Microemulsion systems for glycerol valorization into diesel additives

The depletion of fossil fuel resources and their environmental impact have driven the search for sustainable alternatives such as biomass. Biodiesel production, a key component of this green transition, generates glycerol as a major byproduct, accounting for approximately 10% of the total process mass. Converting this surplus glycerol into high-value chemicals is essential to ensure the economic viability of biorefineries. In particular, the etherification of glycerol with tert-butanol produces di- and tri-tert-butyl glycerol ethers (h-GTBEs), valuable fuel additives that enhance engine performance and reduce particulate emissions. However, this acid-catalyzed reaction is limited by chemical equilibrium, as the water generated during the process promotes the hydrolysis of the desired ethers.

To overcome this limitation, this work develops a microemulsion system designed to protect h-GTBEs from water by partitioning them into an apolar domain. The reaction medium consists of a polar phase (glycerol, tert-butanol, acetonitrile, water, and H₂SO₄ as catalyst), an apolar phase (diesel), and a nonionic surfactant (Synperonic™ 91/6). System stability was evaluated over a temperature range of 25–85 °C, and the composition space was explored to construct a ternary phase diagram. In addition, a gas chromatography–mass spectrometry (GC–MS) method was validated for the quantification of the synthesized ethers.

The formulation remained fully stable up to 84 °C. An optimal catalyst concentration of 7.5 wt.% was identified, as higher concentrations disrupted the microemulsion structure. Experimental results also showed that increasing the water content reduced both glycerol conversion and ether selectivity. Finally, the amount of surfactant was successfully minimized to the range of 0.9–1.9 g, while concentrations below 0.9 g resulted in immediate phase separation.