The Thermodynamics, Mechanism and Kinetics of the Catalytic Conversion of Propylene and Water to Diisopropyl Ether over Amberlyst 15

Abstract

Diisopropyl ether (DIPE) was synthesised in a single step from a feed of propylene and

water over Amberlyst 15 ion exchange resin catalyst. It was produced in a trickle bed

reactor at pressures between 1 bar and 60 bar, at temperatures between 70°C and 160°C

and at overall propylene to water ratios between 1 : 5 and 10 : 1. Reaction proceeded

in the liquid phase within the catalyst particles. The only reactions that occurred in

the system were the hydration of propylene to form isopropanol (IPA) , the alkylation

of IPA with propylene to form DIPE and the bimolecular dehydration of IP A to form

DIPE and water. No side reactions such as propylene oligomerisation were observed.

Starting from a feed of propylene and water the primary reaction product was IPA. IPA

was subsequently consumed in two secondary reactions which produced DIPE. DIPE was

produced either by the alkylation of IPA with propylene or by the bimolecular dehydration

of IPA. It was generally not possible to study the two DIPE formation reactions separately

as they are linked via the propylene hydration reaction. All experimental data was thus

reported in terms of a hydration rate and an etherification rate, the latter being the sum

of the IPA alkylation and the bimolecular IPA dehydration rates.

The reactions to produce IPA and DIPE over Amberlyst 15 proceeded via two different

mechanisms, the so-called Type I and Type II mechanisms. The ratio of apolar (propylene

and DIPE) to polar (water and IPA) species and the overall species concentration in the

reaction medium determined the dominant mechanism. Type I mechanisms predominated

at low ratios of apolar to polar species in the reaction medium. When the ratio of apolar

to polar species about 1:2 the Type II mechanisms became predominant.