Catalysts dealkylation

The catalysts for xylene isomerization with EB dealkylahon are dominated by MFI zeolite. The de-ethylation reaction is particularly facile over this zeolite. There have been several generations of catalyst technology developed by Mobil, now ExxonMobil [84]. The features in their patents include selectivation and two-catalyst systems in which the catalysts have been optimized separately for deethylation of EB and xylene isomerization [85-87]. The crystallite size used for de-ethylation is significantly larger than in the second catalyst used for xylene isomerization. Advanced MHAI is one example. The Isolene process is offered by Toray and their catalyst also appears to be MFI zeoUte-based, though some patents claim the use of mordenite [88, 89]. The metal function favored in their patents appears to be rhenium [90]. Bimetallic platinum catalysts have also been claimed on a variety of ZSM-type zeolites [91]. There are also EB dealkylation catalysts for the UOP Isomar process [92]. The zeolite claimed in UOP patents is MFI in combination with aluminophosphate binder [93]. 

Precious metals (Section 14.4.2.1) are generally more expensive than the other catalyst components, so reduced metal content is an ongoing effort. This is more of an issue with EB isomerization catalysts since they have higher metal content than EB dealkylation catalysts. 

The converse reactions dealkylation and hydrodealkylation are practiced extensively to convert available feedstocks into other more desirable (marketable), products. Two such processes are (1) the conversion of toluene or xylene, or the higher-molecular-weight alkyl aromatic compounds, to benzene in the presence of hydrogen and a suitable presence of a dealkylation catalyst and (2) the conversion of toluene in the presence of hydrogen and a fixed bed catalyst to benzene plus mixed xylenes. 

There are two broad categories of xylene isomerization catalysts EB isomerization catalysts, which convert ethylbenzene into additional xylenes and EB dealkylation catalysts, which convert ethylbenzene to valuable benzene coproduct. The selection of the isomerization catalyst depends on the configuration of the UOP aromatics complex, the composition of the feedstocks and the desired product slate. 

Vasile et al. [21-23] Flow reactor LDPE, HDPE, PP Silica-alumina, ZSM-5 zeolite, dealkylation catalyst... 

The cracking of petroleum products is probably the most common dealkylation reaction. Silica-almnina, silica-magnesia, and a clay (montmorillonite) are common dealkylation catalysts.. ... 

With the EB-dealkylation catalyst, byproduct benzene is produced at high purity by simple distillation. 

Toluene is dealkylated to benzene over a hydrogenation-dehydrogenation catalyst such as nickel. The hydrodealkylation is essentially a hydrocracking reaction favored at higher temperatures and pressures. The reaction occurs at approximately 700°C and 40 atmospheres. A high benzene yield of about 96% or more can be achieved ... 

Dealkylation also can be effected by steam. The reaction occurs at 600-800°C over Y, La, Ce, Pr, Nd, Sm, or Th compounds, Ni-Cr203 catalysts, and Ni-Al203 catalysts at temperatures between 320-630°C. Yields of about 90% are obtained. This process has the advantage of producing, rather than using, hydrogen. 

When the temperature of a carbonate reservoir that is saturated with high-viscosity oil and water increases to 200° C or more, chemical reactions occur in the formation, resulting in the formation of considerable amounts of CO2. The generation of CO2 during thermal stimulation of a carbonate reservoir results from the dealkylation of aromatic hydrocarbons in the presence of water vapor, catalytic conversion of hydrocarbons by water vapor, and oxidation of organic materials. Clay material and metals of variable valence (e.g., nickel, cobalt, iron) in the carbonate rock can serve as the catalyst. An optimal amount of CO2 exists for which maximal oil recovery is achieved [1538]. The performance of a steamflooding process can be improved by the addition of CO2 or methane [1216]. 

Lewis acid catalysts can also effect dealkylation, i.e. the reaction is reversible. Thus ethylbenzene (22) with BF3 and HF, is found to disproportionate ... 

Failure of hexylpyrene as the liquefaction solvent may be due to the easy dealkylation (13) or high carbonization reactivity probably catalyzed by coals. Transalkylation for coal-liquefaction may require the acid-catalyst (14) or high pressure (15). 

Some other processes are based on a severe hydrotreatment followed by a stage for octane recovery. Octgain from ExxonMobil [57] and ISAL from UOP-Intevep [58], Deep desulfurization is achieved by an increase in severity, causing lost in octane by olefins saturation. In the first case, in a second reactor octane number is recovered by a combination of cracking and isomerization reactions. In the latter case, the catalyst employed during desulfurization possess isomerization capabilities inhibiting an excessive octane lost. Other mentioned functionalities of the catalyst include dealkylation and conversion. 

Finally, a third route considers the possibility of removing the steric hindrance prior to desulfurization by including an acid (isomerizing/dealkylating) function on the catalyst so that the bulky substituents can be moved to a different, less harmless, position related to the S atom site. 

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. 

As previously observed [4] on EU-1 catalyst deactivation leads to isomerization selectivity improvement (table 2) whereas dealkylation and disproportionation selectivity decreases. The same effect is observed for ferrierite and ZSM-22 catalysts to a lesser extent. Isomerization selectivity reach more than 70% for these catalysts after 8... 

The product distribution determined for the reactions performed over a broad temperature range (from -176 to 199 °C) under microwave heating was always more or less different from that obtained by conventional method. Thus, a vigorous formation of isobutene under reflux using microwave heating indicates superheating of the catalyst to a higher temperature. This facilitates the dealkylation reaction, which is promoted by elevated temperature. 

HDA [Hydrodealkylation] A proprietary dealkylation process for making benzene from toluene, xylenes, pyrolysis naphtha, and other petroleum refinery intermediates. The catalyst,... 

Litol Also called Houdry-Litol. A process for making benzene by dealkylating other aromatic hydrocarbons. It is a complex process which achieves desulfurization, removal of paraffins and naphthenes, and saturation of unsaturated compounds, in addition to dealkylation. The catalyst contains cobalt and molybdenum. Developed by the Houdiy Process and Chemical Company and Bethlehem Steel Corporation. First installed by the Bethlehem Steel Corporation in 1964. Subsequently used at British Steel s benzole refinery, Teesside, England. 

Xyloflning [Xylol refining] A process for isomerizing a petrochemical feedstock containing ethylbenzene and xylenes. The xylenes are mostly converted to the equilibrium mixture of xylenes the ethylbenzene is dealkylated to benzene and ethylene. This is a catalytic, vapor-phase process, operated at approximately 360°C. The catalyst (Encilite-1) is a ZSM-5-type zeolite in which some of the aluminum has been replaced by iron. The catalyst was developed in India in 1981, jointly by the National Chemical Laboratory and Associated Cement Companies. The process was piloted by Indian Petrochemicals Corporation in 1985 and commercialized by that company at Baroda in 1991. 

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