MTBE and TAME Synthesis

A third class of RD processes that are known to show intricate nonlinear behavior, are processes for the production of fuel ethers methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME). These are produced by etherification of iso-olefins with methanol according to 

The reactions are catalyzed by strong acid ion-exchange resins and are usually carried out in the presence of inert components. For MTBE synthesis the iso-olefin is isobutylene and for TAME synthesis the iso-olefins are 2-methyl-l-butene and 2-methyl-2-butene. Further details on the chemistry of etherification processes are given in Chapter 5. 

First simulation results on steady state multiplicity of etherification processes were obtained for the MTBE process by Jacobs and Krishna [45] and Nijhuis et al. [78]. These findings attracted considerable interest and triggered further research by others (e. g., [36, 80, 93]). In these papers, a column pressure of 11 bar has been considered, where the process is close to chemical equilibrium. Further, transport processes between vapor, liquid, and catalyst phase as well as transport processes inside the porous catalyst were neglected in a first step. Consequently, the multiplicity is caused by the special properties of the simultaneous phase and reaction equilibrium in such a system and can therefore be explained by means of reactive residue curve maps using oo/ -analysis [34, 35]. A similar type of multiplicity can occur in non-reactive azeotropic distillation [8]. 

However, it was shown that for the above conditions the multiplicity regions in the space of the adjustable operating parameters are fairly small for the MTBE process ]73]. This is illustrated in Fig. 10.13 for the pilot plant column treated in ]72, 73]. The bifurcation parameters are the heating rate Q and the reflux ratio R, which can be directly adjusted at the real plant. The parameter range is further decreased if a finite mass transfer between the vapor and the hquid phase is taken into account as shown in ]5, 40] for the column configuration of Jacobs and Krishna ]45]. Moreover, the multiplicity regions even seem to disappear entirely, when finite transport processes are taken additionally into account inside the catalyst [39]. Hence, practical relevance seems to be low. 

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Commercial MTBE (and TAME) synthesis occurs at about 1.5 MPa and 100°C in the liquid phase over an acid resin catalyst that is based on the sulfonic acid group -SO H. The synthesis reaction is sli tly exothermic and limited by equilibrium under the conditions of the commercial operation ... 

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