Pressure-swing or extraction-distillation for the recovery of pure acetonitrile from ethanol ammoxidation process : a comparison of efficiency and cost

Acetonitrile is increasingly used as solvent for the fine chemicals and pharmaceutical industries. Ethanol ammoxidation has been proposed as an alternative way for its production starting from a renewable source. This process leads to a complex mixture of products, which needs an optimized separation train to maximize the recovery and purity of acetonitrile. Pressure swing distillation, operated at 7 and 10 bar, has been compared as for feasibility and economic impact with the extractive distillation using dichloromethane as entrainer. The pressure swing option led to higher CH3CN recovery (95.5%) with respect to extractive distillation (92.1%), irrespectively from the operating pressure. Furthermore, the pressure swing option allowed to tune more easily product purity by adding or removing trays in the stripping section of the high pressure column, leaving water as the only impurity. Similar results were obtained when operating the pressure swing between 1 and 7 bar or 1 and 10 bar, but the operation at 10 bar was characterised by lower installation and operating costs, thus it was considered as optimal. The same economical evaluation was carried out for the extractive distillation option, which revealed more expensive with respect to pressure swing. Different energy integration options have been also compared.