The reactive distillation process for MTBE differs from the conventional process in the combination of the second reaction stage (adiabatic) with the purification column and the elimination of some peripheral equipment. The modified process is depicted in Figure 6.2.
reactive zone one reaction stage only u mater .
Figure 6 2 - Ether Synthesis Via Reactive Distillation
The pretreatment stage is unaffected. The operation of the first reaction stage (isothermal) can also remain unchanged. Although it is technically possible to perform all of the reaction inside a reactive distillation environment, it is not practical to do so due to the difficulty of installing and removing catalyst from inside the column. Retaining the first reaction stage from the conventional process unloads the catalyst inside the column and provides further protection against deactivation. It also reduces the amount of heat liberated inside the column which might otherwise produce problems (e.g. localised flash boiling). Slightly higher conversions can also be achieved by retaining the primary reaction stage.
The purification column used in the reactive distillation process differs from that used in the conventional process with the installation of catalyst on trays or packed sections above the feed point. Some non-reactive stages are still required above and below the reactive section to produce the necessary separation between products and reactants. The reactive distillation column is, therefore, actually a hybrid column that contains a reactive distillation section and two non-reactive distillation sections.
The column operating conditions required in the reactive distillation process are comparable to what would be used in the conventional process. Similar overhead pressures should be used in both reactive and non-reactive distillation columns. A similar reboiler duty should be used too. This produces an increase in the condenser duty as the heat of reaction effectively adds to the column heat input. However, the additional vapour-liquid traffic creatcd by the higher condenser duty (and higher overall heat input) maximises the benefits of adding the catalyst. The only really worthwhile change suggested for the reactive distillation process is to move the feed-point a few stages closer to the condenser. This improves the overall performance of the column by making it easier to achieve high ether product concentrations. Further optimisation can be undertaken but the advantages of reactive distillation should already be evident after these simple changes. The operation of the recovery system should also remain essentially unchanged as the only differences arise through slight compositional changes in the distillate product.
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