(463b) Evaluation of Aromatics Formation in Thermal Cracking of Triglycerides

Liquid fuels produced by biomass conversion offer an alternative to our reliance on fossil sources. Among the process available in the literature, thermal cracking results on a liquid product (bio-oil) with similar characteristics to petroleum crude oil, especially when performed with triglyceride sources. However, undesired compounds, such as carboxylic acids and benzene might be formed as well. Although aromatics may have positive aspects (e.g. increasing the octane number on light fuels), they are toxic and, particularly benzene has its content restricted by local regulations. Moreover, benzene removal involves complex processes, being wiser to avoid its formation.

The aim of this work was to investigate one of the hypothesis for benzene formation, regarding a relationship between the degree of unsaturation of the biomass with the benzene content in bio-oil. Thermal cracking experiments were performed using triglyceride sources with three different degrees of unsaturation, in the same operational conditions. Commercial soybean oil and blends with 10% and 20% of hydrogenated were constituted as samples to be analysed. Density, acid index and iodine index were measured to evaluate the blending effect. The thermal cracking experiments were performed in triplicate at 525 ^oC of temperature and feed mass flow of 300 g/h in a continuous screw reactor operating over steady state conditions. The mass balance shows the liquid yield increased and coke formation decreased with for higher blends.

Benzene content decreased by 14% in the bio-oil produced by the biomass with the lowest degree of unsaturation. Also, the reactions for carboxyl group removal were favorable to the saturated compounds, reducing the acidity index in the biomass with the lowest unsaturation content. Notwithstanding, long-chain paraffinic compounds remained in the products, which suggests that saturated compounds does not crack easily.