Reaction kinetics in production of isopropyl ether catalyzed by ion exchange resin.

Isopropyl ether (IPE) is an excellent solvent for the extraction of many chemicals. It used to be produced as a by-product in isopropyl alcohol (IPA) plants, based on sulfuric acid hydration. IPE, however, ceased to be produced by this method, as catalytic direct hydration of propylene (C₃') took the place of sulfuric acid hydration. At this juncture, a new IPE process, carried out with the reaction of IPA with C₃', using SO₃H type ion exchange resin catalyst, was developed. This paper describes the reaction mechanism and the effects of reaction temperature, LHSV, reaction pressure and mol ratio of the feed (C₃'/IPA), for the purpose of commercializing the new IPE process.<br>Experiments were comprised of reactions using both continuous and batch type reactors and gas chromatographic analyses of the reaction products.<br>Experimental data showed that the rate-determining step of this reaction was chemical and not diffusive, because the influence of linear velocity was not observed (Table 1) and the activation energy was 12.2kcal/mol, calculated by Arrhenius' plotting of the first order rate constants of C₃' (Fig. 3).<br>The rate-determining step was proposed to be the step where C₃' attacks oxonium ion of IPA formed rapidly in the ion exchange resin, in reference to the literatures 5), 6), 7) describing the interaction between alcohols and SO₃H type ion exchange resins.<br>The reaction rate charts were completed (Figs. 4, 5), showing the conversion and space time yield (STY; IPE(g)/catalyst(g)/h) at a given temperature and LHSV.<br>Above the critical temperature of C₃' (91.6°C), conversion decreased as the reaction pressure was lowered below 30kg/cm², but the influence of the reaction pressure was hardly observed above 30kg/cm² (Fig. 6).<br>Figs. 7 and 8 show the equilibrium conversions at temperatures of 112.5°C and 130°, and in accordance with this relation, the exothermic heat of reaction was found to be 11.1kcal/mol.<br>Fig. 9 illustrates the plot of the value of [IPA/(IPA+ C₃')]×100 in the reaction product against the reaction temperature, in the mol ratio of feed (C₃'/IPA)=1, and the value of vertical axis was found to be less than 50 at atemperature above 130°C, which is equivalent to saying that, the higher the reaction temperature, the greater the dehydration reaction of IPA. Accordingly, in order to produce IPE, as selectively as possible, it is necessary to react IPA with C₃' at a temperature below 130°C.<br>When δ C₃' and δ IPA represent the quantities of C₃' and IPA rcacted, rcspectively, Fig. 10 illustrates the plots of δ C₃'/IPE and δ IPA/IPE against the mol ratio of feed (C₃'/IPA). According to Fig. 10, δ C₃'/IPE is less than 1 and δ IPA/IPE is more than 1 at a mol ratio below 1. In other words, dehydration reaction of IPA was found to occur at the mol ratio. On the other hand, the larger the mol ratio, the more the dimers of C₃'(C₆') are produced, as shown in Fig. 10. In conclusion, it is desirable to react IPA with C₃' at a mol ratio ranging from 1 to 2.