The present invention provides process for preparing an alkylate comprising contacting in a reaction zone a hydrocarbon mixture comprising at least an isoparaffin and an olefin with an acidic ionic liquid catalyst under alkylation conditions to obtain an alkylate-comprising effluent, in which process: —solids are formed in the reaction zone; —a solids-comprising effluent comprising hydrocarbons and acidic ionic liquid is withdrawn from the reaction zone; and—at least part of the solids-comprising effluent is treated to remove at least part of the solids to obtain a solids-depleted effluent. The invention further provides a process for treating an acidic ionic liquid comprising at least 0.1 wt % of solids based on the total weight of the acidic ionic liquid, wherein at least part of the solids are removed.