Electrodialysis aided desalination of crude glycerol in the production of biodiesel from oil feed stock

• Electrodialysis (ED) as an alternative process for desalination of crude glycerol
• Optimization of linear velocity to establish design parameters for ED process
• Economic estimation of ED for processing 1 m3/h of crude glycerol feed

Electrodialysis (ED) is a proven membrane process used mainly in desalination of brackish/seawater, salt production and separation of ionizable compounds from aqueous industrial solutions. In the biodiesel industry, trans-esterification reaction produces the fuel along with a mixture of byproducts containing glycerol, methanol, water, soap and unreacted catalyst. Considering the massive scale of crude glycerol formed as a byproduct in the tremendously increasing number of biodiesel industries worldwide, there is a great demand for newer methods for purification of crude to pure glycerol. The present study focuses on the separation of sodium sulfate (Na2SO4) salt formed during neutralization of alkaline catalysts, from the crude glycerol. ED studies were conducted with commercial AMI-7001 and CMI-7000 ion exchange membranes. Limiting current densities (LCDs) were determined at different feed flow rates. The ED cost estimation studies were performed by optimizing a single process parameter, namely, linear velocity. The experimental results demonstrated that the membranes exhibited sufficient chemical and thermal stability and successfully separated more than 95% of Na2SO4 from crude glycerol. ED was observed to be a simple and cost effective technology, which provides a competitive value addition to biodiesel production through byproduct recovery.