Conceptual reactive distillation columns

Melles S., Grievink J. and Schrans S.M. (2000). Optimization of the conceptual design of reactive distillation columns. Chemical Engineering Science 55, 2089-2097. 3.2.4, 6.1.3... 

Flowsheets for processes are sometimes generated without following the hierarchy of properties described previously. As an example, Siirola [20] proposed a reactive-distiUation solution to make methyl acetate. Unit operations that combine the property differences present abrupt departures from common methodologies. With the advent of various pieces of equipment, such as differential side-stream feed reactors (i.e., semicontinuously fed batch reactors), continuous evaporator-reactors (e.g., wiped-film evaporators), and reactive distillation columns, one can consider these unit operations in the development of conceptual designs. As an example, Doherty and Malone [21] have presented systematic methods for reactive distillation design. 

These books deal primarily with the steady-state design of reactive distillation columns. Conceptual approximate design approaches are emphasized. There is little treatment of rigorous design approaches using commercial simulators. The issues of dynamics and control... 

Dragomir R. M. and M. Jobson, Conceptual design of single-feed hybrid reactive distillation columns, Chem. Eng. Sci. 60, 4377 4395 (2005). 

Several hundred papers and patents have appeared in the area of reactive distillation, which are too numerous to discuss. A number of books have dealt with the subject such as (1) Distillation, Principles and Practice by Stichhnair and Fair, (2) Conceptual Design of Distillation Systems by Doherty and Malone," and (3) Reactive Distillation— Status and Future Directions by Sundmacher and Kienle. These books deal primarily with the steady-state design of reactive distillation columns. Conceptual approximate design approaches are emphasized, but there is little treatment of rigorous design approaches using commercial simulators. The issues of dynamics and control stmcture development are not covered. Few quantitative eeonomic comparisons of conventional multiunit processes with reactive distillation are provided. 

Most of the published literature on reactive distillation (RD) has been focussed mainly on aspects such as conceptual design with the aid of residue curve maps, steady-state multiplicity and bifurcations, and development of equilibrium (EQ) stage and rigorous non-equilibrium (NEQ) steady-state and dynamic models [1, 2]. Relatively little attention has been paid to hardware design. In this chapter the concepts underlying the selection of the appropriate hardware for RD columns are discussed. For RD column design, detailed information on hydrodynamics and mass transfer for the chosen hardware is required, but this information is often lacking. Modern tools such as computational fluid dynamics (CFD) can be invaluable aids in hydrodynamic and mass-transfer studies. 

The above flowsheet can be simplified tremendously by catalytic distillation. Figure 7.32 depicts a conceptual configuration. The RD column consists of a reactive zone at the top, and a distillation section at the bottom. The reaction mixture is sent to a purification column, from which ethylbenzene is obtained as top distillate. A side-stream containing PEB is sent to transalkylation for EB recovery. Obviously, the feasibility of this process depends largely on the availability of an active and selective catalyst. For zeolites the optimal operating conditions are about pressure around 3 MPa, temperature less than 200 °C, and reaction rate capable to give a space-time of 5 h" for almost complete ethylene conversion. 

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