ETHERS FROM ETHANOL .4. KINETICS OF THE LIQUID-PHASE SYNTHESIS OF 2 TERT-HEXYL ETHYL ETHERS

Tertiary ethers produced from reactive C-5 and C-6 olefins and ethanol or methanol are being investigated as oxygenate gasoline additives in addition to isobutylene-derived methyl tert-butyl ether and ethyl ter t-butyl ether. The kinetics of liquid-phase etherification and accompa nying isomerization of four reactive C-6 olefin isomers with ethanol c atalyzed by the ion-exchange resin catalyst Amberlyst 15 were determin ed at temperatures from 313 to 353 K and a pressure of 0.69 MPa in a d ifferential packed-bed reactor. Rate expressions in terms of species a ctivities, with the activity coefficients determined by the UNIFAC met hod, were developed to correlate the experimental data over a wide ran ge of compositions. The rate expressions are based on the Langmuir-Hin shelwood-Hougen-Watson formalism involving a dual-site surface etherif ication reaction and a single-site surface isomerization reaction as t he rate-limiting steps, along with the assumption of ethanol as the mo st abundant surface species. The negligibility of olefins and ether ad sorption terms, but the nonnegligibility of vacant sites, was confirme d by independent liquid-phase adsorption experiments. The developed ra te expressions were finally tested in an integral reactor and found to be accurate.