Continuous glycerolysis reaction using microwave energy for high fatty acids feedstock for biodiesel production

• Main Author: Syed Amirul Haziq Bin Syed Isamri
• Published: 2023
• Subjects: Biodiesel; Continuous Flow; Glycerolysis

In production of biodiesel, vegetable oil that use as a feedstock of biodiesel has created long-term competition with the food supply chain as consequently in higher biodiesel prices. The raw materials cost constitutes 60 to 80 percent of the total cost of producing biodiesel. Therefore, using less expensive feedstocks that do not clash with food supply is a good way to reduce the production cost of biodiesel. Hence, this research will focus on waste cooking oil (WCO) as a raw material option for biodiesel production. However, these feedstocks have a high content of free fatty acids that hindering alkali catalyst reaction. Researchers have stated that alkali catalyst reaction can only tolerate free fatty acid (FFA) content in the feedstock up to 1-3% without adversely affecting the process. The FFA content in WCO usually 4-5% which is not suitable for alkali catalyst reaction. Therefore, pre-treatment of non-edible oils to lower the FFA in feedstock for alkali catalyzed transesterification is inevitable. Glycerolysis is one of pre-treatment process which can transform the FFA back to its respective glyceride molecule. There were few works have been reported on glycerolysis reaction with various non-edible oils with and without presence of catalyst. Most of them have reported, glycerolysis reaction has successfully reduced the FFA non-edible oils below 3% which is favorable for alkali catalyst transesterification. Nonetheless, the glycerolysis process is that it continues by slow reaction, occurring at a high temperature and being constrained by equilibrium, having two liquid phases in which the solubility of glycerol in triglyceride is rather restricted. Therefore, in this work a novel approach has been proposed which is utilizing microwave energy instead of conventional heating to accelerate the glycerolysis reaction with lower reaction temperature and reduce the process duration. Besides that, this research also focuses on continuous glycerolysis reaction using microwave energy rather than batch processes which are not ideal for industrial application. The results showed that the optimum condition achieve during experiment were molar ratio (oil to glycerol) of 1:3, microwave power of 440W, flow rate of 60rpm and without a presence of catalyst. The required time to achieve 96.5% of FFA reduction was about 10 minutes. Therefore, it was concluded that the lowest FFA value of WCO can be possibly obtain through this continuous glycerolysis method in a short time.