ABSTRACT
Biodiesel, a monoalkyl ester of long-chain fatty acid, is a clean diesel substitute that can be used in most diesel engines without the need of engine modication. The combustion of biodiesel in engines emits much less air pollutants and greenhouse gases than petrodiesel (Leung, 2001). Most of the feedstocks for biodiesel production comes from vegetable oils, both edible and nonedible, because they are renewable in nature and can be cultivated on a large scale (Patil and Deng, 2009). At present, more than 95% of biodiesel production feedstock comes from edible oils (Gui et al., 2008). However, the use of virgin edible oil has caused some problems in our society, such as competition with the edible oil market, hence raises the market price of both edible oils and biodiesel (Kansedo et al., 2009). Thus, researchers have growing interest in using nonedible oils that are not suitable for human consumption, such as Jatropha curcas seeds, okra seeds, and algae oils (Berchmans and Hirata, 2008; Sahoo and Das, 2009; Anwar et al., 2010; Gao et al., 2010). Nonedible oil crops can be grown in wastelands that are not suitable for food crops, and the cost of cultivation is much lower than normal food crops because these crops can still sustain reasonably high yield even without
16.1 Introduction .......................................................................................................................... 327 16.2 Advantages of Using Waste Oils for Biodiesel Production .................................................. 328
16.2.1 Reduction of Biodiesel Production Cost ................................................................... 328 16.2.2 Solving Problems of Waste Oil Disposal and Treatment ......................................... 330
16.3 Waste Feedstock for Biodiesel Production ........................................................................... 330 16.3.1 Used Frying Oil or Used Cooking Oil...................................................................... 331 16.3.2 Animal Fats .............................................................................................................. 331 16.3.3 Yellow Grease ........................................................................................................... 331 16.3.4 Brown Grease (Trap Grease) .................................................................................... 331
16.4 Production Processes ............................................................................................................ 332 16.4.1 Alkaline-Catalyzed Transesterication .................................................................... 333 16.4.2 Acid-Catalyzed Transesterication .......................................................................... 333 16.4.3 Acid-and Alkali-Catalyzed Two-Stage Transesterication ..................................... 333 16.4.4 Enzyme-Catalyzed Transesterication ..................................................................... 335 16.4.5 Supercritical Methanol Method ................................................................................ 335 16.4.6 Pretreatment .............................................................................................................. 335 16.4.7 Analytical Methods .................................................................................................. 336
16.5 Prospect of Biodiesel Produced from Waste Feedstocks ..................................................... 336 16.6 Conclusions ........................................................................................................................... 336 Acknowledgment ........................................................................................................................... 336 References ...................................................................................................................................... 336
intensive care (Tiwari et al., 2007; Gui et al., 2008). However, most nonedible oils (such as jatropha and rubber seed oil) contain high free fatty acids (FFAs) that may require multiple chemical steps or alternate approaches to produce biodiesel. This inevitably increases the production cost, and the ester yield of biodiesel may be lower than the standard specications for biodiesel (Haas, 2005; Patil and Deng, 2009; Sahoo and Das, 2009). Low-cost animal fats (with high saturated fatty acids) and used cooking oil (UCO) or used frying oil (UFO) can be feasible feedstocks of biodiesel production. The consumption of oils and fats in the world is enormous, estimated to be about 154 million tons/ year (MPOC, 2007). A great amount of it will become UCO/UFO after using, which is not suitable for human consumption. Table 16.1 shows the quantity of waste cooking oil produced in major countries (Gui et al., 2008). The use of these waste oils can signicantly reduce the cost of biodiesel production due to its low price in acquiring.
