of its largest plants) can annually produce 800,000 tons renewable diesel fuel, and over 65% of the feedstock used by this diesel plant is animal fats, including chicken fat.[7][8]
Process
Biodiesel
Rendering Process
Chicken fat is collected from the bodies of chickens and made into oil in rendering process. First, the by-products of chicken are crushed into mixture of powder and liquid, and then the solids are completely removed from the mixture by a screw press. The screw press provides with large pressure to make the fluid pass through a filter screen with very small holes, and the solid residue is left in the filter. The next step is heating the by-products to release the fat from cells, decrease the moisture, and destroy pathogens. In the end, the products are liquid oil and "meat and bone meal", an animal feed.[2][9]
Trans-esterification
Trans-esterification procedure converts the chicken fat to biodiesel and glycerin, which can be used to generate energy as environmental-friendly resources. This procedure contains following five steps.
Glycerin Settling and Separation: Settle glycerin created by base transesterification and separate it from oil using a filter.
Methanol Recovery: Heat the oil to evaporate methanol and cool the vapors to collect liquid methanol.
Washing with Fatty Acid Methyl Esters (FAME) or Dry Bioethanol: Wash the oil at temperature above 70 °C for 4-5 times to clean remaining impurity.
After this procedure, chicken fat finally becomes the fuel that provides power efficiently.[10]
Advantages and Disadvantages
Advantages
Low Cost: Biodiesel can compete with petroleum diesel because of its low price. Besides, chicken fat is almost useless, so it is much cheaper than other feedstocks for biodiesel, such as soybean oil. One pound of soybean oil costs 33 cents, while same amount of chicken fat only costs 19 cents.
Renewability: Now most fuels used by humans is petroleum-based, but fossil oil will be used up someday. Chicken fat is a renewable energy source which can be a substitute of petroleum fuel.
High Cetane Number：The saturated fatty acids in chicken fat lead to the high cetane number of biodiesel, and the high cetane number assists the engine to start in less time and work with less noises.
Low NOx Emission: Nitrogen oxides (NOx) are main components of air pollution. Chicken fat biodiesel has lower NOx emission level than soy-based biodiesel, because the high cetane number of chicken fat biodiesel can reduce NOx in combustion process.[1][2][11]
Disadvantages
High Cloud Point: Biodiesel converted from chicken fat has a high cloud point, because the fatty acid in chicken fat is considerably saturated. Chicken fat is 30-33% saturated, while soybean oil is only 14% saturated. Pure biodiesel can only be used under warm conditions, but this issue could be solved by mixing it with large amount of petroleum diesel.
Low Oxidative Stability: Chicken fat is less stable than vegetable oils, since chicken fat has little antioxidants like vitamin E which is plentiful in vegetable oils. Hence, the biofuel made from chicken fat deteriorates faster in the open air.
Contaminants: Contaminants in chicken fat, such as polymers, may do harm to the engine. Polymers form in the rendering due to the high temperature, and they can increase the viscosity of biodiesel. Other remaining contaminants in processing and purification, like phospholipids, possibly result in precipitation which can reduce the life time of the engine.
High Sulfur Contents: Fuel made from chicken fat contains more than 100 ppm of sulfur, which is much higher than the standard of biodiesel for highway use. The high sulfur contents may cause high sulfur dioxide emission. Sulfur dioxide can react with water and oxygen in the air, and create sulfuric acid which may cause acid rain. Therefore, high sulfur dioxide emission is harmful to the environment.[2][11][12]
^ abWyatt, Victor T.; Hess, Melissa A.; Dunn, Robert O.; Foglia, Thomas A.; Haas, Michael J.; Marmer, William N. (2005-08-01). "Fuel properties and nitrogen oxide emission levels of biodiesel produced from animal fats". Journal of the American Oil Chemists' Society. 82 (8): 585–591. doi:10.1007/s11746-005-1113-2. ISSN0003-021X.
^Nutter, Mary K.; Lockhart, Ernest E.; Harris, Robert S. (1943-11-01). "The chemical composition of depot fats in chickens and turkeys". Oil & Soap. 20 (11): 231–234. doi:10.1007/BF02630880. ISSN0003-021X.
