Sustainable process design for the valorization of bioethanol as platform chemical

Sustainable process design for the valorization of bioethanol as platform chemical I. Rossettia, A. Tripodia, F. Contea and G. Ramisb a Chemical Plants and Industrial Chemistry Group, Dip. Chimica, Università degli Studi di Milano, CNR-ISTM and INSTM Unit Milano-Università, via C. Golgi 19, 20133 Milan; b Dip. Ing. Chimica, Civile ed Ambientale, Università degli Studi di Genova and INSTM Unit Genova, via all’Opera Pia 15A, 16145 Genoa Process design is facing fully new challenges to adapt logical and economic successful schemes to new biorefinery concepts. The search for environmentally sustainable chemical processes needs to cope with limited scale up possibilities, complex reactants or products and new paradigms for the economic assessment of chemical plants. In this frame, we have selected bioethanol as platform chemical and pivot for the production of many intermediates and commodities, focusing on the target production scale of a sugar biorefinery. The examples considered were the production of syngas, hydrogen, bioethylene, bioethylene oxide and bioacetonitrile. After designing a fully integrated plant for each application we proceeded to the economic assessment, finding the key limits for the industrial implementation of the process. In most cases, e.g. for the production of hydrogen and syngas, the cornerstone for the economic feasibility was the availability of a cheaper raw material, i.e. diluted bioethanol (40-50 wt%). The calculated minimum hydrogen selling price was 1.91 USD/kg, to be compared with a present standard value from methane steam reforming of 1.80 USD/kg. This calculation was made for a system capable of producing 7793 ton/year of H2 starting from 40000 ton/year of bioethanol. Also for bioethylene production we have experimentally demonstrated the possibility to use diluted bioethanol even for this dehydration reaction, operating at slightly higher temperature than with anhydrous ethanol. Accordingly, a full process flowsheet was designed, whose economic assessment demonstrated the possibility to produce bioethylene with 1.15-3.03 USD/kg production cost depending on the cost of diluted bioethanol (0.30-1.00 USD/kg), in many scenarios competitive with the current production cost in different countries. Finally, another C2 compound with huge industrial applications is ethylene oxide, which may be in principle obtained in two steps following the route bioethanol  bio-ethylene  bio-ethylene oxide. This is the basis of the CRODA process currently proposed for the production of bio-derived ethylene oxide. Recently, a one-pot synthesis has been proposed, considerably simplifying the production process. Accordingly, we designed from the grass roots a new production plant including the reactive and purification sections to exploit it industrially. Kinetic parameters for the reaction have been derived by regression of experimental literature data with a power law pseudo-homogeneous model and they were used for a preliminary sizing of the reactor. A shell&tube heat exchange reactor was implemented to control the exothermicity of the reaction, with simultaneous steam production and three catalyst layers (200, 500 and 2000 kg) with intercooling. 99.5% ethanol conversion and 84% selectivity to ethylene oxide were achieved, with ca. 100 kmol/h productivity, starting from the feedstock availability of a commercial bio-refinery. The product is first recovered with an absorption column (releasing most N2, CO, O2 and CO2 in gas phase, followed by a stripping column. A further distillation column separates crude ethylene oxide as distillate, while acetaldehyde, diethyl ether and minor impurities as bottom product. Further purification options for ethylene oxide and for the recovery of by-products were also compared to generate different scenarios for the economic assessment of the plant.