The regeneration of HF alkylation acid in an alkylation unit is improved by withdrawing a vapor stream from the HF regenerator tower and condensing the stream to form a liquid fraction which is accumulated in a side distillation zone; the collected liquid fraction, comprising HF acid, water and some stripping medium is distilled in a batch or continuous type operation to drive off the HF acid (along with stripping medium) and the vapor is returned to the regenerator-stripper vessel. The distillation of the sidedraw liquid is continued until the composition of the liquid attains the azeotropic value or as near to that value as desired. The azeotrope, comprising water and acid can then be dropped out of the distillation vessel for disposal by neutralization in the conventional way.