**Biodiesel Production from Castor oil by Two-Step Catalytic Transesterification: Optimization of the Process and Economic Assessment**

#### **Nuria Sánchez 1, José María Encinar 1, Sergio Nogales 1,\* and Juan Félix González 2**


Received: 22 September 2019; Accepted: 16 October 2019; Published: 17 October 2019

**Abstract:** The use of biodiesel and the requirement of improving its production in a more efficient and sustainable way are becoming more and more important. In this research work, castor oil was demonstrated to be an alternative feedstock for obtaining biodiesel. The production of biodiesel was optimized by the use of a two-step process. In this process, methanol and KOH (as a catalyst) were added in each step, and the glycerol produced during the first stage was removed before the second reaction. The reaction conditions were optimized, considering catalyst concentration and methanol/oil molar ratio for both steps. A mathematical model was obtained to predict the final ester content of the biodiesel. Optimal conditions (0.08 mol·L−<sup>1</sup> and 0.01 mol·L−<sup>1</sup> as catalyst concentration, 5.25:1 and 3:1 as methanol/oil molar ratio for first and second step, respectively) were established, taking into account the biodiesel quality and an economic analysis. This type of process allowed cost saving, since the amounts of methanol and catalyst were significantly reduced. An estimation of the final manufacturing cost of biodiesel production was carried out.

**Keywords:** catalyst; sodium hydroxide; fatty acid methyl ester; central composite rotatable design; operational conditions
