It is concluded that the NEQ stage model is more accurate than the EQ stage model. The reason may be that in actual operation, trays rarely, if ever, operate at equilibrium, especially when the solid particles are added in the SCD column. So it is advisable to select the NEQ stage model, or the combination of the EQ stage model and tray efficiency, for the design and optimization of the SCD column, which will help the future scale-up of the SCD techniques in industry.

In FCD and SCD, the requirements of high liquid or catalyst holdup aren't consistent with the requirements of good in situ separation. Apart from this, a new-type side-reactor or external reactor concept is proposed [19], It may belong to the scope of catalytic distillation. In the side-reactor concept the reactor feed is withdrawn from the distillation column and the reactor effluent is returned back to the same column. The side reactor could be a conventional catalytic-packed bed reactor operating in liquid phase and therefore, there are no hardware design problems or conflicting requirements with regard to in situ separation. Furthermore, the reaction conditions within the side reactor (e.g. temperature) can be adjusted independently of those prevailing in the distillation column by appropriate heat exchange.

Four configurations of linking the side reactors to the distillation column can be designed, as shown in Fig. 30. In order to meet the process requirements of conversion, more than one side reactor may be necessary. Apparently, the determination of the optimum number of side reactors, along with the liquid draw-off and feed-back points to the distillation column, need careful attention and consideration. An algorithm to determine an optimum configuration of the side-reactor concept in order to maximize conversion has been developed.

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