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Waste Vegetable Oil
Restaurants use many different oils for frying foods. These oils are subjected to very high temperatures as well as fats and water from various foods. The process of frying food changes the physical and chemical make-up of the oil increasing the acidity and water content. This affects the Transesterification Process - the chemical process of making of biodiesel. Higher FFA’s require more catalyst and alcohol, which in turn increases production costs. Other problems may arise from oils high in water or FFA’s, such as poor fuel from incomplete reaction and the formation of emulsions from a water washing process due to excess soap formation or shortened life of ION exchange resins. WVO with the least amount of water (“under 1%”) and low FFA’S (fewer than 5%”) are desirable.
Places to look for high quality oil would be restaurants that fry low fat foods, vegetables, fish, chicken, and potato chips. Example: Oriental restaurants and shrimp boats etc. The types of WVO to look for are Canola, Soy, Sunflower and Corn Oil in this order from thin to thick. The thickness or viscosity of the oil becomes a concern in cold climates as biodiesel made from heavier oil has “higher viscosity” and poor cold weather performance. Thinner oils will have better cold flow properties and better cold weather performance. Biodiesel made from WVO will usually have a higher viscosity than biodiesel made from virgin oil due to the physical and chemical changes made to WVO in the frying process. This will not be a large temperature difference, but you should expect a few degrees difference.
Non-hydrogenated or partially hydrogenated oils will be the most common type of oils used in restaurants. Some will use completely hydrogenated oil that is solid at room temperature and should be avoided. Non-hydrogenated oil will have better cold flow properties, but will not store as well without adding stabilizers. Partially hydrogenated oil has a higher “cloud point” but will not oxidize as fast. The difference between non-hydrogenated and partially hydrogenated oil is small and both are treated the same when making biodiesel. Hydrogenation results in the conversion of liquid vegetable oils to solid or semi-
solid fats. Complete hydrogenation converts unsaturated fatty acids to saturated ones. Changing the degree of saturation of the fat changes some important physical properties such as the melting point, which is why liquid oils become semi-solid. Since partially hydrogenated vegetable oils are cheaper than animal source fats and are available in a wide range of consistencies, and have other desirable characteristics (e.g., increased oxidative stability. Most restaurants tend to use partially hydrogenated oil due to cost and longer life of oil.
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