Dehydrogenation of Isobutane to Isobutene

The dehydrogenation of isobutane to isobutene proceeds at high temperature (ca. 550°C) and low hydrogen pressure (Ibar). In these conditions, the catalyst is very active (turnover frequency 5 s ) and moderately selective (93%) for commercial appHcations. The side-products are due to the hydrogenolysis properties of the 

This modified catalyst can be considered as totally selective for isobutene. 

Typically, this mechanism involves, after C—H bond activation, a y-H abstraction, followed by the formation of a metallacycle and the cleavage of the C—C bonds. 

Another consequence of the suppression of the hydrogenolysis reactions is the increase in the turnover number measured at the pseudo-stationary part of the curve giving the conversion as a function of time. Since hydrogenolysis reactions are suppressed, the coke formation, responsible for the deactivation of the catalyst is strongly reduced and the result is that the tin-modified catalysts are more active than the unmodified ones (Fig. 18.29). 

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Methyl tert-Butylluther Methyl /-butyl ether (MTBE) is an increasingly important fuel additive. Platinum—tin and other PGM catalysts are used for the dehydrogenation of isobutane to isobutene, an intermediate step in MTBE manufacture. 

The activity of the catalyst is also important, as reflected in the value of Da. If the reaction rate is slow, equilibrium will not be approached and the removal of a product by a membrane will not affect the ultimate yield. This was demonstrated by Raich and Foley, who showed that the very promising results of early studies using the dehydrogenation of cyclohexane to benzene were achieved due to the fast reaction rate which quickly attained equilibrium. Slower reactions, such as the dehydrogenation of isobutane to isobutene, are not helped by a membrane reactor as they are kinetically limited (low Da). 

We wiU present here two examples of such effect the dehydrogenation of isobutane to isobutene and the hydrogenolysis of acids or esters to aldehydes and... 

Liang W. Q., Hughes R. 2005. The catalytic dehydrogenation of isobutane to isobutene in a palladium/silver composite membrane reactor. Catalysis Today 104 238-243. 

The process involves the dehydrogenation of isobutane to isobutene which is reacted with methanol to produce MTBE. Particular attention should be given to the dehydrogenation reactor design and operation. Technical and economic data for the design are attached. 

The application of carbon membrane reactors for the dehydrogenation of cyclohexane into benzene was investigated by Itoh and Haraya. They found a higher conversion for the carbon membrane reactor comparing to the normal reactor, which was caused by the chemical reaction shifti ng to the product side due to the preferential permeation of H2. Sznejer and Sheintuch studied the dehydrogenation of isobutane to isobutene in a membrane reactor equipped... 

Matsuda, T., Koike, I., Kubo, N., Kikuchi, E. (1993). Dehydrogenation of isobutane to isobutene in a palladium membrane reactor. Applied Catalysis A, General, 96, 3. 

Direct propane dehydrogenation is the most economical route to propylene, but the process is very complex. However, performing this reaction on a MSR offers the possibility to reach a propylene selectivity of 73-95%, with conversions between 31 and 24% (over calcium hydroxyapatite or Pt-Sn/Al-SAPO-34 catalyst, at 590 °C, respectively) [30,31]. On the other hand, Karinen et al. [32] performed the dehydrogenation of isobutane to isobutene over a chromia/alumina catalyst in a sandwich-type structured microreactor, at 570 °C under atmospheric pressure, showing good results despite its high endothermicity. 

Comuzzi, C., Primavera, A., Trovarelli, A., Bini, G., and Cavani, F. Thermal stability and catalytic properties of the Wells-Dawson K P2Wi8062 IOH2O heteropoly compound in the oxidative dehydrogenation of isobutane to isobutene. Top. Catal 1999, 9, 251. 

Cavani, R, Comuzzi, C., Dolcetti, G., Etienne, E., Finke, R.G., SeUeri, G., Trifiro, F., and TrovareUi, A. Oxidative dehydrogenation of isobutane to isobutene Dawson-type heteropolyoxoanions as stable and selective heterogeneous catalysts./. Catal 1996,160, 317. 

Takita, Y, Sano, K., Muraya, T., Nishiguchi, H., Kawata, N., Ito, M., Akbay, T., and Ishihara, T. Oxidative dehydrogenation of isobutane to isobutene II. Rare earth phosphate catalysts. Appl. Catal A Gen. 1998,170, 23. 

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