Dealkylation of cumene

The microporosity of a new tubular silicatelayered silicate nanocomposite formed by the intercalation of imogolite in Na -montmorillonite has been characterized by nitrogen and m-xylene adsorption. The nitrogen adsorption data yielded liquid micropore volume of -0.20 cm g as determined by both the t-plot and the Dubinin-Radusikevich methods. The t-plot provided evidence for a bimodal pore structure which we attributed to intratube and intertube adsorption environments. The m-xylene adsorption data indicated a much smaller liquid pore volume (-0.11 cm g ), most likely due to incomplete filling of intratubular pores by the planar adsorbate. The FTIR spectrum of pyridine adsorbed on the TSLS complex established the presence of both Bronsted and Lewis acid sites. The TSLS complex was shown to be active for the acid-catalyzed dealkylation of cumene at 350 C, but the complex was less reactive than a conventional alumina pillared montmorillonite. 

In the present work we examine the microporosity of a TSLS complex formed from synthetic imogolite and natural montmorillonite. Nitrogen adsorption and desorption isotherms are reported and analyzed in terms of microporous volume and surface area. Also, the adsorption isotherm for an organic adsorbate, m-xylene, is reported. Preliminary FTIR results for the chemisorption of pyridine and catalytic studies of the dealkylation of cumene suggest that TSLS complexes are promising microporous acids for shape selective chemical conversions. 

Catalytic dealkylation of cumene was carried out in a fixed bed reactor operated at 350 C and atmospheric pressure. The contact time was 1.5 sec and the WHSV was 0.4g cumene/g/hr. The conversion of cumene was determined using a Hewlett Packard 5890 gas Chromatograph equipped with a Supelco wide bore capillary column. 

The acidic functionality of the TSLS complex was demonstrated in the catalytic dealkylation of cumene. For this model reaction at 350 C the conversion of cumene to benzene was monitored as a function of time on stream (see Figure 8). Included in the study for comparison purposes... 

Figure 8. Catalytic dealkylation of cumene at 350 C over the imogolite-montmorillonite TSLS complex and alumina pillared montmorillonite (APM).

Mathis and Watson Dealkylation of cumene by SiOi-AIjOa catalyst 74-149 5-10 1.5-2.5 0.6 1 M8... 

Other Processes. Borosilicates have been used to catalyze a number of other reactions. Among these are dealkylation of cumene by faujasite-type sieves (11). The sieves used for this reaction were prepared by hydrothermal synthesis and contained some aluminum. The catalytic activity increased as the boron content increased. 

Fjq. 12. Poisoning effect of organic nitrogen compounds on the catalytic dealkylation of cumene catalyst. 

Table 7-6 Effect of the metal ion in faujasite on the dealkylation of cumene [T35]...

A number of acid catalyzed reactions have been examined in which the PILCS were compared to zeolites. Shabtai et al. [47] compared the rates of reaction for dealkylation of cumene and 1-isopropylnaphthalene and for cracking of polycyclic naphthenes catalyzed by a pillared montmorillonite with rates of these reactions catalyzed by a Y-type zeolite. In each case the PILC, whether in the H or rare earth form, was found to have a higher activity. When the reactant molecule was larger than the zeolite windows, the rates of the PILC-catalyzed reaction were much greater than those of the zeolite-catalyzed reaction. Some of the data are summarized in Table V. 

The acidic nature of NiCaY after reduction of the metal can be illustrated by using the model reaction of cracking of cumene. Figure 3 shows the catalytic activity at various temperatures and the yields of the products. The catalyst possesses high activity even at 200°C, where the conversion is 20.5 mole %. At 400° C the activity increases and the conversion reaches 97.1 mole %. At 200°C dealkylation is accompanied by disproportionation with formation of diisopropylbenzene. With increasing temperature the disproportionation decreases, while hydrogenolysis of the alkyl chain is strongly increased. 

The cracking of cumene has received considerable attention in recent years as a reaction typical of one class of cracking reactions, namely dealkylation of aromatics. Among the studies of cumene cracking found in the literature there are several attempts to determine the kinetics of... 

The most striking product result is the extensive formation of propane over very active catalysts. Venuto et al. (99) reported analogously that dealkylation of rf-butylbenzene over rare earth-exchanged X zeolite at 260° gave isobutane as the major gaseous product. Such paraffin formation is presumably the result of hydride transfer reactions to the car-bonium ions formed by initial electrophilic cleavage of the alkylbenzene 100) or by protonation of the olefin. Reasonable hydride donors are cumene and propylene the resultant hydrogen-deficient species are then precursors of residue formation (32, 89). Parafiin formation by treatment of alkylbenzenes with aluminum halides in the presence of cyclohexane or decalin has been known for 30 years 47), and there is ample evidence for hydride transfer between carbonium ions and hydrocarbons 10, 22, 27,53). 

The cracking of Cumene is a typical dealkylation reaction, with two major products, benzene and propylene. The race-earth-exchanged Y(REY) zeolite used here has a bulk density of 2 g/ml, a particle size of 1 pore diameter of 9 A, and a specific surface area... 

Experimental work in a micro scale activity test equipment was performed to derive a testing strategy for the optimization of FCC unit operation due to coke deposition on catalyst. The cracking of cumene over a super-D zeolite catalyst was chosen as the model reaction because the nature of this reaction can represent the cracking of typical commercial FCC feeds such as gas-oils via the dealkylation of branched aromatics. In addition, this reaction can also eliminate any obscurity in catalyst deactivation from other contaminants. 

Some experiments related to radiolysis in the adsorbed state, mostly by Hentz, probably involve interactions with some of these hydrocarbon-transforming sites. Cumene will react Avith irradiated silica-alumina (98) or silica gel (10, 99) to form benzene and small quantities of hydrogen. The process is not catalysis, since repetition of the addition yields no further product (98). Annealing and adsorption experiments with silica-alumina (99a) revealed that at least two (possibly three) groups of sites are responsible for the dealkylation. Of a total of... 

Galich el al. 136) showed that, within an alkali metal-exchanged X series (Table XIX), as cationic radius increased, cumene conversion decreased. Also, the products contained larger amounts of l-methyl-3-ethylbenzene and less toluene, ethylbenzene, and propenylbenzene. The dealkylation of lower temperature (260°) over REX catalyst than did other related dealkylations. The major liquid product was benzene, with small amounts of toluene, ethylbenzene, and cumene. Isobutane was the major gaseous product, and no olefins were observed. 

The spectral chemisorption studies described above have been carried out at room temperature. Tachibana and Okuda 95) succeeded in observing a band at 335 mp of an unstable intermediate during the dealkylation cracking of cumene on silica-alumina at 150°C. The band... 

A test procedure involving an isomerization reaction of an olefin would obviously be most desirable for testing the activity of the acid function of a dual-function catalyst. Such a test appeared out of question because of the certain interference with this reaction by the platinum activity of the samples under study. Cumene (isopropyl benzene) is known to undergo reaction (dealkylation) on acidic catalysts. We have found the reactivity of cumene to be a useful measure of the activity for other acid-catalyzed reactions (4) of at least certain classes of compositions. Furthermore, we have foimd it to be useful on dual-function class catalysts, i.e., to yield a relative measure of their acidic activity despite the simultaneous presence of platinum. 

The influence of the exchanged ions is considerable, as shown by the example of cumene dealkylation on faujasite (Table 7-6). Reasons for the large differences in reactivity are the different charges on the ions, and the decreasing ionic radii from Na to and the associated polarizing power of the ions. 

The rate of transalkylation, after 0.5 h is faster than the rate of isomerization. The formation of cumene is possible either by transalkylation reaction between DIPB isomers and benzene or dealkylation of DIPB isomers as shovm in reactions (1) and (2) respectively. 

Benzene was first isolated by Faraday in 1825 from the liquid condensed by compressing oil gas. It is the lightest fraction obtained from the distillation of the coal-tar hydrocarbons, but most benzene is now manufactured from suitable petroleum fractions by dehydrogenation (54%) and dealkylation processes. Its principal industrial use is as a starting point for other chemicals, particularly ethylbenzene, cumene, cyclohexane, styrene (45%), phenol (20%), and Nylon (17%) precursors. U.S. production 1979 2-6 B gals. 

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