Dehydrogenation, of ethylbenzene

Styrene manufacture by dehydrogenation of ethylbenzene is simple ia concept and has the virtue of beiag a siagle-product technology, an important consideration for a product of such enormous volume. This route is used for nearly 90% of the worldwide styrene production. The rest is obtained from the coproduction of propylene oxide (PO) and styrene (SM). The PO—SM route is complex and capital-iatensive ia comparison to dehydrogenation of ethylbenzene, but it stiU can be very attractive. However, its use is limited by the mismatch between the demands for styrene and propylene oxides (qv). 

Fig. 4. Manufacture of styrene by adiabatic dehydrogenation of ethylbenzene A, steam superheater B, reactor section C, feed—effluent exchanger D,...

Other Technologies. As important as dehydrogenation of ethylbenzene is in the production of styrene, it suffers from two theoretical disadvantages it is endothermic and is limited by thermodynamic equiHbrium. The endothermicity requites heat input at high temperature, which is difficult. The thermodynamic limitation necessitates the separation of the unreacted ethylbenzene from styrene, which are close-boiling compounds. The obvious solution is to effect the reaction oxidatively ... 

A similar but somewhat less ambitious approach is to carry out dehydrogenation of ethylbenzene and oxidation of the hydrogen product alternately in separate reactors containing different catalysts ... 

Another appHcation for this type catalyst is ia the purification of styrene. Trace amounts (200—300 ppmw) of phenylacetylene can inhibit styrene polymerization and caimot easily be removed from styrene produced by dehydrogenation of ethylbenzene using the high activity catalysts introduced in the 1980s. Treatment of styrene with hydrogen over an inhibited supported palladium catalyst in a small post reactor lowers phenylacetylene concentrations to a tolerable level of <50 ppmw without significant loss of styrene. 

Example 4 Styrene from Ethylbenzene The principal reaction in the dehydrogenation of ethylbenzene is to styrene and hydrogen. 

In 1869 Berthelot- reported the production of styrene by dehydrogenation of ethylbenzene. This method is the basis of present day commercial methods. Over the year many other methods were developed, such as the decarboxylation of acids, dehydration of alcohols, pyrolysis of acetylene, pyrolysis of hydrocarbons and the chlorination and dehydrogenation of ethylbenzene." ... 

The generation of caibocations from these sources is well documented (see Section 5.4). The reaction of aromatics with alkenes in the presence of Lewis acid catalysts is the basis for the industrial production of many alkylated aromatic compounds. Styrene, for example, is prepared by dehydrogenation of ethylbenzene made from benzene and ethylene. 

Dehydrogenation of ethylbenzene to styrene occurs over a wide variety of metal oxide catalysts. Oxides of Ee, Cr, Si, Co, Zn, or their mixtures can be used for the dehydrogenation reaction. Typical reaction... 

Problem 16.21 Styrene, the simplest alkenylbenzene, is prepared commercially for use in plastics manufacture by catalytic dehydrogenation of ethylbenzene. How might you prepare styrene from benzene using reactions you ve studied ... 

J.N. Michaels, and C.G. Vayenas, Kinetics of Vapor-Phase Electrochemical Oxidative Dehydrogenation of Ethylbenzene,/. Catal. 85, 477-488 (1984). 

Example 3.3 Fixed-bed reactors are used for the catalytic dehydrogenation of ethylbenzene to form styrene ... 

Example 10.6 A commercial process for the dehydrogenation of ethylbenzene uses 3-mm spherical catalyst particles. The rate constant is 15s , and the diffusivity of ethylbenzene in steam is 4x 10 m /s under reaction conditions. Assume that the pore diameter is large enough that this bulk diffusivity applies. Determine a likely lower bound for the isothermal effectiveness factor. 

Dehydrogenation of ethylbenzene with carbon nanofiber supported iron oxide... 

The results of catalytic activities in the dehydrogenation of ethylbenzene with various iron oxide based catalysts are shown in Fig. l(a-b). The number in the parentheses of the catalyst codes indicates the weight fi-action of metal per gram carbon. On oxidized CNF alone less than 20% conversion of EB is observed after 3 h on stream. The conversion of ethylbenzene... 

Styrene (or viuylbenzene) is prepared technically by the cracking dehydrogenation of ethylbenzene ... 

An efficient oxidation catalyst, OMS-1 (octahedral mol. sieve), was prepared by microwave heating of a family of layered and tunnel-structured manganese oxide materials. These materials are known to interact strongly with microwave radiation, and thus pronounced effects on the microstructure were expected. Their catalytic activity was tested in the oxidative dehydrogenation of ethylbenzene to styrene [25]. 

As an example for an endothermic reaction, we use the dehydrogenation of ethylbenzene, reaction (D) in Section 21.1. This is developed in mare detail in file following example. 

For the dehydrogenation of ethylbenzene at equilibrium, CgH10 (EB) CgHg (S) + H2, calculate and plot /EB eq(T), at P = 0.14 MPa, with an initial molar ratio of inert gas (steam, H20) to EB of r = 15 (these conditions are also indicative of commercial opera-liens). Assume ideal-gas behavior, with Kp = 82 X IQ5 exp( — 15,200IT) MPa. 

For an endothermic, reversible reaction (such as the dehydrogenation of ethylbenzene), as also shown in Section 5.3 and illustrated in Figure 5.2(b), the rate does not exhibit a maximum with respect to T at constant /, but increases monotonically with increasing T. The rate also decreases with increasing / at constant T, as does the rate of an exothermic reaction. 

Consider a fixed-bed catalytic reactor (FBCR), with axial flow, for the dehydrogenation of ethylbenzene (A) to styrene (S) (monomer). From the information given below, calculate the temperature (TIK) in the first-stage bed of the reactor,... 

Styrene is to be produced by the catalytic dehydrogenation of ethylbenzene according to the reaction ... 

Figure 7.24 Photoelectron emission microscopy images of two Fe304 surfaces that were used as model catalyst in the dehydrogenation of ethylbenzene to styrene at 870 K, showing carbonaceous deposits (bright). These graphitic deposits grow in dots and streaks on a surface of low defect density, but form dendritic structures on surfaces rich in point and step detects (from Weiss et al. f731).

A fluidized bed reactor is used to accomplish the catalytic dehydrogenation of ethylbenzene in the presence of steam which serves as an inert diluent. The reaction is... 

Data for the process of dehydrogenation of ethylbenzene to styrene in a tubular packed reactor are given by Jenson Jeffreys (Mathematical Methods in Chemical Rngineering, 424, 1977). The energy and material balances are like... 

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