Hydration of isobutene

Liquid-phase hydration of alkenes has an advantage over vapor-phase hydration because equilibrium conversion of alkene is much higher. Indeed, several homogeneous liquid-phase hydration processes have been commercialized since 1972. These include the manufacture of 2-propanol [7], t-butyl alcohol [8], and 2-butanol [9] by use of heteropolyacid catalysts. A high-silica ZSM-type zeolite has recently been introduced as an industrial catalyst for the heterogeneous liquid-phase hydration of cyclohexene [19]. A sulfonated resin catalyst is applied for the hydration of propene and isobutene. 

---

ILLUSTRATION 3.4 USE OF GUGGENHEIM S METHOD AND A NUMERICAL INTEGRAL PROCEDURE TO DETERMINE THE RATE CONSTANT FOR THE HYDRATION OF ISOBUTENE IN HYDROCHLORIC ACID SOLUTION... 

Ciapetta and Kilpatrick (14) have used a dilato-metric technique to investigate the kinetics of the hydration of isobutene in perchloric acid solution at 25 CC. 

The difference between product isotope effects (r) and rate isotope effects ( / ) was independently recognized by Kreevoy and Kretchmer (1964) and by Gold and Kessick (1964). Equation (52) has been used for predicting the dependence of kn on n for the hydration of isobutene (Gold and Kessick, 1965a, b). 

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. 

Processes have also been developed using 40 to 45 per cent weight solutions and operating at low temperature (CFR, BASF eta), with yields between 90 and 95 per cent and purities above 99 per cent In fact, it has been shown that, at 3CFC. and with a 45 per cent weight sulfuric add solution, the hydration of isobutene is 1500 times faster than that of n-butenes, and 300 times faster than that of 13-butadienc. 

The most numerous cases of homogeneous catalysis are by certain ions or metal coordination compounds in aqueous solution and in biochemistry, where enzymes function catalytically. Many ionic effects are known. The hydronium ion H3O and the hydroxyl ion OH catalyze hydrolyses such as those of esters ferrous ion catalyzes the decomposition of hydrogen peroxide decomposition of nitramide is catalyzed by acetate ion. Other instances are inversion of sucrose by HCl, halogenation of acetone by H and OH , hydration of isobutene by acids, hydrolysis of esters by acids, and others. 

Applications of POMs to catalysis have been periodically reviewed [33 0]. Several industrial processes were developed and commercialized, mainly in Japan. Examples include liquid-phase hydration ofpropene to isopropanol in 1972, vapor-phase oxidation of methacrolein to methacrylic acid in 1982, liquid-phase hydration of isobutene for its separation from butane-butene fractions in 1984, biphasic polymerization of THE to polymeric diol in 1985 and hydration of -butene to 2-butanol in 1989. In 1997 direct oxidation of ethylene to acetic acid was industrialized by Showa Denko and in 2001 production of ethyl acetate by BP Amoco. 

The analysis of isotope effects to give an exponent cq is useful when a Bronsted exponent cannot be obtained by measuring catalytic coefficients for a series of acids. In the hydration of isobutene, general catalysis is unobservable and the reaction is dominated by hydronium ion catalysis. A value of j ca. 0.9 was obtained [44] from eqn. (135) by measuring solvent and product isotope effects. This result is of the expected size, as discussed in Sect. 4.7. 

Tertiary butyl alcohol ( /i° 0.7S56(5>, bpt 013 = 8Z5°Q can be produced by the hydration of isobutene either by dilute sulfuric add (50 to 65 per cent weight) or in the presence of acidic ion exchange resins. Apart from the Shell facility in the United States, which employs sulfuric hydration, no industrial plant of a significant size using this technique exists today. 

In Japan, Mitsui, Petrochemical and Kuraray Isoprene Chemical manufacture 52,000 and 13,000 t/year of tertiary butyl alcohol respectively used for ihe manufacture of methyl methacrylate, employing the reverse operation to the above, namely the hydration of isobutene. 

Processes employing r-butanol carry out the hydration of isobutene in acidic medium, according to the following exothermic reaction ... 

Specific acid catalysis (by H ) was found [F. G. Ciapella and M. Kilpatrick, J. Am. Chem. Soc.. 70 (1948) 639] in the hydration of isobutene general acid-catalysis was not, and for this reason it was thought that the transition state comprised only a proton and the olefin. Schubert et a P, however, showed that formic acid itself could protonate p-methoxy-a-methylstyrene, and hence that general acid catalysis occurred. 

ILLUSTRATION 3.4 Use of Guggenheim s Method and a Numerical Integral Procedure to Determine the Rate Constant for the Hydration of Isobutene in Hydrochloric Acid Solution... 

Though there do not seem to be any generally available technical reports, there are genuine stories of explosions and burn accidents caused by the inadvertent formation and subsequent decomposition of hydrates of hydrocarbons in railway tank cars in the cold climate of Canada. Incidents occurred due to the practice of washing empty tank carr following their use for transporting liquid hydrocarbons. In a cold winter climate, it is possible to form hydrates with small amounts of hydrocarbon residues, which later decompose when the tank car warms up, e.g., when exposed to sunshine. For example, the clathrate hydrate of isobutene (2-methyl-propene, b.p. -6.9" C) needs only 1.12 bar at 273 K to be stable. Precautions were not taken around such nominally clean and empty tankers, and exposure to sparks or naked flames led to flash fires and explosions. While the main content of the tankers was butane, other hydrocarbons were present. In another kind of industrial accident, a worker was killed by H2S gas liberated from H2S hydrate residue in a heavy water production plant, during a shutdown for maintenance. 

TaftRW (1952) The Dependence of the rate of hydration of isobutene on the acidity function, H, and the mechanism for olefin hydration in aqueous acids. J Am Chem Soc 74(21) 5372-5376... 

Rate constants for hydration of isobutene (60) in 19-40% H2SO4, 20-64% H3PO4, and 59% CF3CO2H at 298 K were determined by monitoring substrate consumption from the gas phase under the conditions of the equilibrium substrate distribution between the gas phase and solution. The coefficients of (60) distribution a = [(60)]g/[(60)]s were calculated at 298 K in the H2O-H2SO4, H2O-H3PO4, and... 

The applicability of model <23> as formulated here with consideration of gas flow and pressure variations has been demonstrated by Deckwer [34] for absorption and hydration of isobutene in sulfuric acid and by Deckwer et a1. [35, 36] for CO2 mass transfer. The physical absorption of CO2 in water proved to be a very useful tool to simulate conditions which often prevail in chemical processes, i.e. large amounts of gas are absorbed in a liquid under drastic changes of gas volume flow. As an example Fig. 11 shows CO2 gas phase profiles measured in a BC of 20 cm diameter and 7.2 m height. As shown in Fig. 11, the profiles computed on the basis of model <23> excellently describe the measured data. It is understood that... 

Based on the above information, Keggin-type HPCs demonstrate activity as acid (both Brpnsted and Lewis) and redox (Mo "+ and V +) catalysts. The latter property was initially recognized in 1975 for the oxidation of methacrolein to methacrylic acid using (NH4)2HPMoi204o and the process was industrialized in 1982 [39], The acidic properties of the Keggin structure are utilized in the hydrations of isobutene and 1-nbutene to butyl alcohols in solutions (brought into... 

---