Reactive Distillation Technology - Process Intensification for Green Chemistry - page 248

by constraints such as: common operation range for distillation and reaction (similar
temperature and pressure), proper boiling point sequence (product should be the lightest or
heaviest component, and side or byproducts the mid-boiling ones) and difficulties in
providing proper residence time characteristics [6].
A small number of industrial applications of RD have been around for many decades [1],
but even today the RD crown is carried by the Eastman process, which reportedly replaced
a methyl acetate production plant with a single reactive distillation column (RDC) using
80% less energy at only 20% of the investment costs [7,8]. Nowadays, the application with
the largest number of installations is methyl tertiary butyl ether (MTBE), which is used in
gasoline blending. Other esters, such as ethyl tertiary butyl ether (ETBE), tert-amyl methyl
ether (TAME) and fatty acid methyl ester (FAME), are also now produced by RD [4,5,9].
Considering the large extent of the topic, this chapter aims only to give a brief overview
of RD. For more detailed information, the reader is kindly directed to several topics and
reviews published in the last decade, covering a large range of subjects concerning RD:
process synthesis, conceptual design, control, operation, optimization, equipment and
industrial applications [1,2,4,5,10-15].
9.2 Principles of RD
RD is especially attractive in systems where certain chemical and phase equilibrium
conditions co-exist. The reaction and distillation take place in the same zone of a distillation
column, the reactants being converted with simultaneous separation of the products and
recycle of unused reactants. As the products must be separated from the reactants by
distillation, this implies that the products should be lighter and/or heavier than the reactants.
The ideal case is where one product is the lightest and the other product is the heaviest,
while the reactants are the intermediate boiling components [1]. Moreover, as both
operations occur simultaneously in the same unit, there must be a proper match between
the temperatures and pressures required for reaction and separation [6,16] - as clearly
illustrated by Figure 9.1 (left). If there is no significant overlapping of the operating
conditions of reaction and separation, the combination of reaction and distillation is not
possible (e.g. a high-pressure reaction cannot be combined with a vacuum distillation).
Furthermore, one must also consider that working in the limited overlapping window of
Figure 9.1 Left: overlapping of operating windows for reaction, separation and equipment.
Right: reaction types used in RD [17].