Semicontinuous separation processes combine a single column with one or more middle vessels to perform multi-species separations which normally require multiple columns using traditional continuous methods. The semicontinuous process can be further intensified by incorporating reaction, either in the column or in one or more middle vessels. With this novel process configuration, significant capital cost and/or energy savings may be achieved over traditional batch or continuous designs, particularly at intermediate production rates. Examples of such processes include ternary semicontinuous distillation [1], semicontinuous distillation with auxiliary reaction [2], semicontinuous distillation with reaction in a middle vessel [3], semicontinuous reactive extraction coupled with semicontinuous reactive distillation [4], and others.

Based upon these processes, a set of generalized design heuristics are presented in this work. These include:

1. The classification of semicontinuous processes into three design schemes, and conditions preferable for each.

2. Heuristics for integrating common chemical reaction systems into semicontinuous processes (that is, in the column, in a middle vessel, etc.)

3. Heuristics for handling controllability issues, such as configurations for dynamic set-point tracking and the prevention of flooding and weeping in distillation columns.

4. Process configurations for the transitional modes, when the columns shift from one operation to another.

The heuristics presented in this work will help engineers to determine the configuration, operational recipe, and control structure of semicontinuous processes in the conceptual design stages. Properties such as the order of the relative volatilities of the chemical species, the structure of the chemical reactions, the presence of azeotropes, etc., are the basis for these heuristics.

References

1. Phimister, J. R. and W. D. Seider, "Semicontinuous, middle-vessel distillation of ternary mixtures." AIChE J., 46, 8 (2000): pp. 1508-1520.

2. Adams II, T. A., and W. D. Seider, “Ethyl Lactate Production Using Semicontinuous Distillation with Reaction in an Auxiliary Vessel and Pervaporation,” 2007 AIChE Spring Nat'l. Meet., Houston, TX, Apr 23-27 2007.

3. Adams II, T. A., and W. D. Seider, “Semicontinuous Reactive Distillation for Specialty Chemical Production: Economic Comparison with Batch and Continuous Processing,” 2005 AIChE Fall Nat'l. Meet., Cincinnati, OH, Oct 30-Nov 2 2005; p 6251-6257. Plenary session.

4. Adams II, T. A., and W. D. Seider, “Semicontinuous Process Intensification: Combining Reactive Extraction, Reactive Distillation, And Binary Distillation For Production Of 1,3-Propanediol”, 2007 AIChE Annual Meet., Salt Lake City, UT, Nov 4-9, 2007.