A process includes hydrogenating, in a reaction zone, a highly unsaturated hydrocarbon received from a hydrocarbon stream to yield a product having an unsaturated hydrocarbon, the hydrogenating step occurring in the presence of a hydrogenation catalyst which has a selectivity for conversion of the highly unsaturated hydrocarbon to the unsaturated hydrocarbon of about 90 mol % or greater based on the moles of the highly unsaturated hydrocarbon which are converted to the product, the hydrogenating step occurring in a reaction zone under conditions which include a flow index (IF) in a range of about 0.09 to about 35, wherein the IF is defined as: I F = F × [ CO ] V , wherein F is the flow rate of the hydrocarbon stream into the reaction zone in units of kg/h, [CO] is the concentration of carbon monoxide in the hydrocarbon stream in units of mol %, and V is the volume of the reaction zone in units of ft3.