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.
This work deals with the design of integrated facilities for the production of xylitol and sorbitol from lignocellulosic biomass. Xylitol can be obtained from xylose via fermentation or catalytic hydrogenation. Sorbitol is obtained from glucose, but preferably from fructose, also via fermentation or catalytic hydrogenation. Fructose can be obtained from glucose via isomerization. Thus, a superstructure of alternatives is formulated to process switchgrass, corn stover, miscanthus, and others agricultural and forestry residues. Different pretreatments, such as dilute acid or AFEX for the fractionation of the biomass are evaluated. Next, after hydrolysis, the C5 and C6 sugars are processed separately for which a catalytic or a fermentation stage are considered. Glucose is to be isomerized before it can be processed. Finally, crystallization in a multistage evaporator system is used for purification. The optimization of the system suggests the use of dilute acid and the catalytic system. A system of 3 crystallizers is selected. For a facility that produces 145 kt/yr of xylitol and 157.6 kt/yr of sorbitol, the investment adds up to 120.74 M€ for a production cost of 0.28 €/kg of products. The inverse engineering of biomass was also performed resulting in a composition of 15% water, 20% cellulose, 40% hemicellulose, 15% lignin and 5% ash. The closest biomass corresponds to Sargassum (brown algae), that is capable of producing 230.5 kt/yr of xylitol and 116 kt/yr of sorbitol with investment and production costs of 120.5 M€ and of 0.25 €/kg of products, respectively.
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