Abstract
Pyrolysis, a key waste-to-X technology, enables converting a wide portfolio of biomass waste into valuable chemicals and fuels. However, raw pyrolysis oils are chemically and physically unstable. A multi-step stabilisation is necessary to reduce acidity and the content of reactive components, mainly carbonyls and carboxylic acids. During stabilisation, which involves deoxygenation and hydrogenation as the main steps, an aqueous phase is generated as a by-product. This stream contains mainly water, but relevant amounts of methanol and ethanol (2-8 wt%) are also present, together with minor concentrations of higher alcohols, C1-C4 carboxylic acids, and light esters. The aim of this work is to design and optimise a process to isolate the methanol and ethanol embodied in the aqueous phase and exploit them as intermediates to generate biofuels, biochemicals, and pharmaceutical products. The process consists of a train of four distillation columns to maximise the recovery rate and purity of the two targeted products. COCO-COFE, a CAPE-OPEN process simulator, is used for flowsheet development. The optimal number of theoretical stages and the optimal positioning of the feed to each unit have been optimised, considering a trade-off CAPEX-OPEX as the criterion. Results show that up to 95% and 98% yield can be achieved for methanol and ethanol, respectively. Methanol purity is limited to a maximum of 92 wt% due to the presence of volatile impurities, while ethanol contains residual propanol (6 wt%). The overall heat demand is in the order of 1 MJ/kg feed.