An impeller is applied to a centrifugal fan and includes fan blades and a hub. The preheated aromatic feedstock is contacted with the preheated methanol under alkylation conditions in the reactor in the presence of a catalyst so that the methanol reacts with the aromatic feedstock to produce an effluent comprising para-xylene. The etching solution is made up of a catalytic nanomaterial and an oxidant-etchant solution.