Ethylbenzene, dehydrogenation

Ceria is added as a promoters in the K/Fe-based catalyst used for the dehydrogenation of Ethylbenzene [27-29], which is the most important process for the production of styrene (20.000.000 tons/y) [30], The reaction (eq. 16.6) is highly endothermic (AH= 124.9 KJ/mol ) and thermodinamically limited  

Several studies have been also carried out to develop new and efficient catalysts, not only based on K-Fe oxides [35-37]. One of the strategy to improve the selectivity and activity of the catalyst is to add promoters such as oxides of V, Ce, W, Li, Mg, Ca, Ti, Zr, Ni, and Co. Although at present only a few basic studies have been carried out to understand the role of promoters, it has been suggested that they could influence the number, organization and nature of the reactive centers and contribute either to stabilize the active phase or to accelerate its formation under 

Speculations on the role if ceria have been already reported [5, 44]. It was found that cerium oxide has a positive effect on the nature of the active sites. Cerium ions may enhance the polarization of the Fe-0 bond and increase the basicity of this reaction center, and in addition they may hinder the reduction of Fc203. 

Catalyst S.A. (mVg) Rate b selectivity to styrene Activation Energy (Kcal/mol)  

In accordance with a basic mechanism, the dehydrogenation occurs by abstraction of P-hydrogen to form a jt-adsorbed complex with a scheme of reaction similar to that reported for the ammoxidation of propylene to acrylonitrile [45]  

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Annular flow reactors, such as that illustrated in Figure 3.2, are sometimes used for reversible, adiabatic, solid-catalyzed reactions where pressure near the end of the reactor must be minimized to achieve a favorable equilibrium. Ethylbenzene dehydrogenation fits this situation. Repeat Problem 3.7 but substitute an annular reactor for the tube. The inside (inlet) radius of the annulus is 0.1m and the outside (outlet) radius is 1.1m. 

Example 7.9 Determine AHji for the ethylbenzene dehydrogenation reaction at 973 K and 0.5 atm. 

FIGURE 7.7 Batch reaction trajectory for ethylbenzene dehydrogenation. 

The ethylbenzene dehydrogenation catalyst of Example 3.1 has a first-order rate constant of 3.752 s at 700°C. How does this compare with the catalyst used by Wenner and Dybdal. They reported... 

Peng F, Fu X, Yu H, Wang H (2007). Preparation of carbon nanotube-supported Fe203 catalysts and their catalytic activities for ethylbenzene dehydrogenation. New Carbon Mater. 22 213-217. 

In order to probe the enhanced transport in Def-MCM41, we compared the catalytic performance of various molybdenum oxide/mesoporous material catalysts for ethylbenzene dehydrogenation reaction in Table 2. 

T-Profiling technique Ethylbenzene Dehydrogenation C8H10 c8h8 + h2 600°C Steam Reforming CH4 + H20 CO + 3H2 900°C Hydrogen Cyanide Manufacture CH4 + NH3 HCN + 3H2 1200°C... 

Figure 4.35 A simplified schematic of the SMART process, showing the ethylbenzene dehydrogenation (inset) and hydrogen oxidation energy exchange cycle. 

Conjugated ethylbenzene dehydrogenation by 15% aqueous hydrogen peroxide. 

Oxidative ethylbenzene dehydrogenation by oxygen in an amount equivalent to its concentration in 15% aqueous hydrogen peroxide at complete dissociation of the latter. 

Ethylbenzene dehydrogenation in the simultaneous presence of hydrogen peroxide and molecular oxygen. 

Experimental results on conjugated ethylbenzene dehydrogenation with hydrogen peroxide, shown in Table 4.2 (experiments 1 and 2), indicate that the use of 15% aqueous hydrogen peroxide promotes high yields of styrene for both the missed and the converted ethylbenzene 36.3% and 90%, respectively1. 

In the second series of experiments (Table 4.2, experiments 3-6) on ethylbenzene dehydrogenation by molecular oxygen, styrene yields were much lower than in the first series. On the quartz reactor walls condensation product precipitation in amounts up to 1.7% was observed. Moreover, if molecular hydrogen was absent in the products of conjugated dehydrogenation, the total amount of hydrogen equals 78-82% of the whole volume of gaseous products (2.2% in total products). 

A novel flow strategy for ethylbenzene dehydrogenation in a packed-bed reactor. Chem. 

The activity of granulated rhenium catalyst, obtained from copolymer carbonisate, has been investigated in reactions of cyclohexane or ethylbenzene dehydrogenation in bed -packed quartz tube reactor at the plug flow conditions at temperatures from 650 to 900 K, the reagents feed of 30 - 100 ml/min and initial hydrocarbons partial pressure of 0.5 kPa. 

Figure 5. The temperature dependences of benzene (curve 1) and styrene (curve 2) yields at cyclohexane and ethylbenzene dehydrogenation, respectively, on the catalyst, obtained from copolymer carbonisate, containing 7 mass per cent of Re.

High catalytic activity of catalysts in reactions of reception of cyclohehexane and ethylbenzene dehydrogenation simultaneously with expensive active metal economy, high mechanical durability, and an opportunity of regeneration of the catalyst are achieved due to creation of optimum structure of carbonized material already on the synthesis stage. 

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