Isobutene solubility

Refinery alkylation suffers from the very low isobutene solubility in the acid phase and proceeds near or at the phase boundary between the acid phase and organic phase. 

The initiation of the cationic polymerisation of alkenes is examined in detail by means of simple thermodynamic concepts. From a consideration of the kinetic requirements it is shown that the ideal initiator will yield a stable, singly charged anion and a cation with a high reactivity towards the monomer by simple, well defined reactions. It must also be adequately soluble in the solvent of choice and for the experimental method to be used. The calculations are applied to carbocation salts as initiators and a method of predicting their relative solubilities is described. From established and predicted data for a variety of carbocation salts the position of their ion molecule equilibria and their reactivity towards alkenes are examined by means of Born-Haber cycles. This treatment established the relative stabilities of a number of anions and the reason for dityl, but not trityl salts initiating the polymerisation of isobutene. 

Amberlyst 15 resin was found to catalyze the addition of primary alcohols to olefins. The activity displayed was higher than for soluble anhydrous p-toluenesul-fonic acid. The addition of methanol or -butanol to isobutene is weU-estabhshed as an industrial process [7]. 

Hayduk, W., Asatani, H., and Miyano, Y. Solubilities of propene, butane, isobutane and isobutene gases in n-octane, chlorobenzene and n-butanol solvents, Can. J. Chem. Eng., 66 466-473, 1988. 

Leung, P.C., Zorrilla, C., Pulgjaner, L., and Recasens, F. Solubilities and enthalpies of absorption of isobutene into ferf-butyl alcohol-water mixtures, J. Chem. Eng. Data, 32(2) 169-171, 1987. 

Zhang, C.M., Adesina, A. A., and Wainwright, M.S. Solubility studies of isobutene in tertiary butyl alcohol-t water mixtures,/ Chem. Eng. Data, 47(6) 1476-1480, 2002. 

To get a better insight into the chlorination reaction, we wanted to avoid a heterogeneous process. Instead of polyethylene or polypropylene, we used polyisobutene, which is soluble in carbon tetrachloride, as are its chlorination products. In addition, we were interested in the structure and properties of the chlorinated products, especially in comparison with polyvinyl chloride (PVC) and vinyl chloride/isobutene (VC/IB) copolymers. 

Heteropolyacids are much more active than mineral acids for several types of homogeneous reactions in both organic solvents and aqueous solution [4, 8]. The enhancement is generally greater in organic solvents. For the hydration of isobutene in a concentrated aqueous HPA solution (above 1.5 mol dm-3), the reaction rate is about 10 times greater than for mineral acids [21]. This rate enhancement is attributed to the combination of stronger acidity, stabilization of protonated intermediates, and increased solubility of alkenes [21]. In this case, the selectivity is also much improved with HPA catalysts. 

Both the monomer and polymer are soluble in the solvent in these reactions. Fairly high polymer concentrations can be obtained by judicious choice of solvent. Solution processes are used in the production of c(5-polybutadiene with butyl lithium catalyst in hexane solvent (Section 9.2.7). The cationic polymerization of isobutene in methyl chloride (Section 9.4.4) is initiated as a homogeneous reaction, but the polymer precipitates as it is formed. Diluents are necessary in these reactions to control the ionic polymerizations. Their use is avoided where possible in free-radical chain growth or in step-growth polymerizations because of the added costs involved in handling and recovering the solvents. 

The order in monomer concentration was however difficult to estaWish with confidence due to the poor solubility of the growing ptdymer chains. The above kinetics results can be rationalised by an initiation mechanism based on the formation of an Ad S intermediate, as in the case of cocatalysis by phenols (see Sect. IV-C-4-b), if one assumes that in these specific conditions isobutene and stannic chloride form a strong complex. In other words, if the cmcentration of complex is practically independent of monomer concentration because the reaction... 

The alkylation of phenol was studied with isobutene in the temperature range from 90 - 130°C and high conversion was found as well as in the alkylation of a-methy 1-styrene with 2,3-dimethyl-1-butene. Finally, the catalytic hydrogenolysis of the model substance 1-phenyl-ethanol to ethylbenzene proceeds quantitatively at 30°C without addition of a soluble acid. 

---