Isobutene hydration

Equation (1) consists of various resistance terms. l/Kj a is the gas absorption resistance, while 1/ K,a corresponds to the maleic anhydride diffusion resistance and l/i k represents the chemical reaction resistance. The reaction rate data obtained under the reaction conditions of 250°C and 70 atm were plotted according to equation (1). Although catalytic reaction data with respect to time on stream were not shown here, a linear correlation between reaction rate data and catalyst loading was observed as shown in Fig. 2. The gas absorption resistance (1/ a) was -1.26 h, while the combined reaction-diffusion resistance (lJK,a + 1 T]k) was determined to be 5.57 h. The small negative value of gas absorption resistance indicates that the gas-liquid diffusion resistance was very small and had several orders of magnitude less than the chanical reaction resistance, as similarly observed for the isobutene hydration over Amberlyst-15 in a slurry reactor [6]. This indicates that absorption of malei c anhydride in solvent was a rapid process compared to the reaction rate on the catalyst surface. 

Isobutene hydration HCIO4 3-9 0-9 Gold and Kessick, 1965b... 

Fig. 4. Bate constants as a function of the solvent isotopic composition. The solid lines have been generated from kj, ka, and a( only, (a) Allylmercuric iodide cleavage at 35° k jkD = 3-12 and aj=0-67 (Kreevoy et al., 1966b) (b) Isobutenylmercuric bromide cleavage at 25° kBJkI> = 2-55 and ( = 0-83 (Kreevoy and Landholm, unpublished data) and (c) Isobutene hydration at 25° kmlk1>=l-45 and ce<=0,84 (Gold and Kessick, 1966). The experimental points represent 5% errors in the rate constants and 1 % in the isotopic composition.

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. 

Cation-exchange resins are used as catalysts in the produdion of MTBE (methyl tertiary-butyl ether, 2-methoxy-2-methylpropane) and various other oxygenates and, lately, also in the dimerization of isobutene [30]. Other commercial applications of the cation-exchange resins indude dehydration of alcohols, alkylation of phenols, condensation readions, alkene hydration, purification of phenol, ester hydrolysis and other reactions [31]. The major producers of ion-exchange resins are Sybron Chemicals Incorporated [32] (Lewatit resins), Dow Chemical Company [33] (DOWEX resins), Purolite [28] (Purolite resins), and Rohm and Haas Company [27] (Amberlyst resins). 

Poly([7,8-bis(trifluoromethyl)tetracyclo [4.2.0.02 8.05 7]octane-3,4-diyl]-1,2-ethenediyl), 3457 Poly[borane(l)], 0134 crs-Poly (butadiene), 1480 Poly(l,3-butadiene peroxide), 1528 Poly(butadiyne), 1382 Poly(carbon monofluoride), 0336 Poly(chlorotrifluoroethylene), 0589 Poly(l,3-cyclohexadiene peroxide), 2380 Poly(cyclopentadienyltitanium dichloride), 1837 Poly(diazidophosphazene), 4781 Poly(dibromosilylene), 0282 Poly(difluorosilylene), 4324 Poly(dihydroxydioxodisilane), 4474 Poly(dimercuryimmonium acetylide), 0665 Poly(dimercuryimmonium azide), 4606 Poly(dimercuryimmonium bromate), 0253 Poly (dimercury immonium iodide hydrate), 4449 Poly (dimercury immonium perchlorate), 4006 Poly(dimercuryimmonium permanganate), 4603 Poly (dime thylketene peroxide), see Poly(peroxyisobutyrolactone), 1531 Poly(dimethylsiloxane), 0918 Poly(disilicon nitride), 4752 Poly(ethenyl nitrate), see Poly(vinyl nitrate), 0760 Poly(ethylene), 0778 Poly(ethylene terephthalate), 3256 Poly(ethylidene peroxide), 0831 Poly(furan-2,5-diyl), 1398 Poly(germanium dihydride), 4409 Poly(germanium monohydride), 4407 Poly(isobutene), 1578 Poly(methyl methacrylate peroxide), 1913... 

Figure 1 Examples of industrial processes employing reactive distillation (a) methyl ferf-butyl ether (MTBE) from isobutene and methanol (b) cumene via alkylation of benzene with propylene (c) ethylene glycol via hydration of ethylene oxide.

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). 

The volume of activation, A V, which is — RT 8 lnk)Jdp, has been suggested as a criterion of mechanism (Whalley, 1964). Known volumes of activation for A-SB2 reactions, measured near 25°, seem to be limited to olefin hydration (—12 cm3 mole-1 for isobutene at 35°, Baliga and Whalley, 1965) and allylmercuric iodide cleavage ( — 11 cm3 mole-1 at 25°, Halpem and Tinker, 1965). It is impossible to generalize from so few examples, but, in principle, it seems possible that AV is less dependent on structural ramification than AS, and therefore easier to interpret. Against this must be weighed the experimental difficulties in... 

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. 

In the earliest hydration techniques in saifhric medium, the operation is conducted in the presence of concentrated suUiiiic ac This leads to losses of isobutene as well as add, by the formation of sulfates and polymers. Subsequently, the concentration was reduced to about 60 to 65 per cent w eight Esso, Fermrex etp.k but Che yidd remained iow and product purity did not exceed 96 per cent weight... 

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. 

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