Impact of Glycerin-Derived Oxygenated Additive (TAG) on the Biodiesel Storage Behaviour

November 24, 2025

The rapid expansion of the biodiesel industry generates a substantial surplus of crude glycerin (about 10% of the mass of the processed fat), which undermines its economic and environmental sustainability. Refining this glycerin for pharmaceutical or cosmetic uses proves costly and energy-intensive. This thesis proposes a circular economy strategy: converting the crude glycerin directly into high-value oxygenated additives for incorporation into the biodiesel itself, more specifically triacetin (TAG, glycerol triacetate). Biodiesel samples produced from used frying oil (WFO), via NaOH catalysed methanolysis (the precursor of the active species), were doped with 1%, 3% and 5%(w/w) TAG. Physicochemical characterization of the biodiesel indicated that the presence of TAG increased oxidative stability by extending the induction period of oxidation. Slight modifications were observed: a decrease in the flash point (from 149°C to 145°C) and an increase in density (from 888 to 898 kg/m³ for the 5% TAG sample), while all parameters remained consistent with international biodiesel standards. Accelerated ageing tests in an oven (67 °C, 74 days ≈ , 3.7 years under real-life conditions), in the presence of copper sealing washers, demonstrated greater stability of the additive-enriched biodiesel. The analysis of the Cu washers by X-ray photoelectron spectroscopy revealed a reduction in the atomic ratio Cu²⁺/Cu for the biodiesel with TAG (0.60 versus 0.70 for the non-additivated biodiesel and 0.46 for the un exposed reference ring). The results demonstrate the technical and environmental viability of using triacetin as an additive that valorises glycerin and enhances the performance, stability, and sustainability of biodiesel.

Authors in the community:

• 

  B

  Beatriz Fernandes Leal

  ist196578

Supervisors of this institution:

• 

  R

  Rui Galhano dos Santos

  ist34214

• 

  A

  Ana Paula Vieira Soares Pereira Dias

  ist12794

chemical-engineering - Chemical engineering

por - Portuguese

Instituto Superior Técnico