Phenol → Alpha-Methylstyrene

Participants

Reaction Steps

The current process of choice for commercial phenol production utilizes the autocatalytic cumene/air oxidation to cumene hydroperoxide (CHP) route for over 50% of the world's production of phenol. A key step in this process is the decomposition (cleavage) of CHP produced in the oxidation section of the plant to phenol and acetone using dilute mineral acid (H2SO4) as an acid catalyst. Use of the liquid acid requires subsequent neutralization and purification of the phenol at substantial cost, and a waste stream generation that could be avoided if an effective solid acid catalyst could be used. CHP decomposition is a very exothermic reaction which is normally carried out on a commercial scale in continuous stirred or back-mixed reactors. In such reactors only a small fraction of CHP is unreacted at any given time and the reaction medium consists essentially of the products of decomposition of CHP, i.e., phenol and acetone, plus any solvent (e.g., cumene and/or recycle acetone) and other materials added with CHP to the reactor. During cumene oxidation small amounts of dimethylphenylcarbinol (DMPC) and acetophenone are also formed. In the presence of acid catalyst, DMPC dehydrates to alpha-methylstyrene (AMS), a useful by-product. Very high yields of AMS can be obtained from pure DMPC, e.g., 98% yield upon dehydration over acidic silica at 300° C. In the presence of phenol, however, and more specifically in a phenol/acetone/cumene mixture which is a solvent in the decomposition of CHP/DMPC mixtures, the ultimate AMS yield is normally about 50-60 mol % of the DMPC. Main by-products are AMS dimers and cumylphenol which have no commercial value. Formation of cumylphenol also reduces the phenol yield.

Provenance & Evidence