Acidic ionic liquids of the type [cation] [bis (trifluoromethanesulfonyl)2 N]/AlCl 3 } have been applied to realise for the first time a continuous Friedel-Crafts alkylation reaction in liquid-liquid biphasic reaction mode using a loop reactor concept. Exemplified for the continuous propylation of toluene we have proved that the acidic catalyst layer is successfully immobilised over at least 18 h in the loop reactor. After 8 h time-on-stream, a steady state has been reached followed by at least 10 h time-onstream without any loss of activity or change in selectivity. Our results reveal the high potential of this class of acidic ionic liquids in continuous arene functionalisation reactions.