Optimal Simultaneous Production of Biodiesel (FAEE) and Bioethanol from Switchgrass

Abstract

In this work, we optimize the simultaneous production of biodiesel (fatty acid ethyl esters, FAEE) and ethanol from switchgrass. Two technologies are considered for switchgrass pretreatment: dilute acid and ammonia fiber explosion (AFEX). Next, enzymatic hydrolysis follows any of the pretreaments to obtain fermentable sugars, mainly xylose and glucose. We separate the lignin, and, with the sugars, we consider the production of bioethanol and/or FAEE. Based on a superstructure of alternatives, the problem is formulated as an mixed-integer nonlinear program (MINLP) with simultaneous optimization and heat integration. An economic evaluation is performed and water consumption is calculated. The simultaneous production of bioethanol and FAEE from switchgrass is shown not to be competitive at the current development of the conversion of sugars to FAEE, but it can become promising if the conversion from sugar exceeds 0.5. The optimal solution indicates bioethanol to be the preferred product because of its higher...