A ternary semicontinuous system for the separation of bio-dimethyl ether from methanol and water is presented. The performance of eight potential control configurations, including the application of temperature inferential control, is evaluated. Dynamic simulations of the semicontinuous system and associated control scheme demonstrate that the temperature inferential control configuration is effective in achieving the separation objectives while remaining within operational limits. The semicontinuous system using the inferential temperature control scheme is simulated and shown to be economically preferable to the traditional continuous process for a range of production rates.

Since the year 2000, semicontinuous separation processes have been studied as a unique process intensification technique for the thermal separation of chemical mixtures. Typically, a single separation unit is used for multiple purposes with the aid of an auxiliary storage tank called a middle vessel. The system is operated cyclically but without startup or shutdown phases. As a result, multiple separation steps can be carried out with fewer capital expenses. In several cases, a significant profitability advantage over continuous or batch process alternatives has been shown, particularly for intermediate production capacities. The progress in semicontinuous systems is reviewed, including the development of semicontinuous ternary distillation, liquid-liquid extraction, azeotrope distillation, reactive distillation, and semicontinuous systems with integrated reaction and distillation or extraction. Control and operational strategies for semicontinuous systems are reviewed, as well as heuristics for modeling and simulation.

In this work, a semicontinuous system is investigated for the separation of biomass-derived dimethyl ether from a vapor−liquid mixture. This novel semicontinuous system operates in a cyclic campaign and utilizes one partial condenser column coupled with a middle vessel to achieve the separation typically carried out using two continuous distillation columns. The performance of six control configurations based on composition or temperature inferential control were analyzed. Dynamic simulation results demonstrate the effectiveness of the semicontinuous system and its temperature inferential control configuration in achieving the separation objectives, remaining within operational limits and rejecting fresh feed disturbances. Finally, the semicontinuous system is compared to the traditional continuous system from an economic standpoint with the sensitivity of operating cost to middle vessel product target purity highlighted.