The most common technology used in biodiesel production is the transesterification of vegetable oils and animal fats. Transesterification (also called alcoholysis) is the reaction of fat oil with an alcohol to form esters and glycerol, in presence of catalyst to improve the reaction rate and yield. Although process industry has established long ago that continuous processes are more cost-effective than batch processing, there is still a substantial number of batch processing biodiesel plants in the world. One of the challenges in switching to a continuous process is the simultaneous control requirement of throughput (flow), temperature, and biodiesel concentration.
In the present work, a two-step homogeneous base-catalyzed transesterification process for a continuous biodiesel production plant is studied. The most relevant variables are: reaction temperature, ratio of alcohol to vegetable oil, amount of catalyst, mixing intensity (RPM), catalyst and vegetable oil used. The objective was to design a control strategy incorporating three key loops, overrides, and decoupling based on multivariate control analysis. The designed control strategy is described and simulation-based performance test results are shown.