Results of thermodynamic analysis of reactions occurring during the alkylation of benzene with C-9-C-14 olefins, including the reversible reactions of formation of high-molecular-mass aromatic hydrocarbons, are presented. The thermodynamic relationships revealed have formed the basis for deriving a mathematical model of the alkylation process with allowance for alteration in the activity of the HF catalyst. It has been shown that the buildup of higher aromatic hydrocarbons in the alkylation reactor has a detrimental effect on the properties of HF. Operating modes and controlling parameters of the main stages of the production f linear alkylbenzenes to ensure the maximal efficiency of the process and maintain the activity of the HF catalyst at the optimal level have been determined.