Design and control of a biodiesel production process using sugar catalyst for oil feedstock with different free fatty acid concentrations

• We study plant-wide design of a process to manufacture biodiesel using a heterogeneous sugar catalyst.
• Simultaneous esterification of free fatty acids and transesterification of triglyceride are studied.
• Total annual cost of the process is not significantly changed when the FFA content greater than 15 wt%.
• Significant saving of energy consumption can be realized as compared to a two-step process.
• Proposed control strategy works effectively to hold the product specifications.

This manuscript reports on the plant-wide design and control of a biodiesel process using a sugar catalyst. This catalyst is less expensive and more environmentally friendly than the conventional catalyst because it does not have to be neutralized and there is no resulting waste salt. Also, the acid catalyst can be used for simultaneous esterification of free fatty acids (FFA) and transesterification of triglyceride because there is no concern about the formation of soap, which is a problem with the conventional base catalyst. Two issues are addressed in this work. The first one is to find the effect of FFA content in oil feed to the optimal design of this process. The second one is to investigate the operability of the proposed process. The results show that total annual cost of the plant-wide process is not significantly changed when the FFA content greater than 15 wt%. As compared to a two-step process in literature, the energy consumption per tons of biodiesel production of our proposed process gives significant 65.8% saving for an oil feed with 5 wt% FFA. Dynamic simulations demonstrate that the proposed process can accommodate production rate and feed composition changes using a decentralized plant-wide control structure.