Process design of a direct route from bioethanol to ethylene oxide

PROCESS DESIGN OF A DIRECT ROUTE FROM BIOETHANOL TO ETHYLENE OXIDE Ilenia Rossetti1*, Antonio Tripodi1 and Gianguido Ramis2 1 Chemical Plants and Industrial Chemistry Group, Dipartimento di Chimica, Università degli Studi di Milano, Via Golgi 19, 20133 Milano (MI) , Italy 2 DICCA, Università degli Studi di Genova, via all’Opera Pia 15A, 16100 Genova, Italy *ilenia.rossetti@unimi.it Introduction Currently, ethylene oxide is produced by direct oxidation of ethylene with air or oxygen on supported silver catalysts; annual worldwide production capacity was ca. 1.7 x 107 tons. In the last decades, alternative routes to produce bulk and fine chemicals from renewable sources have been intensely studied. In particular, ethanol seems to be a promising starting reagent and has been used to produce ethylene. The indirect bioethanol-bioethylene-biooxyrane route has already been demonstrated, but it needs two separate plants which, combined with the higher cost of the starting reactant in most countries, would lead to the economic unsustainability of the process. Hence, the aim of this work is to design and simulate the direct one-pot ethylene oxide production starting from bio-ethanol. Starting from the available literature data we have set up a kinetic model and designed the process flow diagram of a completely new production process. Different side opportunities are also discussed for reactants recycles and the valorization of byproducts. Materials and Methods Process design and optimization has been based on the experimental investigation reported elsewhere [1,2] for a Au/γ-Al2O3 catalyst promoted by Li2O and CeOx. The available conversion and selectivity data were regressed according to an originally developed kinetic model. Product recovery and separation was designed to allow the valorization of most byproducts. Pinch analysis was carried out for the energetic optimization of the plant. Results and Discussion A full flowsheet for the direct one-pot conversion of bioethanol to ethylene oxide has been designed for the very first time. Such plant design is capable of converting more than 99% of the starting ethanol into ethylene oxide into the once-through reactive section, with a selectivity around 84%. The overall yield is limited by the ethanol lost in the beer concentration and stripping operation, but this is a minor issue due to the relatively low cost of the reactant. The separation section can recover ca. 98% of ethylene oxide produced in the reactive section, 90% as pure ethylene oxide and 8% as pure ethylene glycol. This products recovery section has been also effectively integrated with the raw materials purification line connecting the following steps: a) the concentrated ethanol is split between the reactor feed and the EO absorber, b) the EO left after its distillation is converted into glycol, c) part of the glycol is re-routed to the ethanol concentrator. With the Pinch Analysis method, the heat consumption achieved after optimization was just 5.5 % higher with respect to the theoretical hot and cold utilities targets. A global as low as 7 °C can be actually achieved considering the substantial contribution of latent heat exchanges. Figure 1. Layout of the designed plant. Significance A novel route for the direct one-pot oxidation of ethanol to ethylene oxide has been designed and scaled-up into a full process: this is the very first design of an innovative one-step conversion route from bioethanol to ethylene oxide. Starting from the review and interpolation of reaction kinetics, a staged, cooled reactor is sized for the air-based oxidation of bioethanol, yielding ethylene oxide in one-step. An efficient strategy for the separation of the product from the gas phase effluent of the reactor is developed, based on absorption in a hydro-alcoholic solution rather than in pure water. This in turn brings a material recycle between the feed and purification section that benefits the atom economy. As the basis of an economic analysis, the energy balances are assessed and analyzed via the Pinch Analysis method. This lets foresee a conversion of 90% of bioethanol into Ethylene Oxide (>99% purity) and 7.7% into marketable ethylene-glycol. References 1. Lippits, M.J., Nieuwenhuys, B.E. Catal. Today 154, 127 (2010). 2. Lippits, M.J., Nieuwenhuys, B.E. J. Catal. 274, 142 (2010).