Styrene Adiabatic dehydrogenation

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

Fina/Badger Styrene Ethylbenzene Two-stage adiabatic dehydrogenation yields high-purity product 50 2000... 

Table 6.11 lists the typical economic data on the manufacture of styrene by adiabatic dehydrogenation of ethylbenzene, and by the method industrialized by Oxtrane. 

Next to ethylene, propylene and vinylchloride, styrene is one of the most important monomers for the production of plastics. The worldwide demand for styrene in 1992 was 18.2 million tonnes and is expected to grow annually with 3-5% to 23.9 million tons in 2000 [42]. Recent production statistics show an annual production of about 1.3 million tons of styrene in the Netherlands. Approximately 75% of this is produced at DOW Benelux in Terneuzen by catalytic adiabatic dehydrogenation of ethylbenzene [42]. 

Both the isothermal and the adiabatic dehydrogenation processes are applied in industrial styrene production. The flow diagram for the BASF dehydrogenation process is shown in Figure 5.6. 

Consider a two-stage fixed-bed catalytic reactor (FBCR), with axial flow, for the dehydrogenation of ethylbenzene (A) to styrene (S) (monomer). From the data given below, for adiabatic operation, calculate the amount of catalyst required in the first stage, W /kg. 

The use of steam has a number of other advantages in the styrene process. The most important of these is that it acts as a source of internal heat supply so that the reactor can be operated adiabatic-ally. The dehydrogenation reaction is strongly endothermic, the heat of reaction at 560°C being (- AH) - 125,000 kJ/kmoL It is instructive to look closely at the conditions which were originally worked out for this process (Fig. 1.7). Most of the.steam, 90 per cent of the total used, is heated separately from the ethylbenzene stream, and to a higher temperature (7I0SC) than is required at the inlet to the... 

Styrene is produced by dehydrogenation of ethylbenzene in an adiabatic, fixed-bed reactor. Although Sheel and Crowe [29] list ten reactions and several products, the major reaction is the conversion of ethylbenzene to styrene, according to the following equation. 

Preliminary results obtained in an effort to model the dehydrogenation of ethylbenzene to styrene in a "membrane reactor" are described below. The unique feature of this reactor is that the walls of the reactor are conprised of permselective membranes through which the various reactant and product species diffuse at different rates. This reaction is endothermic and the ultimate extent of conversion is limited by thermodynamic equilibrium constraints. In industrial practice steam is used not only to shift the ec[uilibrium extent of reaction towards the products but also to reduce the magnitude of the ten erature decrease which accon anies the reaction when it is carried our adiabatically. 

Alkylation takes place in the vapor phase, in the presence of a gaseous dflnent (nitrogen or hydrogen) around 47S°C, at 0.7.10s Pa absolute, with excess toluene (5 1 to 10 1 moles) intended to prevent the formation of inethyldiethylbenzenes. Dehydrogenation takes ptoce in similar conditions to those applied to produce styrene, namely in adiabatic reactors, with catalyst, around 450 to 500°C, and in t he presence of steam. The blend of methylstyrenes currently commercialized by Vow results from the liquid phase alkylation of toluene with aluminum chloride. 

Styrene is produced by the catalytic dehydrogenation of ethyl benzene (EB) in a two-stage fixed-bed adiabatic reactor. Equilibrium and heat capacity data are as given shortly. 

The first and most elementary type of reactor to be considered is the adiabatic. In this case, the reactor is simply a vessel of relatively large diameter. Such a simple solution is not always applicable, however. Indeed, if the reaction is very endothermic, the temperature drop may be such as to extinguish the reaction before the desired conversion is attained—this would be the case with catalytic reforming of naphtha or with ethylbenzene dehydrogenation into styrene. Strongly exothermic reactions lead to a temperature rise that may be prohibitive for several reasons for its unfavorable influence on the equilibrium conversion, as in ammonia, methanol, and SO3 synthesis, or on the selectivity, as in maleic anhydride or... 

Styrene is produced by catalytic dehydrogenation of ethylbenzene. The reaction is endothermic and reversible and takes place with an increase in the number of moles. Consequently, the styrene conversion is favored by high temperatures, low pressures, and by dilution of the feed by means of an inert component, like benzene or more generally steam. The steam also serves as a heat carrier, reducing the temperature drop in adiabatic operation. 

Dehydrogenation of ethylbenzene to form styrene is being studied in an adiabatic tubular reactor packed with a catalyst ... 

Dehydrogenation of ethylbenzene to styrene is normally accomplished in a fixed-bed reactor. A catalyst is packed in tubes to form the fixed bed. Steam is often fed with the styrene to moderate the temperature excursions that are characteristic of adiabatic operation. The steam also serves to prolong the life of the catalyst. Consider the situation in which we model the behavior of this reactor as an isothermal plug flow reactor in which the dehydrogenation reaction occurs homogeneously across each cross section of the reactor. The stoichiometry of the primary reaction is... 

Styrene is produced by the catalytic dehydrogenation of ethylbenzene at 1.2 atm and a temperature of about 575°C, as described by Smith (1981). The reaction is sufficiently endothermic, with an ATR of about —460°C, such that if the reactor were operated adiabati-cally with a feed of pure ethylbenzene, the temperature of the reacting fluid would decrease to such an extent that the reaction rate would be unduly compromised, resulting in a very large reactor volume. To maintain a reasonable temperature, a large amount of steam is added to the feed (typically with a molar ratio of steam to ethylbenzene equal to 20 1), which is preheated to 625°C before entering the reactor (Figure 6.1b). The steam is inert and is easily recovered from the reactor effluent by condensation. The presence of the steam reduces the reaction rate because the styrene concentration is reduced, but the reactor can be operated adiabatically in a simple manner. 

The dehydrogenation reaction is an endothermic reaction, with the heat source supplied either by superheated steam (800—950 °C) mixed with preheated ethylbenzene feedstock prior to exposure to the catalyst (the adiabatic process), or by indirect heat exchange design (the isothermal process). For every mole of ethylbenzene, the process produces one mole of each styrene and hydrogen. This process accounts for over 90% of the total worldwide production of styrene. 

The dehydrogenation of ethyl benzene is endothermic so that heat must be sup-pUed during operation. The two commercial styrene processes either incorporate several adiabatic beds with interbed heat exchange/steam addition or isothermal tubular reactors with a siritable heating mediirm in order to maintain operating... 

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