Conceptual study of transesterification of vegetable oils in the continuous-stirred-tank reactor at unsteady-state and isothermal conditions

The continuous-stirred-tank reactor (CSTR) is favorable for bi-phasic enzymatic reaction due to ease of operation, cost-effective and low downtime. The lack of study on the enzymatic reaction in the CSTR has disfavor this type of reactor compared to batch and packed bed. The purpose of this study is to prove the feasibility of enzyme-catalyzed production of biodiesel in the CSTR using the mathematical model and simulation. The model incorporated the effect of the kinetic, thermal, and operating parameters. Then, it was solved using Polymath 6.1 software. Then, suitable enzyme characteristics and operating conditions are suggested. A high conversion could be achieved by choosing an appropriate lipase and operating conditions. The lipase with K-l > 100 mol/L, K-m < 0.15 mol/L, and Delta G(inac) > 120 kJ/mol were selected as they are resistant to methanol inhibition, showing a high affinity for the oil substrate and thermally stable. For a thermally sensitive enzyme, the operating temperature should remain constant at its optimal level to avoid over denaturation. In addition, the residence time for the triglycerides is prolonged (>20 hr) whereas for the methanol is shortened since it can increase the conversion. This can be achieved by reducing the volumetric flow rate of the triglycerides over the methanol. However, it must not be too low to prevent lower productivity. This article highlights that the production of biodiesel using enzyme-catalyzed reaction can be feasible if an appropriate lipase and operating conditions are employed.