Ethylbenzene in ZSM

Investigation of Diffusion and Counter-diffusion of Benzene and Ethylbenzene in ZSM-5-type Zeolites by a Novel IR Technique... 

Fig. 8 Effect of temperature on the amounts (a, upper part) adsorbed and (b, lower part) desorbed of ethylbenzene in ZSM-5 for different pressure jumps and three final partial pressures (115, 230, and 460 Pa) and effect on the (corrected) diffusivities (vide infra). The uptake curves 1, 2, 3, and 4 were determined at 355, 375, 395, and 415 K, respectively...

Production of p-xylene via p-xylene removal, i.e., by crystallization or adsorption, and re-equilibration of the para-depleted stream requires recycle operation. Ethylbenzene in the feed must therefore be converted to lower or higher boiling products during the xylene isomerization step, otherwise it would build up in the recycle stream. With dual-functional catalysts, ethylbenzene is converted partly to xylenes and is partly hydrocracked. With mono-functional acid ZSM-5, ethylbenzene is converted at low temperature via transalkylation, and at higher temperature via transalkylation and dealkylation. In both cases, benzene of nitration grade purity is produced as a valuable by-product. 

This may be partly the result of increased steric crowding in the transition state of transalkylation. Another contributory factor to the increased selectivity in ZSM-5 is the higher diffusion rate of ethylbenzene vs m-/o-xylene in ZSM-5 and hence a higher steady state concentration ratio [EB]/[xyl] in the zeolite interior than in the outside phase. Diffusional restriction for xylenes vs ethylbenzene may also be indicated by the better selectivity of synthetic mordenite vs ZSM-4, since the former had a larger crystal size. 

Table 1 Diffusivities of benzene and ethylbenzene in fresh and coked H-ZSM-5...

Large amounts of styrene are commercially produced by dehydrogenation of ethylbenzene (EB) in the presence of steam using iron oxide-based catalysts. Carbon dioxide, small amounts of which are formed as a by-product in the ethylbenzene dehydrogenation, was known to depress the catalytic activity of commercial catalyst [7,8]. However, it has been recently reported that several examples show the positive effect of carbon dioxide in this catalytic reaction [5,9,10]. In this study, we investigated the effect of carbon dioxide in dehydrogenation of ethylbenzene over ZSM-5 zeolite-supported iron oxide catalyst. 

With a twofold excess of HNO3 conversion increased to 20 %. Use of > 95 % nitric acid and a 1 1 reactant ratio resulted in an increase in chlorobenzene conversion to 33.4% at 50 °C, although para selectivity dropped substantially (p/o = 1.91). No enhanced para selectivity was observed for toluene and ethylbenzene with ZSM-5, however, when sulfonated ion-exchange resins were used as catalysts a higher fraction of para-substituted products was obtained. 

Factors on dehydrogenation of ethylbenzene to styrene in ZSM-5 type zeolite membrane reactors were studied. About 18% conversion of ethylbenzene increase in the Fe-ZSM-5 membrane reactor can be obtained over the fixed-bed reactor. This result is better than that obtained in the other membrane reactors. The bigger is the permeability and permselectivity of ZSM-5 membranes, the higher is the conversion of ethylbenzene. The order of membrane stability for ethylbenzene dehydrogenation is silicalite-1 > Fe-ZSM-5 > Fe/ZSM-5 > ZSM-5. 

Fig. 5 Loading dependence of corrected diffusivities (Do) for ethylbenzene in H-ZSM-5 at various temperatures, measured by piezometric technique. From Schumacher et al. [20] with permission...

Fig. 3 Set of FTIR spectra indicating successive states of sorption of ethylbenzene into H-ZSM-5 at 415 K (0, 1, 2, 3, 4, 5 after 0, 11.1, 33.3, 55.6, 103.7, and 348 s, respectively). Pressure jump from 0 to 1.15 mbar partial pressure of ethylbenzene in helium stream thickness of the sample wafer 10 mgcm (corresponding to about 0.1 mm)...

The following IR bands being indicative of the adsorbates benzene, ethylbenzene, and p-xylene were monitored at 1478, 1496/1453, and 1516 cm , respectively. Sets of spectra of benzene or p-xylene on H-ZSM-5 analogous to that shown for ethylbenzene (Fig. 3) were monitored and, using the appropriate cahbration curves, the corresponding adsorption and desorption curves of the type displayed for ethylbenzene in Figs. 8a,b obtained (see also discussion of Fig. 29 below). 

A set of such isotherms is shown in Fig. 9 for the system ethylbenzene/ H-ZSM-5. From such sets, in turn, isosteres were constructed and isosteric heats of adsorption, Qiso, determined via the Clausius-Clapeyron equation. This is illustrated in Fig. 10 using the system ethylbenzene/H-ZSM-5 as an example. 

Fig. 20 Uptake curves for ethylbenzene in freshly activated and coked H-ZSM-5 (sample No. 3). The curves obtained after 25.5 and 104 h of time on stream (see Table 6) are omitted for the sake of clarity...

Nagy compared the activity of K-Mor., Cs-Mor., K-ZSM-5, Cs-ZSM-5 in isopropanol conversion. Cs-ZSM-5 yields propene, 2-butenes, 2-pentenes and some aromatic compounds. K-ZSM-5 yields only 2-butenes, toluene and ethylbenzene. CS-ZSM-5 shows a higher basicity and activity in the dehydrogenation of propanol. 

In shape-selective catalysis, the pore size of the zeoHte is important. For example, the ZSM-5 framework contains 10-membered rings with 0.6-nm pore size. This material is used in xylene isomerization, ethylbenzene synthesis, dewaxing of lubricatius oils and light fuel oil, ie, diesel and jet fuel, and the conversion of methanol to Hquid hydrocarbon fuels (21). 

Ethjlben ne Synthesis. The synthesis of ethylbenzene for styrene production is another process in which ZSM-5 catalysts are employed. Although some ethylbenzene is obtained direcdy from petroleum, about 90% is synthetic. In earlier processes, benzene was alkylated with high purity ethylene in liquid-phase slurry reactors with promoted AlCl catalysts or the vapor-phase reaction of benzene with a dilute ethylene-containing feedstock with a BF catalyst supported on alumina. Both of these catalysts are corrosive and their handling presents problems. 

These operations have been gradually replaced by the Mobd-Badger process (28), which employs an acidic ZSM-5 catalyst and produces ethylbenzene using both pure and dilute ethylene sources. In both cases, the alkylation is accomplished under vapor-phase conditions of about 425°C,... 

In recent years alkylations have been accompHshed with acidic zeoHte catalysts, most nobably ZSM-5. A ZSM-5 ethylbenzene process was commercialized joiatiy by Mobil Co. and Badger America ia 1976 (24). The vapor-phase reaction occurs at temperatures above 370°C over a fixed bed of catalyst at 1.4—2.8 MPa (200—400 psi) with high ethylene space velocities. A typical molar ethylene to benzene ratio is about 1—1.2. The conversion to ethylbenzene is quantitative. The principal advantages of zeoHte-based routes are easy recovery of products, elimination of corrosive or environmentally unacceptable by-products, high product yields and selectivities, and high process heat recovery (25,26). 

In this appHcation, ZSM-5 acts as a strong, soHd acid, and may be viewed as supported on the surfaces of the crystalline zeoHte stmcture. The older, Friedel-Crafts aluminum chloride catalyzed process for ethylbenzene produces considerably more by-products and suffers from the corrosivity of the catalyst system. Because of the intermediate pore size of ZSM-5, those reactions that produce coke from larger molecules that cannot enter the ZSM-5 pore stmcture are significantly reduced, which greatly extends catalyst lifetime. 

Another example of catalytic isomerization is the Mobil Vapor-Phase Isomerization process, in which -xylene is separated from an equiHbrium mixture of Cg aromatics obtained by isomerization of mixed xylenes and ethylbenzene. To keep xylene losses low, this process uses a ZSM-5-supported noble metal catalyst over which the rate of transalkylation of ethylbenzene is two orders of magnitude larger than that of xylene disproportionation (12). 

Zeoliltes seem particularly suited to take over the job and in fact are doing so already for aromatic alkylation. Thus in ethylbenzene manufacture (from benzene and ethene) modern processes apply zeolites (H-ZSM-5, H-Y) as the catalyst, substituting conventional processes based on AICI3 or BF3-on-alumina catalysis. Substantial waste reductions are achieved. 

On ferrierite, ZSM-22 and EU-1 zeolite catalysts, 10MR monodimensional zeolite structures (ID), the main reaction is the isomerization of ethylbenzene (figure la). ZSM-5, 10MR three-dimensional structure (3D) zeolite is very selective in dealkylation (90%) (figure lb) and no deactivation was observed within 8 hours of reaction. This particular selectivity of the zeolite ZSM-5 can be partly explained by the presence of strong acid sites and its porous structure that on one hand promotes the containment of molecules in the pores (presence of 8-9A cages at the intersection of channels) and on the other hand prevents the formation of coke and therefore pore blockage. 

Albene [Alcohol benzene] A process for making ethylbenzene from aqueous ethanol and benzene. The aqueous ethanol may contain as little as 30 percent ethanol, such as that obtained by one distillation of liquors from sugar fermentation. The mixed vapors are passed over a catalyst at approximately 350°C. The catalyst ( Encilite-2 ) is a ZSM-5-type zeolite in which some of the aluminum has been replaced by iron. Developed in India jointly by the... 

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