TAME Synthesis

Despite the similar reaction mechanism, a completely different type of behavior was found for the TAME process [71-73]. This is due to the fact that the rate of reaction is one order of magnitude slower for TAME synthesis compared to MTBE synthesis. The behavior of the TAME process is illustrated in Fig. 10.14. In contrast to the MTBE process the TAME column is operated in the kinetic regime of the chemical reaction at a pressure of 2 bar. Under these conditions large parameter ranges with multiple steady states occur. The more detailed analysis by Mohl et al. [73] reveals that steady state multiplicity of the TAME process is caused by self-inhibition of the chemical reaction by the reactant methanol, which is adsorbed preferably on the catalyst surface. Steady state multiplicity is therefore caused by the nonlinear concentration dependence of the chemical reaction rate. Consequently, a similar type of behavior can be observed for an isothermal CSTR. This effect is further in-

Fig. 10.14 TAME process at p = 2 bar. Bifurcation diagram for different reflux ratios R (left), O denotes total reboil. Multiplicity region in the R/Q parameter plane (right)

creased for an RD column with simultaneous reaction and separation. A comparison of the multiplicity regions of an isothermal CSTR, a one-stage RD column, and the pilot plant column shown in Fig. 10.14 has been given [73].

Because of the large multiplicity regions, multiple steady states of the TAME process were also verified experimentally as illustrated in Fig. 10.15 [71, 73, 85]. For this purpose suitable startup strategies were developed by means of dynamic simulation to operate the column directly into the desired steady state. Further, it was

340 350

temperature [KJ

heating rate [kW]

packing of cat. rings il F6 (azcotropic

[ 1 F7 concentration)

packing of inert rings

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