Diesel fuels from vegetable oils

Vegetable oils have heat contents approximately 90% that of diesel fuel and are potential alternate fuel candidates. A major obstacle deterring their use in the direct-injection diesel engine is their inherent high viscosities which are nearly 10 times that of diesel fuel. Solution to the viscosity problem has been approached in three ways: 1) microemulsification, 2) pyrolysis, and 3) transesterification. Microemulsification with short chain alcohols such as methanol and ethanol yields fuels that are clear, thermodynamically stable liquid systems with viscosities near the ASTM specified range for number2 diesel fuel. These micellar systems may be formulated ionically or nonionically. The alcohols are attractive from an economic as well as a renewable resource viewpoint. Methanol has an economic advantage over ethanol, and it can be derived from a large variety of base stocks. These include biomass, municipal waste, natural gas being flared at refineries and from coal. Pyrolysis of vegetable oils is another approach to lowering their viscosity. Soybean and safflower oils were thermally decomposed in both air and nitrogen to obtain fuels for the diesel engine. Using standard ASTM distillation conditions, yields of pyrolysis products were about 75%. GS-MS analysis of the distillates showed the presence of alkanes, alkenes, aromatics,more » and carboxylic acids with carbon numbers ranging from 4 to more than 20. Fuel properties of the thermal decomposition products were substantially improved as evaluated by lower viscosities and higher cetane numbers compared to the unpyrrolyzed vegetable oils. Simple esters from transesterification of vegetable oils perform well in engine tests, and thus show good promise as an alternative or emergency fuel for diesel engines.« less