Integration of deep eutectic solvent and activated carbon in emulsion liquid membrane system for soap removal from crude biodiesel

The present work investigated the soap removal from crude biodiesel (BD) using a new technique known as (DES-based ELM/AC), which is a deep eutectic solvent (DES) -based emulsion liquid membrane with the presence of activated carbon (AC). In this system, the DES was introduced as a stripping phase in the DES-ELMs while the AC was introduced into the membrane phase as due to its interaction with the potassium species in the soap molecules with the presence of active sites on the AC surface. The effect of different parameters on the soap extraction efficiency such as the DES molar ratio, DES: BD ratio, surfactant concentration, mixing speed, duration process, and AC dosage were investigated. The results showed that in comparison to adsorption and DES-based ELM, the synergistic effect provided by DES-based ELM/AC technique showed superior removal efficiency at 97.61%. Highest removal efficiency of 99.75%, which is equivalent to 1.87 ppm soap content in the BD, was achieved at 2 wt% of the surfactant, 0.5 wt% of AC, 1:4 DES molar ratio as stripping phase, 1:1 DES: BD ratio, 400 rpm mixing speed and 6 min extraction time. The soap transport follows the first order kinetic model, with a rate constant of 0.627 min -1. This method offers a viable alternative to the conventional water-based purification process. It demonstrates the effective purification of crude BD without the use of a large amount of water/washing agent in comparison to conventional water washing, thereby offering a more sustainable solution for the purification of BD.