Industrial Applications of Reactive Distillation

Introduction

Reactive distillation (RD) is a combination of separation and reaction in a single vessel. The concept of combining these two important functions for enhancement of overall performance is not new to the chemical engineering world. The recovery of ammonia in the classic Solvay process for soda ash of the 1860s may be cited as probably the first commercial application of RD, as shown in Fig. 1.1. Many old processes have made use of this concept. The production of propylene oxide, ethylene dichloride, sodium methoxide, and various esters of carboxylic acids are some examples of processes in which RD has found a place in some form or the other, without attracting attention as a different class of operation. It was not until the 1980s, thanks to the enormous demand for MTBE (methyl tert-butyl ether), that the process gained separate status as a promising multifunctional reactor and separator.

The commercial success of RD for the production of MTBE was immediately followed by another remarkable achievement with the Eastman Kodak process that condensed the whole chemical plant for methyl acetate in a single RD unit that accepts reactants and delivers pure products. Since this demonstration of its ability to render cost-effectiveness and compactness to the chemical plant, RD has been explored as a potentially important process for several other chemicals and reactions. Along with esterifications and etherification, other reactions such as acetali-zation, hydrogenation, alkylation, and hydration have been explored. This chapter gives an overview of the efforts being made in this direction and suggests some potentially important processes for RD. The objectives of existing and potential applications of RD are to: surpass equilibrium limitation, achieve high selectivity towards a desired product, achieve energy integration, perform difficult separations, and so on. One or more of these benefits are offered by the processes in which RD

Reactive Distillation
Fig. 1.1 Ammonia recovery in Solvay process

is used. Tab. 1 gives a comprehensive list of the reactions that have been investigated as candidates for RD. Tab. 2 suggests some potentially important reactions that should be investigated. Because of the large number of such reactions, it is not possible to describe each reacting system in detail here. The application of RD to the most important reactions is described here to give an overview of the issues related to industrial use of RD.

Table 1.1 Industrially important reactions, either implemented on a commercial scale or have been investigated on laboratory scale, using RD.

Reaction

Catalyst/column internals etc.

Remarks on motives and achievements

Reference

Etherification methanol + isobutene = methyl tert butyl ether (MTBE) Amberlyst-15

methanol + isoamylene = tert amyl methyl ether (TAME) ion-exchange resin ethanol/bioethanol + tert butyl alcohol = ethyl tert butyl Amberlyst-15 pellet ether (ETBE) + water isopropanol + propylene = diisopropyl ether (DIPE)

structured Amberlyst-15 ZSM 12, Amberlyst-36

Zeolite to enhance the conversion of isobutene and [1, 2] achieve separation if isobutene from C4 stream to enhance the conversion of isoamylene [1, 3]

to effectively utilize bioethanol and surpass [4]

equilibrium conversion a two-stage process that uses water and [5]

propylene as feed

Esterification with alcohols/olefins acetic acid + methanol = methyl acetate + water

Dowex 50 W X-8

Amberlyst-15 (baskets on trays)

Katamax packing sulfuric acid butanol + acetic acid = butyl acetate + water cation exchange resin

2-methyl propanol + acetic acid = 2-methyl propyl acetate Katapak-S lactic acid + methanol = methyl lactate + water Dowex 50-W

myristic acid + isopropanol = isopropyl myristate + water recovery of acetic acid from dilute streams [6]

recovery of acetic acid from dilute streams [7]

recovery of dilute acetic acid in carbonylation [9] process manufacture of methyl acetate; overcomes [12]

azeotrope formation; enhances conversion (> 99%)

for recovery of acetic acid from dilute aqueous [13, 14] solutions manufacture of 2-methyl propyl acetate [15]

for recovery of lactic acid from fermentation [16] broth for recovery of myristic acid [17]

Table 1.1 (continued)

Reaction

Catalyst/column internals etc.

Remarks on motives and achievements

Reference

Esterification with alcohols/olefins

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