(27h) Simulation-Based Evaluation of the Pre-Treatment of Acid Raw Materials in Biodiesel Production

Biodiesel is a liquid fuel derived from fatty acid esters (triacylglycerols), whereby if changing its physical-chemical properties, a product similar to petroleum diesel can be obtained¹. In particular, the Brazilian industry commonly uses a transesterification process for biodiesel production through homogeneous catalysis, where the main oil is the soybean derivative. However, the dependence on a single raw material presents risks to this process involving several factors such as financial, logistical, and environmental. The objective of this work is the evaluation of the complementary use of other raw materials for biodiesel production, such as those with high acidity: e.g., waste cooking oil. For this, a pre-treatment stage, presented in Figure 1 in red, has been modeled based on an esterification reaction with a ratio of 40:1 of methanol to oleic acid, representing the content of free fatty acids, and the addition of 10% sulfuric acid (H2SO4) in relation to the mass of oleic acid. The feed stream of methanol with sulfuric acid is reacted with a mixture of oil (85% by mass of triolein/15% by mass of oleic acid), simulating waste cooking oil, at a temperature of 60°C, before entering the esterification reactor².

The process modeling was carried out in the AVEVA Process Simulation (APS) platform, based on the "B3 - Biodiesel Process" example³, where triolein was used to represent low acidity refined oil under alkaline homogeneous catalysis (NaOH) reacting with excess methanol. This process extends beyond the transesterification reaction, also encompassing purification, washing, and drying of biodiesel. The refined oil was included in the stream to ensure a variety and availability of locally easily produced raw materials in Brazilian urban centers, such as residual oils and fats (a byproduct of cooking vegetable oil in food, which undergoes a series of physical and chemical transformations in its composition)⁴. The simulation was able to convert 97.6% of the oleic acid, which corresponds to a reduction in the value of free fatty acids, indicating a reduction in the acidity of residual oils and fats per mass from 15% to 0.21%. The model results presented a satisfactory conversion of oleic acid into triolein in the pre-treatment stage to be used in the alkaline-catalyzed transesterification reactor section.

Keywords: Modeling; Simulation; Esterification; Free Fatty Acids; Biodiesel.

References

¹ CIOLKOSZ, D. (2020), What’s so different about biodiesel fuel? Bioenergy, 739–744.

² YANG, Y. J.; CHAI, M.; TU, Q.; LU, M. (2014) Esterification pretreatment of free fatty acid in biodiesel production, from laboratory to industry. Fuel processing technology, 125, 106-113.

³ AVEVA (2022). AVEVA Process Simulation. B3 - Biodiesel Process. Undocumented examples.

⁴ CARNEIRO, F. L. (2022), Modeling and simulation of biodiesel production from oil and residual fat from the city of Quixadá-CE. Available at: biblioteca.ifce.edu.br/index.asp?codigo_sophia=105952.