Applications transalkylation

Industrial applications of zeolites cover a broad range of technological processes from oil upgrading, via petrochemical transformations up to synthesis of fine chemicals [1,2]. These processes clearly benefit from zeolite well-defined microporous structures providing a possibility of reaction control via shape selectivity [3,4] and acidity [5]. Catalytic reactions, namely transformations of aromatic hydrocarbons via alkylation, isomerization, disproportionation and transalkylation [2], are not only of industrial importance but can also be used to assess the structural features of zeolites [6] especially when combined with the investigation of their acidic properties [7]. A high diversity of zeolitic structures provides us with the opportunity to correlate the acidity, activity and selectivity of different structural types of zeolites. 

In the EBMax process, benzene is fed to the bottom of the liquid-filled multibed reactor. Ethylene is co-fed with the benzene and also between the catalyst beds. Polyethylbenzenes, which are almost exclusively diethylbenzenes, undergo transalkylation with benzene in a second reactor. Mobil-Badger offers both liquid phase and vapor phase transalkylation processes. The vapor phase process removes benzene feed coboilers such as cyclohexane and methylcyclopentane as well as propyl and butylbenzenes. Because the EBMax process produces very low levels of propyl and butylbenzenes, for most applications, the more energy efficient liquid phase process is preferred. Worldwide, there are currently ten licensed EBMax units with a cumulative ethylbenzene production capacity of five million metric tons per year. 

Application Advanced technology to produce high-purity cumene from propylene and benzene using patented catalytic distillation (CD) technology. The CDCumene process uses a specially formulated zeolite alkylation catalyst packaged in a proprietary CD structure and another specially formulated zeolite transalkylation catalyst in loose form. 

Application The UOP Q-Max process produces high-quality cumene (isopropylbenzene) by alkylating benzene with typically refinery- or chemical-grade propylene. The process uses a proprietary zeolite catalyst that is regenerable and noncorrosive. Higher alkylate is converted to cumene via transalkylation, resulting in essentially stoichiometric cumene yield. Minimal impurities are formed, thus providing unsurpassed cumene product quality. 

Transalkylation of alkylbenzenes, polyalkylbenzenes and other arenes can be brought about by a variety of catalysts including Lewis acids, Brpnsted acids and various zeolites and silicates with or without being doped with various transition metals or their oxides. There has been a particularly explosive growth in the volume of literature pertaining to the use of various natural and modified zeolites. Recent developments include the study and applications of shape-selective catalysis by zeolites. Much of the work is patented, and largely applies to industrial processes. 

The equilibrium point lies far to the left and little methyl acetate (CH3COOCH3) is formed if water in not removed. By reactive distillation it is possible to continuously remove water and considerably intensify the reaction. Eastman Chemical pioneered one of the first major applications of reactive distillation, to significantly simplify the production of methyl acetate (Figure 3.7). This unit first went into operation in 1983. Among typical reactions where a by-product prevents the reaction from going to the right are esterification, trans-esterification, hydrolysis, acetalization and amination. Other types of reactions that could benefit from reactive distillation include alkylation/transalkylation/dealkylation, isomerization and chlorination. 

Xvlene Isomerization. The first reported use of borosilicate containing catalysts was for xylene isomerization (12,16). In this application, the purpose is to isomerize a reaction mixture which is lean in p-xylene to an equilibrium mixture from which the p-xylene can then be removed. In addition to the isomerization of xylenes, the catalyst also must convert a portion of the other components present in the feed to allow easier separation of p-xylene from the product mixture. The primary contaminant in the feedstock is ethylbenzene, which is converted via transalkylation to higher molecular weight compounds, which are valuable as gasoline blending components, and benzene. 

Application GT-TransAlk process technology produces benzene and xylenes through transalkylation of the methyl groups from toluene and/or heavy aromatics streams. The technology features a proprietary zeolite catalyst and can accommodate varying ratios of feedstock, while maintaining high activity and selectivity. 

Application The S-TDT process can produce mixed xylenes and benzene in an aromatics complex through disproportionation of toluene and transalkylation of toluene and Cg+ aromatics (Cg+ A) using toluene and Cg+ A as feedstocks. 

The transalkylation of toluene with trimethylbenzenes (TMB) is one of the most important reactions of conversion of methylaromatics aiming at the xylene production. However, with the recent market reduction of benzene as a consequence of environmental restrictions, benzene transalkylation with C9 aromatics emerges as a potentially important reaction for commercial applications and its investigation has attracted increasing attention. 

Mordenite is a promising catalyst for commercial application in the transalkylation of benzene with C9 stream. The reaction should be performed at a H2/HC ratio of 8, mainly because of the selectivity to toluene and xylenes rather than by coke deactivation. In fact, in these conditions, coke produced is soft (hydrogenated) and does not affect the performance of the catalyst. 

Borosilicate Catalysts, BorosHicates, which are prepared by the substitution of B for the Al in ZSM-5, are described as practical catalysts for shape-selective acid catalysis. The preferred application is the processing of Cg aromatics using isomerization, disproportionation, and transalkylation reaction steps. The borosilicate catalyst may also contain a metal additive, such as nickel or noble metal. 

The alkylation of benzene with ethylene in the gas phase was first achieved in 1942. Initially, Al203/Si02 was used as a catalyst, but this was replaced later by P40io/Si02. However, transalkylation is not complete when these catalysts are applied and the yield is unsatisfactory. Since 1980, zeolite catalysts have found application in gas-phase production of ethylbenzene. The Mobil-Badger process uses a ZSM-5-zeolite catalyst at a temperature of 420 to 430 °C and a pressure of... 

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