Biodiesel from tomato seed oil: Transesterification and characterisation of chemical-physical properties

The transesterification process of an oil is influenced by four variables: reaction temperature, reaction time, amount of alcohol and amount of reaction catalyst. The cost of production, yield and chemical-physical characteristics are therefore directly dependent on these variables. In this work, tomato seed oil was transesterified and the influence of the quantities of the alcohol (methanol) and catalyst (potassium hydroxide) was tested. The values of total esters, density, kinematic viscosity, iodine value, acid number, linolenic acid, cetane number and residual glycerides in the different biodiesels produced (Bio from A to F), were studied and compared with the current European regulations EN14214: 2014 (Liquid petroleum products -Fatty acid methyl esters for use in diesel engines and heating applications - Requirements and test methods). The six obtained biodiesels yielded between 72.59 (BioB) and 96.8% (BioE) of the total esters. The presence of non-transesterified oil, besides being a yield index, also negatively affects the viscosity at 40 °C of the produced biodiesel. In fact, the only sample with a value within the legal limit was BioE (4.95 mm2 s-1), while the others showed viscosity values higher than the 5.00 mm2 s-1 established by the European regulation. The density, however, always remained within the specified limits, with values between 880 kg m-3 in BioE and 891 kg m-3 in BioB. The presence of linolenic acid was well below the maximum legal limit in all samples, the iodine value ranged between 119 and 122 g I2 100g-1.