Ethylbenzene in H-ZSM

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)...

Table 2 Isosteric heat, Qiso, and microcalorimetrically measured heat of adsorption, of benzene, ethylbenzene, and p-xylene in H-ZSM-5 ...

Diffusion of Benzene, Ethylbenzene, and p-Xylene in H-ZSM-5 by "Macro"-FTIR... 

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. 

The results of the inverse experiment, viz. counter-diffusion of benzene into H-ZSM-5, previously loaded with ethylbenzene from an ethylbenzene/helium stream at 415 K, are displayed in Fig. 6. 

Application of the IR method proved to be also suitable for the measurement of diffusivities in coking porous catalysts. This was deihonstrated by uptake experiments with ethylbenzene where the sorbent catalyst, H-ZSM-5, was intermittently coked in-situ via dealkylation of ethylbenzene at temperatures (465 K) somewhat higher than the sorption temperature (395 K). Coke deposition was monitored in-situ via the IR absorbance... 

A more recent development in ethylbenzene technology is the Mobil-Badger process,161,314-316 which employs a solid acid catalyst in the heterogeneous vapor-phase reaction (400-45O C, 15-30 atm). A modified H-ZSM-5 catalyst that is regenerable greatly eliminates the common problems associated with... 

The FTIR-TPD profiles (A vs. T) for the desorption of benzene, toluene, and ethylbenzene from high-silica H-ZSM-5 is reported in Figure 4.40 [97], These results were fitted with the complementary error function, that is,... 

Three different zeolites (USY-zeolite, H-ZSM-5 and H-mordenite) were investigated in a computer controlled experimental equipment under supercritical conditions using the disproportionation of ethylbenzene as test reaction and butane or pentane as an inert gas. Experiments were carried out at a pressure of 50 bar, a flow rate of 450 ml/min (at standard temperature and pressure), a range of temperatures (573 - 673 K) and 0.8 as molar fraction of ethylbenzene (EB) in the feed. The results showed that an extraction of coke deposited on the catalysts strongly depends on the physico-chemical properties of the catalysts. Coke deposited on Lewis centres can be more easily dissolved by supercritical fluid than that on Brnsted centres. 

In this paper three zeolite catalysts from Sud-Chemie AG (USY-zeolite Si/Al 2.3-2.5, H-ZSM-5 Si/Al 15 and H-mordenite Si/Al 10) have been investigated in a gradientless reactor under supercritical conditions using the disproportionation of ethylbenzene (EBD) as test reaction and butane or pentane as inert. A previous publication reported investigations on those three catalysts at normal pressure and the details about the geometry of the three zeolites [6]. 

The transformation of n-butane over the Ga and Zn modified ZSM-5 catalysts produced similar aromatic hydrocarbons and gaseous products as over H-ZSM-5. Ethyl benzene was the only aromatic which was not formed with the proton form catalyst. Ga-H-ZSM-5 and Zn-H-ZSM-5 exhibited higher catalytic activity and selectivity to aromatics than the H-ZSM-5 catalyst The amount of cracking products formed for Ga- and Zn- modified catalysts were smaller than for ZSM-5 in its proton form. Toluene constituted almost 50 % of the aromatics formed while benzene, xylenes and ethylbenzene formed the rest The conversion of n-butane and selectivity to aromatic hydrocarbons increased with increasing temperature. The effect of temperature on n-butane conversion and aromatic selectivity over the catalysts is given in Figures 4 and 5. The product selectivity obtained from the transformation of n-butane over the H-ZSM-5, Ga-H-ZSM-5 and Zn-H-ZSM-5 catalysts at 803 K is given in Table 1. 

The significant finding was that the xylene fraction was 99% para. The other fractions are not lost. Toluene can be disproportionated to p-xylene and benzene with H-ZSM-5 treated with a little hexamethyldisiloxane to give 99% p-xylene, so that the usual separation of the ortho- and meta isomers with another zeolite would not be required.177 Benzene can be transalkylated with the higher aromatics to give toluene. Ethylbenzene can be isomerized to p-xylene. Ethylbenzene can be alkylated with ethanol in the presence of a modified ZSM-5 catalyst to produce p diethylbenzene with 97% selectivity.178... 

H-MOR and H-ZSM-5, and noble metal compounds (PdCl2, Pd(N03)2, PdO, PtCl2, orPtCl4) were used. It was demonstrated with the help of several techniques (IR, TPDA, TPE etc.) that the noble metal cations upon solid-state reaction occupy cation sites inside the zeolite structure. After reduction in H2 the thus-obtained materials possessed hydrogenation properties. Provided a suitable balance between the acid function (residual acidic OH groups) and the hydrogenation function (noble metal aggregates) was established, these catalysts were efficient in hydroisomerisation of, for instance, ethylbenzene. 

Cumene conversion under excess of benzene was studied over H-ZSM-11 in the adsorbed phase at 473 K by in situ C MASNMR. To follow the fate of different carbon atoms during the reaction, cumenes labelled with C-isotopes either on a-or on p-positions of the alkyl chain or in the aromatic ring have been synthesized. The primary product of cumene conversion over H-ZSM-11 was found to be n-propylbenzene. It is formed via intermolecular reaction of cumene and benzene. At long reaction times, the formation of n-propylbenzene is accompanied by complete scrambling of both cumene and n-propylbenzene alkyl chain carbon atoms and formation of toluene, ethylbenzene and butylbenzene. The rate of isomerization is higher than the rate of scrambling and fragmentation. 

Moreover, the macro - and micro -FTIR techniques enable us to obtain spectra in situ from a working catalyst, since the cells used (see Sect. 2.1.1) may be operated as flow-through reactors. Thus, coking of zeolite catalysts upon reaction of ethane or ethylbenzene was investigated in situ, and the decrease of diffusivities (e.g., of benzene) in the coking samples was measured as a function of the amount of coke deposited [15]. Similarly, the sorption of para-, meta-, and ortho-diethylbenzene from the gas phase into H-ZSM-5... 

It was confirmed that the presence of the carrier gas (helium) did not affect the diffusion measurements. When helium was replaced by neon, argon, or krypton, no change in the results was observed only xenon caused some deviation of the results (Niessen W, private communication). The main flow could be very rapidly connected with streams of the adsorbates in helium (8 ml min ) in such a way that the total flow and pressure remained constant. The adsorbate partial pressures could be varied, i.e., increased or decreased, almost instantaneously by small jumps. The experiment was started by scanning the spectrum of the pure, activated adsorbent. After a first pressure jump, e.g., from zero to 115 Pa, at a chosen adsorption temperature, the spectrum of the adsorbate/adsorbent was monitored in short intervals. An FTIR spectrometer of Perkin-Elmer type 1800 was employed. An example with sets of spectra of ethylbenzene adsorbed into H-ZSM-5 is shown in Fig. 3. 

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...

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