An improved reactor for an HF alkylation unit of the shell-and-tube heat exchanger type has an axial tube bundle to provide cooling for the reactor and a centrally-located axial sparger system for injecting and dispersing the hydrocarbon reactants into the flow path in the reactor. The sparger comprises an axially-extensive tube with outlet nozzles for the hydrocarbon reactants arranged around the tube, preferably with differing radial angles, at different locations along the length of the sparger.