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Fig. 8.17 Influence of cross-linking of polymer/ceramic ion-exchange catalysts for the dimeri-zation of isobutene during MTBE synthesis at low polymer loading

Influence of Cross-Linking at High Polymer Content

As mentioned above, low polymer loading gives reaction rate curves with the shape observed for commercial macroporous catalysts (maximum for the reaction rate in the region of low methanol concentration).

Different behavior was observed for the samples with higher polymer content. These curves show no maximum (Fig. 8.18). For all tested catalysts, activity for MTBE is nearly the same. Cross-linking in these cases is of minor importance. At low methanol concentrations the rate drops for all samples. The reason for this is that the polymer loading in the pore volume of the carrier causes a transport limitation for isobutene. So the typical activity pattern for macroporous resins cannot be observed. For the operation of an RD column this is beneficial; drastic changes in the rate caused by fluid phase concentration changes do not occur. The whole packing in the column can be approximated with one rate, especially in the concentration range of industrial plants.

As measured for the samples with low polymer content, the selectivity for MTBE rises with increasing cross-linking (Fig. 8.19). Selectivity is in general lower compared with the catalysts with low polymer content. In the methanol concentration range of industrial RD processes, selectivity is high and no by-products were detected. The highly cross-linked catalyst differs from the two other samples. At first no dimer was formed, but when dimerization started it increases with a steeper slope. This behavior is the same as for the low polymer loaded catalyst. A possible reason is the different swelling of the polymer particles resulting in a more swollen resin at low cross-linking. Mass transport of isobutene may become limited in the larger gel particles.

Fig. 8.18 Influence of cross-linking of polymer/ceramic ion-exchange catalysts on the activity of the MTBE synthesis at high polymer loading

Methanol concentration, cMiOH Emol/I]

Fig. 8.19 Influence of cross-linking of polymer/ceramic ion-exchange catalysts for the dimeri-zation of isobutene during MTBE synthesis at high polymer loading

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Methanol concentration, cMiOH Emol/I]

Fig. 8.19 Influence of cross-linking of polymer/ceramic ion-exchange catalysts for the dimeri-zation of isobutene during MTBE synthesis at high polymer loading

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