Biodiesel Production From Non Edible Oils: Standardization and Synthesis

The increase in oil price and the growing interest in environmental issues have recently given a considerable impetus to the research for cleaner and renewable energy sources, in order to ensure a sustainable future. Biodiesel (BD) is a renewable energy source in liquid form that has many advantages over normal diesel, including lower emissions of harmful gases to humans and environment. The BD is produced through the transesterification of triglycerides contained in oils or fats, with methanol and in the presence of an alkaline catalyst, also yielding glycerine as a by-product. Not refined vegetable oils or animal fats, besides tryglicerides, contain also high percentages of free fatty acids (FFA). These last should be as lower as possible to avoid the drawback of soap formation which complicates the reaction and products separation. Although food-grade oils with low acidity can be employed with less practical problems, the use of this feedstock is strongly discouraged to avoid interference with the human food requirement, besides being not competitive cost-wise with the petroleum-based diesel. To overcome this problem, waste materials, such as cooking oil or animal fat, can be employed. These kinds of fats are however characterized by an high content of FFAs and they must be standardized by properly reducing the FFAs content. The authors present the obtained results using different potential feedstock for a sustainable BD production. Besides different kinds of vegetable oils, animal grease and used cooking oil were selected for the experimental tests. In particular, deacidification through esterification with methanol of FFAs is investigated. This last method is particularly convenient in lowering FFA content as yields methyl alkyl esters, i.e. BD. Heterogeneous acid catalysis is preferred for esterification; more in detail, sulfonic ion exchange resins (commercially available from Dow Advanced Materials or Purolite) with different physical and chemical properties were tested in various conditions (stirring velocity, temperature and catalyst amount). Home made catalysts based on zirconia were also employed in esterification reaction. At the moment, the lifetime of the catalyst is the most crucial issue in industrial applications. With the aim of investigating this aspect, 90 consecutive batch deacidification runs, each lasting 6 h, were conducted using crude palm oil or soybean oil as a feedstock and Amberlyst® 46 (Dow Advanced Materials) as a catalyst, leading to very interesting results which have been recently published by the authors on Ind. Eng. Chem. Res. As the catalyst stability depends on the operating mode of the reactor employed, different reactor configurations (batch, semibatch, continuous) were tested.The outcomes of this study allowed one to conceive an optimized and improved equipment configuration, based on a packed-bed reactor with a preliminary emulsificator. Some transesterification experiments were also perform on de-acidified oil in order to validate the whole process.