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Acetonitrile from Bioethanol Ammoxidation: Process Design from the Grass-Roots and Life Cycle Analysis

Tripodi, Antonio, Bahadori, Elnaz, Cespi, Daniele, Passarini, Fabrizio, Cavani, Fabrizio, Tabanelli, Tommaso, Rossetti, Ilenia
ACS sustainable chemistry & engineering 2018 v.6 no.4 pp. 5441-5451
acetonitrile, air, ammonia, ammonium bicarbonate, bioethanol, byproducts, carbon, carbon dioxide, catalysts, climate change, corn, cyanides, economic analysis, ecosystems, ethanol, fossils, life cycle assessment, lignocellulose, markets, nitrogen, nonrenewable resources, process design, raw materials, sugarcane, toxicity, wood
The growing interest for new routes to obtain acetonitrile led to the development of catalysts active toward the ammoxidation of various substrates. Among these, a C2 molecule such as ethanol represents a good choice in terms of atom economy and, being renewable, sets the basis for a long-term sustainable process. This paper describes a fully integrated, newly designed process for the production of acetonitrile from bioethanol, currently not present in the literature. The target is the production and purification of 10 kg/h of acetonitrile, unit of production used for calculations, obtained from ethanol, ammonia, and air as raw materials. All the byproducts, mainly ammonium bicarbonate and sodium cyanide, are considered marketable chemicals and represent an added value, instead of a disposal issue. Their optimized recovery is included in this flowsheet as a basis for the future economic assessment of the system. The process consumes CO₂ without its direct emission. In principle, all the carbon atoms and 90% of the nitrogen atoms are turned into reaction products, and the main loss is gaseous N₂. The process design has been performed by means of the Aspen PLUS process simulator, on the basis of literature data and other experimental results. In addition, for an evaluation of the potential benefits of the innovative biobased route, a life cycle analysis was carried out including all the stages involved in the bioacetonitrile production (from raw materials extraction up to the gate plant). The results were then compared with those achieved for the traditional fossil route (SOHIO process), showing a sensible decrease of the environmental burdens in terms of nonrenewable resources and damage to ecosystems (e.g., toxicity, climate change, etc.). Finally, a simplified sensitivity analysis was carried out by substituting the starting raw material for the production of bioethanol (corn) with other materials conventionally used worldwide, such as sugar cane and wood. The latter option seems to make the system more competitive in terms of carbon neutrality, thanks to the usage of the residual lignocellulosic fraction available on the market.