Catalytic Dehydration of Isomeric Phenylethanols on Alumina in the Presence of Excess Water

In the process of coproduction of propylene oxide and styrene (PO/SM), a stream containing isomeric phenylethanols is fed to the dehydration stage. In this work, the contribution of acid sites of different nature and strength to the activity of aluminum oxide-based catalysts in the dehydration reaction of 1- and 2-phenylethanols occurring in the presence of excess water in the temperature range of 230-300°C is compared. It was found that over the entire studied temperature range: the rate of intramolecular dehydration of the primary alcohol is significantly lower than the rate of dehydration of the secondary alcohol; the dehydrating activity of the catalysts with respect to both alcohols is determined primarily by acid sites of the LAS I and LAS II types; the temperature of manifestation of the dehydrating activity of LAS III type sites with respect to the primary alcohol is ~50°C higher compared to the secondary alcohol. The type of kinetic equation for the target reaction is substantiated, the values ​​of the observed rate constants are calculated. It was found that for both alcohols the change in the pre-exponential factor is directly proportional to the change in the Arrhenius activation energy, while the observed activation energy of the dehydration reaction of the primary alcohol significantly exceeds the activation energy of the dehydration of the secondary alcohol.