Integrated Renewable Production of ETBE from Switchgrass

Abstract

[EN]In this work, we propose the optimization of a flowsheet for the conceptual design of an integrated renewable production of ETBE from ethanol and i-butene from switchgrass. A superstructure embedding a number of alternatives is proposed. Two technologies are considered for switchgrass pretreatment, dilute acid and a novel ammonia fiber explosion (AFEX), so that the structure of the grass is broken down. Only glucose is fermented to produce i-butene, while xylose is fermented to ethanol. Ethanol is purified using a multieffect column followed by molecular sieves and a PSA-membrane system is used to upgrade the i-butene. The problem is formulated as an MINLP, and solved for each pretreatment as an NLP. Finally, an economic evaluation is performed including a sensitivity analysis. Biomass composition determines the byproduct obtained. Dilute acid is the selected pretreatment due to the largest yield to sugars and the possibility of adjusting the production of both i-butene and ethanol for the needs to ETBE. For a facility that produces 90 kt/yr of ETBE, the investment adds up to 160 M€ for a production cost of 0.61€/kg, which is above market price. Even though the results look promising, further experimental and scale up studies are required for validation.